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.

Interaction between sodium dodecylsulfate (SDS) and pluronic L61 in aqueous medium: assessment of the nature and morphology of the formed mixed aggregates by NMR, EPR, SANS and FF-TEM measurements

The interaction of copolymer L61 i.e., (EO)2(PO)32(EO)2 (where EO and PO are ethylene and propylene oxides, respectively) with surfactant SDS (sodium dodecylsulfate) in relation to their self-aggregation, dynamics and microstructures has been physicochemically studied in detail employing the Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), Small-Angle Neutron Scattering (SANS), and Freeze-Fracture Transmission Electron Microscopy (FF-TEM) methods. The NMR self-diffusion study indicated a synergistic interaction between SDS and L61 forming L61-SDS mixed complex aggregates, and deuterium (2H) NMR pointed out the nonspherical nature of these aggregates with increasing [L61]. EPR spectral analysis of the motional parameters of 5-doxyl steraric acid (5-DSA) as a spin probe provided information on the microviscosity of the local environment of the L61-SDS complex aggregates. SANS probed the geometrical aspects of the SDS-L61 assemblies as a function of both [L61] and [SDS]. Progressive evolution of the mixed-aggregate geometries from globular to prolate ellipsoids with axial ratios ranging from 2 to 10 with increasing [L61] was found. Such morphological changes were further corroborated with the results of 2H NMR and FF-TEM measurements. The strategy of the measurements, and data analysis for a concerted conclusion have been presented.

Effects of secondary carbon supplement on biofilm-mediated biodegradation of naphthalene by mutated naphthalene 1, 2-dioxygenase encoded by Pseudomonas putida strain KD9

Polycyclic aromatic hydrocarbons (PAHs) belong to a diverse group of environmental pollutants distributed ubiquitously in the environment. The carcinogenic properties of PAHs are the main causes of harm to human health. The green technology, biodegradation have become convenient options to address the environmental pollution. In this study, we analyzed the biodegradation potential of naphthalene with secondary carbon supplements (SCSs) in carbon deficient media (CSM) by Pseudomonas putida strain KD9 isolated from oil refinerary waste. The rigid-flexible molecular docking method revealed that the mutated naphthalene 1,2-dioxygenase had lower affinity for naphthalene than that found in wild type strain. Moreover, analytical methods (HPLC, qRT-PCR) and soft agar chemotaxis suggest sucrose (0.5 wt%) to be the best chemo-attractant and it unequivocally caused enhanced biodegradation of naphthalene (500 mg L^-1) in both biofilm-mediated and shake-flask biodegradation methods. In addition, the morphological analysis detected from microscopy clearly showed KD9 to change its size and shape (rod to pointed) during biodegradation of naphthalene in CSM as sole source of carbon and energy. The forward versus side light scatter plot of the singlet cells obtained from flow cytometry suggests smaller cell size in CSM and lower florescence intensity of the total DNA content of cells. This study concludes that sucrose may be used as potential bio-stimulation agent.

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.

Understanding the effect of size and shape of gold nanomaterials on nanometal surface energy transfer

Gold Nanomaterials (GNMs) interact with fluorophores via electromagnetic coupling under excitation. In this particular work we carried out (to the best of our knowledge for the first time) a comprehensive study of systematic quenching of a blue emitter 2-Anthracene Sulfonate (2-AS) in the presence of gold nanoparticles of different size and shape. We synthesized gold nanomaterials of four different dimensions [nanoparticle (0D), nanorod (1D), nanotriangle (2D) and nanobipyramids (3D)] and realized the underlying effect on the emitting dipole in terms of steady and time resolved fluorescence. Nanometal Surface Energy Transfer (NSET) has already been proved to be the best long range spectroscopic ruler so far. Many attempts have been made to understand the interaction between a fluorescent molecule and gold nanomaterials. But not a single model can interpret alone the interaction phenomena. We have opted three different models to compare the experimental and theoretical data. Due to the presence of size dependent absorptivity and dielectric function, modified CPS-Kuhn model was proved to be the worthiest to comprehend variance of behavior of an emitting dipole in close proximity to nanometal surface by coupling with the image dipole of gold nanomaterials.

