Showing papers in "Canadian Journal of Chemistry in 2007"
TL;DR: In this article, a computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical software.
Abstract: A computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient (EFG) and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical software. In addition to summarizing tensor magnitudes according to conventions commonly used by solid-state NMR spectroscopists, the program provides Euler angles relating the orientations of the EFG and shielding tensor principal axis systems (PAS). An atomic coordinate file is generated that also contains dummy atoms represent- ing the orientations of the EFG and shielding tensor PASs in the molecular framework. We demonstrate the functional- ity of the program using calculations of the chlorine EFG and shielding tensors for strontium chloride dihydrate and calcium chloride dihydrate. Several models of the chloride environment in these compounds are tested, including those where point charges are used to represent the extended three-dimensional lattices within the self-consistent charge field perturbation approach. The results highlight both the shortcomings and successes of traditional localized orbital-based basis sets in the description of the NMR properties of extended systems. We anticipate that EFGShield will be a useful tool for spectroscopists using quantum chemical software to aid in the interpretation of experimental data.
136 citations
TL;DR: In this article, aldol reactions in brine with high diastereo-and enantioselectivities, using a readily available bifunctional amide catalyst, were developed.
Abstract: Organocatalytic asymmetric direct aldol reactions in brine with high diastereo- and enantioselectivities, using a readily available bifunctional amide catalyst, were developed.Key words: aldol reac...
54 citations
TL;DR: The influence of fission product doping on the structure, composition, and electrochemical reactivity of uranium dioxide has been studied using X-ray diffractometry (XRD), scanning electron microscopy (SEM/EDX), Raman spectroscopy, and XPS.
Abstract: The influence of fission product doping on the structure, composition, and electrochemical reactivity of uranium dioxide has been studied using X-ray diffractometry (XRD), scanning electron microscopy (SEM/EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Experiments were conducted on SIMFUEL specimens with simulated burn-ups (increasing doping levels) of 1.5, 3.0, and 6.0 atom%. As the dopant level increased, the lattice contracted, suggesting the dominant formation of dopant-oxygen vacancy clusters. The smaller than expected lattice contraction can be attributed to the segregation of Zr (one of eleven added dopants) to ABO3 perovskite-type phases that SEM/EDX shows also contain Ba, Ce, and possibly some U. Raman spectroscopy shows that doping leads to a loss of cubic symmetry, possibly associated with tetragonal distortions. Raman mapping confirms this loss of cubic symmetry and suggests the specimen is not uniformly doped. Electrochemical experiments show that these distortions lead...
52 citations
TL;DR: X-ray absorption near edge structure spectroscopy (XANES) analysis has been routinely used to study the complex chemical interactions between additives in engine oil and metallic surfaces during high-temperature and reciprocating wear conditions as discussed by the authors.
Abstract: X-ray absorption near edge structure spectroscopy (XANES) analysis has been routinely used to study the complex chemical interactions between additives in engine oil and metallic surfaces during high-temperature and pres- sure reciprocating wear conditions. XANES analysis provides detailed chemical and structural information on the resul- tant antiwear and tribo films formed on metallic surfaces. The following review will illustrate how XANES analysis on the macro scale can provide the information required to elucidate complex film formation mechanisms, then describes the use of emerging XANES spectromicroscopy to such systems, and concludes by showing the complementary nature of the macro and micro scale spatially resolved XANES analysis; Professor Bancroft has utilized the combination of these to stay at the forefront of XANES research in the field of tribology and in spectroscopy science in general.
51 citations
TL;DR: In this paper, hydrogen peroxide together with MoO3 as catalyst can efficiently and chemoselectivity oxidize sulfides to sulfoxides and sulfones in the presence of other oxidized functional groups in ethanol.
Abstract: Hydrogen peroxide together with MoO3 as catalyst can efficiently and chemoselectivity oxidize sulfides to sulfoxides and sulfones in the presence of other oxidized functional groups in ethanol at 5...
48 citations
TL;DR: In this article, Synchrotron XPS and NEXAFS spectroscopic data for a natural tetrahedrite surface prepared by fracture under UHV were in accord with the composition of the mineral and its expected semi-saliency.
Abstract: Synchrotron XPS and Cu L2,3-edge NEXAFS spectroscopic data for a natural tetrahedrite surface prepared by fracture under UHV were in accord with the composition of the mineral and its expected semi...
