Additive-anchored thermoresponsive nanoscale self-assembly generation in normal and reverse Tetronics®.

Self-assembly of ethylene oxide (EO)-propylene oxide (PO)-based star-shaped block copolymers (BCPs) in the presence of different kinds of additives is investigated in an aqueous solution environment. Commercially available four-armed BCPs, namely Tetronics® (normal: T904 with EO as the terminal end block; and reverse: T90R4 with PO as the terminal end block), each with 40%EO, are used. The effect of various additives such as electrolytes (NaCl and Na2SO4), nonelectrolyte polyols (glucose and sorbitol), and ionic surfactants (viz. anionic-sodium dodecyl sulfate (SDS), cationic-dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecyldimethylammonium propane sulfonate (C12PS)) on these BCPs is examined to observe their influence on micellization behaviour. The presence of salts and polyols displayed interesting phase behaviour, i.e., the cloud point (CP) was decreased, the water structure was affected and the micelles were dehydrated by expelling water molecules, and thus they were likely to promote micelle formation/growth. In contrast, ionic surfactants in small amounts interacted with the BCPs and showed an increase in CPs thereby forming mixed micelles with increasing charges and decreasing micellar sizes, finally transforming to small surfactant-rich mixed micelles. Molecular interactions such as electrostatic and hydrogen bonding involved within the examined entities are put forth employing a computational simulation approach using the Gaussian 09 window for calculation along with the GaussView 5.0.9 programming software using the (DFT)/B3LYP method and 3-21G basis set. The hydrodynamic diameter (Dh) of the micelles is examined using dynamic light scattering (DLS), while the various micellar parameters inferring the shape/geometry are obtained using small-angle neutron scattering (SANS) by the best fitting of the structure factors. It is observed that 10 w/v% T904 remains as spherical micelles with some micellar growth under physiological conditions (37 °C), while 10 w/v% T90R4 remains as unimers and forms spherical micelles in the presence of additives at 37 °C. Furthermore, the additive-induced micellar systems are tested as developing nanovehicles for anticancer (curcumin, Cur) drug solubilization using UV-vis spectroscopy, which shows a prominent increase in absorbance with enhanced solubilization capacity. Additionally, the cytotoxic effect of Cur loaded on the BCP micelles in HeLa cells is studied through confocal microscopy by capturing fluorescence images that depict HeLa cell growth inhibition under the influence of additive-induced micellar systems.

Degradable Polymeric Bio(nano)materials and Their Biomedical Applications: A Comprehensive Overview and Recent Updates.

Degradable polymers (both biomacromolecules and several synthetic polymers) for biomedical applications have been promising very much in the recent past due to their low cost, biocompatibility, flexibility, and minimal side effects. Here, we present an overview with updated information on natural and synthetic degradable polymers where a brief account on different polysaccharides, proteins, and synthetic polymers viz. polyesters/polyamino acids/polyanhydrides/polyphosphazenes/polyurethanes relevant to biomedical applications has been provided. The various approaches for the transformation of these polymers by physical/chemical means viz. cross-linking, as polyblends, nanocomposites/hybrid composites, interpenetrating complexes, interpolymer/polyion complexes, functionalization, polymer conjugates, and block and graft copolymers, are described. The degradation mechanism, drug loading profiles, and toxicological aspects of polymeric nanoparticles formed are also defined. Biomedical applications of these degradable polymer-based biomaterials in and as wound dressing/healing, biosensors, drug delivery systems, tissue engineering, and regenerative medicine, etc., are highlighted. In addition, the use of such nano systems to solve current drug delivery problems is briefly reviewed.

Effect of stoichiometry upon the characteristics of quercetin-arginine cocrystals formulated through solution crystallization.