Internal charge transfer based ratiometric interaction of anionic surfactant with calf thymus DNA bound cationic surfactant: Study I

Cetyl trimethyl ammonium bromide (CTAB) binds calf thymus (ct-) DNA like anionic biopolymers electrostatically and established equilibrium both in the ground as well as in excited state in aqueous medium at pH 7. Anionic sodium dodecyl sulfate (SDS) does not show even hydrophobic interaction with ct-DNA at low concentration. On contrary, SDS can establish well defined equilibrium with DNA bound CTAB in ground state where the same CTAB-DNA isosbestic point reappears. First report of internal charge transfer (ICT) based binding of CTAB with ct-DNA as well as ICT based interaction of anionic SDS with DNA bound CTAB that shows dynamic quenching contribution also. The reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB by SDS.

Micellization and adsorption behaviour of bile salt systems

Variation of enthalpy change with concentration of binary bile salt mixture.

The cholesterol aided micelle to vesicle transition of a cationic gemini surfactant (14-4-14) in aqueous medium

Cholesterol aided micelle to vesicle transition of cationic gemini surfactant (14-4-14) in solution has been investigated.

Micellization and related behavior of sodium dodecylsulfate in mixed binary solvent media of tetrahydrofuran (Tf) and formamide (Fa) with water: a detailed physicochemical investigation

The detailed aggregation behavior of sodiumdodecyl sulfate (SDS) in tetrahydrofuran (Tf)-water (W) and formamide (Fa)-water (W) media at varied volume percent compositions has been investigated. Surface tension (ST), conductance (Cond), viscosity (Visc), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) were used in this study. The presence of nonaqueous solvents affected the critical micelle concentration (CMC) of SDS, the counter-ion binding of the micelle, the energetics of the air/water interfacial adsorption and micellization of the amphiphiles in the bulk, the ion-association (ion-pair, triple-ion, quadruple, etc. between Na(+) and DS(-) ions) as well as the weakly soluble (aggregation less) amphiphile solution. Tf has been observed to produce a "dead zone" or "non-micelle formation zone" in the mixed Tf-W domain of 10-40 vol%. Fa influenced the SDS aggregation up to 70 vol%, at higher proportions (below the Krafft temperature (K(T))), instead of the micelle, "randomly arranged globular assembly" (RAGA) was formed. The correlation of the standard free energy of micellization (ΔG(m)(0)) with different solvent parameters (1) dielectric constant (ε), (2) viscosity (η0), (3) Reichardt parameter (E(T)(30)), (4) Gordon parameter (G), and (5) Hansen-Hildebrand hydrogen bonding parameter (δ(h)) has been attempted. It has been found that δ(h) produced a master correlation between ΔG(m)(0) and δ(h) for different binary mixtures such as Tf-W, Fa-W, Ml-W and Dn-W.

Amphiphile behavior in mixed solvent media I: self-aggregation and ion association of sodium dodecylsulfate in 1,4-dioxane-water and methanol-water media

Mixed aquo-organic solvents are used in chemical, industrial, and pharmaceutical processes along with amphiphilic materials. Their fundamental studies with reference to bulk and interfacial phenomena are thus considered to be important, but such detailed studies are limited. In this work, the interfacial adsorption of sodium dodecylsulfate (SDS, C12H25SO4(-)Na(+)) in dioxane-water (Dn-W) and methanol-water (Ml-W) media in extensive mixing ratios along with its bulk behavior have been investigated. The solvent-composition-dependent properties have been identified, and their quantifications have been attempted. The SDS micellization has been assessed in terms of different solvent parameters, and the possible formation of an ion pair and triple ion of the colloidal electrolyte, C12H25SO4(-)Na(+) in the Dn-W medium has been correlated and quantified. In the Ml-W medium at a high volume percent of Ml, the SDS amphiphile formed special associated species instead of ion association. The formation of self-assembly and the energetics of SDS in the mixed solvent media have been determined and assessed using conductometry, calorimetry, tensiometry, viscometry, NMR, and DLS methods. The detailed study undertaken herein with respect to the behavior of SDS in the mixed aquo-organic solvent media (Dn-W and Ml-W) is a new kind of endeavor.

