43 results on '"Carlos A. Iglesias"'
Search Results
2. Front Cover: Relevance of Palladium to Radiopharmaceutical Development Considering Enhanced Coordination Properties of TE1PA (Chem. Eur. J. 41/2022)
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Julie Pineau, Luís M. P. Lima, Carlos Platas‐Iglesias, Jan Rijn Zeevaart, Cathryn H. S. Driver, Nathalie Le Bris, and Raphaël Tripier
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Organic Chemistry ,General Chemistry ,Catalysis - Published
- 2022
3. Relevance of Palladium to Radiopharmaceutical Development Considering Enhanced Coordination Properties of TE1PA
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Julie Pineau, Luís M. P. Lima, Carlos Platas‐Iglesias, Jan Rijn Zeevaart, Cathryn H. S. Driver, Nathalie Le Bris, and Raphaël Tripier
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Palladium(II) ,Organic Chemistry ,General Chemistry ,Ligands ,Catalysis ,South Africa ,Palladium-109 ,Positron-Emission Tomography ,Cyclam monopicolinate ,Cyclam ,Complexation ,Radiopharmaceuticals ,Palladium ,Chelating Agents ,Radiolabeling - Abstract
[Abstract] The limited use of palladium-103 and -109 radionuclides for molecular radiotherapy is surely due to the lack of appropriate ligands capable of fulfilling all criteria required for application in nuclear medicine. Furthermore, the thermodynamic properties of these complexes in solution remain difficult to establish. The challenge is compounded when considering that radiolabeling of compounds for translation to clinical trials requires fast complexation. Thus, the coordination of Pd(II) and 103/109Pd-nuclides is a huge challenge in terms of molecular design and physicochemical characterization. Herein, we report a comprehensive study highlighting TE1PA, a monopicolinate cyclam – already established in nuclear imaging with 64Cu-PET (positron emission tomography) imaging tracers – as a highly relevant chelator for natural Pd and subsequently 109Pd-nuclide. The structural, thermodynamic, kinetic and radiolabeling studies of Pd(II) with TE1PA, as well as the comparison of this complex with three structurally related derivatives, support palladium-TE1PA radiopharmaceuticals as leading candidates for targeted nuclear medicine. R.T. and N.L.B. acknowledge the Ministère de l′Enseignement Supérieur et de la Recherche and the Centre National de la Recherche Scientifique. J.P. is grateful to the Ligue contre le Cancer, the MAC-group (UBO) and the University of Cape Town for her PhD fellowship; C.H.S.D thanks the Technology Innovation Agency (TIA) seed fund implemented through the South African Nuclear Energy Corporation for financial support. C.P.-I. thanks Centro de Supercomputación de Galicia for providing access to computing facilities. L.M.P.L was financially supported by Project LISBOA-01-0145-FEDER-007660 (Microbiologia Molecular, Estrutural e Celular), funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds through FCT - Fundação para a Ciência e a Tecnologia
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- 2022
4. Synthesis of Orthogonal N -Protected C -Functional Side-Bridged Cyclams to Give Access to Unsymmetrical Constrained BCAs
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Thomas Le Bihan, Carlos Platas-Iglesias, Raphaël Tripier, Hélène Bernard, and Nathalie Le Bris
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chemistry.chemical_compound ,chemistry ,010405 organic chemistry ,Stereochemistry ,Organic Chemistry ,Cyclam ,Physical and Theoretical Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences - Published
- 2019
5. Gadolinium(III)‐Based Dual1H/19F Magnetic Resonance Imaging Probes
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Tanja Savić, Goran Angelovski, David Esteban-Gómez, Carlos Platas-Iglesias, Fabio Carniato, Rosa Pujales-Paradela, and Mauro Botta
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medicine.diagnostic_test ,010405 organic chemistry ,Chemistry ,Gadolinium ,Organic Chemistry ,Relaxation (NMR) ,chemistry.chemical_element ,Magnetic resonance imaging ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,01 natural sciences ,Catalysis ,Imaging phantom ,0104 chemical sciences ,chemistry.chemical_compound ,Nuclear magnetic resonance ,Cyclen ,medicine ,Molecule ,Luminescence - Abstract
We present two novel octadentate cyclen-based ligands bearing one (L1 ) or two (L2 ) phenylacetamide pendants with two CF3 groups either at positions 3 and 5 (L1 ) or 4 (L2 ). The corresponding Gd3+ complexes possess one coordinated water molecule, as confirmed by luminescence lifetime measurements on the EuIII and TbIII analogues. A detailed 1 H and 17 O relaxometric characterization has revealed the parameters that govern the relaxivities of these complexes. The water-exchange rate of the mono-amide derivative GdL1 (kex298 =1.52×106 s-1 ) is faster than that determined for the bis-amide complex GdL2 (kex298 =0.73×106 s-1 ). 1 H and 19 F NMR studies have indicated that the complexes are present in solution almost exclusively as the square-antiprismatic (SAP) isomers. 19 F NMR relaxation studies indicated Gd⋅⋅⋅F distances of 7.4±0.1 and 9.1±0.1 A for GdL1 and GdL2 , respectively. Phantom MRI studies revealed the favorable properties of GdL2 as a dual 1 H/19 F magnetic resonance imaging (MRI) probe, whereas the shorter Gd⋅⋅⋅F distance of GdL1 reduces the signal-to-noise ratio due to the very short transverse relaxation time of the 19 F NMR signal.
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- 2019
6. A Coordination Chemistry Approach to Fine-Tune the Physicochemical Parameters of Lanthanide Complexes Relevant to Medical Applications
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Gyula Tircsó, David Esteban-Gómez, Mariane Le Fur, Olivier Rousseaux, Raphaël Tripier, Ferenc K. Kálmán, Enikő Molnár, Maryline Beyler, Olivier Fougère, Carlos Platas-Iglesias, Chimie, Electrochimie Moléculaires et Chimie Analytique (CEMCA), Institut Brestois Santé Agro Matière (IBSAM), Université de Brest (UBO)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), University of Debrecen Egyetem [Debrecen], Guerbet research group, Guerbet, Departamento de Química Fundamental, and Universidade da Coruña
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Steric effects ,Lanthanide ,Magnetic Resonance Spectroscopy ,Contrast Media ,Gadolinium ,Ligands ,010402 general chemistry ,Lanthanoid Series Elements ,NMR Spectroscopy ,01 natural sciences ,Catalysis ,Dissociation (chemistry) ,Ion ,Coordination complex ,Természettudományok ,Water Exchange ,Lanthanides ,[CHIM]Chemical Sciences ,Molecule ,[CHIM.COOR]Chemical Sciences/Coordination chemistry ,Picolinic Acids ,Kémiai tudományok ,chemistry.chemical_classification ,010405 organic chemistry ,Ligand ,Organic Chemistry ,Water ,General Chemistry ,0104 chemical sciences ,3. Good health ,Kinetics ,Crystallography ,chemistry ,Thermodynamics ,Macrocycles ,Order of magnitude ,MRI - Abstract
International audience; The geometric features of two pyclen-based ligands possessing identical donor atoms but different site organization have a profound impact in their complexation properties toward lanthanide ions. The ligand containing two acetate groups and a picolinate arm arranged in a symmetrical fashion (L1) forms a Gd3+ complex being two orders of magnitude less stable than its dissymmetric analogue GdL2. Besides, GdL1 experiences a much faster dissociation following the acid-catalyzed mechanism than GdL2. On the contrary, GdL1 exhibits a lower exchange rate of the coordinated water molecule compared to GdL2. These very different properties are related to different strengths of the Gd ligand bonds associated to steric effects, which hinder the coordination of a water molecule in GdL2 and the binding of acetate groups in GdL1.
