Showing papers in "Canadian Journal of Chemistry in 1999"
TL;DR: Asymmetric amphiphilic diblock copolymers self-assemble in selective solvents as discussed by the authors, using a sequence of various "crew-cut" aggregate morphologi...
Abstract: Asymmetric amphiphilic diblock copolymers self-assemble in selective solvents. Since 1995, when we first reported the systematic preparation of a sequence of various "crew-cut" aggregate morphologi...
376 citations
TL;DR: In this article, a broad theoretical frame for hydrogen transfer in chemical and biological systems is discussed, including hydrogen tunnelling, coupling between the tunnel modes and the environment, and fluctuational barrier preparation.
Abstract: We discuss a broad theoretical frame for hydrogen transfer in chemical and biological systems Hydrogen tunnelling, coupling between the tunnel modes and the environment, and fluctuational barrier preparation for hydrogen tunnelling are in focus and given precise analytical forms Specific rate constants are provided for three limits, ie, the fully diabatic, the partially adiabatic, and the fully adiabatic limits These limits are all likely to represent real chemical or biological hydrogen transfer systems The rate constants are referred particularly to the driving force and temperature dependence of the kinetic isotope effect (KIE) The origin of these correlations is different in the three limits It is rooted in the tunnel factor and weak excitation of the heavier isotopes in the former two limits, giving a maximum for thermoneutral processes A new observation is that the adiabatic limit also accords with a KIE maximum for thermoneutral processes but the KIE is here reflected solely in the activation Gibbs free energy differences, in this case rooted in the low-frequency environmental nuclear dynamics Three systems of biological hydrogen tunnelling, viz lipoxygenase, yeast alcohol dehydrogenase, and bovine serum amine oxygenase, offer unusual new cases for analysis and have been analysed using the theoretical frames All the systems show large KIEs and strong indications of hydrogen tunnelling They also represent different degrees of fluctuational barrier preparation, with lipoxygenase as the most rigid and bovine serum amine oxygenase as the softest system
229 citations
TL;DR: Experiments showing that water is decomposed by the action of high-energy radiations date back to the first days of the discovery of radioactivity, a century ago as discussed by the authors.
Abstract: Experiments showing that water is decomposed by the action of high-energy radiations date back to the first days of the discovery of radioactivity, a century ago. On the occasion of this anniversar...
129 citations
TL;DR: In this paper, the authors introduced an abstract space of bond critical point properties, called BCP space, to measure the similarity between molecules, and critically examined the departures of BCP spaces.
Abstract: In previous work we introduced an abstract space of bond critical point properties, called BCP space, to measure the similarity between molecules. In this contribution we critically examine the dep...
103 citations
TL;DR: In this article, the reduction potential of acetonitrile of 1-ferrocenyl-4,4, 4-trifluorobutane-1,3-dione was investigated.
Abstract: Formal reduction potentials (E°' values vs. Ag/Ag+ given in parentheses) in acetonitrile of 1-ferrocenyl-4,4,4-trifluorobutane-1,3-dione (ferrocenoyltrifluoroacetone, Hfctfa, 0.394 V), 1-ferrocenyl...
79 citations
TL;DR: In this paper, the zero-point energy changes of the hydrogen bond proton in 1:1 acid-base complexes AHB triple bond were analyzed as a function of the proton energy changes.
Abstract: We have followed by NMR the zero-point energy changes of the hydrogen bond proton in 1:1 acid-base complexes AHB triple bond {AH···B Aδ-···H···Bδ+ A-···HB+} as a function of the proton ...
67 citations
TL;DR: In this article, the redox properties of ferrocene boronic acid in aqueous buffers from pH 4 to pH 12 have been investigated using cyclic voltammetry, and it is shown that the proton transfer equilibrium is under thermodynamic control over the range of scan rates employed (20-5000 mV/s).
