Resonance Raman spectroscopy and quantum chemical modeling studies of protein-astaxanthin interactions in alpha-crustacyanin (major blue carotenoprotein complex in carapace of lobster, Homarus gammarus)

Solid state NMR/Biophysical Organic ChemistryBio-organic Synthesi

Carotenoid blues: Structural studies on carotenoproteins

Solid state NMR/Biophysical Organic Chemistr

A quantum chemistry evaluation of the stereochemical activity of the lone pair in PbII complexes with sequestering ligands

International audienceThe stereochemical activity of the lone pair on PbII complexes is assessed using several theoretical methods, including structural analyses, computations of Fukui functions, natural bond orbitals, electron localization function, investigation of the electron density and of its laplacian. The attention is focused on four octadentate N-carbamoylmethyl-substituted tetraazamacrocycles of various ring sizes ranging from 8 to 14 atoms associated with the PbII cation. The theoretical study illustrates the geometrical constraints imposed by the ring structure which limits the spatial development of the lone pair but without fully preventing it. For a given coordination number, the lone pair activity is strongly correlated to the geometry of the ligand and in particular to the size of the cage that the ligand forms around the PbII cation. Some limitations of the theoretical tools used are also evidenced, among them the necessity to sample around a critical point instead of just analyzing its nature. In the case of the laplacian of the electron density, a visualization method is introduced to moderate the results based only on the nature of a critical point. These limitations should also be related to the difficulty to extend the lone pair concept for the heaviest atoms of the classification

Complexation of some divalent cations with morin: a spectroscopic and theoretical study

International audienc

Protic equilibria as the key factor of quercetin emission in solution. Relevance to biochemical and analytical studies

A detailed spectrofluorimetric study on quercetin in aqueous solution proves that its anionic forms are responsible for a strong fluorescence enhancement observed at pH > 6. Anion fluorescence is also observed in organic solvents with strong hydrogen bond acceptor properties. The results provide a new interpretation of biophysical and analytical literature data where the fluorescence of the anionic forms of quercetin has never been explicitly taken into account. In particular, comparison with published binding studies strongly suggests that quercetin deprotonation and consequent fluorescence enhancement takes place when the flavonoid binds to several biological macromolecules. This observation can be very helpful in the understanding at a molecular level of the interaction between quercetin and the biomolecule

The photo-degradation of mesotrione, a triketone herbicide, in the presence of Cu^II ions

The study focuses first on the complexation of CuII ions with mesotrione. Experimental absorption spectra combined with quantum chemical calculations highlight that CuII ions bind to the molecule in bidentate mode between O1 and O7 atoms. The calculated electronic transitions of the complex show that three of them are mostly ligand-to-ligand electron transfer while the lowest-energy one involves a ligand-to-metal charge transfer (LMCT). The second aim of this work is to explore the effect of CuII complexation on the photo-degradation of mesotrione. The kinetics and mechanisms of the reactions are proposed on the basis of the experimental results. The effect of different parameters such as the irradiation wavelength, the oxygen concentration and the pH of the mixture and also the production of reactive species such as hydroxyl radicals is investigated. The photochemical degradation of mesotrione in water arises from the triplet excited state of the molecule and results in a photo-hydrolysis process. For the complex, by exciting mainly in its LMCT absorption band, an electron transfer between copper and mesotrione probably occurs and the mechanism of mesotrione-CuII photo-degradation differs: in addition to the photo-hydrolysis route, a photo-cyclisation process takes place and the oxidation of the ligand is accompanied by the reduction of CuII ions