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- 2018
7. Morphological Diversity in Nanoporous Covalent Organic Materials Derived from Viologen and Pyrene
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Seema Sharma, Ali Trabolsi, John Carl Olsen, Jésus Raya, Gobinda Das, Dong Suk Han, Tina Skorjanc, Thirumurugan Prakasam, Carlos Platas-Iglesias, and Ramesh Jagannathan
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chemistry.chemical_classification ,Materials science ,Renewable Energy, Sustainability and the Environment ,Nanoporous ,Energy Engineering and Power Technology ,Viologen ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Biomaterials ,chemistry.chemical_compound ,chemistry ,Covalent bond ,Materials Chemistry ,medicine ,Pyrene ,0210 nano-technology ,medicine.drug - Published
- 2017
8. A semantic data lake framework for autonomous fault management in SDN environments
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Álvaro Carrera, Fernando Benayas, Manuel Garcia-Amado, and Carlos A. Iglesias
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Computer science ,business.industry ,Electrical and Electronic Engineering ,Semantic data model ,Software engineering ,business ,Fault management - Published
- 2019
9. Pharmacological Therapy Determines the Gut Microbiota Modulation by a Pomegranate Extract Nutraceutical in Metabolic Syndrome: A Randomized Clinical Trial
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Juan Carlos Espín, Carlos E. Iglesias-Aguirre, Amparo Meoro, María V. Selma, Adrián Cortés-Martín, Ministerio de Economía y Competitividad (España), Fundación Séneca, and Ministerio de Ciencia e Innovación (España)
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Adult ,Male ,Polyphenol ,0301 basic medicine ,medicine.medical_treatment ,Inter-individual variability ,Gut microbiota ,Gut flora ,Pharmacology ,Polymorphism, Single Nucleotide ,Single-nucleotide polymorphisms ,Pomegranate ,03 medical and health sciences ,Nutraceutical ,Pharmacotherapy ,Coumarins ,Humans ,Medicine ,Bifidobacterium ,030109 nutrition & dietetics ,biology ,Plant Extracts ,business.industry ,Prebiotic ,Middle Aged ,medicine.disease ,biology.organism_classification ,Metabolic syndrome ,Crossover study ,Gastrointestinal Microbiome ,Urolithin ,Prebiotics ,030104 developmental biology ,Dietary Supplements ,Female ,business ,Food Science ,Biotechnology - Abstract
Scope: Poly-pharmacological therapy shapes the gut microbiota (GM) in metabolic syndrome (MetS) patients. The effects of polyphenols in poly-medicated MetS patients are unknown. Methods and results: A randomized, placebo-controlled, double-blinded, and crossover trial in poly-medicated MetS patients (n=50) explored whether the effects of a pomegranate extract nutraceutical (PE, 320 mg phenolics/day for 1 month) are affected by the drug therapy. Considering the lipid-lowering (LL-), anti-hypertensive (HP-) and(or) anti-diabetic (AD-) treatments: GM (16S rRNA sequencing), short-chain fatty acids, 40 inflammatory-metabolic and endotoxemia-related biomarkers, associations between biomarkers and GM with 53 cardiometabolic dysfunctions-related single-nucleotide polymorphisms (SNPs), and urolithin metabotypes (UMs) influence are evaluated. Representative SNPs-GM associations after PE include Lactococcus and ClostridiumXIVa with rs5443-GNB3 (G-protein-β-polypeptide-3) and ClostridiumXIVa with rs7903146-TCF7L2 (transcription-factor-7-like-2) and rs1137101-LEPR (leptin-receptor). PE decreases sICAM-1 in LL-patients and the lipopolysaccharide-binding protein in all the patients. PE does not affect the other patients’ markers as a group or stratifying by UMs. After PE, Lactococcus increases in AD-, LL-, and HP-patients, Bifidobacterium increases in LL- and AD-, while Clostridium XIVa decreases in non-LL- and non-HP-patients. Conclusion: The prebiotic effect of PE depends on the medication, mainly on HP-treatments. Targeting GM can complement MetS therapy, but the patients’ drug therapy should be considered individually., Ministerio de Economía y Competitividad. Grant Number: AGL2015-94124-R Fundación Séneca. Grant Number: 20880/PI/18 Ministerio de Ciencia e Innovación. Grant Number: PID2019-103914RB-I00
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- 2021
10. Cover Feature: pH‐Dependent Hydration Change in a Gd‐Based MRI Contrast Agent with a Phosphonated Ligand (Chem. Eur. J. 24/2020)
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David Esteban-Gómez, Isabel Brandariz, Loïc J. Charbonnière, Jérémy Salaam, Aline Nonat, Olivier Jeannin, Fabio Carniato, Cyrille Charpentier, Carlos Platas-Iglesias, and Mauro Botta
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Crystallography ,Chemistry ,Feature (computer vision) ,Ligand ,Gadolinium ,MRI contrast agent ,Organic Chemistry ,chemistry.chemical_element ,Ph dependent ,Cover (algebra) ,General Chemistry ,Catalysis - Published
- 2020
11. Front Cover: Europium(III) Macrocyclic Chelates Appended with Tyrosine‐based Chromophores and Di‐(2‐picolyl)amine‐based Receptors: Turn‐On Luminescent Chemosensors Selective to Zinc(II) Ions (ChemPlusChem 5/2020)
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Gaoji Wang, Carlos Platas-Iglesias, and Goran Angelovski
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Lanthanide ,chemistry ,chemistry.chemical_element ,Amine gas treating ,Chelation ,General Chemistry ,Zinc ,Chromophore ,Luminescence ,Europium ,Photochemistry ,Photoinduced electron transfer - Published
- 2020
12. Macrocyclic Gd3+Complexes with Pendant Crown Ethers Designed for Binding Zwitterionic Neurotransmitters
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Céline Landon, Fatima Oukhatar, Goran Angelovski, Carlos Platas-Iglesias, Éva Tóth, Hervé Meudal, Nikos K. Logothetis, Department for Physiology of Cognitive Processes, Max-Planck-Institut, Centre de biophysique moléculaire (CBM), Université d'Orléans (UO)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), Department of Imaging Science and Biomedical Engineering, University of Manchester [Manchester], Departamento de Química Fundamental, Universidade da Coruña, MR Neuroimaging Agents Group, Max Planck Institute for Biological Cybernetics, Max-Planck-Gesellschaft-Max-Planck-Gesellschaft, and Frapart, Isabelle
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Models, Molecular ,Macrocyclic Compounds ,Magnetic Resonance Spectroscopy ,Stereochemistry ,[SDV]Life Sciences [q-bio] ,Gadolinium ,Ether ,Medicinal chemistry ,Catalysis ,Neurotransmitter binding ,chemistry.chemical_compound ,Coordination Complexes ,Crown Ethers ,Carboxylate ,Amino Acids ,Crown ether ,chemistry.chemical_classification ,Neurotransmitter Agents ,Binding Sites ,Organic Chemistry ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Crown Compounds ,Amino acid ,[SDV] Life Sciences [q-bio] ,chemistry ,Luminescent Measurements ,Potentiometry ,Selectivity - Abstract
International audience; A series of Gd(3+) complexes exhibiting a relaxometric response to zwitterionic amino acid neurotransmitters was synthesized. The design concept involves ditopic interactions 1) between a positively charged and coordinatively unsaturated Gd(3+) chelate and the carboxylate group of the neurotransmitters and 2) between an azacrown ether appended to the chelate and the amino group of the neurotransmitters. The chelates differ in the nature and length of the linker connecting the cyclen-type macrocycle that binds the Ln(3+) ion and the crown ether. The complexes are monohydrated, but they exhibit high proton relaxivities (up to 7.7 mM(-1) s(-1) at 60 MHz, 310 K) due to slow molecular tumbling. The formation of ternary complexes with neurotransmitters was monitored by (1) H relaxometric titrations of the Gd(3+) complexes and by luminescence measurements on the Eu(3+) and Tb(3+) analogues at pH 7.4. The remarkable relaxivity decrease (≈80 %) observed on neurotransmitter binding is related to the decrease in the hydration number, as evidenced by luminescence lifetime measurements on the Eu(3+) complexes. These complexes show affinity for amino acid neurotransmitters in the millimolar range, which can be suited to imaging concentrations of synaptically released neurotransmitters. They display good selectivity over non-amino acid neurotransmitters (acetylcholine, serotonin, and noradrenaline) and hydrogenphosphate, but selectivity over hydrogencarbonate was not achieved.
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- 2015
13. Highly Stable Complexes of Divalent Metal Ions (Mg 2+ , Ca 2+ , Cu 2+ , Zn 2+ , Cd 2+ , and Pb 2+ ) with a Dota‐Like Ligand Containing a Picolinate Pendant
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Carlos Platas-Iglesias, Teresa Rodríguez-Blas, Erika Ruscsák, Imre Tóth, Gyula Tircsó, Martín Regueiro-Figueroa, David Esteban-Gómez, Laura Fra, and Andrés de Blas
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Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Aqueous solution ,chemistry ,Cyclen ,Stability constants of complexes ,Ligand ,Metal ions in aqueous solution ,Inorganic chemistry ,DOTA ,Qualitative inorganic analysis ,Macrocyclic ligand - Abstract
The stability constants of complexes of the macrocyclic ligand do3a-pic4– (H4do3a-pic = 2,2′,2″-{10-[(6-carboxypyridin-2-yl)methyl]-1,4,7,10-tetraazacyclododecane-1,4,7-triyl}triacetic acid) with several divalent metal ions (Pb2+, Cd2+, Zn2+, Cu2+, Ca2+, and Mg2+) have been determined by using pH-potentiometric titrations (I = 0.1 M KCl, 25 °C). The stability of these complexes follows the trend Cu2+ > Cd2+ ≈ Pb2+ ≈ Zn2+ >> Ca2+ >> Mg2+. A particularly high stability constant has been determined for the Cu2+ complex [log KCuL = 23.20(4)]. Analysis of the titration curves indicate the presence of protonated forms of the complexes in solution, with protonation constants of log KM(HxL) = 6.9–2.0 (x = 1, 2, or 3). The structure of the complexes in solution has been investigated by using 1H and 13C NMR spectroscopy and DFT calculations performed in aqueous solution at the TPSSh/6-31G(d) level. In the case of the Pb2+ and Cd2+ complexes, relativistic effects were considered with the use of relativistic effective core potentials. Calculations show that the complexes with the largest metal ions (Pb2+ and Ca2+) are nine-coordinate, with their coordination polyhedra being best described as capped twisted square antiprisms. The Cd2+ and Mg2+ complexes are seven-coordinate, with the metal ions being bound to the four nitrogen atoms of the cyclen unit and the three acetate pendant arms. Finally, in the Cu2+ and Zn2+ complexes, the metal ions are six-coordinated, with the metal ions being asymmetrically placed inside the macrocyclic cavity of the ligand, and the coordination polyhedra can be described as an octahedron and a trigonal prism, respectively.
