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991.
The Raman spectra of neat (C2H5)2CO (pentanone) and its binary mixtures with hydrogen donor solvent (CH3OH), [(C2H5)2CO + CH3OH] having different mole fractions of the reference system, (C2H5)2CO in the range 0.1-0.9 at a regular interval of 0.1 were recorded in the CO stretching region. In neat liquid, the Raman peak appears asymmetric. The asymmetric nature of the peak has been attributed to the CO stretching mode of the two conformers of (C2H5)2CO having C2 and C2v point groups and the corresponding bands at ∼1711 and ∼1718 cm−1, respectively. A careful analysis of the Iiso (isotropic component of the Raman scattered intensity) at different concentrations reveals that upon dilution with methanol, at mole fraction C = 0.6, an additional peak in the CO stretching region is observed at ∼1703 cm−1 which is attributed to the hydrogen bonding with methanol. A peculiar feature in this study is that upon dilution, the peak at ∼1718 cm−1 shows a minimum at C = 0.6, but on further dilution it shows a blue shift. However, the other peak at ∼1711 cm−1 shows a continuous red shift with dilution as well as a maximum at C = 0.7 in the linewidth vs. concentration plot, which is essentially due to competition between motional narrowing and diffusion phenomena. A significant amount of narrowing in the Raman band at ∼1718 cm−1 can be understood in terms of caging effect of the reference molecule by the solvent molecules at high dilution. A density functional theoretic (DFT) calculation on optimized geometries and vibrational frequencies of two conformers of neat (C2H5)2CO in C2 ad C2v forms and the complexes with one and two CH3OH molecules with both the conformers was performed. The experimental results and theoretical calculations together indicate a co-existence of two conformers as well as hydrogen bonded complex with methanol in the binary mixture, [(C2H5)2CO + CH3OH] at intermediate concentrations.  相似文献   
992.
In this work we analyzed the specificity of the amide VI band for different types of secondary structure elements in protein structures. This band involves the bending motion of the CO group of the peptide chain that is typically observed in the spectral region from 590 to 490 cm−1. The infrared absorbance spectra of a set of polypeptide model compounds of well known secondary structure was obtained at defined pH, including poly (l-lysine), poly (l-tyrosine), poly (l-alanine) and poly (l-histidine). In addition spectra of membrane proteins from the respiratory chain, namely the NADH:ubiquinone oxidoreductase, the cytochrome c oxidase and its CuA fragment, the cytochrome bc1 complex, a Rieske-type protein and in addition myoglobin, have been comparatively investigated. The systematic analysis of the amide VI band of the polypeptides and the proteins allowed correlating the signal appearing at ∼525 cm−1 to α-helical structures and signals at ∼545 cm−1 to β-sheet contributions. Random coils have been found to contribute at ∼535 cm−1 while the β-turns were observed at ∼560 cm−1.  相似文献   
993.
Surface pressure (π)-molecular area (A) curves were used to characterize the packing of pseudo-ternary mixed Langmuir monolayers of egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and L-α-dioleoyl phosphatidylethanolamine (DOPE). This pseudo-ternary mixture EPC/DOPE/DOTAP has been successfully employed in liposome formulations designed for DNA non-viral vectors. Pseudo-binary mixtures were also studied as a control. Miscibility behavior was inferred from π-A curves applying the additivity rule by calculating the excess free energy of mixture (ΔG(Exc)). The interaction between the lipids was also deduced from the surface compressional modulus (C(s)(-1)). The deviation from ideality shows dependence on the lipid polar head type and monolayer composition. For lower DOPE concentrations, the forces are predominantly attractive. However, if the monolayer is DOPE rich, the DOTAP presence disturbs the PE-PE intermolecular interaction and the net interaction is then repulsive. The ternary monolayer EPC/DOPE/DOTAP presented itself in two configurations, modulated by the DOPE content, in a similar behavior to the DOPE/DOTAP monolayers. These results contribute to the understanding of the lipid interactions and packing in self-assembled systems associated with the in vitro and in vivo stability of liposomes.  相似文献   
994.
The aim of this investigation is to obtain a polymer-based hybrid material with biodegradability, biocompatibility, and good mechanical properties and this object was realized via. in-situ introduction of the unmodified calcium carbonate (CaCO3) into a poly(l-lactic acid) (PLLA) matrix. As verified by the measurements from scanning electron microscopy (SEM), optical microscopy, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), the hybrid films which possesses a uniform dispersion of calcium carbonate CaCO3 in nano-meter scale, mechanically robustness and thermal stability could be fabricated by a mineralization-alike process. For example, the storage modulus increases from 441 MPa of neat PLLA to 1034 MPa of hybrid film containing 2% (w/w) CaCO3. In addition, the hybrid films display a significant improvement in its UV-exposure resistance.  相似文献   
995.
Treatment of [Ru(CHR)Cl2(PCy3)2] (Cy = cyclohexyl) with Tl[N(Pr2iPO)2] and AgLOEt (LOEt = [CpCo{P(O)(OEt)2}3]) afforded the Ru carbene complexes [Ru(CHPh)(PCy3)Cl{N(Pr2iPO)2}] (1) and [LOEtRu(CHR)(PCy3)Cl] (2), respectively. Chloride abstraction of complex 2 with TlPF6 in MeCN afforded [LOEtRu(CHPh)(PCy3)(MeCN)][PF6] (3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.  相似文献   
996.
