Intramolecular interactions in aminoacyl cyclic-3',5'-nucleotides.

Polymerization of amino-acid acyl cyclic-3',5'-nucleotides is postulated to be the origin of RNA and associated protein in prebiotic molecular evolution. The enthalpy change in the intramolecular interaction between the nucleotide base and the amino-acid side chain determines the stability of the particular complex, resulting in a preferred association (or coding) of a base for a particular amino acid. The compounds studied were glycine acyl cyclic-3',5'-guanylate where the strong hydrogen bond between protonated glycine and guanine N7 gives an enthalpy change of -0.05 h. Similarly, hydrogen bonds in l-lysine acyl cyclic-3',5'-adenylate give an enthalpy change of -0.06 h. Hydrophobic interactions in l-phenylalanine acyl cyclic-3',5'-uridylate give an enthalpy change of -0.02 h and the corresponding value for l-proline acyl cyclic-3',5'-cytidylate is -0.01 h. These interactions were expected to be modified as the genetic code became a duplet and finally a triplet code. The interactions have been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the MP2/6-31G* level.

The reactions of methanimine and cyanogen with carbon monoxide in prebiotic molecular evolution on earth.

A primeval atmosphere is proposed containing simple molecules such as formaldehyde, ammonia, carbon monoxide, cyanogen and hydrogen cyanide, which have been detected in space. Chemical reactions are described for the formation of aziridine-2-one and di-azirine-3-one derivatives as potential precursors for the original synthesis of amino-acids, proteins, pyrimidines, purines, nicotinamide and flavin. The reactions have been shown to be kinetically feasible from the overall enthalpy changes in the ZKE approximation at the MP2/6-31G* level.

Impact of microenvironmental nitrogen dioxide concentrations on personal exposures in Australia.

Indoor and outdoor NO2 concentrations were measured and compared with simultaneously measured personal exposures of 57 office workers in Brisbane, Australia. House characteristics and activity patterns were used to determine the impacts of these factors on personal exposure. Indoor NO2 levels and the presence of a gas range in the home were significantly associated with personal exposure. The time-weighted average of personal exposure was estimated using NO2 measurements in indoor home, indoor workplace, and outdoor home levels. The estimated personal exposures were closely correlated, but they significantly underestimated the measured personal exposures. Multiple regression analysis using other nonmeasured microenvironments indicated the importance of transportation in personal exposure models. The contribution of transportation to the error of prediction of personal exposure was confirmed in the regression analysis using the multinational study database.