Separation and identification of Taxifolin 3-O-glucoside isomers from Chamaecyparis obtusa (Cupressaceae)

Taxifolin 3-O-glucoside isomers, [(2R, 3R)-, (2R, 3S)-, (2S, 3R)- and (2S, 3S)-] were isolated from leaves of Chamaecyparis obtuse (Cupressaceae). Their structures were elucidated on the basis of UV, MS, CD, 1H- and 13C-NMR spectral data, including 2D shift correlation. It was found that the compounds could be distinguished by the use of 1H- and 13C-NMR spectral data.     

Polymerization induced by electron-beam irradiation of octadecyl methacrylate in the form of a multilayer or monolayer

In continuation of the previous series of studies, polymerization of octadecyl methacrylate (ODMA) induced by electron beams has been investigated in a form of its multilayer or monolayer in an attempt to prepare a stable thin polymer film having a regular layer structure. ODMA multilayers were prepared by the Langmuir-Blodgett technique and irradiated with electron beams from a Van de Graaff accelerator. Multiple reflection infrared spectroscopy and x-ray diffractometry revealed that the ODMA multilayer was polymerized to give a thin polymer film having a regular layered structure when irradiated in nitrogen atmosphere, but no indication of polymerization was observed when irradiated in air. A preliminary study on the ODMA monolayer at a nitrogen–water interface indicated that the monolayer was polymerized.     

Rational Design of Macromolecular Structures: Focusing on the Embryonic Stages of Polymerization

Acetate-terminated oligomers of fluoral, chloral and bromal, prepared with the lithium alkoxides of tert-butanol and (-)-borneol, were analyzed by gas chromatography, polarimetry, NMR and mass spectroscopies, and by single crystal x-ray diffraction methods. The configurational and conformational properties of the “embryonic” adducts were found to depend strongly on the relative size of the trihalomethyl side group in these systems. The results of our efforts, summarized here, help to shed new light on the origins of helical geometry and crystalline order in polymers of the perhaloacetaldehydes.     

Preparation and properties of isotactic and syndiotactic poly(methyl methacrylate)s,uniform with respect to molecular weight

Highly isotactic (it-) and highly syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) uniform with respect to molecular weight (stereoregular, uniform PMMAs) were isolated up to the 100mer from it- and st-PMMAs by supercritical fluid chromatography (SFC) and characterized by NMR and mass spectroscopies. Glass transition temperatures (Tg's) of the uniform it- and st-PMMAs were higher than those of the corresponding PMMAs with MWD and with similar molecular weight on average. The Tg values of the uniform it-and st-PMMAs series obeyed the relationship, Tg = Tg∞ - K/M, where M and Tg∞ denote molecular weight and Tg at infinite M, respectively. The reciprocal melting points (1/Tm) of uniform it-PMMA (degree of polymerization, DP = 28–44), obtained from methanol solutions by evaporating the solvent, increased linearly with increasing 1/DP. Extrapolation of the linear relation to 1/DP = 0 gave the Tm of it-PMMA with infinite DP; Tm∞ = 171.1°C. Thermal degradation behavior was studied by thermogravimetry and by SFC analysis of degradation products. In gel-permeation chromatography (GPC) measurements, the it-50mer eluted faster than the st-50mer. Calibration curves for it- and st-PMMAs could be obtained using series of the uniform PMMAs. The instrumental spreading factor determined using it-25mer, it-50mer, st-25mer and st-50mer for our GPC chromatograph was 0.070 ml when the volume of the sample solution was 0.003ml. GPC analysis of a mixture of the it- and st-50mers in tetrahydrofuran indicated formation of a stereocomplex in the solution, and was found quite useful to elucidate the minimum sequence length required for complex formation.     

Solid-state solvolysis of thiophene-substituted trityl-type alcohols: nucleophilic substitution induced by gas-solid contact.

The nucleophilic substitution reaction by gas-solid contact has been investigated. When 9-thienothienylfluoren-9-ol derivatives were coground with dichlorodicyanoquinone (DDQ) and then exposed to methanol vapor, the corresponding 9-methoxyfluorenes were obtained in 15-70% yields. Throughout the whole procedure the solid state was retained. The generation of a radical cation in the coground solids via charge-transfer interaction between the substrate alcohol and DDQ was suggested by the ESR spectrum. The mechanism involving the collapse of the radical cation to generate a proton, which acts as a catalyst to afford the carbocation, was deduced based on the electrochemical oxidation of the substrate in solution. The propagation of the substitution reaction in the solid state has been shown for the carbocation upon contact with methanol vapor. The crystalline inclusion compounds of 9-thienothienylfluoren-9-ol derivatives incorporating methanol as a guest were exposed to HCl gas. This gas-solid reaction also led to the formation of the corresponding methoxy compounds maintaining the solid state. Through this work a new consequence of solid-state cogrinding is deduced.     

13C-Spingitter-Relaxationszeiten von verschiedenen Polymethacrylaten in Lösung

Ohne Zusammenfassung     

A full multiple scattering model for the analysis of time-resolved X-ray difference absorption spectra

A full multiple theoretical model (MXAN) is applied to fit picosecond difference X-ray absorption spectra at the ruthenium L(3) edge upon photoexcitation of aqueous [RuII(bpy)3]2+. We show that fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the (3)MLCT state are in good agreement with recently published values. The implementation of the present approach to L-edge spectra and its high sensitivity opens opportunities for its extension to a large class of experiments where difference X-ray absorption spectra are recorded.