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Focusing on the pertinent research on dual activity (as probes and cancer inhibitors), two novel Eu and Tb lanthanide complexes were prepared in this work alongside their binuclear counterparts holding Cu as the secondary metal. Complexes that did not contain copper were found to be less effective in promoting cancer cell death, in contrast to their bimetallic counterparts, which could function as inhibiting molecules while sequestering Cu from the tumoral environment. The ANOVA test results showed that, for A549 cells, the Eu complexes didn’t present relevant differences, whereas the results for their Tb counterparts were confirmed as being different. All complexes were structurally characterized by using high-resolution mass spectrometry, vibrational, electronic and fluorescence spectroscopy. TD-DFT calculations were carried out to assess the nature of the electronic transitions and ANOVA test to evaluate whether each pair of complexes was similar concerning their activity on the cell lines (null hypothesis). Data showed that the mononuclear Eu and Tb complexes had, as expected, fluorescent properties while their binuclear counterparts (holding Cu) did not. The mononuclear complexes were titrated with Cu2+ confirming their ability to sequester the latter in a tumor microenvironment. All synthesized compounds were pH responsive, although they maintained their structures in the physiological pH range and were investigated in cell viability tests with HeLa (breast) and A549 (lung adenocarcinoma) cancer cell lines towards assessing how they induce cell death. Overall, this work showed that these complexes could play an important role as bioprobes as well as anticancer agents published

In this work, we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study demonstrated that polar and apolar aprotic solvents modulated the reactions in different ways. Experimental data showed that acetonitrile (aprotic polar) could largely hinder the reaction rate, whereas toluene (aprotic apolar) did not. In both cases, product selectivity at isoconversion was not affected. Further insights were obtained by means of neutron diffraction experiments, which confirmed the kinetic data and allowed for the proposal of a model based on substrate–solvent crosstalk by means of hydrogen bonding. In addition, the model was also validated in the ring-opening reaction (overoxidation) of styrene oxide to benzaldehyde, which progressed when toluene was the solvent (reaching 31% styrene oxide conversion) but was strongly hindered when acetonitrile was used instead (reaching only 7% conversion) due to the establishment of H-bonds in the latter. Although this model was confirmed and validated for olefin oxidation reactions, it can be envisaged that it may also be applied to other catalytic reaction systems where reaction control is critical, thereby widening its use.

Fish fraud is a problematic issue for the industry. For it to be properly addressed will require the use of accurate, rapid, and cost-effective tools. In this work, near infrared reflectance spectroscopy (NIRS) was used to predict nutritional values (protein, lipids, and moisture) as well as to discriminate between sources (farmed vs. wild fish) and conditions (fresh or defrosted fish). Samples of five whitefish species—Alaskan pollock (Gadus chalcogrammu), Atlantic cod (G. morhua), European plaice (Pleuronectes platessa), common sole (Solea solea), and turbot (Psetta maxima)—including farmed, wild, fresh, and frozen ones, were scanned by a low-cost handheld near infrared reflectance spectrometer with a spectral range between 900 and 1700 nm. Several machine learning algorithms were explored for both regression and classification tasks, achieving precisions and coefficients of determination higher than 88% and 0.78, respectively. Principal component analysis (PCA) was used to cluster samples according to classes where good linear discriminations were denoted. Loadings from PCA revealed bands at 1150, 1200, and 1400 nm as the most discriminative spectral regions regarding classification of both source and condition, suggesting the absorbance of OH, CH, CH2, and CH3 groups as the most important ones. This study shows the use of NIRS and both linear and non-linear learners as a suitable strategy to address fish fraud and fish QC.

