pH-Induced Biophysical Perspectives of Binding of Surface-Active Ionic Liquid [BMIM][OSU] with HSA and Dynamics of the Formed Complex.

The influence of pH on the human serum albumin (HSA) interaction with ionic liquid (IL)1-butyl 3-methylimidazolium octyl sulfate ([BMIM][OSU]) at its sub-micellar concentration of 5 mM (well below CMC ∼31 mM at 25 °C) in aqueous solution has been monitored employing different methods, viz., circular dichroism (CD), fluorescence, electrokinetic determination of the zeta potential (ZP), nuclear magnetic resonance (NMR), small-angle neutron scattering (SANS), and molecular docking (MD). CD analysis indicated a noticeable reduction of the α-helical content of HSA by IL at pH 3. A significant interaction of the anionic part of IL with HSA was evident from the 1H chemical shifts and saturation transfer difference (STD) NMR. A strong binding between IL and HSA was observed at pH 3 relative to pH 5, revealing the importance of electrostatic and hydrophobic interactions assessed from global binding affinities and molecular correlation times derived from STD NMR and a combined selective/nonselective spin-relaxation analysis, respectively. ZP data supported the electrostatic interaction between HSA and the anionic part of IL. The nature of IL self-diffusion with HSA was assessed from the translational self-diffusion coefficients by pulse field gradient NMR. SANS results revealed the formation of prolate ellipsoidal geometry of the IL-HSA complex. MD identified the preferential binding sites of IL to the tryptophan centers on HSA. The association of IL with HSA was supported by fluorescence measurements, in addition to the structural changes that occurred in the protein by the interaction with IL. The anionic part of IL contributed a major interaction with HSA at the pH levels of study (3, 5, 8, and 11.4); at pH > 8 (effectively 11.4), the protein also interacted weakly with the cationic component of IL.

Radiofrequency and Near-Infrared Responsive Core-Shell Nanostructures Using Layersome Templates for Cancer Treatment.

We report a multifunctional nanotherapeutic platform based on liposomes loaded with drug and iron oxide nanoparticles (IONs) coated with a gold nanoshell synthesized using a polyelectrolyte (layersome) soft templating technique. IONs and gold nanoshells were used to provide combined hyperthermia and triggered drug release via radio frequency (RF) or near-infrared (NIR) stimulation. IONs and the anticancer drug doxorubicin (DOX) were coencapsulated inside liposomes composed of zwitterionic phosphatidylcholine, anionic phosphatidylglycerol, and cholesterol lipids. Coating the magneto-liposomes with positively charged poly-l-lysine enriched the interface with gold anions to form a dense gold nanoshell and protected the structure against deformation and DOX cargo release during shell formation. After modification with thiol-terminated polyethylene glycol, intracellular delivery and release of DOX from the nanostructures was examined in A549 human lung cancer cells. The nanostructures retained their DOX cargo and remained in the cytosol after cellular uptake. Only when triggered by RF or NIR stimuli did the nanostructures release DOX, which then entered the cell nucleus. Compared to the single photothermal therapy or radio frequency treatment, the carriers with combined DOX and RF or NIR stimulation displayed higher therapeutic effect on A549 cells.

Ionic liquid mediated micelle to vesicle transition of a cationic gemini surfactant: a spectroscopic investigation.

In this contribution, we have examined a composition dependent self aggregated structural modification of a catanionic mixture of the surface active ionic liquid (IL) 1-butyl-3-methylimidazolium octyl sulphate and a cationic gemini surfactant (14-5-14) in aqueous medium. We have observed that the hydrodynamic diameter of the aggregates increases with increasing IL concentration and microscopic evidence (HRTEM, FESEM, and LCSM) shows the formation of vesicle like aggregates (Dh ≈ 200 nm) at XIL = 0.5. The steady state fluorescence anisotropy of the membrane binding probe DPH shows a micelle to vesicle transition at this composition. The viscosity of the solution shows a peak at XIL = 0.3, indicating the formation of a worm like micelle as an intermediate of the micelle to vesicle transition. The rotational dynamics shows a stiffer surfactant packing in the vesicles compared to the micelles, whereas, the solvation dynamics measurements indicate a higher abundance of bound type water in the vascular medium compared to that for the micelle. The formed vesicles also show stability towards temperature and biomolecules, which can be used for respective applications.

Unveiling the pH dependent interaction between bolaamphiphiles (dicarboxylic acids) and C10TAB (decyltrimethylammonium bromide) in aqueous medium.

