Accurate Gaussian basis sets for the H2O molecule generated with the molecular improved generator coordinate Hartree–Fock method

The molecular improved generator coordinate Hartree–Fock (MIGCHF) method is used to generate accurate basis sets of primitive Gaussian-type functions for the H₂O molecule. Sequences of increasing size atom centered basis sets are employed to explore the accuracy that can be achieved with this method. Using the O(24s14p8d5f2g1h);H(22s9p5d2f1g) basis set, the HF and second-order electron correlation energies of the H₂O ground state at the experimental geometry are computed as −76.0674680 and −0.3491935 hartree, respectively. The HF energy is in error by 20 μhartree and the second-order correlation energy corresponds to 96.5% of an estimate of the limiting value. The relevance of the present calculations is to show the accuracy that can be achieved in studies of small polyatomic molecules with the MIGCHF method.     

Crystal Structures and Magnetic Studies of Naphthalene Derivatives Containing Nitronly Nitroxides

Crystal structures of new nitronyl nitroxide derivatives 1, 2 and 3 were determined with X‐ray diffraction analysis: 1, monoclinic, C₂/c, a = 1.2404(5) nm, b = 0.9730(5) um, c = 2.7049(10) ran, β = 98.189(15)°, V = 3.2315(24) nm³, Z = 8; 2, or‐thorhombic, Pbca, a = 0.61262(2) nm, b = 1.11426(6) nm, c = 2.30543(13) nm, V = 1.57373(13) nm³, Z = 4; 3, monoclinic, P2(1)/n, a=0.64253(4) nm, b=2.55003(17) nm, c = 1.15497(6) nm, β = 95.000(3)°, V = 1.8852(2) nm³, Z = 4. Their magnetic properties were measured with SQUID and analyzed based on their crystal structures with simple singlet‐triplet, modified one dimensional antiferromagnetic chain and modified singlet‐triplet models respectively: 1, J/k_b= ?2.5 K; 2, J/k_b = 7.8 K, θ = 2.8 K; 3, J/k_b = ?0.96 K, θ = 0.21 K.     

密度泛函理论和从头算方法对富勒烯分子静电势的比较研究

分别在Hartree-Fock和密度泛函B3LYP理论下,用6-31G*基组研究了C60和C70分子的静电势,比较了这方法计算得到上述分子静电势值的大小,静电势图形和静电势差值曲线,分析了富勒烯的电子相关效应.     

Relationship of rotational correlation time from EPR spectroscopy and protein-membrane interaction

A study was carried out to determine if rotational correlation time of spin-labeled hen egg lysozyme (HEL) interacting with ultrafiltration membranes could be used to infer protein-membrane interaction. Polysulfone and cellulosic membranes, which have notably different adsorption properties, and membranes with varying pore sizes were used in this study. Based on this study, it was determined that the rotational correlation time does reflect variations in protein adsorption and pore plugging on membranes. The rotational correlation times for the highly adsorbent polysulfone (2.82 × 10⁻⁸ s) were significantly higher than those obtained from proteins on cellulosic membranes (0.62 × 10⁻⁸ s) and from those in solution (0.17 × 10⁻⁸ s). Rotational correlation time was also increased due to steric hindrance associated with pore plugging, although it was not as significant as the adsorption effect. This study indicates that the rotational time constant can be used to infer the type of protein-membrane interaction.     

Liquid structure of vanadium tetrachloride from neutron diffraction study

Assuming the separation of the intermolecular scattering function into the radial and angular parts and using Egelstaffet al’s orientational model for tetrachlorides, the structure of liquid vanadium tetrachloride has been studied. It has been observed that such a separation is approximate for this liquid and the introduction of a third correction term is required to account for the molecular structure function. The chlorine-chlorine partial structure and effective angleaveraged intermolecular chlorine-chlorine potential in the liquid has been evaluated. Without taking the third correction term, introduced to generate theoretically the molecular structure function, the centre structure function has been obtained in an approximate way from the experimentally observed molecular structure function and from it the centre radial distribution function, centre direct correlation function and the angle-averaged vanadium-vanadium effective potential has been evaluated.     

