Quercetin (QCT), an emerging class of flavonoid known for antioxidant and anti-inflammatory activities, has been studied for its protein stabilizing effect. After demonstrating ethanol (EtOH) - induced structural changes in bovine serum albumin (BSA), the stabilizing effect of QCT was studied using fluorescence, circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopic techniques. Morphological changes were examined using atomic force microscopy (AFM). EtOH triggered blue shift in fluorescence spectra of BSA and its intensity increased at higher percentage of alcohol. A reversal in this trend was recorded in the presence of QCT. This was interpreted as anti-amyloidogenic effect emanating from the binding of QCT to hydrophobic pockets of BSA. The value of binding constant (1.25 x 10⁶ M^-1; 298 K) is suggestive of strong binding affinity of QCT for BSA. The mode of QCT-induced fluorescence quenching was found to be mixed in nature. CD spectra showed that the protein conformation was altered and traces of alpha helix disappeared in the presence of EtOH. Contrarily, disruptive effect of EtOH was not visible upon incorporating QCT. This was further verifiable form the thermal CD data, which showed an upshift in the denaturation temperature of BSA. The data of thioflavin T assay and AFM further substantiated the protective effect of QCT.

Keywords: Binding affinity; Denaturation; Fibrillation; Fluorescence quenching; Helicity.

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檞皮素（QCT），一种具有抗氧化和抗炎作用的类黄酮，已被研究其对蛋白质稳定的效应。在证明乙醇（EtOH）可引起牛血清白蛋白（BSA）结构变化后，使用荧光、圆二色性（CD）和傅里叶变换红外（FTIR）光谱技术研究了QCT的稳定效果。使用原子力显微镜（AFM）检查形态变化。乙醇触发了BSA荧光光谱向蓝移，并且在较高酒精百分比下强度增加。而在QCT存在的情况下，这种趋势发生了逆转。这被解释为QCT与BSA疏水口袋结合产生的抗淀粉样蛋白效应。结合常数值（1.25 x 10⁶ M^-1; 298 K）表明QCT对BSA具有较强的结合亲和力。QCT诱导的荧光淬灭模式被发现是混合型的。CD光谱显示，蛋白质构象发生了改变，并且在乙醇存在时α螺旋痕迹消失。相反，在引入QCT后，乙醇的破坏效应并未显现。这进一步可通过热CD数据验证，该数据显示BSA变性温度有所上升。硫黄素T测定法和AFM的数据进一步证实了QCT的保护作用。

关键词：结合亲和力；变性；纤维化；荧光淬灭；螺旋度。

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