Designing and Testing of an Effective Oil-in-Water Microemulsion Drug Delivery System forIn VivoApplication

The phase behavior of a new psedoternary system of clove oil/Tween 20 has been studied. Several compositions from the single-phase region were selected and their stability toward time, temperature, and electrolytes has been examined. A particular composition(clove oil/Tween 20/water as 5/30/65) was chosen as the drug delivery system from the clear oil-in-water zone of the pseudoternary system. The droplet dimension and the polydispersity state of the particular composition was determined by dynamic light scattering. A bioactive compound quarcetin was encapsulated in the vehicle. The efficacy of the drug in the vehicle was examined against leishmaniasis in hamster models. The hepatotoxicity of the vehicle (o/w microemulsion) with and without the drug quarcetin was examined by estimating serum alkaline phosphatase, glutamate pyruvate transaminase, urea, and creatinine.

New Pharmaceutical Microemulsion System for Encapsulation and Delivery of Diospyrin, a Plant-Derived Bioactive Quinonoid Compound

A new vegetable oil based oil-in-water microemulsion is developed and characterized as a prospective delivery system for in vivo application A particular weight percent composition 5/30/65 (clove oil/Tween-20/water) was selected (V1) from the clear oil-in-water zone of the pseudoternary phase diagram comprising clove oil, polyoxyethylene sorbitan monolaurate (Tween-20), and water. Two modifications of V1, (V2 and V3) were prepared by addition of dipalmitoyl phosphatidyl choline (DPPC), and a mixture of DPPC and cholesterol, respectively. A model drug diospyrin (a plantderived quinonoid compound) was encapsulated in the dispersed clove oil droplets of the three systems and designated as DV1, DV2, and DV3, respectively. The size of the dispersed clove oil droplets ranged between 9-20 nm as determined by dynamic light scattering. The stability of the vehicles, before and after encapsulation, was assessed under varying conditions of time and temperature and was found to be stable for 1 year and over a temperature range of 4-40 degrees C. The ultraviolet-visible spectrum of diospyrin after encapsulation in the compartmentalized medium remained almost identical to that dissolved in chloroform. The single-dose acute toxicity of V1 and DV1 was assessed in vivo by carrying out survival study and enzyme assay in Swiss Albino mice. The vehicle was safe at a volume of 0.05 ml when injected intraperitoneally into the mice.

Biocompatible microemulsions and their prospective uses in drug delivery

Efficacy of lipophilic drugs is often hindered due to their poor aqueous solubility leading to low absorption after in vivo administration. A part of the administered dose is absorbed and reaches the pharmacological site of action and the remainder causes toxicity and undesirable side effects due to unwanted biodistribution. Enhancement in drug efficacy and lowering of drug toxicity could be achieved through encapsulation and delivery of the lipophilic drugs in aqueous based delivery systems. Microemulsions are macroscopically homogeneous pseudoternary and ternary colloidal assemblies having polar and nonpolar micro domains. Their dispersed phases in nanodimension have good shelf-life (due to thermodynamic stability), large surface area, low viscosity (in some compositions), and ultraslow surface tension. These properties qualify them to be prospective drug delivery systems provided they are composed of biocompatible excipients. Due to the existence of polar, nonpolar, and interfacial microdomains, encapsulation of different kinds of drugs is possible. The review entails reports on development and characterization of biocompatible microemulsion systems and their evaluation as probable vehicles for encapsulation, stabilization, and delivery of bioactive natural products and prescription drugs.

