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951.
Koller FO Schreier WJ Schrader TE Malkmus S Schulz C Dietrich S Rück-Braun K Braun M 《The journal of physical chemistry. A》2008,112(2):210-214
The ring-opening and ring-closure reactions of a photochromic indolylfulgimide are investigated with femtosecond vibrational spectroscopy. Spectral signatures due to excited-state decay and vibrational cooling are seen in the mid-IR region. For the ring-opening reaction triggered with visible pulses, a lifetime of the excited electronic state of 4 ps was obtained in polar solution. In a nonpolar solvent, this time constant is reduced to 2 ps. The ring-closure reaction induced with UV pulses displays an excited-state lifetime and thus a building of the photoproduct of roughly 0.5 ps. For all processes, the subsequent cooling occurs on a 15-ps time scale lasting up to approximately 50 ps. The time-resolved IR measurements do not support the existence of any long-living intermediate states. 相似文献
952.
The selective modification of arginine residues by malondialdehyde (MDA) was used to improve the mass spectrometric analysis of arginine oligomers (Arg(x), x = 4, 6, 7, 8, 9) and an arginine-containing dendrimeric peptide. MDA tagging significantly increased the hydrophobicity of the arginine side-chain and resulted in improved retention in RP HPLC of the oligoarginines using formic acid as mobile phase additive. This avoided the use of TFA to generate sufficient retention, as TFA was shown to lead to a dramatically reduced sensitivity (up to ten-fold for Arg(8) and Arg(9)) as a result of the strong signal suppression by ion pairing with multiple basic residues. MDA modification of Arg oligomers not only resulted in improved detection sensitivity for most of the peptides studied (e. g., more than six-fold for Arg(7)), but also greatly enhanced the quality of MS/MS spectra, in line with previous results for other peptides. Furthermore, MDA modification helped to identify major side products in a sample of a dendrimeric peptide, a class of peptides that is typically difficult to analyze by MS. 相似文献
953.
An ab initio potential energy surface of the Xe-H(2)O van der Waals dimer was constructed at the coupled cluster level of theory with single, double, and pertubatively included triple excitations. For the Xe atom, the small-core pseudopotential and augmented correlation-consistent polarized valence quadruple-zeta (aug-cc-pVQZ-PP) basis set was used. Dunning's augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis set was chosen for O and H atoms. Midbond functions were used to supplement the atom-centered basis sets. Rotational spectra of the Xe-H(2)O van der Waals dimer were recorded with a pulsed-nozzle Fourier transform microwave spectrometer. Rotational transitions within two internal rotor states, namely, the 0(00) and 1(01) states, were measured and assigned. Nuclear quadrupole hyperfine structures due to the (131)Xe (I = (3)/(2)), D (I = 1) and (17)O (I = (5)/(2)) nuclei were also observed and analyzed. Information about the molecular structure and the H(2)O angular motions was extracted from the spectroscopic results with the assistance of the ab initio potential. 相似文献
954.
955.
956.
Background
Rosiglitazone (ROZ) and glimepiride (GLM) are antidiabetic agents used in the treatment of type 2 diabetes mellitus. A survey of the literature reveals that only one spectrophotometric method has been reported for the simultaneous determination of ROS and GLM in pharmaceutical preparations. However the reported method suffers from the low sensitivity, for this reason, our target was to develop a simple sensitive HPLC method for the simultaneous determination of ROZ and GLM in their combined dosage forms and plasma. 相似文献957.
