小檗碱质谱碎片离子稳定性分析及碎裂机理的量子化学研究

用量子化学B3LYP/6-31G(d)方法, 研究了小檗碱质谱碎片离子的稳定性规律. 通过几何参数分析、 结合能计算和前线分子轨道分析, 研究碎片离子可能的活性部位及各部位相对反应活性, 并从理论上探讨了质谱碎裂机理. 结合能计算结果表明, 分子离子中C9所连甲氧基的C—O键比C10所连甲氧基的C—O键更容易断裂. 同时发现, 质谱碎裂过程中, 氢的解离促进了羰基的解离, 即质谱中常见的解离CO的过程.     

The Influence of Alkali Metals on the Doping of Poly(p-phenylene) Oligomers

In this study, we report on crystallographic studies that were performed on Na- and K-doped terphenyl and quaterphenyl. The data obtained via X-ray scattering and transmission electron diffraction show that, for both K-doped terphenyl and quaterphenyl samples, there is an increase in the c parameter. However, in regard to Na-doped terphenyl, there is a c parameter decrease along with an a parameter increase, which may be accounted for by the polymerization of this oligomer. Moreover, in order to complete the crystallographic study, a Raman analysis was conducted to describe the localization of the radical anions and the local distortions induced by the electric charges during the doping process.     

双亲半柔性两嵌段共聚物在溶液中自组装形态的模拟退火研究

针对一系列疏溶剂嵌段与溶剂间的相互作用,用模拟退火方法研究了双亲半柔性两嵌段共聚物在溶液中的自组装形态.模拟结果显示共聚物在溶液中均形成核-壳聚集体,其中疏溶剂嵌段形成聚集体的核,亲溶剂嵌段形成聚集体的壳.当上述相互作用较小时,核呈球形,而壳如同长在核上的刺.随着上述相互作用的增大,核逐渐增大.在较大的相互作用时,核呈柱形;而随着相互作用的加大,长在核上的刺逐渐伏贴于核表面.在更大的相互作用时,核又呈球状,壳伏贴于核表面.     

Are measured values of the Auger parameter always independent of charging effects?

In x‐ray photoelectron spectroscopy (XPS) the Auger parameter is often used to study the electronic properties of elements, particularly in insulator materials, because this parameter is assumed to be independent of charging effects. In this paper we report on subtle differences in sample structure and experimental conditions for which the sample potential may not remain constant during the measurements for some spectrometers or experimental arrangements; for such conditions the Auger parameter is not independent of charging. We compare a series of measurements with insulating plate substrates of Al₂O₃ on which different amounts of SnO₂ and Au were deposited. X‐ray photoelectron spectra were collected for different conditions of the sample that was placed either grounded or left floating on a metallic sample holder during measurement. It is found that the Auger parameter is independent of the experimental conditions for Au but substantial differences were found for deposited SnO₂. Surprisingly, measurement artifacts due to charging appeared in the Auger parameter for Sn when the sample holder was grounded but not when it was left floating. In the grounded samples differences up to 0.6 eV in the Auger parameter for Sn were found with respect to the actual value of this parameter measured with substrates where charging effects were not significant. Because no differences in peak broadening have been observed under different measurement conditions, it has been assumed that the shift was not caused by a conventional differential charging phenomenon. Considering the different response of the substrate and the deposited layer on stabilizing the charge when the sample is grounded, we have worked out a possible explanation to account for the observed artifacts. Instrumental specifications should be optimized very carefully, especially if (as here) relatively high charging shifts point to a non‐optimum self‐biasing of the surface potential at the insulating samples. Copyright © 2003 John Wiley & Sons, Ltd.     

Modeling simultaneous saccharification and fermentation of softwood

Simultaneous saccharification and fermentation (SSF) of wood has been modeled for the past 15–20 years, but the substrates used for model evaluation have so far not included pretreated softwood. In the present study, data from lab-scale batch SSF of SO₂-impregnated, steam-pretreated spruce chips were used to evaluate a model found in the literature. The model, which was somewhat modified, consists of a number of nonlinear, coupled ordinary differential equations, which were solved numerically. Some parameter values were fitted to data by use of least-squares minimization. A difficulty in parameter estimation was the lack of cellobiose measurements, something that was relieved by adding assumptions about parameter relations. The simulated concentration profiles agreed well with the measured concentrations of glucose and ethanol. It is therefore concluded that the basic model features apply to softwood SSF. The model predicts rate saturation with respect to enzyme concentration at concentrations above 60 FPU/g cellulose, although this was not observed in the experimental data, which only comprised enzyme concentrations up to 32 FPU/g cellulose.     

