Max Jean-Joseph, Chapados Camille
Département de Chimie-Biologie, Université du Québec à Trois-Rivières, Trois-Rivières, QC G9A 5H7, Canada.
J Chem Phys. 2009 Mar 28;130(12):124513. doi: 10.1063/1.3078382.
The study by Fourier transform infrared attenuated total reflectance spectroscopy at 27 degrees C of methanol (MeOH) and hexane mixtures is presented. In the 0-0.25 and 0.75-1.00 molar fractions, the mixtures form homogeneous solutions, whereas from 0.25 to 0.75, the mixtures are inhomogeneous forming two phases. These mixtures have the near 3300 cm(-1) OH stretch band only slightly displaced throughout the whole concentration range indicating very little variation in the H-bonding condition. This result is very different from that of MeOH in CCl(4) where the OH stretch bands are scattered in a wide frequency range. Factor analysis applied to the MeOH/hexane spectra gave seven principal factors (one hexane and six methanol factors) and retrieved their principal spectra and abundances. In the inhomogeneous region, the two phase volumes changed inversely with concentration, but their factor compositions are invariable at 1:3 and 3:1 molar ratios. Five of the six principal methanol factors have the O-H and the C-O stretch bands situated near, respectively, 3310 and 1025 cm(-1) with little displacement in the whole concentration range. The sixth factor observed at 3654 cm(-1) (full width at half height<40 cm(-1)) was assigned to free methanol OH by Max and Chapados [J. Chem. Phys. 128, 224512 (2008)]. This species concentration is very low but constant at around 0.01 M in the methanol range of 0.5-2.5 M. The main OH stretch bands (approximately 3300 cm(-1)) were simulated with six Gaussian components that were assigned to different hydrogen-bonding situations. These form reverse micelles at low methanol concentrations and micelles at high concentrations that persist in pure methanol. A very different state of affairs exists in MeOH in CCl(4) where free OH groups are formed in almost all mixtures except in pure MeOH. Since hexane is a better model of a lipidic milieu than CCl(4), the results for MeOH/hexane give a better representation of the fate of alcoholic OH groups in such a milieu.
本文介绍了在27摄氏度下用傅里叶变换红外衰减全反射光谱法对甲醇（MeOH）和己烷混合物进行的研究。在摩尔分数为0 - 0.25和0.75 - 1.00时，混合物形成均相溶液，而在0.25至0.75之间，混合物不均匀，形成两相。这些混合物在整个浓度范围内，近3300 cm⁻¹的OH伸缩带仅有轻微位移，表明氢键条件变化很小。这一结果与甲醇在四氯化碳（CCl₄）中的情况非常不同，在CCl₄中OH伸缩带分散在很宽的频率范围内。对MeOH/己烷光谱应用因子分析得到七个主因子（一个己烷因子和六个甲醇因子），并得到了它们的主光谱和丰度。在非均相区域，两相体积随浓度呈反比变化，但它们的因子组成在1:3和3:1的摩尔比下不变。六个主要甲醇因子中的五个，其O - H和C - O伸缩带分别位于3310和1025 cm⁻¹附近，在整个浓度范围内位移很小。在3654 cm⁻¹处观察到的第六个因子（半高宽<40 cm⁻¹）被马克斯和查帕多斯 [《化学物理杂志》128, 224512 (2008)] 归为游离甲醇OH。该物种浓度非常低，但在0.5 - 2.5 M的甲醇范围内约为0.01 M且恒定。主要的OH伸缩带（约3300 cm⁻¹）用六个高斯分量进行了模拟，这些分量被分配到不同的氢键情况。它们在低甲醇浓度下形成反胶束，在高浓度下形成胶束，且在纯甲醇中持续存在。在甲醇在CCl₄中的情况则大不相同，除了纯甲醇外，几乎所有混合物中都会形成游离OH基团。由于己烷比CCl₄更能模拟脂质环境，因此MeOH/己烷的结果能更好地反映醇羟基在这种环境中的命运。
