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The interaction between ilaprazole and bovine serum albumin (BSA) has been investigated in the absence and presence of four popular flavonoids with different C-ring structures, quercetin, luteolin, taxifolin, and (+)-catechin, by means of fluorescence spectroscopy. The results indicated that ilaprazole had a strong ability to quench the intrinsic fluorescence of BSA, and site marker competitive experiments indicated that the binding of ilaprazole to BSA primarily took place in subdomain IIA. The quenching process of ilaprazole with BSA was easily affected by flavonoids,; however, they did not change the quchenching mechanism of ilaprazole with BSA, whereas all of the fluorescence quenching was initiated by a static quenching procedure combining with nonradiative energy transfer. The presence of flavonoids decreased the quenching constants of ilaprazole with BSA from 2.2 to 23.7% and decreased the binding constants from 73.7 to 98.3%, which depended on the different flavonoids' structures. The decreased binding constants and unchangeable spatial distance of ilaprazole with BSA by the introduction of quercetin, luteolin, and taxifolin may result from the competition of flavonoids and ilaprazole binding to BSA, whereas in the presence of (+)-catichin, decreased binding constants and increased spatial distance possibly resulted from the formation of a ternary ilaprazole-BSA-(+)-catechin complex. All of these results may have relevant consequences in rationalizing the interferences of common food to gastric ulcer treatments.

The effects of 1:1 flavonoid-Cu(2+) complexes of four flavonoids with different C-ring substituents, quercetin (QU), luteolin (LU), taxifolin (TA), and (+)-catechin (CA), on bovine serum albumin (BSA) were investigated and compared with corresponding free flavonoids by spectroscopic analysis in an attempt to characterize the chemical association taking place. The results indicated that all of the quenching mechanisms were based on static quenching combined with nonradiative energy transfer. Cu(2+) chelation changed the binding constants for BSA depending on the structures of flavonoids and the detected concentrations. The reduced hydroxyl groups, increased steric hindrance, and hydrophilicity of Cu(2+) chelation may be the main reasons for the reduced binding constants, whereas the formation of stable flavonoid-Cu(2+) complexes and synergistic action could increase the binding constants. The changed trends of critical energy transfer distance (R(0)) for Cu(2+) chelation were contrary to those of binding constants.

The aqueous extract of Eucommia ulmoides leaves has been commonly known as Du-zhong tea as a functional health food for the treatment of hypertension, hypercholesterolemia, and fatty liver. This study developed a centrifugal ultrafiltration-high-performance liquid chromatography (HPLC) method for screening and identification of bioactive compounds in E. ulmoides leaves binding with bovine serum albumin (BSA). Six active compounds were screened, isolated, and elucidated by their ultraviolet (UV), electrospray ionization-mass spectrometry (ESI-MS), and nuclear magnetic resonance (NMR) data as geniposidic acid (1), caffeic acid (2), chlorogenic acid (3), quercetin-3-O-sambubioside (4), rutin (5), and isoquercitrin (6). The interaction between active compounds and BSA was investigated in the absence and presence of other compounds by quenching the intrinsic BSA fluorescence. The results indicated that the structures significantly affected the binding process. The values of binding constants for compounds 2-6 were in the range of 10(5)-10(6) mol L(-1), while geniposidic acid (1) hardly quenching the BSA intrinsic fluorescence. However, the quenching process of geniposidic acid was easily affected in the presence of other active compounds. The formation of the geniposidic acid-phenylpropanoid (flavonoid) complex could increase the binding affinity of geniposidic acid with BSA; however, the increased steric hindrance of the complex may make phenylpropanoid or flavonoid dissociate from BSA and then decrease their affinities.

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