Aggregation of trichogin analogs in weakly polar solvents: PELDOR and ESR studies

Abstract

The technique of pulsed electron-electron double-resonance is used to study the self-aggregation of spin labeled trichogin GA IV analogs in weakly polar solvents. The dipole-dipole spinspin relaxation of spin labels has been experimentally studied in glassy solutions of spin-labeled peptides frozen to 77 K in the mixtures of chloroform-toluene, chloroform-decalin, tetrachloromethanetoluene, dichloroethan-toluene depending on the label position in peptide and the structure of terminal groups. It is shown that the studied trichogin analogs in weakly polar solvents form aggregates whose structure depends on solvent properties and peptide structure. It is also demonstrated that the distances between spin labels which can be measured in aggregates amount to the values of 2.3, 2.6 and 3.3 nm. The lower estimate is given for the average number of peptide molecules in aggregates to within 3.1–4.3 depending on peptide structure and solvent composition.