Showing papers in "Canadian Journal of Chemistry in 1998"
TL;DR: In this paper, a series of β -chalcogenovinylaldehydes, 1,6-dioxa-6a-chalcogenopentalenes, and bim...
Abstract: Ab initio (RHF/LanL2DZ, MP2(fc)/LanL2DZ, MP2(fc)/6-31G**, and MP2(fc)/6-311++G**) calculations were performed for a series of β -chalcogenovinylaldehydes, 1,6-dioxa-6a-chalcogenopentalenes, and bim...
136 citations
TL;DR: In this article, the molecular weight of chitosan samples was determined in a solvent system of 0.25 M CH3COOH/0.25M CH3COONa, using viscometry and gel permeation chromatography (GPC) with a TSK-gel column.
Abstract: Starting from a chitosan sample with a degree of deacetylation of 71%, three separate sample sets were generated by successive deacetylation and reacetylation processes. The degree of deacetylation of samples was determined by UV spectrometry supported by thermogravimetric analysis. The molecular weight of chitosan samples was determined in a solvent system of 0.25 M CH3COOH/0.25 M CH3COONa, using viscometry and gel permeation chromatography (GPC) with a TSK-gel column. The first set of samples had a similar degree of deacetylation (DDA) but differing molecular weights. The second set of samples had a similar molecular weight but differing degrees of deacetylation. The Mark-Houwink-Sakurada constants used for the determination of viscosity average molecular weight and the universal calibration of the GPC system were K =1 .40 ◊1 0 -4 dL/g and a = 0.83. Results showed that molecular weights determined from both techniques are in good accord only at lower degrees of deacetylation. This may be attributed to the fact that the chemical structure of chitosan samples could have been largely altered with increasing or decreasing degree of deacetylation. Nevertheless, the trend with which the molecular weights vary with the deacetylation time is consistent over a limited DDA range. A literature review of molecular weight analysis of chitosan is included.
116 citations
TL;DR: A sensor system based on the optical phenomenon of surface plasmon resonance (SPR), which employs either photothermal deflection spectroscopy (PDS) or a photodiode array (PDA) for detection, was proposed in this paper.
Abstract: A sensor system based on the optical phenomenon of surface plasmon resonance (SPR), which employs either photothermal deflection spectroscopy (PDS) or a photodiode array (PDA) for detection, was de...
78 citations
TL;DR: In this article, the aziridination of olefins with {(4-nitrophenylsulfonyl)imino}phenyl-lambda-3-iodane, NsN==IPh (1c), in the presence of [Rh2(OAc)4] proceeds in yields of up to 85% when the olefin is used in large scales.
Abstract: The aziridination of olefins with {(4-nitrophenylsulfonyl)imino}phenyl-lambda3-iodane, NsN==IPh (1c), in the presence of [Rh2(OAc)4] proceeds in yields of up to 85% when the olefin is used in large...
74 citations
TL;DR: In this paper, a phase mask was used to inscribe a 1.5 mm, high-reflectivity polarization-independent Bragg grating into a ridge wave guide.
Abstract: The solution sol-gel method is used to produce thin films of photosensitive hybrid organic-inorganic glass on silicon. Glasses consisted of photoinitiator, methacryloxypropyltrimethoxysilane, methacrylic acid, and zirconium oxide. Clear, low optical loss films are obtained, indicating nanophase homogeneity in the samples. The nanocomposite films are shown to be suitable for fabricating optical components such as ridge wave guides and Bragg diffraction gratings. The increase in the refractive index of the glass relative to the surrounding material during photolithographic processing is identified as a key material parameter in device fabrication. Accordingly, electronic and vibrational spectroscopy are used to provide insight into the structural changes that occur when glasses are irradiated with continuous narrow band 4.9 eV and pulsed 6.4 eV light. Arguments are advanced, linking the changes in refractive index to collateral densification leading to volume compaction of the silicate network during organic free-radical polymerization. This was shown by following the time evolution of relevant IR absorption bands. Free silanol and unreacted methoxysilane are consumed in the process. Matrix densification is indicated by shifts to low wave number in the transverse optical phonon mode associated with decreasing Si-O-Si bond angles of the antisymmetric stretching vibration (compression). Growth in the Si-O-Si framework is observed through increased intensity in this IR absorption. Similar behaviour is observed for films irradiated with 6.4 eV light from an excimer laser. A phase mask in combination with pulsed 6.4 eV light is used to inscribe a 1.5 mm, high-reflectivity polarization-independent Bragg grating into a ridge wave guide. The high reflectivity is thought to arise from a periodic modulation of the volume compaction of the matrix. Overall, the organic component of the glass confers unique properties on the material that allow it to be densified even with 4.9 eV light. By comparison, sol-gel silica with no organic component must be densified at nearly twice the photon energy.