43 citations
TL;DR: New types of asymmetrical photochromic diarylethene derivatives having a pyrazole unit, namely 1-[1,3,5]trimethyl-1-pyrazol-4-yl], 2-[2-methyl-5-(4-methoxylphenyl)-1-thien-3-yl]perfluorocyclopentene
Abstract: New types of asymmetrical photochromic diarylethene derivatives having a pyrazole unit, namely 1-[1,3,5-trimethyl-1-pyrazol-4-yl],2-[2-methyl-5-(4-methoxylphenyl)-1-thien-3-yl]perfluorocyclopentene
43 citations
TL;DR: In this article, the authors used the ESI-MS data and molecular modeling calculations to gain mechanistic, conformational, and domain-specific information from the acid-induced demetallation reactions of human metallothionein.
Abstract: Electrospray ionization mass spectrometry (ESI-MS) data and molecular modeling calculations were used to gain mechanistic, conformational, and domain-specific information from the acid-induced demetallation reactions of human metallothionein. The recombinant proteins studied were the single α- and β-rhMT-1a domains and the βα- and αβ-rhMT-1a two-domain species, based on the human metallothionein 1a sequence. Complete molecular models (MM3/MD) for all the fully metallated and demetallated species using a modified force field are reported for the first time. Basic residues that contribute to the ESI-MS charge states are identified from the molecular models. Demetallation took place under equilibrium conditions within a narrow pH range. For the two-domain proteins, these results support a demetallation mechanism involving the initial complete demetallation of one domain followed by the other for both βα-rhMT and αβ-rhMT. Based on the stability of the separate domains, the β domain is predicted to demetallate first in the two-domain rhMTs. Both the α domain and the β domain were observed to bind an excess of one Cd2+ ion. The metallated rhMT structures were shown to have very stable conformations, but only when fully metallated. Two or more conformations were observed at low pH in the ESI-MS data, which are interpreted as arising from the presence of structure, as opposed to a random coil, in the apo-rhMT. This is the first report of the existence of a structure in the two-domain metal-free apo-MT proteins. Only at extremely low pH does the structure open fully to give the highest charge distribution, which is associated with a random coil. Pre-existing structural features in the apo-MT would explain why the metallation reactions occur so rapidly.Key words: recombinant human metallothionein-1 (rhMT1), electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), molecular mechanics/molecular dynamics (MM3/MD).
41 citations
TL;DR: In this article, three kinds of scanning probe microscopy techniques, atomic force microscopy (AFM), confocal microscopy and scanning electrochemical microscopy, were used to study live cells in the physiological environment.
Abstract: In this report, three kinds of scanning probe microscopy techniques, atomic force microscopy (AFM), confocal microscopy (CM), and scanning electrochemical microscopy (SECM), were used to study live cells in the physiological environment. Two model cell lines, CV-1 and COS-7, were studied. Time-lapse images were obtained with both contact and tapping mode AFM techniques. Cells were more easily scratched or moved by contact mode AFM than by tapping mode AFM. Detailed surface structures such as filamentous structures on the cell membrane can be obtained and easily discerned with tapping mode AFM. The toxicity of ferrocenemethanol (Fc) on live cells was studied by CM in reflection mode by recording the time-lapse images of controlled live cells and live cells with different Fc concentrations. No significant change in the morphology of cells was caused by Fc. Cells were imaged by SECM with Fc as the mediator at a biased potential of 0.35 V (vs. Ag/AgCl with a saturated KCl solution). Cells did not change visib...
40 citations
TL;DR: In this paper, it was shown that the binary transition from the optically excited π π* state to the Biradical state occurs through a state switch to the ground state at a lower energy, which is defined by an electronic configuration in which one unpaired electron occupies a π * orbital confined to the five-membered ring.
Abstract: Coupled-cluster calculations of increasing accuracy (approximate doubles: CC2; doubles: EOM-CCSD; connected triples: CR-EOM-CCSD(T)) for CIS-optimized potential energy profiles of adenine and its derivatives indicate that the ultrafast internal conversion of the optically excited π π* state occurs through a state switch to a biradical state, which intersects the ground state at a lower energy. The electronic nature of the biradical state is defined by an electronic configuration in which one unpaired electron occupies a π* orbital confined to the five-membered ring. The second unpaired electron is localized very strongly on a p-type C2 atomic orbital of the six-membered ring. The biradical state minimum has a strongly puckered six-membered ring and a C2–H bond, which is twisted nearly perpendicular to the average ring plane. Consistent with the biradical-mediated internal conversion, the π π* state lifetime is extremely short in adenine and 9-methyladenine, which have barrierless crossing to the biradical...
