Showing papers in "Canadian Journal of Chemistry in 2002"

Thermodynamic binding studies of cell surface carbohydrate epitopes to galectins-1, -3, and -7: Evidence for differential binding specificities

Abstract: Binding of a series of sialylated and non-sialylated cell surface carbohydrates to bovine heart galectin-1, recombinant murine galectin-3, and recombinant human galectin-7 was investigated by isoth...

Ligand scrambling reactions of cyano(thione)gold(I) complexes and determination of their equilibrium constants

Abstract: Ligand scrambling reactions in cyano(thione)gold(I) complexes ((>C=S-Au-CN)) to form (Au(>C=S)2) + and (Au(CN)2) - species have been investigated for a series of thiones in DMSO using 13 C and 15 N NMR spectroscopy. Rapid approach to equilibrium occurred and resulted in distinct signals for the (>C=S-Au-CN) and (Au(CN)2) - com- plexes, both in 13 C and 15 N NMR. Equilibrium constants (Keq) were determined for scrambling of all the complexes by integrating the CN resonances in the 13 C NMR recorded at 298 K. The influence of various factors (initial concentra- tion, ionic strength, temperature, and solvent polarity) on the Keq value was examined for a representative complex (ImtAuCN (Imt = Imidazolidine-2-thione)).

Glucosyltransferases acting on starch or sucrose for the synthesis of oligosaccharides

Abstract: In this work we review the extraordinary biotechnological potential of two glycosyltransferases, cyclodextrin glucanotransferase and dextransucrase, especially their utility in the synthesis of oli...

Second-generation MS-based high-throughput screening system for enantioselective catalysts and biocatalysts

Abstract: A high-throughput method is described, where the enantioselectivity of approximately 10 000 catalysts or biocatalysts can be determined per day. The method is based on electrospray mass spectrometr...

Synthesis, characterization, and X-ray crystal structures of Co(II) and La(III) complexes of a pyridine containing self-assembling system and solution studies of the Co(II) complex

Abstract: The complexes [pyda.H]2[Co(pydc)2]·H2O (I) and [pyda·H]2[La2(pydc)4(H2O)4].2H2O (II) were prepared from the complexation of a novel pyridine containing self-assembling system LH2, ([pyda·H2]2+[pydc...

1-Propanol hydrate by IR spectroscopy

Abstract: The mid-IR attenuated total reflectance (mid-IR–ATR) spectra of a series of 1-propanol and water mixtures were obtained. Factor analysis (FA) applied to spectra gave the spectra of three principal ...

Aspects of the hydrolysis of formamide: revisitation of the water reaction and determination of the solvent deuterium kinetic isotope effect in base

Abstract: A study of the hydrolysis of formamide is reported with the aims of isolating the water reaction for hydrolysis from the acid and base hydrolysis terms and determining the solvent deuterium kinetic...

Studies of a benzoporphyrin derivative with Pluronics

Abstract: The synthetic route for the benzoporphyrin derivatives produces two regioisomers in equimolar quantities (ring A and B isomers). A derivative of the A-ring product, BPD-MA (benzoporphyrin-derivative monoacid ring A, verteporfin), has recently been approved in North America and Europe for the treatment of age-related macular degen- eration. The B-ring isomers, contrary to the A-ring isomers, exhibit high aggregation in many formulations, which re- sults in inadequate drug delivery for clinical uses. To avoid aggregation, a non-ionic surfactant polymer such as a Pluronic — poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) — may be used as a formulation excipient. The triblock polymer investigated here is designated P123 (or poloxamer 403). When used to formulate a monoacid benzoporphyrin B-ring derivative (2), a critical micelle concentration of P123 in water occurred at approxi- mately 0.015 to 0.03%. The apparent pKa of compound 2 was dependent on its concentration in P123, and decreased as the molar ratio (P123:2) increased. High concentrations of P123 and neutral pH were found to be the best condi- tions to maintain the drug in its monomeric form. Kinetic studies suggest that the aggregate of 2 contains several mol- ecules, and is formed by a catalyzed self-assembly process. Samples with 1 mg mL -1 of drug, at pH = 7.4, and 4.8% of Pluronic showed satisfactory capacity to load and keep monomers stable. This formulation has potential PDT appli- cations.