Preparation of prospective plant oil derived micro-emulsion vehicles for drug delivery

Biocompatible oil-in-water (o/w) micro-emulsions can be prospective drug delivery vehicles for their capability to solubilize lipophilic (oil soluble) drugs in the dispersed oil. Plant oils are considered suitable for such a purpose. In this study, we have attempted to examine the dispersion of corn, cottonseed, clove, orange and peppermint oils, as well as isopropyl myristate (IPM) in water continuum in presence of surfactants Tween-20, Brij-30 and Brij-92 and co-surfactants ethanol (EtOH) and isopropyl alcohol (iPrOH). Both ternary (oil/surfactant/water) and psedoternary (oil/surfactant + co-surfactant/water) phase diagrams were constructed. The ternary systems produced larger micro-emulsion forming zones than the psedo-ternary systems. The combinations peppermint oil/iPrOH/water, IPM/iPrOH/water and 1:1 (v/v) peppermint oil + IPM/iPrOH/water were found to form fair proportion of single-phase surfactant-less micro-emulsion. The surfactant-aided ternary systems produced larger clear microemulsion zones, compared to pseudo-ternary systems, while the behaviour of surfactant-less systems was intermediate. The prepared systems had shelf life of 1 year and they withstood temperature variations in the range of 4-40 degrees C.

Enhanced in vitro percutaneous absorption and in vivo anti-inflammatory effect of a selective cyclooxygenase inhibitor using microemulsion

Celecoxib, a specific COX-2 inhibitor, was recently approved for the treatment of rheumatoid and osteoarthritis, acute pain, familial adenomatous polyposis and primary dysmenorrhea. Oral administration of celecoxib is effective against ultraviolet B radiation (UVB)-induced skin carcinogenesis; however, its clinical use is restricted because of its failure to block the characteristic cutaneous inflammatory response and lower availability at the site of inflammation. Topical application of celecoxib has been effective compared with oral in certain clinical conditions. The present study was undertaken to develop and investigate the development of microemulsion system (isopropyl myristate/medium-chain glyceride/polysorbate 80/water) for topical delivery of celecoxib. The pseudoternary phase diagram was constructed with constant surfactant concentration, and several compositions were identified and characterized by using dynamic light scattering. The in vitro permeation rate of celecoxib through rat skin was determined for microemulsions, microemulsion gel, and cream by using the modified Franz-type diffusion cell. In all formulations tested, celecoxib permeated more quickly, and the microemulsions increased the permeation rate of celecoxib up to 5 and 11 times compared with those of microemulsion gel and cream, respectively. Increasing the concentration of medium-chain mono-/di-glyceride in microemulsion imparted increased droplet size and viscosity and decreased diffusion coefficient. In vivo anti-inflammatory study suggested that the developed microemulsion formulations might serve as potential drug vehicle for the prevention of UVB-induced skin cancer.

Formulation and physicochemical characterization of microemulsion system using isopropyl myristate, medium-chain glyceride, polysorbate 80 and water

The phase behavior of the system isopropyl myristate/medium-chain glyceride/polysorbate 80/water forming both w/o and o/w microemulsions has been studied to develop microemulsion comprising of pharmaceutical excipients. The pseudo-ternary phase diagrams with large monophasic zones and gel formation were realized and several compositions were identified in the phase diagram for rheological, dynamic light scattering (DLS) and calorimetric measurements. The identified systems at different temperatures behaved as Newtonian fluid and the activation parameters for their viscous flow were evaluated. From DLS measurements, hydrodynamic diameter, polydispersity and diffusion coefficient of the microheterogeneous dispersions were determined. The free energy, enthalpy and entropy of solution of the w/o and o/w microemulsions were determined from calorimetric measurements.

