Study on Mixed Micelles of Cationic Gemini Surfactants Having Hydroxyl Groups in the Spacers with Conventional Cationic Surfactants: Effects of Spacer Group and Hydrocarbon Tail Length

Study of interactions of the cationic 12–2–12 Gemini surfactant with saccharides in aqueous solution: volumetric, compressibility and viscometric analysis

In the present study, the interaction behaviour of 12–2–12 Gemini surfactant in aqueous saccharide solutions (lactose and maltodextrin solutions) is investigated using density, sound velocity and viscosity measurements. The density and sound velocity data were used to determine the volume and compressibility parameters. The effects of temperature and concentration/strength of the solutions on the interaction behaviour were analysed by conductivity studies over a wide temperature (293.15–313.15) K and concentration range of the saccharides as well as of the surfactant. It was found that predominantly hydrophobic interactions together with ionic/hydrophilic interactions between 12–2–12 Gemini surfactant and the saccharides maltodextrin and lactose play a role. In addition, the structural changes in the 12–2–12 Gemini solutions induced by lactose and maltodextrin were investigated by viscosity measurements. The results confirm the observations from the volume and compressibility studies. The study of the different hydrophobic/hydrophilic interactions in the Gemini surfactant-sacharide-water mixtures are very helpful to understand the structural behaviour of Gemini surfactants in the view of their biological significance.

Physical-Chemical Characterization of Bilayer Membranes Derived from (±) α-Tocopherol-Based Gemini Lipids and Their Interaction with Phosphatidylcholine Bilayers and Lipoplex Formation with Plasmid DNA

Membrane formation and aggregation properties of two series of (±) α-tocopherol-based cationic gemini lipids without and with hydroxyl functionalities at the headgroup region (TnS n = 3, 4, 5, 6, 8, and 12; THnS n = 4, 5, 6, 8, and 12) with varying polymethylene spacer lengths were investigated extensively while comparing with the corresponding properties of the monomeric counterparts (TM and THM). Liposomal suspensions of each cationic lipid were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), zeta potential measurements, and small-angle X-ray diffraction studies. The length of the spacer and the presence of hydroxyl functionalities at the headgroup region strongly contribute to the aggregation behavior of these gemini lipids in water. The interaction of each tocopherol lipid with a model phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)-derived vesicles, was thoroughly examined by differential scanning calorimetry (DSC) and 1,6-diphenyl-1,3,5-hexatriene (DPH)-doped fluorescence anisotropy measurements. The binding efficiency of the cationic tocopherol liposomes with plasmid DNA (pDNA) was followed by an ethidium bromide (EB) exclusion assay and zeta potential measurements, whereas negatively charged micellar sodium dodecyl sulfate (SDS)-mediated release of the pDNA from various preformed pDNA-liposomal complexes (lipoplex) was studied by an ethidium bromide (EB) reintercalation assay. The structural transformation of pDNA upon complexation with liposome was characterized using circular dichroism (CD) spectroscopic measurements. Gemini lipid-pDNA interactions depend on both the presence of hydroxyl functionalities at the headgroups and the length of the spacer chain between the headgroups. Succinctly, we performed a detailed physical-chemical characterization of the membranes formed from cationic monomeric and gemini lipids bearing tocopherol as their hydrophobic backbone and describe the role of inserting the -OH group at the headgroup of such lipids.

Role of Different States of Solubilized Water on Solvation Dynamics and Rotational Relaxation of Coumarin 490 in Reverse Micelles of Gemini Surfactants, Water/12-s-12.2Br- (s = 5, 6, 8)/n-Propanol/Cyclohexane

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-s-12 (s = 5, 6, 8).2Br^-/n-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 (W _o) 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 W _o 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.

Stability issues and approaches to stabilised nanoparticles based drug delivery system

Nanoparticles form the fundamental building blocks for many exciting applications in various scientific disciplines due to its unique features such as large surface to mass ratio, targeting potential, ability to adsorbed and carry other compound which makes them suitable for biomedical applications. However, the problem of the large-scale synthesis of nanoparticles remains challenging due to physical instability associated with nanoparticles which lead to generation of aggregates particles with high polydispersity index (PDI) indicating low particle homogeneity and eventually loss of their special nanoscale properties. The stabilisation concept can be generated by repulsive electrostatic force, which nanoparticles experience, when they are surrounded by a double layer of electric charges. Selection of proper stabiliser will govern the stability of NPs and ultimately development of optimised drug delivery system. This review summarises mechanism of physical instability issues likely to be encountered during the development of nanoformulations. It also discusses potential stabilising agents used so far and their mechanism in achieving stable nanosystems.

An Interaction of Anionic- and Cationic-Rich Mixed Surfactants in Aqueous Medium through Physicochemical Properties at Three Different Temperatures

The mixed micellization of aqueous binary mixtures of DTAB-rich and SDS-rich surfactants, comprising sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) is studied in aqueous solution by using the physicochemical properties (PCPs) at three different temperatures (T = 293.15, 298.15, and 303.15 K) and P=0.1  MPa. The DTAB concentration is varied from 0.0001 to 0.03 M/mol·L−1 in the ∼0.01 M/mol·L−1 SDS solution, while the concentration of SDS is varied from 0.001 to 0.015 M/mol·L−1 in the ∼0.005 M/mol·L−1 DTAB. The stable formulations have been obtained by employing the DTAB-rich and SDS-rich surfactants solutions in 3 : 1 ratio. Therefore, different phases and aggregated states formed in the ternary combinations of DTAB/SDS/H2O have been identified and described. The calculated PCPs have been utilized for determining the nature of the solute-solvent interaction (SLS0I). With increasing surfactants concentration, the polarisation of the solution also increases along with an increase in relative viscosity (ηr), viscous relaxation time (τ), and surface excess concentration (Γmax). However, the surface area of the molecule (Amin), hydrodynamic volume (Vh), and hydrodynamic radius (Rh) decrease along with an increase in surfactants concentration.