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- 2014
14. Spectroscopic properties of a family of mono‐ to trinuclear lanthanide complexes
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David Esteban-Gómez, Raphaël Tripier, Loïc J. Charbonnière, Carlos Platas-Iglesias, Aurora Rodríguez-Rodríguez, Mohamadou Sy, Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Departamento de Química Fundamental, Universidade da Coruña, Chimie, Electrochimie Moléculaires et Chimie Analytique (CEMCA), Institut Brestois Santé Agro Matière (IBSAM), and Université de Brest (UBO)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)
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Lanthanide ,Polynuclear complexes ,Luminescence ,Absorption spectroscopy ,010405 organic chemistry ,Picolinic acid ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,Macrocyclic ligands ,Ultraviolet visible spectroscopy ,chemistry ,Cyclen ,Excited state ,Lanthanides ,[CHIM]Chemical Sciences ,UV/Vis spectroscopy ,Spectroscopy - Abstract
[Abstract] A series of mono‐, di‐, and trinuclear complexes of Eu and Tb was designed to study the influence of the number of Ln emitting centers on the luminescence properties of discrete polynuclear complexes. The complexes are based on a cyclen scaffold, functionalized by two picolinic acid pendant arms. These coordinating units are separated by a 1,3‐dimethylbenzene spacer for the dinuclear complex and a 1,3,5‐trimethylbenzene bridge in the case of the trinuclear complex. The synthesis and characterization of the ligands are presented, together with the preparation and spectroscopic characterization of the complexes. The luminescence properties of the complexes were determined by UV/Vis absorption spectroscopy and steady‐state and time‐resolved luminescence spectroscopy in buffered aqueous solutions. Comparison of the electronic absorption spectra showed that the absorption properties can almost be considered as extensive parameters within experimental error, as expected for electronically non‐conjugated systems. A small drop of both the excited state luminescence lifetimes and the luminescence quantum yields was observed for the trinuclear complexes in the case of Tb. To understand this behavior, theoretical HF (Hartree–Fock) calculations were performed for the three complexes. Models indicate that the average intermetallic distance in the dinuclear complex is almost the same as in the trinuclear one, disfavoring a possible distance dependence of the observed phenomena. Francia. Agence Nationale de la Recherche; ANR P2N 2012
- Published
- 2017
15. 1,4,7‐triazacyclononane‐based bifunctional picolinate ligands for efficient copper complexation
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Véronique Patinec, David Esteban-Gómez, Raphaël Tripier, Carlos Platas-Iglesias, Mélissa Roger, Rita Delgado, Amaury Guillou, Luís M. P. Lima, Chimie, Electrochimie Moléculaires et Chimie Analytique (CEMCA), Institut Brestois Santé Agro Matière (IBSAM), Université de Brest (UBO)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC), Instituto de Tecnologia Química e Biológica António Xavier (ITQB), Universidade Nova de Lisboa = NOVA University Lisbon (NOVA), Departamento de Química Fundamental, and Universidade da Coruña
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Inorganic chemistry ,Potentiometric titration ,chemistry.chemical_element ,Imaging agents ,[CHIM.INOR]Chemical Sciences/Inorganic chemistry ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,law.invention ,Inorganic Chemistry ,chemistry.chemical_compound ,Macrocyclic ligands ,N ligands ,law ,[CHIM.COOR]Chemical Sciences/Coordination chemistry ,Electron paramagnetic resonance ,Bifunctional ,010405 organic chemistry ,Chemistry ,Copper ,0104 chemical sciences ,Crystallography ,Stability constants of complexes ,Potentiometry ,Chemical stability ,Cyclic voltammetry - Abstract
International audience; Three 1,4,7-triazacyclononane-based (tacn-based) ligands containing picolyl and picolinate pendant arms (no3py, no2pa1py, and no3pa) were synthesized, and their copper(II) complexation properties were studied to evaluate their potentials as chelators for copper radioisotopes. The thermodynamic stability constants of the complexes were determined by potentiometric titrations. These studies evidenced the formation of mononuclear species for no3py and mono- and dinuclear species for no2pa1py and no3pa. The pCu values decreased as the number of carboxypicolyl arms increased. The [Cu(no3py)]2+ complex presented a very high stability constant (log KCuL = 27.4) and a very high selectivity towards Zn2+ ions (log KZnL = 17.25). Vis/NIR (NIR = near-infrared) absorption and electron paramagnetic resonance (EPR) spectroscopy indicated that the three complexes present distorted octahedral geometries with two paramagnetic species, which were identified as the Δ(δδδ) and Λ(δδδ) isomers [and their corresponding enantiomeric forms Λ(λλλ) and Δ(λλλ)] by DFT calculations. The electrochemical properties were investigated by cyclic voltammetry, which revealed quasireversible behavior for the [Cu(no3py)]2+ complex but irreversible Cu2+/Cu+ systems for [Cu(no2pa1py)] and [Cu(no3pa)]–.
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- 2017
16. Supramolecular Luminescent Lanthanide Dimers for Fluoride Sequestering and Sensing
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Aline Nonat, Maryline Beyler, Katia Nchimi Nono, Loïc J. Charbonnière, Raphaël Tripier, Martín Regueiro-Figueroa, Tao Liu, Sarah Cianférani‐Sanglier, Carlos Platas-Iglesias, Franck Camerel, Olivier Jeannin, François Debaene, Département Sciences Analytiques et Interactions Ioniques et Biomoléculaires (DSA-IPHC), Institut Pluridisciplinaire Hubert Curien (IPHC), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Sciences et ingénierie en biologie santé (SCINBIOS), Université de Brest (UBO)-Institut National de la Santé et de la Recherche Médicale (INSERM), Departamento de Quimica Inorganica e Ingenieria Quimica (Cordoba, Spain), Universidad de Córdoba = University of Córdoba [Córdoba], Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Chimie, Electrochimie Moléculaires et Chimie Analytique (CEMCA), Université de Brest (UBO)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut Brestois Santé Agro Matière (IBSAM), Université de Brest (UBO), Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Institut National de la Santé et de la Recherche Médicale (INSERM)-Université de Brest (UBO), University of Córdoba [Córdoba], Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Institut Brestois Santé Agro Matière (IBSAM), and Université de Brest (UBO)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)
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Lanthanide ,Dimer ,Supramolecular chemistry ,chemistry.chemical_element ,Photochemistry ,010402 general chemistry ,Lanthanoid Series Elements ,01 natural sciences ,Chemistry Techniques, Analytical ,Catalysis ,Supramolecular assembly ,Fluorides ,chemistry.chemical_compound ,dimers ,Cyclen ,luminescence ,lanthanides ,Sequestering Agents ,sensing ,Luminescent Agents ,Molecular Structure ,fluoride ,[CHIM.ORGA]Chemical Sciences/Organic chemistry ,010405 organic chemistry ,Water ,General Chemistry ,[CHIM.MATE]Chemical Sciences/Material chemistry ,General Medicine ,0104 chemical sciences ,chemistry ,Luminescence ,Europium ,Dimerization ,Fluoride - Abstract
International audience; Lanthanide complexes (Ln=Eu, Tb, and Yb) that are based on a C2-symmetric cyclen scaffold were prepared and characterized. The addition of fluoride anions to aqueous solutions of the complexes resulted in the formation of dinuclear supramolecular compounds in which the anion is confined into the cavity that is formed by the two complexes. The supramolecular assembly process was monitored by UV/Vis absorption, luminescence, and NMR spectroscopy and high-resolution mass spectrometry. The X-ray crystal structure of the europium dimer revealed that the architecture of the scaffold is stabilized by synergistic effects of the Eu[BOND]F[BOND]Eu bridging motive, π stacking interactions, and a four-component hydrogen-bonding network, which control the assembly of the two [EuL] entities around the fluoride ion. The strong association in water allowed for the luminescence sensing of fluoride down to a detection limit of 24 nM.
- Published
- 2014
17. Radical-Cation Dimerization Overwhelms Inclusion in [n]Pseudorotaxanes
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Parastoo Dalvand, Thirumurugan Prakasam, Ali Trabolsi, Zouhair Asfari, Shaikha S. AlNeyadi, Selbi Nuryyeva, Albert C. Fahrenbach, Kuldeep Wadhwa, Carlos Platas-Iglesias, Mourad Elhabiri, John Carl Olsen, and Katia Nchimi-Nono
- Subjects
Models, Molecular ,Molecular switch ,Molecular Structure ,Rotaxanes ,Organic Chemistry ,Viologen ,General Chemistry ,Photochemistry ,Catalysis ,chemistry.chemical_compound ,Crystallography ,Monomer ,chemistry ,Radical ion ,Covalent bond ,Cations ,Intramolecular force ,medicine ,Molecule ,Dimerization ,Phosphazene ,medicine.drug - Abstract
Suppression of the dimerization of the viologen radical cation by cucurbit[7]uril (CB7) in water is a well-known phenomenon. Herein, two counter-examples are presented. Two viologen-containing thread molecules were designed, synthesized, and thoroughly characterized by (1)H DOSY NMR spectrometry, UV/Vis absorption spectrophotometry, square-wave voltammetry, and chronocoulometry: BV(4+), which contains two viologen subunits, and HV(12+), which contains six. In both threads, the viologen subunits are covalently bonded to a hexavalent phosphazene core. The corresponding [3]- and [7]pseudorotaxanes that form on complexation with CB7, that is, BV(4+)⊂(CB7)2 and HV(12+)⊂(CB7)6, were also analyzed. The properties of two monomeric control threads, namely, methyl viologen (MV(2+)) and benzyl methyl viologen (BMV(2+)), as well as their [2]pseudorotaxane complexes with CB7 (MV(2+)⊂CB7 and BMV(2+)⊂CB7) were also investigated. As expected, the control pseudorotaxanes remained intact after one-electron reduction of their viologen-recognition stations. In contrast, analogous reduction of BV(4+)⊂(CB7)2 and HV(12+)⊂(CB7)6 led to host-guest decomplexation and release of the free threads BV(2(·+)) and HV(6(·+)), respectively. (1)H DOSY NMR spectrometric and chronocoulometric measurements showed that BV(2(·+)) and HV(6(·+)) have larger diffusion coefficients than the corresponding [3]- and [7]pseudorotaxanes, and UV/Vis absorption studies provided evidence for intramolecular radical-cation dimerization. These results demonstrate that radical-cation dimerization, a relatively weak interaction, can be used as a driving force in novel molecular switches.
- Published
- 2014
18. Dual-Frequency Calcium-Responsive MRI Agents
- Author
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Goran Angelovski, Gisela E. Hagberg, Pascal Kadjane, Mathias Hoehn, Vincent Truffault, Philipp Boehm-Sturm, Nikos K. Logothetis, and Carlos Platas-Iglesias
- Subjects
Magnetic Resonance Spectroscopy ,Molecular Structure ,medicine.diagnostic_test ,Chemistry ,Organic Chemistry ,Contrast Media ,Magnetic resonance spectroscopic imaging ,chemistry.chemical_element ,Magnetic resonance imaging ,General Chemistry ,Calcium ,Magnetic Resonance Imaging ,Signal ,Catalysis ,Nuclear magnetic resonance ,medicine ,Dual frequency - Abstract
Responsive or smart magnetic resonance imaging (MRI) contrast agents are molecular sensors that alter the MRI signal upon changes in a particular parameter in their microenvironment. Consequently, they could be exploited for visualization of various biochemical events that take place at molecular and cellular levels. In this study, a set of dual-frequency calcium-responsive MRI agents are reported. These are paramagnetic, fluorine-containing complexes that produce remarkably high MRI signal changes at the (1)H and (19)F frequencies at varying Ca(2+) concentrations. The nature of the processes triggered by Ca(2+) was revealed, allowing a better understanding of these complex systems and their further improvement. The findings indicate that these double-frequency tracers hold great promise for development of novel functional MRI methods.
