Mechanism of thermal energy charge transfer reactions: rare gas ions reacting with NH3 and PH3

Absolute rate constants and approximate product distributions are presented for the reactions of He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺, CO⁺ and CO⁺₂ with NH₃ and PH₃. In all cases, electron transfer is the dominant reaction channel. Hydrogen atom transfer is observed in several systems, but only as a minor product, even when this channel is very exothermic. The magnitude of the absolute rate constants can be correlated with the Franck-Condon factors associated with the reactions in most cases. Several exceptions to this general rule are observed that could not be readily predicted a priori. It is speculated that these reactions proceed via a collision complex.     

Structural Investigation of Guest-to-Host and Ligand-Ligand Interactions in Werner Clathrates of [Ni(4-Etpy)4(NCS)2]⋅ nG Type (G = Naphthalene Derivatives). The Crystal Structure of [Ni(4-Etpy)4(NCS)2]⋅1-Methylnaphthalene

The stoichiometry and spectral properties of [Ni(4-Etpy)4(NCS)2]nG clathrates have been studied where n = 2 for G = 1-BrN (N = naphthalene), n = 1 or 2 for G = 1-MeN, and n = 0.5 for 2-MeN and 2-BrN. The complexes under study show electronic absorption spectra typical of an octahedral environment of the Ni(II) central atom. The differences found in IR spectra for the (CN) and (Ni–-NNCS) vibrations are discussed. The crystal structure of [Ni(4-Etpy)4(NCS)2]1-MeN was determined by X-ray diffraction and refined to R = 0.0586. Discrete non-centrosymmetric [Ni(4-Etpy)4(NCS)2] molecules form layers of a host structure and the space between the layers is occupied by 1-MeN. The relationship between interatomic distances in the host complex of similar clathrates are discussed.     

α-phosphoryl sulfoxides. X. A general synthesis of optically active α-chlorovinyl sulfoxides

A general and efficient synthesis of enantiomeric α-chlorovinyl p-tolyl sulfoxides 1 using (+)-(S)_C(S)_S-α-chloro-α-dimethoxyphosphorylmethyl p-tolyl sulfoxide as a key substrate for the Horner-Wittig reaction with carbonyl compounds is described. The ratio of geometrical isomers of 1 was determined and briefly investigated. The X-ray diffraction structures of (Z)-1-chloro-1-p-tolylsulfinyl-2-phenyl-ethene and (Z)-1-chloro-1-p-tolylsulfinyl-2-(2-thienyl)-ethene are reported.     

Extraction and analysis of phenolics in food

Phenolics are ubiquitous compounds found in all plants as their secondary metabolites. These include simple phenols, hydroxybenzoic acid and cinnamic acid derivatives, flavonoids, coumarines and tannins, among others. The extraction of phenolics from source materials is the first step involved in their analysis. While chemical methods are used for determination of total content of phenolics, chromatographic and spectrometric analyses are employed for identification and quantification of individual compounds present. This paper provides a summary of background information and methodologies used for the analysis of phenolics in foods and nutraceuticals.     

Syntheses and PE-Spectroscopic Investigations of 2,6- and 3,5-Bridged 1,4-Dimethylidenecyclohexanes

Three 1,4-dimethylidenecyclohexanes, bridged in the 2,6- and 3,5-positions by two ethano ( 4 ), one ethano and one propano ( 5 ), and two propano bridges ( 6 ) have been synthesized. The interaction of the two exocyclic methylidene groups has been investigated by He(I) photoelectron (PE) spectroscopy. It revealed a slightly larger energy difference (0.8 eV) for 4 and 5 as compared to the parent 1,4-dimethylidenecyclohexane ( 7 ) (0.7 eV). The interpretation of the PE spectra was based on the comparison with PE data of related systems and with the results of semiempirical calculations on 4–6 .     

INDUCTION OF DNA-PROTEIN CROSS-LINKS IN CHINESE HAMSTER CELLS BY THE PHOTODYNAMIC ACTION OF CHLOROALUMINUM PHTHALOCYANINE AND VISIBLE LIGHT

Abstract— Chloroaluminum phthalocyanine (CAPC) is an efficient photosensitizer for the inactivation of Chinese hamster V79 cells. In order to investigate possible molecular mechanisms in the photo-dynamic action of CAPC and visible light, the induction and repair rate of two classes of DNA lesions have been determined, i.e. DNA single-strand breaks and DNA-protein cross-links. In cells pretreated with 1 μ.M CAPC, a fluence of 12 kJ/m² of red light (>600 nm) kills approximately 50% of the cells and induces 3 to 3.5 Gy-equivalents of single-strand breaks. The repair of these breaks was slower than the repair of single-strand breaks induced by -irradiation. The photodynamic action of CAPC also induces a large number of DNA-protein cross-links which, in contrast to -radiation-induced DNA-protein cross-links, do not appear to be repaired during 4 h of post-treatment incubation in fresh medium. These studies suggest that DNA may be an important target for the cytotoxicity of CAPC + red light.     

Regioselectivity in SNH reactions of some 3-nitro-1,8-naphthyridines with chloromethyl phenyl sulfone

A number of 2-X-3-nitro-1,8-naphthyridines (X= H,D,OH,Cl,NH₂, OEt) react with the anion of chloromethyl phenyl sulfone exclusively into 2-X-3-nitro-4-(phenylsulfonylmethyl)-1,8-naphthyridines in high yield. The reaction is found by quantum chemical calculations to be controlled by the interactions of the HOMO of the nucleophile with the LUMO of the substrate, and not by charge.     

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO

The electronic dipole transition moment functions of the A ²Π-X ²Σ⁺, B ²Σ⁺-X ²Σ⁺ and B ²Σ⁺-A ²Π transitions and the dipole moment function of the X ²Σ⁺ state of CO⁺ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B ²Σ⁺ and A ²Π. Radiative lifetimes of vibrational levels of the X ²Σ⁺ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B ²Σ⁺ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A ²Π state are in excellent agreement with lifetimes measured with an ion trap technique.     

A Study of PbTiO3 Crystallization in Pure and Composite Nanopowders Prepared by the Sol-Gel Technique

Summary.  In this investigation the crystallization of PbTiO₃ upon annealing of pure nanopowders and PbTiO₃–SiO₂ (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the start of PbTiO₃ crystallization in pure PbTiO₃ powders was detected at 400°C. Distinct crystallization of PbTiO₃ in PbTiO₃–SiO₂ nanocomposites starts at 700°C, whereas SiO₂ remains amorphous. There are indications that an interface interaction between the PbTiO₃ and the SiO₂ phase plays an important role in hindering the crystallization of PbTiO₃. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line profiles. The average size of PbTiO₃ nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites (coherently scattering regions). Received October 4, 2001. Accepted (revised) December 14, 2001