Self-aggregation of alkyltrimethylammonium bromides (C10-, C12-, C14-, and C16TAB) and their binary mixtures in aqueous medium: a critical and comprehensive assessment of interfacial behavior and bulk properties with reference to two types of micelle formation

The detailed interfacial adsorption and micellization behavior of pure and mixed alkyltrimethylammonium bromides (ATABs: C10-, C12-, C14-, and C16TAB) were studied using tensiometric, conductometric, fluorimetric, viscometric, and calorimetric methods. The critical micellar concentration (CMC), thermodynamics of adsorption and micellization, counterion binding, aggregation number, and micellar polarity were determined. It was observed that the studied 1:1 molar mixtures of C10-C12TAB, C10-C14TAB, and C10-C16TAB, and the mixtures C12-C14TAB and C12-C16TAB at different mole ratios produced two CMCs that were supported by the conductometric, calorimetric and viscometric methods. Compared to the first micelle, the second micelle condensed more counterions and produced a higher aggregation number, but their interior polarity states were the same. The surface excess, area minimum of the ATABs at the CMC and Gibbs free energy of adsorption were evaluated and compared. The ideality/nonideality states of the mixed micelles formed in solution were tested in the light of Clint and Rubingh's formalisms; the mixed systems were found to undergo moderate to weak synergistic interaction. The contributions of the terminal methyl group, the intermediate methylene groups, and the hydrophilic tetramethylammonium group toward the standard Gibbs free energy, enthalpy, and entropy of the micellization processes were deciphered and discussed.

Self-aggregation of binary mixtures of alkyltriphenylphosphonium bromides: a critical assessment in favor of more than one kind of micelle formation

The micellization behavior of binary combinations of alkyltriphenylphosphonium bromides (ATPBs) with alkyl chain carbons 10, 12, 14, and 16 has been studied by conductometry and calorimetry. The combinations C(10)-C(12), C(10)-C(14), C(10)-C(16), C(12)-C(14), C(12)-C(16), and C(14)-C(16) were found to form two cmc's by both the methods, with good agreement, except C(14)-C(16)TPB, which has evidenced only a single cmc by calorimetry for all combinations. The combinations C(10)-C(12) (for both cmc(1) and cmc(2)) and C(10)-C(14)TPB (for cmc(2)) formed ideal mixtures, whereas the rest were nonideal. In the nonideal binary mixtures, the ATPB components showed antagonistic interaction with each other. The cmc, interaction parameter (beta), mixed micellar composition, extent of counterion binding, and thermodynamic parameters for the micellization process have been reported and discussed. The enthalpy of mixed micelle formation has been found to have a fair correlation with a Clint-type relation applicable to ideal binary mixtures of surfactants.

Topical delivery of celecoxib using microemulsion

The topical delivery of celecoxib has been studied using microemulsion as the vehicle for the treatment of UV B induced skin cancer. Pseudotemary phase diagrams were constructed at different oil to cosurfactant ratios to identify the formulation variables for microemulsion formation, and the effect of these variables on skin permeation of celecoxib was evaluated with excised rat skin. Topical anti-inflammatory effect of celecoxib has been assessed using the arachidonic acid induced ear oedema model. Formulation E consisting of 3% celecoxib, 22% propylene glycol dicaprylate/dicaprate + caprylic/capric mono-/di-glycerides (2:1), 30% polysorbate 80 and water (all w/w) showed higher permeation rate and significant anti-inflammatory activity. The studied microemulsion formulations have a prospect for use as a potential vehicle for treatment of UV B induced skin cancer.

Formulation Design of Self-Microemulsifying Drug Delivery Systems for Improved Oral Bioavailability of Celecoxib

Celecoxib is a hydrophobic and highly permeable drug belonging to class II of biopharmaceutics classification system. Low aqueous solubility of celecoxib leads to high variability in absorption after oral administration. Cohesiveness, low bulk density and compressibility, and poor flow properties of celecoxib impart complications in it's processing into solid dosage forms. To improve the solubility and bioavailability and to get faster onset of action of celecoxib, the self-microemulsifying drug delivery system (SMEDDS) was developed. Composition of SMEDDS was optimized using simplex lattice mixture design. Dissolution efficiency, t(85%), absorbance of diluted SMEDDS formulation and solubility of celecoxib in diluted formulation were chosen as response variables. The SMEDDS formulation optimized via mixture design consisted of 49.5% PEG-8 caprylic/capric glycerides, 40.5% mixture of Tween20 and Propylene glycol monocaprylic ester (3:1) and 10% celecoxib, which showed significantly higher rate and extent of absorption than conventional capsule. The relative bioavailability of the SMEDDS formulation to the conventional capsule was 132%. The present study demonstrated the suitability of mixture design to optimize the compositions for SMEDDS. The developed SMEDDS formulations have the potential to minimize the variability in absorption and to provide rapid onset of action of celecoxib.