The dynamics of 2-methoxybenzaldehyde, 4-methoxybenzaldehyde, and 4-ethoxybenzaldehyde in the solid state are assessed through INS spectroscopy combined with periodic DFT calculations. In the absence of experimental data for 4-ethoxybenzaldehyde, a tentative crystal structure, based on its similarity with 4-methoxybenzaldehyde, is considered and evaluated. The excellent agreement between calculated and experimental spectra allows a confident assignment of the vibrational modes. Several spectral features in the INS spectra are unambiguously assigned and torsional potential barriers for the methyl groups are derived from experimental frequencies. The intramolecular nature of the potential energy barrier for methyl rotation about O– CH3 bonds compares with the one reported for torsion about saturated C–CH3 bonds. On the other hand, the intermolecular contribution to the potential energy barrier may represent 1/3 of the barrier height in these systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Fucus vesiculosus is a brown macroalgae used in food and generally considered safe to be consumed, according to EU Directive (EC 258/97). The aim of this study is to analyze the effect of food preparation on F.vesiculosus of different origins on what concerns its chemical constituents and final bioactivities. The aqueous extract of the seaweeds were obtained at different temperatures, similar to food preparation and then purified by SPE. The compound identification was carried out by Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS/MS) and algae extracts microstructure were observed by Scanning Electron Microscopy (SEM). The activities were determined by using antioxidant activity, inhibition of acetylcholinesterase (AChE) and 3-hidroxi-3-methyl-glutaril-CoA (HMG-CoA) reductase (HMGR) together with Caco-2 cells line simulating the intestinal barrier. The activity of AChE and the HMGR were inhibited by the extracts giving IC50 values of 15.0 &plusmn, 0.1 &micro, g/mL and 4.2 &plusmn, g/mL, respectively and 45% of the cholesterol permeation inhibition. The main compounds identified were phlorotannins and peptides derivatives. The mode of preparation significantly influenced the final bioactivities. Moreover, the in vitro results suggest that the preparation of F. vesiculosus as a soup could have hypercholesterolemia lowering effect.

This work presents a comprehensive spectroscopic analysis of crystalline isoniazid, one of the main drugs in tuberculosis chemotherapy, using a blend of spectroscopic and computational methods. Mid- and far-infrared, Raman, and inelastic neutron scattering spectroscopies, with contribution of isotopic substitution are combined with discrete and periodic DFT quantum chemical calculations. This combined approach successfully reproduces the whole spectral range, allowing a sound assignment of all the vibrational bands. Previous misassignments have been corrected and several spectral features of isoniazid crystal are reported for the first time. Virtues and limitations of the computational approach (periodic and discrete) are also discussed in light of the present state-of-the-art in the field.

Au nanoparticles (AuNPs) were immobilized on S-containing amino acids (cysteine and methionine) Mg/Al hydrotalcite clay in both bulk and exfoliated (colloidal) forms. The Au nanoparticles were prepared by a biomimetic method using an anti-oxidant tea extract to reduce the Au salt solution. The performance of bulk and exfoliated clays with Au nanoparticles in aerobic olefin epoxidation was assessed with very interesting results. Both catalysts were very active towards the epoxide products; selectivity was found to be dependent on the catalyst form. The exfoliated catalysts yielded higher product stereoselectivity in the case of limonene epoxidation. These results can be explained by the existence of a confined environment around the AuNPs structures provided by the clay nanosheets wrapping the nanoparticles, modulating how substrates interact with the catalytic active centres. Based on experimental data mechanistic proposals were also rationalized for these catalysts showing how they assist the catalytic process.

The structure and dynamics of crystalline 4-(dimethylamino) benzaldehyde, 4DMAB, are assessed through INS spectroscopy combined with periodic DFT calculations. The excellent agreement between experimental and calculated spectra is the basis for a reliable assignment of INS bands. The external phonon modes of crystalline 4DMAB are quite well described by the simulated spectrum, as well as the modes involving low-frequency molecular vibrations. Crystal field splitting is predicted and observed for the modes assigned to the dimethylamino group. Concerning the torsional motion of methyl groups, four individual bands are identified and assigned to specific methyl groups in the asymmetric unit. The torsional frequencies of the four methyl groups in the asymmetric unit fall in a region of ca. 190 ± 20 cm−1, close to the range of values observed for methyl groups bonding to unsaturated carbon atoms. The hybridization state of the X atom in X-CH3 seems to play a key role in determining the methyl torsional frequency.

Undaria pinnatifida is a brown alga, largely used as food in oriental countries. The purpose of this work was to analyze several bioactivities that might be present in different food preparations, relating them with the compounds present in the extracts. Aqueous extracts cooked, like a soup, as well as used in a salad, by simulating U. pinnatifida digestion with pancreatin were prepared. The soup preparation had anti-acetylcholinesterase activity as well as 3-hydroxy3-methyl-glutaryl coenzyme A reductase inhibition capacity, the use of 1 mg/mL, for both enzymes, caused 50% enzyme activity inhibition. The extracts produced changes in HepG2 cell proteome, mainly in the 148 kDa proteins. U. pinnatifida in salads hardly released phlorotannins to the digestive tract. The in vitro studies suggested that a soup prepared from this seaweed could deliver bioactive compounds, phlorotannins and small peptides that may facilitate the gastro-intestinal motility and reduce the cholesterol biosynthesis. info:eu-repo/semantics/publishedVersion

Layered double hydroxides (LDHs) have attracted attention as green materials due to their catalytic ability in benign aqueous solvents. We here demonstrate the synthesis of colloidal Co–Al LDH nanoclusters with an average size of

