Showing papers in "Canadian Journal of Chemistry in 1995"
TL;DR: In this article, an evaluation of approximate density functional theory as a practical tool in studies on organometallic energetics and kinetics is given, covering electronic excitations and ionization.
Abstract: An evaluation is given of approximate density functional theory as a practical tool in studies on organometallic energetics and kinetics. The evaluation covers electronic excitations and ionization...
243 citations
TL;DR: In this paper, family-independent relationships between computed molecular surface properties and solute hydrogen bond acidity/basicity and solutes-induced methanol O-H infrared frequency shifts are presented.
Abstract: Family-independent relationships between computed molecular surface properties and solute hydrogen bond acidity/basicity and solute-induced methanol O–H infrared frequency shifts are presented. The...
160 citations
TL;DR: In this article, aqueous solutions of L-asparagine, L-glutamine, glycyl glycine, gly glycyl-L-valine and glycylDL-leucine at 288.15, 298, 313.15 and 328.15 K were measured for the CH(NH2)CO2H, CH2, OH, COOH, CONH2, and CONH groups.
Abstract: Densities and heat capacities have been measured for aqueous solutions of L-asparagine, L-glutamine, glycylglycine, glycyl-L-valine, glycyl-L-asparagine, and glycyl-DL-leucine at 288.15, 298.15, 313.15, and 328.15 K. These data have been used to calculate apparent molar volumes, V2,o, and apparent molar heat capacities, Cp,2,o, which in turn have been used to obtain standard state volumes, and heat capacities, The semi-empirical modelling procedures of Helgeson, Kirkham, and Flowers have been used to subdivide the calculated standard state volume and heat capacity data into solvation and nonsolvation contributions. The nonsolvation components of the standard state properties are used in group additivity analyses. These analyses yield structural contributions to standard state volumes and heat capacities for the CH(NH2)CO2H, CH2, OH, COOH, CH, CONH2, and CONH groups. The temperature dependences of these contributions are discussed. Some comments are reported concerning the practicality of using the thermod...
96 citations
TL;DR: In this article, the reversible optical storage properties of poly[4′-[[(2methacryloyloxy)ethyl]ethylamino]azobenzene] (pMAEA) were investigated.
Abstract: Poly[4′-[[(2-methacryloyloxy)ethyl]ethylamino]azobenzene] (pMAEA) was prepared. Its reversible optical storage properties were studied and compared with the properties of previously reported poly[4...
93 citations
TL;DR: In this paper, the partial molar volumes and their derivatives with respect to temperature have been used for extending the understanding of molecular interactions in completely miscible (water + organic) systems.
Abstract: Densities of completely miscible (water + methyldiethanolamine) and (water + ethyldiethanolamine) systems have been measured over the full range of compositions at temperatures from 25 to 80°C. Results of these measurements have been used in calculating excess molar volumes and partial molar volumes of each component. We have also identified different measures of the thermal expansion of these systems and have calculated some of these derivative quantities. The partial molar volumes and their derivatives with respect to temperature provide a basis for extending our understanding of molecular interactions in these (water + organic) systems.
92 citations
TL;DR: In this paper, a poly(3-alkylthiophenes) undergo simultaneous photobleaching, cross-linking, and chain scission when irradiated in air with UV or visible light.
Abstract: Films of poly(3-alkylthiophenes) undergo simultaneous photobleaching, cross-linking, and chain scission when irradiated in air with UV or visible light. The quantum yields of the latter two process...
71 citations
TL;DR: Fluorescently labeled amphiphilic poly-(N-isopropylacrylamides) (PNIPAM) substituted with a N-[4-(1-pyrenyl)butyl]-N-n-octadecyl group at the chain end were prepared by free-radical polymerization as mentioned in this paper.
Abstract: Fluorescently labeled amphiphilic poly-(N-isopropylacrylamides) (PNIPAM) substituted with a N-[4-(1-pyrenyl)butyl]-N-n-octadecyl group at the chain end were prepared by free-radical polymerization ...