Kinetics in microemulsion V. Glucose oxidase catalyzed oxidation of beta-D-glucose in aqueous, micellar and water-in-oil microemulsion media

The oxidation of beta-D-glucose by the enzyme glucose oxidase was studied in aqueous medium, in solutions of surfactants AOT (2-ethylhexylsulfosuccinate, sodium salt) TX-100 (polyethylene glycol p-tert octyl phenyl ether) and in w/o microemulsion medium (water/AOT/decane) at different water/AOT mole ratio (omega), pH, temperature and in presence of additives. The time-dependent activities of the enzyme in aqueous and microemulsion media were determined. The catalytic process was retarded in the presence of TX-100 and AOT. In microemulsion medium, kcat values exhibited a deformed W-shaped profile with omega. At pH 7, a maximum value of kcat was observed at omega = 10.6. The kcat values were found to be higher in microemulsion medium than in aqueous medium at both pH's 7 and 8. Activation parameters for the kinetic process were evaluated together with the thermodynamics of the enzyme-substrate Michaelis complex. The deltaG* was lower, whereas deltaH* and deltaS* were higher in microemulsion than in water. The Michaelis constant, KM was also lower in microemulsion. The inhibition effects of the additives, NaNO3 and NaC were studied in both aqueous and microemulsion media by examining their influences on catalytic constant, kcat and Michaelis constant KM. In microemulsion, both the additives NaNO3 and NaC produced non-competitive inhibition.

Thermal oscillations in the bromate – oxalic acid – MnSO4 – H2SO4 – acetone system: A calorimetric study

The oscillatory reaction of potassium bromate, oxalic acid, and MnSO4 in the presence of acetone in aq H2SO4 solutions has been studied calorimetrically at different concentrations of substrates. Acetone and oxalic acid have been found to accelerate the reaction by increasing the oscillation frequency. On the other hand, MnSO4 has a retarding effect; the frequency of oscillation decreases systematically with increasing concentration of MnSO4. Potassium bromate shows mixed behavior in this respect. The total heat evolved during the reaction per mol of oxalic acid consumed has been evaluated, which can be used to calculate the concentrations of the various reactants at different stages of the reaction. The effects of different electrolytes (KCl, NaCl, BaCl2, CaCl2, SrCl2, NaBr, NaI, KNO3, NaNO3, and Ca(NO3)2) and solvents (dimethylformamide, 1,4-dioxane, acetonitrile, and tetrahydrofuran) on the extents of oscillation and the enthalpy change for the process have been also examined.Key words: Belousov–Zhabotinsky reaction, oscillatory reaction, oxalic acid, calorimetry, acetone.

Studies on surfactant-biopolymer interaction. I. Microcalorimetric investigation on the interaction of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) with gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA)

The interaction of the surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with the biopolymers gelatin (Gn), lysozyme (Lz) and deoxyribonucleic acid (DNA) was studied by isothermal titration microcalorimetry at varied biopolymer concentration, pH and temperature. The nature of interaction of the surfactants with the biopolymers was assessed from the observed enthalpy-[surfactant] profiles. The biopolymer-induced aggregation of the surfactants was observed. The enthalpies of aggregation of amphiphiles, binding of aggregates with macromolecules, organisational change of bound aggregates, and threshold concentrations for micelle formation of surfactants in the presence of biopolymers were estimated. The results collected on the three biopolymers were analysed and compared.