A Co/Al layered double hydroxide material was synthesized in both bulk and exfoliated (colloidal) forms. Anion exchange with methionine allowed immobilization of Au nanoparticles previously prepared by a biomimetic method using an anti-oxidant tea aqueous extract to reduce the Au salt solution. The catalytic performance of bulk and exfoliated clays Au-hybrid materials was assessed in aerobic olefin epoxidation. Both catalysts were very active towards the epoxide products and with very interesting substrate conversion levels after 80 h reaction time. The Au-exfoliated material, where the nanosheets work as large ligands, yielded higher product stereoselectivity in the case of limonene epoxidation. This arises from a confined environment around the Au nanoparticles wrapped by the clay nanosheets modulating access to the catalytic active centres by reagents. Mechanistic assessment was also accomplished for styrene oxidation by DFT methods.

A 2:1 Co/Al layered double hydroxide (LDH) material was synthesized with Cl– anions intercalated and then anion exchanged with deprotonated methionine. This allowed further immobilization of Au nanoparticles. The catalytic performance of the set of three LDH materials for comparative benchmarking was assessed in the aqueous reduction of nitroaromatic compounds and of rhodamine dyes in the presence of NaBH4. All catalysts were found to be very active for the nitro-to-amine reduction. The same was observed for the dyes, where reduction rhodamine 6G was faster than that of rhodamine B, for all catalysts. While the Au-containing catalyst was apparently the one showing the best catalytic activity the LDH with Cl– was found to follow it closely in terms of catalytic performance. In addition, while the LDH catalyst with Au was prone to deactivation by amine products in recycling experiments, the LDH catalyst with Cl– was almost insensitive to that, which is a large advantage. These results showed that using a catalyst based on first-row metals for efficient processes is possible and addresses current sustainable and environmental concerns.

Iron oxide magnetic nanoparticles were synthesized with different sizes (11 and 30 nm). Subsequently they were shelled with a silica layer allowing grafting of an organic phosphine ligand that coordinated to the [MoI2(CO)3] organometallic core. The silica layer was prepared by the Stöber method using either mechanical (both 11 and 30 nm nanoparticles) or ultrasound (30 nm only) stirring. The latter nanoparticles once coated with silica were obtained with less aggregation, which was beneficial for the final material holding the organometallic moiety. The Mo loadings were found to be 0.20, 0.18, and 0.34 mmolMo·g−1 for MNP30-Si-phos-Mo,MNP11-Si-phos-Mo, and MNP30-Sius-phos-Mo, respectively, with the ligand-to-metal ratio reaching 4.6, 4.8, and 3.2, by the same order, confirming coordination of the Mo moieties to two phos ligands. Structural characterization obtained from powder X-ray diffraction (XRD), scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) analysis, and Fourier-transform infrared (FTIR) spectroscopy data confirmed the successful synthesis of all nanomaterials. Olefin epoxidation of several substrates catalyzed by these organometallic nano-hybrid materials using tert-butyl hydroperoxide (tbhp) as oxidant, achieved very good results. Extensive testing of the catalysts showed that they are highly active, selective, recyclable, and efficient concerning oxidant consumption.

A thorough vibrational portrait of 4-fluorobenzaldehyde is presented, covering Infrared (Mid- and Far-), Raman and Inelastic Neutron Scattering (INS) spectra. Periodic DFT calculations (CASTEP) of a model 4FB crystal proved useful for vibrational assignment, yielding estimates of experimental spectra with near one-to-one correspondence – including the correct estimation of overtone and combination modes. A striking similarity among the Far-IR spectrum of liquid 4FB and that estimated based on a periodic structure indicates that the solid-liquid transition induces soft structural changes which leave most vibrational modes unaffected – except for those directly involved in Csingle bondH…O bonding, where crystal field splitting is observed. published

Bacterial nanocellulose (BC)-based composites containing poly(2-hydroxyethyl methacrylate) (PHEMA), poly(methacroylcholine chloride) (PMACC) or poly(methacroylcholine hydroxide) (PMACH) were characterized by inelastic neutron scattering (INS) spectroscopy, combined with DFT (density functional theory) calculations of model systems. A reasonable match between calculated and experimental spectral lines and their intensities was used to support the vibrational assignment of the observed bands and to validate the possible structures. The differences between the spectra of the nanocomposites and the pure precursors indicate that interactions between the components are stronger for the ionic poly(methacrylate) derivatives than for the neutral counterpart. Displaced anions interact differently with cellulose chains, due to the different ability to compete with the O&ndash, H&middot, &middot, O hydrogen bonds in cellulose. Hence, the INS is an adequate technique to delve deeper into the structure and dynamics of nanocellulose-based composites, confirming that they are true nanocomposite materials instead of simple mixtures of totally independent domains.

