Micellization behavior of cationic surfactant dodecyldimethylethylammonium bromide (DDAB) in the presence of papain

Application of Flue Gas Foam-Assisted Steam Flooding in Complex and Difficult-to-Produce Heavy Oil Reservoirs

In order to study the mechanism of improving recovery efficiency of complex difficult-to-recover heavy oil reservoirs and explain the interaction and migration law of flue gas, foam, and steam, this paper designed the experiment of flue gas influence on heavy oil flow and the experiment of flue gas foam displacement in complex difficult-to-recover heavy oil model. The results show that the flue gas has expansion and an energy enhancement effect. Moreover, the interfacial tension of heavy oil can be reduced, and the higher the CO2 content in flue gas, the more beneficial it is to reduce the interfacial tension. When there is an interlayer in the reservoir, the gas can form a "puncture" in the interlayer, which provides a channel for the subsequent upward expansion of steam, so that the upper part of the interlayer can be used to expand the steam sweep range. The main mechanism of improving heavy oil recovery with flue gas foam is that the foam regulates fluid mobility and improves the thermal sweep efficiency of steam. In addition, the injected foam can emulsify with heavy oil, reduce the viscosity of heavy oil, and improve the fluidity of heavy oil. Finally, the maximum oil production rate increased from 1.809 to 2.455 g/min, and the recovery rate increased from 44.3 to 68.8%.

Effect of Electrolytes on Solution and Interfacial Behaviors of Double Chain Cationic-Nonionic Surfactant Mixtures for Hydrophobic Surface Wetting and Oil/Water Emulsion Stability Applications

The solution behaviors of the binary mixture of double chain cationic surfactant didodecyldimethylammonium bromide (DDAB) with nonionic surfactants of varied head groups, EO-9 and EO-40, in the presence and absence of electrolytes were studied and found nonideal behavior. The different physicochemical properties such as Gibb's surface excess (Γ), minimum area per molecule (A_min), and interaction parameters at bulk (β^M) and interface (β^σ) were calculated. In the presence of nonionic surfactants, lowering of CMC, CVC, and surface tension at these two concentrations of DDAB were observed. The β^M and β^σ values indicate strong interaction between DDAB and EO-40 mixed system. Further, addition of electrolytes to the mixed systems show increased interaction and change of physicochemical properties because of the combination of electrical and salting out effects.

Enhanced Cellular Uptake and Gene Silencing Activity of Survivin-siRNA via Ultrasound-Mediated Nanobubbles in Lung Cancer Cells

PURPOSE

Paclitaxel is a first-line drug for the therapy of lung cancer, however, drug resistance is a serious limiting factor, related to overexpression of anti-apoptotic proteins like survivin. To overcome this phenomenon, developing novel ultrasound responsive nanobubbles - nanosized drug delivery system- for the delivery of paclitaxel and siRNA in order to silence survivin expression in the presence of ultrasound was aimed.

METHODS

Paclitaxel-carrying nanobubble formulation was obtained by modifying the multistep method. Then, the complex formation of the nanobubbles - paclitaxel formulation with survivin-siRNA, was examined in terms of particle size, polydispersity index, zeta potential, and morphology. Furthermore, siRNA binding and protecting ability, cytotoxicity, cellular uptake, gene silencing, and induction of apoptosis studies were investigated in terms of lung cancer cells.

RESULTS

Developed nanobubbles have particle sizes of 218.9-369.6 nm, zeta potentials of 27-34 mV, were able to protect siRNA from degradation and delivered siRNA into the lung cancer cells. Survivin expression was significantly lower compared with the control groups and enhanced apoptosis was induced by the co-delivery of survivin-siRNA and paclitaxel. Furthermore, significantly higher effects were obtained in the presence of ultrasound induction.

CONCLUSION

The ultrasound responsive nanobubble system carrying paclitaxel and survivin-siRNA is a promising and effective approach against lung cancer cells.

Investigation of binding interactions between BSA and [EPMpyr][Sal] through spectroscopy studies, thermophysical and thermodynamic properties

The intensity of research, probing the interactions between proteins and ionic liquid (IL), has been increasing and parallels the fast-growing applications of ILs in biotechnology. The specific aspects which have attracted the involvement of researchers are stabilization, separation, biochemical and enzymatic reactions of proteins. In this work the synthesis of IL, epoxypropyl and N-methyl substituted 2‑oxopyrrolidinium cation with salicylate anion, [EPMpyr][Sal], and its interaction with aqueous BSA{BSA_(aq)-[EPMpyr][Sal]}. Measurements of thermophysical properties (density (ρ), and speed of sound (u)) showed that both moderately strong and weak interactions occur on treatment of BSA with that chosen IL. H-bond formation, dipole-dipole interactions and ionic interactions occurring in this system were investigated via thermophysical and thermodynamic properties as well as spectroscopic data. Thermodynamic data (excess molar volume (V_m^E), isentropic compressibility (k_s), deviation in isentropic compressibility (∆k_s) and intermolecular free length (L_f)) showed that there were stronger interaction between IL and BSA at higher temperature. The data from all the studies were correlated with Redlich Kister polynomial equation. The blue shift observed in the fluorescent spectra was interpreted to indicate that thetryptophan (Trp) residue of BSA moves to a more hydrophobic environment. It was also observed that the addition of more IL to BSA resulted in denaturation of BSA due to high hydrophobic nature of IL. Circular dichroism studies show that there were significant changes in the fine structure of BSA on interaction with IL. From the FTIR spectra the position of H-bond in the secondary structure of BSA was deduced.

Behavior of papain in mixed micelles of anionic-cationic surfactants having similar tails and dissimilar head groups

The mixed micellar behavior of anionic surfactant, sodium dodecylsulfate (SDS) and cationic surfactant, dodecylethyldimethylammonium bromide (DDAB) at varying mole fractions of DDAB, i.e. alpha(DDAB) in aqueous solution of papain has been investigated with the aid of spectroscopy and physiochemical measurements. Thermodynamic parameters have been computed over the entire mole fraction range of DDAB. The Clint equation and the regular approximation method have been used to investigate the interactions between mixed surfactants in the presence of protein. The two surfactants have similar tails, however, the charges on respective polar head groups are expected to have significant effect on their colloidal behavior. The cmc values of mixed surfactants have been estimated from fluorescence, conductivity, surface tension, ultrasonic speed and density measurements. The results show that lower and higher mole fractions of DDAB give negative departure from ideality whereas intermediate mole fractions have positive deviation. The aggregation number, N(agg) of mixed micelles has also been calculated. The turbidity or cloudiness at intermediate mole fractions demonstrates a reduction in the background free monomer concentration due to neutralization of the monomers of opposite charge. The effect of concentration of papain on mixed micellar behavior indicates that with increase in the concentration of protein, the cac and cmc values increase. The unfolding of polypeptide chain in the presence of mixed surfactant has been observed.