摘要:

Tricarbonylrhenium(I) halide complexes of the nonracemic chiral ligand 2-[(4R,5R)-dimethyl-1,3-dioxan-2-yl]pyridine (L), namelyfac-[ReX(CO)3L] (X = Cl, Br, or I), have been prepared and their latent fluxionality studied by dynamic NMR techniques in the slow and intermediate exchange regimes. In solution, these complexes give rise to four diastereoisomers, depending on the configuration at the metal and at the acetal-carbon atom, respectively; the relative populations are in the orderSR>RR>>;RS>SS. At moderate temperatures, a reversible "acetal ring flip" leads toformalinversion of configuration at the acetal-carbon atom; the free energies of activation are in the range 84-88 kJ mol-1at 298 K. Above ca. 370 K, reversible ligand dissociation also occurs, leading to an exchange of all four diastereoisomers on the NMR chemical shift time-scale.Key words: dynamic NMR, fluxionality, tricarbonylrhenium(I) complexes, chiral acetal ligands.

ISSN:0008-4042    

DOI:10.1139/v99-152

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In solution in acetone at room temperature, tris(perfluoropropanoyl and perfluorobutanoyl)benzoylmethanate complexes of rhodium(III) are shown by19F NMR spectroscopy to exist as nearly statistical 1:3 mixtures of their respectivefacandmeroctahedral isomers, whereas the analogous perfluoroalkanoylthiobenzoylmethanate complexes have afac-octahedral structure. For all four complexes studied, vicinal F-F coupling constants are too small (0-3 Hz) to lead to resolved multiplet peaks, so that perfluoroethyl groups show singlet resonances for their CF3groups. Since four-bond coupling constants are significantly larger, ~9 Hz, perfluoropropyl groups show the expected multiplet resonances for their CF3groups. In acetone, AB patterns, with geminal coupling constants equal to approx. 270 Hz, are observed for the CF2groups next to the chelate ring (except for the perfluoropropanoylthiobenzoylmethanate complex). (These observations are modified by solvent. In toluene, one of the AB patterns of amer-octahedral complex collapses to a single peak.) The AB spectra, which are subject to substituent and solvent effects, can be interpreted in terms of perfluoroalkyl groups rotating rapidly about the Cring-Calkylbond, with an unsymmetric double potential well, giving unequal rotamer populations. Changes in the spectra were not noticeable over the temperature range accessible in the acetone and toluene solvents used.Key words: rotation, perfluoroalkyl groups, fluorine NMR spectra, fluorine-fluorine coupling constants, fluorinated&bgr;-diketonate complexes, monothio-beta-diketonates, rhodium complexes.

ISSN:0008-4042    

DOI:10.1139/v99-133

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The enzyme citrate synthase fromE. coliis a protein with a molecular weight (Mr) of 47 885 Da (wild type). This enzyme has been studied extensively, and its amino acid sequence has been characterized. This model protein has been used in this work for development and validation of methods involving capillary electrophoresis (CE) and electrospray ionization mass spectrometry (ESI-MS). TheMrdeterminations were conducted using sample infusion ESI-MS, and the tryptic digestion products of wild-type citrate synthase were characterized by on-line CE-ESI-MS coupled with a sheathless interface. On-line experiments were conducted on two different mass spectrometers, a Quattro-LC triple quadrupole instrument equipped with a Z-SprayTMsource (Micromass), and a reflecting time-of-flight (TOF) mass spectrometer built in-house in the Time-of-Flight Laboratory, Department of Physics, University of Manitoba. This is the first article to be written on the interfacing of a Z-SprayTMsource with CE. Unmodified fused silica capillaries gold-coated sheathless interfaces were used. The on-line CE separations yielded theoretical plate numbers greater than 104on average. Selected ion electrophorograms (SIE) of the tryptic peptides recorded on the Quattro-LC displayedS/Nratios ranging from ca. 14 to 120 on raw data. These SIE enabled identification of each peptide. The use of reflecting time-of-flight mass spectrometry (TOFMS) afforded mass resolution values of ca. 6000 (m/deltamFWHM), which enabled isotopic resolution of the peptide components. CE-ESI-MS and CE-ESI-TOFMS experiments enabled the generation of a complete tryptic map of citrate synthase.Key words: capillary electrophoresis, electrospray ionization, mass spectrometry, citrate synthase, tryptic digestion, triple quadrupole analyzer, time-of-flight analyzer.

