Removal of dependencies from nearly complete basis sets. Calculations on the helium dimer

A method is devised for dealing with almost linearly dependent basis sets that contain large sets of bond functions. Using the largest of such basis sets, LARSAT, the second-order Møller-Plesset polarization dispersion energy of the helium dimer is calculated to be - 17.08 K at R = 5.6 bohrs. MR-SDCI calculations, employing a set of 37 reference configurations, were performed for the helium dimer with several basis sets at 4.0 and 5.6 bohrs. Size-extensivity corrections were included to take into account the R dependency of the size-extensivity error in MR-SDCI calculations. The He₂ interaction energies computed with basis LARSAT are - 10.92 K at 5.6 bohrs and 295.1 K at 4.0 bohrs. The 37-MR-SDCI calculations with basis LARSAT almost reproduce the He₂ full configuration interaction (CI) interaction energies computed with the same basis, at notably smaller cost. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 805–815, 1997     

Fluctuating Interfaces in Liquid Crystals

Summary: We review and compare recent work on the properties of fluctuating interfaces between isotropic and nematic liquid-crystalline phases. Molecular dynamics and Monte Carlo simulations have been carried out for systems of ellipsoids and hard rods with aspect ratio 15:1, and the fluctuation spectrum of interface positions (the capillary wave spectrum) has been analyzed. In addition, the capillary wave spectrum has been calculated analytically within the Landau-de Gennes theory. The theory predicts that the interfacial fluctuations can be described in terms of a wave vector dependent interfacial tension, which is anisotropic at small wavelengths (stiff director regime) and becomes isotropic at large wavelengths (flexible director regime). After determining the elastic constants in the nematic phase, theory and simulation can be compared quantitatively. We obtain good agreement for the stiff director regime. The crossover to the flexible director regime is expected at wavelengths of the order of several thousand particle diameters, which was not accessible to our simulations.     

Seebeck coefficients of half-metallic ferromagnets

In this article the Co₂ based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arc melting and consequent annealing. Band structure calculations were performed which revealed the compounds to be half-metallic ferromagnets. Magnetometry was performed on the samples and the Curie temperatures and the magnetic moments were determined. The Seebeck coefficients were measured from low to ambient temperatures for all compounds. For selected compounds high temperature measurements up to 900 K were performed.     

A comment on “Accurate ab initio determination of binding energies for rare-gas dimers by basis set extrapolation”

In this work we comment on an extrapolation scheme presented by Lee in Theoretical Chemistry Accounts, which is based on an extrapolation of energy differences instead of actual energies. In particular, we show that a very similar scheme had been introduced already in 1999, and used to estimate the MP5, CCSDT and FCI complete basis set limits of He₂. Comment to the article “Accurate ab initio determination of binding energies for rare-gas dimers by basis set extrapolation” by J.S. Lee, Theor Chem Acc (2005) 113: 87–94     

Reaction monitoring of enzyme-catalyzed ester cleavage by time-resolved fluorescence and electrospray mass spectrometry: method development and comparison

Two complementary methods for reaction monitoring of the esterase-catalyzed cleavage of bis(2-pyridylmethyl)(2-acetoxyphenyl)amine are developed and compared. While enzyme-amplified lanthanide luminescence (EALL) allows for the time-resolved fluorescence determination of the intrinsically non-fluorescent product, both substrate and product of the enzymatic reaction may be determined simultaneously by electrospray mass spectrometry (ESI-MS). Excitation wavelength for the Tb(III) complex of the reaction product is 297 nm and emission was detected at 545 nm, which is the characteristic emission wavelength of the terbium(III) ion. In contrast to other EALL techniques, the presented method allows for the direct monitoring of an enzymatic conversion without any further sample preparation (e.g., rebuffering). For the mass spectrometric measurements the mass traces were set to m/z=306, 328, 348, and 370 for the protonated ester, the resulting phenol and their sodium adducts, respectively.     

Synthesis, Characterization, and Biological Activity of Amino Acid Derivatives of the Heteropolytungstophosphoric Acid

Compounds of phosphotungstic acid (WPA) containing the amino acids alanine (WPA–Ala) or glycine (WPA–Gly) as counter cations were synthesized and characterized by elemental analysis, thermal analysis, and IR spectroscopy. Cellular toxicity was assessed by the trypan blue exclusion method, and the antiviral activity of WPA and the modified WPA compounds was tested against herpes simplex viruses (HSV) type 1 and type 2. Biological assays indicate that the newly synthesized compounds exhibit no evident cytotoxic effects on Vero cells and negligible antiviral activity against HSV-1 and HSV-2.     

Development and optimization of an analytical method for the determination of UV filters in suntan lotions based on microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) has been applied to the separation of some UV filters (Eusolex 4360, Eusolex 6300, Eusolex OCR, Eusolex 2292, Eusolex 6007, Eusolex 9020, Eusolex HMS, Eusolex OS, and Eusolex 232) commonly found in suntan lotions. The composition of the microemulsion employed was optimized with respect to the best possible separation of the selected analytes using artificial neural networks (ANNs). Two parameters namely the composition of the mixed surfactant system comprising the anionic sodium dodecyl sulfate (SDS) and neutral Brij 35 and the amount of organic modifier (2-propanol) present in the aqueous phase of the microemulsion were modeled. Using an optimized MEEKC buffer consisting of 2.25 g SDS, 0.75 g Brij 35, 6.6 g 1-butanol, 0.8 g n-octane, 17.5 g 2-propanol, and 72.1 g of 10 mM borate buffer (pH 9.2), eight target analytes could be separated in under 25 min employing a diode-array detector to segregate the overlapping signals obtained for Eusolex 9020 and Eusolex HMS. Detection limits from 0.8 to 6.0 nug/mL were obtained and the calibration plots were linear over at least one order of magnitude. The optimized method could be applied to the determination of Eusolex 6300 and Eusolex 9020 in a commercial suntan lotion.