Crystallographic Study on the Complex of  Catechins and Caffeine

DONG Yanru; CAO Yanyan; LU Jiachun; MEI Sifan; HE Run; CHEN Ping

doi:10.13305/j.cnki.jts.20201127.001

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Journal of Tea Science ›› 2021, Vol. 41 ›› Issue (1) : 80-89. DOI: 10.13305/j.cnki.jts.20201127.001

Research Paper

Crystallographic Study on the Complex of Catechins and Caffeine

DONG Yanru, CAO Yanyan, LU Jiachun, MEI Sifan, HE Run, CHEN Ping^*

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Abstract

Through HPLC analysis, it was found that catechins and caffeine accounted for more than 88% of the total mass of green tea cream. The CATs-CAF, a simplified green tea cream system, was established by two ester catechins that with the highest content in green tea cream, and their corresponding non-ester catechins complexed with caffeine. The distribution ratio of 4 catechins in precipitate was that EC∶ECG∶EGC∶EGCG≈1∶2∶1∶2. Single crystals were prepared by complexing ECG and EC respectively with caffeine and observed under scanning electron microscopy to record their micro-morphology before and after complexation. Using X-ray single-crystal diffraction to analyze the stereochemical structure, the results show that two needle crystals were formed by intermolecular hydrogen bonding and face-to-face π-π stacking. EC formed O-H...O type hydrogen bonds with adjacent EC and CAF molecules, and π-π stacking occurred between the A ring of EC and the six-membered ring of CAF to form a 1∶1 complex of EC-CAF. While the ECG could form O-H...O and O-H...N type hydrogen bonds with adjacent ECG and CAF molecules, and the π-π stacking of ECG-CAF occurred among all aromatic rings to form a 2∶4 complex, in which the ring A and B of each ECG shared the six-membered ring of CAF separately with the ring B and A of the adjacent ECGs, while the D ring of ECG and the six-membered ring of CAF extended on the a axis in two arrangements.

Key words

complexation mechanism / scanning electron microscope / tea cream / X-ray single crystal diffraction

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DONG Yanru, CAO Yanyan, LU Jiachun, MEI Sifan, HE Run, CHEN Ping. Crystallographic Study on the Complex of Catechins and Caffeine[J]. Journal of Tea Science. 2021, 41(1): 80-89 https://doi.org/10.13305/j.cnki.jts.20201127.001

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