Competitive inhibition constants Ki for a series of phenol-ring-substituted derivatives of alpha-(2-hydroxyphenyl)benzenepropanoic acid have been ascertained by observing their influence on the catalytic hydrolysis of a peptide substrate by the zinc enzyme carboxypeptidase A. The pH-dependence of Ki shows that binding is maximal between two pKa values: one is that of the phenol group of the inhibitor, and the other uniformly has a value of 6, the pKa of a Zn(2+)-bound water molecule on the enzyme in the absence of substrate or inhibitor. This is the dependence expected if phenolate binds to the Zn2+ displacing its bound H2O/HO-. A log-log plot of the dissociation constants for the productive forms of inhibitor plus enzyme versus the acid dissociation constants of the phenolic residues in the inhibitors yields a straight line with a slope of +0.76. This number indicates that the active-site metal ion has special capacity for dispersing negative charge, such as builds up on the oxygen atom of a carboxamide group undergoing nucleophilic addition.

The Raman and infra-red spectra of 2-propene-1-sulphonyl chloride, 1-propene-1-sulphonyl chloride, 2-phenyl ethane and 2-phenyl ethane sulphonyl chlorides, and the infra-red spectrum of sodium 2-phenyl ethane sulphonate have been recorded. The constancy of sulphonyl, S-Cl, C-S, and C=C vibrations indicates the absence of conjugation in the ground state between C=C and S=O. The ultraviolet spectra of the styrene derivatives indicate a strong electronic interaction in the excited state. The 1-propene-1-sulphonyl chloride prepared by the method of Lambert and Rose (1949) is shown to be the trans-compound. �� The constancy of the symmetric and asymmetric frequencies of the SO3 group in the ions CH3S03-, NH2SO3-, and HOS03- also shows that there is no strong inter- action between the lone pairs of electrons on the nitrogen or oxygen and the sulphur-oxygen π-bond system.

The symmetric and asymmetric SO2 stretching frequencies (1190, 1365 cm-1) and the SO2 deformation frequency (565 cm-1) in esters of arylsulphonic acids are similar to those for sulphonyl chlorides. A frequency of about 800 cm-1 can be correlated with the presence of the SO2.OR group and is probably the S-OR bond stretching vibration. The corresponding frequencies in methyl methane sulphonate are slightly lower. A doubling of some frequencies is attributed to the occurrence of rotational isomerism in the sulphonic ester group. The frequency noted by Ham and Hambly (1953b) and suggested as characteristic of aromatic sulphonyl derivatives corresponds to a very constant vibration 1098-1099 cm-1 in the aromatic esters studied.

A seven parameter valence force is used to account for the 15 planar frequencies of H2CO, HDCO, D2CO with an average deviation of less than 0.8%. Bond moments and dipole derivatives have been recalculated.

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