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Luminomagnetic composites have been synthesized that allow for an individual tuning of luminescence intensity, chromaticity and magnetization by combination of superparamagnetic, citrate‐stabilized iron oxide nanoparticles with the luminescent MOFs 3∞[Ln2(BDC)3(H2O)4] (Ln=Eu, Tb; BDC2−=terephthalate). The components are arranged to a concept of inverse structuring compared to previous luminomagnetic composites with MOF@magnetic particle (shell@core) composition so that the luminescent MOF now acts as core and is covered by magnetic nanoparticles forming the satellite shell. Thereby, the magnetic and photophysical properties are individually tuneable between high emission intensity (1.2 ⋅ 106 cps mg−1) plus low saturation magnetization (6 emu g−1) and the direct opposite (0.09 ⋅ 106 cps mg−1; 42 emu g−1) by adjusting the particle coverage of the MOF. This is not achievable with a core‐shell structure having a magnetic core and a dense MOF shell. The composition of the composites and the influence of different synthesis conditions on their properties were investigated by SEM/EDX, PXRD, magnetization measurements and photoluminescence spectroscopy.

Herein, we report on the successful creation of a luminescent micron-sized magnet.

Tuning the morphology of supraparticles can crucially influence their final properties and is, thus, important for their application in chemical, pharmaceutical, and food industries. The present study reveals how varied nanoparticle sizes, concentrations, and weight ratios in multicomponent dispersions influence the morphology of supraparticles assembled by these nanoparticle building blocks via spray‐drying. In a droplet containing monodisperse nanoparticles, smaller nanoparticles form a coherent elastic shell due to lower cohesive forces. As the solvent enclosed in the shell evaporates less easily due to the narrow pores between the nanoparticles, this ultimately results in rather non‐spherical supraparticles, while larger nanoparticles tend to yield spherical supraparticles. When small nanoparticles outweigh large ones in binary or trinary dispersions, the small nanoparticles form the outer shell that shrinks into a mushroom cap‐like shape upon drying of the spray‐droplet, while larger nanoparticles stay in the center of the droplet, resulting in non‐spherical supraparticles. Furthermore, the findings give a more systematic insight into structures that potentially arise from multimodal‐sized building blocks, thus, paving the way to tune the supraparticle morphology upon spray‐drying, when working with more complex, multicomponent dispersions.

International audience; We report a macrocyclic ligand (H) based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing three acetate pendant arms and a benzyl group attached to the fourth nitrogen atom of the macrocycle. The X-ray structures of the Y and Tb complexes reveal nine coordination of the ligand to the metal ions through the six nitrogen atoms of the macrocycle and three oxygen atoms of the carboxylate pendants. A combination of NMR spectroscopic studies (H, C, and Y) and DFT calculations indicated that the structure of the Y complex in the solid state is maintained in an aqueous solution. The detailed study of the emission spectra of the Eu and Tb complexes revealed Ln-centered emission with quantum yields of 7.0 and 60%, respectively. Emission lifetime measurements indicate that the ligand offers good protection of the metal ions from surrounding water molecules, preventing the coordination of water molecules. The Y complex is remarkably inert with respect to complex dissociation, with a lifetime of 1.7 h in 1 M HCl. On the other hand, complex formation is fast (∼1 min at pH 5.4, 2 × 10 M). Studies using the Y-nuclide confirmed fast radiolabeling since [Y]Y is nearly quantitatively formed (radiochemical yield (RCY) > 95) in a short time over a broad range of pH values from ca. 2.4 to 9.0. Challenging experiments in the presence of excess ethylenediaminetetraacetic acid (EDTA) and in human serum revealed good stability of the [Y]Y complex. All of these experiments combined suggest the potential application of H derivatives as Y-based radiopharmaceuticals.