Radiolysis of liquid water: An attempt to reconcile Monte-Carlo calculations with new experimental hydrated electron yield data at early times

Abstract: A re-examination of our Monte-Carlo modeling of the radiolysis of liquid water by low linear-energy-transfer (LET ~ 0.3 keV µm–1) radiation is undertaken herein in an attempt to reconcile the results of our simulation code with recently revised experimental hydrated electron (e–aq) yield data at early times. The thermalization distance of subexcitation electrons, the recombination cross section of the electrons with their water parent cations prior to thermalization, and the branching ratios of the different competing mechanisms in the dissociative decay of vibrationally excited states of water molecules were taken as adjustable parameters in our simulations. Using a global-fit procedure, we have been unable to find a set of values for those parameters to simultaneously reproduce (i) the revised e–aq yield of 4.0 ± 0.2 molecules per 100 eV at "time zero" (that is, a reduction of ~20% over the hitherto accepted value of 4.8 molecules per 100 eV), (ii) the newly measured e–aq decay kinetic profile from 100 ...

Investigation of the reactivity difference between thioglycoside donors with variant aglycon parts

Abstract: The reactivity of perbenzoylated thioglycosides with various thiol aglycons has been compared and quantified using competitive glycosylation experiments. Methyl 2,3,4-tri-O-benzyl-α-D-glucopyranosi...

Size dependence of the solubility of nonpolar compounds in different solvents

Abstract: At 25°C, plots of the standard Gibbs energy change associated with the solvation of noble gases and aliphatic hydrocarbons vs. the size of the solutes prove to be approximately linear with a negative slope for common organic solvents but not for water. In the latter case, the plot has a characteristic V-shape. The slope is negative for noble gases, methane, and ethane, but is positive for larger alkanes. This means that the solubility of nonpolar solutes increases with solute size in every solvent except water. The solvation thermodynamics of noble gases and aliphatic hydrocarbons in five solvents (water, ethanol, benzene, c-hexane, and n-hexane) are analyzed in detail by a general theory, which is rederived to avoid risky misunderstandings. The calculations are performed in the same manner for all solvents, using simple formulas where the physical reliability is well established and the results are consistent. The work of cavity creation increases with solute size in every solvent, but to a far greater e...

Dioxygenase-catalyzed cis-dihydroxylation of pyridine-ring systems

Abstract: Toluene dioxygenase-catalyzed dihydroxylation, in the carbocyclic rings of quinoline, 2-chloroquinoline, 2-methoxyquinoline, and 3-bromoquinoline, was found to yield the corresponding enantiopure c

The neutral diradical 5,5'-bis(1,3,2,4-dithiadiazolyl) [-], the first main group radical to exhibit a dramatic increase in paramagnetism on mechanical grinding

Abstract: Reduction of [()2][As6]2 with triphenylantimony and tetrabutylammonium chloride produced the diradical 5,5'-bis(1,3,2,4-dithiadiazolyl) [-] in high yield as a black solid with widely ranging magnetic susceptibilities (e.g., 0.6 to 2.6 μB), which on oxidation with AsF5 regenerated [()2][AsF6]2. The identity of [-] was established from EPR, vibrational, and mass spectra. Ab initio molecular orbital [MPW1PW91/6-311G(2df)] calculations show the lowest energy structure to consist of two coplanar rings separated by a C—C single bond (1.444 A), reflected in the comparison of the vibrational spectra of the diradical with that of [()2][AsF6]2 and the calculated spectra. Confidence in the calculated [MPW1PW91/6-311G(2df)] structure of the diradical is supported by the excellent agreement between the calculated and X-ray single crystal structure geometries of []2 and [()2]2+ in [()2][AsF6]2. The molecular orbitals indicate the diradical is essentially disjoint, confirmed by a very small (0.07 kJ mol–1) GVB-PP(TC-SCF...

The core oligosaccharide component from Mannheimia (Pasteurella) haemolytica serotype Al lipopolysaccharide contains L-glycero-D-manno- and D-glycero-D-manno-heptoses: Analysis of the structure and conformation by high-resolution NMR spectroscopy

Abstract: Previous studies from our laboratory have indicated that the lipopolysaccharide (LPS) from Mannheimia haemolytica serotype A1 contains both L-glycero-D-manno-heptose and D-glycero-D-manno-heptose r...

The coordination chemistry of o,o'-i-Pr2C6H3-bis(imino)acenaphthene to group 13 trihalides

Abstract: The preparation of several complexes of the diimine ligand o,o'-i-Pr2C6H3-bis(imino)acenaphthene (Ar-BIAN (1)) with group 13 trihalides (EX3, E = B, Al, Ga; X = Cl, Br) is reported. Four compounds ...

Sialoside clusters as potential ligands for siglecs (sialoadhesins)

Abstract: Clusters of O- and S-linked α-sialosides with valencies of two to four were constructed to serve as potential multivalent inhibitors towards sialoadhesins (siglecs). Thus, O- and S-prop-2-ynyl α-si...

Sequential dehydrochloride coupling of trichlorophosphine with 2,6-di-isopropylaniline: aminophosphine precursors to phosphetidines

Abstract: Various stoichiometric combinations of PCl3 with DippNH2 (Dipp = 2,6-di-isopropylphenyl) have been examined using 31P NMR spectroscopy. The dehydrochloride coupling reaction is mediated by the mode...

