In aqueous solutions containing equimolar concentrations of cytidine and glycylglycine, the presence of zinc chloride results in the formation of a ternary complex, in which cytidine is bound to the metal ion through N3, and the metal ion in turn is chelated to glycylglycinate through the amino and amide groups, leaving the carboxylate anion uncomplexed. When the zinc salt is replaced by mercury(I1) nitrate, no ternary complex is formed ; only the binary complexes mercury(I1)-cytidine and niercury(I1)-glycylglycinate. In the absence of glycylglycine, the cytidine H5 and Hg signals are shifted in opposite directions on the addition of mercury(I1) nitrate, and this is attributed to an increase in restriction of rotation of the amino group because of mercury(I1) complexation. In the presence of glycylglycine, the extent of mercuration of cytidine decreases because of the competition for mercury(I1) by glycylglycinate to form the peptide complex.
Articles you may be interested inContinuous monitoring of the zinc-phosphate acid-base cement setting reaction by proton nuclear magnetic relaxationThe rates of acid-and base-catalyzed exchange of protons in water have been redetermined. Rather than employ 170-enriched water, as in Meiboom's method, we have taken advantage of our observation that T2 is frequency dependent in order to simplify the analysis. The acid-catalyzed rate constant for proton exchange, kl' was found to be 7.9X10 9 liter mole-I. sec-l and the base-catalyzed rate constant, k2, to be 4.5X10 9 liter mole-l·secl • The activation energy for kl was 2.6 kcal, while that for k2 was 2.7 kcal. Our results are compared with those of others as well as with the related anomalous conductance of water. Further studies on the properties of water are suggested by the observation that T2 is frequency dependent.
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