Latosińska Jolanta Natalia, Latosińska Magdalena, Tomczak Marzena Agnieszka, Medycki Wojciech
Faculty of Physics, Adam Mickiewicz University , Umultowska 85, 61-614 Poznań, Poland.
J Phys Chem A. 2014 Mar 27;118(12):2209-19. doi: 10.1021/jp411981s. Epub 2014 Mar 14.
Molecular relaxation in antibacterial/antifungal agent: chloroxylenol (4-chloro-3,5-dimethylphenol, PCMX) in the solid state was studied by the (1)H NMR and quantum chemistry calculations. The temperature dependencies of the proton spin-lattice relaxation time (T1) in the ranges 15-273 K (at 24.667 MHz), 77-295 K (at 15 MHz), and 112-291 K at 90 MHz and the second moment (M2) of (1)H NMR resonant line in the range 106-380 K were measured. The two minima in the temperature dependence of T1 revealed two activation processes, whereas the M2 dependence in the studied range was quite flat and revealed the only significant reduction at 380 K. The low temperature part of T1(T) dependence indicated the occurrence of two processes characteristic of methyl bearing solids; the quantum mechanics governed incoherent tunneling (responsible for the low temperature flattening of T1) and the classical Arrhenius dependence governed hindered rotation (related to the wide low temperature minimum of 0.066 s at 57 K, 24.667 MHz). The 2D potential energy surface obtained using DFT/B3LYP/6-311++G(2d,p) calculations revealed the inequivalence of methyl groups and the lack of their interplay/coupling. The activation energies of classical hindered rotation are 3.35 and 2.5 kJ/mol, whereas temperatures at which the proton tunneling T(tun) finally ceases are 52 and 63 K, for inequivalent methyl groups. C(p)(T) required for the estimation of T(tun) was calculated purely theoretically on the basis of the Einstein and Debye models of specific heat and 51 modes of atomic vibrations, 4 internal rotations, and 3 torsions calculated by DFT. The -CH3 motion (tunneling and classical) results in the reduction in the (1)H NMR line second moment from 17.3 G(2) (rigid) to approximately 11.05 G(2). The pointed high temperature minimum T1(T) of 0.109 s at 89 K, 24.667 MHz, which shifts with frequency, was assigned to small-angle libration jumps, by the Θ2 = ±15° between two positions of equilibrium. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points is 10.5 kJ/mol. The reduction in the (1)H NMR line second moment assigned to this motion is much lower (due to order parameter s = 0.64) and equal to 1.6 G(2). The high temperature reduction from 9.6 G(2) to 0.9 G(2) at 380 K is a result of the phase transition connected with melting (385-389 K).
抗菌/抗真菌剂中分子弛豫的研究：通过¹H NMR和量子化学计算研究了固态的对氯间二甲苯酚（4-氯-3,5-二甲基苯酚，PCMX）。测量了质子自旋晶格弛豫时间（T1）在15 - 273 K（24.667 MHz）、77 - 295 K（15 MHz）和112 - 291 K（90 MHz）范围内的温度依赖性，以及¹H NMR共振线的二阶矩（M2）在106 - 380 K范围内的温度依赖性。T1温度依赖性中的两个最小值揭示了两个活化过程，而在所研究范围内M2的依赖性相当平缓，仅在380 K时有显著降低。T1（T）依赖性的低温部分表明存在两个甲基固体特有的过程；量子力学控制的非相干隧穿（导致T1的低温平坦化）和经典的阿仑尼乌斯依赖性控制的受阻旋转（与57 K、频率24.667 MHz时0.066 s的宽低温最小值相关）。使用DFT/B3LYP/6 - 311++G(2d,p)计算得到的二维势能面揭示了甲基的不等价性以及它们之间缺乏相互作用/耦合。对于不等价甲基，经典受阻旋转的活化能分别为3.35和2.5 kJ/mol，而质子隧穿T（tun）最终停止的温度分别为52和63 K。基于比热的爱因斯坦和德拜模型以及DFT计算的51种原子振动模式、4种内旋转和3种扭转，纯理论计算了估计T（tun）所需的C(p)(T)。-CH3运动（隧穿和经典运动）导致¹H NMR线二阶矩从17.3 G²（刚性）降低到约11.05 G²。在89 K、24.667 MHz时出现的0.109 s的尖锐高温最小值T1（T）随频率移动，被归因于在两个平衡位置之间Θ2 = ±15°的小角度摆动跳跃。根据理论模型与实验点的拟合估计，该运动的活化能为10.5 kJ/mol。归因于该运动的¹H NMR线二阶矩的降低要低得多（由于序参量s = 0.64），等于1.6 G²。在380 K时从9.6 G²到0.9 G²的高温降低是与熔化（385 - 389 K）相关的相变的结果。