We report a macrocyclic ligand (H

We present a detailed study of the lanthanide(III) complexes with cyclen-based ligands containing phenylacetamide pendants that incorporate CF3 group(s) at different distances from the metal ion. The complexes exhibit square-antiprismatic coordination in solution, as demonstrated by analysis of the Yb3+-induced paramagnetic shifts and the X-ray structure of the [YbL3] complex. Luminescence lifetime measurements and a detailed 1H and 17O relaxometric characterization confirmed the presence of an inner-sphere H2O molecule. The Tm3+ complexes provide chemical-exchange saturation-transfer response upon saturation at the frequency of the amide protons. A 19F relaxation study provided accurate estimates of the Ln···F distances that were used to rationalize the efficiency of the complexes as 19F magnetic resonance imaging (MRI) probes, which was tested in vitro using MRI phantom studies.

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.

Two macrocyclic triamide octadentate chelator scaffolds L1 and L2 were synthesized, characterized by several spectroscopic techniques, and their pKa values were determined by potentiometric titration. Using these ligands, two water soluble paramagnetic Eu(III) complexes, [EuL1(OH2)](NO3)3·H2O (EuL1) and [EuL2(OH2)](NO3)3·H2O (EuL2) were synthesized and characterized in the solid state and in solution. Single crystal X ray diffraction measurement of [EuL1(OH2)](NO3)3.H2O (EuL1) reveals octadentate binding of the ligand to Eu(III) and ninth coordination being completed by an oxygen atom of a solvent molecule (H2O). X-ray diffraction data of [EuL2(OH2)](NO3)3·H2O (EuL2) were severely disordered and hence its chloride analogue [EuL2(DMF)]Cl3·H2OMeOH (EuL2-Cl) was synthesized and characterized using single-crystal X-ray diffraction measurements. The crystal data of [EuL2(DMF)](Cl)3·H2OMeOH (EuL2-Cl) reveal octadentate binding of the ligand to Eu(III), with the ninth coordination being completed by an oxygen atom of a solvent molecule (DMF). Luminescence measurements confirm the presence of a water molecule coordinated to Eu(III) in aqueous solution. The stability of the Eu(III) complexes was investigated using spectrophotometric molar ratio method. Cyclic voltammetry studies obtained from aqueous solutions of the Eu(III) complexes show reversible one electron reduction processes at the glassy carbon electrode with E1/2 = −0.799 V and −0.777 V (versus Ag/AgCl) for the complexes of L1 and L2. © 2018 Elsevier B.V.

We report a series of pentadentate ligands based on a 1,4,7-triazacyclononane-1,4-diacetic acid (H2NO2A) containing different substituents attached to the third nitrogen atom of the macrocyclic unit. Detailed 1H Nuclear Magnetic Relaxation Dispersion (NMRD) characterisation of the corresponding Mn2+ complexes suggests the formation of six-coordinate species in solution containing an inner-sphere water molecule. This was confirmed by recording the transverse 17O relaxation time and chemical shift measurements. The water exchange rate of the coordinated water molecule was found to be strongly influenced by the nature of the substituent R at position 7 of the triazacyclononane unit (R = Me, k298ex = 62.6 × 107 s-1; R = Bz, k298ex = 4.4 × 107 s-1; R = 1-phenylethyl, k298ex = 2.6 × 107 s-1). The decreasing exchange rates are explained by the increasing bulkiness of the substituent, which hinders the approach of the entering water molecule in an associatively activated water exchange mechanism. This is supported by DFT calculations (M062X/TZVP), which confirm the associative nature of the water exchange reaction. A potentially decadentate ligand containing two NO2A units linked by a xylenyl spacer in the meta position was also synthesised. The corresponding binuclear Mn2+ complex contains two metal ions with different hydration numbers, as evidenced by 1H NMRD and 17O NMR measurements. DFT calculations show that this is related to the presence of a bridging bidentate μ-η1-carboxylate group connecting the two metal centers. The results reported in this work provide a straightforward strategy to control the exchange rate of the coordinated water molecule in this family of MRI contrast agent candidates.

