Radiation chemical studies of protein reactions: Effect of radiation on the breaking of secondary bonding in protein

The effect of radiation on the breaking of secondary bonding in protein was studied by measuring the viscosity change at different radiation doses and urea concentrations. An experimental equation for the viscosity change was obtained, and the observed behavior was explained on the basis of the molecular mechanism. The general equation for the viscosity change is given by η_red = A(X ? Be^?kx) + C log R, where η_red is the reduced viscosity of the solution, R is the dose of γ-radiation, X is the concentration of urea, and A, B, C, and k are adjustable constants.     

Products of the gas-phase reactions of aromatic hydrocarbons: Effect of NO2 concentration

The formation yields of selected products of the OH radical-initiated reactions of toluene, o-xylene, and 1,2,3,-trimethylbenzene have been measured in the absence of NO_x and in the presence of varying concentrations of NO and NO₂. The formation yield of o-cresol from toluene increased from 0.123 ± 0.022 in the absence of NO_x to 0.160 ± 0.008 for an average NO₂ concentration of 1.7 × 10¹⁴ molecule cm³. The formation yield of 2,3-butanedione from o-xylene was 0.092 ± 0.013 in the absence of NO_x, and in the presence of NO_x decreased from 0.16 at an average NO₂ concentration of (7–8) × 10¹² molecule cm^?3 to 0.09 at an average NO₂ concentration of ca. 7 × 10¹³ molecule cm^?3. The formation yield of 2,3-butanedione from 1,2,3-trimethylbenzene increased from 0.18 in the absence of NO_x to 0.444 ± 0.053 in the presence of ca. (0.16–3.6) × 10¹³ molecule cm^?3 of NO₂. These product data are consistent with literature kinetic data showing that the hydroxycyclohexadienyl radicals formed by OH radical addition to the aromatic ring react with both O₂ and NO₂ and with the NO₂ reaction rate constants being ca. 10⁵ higher than the O₂ reaction rate constants at room temperature. Under typical tropospheric conditions the reactions of the hydroxycyclohexadienyl radicals with O₂ will dominate over their reactions with NO₂. © 1994 John Wiley & Sons, Inc.     

Calorimetric studies of adsorption of aromatic hydrocarbons on silicalite

Conclusions Complex relationships between the differential adsorption heats and the degree of filling are observed when benzene and toluene are adsorbed on silicalite. A possible reason for this phenomenon is either a redistribution or a reorientation of the adsorbed molecules when the degree of filling exceeds 0.5.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2820–2823, December, 1982.The authors express their gratitude to Dr. Fahlke for synthesizing and supplying the silicalite sample.     

Radiation chemical and magnetic resonance studies of aqueous agarose gels containing ferrous ions

Aqueous agarose gels containing ferrous ions sustain a radiolytic chain reaction, producing Fe³⁺. G(Fe³⁺)-values up to 156 have been observed, independent of dose rate between 0.434 and 3.74 Gy min^-1. Dissolved oxygen is needed to maintain the chain reaction, and initial ferric yields are increased if the gel is oxygen saturated, or if the Fe²⁺ concentration is decreased. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production, permitting visualizing of dose levels in these gels by magnetic resonance imaging techniques. There is a potential for application to radiation therapy treatment planning.     

Theoretical studies on the carcinogenicity of polycyclic aromatic hydrocarbons

The distinct molecular regions of a set of 28 polycyclic aromatic hydrocarbons (PAHs) showing varying degrees of carcinogenic activity (CA) have been analyzed on the basis of their calculated molecular electrostatic potential (MESP) at B3LYP/6-31+G(d,p) level of theory. The MESP, being a property directly related to electron density, clearly distinguishes the electron dense centers in the molecule into K, L, M, and newly defined N regions. Further, a quantitative structure activity relationship (QSAR) model of carcinogenicity is developed using the volume of MESP lobes at the named regions for a set of 17 carcinogenic molecules with experimentally known CA index. The QSAR equation suggested that all the geometrical regions are significant in determining the carcinogenic property of PAHs. The model clearly showed that K and M regions have activating carcinogenic effect whereas L and N regions have deactivating carcinogenic effect. The CA showed considerable enhancement when any three distinct regions are present in a PAH. On the other hand, all the PAH systems with only one type of region are inactive irrespective of whether the region is activating or deactivating. Similarly, molecules showing the presence of two types of regions are either inactive or weakly active. The essential features of both the "K, L region" and the "bay region" theories of carcinogenesis are well evident in the new QSAR model, as the former theory works on the basis of activating K and deactivating L regions whereas the latter theory is related with the activating M region.     