OBJECTIVE: The aim of this study is to demonstrate the effect of stoichiometry upon characteristics of quercetin-arginine (QCT-Arg) cocrystals. SIGNIFICANCE: Quercetin (QCT) is a most abundant flavonoid in vegetables and fruits and has been widely used as an antioxidant. However, its oral bioavailability remains low due to poor aqueous solubility. We illustrate that QCT-Arg cocrystals formulated through an optimized stoichiometry can be a useful approach for its solubilization. METHOD: Cocrystals were prepared using solvent evaporation method. Characterizations were performed through microscopic, spectroscopic, and thermal techniques. The stoichiometry was confirmed from the binary phase diagram which was prepared using thermograms derived from differential scanning calorimetric experiments. RESULT: Cocrystal formation was accompanied by the conversion of isotropic phase into anisotropic one. Thread-like cocrystals were formed, regardless of QCT-Arg stoichiometry and solvent's polarity. Spectral analyses suggested that cocrystal structure was held together by hydrogen bonding between QCT and Arg. We ruled out the existence of eutectic mixture based on the observation of two eutectic points in the binary phase diagram. CONCLUSION: Morphology of cocrystals remained unaffected by the solvent type, stoichiometry and the presence of surfactant. We noticed that the cocrystals could improve the aqueous solubility of QCT.

Salt induced micellization conduct in PEO-PPO-PEO-based block copolymers: a thermo-responsive approach.

The nanoscale self-assembly behavior in ethylene oxide (EO) and propylene oxide (PO)-based block copolymers (BCPs) commercially available as Pluronics®: L44 (PEO10-PPO23-PEO10) and F77 (PEO53-PPO34-PEO53) is put forth in aqueous solution and in the presence of sodium salts NaCl and Na2SO4. The moderate hydrophilicity of L44 is attributed to its low molecular weight PPO segment, while the high percentage of PEO content in F77 contributes to its extreme hydrophilicity. The impact of sodium salts (NaCl and Na2SO4) on the self-assembly is investigated to understand their influence and role in micellization, by employing various physicochemical techniques such as phase behavior conduct, calorimetry, tensiometry, scattering, and spectral analysis. The results indicate that at a low temperature range of 20-30 °C, Pluronics® solutions with a concentration of 10% w/v remain molecularly dissolved as individual units called unimers (Gaussian chain), which have a hydrodynamic size (Dh) of approximately 4-6 nm. Additionally, loose clusters of a few hundred nanometers in size are also observed. Though, at higher concentrations of BCPs and in the presence of salt or elevated temperatures, the examined micellar structures exhibit a higher degree of organization i.e., spherical or ellipsoidal in terms of size and shape. Also, the solubilization enhancement of a hydrophobic dye called orange OT within the examined micellar system is also undertaken using a spectral approach.

Comparative Effect of Physiological Salts upon Micellization of T1304 and T1307.

We present a comprehensive investigation on the interaction of tetronics (T1304 and T1307) with some important physiological salts (NaH2PO4, KH2PO4, Na2CO3, NaCl, and KI). Thermodynamic and microstructural aspects of these interactions were studied as a function of the solution temperature, pH and salt concentration. Characterizations were performed using turbidimetric, calorimetric, and scattering techniques. We show that, at ambient temperature, T1304 molecules aggregated to form spherical core-shell aggregates displaying a unimodal distribution pattern. On the other hand, unimers and large clusters dominated in the case of highly hydrophilic T1307. Its micellization was promoted in the presence of salts as per the following trend: NaCl < KH2PO4 < NaH2PO4 ≪ Na2CO3. Aggregation was found to be endothermic, and hydrophobic interactions (TΔSmic > ΔHmic) prevailed. The enthalpy-entropy compensation plot was found to be linear for both copolymers. Demicellization occurred in the presence of KI as it facilitated the buildup of water structures around the copolymer chains. This could be verified from the increase in the cloud point, critical micelle concentration, and free energy. Overall, the temperature and salts inflicted a stronger hydrophobic effect upon T1304 in comparison to T1307.

Structural Changes in Liposomal Vesicles in Association with Sodium Taurodeoxycholate.

