(1) The antibiotic activity of carboxylic acid changes remarkably with the species of micro-organisms. Twenty six carboxylic acids (mainly phenol carboxylic acid) were tested toward four kinds of micro-organisms, namely
Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae and
Aspergillus niger. It is difficult to systemize the activity by the relative position of phenolic hydroxyl and carboxyl groups on aromatic nucleus.
There have been identified the alkali degradation products of softwood lignin, namely phydroxybenzoic acid, vanillic acid, protocatechuic acid, syringic acid etc. Comparing the relation between the chemical structure of the above phenol carboxylic acids and the antibiotic activity toward micro-organism, it is summarized that the activity of carboxylic acid ester is higher than that of free carboxylic acid, and methoxyl group brings a considerable reduction in the activity.
(2) Lignosulfonate and thiolignin do not give the antibiotic activity. In order to give the activity to industrial lignin, the introduction of phenol carboxylic acid type structure into lignin was tried by the use of alkali fusion method. Within the limit of research, so far, the ethanol soluble fraction from alkali fused lignin shows comparatively high activity, although the activity toward
Aspergillus niger was not observed. It should be emphasized here, however, that there is no proof of the formation of phenol carboxylic acid type structure in alkali fused lignin.
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