- Published
- 2014
19. Simultaneous Self-Assembly of a [2]Catenane, a Trefoil Knot, and a Solomon Link from a Simple Pair of Ligands
- Author
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François Debaene, Loïc J. Charbonnière, Thirumurugan Prakasam, Zouhair Asfari, John Carl Olsen, Mourad Elhabiri, Carlos Platas-Iglesias, Matteo Lusi, Ali Trabolsi, and Sarah Cianférani‐Sanglier
- Subjects
Models, Molecular ,Protein Folding ,Molecular Structure ,Chemistry ,Protein Conformation ,Catenane ,Catenanes ,Dynamic covalent chemistry ,General Chemistry ,General Medicine ,Ligands ,Catalysis ,Protein Structure, Secondary ,Crystallography ,Simple (abstract algebra) ,Self-assembly ,Link (knot theory) ,Trefoil knot - Abstract
A topological triptych: Three molecular links, a [2]catenane, a trefoil knot, and a Solomon link, were obtained in one pot through the self-assembly of two simple ligands in the presence of Zn(II). The approach relied on dynamic covalent chemistry and metal templation.
- Published
- 2013
20. Water exchange rates and mechanisms in tetrahedral [Be(H2O)4]2+ and [Li(H2O)4]+ complexes using DFT methods and cluster‐continuum models
- Author
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Carlos Platas-Iglesias, Laura Caneda-Martínez, Rosa Pujales-Paradela, Martín Regueiro-Figueroa, David Esteban-Gómez, and Andrés de Blas
- Subjects
Coordination sphere ,010405 organic chemistry ,Chemistry ,Coordination number ,Thermodynamics ,Water exchange ,Lithium ,010402 general chemistry ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Transition state ,0104 chemical sciences ,Ion ,Berylium ,Density functional calculations ,Computational chemistry ,Tetrahedron ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry - Abstract
[Abstract] The water exchange reactions in aquated Li+ and Be2+ ions were investigated with density functional theory calculations performed using the [Li(H2O)4]+·14H2O and [Be(H2O)4]2+·8H2O systems and a cluster‐continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five‐coordinated transition states responsible for the associative (A) or associative interchange (Ia) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted Iamechanism for the water exchange in [Be(H2O)4]2+·8H2O that gives an average residence time of water molecules in the first coordination sphere of 260 μs. For [Li(H2O)4]+·14H2O the water exchange reaction is predicted to follow an A mechanism with a residence time of inner‐sphere water molecules of 25 ps. Ministerio de Economía y Competitividad; CTQ2013‐43243‐P Ministerio de Economía y Competitividad; CTQ2015‐71211‐REDT
- Published
- 2016
21. Exceptionally inert lanthanide(III) PARACEST MRI contrast agents based on an 18-membered macrocyclic platform
- Author
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Paulo Pérez-Lourido, Rufina Bastida, Goretti Castro, Carlos Platas-Iglesias, Alejandro Macías, David Esteban-Gómez, Laura Valencia, and Martín Regueiro-Figueroa
- Subjects
Lanthanide ,Aqueous solution ,Chemistry ,Metal ions in aqueous solution ,Organic Chemistry ,Inorganic chemistry ,General Chemistry ,Crystal structure ,Nuclear magnetic resonance spectroscopy ,Catalysis ,Dissociation (chemistry) ,Crystallography ,NMR spectroscopy ,Lanthanides ,Proton NMR ,Macrocyclic ligand ,Macrocycles ,CEST ,MRI - Abstract
[Abstract] We report a macrocyclic ligand based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing four hydroxyethyl pendant arms (L1) that forms extraordinary inert complexes with Ln3+ ions. The [EuL1]3+ complex does not undergo dissociation in 1 M HCl over a period of months at room temperature. Furthermore, high concentrations of phosphate and Zn2+ ions at room temperature do not provoke metal-complex dissociation. The X-ray crystal structures of six Ln3+ complexes reveal ten coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and the four oxygen atoms of the hydroxyethyl pendant arms. The analysis of the Yb3+- and Pr3+-induced paramagnetic 1H NMR shifts show that the solid-state structures are retained in aqueous solution. The intensity of the 1H NMR signal of bulk water can be modulated by saturation of the signals of the hydroxy protons of Pr3+, Eu3+, and Yb3+ complexes following chemical-exchange saturation transfer (CEST). The ability of these complexes to provide large CEST effects at 25 and 37 °C and pH 7.4 was confirmed by using CEST magnetic resonance imaging experiments. Ministerio de Ciencia e Innovación; CTQ2011-24487 Ministerio de Economía y Competitividad; CTQ2013-43243-P
- Published
- 2015
22. The Solution Structure and Dynamics of MRI Probes Based on Lanthanide(III) DOTA as Investigated by DFT and NMR Spectroscopy
- Author
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Carlos Platas-Iglesias
- Subjects
Inorganic Chemistry ,Lanthanide ,Paramagnetism ,chemistry.chemical_compound ,Molecular geometry ,Cyclen ,Chemistry ,Computational chemistry ,Proton NMR ,DOTA ,Density functional theory ,Nuclear magnetic resonance spectroscopy - Abstract
Paramagnetic lanthanide(III) complexes stable in aqueous solutions have gained increasing interest in the recent years due to their importance as contrast agents in magnetic resonance imaging (MRI). Lanthanide(III) complexes with macrocyclic ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) are widely used for the design of MRI probes because of their high thermodynamic stability and kinetic inertness. The rational design of more efficient contrast agents requires a better understanding of the structure and dynamics of these systems in solution. This contribution reviews the work of the author and his collaborators on the solution structure and dynamics of lanthanide(III) complexes with different cyclen-based ligands and closely related systems. DFT calculations provide molecular geometries and relative energies of the different stereoisomers of these complexes in good agreement with the experimental data. The conformational analysis performed with the aid of density functional theory (DFT) calculations was validated with the investigation of the YbIII-induced 1H NMR paramagnetic shifts, which encode information on the position of the observed NMR nuclei with respect to the LnIII ion. Additionally, DFT calculations provide a better understanding of the dynamic processes responsible for the interconversion between the square-antiprismatic (SAP) and twisted-square-antiprismatic (TSAP) isomers of these complexes in solution, which might proceed through the inversion of the cyclen unit or the rotation of the pendant arms. The activation barriers obtained from theoretical calculations show a good agreement with the experimental values obtained from variable-temperature NMR spectroscopy. The work presented in this paper shows that DFT calculations in combination with NMR spectroscopy provide detailed information on the structure and dynamics of lanthanide(III) complexes at the molecular level and represent a powerful tool for the characterization of lanthanide(III) complexes relevant to the field of MRI contrast agents.
- Published
- 2011
23. Lead(II) Complexes of Lateral Macrobicyclic Receptors That Incorporate a Crown Moiety and a Pyridine Head Unit
- Author
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Andrés de Blas, Teresa Enríquez-Pérez, Marta Mato-Iglesias, Carlos Platas-Iglesias, Raquel Ferreirós-Martínez, David Esteban-Gómez, and Teresa Rodríguez-Blas
- Subjects
N,O ligands ,Cryptands ,Chemistry ,Ligand ,Stereochemistry ,Cryptand ,Protonation ,Crystal structure ,Crown Compounds ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Lead ,Intramolecular force ,Pyridine ,Moiety ,Macrocycles ,Crown compounds - Abstract
[Abstract] The coordinative properties towards lead(II) of two lateral macrobicyclic receptors that incorporate either a 1,10‐diaza‐[15]crown‐5 (L7) or a 4,13‐diaza‐[18]crown‐6 (L8) fragment are reported. Spectrophotometric titrations performed in acetonitrile solution indicate only the formation of mononuclear complexes in solution. The X‐ray crystal structures of the two receptors show that the conformation adopted by the ligand is imposed by the presence of intramolecular hydrogen‐bonding interactions that involve the secondary amine groups and the pivotal nitrogen atoms. The solid‐state structure of [Pb(L7)(NCS)](SCN)·0.5H2O shows that the metal ion is asymmetrically coordinated inside the macrobicyclic cavity. The PbII ion is coordinated to the nitrogen atom of the pyridine unit, the two secondary amine atoms, two oxygen atoms of the crown moiety, and a nitrogen atom of an isothiocyanate group. The distances between the PbII ion and the two pivotal nitrogen atoms as well as one of the oxygen atoms of the crown moiety are too long (>2.92 Å) to be considered unequivocal bonds, and should be regarded only as weak interactions. The protonation constants of L7 and L8 as well as the stability constants of their PbII complexes were investigated by using potentiometric titrations in 95 % methanol (I = 0.1 M, nBu4NClO4, 25 °C). The two receptors undergo two protonation processes in the pH range investigated (2.0 < pH < 12.0), which correspond to the protonation of the nitrogen atoms of the oxa–aza moiety. The log KPbL value obtained for L7 [9.906(1)] is approximately 1.1 log K units higher than the one determined for L8 [8.75(1)]. Xunta de Galicia; PGIDIT06TAM10301PR Xunta de Galicia; INCITE09E1R103013ES
- Published
- 2010
24. Structure and Dynamics of Lanthanide(III) Complexes with an N ‐Alkylated do3a Ligand (H 3 do3a = 1,4,7,10‐Tetraazacyclododecane‐1,4,7‐triacetic Acid): A Combined Experimental and DFT Study
- Author
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Andrés de Blas, Teresa Rodríguez-Blas, Martín Regueiro-Figueroa, Carlos Platas-Iglesias, and David Esteban-Gómez
- Subjects
Inorganic Chemistry ,Lanthanide ,chemistry.chemical_compound ,Crystallography ,Cyclen ,chemistry ,Stereochemistry ,Ligand ,Molecule ,DOTA ,Density functional theory ,Carboxylate ,Alkylation - Abstract
Lanthanide(III) complexes with 10-benzyl-1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane (H 3 L) have been investigated as model compounds of N-alkylated Ln III -do3a complexes (H 3 do3a = 1,4,3,10-tetraazacyclododecane-1,4,7-triacetic acid) with potential application in molecular imaging. The X-ray structures of the [{Ln(L)(H 2 O)} 2 ]·18H 2 O complexes (Ln = Eu or Tb) show that the metal ion is directly bound to the seven donor atoms of the ligand, with the nine-coordination sphere completed by an oxygen atom of an inner-sphere water molecule and an oxygen atom of a carboxylate group from a neighboring [Ln(L)] unit. This results in the formation of tetrameric units through the sharing of carboxylic groups between adjacent [Ln(L)(H 2 O)] complexes. Luminescence lifetime measurements recorded in H 2 O and D 2 O provide a number of coordinated water molecules (q) of 1.2, which indicates that the major species that exists in solution contains one inner-sphere water molecule. The conformational properties of the [Ln(L)(H 2 O)] complexes (Ln = Gd or Lu) have been investigated by using density functional theory (DFT) calculations (B3LYP model). Our results indicate that the Δ(λλλλ) conformation is more stable than the Δ(δδδδ) one for both complexes. The interconversion between these two isomers may proceed either through the inversion of the five-membered rings formed upon coordination of the 1,4,7,10-tetraazacyclododecane (cyclen) unit, or through the stepwise rotation of the three acetate pendant arms. According to our calculations, the activation free energy for the arm-rotation process (5.6 kcalmol -1 ) is much lower than that of the ring-inversion path (14.6 kcalmol -1 ), which in turn is very similar to those determined experimentally for Ln III (dota) complexes. Thus, a low energy barrier for the arm-rotation process appears to be responsible for the relatively fast isomer interconversion observed for Ln III (N-alkylated do3a) complexes.
