摘要:

Reaction of thiirane 1,1-dioxide (1) with aqueous barium hydroxide gives chiefly barium ethanesulfonate (3) together with some ethylene and barium sulfite, and only a small amount (<5%) of barium 2-hydroxyethanesulfinate (2), the material previously described by Hesseetal. as the major product of this reaction. Reaction of1with potassium hydroxide proceeds analogously except for the formation of barium 2-sulfinatoethanesulfonate (6) from reaction of potassium sulfite with unreacted1. This revision, when taken with what is already known of the final step of the Ramberg–Bäcklund reaction, provides a consistent picture of the reaction of thiirane 1,1-dioxides with hydroxide. For this reaction we suggest a common intermediate with a pentacoordinated sulfur for formation of both the sulfonate anion and the olefin, though an attempt to confirm the existence of such a species using H218O was unsuccessful.

ISSN:0008-4042    

DOI:10.1139/v85-001

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Steady-state γ-radiolysis of deaerated aqueous solutions of thymidine has been carried out in the presence of 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl (TAN), a well-known radiosensitizing agent. The eight main radiation-induced TAN addition products to thymidine have been isolated and characterized by1H and13C nmr, cd, and fast-atom bombardment mass spectrometry measurements.

ISSN:0008-4042    

DOI:10.1139/v85-002

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

γ-Irradiation of oxygen-free, aqueous solutions of 2′-deoxythymidine in the presence of the organic nitroxide free radical, 2,2,6,6-tetramethyl-1,4-piperidone-N-oxyl (TAN), leads to a complex mixture of products in which the TAN moiety is linked to the C5 or C6 position of a 5,6-saturated thymine ring. Extensive1H and13C nmr data are provided for the eight TAN–dT adducts which are produced in the largest amounts. The results show that the conformational properties of the sugar moiety are dependent on the point of attachment of the TAN group and the configuration of the saturated thymine ring.

ISSN:0008-4042    

DOI:10.1139/v85-003

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The spin–spin coupling over six bonds between19F and13C nuclei on the sidechain in thirteen 4-fluorophenyl derivatives appears to be mediated by a σ–π mechanism. Its magnitude depends somewhat on the hybridization state of the carbon atom carrying the coupled nucleus, as well as on the electronegativity of substituents attached to this carbon atom. A consistent behaviour of this coupling is observed if its value is assumed to be proportional to sin2θ, where θ is the angle by which the bond carrying the coupled carbon nucleus twists out of the ring plane. However, in 4-fluorostyreneis a π electron coupling in the planar form, so that its magnitude decreases as the vinyl group twists out of the benzene plane. The σ–π contribution to this coupling is smaller than the π component.is used to assess the conformational preferences of a number of compounds, including 4-fluoro-α-methylstyrene, 4,4′-difluorodiphenylmethane, 1,1-dichloro-2,2-bis(4-fluorophenyl)ethane, and 1-(4-fluorophenyl)-N-methylcyclohexylamine.

ISSN:0008-4042    

DOI:10.1139/v85-004

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Hydrogen, hydrogen sulphide, mercaptoethanol disulphide, and ethanol yields from the radiolysis of 2-mercaptoethanol are consistent with the same mechanism postulated for other sulphydryl-containing molecules. In all cases studiedgHin neutral solution appears to be enhanced (gH = 0.7–0.9 molecule per 100 eV). However, there is no basis for attributing this to reaction [10] which was postulated in earlier work:but is not supported by independent data from H atom studies.

ISSN:0008-4042    

DOI:10.1139/v85-005

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The oxidation of captopril (CpSH, 1-(D-3-mercapto-2-methylpropanoyl)-1-proline) by glutathione disulfide (GSSG) via thiol/disulfide exchange to form, in the first step, CpSSG and GSH and, in the second step, CpSSCp and GSH, has been studied in aqueous solution by1H nmr. Due to slow rotation around the amide bond(s) of CpSH and CpSSCp and of the captopril part of CpSSG, separate resonances are observed for thecisandtransconformations across these bonds. Conformational equilibrium constants were estimated as a function of pH for CpSH, CpSSCp, and CpSSG from the intensities of resonances for thecisandtransisomers. These equilibrium constants were used in the determination of equilibrium constants for the two steps in the oxidation of CpSH by GSSG. The results suggest that CpSH has a greater tendency to reduce disulfide bonds by thiol/disulfide exchange at physiological pH, and thus form mixed disulfides, than do the thiol groups in amino acids. Also, the conformational equilibrium constants indicate that, at physiological pH, approximately two thirds of the captopril, either free or in a disulfide form, has thetransconformation.

ISSN:0008-4042    

DOI:10.1139/v85-006

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The anesthetic potency ofn-alcohols exhibits a somewhat irregular dependence on the length of the hydrocarbon chain. An attempt has therefore been made to ascertain if this is related to the relative tendency for hydrogen bond formation by these alcohols. No such relationship was found. The result was rather that the degree of association by hydrogen bond formation of dissolved alcohols appears to be independent of the chain length, that is of the extent of other interactions that exist in these solutions.

ISSN:0008-4042    

DOI:10.1139/v85-007

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Conductimetric and potentiometric measurements in aqueous solution as a function of temperature show that cupric ions promote the deprotonation of the hydroxy side chain ofthreoanderythroβ-phenylserines. Thethreoligand yields at 298 K the formation constants: Cu(L),K1 = 7.99; Cu(L)2,K2 = 6.71; Cu(L2H−1),K3 = −9.51; Cu(L2H−2),K4 = −10.83. Theerythroisomer yields the corresponding constants:K1 = 7.70,K2 = 6.70,K3 = −9.82, andK4 = −11.20. Thermodynamic parameters for the first two complexation steps are −ΔH = 21.3 and 44.7 kJ mol−1; ΔS = 82 and 132 J K−1mol−1, respectively, for thethreoform and −ΔH = 20.7 and 44.1, ΔS = 79 and 129 for theerythroform. Deprotonation of the complexes corresponds to an additional enthalpy of −21 kJ mol−1. These results and the structures of the complexes are discussed.

ISSN:0008-4042    

DOI:10.1139/v85-008

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The epr spectra at various frequencies of copper(II) acetate anhydrous, monohydrate, monoacetic acid, and water – acetic acid adduct are presented and analysed. The presence of copper hyperfine splittings in the solid state epr spectra of this series of compounds is discussed. The frozen solution spectrum of copper(II) acetate in acetic acid solution containing ~2% water shows an exceptional resolution ofhyperfine of 24 G. This is attributed to a key intermediate which explains the monomer–dimer dissociation mechanism. The influence of distortions on the structures of these compounds is presented.

ISSN:0008-4042    

DOI:10.1139/v85-009

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Niobium(IV) methoxide was synthesized by prolonged electroreduction of niobium pentachloride in methanol. Electron paramagnetic resonance spectra at room temperature and 77 K show the expected 10-line patterns of93Nb atand ΔMs = 2 absorptions indicating the presence of dimer species. The spectroscopic parameters obtained in the presence of a series of phosphorus donor ligands are presented and discussed in terms of mononuclear and dinuclear structures.

ISSN:0008-4042    

DOI:10.1139/v85-010

出版商:NRC Research Press    

年代:1985

数据来源: NRC