The present work emphasizes the value of periodic density functional theory (DFT) calculations in the assessment of the vibrational spectra of molecular crystals. Periodic calculations provide a nearly one-to-one match between the calculated and observed bands in the inelastic neutron scattering (INS) spectrum of crystalline 4-phenylbenzaldehyde, thus validating their assignment and correcting previous reports based on single molecule calculations. The calculations allow the unambiguous assignment of the phenyl torsional mode at ca. 118&ndash, 128 cm&minus, 1, from which a phenyl torsional barrier of ca. 4000 cm&minus, 1 is derived, and the identification of the collective mode involving the antitranslational motion of CH&middot, &middot, O bonded pairs, a hallmark vibrational mode of systems where C-H&middot, O contacts are an important feature.

The suitability of porous materials to immobilize and release under control bioactive molecules prompted us to design and study delivery systems of Vitamin A (VitA). This molecule, relevant in several physiological functions, is easily oxidized. Commercial VitA was immobilized in two different clays, montmorillonite K-10 (MMT) and sepiolite (SEP), and in MCM-41, by impregnation. Characterization of the resulting hybrid materials by XRD, FTIR and 13C and 29Si (MAS) NMR spectroscopies revealed its presence. The photo-stability tests showed decreased degradation of VitA in the clays, compared to MCM-41 and the pure VitA, while thermostability is observed until ∼100 °C. The kinetics of the release depended on the structural features of the support material and the pH. Sepiolite originated a classic profile of increasing amount of VitA with time, indicating that no oxidation was taking place. In both montmorillonite and MCM-41 the amount of released VitA dropped after ∼2 hours, reflecting oxidation. Oxidation and degradation products obtained when VitA was immobilized in MCM-41, both under nitrogen and in air, were identified by mass spectrometry experiments. Sepiolite is therefore a suitable material to use in controlled release of VitA, since it appears to prevent oxidation.

Metal oxide nanoparticles MoO 2 with tremella-like morphology have been synthesized and characterized. The solvothermal synthesis method is a new procedure starting from MoO 3 mixed with ethylenediamine and hydroquinone as reducing and assisting agents, respectively. Characterization by powder XRD and TEM microscopy made possible to estimate that the nanosheets have ca. 12 nm and aggregate to form tremella-like structures. The resulting MoO 2 nanoparticles were used as catalyst for epoxidation of several olefins. The use of tert -butylhydroperoxide (TBHP) and cumenehydroperoxide (CHP) as oxygen sources was screened under different reaction conditions, namely, solvent and temperature. The results from the catalytic experiments show that this catalyst is very active leading to very high conversion and product selectivity. Efficiency tests evidence that for some transformations the MoO 2 nanoparticles can work under olefin:oxidant stoichiometric ratios which is certainly an advantage, although induction periods are observed under these conditions. The induction periods are directly correlated with the amount of oxidant and tend to decrease with increasing concentration of the oxidant. The catalyst is also recyclable without severe loss of activity and no major structural changes as well. This catalyst also levels its performance with related systems found in the literature.

Molybdenum trioxide (MoO3) nanoparticles with an average size below 100 nm were prepared by solvothermal synthesis of nano-crystalline molybdenum dioxide (MoO2) and subsequent thermal oxidative annealing. The successful preparation of this type of nanoparticles was confirmed by evidence obtained from characterization by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis and Fourier transform infrared spectroscopy (FTIR). The MoO3 nanoparticles were tested as catalytic precursor in the epoxidation of cis-cyclooctene, styrene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (tbhp) as oxygen source under different reaction conditions, namely, various solvents and temperatures. The catalytic studies show that the MoO3 nanoparticles perform selective epoxidation of the tested substrates with very high yield, especially at high temperature and using toluene as solvent. Furthermore, the catalyst remains active across several reaction cycles with virtually no loss of activity.

New asymmetric Cu(II)/Cu(II) and Ni(II)/Ni(II) binuclear Schiff base complexes were synthesised via a one-pot reaction introducing two different aldehyde building blocks (R = H, t-Bu). These complexes were successfully electropolymerised to afford new metallopolymers using different sweep scan rates (50, 100 and 200 mV s−1) between 0 and 1.4 V. Surface coverage – (Γ) values were determined assuming ligand-based conduction and are of about 10−7 mol cm−2 for both polymers. Atomic force microscopy (AFM) images showed morphological differences between Cu(II) and Ni(II) polymers with root mean square roughness (Rq) higher for the former. DFT studies support the ligand based electropolymerisation mechanism, based on the electron density of the cation at the para position of the phenolate ring, and suggest that copper dimers prefer slipped square planar geometry, with one Cu–O weak bond between adjacent units, rather than stack as in Ni(II) dimers, in agreement with the AFM observations.