- Published
- 2010
25. Towards Selective Recognition of Sialic Acid Through Simultaneous Binding to Its cis-Diol and Carboxylate Functions
- Author
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Teresa Rodríguez-Blas, Andrés de Blas, Carlos Platas-Iglesias, David Esteban-Gómez, Kristina Djanashvili, and Martín Regueiro-Figueroa
- Subjects
chemistry.chemical_classification ,Stereochemistry ,Chemistry ,Organic Chemistry ,Synthon ,Nitro compound ,Nuclear magnetic resonance spectroscopy ,Sialic acid ,chemistry.chemical_compound ,Thiourea ,Moiety ,Carboxylate ,Physical and Theoretical Chemistry ,Phenylboronic acid - Abstract
A series of receptors containing phenylboronic acid and urea or thiourea units have been designed for simultaneous recognition of the cis-diol and carboxylate functions of sialic acids, which are known to be overexpressed on the surfaces of tumor cells. The interaction of the receptors with 5-acetylneuraminic acid (Neu5Ac) and 2-α-O-methyl Neu5Ac (MeNeu5Ac) in DMSO solution has been investigated bymeans of spectrophotometric titrations and 1H, 13C, and 11B NMR spectroscopy. Additionally, we have also investigated the binding of these receptors with competing monosaccharides such as D-(+)-glucose, D-fructose, methyl α-D-galactoside, and methyl α-D-mannoside. Our results show that 2-{[3-(4-nitrophenyl)thioureido]methyl}phenylboronic acid (3a) recognizes both Neu5Ac and MeNeu5Ac with good selectivity with regard to the remaining monosaccharides investigated. DFT calculations performed at the B3LYP/6-31G(d) level show that this selectivity is due to a cooperative two-site binding of Neu5Ac through 1) ester formation by interaction at the phenylboronic acid function of the receptor and 2) hydrogen-bond interaction between the thiourea moiety and the carboxylate group of Neu5Ac. Compound 3a can therefore be considered a promising synthon for the design of contrast agents for magnetic resonance imaging of tumors. In contrast, the analogue of 3a containing a urea moiety – compound 3b – displays strong binding to all monosaccharides investigated, due to two-site binding through interaction on the phenylboronic acid function of the receptor and a hydrogen-bond interaction between the urea moiety and the sugar hydroxy groups.
- Published
- 2010
26. Solid‐State and Solution Structure of Lanthanide(III) Complexes with a Flexible Py‐N 6 Macrocyclic Ligand
- Author
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Laura Valencia, Cristina Núñez, Marta Mato-Iglesias, Rufina Bastida, Carlos Platas-Iglesias, Paulo Pérez-Lourido, and Alejandro Macías
- Subjects
Inorganic Chemistry ,Lanthanide ,Crystallography ,chemistry.chemical_compound ,Denticity ,Stereochemistry ,Chemistry ,Ligand ,Metal ions in aqueous solution ,Pyridine ,Density functional theory ,Macrocyclic ligand ,Acetonitrile - Abstract
Lanthanide complexes of a hexaaza macrocyclic ligand containing a pyridine head unit (L) were synthesized (Ln = La–Lu, except Pm). The solid-state structures of the corresponding La, Ce, Pr, Nd, and Lu complexes were determined by single-crystal X-ray crystallography, and they reveal the presence of three different mononuclear complexes with three different conformations of the macrocycle and coordination environments around the metal ions. In all complexes the lanthanide ion is coordinated in an endomacrocyclic manner to the six nitrogen donor atoms of the ligand. In the La, Ce, and Pr complexes the metal ions show a 12-coordinate mononuclear environment in which 3 nitrate anions coordinate in a bidentate fashion. However, in the Nd analogue the metal ion displays a 10-coordinated environment with the coordination of 2 bidentate nitrate groups, whereas Lu shows a 9-coordinate environment interacting with 2 nitrate ligands, one of them acting as bidentate and the second one coordinating in a monodentate fashion. The 1H and 13C NMR spectra of the complexes recorded in CD3CN suggest that the complexes adopt in solution a similar structure to that observed for the Nd complex in the solid state. The [Ln(L)(NO3)3] and [Ln(L)(NO3)2]+ complexes were characterized by density functional theory (DFT) calculations (B3LYP model). The structures obtained from these calculations for La, Ce, Pr, and Nd are in good agreement with the experimental solid-state structures. The relative stabilities of the [Ln(L)(NO3)2]+ complexes with respect to the [Ln(L)(NO3)3] ones (Ln = La, Nd, Gd, Ho, or Lu) were studied both in vacuo and in acetonitrile solution (PCM model) at the same computational level. Our calculations indicate that in solution the [Ln(L)(NO3)2]+ species is the most stable one along the whole lanthanide series, in agreement with the NMR spectroscopic data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
- Published
- 2009
27. Anion Coordination Effect on the Nuclearity of Co II , Ni II , Cu II , and Zn II Complexes with a Benzimidazole Pendant‐Armed Crown
- Author
-
Andrés de Blas, Lea Vaiana, Marta Mato-Iglesias, Carlos Platas-Iglesias, David Esteban-Gómez, and Teresa Rodríguez-Blas
- Subjects
chemistry.chemical_classification ,Metal ions in aqueous solution ,Inorganic chemistry ,Crown Compounds ,Inorganic Chemistry ,chemistry.chemical_compound ,Trigonal bipyramidal molecular geometry ,Crystallography ,Perchlorate ,chemistry ,Octahedral molecular geometry ,Counterion ,Acetonitrile ,Crown ether - Abstract
The study presented in this paper provides a rare example of a macrocyclic receptor allowing the formation of mono- or binuclear complexes on the same first-row transition-metal guest cation depending on the nature of the counterion present. Reaction of N,N′-bis(benzimidazol-2-ylmethyl)-4,13-diaza-18-crown-6 (L4) with CoII, NiII, CuII, or ZnII perchlorates leads to the formation of the expected mononuclear complexes with the metal ion showing a distorted octahedral coordination environment. In these complexes, the metal ion is placed at one end of the macrocyclic cavity, and two of the oxygen atoms of the crown ether moiety remain uncoordinated. 1H and 13C NMR spectroscopic studies on the diamagnetic [Zn(L4)]2+ complex indicate that the asymmetric coordination of the metal ion inside the macrocyclic cavity is maintained in acetonitrile solution, but translocation of the ZnII ion from one end of the macrobicyclic cavity to the second one occurs. However, reaction of L4 with CoII, NiII, or CuII perchlorates in the presence of chloride anions results in the formation of binuclear complexes where the metal ion is either five-coordinate in a distorted trigonal bipyramidal coordination environment (Co or Cu) or six-coordinate in a distorted octahedral geometry (Ni), and a chloride anion coordinates to each of the two metal ions in all cases. The ZnII ion behaves in a different way, and addition of chloride anions to the ZnII perchlorate in the presence of L4 does not lead to the formation of a binuclear complex. The formation of these binuclear systems was followed by spectrophotometric titrations of the mononuclear [M(L4)](ClO4)2 complexes with [nBu4N]Cl in acetonitrile solution indicating the formation of a [M2(L4)(Cl)]2+ intermediate species, followed by the formation of the binuclear complex [M2(L4)(Cl)2]2+ (M = Co, Ni, or Cu). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
- Published
- 2009
28. Metal Ion Complementarity: Effect of Ring‐Size Variation on the Conformation and Stability of Lead(II) and Cadmium(II) Complexes with Pendant‐Armed Crowns
- Author
-
Martín Regueiro-Figueroa, Andrés de Blas, David Esteban-Gómez, Carlos Platas-Iglesias, and Teresa Rodríguez-Blas
- Subjects
Conformational change ,Chemistry ,Inorganic chemistry ,Crystal structure ,Inorganic Chemistry ,Metal ,Ring size ,Crystallography ,chemistry.chemical_compound ,visual_art ,visual_art.visual_art_medium ,Titration ,Density functional theory ,Selectivity ,Acetonitrile - Abstract
The binding tendencies of the pendant-armed crown ethers L1–L3 [L1 = N,N′-bis(benzimidazol-2-ylmethyl)-1,7-diaza-12-crown-4, L2 = N,N′-bis(benzimidazol-2-ylmethyl)-1,10-diaza-15-crown-5) and L3 = N,N′-bis(benzimidazol-2-ylmethyl)-4,13-diaza-18-crown-6] towards PbII and CdII have been investigated. The X-ray crystal structure of [Cd(L3)](ClO4)2·EtOH shows that, in the solid state, the CdII ion is eight-coordinate and fits quite well into the crown hole, favouring an anti arrangement of the organic receptor. NMR measurements recorded in acetonitrile solution indicate that increasing the crown size induces a conformational change in the series of CdII complexes. The conformation goes from a syn arrangement for L1 to an anti arrangement for L3, passing through a syn [lrarr2] anti equilibrium in the complex derived from L2. On the contrary, no conformational change was observed for the corresponding PbII complexes, which have a syn conformation in all cases. These results have been confirmed by means of density functional theory (DFT) calculations performed by using the B3LYP model. The binding constants obtained from UV/Vis titration experiments in DMSO solution demonstrate that a decrease in the crown size provokes a 102-fold enhancement of the stability for this series of CdII complexes, whereas for PbII a gradual decrease of the binding constants is observed. Receptor L1 shows a certain degree of selectivity for CdII over PbII, with a selectivity factor > 102. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
- Published
- 2007
29. Effect of Protonation and Interaction with Anions on a Lead(II) Complex with a Lateral Macrobicycle Containing a Phenol Schiff‐Base Spacer
- Author
-
Andrés de Blas, Teresa Rodríguez-Blas, Fernando Avecilla, Carlos Platas-Iglesias, and David Esteban-Gómez