62 citations
TL;DR: In this paper, the completeness profile is used to provide a visual assessment of the quality of one-electron basis sets, illustrated by examples of a number of basis sets for the carbon atom.
Abstract: The completeness profile is used to provide a visual assessment of the quality of one-electron basis sets. The approach is illustrated by examples of a number of basis sets for the carbon atom. New...
56 citations
TL;DR: In this article, the reaction of the homoleptic yttrium amido complex Y[N(SiMe3)2]3 with C5Me4HSiMe2N(H)-t-C4H9, Cp*HSiNHR, at 100 °C, resulted in elimination of 2 equivalents of HN (SiMe 3)2 and attachment of the Cp-amido donor to Yttrium.
Abstract: Reaction of the homoleptic yttrium amido complex Y[N(SiMe3)2]3 with C5Me4HSiMe2N(H)-t-C4H9, Cp*HSiNHR, at 100 °C resulted in elimination of 2 equivalents of HN(SiMe3)2 and attachment of the Cp-amido donor to yttrium. The product (Cp*SiNR)YN(SiMe3)2, 1, was isolated in 40% yield and was characterized crystallographically (triclinic, space group a = 8.9759(23) A, b = 9.504(7) A, c = 18.294(6) A, V = 1423.4(12) A3, Z = 2, R = 0.061, Rw = 0.053). Metrical parameters associated with the N(SiMe3)2 ligand were suggestive of weak β-SiC agostic interactions that stabilize the electron-deficient yttrium center. Alkylation of 1 resulted in unstable alkyl derivatives that could not be isolated. Keywords: cyclopentadienyl-amido, amine elimination, yttrium complex.
53 citations
TL;DR: In this paper, the UV-visible absorption properties of seven anilino class squaraine dyes in dimethyl sulfoxide (DMSO) water mixtures were investigated.
Abstract: In characterizing the UV–visible absorption properties of a series of seven anilino class squaraine dyes in dimethyl sulfoxide (DMSO) – water mixtures, spectral features characteristic of aggregati...
53 citations
TL;DR: In this paper, a new method was developed for analyzing the diffusion of oxygen in thin polymer films via fluorescence quenching measurements, which involved approximations of approximability.
Abstract: A new method is developed for analyzing the diffusion of oxygen in thin polymer films via fluorescence quenching measurements. We begin by reviewing previous methods, all of which involve approxima...
TL;DR: In this article, the two concerted rearrangement processes and competing homolytic reactions are explored using molecular orbital calculations at levels up to MP4SDQl6- 31G*lIMP216-31G*.
Abstract: The rearrangement of organic thionitrate to sulfenyl nitrite potentially mediates the release of nitric oxide from organic nitrates, such as nitroglycerin, in the presence of thiol. The biological activity of these nitrovasodilators is proposed to result from release of nitric oxide in vivo. The thionitrate rearrangement bears analogy to the rearrangement of peroxynitrous acid to nitric acid, which has been proposed to mediate the biological toxicity of nitric oxide and superoxide. In this paper, the two concerted rearrangement processes and competing homolytic reactions are explored using molecular orbital calculations at levels up to MP4SDQl6- 31G*lIMP216-31G*. Examination of structure and energy for all conformers and isomers of RSONO, (R = H, Me), models for organic thionitrates and their isomers, demonstrates that structures corresponding to thionitrates and sulfenyl nitrates are of similar energy. Free energies of reaction for homolysis of these compounds are low (AGO < 19 kcallmol), whereas the bamer for concerted rearrangement is large (AGf (aq.) = 56 kcaVmo1). The larger bamer for concerted rearrangement of peroxynitrous acid to nitric acid (aGz(aq.) = 60 kcallmol) again compares unfavourably with homolysis (AGO c 11 kcallmol for homolysis to NO2 or 'NO). The transition state structures, confirmed by normal mode and intrinsic reaction coordinate analysis, indicate that considerable structural reorganization is required for concerted rearrangement of the ground state species. These results suggest that concerted rearrangement is not likely to be a viable step in either biological process. However, rearrangement via homolysis and radical recombination may provide an energetically accessible pathway for peroxynitrous acid rearrangement to nitric acid and rearrangement of thionitrate to sulfenyl nitrite. In this case, NO, will be a primary product of both reactions.
