摘要:

A series of copolymers of 4'-[[[2-(methacryloyloxy)ethyl]ethyl]amino]-4-nitroazobenzene (DR1M) and an optically "inert" styrene comonomer were tested for photoinduced birefringence. The level of saturated birefringence increased linearly with the content of DR1M in the copolymer. The birefringence per mole of azo chromophore was constant along the copolymer series.Key words: azobenzene, photoinduced birefringence, copolymers,trans-cisisomerization.

ISSN:0008-4042    

DOI:10.1139/v00-034

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Reliable atomic properties can be obtained via the theory of "Atoms in Molecules" (AIM) via integration over a finite volume. These integrations are challenging because of the variety and complexity of the shape of the AIM atoms. In practice the integration of a large number of atoms (100-1000, sampled from many molecules) yields integration errorsL(Ω) of varying magnitude. We prove that it is impossible to predict the size of an angular Gauss-Legendre grid (outside the &bgr; sphere) that guarantees a pre-set error. Hence it is incorrect to assume that a large grid (~23 000 angular grid points) will automatically yield a lowL(Ω) value. The erratic relationship between the integration error and the grid size prompts a statistical interpretation of atomic integration, at a purely practical level. More importantly we have investigated the relationship betweenL(Ω) and seven atomic properties which include volume, energy, and the magnitudes of five electrostatic multipole moments. The electronic population (N(Ω)) and the volume (v(Ω)) of carbon is linearly correlated withL(Ω), enabling the interpolation or extrapolation ofN(Ω) andv(Ω). Other properties of carbon and other atoms (N, O, and S) yield low correlation coefficients but occasionally trends can be observed. For example, we find that some properties are systematically underestimated ifL(Ω) is negative. This work has led to an estimate of safe error bars of atomic properties for atoms occurring in biological molecules with reasonably sized integration grids. The most stable properties were found to be the energy and the population. Finally, we have observed that the influence of the grid orientation is less ifL(Ω) is small, and that population and energy are the least affected.Key words: electron density, topology, atoms in molecules, atomic properties, amino acids.

ISSN:0008-4042    

DOI:10.1139/v00-026

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Excess molar volumes (VEm) and dynamic viscosities (η) for five (alkoxyethanol + propylamine) mixtures have been measured as a function of composition at 298.15 K and atmospheric pressure. The alkoxyethanols were 2-methoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol, and 2-{2-(2-methoxyethoxy)ethoxy}ethanol. The excess molar volumesVEmare all negative over the whole composition range. The viscosity data have been correlated by the methods of Kendall and Monroe, Grunberg and Nissan, Tamura and Kurata, Hind, Katti and Chaudry, and with McAllister correlations. From the experimental data, deviations in the viscosity (&Dgr;η) have been calculated. The results are discussed in terms of the interaction between components.Key words: excess volume, viscosity, binary mixtures.

ISSN:0008-4042    

DOI:10.1139/v00-027

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Acid-catalyzed hydrolysis of acetophenone dimethyl acetal (ADMA) and trimethyl orthobenzoate (TMOB) is retarded by cyclodextrins (CDs): &agr;-CD, &bgr;-CD, hb-&bgr;-CD = "hydroxypropyl-&bgr;-cyclodextrin", and &ggr;-CD. The observed first order rate constants (kobs) vary with [CD] in the manner expected for 1:1 binding between the substrates and the CDs. Similar behaviour was found recently for the hydrolysis of benzaldehyde dimethyl acetal (BDMA). With &bgr;-CD and hp-&bgr;-CD, the binding of all three substrates (BDMA, ADMA, TMOB) is strong and the CD-bound forms have very little reactivity. By contrast, substrate binding by &agr;-CD is much weaker, and the CD-bound forms have appreciable, though reduced, reactivity. Substrate binding by &ggr;-CD is also relatively weak, but the bound substrates have very low reactivities. The hydrolysis reactions of ADMA, TMOB, and BDMA have been evaluated as kinetic probes of the binding of guests to CD hosts. For &agr;-CD, &bgr;-CD, and hp-&bgr;-CD, the addition of guests reduces the amount of free CD and thereby alleviates retardation of the hydrolysis by the CD. The resultant increases in hydrolysis rates can be analyzed to provide estimates of CD-guest dissociation constants,KG. For aliphatic alcohols and ketones binding to &bgr;-CD and hp-&bgr;-CD, all three probe reactions provide values ofKGthat agree well with each other and with literature values determined by other methods. The approach does not work well with &agr;-CD because of its much weaker binding of the kinetic probes and their less pronounced dependence ofkobson [&agr;-CD]. In the case of &ggr;;-CD, the approach cannot be used because added guests cause a further lowering in the rate of hydrolysis, suggesting the formation of an unreactive ternary (substrate·CD·guest) complex.Key words: acetal, hydrolysis, cyclodextrin, host-guest, binding.

ISSN:0008-4042    

DOI:10.1139/v00-033

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Excess molar volumes (VEm) and viscosities (η) for mixtures of triethylene glycol dimethyl ether + dichloromethane, + trichloromethane, and + tetrachloromethane have been determined at 298.15 K and atmospheric pressure over the whole concentration range. From the experimental results, deviations in viscosities (&Dgr; ln η) have been calculated. These properties were fitted to the polynomial relations to obtain the coefficients and the standard deviations. The results have been analysed in terms of molecular interactions between components.Key words: experiments, data, excess volume, viscosity deviation, binary mixtures.

