Phase-separation of cellulose from ionic liquid upon cooling: preparation of microsized particles

Cellulose - Cellulose is an historical polymer, for which its processing possibilities have been limited by the absence of a melting point and insolubility in all non-derivatizing molecular...     

Electron attachment to oxygen and oxygen/ozone clusters studied in a high-resolution crossed beams experiment

Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O₂)_n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O₂)_n +e → O ₂ ^? varies inversely with the electron energy, indicative of s-wave electron capture to (O₂)_n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O₃) _m ^? including the O ₃ ^? monomer while oxygen cluster ions (O₂) _n ^? appear with comparatively low intensity.     

Quenching of I(2P½) by R-OH compounds. Influence of the alkyl group on the quenching efficiency

The deactivation of I(²P_½) by R-OH compounds (R = H, C_nH_2n+1) was studied using time-resolved atomic absorption at 206.2 nm. The second-order quenching rate constants determined for H₂O, CH₃OH, C₂H₅OH, n-C₃H₇OH, i-C₃H₇OH, n-C₄H₉OH, i-C₄H₉OH, s-C₄H₉OH, t-C₄H₉OH, are respectively, 2.4 ± 0.3 × 10⁻¹², 5.5 ± 0.8 × 10⁻¹², 8 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 11.1 ± 0.9 × 10⁻¹², 9.8 ± 0.9 × 10⁻¹², 7.1 ± 0.7 × 10⁻¹², and 4.1 ± 0.4× 10⁻¹² cm³ molec⁻¹ s⁻¹ at room temperature. It is believed that a quasi-resonant electronic to vibrational energy transfer mechanism accounts for most of the features of the quenching process. The influence of the alkyl group and its role in the total quenching rate is also discussed. © 1997 John Wiley & Sons, Inc.     

Hexane dehydrogenation to hexenes: a general indicator for deactivation of Pt catalysts in “skeletal” reactions

The comparative evaluation of dehydrogenation yields and selectivities of skeletal reactions from n-hexane reactions on monofunctional Pt catalysts is a good universal indicator of catalyst deactivation, independently of the presence and the nature of the support. Four regions could be defined with increasing carbon accumulation, causing "beneficial", "selective", "nonselective" and "severe" deactivation.     

Toward the development of new photolabile protecting groups that can rapidly release bioactive compounds upon photolysis with visible light

The synthesis and characterization of a new photolabile protecting group (caging group) for carboxylic acids, the 2-(dimethylamino)-5-nitrophenyl (DANP) group, is described. This compound has a major absorption band in the visible wavelength region with a maximum near 400 nm (epsilon400 = 9077 M(-1) cm(-1) at pH 7.4 and 21 degrees C). The caging group is attached through an ester linkage to the carboxyl functionality of beta-alanine, which activates the inhibitory glycine receptor in the mammalian central nervous system. Such caged compounds play an important role in transient kinetic investigations of fast cellular processes. Upon photolysis of DANP-caged beta-alanine, the caging group is released within 5 micros. Quantum yields of 0.03 and 0.002 were obtained in the UV region (308 and 360 nm) and the visible region (450 nm), respectively. Laser-pulse photolysis experiments, using 337 or 360 nm light, were performed with the caged compound equilibrated with HEK 293 cells transiently transfected with cDNA encoding the alpha1 homomeric, wild-type glycine receptor. The experiments demonstrated that neither DANP-caged beta-alanine nor its byproducts inhibit or activate the glycine receptors on the cell surface. Under physiological conditions, the DANP-caged beta-alanine is water-soluble and stable and can be used for transient kinetic measurements.     

A 50% n-octylmethyl, 50% diphenyl-polysiloxane as stationary phase with unique selectivity for gas chromatography

An n-octylmethyl, diphenyl-polysiloxane called SOP-50-Octyl was prepared by a condensation reaction of bis(dimethylamino) n-octylmethylsilane with diphenylsilanediol. The resulting copolymer was a gum with high molecular weight and was obtained with a yield of 80%. 1H and 29Si NMR spectroscopy revealed that the copolymer was a 52% octylmethyl, 48% diphenyl-polysiloxane with random microstructure. Small cyclic impurities could be almost quantitatively removed via a purification step. SOP-50-Octyl was used as stationary phase for the preparation of wall coated open tubular fused silica capillary columns for gas-liquid chromatography. The capillary columns exhibited high separation efficiency and high inertness. The stationary phase offered a unique selectivity due to its unique composition. The Rohrschneider-McReynolds constants indicated a low overall polarity in spite of the high phenyl content, as the polarity was distinctly decreased by the octyl substituent. Furthermore, the octyl substituent was responsible for a high column bleed, reducing the maximum allowable operating temperature to 280 degrees C. The elution temperatures of apolar compounds were increased due to increased interaction of the octyl substituent with the analytes. Some applications with volatile and semi-volatile organic compounds illustrate that SOP-50-Octyl is an excellent choice for confirmational analyses.     

Strain fields at contacts between small particles

Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results.     

Can a single oxidant with two spin states masquerade as two different oxidants? A study of the sulfoxidation mechanism by cytochrome p450

Density functional calculations were performed on the sulfoxidation reaction by a model compound I (Cpd I) of cytochrome P450. By contrast to previous alkane hydroxylation studies, which exhibit a dominant low-spin (LS) pathway, the sulfoxidation follows a dominant high-spin (HS) reaction. Thus, competing hydroxylation and sulfoxidation processes as observed for instance by Jones et al. (Volz, T. J.; Rock, D. A.; Jones, J. P. J. Am. Chem. Soc. 2002, 124, 9724) are the result of a two-state reactivity scenario, whereby the hydroxylation originates from the LS pathway and the sulfoxidation from the HS pathway. In this manner, two spin states of a single oxidant (Cpd I) can be disguised as two different oxidants. The calculations rule out the possibility that a second oxidant (the ferric peroxide, Cpd 0 species) interferes in the observed results of Jones et al.