Abstract In this work, complex investigations of crystalline L-carnosine (Car) and its solutions in water and aqueous buffer solvent have been conducted by the methods of differential scanning calorimetry (DSC), Knudsen’s effusion mass spectrometry (KEMS), calorimetry of dissolution, and densimetry. DSC and KEMS have revealed no phase transitions in the temperature range 208–471 K. The phenomenon that the sublimation of Car is accompanied by cyclization of fragment ions in the temperature range (298–360) K has been observed. Calorimetric and volumetric methods were employed to investigate molecular interactions of L-carnosine in water (pH 5.4) and in aqueous buffer solutions (pH 7.4) at various temperatures. The effects of solute structure, concentration, pH and temperature on the thermodynamic properties derived were discussed. In case of aqueous solutions with different pH values, the data have been discussed in terms of predominant types of molecular interactions (hydrophilic, hydrophobic, ionic and zwitterionic) on the basis of co-spheres overlap model. For neutral molecule of carnosine, DFT theoretical calculations at B3LYP/6–31++G(d,p) level of theory have been performed. Analysis of natural bond orbitals (NBO) has been carried out for the four most stable conformers.

中文翻译：

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结晶L-肌肽及其水溶液的热力学性质

摘要 在这项工作中，通过差示扫描量热法 (DSC)、克努森渗出质谱法 (KEMS)、溶解量热法、和密度测量。DSC 和 KEMS 显示在 208-471 K 温度范围内没有相变。已经观察到 Car 升华伴随着碎片离子在 (298-360) K 温度范围内环化的现象。采用量热法和体积法研究 L-肌肽在不同温度下的水 (pH 5.4) 和水性缓冲溶液 (pH 7.4) 中的分子相互作用。讨论了溶质结构、浓度、pH 和温度对所得热力学性质的影响。在具有不同 pH 值的水溶液的情况下，根据共球重叠模型，根据主要类型的分子相互作用（亲水性、疏水性、离子性和两性离子性）讨论了数据。对于中性肌肽分子，已经进行了 B3LYP/6-31++G(d,p) 理论水平的 DFT 理论计算。对四种最稳定的构象异构体进行了自然键轨道 (NBO) 分析。