摘要:

A method has been devised to approximate both the hydrate formula numbernand the standard thermodynamic functions for hydrate dissociation from the temperature change of the hydrate former fugacity along a univariant three-phase (hl1g) equilibrium line. Thermodynamic equations are derived, their validity discussed, and an iterative method for their solution is described. The univariant (hl1g) equilibrium dissociation of deuterium sulfide D-hydrate (D2S·nD2O phase h) into gaseous deuterium sulfide (g) and liquid deuterium oxide (l1) has been treated to give approximate formulae and dissociation constants at 58 temperatures from 2.798 to 30.666°C. Dissociation equilibrium constantsKp(h–> l1g) have been represented as a function of temperature by a four-parameter equation which yields both values and standard errors (i) for &Dgr;Hot(h–> l1g) and &Dgr;Cpot(h–> l1g) the standard enthalpy and heat capacity changes for D-hydrate dissociation and (ii) forn = rthe approximate formula number of the D-hydrate at each experimental temperature. The formula D2S·6.115D2O with standard error 0.018D2O is found for deuterium sulfide D-hydrate at lower quadruple pointQ(hs1l1g) 3.392°C; an approximate formula D2S·5.840D2O with SE 0.019D2O is found at upper quadruple pointQ(hs1l2g) 30.770°C.Key words: clathrate D-hydrate of deuterium sulfide, deuterium sulfide D-hyfrate, formula of deuterium sulfide D-hydrate, thermodynamics of clathrate hydrate dissociation, dissociation equilibrium constant of deuterium sulfide D-hydrate, standard enthalpy, and heat capacity changes for dissociation of deuterium sulfide D-hydra

ISSN:0008-4042    

DOI:10.1139/v99-219

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The reactions of PhBCl2with Li[CE(NtBu)(nBu)] or Li[CS(NtBu)(NHtBu)] (1:1 molar ratio) in toluene at 23°C produced the heterocycles Ph(Cl)B(&mgr;-NtBu)(&mgr;-E)C(nBu) (1a, E = NtBu;1b, E = O;1c, E = S) or Ph(Cl)B(&mgr;-NtBu)(&mgr;-S)C(NHtBu) (2), which were characterized by1H,11B and13C NMR and by mass spectra. X-ray structural determinations revealed that1a,1cand2contain four-membered rings. In2the thioamidate ligand adopts anN,Sbonding mode. Crystal data:1a, monoclinic, space groupP21,a= 8.816(3),b= 11.311(2),c= 10.168(3) Å, &bgr; = 98.86(3)°,V= 1001.7(5) Å3,Z= 2,R= 0.042, andRw= 0.020;1c, monoclinic, space groupP21/n,a= 7.617(2),b= 11.200(1),c= 19.568(2), &bgr; = 90.74(2)°,V= 1669.1(5) Å3,Z= 4,R= 0.046, andRw= 0.059;2, monoclinic, space groupP21/a,a= 11.357(2),b= 12.289(2),c= 12.620(3) Å, &bgr; = 95.43(2)°,V= 1753.4(5) Å3,Z= 4,R= 0.043, andRw= 0.027.Key words: boron, amidinate, oxoamidate, thioamidate, X-ray st