Reduction Responsive Nanovesicles Derived from Novel α-Tocopheryl-Lipoic Acid Conjugates for Efficacious Drug Delivery to Sensitive and Drug Resistant Cancer Cells

Two novel α-tocopheryl-lipoic acid conjugates (TL1 and TL2) were synthesized for the anticancer drug, doxorubicin (DOX), delivery. Both conjugates were able to form stable nanovesicles. The critical aggregation concentration (CAC) was determined using 4-(N,N-dimethylamino)cinnamaldehyde (DMACA) as a fluorescence probe. Formation of highly packed nanovesicles was characterized by 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence anisotropy and microviscosity measurements. The morphologies of nanovesicles were visualized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The response of nanovesicles to reducing environment of cells was probed by the addition of dithiothreitol (DTT), which was followed by the increase in the hydrodynamic diameter under dynamic light scattering (DLS) measurements. The encapsulation efficiency of a commonly used anticancer drug, doxorubicin (DOX), in nanovesicles was found to be ∼60% and ∼55% for TL1 and TL2, respectively (TL1-DOX and TL2-DOX). Also, the cumulative drug (DOX) release from DOX-encapsulated nanovesicles in response to biological reducing agent glutathione (GSH) was ∼50% and ∼40% for TL1-DOX and TL2-DOX, respectively, over a period of 10 h. Both TL1-DOX and TL2-DOX delivered the anticancer drug, doxorubicin (DOX), across the DOX-sensitive and DOX-resistant HeLa (HeLa-DOX^R) cells in an efficient manner and significantly more efficaciously than the drug alone treatments, especially in HeLa-DOX^R cells. The nanovesicle mediated DOX treatment also showed significantly higher cell death when compared to DOX alone treatment in HeLa-DOX^R cells. Blood compatibility of the nanovesicles was supported from clotting time, hemolysis, and red blood cell (RBC) aggregation experiments for their potential in vivo applications. Concisely, we present biocompatible and responsive nanovesicles for efficacious drug delivery to drug-sensitive and drug-resistant cancer cells.

The effect of hydroxyl on the solution behavior of a quaternary ammonium gemini surfactant

The influence of the introduction of a hydroxyl group into the system is studied at the macro and micro levels.

Solvation dynamics and rotational relaxation of coumarin 153 in mixed micelles of Triton X-100 and cationic gemini surfactants: effect of composition and spacer chain length of gemini surfactants

To demonstrate simultaneously how the solvation dynamics and rotational relaxation in nonionic micelles change with the composition of a gemini surfactant and how this change depends on spacer chain length of gemini surfactants.

Effect of Polymethylene Spacer of Cationic Gemini Surfactants on Solvation Dynamics and Rotational Relaxation of Coumarin 153 in Aqueous Micelles

The present work demonstrates the solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in the micelles of a series of cationic gemini surfactants, 12-s-12, 2Br(-) containing a hydrophobic polymethylene spacer with s = 3, 4, 6, 8, 12. Steady-state and time-correlated single-photon counting (TCSPC) fluorescence spectroscopic techniques have been used to carry out this study. Steady-state and TCSPC fluorescence data suggest that C-153 molecules are located at the Stern layer of micelles. While probe molecules feel more or less the same micropolarity in the micellar phase, the microviscosity of micelles decreases with spacer chain length. Solvation dynamics at the Stern layer is bimodal in nature with fast solvation as a major component. Counter ions and water molecules bonded with the polar headgroups of surfactant molecules are responsible for the slow component. Average solvation time increases with spacer chain length because of the increased degree of counter ion dissociation. Some water molecules are involved in the solvation of counter ions themselves, resulting in the decrease in "free" water molecules to be available for the solvation of C-153. The hydrophobic spacer chain also has an effect on increasing the solvation time with increasing chain length. The average rotational relaxation time for C-153 decreases with spacer chain length with a rapid decrease at s > 4. The anisotropy decay of C-153 in micelles is biexponential in nature. The slow rotational relaxation is due to the lateral diffusion of C-153 in micelles. Lateral diffusion is much faster than the rotational motion of a micelle as a whole. The rotational motion of the micelle as a whole becomes faster with the decreasing size of micelles.

Effects of concentration, temperature and solvent composition on density and apparent molar volume of the binary mixtures of cationic-anionic surfactants in methanol-water mixed solvent media

The accurate measurements on density of the binary mixtures of cetyltrimethylammonium bromide and sodium dodecyl sulphate in pure water and in methanol(1) + water (2) mixed solvent media containing (0.10, 0.20, and 0.30) volume fractions of methanol at 308.15, 318.15, and 323.15 K are reported. The concentrations are varied from (0.03 to 0.12) mol.l^-1 of sodium dodecyl sulphate in presence of ~ 5.0×10^-4 mol.l^-1 cetyltrimethylammonium bromide. The results showed almost increase in the densities with increasing surfactant mixture concentration, also the densities are found to decrease with increasing temperature over the entire concentration range, investigated in a given mixed solvent medium and these values are found to decrease with increasing methanol content in the solvent composition. The concentration dependence of the apparent molar volumes appear to be negligible over the entire concentration range, investigated in a given mixed solvent medium and the apparent molar volumes increase with increasing temperature and are found to decrease with increasing methanol content in the solvent composition.