Comparison of anti-bacterial activity of three types of di-O-caffeoylquinic acids in Lonicera japonica flowers based on microcalorimetry

The anti-bacterial activities of three types of di-O-caffeoylquinic acids(diCQAs) in Lonicera japonica flowers,a traditional Chinese medicine(TCM),on Bacillus shigae growth were investigated and compared by microcalorimetry.The three types of diCQAs were 3,4-di-O-caffeoylquinic acid(3,4-diCQA),3,5-di-O-caffeoylquinic acid(3,5-diCQA),and 4,5-di-O-caffeoylquinic acid(4,5-diCQA).Some qualitative and quantitative information of the effects of the three diCQAs on metabolic power-time curves,growth rate constant k,maximum heat-output power Pm,and the generation time tG,total heat output Qt,and growth inhibitory ratio I of B.shigae were calculated.In accordance with a thermo-kinetic model,the corresponding quantitative relationships of k,Pm,Qt,I and c were established.Also,the half-inhibitory concentrations of the drugs(IC50) were obtained by quantitative analysis.Based on the quantity-activity relationships and the IC50 values,the sequence of inhibitory activity was 3,5-diCQA 4,5-diCQA 3,4-diCQA.The results illustrate the possibility that the caffeoyl ester group at C-5 is the principal group that has a higher affinity for the bacterial cell,and that the intramolecular distance of the two caffeoyl ester groups also has an important influence on the anti-bacterial activities of the diCQAs.