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(III) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(III) ions thanks to μ2–η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(III) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(III) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(III) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (e = 8770 M−1 cm−1) that was attributed to the Bi(III)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl−, Br−, I− and N3−, respectively.

International audience; We report a detailed study of the thermodynamic stability and dissociation kinetics of lanthanide complexes with two ligands containing a cyclen unit, a methyl group, a picolinate arm, and two acetate pendant arms linked to two nitrogen atoms of the macrocycle in either cis (1,4-H3DO2APA) or trans (1,7-H3DO2APA) positions. The stability constants of the Gd3+ complexes with these two ligands are very similar, with log KGdL values of 16.98 and 16.33 for the complexes of 1,4-H3DO2APA and 1,7-H3DO2APA, respectively. The stability constants of complexes with 1,4-H3DO2APA follow the usual trend, increasing from log KLaL = 15.96 to log KLuL = 19.21. However, the stability of [Ln(1,7-DO2APA)] complexes decreases from log K = 16.33 for Gd3+ to 14.24 for Lu3+. The acid-catalyzed dissociation rates of the Gd3+ complexes differ by a factor of ∼15, with rate constants (k1) of 1.42 and 23.5 M–1 s–1 for [Gd(1,4-DO2APA)] and [Gd(1,7-DO2APA)], respectively. This difference is magnified across the lanthanide series to reach a 5 orders of magnitude higher k1 for [Yb(1,7-DO2APA)] (1475 M–1 s–1) than for [Yb(1,4-DO2APA)] (5.79 × 10–3 M–1 s–1). The acid-catalyzed mechanism involves the protonation of a carboxylate group, followed by a cascade of proton-transfer events that result in the protonation of a nitrogen atom of the cyclen unit. Density functional theory calculations suggest a correlation between the strength of the Ln–Ocarboxylate bonds and the kinetic inertness of the complex, with stronger bonds providing more inert complexes. The 1H NMR resonance of the coordinated water molecule in the [Yb(1,7-DO2APA)] complex at 176 ppm provides a sizable chemical exchange saturation transfer effect thanks to a slow water exchange rate of (15.9 ± 1.6) × 103 s–1.; L'arrangement des atomes donneurs de ligand autour de l'ion lanthanide provoque des différences dramatiques dans les stabilités thermodynamiques et la cinétique de dissociation des complexes de lanthanides, comme le démontre l'étude des complexes avec deux ligands à base de régioisomères du cyclen, contenant un bras picolinate et deux bras acétate soit en position 1,7 ou 1,4 de la structure macrocyclique.

We present a detailed study of the lanthanide(III) complexes with cyclen-based ligands containing phenylacetamide pendants that incorporate CF

Reinforced cross-bridged Ni2+-cyclam complexes were functionalised with pendant arms containing both amide protons and CF3 groups that lead to a dual 1H/19F response. The resulting complexes possess very high inertness favourable for MRI applications. The paramagnetism of the Ni2+ ion shifts the amide resonance 56 ppm away from bulk water favouring the chemical exchange saturation transfer (CEST) effect and shortening the acquisition times in 19F magnetic resonance imaging (MRI) experiments, thus enhancing the signal-to-noise ratios compared to the fluorinated diamagnetic reference.

Reinforced cross-bridged Ni2+-cyclam complexes were functionalised with pendant arms containing both amide protons and CF3 groups that lead to a dual 1H/19F response. The resulting complexes possess very high inertness favourable for MRI applications. The paramagnetism of the Ni2+ ion shifts the amide resonance 56 ppm away from bulk water favouring the chemical exchange saturation transfer (CEST) effect and shortening the acquisition times in 19F magnetic resonance imaging (MRI) experiments, thus enhancing the signal-to-noise ratios compared to the fluorinated diamagnetic reference.