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Schiff base ,chemistry ,Hydrogen bond ,Imine ,Inorganic chemistry ,Protonation ,Chirality (chemistry) ,Acetonitrile ,Lone pair ,Coordination geometry - Abstract
The macrobicycle receptor L4, derived from 1,10-diaza-15-crown-5 incorporating a phenol Schiff-base spacer, forms stable complexes with lead(II). In [Pb(L4)(ClO4)](ClO4)·CH3CN (1), the lead(II) ion is asymmetrically placed at the one end of the macrobicyclic cavity, because of the intramolecular hydrogen bonding interaction that occurs between an imine nitrogen atom and the phenol group. This asymmetric position of the metal ion inside the macrobicyclic cavity induces chirality in this system. Variable temperature 1H NMR spectroscopic experiments indicate that the asymmetric coordination of the metal ion inside the macrocyclic cavity is maintained in acetonitrile solution, but a translocation of the PbII ion from one end of the macrobicyclic cavity to the second one occurs. This dynamic behaviour, which corresponds to the interconversion between the two possible enantiomeric forms of the complex, is fast on the NMR timescale at 320 K but slow at low temperatures, and we have estimated an activation barrier of ΔG‡ = 68 ± 2 kJ mol–1. We have also studied the effect of the protonation on 1 by NMR and UV/Vis spectroscopy in CH3CN solutions at room temperature, finding that diprotonation causes demetallation of the complex without receptor destruction, recovering L4 in its protonated form. On the other hand, the interaction of compound 1 with anions such as NO3– and SCN– has been evaluated by using spectrophotometric titrations in acetonitrile solution, finding log K values of 5.83(1) for NO3– and 6.27(2) forSCN–. The [Pb(L4)]2+, [Pb(L4)(NO3)]+, [Pb(L4)(NCS)]+ and [Pb(L4)(SCN)]+ systems were characterized by means of density functional theory calculations (DFT) performed by using the B3LYP model, and the coordination geometry as well as the role of the PbII lone pair has been investigated and discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
- Published
- 2007
30. Zeolite GdNaY Nanoparticles with Very High Relaxivity for Application as Contrast Agents in Magnetic Resonance Imaging
- Author
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Robert N. Muller, Carlos F. G. C. Geraldes, Luce Vander Elst, Carlos Platas-Iglesias, Wuzong Zhou, Joop A. Peters, and Thomas Maschmeyer
- Subjects
Aqueous solution ,Gadolinium ,Organic Chemistry ,Relaxation (NMR) ,Analytical chemistry ,Nanoparticle ,chemistry.chemical_element ,General Medicine ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Dispersion (geology) ,Catalysis ,Ion ,law.invention ,chemistry ,law ,Electron paramagnetic resonance ,Zeolite - Abstract
In this paper we explore Gd(3+)-doped zeolite NaY nanoparticles for their potential application as a contrast agent in magnetic resonance imaging (MRI). The nanoparticles have an average size of 80-100 nm, as determined by TEM and XRD. A powdered sample loaded with La3+ was characterised by means of multinuclear solid-state NMR spectroscopy. The NMR dispersion (NMRD) profiles obtained from aqueous suspensions of samples with Gd3+ doping ratios of 1.3-5.4 wt% were obtaining at different temperatures. The relaxivity increases drastically as the Gd3+ loading decreases, with values ranging between 11.4 and 37.7 s-1 mM-1 at 60 MHz and 37 degrees C. EPR spectra of aqueous suspensions of the samples suggest that an interaction between neighbouring Gd3+ ions within the same particle produces a significant increase in the transversal electronic relaxation rates in samples with a high Gd3+ content. The experimental NMRD and EPR data are explained with the use of a model that considers the system as a concentrated aqueous solution of Gd3+ in the interior of the zeolite that is in exchange with the bulk water outside the zeolite. The results obtained indicate that the Gd3+ ion is immobilised in the interior of the zeolite and that the relaxivity is mainly limited by the relatively slow diffusion of water protons from the pores of the zeolite channels into the bulk water.
- Published
- 2002
31. ChemInform Abstract: Full Control of the Regiospecific N-Functionalization of C-Functionalized Cyclam Bisaminal Derivatives [(V) and (VII)] and Application to the Synthesis of Their TETA (XIII), TE2A (XII), and CB-TE2A Analogues (XV)
- Author
-
Raphaël Tripier, Zakaria Halime, Hélène Bernard, Nathalie Camus, Nathalie Le Bris, and Carlos Platas-Iglesias
- Subjects
chemistry.chemical_compound ,Chemistry ,Cyclam ,Surface modification ,Organic chemistry ,General Medicine ,Condensation reaction ,Medicinal chemistry - Published
- 2014
32. Understanding stability trends along the lanthanide series
- Author
-
David Esteban-Gómez, Teresa Rodríguez-Blas, Carlos Platas-Iglesias, Martín Regueiro-Figueroa, and Andrés de Blas
- Subjects
Models, Molecular ,Lanthanide ,Computational chemistry ,Binding energy ,Ligands ,Lanthanoid Series Elements ,Catalysis ,Metal ,chemistry.chemical_compound ,Lanthanides ,Isostructural ,Methylene ,Molecular Structure ,Ligand ,Organic Chemistry ,General Chemistry ,Dipicolinic acid ,Bond length ,Ligand effects ,Density functional calculations ,chemistry ,visual_art ,visual_art.visual_art_medium ,Physical chemistry ,Complex stability - Abstract
[Abstract] The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA4− (H4TETA=2,2′,2′′,2′′′‐(1,4,8,11 tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetraacetic acid), BCAED4− (H4BCAED=2,2′,2′′,2′′′ {[(1,4‐diazepane‐1,4‐diyl)bis(ethane‐2,1‐diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C62− (H2BP18C6=6,6′‐[(1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐7,16 diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calculations. Geometry optimizations performed at the TPSSh/6‐31G(d,p) level, and using a 46+4fn ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the experimental values observed in the X‐ray structures. The contractions of the Ln3+ coordination spheres follow quadratic trends, as observed previously for different isostructural series of complexes. We show here that the parameters obtained from the quantitative analysis of these data can be used to rationalize the observed stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calculating the free energy for the reaction [La(L)]n+/−(sol)+Ln3+(sol)→[Ln(L)]n+/ (sol)+La3+(sol). A parameterization of the Ln3+ radii was performed by minimizing the differences between experimental and calculated standard hydration free energies. The calculated stability trends are in good agreement with the experimental stability constants, which increase markedly across the series for BCAED4−complexes, increase smoothly for the TETA4− analogues, and decrease in the case of BP18C62− complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the absolute values of hydration energies along the 4f period. Xunta de Galicia; CN2012/011
- Published
- 2014
33. High relaxivity Mn2+-based MRI contrast agents
- Author
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Mauro Botta, Andrés de Blas, Teresa Rodríguez-Blas, Gabriele A. Rolla, Martín Regueiro-Figueroa, David Esteban-Gómez, and Carlos Platas-Iglesias
- Subjects
NMR imaging ,Stereochemistry ,Serum albumin ,Contrast Media ,Plasma protein binding ,Catalysis ,Contrast agents ,Coordination complex ,chemistry.chemical_compound ,Coordination Complexes ,medicine ,Humans ,Molecule ,Methylene ,Serum Albumin ,chemistry.chemical_classification ,Manganese ,biology ,Chemistry ,Organic Chemistry ,Human serum albumin ,General Chemistry ,Dipicolinic acid ,Magnetic Resonance Imaging ,Solvent ,Crystallography ,biology.protein ,Coordination compounds ,Protein Binding ,medicine.drug - Abstract
[Abstract] Stable Mn2+ mono- and binuclear complexes containing pentadentate 6,6′-((methylazanediyl)bis(methylene)) dipicolinic acid coordinating units give remarkably high relaxivities due to the presence of two inner-sphere water molecules. The mononuclear derivative binds human serum albumin (HSA) with an association constant of 3372 M−1, which results in the replacement of the coordinated water molecules by donor atoms of protein residues. The dinuclear analogue also binds HSA while leaving one of the Mn2+ centres exposed to the solvent with two coordinated water molecules. Thus, this complex shows remarkably high relaxivities upon protein binding (39.0 mM−1 s−1 per Mn, at 20 MHz and 37 °C). Galicia. Consellería de Cultura, Educación e Ordenación Universitaria; EM 2012/088 Galicia. Consellería de Cultura, Educación e Ordenación Universitaria; CN 2012/011
- Published
- 2014
34. Determination of paramagnetic lanthanide(III) concentrations from bulk magnetic susceptibility shifts in NMR spectra
- Author
-
Daniele M. Corsi, Herman van Bekkum, Joop A. Peters, and Carlos Platas-Iglesias
- Subjects
Lanthanide ,NMR spectra database ,Paramagnetism ,Chemistry ,Chemical shift ,education ,Analytical chemistry ,Proton NMR ,Resonance ,General Materials Science ,General Chemistry ,Inductively coupled plasma ,Magnetic susceptibility - Abstract
The bulk magnetic susceptibility (BMS) shifts of 1H NMR resonance signals for inert reference compounds caused by the addition of paramagnetic lanthanide(III) compounds were exploited in order to determine lanthanide(III) concentrations in solution. The BMS shifts of an inert reference compound in the samples were measured by comparing the chemical shifts with those of an external reference. The concentration values obtained were in good agreement with results acquired from inductively coupled plasma analysis. Copyright © 2001 John Wiley & Sons, Ltd.
