由水溶液形成的碳水化合物薄膜的振动圆二色性

Petrovic Ana G, Bose Pranati K, Polavarapu Prasad L

Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA.

Carbohydr Res. 2004 Nov 15;339(16):2713-20. doi: 10.1016/j.carres.2004.09.014.

Vibrational circular dichroism (VCD) spectra in the entire 2000-900 cm(-1) region have been recorded, for the first time, for films of carbohydrates prepared from aqueous solutions. Eight different carbohydrates, alpha-D-glucopyranosyl-(1-->4)-D-glucose, cyclomaltohexaose, alpha-D-glucopyranosyl alpha-D-glucopyranoside, beta-D-glucopyranosyl-(1-->6)-D-glucose, beta-D-glucopyranosyl-(1-->4)-D-glucose, D-glucose, and both enantiomers of 6-deoxygalactose and of allose, were investigated. The VCD spectra obtained for films are found to be identical to the corresponding spectra obtained for aqueous solutions of carbohydrates. These measurements demonstrate several advantages of significant importance. The strong infrared absorption of water has prevented, in the past, the pursuit for routine applications of VCD in determining the structures of carbohydrates in aqueous solutions. This limitation is not present for film studies because water solvent is removed in the process of preparing the films. Also, strong infrared absorption of water at 1650 cm(-1) requires the use of very short-pathlength (6 microm) cells for measurements on aqueous solutions. This requirement and concomitant inconveniences (such as laborious assembling of a demountable liquid cell or purchasing an expensive variable pathlength liquid cell) have been eliminated for film measurements. The removal of interfering water absorption in film studies resulted in higher light throughput and better signal-to-noise ratios for VCD measurements. Another point of significance is that the amount of carbohydrate sample required for VCD measurements on films is approximately one to two orders of magnitude smaller than that required for corresponding VCD measurements on aqueous solutions. Since carbohydrate samples can now be studied as films, VCD spectroscopy becomes much more broadly applicable for carbohydrates than previously believed. The present work, in combination with other film measurements in our laboratory, indicate that VCD studies on films can be used more generally, providing a convenient and powerful approach for probing structural information for biologically important compounds.

首次记录了由水溶液制备的碳水化合物薄膜在整个2000 - 900 cm⁻¹区域的振动圆二色性（VCD）光谱。研究了八种不同的碳水化合物，即α-D-吡喃葡萄糖基-(1→4)-D-葡萄糖、环麦芽六糖、α-D-吡喃葡萄糖基α-D-吡喃葡萄糖苷、β-D-吡喃葡萄糖基-(1→6)-D-葡萄糖、β-D-吡喃葡萄糖基-(1→4)-D-葡萄糖、D-葡萄糖以及6-脱氧半乳糖和阿洛糖的两种对映体。发现薄膜的VCD光谱与碳水化合物水溶液的相应光谱相同。这些测量显示出几个极其重要的优点。过去，水的强红外吸收阻碍了VCD在确定水溶液中碳水化合物结构的常规应用。对于薄膜研究不存在这个限制，因为在制备薄膜的过程中除去了水溶剂。此外，水在1650 cm⁻¹处的强红外吸收要求在水溶液测量时使用非常短的光程（6微米）的样品池。对于薄膜测量，这个要求以及随之而来的不便（例如可拆卸液体样品池的费力组装或购买昂贵的可变光程液体样品池）都已消除。薄膜研究中干扰性水吸收的消除导致VCD测量具有更高的光通量和更好的信噪比。另一个重要点是，薄膜VCD测量所需的碳水化合物样品量比相应的水溶液VCD测量所需的量大约小一到两个数量级。由于现在可以将碳水化合物样品作为薄膜进行研究，VCD光谱学对于碳水化合物的适用性比以前认为的要广泛得多。目前的工作与我们实验室的其他薄膜测量相结合，表明对薄膜的VCD研究可以更广泛地使用，为探测生物重要化合物的结构信息提供了一种方便而强大的方法。