Special Topic 5.1 Electron transfer in biopolymers

The distance dependence of the individual hopping steps is smaller in DNA than in peptides because DNA is more efficient than the peptides as a mediator of the charge transport. On the other hand, peptides are more flexible than DNA double strands and the distances between side-chains of amino acids in peptides can be reduced by conformational changes. The influence of peptide sequence and tertiary structure still remains to be investigated in detail. Investigations of ribonucleotide reductase, DNA photolyase and photosystem II point to the importance of aromatic amino acids such as tyrosine and tryptophan for ET in these proteins. 

The electrical current across a few DNA molecules at least 600 nm long has been measured as a function of the potential applied.381 

The acidity of excited molecules often differs substantially from that in the ground state and the ionization of excited acids may occur adiabatically (Section 2.3), yielding the 

In order to place the transition energies /i(l o(AH) and /i(l (I(A ), which are determined from the absorption spectra of AH and A, on the free energy scale, we ignore volume and entropy effects, that is, we assume that the changes in volume and entropy associated with ionization in the ground state, Aionym(AH) and Aion5 m(AH), are similar to those in the excited state (Equation 5.9). 

Case Study 5.1 Mechanistic photochemistry - adiabatic proton transfer reactions of 2-naphthol and 4-hydroxyacetophenone 

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