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Kinetics for interaction of the thione unit in 4-thio-2'-deoxyuridine and 4-thiouridine 5'-monophosphate with rapidly reacting gold(III) complexes

Ericson, Anna LU ; Arthur, John C. ; Coleman, Robert S.; Elding, Lars Ivar LU and Elmroth, Sofi LU (1998) In Journal of the Chemical Society. Dalton Transactions 1998. p.1687-1692
Abstract
Reactions of 4-thio-2′-deoxyuridine d(s4U) and 4-thiouridine 5′-monophosphate s4UMP with trans-[AuY2Cl2]+/– (Y = CN– or NH3) have been investigated by conventional and high-pressure stopped-flow spectrophotometry in aqueous solution with 2.9 ⩽ pH ⩽ 7.0. For a given combination of metal complex and sulfur donor the observed second-order rate constants decreased with increasing pH. In the pH range 2.9 to 5.5 this decrease is mainly due to displacement of the pH-dependent equilibrium trans-[AuY2Cl2]+/– + H2O ⇌ trans-[AuY2Cl(OH)]+/– + Cl– + H+ and formation of an increasing fraction of the less reactive gold(III) hydroxo complex. The activation parameters ΔH ‡, ΔS ‡ and ΔV ‡ at pH 4.0 for substitution of chloride for thione at... (More)
Reactions of 4-thio-2′-deoxyuridine d(s4U) and 4-thiouridine 5′-monophosphate s4UMP with trans-[AuY2Cl2]+/– (Y = CN– or NH3) have been investigated by conventional and high-pressure stopped-flow spectrophotometry in aqueous solution with 2.9 ⩽ pH ⩽ 7.0. For a given combination of metal complex and sulfur donor the observed second-order rate constants decreased with increasing pH. In the pH range 2.9 to 5.5 this decrease is mainly due to displacement of the pH-dependent equilibrium trans-[AuY2Cl2]+/– + H2O ⇌ trans-[AuY2Cl(OH)]+/– + Cl– + H+ and formation of an increasing fraction of the less reactive gold(III) hydroxo complex. The activation parameters ΔH ‡, ΔS ‡ and ΔV ‡ at pH 4.0 for substitution of chloride for thione at trans-[AuY2Cl2]+/– indicate an associative interchange process. When the thione-containing nucleotide reacts with the cation, steric and electrostatic interactions between the metal complex and the phosphate group oppose each other and the rate of the reaction of trans-[Au(NH3)2Cl2]+ with s4UMP is approximately the same as with d(s4U). Thus, the electrostatic outer-sphere interaction with a single phosphate group adjacent to the kinetically preferred binding site is not sufficient to induce a reactivity that significantly exceeds that of direct interaction between the thione and the rapidly reacting gold(III) centre. In contrast, reaction of trans-[Au(CN)2Cl2]– with s4UMP is significantly slower than with d(s4U), most likely due to the combined effect of electrostatic repulsion and steric blocking. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Inorganic chemistry, Gold(III) complexes, Thiones, Stopped-flow kinetics, Activation parameters, Reaction mechanism
in
Journal of the Chemical Society. Dalton Transactions
volume
1998
pages
6 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:33748988510
ISSN
1472-7773
DOI
10.1039/A708564H
language
English
LU publication?
yes
id
4cccb125-1157-42c6-887b-e93a586989ca
date added to LUP
2016-12-18 19:01:20
date last changed
2017-08-27 06:32:03
@article{4cccb125-1157-42c6-887b-e93a586989ca,
  abstract     = {Reactions of 4-thio-2′-deoxyuridine d(s4U) and 4-thiouridine 5′-monophosphate s4UMP with trans-[AuY2Cl2]+/– (Y = CN– or NH3) have been investigated by conventional and high-pressure stopped-flow spectrophotometry in aqueous solution with 2.9 ⩽ pH ⩽ 7.0. For a given combination of metal complex and sulfur donor the observed second-order rate constants decreased with increasing pH. In the pH range 2.9 to 5.5 this decrease is mainly due to displacement of the pH-dependent equilibrium trans-[AuY2Cl2]+/–  +  H2O  ⇌  trans-[AuY2Cl(OH)]+/–  +  Cl–  +  H+ and formation of an increasing fraction of the less reactive gold(III) hydroxo complex. The activation parameters ΔH  ‡, ΔS  ‡ and ΔV  ‡ at pH 4.0 for substitution of chloride for thione at trans-[AuY2Cl2]+/– indicate an associative interchange process. When the thione-containing nucleotide reacts with the cation, steric and electrostatic interactions between the metal complex and the phosphate group oppose each other and the rate of the reaction of trans-[Au(NH3)2Cl2]+ with s4UMP is approximately the same as with d(s4U). Thus, the electrostatic outer-sphere interaction with a single phosphate group adjacent to the kinetically preferred binding site is not sufficient to induce a reactivity that significantly exceeds that of direct interaction between the thione and the rapidly reacting gold(III) centre. In contrast, reaction of trans-[Au(CN)2Cl2]– with s4UMP is significantly slower than with d(s4U), most likely due to the combined effect of electrostatic repulsion and steric blocking.},
  articleno    = {7/08564H},
  author       = {Ericson, Anna and Arthur, John C.  and Coleman, Robert S. and Elding, Lars Ivar and Elmroth, Sofi},
  issn         = {1472-7773},
  keyword      = {Inorganic chemistry,Gold(III) complexes,Thiones,Stopped-flow kinetics,Activation parameters,Reaction mechanism},
  language     = {eng},
  pages        = {1687--1692},
  publisher    = {Royal Society of Chemistry},
  series       = {Journal of the Chemical Society. Dalton Transactions},
  title        = {Kinetics for interaction of the thione unit in  4-thio-2'-deoxyuridine and 4-thiouridine 5'-monophosphate with rapidly reacting gold(III) complexes},
  url          = {http://dx.doi.org/10.1039/A708564H},
  volume       = {1998},
  year         = {1998},
}