Fungistatic Activity of t-Butylhalophenols for Growth of Aspergillus niger

Abstract

The relationship between chemical structures of 16 kinds of t-butylhalophenols and their fungistatic activity toward Aspergillus niger, in the range of pH 3.7, 5.2 and 7.0, was investigated by using the agar plate filter paper disc method. The inhibition of fungal growth was estimated in terms of initial strength of activity (IS), which was obtained by measuring the diameter of the inhibition zone in each sample, and its durability. As a control, the IS value of 4-chloro-m-cresol (1) obtained at pH 5.2 with incubation for 3 days was defined as 100. The durability was estimated as the period required for the initial inhibition zone to disappear under continuous incubation.The relationship between the fungistatic activity and the chemical structures of tested compounds was as follows. The o-t-butyl-4-halophenols and m-t-butyl-4-halophenols were much more effective than the corresponding 2-halogenated isomers, and the activity was greatly superior to that of p-t-butyl-2-halophenols. The IS values of 2-t-butyl-4-chlorophenol (6), 2-t-butyl-4-bromophenol (12) and 3-t-butyl-4-chlorophenol (8) were mostly higher than that of 1, but their durability was inferior to that of 1. However, 3-t-butyl-4-bromophenol (14) was superior to 1 in both the IS value and the durability at all pH levels. When 14 was derived to 2, 4-dibromo-5-t-butylphenol (17) by means of bromination, its durability was somewhat improved but its IS values were reduced to 0.5-0.7 times that of 14. The activity of 2, 6-di-t-butyl-4-bromophenol (16) derived from 12, which showed the greatest IS among all the tested compounds, was not effective at any pH level due to the complete loss of activity. The influence of pH upon the fungistatic activity of the compounds is discussed.