Evidence against the hopping mechanism as an important electron transfer pathway for conformationally constrained oligopeptides.
ABSTRACT The rate constant of intramolecular electron transfer through oligopeptides based on the alpha-aminoisobutyric acid residue was determined as a function of the peptide length and found to depend weakly on the donor-acceptor separation. By measuring the electron-transfer activation energy and estimating the energy gap between donor and bridge, we were able to discard the electron hopping mechanism.
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ABSTRACT: Understanding the interaction of nanoparticles with cell membranes is a high-priority research area because of the possible biomedical applications. We describe our findings concerning the interaction of Au144 monolayer-protected clusters (MPCs) with biomimetic membranes, and their permeabilizing effect as a function of the transmembrane potential. We synthesized Au144(SCH2CH2Ph)60 and modified the capping monolayer with 8-mercaptooctanoic acid (Au144COOH) or thiolated trichogin (Au144TCG), a channel-forming peptide. The interactions of these MPCs with mercury-supported lipid mono- and bilayers were studied with a combination of electrochemical techniques specifically sensitive to changes of the properties of biomimetic membranes and/or charge-transfer phenomena. Permeabilization effects were evaluated through the influence of MPCs' uptake on the reduction of cadmium(II) ions. Main outcome is that the nature and properties of the Au144 capping molecules play a crucial role in controlling how MPCs interact with membranes. The native MPC causes a small effect, whereas both Au144COOH and Au144TCG interact significantly with the lipid monolayer, and show electroactivity. However, whereas Au144COOH penetrates the membrane, Au144TCG pierces the membrane with its peptide appendage, while remaining outside of it. Both clusters promote Cd2+ reduction, although with apparently different mechanisms. Because of the different way they interact with the membrane, whereas Au144COOH is more effective on Cd2+ reduction when interacting with the lipid bilayer, Au144TCG performs particularly well when piercing the lipid monolayer.Langmuir : the ACS journal of surfaces and colloids. 06/2014;
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ABSTRACT: We synthesized two molecular systems in which an endofullerene C60 , incarcerating one hydrogen molecule (H2 @C60 ), and a nitroxide radical are connected by a folded 310 -helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear-spin relaxation rates and the para → ortho conversion rate of the incarcerated hydrogen molecule were determined by (1) H NMR spectroscopy. The experimental results were analyzed using DFT-optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H2 @C60 / nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para → ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear-spin relaxation rates are in excellent agreement with the Solomon-Bloembergen equation predicting a 1/r(6) dependence. This article is protected by copyright. All rights reserved.Photochemistry and Photobiology 10/2013; · 2.29 Impact Factor
- Angewandte Chemie. 01/2007; 119(18):3258-3273.