Liposomes composed of soy lecithin (SL) have been studied widely for drug delivery applications. The stability and elasticity of liposomal vesicles are improved by incorporating additives, including edge activators. In this study, we report the effect of sodium taurodeoxycholate (STDC, a bile salt) upon the microstructural characteristics of SL vesicles. Liposomes, prepared by the thin film hydration method, were characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), electron microscopy, and rheological techniques. We noticed a reduction in the size of vesicles with the incremental addition of STDC. Initial changes in the size of spherical vesicles were ascribed to the edge-activating action of STDC (0.05 to 0.17 µM). At higher concentrations (0.23 to 0.27 µM), these vesicles transformed into cylindrical structures. Morphological transitions at higher STDC concentrations would have occurred due to its hydrophobic interaction with SL molecules in the bilayer. This was ascertained from nuclear magnetic resonance observations. Whereas shape transitions underscored the deformability of vesicles in the presence of STDC, the consistency of bilayer thickness ruled out any dissociative effect. It was interesting to notice that SL-STDC mixed structures could survive high thermal stress, electrolyte addition, and dilution.

Stabilization of lysozyme in aqueous dispersion of graphene oxide sheets.

This study examines the effect of surface oxygen groups upon ability of graphene oxide (GO) sheets in suppressing the fibrillation of lysozyme (LYZ). Graphite was oxidized using 6 and 8 wt equivalents of KMnO4, and as produced sheets were abbreviated as GO-06 and GO-08, respectively. Particulate characteristics of sheets were characterized by light scattering and electron microscopic techniques, and their interaction with LYZ was analysed by circular dichroism (CD) spectroscopy. After ascertaining acid-driven conversion of LYZ to fibrillary form, we have shown that the fibrillation of dispersed protein can be prevented by adding GO sheets. Inhibitory effect could be attributed to binding of LYZ over the sheets via noncovalent forces. A comparison between GO-06 and GO-08 samples showed superior binding affinity of the latter. Higher aqueous dispersibility and density of oxygenated groups in GO-08 sheets would have facilitated the adsorption of protein molecules, thus making them unavailable for aggregation. Pre-treatment of GO sheets with Pluronic 103 (P103, a nonionic triblock copolymer), caused reduction in the adsorption of LYZ. P103 aggregates would have rendered the sheet surface unavailable for the adsorption of LYZ. Based on these observations, we conclude that fibrillation of LYZ can be prevented in association with graphene oxide sheets.

Rationalizing the Design of Pluronics-Surfactant Mixed Micelles through Molecular Simulations and Experiments.

Aqueous systems comprising polymers and surfactants are technologically important complex fluids with tunable features dependent on the chemical nature of each constituent, overall composition in mixed systems, and solution conditions. The phase behavior and self-assembly of amphiphilic polymers can be changed drastically in the presence of conventional ionic surfactants and need to be clearly understood. Here, the self-aggregation dynamics of a triblock copolymer (Pluronics L81, EO3PO43EO3) in the presence of three cationic surfactants (with a 12C long alkyl chain but with different structural features), viz., dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and ethanediyl-1,2-bis(dimethyldodecylammonium bromide) (12-2-12), were investigated in an aqueous solution environment. The nanoscale micellar size expressed as hydrodynamic diameter (Dh) of copolymer-surfactant mixed aggregates was evaluated using dynamic light scattering, while the presence of a varied micellar geometry of L81-cationic surfactant mixed micelles were probed using small-angle neutron scattering. The obtained findings were further validated from molecular dynamics (MD) simulations, employing a simple and transferable coarse-grained molecular model based on the MARTINI force field. L81 remained molecularly dissolved up to ∼20 °C but phase separated, forming turbid/translucent dispersion, close to its cloud point (CP) and existed as unstable vesicles. However, it exhibited interesting solution behavior expressed in terms of the blue point (BP) and the double CP in the presence of different surfactants, leading to mixed micellar systems with a triggered morphology transition from unstable vesicles to polymer-rich micelles and cationic surfactant-rich micelles. Such an amendment in the morphology of copolymer nanoaggregates in the presence of cationic surfactants has been well observed from scattering data. This is further rationalized employing the MD approach, which validated the effective interactions between Pluronics-cationic surfactant mixed micelles. Thus, our experimental results integrated with MD yield a deep insight into the nanoscale interactions controlling the micellar aggregation (Pluronics-rich micelles and surfactant-rich micelles) in the investigated mixed system.