Development of stable self-assembled nanostructures (especially vesicles and liposomes), and understanding their physicochemical behaviors in aqueous solution is a long-standing topic of interest in chemical and biochemical research. In this progressive area, we report for the first-time formation of mixed micelles (at pH 12), and vesicles of anionic bolaamphiphiles (dicarboxylic acids viz. [Formula: see text] , with moderate values of n 10, 11, 12, and 14) in combination with a cationic surfactant decyltrimethylammonium bromide (C10TAB) in buffered aqueous medium at different pH (6.0, 6.5, 6.8, and 8.0 for bola 10, 11, 12, and 14, respectively). Three pH dependent states of the solutions are observed: clear (high pH > 8), turbid and translucent (mid pH ≈ 6-8), and viscous inhomogeneous oil-like state (low pH < 6). The micelle size varies from 6.24 to 7.43 nm at pH 12, for vesicles the values are large (220-296 nm), and small (∼30-70 nm) in the pH range of 6.0-8.0. The self-assembly formation properties of their mixtures are herein investigated using different techniques viz. UV-vis spectroscopy, fluorescence spectroscopy, dynamic light scattering, laser confocal scanning microscopy, and isothermal titration calorimetry. The formed vesicles are fairly polydisperse, and show overall spherical shape. Formation of the bilayer assemblies, and their conversion to mixed micelles by the temperature effect are observed from steady state fluorescence anisotropy measurements. Micellization of the mixed bola-C10TAB species is endothermic and fairly entropy controlled; their formation/deformation is pH sensitive. They have spherical morphologies, and once formed at the right pH they are found to be very stable in terms of time. Thus, these vesicles have prospects for encapsulation and delivery of materials like drugs, and other substrates by controling the acid-base conditions of the system environment. The formed mixed micelles, and vesicles are expected to be low toxic, and thus green materials in nature with wider application possibilites.

Physicochemical Understanding of Self-Aggregation and Microstructure of a Surface-Active Ionic Liquid [C4mim] [C8OSO3] Mixed with a Reverse Pluronic 10R5 (PO8EO22PO8).

Physicochemical studies on aqueous mixtures of ionic liquids (ILs) and reverse pluronics are limited. Self-aggregation dynamics and microstructure of a surface-active IL (SAIL), 1-butyl-3-methylimidazolium octylsulfate [C4mim] [C8OSO3], in the presence of a reverse pluronic, PO8EO22PO8 (known as 10R5), were studied using isothermal titration calorimetry (ITC), high-resolution nuclear magnetic resonance (NMR), and small-angle neutron scattering (SANS) methods. Also, cryo-/freeze-fracture transmission electron microscopy was employed to determine the microstructures of SAIL/10R5 mixtures. The ITC and NMR results revealed facilitation of SAIL aggregation in the presence of 10R5 forming mixed aggregates as well as free SAIL micelles. 2H spin relaxation rate data pointed out the onset of slow dynamics of the aqueous SAIL/10R5 mixture with an increase in either the former or the latter. Globular morphologies of the mixed species as well as their individual components were corroborated from the measurements. The preferential location of interaction of the SAIL with the 10R5 was identified from 13C NMR chemical shift findings to be in the interfacial region of the assembled SAIL. The formed species were mixed interacted aggregates but not mixed micelles that arise from mixed surfactants. The physicochemical information acquired herein would enrich the literature on the 10R5/SAIL mixed microheterogeneous systems having importance in the making of useful green drug carrier systems and templates for the synthesis of nanomaterials.

Enthalpy-Entropy Compensation (EEC) Effect: Decisive Role of Free Energy.

The "enthalpy-entropy compensation" (EEC) effect has been a long-standing fascinating yet unresolved phenomenon in chemical thermodynamics. The reasons for the observation of EEC are not clear. Various views such as empirical, extrathermodynamic, error-related, solvation, and so forth as reasons for the H/S linear correlation are floating. Statistical reasons and a hidden Carnot's cycle (involving microscopic "heating and cooling" machines) have also been proposed recently for the observation of EEC. In this work, we have attempted a different line of approach to understand and explain the phenomenon. In the EEC treatment, the enthalpy (ΔH) and entropy (ΔS) values of "similar processes" are considered keeping aside the role of the other important thermodynamic parameter, that is, the free energy (ΔG). Considering ΔG along with ΔH and ΔS, it is established that the conventional EEC plot is not appropriate and mathematically sound. Consideration of ΔG may account for correlations of different kinds, linear, nonlinear, and so forth. Reports of non- or anticompensation phenomenon also prevail in the literature. A realistic account of the role of ΔG along with ΔH and ΔS in the understanding of such EEC correlations using authentic literature data is presented and discussed herein. EEC has several facets. Planned studies on similar systems with a wide range of ΔG values are required for realistic evaluation of the EEC and antienthalpy entropy compensation manifestations.