ISSN:0008-4042    

DOI:10.1139/v99-221

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A kinetic model is presented for the pyrolysis of ethylene at pressures ranging from 0.8 to 27 kPa and temperatures from 774 to 1023 K. The model is based on experimental measurements of C2H2, C2H6, C3H6, 1-C4H8, and 1,3-C4H6. In this temperature range the reaction is initiated by the disproportionation of C2H4and the observed products result from reactions of the C2H3and C2H5radicals produced in this process. The C2H2and 1,3-C4H6result from reactions of C2H3while C2H6, C3H6, and 1-C4H8result from reactions of C2H5. C2H2is produced exclusively by the decomposition of the C2H3radical. This process is in its falloff region throughout the range of experimental conditions examined and the yield of C2H2provides a measure of the degree of falloff. The production of 1,3-C4H6is controlled by the reaction C4H7–> C4H6+ H. The rate constants for this reaction were independent of pressure and are given as a function of temperature byk= 2.2 × 1013exp (-19.6 × 103/T). Production of C2H6is controlled by the reaction C2H5+ C2H4–> C2H6+ C2H3. The rate constant for this reaction is given as a function of temperature byk= 5.83 × 1011exp (-14.6 × 103/T). C3H6is produced by decomposition of 2-C4H9and is controlled kinetically by the isomerization reaction 1-C4H9–> 2-C4H9. The temperature dependence of the rate constants obtained for this reaction leads to a preexponential factor of approximately 3 × 1016and an activation energy of approximately 200 kJ mol-1. The yield of 1-C4H8is controlled by 1-C4H9–> 1-C4H8+ H. The rate constants for this reaction were independent of pressure and are given as a function of temperature byk= 2.97 × 1012exp (-17.1 × 103/T).Key words: kinetic modeling, ethylene pyr

ISSN:0008-4042    

DOI:10.1139/v99-217

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The title compound is one of a large number of compounds related to the drug suramin which have been found to have anti-HIV properties. However, its toxicity to uninfected cells is high. We crystallized the compound, determined its structure, and investigated the molecular basis for its high toxicity. The crystals are monoclinic,C2/c,a= 28.614(1),b= 10.031(0),c= 24.051(1) Å, &bgr; = 98.36(2)°,Z= 8, convergence atR= 0.066 for 4264 reflections withI> 2&sgr;(I). The oxygen atoms of one of the sulfonate groups are disordered, as are several water molecules. Stereochemical comparisons with a segment of B-DNA have yielded a plausible explanation for the molecule's toxicity.Key words: crystal structure, cellular toxicity, stereochemistry, NF-03

ISSN:0008-4042    

DOI:10.1139/v99-222

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A new podocarpane diterpene, 7&agr;,15-dihydroxypodocarp-8(14)-en-13-one (1) and eight new abietane diterpenes, abiet-8(14)-en-7&agr;,13&bgr;,15,18-tetraol (2), 7&agr;,13&bgr;,15-trihydroxyabiet-8(14)-en-18-oic acid (3), 13&bgr;,18-dihydroxyabiet-8(14)-en-7-one (4), 13&bgr;,15,18-trihydroxyabiet-8(14)-en-7-one (5), 7-oxo-13&bgr;-methoxyabiet-8(14)- en-18-oic acid (7), abiet-8(14)-en-7&agr;,12&agr;,13&bgr;,18-tetraol (8), 7&agr;,12&agr;,13&bgr;-trihydroxyabiet-8(14)-en-18-oic acid (9), and abiet-8(14)-en-7&agr;,12&agr;,13&bgr;,15,18-pentaol (10) were isolated from the CHCl3extract of the cones ofLarix kaempferi. Their structures were determined on the basis of chemical and spectral evidence. The inhibitory effects of compounds1-4and7-9on Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), were examined for a primary screening for anti-tumor promotors.Key words:Larix kaempferi, Pinaceae, cones, abietane, EBV-EA.

ISSN:0008-4042    

DOI:10.1139/v99-218

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

It is shown that chiral zeroes are integral to all pseudoscalar functions, and that these functions, and thus the chirality properties that are described by them, are therefore normally unsuitable as chirality measures. The multidimensional nature of chirality properties is explored. Chirality measures for nonrigid objects and stochastic systems are discussed. It is shown that if the chirality of a nonrigid object is described as a time average of the chirality measures of its instant configurations, this time average is nonzero not only for chiral but also for achiral molecules. This paradox can be resolved if chirality measures are properly applied to nonrigid objects.Key words: chirality, chiral zeroes, chirality measures, chirality properties.