Self-assembly of bile salts and their mixed aggregates as building blocks for smart aggregates.

The present communication offers a comprehensive overview of the self-assembly of bile salts emphasizing their mixed smart aggregates with a variety of amphiphiles. Using an updated literature survey, we have explored the dissimilar interactions of bile salts with different types of surfactants, phospholipids, ionic liquids, drugs, and a variety of natural and synthetic polymers. While assembling this review, special attention was also provided to the potency of bile salts to alter the size/shape of aggregates formed by several amphiphiles to use these aggregates for solubility improvement of medicinally important compounds, active pharmaceutical ingredients, and also to develop their smart delivery vehicles. A fundamental understanding of bile salt mixed aggregates will enable the development of new strategies for improving the bioavailability of drugs solubilized in newly developed potential hosts and to formulate smart aggregates of desired morphology for specific targeted applications. It enriches our existing knowledge of the distinct interactions exerted in mixed systems of bile salts with variety of amphiphiles. By virtue of this, researchers can get innovative ideas to construct novel nanoaggregates from bile salts by incorporating various amphiphiles that serve as a building block for smart aggregates for their numerous industrial applications.

Amphiphilic Block Copolymers: Their Structures, and Self-Assembly to Polymeric Micelles and Polymersomes as Drug Delivery Vehicles.

Self-assembly of amphiphilic block copolymers display a multiplicity of nanoscale periodic patterns proposed as a dominant tool for the 'bottom-up' fabrication of nanomaterials with different levels of ordering. The present review article focuses on the recent updates to the self-association of amphiphilic block copolymers in aqueous media into varied core-shell morphologies. We briefly describe the block copolymers, their types, microdomain formation in bulk and micellization in selective solvents. We also discuss the characteristic features of block copolymers nanoaggregates viz., polymer micelles (PMs) and polymersomes. Amphiphilic block copolymers (with a variety of hydrophobic blocks and hydrophilic blocks; often polyethylene oxide) self-assemble in water to micelles/niosomes similar to conventional nonionic surfactants with high drug loading capacity. Double hydrophilic block copolymers (DHBCs) made of neutral block-neutral block or neutral block-charged block can transform one block to become hydrophobic under the influence of a stimulus (physical/chemical/biological), and thus induced amphiphilicity and display self-assembly are discussed. Different kinds of polymer micelles (viz. shell and core-cross-linked, core-shell-corona, schizophrenic, crew cut, Janus) are presented in detail. Updates on polymerization-induced self-assembly (PISA) and crystallization-driven self-assembly (CDSA) are also provided. Polyion complexes (PICs) and polyion complex micelles (PICMs) are discussed. Applications of these block copolymeric micelles and polymersomes as nanocarriers in drug delivery systems are described.

Self-Assembly and Micellar Transition in CTAB Solutions Triggered by 1-Octanol.

This study exploits higher-order micellar transition ranging from ellipsoidal to rodlike to wormlike induced by 1-octanol (C8OH) in an aqueous solution of cetyltrimethylammonium bromide (CTAB), characterizing phase behavior, rheology, and small-angle neutron scattering (SANS). The phase diagram for the ternary system CTAB-C8OH-water was constructed, which depicted the varied solution behavior. Such performance was further inferred from the rheology study (oscillatory-shear frequency sweep (ω) and viscosity (η)) that displayed an interesting solution behavior of CTAB solutions as a function of C8OH. It was observed that at low C8OH concentrations, the solutions appeared viscous/viscoelastic fluids that changed to an elastic gel with an infinite relaxation time at higher concentrations of C8OH, thereby confirming the existence of distinct micelle morphologies. Small-angle neutron scattering (SANS) provided various micellar parameters such as aggregation numbers (Nagg) and micellar size/shape. The experimental results were further validated with a computational simulation approach. The molecular dynamic (MD) study offered an insight into the molecular interactions and aggregation behavior through different analyses, including radial distribution function (RDF), radius of gyration (Rg), and solvent-accessible surface area (SASA).

Glucose-induced self-assembly and phase separation in hydrophilic triblock copolymers and the governing mechanism.