TL;DR: The molecular orientation is generally expressed by an order parameter, which depends on both the angular position and the shape of the orientation distribution as mentioned in this paper, which is an average made-up parameter.
Abstract: The molecular orientation is generally expressed by an "order parameter," which depends on both the angular position and the shape of the orientation distribution. This parameter is an average made...
TL;DR: In this paper, available data on the oxidation of nitrilotriacetic acid (NTA), ethylenedinitrilotetric acid (EDTA), N-hydroxyethylethylenediaminetriacic acid (HEDTA) and other aminopolycarboxylate chelati...
Abstract: Available data on the oxidation of nitrilotriacetic acid (NTA), ethylenedinitrilotetraacetic acid (EDTA), N-hydroxyethylethylenediaminetriacetic acid (HEDTA), and other aminopolycarboxylate chelati...
TL;DR: The median filter provides a means for dealing with "spiky" noise and separating peaks from a slowly changing baseline, even when the exact nature of the drift and noise distribution is not known.
Abstract: The properties and application of the median filter are investigated using both simulated and real data for signals evolving with time. Comparison is made with existing numerical techniques for dri...
TL;DR: In this paper, the 1H NMR signals of the Ru(III) species present in solution are considerably broadened and shifted by paramagnetism, but they can be used to follow chloride displacement in the trans-[RuCl4Im2]− ion.
Abstract: The 1H NMR signals of the Ru(III) species present in solution are considerably broadened and shifted by paramagnetism, but they can be used to follow chloride displacement in the trans-[RuCl4Im2]− ion. This anion remains predominant for several hours at room temperature in D2O, but its signals are progressively replaced by those of a monoaqua [RuCl3(D2O)Im2] complex. Over a period of days, two new sets of peaks appear, corresponding to two isomers of [RuCl2(D2O)2Im2]+. The same behaviour is observed for the 1-methyl-and 4-methylimidazole analogues. These reactions can be driven backwards by addition of KCl, but [RuCl4Im2]− is not quantitatively regenerated in solution even for 6 M NaCl. Within several months, the [RuCl2(D2O)2Im2]+ isomers further aquate to a single species [RuCl(D2O)3Im2]2+. In CD3OD, displacement of the first chloride of [RuCl4Im2]− takes place faster, over several hours, but substitution stops at the [RuCl3(CD3OD)Im2] stage. In DMSO, substitution occurs very slowly. The [RuCl3(DMSO)Im2]...
TL;DR: Uridine 5′-(5a-carba-α-D-galactopyranosyl diphosphate), the carbocyclic analog of UDP-Galactose where the ring oxygen of the galactose residue is replaced by a methylene group, was chemically synthesized as a potential inhibitor of galactosyltransferases.
Abstract: Uridine 5′-(5a-carba-α-D-galactopyranosyl diphosphate), the carbocyclic analog of UDP-galactose where the ring oxygen of the galactose residue is replaced by a methylene group, was chemically synthesized as a potential inhibitor of galactosyltransferases. It was found to be a competitive inhibitor of UDP-galactose: N-acetylglucosamine β(1 → 4)-galactosyltransferase from bovine milk (EC 2.4.1.22) with a Ki value of 58 µM, similar to the Km value for UDP-galactose (25 µM). Keywords: carbocycles, UDP-5a-carbagalactose, galactosyltransferase, glycosyltransferase inhibitor.
TL;DR: The acidity and keto-enol tautomerism of a series of symmetrical β-diketones (RCOCH2COR (1)) and two series of unsymmetrical β -dikets (RCOCH2COCH3 (7a−7f) and RCOCH 2COC6H5 (8a−8f)) have been investigated in aqueous solution at 25 °C and ionic strength 0.1 as mentioned in this paper.
