کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1318147 | 976662 | 2007 | 9 صفحه PDF | دانلود رایگان |
Previously published stability constants of several metal ion (M2+) complexes formed with thiouridines and their 5′-monophosphates, together with recently obtained logKM(U)M versus pKUH plots for M2+ complexes of uridinate derivatives (U−) allowed now a quantitative evaluation of the effect that the exchange of a (C)O by a (C)S group has on the stability of the corresponding complexes. For example, the stability of the Ni2+, Cu2+ and Cd2+ complexes of 2-thiouridinate is increased by about 1.6, 2.3, and 1.3 log units, respectively, by the indicated exchange of groups. Similar results were obtained for other thiouridinates, including 4-thiouridinate. The structure of these complexes and the types of chelates formed (involving (N3)− and (C)S) are discussed. A recently advanced method for the quantification of the chelate effect allows now also an evaluation of several complexes of thiouridinate 5′-monophosphates. In most instances the thiouracilate coordination dominates the systems, allowing only the formation of small amounts of phosphate-bound isomers. Among the complexes studied only the one formed by Cu2+ with 2-thiouridinate 5′-monophosphate leads to significant amounts of the macrochelated isomer, which means that in this case Cu2+ is able to force the nucleotide from the anti to the syn conformation, allowing thus metal ion binding to both potential sites and this results in the formation of about 58% of the macrochelated isomer. The remaining 42% are species in which Cu2+ is overwhelmingly coordinated to the thiouracilate residue; Cu2+ binding to the phosphate group occurs in this case only in trace amounts.
Journal: Journal of Inorganic Biochemistry - Volume 101, Issue 4, April 2007, Pages 727–735