Thermodynamic analysis on the cononsolvency of poly (vinyl alcohol) in water–DMSO mixtures through the ternary interaction parameter

Isothermal phase diagrams for the semicrystalline poly (vinyl alcohol) (PVA) in solutions composed of water and dimethylsulfoxide (DMSO) was studied at 25 °C. From the observed phase behavior, PVA was soluble in either water or DMSO individually but crystallization-induced gelation and liquid–liquid demixing were observed in water–DMSO mixtures. Flory–Huggins formalism including three binary interaction parameters and one ternary interaction parameter was used to study the phenomenon of the cononsolvency, i.e. the formation of nonsolvents by mixing two solvents. The equilibrium crystallization line in the DMSO-rich region and the total calculated binodals agreed well with the measured results when a composition-dependent ternary interaction parameter was included into calculations. In contrast, calculations yielded crystallization-induced gelation in the water-rich region, but experiments indicated that PVA remained well dissolved even 1 year after preparation. The discrepancy was explained by the temperature-induced changes in the relative interaction between water and PVA. In addition, the role of the ternary interaction parameter in the cononsolvent ternary polymer systems was discussed. It was found the contribution of the ternary interaction parameter in the cononsolvent system under study is to decline the degree of the cononsolvency. The driving force for cononsolvency is the strong interaction between water and DMSO to form the stable DMSO hydrate to exclude PVA segments in the vicinity of the hydrate.     

Improved order parameter (alignment) determination in cellulose nanocrystal (CNC) films by a simple optical birefringence method

Birefringence, based on the crystal orientation of a cellulose nanocrystal (CNC) film, has been investigated for the determination of crystal orientation. The prime focus of our study is to establish a simple and low-cost experimental technique using a standard UV–Vis spectrometer to determine the order parameter (S) for both isotropic and anisotropic configurations. Self-standing CNC films of various order parameters (S: 0–0.95) were prepared using shear flow with varying shear rates. The transmitted light intensity of CNC films between cross polarizers for the bright and dark fields were measured to determine the linear dichroitic ratio, which were used to calculate the order parameters of different crystalline arrangements. Two-dimensional X-ray diffraction results were compared to the birefringence technique to explore the presence of short-range amorphous order, which is significant in higher order parameter (S > 0.60) specimens. Thus, the new birefringence technique was shown to obtain a more accurate measurement of order parameter with an easier method using more common and lower cost equipment.     

Ortho effect in fluorobenzenes: cross-correlated relaxation and quantum chemical studies

An early solid-state NMR study of the shielding tensors in substituted fluorobenzenes had indicated the presence of the 'ortho effect'. This was confirmed recently in the liquid state from a study of cross-correlated relaxation, which gives a handle on the shielding tensor. We report here a combined experimental and computational study on substituted fluorobenzenes where the ortho substituent is varied systematically. Experimental measurements of the longitudinal relaxation of 19F indicate the cross-correlation between the chemical shift anisotropy (CSA) of fluorine and its dipolar interaction with the ortho proton, and provide a measure of the CSA orientation parameter. This parameter is obtained also from quantum chemical calculations of the 19F CSA tensor. We establish a correlation between the CSA orientation parameter and linear free energy parameters by resorting to a multi-parameter regression analysis. Excellent correlation is obtained for most of these substituents only when a parameter for the ortho effect is included.     

环己醇脱氢催化反应本征动力学研究

采用管式连续流动固定床积分反应器,对环己醇在Cu－Co/MgO催化剂上的脱氢反应本征动力学进行了研究,求出幂式速率模型各项参数,得到反应的表观活化能为44.28kJ/mol.将上述实验数据与由似平衡浓度法导出的速控步骤的数学模型相关联,求出各有关参数和物种的吸附烙.结果表明,以环己醇吸附和表面反应为速控步骤的模型可较好地进行关联.对上述模型进行了方差和残差分析,误差在宏观动力学研究允许范围内,实验无系统误差.方差分析表明,表面反应为速控步骤的模型对描述反应具有相对最小误差.     

