摘要:

The signs and magnitudes of the long-range coupling constants between the formyl and ring protons over five, six, seven, and eight bonds in phenyl formate and its 4-fluoro, 4-methyl, and 4-nitro derivatives are reported. These numbers are combined with CNDO/2 and INDO MO FPT computations of their conformational dependence and with STO-3G MO populational distributions to provide a description of the conformational behaviour of these molecules. TheZconformers, predominantly nonplanar and having the carbonyl group pointing towards the ring, appear to account for more than 95% of the molecules in CS2solution at 300 K. In polar solvents, significant populations of theEconformers are indicated by the long-range coupling constants. The long-range coupling constants for the formyl proton in 2,6-dichlorophenyl formate are consistent with geometry-optimized STO-3G MO computations, which imply that theZconformation, with the aldehyde group lying near the plane perpendicular to the benzene plane, is again at least 95% abundant at 300 K. The proton chemical shifts are also consistent with these conclusions.

ISSN:0008-4042    

DOI:10.1139/v88-289

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A trimethylsilyl enol ether (34) derived from camphor (1) undergoes intramolecular Mukaiyama reaction to provide a tricyclic ketone (36) that can serve as a key intermediate in a new enantiospecific synthesis of longiborneol (11) and longifolene (12).

ISSN:0008-4042    

DOI:10.1139/v88-290

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A sulfhydryl-specific fluorescent reagent, 7-diethylamino-3-((4′-iodoacetylamino)phenyl)-4-methylcoumarin (DCIA) was used to label cysteine residues on tropomyosin (TM) from rabbit cardiac and rabbit skeletal muscles. The emission maximum at 486 nm, the high degree of fluorescence polarization, and the limited accessibility of the bound probe to quenching by iodide suggest that the probe is bound in the hydrophobic cleft between polypeptide chains of the TM coiled coil, as well as being bound covalently at a cysteine residue. The labelled TMs retain their abilities to bind F-actin and are able to interact with deoxyribonuclease I. They, however, show a reduced tendency to aggregate into filaments in low ionic strength solutions.

ISSN:0008-4042    

DOI:10.1139/v88-291

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

A series of tris(benzohydroxamato)metal(III) complexes has been prepared and characterized wherein the metals are aluminum, gallium, and indium. The complexes are synthesized in high yield from aqueous solution. The indium complex, as its ethanol solvate In(C7H6NO2)3•C2H5OH, has been studied by single crystal X-ray diffraction. The crystals are monoclinic witha = 11.091(2),b = 18.065(3),c = 12.861(2) Å, β = 105.55(1)°,Z = 4, and space groupP21/n. The structure was solved by Patterson and Fourier methods and was refined by full-matrix least-squares procedures toR = 0.038 andRw = 0.037 for 2579 reflections withI ≥ 3σ(I). Bond lengths and angles in the compound were normal, although there is a strong In—O(C) interaction; the arrangement of the three ligands ismer. There is extensive hydrogen bonding involving all possible donors. All three complexes have been studied by mass spectrometry, and by infrared and nuclear magnetic resonance (1H,27Al) spectroscopies. Parallel studies have been attempted with acetohydroxamic acid.

ISSN:0008-4042    

DOI:10.1139/v88-292

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Ac-tubulin-α(430–441)-amide, a synthetic fragment of tubulin, has been studied by 300-MHz1H nuclear magnetic resonance spectroscopy in 80% CD3OH/20% D2O solution at neutral pH. The results, based on two-dimensional phase-sensitive techniques such as COSY, RELAY, and ROESY, reveal that the dodecapeptide exists in a non-random conformation. The conformation can be described as an α helix for the N-terminal five residues, followed by an extended section. The extended part exhibits a significant change in the nuclear Overhauser enhancement (nOe) pattern between units number 9 and 10. Together with long-range nOe data this can be attributed to a folding back that allows the close proximity of the C-terminal half of the extended chain and amino acids 3 to 5 of the α-helical turn. The existence of an α helix is in good agreement with previously published circular dichroism data.

ISSN:0008-4042    

DOI:10.1139/v88-293

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The anisotropy of the indirect31P,199Hg spin–spin coupling constant, ΔJ, in solid [HgP(o-tolyl)3(NO3)2]2is obtained from an analysis of the31P nuclear magnetic resonance powder pattern. The value of ΔJ, 5170 ± 250 Hz, is large and indicates that mechanisms other than the Fermi contact mechanism are important for this spin–spin coupling. The powder spectrum also indicates that the absolute sign of1J(31P,199Hg) is positive.

