Regular Article

Theoretical Chemistry Accounts

, Volume 130, Issue 2, pp 279-297

First online:

Quantum chemical studies on the role of water microsolvation in interactions between group 12 metal species (Hg2+, Cd2+, and Zn2+) and neutral and deprotonated cysteines

  • Seiji MoriAffiliated withFaculty of Science, Ibaraki UniversityFrontier Research Center for Applied Atomic Sciences, Ibaraki University Email author 
  • , Takahiro EndohAffiliated withFaculty of Science, Ibaraki University
  • , Yuki YaguchiAffiliated withFaculty of Science, Ibaraki University
  • , Yuuhei ShimizuAffiliated withFaculty of Science, Ibaraki University
  • , Takayoshi KishiAffiliated withFaculty of Science, Ibaraki University
  • , Tetsuya K. YanaiAffiliated withFaculty of Science, Ibaraki University

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Abstract

Interactions of group 12 metal(II) species (Hg2+, Cd2+, Zn2+, Hg(H2O) n 2+ , Cd(H2O) n 2+ , and Zn(H2O) n 2+ (n = 1, 2) with neutral (RSH), deprotonated (RS), and doubly deprotonated cysteine species (abbreviated as “H2cys”, “Hcys”, and “cys2−”, respectively) are examined with the Becke three-parameter Lee–Yang–Parr (B3LYP) hybrid functional after preliminary screening in a conformation analysis with the Parameterized Model number 3 (PM3) semiempirical method. Effects of water on aqueous solution are evaluated by microsolvation and polarized continuum model (PCM) approaches. In the most stable conformations of M(H2cys)2+ and M(Hcys)+ complexes (M = Hg2+, Cd2+, and Zn2+), the SH group of the cysteine moiety is already deprotonated and undergoes strong binding with the metal ion. Among Hg(H2cys)2+ complexes, cysteine complexes of Hg2+ without deprotonation of the SH group and mercury(II) carboxylato-type structures are at least 83 and 117 kJ/mol less stable in energy than the most stable complex (B3LYP/6-311++G(d,p)-SDD+d+f//B3LYP/6-31G(d)-SDD+d). Although Zn2+ binds more strongly than Hg2+ to a H2cys molecule at the high-level CCSD(T)/6-311++G(d,p)-SDD+d+f//B3LYP/6-311++G(d,p)-SDD+d+f level, [Hg(H2O)2]2+ is stronger than [Zn(H2O)2]2+ because the deformation of [Zn(H2O)2]2+ required to bind to cys is much more than in [Hg(H2O)2]2+. Complexes with a deprotonated cysteine, M(Hcys)+ and M(cys), prefer a multidentate structure.

Keywords

Mercury Cadmium Zinc Cysteine Molecular interaction Density functional calculations