Institute of Condensed Matter Physics, Technische Universität Darmstadt, Hochschulstr. 6, 64289 Darmstadt, Germany.
J Chem Phys. 2022 Aug 21;157(7):074705. doi: 10.1063/5.0105062.
We perform differential scanning calorimetry, broadband dielectric spectroscopy (BDS), and nuclear magnetic resonance (NMR) studies to understand the molecular dynamics in mixtures of ethylene glycol with elastin or lysozyme over broad temperature ranges. To focus on the protein-solvent interface, we use mixtures with about equal numbers of amino acids and solvent molecules. The elastin and lysozyme mixtures show similar glass transition steps, which extend over a broad temperature range of 157-185 K. The BDS and NMR studies yield fully consistent results for the fastest process P1, which is caused by the structural relaxation of ethylene glycol between the protein molecules and follows an Arrhenius law with an activation energy of E = 0.63 eV. It involves quasi-isotropic reorientation and is very similar in the elastin and lysozyme matrices but different from the α and β relaxations of bulk ethylene glycol. Two slower BDS processes, viz., P2 and P3, have protein-dependent time scales, but they exhibit a similar Arrhenius-like temperature dependence with an activation energy of E ∼ 0.81 eV. However, P2 and P3 do not have a clear NMR signature. In particular, the NMR results for the lysozyme mixture reveal that the protein backbone does not show isotropic α-like motion on the P2 and P3 time scales but only restricted β-like reorientation. The different activation energies of the P1 and P2/P3 processes do not support an intimate coupling of protein and ethylene glycol dynamics. The present results are compared with previous findings for mixtures of proteins with water or glycerol, implying qualitatively different dynamical couplings at various protein-solvent interfaces.
我们进行了差示扫描量热法、宽频介电谱（BDS）和核磁共振（NMR）研究，以了解在广泛的温度范围内乙二醇与弹性蛋白或溶菌酶混合物中的分子动力学。为了关注蛋白质-溶剂界面，我们使用氨基酸和溶剂分子数量大致相等的混合物。弹性蛋白和溶菌酶混合物显示出相似的玻璃化转变步骤，这些步骤在 157-185 K 的宽温度范围内延伸。BDS 和 NMR 研究为最快的过程 P1 提供了完全一致的结果，该过程是由蛋白质分子之间乙二醇的结构弛豫引起的，遵循阿伦尼乌斯定律，活化能 E = 0.63 eV。它涉及准各向同性的重新取向，在弹性蛋白和溶菌酶基质中非常相似，但与本体乙二醇的α和β弛豫不同。两个较慢的 BDS 过程，即 P2 和 P3，具有蛋白质依赖性的时间尺度，但它们表现出类似的阿伦尼乌斯温度依赖性，活化能 E∼0.81 eV。然而，P2 和 P3 没有明确的 NMR 特征。特别是，溶菌酶混合物的 NMR 结果表明，在 P2 和 P3 时间尺度上，蛋白质主链没有各向同性的α样运动，而只有受限的β样重排。P1 和 P2/P3 过程的不同活化能不支持蛋白质和乙二醇动力学的紧密耦合。目前的结果与以前关于蛋白质与水或甘油混合物的发现进行了比较，表明在各种蛋白质-溶剂界面上存在定性不同的动力学耦合。