ISSN:0008-4042    

DOI:10.1139/v99-138

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Spectral parameters, order parameters, and structural parameters, including the vibrationally correctedralphastructure of the partially oriented solutesp-xylene,p-chlorotoluene,p-dichlorobenzene, toluene, and chlorobenzene dissolved in three liquid crystal mixtures, are reported. For samples containing the three solutesp-xylene,p-dichlorobenzene, and 1,3,5-trichlorobenzene, multiple quantum (MQ) nuclear magnetic resonance was used to aid in the analysis of the complex high-resolution spectra of thep-xylene. The high-resolution spectra of 1,3,5-trichlorobenzene andp-dichlorobenzene were easily identified and analyzed once the calculatedp-xylene spectrum was subtracted from the experimental one. The methyl groups ofp-xylene,p-chlorotoluene, and toluene have similar geometries when the structure is determined from dipolar couplings corrected for harmonic vibrations.Key words: nematic liquid crystal, NMR, molecular structure, order parameter.

ISSN:0008-4042    

DOI:10.1139/v99-144

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

We report a67Zn nuclear magnetic resonance (NMR) study of compounds containing zinc ions coordinated by oxygen, nitrogen, and sulfur ligands. New information concerning67Zn nuclear quadrupole coupling constants (NQCC) and chemical shift was obtained from magic-angle spinning (MAS) spectra of solid compounds containing both natural abundance and enriched67Zn isotopes. Rapid ligand exchange processes of [Zn(thiourea)4]2+in aqueous solutions were also observed.Key words:67Zn NMR, nuclear quadrupolar coupling constant, ligand exchange.

ISSN:0008-4042    

DOI:10.1139/v99-154

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The formyl rotational energetics, solvent effects on the energetics and formyl-proton spin-spin coupling behavior of 2,6-dichlorobenzaldehyde were studied by using dipolar couplings analysis and the temperature dependence of the spin-spin couplings. The general form of the rotational potential was taken from molecular mechanics and the conjugative sin2Θ-type component (where Θ is the formyl-ring dihedral angle) was then optimized using the dipolar couplings obtained by analyzing1H NMR and13C proton satellite spectra in a liquid crystal solvent. The optimization based on the dipolar couplings gave the following rotational free energy potential:V(Θ) = 4.5 cos6Θ + 10.7 (± 2.0) sin2Θ, in kJ/mol. The analysis based on the temperature dependence of6Jdata allowed estimation of solvent effects on the potential. For example, the potentials in acetone and in acetonitrile differ by a 1.0 sin22Θ (in kJ/mol). The chloroform solvent effect can be described by term of -1.0 cos6Θ. When the formyl-proton six-bond coupling data was fit, assuming it obeyed the expression6J(Θ) =6J90sin2Θ +6J0and assuming6J0= 0.015 Hz, the analysis yielded6J90of -0.48 (± 0.03) Hz. The scalar coupling temperature dependence method was applied also to the conformational analysis of 2,6-dinitrobenzaldehyde.Key words: spin-spin coupling, dipolar coupling, solvent effect, rotational barrier, benzaldehyde.

ISSN:0008-4042    

DOI:10.1139/v99-198

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A series of functionalized polynorbornenes containing pendent ether- or ester-bridged poly(aromatic ether) chains were prepared. The ether-bridged norbornene complex was synthesized via cyclopentadienyliron-mediated nucleophilic aromatic substitution reactions. This methodology, combined with that of dicyclohexylcarbodiimide-mediated coupling, allowed for the formation of novel oligomeric aryl ether and ester substituted norbornene complexes. Photolytic demetallation gave the monomers in good yields. Structural identification of theexoandendoisomers of both the metallated and demetallated norbornene derivatives was accomplished using HH and CH COSY NMR techniques. Ring-opening metathesis polymerization (ROMP) of these monomers using RuCl3(hydrate) and (Cy3P)2Cl2Ru=CHPh allowed for the preparation of the functionalized polynorbornenes. Thermal analysis of the resulting polymeric materials demonstrated greater thermal stability as the number of aryl ether groups increased.Key words: aromatic ethers, cyclopentadienyliron, polynorbornene, ROMP, ruthenium catalysts.

ISSN:0008-4042    

DOI:10.1139/v99-164

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Deuterium and nitrogen-15 NMR spectroscopy has been used to measure the2H quadrupolar coupling and15N chemical shift tensors in solid hydroxylammonium chloride, NH3OH+Cl-, (HAC). In addition, the NH3and OH dynamics have been investigated by variable temperature2H line shapes andT1measurements. The Arrhenius activation energy for NH3rotation is 22.5 ± 1.8 kJ/mol with a pre-exponential factor of 8 ± 3 × 1012s-1from line shapes and 21.3 ± 2 kJ/mol with an infinite temperature correlation time, &tgr;inf,, of 5.0 ± 0.4 × 10-14s from theT1analysis. The latter value corresponds to a pre-exponential factor of 6.7 ± 0.5 × 1012s-1, if a three-site exchange is assumed. There was no evidence for OH reorientation up to 405 K, indicating a rather strong OH···Cl hydrogen bond. Previously reported inconsistencies between crystal structure and molecular orbital derived N-O bond lengths are cleared up by performing geometry optimizations with large basis sets and taking electron correlation into account. The internal rotational potential for the isolated HA cation is calculated to be 5.8 kJ/mol at the MP2/6-31G** level, with thetransgeometry preferred. Calculations that employ the neutron diffraction geometry and include the Cl-anions that surround the HA+cation yield an upper limit for the activation energy for NH3group rotation of 62 kJ/mol. Analysis of the deuterium spectrum andT1data yield nuclear quadrupolar coupling constants of 160 ± 5 kHz and 194 ± 5 kHz (η = 0.50 ± 0.05) for the ND3and OD deuterons, respectively. Density functional calculations of the deuterium and nitrogen-14 nuclear quadrupolar coupling constants at the B3LYP level show that it is necessary to include the influence of the surrounding chloride anions. We have also shown that it is possible to obtain accurate proton chemical shifts from the deuterium MAS spectrum of solid HAC-d4.Key words: solid state NMR, molecular dynamics, nitrogen 15 chemical shift anisotro