Ya-Ting Hsieh Nai-Tzu Kuo Eamor M. Woo 《Journal of Thermal Analysis and Calorimetry》2012,107(2):745-756
Abstract
Thermal behavior, miscibility, and crystalline morphology in blends of low-molecular-weight poly(l-lactic acid) (LMw-PLLA) or high-molecular-weight PLLA (HMw-PLLA) with various polyesters such as poly(butylene adipate) (PBA), poly(ethylene adipate) (PEA), poly(trimethylene adipate) (PTA), or poly(ethylene succinate) (PESu), respectively, were explored using differential scanning calorimeter (DSC), and polarized-light optical microscopy (POM). Phase behavior in blends of PLLA with other polyesters has been intriguing and not straight forward. Using a low- and high molecular weight PLLA, this study aimed at mainly using thermal analyses for probing the phase behavior, phase diagrams, and temperature dependence of blends systems composed of PLLA of two different molecular weights (low and high) with a series of aliphatic polyesters of different structures varying in the (CH2/CO) ratio in main chains. The blends of LMw-PLLA/PEA and LMw-PLLA/PTA show miscibility in melt and amorphous glassy states. Meanwhile, the LMw-PLLA/PESu blend is immiscible with an asymmetry-shaped upper critical solution temperature (UCST) at 220–240 °C depending on the blend composition. In contrast to miscibility in LMw-PLLA/PTA and LMw-PLLA/PEA blends, HMw-PLLA with polyesters are mostly immiscible; and HMw-PLLA/PTA blend is the only one showing an asymmetry-shaped UCST phase diagram with clarity points at 195–235 °C (depending on composition). Reversibility of UCST behavior, with no chemical transreactions, in these blends was proven by solvent recasting, gel permeation chromatography, and Fourier transform infrared spectroscopy (FT-IR). Crystalline morphology behavior of the LMw-PLLA/PEA and LMw-PLLA/PTA blends furnishes addition evidence for miscibility in the amorphous phase between LMw-PLLA and PTA or PEA. 相似文献958.
Igor E. Paukov Yulia A. Kovalevskaya Alexei E. Arzamastcev Natalia A. Pankrushina Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2012,108(1):243-247
Heat capacity of methacetin (N-(4-methoxyphenyl)-acetamide) has been measured in the temperature range 5.8–300 K. No anomalies in the C
p(T) dependence were observed. Thermodynamic functions were calculated. At 298.15 K, the values of entropy and enthalpy are equal
to 243.1 J K−1 mol−1 and 36360 J mol−1, respectively. The heat capacity of methacetin in the temperature range 6–10 K is well fitted by Debye equation C
p = AT
3. The thermodynamic data obtained for methacetin are compared with those for the monoclinic and orthorhombic polymorphs of
paracetamol. 相似文献
959.
Mahesh Datt Bhatt Akihisa Baba Takeaki Sakurai Katsuhiro Akimoto 《Journal of Solid State Electrochemistry》2012,16(3):1141-1149
We have performed ultraviolet photoelectron spectroscopy measurements and density functional theory calculations to study
the electronic structure at the interface between organic semiconductor (3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1,2,4-triazole
(TAZ)) and metals (Ca, Mg, Ag, and Au). The basic mechanism of interface states at organic–metal interfaces can be understood
by controlling the injection of charge carriers at these interfaces. The position of highest occupied molecular orbital relative
to the Fermi level and the magnitude of the interface dipole are measured for each organic–metal interface. For TAZ on Ca,
Mg, and Ag, interface states are observed near the Fermi level. However, no interface state is observed for TAZ on Au. It
is analyzed qualitatively that the interface state is formed due to interaction of TAZ lowest unoccupied molecular orbital
composed of C2p and metal s levels. It is suggested that the interface state plays an important role in charge transport at
the interface. The mechanism of formation of interface states and electrical properties are discussed. 相似文献
960.
SmAlO3 nanopowder synthesized by a citrate precursor method using citric acid as a chelating agent and ethylene glycol as an esterifying
agent was reported in this paper. The phase purity of the as-prepared powder was examined using thermogravimetry (TG) analysis
and differential scanning calorimetry (DSC) analysis, Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction
(XRD) studies showed that pure SmAlO3 phase with orthorhombic perovskite structure could be synthesized at 800 °C for 2 h without any detectable intermediate phase.
The average particle size calculated from transmission electron microscopy (TEM) investigation for the powder synthesized
at 900 °C was as low as 45 nm. The nanopowder was sintered to a density of 97% of the theoretical density at 1,550 °C for
2 h and the bulk ceramics exhibited excellent microwave dielectric properties as follows: a dielectric constant of 20.54,
a quality factor of 75,380 GHz and a temperature coefficient of resonate frequency of −69.2 ppm/K. 相似文献