Anchor dependency for non-glycerol based cationic lipofectins: mixed bag of regular and anomalous transfection profiles

Although detailed structure-activity, physicochemical and biophysical investigations in probing the anchor influence in liposomal gene delivery have been reported for glycerol-based transfection lipids, the corresponding investigation for non-glycerol based simple monocationic transfection lipids have not yet been undertaken. Towards this end, herein, we delineate our structure-activity and physicochemical approach in deciphering the anchor dependency in liposomal gene delivery using fifteen new structural analogues (lipids 1-15) of recently reported non-glycerol based monocationic transfection lipids. The C(14) analogues in both series 1 (lipids 1-6) and series 2 (lipids 7-15) showed maximum efficiency in transfecting COS-1 and CHO cells. However, the C(12) analogue of the ether series (lipid 3) exhibited a seemingly anomalous behavior compared with its transfection efficient C(10) and C(14) analogues (lipids 2 and 4) in being completely inefficient to transfect both COS-1 and CHO cells. The present structure-activity investigation also convincingly demonstrates that enhancement of transfection efficiencies through incorporation of membrane reorganizing unsaturation elements in the hydrophobic anchor of cationic lipids is not universal but cell dependent. The strength of the interaction of lipids 1-15 with DNA was assessed by their ability to exclude ethidium bromide bound to the DNA. Cationic lipids with long hydrophobic tails were found, in general, to be efficient in excluding EtBr from DNA. Gel to liquid crystalline transition temperatures of the lipids was measured by fluorescence anisotropy measurement technique. In general (lipid 2 being an exception), transfection efficient lipids were found to have their mid transition temperatures at or below physiological temperatures (37 degrees C).

Physicochemical Investigations of Microemulsification of Coconut Oil and Water Using Polyoxyethylene 2-Cetyl Ether (Brij 52) and Isopropanol or Ethanol

The microemulsification of coconut oil/polyoxyethylene 2-cetyl ether/2-propanol or ethanol/water was investigated. The phase behaviors of the mixed system were examined. The shear viscosity at different temperatures was measured to derive activation parameters for the viscous flow. The diffusion coefficient of the microemulsions at different compositions was determined by the DLS method. The energetics of solubilization of water into oil + Brij + alkanol as well as of oil into water + Brij + alkanol forming w/o and o/w microemulsions, respectively, were calorimetrically determined.

Physicochemical investigations on microemulsification of eucalyptol and water in presence of polyoxyethylene (4) lauryl ether (Brij-30) and ethanol

The microemulsification of eucalyptol/polyoxyethylene(4)lauryl ether (Brij-30)/ethanol/water has been investigated. The phase behaviours of the mixed system in pseudoternary and tetrahedral representations have been examined to understand the topological nature of the multicomponent mixtures. Phase volumes of the heterogeneous combinations have been estimated to understand the mixing efficacy of the combinations. Shear viscosities of different monophasic compositions have been measured at different shear rates and temperatures, and the activation parameters for the viscous flow have been evaluated. The dimensions of the nanodispersions of w/o and o/w types, their diffusion coefficients and the polydispersity have been determined by the DLS method. The energetics of solubilisation (dissolution) of water in oil+Brij-30+ethanol as well as oil in water+Brij-30+ethanol forming w/o and o/w microemulsions, respectively, have been calorimetrically determined. Considering the phase separation point to be the point of maximum solubility, the energetic parameters (enthalpy, free energy and entropy) of the microemulsification process have been estimated.

Adsorption Behaviors of L-Histidine and DL-Tryptophan on Cholesterol, Silica, Alumina, and Graphite

The adsorption of L-histidine (L-His) and DL-tryptophan (DL-Trp) on cholesterol, silica, alumina, and graphite surfaces from aqueous solution at pH 9.2 has been studied in the temperature range of 25 to 50 degrees C. The data have been analyzed, wherever applicable, by Langmuir and Hill equations to obtain (1) the monolayer adsorption capacity (x(m)) and the equilibrium constant (k') for the adsorption and desorption processes and (2) the Hill coefficient (n) at different temperatures. The results of adsorption on different kinds of adsorbents have been compared. The energetic parameters for the adsorption process have also been evaluated and compared. Copyright 2001 Academic Press.