Abstract: The redox properties of ferrocene boronic acid in aqueous buffers from pH 4 to pH 12 have been investigated using cyclic voltammetry. It is shown that the proton transfer equilibrium is under thermodynamic control over the range of scan rates employed (20-5000 mV/s), leading to pKa values of 10.8 and 5.8 for the ferrocene and ferrocenium forms, respectively. In the presence of sorbitol, fructose, or glucose, the voltammetric behaviour of ferrocene boronic acid at pH 7 is consistent with reversible formation of a carbohydrate - boronic acid complex. However, in all cases, the complexation-dissociation is under kinetic control. Analysis of the voltammetric response as a function of scan rate and carbohydrate concentration, together with an independent spectroscopic determination of the binding constant to the ferrocene form, allows all of the kinetic and thermodynamic constants for each system to be determined. In general, it is found that the binding constants ferrocenium form are about two orders of magnitude greater than those for the ferrocene form. It is possible that this redox dependent switching of the carbohydrate binding can be exploited in amperometric or potentiometric sensing devices.
64 citations
TL;DR: In this article, the authors proposed the following classes of compounds: benzyl (4-MeO, 4-Me, and 4-methoxy-1-naphthylmethyl), phenethyl (4Me2N, 4MeO), 3,4-(MeO)2), 4-F, 3-meO, 2,6-Me2, parent, and cumyl(4-me2N).
Abstract: Benzyl (4-MeO, 4-Me, and 4-methoxy-1-naphthylmethyl), phenethyl (4-Me2N, 4-MeO, 3,4-(MeO)2, 4-Me, 3-Me, 4-F, 3-MeO, 2,6-Me2, parent, and 4-methoxy-1-naphthylethyl) and cumyl (4-Me2N, 4-MeO, 4-Me, p...
54 citations
TL;DR: In this article, the pyrone ligands are bound to molybdenum in a cis bidentate fashion via the deprotonated hydroxyl groups and the ketone moieties.
Abstract: We have prepared a number of complexes of the type cis-MoO2L2 where L represents a hydroxypyronato or hydroxypyridinonato ligand. Both the maltol (3-hydroxy-2-methyl-4-pyrone, Hma) and kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone, Hka) complexes, cis-MoO2(ma)2 (1) and cis-MoO2(ka)2 (2), have been characterized by X-ray diffraction studies. The pyrone ligands are bound to molybdenum in a cis bidentate fashion via the deprotonated hydroxyl groups and the ketone moieties. Crystals of 1 are orthorhombic, a = 12.107 (1), b = 8.6169 (8), c = 16.472 (1) A, Z = 4, space group Pca21, and those of 2 are monoclinic, a = 8.4591 (5), b = 16.3453 (10), c = 10.2954 (7) A, β = 103.0320 (10)°, Z = 4, space group P21/c. Hydroxypyridinone molybdenum complexes have been prepared for both maltol and kojic acid derivatives with the substituents Me, n-Pr, CH2Ph, Ph at the ring nitrogen. Crystals of the 3-hydroxy-2-methyl-1-phenyl-4-pyridinone (Hppp) derivative, MoO2(ppp)2 (9), are monoclinic, a = 10.9476 (6), b = 13.5353 (9),...
53 citations
TL;DR: In this paper, density, heat capacity, and isentropic compressibility data for aqueous methanol, ethanol, and propan-1-ol by Benson's group were used to evaluate two kinds of fluctuations; mean-square fluctuation...
Abstract: Density, heat capacity, and isentropic compressibility data for aqueous methanol, ethanol, and propan-1-ol by Benson's group were used to evaluate two kinds of fluctuations; mean-square fluctuation...
51 citations
TL;DR: In this paper, the effects of transition and alkaline earth metals on the reactions of peroxide with diffe cation was investigated, and it was shown that peroxide bleaching is significantly affected by transition and earth metals.
Abstract: Peroxide bleaching is significantly affected by transition and alkaline earth metals. Isolating the effects of different transition and alkaline earth metals on the reactions of peroxide with diffe...
TL;DR: The tertbutyl and 1-arylethyl ethers of salicylic acid are hydrolyzed with efficient general acid catalysis by the ortho-COOH group as discussed by the authors.
