Optical Spectroscopic and TEM Studies of Catanionic Micelles of CTAB/SDS and Their Interaction with a NSAID

Abstract

If a vesicle is a better model of a membrane in the context of the hydrophobic effect, then from the charge distribution point of view, a catanionic micelle is a closer model to a biomembrane. We have prepared and characterized two different types of catanionic micelles of sodium dodecyl sulfate (SDS) and cetyl N,N,N-trimethylammonium bromide (CTAB) having different surface charge ratios using optical spectroscopy and transmission electron microscopy. The average size of both types of mixed micelles was found to be much larger than that of micelles containing uniformly charged headgroups. Catanionic micelles containing higher concentrations of positively charged headgroups (CTAB) are larger in size, less compact, and more polar compared to the micelles containing higher concentrations of negatively charged headgroups (SDS). We have used these catanionic micelles as membrane mimetic systems to understand the interaction of piroxicam, a nonsteroidal anti-inflammatory drug (NSAID) of the oxicam group, with biomembranes. In continuation of our work on membrane mimetic systems, we have used spectral properties of the drug itself to understand the effect of the presence of mixed charges on the micellar surface in guiding the interaction of catanionic micelles with piroxicam. Our earlier studies of the interaction of piroxicam with micelles having uniform surface charges have shown that the charge on the micellar surface not only dictates which prototropic form of the drug will be incorporated in the micelles but also induces a switch-over between different prototropic forms of piroxicam. The equilibrium of this switch-over is extremely sensitive to the environment. In this study, we demonstrate how even small changes in the electrostatic forces obtained by doping the uniformly charged surface of the micelles with oppositely charged headgroups (as in catanionic micelles) are capable of fine-tuning this equilibrium. This implies that the surface charge of biomembranes, which are quite diverse in vivo, might play a significant role in selecting a particular form of the drug to be presented to its targets.

The Viscous Properties of Anionic/Cationic and Cationic/Nonionic Mixed Surfactant Systems

“…2 with a straight line. These results are consistent with Chakraborty and Sarkar study [20]. The dependences of relative viscosity on the mole fraction of CTAB in CTAB-Brij mixed systems are shown in Fig.…”

“…In both cases, the doping with surfactants having oppositely charged headgroups reduces headgroup repulsion and thereby promotes aggregate growth. The increase of viscosity is consistent with Chakraborty and Sarkar study [20]. They have reported that average size of both types of mixed micelles (SDS rich and CTAB rich) is much larger than that of micelles containing more uniformly charged headgroups.…”

“…In recent years there have been many papers aimed at the study of the phase behavior of cationic and anionic surfactant mixtures [17][18][19]. Cationic and anionic mixed micelles with different surface charge have been studied by Chakraborty and Sarkar [20] using optical spectroscopy and transmission electron microscopy. Schubert et al [21] treated cationic/anionic surfactant mixtures as wormlike micelles with electrostatic interaction.…”

Interaction of oxicam NSAIDs with DMPC vesicles: differential partitioning of drugs

“…Additionally, surface charge also induces a switch over between prototropic forms like global neutral and anionic forms of piroxicam. Even small changes in the surface charges obtained by doping a small amount of opposite charges on the surface of the micelles (as in case of mixed micellar systems) were capable of fine tuning the equilibrium of this switch over or conversion (Chakraborty and Sarkar, 2004). It was also found that none of the different structural forms of the drugs interacted with neutral micelles formed either by Triton X-100 and Tween 40 separately (Chakraborty et al, 2003).…”

Low‐Temperature Synthesis of Star‐Shaped PbS Nanocrystals in Aqueous Solutions of Mixed Cationic/Anionic Surfactants

“…We tentatively suggest that mixed CTAB/ SDS micelles in the reaction solution at 80°C may directly participate in the shape-controlled synthesis of PbS nanostars, since mixed micelles are generally the predominant structures in clear solutions of CTAB/SDS mixtures at mixing ratios far away from 1:1. [14] It has been documented that in mixed CTAB/SDS solutions, relatively larger catanionic vesicles and surfactant salts rather than mixed micelles tend to form at the equimolar mixing ratio (CTAB/SDS = 1:1). [15] Therefore, in the equimolar CTAB/SDS solution, a wide variety of microstructures possibly coexist, especially at the early stage of the reaction when the solution is heated to 80°C.…”