Dasgupta Antara, Das Debapratim, Das Prasanta Kumar
Department of Biological Chemistry and Center for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India.
Langmuir. 2007 Apr 10;23(8):4137-43. doi: 10.1021/la063567n. Epub 2007 Mar 10.
Interfacial concentrations and/or space: which one is the predominant factor in regulating lipase activity at the water-oil interface? This work is an endeavor toward probing the relationship between lipase activity and interfacial concentrations in cationic water-in-oil (W/O) microemulsions through quantitative study by a chemical trapping method. The interfacial concentrations of water ([H2Oi]), bromide ([Bri-]), and n-hexanol ([HexOHi]) were estimated in the W/O microemulsions of six surfactants with varying headgroup architecture and hydrophilicity across a wide W0 ([H2O]/[surfactant]) range. The surfactants were prepared by the replacement of methyl groups of cetyltrimethylammonium bromide (1) by n-propyl (2-4), one hydroxyethyl (5), and one methoxyethyl (6) group. The estimated [H2Oi] was found not to change much (30.0-36.7 M) with the variation in headgroup hydrophilicity or size from 1-5. However, [Bri-] was found to increase with a decrease in the degree of dissociation (alpha), being higher for 1 and 5 (2.4-3.3 M) and relatively lower (0.9-1.9 M) for others depending on W0. Interestingly, [H2Oi] was found to be little higher (41.5-42.2 M) in the case of 6. The present study elucidates the importance of interfacial water and counterion concentrations in modulating the lipase activity in reverse micelles. In our previous report, the lipase activity was found to increase from 1-4 and in 6, whereas that observed in 5 was comparable with 1, being largely regulated by the surfactant head group size (Das, D.; Roy, S.; Mitra, R. N.; Dasgupta, A.; Das, P. K. Chem.-Eur. J. 2005, 11, 4881). The only other parameter that increased distinctly with lipase activity is the headgroup size, not [H2Oi]. Thus, the role of [H2Oi] in comparison to the surfactant's headgroup size is not found to be that significant. Moreover, the lower [Bri-] in 2-4 and 6 perhaps enhances the probability of enzyme and substrate localization at the interface, leading to higher lipase activity.
界面浓度和/或空间：哪一个是调节水-油界面脂肪酶活性的主要因素？这项工作旨在通过化学捕获法进行定量研究，探究阳离子油包水（W/O）微乳液中脂肪酶活性与界面浓度之间的关系。在六种具有不同头基结构和亲水性的表面活性剂的W/O微乳液中，在较宽的W0（[H2O]/[表面活性剂]）范围内估算了水（[H2Oi]）、溴化物（[Bri-]）和正己醇（[HexOHi]）的界面浓度。这些表面活性剂是通过用正丙基（2-4）、一个羟乙基（5）和一个甲氧基乙基（6）取代十六烷基三甲基溴化铵（1）的甲基制备的。发现随着头基亲水性或尺寸从1到5的变化，估算的[H2Oi]变化不大（30.0 - 36.7 M）。然而，发现[Bri-]随着解离度（α）的降低而增加，对于1和5较高（2.4 - 3.3 M），对于其他的则相对较低（0.9 - 1.9 M），这取决于W0。有趣的是，在6的情况下，[H2Oi]略高（41.5 - 42.2 M）。本研究阐明了界面水和抗衡离子浓度在调节反胶束中脂肪酶活性方面的重要性。在我们之前的报告中，发现脂肪酶活性从1到4以及在6中增加，而在5中观察到的与1相当，主要受表面活性剂头基尺寸调节（达斯，D.；罗伊，S.；米特拉，R. N.；达斯古普塔，A.；达斯，P. K. 《化学 - 欧洲杂志》2005年，11卷，4881页）。唯一另一个随脂肪酶活性明显增加的参数是头基尺寸，而不是[H2Oi]。因此，与表面活性剂头基尺寸相比，[H2Oi]的作用并不显著。此外，2 - 4和6中较低的[Bri-]可能增加了酶和底物在界面处定位的概率，导致更高的脂肪酶活性。
