Genistein complexes with amines. Part II: ab initio study of the complexes with piperazine and triethylamine

The piperazine and triethylamine complexes of genistein, exhibiting high immunosuppressant activity, were ab initio modeled at RHF/6-31G^** level and results were compared with those obtained for genistein–morpholine complexes by X-ray, NMR, and theoretical methods. The most stable genistein–piperazine complex is formed due to hydrogen bonding of genistein's OH group at position C7 to piperazine's nitrogen atom. In the most stable genistein–triethylamine complex genistein's OH group at position C4′ (position para to phenyl substituent) and trimethylamine nitrogen atom are engaged in hydrogen bond formation. The calculations confirmed our previous NMR conclusion that piperazine is more strongly complexed by genistein than is morpholine or triethylamine. The theoretical ¹³C NMR spectra correlate fairly well with the experimental spectra.     

DFT study of vibrational circular dichroism spectra of D-lactic acid-water complexes

This paper presents a discussion of the interaction energies, conformations, vibrational absorption (VA, harmonic and anharmonic) and vibrational circular dichroism (VCD) spectra for conformers of monomeric chiral d(-)-lactic acid and their complexes with water at the DFT(B3LYP)/aug-cc-pVDZ and DFT(B3LYP)/aug-cc-pVTZ levels. A detailed analysis has been performed principally for the two most stable complexes with water, differing by lactic acid conformation. The VCD spectra were found to be sensitive to conformational changes of both free and complexed molecules, and to be especially useful for discriminating between different chiral forms of intermolecular hydrogen bonding complexes. In particular, we show that the VCD modes of an achiral water molecule after complex formation acquire significant rotational strengths whose signs change in line with the geometry of the complex. Using the theoretical prediction, we demonstrate that the VCD technique can be used as a powerful tool for structural investigation of intermolecular interactions of chiral molecules and can yield information complementary to data obtained through other molecular spectroscopy methods.     

HCl solvation at the surface and within methanol clusters/nanoparticles II: Evidence for molecular wires

Condensed-phase solvation of HCl on and within methanol nanoparticles was investigated by Fourier transform infrared (FTIR) spectroscopy, on-the-fly molecular dynamics as implemented in the density functional code Quickstep (which is part of the CP2K package), and ab initio calculations. Adsorption and solvation stages are identified and assigned with the help of calculated infrared spectra obtained from the simulations. The results have been further checked with MP2-level ab initio calculations. The range of acid solvation states extends from the single-coordinated slightly stretched HCl to proton-sharing with Zundel-like methanol O...H+...X- states, and finally to MeOH2+...Cl- units with full proton transfer. Furthermore, once the proton moves to methanol, it is mobilized along methanol molecular chains. Since the proton dynamics reflects the evolving local structures, the "proton" spectra display broad bands usually with underlying continua.     

On the improvement of expectation values in the uncoupled SCF and HF perturbation theories

The exact derivation of the formula for the first-order ‘correlation’ correction to the second-order uncoupled Hartree-Fock energies, computed with approximate Hartree-Fock orbitals, is presented. A comparison with the corresponding formula derived under the assumption of the exact solution of the Hartree-Fock equations indicates that also the second-order perturbed orbitals do contribute. However, their contribution can be expressed in terms of the first-order correction to the SCF orbitals which accounts for the difference between the Hartree-Fock and SCF solution. These additional terms can be either positive or negative and can influence significantly the final result for the correlation-corrected second-order energies.     

Cysteine conformations revisited

Based on the B3LYP and MP2/aug-cc-pVDZ calculations, 51 cysteine conformers were found to be stable in the gas phase. The calculations were repeated for the most stable eight structures by using the aug-cc-pVTZ basis set. To estimate the influence of water on the cysteine conformation, the IEF-PCM/B3LYP/aug-cc-pVDZ calculations were carried out and showed 44 neutral and 12 zwitterion conformers to be stable in the water solution. The most stable cysteine structure in water appeared to be the zwitterionic conformer quite similar to the molecule observed in the crystal state.     