The solids choline chloride and urea, mixed in a 1 : 2 molar proportion, form the iconic deep eutectic solvent “Reline”. A combination of computational and vibrational spectroscopy tools, including inelastic neutron scattering (INS), have been used to probe intermolecular interactions in the eutectic mixture. Reline's experimental spectra were estimated using discrete and periodic ab initio calculations of a molecular aggregate with two choline chloride and four urea units. This is the minimum size required to achieve satisfactory agreement with experiment, as smaller clusters cannot represent all of reline's significant intermolecular interactions. The INS spectrum of reline, compared with that of pure choline chloride, reveals a displacement of chloride anions away from their preferred positions on top of choline's methyl groups, whose torsional movement becomes less hindered in the mixture. Urea, which adopts a planar (sp2) shape in the crystal, becomes non-planar (sp3) in reline, a feature herein discussed for the first time. In reline, urea molecules form a wide range of hydrogen bonds, from soft contacts to stronger associations, the latter being responsible for the deviation from ideality. The chloride's interactions with choline are largely conserved at the hydroxyl end while becoming weaker at the cationic headgroup. The interplay of soft and strong interactions confers flexibility to the newly formed hydrogen-bond network and allows the ensemble to remain liquid at room temperature.

The organometallic fragment [MoI 2 (CO) 3 ] was coordinated to magnetic iron oxide nanoparticles of different sizes (average size of 11 and 30 nm) which have been previously coated with a silica shell and grafted with a pyridine derivative ligand. The Mo loading was found to be approximately 0.37 wt-% Mo and 0.57 wt-% Mo, corresponding to 0.150 mmol Mo g −1 and 0.230 mmol Mo g −1 for materials MNP 30 -Si-inic-Mo and MNP 11 -Si-inic-Mo , respectively. Preparation of these organometallic decorated magnetic nanoparticles was further confirmed by evidence obtained from extensive characterization by powder XRD, SEM/TEM analysis, as well as from data of 57 Fe Mossbauer and FTIR spectroscopy. Olefin epoxidation of a variety of substrates promoted by these organometallic nano-hybrid materials using tbhp as oxidant, was performed with very good results. The catalytic studies show that the catalysts yield selectively the desired epoxides of a series of olefins. In addition, these catalysts are found to work under a wide temperature range and over several catalytic cycles without notorious performance loss in most cases.

Helical mesoporous materials of the MCM-41 type are important materials that can be prepared by onepot synthesis procedures with a co-surfactant. A control of the characteristics at a local level is of the most important in the view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared both helical and regular channel materials from Si-based MCM-41 type. Afterward, a bpy derivative was used as ligand to coordinate MoII/VI. The complexes and the new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, 1-octene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general good. The major achievement of these catalysts is an outstanding stereocontrol of the reaction products. In addition, these catalysts were found to be very effective under several circumstances. This is certainly an important contribution for such concept and may render such materials further applications where chiral recognition is important.

International audience; Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

MCM-41 based materials were prepared with immobilized Mo II and Mo VI active sites based on [MoI 2 (CO) 3 ] and [MoO 2 Cl 2 ] cores, respectively, using a 2-aminopyridine glycidyloxypropyl derivative as anchoring ligand. Suitable characterization by powder X-ray diffraction, FTIR and, 13 C and 29 Si solid state NMR spectroscopy was accomplished. All new materials were successfully used in photodegradation experiments of rhodamine B under aerobic conditions. Control experiments using neat MCM-41 and direct photolysis of rhodamine B were also carried out. All experiments were run without any external source of oxygen other than air. Photocatalytic results show that the presence of Mo and its oxidation state is not innocent in this process. In addition, Mo catalysts act most probably by quenching rhodamine B excited state leading to extended degradation of the dye, through secondary photochemistry, beyond a simple de-ethylation process. Density functional theory (DFT) results corroborate with this showing that when rhodamine B is in excited state the xanthene moiety bond orders change.

