Glycine-Zn+/Zn2+ and their hydrates: On the number of water molecules necessary to stabilize the switterionic glycine-Zn+/Zn2+ over the nonzwitterionic ones

Abstract

Several interaction modes of glycine with one Zn ϩ or Zn 2ϩ and further with one and even two H 2 O molecules in the gas phase are studied at the hybrid three-parameter B3LYP and Hartree-Fock level, respectively. On the basis of these optimized geometries, single point calculations are performed using different theoretical methods and larger basis sets. The calculated results imply that the most stable glycine-Zn ϩ isomer is a five-membered ring with Zn ϩ bound to both amino nitrogen and carbonyl oxygen ͑NO͒ of glycine, and the next most stable glycine-Zn ϩ species is a four-membered ring with Zn ϩ coordinated at both oxygen ends ͑OO͒ of the zwitterionic glycine. The binding energy of the most stable glycine-Zn ϩ is 68.5 kcal/mol calibrated at the BHLYP/6-311ϩG*//6-311ϩG* level. On the contrary with glycine-Zn ϩ isomers, the most stable glycine-Zn 2ϩ species holds the similar coordination mode to that of next most stable glycine-Zn 2ϩ complex, while the next most stable glycine-Zn 2ϩ exhibits the similar coordination mode to that of the most stable glycine-Zn ϩ . The binding strength of these glycine-Zn 2ϩ isomers are all far more than those of their corresponding counterparts of glycine-Zn ϩ isomers, such as the binding energy of the most stable glycine-Zn 2ϩ being 234.4 kcal/mol, showing stronger electrostatic interaction. The reoptimization for the two most stable modes with the different valent states ͑ϩ1,ϩ2͒ to combine a H 2 O molecule at their each end of Zn ion show that the relative energy ordering does not change, and also resembles their no-H 2 O-combined counterparts. However, an interesting and important observation has been first obtained that single hydration effect can strikingly strengthen the stability of the monovalent OO form though it is still higher by 0.1 kcal/mol in energy than the NO counterpart. Hydration effect of double waters can reverse their relative stability due to the strong hydrogen bond effect in the OO form. Different from the case of the two monovalent hydrated complexes, calculated results for the divalent zinc ion chelated complexes show that with or without single hydration hardly change the value of their relative energy, and hydration strength and glycine deformation difference induced with or without hydration in the two different modes display surprising similarity. So we predict that the further hydration basically do not yield any effect on the relative stability. The prediction for the hydration effect on the glycine-Zn ϩ /Zn 2ϩ system would be also suitable for its analogs, such as glycine-Cu ϩ /Cu 2ϩ and glycine-Ni ϩ /Ni 2ϩ systems, and even suitable for other similar transition metal ion-chelated glycine systems.

Binding energies of water to lithiated valine: Formation of solution-phase structure in vacuo

“…For Gly⅐Ni ϩ and Gly⅐Cu ϩ , the nonzwitterion forms are ϳ14 and 10 kcal/mol more stable, respectively [31,32]. Attachment of divalent alkaline earth metal ions (except Be 2ϩ ) [33], Cu 2ϩ [32] and Zn 2ϩ [29] can make the zwitterion or salt-bridge form of glycine more stable by 5-12 kcal/mol.…”

“…The zwitterion form can be made more stable by attaching a metal ion or an electron to it. Calculations indicate that an attached alkali metal cation [23][24][25][26][27], silver (I) ion [28], or zinc (I) ion [29] can lower the relative energy of the zwitterion or salt-bridge form of glycine to only 1-4 kcal/mol higher in energy than the nonzwitterion or charge-solvated form of these ions. Experimental evidence indicates that only the chargesolvated form exists in the gas phase [26,30].…”

Effect of regular hydration on gas phase structural stability of [zwitterionic alanine+M+] (M+=Li+, Na+, K+) complexes: A quantum chemical study

“…A number of studies [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] have been done to investigate the role of monovalent and divalent metal cations and also with explicit addition of water molecules on the structural stability of Ala and ZAla in both, gas phase as well as aqueous medium. In our recent study [43], the theoretically calculated Raman spectra of hydrogen bonded complexes of ZGly with 1-5 water molecules were compared to the experimentally recorded Raman spectra of Gly in aqueous medium and we observed that the calculated Raman spectra of ZGly with five water molecules were found to be in good agreement with the experimentally recorded Raman spectra in aqueous medium.…”

Comparative Study of Different Methods to Determine the Role of Reactive Oxygen Species Induced by Zinc Oxide Nanoparticles

“…One of the possible mechanisms of free radical induction by ZnO nanoparticles was proposed by Ai and co-workers (2003) which is that sequential oxidation-reduction reaction may occur at ZnO particle surface to produce reactive species such as H 2 O 2 and hydroxyl radical (Ai, 2003). Some limitations of utilising this probe exist, even though it is often assumed that H 2 O 2 (in presence of cellular peroxidases and similar catalysts) and hydroxyl radicals (˙OH) can oxidise DCFH (Ai, 2003).…”