Structural and therapeutic properties of salicylic acid-solubilized Pluronic solutions and hydrogels

Salicylic acid (SA) finds extensive applications in the treatment of rheumatic and skin diseases because of its analgesic, anti-inflammatory and exfoliating properties. As it is lipophilic in nature, there is a need for appropriate delivery systems to harness these properties for different applications. Herein, we examined the suitability of Pluronic P123/F127 micellar systems as delivery media by investigating the structural, flow and antimicrobial properties of P123/F127-SA solutions and hydrogels using DLS, SANS, rheological and zone inhibition measurement techniques. SA modulates the aggregation characteristics of these surfactant systems and brings about spherical-to-worm-like micelle-to-vesicular structural transitions in the hydrophobic Pluronic P123 system, a spherical-to-worm-like micellar transition in the mixed P123/F127 system and an onset of inter-micellar attraction in the hydrophilic Pluronic F127 system. SA-solubilized systems of both hydrophobic and hydrophilic Pluronics inhibit the growth of Gram-positive and Gram-negative bacteria with comparable MIC values. This suggests that the interaction of SA molecules with the bacterial cell membrane remains unobstructed upon encapsulation in Pluronic micelles. F127 hydrogel-based SA formulations with rheological properties suitable for topical applications and up to 15% SA loading were prepared. These will be useful SA ointments as F127 is an FDA-approved excipient for topical drug delivery applications. The results indicate that Pluronics remain effective as delivery agents for SA and exhibit interesting structural polymorphism upon its solubilization.

Studying the structural organization of non-membranous protein hemoglobin in a lipid environment after reconstitution

In our current work we have developed a supported 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer with embedded hemoglobin, reconstituted via detergent-mediated method. Microscopic studies revealed that the hemoglobin molecules could be visualized without any labelling agents. The reconstituted proteins assemble themselves as supramolecular structures to adapt to lipid bilayer environment. The nonionic detergent, n-octyl-β-d-glucoside (NOG) used for insertion of hemoglobin played an important role in formation of these structures. When concentrations of lipid, protein and detergent were raised by four folds, we observed phase separation by protein molecules within bilayer via protein-protein assembly. This phase separation process exhibited extremely slow kinetics to form large stable domains with correlation times in the order of minutes. Confocal Z-scanning images showed that these supramolecular structures generated membrane deformities. UV-Vis, Fluorescence and Circular Dichroism (CD) measurement indicated minor structural change to expose the hydrophobic regions of the protein to adjust the hydrophobic stress of the lipid environment whilst Small Angle Neutron Scattering (SANS) results indicated that the hemoglobin molecules retained their overall tetrameric form in the system. In conclusion, we state that this investigation allowed us to closely inspect some rare but noteworthy phenomena like the formation of supramolecular structures, large domain formation and membrane deformation etc.

Pluronic Induced Interparticle Attraction and Re-entrant Liquid-Liquid Phase Separation in Charged Silica Nanoparticle Suspensions

Tuning surface properties of nanoparticles by introducing charge, surface functionalization, or polymer grafting is central to their stability and applications. Here, we show that introducing non-DLVO forces like steric and hydrophobic effects in charged silica nanoparticle suspensions through interaction with a nonionic surfactant brings about interesting modulations in their interparticle interaction and phase behavior. The Ludox TM-40 negatively charged silica suspensions thus exhibit liquid-liquid phase separation driven by the onset of interparticle attraction in the system in the presence of the triblock copolymer Pluronic P123. The observed phase separations are thermoresponsive in nature, as they are associated with lower consolute temperatures and a re-entrant behavior as a function of temperature. The nanoparticle-Pluronic system thus undergoes transformation from one-phase to two-phase and then back to one-phase with monotonic increase in temperature. Evolution of the interparticle interaction in the composite system is investigated by dynamic light scattering (DLS), small angle neutron scattering (SANS), zeta potential, rheological, and fluorescence spectroscopy studies. Zeta potential studies show that the charge interaction in the system is partially mitigated through adsorption of a Pluronic micellar layer on the nanoparticle surfaces. Contrast-matching SANS studies suggest that hydrophobic interactions between the adsorbed micellar layer bring about the onset of interparticle attraction in the system. The results are unique and not reported hitherto in charged silica nanoparticle systems.

Chain-folding regulated self-assembly, outstanding bactericidal activity and biofilm eradication by biomimetic amphiphilic polymers

Chain-folding regulated hierarchical self-assembly of cationic host defense peptide mimicking amphiphilic polyurethanes exhibit excellent antibacterial activity and biofilm killing.