We developed a method for simultaneously determining l-citrulline and l-arginine levels in serum and tissue samples using RP-HPLC with ultraviolet (UV) detection. The serum was deproteinized by trichloroacetic acid and heat; the tissue was homogenized by trichloroacetic acid and deproteinized as the same as serum. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out. The linearity for l-arginine and l-citrulline ranged from 0 to at least 1000 μmol/L. R2 values were above 0.9999 for both. LODs for l-arginine and l-citrulline were 0.0462 μmol/L and 0.0195 μmol/L, respectively, while LOQs were 0.530 μmol/L and 0.417 μmol/L, respectively. Intra- and inter-day CVs were less than 3.5% and 7.5% in serum, respectively. The average recovery was from 85.5% to 116.5% in serum. Intra-assay CVs were 3.8% and 10.3%, and inter-assay CVs were 13.7% and 10.7% for l-arginine and l-citrulline respectively in tissue. The average recovery was from 92.8% to 113.5% in tissue. This is a reliable and convenient analytical method which is suitable for most clinical laboratories.  相似文献   
997.
Nanocrystalline tungsten oxides (WO3−δ) are currently receiving a lot of attention because of their interesting electrical, magnetic, optical and mechanical properties. In this report, we present the synthesis of PEG assisted tungsten oxide (WO3) nanoparticles by simple household microwave irradiation (2.45 GHz) method. The samples were characterized using powder X-ray diffraction (XRD), thermal analysis (TG/DTA), transmission electron microscopy (TEM), UV-visible diffusion reflectance spectroscopy (UV-VIS-DRS), cyclic voltammetry and electrochemical impedance spectroscopy. Powder XRD results revealed that both the samples prepared with and without surfactant crystallize in the orthorhombic structure corresponding to WO3·H2O phase. Subsequent annealing under identical conditions (600 °C/air/6 h) led to significantly different products i.e. monoclinic W17O47 from surfactant free sample and orthorhombic WO3 from PEG assisted sample. Blue emission was observed through UV-VIS-DRS with blue shift and the band gap energy was estimated as 2.7 and 3.28 eV for PEG assisted as prepared (WO3·H2O) and annealed samples (WO3) respectively. Electrochemical measurements have been performed on all the samples deposited on the surface of glassy carbon (GC) electrode which showed high sensitivity and good selectivity for PEG assisted sample (WO3·H2O) for the direct detection of l-dopa.  相似文献   
998.
New azadioxaphosphabicyclo[3.3.0]octane ligands showing a trans arrangement with regard to the two five-membered heterocycles, were obtained as a mixture of three conformers, in agreement with molecular modelling studies. The stability of oxaphosphane ligands was studied under basic catalytic conditions, monitored by NMR spectroscopy. Palladium catalytic systems containing these ligands were active in Suzuki C-C cross-coupling reactions between phenylboronic acid and aryl halides (bromide and chloride derivatives) bearing electron-donor or electron-withdrawing substituents, in both organic and ionic liquid solvents. The catalytic systems showed a high stability even under the most severe reaction conditions used in this work. The ionic liquid catalytic phase could be recycled up to ten times without significant activity loss.  相似文献   
999.
A stereoselective total synthesis of (−)-cleistenolide (1) derived from d-(−)-isoascorbic acid has been described. The new synthetic strategy involves highly diastereoselective reduction, one-pot protection of required benzoyl, acetyl groups, and the RCM reaction by using Grubbs catalyst are the key steps with considerable yields.  相似文献   
1000.
The hydrolytic reactions between various Pt(II) complexes of the type [Pt(L)Cl2] and [Pt(L)(CBDCA-O,O′] (L is ethylenediamine, en; (±)-trans-1,2-diaminocyclohexane, dach; (±)-1,2-propylenediamine, 1,2-pn and CBDCA is the 1,1-cyclobutanedicarboxylic anion) and the N-acetylated l-methionylglycine dipeptide (MeCOMet-Gly) were studied by 1H NMR spectroscopy. All reactions were realized at 37 °C with equimolar amounts of the Pt(II) complex and the dipeptide at pH 7.40 in 50 mM phosphate buffer in D2O. Under these experimental conditions, a very slow cleavage of the Met-Gly amide bond was observed and this hydrolytic reaction proceeds through the intermediate [Pt(L)(H2O)(MeCOMet-Gly-S)]+ complex. In general, it can be concluded that faster hydrolytic cleavage of the MeCOMet-Gly dipeptide was observed in the reaction with the chloride complex than with corresponding CBDCA Pt(II) complexes. The steric effects of the Pt(II) complex on the hydrolytic cleavage of the amide bond in the MeCOMet-Gly dipeptide were also investigated by 1H NMR spectroscopy. It was found that the rate of hydrolysis decreases as the steric bulk of the CBDCA and chlorido Pt(II) complexes increase (en > 1,2-pn > dach). These results contribute to a better understanding of the toxic side effects of Pt(II) antitumor drugs and should be taken into consideration when designing new potential Pt(II) antitumor drugs with preferably low toxic side effects.  相似文献   
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