38 citations
TL;DR: In this paper, a solvent-free procedure for the preparation of bis(indolyl)methanes via electrophilic substitution reactions of indoles with aldehydes and ketones is described.
Abstract: A simple and efficient solvent-free procedure for the preparation of bis(indolyl)methanes via electrophilic substitution reactions of indoles with aldehydes and ketones is described. The reactions took place in the presence of a catalytic amount of silica chloride at room temperature. The advantages of this method are high yields, short reaction times, low cost, and compliance with green-chemistry protocols.Key words: silica chloride, indole, carbonyl compound, solvent-free, bis(indolyl)methane.
TL;DR: In this paper, Monte Carlo simulations are used to investigate the effects of acidity (pH) on the primary yields of various chemical species produced in the radiolysis of de-aerated aqueous sulfuric acid solutions over the range from neutral solution to 0.4 mol/L H2SO4.
Abstract: Monte Carlo simulations are used to investigate the effects of acidity (pH) on the primary yields of various chemical species produced in the radiolysis of de-aerated aqueous sulfuric acid solutions over the range from neutral solution to 0.4 mol/L H2SO4. The effects of the quality of radiation, measured in terms of linear energy transfer (LET), have also been studied for LET varying from ~0.3 to 15 keV/µm at ambient temperature. Our results show that an increase in acidity (1 < pH < 4) leads to an increase in the yield of the "reducing" free radicals (hydrated electron and H atom) and a slight increase in G·OH and , while there is a slight decrease in At pH < 1, OH radicals react with HSO4- anions to form SO4·– radicals, resulting in a steep decrease in G.OH. By contrast, in the range of pH from ~4 to 7, the calculated yield values are independent of sulfuric acid concentration. In both neutral water and 0.4 mol/L H2SO4 (pH 0.46) solutions, the primary molecular yields increase upon increasing LET to ~...
TL;DR: In this paper, the chemical, crystalline, and non-crystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive X- ray analysis (SEM-EDX), micro-X-ray diffraction (µXRD), and calcium K-edge micro X-ray absorption near edge structure spectroscopy.
Abstract: Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete met- als through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the na- ture and formation mechanism of these precipitates. The chemical, crystalline, and noncrystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive X- ray analysis (SEM-EDX), micro-X-ray diffraction (µXRD), and calcium K-edge micro X-ray absorption near edge structure (µXANES) spectroscopy. Zinc is predominantly incorporated in calcite and cadmium in calcite and vaterite. Aragonite, which occurs occasionally, does not seem to contain trace metals. In addition to being precipitated in its three possible polymorphic forms, calcite, aragonite, and vaterite, calcium is also speciated as amorphous CaCO3 and possibly organic Ca in some grains. Most often, a particular grain consists of two or more crystalline and noncrystalline phases. The observed variability of intra- and inter-grain elemental and phase composition suggests that this biomineralization process is not constrained by biological factors but instead results from thermodynamically and kinetically controlled reactions. This study illustrates the potential of laterally resolved X-ray synchrotron radiation techniques (µXRD and µXANES) to study biomineralization and metal immobilization processes in plants.
TL;DR: A wide variety of phosphonium ionic liquids containing fluorous ponytails were synthesized by the reaction of Rfn-(CH2)2-I with trialkylphosphines (R3P; R
Abstract: A wide variety of phosphonium ionic liquids containing fluorous ponytails Rfn (Rfn = –(CF2)n–1CF3; n = 4, 6, 10) are synthesized by the reaction of Rfn-(CH2)2-I with trialkylphosphines (R3P; R = Me...
TL;DR: In this article, ammonium thiocyanate was used in the presence of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in methanol solution.
Abstract: Thiocyanation of various aromatic and heteroaromatic compounds has been achieved using ammonium thiocyanate in the presence of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in methanol solution at roo...
TL;DR: In this paper, the mechanisms of gold precipitation by the interaction of cyanobacteria and gold(III) chloride aqueous solutions (7.6 mmol/L final gold) have been studied at 25, 60, and 90 degrees.
Abstract: The mechanisms of gold precipitation by the interaction of cyanobacteria (Plectonema boryanum UTEX 485) and gold(III) chloride aqueous solutions (7.6 mmol/L final gold) have been studied at 25, 60,...
TL;DR: In this article, an ionic liquid-based route to 1,2-haloamines, 1 2-azidoamines and 1 2 -thiocyanoamines was developed.