71 citations
TL;DR: In this article, the complex interaction of softwood residual kraft lignin with oxygen at elevated temperatures, pressures, and pH's was investigated by isolating and systematically oxidizing the Lignin, as a function of time and temperature.
Abstract: The complex interaction of softwood residual kraft lignin with oxygen at elevated temperatures, pressures, and pH's was investigated by isolating and systematically oxidizing the lignin, as a function of time and temperature. The isolation of the oxidized lignin was carried out using a multistep procedure developed specifically to recover all species. Detailed quantitative 31 P NMR measurements provided, for the first time, three-dimensional plots describing the formation and (or) elimination of the various functional groups. Oxidative demethoxylation reactions were found to induce the formation of catechols, which are, most likely, reactive intermediates of the oxidation. The rate of carboxylic acid formation and guaiacyl phenol elimination was found to follow two distinct phases: a rapid initial phase followed by a slower phase. More specifically, the rate of carboxylic acid group formation was found to dramatically increase as the reaction temperature increased, analogous to the profiles obtained for the elimination of guaiacyl phenolic units. At reaction temperatures typical of conventional commercial oxygen delignification installations (80-100°C), only minor oxidation was found to occur within the lignin. At these temperatures, increasing the reaction time did not significantly aid the formation of carboxylic acid groups on lignin despite the idealized two- phase homogeneous conditions. The technological ramifications of these data imply that a three-phase oxygen delignification system, operating at temperatures below 100°C, causes only minor oxidative changes to the structure of the lignin in the fibre. It was also possible to isolate the effect of alkali and temperature on the structure of residual kraft lignin through experiments in which pressurized oxygen was replaced by nitrogen. These data revealed a concealed set of alkali-induced condensation and fragmentation reactions.
70 citations
69 citations
TL;DR: In this article, a photoactive copolymer derived from fluorenes derived from palladium-catalyzed Suzuki couplings has been described, and poly((4,4prime-biphenylene)-2,7-(9,9-dioctylfluorene)) an...
Abstract: Electroactive and photoactive copolymers derived from fluorenes have been prepared from palladium-catalyzed Suzuki couplings. For instance, poly((4,4prime-biphenylene)-2,7-(9,9-dioctylfluorene)) an...
69 citations
TL;DR: Ring-opening polymerization (ROP) of strained ring-tilted metallocenophanes can be achieved thermally, via anionic or cationic initiation, or by the use of transition-metal catalysts.
Abstract: Ring-opening polymerization (ROP) of strained ring-tilted metallocenophanes can be achieved thermally, via anionic or cationic initiation, or by the use of transition-metal catalysts and provides access to a wide range of high molecular weight (Mw = 10 5 n10 6 , Mn >1 0 5 ) poly(metallocenes). These materials possess a variety of interesting properties and many are very easy to prepare. This article provides an overview of our work, giving background to and an account of the initial discovery, and discusses work on the synthesis and properties of new poly(metallocenes) and related materials with particular emphasis on recent research directions.
69 citations
TL;DR: The first reagent-controlled asymmetric halolactonizations were described in this article, where complexes of I+ with O-acyl-and O-aryldihydroquinidines were used to promote the asymmetric H-Lactonization of prochiral H-cliques.
Abstract: The first reagent-controlled asymmetric halolactonizations are described. Complexes of I+ with O-acyl- and O-aryldihydroquinidines are used to promote the asymmetric halolactonization of prochiral ...
69 citations
TL;DR: In this article, it was shown that the proper open systems predicted by the quantum action principle define the atom and that this definition accounts for the retention of an atom's chemical identity by enabling one to replace the quantum mechanical observables for force and energy with dressed, real space density distributions whose forms parallel the transferable topology of the electron density distribution.
Abstract: Dalton made a bold assumption in his atomic hypothesis by stating that atoms retained their mass and their identity in chemical combination. Its vindication had to await Rutherford's nuclear model of the atom. The continuing evolution of chemistry led to the realization that atoms exhibit not only a unique mass but also characteristic additive properties, thereby making it possible to recognize their presence in a molecule and to predict the molecule's static and reactive properties. The theoretical vindication of the model of a functional group as the carrier of chemical information had to await the work of Feynman and Schwinger. Their generalization of physics leads to a unique definition of an atom as an open quantum system and makes possible the renormalization that is required to account for the short-range nature of the forces that enable one to identify a given group in any environment. The lecture will demonstrate that the proper open systems predicted by the quantum action principle define the atom and that this definition accounts for the retention of an atom's chemical identity by enabling one to replace the quantum mechanical observables for force and energy with dressed, real space density distributions whose forms parallel the transferable topology of the electron density distribution.
