Herein, we report the aggregation behavior of catanionic mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in solution and at the air/water interface obtained by the Langmuir-Blodgett (LB) technique. We employed Fourier transform infrared spectroscopy, in situ phase-contrast inverted microscopy, scanning electron microscopy, and atomic force microscopy to characterize the systems in solution, at the air/water interface, and in LB films. We found spherical vesicles at the SDS/CTAB ratio of 35/65 in aqueous solution and an ordered aggregated morphology called surface micelles at SDS/CTAB ratios of 35/65 to 65/35 at the air/water interface. Other mixtures (SDS/CTAB = 90/10, 10/90) were found to contain mostly disordered aggregated microstructures. An in situ time-dependent study of surface micelle formation at the air/water interface showed micelle ripening through the fusion of smaller micelles. These micelles were successfully immobilized on a glass substrate by the LB technique. Overall, the study might find application in the fundamental science of the physical chemistry of surfactant systems, as well as in the preparation of drug delivery system.
Here we report the fibrillation of egg white ovalbumin (OVA) induced by the biomineralization of two alkali halides (KCl, NaCl) in the Langmuir-Blodgett (LB) film of OVA. The pressure-area isotherm of OVA shows the salt-induced increment of apparent area/monomer of OVA. Fibrillation of OVA in the LB film is monitored by FE-SEM imaging. Formation of fibrillar aggregates is concomitant with an increase of salt concentration. HR-TEM and EDX measurements allowed us to identify nanostructured crystals of salt, which are associated with this fibrillar structure. FTIR spectroscopic study of the amide band in LB films as well as CD spectroscopy in solution qualitatively indicates the increase in β-sheet to α-helix ratio in the presence of salt, indicating unfolding of protein. We suggest that the ion attachment to the peptide chain leads to unfolding and that subsequent recrystallization in the transferred monolayer leads to fibrillation of protein as well as biomineralization of alkali halide salts. This finding demonstrates that the fibrillation of OVA is induced by the biomineralization of alkali halides.
The interaction between a protein/enzyme and a lipid is critical for pharmacological activity. Here, we study the interaction between insulin and the 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) lipid anionic vesicle by successfully entrapping the insulin molecule into DPPG vesicles, which are biocompatible liposomes. For the insulin-DPPG complex system, steady state emission spectroscopy at room temperature (300 K) shows a new broad and structured peak between 400 nm and 500 nm along with the tyrosine fluorescence peak at 303 nm. Temperature dependent and time resolved spectroscopy reveal that the peak between 400 nm and 500 nm in the insulin-DPPG system arises due to the tyrosine phosphorescence phenomenon. This phosphorescence peak is the signature of insulin entrapment into the liposome. A molecular dynamics study of the tyrosine-DPPG system shows that the rigidity of tyrosine increases in the lipid layer. Dynamic light scattering (DLS), and zeta potential studies also establish the attachment of insulin with the anionic liposome.
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