Unusual Growth and Hydration Characteristics of Oil Solubilized Micelles in Aqueous Pluronic Systems

Lipophile induced modulations of self-assembly characteristics in aqueous Pluronic systems merit attention because of wide-ranging uses of Pluronics as solubilizing agents of lipophilic substances. In this paper, we report unusual evolutions of structural and hydration properties in lavender essential oil (LO) solubilized Pluronic P85 aqueous micellar systems as a function of micellar volume fraction and temperature. Our DLS, SANS, and viscometry studies show that the spherical-to-wormlike micellar structural transition observed in 1% P85 solutions upon solubilization of LO quite unexpectedly gets suppressed with increased P85 concentration to ≥5%. Detailed SANS studies reveal that the core sizes of the oil solubilized micelles cannot attain the threshold value required for the onset of structural transition at higher copolymer concentrations due to their progressive shrinking with an increase in P85 concentration. Oil solubilized P85 solutions show two cloud points and very interestingly exhibit micellar growth upon cooling to their lower cloud points. Steady state fluorescence studies explain this based on increasing dehydration of micellar corona with a decrease in temperature, very much opposite to what is observed in pure aqueous Pluronic systems. The results give new insight into viscous flow properties and low temperature storage possibilities of oil solubilized aqueous Pluronic systems.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH₂ - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

Polymer-mediated interaction between nanoparticles during hydration and dehydration: a small-angle X-ray scattering study

Polymer-mediated interactions such as DNA-protein binding, protein aggregation, and filler reinforcement in polymers play crucial roles in many important biological and industrial processes. In this work, we report a detailed investigation of interactions between nanoparticles in the presence of high volume fractions of an adsorbing polymer. Small-angle X-ray scattering (SAXS) revealed the existence of a stable gel-like structure in the polymer-nanoparticle dispersion, whereby anchored polymer molecules on nanoparticles acted as bridging centres, while basic interactions between nanoparticles remained repulsive. Time-resolved SAXS measurements showed that the local volume fraction of nanoparticles increased during the drying of the dispersion owing to the shrinkage of the gel-like structure. Further, nanoparticle clusters in the dehydrated composite films showed percolated networks of nanoparticles, except for 5% loading that showed a phase-separated morphology as the volume fraction of nanoparticles remained lower than the percolation threshold. A significant restructuring of nanoparticle clusters occurred upon the hydration of nanocomposite films caused by the expansion of polymer networks induced by hydration forces. Temporal evolution of the volume fraction of nanoparticles during dehydration unveiled three distinct stages similar to the logistic growth function and this was attributed to the evaporation of free, intermediate, and bound water in the different stages. A plausible mechanism was elucidated based on the spring action analogy between anchored polymer chains and nanoparticles during hydration and dehydration processes.

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.

Ubiquity of complex coacervation of DNA and proteins in aqueous solution

We report complex coacervation between a primarily hydrophobic protein, elastin, and a strong polyanion DNA (2 kbp) in aqueous and salty solutions at room temperature, 25 °C. The associative interaction at fixed elastin and varying DNA concentration, thereby maintaining a mixing ratio of r = [DNA] : [elastin] = 0.0027 to 0.093, was probed. What distinguishes this study from protein-DNA coacervation reported earlier is that the protein used here was mostly a hydrophobic polyampholyte with low linear charge density, and its complementary polyelectrolyte, DNA, concentration was chosen to be extremely small (1-35 ppm). The interaction profile was found to be strongly hierarchical in the mixing ratio, defined by three distinct regions: (i) Region I (r < 0.02) was defined as the onset of primary binding leading to condensation of DNA; (ii) Region II (0.02 < r < 0.08) indicated secondary binding which led to the formation of fully charge neutralized complexes signaling the onset of coacervation; and (iii) Region III (0.08 < r < 0.12) revealed growth of insoluble complexes of large size facilitating liquid-solid phase separation. The degree of complex coacervation was suppressed in the presence of a monovalent salt implying that screened Coulomb interactions governed the binding. Small angle neutron scattering data attributed an amorphous structure to the coacervates. The elastin-DNA system belongs to a rare class of interacting biopolymers where very weak electrostatic interactions may drive coacervation, thereby implying that coacervation between DNA and proteins may be ubiquitous.

Versatile surface-active ionic liquid: construction of microemulsions and their applications in light harvesting

This article outlines a sustainable method towards the synthesis of advanced materials such as core/shell Quantum Dots (QDs) and their in situ stabilization using microemulsions (MEs). QDs are versatile materials which show unusual optical properties. We have constructed MEs consisting of an Ionic Liquid (IL) based surfactant i.e. choline dioctylsulfosuccinate, [Cho][AOT] as an emulsifier, toluene as a nonpolar phase and water as a polar phase. The system forms a large single-phase region in the phase diagram without any co-surfactant. Spontaneous formation of micelles has been observed and studied through tensiometry and fluorescence and isothermal titration calorimetry (ITC). The exceptional swelling behaviour of the MEs was studied using Dynamic Light Scattering (DLS) and small angle neutron scattering (SANS). In ME droplets, i.e. Reverse Micelles (RMs), we successfully synthesized spherical core/shell QDs (size ∼3 to ∼6 nm) with precise control over the size and morphology. The QDs have been characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Powder X-ray Diffraction (PXRD). QDs stabilized in MEs exhibited excellent optical properties and can be suitably used as light harvesting materials for diverse applications.