ISSN:0008-4042    

DOI:10.1139/v88-294

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The technique of optical–optical double resonance has been applied to a study of theion-pair state of Br2. Two pulsed dye lasers excite the molecules from the ground state to theion-pair state stepwise through thestate in the pump-probe scheme:. Theemission identified at around 215 nm is used to detect the double resonance signals when the probe laser frequency (ν2) is scanned by fixing the pump laser frequency (v1) to appropriatetransitions. The emission spectra are resolved to establish the absolute vibrational numbering of the ion-pair state in terms of the Franck–Condon calculations. The Dunham coefficients of thestate obtained in a global least-squares fit analysis of 377 transitionsareY00 = 57929.724(24),Y10 = 212.227(23),Y20 = −1.5683(56),Y30 = 1.606(40) × 10−2,Y01 = 0.0465652(89),Y11 = −4.500(36) × 10−4,Y21 = 1.133(41) × 10−5, andY02 = −9.37(94) × 10−9for79Br2isotope species (all in cm−1with 3σ in parentheses).

ISSN:0008-4042    

DOI:10.1139/v88-295

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Spin adduct yields in the photoreduction of menadione (2-methylnaphthoquinone) in isotope labeled micellar solutions were measured as functions of the external magnetic field. As surfactants, ordinary SDS, perdeuteriated SDS, and a mixture of the two were employed. In a mixed micellar solution, a normal isotope effect on the spin adduct yield was observed. On the other hand, in the pure micellar solutions with each of the former two surfactants, a reversed isotope effect was observed. These two apparent isotope effects depend on the external magnetic field and were separated into two independent isotope effects: one is the primary isotope effect on the hydrogen abstraction step and the other is the secondary magnetic isotope effect on the intersystem crossing step of the intermediate radical pair.

ISSN:0008-4042    

DOI:10.1139/v88-296

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The synthesis and X-ray structure determination ofN,N′-di(o-tolyl)piperazineN,N′-dioxide tetrahydrate,I,N,N′-di(p-tolyl)piperazineN,N′-dioxide tetrahydrate,II, andN,N′-di(p-chlorophenyl)piperazineN,N′-dioxide tetrahydrate,III, are described. CompoundIcrystallizes in space groupwitha = 7.778(1),b = 7.915(2),c = 8.919(2) Å, α = 106.25(2), β = 99.56(1), γ = 108.80(2)°, andZ = 1. CompoundIIcrystallizes in space groupwitha = 6.558(1),b = 7.134(2),c = 11.610(3) Å; α = 73.23(2), β = 78.08(2), γ = 72.67(2)°, andZ = 1. CompoundIIIcrystallizes in space groupP21/cwitha = 9.159(3),b = 12.390(4),c = 8.339(4) Å, β = 97.38(3)°, andZ = 2. The structures ofI–IIIwere solved by the direct method and refined toR = 0.049 (1749 observed MoKα reflections), 0.055 (2651 observed reflections), and 0.035 (1827 observed reflections), respectively. In each case, theN,N′-dioxide molecule occupies a site of symmetry. The piperazine ring takes the chair form, with two N—O bonds oriented axially in atransconfiguration. The structures are characterized by strong hydrogen bonding between the water molecules, as well as between theN-oxide groups and water molecules, giving rise to puckered layers composed of various combinations of edge-sharing four-membered, six-membered, ten-membered, and twelve-membered rings. The aryl rings, which protrude on both sides of each puckered layer, constitute hydrophobic regions separating the hydrophilic layers in the crystal packing.

ISSN:0008-4042    

DOI:10.1139/v88-297

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The proton and fluorine second moments and the spin-lattice relaxation timesT1(at 25.75 MHz) were measured in the solid complex trimethylamine–trifluoroborane from 53 to 300 K. There is a cross-relaxation effect between1H and19F below 120 K. TheirT1minima near 140 K led to activation energies of 10.6 and 11.1 kJ mol−1for the reorientation of the methyl and the trifluoride groups, respectively. An additional minimum observed in theT1of protons at about 240 K was attributed to the reorientation of the trimethylamine group about the N—B bond with an activation energy of 25.0 kJ mol−1. A comparison of these potential parameters with those in other trimethylamine complexes led to a notion that the activation energies for the reorientation of the (CH3)3N group in the trimethylamine–trifluoroborane complex are mainly governed by the intramolecular steric effect.

ISSN:0008-4042    

DOI:10.1139/v88-298

出版商:NRC Research Press    

年代:1988

数据来源: NRC