Dynamical structure of aqueous solutions of biological substance by microwave dielectric relaxation

1.利用TDR和波导法测量了乙醇/水和乙二醇/水混合物在0.1V/GHz[小于或等于]89的频率范围内的复介电谱。在0.3[小于或等于]X(醇的摩尔分数)[小于或等于]1.0时，除了主要的低频过程(j=1)被指定为氢键系统的协同动力学外，还需要两个附加的德拜项(j=2和j=3)，松弛时间分别为τ_2~10-20ps和τ_3~1-2ps。这可分别归结为单H键醇单体在链结构末端的运动和自由羟基的翻转运动。在X&lt；0.3处，j=2过程不再是可分离的。由Δ的松弛时间求出了超额活化自由能ΔG^E、焓、ΔH^E和熵ΔS^E以及它们的偏摩尔量ΔG^E、ΔH^E和…S^E_i(i=醇和水更多VE进程，τ_1。在X[大于或等于]X_b(例如X_b~0.15(异丙醇/水)，ΔH^E_A和ΔS^E_A几乎为零，表明生成与纯醇类似的锯齿形氢键醇链。ΔH^E_A和ΔS^E_A(Ex.对于异丙醇/水，在X~0.03和~0.07处)被解释为氢键数目和强度的同时增加，并支持在中间区，由于溶质-溶质相互作用，水分子被从非极性基团的第一配位壳层推入本体。比较了异丙醇/水和正丙醇/水的反应结果，发现不仅非极性头基的大小，而且醇的空间位阻也是控制氢键体系协同动力学的关键因素。我们在0.1v/℃频率范围内对甘氨酸、L-丙氨酸、L-亮氨酸、L-亮氨酸、L-异亮氨酸、L-丝氨酸、L-苏氨酸、L-脯氨酸、L-半胱氨酸、L-蛋氨酸和L-苯丙氨酸的水溶液进行了深入的研究。发现了三个弛豫过程：两性氨基酸分子的旋转扩散(τ_1~40-110ps)、主体水的协同动力学(τ_2~8-11ps)和单氢键水分子的快速旋转(τ_3~1-2ps)。将Cavell方程分别应用于溶质和溶剂过程，推导出各氨基酸的偶极矩和有效水化数Z，Z对应于每个溶质中不能对溶剂松弛过程有贡献的水分子数。用斯托克斯-爱因斯坦-德拜方程由τ_1估算的氨基酸分子的有效摩尔体积与其偏摩尔体积的比较表明，在流体动力滑移边界条件下，氨基酸分子的形状因子f_⊥随侧链基团的大小而线性增加，但具有刚性环状结构的氨基酸除外。较少

1. We determined the complex dielectric spectra of alcohol/water and ethylene glycol/water mixtures in the frequency range of 0.1【less than or equal】v/GHz【less than or equal】89 using TDR and wave guide interferometry. At 0.3【less than or equal】X (molar fraction of alcohol)【less than or equal】1.0, besides the dominating low-frequency process (j=1), assigned to the cooperative dynamics of the H-bond system, two additional Debye terms (j=2 and j=3) with the relaxation times of τ_2〜10-20ps and τ_3〜1-2ps are required to reproduce the high-frequency part of the spectrum. These can respectively be assigned to the motion of singly H-bonded alcohol monomers at the ends of the chain structure and the flipping motion of free OH. At X<0.3, the j=2 process becomes no longer separable.2. The excess activation free energy, ΔG^E, enthalpy, ΔH^E, and entropy, ΔS^E, and their partial molar quantities, ΔG^E_i, ΔH^E_i, and ΔS^E_i (i=alcohol and water) were derived from the relaxation time of the cooperati … More ve process, τ_1. In X【greater than or equal】X_b (ex. X_b〜0.15, for 2-propanol/water), ΔH^E_A and ΔS^E_A become nearly zero, suggesting the generation of zigzag H-bonded alcohol chains similar to the pure alcohol. The two pertinent maxima in ΔH^E_A and ΔS^E_A (ex. at X〜0.03 and 〜0.07 for 2-propanol/water) are interpreted as a simultaneous increase of the number and strength of H-bond and support the view that in the intermediate region, water molecules are pushed out of the first coordination shell of the non-polar group into the bulk due to solute-solute association, called hydrophobic interaction. The comparison of the result of 2-propanol/water to that of 1-propanol/water revealed that not only the size of non-polar head group but the steric hindrance to alcohol OH are the key factor that controls the cooperative dynamics of H-bond system.3. We thoroughly investigated aqueous solutions of amino acids; glycine, L-alanine, L-valine, L-leucine, L-isoleucine, L-serine, L-thoreonine, L-proline, L-cysteine, L-methionine, and L-Phenylalanine using DRS at 25℃ in the frequency range 0.1【less than or equal】v/GHz【less than or equal】89. The three relaxation processes; the rotational diffusion of zwitterionic amino acid molecules (τ_1〜40-110ps), the cooperative dynamics of bulk water (τ_2〜8-11ps), and a fast rotation of singly H-bonded water molecules (τ_3〜1-2ps) were detected. Applying the Cavell equation respectively to the solute and solvent processes, the dipole moment of each amino acid and the effective hydration number, Z, corresponding to the number of water molecules per solute that cannot contribute to the solvent relaxation processes, were deduced. A comparison of the effective molar volume of amino acid molecules as a rotational species estimated from τ_1 using the Stokes-Einstein-Debye (SED) equation to their partial molar volume, revealed that the shape factor of the amino acids under the hydrodynamic slip boundary condition, f_⊥, representing deviation from a spherical shape, increases linearly with the size of the side chain group except the case of L-proline that possesses a rigid ring-like structure. Less