ISSN:0008-4042    

DOI:10.1139/v99-156

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Ru(hfac)3(2) was synthesized via peroxide oxidation of the Ru(II) species [Na][Ru(hfac)3] (1) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate). Treatment of either1or2with CF3SO3H in MeCN generatedcis-Ru(hfac)2(MeCN)2(3). Ru(acac)2(hfac) (4) (acac = acetylacetonate) was generated by addition of hfac to an EtOH solution ofcis-[Ru(acac)2(MeCN)2][CF3SO3]. Subsequent treatment of4with CF3SO3H in MeCN yieldedcis-Ru(acac)(hfac)(MeCN)2(7). Syntheses of [Na][Ru(hfac)2(acac)] (5) and Ru(hfac)2(acac) (6) are also reported. The complexes were characterized generally by elemental analysis, cyclic voltammetry, UV-vis, NMR, and IR spectroscopies. The structures of2,3, and7were established by X-ray crystallographic analyses. Crystals of2are monoclinic witha= 8.7781(4),b= 13.0760(11),c= 19.1857(5) Å, &bgr; = 92.2275(5)°,Z= 4, and space groupP21/n; those of3are monoclinic witha= 25.731(4),b= 8.8332(13),c= 18.1955(4) Å, &bgr; = 93.3395(6)°,Z= 8, and space groupC2/c; and those of7are triclinic witha= 7.6812(9),b= 10.680(2),c= 12.578(2) Å, &agr; = 88.062(6)°, &bgr; = 83.874(3)°, &ggr; = 69.5898(15)°,Z= 2, and space groupPbar over 1. The structures were solved by Patterson methods and refined by full-matrix least-squares procedures toR(F) = 0.036, 0.035, and 0.068 (Rw(F2) = 0.061,Rw(F) = 0.052, andRw(F) = 0.089), respectively.Key words: ruthenium, &bgr;-diketonato complexes, acetylacetonate, 1,1,1,5,5,5-hexafluoroacetylacetonate, acetonitrile co

ISSN:0008-4042    

DOI:10.1139/v99-175

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Collagen type I and III deposition in the cardiac extracellular matrix contributes significantly to myocardial dysfunction. Diffuse and focal fibrosis is believed to accompany human congestive cardiomyopathy (CCM) associated with congestive heart failure (CHF). The left ventricle collagen remodeling that occurs in the hamster model of CCM is marked by left ventricle fibrosis, hypertrophy and dilation, proceeded by CHF post 150 days of age. The objectives of our study were to (i) evaluate changes in collagen deposition in the right (RV) and left (LV) ventricular tissue of cardiomyopathic (CMP) and control (CON) myocardium using FTIR ATR spectroscopy, (ii) classify the normal and diseased heart tissue using linear discriminant analysis (LDA) aided by a genetic algorithm (GA) selection of spectroscopically diagnostic regions in the mid-IR region, (iii) rationalize the spectroscopic differences between left/right ventricle tissue as well as CON/CMP tissue according to the pathophysiology documented for the UM-X7.1 strain of CMP hamsters. The presence of collagen in the tissue was confirmed spectroscopically by observation of the collagen IR fingerprint in the 1000-1800 cm-1region. Difference spectroscopy was utilized to substantiate which tissue under comparison exhibited pronounced collagen content. Multivariate analysis (LDA) was carried out on user-selected spectral subregions and compared to class separation based on spectral subregions chosen nonsubjectively by a GA. Our study confirmed that the animals experienced LV collagen remodeling denoted by focal rather than diffuse fibrosis. In addition, RV collagen remodeling, denoted by decreased RV collagen content, appeared to accompany the increased LV collagen deposition found for the CMP animals.Key words: FTIR spectroscopy, collagen, cardiomyopathy, genetic algorithm, linear discriminant analysis.

ISSN:0008-4042    

DOI:10.1139/v99-178

出版商:NRC Research Press    

年代:1999

数据来源: NRC