The [Mo VI O 2 Cl 2 (thf) 2 ] and [Mo II I 2 (CO) 3 (MeCN) 2 ] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were prepared in one pot synthesis, containing the bidentate N , N ′-ligand ( glypy ) in the material. In a second approach, the ordered mesoporous silica MCM- glypy was prepared using a tethered approach by a stepwise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N 2 adsorption, and solid-state CP MAS NMR ( 13 C, 29 Si). All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert -butylhydroperoxide (TBHP) at 328 K. Selectivity to octene and cyclooctene epoxides was complete. The new PMO materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis.

The purpose of this study was to develop a simple biological method for the synthesis of Ag nanoparticles (AgNPs) using Lippia citriodora leaves aqueous extract as reducing agent. Transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD), and visible absorption spectroscopy (UV-vis) confirmed the reduction of silver ions to AgNPs. Stable, spherical crystalline AgNPs with well defined dimensions (average size of 15-30 nm) were obtained, on treating aqueous silver nitrate with the plant leaf aqueous extract. The kinetic of particles formation was proportional to the effect of reducing agent concentration and was enhanced by the increase of temperature from 25 degrees C to 95 degrees C. Time, temperature and extract concentration did not influence significantly the shape and size of nanoparticles. In order to identify the compounds responsible for the bioreduction of silver ions and stabilization of the AgNPs formed, we investigated the constituents of L. citriodora aqueous extract by high performance liquid chromatography (HPLC) and mass spectrometry (MS). The main compounds found were verbascoside, isoverbascoside, chrysoeriol-7-O-diglucoronide and luteonin-7-O-diglucoronide. The data obtained suggests that the isoverbascoside compound is responsible for Ag(+) ions reduction and act as capping agents of the nanoparticles afterwards.

Metalloligands of stoichiometry [AuCl(P−N)] have been obtained by the reaction of the heterofunctional phosphines P−N = PPh2py, PPh2CH2CH2py, or PPhpy2 with [AuCl(tht)] (tht = tetrahydrothiophene). Reactions of these metalloligands with several metal compounds have afforded heteropolynuclear species which exhibit luminescent properties. The stoichiometries depend on the molar ratio and the heterometal. Thus, the reaction with [Cu(NCMe)4]+ in a molar ratio 2:1 gives the trinuclear compounds [Au2CuCl2(P−N)2]+, in which the structure and Au···Cu interactions depend on the phosphine ligand. With rhodium and iridium derivatives the reactivity is different leading to complexes of the type [AuMCl2(cod)(P−N)] for P−N = PPh2py, PPhpy2, and [Au2M2Cl(cod)2(P−N)2]Cl with PPh2CH2CH2py. Using [MCl2(NCPh)2] (M = Pd, Pt) in a 2:1 molar ratio yields [Au2MCl4(P−N)2] and in a 1:1 molar ratio [AuPdCl3(μ3-PPhpy2)]. Several compounds have been characterized by X-ray diffraction showing in many cases short Au···M distances. The luminescence of these derivatives has been studied. The metalloligands display bands assigned to intraligand (IL) transitions. For the bimetallic (Au/M) systems the luminescence depends on the heterometal present and on the metallophilic interactions. The most important excitations in the relevant energy range were assigned essentially a MMLCT character (from Rh/Ir and Au to ligands) based on density functional theory (DFT) calculations in selected complexes. The luminescence behavior in Rh/Ir [AuMCl2(cod)(PPh2py)] complexes was interpreted on the basis of the different nature of the half occupied orbitals in the triplet state., We thank the Dirección General de Investigación Científica y Técnica (CTQ2007-67273-C02-01) for financial support. M.J.C. and P.D.V. acknowledge FCT, POCI, and FEDER (project PTDC/QUI/58925/2004) for financial support.

New hydrotalcite clay materials functionalized with molybdenum(II) complexes holding potential catalytic properties were prepared by a stepwise procedure. The material was first calcined at 823 K for 4 h, to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a solution of either tryptophane (trpH) or phenylalanine (pheH) in a KOH aqueous solution of dmf at 343 K. Subsequent impregnation with a solution of the organometallic precursor [MoI 2 (CO) 3 (NCCH 3 ) 2 ] led to substitution of the nitriles by the ligands affording the organometallic derivatized clays. The equivalent homogeneous phase complexes [MoI 2 (CO) 3 L] (L = trpH or pheH) were also prepared for comparison purposes. All the materials were characterized by powder X-ray diffraction, FTIR and 13 C CP MAS-DD solid state NMR. The complexes were also characterized by FTIR, UV/vis, elemental analysis, and 1 H and 13 C solution NMR accordingly. Both the complexes and these new materials, the latter containing 3.90 wt.% and 5.42 wt.% of Mo, respectively for HT–trp–Mo and HT–phe–Mo materials, catalyzed the epoxidation of cyclooctene and styrene at 328 K. The heterogeneous catalytic systems performed better showing that the presence of the clay is not innocent. In addition, further oxidation of styrene yielding benzaldehyde has occurred. A possible mechanism is proposed based on the detection of two reaction intermediaries by GC/MS. The heterogeneous catalysts also show superior handling capabilities due to Mo increased resistance to moisture and to separation from reaction medium.

