C.W. Tsang

Alkali metal cation-ligand affinities: Basis set superposition correction for the Gaussian protocols

The effect of basis set superposition error (BSSE) on Gaussian-2 and Gaussian-3 calculated alkali metal cation-ligand affinities has been studied. For these systems, we found that the standard Boys–Bernadi full counterpoise (CP) method often leads to correction terms that are physically incorrect. This problem may be rectified by using the geometry corrected counterpoise (GCP) method. The relationship between CP, GCP corrections, and deformation energy is discussed. In order to yield good agreement with existing experimental Li+ and Na+ ligand affinities, we recommend the adoption of either the G3 (with GCP correction) or the G2(MP2,SVP)-FC (without GCP correction) protocols. In the case of K+, the GCP correction is of negligible magnitude, and hence GCP corrections may be omitted in the G2(MP2,SVP)-ASC affinity calculations for these complexes.

A theoretical study of potassium cation-glycine (K+-Gly) interactions

Abstract The structures and binding affinities of potassium cation (K + ) bound complexes of glycine (Gly) are established using a B3-LYP density functional based energetic protocol ‘EP(K + )’. Ten stable isomers on the potential energy surface have been located and the most stable mode of binding involves a bidentate interaction between the cation with OC and −OH. The dipole moment of the glycine ligand plays a dominant role in governing the relative stability of binding modes, while the effect of ligand polarizability plays a less important role. We found that the stabilization energies (raw interaction energies) of these complexes can be well approximated by a linear function of the ‘dipole interaction parameter’ and ‘polarizability interaction parameter’.

Theoretical studies of the structure and stability of (Ag(C6H6)n+ (n = 1 and 2)

Abstract Ab initio molecular orbital techniques are used to probe the structure and stability of Ag(C 6 H 6 ) + and Ag(C 6 H 6 ) 2 + recently observed in electrospray ionization mass spectra. Of all the Ag(C 6 H 6 ) + structures investigated, the C 6v complex is the most stable. Our calculated first binding energy of benzene to Ag + is in agreement with the experimental value and the second binding enegy of benzene to Ag + is estimated to be 114 (10) kJ mol −1 .

Interaction of Ca2+ with mannose: a density functional study

Abstract Five stable binding modes between Ca 2+ and β- d -mannose have been identified using hybrid density functional method. The most stable mode of binding involves the simultaneous interaction of Ca 2+ with four oxygen atoms on the mannose, while some bidentate interactions are of comparable strength to the tridentate interaction. By partitioning the total interaction energy into “stabilization” and “deformation” energies, the effect of Ca 2+ co-ordinate number, Ca 2+ –O bonding distances, intramolecular hydrogen bonding and conformational strain upon complexation on the relative stability of different binding modes are analyzed. Biological relevance of our present study is also discussed.

Interaction of alkali metal cations and short chain alcohols: effect of core size on theoretical affinities

Abstract The effect of core size on the calculated binding energies of alkali metal cations (Li + , Na + , K + ) to methanol, ethanol, n -propanol, i -propanol, n -butanol, i -butanol, s -butanol, and t -butanol are evaluated using G2(MP2,SVP) protocol. The K + affinities, reported for the first time, were found to be negative if a core size larger than that of neon (2s 2 2p 6 ) was used. Given this, we suggest that the 1s 2 , 2s 2 2p 6 , and 3s 2 3p 6 electrons have to be included in the electron correlation treatment for Li + , Na + and K + containing species, respectively. With these core sizes, our G2(MP2,SVP) Li + and Na + affinities are in excellent agreement with values obtained from the newly developed G3 protocol. The nature of alkali metal cation–alcohol interaction is also discussed.

Theoretical binding energies of lithium ions to short-chain alcohols

Abstract The binding energies of lithium ion to methanol, ethanol, n -propanol, i -propanol, n -butanol, i -butanol, s -butanol and t -butanol are calculated using an ab initio molecular orbital method. The calculated enthalpy and Gibbs free energy is in excellent agreement with experimental values reported recently by M.T. Rodgers and P.B. Armentrout [J. Phys. Chem. A 101 (1997) 1238]. Based on our theoretical calculated results, it is recommended that the widely accepted Li + affinity scale of R.W. Taft, F. Anvia, J.-F. Gal, S. Walsh, M. Capon, M.C. Holmes, K. Hosn, G. Oloumi, R. Vasanwala and S. Yazdani [Pure Appl. Chem. 62 (1990) 17] should decrease by 15±2 kJ mol −1 .