title: Extent of metal ion-sulfur binding in complexes of thiouracil nucleosides and nucleotides in aqueous solution.
abstract: Previously published stability constants of several metal ion (M2+) complexes formed with thiouridines and their 5'-monophosphates, together with recently obtained log K(M(U))(M) versus pK(U)(H) 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.
authors.affiliation: Department of Chemistry, Graduate School of Sciences, Nagoya University, Nagoya 464-8602, Japan. b42170a@nucc.cc.nagoya-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Odani
authors.forename: Henryk
authors.initials: H
authors.lastname: Kozlowski
authors.forename: Jolanta
authors.initials: J
authors.lastname: Swiatek-Kozlowska
authors.forename: Justyna
authors.initials: J
authors.lastname: Brasuń
authors.forename: Bert P
authors.initials: BP
authors.lastname: Operschall
authors.forename: Helmut
authors.initials: H
authors.lastname: Sigel
mesh_terms: D002104:Cadmium / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D009705:Nucleosides / Q000737:chemistry*; D009711:Nucleotides / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*; D013889:Thiouracil / Q000737:chemistry*; D013891:Thiouridine / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D008670:Metals; D009705:Nucleosides; D009711:Nucleotides; D009942:Organometallic Compounds; D002104:Cadmium; D014867:Water; D013891:Thiouridine; D013889:Thiouracil; D013455:Sulfur; D009532:Nickel