Department of Physical Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic.
Central Laboratories, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic.
Molecules. 2021 Jul 15;26(14):4298. doi: 10.3390/molecules26144298.
In an effort to establish reliable thermodynamic data for proteinogenic amino acids, heat capacities for l-histidine (CAS RN: 71-00-1), l-phenylalanine (CAS RN: 63-91-2), l-proline (CAS RN: 147-85-3), l-tryptophan (CAS RN: 73-22-3), and l-tyrosine (CAS RN: 60-18-4) were measured over a wide temperature range. Prior to heat capacity measurements, thermogravimetric analysis was performed to determine the decomposition temperatures while X-ray powder diffraction (XRPD) and heat-flux differential scanning calorimetry (DSC) were used to identify the initial crystal structures and their possible transformations. Crystal heat capacities of all five amino acids were measured by Tian-Calvet calorimetry in the temperature interval from 262 to 358 K and by power compensation DSC in the temperature interval from 307 to 437 K. Experimental values determined in this work were then combined with the literature data obtained by adiabatic calorimetry. Low temperature heat capacities of l-histidine, for which no literature data were available, were determined in this work using the relaxation (heat pulse) calorimetry from 2 K. As a result, isobaric crystal heat capacities and standard thermodynamic functions up to 430 K for all five crystalline amino acids were developed.
为了建立可靠的蛋白质氨基酸热力学数据，我们对 l-组氨酸（CAS RN：71-00-1）、l-苯丙氨酸（CAS RN：63-91-2）、l-脯氨酸（CAS RN：147-85-3）、l-色氨酸（CAS RN：73-22-3）和 l-酪氨酸（CAS RN：60-18-4）的热容进行了广泛温度范围内的测量。在进行热容测量之前，进行了热重分析以确定分解温度，而 X 射线粉末衍射（XRPD）和热流差示扫描量热法（DSC）用于确定初始晶体结构及其可能的转变。通过 Tian-Calvet 量热法在 262 至 358 K 的温度范围内以及通过功率补偿 DSC 在 307 至 437 K 的温度范围内测量了所有五种氨基酸的晶体热容。本工作中确定的实验值随后与通过绝热量热法获得的文献数据相结合。对于 l-组氨酸，由于没有文献数据，本工作使用从 2 K 开始的弛豫（热脉冲）量热法确定了其低温热容。结果，为所有五种结晶氨基酸开发了高达 430 K 的等压晶体热容和标准热力学函数。