Is There a Single Ideal Parameter for Halogen-Bonding-Based Lewis Acidity?

Halogen-bond donors (halogen-based Lewis acids) have now found various applications in diverse fields of chemistry. The goal of this study was to identify a parameter obtainable from a single DFT calculation that reliably describes halogen-bonding strength (Lewis acidity). First, several DFT methods were benchmarked against the CCSD(T) CBS binding data of complexes of 17 carbon-based halogen-bond donors with chloride and ammonia as representative Lewis bases, which revealed M05-2X with a partially augmented def2-TZVP(D) basis set as the best model chemistry. The best single parameter to predict halogen-bonding strengths was the static σ-hole depth, but it still provided inaccurate predictions for a series of compounds. Thus, a more reliable parameter, Ω_σ*, has been developed through the linear combination of the σ-hole depth and the σ*(C−I) energy, which was further validated against neutral, cationic, halogen- and nitrogen-based halogen-bond donors with very good performance.     

EFFECTS OF INTERFACIAL POLYUREA FILM ON THE STABILITY OF OIL IN WATER EMULSIONS

The stability of oil in water emulsions containing a triisocyanate soluble in the oil phase was investigated. The oil component was either di-n-butyl phthalate (DBP) or a mixture of DBP with liquid paraffin. The time required for the average size parameter to reach a constant value was studied. It was found that the polyurea film produced by an interfacial polymerization reaction between water and a triisocyanate contributed to make the stable emulsions. The effects of drop size, temperature, polarity of oil phase, triisocyanate concentration, and mechanical stirring on the stability of the emulsions were established in this study. The film thickness at the point where the average size parameter reached a constant value was found to be of the order of 0. 002 ～ 0. 004μ.     

Formation of parallel strips in thin films of polystyrene/poly(vinyl pyrrolidone) blends via spin coating on unpatterned substrates

Patterns of parallel strips, consisting of alternating polystyrene (PS) and poly(vinyl pyrrolidone) (PVP) regions, were observed in thin films spin cast from a PS/PVP/chloroform solution on unpatterned substrates. The formation of anisotropic patterns, manifested not only in thickness variation but also in composition variation, was found to be driven by Marangoni instability, with the PS and PVP streams flowing toward the preferred regions as the phase separation induced by solvent evaporation proceeded. The initial viscosity of the polymer solution and the thickness of the spin-cast films were lumped into one single parameter to study the phase morphology development at various initial polymer solution concentrations. Interestingly, the ratio of the square of the film thickness to the viscosity, a parameter loosely related to the Marangoni number, was found to reach a maximum value at the concentration where the strip patterns were most well-developed.     

热重法对含羧甲磺酰基偶氮染料的脱羧动力学研究

热重法对含羧甲磺酰基偶氮染料的脱羧动力学研究匡春香，潘鑫（大连理工大学化工学院大连１１６０１２）杨青（辽宁师范大学化学系大连１１６０２２）关键词热重法，染料，脱羧，动力学本文用热重法研究了四支含羧甲磺酰基偶氮染料（Ⅰ～Ⅳ）的脱羧反应，获得了脱羧温度，...     

A new three-particle-interaction model to predict the thermodynamic properties of different electrolytes

In this study, Guggenheim charging process, which involves the radial Boltzmann distribution, was introduced to develop a new predictive model with three parameters, ion–ion distance parameter, ion–solvent parameter, and solvation parameter. In this model, the ion–ion and ion–solvent molecule interaction are all included in the charging process, and it is independent of the temperature and solvent. This new model was applied to correlate the experimental data from literatures for 208 electrolytes aqueous solution at T = 298.15 K of which the concentration range is wide. The calculated results agreed well with the experimental ones for most electrolytes, especially for the prediction in high ionic strength. The estimation of solvation parameter S also gave that the solvation tendency for cations and anions follow a trend, which is in consistent with results published in literature. Investigations were also been made in calculations for electrolytes solutions at other temperatures and non-aqueous system, which proved this model was also feasible.     

