Department of Physics, Faculty of Philosophy, Sciences and Letters of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil.
Department of Physics, School of Sciences and Technology, São Paulo State University (UNESP), Presidente Prudente, SP, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 Jun 5;198:71-77. doi: 10.1016/j.saa.2018.02.059. Epub 2018 Feb 23.
The bioactivity of propolis against several pathogens is well established, leading to the extensive consumption of that bee product to prevent diseases. Brazilian green propolis, collected by the species Apis mellifera, is one of the most consumed in the world. The chemical composition of green propolis is complex and it has been shown that it displays antioxidant, antimicrobial, anti-inflammatory and antitumor activities, especially due to the high content of Artepillin C. The molecule is a derivative of cinnamic acid with two prenylated groups, responsible for the improvement of the affinity of the compound for lipophilic environment. A carboxylic group (COOH) is also present in the molecule, making it a pH-sensitive compound and the pH-dependent structure of Artepillin C, may modulate its biological activity related to interactions with the cellular membrane of organisms and tissues. Molecular properties of Artepillin C on aqueous solution were examined by optical absorption, steady state and time-resolved fluorescence spectroscopies. Acid-base titration based on the spectral position of the near UV absorption band, resulted in the pKa value of 4.65 for the carboxylic group in Artepillin C. In acidic pH, below the pKa value, an absorption band raised around 350nm at Artepillin C concentration above 50μM, due to aggregation of the molecule. In neutral pH, with excitation at 310nm, Artepillin C presents dual emission at 400 and 450nm. In pH close to the pKa, the optical spectra show contribution from both protonated and deprotonated species. A three-exponential function was necessary to fit the intensity decays at the different pHs, dominated by a very short lifetime component, around 0.060ns. The fast decay resulted in emission before fluorescence depolarization, and in values of fluorescence anisotropy higher than could be expected for monomeric forms of the compound. The results give fundamental knowledge about the protonation-deprotonation state of the molecule, that may be relevant in processes mediated by biological membranes.
蜂胶对几种病原体的生物活性已得到充分证实，这导致了该蜂产品的广泛消费，以预防疾病。巴西绿蜂胶是世界上消费最多的蜂胶之一，由蜜蜂物种 Apis mellifera 采集。绿蜂胶的化学成分复杂，已显示其具有抗氧化、抗菌、抗炎和抗肿瘤活性，尤其是由于 Artepillin C 的高含量。该分子是肉桂酸的衍生物，具有两个 prenylated 基团，负责提高化合物对亲脂环境的亲和力。分子中还存在一个羧酸基团 (COOH)，使其成为一种 pH 敏感的化合物，Artepillin C 的 pH 依赖性结构可能调节其与生物体和组织细胞膜相互作用相关的生物活性。通过光吸收、稳态和时间分辨荧光光谱研究了 Artepillin C 在水溶液中的分子性质。基于近紫外吸收带光谱位置的酸碱滴定，得出 Artepillin C 中羧酸基团的 pKa 值为 4.65。在低于 pKa 值的酸性 pH 下，当 Artepillin C 浓度高于 50μM 时，由于分子聚集，会在 350nm 左右产生一个吸收带。在中性 pH 下，用 310nm 激发，Artepillin C 在 400nm 和 450nm 处呈现双发射。在接近 pKa 的 pH 下，光谱显示出质子化和去质子化物种的共同贡献。需要使用三个指数函数来拟合不同 pH 值下的强度衰减，主要由一个非常短的寿命分量主导，约为 0.060ns。快速衰减导致发射发生在荧光偏振之前，并且荧光各向异性值高于化合物单体形式的预期值。这些结果提供了关于分子质子化-去质子化状态的基本知识，这在生物膜介导的过程中可能很重要。