- Published
- 2001
35. Self‐aggregated dinuclear lanthanide(III) complexes as potential bimodal probes for magnetic resonance and optical imaging
- Author
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Teresa Rodríguez-Blas, Aline Nonat, Mauro Botta, Loïc J. Charbonnière, Gabriele A. Rolla, Andrés de Blas, David Esteban-Gómez, Carlos Platas-Iglesias, and Martín Regueiro-Figueroa
- Subjects
Lanthanide ,Tris ,Luminescence ,010405 organic chemistry ,Ligand ,Gadolinium ,Organic Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Crystallography ,Magnetic resonance imaging ,chemistry ,Europium ,Pyridine ,Lanthanides ,Hydroxymethyl - Abstract
[Abstract] Homodinuclear lanthanide complexes (Ln=La, Eu, Gd, Tb, Yb and Lu) derived from a bis‐macrocyclic ligand featuring two 2,2′,2′′‐(1,4,7,10‐tetraazacyclododecane‐1,4,7 triyl)triacetic acid chelating sites linked by a 2,6‐bis(pyrazol‐1‐yl)pyridine spacer (H2L3) were prepared and characterized. Luminescence lifetime measurements recorded on solutions of the EuIII and TbIII complexes indicate the presence of one inner‐sphere water molecule coordinated to each metal ion in these complexes. The overall luminescence quantum yields were determined (∅H2O=0.01 for [Eu2(L3)] and 0.50 for [Tb2(L3)] in 0.01 MTRIS/HCl, pH 7.4; TRIS=tris(hydroxymethyl)aminomethane), pointing to an effective sensitization of the metal ion by the bispyrazolylpyridyl unit of the ligand, especially with Tb. The nuclear magnetic relaxation dispersion (NMRD) profiles recorded for [Gd2(L3)] are characteristic of slowly tumbling systems, showing a low‐field plateau and a broad maximum around 30 MHz. This suggests the occurrence of aggregation of the complexes giving rise to slowly rotating species. A similar behavior is observed for the analogous GdIII complex containing a 4,4′ dimethyl‐2,2′‐bipyridyl spacer ([Gd2(L1)]). The relaxivity of [Gd2(L3)] recorded at 0.5 T and 298 K (pH 6.9) amounts to 13.7 mM−1 s−1. The formation of aggregates has been confirmed by dynamic light scattering (DLS) experiments, which provided mean particle sizes of 114 and 38 nm for [Gd2(L1)] and [Gd2(L3)], respectively. TEM images of [Gd2(L3)] indicate the formation of nearly spherical nanosized aggregates with a mean diameter of about 41 nm, together with some nonspherical particles with larger size. Ministerio de Educación y Ciencia; CTQ2009‐10721 Xunta de Galicia; IN845B‐2010/063
- Published
- 2013
36. Hyperfine coupling constants on inner‐sphere water molecules of GdIII‐based MRI contrast agents
- Author
-
Andrés de Blas, David Esteban-Gómez, Lothar Helm, Teresa Rodríguez-Blas, and Carlos Platas-Iglesias
- Subjects
Lanthanide ,Gadolinium DTPA ,Models, Molecular ,F‐group elements ,Contrast Media ,Model system ,Inner sphere electron transfer ,Ion ,chemistry.chemical_compound ,Hyperfine coupling ,Heterocyclic Compounds, 1-Ring ,Hyperfine couplings ,Computational chemistry ,Heterocyclic Compounds ,Lanthanides ,Organometallic Compounds ,MRI contrast agents ,DOTA ,Molecule ,Physical and Theoretical Chemistry ,Water ,Magnetic Resonance Imaging ,Atomic and Molecular Physics, and Optics ,Density functional calculations ,chemistry ,Physical chemistry ,Solvent effects - Abstract
[Abstract] Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner‐sphere water molecules of [Gd(H2O)8]3+ and different GdIII‐based magnetic resonance imaging contrast agents such as [Gd(DOTA)(H2O)]−, [Gd(DTPA)(H2O)]2−, [Gd(DTPA‐BMA)(H2O)] and [Gd(HP‐DO3A)(H2O)]. DFT calculations performed on the [Gd(H2O)8]3+ model system show that both hybrid‐GGA functionals (BH&HLYP, B3PW91 and PBE1PBE) and the hybrid meta‐GGA functional TPSSh provide 17O HFCCs in close agreement with the experimental data. The use of all‐electron relativistic approaches based on the DKH2 approximation and the use of relativistic effective core potentials (RECP) provide results of essentially the same quality. The accurate calculation of HFCCs on the [Gd(DOTA)(H2O)]−, [Gd(DTPA)(H2O)]2−, [Gd(DTPA‐BMA)(H2O)] and [Gd(HP‐DO3A)(H2O)] complexes requires an adequate description of solvent effects. This was achieved by using a mixed cluster/continuum approach that includes explicitly two second‐sphere water molecules. The calculated isotropic 17O HFCCs (Aiso) fall within the range 0.40–0.56 MHz, and show deviations from the corresponding experimental values typically lower than 0.05 MHz. The Aiso values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the GdIII ion, as well as by the orientation of the water molecule plane with respect to the Gd‐O vector. 1H HFCCs of coordinated water molecules and 17O HFCCs of second‐sphere water molecules take values close to zero. Ministerio de Educación y Ciencia; CTQ2009‐10721 Xunta de Galicia; IN845B‐2010/063
- Published
- 2012
37. ChemInform Abstract: The Solution Structure and Dynamics of MRI Probes Based on Lanthanide(III) DOTA as Investigated by DFT and NMR Spectroscopy
- Author
-
Carlos Platas-Iglesias
- Subjects
Lanthanide ,chemistry.chemical_compound ,Paramagnetism ,Molecular geometry ,Cyclen ,Chemistry ,Computational chemistry ,Proton NMR ,DOTA ,Density functional theory ,General Medicine ,Nuclear magnetic resonance spectroscopy - Abstract
Paramagnetic lanthanide(III) complexes stable in aqueous solutions have gained increasing interest in the recent years due to their importance as contrast agents in magnetic resonance imaging (MRI). Lanthanide(III) complexes with macrocyclic ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) are widely used for the design of MRI probes because of their high thermodynamic stability and kinetic inertness. The rational design of more efficient contrast agents requires a better understanding of the structure and dynamics of these systems in solution. This contribution reviews the work of the author and his collaborators on the solution structure and dynamics of lanthanide(III) complexes with different cyclen-based ligands and closely related systems. DFT calculations provide molecular geometries and relative energies of the different stereoisomers of these complexes in good agreement with the experimental data. The conformational analysis performed with the aid of density functional theory (DFT) calculations was validated with the investigation of the YbIII-induced 1H NMR paramagnetic shifts, which encode information on the position of the observed NMR nuclei with respect to the LnIII ion. Additionally, DFT calculations provide a better understanding of the dynamic processes responsible for the interconversion between the square-antiprismatic (SAP) and twisted-square-antiprismatic (TSAP) isomers of these complexes in solution, which might proceed through the inversion of the cyclen unit or the rotation of the pendant arms. The activation barriers obtained from theoretical calculations show a good agreement with the experimental values obtained from variable-temperature NMR spectroscopy. The work presented in this paper shows that DFT calculations in combination with NMR spectroscopy provide detailed information on the structure and dynamics of lanthanide(III) complexes at the molecular level and represent a powerful tool for the characterization of lanthanide(III) complexes relevant to the field of MRI contrast agents.
