摘要:

The stopped-flow technique has been used to study the pre-steady-state kinetics of the hydrolysis ofN-carbobenzoxy-L-alanine-p-nitrophenyl ester catalyzed by trypsin. By working under conditions such that the enzyme concentration is much greater than that of the substrate, it has been possible to measurethe rate constant for the conversion of the enzyme-substrate complex into the acyl enzyme. The pHdependence ofreveals a pKb′ value of 6.9 for the conversion of complex into acyl enzyme, in agreement with deductions from steady-state investigations. The pHdependence of(equal tok−1 + k2)/k1) has also been determined. The results provide direct evidence for the existence of an enzyme-substrate complex for this reaction.The work has been done in various mixtures of water and isopropyl alcohol. The logarithms of the rate constantsandvary linearly with 1/D, showing a decrease with increasing alcohol concentration;increases with alcohol concentration. The solvent results suggest that addition of alcohol affects the hydrophobic bonding in the protein and leads to unfolding of the enzyme.

ISSN:0008-4042    

DOI:10.1139/v70-298

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

The γ-radiolysis of N2O at 77 °K, or vapor phase irradiation with 1 MeV He+ions followed by condensation at 77 °K, results in the formation and trapping of at least 4 paramagnetic species. Using isotopically labelled N2O these are identified as N2O+, NO2, NO3, and N. The latter assignment is reasonable on spectroscopic grounds but since this species arises exclusively from the central nitrogen of N2O it is difficult to describe its formation from established chemical reactions. The addition of H2O to the vapor phase experiments resulted in the trapping of O2−, while the addition of tetranitromethane or NO indicated the existence of O2−and O atoms, respectively. Possible reaction mechanisms are indicated.

ISSN:0008-4042    

DOI:10.1139/v70-299

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

Methyl fluoride and fluoroform have been irradiated with gamma rays from a 1200-Ci60Co source. Ionization currents were measured using a Pyrex parallel-plate-type ionization chamber.Wvalues of 27.2 and 28.0 eV were determined for the two gases, CH3F and CHF3, respectively. The method employed was a comparative one, making use of the Bragg–Gray theory of cavity ionization.G(H2) yields of 4.20 and 1.25 for CH3F and CHF3, respectively, were then calculated from the aboveWvalues and the measured ion-pair yields for hydrogen. The formation of hydrogen is probably due to the fact that the C—H bonds in these compounds are weaker than the C—F bonds.

ISSN:0008-4042    

DOI:10.1139/v70-300

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

Reaction between a reduced solution ofcis-[Ru(trien)Br2]Br•2H2O and gaseous nitrogen yields the dimeric species [(trien)RuXN2XRu(trien)]X2where X = added anion I, Br and trien = triethylene tetraamine. In solution, the halides undergo solvolysis, before bridge splitting occurs, giving the monomeric [Ru(trien)N2H2O]2+ion. The rate of formation of monomer is pHdependent, being faster in base.

ISSN:0008-4042    

DOI:10.1139/v70-301

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

It is suggested that given two molecules potentially capable of being involved in the same reaction, one as a product and one as a reactant, it seems reasonable that the calculated difference in energy between these molecules may become relatively constant with smaller basis sets than the calculated energies themselves. To examine this suggestion, and at the same time to provide information on small molecules containing bonds related to the nitrile bond, a number of linear combination of atomic orbitals-molecular orbitals-self consistent field (l.c.a.o.-m.o.-s.c.f.) calculations using small or intermediate sizes of basis sets of Gaussian orbitals were performed on H2CNH, H2CN−, H2CNH2+, H2CN+, and HCN. The change of energy in passing from one molecule to another is shown to converge to a reasonably constant value for smaller basis sets than are required for convergence of individual molecular energies.

ISSN:0008-4042    

DOI:10.1139/v70-302

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

A simple procedure has been developed for the stereospecific synthesis of some 2-chloro-2-deoxy pentoses. Treatment of β-D-xylopyranosyl chloride 2,3,4-tri(chlorosulfate) with aluminum chloride (> 1 mole equivalent) resulted in specific chloro-displacement of the C-2 chlorosulfate group via a mechanism involving anomeric chlorine migration, which occurred to the extent of almost 100%. The resultant crystalline 2-chloro-2-deoxy-α-D-lyxopyranosyl chloride 3,4-di(chlorosulfate) when treated with sodium iodide yielded crystalline 2-chloro-2-deoxy-D-lyxose. Similarly α-D-lyxpoyranosyl chloride 2,3,4-tri(chlorosulfate) yielded 2-chloro-2-deoxy-a-D-xylopyranosyl chloride 3,4-di(chlorosulfate) from which pure 2-chloro-2-deoxy-D-xylose was obtained by a modified procedure. The structures of these compounds have been confirmed and the mechanism is discussed.

ISSN:0008-4042    

DOI:10.1139/v70-303

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

Irradiation of 1-p-substitutedphenyl-4-phenyl-1,3-butadienes gave mixtures of 1-p-substituted-phenylnaphthalenes and 7-substituted-1-phenylnaphthalenes. Photocyclization of 1-m-substituted-phenyl-4-phenyl-1,3-butadienes gave 1-m-substitutedphenylnaphthalenes, 6-substituted-1-phenylnaphthalenes, and 8-substituted-1-phenylnaphthalenes. Characterization of the photoproducts was achieved through synthesis by an independent method.

ISSN:0008-4042    

DOI:10.1139/v70-304

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

The reaction that occurs between adrenalin (1) and phenols in the presence of hydrochloric acid, to form potentially physiologically active β,β-diphenylethylamine derivatives, is described. The products obtained include adrepine (7), formed from1alone, and others obtained by the interaction of1with a second phenolic component, such as epinine or 4-methylcatechol. The nuclear magnetic resonance and mass spectroscopic data obtained for these products and a number of related compounds are presented and discussed.

ISSN:0008-4042    

DOI:10.1139/v70-305

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

The reduction of 2,3-dimethyl-4-(o-nitrophenylthio)-1-phenyl-3-pyrazolin-5-one by sodium borohydride and palladium–charcoal gave the corresponding hydroxylamine. The action of hydrochloric acid on this hydroxylamine gave thep-chloroamine. In a similar manner, treatment of some 2H-1,4-benzothiazine and -benzoxazine hydroxamic acids with hydrochloric acid resulted in the formation of 7-chloro-2H-1,4-benzothiazine and -benzoxazine lactams.

ISSN:0008-4042    

DOI:10.1139/v70-306

出版商:NRC Research Press    

年代:1970

数据来源: NRC

摘要:

Hammett free energy correlations are reported for the decomposition reactions of tetra-alkylammonium halides in chloroform and acetone solution. All the salts contained a substituted benzyl group attached to the nitrogen atom and decomposed to yield a benzyl iodide and dimethylaniline as the only products.The curved Hammett plots for para-substituted benzyl compounds are compared to the linear plot found previously for a series of salts each containing a para-substituted phenyl group, and it is concluded that curved Hammett plots cannot be used as evidence for a change of mechanism, unless direct conjugative effects between substituent and reaction site are absent.

ISSN:0008-4042    

DOI:10.1139/v70-307

出版商:NRC Research Press    

年代:1970

数据来源: NRC