Thermal and microwave synthesized SPIONs: Energy effects on the efficiency of nano drug carriers

Superparamagnetic iron oxide nanoparticles (SPIONs) were optimally synthesized employing two energy sources viz. thermal and microwave using low temperature co-precipitation process. Both methods yielded particles with optimum physicochemical properties for biomedical applications like smaller size (~6--7 nm), narrow size distribution (standard deviation ~1.6-1.7 nm) and good magnetic parameters (saturation magnetisation ~53 emu/g at 9 T). Simplified process made use of domestic oven. After coating by amino acid serine, successful loading (>8 wt%) of drug Doxorubicin was achieved for both SPIONs. Microwave sample showed equivalently efficient drug loading despite half the serine coating. Findings were confirmed by various techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), Vibrating sample magnetometer (VSM) and thermo gravimetric analysis (TGA) etc. Differences in thermal homogeneities and efficiency of heat transfer between two energy modes affected the properties of synthesized SPIONs. Differences were observed in amount of serine coating, drug release behaviour and in vitro experiments on A549 cells like internalisation and cell viability data. About 59 and 39% pH and time dependent drug release at pH 5 was obtained for thermal and microwave sample respectively. In vitro experiments confirmed the successful internalisation and cell death, supporting the suitability of SPIONS as efficient targeted drug carriers. Despite lesser drug release, microwave sample showed comparable in vitro results. Study emphasizes the role and importance of energy in affecting the efficiency and functional behaviour of SPIONs as nano drug carriers. Being biocompatible and magnetic these particles can be applied successfully as efficient targeted drug delivery agents.

Synthesis, thermal and surface activity of cationic single chain metal hybrid surfactants and their interaction with microbes and proteins

A series of water-soluble metal functionalized surfactants have been prepared using commercially available surfactant cetyl pyridinium chloride and transition metal salts. These complexes were characterized in the solid state by elemental analysis, FTIR, 1H NMR and thermogravimetric analysis. The interfacial surface activity and aggregation behaviour of the metallosurfactants were analysed through conductivity, surface tension and small angle neutron scattering measurements. Our results show that the presence of metal ions as co-ions along with counter ions favours micellization at a low critical micellization concentration (CMC). Small angle neutron scattering revealed that the metallomicelles are of a prolate ellipsoidal shape and exhibit strong counterion binding. This article further describes the interaction of the metallosurfactants with transport protein Bovine Serum Albumin (BSA) using different spectroscopic techniques. A spectroscopic study was used to study the binding, interaction and quenching mechanism of BSA with the metallosurfactants. Gel electrophoresis (SDS-PAGE) and circular dichroism (CD) investigated the structural and conformational changes produced in BSA due to the metallosurfactants. The results indicate that there is an alteration in the secondary structure of BSA due to the electrostatic interaction between positive head groups and metal co-ions of the metallosurfactants and negatively charged amino acids of BSA. As the concentration increases, the α-helicity of BSA decreases and all the three studied metallosurfactants gave comparable results. Finally, the in vitro cytotoxicity and antimicrobial activity of the metallosurfactants were evaluated against erythrocytes and microorganisms, which showed prominent effects related to the presence of a metal ion in metallomicelles of the hybrid surfactants.

Mixing ratio dependent complex coacervation versus bicontinuous gelation of pectin with in situ formed zein nanoparticles

We report on the competitive phenomenon of complex coacervation versus bicontinuous gelation between pectin (P, a polyanionic carbohydrate, [P] = 0.01-2% (w/v)) and zein nanoparticles (Z, a hydrophobic protein and a weak polyampholyte, [Z] = 0.1 and 0.5% (w/v), in an ethanolic solution of effective concentration 4 and 27% (v/v)), which was studied below (pH ≈ 4), and above (pH ≈ 7.4) the pI (≈ 6.2) of zein at room temperature, 25 °C. The uniqueness of this study arises from the interaction protocol used, where the pectin used was in the extended polyelectrolyte (persistence length ≈ 10 nm) conformation while zein was used as a charged globular nanoparticle (size ≈ 80-120 nm) that was formed in situ. Their mixing ratio, r = [P] : [Z] (w/w), was varied from 0.02 to 4.0 (for [Z] = 0.5% (w/v)), and from 0.1 to 7.5 (for [Z] = 0.1% (w/v)) in the ionic strength range 10-4 to 10-2 M NaCl. Zeta potential data revealed that at pH ≈ 4, the complementary binding condition, r = 1 : 1 (equivalent to 1 : 5 molecule/nanoparticle) demarcated the coacervate from the gel region. The measured rigidity (G0, low frequency storage modulus) of these materials revealed the following: for r < 1, (low pectin content samples, coacervate region) the material had lower values of Gcoac0, whereas for r > 1, an excess of pectin facilitated gelation with Ggel0 ≫ Gcoac0. Above pI, surface patch binding caused associative interactions and complex coacervation though both biopolymers had similar net charge. The network density was used as a descriptor to distinguish between the coacervate and gel samples. Their microstructures were probed by small angle neutron scattering (SANS), and viscoelastic properties by rheology. Simple modeling shows that formation of the interpolymer complex was favored in higher protein containing samples. Mixing ratio dependent selective coacervation (a kinetic process) and bicontinuous gelation (a thermodynamic process) are rarely seen to coexist in biopolymer interactions.