Abstract: Ionic liquids, containing a variety of functionalities such as halo, azido, and thiocyano, efficiently cleave aziridines and epoxides to the corresponding products in high yields. The cleavages are regio- and stereo-selective. The reactions are complete in 1 h at 60 °C and do not require any other catalyst or organic solvent. Thus, a convenient synthetic route to 1,2-haloamines, 1,2-azidoamines, 1,2-thiocyanoamines, 1,2-azidoalcohols, and 1,2-thiocyanoalcohols is developed.Key words: aziridine, epoxide, ionic liquid, cleavage, regioselectivity, stereoselectivity
TL;DR: A simple, clean and efficient procedure for the green synthesis of some N-alkyl derivatives of sulfonamides is described in this article, using a simple microwave-assisted Michael addition.
Abstract: A simple, clean, and efficient procedure for the green synthesis of some N-alkyl derivatives of sulfonamides is described. Microwave-assisted Michael addition of sulfonamides to α,β-unsaturated est...
TL;DR: In this article, seven highly polar trisulfated triterpene glycosides belonging to the frondoside A7 group were isolated from the North Atlantic sea cucumber Cucumaria frondosa.
Abstract: Seven highly polar trisulfated triterpene glycosides belonging to the frondoside A7 group have been isolated from the North Atlantic sea cucumber Cucumaria frondosa. The structures of five new glyc...
TL;DR: The modified oligomers showed that the 5-hydroxymethyl group is compatible with triplex and duplex formation, and was compatible with Fmoc-based oligopeptide synthesis.
Abstract: We have investigated the chemistry for the incorporation of C5-hydroxymethyl-uracil and -cytosine in peptide nucleic acid (PNA) and the subsequent effect of this modification on PNA hybridization b...
TL;DR: The reaction of the anionic gallium(I) N-heterocyclic carbene analogue with the solution stable digermene 5 results in the formation of the gallium NHC- germylene complex 8 as discussed by the authors.
Abstract: The reaction of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue 3 with the solution stable digermene 5 results in the formation of the gallium NHC – germylene complex 8. The gallium NH...
TL;DR: In this article, a novel silica-supported zinc chloride catalyst was proposed for the Biginelli reaction and the key features of the catalyst include rapid reaction with 100% conversion of aldehyde, g...
Abstract: A novel silica-supported zinc chloride catalyst was prepared and investigated for the Biginelli reaction. The key features of the catalyst include rapid reaction with 100% conversion of aldehyde, g...
TL;DR: In this paper, the effect of several calcium-containing detergents on the tribological and tribochemical performance of a zinc dialkyldithiophosphate (ZDDP) lubricating oil additive in a low-sulfur base stock, 100N, was evaluated in a pin-on-disc configuration.
Abstract: A Plint friction and wear tester was used to investigate the effect of several calcium-containing detergents on the tribological and tribochemical performance of a zinc dialkyldithiophosphate (ZDDP) lubricating oil additive in a low-sulfur base stock, 100N. Thus, the friction and wear behavior of a steel-on-steel contact lubricated by 100N oil containing ZDDP alone and ZDDP–detergent mixtures at 100 °C was evaluated in a pin-on-disc configuration. The wear scar width of the upper steel pins was determined using an optical microscope, while the tribofilms formed on the lower steel discs were analyzed using X-ray absorption near edge structure (XANES) spectroscopy and X-ray photoelectron spectroscopy (XPS). At the same time, the thermal-oxidation films of the oil blends containing different additives were also prepared on the same steel discs and analyzed using XANES spectroscopy for comparative studies. It was found that in simple formulations the three kinds of calcium-containing detergents improved the f...
TL;DR: In this article, a reaction mechanism for the formation of the reported 4-azaisoindoles is proposed, which is based on the Friedlander reaction of 3-amino-4-cyanopyrroles with a series of cyclic ketones.
Abstract: The regioselective Friedlander reaction of 3-amino-4-cyanopyrroles with a series of cyclic ketones has enabled the first reported synthesis of substituted 4-azaisoindoles. Structurally, this new class of compounds stands for the first reported 4-azaisoindole tacrine analogues. A reaction mechanism for the formation of the reported 4-azaisoindoles is proposed.Key words: 4-azaisoindoles, tacrine, Friedlander reaction, pyrroles, mechanism.
TL;DR: It is found that it is possible to N-arylate electron-deficient pyrroles and indoles having no carbonyl group α to the nitrogen ring in good to excellent yields under the Chan and Lam conditions using N-Ethyldiisopropylamine (DIEA) base as a substitute for triethylamine and pyridine.