Finite-field many-body perturbation theory IV. Basis set optimization in MBPT calculations of molecular properties. Molecular quadrupole moments

The choice of truncated basis sets and their optimization for MBPT calculations of molecular properties are discussed. It is pointed out that computing the correlation corrections to some kth order property by using the MBPT approach requires the knowledge of accurate perturbed orbitals through the kth order. Hence, it is argued that the basis set functions can be optimized with respect to the perturbed energies calculated within the coupled Hartree-Fock method. The proposed procedure is illustrated by MBPT calculations of quadrupole moments of H₂ and FH. Additionally, also some estimates of the quadrupole polarizability tensor components for these molecules are obtained.     

Infrared spectra and structure of substituted unsaturated carbonyl compounds: XVII. Enamino ketone and aldehyde quaternary ammonium salts

The β-trialkylammonium chloride derivatives of several α,β-unsaturated carbonyl compounds have been shown by infrared spectra to exist in the s-cis and s-trans rotational forms. The equilibrium between these two forms shifts towards the s-cis with the increasing steric requirements of the alkyl substituent linked to carbonyl. The CO and CC stretching frequencies are shifted to higher values as compared with other types of α,β-unsaturated ketones.     

Reduced–size polarized basis sets for calculations of molecular electric properties. III. Second–row atoms

Reduced–size polarized (ZmPolX) basis sets are developed for the second–row atoms X = Si, P, S, and Cl. The generation of these basis sets follows from a simple physical model of the polarization effect of the external electric field which leads to highly compact polarization functions to be added to the chosen initial basis set. The performance of the ZmPolX sets has been investigated in calculations of molecular dipole moments and polarizabilities. Only a small deterioration of the quality of the calculated molecular electric properties has been found. Simultaneously the size of the present reduced–size ZmPolX basis sets is about one-third smaller than that of the usual polarized (PolX) sets. This reduction considerably widens the range of applications of the ZmPolX sets in calculations of molecular dipole moments, dipole polarizabilities, and related properties.     

Polarized basis sets and the calculation of infrared intensities from nuclear electric shielding tensors

The idea of the basis set polarization which follows from the known dependence of basis set functions on the perturbation strength is applied to the calculation of the dipole moment derivatives with respect to nuclear displacements. The differentiation of the dipole moment function is replaced by the straightforward evaluation of derivatives of the intramolecular electric field with respect to the external electric field strength. The method and its efficiency are illustrated by a series of calculations of the dipole moment derivatives for the water molecule. Already a polarized basis set of 26 CGTO's derived from the minimal CGTO basis set provides fairly reasonable results.     

Ionization potentials and electron affinities of Cu,Ag, and Au: Electron correlation and relativistic effects

The electron correlation and relativistic effects on ionization potentials and electron affinities of Cu, Ag, and Au are investigated in the framework of the coupled cluster method and different 1-component approximations to the relativistic Dirac-Coulomb Hamiltonian. The first-order perturbation approach based on the massvelocity and Darwin terms is found to be sufficiently accurate for Cu and Ag while it fails for Au. The spin-averaged Douglas-Kroll no-pair method gives excellent results for the studied atomic properties. The ionization potentials obtained within this method and the coupled cluster scheme for the electron correlation effects are 7.733(7.735) eV for Cu, 7.461(7.575) eV for Ag, and 9.123(9.225) eV for Au (experimental values given in parentheses). The calculated (experimental) electron affinity results for Cu, Ag, and Au are 1.236(1.226), 1.254(1.303), and 2.229(2.309) eV, respectively. There is a marked relativistic effect on both the ionization potential and electron affinity of Ag which sharply increases for Au while Cu exhibits only a little relativistic character. A similar pattern of relativistic effects is also observed for electric dipole polarizabilities of the coinage metal atoms and their ions. The coupled cluster dipole polarizabilities of the coinage metal atoms calculated in this article in the Douglas-Kroll no-pair formalism (Cu: 46.50 au; Ag: 52.46 au; Au: 36.06 au) are compared with our earlier data for their singly positive and singly negative ions. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 557–565, 1997