Abstract: The acidity and keto–enol tautomerism of a series of symmetrical β-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl (d), 3-(N-methyl)pyridinio (e), and 4-(N-methyl)pyridinio (f)) and two series of unsymmetrical β-diketones (RCOCH2COCH3 (7a–7f) and RCOCH2COC6H5 (8a–8f)) have been investigated in aqueous solution at 25 °C and ionic strength 0.1. Values of were measured spectrophotometrically, and the acidities of the enols were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-catalyzed protonation of the enolateconjugate bases. These data in turn allowed the calculation of the acidities of the keto tautomers and the equilibrium constants for enolization (KE = [Enol]/[Keto]). In general, KE is greater for the symmetrical ketones(1) than for the corresponding R-substituted unsymmetrical ketones (7 and 8). KE is much more sensitive to the nature of the R substituent in these three series of β-diketones than in the corresponding serie...
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TL;DR: The synthesis of a [2,3-13C2] bond-labeled sample of 1-deoxy-D-xylulose has been reported in this article, which is a precursor of thiamin and pyridoxine (Vitamin B6) in bacteria.
Abstract: 1-Deoxy-D-xylulose (= 1-deoxy-D-theropentulose) is a precursor of thiamin (Vitamin B1) and of pyridoxine (Vitamin B6) in bacteria. The synthesis of a [2,3-13C2] bond-labeled sample of the compound,...
TL;DR: The crystal structure of bright red crystals of the bidimensional polynuclear diamagnetic diamagnetic (µ-chloro)(µ -pyrazine)copper(I) complex has been analyzed from X-ray diffraction data.
Abstract: The crystal structure of bright-red crystals of the bidimensional polynuclear diamagnetic (µ-chloro)(µ-pyrazine)copper(I) complex has been analyzed from X-ray diffraction data. The structure was so...
TL;DR: In this article, the tetraazamacrocycles were synthesized by using p-toluenesulfonyl chloride as a protective group and obtained the [14(ane) N4] and [15(ane), N4], respectively.
Abstract: Syntheses of tetraazamacrocycles have been carried out by using p-toluenesulfonyl chloride as protective group. The [14(ane) N4] and [15(ane) N4] were also obtained by the template synthesis. Mono-...
TL;DR: The structures and stereochemistry of 14 taxanes isolated from Taxuscanadensis have been rigorously established by high-resolution NMR techniques and mass spectrometry as mentioned in this paper.
Abstract: The structures and stereochemistry of 14 taxanes isolated from Taxuscanadensis have been rigorously established by high-resolution NMR techniques and mass spectrometry. Taxuscanadensis is the only yew that accumulates 9-dihydro-13-acetylbaccatin III (also called 7,9-deacetylbaccatin VI) as the most abundant taxane. Five 9-dihydrotaxanes derived from the Canadian yew are novel natural products not reported in the needles of other species of yew (8–11, 14, Fig. 1). Keywords: Taxuscanadensis, Taxaceae, taxanes, 9-dihydro-13-acetylbaccatin III, taxol.
TL;DR: In this paper, the selectivity of conjugated enones to the corresponding carbonyl compounds has been investigated in aqueous methanol under constant current at nickel boride, fractal nickel, and Raney nickel electrodes made of pressed powders.
Abstract: The selectivity of the electrocatalytic hydrogenation (ECH) of conjugated enones to the corresponding carbonyl compounds has been investigated in aqueous methanol under constant current at nickel boride, fractal nickel, and Raney nickel electrodes made of pressed powders. The influence of various parameters (water percentage, pH, concentration of substrate, and current density) on the selectivity of the carbon–carbon double bond hydrogenation was studied with cyclohex-2-en-1-one at nickel boride electrodes. Under given electrolysis conditions, fractal nickel electrodes were found to give the highest selectivity. The selectivity of the ECH of a variety of conjugated enones at fractal nickel electrodes was determined under electrolysis conditions that gave the best selectivity with cyclohexenone at nickel boride electrodes. Keywords: electrocatalytic hydrogenation, α,β-unsaturated ketones, selective hydrogenation, nickel based cathodes.