- Published
- 2012
38. Manganese‐Enhanced MRI Contrast Agents: From Small Chelates to Nanosized Hybrids The Development of Iron(II) Complexes as ParaCEST MRI Contrast Agents Lanthanide Complexes as Paramagnetic Probes for 19 F Magnetic Resonance The Solution Structure and Dynamics of MRI Probes Based on Lanthanide(III) DOTA as Investigated by DFT and NMR Spectroscopy (Eur. J. Inorg. Chem. 11/2012)
- Author
-
Delphine Felder-Flesch, Ilya Kuprov, David Parker, Carlos Platas-Iglesias, Marie Kueny-Stotz, and Janet R. Morrow
- Subjects
Lanthanide ,medicine.diagnostic_test ,Chemistry ,Magnetic resonance imaging ,Nuclear magnetic resonance spectroscopy ,Solution structure ,Inorganic Chemistry ,Paramagnetism ,chemistry.chemical_compound ,Nuclear magnetic resonance ,medicine ,DOTA ,Chelation ,Manganese enhanced mri - Published
- 2012
39. Definition of an intramolecular Eu‐to‐Eu energy transfer within a discrete [Eu2L] complex in solution
- Author
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Carlos Platas-Iglesias, Andrés de Blas, Loïc J. Charbonnière, Teresa Rodríguez-Blas, David Esteban-Gómez, Martín Regueiro-Figueroa, and Aline Nonat
- Subjects
Lanthanide ,Magnetic Resonance Spectroscopy ,Luminescence ,Metal ions in aqueous solution ,Analytical chemistry ,Ligands ,Lanthanoid Series Elements ,Catalysis ,Bipyridine ,chemistry.chemical_compound ,Macrocyclic ligands ,2,2'-Dipyridyl ,Europium ,Lanthanides ,Molecule ,Methylene ,Chemistry ,Ligand ,Organic Chemistry ,General Chemistry ,Solutions ,Crystallography ,Energy Transfer ,Energy transfer ,Intramolecular force ,Spectrophotometry, Ultraviolet ,Density functional theory - Abstract
[Abstract] Ligand L, based on two do3a moieties linked by the methylene groups of 6,6′‐dimethyl‐2,2′‐bipyridine, was synthesized and characterized. The addition of Ln salts to an aqueous solution of L (0.01 M Tris‐HCl, pH 7.4) led to the successive formation of [LnL] and [Ln2L] complexes, as evidenced by UV/Vis and fluorescence titration experiments. Homodinuclear [Ln2L] complexes (Ln=Eu, Gd, Tb, Yb, and Lu) were prepared and characterized. The 1H and 13C NMR spectra of the Lu and Yb complexes in D2O solution (pD=7.0) showed C1 symmetry of these species in solution, pointing to two different chemical environments for the two lanthanide cations. The analysis of the chemical shifts of the Yb complex indicated that the two coordination sites present square antiprismatic (SAP) coordination environments around the metal ions. The spectroscopic properties of the [Tb2L] complex upon ligand excitation revealed conventional behavior with τH2O=2.05(1) ms and ϕH2O=51 %, except for the calculation of the hydration number obtained from the luminescent lifetimes in H2O and D2O, which pointed to a non‐integer value of 0.6 water molecules per TbIII ion. In contrast, the Eu complex revealed surprising features such as: 1) the presence of two and up to five components in the 5D0→7F0 and 5D0→7F1 emission bands, respectively; 2) marked differences between the normalized spectra obtained in H2O and D2O solutions; and 3) unconventional temporal evolution of the luminescence intensity at certain wavelengths, the intensity profile first displaying a rising step before the occurrence of the expected decay. Additional spectroscopic experiments performed on [Gd2−xEuxL] complexes (x=0.1 and 1.9) confirmed the presence of two distinct Eu sites with hydration numbers of 0 (site I) and 2 (site II), and showed that the unconventional temporal evolution of the emission intensity is the result of an unprecedented intramolecular Eu‐to‐Eu energy-transfer process. A mathematical model was developed to interpret the experimental data, leading to energy‐transfer rates of 0.98 ms−1 for the transfer from the site with q=0 to that with q=2 and vice versa. Hartree–Fock (HF) and density functional theory (DFT) calculations performed at the B3LYP level were used to investigate the conformation of the complex in solution, and to estimate the intermetallic distance, which provided Förster radii (R0) values of 8.1 Å for the energy transfer from site I to site II, and 6.8 Å for the reverse energy transfer. These results represent the first evidence of an intramolecular energy‐transfer equilibrium between two identical lanthanide cations within a discrete molecular complex in solution. Ministerio de Educación y Ciencia; CTQ2009–10721 Xunta de Galicia; IN845B‐2010/063
- Published
- 2012
40. Macrocyclic receptor showing improved PbII/ZnII and PbII/CaII selectivities
- Author
-
Raquel Ferreirós-Martínez, Teresa Rodríguez-Blas, Carlos Platas-Iglesias, David Esteban-Gómez, and Andrés de Blas
- Subjects
Ligand ,Chemistry ,Metal ions in aqueous solution ,Inorganic chemistry ,Crystal structure ,Carbon-13 NMR ,Inorganic Chemistry ,NMR spectra database ,Crystallography ,Lead ,Proton NMR ,Selectivity ,Macrocycles ,Lone pair ,Coordination geometry ,Cadmium ,Crown compounds - Abstract
[Abstract] Herein we report on the macrocyclic receptor N,N′‐bis[(6‐carboxy‐2‐pyridyl)methyl]‐1,10‐diaza‐15‐crown‐5 (H2bp15c5) and its coordination properties towards ZnII, CdII, PbII, and CaII. The stability constants of these complexes determined by pH‐potentiometric titration at 25 °C in 0.1 M KNO3 vary in the following order: PbII > CdII >> ZnII > CaII. As a result, bp15c5 presents very important PbII/ZnII and PbII/CaII selectivities. These results are in contrast to those reported for the related receptor derived from 1,7‐diaza‐12‐crown‐4, which provides very similar complex stabilities for ZnII and PbII. The X‐ray crystal structure of [Cd(Hbp15c5)]+ shows heptadentate binding of the ligand to the metal ion, with two oxygen atoms of the macrocyclic unit remaining uncoordinated. The 1H NMR spectra of the complexes formed with PbII, ZnII, and CaII (D2O) show very broad peaks in the region 2–5 ppm, indicating an important degree of flexibility of the crownmoiety in these complexes. On the contrary, the 1H and 13C NMR spectra recorded for the CdII complex are well resolved and could be fully assigned. A detailed conformational investigation using theoretical calculations performed at the DFT (B3LYP) level predict a minimum energy conformation for [Cd(bp15c5)] that is very similar to that observed in the solid state. Analogous calculations performed on the [M(bp15c5)] (M = Zn or Pb) systems predict hexadentate binding of the ligand to these metal ions. In the case of the PbII complex our calculations indicate that the 6s lone pair is stereochemically active, which results in a hemidirected coordination geometry around the metal ion. The minimum energy conformations calculated for the ZnII, CdII, and PbII complexes are compatible with the experimental NMR spectra obtained in D2O solution. Xunta de Galicia; PGIDIT06TAM10301PR Xunta de Galicia; INCITE09E1R103013ES
- Published
- 2010
41. Receptor versus counterion: capability of N,N′‐Bis(2‐aminobenzyl)‐diazacrowns for giving endo‐ and/or exocyclic coordination of ZnII
- Author
-
David Esteban-Gómez, Teresa Rodríguez-Blas, Carlos Platas-Iglesias, Lea Vaiana, Fernando Avecilla, and Andrés de Blas
- Subjects
chemistry.chemical_classification ,Ionic radius ,Coordination sphere ,Ligand ,Inorganic chemistry ,chemistry.chemical_element ,Zinc ,Coordination modes ,Inorganic Chemistry ,chemistry.chemical_compound ,Perchlorate ,Crystallography ,Macrocyclic ligands ,Density functional calculations ,chemistry ,Transition metal ,Counterion ,Acetonitrile ,Crown compounds - Abstract
The structure of Zn II complexes with receptors L 1 and L 2 [L 1 = N,N'-bis(2-aminobenzyl)-1,10 -diaza-15-crown-5 and L 2 = N,N'-bis(2-aminobenzyl)-4,13-diaza-18-crown-6] was studied both in the solid state and in acetonitrile solution. Both receptors form mononuclear Zn II complexes in this solvent, while no evidence for the formation of dinuclear complexes was obtained. This is in contrast with previous investigations that demonstrated the formation of dinuclear complexes of L 2 with first-row transition metals such as Ni II , CO II and Cu II . Compounds of formula [Zn(L 1 )](ClO 4 ) 2 (1), [Zn(L 1 )](NO 3 ) 2 ·2CH 3 CN (2), [Zn(L 2 )](ClO 4 ) 2 (3) and [Zn(L 2 )-(NO 3 ) 2 ] (4) were isolated and structurally characterised by X-ray diffraction analyses. L 1 forms seven-coordinate Zn II complexes in the presence of both nitrate and perchlorate anions, as a consequence of the good fit between the macrocyclic cavity and the ionic radius of the metal ion. The Zn II ion is deeply buried into the receptor cavity and the anions are forced to remain out of the metal coordination sphere. The cation [Zn(L 1 )] 2+ present in 1 and 2 is one of the very few examples of seven-coordinate Zn complexes. Receptor L 2 provides a very rare example of a macrocyclic receptor allowing endocyclic and exocyclic coordination on the same guest cation, depending on the nature of the anion present. Thus, in 3 the Zn II ion is endocyclically coordinated, placed inside the crown hole coordinated to four donor atoms of the ligand in a distorted tetrahedral environment, whereas in 4, the presence of a strongly coordinating anion such as nitrate results in an exocyclic coordination of Zn II , which is directly bound only to the two primarily amine groups of L 2 and two nitrate ligands. Spectrophotometric titrations of [Zn(L 2 )] 2+ with tetrabutylammonium nitrate in acetonitrile solution demonstrate the stepwise formation of 1:1 and 1:2 adducts with this anion in acetonitrile solution. The [Zn(L 1 )] 2+ , [Zn(L 2 )] 2+ and [Zn(L 2 )(NO 3 ) 2 ] systems were characterised by means of DFT calculations (B3LYP model). The calculated geometries show an excellent agreement with the experimental structures obtained from X-ray diffraction analyses. Calculated binding energies of the macrocyclic ligands to Zn II are also consistent with the experimental data.
- Published
- 2007
42. Inside Cover: Simultaneous Self-Assembly of a [2]Catenane, a Trefoil Knot, and a Solomon Link from a Simple Pair of Ligands (Angew. Chem. Int. Ed. 38/2013)
- Author
-
Zouhair Asfari, Loïc J. Charbonnière, John-Carl Olsen, Thirumurugan Prakasam, Ali Trabolsi, Sarah Cianférani‐Sanglier, Carlos Platas-Iglesias, Mourad Elhabiri, Matteo Lusi, and François Debaene
- Subjects
Simple (abstract algebra) ,Chemistry ,Stereochemistry ,Catenane ,Cover (algebra) ,General Chemistry ,Self-assembly ,Link (knot theory) ,Catalysis ,Trefoil knot - Published
- 2013
43. Effect of Protonation and Interaction with Anions on a Lead(II) Complex with a Lateral Macrobicycle Containing a Phenol Schiff‐Base Spacer (Eur. J. Inorg. Chem. 12/2007)
- Author
-
Andrés de Blas, David Esteban-Gómez, Fernando Avecilla, Teresa Rodríguez-Blas, and Carlos Platas-Iglesias
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,Schiff base ,Research groups ,chemistry ,Computational chemistry ,Ligand ,Lead pollution ,Inorganic chemistry ,Phenol ,Protonation - Abstract
The cover picture shows a crown-based lateral macrobicycle designed by our research group as a potential ligand for PbII complexation. Lead is recognized worldwide as a serious environmental pollutant, and although it is a natural component of soil, water and vegetation, anthropogenic emissions have contributed to the dramatic increase in its level in the environment. The removal of lead from the environment and biological systems is the aim of many research groups. In particular, we are interested in the design of PbII-complexing agents based on crown frameworks. In this picture, the complexed PbII ion has been replaced by our beautiful but polluted blue planet. The cover picture symbolizes the need for innovative ideas to solve the problem of environmental lead pollution – one solution includes the design of selective complexing agents. Details are discussed in the article by A. de Blas, T. Rodr�guez-Blas et al. on p. 1635 ff.
- Published
- 2007
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