5-O-Caffeoylquinic acid: A spectroscopic study and biological screening for antimicrobial activity

5-O-Caffeoylquinic acid (5-CQA, chlorogenic acid) is one of the major chlorogenic acids present in many fruits, vegetables and herbs. Because of its high biological importance and the widespread confusion in the literature concerning the nomenclature of caffeoylquinic acids, the comprehensive structural, spectroscopic and biological studies are necessary. In this work the FT-IR, FT-IR ATR, FT-Raman, UV, 1H (400.15 MHz), 13C (100.63 MHz) and 2D (COSY, HSQC, HMBC) NMR, as well as theoretical (at B3LYP/6-311++G(d,p) level) studies of 5-O-caffeoylquinic acid were carried out. Accurate geometrical parameters as well as atomic charges are reported. Full and proper assignments of bands on vibrational as well as 1H and 13C NMR spectra are made. In addition, 5-CQA was tested for its minimum inhibitory concentration (MIC) against Escherichia coli, Staphylococcus aureus, Enterococcus faecium, Proteus vulgaris, Pseudomonas aeruginosa, Klebsiella pneumoniae and Candida albicans. The obtained MIC values were in the range 5-10 mg/ml. Out of the tested microorganisms, 5-CQA possesses the strongest antimicrobial activity against Klebsiella pneumonia.