TL;DR: In this paper, the mixing and the structural properties of model mixtures formed by the main lipids of the stratum corneum have been examined by infrared spectroscopy, showing that the mixture exhibits a rich polymorphism, ranging from crystalline domains with heterogeneous lipid composition and orthorhombic chain packing, to a fluid and homogeneous phase.
Abstract: The stratum corneum, the top layer of the epidermis, is the material that constitutes the membrane enveloping our body. The lipids that are present are responsible for the permeability properties of the skin and, as a consequence, are essential to maintain the hydration of the internal components and to protect our body from external agents. In the present work, the mixing and the structural properties of model mixtures formed by the main lipids of the stratum corneum have been examined by infrared spectroscopy. The model is formed by an equimolar mixture of ceramides (type III), cholesterol, and perdeuterated palmitic acid. Binary mixtures as well as mixtures for which the ceramides were substituted by sphingomyelin, a ceramide precursor, have also been studied. The results indicate that the stratum corneum model mixture exhibits a rich polymorphism, ranging from crystalline domains with heterogeneous lipid composition and orthorhombic chain packing, to a fluid and homogeneous phase. To obtain this particular behaviour, the three components are essential and the specific role of each species is discussed. In addition, the results reveal that the homogeneous lipid distribution observed for temperatures higher than 70°C can be maintained at low temperatures, leading to the formation of a metastable phase. Several weeks are needed to obtain the thermodynamically stable phase if the sample is incubated at 5°C. However, it is rapidly induced by annealing the sample at 40°C. Resume : Le stratum corneum, la couche superieure de l'epiderme, est le materiau constituant la membrane enveloppant notre corps. Les lipides qu'on y retrouve sont responsables des proprietes de permeabilite de la peau et, en consequence, sont necessaires au maintien de l'hydratation des composantes internes et a la protection du corps contre les agents externes. Dans le present travail, les proprietes de melange et structurales de melanges modeles constitues des principaux lipides du stratum corneum ont ete examinees par spectroscopie infrarouge. Le modele utilise est constitue d'un melange equimolaire de ceramides (de type III), de cholesterol et d'acide palmitique perdeutere. Des melanges binaires ainsi que des melanges pour lesquels les ceramides sont replaces par la sphingomyeline, un precurseur des ceramides, ont ete aussi etudies. Les resultats montrent que le melange modele du stratum corneum montre un riche polymorphisme, allant de domaines cristallins heterogenes du point de vue de leur composition en lipide et ou les chaines possedent un empilement orthorhombique, a une phase fluide homogene. Pour obtenir ce comportement, les trois composantes sont essentielles et le role specifique de chaque espece est discute. De plus, les resultats revelent que la distribution homogene des lipides obtenue a des temperatures superieures a 70°C peut etre maintenue a basses temperatures, conduisant a la formation d'une phase metastable. Plusieurs semaines sont necessaires pour obtenir la phase thermodynamiquement stable si l'echantillon est maintenu a 5°C. Cependant, celle-ci est rapidement induite par un recuit a 40°C. Mots cles : stratum corneum, lipide, spectroscopie infrarouge, ceramide.
TL;DR: In this article, the addition of indole and methyl indole at both high and ambient pressures to a series of Michael acceptors under the influence of ytterbium triflate was investigated.
Abstract: The addition of indole and methyl indole at both high and ambient pressures to a series of Michael acceptors under the influence of ytterbium triflate was investigated. Under ambient pressure the m...
TL;DR: The carcinogens 4-aminobiphenyl and 2-aminofluorene are metabolized to hydroxylamine esters that undergo N-O heterolysis to produce arylnitrenium ions that react with DNA, especially at guanine residues, which completely parallels that of carbenium ions.
Abstract: The carcinogens 4-aminobiphenyl and 2-aminofluorene are metabolized to hydroxylamine esters that undergo N-O heterolysis to produce arylnitrenium ions that react with DNA, especially at guanine residues. These nitrenium ions and a number of their derivatives have been studied by the laser flash photolysis technique, to provide direct kinetic information about the lifetimes of the electrophiles in water and their reactivities with added nucleophiles. Arylnitrenium ions ArNH+ are longer-lived in water than arylcarbenium analogs ArCH2+, in some cases significantly longer-lived. The nitrenium ions do react with azide ion at the diffusion limit (providing the cation is not highly stabilized). This behaviour completely parallels that of carbenium ions. The biphenylyl- and fluorenylnitrenium ions react with guanine derivatives such as 2-deoxyguanosine (dG) with rate constants that are close to or at the diffusion limit (2 × 109 M-1 s-1) for the more reactive cations. Thus, in spite of cation lifetimes of the ord...
