Nonradiative energy transfer in oligopeptide chains generated by a monte‐cralo mehod including long‐range interactions

Abstract

Abstract A Monte‐Carlo method including long‐range interactions is used to oligopeptide chains in random‐coil state. The chains are composed of 4, 9, or 14 repeating units and are labeled with the luminopheres tyrosine or tryptophan. Interactions with a solvent (water) are taken into account in the calculations through modifications of the semiempirical potential‐energy functions. The chains represent oligopeptides composed of hydrophobic or hydrophilic amino acid residues. Various properties relavent to the interpretaiton of nonradiative enrgy‐transfer experiments, such as the average value of the orientation factor for dipole‐dipole interaction of the luminophores, 〈 k 2 〉, the distribution function of the distances between the luminophores f ( r l ), the efficiences of energy transfer in the static and dyamic averaging regimes, 〈 T 〉 s amnd 〈 T 〉 d , as well as the fluorescence decay I(t) of the donor luminophore in various averaging conditions, are computed. It is shown that, for all chains considered, 〈 k 2 〉 is not vary far form 0.67 and that 〈 T 〉 s and 〈 T 〉 d have completely different values. Due to the small extent of correlation between the distances r l and the mutual orientations of the lumninophores, the decay kinetics 〈 I ( t ) s corresponding to a static averaging regime can be expressed in terms of distribution functions f ( r l ). These results are in agrrement with those obtained previously for the unperturbed chain model.