The synthesis of a carbohydrate-like dihydrooxazine and tetrahydrooxazine as putative inhibitors of glycoside hydrolases: A direct synthesis of isofagomine.

Abstract: The treatment of benzyl 2,3-O-isopropylidene-β-L-xylopyranoside with N-hydroxyphthalimide under Mitsunobu conditions, followed by protecting-group interchange, gave benzyl 4-O-[(tert-butoxycarbonyl...

2000 John C. Polanyi Award Lecture Mother Nature and the molecular Big Bang

Abstract: Biological molecules are mesoscopic systems that bridge the quantum and classical worlds. At the single molecule level, there are often more than 1 × 104 degrees of freedom that are involved in protein-mediated processes. These molecules are sufficiently large that the bath coordinate convolved to the reaction at an active site is defined by the surrounding protein tertiary structure. In this context, the very interatomic forces that determine the active protein structures create a strongly associated system. Thus, the bath fluctuations leading to reactive crossings involve highly hindered motions within a myriad of local minima that would act to cast the reaction dynamics into the high viscosity limit appropriate to glasses. However, the time scales observed for biological events are orders of magnitude too fast to meet this anticipated categorization. In this context, the apparent deterministic nature of biological processes represents an enormous challenge to our understanding of chemical processes. So...

Synthesis of 1,4-anhydro-D-xylitol heteroanalogues of the naturally occurring glycosidase inhibitor salacinol and their evaluation as glycosidase inhibitors

Abstract: The syntheses of two 1,4-anhydro-D-xylitol heteroanalogues (8 and 9) of the naturally occurring sulfonium ion, salacinol (3), containing a sulfur or nitrogen atom in the ring are described. Salacin...

Environmental photodegradation of pyrimidine fungicides — Kinetics of the visible-light- promoted interactions between riboflavin and 2- amino-4-hydroxy-6-methylpyrimidine

Abstract: To clarify the evolution of pyrimidine fungicides under natural aquatic environmental conditions, the visible-light-promoted degradation of the model fungicide 2-amino-4-hydroxy-6-methylpyrimidine ...

The activation of fibroblast growth factors by heparin: Synthesis and structural study of rationally modified heparin-like oligosaccharides

Abstract: Heparin-like hexasaccharide 3 and octasaccharide 4 have been synthesized using a convergent block strategy and their solution conformations have been determined by NMR spectroscopy Both oligosacch

Biomimetic reactions in organic synthesis: Semi-pinacol rearrangements of some spirocyclic epoxyalcohols derived from Juliá-Colonna asymmetric epoxidations

Abstract: Epoxy tert-alcohols have been prepared from (E)-enones in a two-step approach consisting of Julia–Colonna asymmetric epoxidation followed by Grignard alkylation of the epoxyketone. On treatment wit...

Synthesis, structure, and electrochemistry of cobalt(III) complexes with bis(benzoylacetone)ethylenediimine Schiff base

Abstract: A series of complexes of the type trans-[Co((BA)2en)(amine)2]ClO4 — where (BA)2en is the bis(benzoylacetone)ethylenediimine dianion and the amines are morpholine (mrpln) 1, aniline (aniln) 2, benzylamine (bzlan) 3, piperidine (pprdn) 4, p-toluidine (p-toldn) 5, and pyrrolidine (prldn) 6 — has been synthesized and characterized by elemental analysis, UV–vis, 1H NMR, and 13C NMR spectroscopy. The crystal and molecular structure of trans-[Co((BA)2en)(mrpln)2]ClO4 (1) has been determined by X-ray crystallography. The electrochemical reduction of these complexes at a glassy-carbon electrode, in the potential range of 0.5 to –2.0 V (vs. Ag/AgCl), in acetonitrile solution, indicates that the first reduction potential of Co(III/II) is irreversible, which is accompanied by the dissociation of the axial amine–cobalt bonds. This potential is dependent on the pKa of the axial amines. The second reduction potential of Co(II/I) shows reversible behavior and is also independent of the axial amine pKa. These results indi...