We report a series of pentadentate ligands based on a 1,4,7-triazacyclononane-1,4-diacetic acid (H2NO2A) containing different substituents attached to the third nitrogen atom of the macrocyclic unit. Detailed 1H Nuclear Magnetic Relaxation Dispersion (NMRD) characterisation of the corresponding Mn2+ complexes suggests the formation of six-coordinate species in solution containing an inner-sphere water molecule. This was confirmed by recording the transverse 17O relaxation time and chemical shift measurements. The water exchange rate of the coordinated water molecule was found to be strongly influenced by the nature of the substituent R at position 7 of the triazacyclononane unit (R = Me, k298ex = 62.6 × 107 s-1; R = Bz, k298ex = 4.4 × 107 s-1; R = 1-phenylethyl, k298ex = 2.6 × 107 s-1). The decreasing exchange rates are explained by the increasing bulkiness of the substituent, which hinders the approach of the entering water molecule in an associatively activated water exchange mechanism. This is supported by DFT calculations (M062X/TZVP), which confirm the associative nature of the water exchange reaction. A potentially decadentate ligand containing two NO2A units linked by a xylenyl spacer in the meta position was also synthesised. The corresponding binuclear Mn2+ complex contains two metal ions with different hydration numbers, as evidenced by 1H NMRD and 17O NMR measurements. DFT calculations show that this is related to the presence of a bridging bidentate μ-η1-carboxylate group connecting the two metal centers. The results reported in this work provide a straightforward strategy to control the exchange rate of the coordinated water molecule in this family of MRI contrast agent candidates.

The indispensable transformation to a (more) sustainable human society on this planet heavily relies on innovative technologies and advanced materials. The merits of nanoparticles (NPs) in this context are demonstrated widely during the last decades. Yet, it is believed that the impact of particle‐based nanomaterials to sustainability can be even further enhanced: taking NPs as building blocks enables the creation of more complex entities, so‐called supraparticles (SPs). Due to their evolving phenomena coupling, emergence, and colocalization, SPs enable completely new material functionalities. These new functionalities in SPs can be utilized to render six fields, essential to human life as it is conceived, more sustainable. These fields, selected based on an entropy‐rate‐related definition of sustainability, are as follows: 1) purification technologies and 2) agricultural delivery systems secure humans “fundamental needs.” 3) Energy storage and conversion, as well as 4) catalysis enable the “basic comfort.” 5) Extending materials lifetime and 6) bringing materials back in use ensure sustaining “modern life comfort.” In this review article, a perspective is provided on why and how the properties of SPs, and not simply properties of individual NPs or conventional bulk materials, may grant attractive alternative pathways in these fields.

[Abstract] We have reported here a series of ligands containing pentadentate 6,6′-(azanediylbis(methylene))dipicolinic acid units that differ in the substituent present at the amine nitrogen atom (acetate: H3DPAAA; phenyl: H2DPAPhA; dodecyl: H2DPAC12A; 4-hexylphenyl: H2DPAC6PhA). The protonation constants of the hexadentate DPAAA3− and pentadentate DPAPhA2−ligands and the stability constants of their Mn2+ complexes were determined using pH-potentiometry (25 °C, 0.15 M NaCl). The mono-hydrated [Mn(DPAAA)]− complex (logKMnL = 13.19(5)) was found to be considerably more stable than the bis-hydrated [Mn(DPAPhA)] analogue (logKMnL = 9.55(1)). A detailed 1H and 17O NMR relaxometric study was carried out to determine the parameters that govern the proton relaxivities of these complexes. The [Mn(DPAC12A)] complex, which contains a dodecyl lipophilic chain, forms micelles in solution characterized by a critical micellar concentration (cmc) of 96(9) μM. The lipophilic [Mn(DPAC6PhA)] and [Mn(DPAC12A)] derivatives form rather strong adducts with Human Serum Albumin (HSA) with association constants of 7.1 ± 0.1 × 103 and 1.3 ± 0.4 × 105 M−1, respectively. The X-ray structure of the complex {K(H2O)4}{[Mn(DPAAA)(H2O)]}2 shows that the Mn2+ ion in [Mn(DPAAA)]− is coordinated to the six donor atoms of the ligand, a coordinated water molecule completing the pentagonal bipyramidal coordination environment. Ministerio de Economía y Competitividad; CTQ2015-71211-REDT Ministerio de Economía y Competitividad; CTQ2016-76756-P