Mechanically robust dual responsive water dispersible-graphene based conductive elastomeric hydrogel for tunable pulsatile drug release

Nanohybrid hydrogels based on pristine graphene with enhanced toughness and dual responsive drug delivery feature is opening a new era for smart materials. Here pristine graphene hydrogels are synthesized by in situ free radical polymerization where graphene platelets are the nanobuiliding blocks to withstand external stress and shows reversible ductility. Such uniqueness is a mere reflection of rubber-like elasticity on the hydrogels. These nanobuilding blocks serve also the extensive physisorption which enhances the physical crosslinking inside the gel matrix. Besides the pH-responsive drug release features, these hydrogels are also implemented as a pulsatile drug delivery device. The electric responsive drug release behaviours are noticed and hypothesized by the formation of conducting network in the polyelectrolytic hydrogel matrix. The hydrogels are also tested as good biocompatibility and feasible cell-attachment during live-dead cell adhesion study. The drug release characteristics can also be tuned by adjusting the conducting filler loading into the gel matrix. As of our knowledge, this type of hydrogels with rubber-like consistency, high mechanical property, tunable and dual responsive drug delivery feature and very good human cell compatible is the first to report.

Pluronic®-bile salt mixed micelles

The present study was aimed to examine the interaction of two bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) with three ethylene polyoxide-polypropylene polyoxide (PEO-PPO-PEO) triblock copolymers with similar PPO but varying PEO micelles with a focus on the effect of pH on mixed micelles. Mixed micelles of moderately hydrophobic Pluronic^® P123 were examined in the presence of two bile salts and compared with those from very hydrophobic L121 and very hydrophilic F127. Both the bile salts increase the cloud point (CP) of copolymer solution and decreased apparent micelle hydrodynamic diameter (D_h). SANS study revealed that P123 forms small spherical micelles showing a decrease in size on progressive addition of bile salts. The negatively charged mixed micelles contained fewer P123 molecules but progressively rich in bile salt. NaDC being more hydrophobic displays more pronounced effect than NaC. Interestingly, NaC shows micellar growth in acidic media which has been attributed to the formation of bile acids by protonation of carboxylate ion and subsequent solubilization. In contrast, NaDC showed phase separation at higher concentration. Nuclear Overhauser effect spectroscopy (NOESY) experiments provided information on interaction and location of bile salts in micelles. Results are discussed in terms of hydrophobicity of bile salts and Pluronics^® and the site of bile salt in polymer micelles. Proposed molecular interactions are useful to understand more about bile salts which play important role in physiological processes.

Sodium deoxycholate mediated enhanced solubilization and stability of hydrophobic drug Clozapine in pluronic micelles

In this report, the solubilization behaviour of a hydrophobic drug Clozapine (CLZ) in micellar suspensions of pluronics having different hydrophilic lipophilic balance (HLB) ratios viz. P84, F127 and F108 in the absence and presence of bile salt sodium deoxycholate (SDC) has been studied. UV-Vis spectroscopy has been exploited to determine the solubilization capacity of the investigated micellar systems in terms of drug loading efficiency, average number of drug molecules solubilized per micelle (n_s), partition coefficient (P) and standard free energy of solubilization (∆G^°). The morphological and structural changes taking place in pluronics in different concentration regimes of SDC and with the addition of drug CLZ has been explored using dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements. The SANS results revealed that aggregation behaviour of pluronic-SDC mixed micelles gets improved in the presence of drug. The micropolarity measurements have been performed to shed light on the locus of solubilization of the drug in pure and mixed micellar systems. The compatibility between CLZ and drug carriers (pluronics and SDC) was confirmed using powder X-ray diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR) techniques. Among the investigated systems, P84-SDC mixed system was found to be highly efficient for CLZ loading. The long term stability data indicated that CLZ loaded P84-SDC mixed micellar formulation remained stable for 3months at room temperature. Further, it was revealed that the CLZ loaded P84-SDC mixed micelles are converted into CLZ loaded pure P84 micelles at 30-fold dilutions which remain stable up to 48-fold dilutions. The results from the present studies suggest that P84-SDC mixed micelles can serve as suitable delivery vehicles for hydrophobic drug CLZ.

PEG coated vesicles from mixtures of Pluronic P123 and l-α-phosphatidylcholine: structure, rheology and curcumin encapsulation

PEG coated vesicles are important vehicles for the passive targeting of anticancer drugs. With a view to prepare PEG decorated vesicles using co-assembly of block copolymers and lipids, here we investigated the microstructure of aggregates formed in mixtures comprising lipids (l-α-phosphatidylcholine) and block copolymers (Pluronic P123), in the polymer rich regime. DLS and SANS studies show that the structure of the aggregates can be tuned from micelles to rod-like micelles or vesicles by changing the lipid to polymer composition. Rheological studies on gels formed by mixtures of polymer and lipid suggest incorporation of the lipid into the polymer matrix. The encapsulation efficiencies of polymer incorporated liposomes for curcumin and doxorubicin hydrochloride (DOX) are evaluated at different drug to carrier ratios. The pH dependent sustained release of both the drugs from the PEGylated liposomes suggests their application in the development of cost effective formulations for anticancer drug delivery.

