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

Abstract 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 P m , and the generation time t G , total heat output Q t , and growth inhibitory ratio I of B. shigae were calculated. In accordance with a thermo-kinetic model, the corresponding quantitative relationships of k, P m , Qt, I and c were established. Also, the half-inhibitory concentrations of the drugs (IC 50 ) were obtained by quantitative analysis. Based on the quantity-activity relationships and the IC 50 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.