FT-IR study of the proton polarizability of hydrogen bonds and of the hydrogen-bonded systems in a di-Mannich base of 5,5′-dimethoxy-2,2′-biphenol

The mono- as well as the di-Mannich bases of 5,5′-dimethoxy-2,2′-biphenol are studied by FT-IR spectroscopy. It is shown that in these bases the protons remain localized at the phenol O atom. This result is in contrast to those obtained earlier for more acidic biphenols in which the protons are not localized but fluctuate and the relevant hydrogen bonds show large polarizability. An intense infrared continuum in the FT-IR spectrum of the mono-protonated di-Mannich base of 5,5′-dimethoxy-2,2′-biphenol demonstrates that the intramolecular hydrogen bond in this compound shows large proton polarizability.     

Breit-Pauli and direct perturbation theory calculations of relativistic helium polarizability.

Large Gaussian-type geminal wave function expansions and direct perturbation theory (DPT) of relativistic effects have been applied to calculate the relativistic contribution to the static dipole polarizability of the helium atom. It has been demonstrated that DPT is superior for this purpose to traditional Breit-Pauli calculations. The resulting value of the molar polarizability of 4He is 0.517254(1) cm3 x mol(-1), including a literature estimate of QED effects. As a by-product, a very accurate value of the nonrelativistic helium second hyperpolarizability, gamma = 43.104227(1) atomic units (without the mass-polarization correction), has been obtained.     

Synthesis, molecular structure, spectral properties and antifungal activity of polymethylene-α,ω-bis(N,N- dimethyl-N-dodecyloammonium bromides)

Hexamethylene-1,6-bis-(N,N-dimethyl-N-dodecylammonium bromide), pentamethylene-1,5-bis(N,N-dimethyl-N-dodecylammonium bromide), tetramethylene-1,4-bis(N,N-dimethyl-N-dodecylammonium bromide), trimethylene-1,3-bis(N,N-dimethyl-N-dodecylammonium bromide) and ethylene-1,2-bis(N,N-dimethyl-N-dodecylammonium bromide) have been obtained and characterized by FTIR and NMR spectroscopy. DFT calculations have also been carried out. The optimized bond lengths, bond angles and torsion angles calculated by Hartree-Fock/3-21G(d,p) approach have been presented. MIC values for A. niger, P. chrysogenum, C. albicans have been determined and the relationship between MIC and spacer length has been discussed.     

Pair potential for helium from symmetry-adapted perturbation theory calculations and from supermolecular data

Symmetry-adapted perturbation theory (SAPT) was applied to the helium dimer for interatomic separations R from 3 to 12 bohrs. The first-order interaction energy and the bulk of the second-order contribution were obtained using Gaussian geminal basis sets and are converged to about 0.1 mK near the minimum and for larger R. The remaining second-order contributions available in the SAPT suite of codes were computed using very large orbital basis sets, up to septuple-zeta quality, augmented by diffuse and midbond functions. The accuracy reached at this level was better than 1 mK in the same region. All the remaining components of the interaction energy were computed using the full configuration interaction method in bases up to sextuple-zeta quality. The latter components, although contributing only 1% near the minimum, have the largest uncertainty of about 10 mK in this region. The total interaction energy at R=5.6 bohrs is -11.000+/-0.011 K. For R< or =6.5 bohrs, the supermolecular (SM) interaction energies computed by us recently turned out to be slightly more accurate. Therefore, we have combined the SM results for R< or =6.5 bohrs with the SAPT results from 7.0 to 12 bohrs to fit analytic functions for the potential and for its error bars. The potential fit uses the best available van der Waals constants C(6) through C(16), including C(11), C(13), and C(15), and is believed to be the best current representation of the Born-Oppenheimer (BO) potential for helium. Using these fits, we found that the BO potential for the helium dimer exhibits the well depth D(e)=11.006+/-0.004 K, the equilibrium distance R(e)=5.608+/-0.012 bohrs, and supports one bound state for (4)He(2) with the dissociation energy D(0)=1.73+/-0.04 mK, and the average interatomic separation R=45.6+/-0.5 A.     

Mass spectrometric and PM5 study of N-(2-pyridyl)-aminomethyldiphoshonic acids and their complexes with alkali cations

Four N-(2-pyridyl)aminomethyldiphoshonic acids have been synthesized and the formation of the complexes between them and alkali cations were studied by the electrospray ionization mass spectrometry (ESI MS). The ESI spectra have evidenced formation of various types of complexes of the acids and monovalent cations, directly related to the formation of respective mono- and disalts of the acids. The main fragmentation path of the acids and their complexes is realized by the elimination of H₂O or H₃PO₃ molecules. The structures of the acids and their complexes with monovalent cations have been calculated by the PM5 method. The structure and the stabilization role of the intramolecular hydrogen bonds for the complexes are discussed.     

On the multipole structure of exchange dispersion energy in the interaction of two helium atoms

The exchange dispersion energy for the interaction of two helium atoms is expressed as a sum of multipole components. In contrast to the analogous expansion for the dispersion energy the derived series converges very slowly and the rate of convergence does not improve with an increasing interatomic distance. Numerical calculations show that at the van der Waals minimum the first term of the series, referred to as dipole-dipole exchange energy, represents merely 17 per cent of the exchange dispersion energy. Moreover, even the inclusion of dipole-quadrupole and quadrupole-quadrupole terms can account for only half of the total exchange dispersion interaction. The above difficulty can be avoided by expanding the dispersion pair function in terms of ionic type or explicitly correlated functions.     

A new functional for variational calculation of atomic and molecular second-order correlation energies

Second-order correlation energies for atoms and molecules are calculated with a novel variational functional that is closely related to the one used before but neglects the most time-consuming terms. Consequently much larger basis sets could be used. Results for He, Be, H₂ and LiH obtained with an explicitly correlated gaussian geminal basis are better than the best published results by 0.32, 0.06, 3.3, and 6.2% and are estimated to be accurate to within a fraction of 1%.     

Radiative corrections to the polarizability of helium

The complete alpha(3) QED correction to the helium atom polarizability is computed assuming an infinite nuclear mass and found to be equal to 0.000030666(3) a.u., with the contribution from the electric-field dependence of the Bethe logarithm amounting to 0.000000193(2) a.u. After including the alpha(2) and alpha(3) corrections for the nuclear recoil and the leading part of the alpha(4) QED correction, we find that the molar polarizability of 4He is 0.51725419(9)(4) cm(3)/mol. The first of the two error bounds is dominated by the uncertainty of alpha(4) and higher-order QED corrections and the second reflects the uncertainty of the Avogadro constant.