C-H ... O hydrogen bonding in solutions of methylated nucleic acid base analogs as revealed by NMR.

Formation and thermodynamic characteristics of C-H ... O hydrogen bonding of methylated uracils and caffeine have been studied by nmr along two lines. 1. The concentration and temperature dependencies of the PMR spectra of 1,3-dimethyluracil (m2 1,3Ura), 1,3-dimethylthymine (m2 1,3Thy), and 1,3,6-trimethyluracil (m3 1,3,6Ura) in chloroform at high concentrations of base analogs indicated the self-association of m2 1,3Ura and m2 1,3Thy via C(6)H ... O hydrogen bonding and the competitive formation of C-H ... O bonds between carbonyl oxygens and chloroform. The intermolecular interaction energy and the arrangement of molecules in the local minima of various m2 1,3Ura dimers were calculated by the method of atom-atom potentials. The deepest minimum for the m2 1,3Ura coplanar dimer corresponds to a C(6)-H ... O hydrogen-bond formation. 2. At low concentration of m2 1,3Ura and caffeine in CCl4, C(6)-H ... O bonding for m2 1,3Ura and C(8)-H ... O bonding for caffeine with oxygens of dimethyl sulfoxide (DMSO) and acetone were observed. The association constants of these complexes were obtained at different temperatures. The enthalpies delta H, of the m2 1,3Ura-DMSO, m2 1,3Ura-accetone, caffeine-DMSO, and caffeine-acetone complexes were -2 +/- 0.1 kcal/mol. The calculations showed that the deepest minimum of the caffeine-acetone coplanar complex corresponds to C(8)-H ... O bonding with energy of -3.5 kcal/mol and that of the m2 1,3Ura-acetone complexes corresponds to C(6)-H ... O bonding with energy of -3.4 kcal/mol. The approximate correction for the solvent effect provides good agreement of the experimental data with the calculations.

[Structural analysis of translating ribosomes. Proton magnetic resonance method]. / Strukturnye issledovaniia transliruiushchikh ribosom. III. Metod protonnogo magnitnogo rezonansa.

Comparison has been made of the proton magnetic resonance (PMR) spectra of translating ribosomes in the pre-translocation and post-translocation states as well as of the complexes of translating ribosomes with elongation factors Tu (EF-Tu) or G (EF-G) in the presence of the uncleavable analogue of GTP--guanylyl-imidodiphosphate (GMP-PNP). It is shown that proteins L7/L12 within the translating ribosomes possess a high intramolecular mobility both in the pre-translocation and in the post-translocation states. The interaction of EF-G with translating ribosomes results in a decrease of the mobility of the L7/L12 proteins. The interaction of EF-Tu with translating ribosomes leads to slight changes in the PMR spectra different from the changes caused by EF-G.

[NMR-intrascopy - new method of biophysical investigation]. / IaMR-introskopiia -- novyi metod biofizicheskogo issledovaniia.

During the past few years new techniques have been developed in nuclear magnetic resonance (NMR) which make it possible to form two dimensional cross-sectional images related to the distribution of protons in biological structures. The methods are non-invasive and of low radiation hazard and could therefore have some clinical value in medical diagnosis. Several methods of producing NMR images are discussed and examples of biological application are given.

[Extraction of deuterated compounds from Chlorella sp. K. grown in D20]. / Poluchenie deiterirovannykh soedinenii iz Chlorella sp. K., vyrashchennoi v D20

A comparison of the three known methods made it possible to work out methods of complex extraction of deutero amino acids, deutero sugars and deutero vitamins from algae Chlorella sp. K., grown autotrophically in heavy water. An analysis of the isotopic composition of deutero amino acids by PMR indicates that treatment with HCl introduces 1H into side chains of some amino acids by chemical exchange (C2, 6H of tyrosine, C2H of histidine, rho-H of phenylalanin, beta-CH2-aspartate and gamma-CH2-glutamate. These exchanges made the amino acids convenient to be used as the substrates for the growth of heterotrophic selective deuterated organisms as a source of selective deuterated proteins.