Poly(ethylene oxide, EO)-poly(propylene oxide, PO)-poly(ethylene oxide, EO)-based triblock copolymers (BCPs) with 80% hydrophilicity stay molecularly dissolved as Gaussian chains at ambient temperature, even at fairly high concentrations (>5 %w/v). This study presents the plausible micellization behaviour of such very-hydrophilic Pluronics® - F38, F68, F88, F98, and F108 - incited upon the addition of glucose at low concentrations and temperatures. The outcomes obtained from phase behaviour and scattering studies are described. At temperatures near to ambient temperature, these BCPs form micelles with a central core made of a PO block, surrounded by a corona of highly hydrated EO chains. The phase transitions in these hydrophilic Pluronics® in the presence of glucose are demonstrated via the dehydration of the copolymer coil, leading to a decrease in the I1/I3 ratio, as determined using fluorescence spectroscopy. The temperature-dependent cloud point (CP) showed a marked decrease with an increase in the PO molecular weight and also in the presence of glucose. The change in solution relative viscosity (ηrel) caused by glucose is due to the enhanced dehydration of the EO block of the BCP amphiphile. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) investigations suggested that the dimensions of the hydrophobic core increase during the dehydration of the EO-PO blocks upon a temperature increase or after adding varying concentrations of glucose, thereby resulting in a micellar shape transition. It has been observed that added glucose influences the phase behaviour of BCPs in an analogous way to the influence of temperature. Also, plausible interactions between the EO-PO blocks and glucose were suggested based on the evaluated optimized descriptors obtained from a computational simulation approach. In addition, the core-shell blended micelles obtained using these BCPs are successfully utilized for drug (curcumin, Cur) solubilization based on the observed peak intensities from UV-visible spectroscopy. The loading of Cur into glucose-containing and glucose-free hydrophilic Pluronic® micelles shows how the radius of the micellar core (Rc) increases in the presence of glucose, thereby indicating Cur solubility enhancement for the Pluronic® micelles. Various kinetics models were employed, demonstrating a drug release profile that enables this approach to be used as an ideal platform for drug delivery.

Advances on nanoformulation approaches for delivering plant-derived antioxidants: A case of quercetin.

Oxidative stress has been implicated in tumorigenic, cardiovascular, neuro-, and age-related degenerative changes. Antioxidants minimize the oxidative damage through neutralization of reactive oxygen species (ROS) and other causative agents. Ever since the emergence of COVID-19, plant-derived antioxidants have received enormous attention, particularly in the Indian subcontinent. Quercetin (QCT), a bio-flavonoid, exists in the glycosylated form in fruits, berries and vegetables. The antioxidant potential of QCT analogs relates to the number of free hydroxyl groups in their structure. Despite presence of these groups, QCT exhibits substantial hydrophobicity. Formulation scientists have tested nanotechnology-based approaches for its improved solubilization and delivery to the intended site of action. By the virtue of its hydrophobicity, QCT gets encapsulated in nanocarriers carrying hydrophobic domains. Apart from passive accumulation, active uptake of such formulations into the target cells can be facilitated through well-studied functionalization strategies. In this review, we have discussed the approaches of improving solubilization and bioavailability of QCT with the use of nanoformulations.

Micellar assembly leading to structural growth/transition in normal and reverse Tetronics® in single and mixed solution environment.