Photophysics of thionine dye in aqueous and liposome media in presence of different reducing agents

The photoelectrochemical and spectral (both absorption and fluorescence) studies of thionine, a cationic phenothiazine dye, have been carried out in aqueous and phosphatidylcholine liposome media in the presence of different reducing agents, such as I(-), Br(-), Cl(-) and Fe(2+). The results show that the photovoltage generation from photoelectrochemical studies and Stern-Volmer quenching constant studied by fluorescence quenching support the photoinduced electron transfer from the reducing agent to the singlet excited thionine dye. Moreover, a good correlation between photovoltages/Stern-Volmer quenching constants vs. reduction potentials of the reducing agents also confirms the above electron transfer in the photoexcited state.

Phase behaviours and conductivity study of water/CPC/alkan-1-ol (C4and C5)/1-hexane water/oil microemulsions with reference to their structure and related thermodynamics

The microemulsion forming systems of water/cetylpyridinium chloride/butan-1-ol/n-hexane, and water/cetylpyridinium chloride/pentan-1-ol/n-hexane have been studied with respect to their phase behaviours and percolation of conductance to derive information on their droplet physicochemical characteristics (dimension, interfacial area and composition, and number density). This was carried out at different water contents at specific ratios of surfactant and cosurfactant and at various temperatures. From the information collected, the energetics of the transfer of the alkanol (butan-1-ol and pentan-1-ol) from the continuous oil-phase to the interfacial region (the interphase) have been estimated. At the conductance percolation threshold, the droplets cluster or associate, can be considered to form a pseudophase similar to surfactants forming micelles. Based on this concept, the energetics of the clustering process have been evaluated, and the results are discussed in comparison with other recently studied systems.Key words: energetics of clustering, percolation, phase diagrams, microemulsions and thermodynamics of transfer.

Mixed Micelles of Sodium Deoxycholate and Polyoxyethylene Sorbitan Monooleate (Tween 80)

The results of studies on the interaction of binary mixtures of sodium deoxycholate (NaDC) and polyoxyethylene sorbitan monooleate (Tween 80) in bulk and at the air/water interface obtained from conductance, surface tension, and fluorescence measurements are described. The critical micelle concentration (CMC), thermodynamics of micellization, free energy of interfacial adsorption, minimum average area occupied by the surfactant species at the interface, micellar polarity, and aggregation number of the mixed aggregates have been determined. The mixed micellar composition and the estimation of the interacting forces involved are evaluated on the basis of recent theoretical models. The estimated interaction parameter indicates an overall attractive force in the mixed state, and the proportion of NaDC in the mixed micelle is found to be lower compared to the stoichiometric compositions. The mixed aggregates with higher mole fractions of NaDC show less stability in comparison with those having higher proportions of the nonionic component. Copyright 1999 Academic Press.

Interfacial and Micellization Behaviors of Binary and Ternary Mixtures of Amphiphiles (Tween-20, Brij-35, and Sodium Dodecyl Sulfate) in Aqueous Medium

The formation of micelles of Tween-20 and Brij-35 as well as of SDS, Tween-20, and Brij-35 mixed in different proportions in aqueous medium has been physicochemically investigated. The critical micellar concentration (CMC), micellar aggregation number, counterion binding by micelles, micellar polarity, free energies of micellization and interfacial adsorption, and entropy of micellization have been evaluated by conductometric, tensiometric, and fluorimetric measurements. The solution composition has been found to have a complex say on the measured physicochemical parameters. The enthalpies of micellization of both Tween-20 + Brij-35 and SDS + Tween-20 + Brij-35 mixed surfactant systems have been found to be negligibly small. Attempts to understand the properties of mixed micelles (composition, mutual synergism, component activity coefficients, and CMC) have been made with the help of the propositions of Clint, Rubingh, and Rubingh and Holland. The mixed binary and ternary systems can be adequately described by these theories. Copyright 1998 Academic Press.