We present two novel octadentate cyclen-based ligands bearing one (L

[Abstract] We report a pentadentate ligand containing a 2,2′-azanediyldiacetic acid moiety functionalized with a picolinate group at the nitrogen atom (H3paada), as well as a lipophylic derivative functionalized with a dodecyloxy group at position 4 of the pyridyl ring (H3C12Opaada). The protonation constants of the paada3− ligand and the stability constant of the Mn(II) complex were determined using a combination of potentiometric and spectrophotometric titrations (25 °C, 0.15 M NaCl). A detailed relaxometric characterisation was accomplished by recording 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O chemical shifts and relaxation rates. These studies provide detailed information on the microscopic parameters that control their efficiency as relaxation agents in vitro. For the sake of completeness and to facilitate comparison, we also characterised the related [Mn(nta)]− complex (nta = nitrilotriacetate). Both the [Mn(paada)]− and [Mn(nta)]− complexes turned out to contain two inner-sphere water molecules in aqueous solution. The exchange rate of these coordinated water molecules was slower in [Mn(paada)]− (k298ex = 90 × 107 s−1) than in [Mn(nta)]− (k298ex = 280 × 107 s−1). The complexes were also characterised using both DFT (TPSSh/def2–TZVP) and ab initio CAS(5,5) calculations. The lipophylic [Mn(C12Opaada)]− complex forms micelles in solution characterised by a critical micellar concentration (cmc) of 0.31 ± 0.01 mM. This complex also forms a rather strong adduct with Bovine Serum Albumin (BSA) with an association constant of 5.5 × 104 M−1 at 25 °C. The enthalpy and entropy changes obtained for the formation of the adduct indicate that the binding event is driven by hydrophobic interactions. Authors R. P.-P., I. B., E. I., C. P.-I. and D. E.-G. thank Ministerio de Economía y Competitividad (CTQ2016-76756-P) and Xunta de Galicia (ED431B 2017/59 and ED431D 2017/01) for generous financial support and Centro de Supercomputación of Galicia (CESGA) for providing the computer facilities. R. P.-P. thanks Ministerio de Economía y Competitividad for a PhD FPI grant (BES-2014-068399) and a fellowship for a short term stay in Alessandria (EEBB-I-18-13075). R. U.-V. thanks Xunta de Galicia for a PhD grant (ED481A-2018/314). M.B. and F.C. are grateful to Università del Piemonte Orientale for financial support (Ricerca locale 2016). This work was carried out within the framework of the COST CA15209 Action “European Network on NMR Relaxometry” Xunta de Galicia; ED431B 2017/59 Xunta de Galicia; ED431D 2017/01 Xunta de Galicia; ED481A-2018/314

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(iii) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(iii) ions thanks to μ2-η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(iii) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(iii) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(iii) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (ε = 8770 M-1 cm-1) that was attributed to the Bi(iii)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl-, Br-, I- and N3-, respectively.

We have reported here a series of ligands containing pentadentate 6,6'-(azanediylbis(methylene))dipicolinic acid units that differ in the substituent present at the amine nitrogen atom (acetate: H

Transition metal ions such as MnII and FeIII can also be exploited in the design of efficient T1 contrast agents. This chapter investigates the differences and similarities between GdIII and transition metal complexes with respect to their application as MRI contrast agents. The significance and determination of the magnetic moments of paramagnetic complexes and of the number of inner-sphere water molecules (q) in transition metal complexes are described.

[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