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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Complex Mechanism of Relaxation in Solid Chloroxylenol (Antibacterial/Antifungal Agent) Studied by ~1H NMR Spectroscopy and Density Functional Theory Calculations
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Complex Mechanism of Relaxation in Solid Chloroxylenol (Antibacterial/Antifungal Agent) Studied by ~1H NMR Spectroscopy and Density Functional Theory Calculations

机译：〜1H NMR光谱和密度泛函理论计算研究固态氯氧酚（抗菌/抗真菌剂）松弛的复杂机理

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Molecular relaxation in antibacterial/antifungal agent: chloroxylenol (4-chloro- 3,5-dimethylphenol, PCMX) in the solid state was studied by the ~1H NMR and quantum chemistry calculations. The temperature dependencies of the proton spin-lattice relaxation time (T_1) 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 ~1H NMR resonant line in the range 106-380 K were measured. The two minima in the temperature dependence of T_1 revealed two activation processes, whereas the M_2 dependence in the studied range was quite flat and revealed the only significant reduction at 380 K. The low temperature part of T_1(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 T_1) 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 -CH_3 motion (tunneling and classical) results in the reduction in the ~1H NMR line second moment from 17.3 G~2 (rigid) to approximately 11.05 G~2. The pointed high temperature minimum T_1(T) of 0.109 s at 89 K, 24.667 MHz, which shifts with frequency, was assigned to small-angle libration jumps, by the Θ_2 = ±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 ~1H 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 G2 to 0.9 G~2 at 380 K is a result of the phase transition connected with melting (385-389 K).
机译：抗菌/抗真菌剂中的分子弛豫：通过〜1H NMR和量子化学计算，研究了固态的氯酚（4-氯-3,5-二甲基苯酚，PCMX）。质子自旋晶格弛豫时间（T_1）在15-273 K（在24.667 MHz时），77-295 K（在15 MHz时）和112-291 K在90 MHz和第二矩（在106-380 K范围内测量了〜1H NMR共振线的M2）。 T_1的温度依赖性的两个最小值显示了两个激活过程，而在研究范围内，M_2依赖性相当平坦，并且在380 K时显示出唯一的显着降低。T_1（T）依赖性的低温部分表明发生了两个活化过程。含甲基固体的工艺特征;量子力学控制了非相干隧穿（负责T_1的低温平坦化），而经典的阿伦尼乌斯依赖性则控制了受阻旋转（与在57 K，24.667 MHz处的0.066 s的低温最小值相关）。使用DFT / B3LYP / 6-311 ++ G（2d，p）计算获得的2D势能面揭示了甲基的不等价性以及它们之间的相互作用/偶联。对于不等价的甲基，经典受阻旋转的活化能为3.35和2.5 kJ / mol，而质子隧穿T_（tun）最终停止的温度为52和63K。估计T_（tun）所需的C_p（T）纯粹是在理论上基于比热的爱因斯坦和德拜模型，51种原子振动模式，4个内部旋转和3种由DFT计算的扭转而得出的。 -CH_3运动（隧穿和经典运动）导致〜1H NMR线的第二矩从17.3 G〜2（刚性）降低到大约11.05 G〜2。在89 K，24.667 MHz处随频率变化的0.109 s的尖峰高温最小值T_1（T）随频率变化，通过两个平衡点之间的Θ_2=±15°分配给小角度的自由跃迁。根据理论模型对实验点的拟合估计的该运动的激活能为10.5 kJ / mol。分配给该运动的〜1H NMR线第二矩的减小要低得多（由于阶跃参数s = 0.64），等于1.6 G〜2。 380 K时从9.6 G2高温还原到0.9 G〜2是相变与熔化（385-389 K）有关的结果。

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