DNA ionogel: Structure and self-assembly

DNA dissolved in ionic liquid (IL) solution (1-ethyl-3-methylimidazolium chloride, [C2mim][Cl]) showed a transition to the gel phase ([DNA] ≥ 1% (w/v)). The gelation time was 400 s for the 1% [IL] sample which reduced to 260 s for 5% [IL] concentration. Gelation times, obtained from the viscosity and ergodicity breaking from the dynamic structure factor data, were remarkably identical to each other. Correspondingly, the gelation temperature which was ∼60 °C increased to 67 °C with [IL] content. The small angle neutron scattering (SANS) structure factor profile revealed the presence of the following three distinct length scales: (a) mesh size, ξ ≈ 3 ± 0.5 nm for ionogels, and ≈0.73 ± 0.06 nm, for sol; (b) cross-sectional radius of DNA strand, R_c ≈ 1.6 ± 0.1 nm; and (c) the characteristic inter-cluster distance ≈33 ± 5 nm. Physical conformation of the DNA-IL complexes remained close to the Gaussian coil definition. It was observed that without IL, in the sol phase, the system was completely ergodic and did not gel, while on addition of IL a sudden transition to the non-ergodic (arrested) gel phase occurred. This was due to the formation of an amorphous network of DNA-IL complexes preceding gelation. In summary, it is shown that the DNA ionogels can be prepared with a tunable gel strength (27-70 Pa) and gelation temperature (60-67 °C). Further, the relaxation dynamics was found to be hierarchical in IL content of the gel, revealing considerable self-organization.

Aggregation and Rheological Behavior of the Lavender Oil-Pluronic P123 Microemulsions in Water-Ethanol Mixed Solvents

The effect of lavender oil on aggregation characteristics of P123 in aqueous-ethanolic solutions is investigated systematically by DLS, SANS, and rheology. The solubilization capacity of the P123 based formulations toward Lavender oil increased by increasing P123 concentration. The study unveiled the importance of the short chain alcohol-ethanol, as solubilization enhancer. The apparent hydrodynamic radius (R_h) increased significantly with an increase in lavender oil concentration up to maximum oil solubilization capacity of the copolymer at a particular ethanol concentration. DLS measurements on 5, 10, and 15 wt% P123 in the presence of 25% ethanol revealed the presence of large-sized micellar clusters in addition to the oil swollen micelles. The core size (R_C), radius of hard sphere (R_HS), and aggregation number (N) obtained from SANS profiles showed considerable enhancement with the addition of lavender oil confirming penetration of oil inside the copolymer. Rheological studies showed that viscosity also increased significantly with the addition of lavender oil near the maximum loading limit of the P123 concentration. Quite interestingly, the sol-gel transition temperature displayed a strong dependence on both P123 as well as oil concentration and decreased almost linearly by increasing oil concentration. This study demonstrates the use of a biocompatible and temperature sensitive self-assembled P123 based formulation for lavender oil solubilization that can be beneficial in the cosmetic industry wherein controlled release of fragrances and so forth is demanded.

Morphological changes in human serum albumin in the presence of cationic amphiphilic drugs

Binding of cationic amphiphilic drugs results in unfolding of human serum albumin.

Solvent hydrophobicity induced complex coacervation of dsDNA and in situ formed zein nanoparticles

Zein, a predominantly hydrophobic protein, was sustained as a stable dispersion in ethanol-water (80 : 20, % (v/v)) binary solvent at room temperature (25 °C). Addition of aqueous dsDNA solution (1% (w/v)) to the above dispersion prepared with the protein concentration of C_zein = 0.01-0.5% (w/v) caused a concomitant change in ethanol content from 14-35% (v/v), which in turn generated zein nanoparticles in situ of size 80-120 nm increasing with water content. The subsequent associative interaction between DNA (polyanion; 2000 bps) and the positively charged zein nanoparticles, (at pH = 4) was driven by Coulombic forces, and by the solvent hydrophobicity due to the ethanol content of the binary solvent. Experimentally, two interesting regions of interaction were observed from turbidity, zeta potential, particle sizing, and viscosity data: (i) for C_zein < 0.2% (w/v), zein nanoparticles of size 80 nm bind to dsDNA (primary complex) causing its condensation (apparent hydrodynamic size decreased from ≈2100 to 560 nm), and (ii) for 0.2% < C_zein < 0.5% (w/v) larger nanoparticles (>80 nm) were selectively bound to primary complexes to form partially charge neutralized interpolymer soluble complexes (secondary complexes), followed by complex coacervation. During this process, there was depletion of water in the vicinity of the nucleic acid, which was replaced by hydration provided by the ethanol-water binary solvent. Equilibrium coacervate samples were probed for their microstructure by small angle neutron scattering, and for their viscoelastic properties by rheology. The interplay of solvent hydrophobicity, electrostatic interaction, and zein nanoparticle size dependent charge neutralization had a commensurate effect on this hitherto unexplored coacervation phenomenon.