Computational studies of the 3-Dimensional structure of cyclopenta polycyclic aromatic hydrocarbons containing a gulf region

Recently, some cyclopenta-fused polyaromatic hydrocarbons, an environmentally relevant subclass of chemicals, have been shown to have carcinogenic activity in animals. It has been suggested that benz[l] aceanthrylene ( I ), an active member of this subclass with a gulf region, has a trans dihydrodiol metabolite that is nonplanar and has two distinct spatial configurations. We have used MMP 2(85) and AM 1 to investigate the three-dimensional structure of this dihydrodiol and other similar derivatives of ( I ) and have found that although ( I ) is somewhat nonplanar the relevant derivatives are all nearly planar. Further, we have computed potential functions for the bending of the angular ring in the gulf region using MMP 2(85), AM 1, and ab initio computed energies for AM 1 spatial configurations and find that these molecules all have only a single potential minimum. We have performed the same calculations for benzo[c]phenanthren and its 1,12 dimethyl derivative, molecules with a similar gulf region for which crystallographic data exists. In agreement with that data, we find that two distinct spatial configurations exist separated by significant barries. The differences between the results generated by the three different methods of computation will be discussed.     

Recent developments on the mechanism of chemical carcinogenesis by aromatic hydrocarbons

This paper presents a critical discussion of recent discoveries on the metabolic transformations of polycyclic aromatic hydrocarbons and their interactions with nucleic acids in the light of quantum-mechanical theories of chemical carcinogenesis.     

Studies on the permeation of aromatic hydrocarbons through liquid surfactant membranes

The effect of operating parameters on the batch scale permeation of hydrocarbons from benzene—heptane mixtures and a straight run naphtha through liquid membrane is reported. The thirteen operating parameters studied include: mixing intensity, surfactant concentration, treat ratios, contact times, temperature and additives. The variations observed in the two key properties of selectivity and aromatic recoveries as well as in product compositions with change in operating parameter is discussed. Surfactant concentration contact time during permeation, type and concentration of additive used appear to exert a marked effect on the enrichment obtained. The careful optimization of operating parameters give selectivities as high as 50 and aromatic recoveries of 75% in one stage at 30°C. Comparison of data with batch liquid—liquid extraction data from extraction of similar feed mixtures with the most widely used solvent, sulpholane, under typical industrial conditions, has shown that selectivities and aromatic recoveries in liquid membrane permeation (LMP) are much higher. Batch scale LMP experiments with straight run naphtha as feed show that under optimum conditions of membrane stability and operating parameters the dearomatization of naphtha from an initial aromatic level of 22 vol.% to 10.5 vol.% is possible in one stage at 30°C with a raffinate yield of 63%. The results obtained on benzene—heptane model mixture compare fairly well with those obtained on naphtha feed.     

Analysis of high-molecular-mass polycyclic aromatic hydrocarbons in environmental samples using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) with molecular masses higher than 300 u were analysed using LC-atmospheric pressure chemical ionization (APCI) MS in extracts of environmental samples from Hamilton, Canada including zebra mussels from Hamilton Harbour, air particulate and coal tar. The LC-APCI-MS profiles of three molecular mass classes of PAHs (326 u, 350 u and 374 u) were compared to identify potential sources of PAH contamination in Hamilton Harbour. The Hamilton air particulate profile was also compared with an urban air reference standard (NIST SRM 1649) from Washington, DC, USA. Profiles of all extracts were similar and suggested an environmental predominance of PAHs within the three isomeric molecular mass classes studied. However, PAHs of molecular mass 326 u and 350 u were detected in extracts of coal tar and zebra mussels from Hamilton Harbour but were not detected in Hamilton air. These results indicated that some high-molecular-mass PAHs may be characteristic of contamination by coal tar.     

Model quantum chemical studies of the electronic structure and aspects of reactivity of diol epoxides of aromatic hydrocarbons

This paper offers a unified presentation of the main ring conformers of the diol expoxides, triol carbonium ions, and tetrols related to the “bay-region” benzo ring of carcinogenic metabolites of PAH and brings forward quantitative information through ab initio SCF computations about their relative energies. It substantiates and evaluates the energy of the syn epoxide-OH4 hydrogen bond and, on the contrary, refutes the significance of an O ?H? O or an O^? ?H? O bond in the triol carbonium ions. It provides an explanation for the similar rates of acid-catalyzed hydrolysis of the syn and anti diol expoxides. It evaluates the stabilization of the triol carbonium ions due to the presence of a neighboring double bond and accounts for the spontaneous opening of protonated epoxides. Finally it accounts for cis hydrolysis of the syn diol epoxide and trans hydrolysis of the anit diol epoxide under acid conditions.     

