Glass Transition and Dynamics in Lysozyme-Water Mixtures Over Wide Ranges of Composition
Glass Transition and Dynamics in Lysozyme-Water Mixtures Over Wide Ranges of Composition
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DOI：
10.1007/s11483-010-9201-0
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发表时间：
2011-06-01
期刊：
影响因子：
3
通讯作者：
Pissis, Polycarpos
中科院分区：
文献类型：
--
作者：
Panagopoulou, Anna;Kyritsis, Apostolos;Pissis, Polycarpos
差示扫描量热法（DSC）和两个介电技术，宽带介电弛豫光谱和热刺激去极化电流（TSDC），研究玻璃化转变和水和蛋白质动力学的混合物中的水和一种球状蛋白质，溶菌酶，在宽范围的水含量，无论是解决方案，和水合固体样品。此外，在室温下进行水平衡吸附等温线（ESI）测量。主要目的是通过不同的技术相互关联的结果，并确定各种工艺的临界含水量。根据ESI测量，直接结合到主要水合位点的水的含量被确定为0.088（克水/克干蛋白质），对应于71个水分子/蛋白质分子，并且其中聚集变得显著的水的含量为约0.25。水的结晶和熔化事件首先观察到在水含量分别为0.270和0.218，和未结晶水的量被发现随着水含量的增加而增加。两个群体的冰晶观察DSC，初级和散装冰晶，这引起两个单独的弛豫介电测量。此外，未结晶水的松弛被观察到，叠加在蛋白质表面上的极性基团的局部松弛。发现通过DSC和TSDC彼此相当一致地测定的玻璃化转变温度随着水含量的增加而显著降低，并且对于高于约0.25的水含量稳定在约-90 ° C。这是本研究的新结果，对低温保护和药剂学具有潜在影响。
Differential scanning calorimetry (DSC) and two dielectric techniques, broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents (TSDC), were employed to study glass transition and water and protein dynamics in mixtures of water and a globular protein, lysozyme, in wide ranges of water content, both solutions, and hydrated solid samples. In addition, water equilibrium sorption isotherms (ESI) measurements were performed at room temperature. The main objective was to correlate results by different techniques to each other and to determine critical water contents for various processes. From ESI measurements the content of water directly bound to primary hydration sites was determined to 0.088 (grams of water per grams of dry protein), corresponding to 71 water molecules per protein molecule, and that where clustering becomes significant to about 0.25. Crystallization and melting events of water were first observed at water contents 0.270 and 0.218, respectively, and the amount of uncrystallized water was found to increase with increasing water content. Two populations of ice crystals were observed by DSC, primary and bulk ice crystals, which give rise to two separate relaxations in dielectric measurements. In addition, the relaxation of uncrystallized water was observed, superimposed on a local relaxation of polar groups on the protein surface. The glass transition temperature, determined by DSC and TSDC in rather good agreement to each other, was found to decrease significantly with increasing water content and to stabilize at about -90 degrees C for water contents higher than about 0.25. This is a novel result of this study with potential impact on cryoprotection and pharmaceutics.