TL;DR: A general synthetic route to 2-alkyl and 2,2-dialkyl-1,3-dioxan-5-ones, using tris(hydroxymethyl)-nitromethane as the starting material, is described in this article.
Abstract: A general synthetic route to 2-alkyl- and 2,2-dialkyl-1,3-dioxan-5-ones, using tris(hydroxymethyl)-nitromethane as the starting material, is described. Deprotonation of these compounds was studied....
TL;DR: Schiff bases from ferrocene aldehyde and α-amino acidates react with PdCl2 or Na2PdCl4 to give N,O-chelate complexes as discussed by the authors.
Abstract: Schiff bases from ferrocene aldehyde and α-amino acidates react with PdCl2 or Na2PdCl4 to give N,O-chelate complexes (2a–e, 3). The related N-ferrocenylmethylen-α-amino acid esters give, with Pd(OA...
TL;DR: The notion of division between active and dormant electrons has been well received and widely used in the chemists' way of thinking as mentioned in this paper, and the core-valence separation in atoms is the best-known example.
Abstract: The notion of division between active and dormant electrons has been well received and widely used in the chemists' way of thinking. The core–valence separation in atoms is the best-known example. ...
TL;DR: Raman spectra of the oxidized and neutral forms of polypyrrole show a relative intensity shift from the high wave number to the low wave number region as the source wavelength is increased as mentioned in this paper.
Abstract: Raman spectra of the oxidized and neutral forms of polypyrrole show a relative intensity shift from the high wave number region to the low wave number region as the source wavelength is increased f...
TL;DR: S,S-[1,2-Bis(tetrahydroindenyl)ethane]titanium-based catalysts were used, in conjunction with either diphenyl- or methylphenylsilane, to effect the catalytic hydrosilation of a wide variety of dials as mentioned in this paper.
Abstract: S,S-[1,2-Bis(tetrahydroindenyl)ethane]titanium-based catalysts were used, in conjunction with either diphenyl- or methylphenylsilane, to effect the catalytic hydrosilation of a wide variety of dial...
TL;DR: The Onsager-Samaras version of Wagner's theory of surface tension of solutions of 1:1 salts has been modified to include ion-induced dipole terms in the image potential as mentioned in this paper.
Abstract: The Onsager–Samaras version of Wagner's theory of surface tension of solutions of 1:1 salts has been modified to include ion-induced dipole terms in the image potential. Effective solvated ionic po...
TL;DR: In this paper, the crystal and molecular structures of this salt were solved by X-ray diffraction techniques using 2634 counter data with I < 2σ(I). Refinement of 278 variables by full-matrix least squares converged at an agreement factor R = 0.023.
Abstract: The complex [Au2(μ-dppm)(C≡Ct-Bu)2], 1, dppm=Ph2PCH2PPh2, is formed by reaction of [AuC≡Ct-Bu] with dppm. Compound 1, as an acetone solvate, crystallizes in the monoclinic space group P21/c with cell dimensions a = 14.047(1), b = 16.124(1), c = 17.140(3) A, β = 103.17(2)° and four formula units per cell. The crystal and molecular structures of this salt were solved by X-ray diffraction techniques using 2634 counter data with I > 2σ(I). Refinement of 278 variables by full-matrix least squares converged at an agreement factor R = 0.023. Thermolysis of complex 1 in refluxing toluene led to intermolecular elimination of t-BuC≡CH, by combination of a t-BuC≡C ligand of one molecule of 1 with a proton from the CH2P2 group of a second, and formation of the stable tetragold(I) complex [Au4(μ3-Ph2PCHPPh2)(μ-dppm)(C≡Ct-Bu)3], 2, which was characterized by its spectroscopic properties. Keywords: acetylide complexes, gold complexes, X-ray crystallography, nmr spectroscopy, bis(diphenylphosphino)methane.