Isabelle Ortmans

Ru(II) polypyridine complexes with a high oxidation power. Comparison between their photoelectrochemistry with transparent SnO2 and their photochemistry with desoxyribonucleic acids

Abstract The compounds which are discussed in the present review are highly oxidizing Ru(II) complexes, based on various polyazaaromatic ligands, and acting as efficient electron acceptors in the excited state. The photoinduced charge transfer process and the following associated kinetic steps are characterized for the whole series of complexes by quite different techniques and methods. Thus their behaviour in the presence of reductants such as hydroquinone and mononucleotides (guanosine-5′-monophosphate and adenosine-5′-monophosphate) are examined by flash photolysis, spectroelectrochemistry and photoelectrochemistry. It is explained how the light-initiated electron transfer process can be applied for spectral supersensitization of wide band gap SnO 2 semiconductor electrodes. Moreover, it is shown that such a knowledge of the behaviour of these photoredox reactions leads to interesting applications of these oxidizing complexes in a biological area, i.e. for the study of nucleic acids. Thus it is illustrated how these compounds can be used as promising photoreagents of DNA. The easy modulation of their size and shape, and their irreversible anchoring on the DNA bases, triggered by the reductive photoelectron transfer process from the guanine bases to the excited complex, allow one to regard these complexes as attractive molecular tools for DNA study and maybe as future possible drugs activatable under visible light.

Refolding simulations of an isolated fragment of barnase into a native‐like β hairpin: Evidence for compactness and hydrogen bonding as concurrent stabilizing factors

Experimental evidence and theoretical models both suggest that protein folding is initiated within specific fragments intermittently adopting conformations close to that found in the protein native structure. These folding initiation sites encompassing short portions of the protein are ideally suited for study in isolation by computational methods aimed at peering into the very early events of folding. We have used Molecular Dynamics (MD) technique to investigate the behavior of an isolated protein fragment formed by residues 85 to 102 of barnase that folds into a β hairpin in the protein native structure. Three independent MD simulations of 1.3 to 1.8 ns starting from unfolded conformations of the peptide portrayed with an all‐atom model in water were carried out at gradually decreasing temperature. A detailed analysis of the conformational preferences adopted by this peptide in the course of the simulations is presented. Two of the unfolded peptide conformations fold into a hairpin characterized by native and a larger bulk of nonnative interactions. Both refolding simulations substantiate the close relationship between interstrand compactness and hydrogen bonding network involving backbone atoms. Persistent compactness witnessed by side‐chain interactions always occurs concomitantly with the formation of backbone hydrogen bonds. No highly populated conformations generated in a third simulation starting from the remotest unfolded conformer relative to the native structure are observed. However, nonnative long‐range and medium‐range contacts with the aromatic moiety of Trp94 are spotted, which are in fair agreement with a former nuclear magnetic resonance study of a denaturing solution of an isolated barnase fragment encompassing the β hairpin. All this lends reason to believe that the 85–102 barnase fragment is a strong initiation site for folding. Proteins 29:212–227, 1997.

Oligonucleotides Derivatized with Luminescent and Photoreactive RU(II) Complexes: Models for Photoelectron Transfer and Photocrosslinking

Abstract In this work we examined different aspects of the photo-reaction of Ru(TAP)2 (DIP)2+ (TAP = 1,4,5,8-tetraazaphenanthrene; DIP = 4,7 diphenylphenanthroline) with guanine by studying synthetic oligonucleotide conjugates in which the metal complex is tethered to the oligonucleotide.