Effect of viscosity of a liquid membrane containing oleyl alcohol on the pertraction of butyric acid

Solvent formulation is important in the optimization of the mass-transfer through supported liquid membranes (SLM) in pertraction and membrane extraction. Oleyl alcohol (OA) is frequently used as the solvent or diluent in the extraction of carboxylic acids. A disadvantage of OA is its relatively high viscosity of 28.32 mPa s at 25°C. This can be decreased by the application of a less viscous OA diluent, e.g. dodecane. The relationship between the ratio of the distribution coefficient of butyric acid (BA), D _F, and the viscosity of OA-dodecane solvents, µ, as extraction and transport characteristics, and the overall mass-transfer coefficient, K _p, through SLMs was analyzed. Dependence of the D _F/µ ratio on the OA concentration showed a maximum at the OA concentration of 15 mass % to 30 mass %. The OA concentration dependence of K _p for SLMs exhibited also a maximum at about 30 mass % and 20 mass % of OA at the BA concentration driving force of 0.12 kmol m^?3 and 0.3 kmol m^?3, respectively. Shifting of the maximum in K _p dependences towards lower OA concentrations by increasing the BA concentration driving force is in agreement with the D _F/µ ratio dependence. Using pure OA as the solvent or diluent is not preferable and a mixture of a low viscosity diluent with the OA concentration below 40 mass % should be used. The presented results show the potential of the D _F/µ ratio in the screening and formulation of solvents in extraction and SLM optimization.     

预测氯代芳烃对戈卑鱼毒性的理论研究

为建立氯代芳烃对戈卑鱼毒性相关的QSAR模型,分析了22种氯代芳烃的结构特征,计算了各个分子的分子连接性指数.通过多元线性逐步回归分析研究,筛选了其中4种分子连接性指数~0X,~2X,~3X和~4X_(PC),建立了这4种指数与氯代芳烃对戈卑鱼毒性的定量结构-活性相关的QSAR模型,方程的相关系数R=0.979,判定系数R_(adj)~2=0.959,标准误差S=0.134,经检验该模型具有良好的稳定性和预测能力.     

High temperature normal phase liquid chromatography of aromatic hydrocarbons on bare zirconia

The normal phase HPLC behavior of a bare zirconia column was studied at temperatures up to 200 °C using a hexane mobile phase. The use of elevated column temperatures significantly decreased the retention of twenty five aromatic model compounds according to the van't Hoff equation (>30-fold decrease for some compounds). Large improvements in peak shape, efficiency (>2.2-fold), aromatic group-type selectivity, and column re-equilibration times (>5-fold) were obtained at elevated temperatures. The thermal decomposition of two polar nitrogen compounds (indole and carbazole) was observed in a hexane/dichloromethane mobile phase at temperatures greater than 100 °C. The first order decomposition of carbazole was studied in further detail.     

Retention properties of the fluorinated bonded phase on liquid chromatography of aromatic hydrocarbons

The unique characteristics of a bonded-fluoroalkylsilane column, Fluofix, are described by comparison with those of a bonded octylsilane column, C8, in the reversed-phase chromatography of aromatic hydrocarbons. The selectivity of homologous aromatics on the fluorinated column varied with the methanol concentration in the eluent. At a larger proportion of methanol than 80:20 (v/v) the larger aromatics eluted faster than the smaller ones. However, with less methanol, the aromatics were eluted in order of their molecular size, as usually reported for a conventional hydrocarbonaceous column. A dependence of the retention mechanism on the composition of the eluent was suggested by the decrease in the entropy-enthalpy compensation temperature, beta, with increase of methanol concentration in the eluent. In order to explain the concentration dependence of the retention, the molecular interaction energy in the retention process was calculated by computer simulation. The interaction energy between aromatics and the stationary ligand on the Fluofix column was smaller than that on the C8 column and comparable to the interaction energy between the aromatics and methanol. At higher methanol concentrations, solute-fluorinated ligand complex formation was obstructed by the methanol molecules solvating the solute, reducing the retention of the larger aromatics.     

Physical and chemical studies on cement containing sugarcane molasses

Molasses is generally used as a grinding aid in cement and as a water reducer and retarder in concrete. In China, the output primarily consists of sugarcane molasses. In this paper, the effects of sugarcane molasses on the physical performance and hydration chemistry of conventional Portland cement were investigated. The setting times, the normal consistency of cement pastes, the compressive strengths and fluidities of the mortars were respectively determined according to Chinese Standard GB/T 1346, GB/T17671 and GB/T 2419. The effect of molasses on the hydration kinetics of cement was investigated using a calorimeter. The hydration products and pore size distribution of the cement pastes were analysed by X-ray powder diffraction, differential scanning calorimetry and a mercury injection apparatus. The results show that a small amount of sugarcane molasses retards the setting and hardening of cement paste and increases the fluidity of cement mortar, while excess molasses accelerates the setting and hardening. Molasses improves significantly the compressive strength at 3d due to the decrease of porosity. The addition of 1.0 % molasses accelerates the formation of ettringite, prevents the second hydration of aluminate phase and delays the hydration of C₃S.     

Volumetric studies on the binary mixtures of furan with some aromatic hydrocarbons

Molar excess volumes of mixing for the binary mixtures of furan with benzene, toluene, ethylbenzene, o-, m-, and p-xylenes have been calculated from the precise experimental density data at 25°C over the entire composition range. The results have been discussed in terms of molecular interactions and geometric effects in the binary mixtures.