Reaction of [MnIII(acac)3] and [VIVO(acac)2] with the 1,4-diazabutadiene (DAB) ligands Ph–DAB–(CH2)3R [R = Si(OEt)3(1a); H (1b)] (L) leads to complexes of the type [MnII(acac)2L] and [VIVO(acac)L]Cl in good yields. These complexes were characterised by spectroscopic techniques, and magnetic measurements showed that in the case of the manganese the metal was reduced during the reaction with the nitrogen ligand. The oxovanadium and manganese complexes bearing the ligand with triethoxysilyl groups Ph–DAB–(CH2)3Si(OEt)3(1a) were immobilised in ordered MCM-41 by carrying out a grafting reaction. Tethered complexes of the same type were prepared by treating MCM-41 first with a toluene solution of 1a under reflux; manganese(III) and oxovanadium(IV) precursors were then introduced into the MCM-41-ligand by pore volume impregnation of complex solutions. The modified materials were characterised by powder X-ray diffraction, solid-state NMR (13C, 29Si), FTIR, thermogravimetric studies and low temperature nitrogen adsorption isotherms. The grafted materials contained 0.7 wt% Mn and 0.8 wt% V, while higher metal loadings were achieved when the materials were prepared by tethering (2.9 wt% Mn and 2.4 wt% V). The modified materials are active catalysts for the oxidation of cis-cyclooctene using tert-butylhydroperoxide as oxygen donor, at 328 K, yielding 1,2-epoxycyclooctane as the main reaction product and 1,2-cyclooctanediol as a by-product. The vanadium-containing materials are more efficient epoxidation catalysts than the manganese ones. The catalytic behaviour of the heterogenised catalysts was also compared with that observed in homogeneous phase for the complexes [Mn(acac)2L] and [VO(acac)L]Cl. The vanadium catalysts exhibited the highest catalytic activity, whereas the manganese catalysts were the least active and selective to epoxide formation.

[MoX 2 (CO) 3 (pyca)] (X = I, Br) complexes bearing the ligand C 5 H 4 NCH N(CH 2 ) 2 CH 3 (pyca, 2 ) were prepared and characterized by elemental analysis as well as FTIR and 1 H and 13 C solution NMR spectroscopy. Using the modified ligand C 5 H 4 NCH N(CH 2 ) 3 Si(OEt) 3 (pycaSi, 3 ), they were immobilized in MCM-41 ( MCM ) and in mesoporous materials (i.e., periodic mesoporous organosilica [PMO]) and then characterized by powder X-ray diffraction, N 2 adsorption analysis, FTIR, and 29 Si MAS and CP MAS and 13 C CP MAS solid-state NMR spectroscopy. These new materials and complexes were tested in the oxidation of cyclohexene, cyclooctene, and styrene and in the polymerization of styrene and norbornene. All were good catalyst precursors for olefin epoxidation with TBHP ( t -butylhydroperoxide), leading selectively to epoxides with high conversions and TOFs and achieving high conversions in the second run. This finding, combined with the fact that the materials outperformed the homogeneous complexes, make these catalysts very attractive. They combine the selectivity and activity of the homogeneous species with the features of materials. The iodine-containing materials performed better for styrene (100% conversion), and the bromine-containing materials displayed higher conversion for cyclooctene.

[MX 2 (CO) 3 (DAB)] (M = Mo, W; X = I, Br) ( 5 – 8 ) complexes bearing the 1,4-diazobutadiene (DAB) ligand RN C(Ph) C(Ph) NR [R = (CH 2 ) 3 Si(OEt) 3 ] were immobilized in MCM-41 mesoporous silica. The tethering, stepwise procedure started with treatment of the MCM-41 mesoporous material with a toluene solution of the 1,4-diazobutadiene ligand, under reflux. The molybdenum and tungsten organometallic cores were subsequently introduced into the ligand-silicas by pore volume impregnation of a solution of the complexes [MX 2 (CO) 3 (NCMe) 2 ] (M = Mo, W; X = Br, I). The modified materials were extensively characterized by several techniques, such as FTIR, solid-state MAS and CP MAS NMR ( 13 C, 29 Si), powder XRD, and nitrogen adsorption–desorption measurements. These new materials (containing 2.6–2.9 wt.% Mo or 0.4–0.6 wt.% W) catalyze the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and norbornadiene at 328 K, in contrast with the very low activity exhibited by the precursor complexes and with their behavior at lower temperature. Addition of AlCl 3 as a co-catalyst enhanced the catalytic performance of the material MCM-DAB-MoBr 2 ( 12 ) in the ROMP of NBE.

