摘要:

In order to extend existing ideas on isotropic spin transfer mechanisms in bipyridine–metal complexes, a series of unsymmetrical methyl-substituted bipyridine ligands, and their nickel(II) and cobalt(II) complexes, have been prepared, and their1H nmr isotropic shifts measured experimentally. Simulating different electron spin density transfer mechanisms, from direct σ-electron density transfer to indirect π-mechanisms involving spin polarization or hyperconjugation, various INDO calculations have been performed on model cations and anions of the free ligand, producing good agreement with the experimental results.

ISSN:0008-4042    

DOI:10.1139/v81-252

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Deuterium longitudinal relaxation time is used for assessing the interaction between bovine serum albumin (BSA) and some drugs. The study of unenriched compounds by means of a reference equilibrium is successfully applied.The deuterium relaxation rate of pyridine versus the pH profile allows a better understanding of the nature of the interactions. Some experimental aspects are discussed.

ISSN:0008-4042    

DOI:10.1139/v81-253

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Two phase acid–base titrations of amines from tributyl to tridodecyl and their salts have been performed for the nitrobenzene–water system. Hydrolysis constants were determined and from these anion-exchange constants were calculated. For these series of salts values of hydrolysis and anion-exchange constants were independent of the amine and strongly influenced by the nature of the anions.

ISSN:0008-4042    

DOI:10.1139/v81-254

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

It is shown by X-ray crystallography that 2-nitrosoquinoxaline crystallizes as a dimer, the structure of which is established. In solution the monomeric form predominates and the dimerisation equilibrium constant is measured. The electrochemical reduction of 2-nitrosoquinoxaline in acidic medium leads to the oxime of quinoxaline (1H)-2-one (3) through the intermediate hydroxylamine.3is electrochemically reoxidized directly to 2-nitrosoquinoxaline.

ISSN:0008-4042    

DOI:10.1139/v81-255

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

5,5-Dimethylcyclohexane-1,3-dione and its derivatives were shown to isomerize to give 5,6-dihydropyran-4-ones on irradiation in FSO3H or 98% H2SO4. The 2,2-dimethyl derivative, lacking hydrogen on C2, failed to give any products under the same conditions. A similar type of isomerization was also observed with thiolane-2,4-dione and its derivatives, while no photoisomerization was observed with their nitrogen or oxygen analogs. A possible reaction mechanism is proposed.

ISSN:0008-4042    

DOI:10.1139/v81-256

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

When five- and six-membered cyclic β-dicarbonyl compounds having an acetyl group on the 2-position were irradiated in methanol in the presence of TiCl4, a coupling reaction between the acetyl carbonyl atom and the α-carbon atom of the methanol took place, giving γ-ketoaldehydes or dihydrofurans as the main product.

ISSN:0008-4042    

DOI:10.1139/v81-257

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The synthesis of a series of macrocyclic polyethers (crown ethers) of interest as carriers for the countertransport of metal ions and protons across artificial membranes is described. Thallium mediated cyclization of oligoethyleneglycol diiodides with (+)–N,N,-N′,N′-tetramethyltartaramide gave 15-crown-5 and 18-crown-6 diamides which were converted, via the diacids and anhydrides, to crown ether monoamides bearing long chain alkyl groups (octyl, tetradecyl, and octadecyl). The alkali metal salts and complexes of these carriers are soluble in nonpolar solvents and alkali metal ions are extracted from aqueous solutions into chloroform solutions of the carriers. Acidity constants and stability constants for complex formation in methanol/water (90:10 v/v) solutions have been determined using a combination of ion selective electrode and pH-metric techniques. Deprotonation of the ligand carboxylic acid group results not only in more stable complexes but also more selective complexation. Implications for membrane transport are discussed.

ISSN:0008-4042    

DOI:10.1139/v81-258

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

An artificial membrane system based on a series of macrocyclic polyether carriers (crown ethers) is described. Under the influence of a proton gradient the carriers move alkali metal ions from basic to acidic solution through a chloroform membrane phase. Transport occurs against the concentration gradient of the transported ion as a result of a coupled counterflow of protons. Different transport behaviors are observed depending upon the metal ion concentration. At high metal ion concentration the amount transported is a linear function of time; at lower metal ion concentration the amount transported is a complex function of time which may be described as the result of a pair of consecutive first order processes. Effects of metal ion, carrier, and proton concentration on transport rate are considered. The rate increases with increasing metal ion or carrier concentration but is essentially independent of the pH of either aqueous phase. Increased lipophilicity of the carrier also results in a rate increase. Carriers derived from 18-crown-6 transport potassium selectively and all ions more rapidly than 15-crown-5 derivatives which are, however, selective for sodium. The overall efficiency of the system is discussed in terms of competing "leak" reactions, either of cations from the basic phase or of anions from the acidic phase.

ISSN:0008-4042    

DOI:10.1139/v81-259

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v81-261

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The epr spectral parameters for someradicals have been measured over a range of temperatures. These radicals are probably non-planar at nitrogen. Their OR groups are in the eclipsed position with respect to the N 2pzorbital, a conformational preference which is attributed to a combination of steric factors and the anomeric effect. Forthe H hyperfine splittings (hfs) are of unusually small magnitude. It is pointed out that all other knownalso have anomalously low H hfs. It is suggested that this is due to the anomeric effect which not only promotes the eclipsed conformation but also causes the OR group to bend towards the semioccupied orbital, thereby movingHand R2towards the nodal plane of this orbital.

ISSN:0008-4042    

DOI:10.1139/v81-262

出版商:NRC Research Press    

年代:1981

数据来源: NRC