ISSN:0008-4042    

DOI:10.1139/v00-028

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Experimental solubilities are reported at 25.0°C for diphenyl sulfone dissolved in 25 different organic nonelectrolyte solvents containing ether-, chloro-, hydroxy-, ester, methyl-, andtert-butyl-functional groups. Results of these measurements, combined with previously reported diphenyl sulfone solubilities taken from the chemical literature, are used to test the applications and limitations of expressions derived from Mobile Order theory. For the 34 solvents for which predictions could be made, computations show that mobile order theory does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 49.3%. In comparison, the average absolute deviation is 5 500% when ideal solution behavior is assumed.Key words: diphenyl sulfone solubilities, organic nonelectrolyte solvents, solubility predictions

ISSN:0008-4042    

DOI:10.1139/v00-041

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The synthesis of [Ln{N(SiMe3)2}2(THF)(µ-Cl)]2(Ln = Ce,1; Nd,2) by reaction of sodium bis(trimethylsilyl)amide (2 equiv.) with LnCl3is reported. The same complexes were also isolated from the ligand redistribution reactions of Ln[N(SiMe3)2]3and LnCl3(2:1 ratio) in THF at 80°C. The crystal structure of2, determined by X-ray diffraction, revealed a centrosymmetric dimer with bridging chlorides and pentacoordinate metal centres.1H NMR studies show that the solid state structure is not maintained in solution. NMR evidence for the presence of Ln[N(SiMe3)2]3and two other bis(trimethylsilyl)amide containing species, presumably Ln[N(SiMe3)2]Cl2(THF)xand Ln[N(SiMe3)2]2Cl(THF)y, is presented.Key words: lanthanide, amide, neodymium, cerium, crystal structure, X-ray, nuclear magnetic resonance, redistribution

ISSN:0008-4042    

DOI:10.1139/v00-036

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Experimental solubilities are reported at 25.0°C for hexachlorobenzene dissolved in 42 different organic nonelectrolyte solvents containing ether-, chloro-, hydroxy-, ester, methyl-, andtert-butyl-functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order model. For the 33 solvents for which predictions could be made computations show that Mobile Order model does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 210%. In comparison, the average absolute deviation is 2 060% when ideal solution behavior is assumed.Key words: hexachlorobenzene solubilities, organic nonelectrolyte solvents, solubility predictions

ISSN:0008-4042    

DOI:10.1139/v00-040

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents

ISSN:0008-4042    

DOI:10.1139/v00-042

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The detritiation kinetics of the Cr(III) complexes1and3-6have been studied in aqueous buffers at 35°C, using the liquid scintillation counting technique. Results for5and6provide benchmark kinetic data for N-T/N-H exchange under the experimental conditions of the study and have aided in the delineation of N-T/N-H from C-T/C-H exchange in the parallel reactions observed experimentally. Curved first-order plots obtained for1,3, and4were treated to yield rate constants for two parallel exchange reactionskobsA  andkobsB  for the "fast" and "slow" processes, respectively. The "fast" process has been assigned to C(2)-H exchange in1, competing N-H and C(2)-H exchange in3, and N-H exchange in4. In all cases, the "slow" process is associated with C(4,5)-H exchange. Identification of exchange sites in1,3, and4was made possible by the consideration of the results of an IR spectroscopic study of hydrogen-deuterium exchange, comparison of the extent of3H incorporatation in different complexes in the tritiation experiments, and a careful analysis of the exchange kinetic data. Analysis of the rate data indicates that Cr(III) significantly enhances C(2)-H exchange in1and3, while C(4,5)-H exchange, hitherto reported in the literature only under drastic reaction conditions, was observed for1,3, and4under the mild conditions of the present study. Quantitation of the effect of Cr(III) coordination on3H exchange in imidazole-type nuclei was achieved fully in1; givingkM+values of 6 × 103and 7 × 102M-1s-1for C(2)-H and C(4,5)-H exchange, respectively. Using the literature value forkH+, the second-order rate constant for C(2)-H exchange under H+catalysis, 2.9 × 102M-1s-1, it follows that Cr(III) is ca. 20 times better as a catalyst for C(2)-H exchange in 1-methylimidazole than H+, providing the first example of a metal ion being more effective than a proton in these processes. Comparison of the results obtained with1with literature results for2shows a very large (ca. 3 × 105-fold) difference in the catalytic activities of Cr(III) and Co(III), favouring the former. The dichotomy in the effectiveness of the two metal ions in catalyzing3H exchange in the imidazole nucleus has been ascribed to differences in (i) extent of Mn+—N bond polarization (and the consequent effect on ligand C-H acidity); (ii) electronic configuration; (iii) crystal field stabilization and activation energies; and (iv) importance of metal-ligand &pgr; back-bonding. The study highlights the diversity of factors and complexity of interactions involved in determining the role of metal ions in biological systems, especially where such processes involve complex formation between metal ions and heterocyclic fragments of biomolecules.Key words: metal ion-biomolecule interactions, methylimidazole, isotopic hydrogen exchange, catalysis by chr

ISSN:0008-4042    

DOI:10.1139/v00-031

出版商:NRC Research Press    

年代:2000

数据来源: NRC