NEEM - Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, 36036-900, Brazil.
J Phys Chem A. 2011 Aug 4;115(30):8511-9. doi: 10.1021/jp2028142. Epub 2011 Jul 14.
In the present study, the inclusion processes of β-carotene, astaxanthin, lycopene, and norbixin (NOR) into the β-cyclodextrin (β-CD) cavity were investigated by means of Raman spectroscopy and quantum mechanics calculations. The Raman ν(1) band assigned to C═C stretching was sensitive to the host-guest interaction and in general undergoes a blue shift (3-13 cm(-1)) after inclusion takes place, which is the consequence of the localization of single and double bonds. This is supported by the molecular modeling prediction, which inclusion complexes show the ν(1) band blue shifted by 1-8 cm(-1). The calculated complexation energies was small for most of derivatives and was found to be -11.1 kcal mol(-1) for inclusion of AST and +0.27 kcal mol(-1) for NOR. The stability order was qualitatively correlated to topological parameters accounting for the opening angle of the chain. This means that after inclusion the guest molecules assume a slightly more extended conformation, which enhances the host-guest contact, improving the interaction energy. The results discussed here clearly demonstrate the matrix effect on the carotenes' spectroscopic profile and should contribute to fully characterize the raw samples.
在本研究中，通过拉曼光谱和量子力学计算研究了β-胡萝卜素、虾青素、番茄红素和叶黄素（NOR）纳入β-环糊精（β-CD）空腔的包合过程。ν(1)带分配给 C=C 伸缩振动对主客体相互作用敏感，通常在包合发生后发生蓝移（3-13 cm(-1))，这是单键和双键定位的结果。分子建模预测支持这一点，表明包含复合物的 ν(1)带蓝移 1-8 cm(-1)。对于大多数衍生物，计算出的络合能很小，AST 的络合能为-11.1 kcal mol(-1)，NOR 的络合能为+0.27 kcal mol(-1)。稳定性顺序与拓扑参数定性相关，这些参数与链的开口角度有关。这意味着，包合后，客体分子呈现出略微扩展的构象，从而增强了主客体接触，提高了相互作用能。这里讨论的结果清楚地表明了基质对类胡萝卜素光谱特征的影响，这应该有助于充分表征原始样品。
