Effect of Hydroxyl Group Substituted Spacer Group of Cationic Gemini Surfactants on Solvation Dynamics and Rotational Relaxation of Coumarin-480 in Aqueous Micelles

Abstract

The solvation dynamics and rotational relaxation of Coumarin 480 (C-480) have been investigated in the micelles of a series of gemini surfactants, 12-4(OH)n-12 (n = 0, 1, and 2), with increasing hydroxyl group substitution within the spacer group. Steady-state and time-correlated single photon counting (TCSPC) fluorescence spectroscopic techniques have been used to carry out such study. Steady-state and TCSPC fluorescence data support the location of probe molecule at the Stern layer. The solvation dynamics is found to be slower on hydroxyl substitution of spacer group due to the formation of hydrogen bonds between water molecules and hydroxyl group(s) of spacer group. Such kind of hydrogen bonding protects the probe molecule from its contact with water molecules and also results in restricted mobility of water molecules. The average rotational relaxation time increases on increasing number of substituted hydroxyl group on a spacer group. It is because of formations of more and more close packed micelles and larger extent of intermolecular hydrogen bonding interactions between C-480 and hydroxyl group(s). For micelles of each of 12-4-12 and 12-4(OH)-12, the slow rotational relaxation is dominated by the lateral diffusion of the fluorophore along the spherical surface of the micelle. However, for 12-4(OH)2-12, the slow rotational relaxation is mainly due to the rotational motion of the micelle as a whole. Because of high microviscosity of micelles of 12-4(OH)2-12 and greater extent of hydrogen bonding interactions with C-480, the relaxation time corresponding to the lateral diffusion of the fluorophore is very high in this case.

Structural, biocomplexation and gene delivery properties of hydroxyethylated gemini surfactants with varied spacer length

“…Comparison of hydroxyalkylated geminis with conventional m-s-m analogs provide evidences that introducing hydroxyalkyl fragments markedly modifies functional activity (solubilization, catalytic, etc.) and physicochemical properties of systems (Fig.S1, Table 1) [12,27,33,64]. In particular, larger cmc decrease, lower isoelectric values, smaller aggregates with higher surface curvature and charge density, and more facile dehydration of polar groups occur in the case of hydroxyalkylated surfactants.…”

“…While the role of the spacer architecture in the DNA-surfactant complexation is exemplified in literature [26][27][28][29], there is some disagreement in these data. Superior results were obtained for ethanediyl-and propanediyl versus the longer (-CH 2 -) 5 and (-CH 2 -) 12 polymethylene spacers in ref.…”

“…The introduction of OH-group in both spacer and head groups may affect the structural behavior of single surfactant solution and its complexes with DNA [12,27,33]. This influence is probably mediated through solvation of head groups, changes in their size and the surface curvature of aggregates, which in turn modify the coverage of DNA molecules.…”

Effect of Polar Organic Solvents on Self‐Aggregation of Some Cationic Monomeric and Dimeric Surfactants

“…The 12-4(OH)-12 gemini surfactant has a lower CMC than 12-4-12, as shown in Table 1. Saha et al [35,36] reported a decrease in the CMC of gemini surfactants with increasing hydroxyl group substitution on the spacer group. They rationalized this observation on the basis that the effect of increasing spacer chain length is dominant over the substituted hydroxyl group effect.…”

“…The gemini surfactants, viz., C 16 -12-C 16 , 2Br -; C 16 -4-C 16 , 2Br -; C 12 -4-C 12 , 2Br -and C 12 -4(OH)-C 12 , 2Br -were synthesized following the same method as reported in the literature [33][34][35][36]. CDEEAB, CDMEAB and TDEEAB were obtained from Prof. R.M.…”