Ghent University, Faculty of Bioscience Engineering, Particle and Interfacial Technology Group, Coupure Links 653, B-9000 Gent, Belgium.
J Pharm Biomed Anal. 2010 Feb 5;51(3):583-9. doi: 10.1016/j.jpba.2009.09.025. Epub 2009 Sep 27.
Polysorbate surfactants (commercially available as Tween) are widely used in pharmaceutical, cosmetic and food products. They are generally considered as esters of ethoxylated sorbitan with fatty acids. Diffusion H1 NMR spectroscopy on a solution of polysorbate 20 in D2O revealed that only one diffusion coefficient was found for the fatty acyl part. Using the Stokes-Einstein equation, it became obvious that this diffusion behavior was caused by micelles. On the other hand, two significantly different diffusion coefficients were found for the methylene groups of ethylene oxide (EO). This indicates the presence of two distinct EO containing species in solution. Since the slowest diffusing EO species has the same diffusion coefficient as the fatty acyl part, it corresponds to the micellar (i.e. fatty acyl bound) ethoxylates. The diffusion coefficient of the fastest diffusing EO species was a factor of four larger than that of the slowly diffusing species and was attributed to water-soluble non-esterified ethoxylates. A solution of polysorbate 20 in the presence of NaOD was prepared to investigate if hydrolysis of the sorbitan ester could be the reason for the occurence of these hydrophilic ethoxylates. It was found that alkaline hydrolysis does lead to an increasing fraction of non-esterified ethoxylates, but is not the cause of its presence in untreated polysorbate samples since these species were also found in solutions of polyethylene glycol oleyl ether (commercially available as Brij), which are not susceptible to hydrolysis. Fractionation of the EO species present in polysorbate 20 into an amphiphilic and a hydrophilic fraction was only partly obtained by activated carbon adsorption. On the other hand, sequential extraction of aqueous polysorbate solutions by ethyl acetate and chloroform enabled a nearly complete fractionation. H1 NMR spectroscopy proved to be very useful since it allows in situ determination of the global composition of a surfactant sample, as well as quantification of both the amphiphilic and hydrophilic ethoxylate fractions via diffusion measurements.
聚山梨酯表面活性剂（商品名为 Tween）广泛应用于制药、化妆品和食品产品中。它们通常被认为是聚氧乙烯山梨糖醇酯与脂肪酸的酯。在 D2O 溶液中的聚山梨酯 20 的扩散 H1 NMR 光谱显示，仅发现一个脂肪酸部分的扩散系数。使用 Stokes-Einstein 方程，很明显这种扩散行为是由胶束引起的。另一方面，对于环氧乙烷（EO）的亚甲基，发现了两个明显不同的扩散系数。这表明在溶液中存在两种不同的含 EO 物质。由于最慢扩散的 EO 物质具有与脂肪酸部分相同的扩散系数，因此它对应于胶束（即脂肪酸结合的）乙氧基化物。最快扩散的 EO 物质的扩散系数比缓慢扩散的物质大四倍，归因于水溶性非酯化乙氧基化物。制备了含有 NaOD 的聚山梨酯 20 溶液，以研究山梨醇酯的水解是否可能是这些亲水性乙氧基化物出现的原因。发现碱性水解确实会导致非酯化乙氧基化物的比例增加，但不是未处理的聚山梨酯样品中存在这些物质的原因，因为这些物质也存在于聚氧乙烯油醚（商品名为 Brij）的溶液中，不易水解。通过活性炭吸附，仅部分地将聚山梨酯 20 中存在的 EO 物质分为亲脂性和亲水性两部分。另一方面，通过乙酸乙酯和氯仿的顺序提取水溶液中的聚山梨酯溶液，可以实现几乎完全的分离。H1 NMR 光谱非常有用，因为它允许原位确定表面活性剂样品的总体组成，以及通过扩散测量定量确定亲脂性和亲水性乙氧基化物部分。
