Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700 032, India.
Langmuir. 2012 Jan 24;28(3):1715-24. doi: 10.1021/la2035906. Epub 2012 Jan 12.
The present work reports covalent functionalization of single-walled carbon nanotubes (f-SWNTs) to introduce hydrophilicity to the otherwise amphiphobic nanotubes. The charge and spacer length of the functional moiety were varied by using quaternized ethylene diamine, 6-aminocaproate, quaternized (ethylenedioxy)bis(ethylamine), and a poly(ethylene glycol) (PEG) unit (f-SWNT-1 to f-SWNT-4, respectively). These f-SWNTs with varying degrees of hydrophilicity were incorporated within cetyltrimethyl ammonium bromide (CTAB) reverse micelles to develop stable self-assembled nanohybrids. An optimum hydrophilicity on the SWNT surface led to interfacial localization of f-SWNTs resulting in the augmentation of space at the interface. A surface-active enzyme, lipase, localized at this enhanced interface of f-SWNT-containing CTAB reverse micelles exhibited significant activation (2.5-fold) compared to that in the absence of the nanoconstructs. This improvement in lipase activity was mainly due to the smooth occupancy of lipase and also presumably because of the increase in the concentrations of both substrate and the enzyme at the augmented interface. Interestingly, the f-SWNTs that activate lipase in reverse micelles deactivate the same enzyme in water. The dispersion of f-SWNTs in water and its matching integration at the interface of reverse micelles were confirmed through transmission electron microscopic (TEM) investigations. The interfacial localization of these nanoconstructs was also established from the distinct fluorescence behavior of a hydrophobic fluorescent probe, fluorescein isothiocyanate (FITC), adsorbed onto the f-SWNT surface. In concurrence with the observed lipase activity, the corresponding changes in the enzyme conformation within f-SWNTs integrated reverse micelle as well as in aqueous medium were studied by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy.
本工作报道了单壁碳纳米管（SWNTs）的共价功能化，以向原本疏水的纳米管引入亲水性。通过使用季化乙二胺、6-氨基己酸、季化（乙二氧基）双（乙胺）和聚（乙二醇）（PEG）单元（分别为 f-SWNT-1 至 f-SWNT-4），改变功能部分的电荷和间隔长度。这些具有不同亲水性程度的 f-SWNTs 被掺入十六烷基三甲基溴化铵（CTAB）反胶束中，以开发稳定的自组装纳米杂化物。SWNT 表面的最佳亲水性导致 f-SWNTs 在界面处定位，从而增加界面处的空间。定位在含有 f-SWNT 的 CTAB 反胶束的增强界面处的表面活性酶，脂肪酶，与不存在纳米结构相比，表现出显著的激活（2.5 倍）。脂肪酶活性的这种提高主要归因于脂肪酶的顺利占据，也可能是由于在增强的界面处底物和酶的浓度增加。有趣的是，在反胶束中激活脂肪酶的 f-SWNTs 在水中使相同的酶失活。通过透射电子显微镜（TEM）研究证实了 f-SWNTs 在水中的分散及其在反胶束界面处的匹配集成。通过吸附在 f-SWNT 表面上的疏水性荧光探针异硫氰酸荧光素（FITC）的明显荧光行为，也确定了这些纳米结构的界面定位。与观察到的脂肪酶活性一致，还通过圆二色性（CD）和傅里叶变换红外（FTIR）光谱研究了在 f-SWNTs 整合反胶束以及在水介质中酶构象的相应变化。
