Electronic tunneling paths in proteins

Probing Interfacial Organization in Surface Monolayers Using Tethered Pyrene. 1. Structural Mediation of Electron and Proton Access to Adsorbates

We have synthesized and characterized a family of self-assembled monolayers containing pyrene derivatives on gold and indium-doped tin oxide (ITO) substrates. The covalently bound pyrene functionalities serve as either spectroscopic or electrochemical probes of their immediate environment, and we explore their electrochemical response in this paper. When these compounds are the only constituents bound to the interfaces, the molecules enjoy significant structural freedom. The addition of aliphatic adsorbates to the interfaces serves to place the pyrene derivatives in a more restricted environment. Cyclic voltammetry shows that the organization of a monolayer with pyrene derivatives, and the position of the terminal pyrene within such monolayer, depend sensitively on the length of the pyrene tether and the presence or absence of aliphatic interfacial species, as well as the identity of the substrate.

Couplage électronique et transferts de charges dans l'ADN : étude du contrôle énergétique

The influence of the energetic gap on the effective distance-decay rate of electronic coupling (βeff) in DNA is investigated in the context of the superexchange mechanism. The DNA double helix is described by a tight-binding electronic Hamiltonian model, in which all orbitals have the same energy and interact with one another through an exponentially decaying function of distance. Our numerical results concerning the βeff values obtained for two different DNA molecules are analyzed within the theoretical framework of the "continuous-medium approximation," previously developed by Lopez-Castillo et al. (J.-M. Lopez-Castillo, A. Filali-Mouhim, I.L. Plante, and J.-P. Jay-Gerin. J. Phys. Chem. 99 : 6864-6875, 1995). We find that the intervening DNA bridge between the donor and acceptor sites is defined by a unique dimensionless control parameter Γ/E, where E is the energy of the orbitals of this medium with respect to those of the redox site orbitals (energetic gap) and Γ is the electronic band width of the bridge considered as a continuous medium. In the narrow-band regime, our "through-space" coupling model predicts βeff values that are in good order of magnitude agreement with those calculated by other theoretical approaches as well as with those obtained from experiment. Moreover, under equivalent energetic conditions, the DNA-mediated transfers of holes and electrons differ considerably. This difference depends upon the sign of the parameter Γ/E.Key words: DNA, electronic coupling, effective distance-decay rate, energetic gap, superexchange mechanism, continuous-medium approximation, long-distance electron and hole transfers.

Resonance effects in strongly exothermic long-range electron transfer and their possible implications for the behaviour of site-directed mutant proteins

Long-range electron transfer investigations of hemoproteins, blue copper and iron-sulphur proteins frequently rest on electronically excited metal centres. When the excitation energy approaches the oxidation or reduction potentials of intermediate residues the superexchange view normally used, however, fails and a variety of new dynamic features arise. These all involve population of the intermediate cation or anion residue states which can be partially or wholly vibrationally relaxed. We discuss suitable views and a new theoretical formalism for these phenomena. We also note some important implications for site-directed mutagenesis in long-range, strongly exothermic electron transfer processes.