Conformational dependence of the n→π* rotatory strength in dissymmetric carboxylic acid compounds

The conformational dependence of the chiroptical properties associated with electronic transitions in α-hydroxy, α-fluoro, α-chloro, and α-mercapto carboxylic acids is examined with a theoretical model in which rotatory strengths are calculated directly from molecular orbitals calculated using INDO and CNDO semi-empirical molecular orbital models, and excited state wave functions constructed in the virtual orbital-configuration interaction approximation. Binding energies, ground state dipole moments, and vertical ionization potentials (calculated according to Koopman's theorem) are calculated, as well as transition energies, dipole strengths, oscillator strengths, rotatory strengths and dissymmetry factors. Special emphasis is placed on correlating the signs of the rotatory strengths calculated for the lowest energy singlet-singlet transitions with conformational isomerism about the C(α)-COOH band of acyclic α-substituted carboxylic acids. The calculated results for S-lactic acid are in agreement with and strongly support the empirically based spectra-structure relationships previously proposed for S-lactic acid and its derivatives. The calculated results for 2(S)-chloropropionic acid do not agree with previously proposed spectra-structure relationships and this finding is discussed. The results obtained for 2(S)-mercaptopropionic acid are in partial agreement with experiment and spectra-structure relationships in this case involve some uncertainty.     

Inhibition of UV-induced immune suppression and interleukin-10 production by plant oligosaccharides and polysaccharides

Application of Aloe barbadensis poly/oligosaccharides to UV-irradiated skin prevents photosuppression of delayed-type hypersensitivity (DTH) responses in mice. We tested the hypothesis that these carbohydrates belong to a family of biologically active, plant-derived polysaccharides that can regulate responses to injury in animal tissues. C3H mice were exposed to 5 kJ/m2 UVB from unfiltered FS40 sunlamps and treated with between 1 pg and 10 micrograms tamarind xyloglucans or control polysaccharides methylcellulose or dextran in saline. The mice were sensitized 3 days later with Candida albicans. Tamarind xyloglucans and purified Aloe poly/oligosaccharides prevented suppression of DTH responses in vivo and reduced the amount of interleukin (IL)-10 observed in UV-irradiated murine epidermis. Tamarind xyloglucans were immunoprotective at low picogram doses. In contrast, the control polysaccharides methylcellulose and dextran had no effect on immune suppression or cutaneous IL-10 at any dose. Tamarind xyloglucans and Aloe poly/oligosaccharides also prevented suppression of immune responses to alloantigen in mice exposed to 30 kJ/m2 UVB radiation. To assess the effect of the carbohydrates on keratinocytes, murine Pam212 cells were exposed to 300 J/m2 UVB radiation and treated for 1 h with tamarind xyloglucans or Aloe poly/oligosaccharides. Treatment of keratinocytes with immunoprotective carbohydrates reduced IL-10 production by approximately 50% compared with the cells treated with UV radiation alone and completely blocked suppressive activity of the culture supernatants in vivo. The tamarind xyloglucans also blocked UV-activated phosphorylation of SAPK/JNK protein but had no effect on p38 phosphorylation. These results indicate that animals, like plants, may use carbohydrates to regulate responses to environmental stimuli.     

The Interaction of Benzyl Alcohol with Trimethoxyboroxine : Amine Adducts of Triarylboroxines as Model Compounds

The interaction of benzyl alcohol with trimethoxyboroxine has been investigated by hydrogen-1 and carbon-13 NMR and IR spectroscopy. These techniques indicate formation of a weak Lewis acid/base adduct, additionally stabilized by a hydrogen-bonding interaction, which undergoes rapid ligand exchange at room temperature. The system has been modelled by the synthesis and characterization of a series of amine-triarylboroxine adducts. These adducts rapidly undergo ligand dissociation-recombination in solution with ΔG⁺ of ca. 40-50 kJ/mol.     

Mid-infrared pulses generated from the mixing output of an amplified, dual-wavelength Ti:sapphire system

We demonstrate the generation of femtosecond mid-infrared pulses by direct difference-frequency mixing in a AgGaS(2) crystal of two intense pulses from a dual-wavelength oscillator that have been simultaneously amplified in a single regenerative amplifier. A pulse energy of as much as 1.6 muJ was achieved at wavelengths of 9-11 mum.     

Angularly correlated two-electron repulsion operators

The Bohr model for two-electron atoms is modified to include angular correlation effects in an empirical fashion. An extension of the model to two-centers is given. Simple expressions for one- and two-center Coulomb repulsion integrals are derived and compared with semi-empirical approximations.

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Zusammenfassung Die Bohrsche Modellvorstellung für ein Atom mit zwei Elektronen wird so modifiziert, daß die Winkelkorrelation empirisch berücksichtigt wird. Die Erweiterung dieses Modells auf zwei Zentren wird angegeben. Einfache Ausdrücke für Ein- und Zweizentren-Coulombintegrale werden abgeleitet und mit semiempirischen Näherungen verglichen.

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Based on a thesis submitted by RWS to the State University of New York at Albany in partial fulfillment of the requirements for the degree of Ph. D.