Abstract: The tert-butyl (1) and 1-arylethyl ethers (2) of salicylic acid are hydrolyzed with efficient general acid catalysis by the ortho-COOH group. The half-life of the neutral COOH form of the tert-buty...
TL;DR: In this paper, the liquidus surfaces and thermal windows of four ternary systems implying consecutive n-alkanes (for n between 14 and 21 carbon atoms) have been studied combining Differential Scanning Calorimetry (DSC), X-ray experiments, and calculation using the program Txy-CALC.
Abstract: The liquidus surfaces and thermal windows of four ternary systems implying consecutive n-alkanes (for n between 14 and 21 carbon atoms) have been studied combining Differential Scanning Calorimetry (DSC), X-ray experiments, and calculation using the program Txy-CALC. From the DSC measurements, the transition temperatures as well as the melting enthalpies have been determined. X-ray experiments performed at temperatures just below melting have shown that there is almost complete syncrystallization in the rotator form RI. The calculation of the RI –> L liquidus surfaces has been made with temperature-independent as well as temperature-dependent excess Gibbs energies. In both cases, the agreement between experimental and calculated data is very good, the average temperature difference being within the uncertainty of the former.Key words: n-alkanes, ternary mixtures, liquidus and solidus surfaces, rotator phase, thermodynamic analysis.
TL;DR: The two keto tautomers of phenol (1), cyclohexa-2,4-dienone (2) and cyclohexylcyclohexane-2.5-diamone (3) were generated by flash photolysis of appropriate precursors in aqueous solution, and the pH-rate was measured as mentioned in this paper.
Abstract: The two keto tautomers of phenol (1), cyclohexa-2,4-dienone (2) and cyclohexa-2,5-dienone (3), were generated by flash photolysis of appropriate precursors in aqueous solution, and the pH-rate prof...
TL;DR: In this article, the rate laws for the CrVI oxidation reactions are expressed by -d[CrVI]/dt = kH[H+]2 [ribose][CrVI], where kH = (5.9 ± 0.1) × 10-2 mol-1 dm3 s-1 and kH' = (4.2 ± 0 1.5)
Abstract: The oxidation of D-ribose and 2-deoxy-D-ribose by CrVI yields the aldonic acid and Cr3+ as final products when an excess of sugar over CrVI is used. The redox reaction occurs through CrVI–>CrIII and CrVI–>CrV–>CrIII paths. The complete rate laws for the CrVI oxidation reactions are expressed by -d[CrVI]/dt = kH[H+]2 [ribose][CrVI], where kH = (5.9 ± 0.1) × 10-2 mol-3 dm9 s-1, and -d[CrVI]/dt = (k0 + kH'[H+]2) [2-deoxyribose][CrVI], where k0 = (1.3 ± 0.5) × 10-3 mol-1 dm3 s-1 and kH' = (4.2 ± 0.1) × 10-2 mol-3 dm9 s-1, at 33°C. An intermediate sugar alkoxide radical could be trapped with DMPO and observed by EPR as a multiline signal at g = 2.003. CrV is formed in a rapid step by reaction of the sugar radical with CrVI. CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxochromate(V) intermediates are formed, and the distribution of these CrV species in the reaction mixture essentially depends on the solution acidity.Key words: ribose, 2-deoxyribose, ch...
TL;DR: In this article, the reaction of aniline and six of its derivatives with 4,6-dinitrobenzofuroxan (DNBF) in water -dimethyl sulfoxide mixtures.
Abstract: Kinetic results are reported for reaction of aniline and six of its N- and ring-substituted derivatives with 4,6-dinitrobenzofuroxan (DNBF) in water - dimethyl sulfoxide mixtures. In acidic solutio...
TL;DR: In this article, a short comparative study with results for mixtures with higher 1-alkanols and polyethers is presented, showing that the dominant contribution of free volume effects on interactional effects, particularly when the ethers are of the type CH3-(O-CH2CH2)m-CH3.
