NMR studies of electrostatic potential distribution around biologically important molecules

A new experimental approach has been developed to study the distribution of local electrostatic potential around specific protons in biologically impo rtant molecules. The approach is the development of a method denoted as "sp in label/spin probe," which was proposed by one of us (Likhtenshtein et al. , 1972. Mol. Biol. 6:498-507). The proposed method is based upon the quanti tative measurement of the contribution of differently charged nitroxide pro bes to the spin lattice relaxation rate (1/T-1) of protons in the molecule of interest, followed by calculation of local electrostatic potential using the classical Debye equation. In parallel, the theoretical calculation of potential distribution with the use of the MacSpartan Plus 1.0 program has been performed. Application of the method to solutions of simple organic mo lecules (aliphatic and aromatic alcohols, aliphatic carboxylates (propionat e anion), and protonated ethyl amine and imidazole) allowed us to estimate the effective potential around the molecules under investigation. These wer e found to be in good agreement with theoretically expected values. This te chnique was then applied to zwitterionic amino acids bearing neutral and ch arged side chains (glycine, lysine, histidine, and aspartic acid). The reli ability of the general approach is proved by the data presented in this pap er. Application of this new methodology can afford insight into the biochem ical significance of electrostatic effects in biological systems.