Syntheses and X-ray structures of boraamidinate complexes of lithium, phosphorus, and tellurium

Abstract: The dilithiated boraamidinate complexes {Li2[RB(N-t-Bu)2]}2 (1a, R = Ph; 1b, R = t-Bu), prepared by the reaction of B[N(H)-t-Bu]3 with three equivalents of LiR, are shown by X-ray crystallography to have dimeric structures consisting of a distorted Li4N4 cube capped on two opposite faces by RB units Reactions of 1a with TeCl4 or PX3 (X = Cl, Br) yielded complexes PhB(μ-N-t-Bu)2TeCl2 (2) and PhB(μ-N-t-Bu)2PX (4a, X = Cl; 4b, X = Br), respectively The structures of 2 and 4b were determined by X-ray crystallography In the solid state, complex 2 forms a dimer with weak Te···Cl contacts (32411(6) A) Complex 4b is monomeric with a P—Br bond length of 23047(11) A The reactions of 2 and 4a with the appropriate amounts of Li[N(H)-t-Bu] produce the monomeric tellurium imide PhB(μ-N-t-Bu)2Te=N-t-Bu and the amido derivative PhB(μ-N-t-Bu)2PN(H)-t-Bu (4c), respectively The X-ray structure of 4c was determined Deprotonation of 4c with n-BuLi produces the dimeric monolithium derivative {Li[PhB(μ-N-t-Bu)2PN-t-Bu]

L'échelle pKHB de basicité de liaison hydrogène des amines tertiaires aliphatiques

Abstract: The hydrogen bond acceptor strength of 40 tertiary amines has been measured by Fourier transform – infrared (FTIR) spectrometry from their 1:1 complexation constant towards 4-fluorophenol in CCl4 at 25°C (the pKHB scale). Also measured was the frequency shift, Δν(OH), of the ν(OH) band of methanol hydrogen-bonded to these amines. The comparison of the thermodynamic hydrogen bond basicity scale, pKHB, with the spectroscopic one, Δν(OH), and with the Bronsted pKa scale, points to the great sensitivity of pKHB to steric effects. The pKHB scale of tertiary amines extends from 2.71 for quinuclidine to –0.34 for N,N-diisopropyl-3-pentylamine. The main factors governing this important variation (17 kJ·mol–1 on the Gibbs energy scale) are the electron-withdrawing inductive effect and various kinds of steric effects (e.g., opening of the CNC angles and hindrance to OH fixation on the nitrogen lone pair). Infrared (IR) spectra show the attachment of 4-fluorophenol to the nitrile nitrogen of Me2NCH2CN and Me2NCH2CH2...

Novel terpenoids from the Sea Hare Aplysia punctata

Abstract: The structures of 23 compounds isolated from the sea hare Aplysia punctata have been determined by spectroscopic means. These include four new diterpenes (1–4): 1, neopargueroldione, is a tricyclic...

Reciprocal donor acceptor selectivity (RDAS): A new concept for "matching" donors with acceptors

Abstract: Lemieux's extensive work on replacement reactions at the anomeric center helped to establish the fact that the O-2-protecting group of a donor exerts powerful control over stereoselectivity in glyc...

Kinetics and mechanism of the oxidation of disaccharides by CrVI

Abstract: The oxidation of D-lactose, D-maltose, D-melibiose, and D-cellobiose by Cr VI yields the corresponding aldobionic acid and Cr 3+ as final products when an excess of reducing disaccharide over Cr VI is used. The rate law for the Cr VI oxidation reaction is expressed by -d(Cr VI )/dt = kH (disaccharide)(Cr VI ), where the second-order kinetic con- stant, kH, depends on (H + ). The relative reactivity of the disaccharides with Cr VI is expressed as follows: Mel > Lac > Cel > Mal, at 33°C. In acid medium, intermediate Cr V forms and reacts with the substrate faster than Cr VI . The EPR spectra show that five- and six-coordinate oxo-Cr V intermediates are formed, with the disaccharide acting as bidentate ligand. Five-coordinate oxo-Cr V species are present at any (H + ), whereas six-coordinate ones are observed only at pH < 2, where they rapidly decompose to the redox products. In the pH 3-7 range, where hexa-coordinate oxo-Cr V species are not observed, Cr V complexes are stable enough to remain in solution from several days to several months.

SiCl4ethanol as a trimerization agent for organometallics: convenient syntheses of the symmetrically substituted arenes 1,3,5-C6H3R3 where R = (C5H4)Mn(CO)3 and (C5H4)Fe(C5H5)

Abstract: Trimerization of acetylferrocene and of (acetylcyclopentadienyl)tricarbonyl-manganese proceeds efficiently in the presence of ethanol and tetrachlorosilane. The resulting 1,3,5-trisubstituted benzenes have been characterized by X-ray crystallography and compared with the structure of (1,3,5-triphenylbenzene)tris(tricarbonylchromium). The efficacy of EtOH–SiCl4 as a combined reagent for the trimerization of polycyclic ketones is also discussed. Finally, the synthesis and structure of [CpMn(CO)2]2(µ-C=CHPr), derived from the reaction of cymantrene with butyllithium and phenylacetyl chloride at room temperature, is described.Key words: ketone, condensation, cyclization, organometallics, arenes.