Abstract: Excess molar volumes VmE at 298.15 K and atmospheric pressure for methanol and ethanol + 2,5-dioxahexane, + 3,6-dioxaoctane, + 2,5,8-trioxanonane, + 3,6,9-trioxaundecane, + 5,8,11-trioxapentadecane, + 2,5,8,11-tetraoxadodecane, and + 2,5,8,11,14-pentaoxapentadecane have been obtained from densities measured with an Anton-Paar DMA 602 vibrating-tube densimeter. All the excess volumes are negative over the whole mole fraction range.The VmE curves are shifted to the region rich in the alkanol, increasing their asymmetry with the number of oxygen groups in the polyethers. Results seem to remark the predominant contribution of free volume effects on interactional effects, particularly when the ethers are of the type CH3-(O-CH2CH2)m-CH3. In the case of polyethers with longer n-alkyl chain ends, self-association of methanol and ethanol is more relevant. A short comparative study with results for mixtures with higher 1-alkanols and polyethers is also presented.Key words: experimental, excess volumes, 1-alkanols, ...
TL;DR: Two-dimensional NOE spectroscopy (NOESY) experiments have been used to examine the dissolution of two typical solubilizates (1-butanol and benzene) in anionic sodium dodecyl sulfate (SDS) micelles and of benzene in cationic dodecayltrimethyammonium (DTAB) miceLLes as discussed by the authors.
Abstract: Two-dimensional NOE spectroscopy (NOESY) experiments have been used to examine the dissolution of two typical solubilizates (1-butanol and benzene) in anionic sodium dodecyl sulfate (SDS) micelles and of benzene in cationic dodecyltrimethyammonium (DTAB) micelles. In all cases, significant, positive NOESY cross peaks were obtained that appeared to correlate well with the expected locus of solubilization of these solubilizates in these surfactant systems. The NOESY technique, which is a noninvasive experiment, is found to provide significant insight in terms of the solubilization of these molecules in the interior of ionic micelles.
TL;DR: In this article, a series of symmetrical anilino-based squaraines with increasing N-alkyl chain length was examined for aggregation behavior of squaraine dyes in DMSO-water mixtures.
Abstract: In continuing studies of the aggregation behaviour of squaraine dyes in DMSO-water mixtures, we have examined a series of symmetrical anilino-based squaraines with increasing N-alkyl chain length (...
TL;DR: In this article, the apparent molar volumes (Vϕ) of ω-amino acids were determined in aqueous guanidine hydrochloride (6 m GuHCl) and sodium sulphate (2 m Na2SO4) solutions at 288.15 and 298.15 K using a vibra...
Abstract: Apparent molar volumes (Vϕ) of some ω-amino acids have been determined in aqueous guanidine hydrochloride (6 m GuHCl) and sodium sulphate (2 m Na2SO4) solutions at 288.15 and 298.15 K using a vibra...
TL;DR: In this paper, the absorption and emission spectra and the fluorescence lifetimes and quantum yields of alloxazine and several of its N- and C- methyl-substituted derivatives, including two isoalloxazines, have been measured in a nonpolar solvent (1,2-dichloroethane), a polar aprotic solvent (acetonitrile), and a polar protic solvent(ethanol).
Abstract: The absorption and emission spectra and the fluorescence lifetimes and quantum yields of alloxazine and several of its N- and C- methyl-substituted derivatives, including two isoalloxazines, have been measured in a nonpolar solvent (1,2-dichloroethane), a polar aprotic solvent (acetonitrile), and a polar protic solvent (ethanol). The excited state decays are all single exponential, suggesting that only one emitting species is present in all cases. The spectroscopic data show that the emitting species is the π,π* electronic excited state corresponding to the ground state of the absorbing molecule; there is no evidence of excited state proton transfer for any of these solutes in any of the three solvents. The longer lifetimes and larger fluorescence quantum yields of the isoalloxazines compared with the alloxazines can be attributed exclusively to significantly slower rates of radiationless relaxation in the excited isoalloxazines. The remission and emission spectra of these same compounds adsorbed on cellulose are similar to the corresponding absorption and emission spectra in homogeneous solution, suggesting that the emitting species are the same in the adsorbed state as they are in homogeneous solution. However, the adsorbed excited species exhibit non- exponential temporal decay, attributed to inhomogeneities in the binding of the chromophore to cellulose. The emission spectra of polycrystalline samples of alloxazine and lumichrome suggest the possible occurrence of double intermolecular excited state proton transfer, but this interpretation is not supported by the further photophysical data obtained here.