The effect of temperature, composition and alcohols on the microstructures of catanionic mixtures of sodium dodecylsulfate and cetyltrimethylammonium bromide in water

The influence of mixing protocol, composition, temperature, ageing and added alcohols on the characteristics of the microstructures of sodium dodecylsulfate (SDS) + cetyltrimethylammonium bromide (CTAB) mixtures has been investigated in this paper. In this catanionic mixture (1 weight% total surfactant content) temperature induced microstructural transition occurs, which is (i) a micelle-to-vesicle transition (MVT) if α_SDS (mole fraction of SDS) = 0.7, 0.8 or 0.9 and (ii) a vesicle-to-micelle transition (VMT) if α_SDS = 0.1, 0.2 or 0.3. In the mixture of α_SDS = 0.7, specific conductivity and dynamic light scattering measurements also support the occurrence of MVT. Transition electron microscopy and small angle neutron scattering measurements were also made to assess the characteristics of the microstructures. Alcohols added to the mixture of α_SDS = 0.7 reduced the size of the vesicle, while only monohydric alcohols suppressed the temperature induced transition indicating that the number and location of -OH groups of the alcohols have a dramatic modulating influence on the structural transition occurring in catanionic mixtures. The influence of the alcohols is explained in terms of changes produced in the dielectric constant and hydrophobicity of the medium.

Vesicle to micelle transition in the ternary mixture of L121/SDS/D2O: NMR, EPR and SANS studies

Proposed model depicting vesicle to mixed micelle transformation in a ternary mixture of L121/SDS/D₂O.

Hierarchical Internal Structures in Gelatin-Bovine Serum Albumin/β-Lactoglobulin Gels and Coacervates

Herein, we report the comparative study of gels and complex coacervates of bovine serum albumin (BSA) and beta-lactoglobulin (β-Lg) with gelatin close to their common pI. Surface patch binding produced a range of new soft matter phases (interpolymer complexes) such as opaque coacervates (charge neutralized complexes) and transparent gels (overcharged complexes). We emphasize on the comparative study of the microstructure of coacervates and gels formed at different mixing ratios using small angle scattering (SANS) data. It was found that phase states were entirely defined by the mixing ratio r = [GB]:[β-Lg or BSA]. Thermo-viscoelastic profiles of aforesaid samples revealed a smaller storage modulus and lower melting temperature for coacervates compared to gels. Thermally activated samples generated additional phases that were also probed by SANS and rheology. Thus, it is established that intermolecular association between globular proteins and a random coil polypeptide can generate various soft matter states that may facilitate harvesting of novel biomaterials.

Surface and Aggregation Behavior of Pentablock Copolymer PNIPAM7-F127-PNIPAM7 in Aqueous Solutions

The triblock Pluronic F127 was modified by introducing poly(N-isopropylacrylamide) (PNIPAM) at both the poly(ethylene oxide) ends, and the pentablock copolymer so-prepared was characterized by gel permeation chromatography and (1)H NMR. The degree of polymerization of NIPAM blocks at the two ends was 7. The solution behavior and microstructure of copolymer aggregates in water and aqueous salt solution were examined and compared with F127 by UV-visible absorption spectroscopy, microdifferential scanning calorimetry, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The behavior of the pentablock copolymer at the air/water interface was determined by Langmuir film balance. Two lower critical solution temperatures were observed for pentablock copolymer, corresponding to poly(propylene oxide) and PNIPAM blocks, respectively. DLS studies show that micelle size increased with increase in temperature and in the presence of salt. SANS measurements provided temperature-dependent structural evolution of copolymer micelles in water and salt solution. The copolymer displays an isotherm with four classical regions (pancake, mushroom, brush, and condensed state). The study has potential applications in controlled drug delivery due to the tunable phase behavior and biocompatibility of the copolymer.

Trends in small angle neutron scattering of actinide–trialkyl phosphate complexes: a molecular insight into third phase formation

SANS as a molecular probe was used to investigate and quantify the aggregation tendency of metal complexes, facilitating the prediction of third phase formation.

Hybrid surfactants decorated with copper ions: aggregation behavior, antimicrobial activity and anti-proliferative effect

In the present study, the emphasis is laid on the self aggregation behavior and biological activity of copper based inorganic–organic hybrids in aqueous media.

Aggregation and surface behavior of aqueous solutions of cis-bis(1,3-diaminopropane)bis(dodecylamine)cobalt(iii) nitrate. A double-chained metallosurfactant

Metallosurfactants or amphiphilic metal complexes are emerging as a new class of material with a range of properties inherent to both metal complexes and surfactants.

