Comparison of the Dynamics of Water Molecules in Crystals of Proton-Ordered Ice IX and Its Proton-Disordered Analog III

A computer simulation of proton-ordered ice IX and its proton-disordered analog III (768 molecules, 90 K) was carried out by the molecular dynamics method using Poltev–Malenkov's potential. For ice IX, the differences in the dynamic characteristics of molecules with O(1) and O(2) are much wider than those in the case of ice III. The libration spectrum of ice IX has a number of distinct acute peaks, and the spectrum of ice III is strongly smoothed. These peculiarities are explained by the proton ordering of ice IX and disordering of ice III. The latter is responsible for the great differences in the short- and especially long-range environment of water molecules in ice crystals and hence for the presence of many molecules with different dynamic characteristics. Thus averaging over a large number of different vibrational spectra of molecules leads to a smoothed total spectrum in the case of the proton-disordered crystal modification of ice.     

Optimum gas chromatographic conditions in wall-coated capillary columns. Extended and simplified forms of the Golay-equation

Band broadening in capillary columns is satisfactorily described by the Golay-equation extended to situations of appreciable pressure drop by Giddings. In practice, however, several simplifications are often made. The effect of these simplifications on the calculated values of the minimum plate height and optimum carrier gas velocity are treated systematically.     

毛细管电色谱中双电层叠加的研究

通过流动相中电解质浓度对毛细管电色谱柱效能的流动相平均线速度的影响，研究了ＣＥＣ中双电层叠加现象。提出选择合适电解质组成的浓度及在制备色谱柱过程中避免细小和破碎的固定相颗粒进入柱中，以有效地减小双电层叠加作用。     

冷态德士古气化炉流场与停留时间分布的研究

测定了德士古气化炉的冷态速度分布和停留时间分布。结果表明：德士古气化炉内在轴向２．５～３．０倍直径范围内存在回流，最大回流量为射流量的３．５倍左右；在平均停留时间之前，已有５０％左右的物料逸出炉外。本文指出，德士古气化炉中存在的问题，如结渣、耐火砖寿命短、有效气体成分偏低均与炉内流场有关。     

π-Bindungsbeitrag in Boranen, 2. Mitt.:Ab initio- und Kraftfeld-Rechnungen von Vinyldifluorboran

Ab initio calculations on vinyldifluoroborane yield a -contribution of 23 kJ/mol (5.5 kcal/mol) mainly due to the C=C bond and not to the lone pairs of the fluorine atoms. The rotational barrier was also determined. The force field calculations favour the interpretation of the bond structure derived from the theab initio results.

     

The Conductance- and Capacitance-Frequency Characteristics of the Rectifying Junctions Formed by Sublimation of Organic Pyronine-B on p-Type Silicon

The rectifying junction characteristics of the organic compound pyronine-B film on a p-type Si substrate has been studied. The pyronine-B has been sublimed on the top of p-Si surface. The barrier height and ideality factor values of 0.79±0.04 and 1.13±0.06 eV for this structure have been obtained from the forward bias current-voltage (I-V) characteristics. From the low capacitance-frequency (C-f) characteristics as well as conductance-frequency (G-f) characteristics, the energy distribution of the interface states and their relaxation time have been determined in the energy range of (0.53−E_v)-(0.79−E_v) eV taking into account the forward bias I-V data. The interface state density N_ss ranges from 4.93×10¹⁰ cm⁻² eV⁻¹ in (0.79−E_v) eV to 3.67×10¹³ cm⁻² eV⁻¹ in (0.53−E_v) eV. Furthermore, the relaxation ranges from 3.80×10⁻³ s in (0.53−E_v) eV to 4.21×10⁻⁴ s in (0.79−E_v) eV. It has been seen that the interface state density has an exponential rise with bias from the midgap towards the top of the valence band. The relaxation time shows a slow exponential rise with bias from the top of the valence band towards the midgap.     

Binding studies of sodium dodecyl benzene sulphonate with poly(N-vinyl-2-pyrrolidone)

The binding of sodium dodecyl benzene sulphonate (SDBS) with poly(N-vinyl-2-pyrrolidone) (PVP) has been investigated at 303.15 and 313.15 K using equilibrium dialysis, surface tension, viscosity, ultrasound velocity and ultrasound absorption techniques. From each of these studies four distinct regions of SDBS-PVP interactions were observed. Interaction of SDBS with PVP was found to involve the binding of surfactant dimers with the polymer molecule followed by usual micellization. The binding data has been analyzed in terms of various models of polymer-surfactant interaction.     

甲烷二氧化碳介质阻挡放电转化产物分布研究

针对介质阻挡放电甲烷二氧化碳转化实验,分析了反应的产物分布,探讨了进料组成和反应器结构对反应的影响.反应产物包括:高H2/CO摩尔比的合成气、气态烃、高辛烷值的汽油组分、醇和酸等含氧有机物.对所述电极结构,产物的选择性随碳数增加而降低;高的甲烷进料浓度有利于烃的生成,对醇和酸的最佳甲烷进料体积分数范围在67.4％～75.1％;放电间隙越小,原料转化率和烃、酸的选择性越大,大的放电间隙对醇的生成有利.     

S1←S0 Vibronic spectra and the structure of acetyl fluoride-h3 and acetyl fluoride-d3 molecules

UV absorption spectra of acetyl fluoride-h₃ and -d₃ (CH₃COF and CD₃COF) molecules in the region of S₁S₀ electronic transitions are investigated. The origins (0⁰ ₀ or 14^0± ₀) of these transitions are observed at 39912 and 39904 cm^–1, respectively, and some of the fundamental frequencies of these molecules in the s₀ and S₁ states are determined. In particular, the systems of torsion and inversion (out-of-plane C=O vibrations) energy levels are studied. The geometric parameters of an acetyl fluoride-h₃ molecule in the S₁ state are estimated by the theoretical simulation of the rotational contours of the 0⁰ ₀ (14^0± ₀) band. These data are used to evaluate the potential barriers to internal rotation in the S₀ and S₁ states, which were found to be 360 and 560 cm^–1 for acetyl fluoride-h₃ and 380 and 770 cm^–1 for acetyl fluoride-d₃, respectively, as well as the potential barriers to inversion in the S₁ states, which were found to be 2090 and 2370 cm^–1 for acetyl fluoride-h₃ and acetyl fluoride-d₃, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1957–1964, November, 1994.In conclusion, the authors would like to acknowledge T. S. Kuznetsova for the synthesis and purification of the AF samples.The research presented here was supported in part by the International Science Foundation under grant No. MJ 1000.     

Concerning the Thermal Diastereomerization of the Green Fluorescent Protein Chromophore

Summary. Two model compounds for the green fluorescent protein chromophore were prepared. One of them incorporates the natural 4-hydroxybenzylidene group of the natural tyrosin derived chromophore, the other one bears a methyl group instead of the hydroxy group. Whereas the photochemically prepared (E)-diastereomer of the first compound very effectively reverted thermally (room temperature) to the thermodynamically stable (Z)-diastereomer, the (E)-diastereomer of the second derivative proved to be stable even at elevated temperatures for more than a day. This finding can be rationalized by constructing the appropriate resonance structures showing that only in the first case an effective delocalization enables partial single bond character of the benzylidene double bond. From the standpoint of chemical etiology, only Nature’s choice of the tyrosin derived chromophore of the green fluorescent protein provides an efficient radiationless thermal relaxation channel for the unwanted photo-diastereomerization product formed after excitation besides the dominating fluorescence channel of its chromophore.