Effect of solvent quality on kinetics of tethered layer formation

We conducted a study of the effect of solvent quality on the kinetics of formation of a layer of polymer chains tethered to a solid substrate. In these experiments, tethering was accomplished by means of chemical bond formation between reactive sites on the surface and the end‐functional groups of the polymer chains in solution. All experimental variables were held constant except for the χ‐parameter between the polymer and solvent. Variation in the χ‐parameter was achieved by use of a series of nonpolar, organic solvents. The distinct three‐regime kinetics, typical of tethering reactions run in a good solvent and in the absence of segmental adsorption, was observed over the range of values for the χ‐parameter. As expected, an increase in the χ‐parameter (a decrease in solvent quality) did result in increased tethering density, but, contrary to expectation, no increase in tethering rate was observed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5530–5537, 2004     

Determination of the stability and magnetic properties of Fe–Pd nitride using the generalised gradient approximation (GGA)

In this study, an electronic structure calculation of the substituted nitride PdFe₃N was conducted, and a posterior understanding of its structural and magnetic properties was obtained. A first principle method was applied to study the lattice parameter variation in relation to the energy of solid formation. After the equilibrium parameter was found, some properties of the ground state, such as the magnetic moment and the bulk modulus, were calculated. Preliminary observations show that the material properties of γ′-Fe₄N vary significantly with the insertion of the palladium atom in the matrix as well as when the material is subjected to applied pressure. The density of states shows a strong interaction between the s states of nitrogen and, primarily, the s and p states of iron, presenting a weak interaction with the palladium atoms. The analysis of such properties illustrates why these nitrides have a promising future for use in technological applications.     

Comparison of two methods for predicting aqueous solubility.

This study compares the solubility predictions of the two parameter general solubility equation (GSE) of Jain and Yalkowsky with the 171 parameter Klopman group contribution approach. Melting points and partition coefficients were obtained for each of the compounds from Klopman's test set. Using these two variables, the solubility of each compound was calculated by the GSE and compared to the values predicted by Klopman. Both methods give reasonable solubility predictions. The data of Klopman produced an average absolute error (AAE) of 0.71 and a root-mean-square error (RMSE) of 0.86, while the GSE had an AAE of 0.64 and a RMSE of 0.92.     

Twin nematic phenylbenzoates in a.c. electric fields

The orientational behaviour of nematic compounds having twin phenylbenzoate mesogens was examined under a wide range of a.c. electric fields (0-2 V mum-1 and 10Hz-50 kHz). For this study, crossed polarizing optical microscopy (POM) and real-time X-ray diffraction (RTXRD) measurements were employed to investigate optical and orientational response. These nematic compounds have a positive dielectric anisotropy and a relatively low epsilon// relaxation frequency which allowed study in both homeotropic and planar orientations over a controllable frequency range. The optical behaviour and X-ray results corresponded well, providing a tool for understanding the orientational behaviour of these liquid crystals. For homeotropic alignment, an electric field of over 1 V mum-1 was required in order to obtain good orientation. However, homeotropic orientation depended on a delicate balance between thermal fluctuations and dielectric torque imposed by the electric field, which are both strongly related to the elasticity of the LC domains. Due to this effect, the highest orientation parameter achieved for homeotropic orientation was only 0.48, which indicated that this state was still non-equilibrium. On the other hand, for planar orientation, a uniform texture with orientation parameter of 0.65 was easily obtained even at electric fields as low as 0.2 V mum-1. The application of an electric field stronger than 1 V mum-1 induced a distortion in the texture, and reduced the orientation parameter to 0.45 for planar alignment.     

Analysis of human brain tissue, brain tumors and tumor cells by infrared spectroscopic mapping

This study uses infrared (IR) spectroscopic, point detection, mapping procedures to examine tissue samples from normal brain specimens and from astrocytic gliomas, the most frequent human brain tumors. Model systems were derived from cultured glioma cell lines. IR spectra of normal tissue sections distinguished white matter from gray matter by increased spectral contributions from lipids and cholesterol. Qualitatively the same differences were found in IR spectra of low and high grade glioma tissue sections pointing to a significant reduction of brain lipids with increasing malignancy. Whereas spectral contributions of proteins and lipids were similar in IR spectra of glioma cells and tissues, nucleic acid bands were more intense for cells suggesting higher proliferative activities. For statistical analyses of IR spectroscopic maps from 71 samples, a parameter for the lipid to protein ratio was introduced involving the CH(2) symmetric stretch band with lipids as main contributors and the amide I band of proteins. As this parameter correlated with the grade of gliomas obtained from standard histopathological examination, it was applied to classify brain tissue sections based on IR spectroscopic mapping.