This study scrutinizes the self-association of ethylene oxide (EO)-propylene oxide (PO)-based star-shaped block copolymers as normal Tetronic® (T904) and reverse Tetronic® R (T90R4) with varying molecular characteristics and different hydrophilic-hydrophobic ratios in an aqueous solution environment. These thermo-responsive solutions appear clear, transparent or bluish up to 10%w/v, which anticipated the probable transition of unimers to spherical or ellipsoidal micelles which is complemented by scattering experiments. In a single-solution environment, 10%w/v T904 formed star-shaped micelles at ambient temperature and exhibited a micellar growth/transition with temperature ageing. While 10%w/v T90R4 exists as unimers or a Gaussian coil over a wide range of temperature. Very interestingly, close to the cloud point (CP) flower-shaped spherical and ellipsoidal micelles were formed. A similar proposed micellar scheme was also examined for mixed systems T904 : T90R4 in varying ratios (1 : 0, 3 : 1, 1 : 1, 1 : 3 and 0 : 1) giving an account to the solution behavior of the mixtures. An amalgamation of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) techniques achieved the thorough extraction of the structural parameters of the micellar system. The hydrodynamic diameter (Dh) of the micelles with temperature variation was evaluated from dynamic light scattering (DLS) while the structure factor of the micelles was found by employing small-angle neutron scattering (SANS). Furthermore, the single and mixed micellar systems were quantitatively and qualitatively examined for anticancer drug solubilization using UV-vis spectroscopy for their superior use as potential nanocargos.

Immunomodulation and Anticancer Immunity: Reviewing the Potential of Probiotics and Their Delivery with Macromolecular Carriers.

Probiotics colonize in the gastrointestinal tract and regulate the homeostasis in healthy human hosts. These protect the host against putrefactive organisms and secrete soluble factors exhibiting important transductive roles. However, constitutive processes in human host are deregulated following dysbiosis caused during prolonged exposure to cytotoxic agents and pollutants. Apart from restoring the homeostasis, probiotic administration has shown to minimize carcinogenesis and post-surgery complications in cancer patients. Moreover, ability of microbial cells to colonize at tumor foci can be harnessed to deliver genes, therapeutic proteins and antibodies in a selective manner. In this review, we have discussed immunomodulatory roles of probiotics in context to cancer prevention. The article further proposes the use of dietary interventions for boosting anticancer immunity and as an alternative to detrimental chemotherapeutic agents. After summarizing clinical evidences on probiotic efficacy, formulation approaches have been described for effective delivery of the microorganisms. The literature shows that polysaccharide matrices can be employed to achieve the survivability of probiotics. Formulation approaches have been reviewed together with the risks associated with the migration of live microorganisms to systemic circulation and their ability of transmitting antibiotic resistance factors into human pathogens.

Oxidation state of graphene oxide nanosheets drives their interaction with proteins: A case of bovine serum albumin.

In the present study, we explored the interaction of bovine serum albumin (BSA) with oxidized graphene oxide (GO) nanosheets. Nanosheets, synthesized with 4, 6, 8, 10 and 12 wt equivalents of KMnO4 as oxidant, were coded as GO-4, GO-6, GO-8, GO-10 and GO-12, respectively. After incubating sheets with a fixed concentration of BSA at room temperature, interactions were monitored with time. The analysis is based on UV-vis spectroscopy, fluorescence quenching, dynamic light scattering (DLS), small angle neutron scattering (SANS), Fourier transform infrared (FTIR) spectroscopy and circular dichroism (CD) techniques. Binding of BSA over sheets was recorded in the following order; GO-04 >> GO-06 > GO-08 > GO-10 ≈ GO-12. Our observations suggest that these interactions are largely regulated by the availability of pure graphitic domains and density of oxygen functionalities on sheet surface. This led us to the conclusion that GO-protein interactions can be minimized by modulating the extent of sheet oxidation. Moreover, we show that adsorption of proteins as colloidal aggregates contributes to improved biosafety of sheets. The protein molecule did not exhibit depletive changes in its conformation. However, from the viewpoint of drug delivery applications, density of oxygen groups must be optimized for maximizing the loading efficiency of oxidized sheets.

Fate of Photoinduced Electron Transfer Reactions with Temperature- and pH-Induced Assembly/Disassembly of Star Block Copolymer Micelles.

