Aggrawal Rishika, Kumari Sunita, Gangopadhyay Subhashis, Saha Subit Kumar
Department of Chemistry, Birla Institute of Technology & Science (BITS), Pilani, Pilani Campus, Pilani, Rajasthan 333031, India.
Department of Physics, Birla Institute of Technology & Science (BITS), Pilani, Pilani Campus, Pilani, Rajasthan 333031, India.
ACS Omega. 2020 Mar 17;5(12):6738-6753. doi: 10.1021/acsomega.0c00035. eCollection 2020 Mar 31.
The present study demonstrates how the different states of solubilized water viz. quaternary ammonium headgroup-bound, bulklike, counterion-bound, and free water in reverse micelles of a series of cationic gemini surfactants, water/12--12 ( = 5, 6, 8).2Br/-propanol/cyclohexane, control the solvation dynamics and rotational relaxation of Coumarin 490 (C-490) and microenvironment of the reverse micelles. The relative number of solubilized water molecules of a given state per surfactant molecule decides major and minor components. A rapid increase in the number of bulklike water molecules per surfactant molecule as compared to the slow increase in the number of each of headgroup- and counterion-bound water molecules per surfactant molecule with increasing water content ( ) in a given reverse micellar system is responsible for the increase in the rate of solvation and rotational relaxation of C-490. The increase in the number of counterion-bound water molecules per surfactant molecule and the concomitant decrease in the number of bulklike water molecules per surfactant molecule with increasing spacer chain length of gemini surfactants at a given are ascribed to the slower rates of both solvation and rotational relaxation. Relative abundances of different states of water have a role on the microenvironment of the reverse micelles as well. Thus, a comprehensive effect of different states of water on dynamics in complex biomimicking systems has been presented here.
本研究展示了一系列阳离子双子表面活性剂水/12-12（=5、6、8）.2Br/-丙醇/环己烷反胶束中增溶水的不同状态，即季铵头基结合水、类本体水、抗衡离子结合水和自由水，如何控制香豆素490（C-490）的溶剂化动力学和旋转弛豫以及反胶束的微环境。每个表面活性剂分子给定状态的增溶水分子相对数量决定了主要和次要成分。在给定的反胶束体系中，随着水含量（）增加，每个表面活性剂分子的类本体水分子数量快速增加，而每个表面活性剂分子结合头基和抗衡离子的水分子数量增加缓慢，这导致了C-490溶剂化速率和旋转弛豫速率的增加。在给定的情况下，随着双子表面活性剂间隔链长度增加，每个表面活性剂分子抗衡离子结合水分子数量增加，同时每个表面活性剂分子类本体水分子数量减少，这归因于溶剂化和旋转弛豫速率都变慢。不同水状态的相对丰度对反胶束的微环境也有作用。因此，本文展示了不同水状态对复杂仿生系统动力学的综合影响。