The presence of C—H···O hydrogen bonds in liquid cyclohexanone is concluded from a combined theoretical and vibrational spectroscopic study. The two bands present in the νCO region, clearly observed in the Raman spectrum, are assigned to ‘free’ and ‘bonded’ carbonyl groups from their temperature-dependent and solvent-dependent relative intensities. In addition, a band exhibiting the same intensity dependence in the νC–H region is tentatively assigned to the blue-shifted νC–H···(O) mode. Copyright © 2003 John Wiley & Sons, Ltd.

Three new mononuclear oxovanadium(IV) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino} acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(V)(-1) h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.

A regular MCM-41 type mesostructured silica was used as a support for the incorporation of the highly luminescent tris(beta-diketonate) complex Eu(tta)(3)ephen yielding the hybrid MCM-Eu material. Suitable characterization by powder X-ray diffraction (XRD), thermogravimetric analyses (TGA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), C-13 and Si-21 solid state NMR spectroscopy and photoluminescence was accomplished. The combination of ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence techniques shows that the complex incorporation seems to modify essentially the second Eu3+ coordination shell. For a material that has a simply impregnated lanthanide complex, the herein reported maximum D-5(0) quantum yield value of 0.31 is a significantly high value, being almost in the same scale of the values obtained for the materials with covalently bonded complexes. A detailed theoretical photoluminescence study of the MCM-Eu with the recently developed Luminescence Package - LUMPAC is presented. The high accuracy of the theoretical calculations is achieved through the comparison with the experimental values. Aiming at a deeper understanding of the photoluminescence process, the ligand-to-Eu3+ intramolecular energy transfer and back-transfer rates were also predicted. The dominant pathway involves the energy transfer between the lowest energy ligand triplet and the D-5(0) level (9.70 x 10(7) s(-1)).

The -substituted -diketonate [Ln(3Cl-acac)(3)(H2O)(2)] [Ln=Tb, Gd] complexes (with 3Cl-acac(-) being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)(3)(H2O)(2)] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)(3)(H2O)(2)], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)(3)(H2O)(2). Additionally, the possibility of Tb(3Cl-acac)(3)(H2O)(2) to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370nm) with the Tb(3Cl-acac)(3)(H2O)(2) complex.

Following a computational-experimental approach, a highly luminescent beta-diketonate-europium(III) complex containing 2-thenoyltrifluoracetonate (tta(-)) and 5,6-epoxy-5,6-dihydro-[1,10] phenanthroline (ephen) ligands, Eu(tta)(3)ephen (II), was theoretically studied by DFT/TD-DFT calculations, synthesized from Eu(tta)(3)(H2O)(2)(I) and fully characterized by high resolution mass spectrometry, TGA analysis, vibrational, UV-Vis and photoluminescence spectroscopy. For intramolecular energy transfer analysis purpose, Ln(NO3)(3)(ephen)(2) [Ln = Eu (III), Gd (IV)] complexes were also synthesized and complexes I and III were theoretically studied. The organic-inorganic tri-ureasil matrix was used as a support for the immobilization of complex II and two hybrid samples were synthesized as a monolith (MtU5Eu-II) and as a thin film (FtU5Eu-II), characterized and its photoluminescence properties were compared with those of complex II. The photophysical properties of complex II benefit from the synergy between the excited-states of both ligands that create efficient energy transfer pathways to optimize the Eu3+ sensitization contributing to the large emission quantum yield (82 +/- 8%), which is one of the highest so far reported for solid lanthanide beta-diketonate complexes. Moreover, although the incorporation of complex II into the hybrid matrix is disadvantageous from the quantum yield point of view, MtU5Eu-II and FtU5Eu-II exhibit the highest emission quantum yields reported so far for Eu3+-containing hybrids (63 +/- 6% and 48 +/- 5%, respectively). Additionally, a significant improvement in the photostability under UV irradiation of the incorporated complex II is observed. The possibility of FtU5Eu-II to be used as a luminescent solar concentrator was evaluated and an optical conversion efficiency of similar to 9% as well as an ability to boost up the Si-photovoltaic cell output to 0.5% were verified.