Abstract: We have found that it is possible to N-arylate electron-deficient pyrroles and indoles having no carbonyl group α to the nitrogen ring in good to excellent yields under the Chan and Lam conditions ...
TL;DR: In this paper, a recommended isotropic dipole oscillator strength distribution (DOSD) was constructed for the ethylene molecule through the use of quantum mechanical constraint techniques and experimental dipole OSS data; the data employed are recent experimental results not available at the time of the original constrained DOSD analysis of this molecule.
Abstract: A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the ethylene molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength (DOS) data; the DOS data employed are recent experimental results not available at the time of the original constrained DOSD analysis of this molecule. The constraints are furnished by molar refractivity data and the Thomas–Reiche–Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums, and mean excitation energies for ethylene. Pseudo-DOSDs for this molecule, and for propene and 1–butene, which are based on an earlier constrained DOSD analysis for these molecules, are developed. They are used to obtain reliable results for the isotropic dipole–dipole dispersion-energy coefficients C6, for the interactions of the alkenes with each other and with 47 other species, and the triple-dipole dispersion-energ...
TL;DR: A catalytic amount of ruthenium(III) acetylacetonate (2 mol%) [Ru(acac)3] enables solvent-free acetylation of phenols, alcohols, and amines at ambient temperature in good to excellent yields.
Abstract: A catalytic amount of ruthenium(III) acetylacetonate (2 mol%) [Ru(acac)3] enables solvent-free acetylation of phenols, alcohols, and amines at ambient temperature in good to excellent yields. Furth...
TL;DR: In this article, seven gallate-based compounds based on gallate were synthesized and characterized by elemental analysis, 1H NMR, and MS spectra, and compound 6 was structurally determined by single-crystal X-ray diffraction for the first time.
Abstract: Seven compounds (1–7) based on gallate were synthesized and characterized by elemental analysis, 1H NMR, and MS spectra. 2-(3,5-Dibenzyloxy-4-methoxy)phenyl-2-propanol (6) was a new compound. Methyl 3,5-dihydroxy-4-methoxybenzoate (3), methyl 3,5-dibenzyloxy-4-methoxybenzoate (4), 3,5-dibenzyloxy-4-methoxybenzyl alcohol (5), and compound 6 were structurally determined by single-crystal X-ray diffraction for the first time. Crystallographic data for 3: space group P212121; a = 4.0750(8) A, b = 7.5880(15) A, c = 29.802(6) A; V = 921.5(3) A3; Z = 4. 4: space group P-1; a = 10.068(2) A, b = 10.499(2) A, c = 11.388(2) A; α = 76.84(3)°, β = 66.79(3)°, γ = 64.10(3)°; V = 993.0(3) A3, Z = 2. 5: space group P-1; a = 8.1410(16) A, b = 8.7590(18) A, c = 12.879(3) A; α = 91.66(3)°, β = 94.69(3)°, γ = 91.73(3)°; V = 914.4(3) A3; Z = 2. 6: space group P21/c; a = 5.8100(12) A, b = 15.778(3) A, c = 23.237(5) A; β = 96.09(3)°; V = 2118.1(7) A3; Z = 4. All of the seven compounds were evaluated for the inhibition of growth ...
TL;DR: A series of geometry, frequency, and energy calculations of aquabismuth(III) complexes were carried out at up to the MP2/CEP-121G* level.
Abstract: A series of geometry, frequency, and energy calculations of aquabismuth(III) complexes were carried out at up to the MP2/CEP-121G* level. A thorough examination of all species up to and including enneacoordinate species was carried out. The structures of the complexes are compared with experimental data where available. Deviations from the most highly symmetric structures are consistent with the inert-pair effect. In addition, protonated bismuth–oxo clusters of the stoichiometry Bi6O8–n(OH)n(2+n)+, n = 0–4 are examined. The Raman spectrum of bismuth perchlorate with added perchloric and hydrochloric acid is measured.Key words: bismuth, aqua complexes, ab initio, Raman spectra.
TL;DR: The structure of metallurgical or smelter-grade aluminas (MGAs) is complex and poorly understood as discussed by the authors, and the structure of MGAs is poorly understood.
Abstract: The structure of metallurgical- or smelter-grade aluminas (MGAs) is complex and poorly understood. Ultra-high-field solid-state 27Al NMR results on industrial as well as on laboratory-prepared alum...