TL;DR: In this paper, it was shown that [Fe(2methylimidazolate)2·0.13(FeCp2)]x,1, is orthorhombic, a = 8.0654(11), b = 15.3504(5), c = 19.3388(9) A, Z = 8, space group Pnnm.
Abstract: Crystals of [Fe (2methylimidazolate)2·0.13(FeCp2)]x,1, are orthorhombic, a = 8.0654(11), b = 15.3504(5), c = 19.3388(9) A, Z = 8, space group Pnnm. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R (F, I 3σ(I)) = 0.057 (Rw (F2, all data) = 0.142). The structure involves tetrahedral iron(II) centers linked in chains by single imidazolate ligand bridges. The chains are cross-linked by additional imidazolates to generate a complex 3-D network of linear channels in which ferrocene molecules are trapped. [Cu(1,2,4-triazolate)2]x, 2, is shown by indirect evidence to have a polymeric structure in which copper(II) ions are bridged by triazolate ligands. Magnetic susceptibilities were measured on powdered samples over the temperature range 2-300 K at applied fields of 0-55 000 G. Both materials exhibit antiferromagnetic exchange at temperatures above a magnetic phase transition: 27 K for 1 and 35 K for 2. At temperatures below these transitions the compounds exhibi...
TL;DR: A large part of the development of mathematics was driven by the desire to understand why objects in nature are found in a myriad of shapes and sizes and why certain forms are preferred over others as mentioned in this paper.
Abstract: A large part of the development of mathematics was driven by the desire to understand why objects in nature are found in a myriad of shapes and sizes and why certain forms are preferred over others...
TL;DR: Protonation of ferrocene has been suggested to take place on carbon (exo-protonation) or iron (endorion), but experiments have not been conclusive because of interfering exchange reactivities as discussed by the authors.
Abstract: Protonation of ferrocene has been suggested to take place on carbon (exo-protonation) or iron (endo-protonation). However, experiments have not been conclusive because of interfering exchange react...
TL;DR: In this article, the formation constants for the hydrogen-bonded complexes between phenol (donor) and selected carbonyl or phosphoryl compounds (acceptors) were determined from IR Δν shifts.
Abstract: Formation constants for the hydrogen-bonded complexes between phenol (donor) and selected carbonyl or phosphoryl compounds (acceptors) were determined from IR Δν shifts. The P=O group is about two ...
TL;DR: The ligands L = pyridine- or quinoline-carboxylic acid easily give complexes trans-[PdCl2L2], which self-assemble through hydrogen bonding between carboxyric acid groups to give one-dimensional pol...
Abstract: The ligands L = pyridine- or quinoline-carboxylic acid easily give complexes trans-[PdCl2L2], which self-assemble through hydrogen bonding between carboxylic acid groups to give one-dimensional pol...
TL;DR: In this article, synthetic studies directed toward various classes of compounds including taxoids and enediyne systems are described, including tether-controlled imtramolecular Diels-Alder reactions, carbometallation routes to dienes and furans, the use of carbohydrate building blocks, pentadienyl indium reagents for tandem cycloadditions to steroid and triterpenoid skeletons, and the synthesis of taxamycins and revolveneynes and related cyclophanes.
Abstract: Synthetic studies directed toward various classes of compounds including taxoids and enediyne systems are described. These investigations include tether-controlled imtramolecular Diels-Alder reactions, carbometallation routes to dienes and furans, the use of carbohydrate building blocks, pentadienyl indium reagents for tandem cycloadditions to steroid and triterpenoid skeletons, and the synthesis of taxamycins and revolveneynes and related cyclophanes.Key words: cycloaddition, taxoids, enediyne, cyclophanes, carbometallation.