Electrolyte effect on the phase behavior of silica nanoparticles with lysozyme and bovine-serum-albumin proteins

Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) studies have been carried out to investigate the effect of an electrolyte on the phase behavior of anionic silica nanoparticles with two globular proteins-cationic lysozyme [molecular weight (MW) 14.7 kDa] and anionic bovine serum albumin (MW 66.4 kDa). The results are compared with our earlier published work on similar systems without any electrolyte [I. Yadav, S. Kumar, V. K. Aswal, and J. Kohlbrecher, Phys. Rev. E 89, 032304 (2014)]. Both the nanoparticle-protein systems transform to two phase at lower concentration of protein in the presence of an electrolyte. The autocorrelation function in DLS suggests that the diffusion coefficient (D) of a nanoparticle-protein system decreases in approaching two phase with the increase in protein concentration. This variation in D can be attributed to increase in attractive interaction and/or overall increase in the size. Further, these two contributions (interaction and structure) are determined from the SANS data. The changes in the phase behavior of nanoparticle-protein systems in the presence of an electrolyte are explained in terms of modifications in both the repulsive and attractive components of interaction between nanoparticles. In a two-phase system individual silica nanoparticles coexist along with their fractal aggregates.

Extractant mediated nano-aggregate formation in Triton X-114 aided cloud formation: structural insights from TEM and SANS studies

Nanoaggregate formation by self assembly was noticed during the cloud formation of Triton X-114 in the presence of dibenzoylmethane (DBM), thenoyltrifluoroacetone (HTTA) and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and tributyl phosphate (TBP).

Interactions in globular proteins with polyampholyte: coacervation route for protein separation

Representative model of protein–protein separation in a BSA–GB–β-Lg aqueous solution.

Effect of sodium salicylate and sodium deoxycholate on fibrillation of bovine serum albumin: comparison of fluorescence, SANS and DLS techniques

Adsorbed sodium salicylate (NaSal) and sodium deoxycholate (NaDC) retard the thermal denaturation of bovine serum albumin.

Controlling the aggregation of sodium dodecylsulphate in aqueous poly(ethylene glycol) solutions

The role of PEG's of different molecular weights on the self-assembly of SDS and the role of added NaCl has been addressed opening new scopes for further studies.

TBP induced double cloud point in aqueous EO13PO30EO13 solutions: investigating the evolution of associated micellar characteristics as a function of temperature

TBP solubilized Pluronic L64 solutions exhibit inter-micellar attraction driven micellar cluster formation upon cooling, which is unique in non-ionic micellar systems.

Physicochemical perspectives (aggregation, structure and dynamics) of interaction between pluronic (L31) and surfactant (SDS)

The influence of the water soluble non-ionic tri-block copolymer L31 on the microstructure and self-aggregation dynamics of the anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution was investigated.

Pluronic copolymer encapsulated SCR7 as a potential anticancer agent

Nonhomologous end joining (NHEJ) of DNA double strand breaks (DSBs) inside cells can be selectively inhibited by 5,6-bis-(benzylideneamino)-2-mercaptopyrimidin-4-ol (SCR7) which possesses anticancer properties. The hydrophobicity of SCR7 decreases its bioavailability which is a major setback in the utilization of this compound as a therapeutic agent. In order to circumvent the drawback of SCR7, we prepared a polymer encapsulated form of SCR7. The physical interaction of SCR7 and Pluronic® copolymer is evident from different analytical techniques. The in vitro cytotoxicity of the drug formulations is established using the MTT assay.

Influence of hydrotropic coions on the shape transitions of sodium dioctylsulfosuccinate aggregates in an aqueous medium

The slope change of the CH plot is a manifestation of the shape change of the ionic micelles. However, binding of the salicylate coion to ionic micelles is an exception to this inference.

pH-switchable structural evolution in aqueous surfactant-aromatic dibasic acid system

Structural transitions triggered by pH in an aqueous micellar system comprising of a cationic surfactant (cetylpyridinium chloride) and an aromatic dibasic acid (phthalic acid) was investigated. Reversible switching between liquid-like and gel-like states was exhibited by the system on adjusting the solution pH. Self-assembled structures, responsible for the changes in flow properties were identified using rheology, light scattering techniques and cryogenic Transmission Electron Microscopy (cryo-TEM). High-viscosity, shear-thinning behavior and Maxwell-type dynamic rheology shown by the system at certain pH values suggested the growth of spheroidal/short cylindrical micelles into long and entangled structures. Light scattering profiles also supported the notion of pH-induced microstructural transitions in the solution. Cryo-TEM images confirmed the presence of spheroidal/short cylindrical micelles in the low-viscosity sample whereas very long and entangled thread-like micelles in the peak viscosity sample. pH-dependent changes in the micellar binding ability of phthalic acid is proposed as the key factor regulating the morphological transformations and related flow properties of the system.

Micellar solution with pH responsive viscoelasticity and colour switching property

Macroscopic properties of amphiphilic systems can be reversibly controlled by tailoring micellar morphology via appropriate choice of additive and external stimulus.

