Studies on Hydrophobic Effect and Micelle Formation of Some Surfactant-Cr(III)-Cetylamine Complexes in Non-aqueous Solvents

Effect of Hydrophobicity and Salt on the Temperature Responsiveness of Polymeric Micelles Consisting of Hydrophobic and Sulfobetaine Chains

The effect of the hydrophobicity of the core part and salt on the temperature responsiveness of polymeric micelles composed of sulfobetaine and hydrophobic blocks was investigated. Poly(sulfopropyl dimethylammonium propylacrylamide) (PSPP) was used as the sulfobetaine; poly(2-ethylhexyl acrylate) (PEHA), poly(n-butyl acrylate) (PnBA), poly(ethyl acrylate) (PEA), or poly(n-hexyl acrylate) (PnHA) was used as the hydrophobic polymer. Measurement of the transmittance revealed that the transition temperature of the sulfobetaine homopolymer could be controlled by adjusting the concentration, the degree of polymerization (DP), and the concentration of the added salt. The effect of the anionic species of the added salt due to the chemical structural properties of the sulfobetaine chain was consistent with the order of ionic species with strong structural destruction in the Hofmeister series. The temperature response and micelle formation behavior of the polymeric micelles according to the hydrophobicity of the core part and the preparation method were examined by static light scattering (SLS), fluorescence measurement with pyrene, dynamic light scattering (DLS), transmittance, and atomic force microscopy (AFM). Micelles that had EHA (solubility in water was 0.01 g/100 mL) as the core and did not show temperature responsiveness expressed temperature responsiveness at a lower hydrophobicity (solubility of nBA in water was 0.14 g/100 mL). nBA-b-SPP did not show temperature responsiveness due to the block ratio. However, when micelles were prepared by dialysis, smaller and more stable micelles could be formed in an equilibrium state, and temperature responsiveness was observed. Their transition temperature can be controlled by adjusting the ratio of the sulfobetaine blocks, the hydrophobicity of the core part, the concentration of the polymer aqueous solution, and the concentration of the added salt. Furthermore, like the sulfobetaine homopolymer, the effect depended on the anionic species of the added salt.

Furosemide–Cetyltrimethylammonium Bromide Interactions in Aqueous Dimethylsulfoxide Solutions: Physico–Chemical Studies

Interaction of a cardiovascular drug, Furosemide with cetyltrimethylammonium bromide (CTAB) has been studied in aqueous solutions of Dimethylsulfoxide (DMSO) with the help of density, speed of sound and conductivity measurements over a range of temperatures 293.15–313.15 K at interval of 5 K. The interaction parameters viz. apparent molar volume, Vϕ and apparent molar isentropic compression, κs , ϕ have been enumerated from density and speed of sound data. Also, variation in the micellization behavior has been explored by calculating critical micelle concentration, CMC. It has been observed that micellization tendency of the surfactant decreases in the presence of DMSO as compared to pure aqueous system. Moreover, the CMC values shift toward lower concentration with increase in Furosemide content because of increase in hydrophobic hydration which may be to hydrophobicity of drug molecule. The dependence of CMC in mole fraction (Xcmc ) values on the temperature has been analyzed in terms of thermodynamics of the system by reporting the standard thermodynamic parameters i.e. standard Gibb’s free energy ( Δ G m o ) , $(\Delta G_m^o),$ enthalpy ( Δ H m o ) $(\Delta H_m^o)$ and entropy ( Δ S m o ) $(\Delta S_m^o)$ of micellization for CTAB in mixed solvent systems. The entropies of micellization are all positive, and they compensate the enthalpies of the process. Compensation temperature, Tc has also been evaluated from enthalpy–entropy compensation whose values lies in Lumrys range (270–300 K).

Methyl groups of trimethylamine N-oxide orient away from hydrophobic interfaces

The molecular orientation of trimethylamine N-oxide (TMAO), a powerful protein stabilizer, was explored at aqueous/hydrophobic interfaces using vibrational sum frequency spectroscopy (VSFS). The systems studied included the octadecyltrichlorosilane (OTS)/water interface, which represents an aqueous solution in direct contact with a hydrophobic medium. Surprisingly, the measurements revealed that the methyl groups of TMAO pointed into the aqueous phase and away from the OTS. This orientation may arise from the more hydrophilic nature of methyl groups attached to a strongly electron-withdrawing atom such as a quaternary nitrogen. Additional studies were performed at the air/water interface. This interface showed a high degree of TMAO alignment, but the dangling OH from water was present even at 5 M TAMO. Moreover, the addition of this osmolyte modestly increased the surface tension of the interface. This meant that this species was somewhat depleted at the interface compared to the bulk solution. These findings may have implications for the stabilizing effect of TMAO on proteins. Specifically, the strong hydration required for the methyl groups as well as the oxide moiety should be responsible for the osmolyte's depletion from hydrophobic/aqueous interfaces. Such depletion effects should help stabilize proteins in their folded and native conformations on entropic grounds, although orientational effects may play an additional role.