TL;DR: Ostwald solubility coefficients, as log L, for solutes in water and ethanol have been combined to give log PEtOH for partition between the two pure solvents.
Abstract: Ostwald solubility coefficients, as log L, for solutes in water and ethanol have been combined to give log PEtOH for partition between the two pure solvents. Sixty-four such values have been correl...
TL;DR: In this article, a 1H NMR chemical shift ( delta ) study of a homologous series of hydrocarbon (hc) (CxH2x + 1CO2Na, x = 5, 7, 9, 11, 13) surfactants (S) has been carried out in water and in binary solvent (D2O + cyclodextrin (CD)) systems at 22°C.
Abstract: A 1H NMR chemical shift ( delta ) study of a homologous series of hydrocarbon (hc) (CxH2x + 1CO2Na, x = 5, 7, 9, 11, 13) surfactants (S) has been carried out in water and in binary solvent (D2O + cyclodextrin (CD)) systems at 22°C. Complementary 1H NMR chemical shift ( delta ) data of the cyclodextrins in binary (D2O + S) systems containing hc surfactants have also been obtained. Complex induced shift (CIS) values for selected host or guest protons were found to increase as the alkyl chain (Cx) length of the surfactant increased. The CIS values are found to depend on the following factors: (i) the magnitude of the binding constant (Ki, i = 1:1, 2:1), (ii) the chain length of the surfactant, (iii) the mole ratio of the host to guest species, (iv) the host-guest stoichiometry, and (v) the host-guest inclusion geometry. The CIS values of the CD-S systems have been analyzed using equilibrium models in which 1:1 complexes, 1:1 plus 2:1 complexes, and uncomplexed species are present. Differences in the binding ...
Abstract: A series of cation-exchange membranes were obtained by photoinitiated grafting of acrylic acid onto a polypropylene microporous support having 0.2 µm diameter pores. The poly(acrylic acid) was shown to be contained within the pores of the membrane. The ion-exchange capacities of these "pore-filled" membranes ranged from 65 to 80% of the theoretical values calculated on the basis of their measured graft yields, with water contents ranging from 72 to 77%. The membranes exhibited a chemical valve effect of flux as a function of pH. Treatment of a poly(acrylic acid) grafted membrane with a solution containing ferrous ions resulted in a large uptake of iron (>24% by weight of iron with a membrane containing 152% graft yield of poly(acrylic acid)). Subsequent alkaline (pH 14) oxidation at 70°C with either oxygen or hydrogen peroxide led to the formation of a superparamagnetic nanocrystalline form of ferrihydrite, 5Fe2O3 ·9H2O. The oxide was identified by temperature-dependent Mossbauer spectroscopy recorded fro...
TL;DR: In this paper, gold complex ions [AuCl4]- were reduced from aqueous solution to produce nanoparticles of gold upon the surface of porous silicon, using porous silicon as a reducing agent and a substrate.
Abstract: Utilizing porous silicon as a reducing agent and a substrate, gold complex ions [AuCl4]- were reduced from aqueous solution to produce nanoparticles of gold upon the surface of porous silicon. Scan...
TL;DR: Using the published method of Wiedenbruch, bis(pentafluorophenyl)zinc, 1, was prepared from anhydrous ZnCl2 and 2 equiv. of LiC6F5 in diethyl ether as discussed by the authors.
Abstract: Using the published method of Wiedenbruch, bis(pentafluorophenyl)zinc, 1, was prepared from anhydrous ZnCl2 and 2 equiv. of LiC6F5 in diethyl ether. Base-free 1 was obtained in 60-65% yield by repe...
TL;DR: Escherichia coli β-galactosidase molecules were incubated with fluorogenic substrate in a capillary and individual randomly distributed peaks of product were observed, each representing the activity of an individual enzyme molecule.
Abstract: Escherichia coli β-galactosidase molecules were incubated with fluorogenic substrate in a capillary. Upon flushing the reactor contents past the detector, individual randomly distributed peaks of p...
TL;DR: In this article, tridentate azomethine ligands derived from salicylaldehyde with phenylboronic acid were synthesized by reaction of tridentates with trichlorobicyclic structures.
Abstract: Three boronates have been synthesized by reaction of tridentate azomethine ligands derived from salicylaldehyde with phenylboronic acid. The [5.4.0], [4.4.0], and [4.3.0]heterobicyclic structures o...
