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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Solvent Effect on Anthranilic Acid Spectroscopy
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Solvent Effect on Anthranilic Acid Spectroscopy

机译：邻氨基苯甲酸光谱的溶剂效应

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The spectroscopy of anthranilic acid (AA) was examined in neat and binary solvents of varying polarity and hydrogen bonding strength in order to understand the role of water in solvating the polar sites of the molecule. With the exception of water, the Stokes shift of AA in different solvents was found to be linearly correlated with the normalized molar transition energy of solvent polarity (E_N~T), indicating the major role of the hydrogen bonding effect in solution. Analysis of the absorption and fluorescence spectra reveals that AA exists as an anion in neutral water. The pK_a (4.50) and pK_a~* (4.44) values were estimated from the spectral shift in the absorption and fluorescence spectra measured in different pH solutions. The shortest fluorescence lifetime was measured in cyclohexane and is attributed to intramolecular hydrogen dislocation/transfer in the excited state. The lifetime values in polar solvents point to the dominant effect of the hydrogen-bond donating strength (α value) of the solvent. The number of water molecules solvating the polar region of the neutral form of AA was estimated to be three from the absorbance change in dioxane/ buffer (pH 3.5) binary mixtures. The structures of AA:water complexes were calculated from density functional theory using the B3LYP method with a 6-311++G(2d,p) basis set. A stepwise addition of water molecules (1?3) to the polar region of AA leads to a preferential solvation of the COOH group of the molecule in a closed-cyclic geometry. It is worth noting that the spectral shift as a function of pH suggests the suitability of AA as a probe to estimate the local acidity of binding sites in macromolecules in the pH range 3.0?7.0.
机译：为了了解水在溶剂化分子极性位点中的作用，在不同极性和氢键强度的纯净和二元溶剂中检查了邻氨基苯甲酸（AA）的光谱。除水外，发现AA在不同溶剂中的斯托克斯位移与溶剂极性的归一化摩尔跃迁能（E_N〜T）呈线性相关，表明溶液中氢键作用的主要作用。吸收光谱和荧光光谱分析表明，AA在中性水中以阴离子形式存在。 pK_a（4.50）和pK_a〜*（4.44）值是根据在不同pH溶液中测得的吸收光谱和荧光光谱的光谱位移估算的。在环己烷中测得的荧光寿命最短，这归因于在激发态下分子内氢的位错/转移。在极性溶剂中的寿命值表明了溶剂氢键给体强度（α值）的主要作用。从二恶烷/缓冲液（pH 3.5）二元混合物的吸光度变化估计，溶解AA中性形式极性区域的水分子数量为3。 AA：水络合物的结构是使用B3LYP方法和6-311 ++ G（2d，p）基集根据密度泛函理论计算的。将水分子（1〜3）逐步添加到AA的极性区域中导致在闭环几何形状中分子的COOH基团的优先溶剂化。值得注意的是，光谱偏移随pH的变化表明，AA作为探针来估计pH范围为3.0-7.0的大分子中结合位点的局部酸度是合适的。

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