Enthalpy-Entropy Compensation (EEC) Effect: A Revisit.

A short account of the developments and perspectives of IKR (iso-kinetic relation) and EEC (enthalpy (H) - entropy (S) compensation) has been presented. The IKR and EEC are known to be extra thermodynamic or empirical correlations though linear H-S correlation can be thermodynamically deduced. Attempt has also been made to explain the phenomena in terms of statistical thermodynamics. In this study, we have briefly revisited the fundamentals of both IKR and EEC from kinetic and thermodynamic grounds. A detailed revisit of the EEC phenomenon on varied kinetic and equilibrium processes has been also presented. Possible correlations among the free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes of different similar and nonsimilar chemical processes under varied conditions have been discussed with possible future projections.

Micellization of cetyltrimethylammonium bromide: effect of small chain Bola electrolytes.

Sodium dicarboxylates (or Bola salts) with methylene spacers 0, 2, 4, 6, 8, and 10 were studied in aqueous solution to investigate their influence on the micellization of cetyltrimethylammonium bromide (CTAB). Since bolas with spacer length ≤12 are known not to micellize in general, the herein used sodium dicarboxylates were treated as 2:1 amphiphilic electrolytes which reduced surface tension of water (except sodium oxalate with zero spacer) without self-association. Their concentration dependent conductance was also linear without breaks. The bolas affected the micellization of CTAB but acted like salts to decrease its CMC. Their combinations did not form bilayer aggregates as found in vesicles. Nevertheless, they synergistically interacted with CTAB at the air/water interface as revealed from Rosen's thermodynamic model. Hydrodynamic radius (Rh), Zeta-potential (ζ), and electrical double layer behavior of bola interacted CTAB micelles were assessed. From SANS measurements, micelle shape, shape parameters, aggregation number (Nagg), surface charge of the bola influenced CTAB micelles were also determined. NMR study as well supported the non-mixing of bolas with the CTAB micelles. They interacted in solution like "amphiphilic electrolytes" to influence the surface and micelle forming properties of CTAB.

Self-aggregation of MEGA-9 (N-nonanoyl-N-methyl-D-glucamine) in aqueous medium: physicochemistry of interfacial and solution behaviors with special reference to formation energetics and micelle microenvironment.

Self-aggregation of MEGA-9 (N-nonanoyl-N-methyl-D-glucamine), a nonionic sugar-based surfactant, was studied with respect to the effect of salt (NaCl) and ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) on its critical micelle concentration (cmc), aggregation number, hydrodynamic dimensions, energetics of micellization, and micellar microenvironment. Fluorimetry (both steady state and time resolved) was used to understand the microenvironments under the influence of additives. NaCl was found to decrease cmc, increase aggregation number (N), increase micellar size, and decrease enthalpy of micelle formation; the IL effect on the parameters was mostly opposite. The microscopic properties of micelles were probed using two fluorophores: one nonpolar C-153 (2,3,5,6-1H,4H-tetrahydro-8-trifluormethylquinolizino-(9,9a,1-gh)coumarin) and the other fairly polar ANS (8-anilinonaphthalene-1-sulfonate); they delivered information on the palisade layer and the peripheral region of the micelle interface, respectively. Energy of activation and entropy of activation of the dynamics of the probes were evaluated from their decay time, lifetime, and rotational movements in the regions of residency in the micelles. Density functional theory (DFT) calculations showed that the ternary combination MEGA-9/IL/H2O had the maximum interaction energy compared to any of the binary combinations. Thus, the ionic liquid reduced MEGA-9 self-association to a large extent.

Types of interaction of meso-tetraphenylporphyrin with alkali and alkaline-earth metal ions.

The cavity in a porphyrin can accommodate metal ions through electron donor-acceptor (EDA) interaction in acetonitrile media without any specially designed fabrication with the porphyrin subunit. Alkali metal ion forms a complex with meso-tetraphenylporphyrin (TP) in 2:1 stoichiometry, while the bivalent Mg(2+) ion follows a 1:1 stoichiometry. A fluorescence interaction study indicated that TP can behave like a chemosensor for these ions present in the blood electrolytes. Specifically, for the alkali metal ions intensity-based sensing was observed, due to inhibition of photoinduced electron transfer (PET), entailing enhancement of fluorescence intensity, and for the alkaline-earth Mg(2+) a mixed quenching was observed. Na(+) and K(+) ions can be differentiated depending upon the extent of fluorescence enhancement.