TL;DR: In organoammonium cations containing two or more N atoms, the H(N) atom introduced by the protonation may engage in an N→H(N)...Y bond to an external acceptor (anion or solvent molecule); in an int...
Abstract: In organoammonium cations containing two or more N atoms, the H(N) atom introduced by the protonation may engage in an N→H(N)...Y bond to an external acceptor (anion or solvent molecule); in an int...
TL;DR: In this paper, the results of a flash photolysis irradiation of 4-Azido-X-substituted biphenyls (X' = 4'-MeO, 4'Me, 4', MeO+F, 4'-F, 3'-Me, 3'Me+H, H, 3',MeO+3', 3'-Cl, 3´Cl, 4´CF3) were shown to be quenched by azide ion at diffusion limit.
Abstract: 4-Azido-X'-substituted biphenyls (X' = 4'-MeO, 4'-Me, 4'-F, 3'-Me, 4'-Cl, H, 3'-MeO, 3'-Cl, 4'-CF3) have been prepared and subjected to 248 nm flash photolysis irradiation in 20:80 acetonitrile:water. Transient X'-substituted 4-biphenylylnitrenium ions 10 (Ar C6H4-N + H) are observed, with lifetimes ranging from 0.6 ms (4'-MeO) to 26 ns (4'-CF3). These cations are quenched by azide ion, with values of kaz ranging from 6 to 10 x 109 M-1 s-1, with the majority in the range (9-10) x 109. This near constant kaz provides further evidence that arylnitrenium ions are quenched by azide ion at the diffusion limit. The solvent reactivities, plotted in a single-parameter Hammett plot against σ sup + (X), exhibit a poor correlation, with the points for the para π-electron donors deviating from the correlation line based on the other substituents in the direction of requiring a more negative substituent parameter. The data are more satisfactorily fit to the two-parameter Yukawa-Tsuno equation; the parameter r + obtain...
TL;DR: The lithium pK scale has been extended to 25 indicators with a pK range of 9.7-24.4 as discussed by the authors, compared with the cesium ion pair acidities.
Abstract: The lithium pK scale has been extended to 25 indicators with a pK range of 9.7-24.4. The resulting scale is compared with the cesium ion pair acidities and to ionic pK's in DMSO and aqueous DMSO.Ke...
TL;DR: The crystal structure of the title compound was determined at 250 K in space group I 4 bar 2m, a = 20.661(5) A, c = 6.764(7) A, Z = 8.
Abstract: The crystal structure of the title compound was determined at 250 K in space group I 4 bar 2m, a = 20.661(5) A , c = 6.764(7) A , Z = 8. The individual dithiadiazole rings form two sets of contraro...
TL;DR: In this paper, a self-modeling curve resolution (SMCR) algorithm is proposed to extract spectral and concentration information for unknown components in a series of mixture spectra, which is applicable to problems in chromatography, equilibrium studies, and kinetics, among others.
Abstract: A new procedure to extract spectral and concentration information for unknown components in a series of mixture spectra is described. The algorithm, a form of self-modeling curve resolution (SMCR), requires no assumptions about the mixture data except for linear additivity and non-negativity of component spectra, and non-negativity of concentrations. It provides permissible bands for the spectra and concentration profiles of individual components in the mixtures and is applicable to problems in chromatography, equilibrium studies, and kinetics, among others. The new method employs a nonlinear optimization procedure and is substantially more efficient than similar methods that have been previously reported. The SMCR algorithm is demonstrated by applying it to the autocatalytic oxidation of oxalic acid by permanganate in the presence of sulfuric acid. The reaction was monitored spectroscopically between 200 and 1000 nm under four different reaction conditions. Results verified the presence of two reaction intermediates previously proposed in the literature and confirmed their spectral properties. Concentration profiles for the intermediates are described.
TL;DR: In this paper, the reaction of S-nitrosothiols with their corresponding thiols (RSH) present in a large excess (>20-fold) proceed readily to give the disulfide.
Abstract: Reactions of S-nitrosothiols (RSNO) with their corresponding thiols (RSH) present in a large excess (>20-fold) proceed readily to give the disulfide. Ammonia is formed together with some nitrite an...
TL;DR: A survey of crystal structures containing the xanthine ring showed that caffeine-like molecules tend to stack in parallel in a variety of stacking geometries, suggesting that a stacked pair of caffe...
Abstract: A survey of crystal structures containing the xanthine ring shows that caffeine-like molecules tend to stack in parallel in a variety of stacking geometries, suggesting that a stacked pair of caffe...