Enhanced efficacy of pluronic copolymer micelle encapsulated SCR7 against cancer cell proliferation

5,6-Bis(benzylideneamino)-2-mercaptopyrimidin-4-ol (SCR7) is a new anti cancer molecule having capability to selectively inhibit non-homologous end joining (NHEJ), one of the DNA double strand break (DSB) repair pathways inside the cells. In spite of the promising potential as an anticancer agent, hydrophobicity of SCR7 decreases its bioavailability. Herein the entrapment of SCR7 in Pluronic copolymer is reported. The size of the aggregates was determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) which yields an average diameter of 23 nm. SCR7 encapsulated micelles (ES) were also characterized by small-angle neutron scattering (SANS). Evaluation of its biological properties by using a variety of techniques, including Trypan blue, MTT and Live-dead cell assays, reveal that encapsulated SCR7 can induce cytotoxicity in cancer cell lines, being more effective in breast cancer cell line. Encapsulated SCR7 treatment resulted in accumulation of DNA breaks within the cells, resulting in cell cycle arrest at G1 phase and activation of apoptosis. More importantly, we found ≈ 5 fold increase in cell death, when encapsulated SCR7 was used in comparison with SCR7 alone.

Structure and interaction in the polymer-dependent reentrant phase behavior of a charged nanoparticle solution

Small-angle neutron scattering (SANS) studies have been carried out to examine the evolution of interaction and structure in a nanoparticle (silica)-polymer (polyethylene glycol) system. The nanoparticle-polymer solution interestingly shows a reentrant phase behavior where the one-phase charged stabilized nanoparticles go through a two-phase system (nanoparticle aggregation) and back to one-phase as a function of polymer concentration. Such phase behavior arises because of the nonadsorption of polymer on nanoparticles and is governed by the interplay of polymer-induced attractive depletion with repulsive nanoparticle-nanoparticle electrostatic and polymer-polymer interactions in different polymer concentration regimes. At low polymer concentrations, the electrostatic repulsion dominates over the depletion attraction. However, the increase in polymer concentration enhances the depletion attraction to give rise to the nanoparticle aggregation in the two-phase system. Further, the polymer-polymer repulsion at high polymer concentrations is believed to be responsible for the reentrance to one-phase behavior. The SANS data in polymer contrast-matched conditions have been modeled by a two-Yukawa potential accounting for both repulsive and attractive parts of total interaction potential between nanoparticles. Both of these interactions (repulsive and attractive) are found to be long range. The magnitude and the range of the depletion interaction increase with the polymer concentration leading to nanoparticle clustering. At higher polymer concentrations, the increased polymer-polymer repulsion reduces the depletion interaction leading to reentrant phase behavior. The nanoparticle clusters in the two-phase system are characterized by the surface fractal with simple cubic packing of nanoparticles within the clusters. The effect of varying ionic strength and polymer size in tuning the interaction has also been examined.

Hierarchical surface charge dependent phase states of gelatin-bovine serum albumin dispersions close to their common pI

We report interaction between bovine serum albumin ([BSA] = 1% (w/v)) and gelatin B ([GB] = 0.25-3.5% (w/v)) occurring close to their common isoelectric pH (pI). This interaction generated distinguishable multiple soft matter phases like opaque coacervates (phase I) and transparent gels (phase II), where the former are composed of partially charge neutralized intermolecular complexes (zeta potential, ζ ≤ 0) and the latter of overcharged complexes (ζ ≥ 0) that organized into a network pervading the entire sample volume. These phase states were completely governed by the protein mixing ratio r = [GB]:[BSA]. Coacervates, when heated above 32 °C, produced thermoirreversible turbid gels (phase III), stable in the region 32 ≥ T ≤ 50 °C. When the transparent gels were heated to T ≥ 34 °C, these turned into turbid solutions that did form a turbid fragile gel (phase IV) upon cooling. Mechanical and thermal behaviors of aforesaid coacervates (phase I) and gels (phase II) were examined; coacervates had lower storage modulus and melting temperature compared to gels. Cole-Cole plots attributed considerable heterogeneity to coacervate phase, but gels were relatively homogeneous. Raman spectroscopy data suggested differential microenvironment for these phases. Coacervates were mostly hydrated by partially structured water with degree of hydration dependent on gelatin concentration whereas for gels hydration was invariant of [GB]. Small-angle neutron scattering (SANS) data gave static structure factor profiles, I(q), versus wavevector q, that were remarkably different. For transparent gels, data could be split into two distinct regions: (i) 0.01 < q < 0.1 Å(-1), I(q) = IOZ(0)/(1 + q(2)ζgel(2))(2) (Debye-Bueche function) with ζgel = 9-13 nm, and (ii) 0.1 < q < 0.35 Å(-1), I(q) = IOZ(0)/(1 + q(2)ξgel(2)) (Ornstein-Zernike function) with ξgel = 3.1 ± 0.6 nm. Similarly, for coacervate, the aforesaid two q-regions were described by (i) I(q) = IPL(0)q(-α) with α = 1.7 ± 0.1 and (ii) I(q) = IOZ(0)/(1 + q(2)ξcoac(2)) with ξcoac = 1.6 ± 0.2 nm, a value close to the persistence length of gelatin chain (lp ≈ 2 nm). Phase transition from one equilibrium state to another, i.e., phase I to II, was hierarchical in the charge state of the protein-protein complex. Within the same charge state, transition from phase I to III and from phase II to IV was thermally activated. The aforesaid mechanisms are captured in a unique ζ-T phase diagram.