The assembly/disassembly of star block copolymers induced by changes in temperature or pH of the medium is anticipated to have interesting implications for hosting/releasing drugs and tuning chemical reactions. This study investigates the possibility of employing the dually sensitive self-assembly of an ethylene oxide-propylene oxide star block copolymer, Tetronic T904, to influence photoinduced electron transfer (ET) reactions, on switching from the assembled state (micelle) when temperature is above the critical micelle temperature (CMT) and pH of the medium is above the pKa of T904 to the dissociated (unimer) state when either the temperature is below the CMT or the polymer is protonated. Steady-state and time-resolved fluorescence techniques have been used to characterize the microenvironments of the reactants in T904 solutions under different temperature and pH conditions and to determine ET rate constants. Interestingly, the bimolecular ET rate constants in both assembled and disassembled states of T904 depict a bell-shaped correlation with the driving force of the reaction, in accordance with Marcus inversion behavior instead of the usual Rehm-Weller behavior seen in conventional solvents. The assembly/disassembly of T904 stimulated by temperature or pH affects the micropolarity in the reactant environment, the magnitude of ET rate constants, and the position of inversion on the exergonicity scale.

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants.

The self-assembly in aqueous solutions of three quaternary salt-based C16-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (Nagg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.

Tuning Cationic Micelle Properties with an Antioxidant Additive: A Molecular Perspective.

In this work, we characterize the micellization and morphology transition induced in aqueous cetyltrimethylammonium bromide (CTAB) solution by the addition of the antioxidant propyl gallate (PG) using tensiometry, rheology, and small-angle neutron scattering (SANS) techniques combined with the molecular dynamics (MD) simulation approach. The adsorption of CTAB at the air-water interface in the presence of varying [PG] revealed a progressive decrease in the critical micelle concentration (CMC), while the changes in different interfacial parameters indicated enhancement of the hydrophobicity induced by PG in the CTAB micellar system. The dynamic rheology behavior indicated an increase in the flow viscosity (η) as a function of [PG]. Moreover, the rheological components (storage modulus, G', and loss modulus, G″) depicted the viscoelastic features. SANS measurements depicted the existence of ellipsoidal micelles with varying sizes and aggregation number (Nagg) as a function of [PG] and temperature. Computational simulation performed using density functional theory (DFT) calculations and molecular dynamics (MD) provided an insight into the atomic composition of the examined system. The molecular electrostatic potential (MEP) analysis depicted a close proximity of CTAB, i.e., emphasized favorable interactions between the quaternary nitrogen of CTAB and the hydroxyl group of the PG monomer, further validated by the two-dimensional nuclear Overhauser enhancement spectroscopy (2D-NOESY), which showed the penetration of PG inside the CTAB micelles. In addition, various dynamic properties, viz., the radial distribution function (RDF), the radius of gyration (Rg), and solvent-accessible surface area (SASA), showed a significant microstructural evolution of the ellipsoidal micelles in the examined CTAB-PG system, where the changes in the micellar morphology with a more elongated hydrophobic chain and the increased Rg and SASA values indicated the notable intercalation of PG in the CTAB micelles.

Adsorption of P103 Nanoaggregates on Graphene Oxide Nanosheets: Role of Electrostatic Forces in Improving Nanosheet Dispersion.

Graphene oxide (GO) nanosheet suspension is not stable in physiological ionic fluids. To improve stability, surfactants such as Pluronic 103 (P103) have been tested. Going further, this work investigated whether conferring positive surface charge to the surfactant may improve the adsorption ability of P103 micelles on GO sheets. Positive charge on the surfactant was induced by adding dodecyltrimethylammonium bromide (DTAB, a cationic surfactant) in P103 micelles. Subsequent changes in aggregation parameters were investigated through dynamic light scattering and small-angle neutron scattering studies. DTAB incorporation was accompanied by a steady increase in the ζ potential and mixed micelle formation. At high surface charge density, the interaction between adjacent head groups was distorted, which led to dissociation of mixed micelles. Structural developments during the adsorption of mixed micelles on the sheet surface (mass fractal formation) were monitored in terms of changes in the scattering features of aggregates. These fractals emerged as a result of electrostatic interactions. Our observations point toward the existence of small-sized building blocks at low DTAB concentration (≤4 mM). With a superior adsorption, mixed micelles are expected to occupy the intersheet space and maintain a hydration layer. However, at a higher DTAB concentration (≥10 mM), micelles dissociate to produce DTAB-rich unimers and P103-rich loose aggregates. At this point, sheets tend to aggregate in the solvent, regardless of fractal formation.