摘要:

The high cost of nicotinamide coenzymes currently acts as a deterrent to the widespread adoption of alcohol dehydrogenases as chiral catalysts for effecting stereospecific and selectiveoxidoreductions on a preparative scale. Attempts to overcome this problem generally involve using catalytic amounts of coenzyme together with an auxiliary system capable of continuously regenerating its active forminsitu. Flavin mononucleotide has been found to be an effective, convenient, and inexpensive reagent forinsiturecycling of NAD+. Using horse liver alcohol dehydrogenase-catalyzed oxidation of cyclohexanol as a representative process, up to 50-fold NAD+-regeneration levels have been achieved. This method is the most satisfactory and practical oxidative-mode recycling procedure yet developed for routine laboratory applications.

ISSN:0008-4042    

DOI:10.1139/v76-420

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The rates of H-transfer between various 1,4-dihydropyridines and pyridinium salts (including NADH and NAD+), and from 1,4-dihydropyridines to FMN, have been measured. The reactions are found to be sufficiently slow for H-transfer to be rate-determining to a significant extent when such Systems are applied for nicotinamide coenzyme recycling purposes. The rates of H-transfer parallel the magnitudes of the donor–acceptor redox potential differences (ΔE0′); ΔE0′ values may therefore be used as qualitative guides in formulating and selecting redox couples of NAD/H recycling value. On the basis of deuterium isotope effects, it is concluded that formation of a complex prior to H-transfer is not rate determining for 1,4-dihydropyridine–NAD+reactions. This behavior is in contrast to that of other model alcohol dehydrogenase Systems.

ISSN:0008-4042    

DOI:10.1139/v76-421

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The pyrolysis of C6H5I has been studied by the toluene carrier technique over the temperature range 861–955 K using contact times of 0.54–3.28 s and total pressures of 2.5–4.13 kPa. Percent decomposition based on analysis for residual C6H5I ranged from 5.6–93.3%. Only trace quantities of I2were observed and when HI was trapped out the only other gaseous products were small quantities of hydrogen and methane in about a 2:1 ratio. Within the limits of the experimental method the decomposition was found to be homogeneous and first order.The Arrhenius equation obtained for reaction 1 isMaking an approximate correction of the activation energy to 298 K then gives

ISSN:0008-4042    

DOI:10.1139/v76-422

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

It is shown that β-, γ-, and δ-substituent effects on13C chemical shifts may be better understood by assuming that the upfield shifts caused bygaucheγ-substituents are not due to non-bonded interactions introduced with the γ-group, but that they are due to the removal of the hydrogen on the β-substituent.

ISSN:0008-4042    

DOI:10.1139/v76-423

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A study by11B and1H nmr of the scrambling reactions between the boron trihalides BX3(X = I, Br, Cl, F) and the trialkylborane BR3(R = C3H7, C4H9) shows that the mixed species, on equilibrium are non uniformly favoured. The effects of Lewis acidity and steric hindrance are discussed.

ISSN:0008-4042    

DOI:10.1139/v76-424

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

The X-ray crystal structure of thiamine iodide hydroiodide, C12H18N4OSI2, has been determined. The unit cell parameters are:a = 13.835(7),b = 7.442(4),c = 20.243(9) Å, β = 120.52(7)°, monoclinic space groupP21/c,Z = 4. A total of 1445 reflections havingF2 > 2σ(F2), 2θ < 40° were collected on a Picker 4-circle diffractometer with MoKα radiation by the 2θ scan technique. The structure was solved by the heavy-atom method. The iodide and sulphur atoms were refined anisotropically; only positional parameters were refined for the hydrogen atoms. Successive full-matrix least-squares refinements yielded an unweightedR-factor of 0.054. The pyrimidine ring is protonated on the ring nitrogen opposite the amino group. The relative disposition of the pyrimidine and thiazolium rings is similar to that observed in most other thiamine structures. The β-hydroxyethyl side chain of the thiazolium ring is folded in such a way that there is a short S … O contact, 2.97 Å in length. The iodide ions are involved in a number of weak hydrogen bonds.

ISSN:0008-4042    

DOI:10.1139/v76-425

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Precision isotope ratio mass spectrometry has been used to determine the relative vapour pressures of the four principal isotopic species of liquid carbon disulfide. Relative to the principal species12C32S32S = 1.000000, the vapour pressures of the other species are:12C32S34S = 0.999855, and13C32S32S = 1.00162. A value of 0.999927for12C32S33S is deduced by application of the rule of the geometric mean. The results are invariant with temperature between −20 and +56 °C. Qualitatively similar effects have been reported earlier for13C and18O substitution in12C16O2, a chemical analogue of CS2.

ISSN:0008-4042    

DOI:10.1139/v76-426

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

A general route leading to 5- to 8-membered cyclic sulfinate esters (sultines) is described. The method is based on the reaction oftert-butyl hydroxyalkyl sulfoxides with SO2Cl2in an inert solvent.

ISSN:0008-4042    

DOI:10.1139/v76-427

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Photoelectron spectra show that in CH3SCH2COCH3the sulfur and carbonyl lone pair orbitalsare both stabilized with respect to the compounds containing S or CO only. This is in keeping with the observed values of the basicity constants. The ultraviolet absorption spectra contain the expectedandbands and give evidence for a significant amount of mixing between the excited orbitals.

ISSN:0008-4042    

DOI:10.1139/v76-428

出版商:NRC Research Press    

年代:1976

数据来源: NRC

摘要:

Measurement of freezing point depressions for the non-electrolytes, CCl4. CH3SO2F, and (CF3CO)2O permit calculation of the cryoscopic constant for trifluoroacetic acid, HOTFA. Water is shown to give freezing point depressions lower than those for non-electrolytes and this is attributed to association. Freezing point depressions for NaOTFA, KOTFA, and CsOTFA have been measured and accounted for in terms of ion-pair dissociation constants previously determined from electrical conductivity measurements. The results cast doubt on the existence of triple ions in this solvent.

ISSN:0008-4042    

DOI:10.1139/v76-429

出版商:NRC Research Press    

年代:1976

数据来源: NRC