ISSN:0008-4042    

DOI:10.1139/v99-223

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Two dimensional deuterium NMR measurements are reported for three different onium salts (CH3)3SeNO3-d3, (CH3)3TeI-d3, and (CH3)3SI-d9. In these molecular solids with the general structure (CH3)3E+X-, three methyl groups are attached to the E atom. There is the possibility of reorientation of the methyls about their C3axes and reorientation of the whole tri-methyl group about the C'3axis. From an analysis of the 2D NMR exchange spectra the angle between the E-C bonds and the rotation axis for trimethyl reorientation were determined. Exchange rates and spin lattice relaxation times are given for several temperatures, to show how the mixing times for the experiments were selected. The data presented for (CH3)3TeI-d3, demonstrate that 2D techniques are sensitive to motions on a time scale an order of magnitude slower than that accessible using 1D line shape techniques.Key words: deuterium NMR, molecular motion, onium salts, two dimensional spectra.

ISSN:0008-4042    

DOI:10.1139/v99-226

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Humic substances (HS) were extracted with the aid of 0.1 M Na4P2O7and 0.5 M NaOH solutions from the sediments of four lakes located in the Sudbury area in Ontario, Canada, namely, Tilton, Clearwater, Silver and Ramsey Lake. The humic acid (HA) and fulvic acid (FA) extracts, purified and characterized using classical methods i.e., elemental analysis, FTIR spectroscopy, and CPMAS13C NMR (see N. Belzile, H.A. Joly, and H. Li. (1997)), were submitted to pyrolysis - gas chromatography - mass spectrometry (Py-GC-MS). The pyrolysates of the HA and FA extracts were found to be complex mixtures of at least 200 compounds. Results based on statistical analysis of the abundances of pyrolysis products (of known origin) revealed trends similar to those obtained from the classical bulk characterization techniques. The Py-GC-MS technique supported the observation, obtained from classical methods, that the chemical composition of HA extracts varied less significantly among the four lake sediments than for the FA extracts. The abundances of lignin and carbohydrate pyrolysates showed the highest variation among the FA extracts. Pyrolysis products originating from lignin, carbohydrates, proteins, and fatty acids were identified.Key words: humic substances, humic acid, fulvic acid, pyrolysis, pyrolysis – gas chromatography – mass spectrometry, lake sediment

ISSN:0008-4042    

DOI:10.1139/v99-228

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The titration of NaOH by HCl is achieved through infrared spectral measurement of the various mixtures. Factor Analysis (FA) is used to separate the spectra. Four principal spectra were necessary to perform the analysis: pure water, 2.09 M HCl, 2.23 M NaOH, and 2.60 M NaCl solvated water. Each of the 18 experimental spectra obtained was determined to be a linear combination of these principal spectra. The composition of the solutions retrieved from the IR analysis is identical to what was determined by the mass balance. The mean activity coefficient of HCl was calculated using the concentration of HCl obtained by IR and the activity obtained by pH measurements. It was found that the mean activity coefficient increased by a factor greater than 2 in the presence of 1 M NaCl. Because the water molecules associated to the ionic pair H+/Cl-, as observed by IR, are unmodified by the presence of the salt, such an increase cannot be attributed to a modification of the strong association of the water molecules to the pair of ions.Key words: infrared spectroscopy; ATR; liquid; acidic solutions; alkaline solutions; aqueous solutions; factor analysis; principal spectra; HCl-, NaOH-, NaCl-solvated water; activity coefficient; IR titration.

ISSN:0008-4042    

DOI:10.1139/v99-231

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The contribution of stilbene-parahydroquinone structures, formed from &bgr;-5 units during refining and bleaching, in photoreversion of peroxide-bleached high-yield pulps, was studied using 4'-benzyloxy-2,5-dihydroxy-3,3'-dimethoxystilbene (I), as a model compound. The various photoproducts formed during irradiation ofIin solution or adsorbed on cellulose paper were identified. Isomerization of the stilbene double bond and oxidation of the hydroquinone into quinone were observed in solution, whereas in the solid state only the formation of the quinone was found to operate. Our attempts to detect and quantify stilbene-hydroquinones forming from &bgr;-5 units created on peroxide bleached mechanical pulp were not met with success.Key words: lignin, stilbene, hydroquinone, lignin model compound, pulp, photoyellowing.

ISSN:0008-4042    

DOI:10.1139/v99-230

出版商:NRC Research Press    

年代:2000

数据来源: NRC