New unsymmetrical difluoroaromatic compounds and estimation of their reactivities in nucleophilic substitution

A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on ¹⁹F and ¹³C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the C_ipso atoms correlate linearly with the experimental chemical shifts in the ¹⁹F and ¹³C NMR spectra. Difluoroaromatic compounds, which are characterized by _F > –110 and _C > 163 and by the charge density on the C_ipso atom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers.     

Comparison of the effective core potential and model potential methods in studies of electron correlation energy in molecules: Dihalides and halogen hydrides

Summary The effective core potential and model potential methods were used in post-SCF calculations on HC1, HBr, Cl₂, and Br₂ in order to gain insight into the effect of insufficient representation of inner nodes in the valence orbitals of the approximate methods. The results show that while the correlation energy may be slightly overestimated (by 1–7%), both the electric moment functions and the quantities depending on energy differences are consistently similar for the methods studied and close to the results from all-electron calculations.Dedicated to Prof. Klaus Ruedenberg     

Fluorescence correlation spectroscopy of water-in-oil microemulsions: an application in specific characterisation of droplets containing biomolecules

Fluorescence correlation spectroscopy (FCS) has been successfully used to characterise water-in-oil (w/o) microemulsions. The investigated systems were stabilised by sodium bis-2-ethylhexyl sulphosuccinate (AOT) and the measured diffusion times have been related to the radii of the aggregated species, which for some systems, were separately determined by small-angle neutron scattering (SANS). We demonstrate that FCS is capable of measuring hydrodynamic radii of microemulsions rapidly and at surfactant concentrations lower than previously reported for other techniques. FCS was also used to specifically interrogate microemulsion droplets containing a fluorescently-labelled biomolecule, specifically phalloidin, a peptide fungal toxin from Amanita phalloides, and the enzyme -chymotrypsin (-CT). The microemulsion droplets are only marginally increased in size if a small peptide (phalloidin) is included in the water phase, whereas the droplet size is significantly increased when a larger protein (-CT) is included.     

Improved third-order Møller-Plesset perturbation theory

Based on a partitioning of the total correlation energy into contributions from parallel‐ and antiparallel‐spin pairs of electrons, a modified third‐order Møller–Plesset (MP) perturbation theory is developed. The method, termed SCS–MP3 (SCS for spin‐component‐scaled) continues previous work on an improved version of MP2 (S. Grimme, J Chem Phys 2003, 118, 9095). A benchmark set of 32 isogyric reaction energies, 11 atomization energies, and 11 stretched geometries is used to assess to performance of the model in comparison to the standard quantum chemical approaches MP2, MP3, and QCISD(T). It is found, that the new method performs significantly better than usual MP2/MP3 and even outperforms the more costly QCISD method. Opposite to the usual MP series, the SCS third‐order correction uniformly improves the results. Dramatic enhancements are especially observed for the more difficult atomization energies, some of the stretched geometries, and reaction and ionization energies involving transition metal compounds where the method seems to be competitive or even superior to the widely used density functional approaches. Further tests performed for other complex systems (biradicals, C₂₀ isomers, transition states) demonstrate that the SCS–MP3 model yields often results of QCISD(T) accuracy. The uniformity with which the new approach improves for very different correlation problems indicates significant robustness, and suggests it as a valuable quantum chemical method of general use. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1529–1537, 2003     

Comparison of methods to enhance flame ionization detector (FID) signals in gas chromatography

The performances of some numerical methods to improve the signal to noise ratio are compared and applied to enhance noisy signals obtained in gas chromatography with capillary columns and a flame Ionization detector. Several methods have been considered: cutoffs In the Fourier transform of the recorded signal; real time numerical filtering; theoretical model curve fitting; and the correlation of a chromatogram recorded from a pseudorandomly injected sample with the pseudorandom injection function. Numerical real time filtering is shown to be the most convenient method when the main periodic component of the noise has been determined by Fourier analysis.