Cloud Point Studies Research Articles

A recent overview of surfactant-drug interactions and their importance.

This review focuses on the self-aggregation properties of different drugs, as well as on their interaction with anionic, cationic, and gemini surfactants. The interaction of drugs with surfactants has been reviewed concerning conductivity, surface tension, viscosity, density, and UV-Vis spectrophotometric measurements, and their relation with critical micelle concentration (CMC), cloud point, and binding constant. The conductivity measurement technique is used for the micellization of ionic surfactants. Cloud point studies can be used for the non-ionic, and also for certain ionic surfactants. Usually, surface tension studies are mostly employed for non-ionic surfactants. The degree of dissociation that is determined is used to evaluate thermodynamic parameters of micellization at various temperatures. The effect of external parameters like temperature, salt, solvent, pH, etc., is discussed for thermodynamics parameters using recent experimental works on drug-surfactant interactions. Consequences of drug-surfactant interaction, condition of drugs during interaction with surfactants, and applications of drug-surfactant interaction are being generalized which reflects current and future potential uses of drug-surfactant interactions.

Conductivity and cloud point studies of the interaction of lomefloxacin hydrochloride with anionic and nonionic surfactants in electrolytes solution

The interaction of lomefloxacin hydrochloride (LMFH) drug (utilized to treat different bacterial infections) with anionic (sodium dodecyl sulfate (SDS)) and nonionic (triton X-100 (TX-100)) surfactants in electrolytes media has been carried out applying the conductometric and cloud point (CP) measurement methods. SDS is very useful to prohibit different viral infections and to extract DNA/RNA. Two critical micelle concentrations (cmc) were observed for LMFH + SDS mixtures within the investigated surfactant concentration. The cmc values of SDS increase monotonically with the increase of the LMFH concentration. The cmc values of LMFH + SDS mixtures were reduced as the ionic strength of electrolytes increases. In the case of the LMFH + SDS mixture, the cmc values showed reverse U-shaped change with the augmentation of temperature in the electrolyte medium. The extent of counterion binding (β) varies significantly with the change of ionic strength of the electrolytes and concentration of the drug. The CP values of the LMFH + TX-100 mixture was increased and decreased with the enhancing of LMFH and electrolyte concentrations respectively. The standard Gibbs free energy changes both for first and second micellization (ΔG1,mo &ΔG2,mo) were attained to be negative throughout the study suggesting spontaneous micellization of LMFH + SDS mixture in all the cases. The ΔG1,mo &ΔG2,mo values increase with the increase of temperature. Again, ΔG2,mo > ΔG1,mo signify that second micellization is more spontaneous. The positive free energy changes of the LMFH + TX-100 mixture reveal the nonspontaneous nature of the clouding process. The non-spontaneity of clouding experiences a reduction with the rise of TX-100 concentration. The other thermodynamic parameters, transfer properties as well as entropy-enthalpy compensation parameters of micellization and clouding processes have been assessed. The intrinsic enthalpy (ΔHmo,∗) values reveal that micelle is more stable in electrolyte media.

Spectroscopic and cloud point studies of the interaction and thermodynamics of ciprofloxacin hydrochloride+surfactants mixture in different solvents: Effect of temperature and composition

Spectroscopic and cloud point studies of the interaction and thermodynamics of ciprofloxacin hydrochloride+surfactants mixture in different solvents: Effect of temperature and composition

Interaction of methylparaben and propylparaben with P123/F127 mixed polymeric micelles

This paper reports the interaction between Pluronic F127, P123 and their mixed micelles with methylparaben and propylparaben. The UV studies revealed that, the spectral behavior of mixed micelle of F127 and P123 with parabens lay between their individual micellar behaviors. The cloud point studies have shown similar results. It was observed that the intensity of fluorescence spectra, compared with the single micelle-drug combinations was much higher with the mixed micelle-methylparaben combinations and lower with the mixed micelle-propylparaben combinations. The number of binding sites was calculated. Static nature of quenching was observed. The dissociation constant KD for methylparaben - mixed pluronic and propylparaben - mixed pluronic combinations were 21.18 × 10-3 L mol-1 and 32.57 × 10-3 L mol-1 respectively. This suggests that there was stronger binding between methylparaben and mixed micelle compared to propylparaben and mixed micelle. Dynamic light scattering studies indicated that the addition of NaCl to the mixed micelle and parabens facilitated the micellar aggregation and better encapsulation efficiency for the drug. Scanning electron microscope images showed the incorporation of methylparaben and propylparaben molecules into the surface cavities of mixed micelle, pointing towards the change in morphology. This is probably the first report on interaction study of parabens with mixed micelles.

RHEOLOGICAL PROPERTIES OF BRINE/VEGETABLE OIL/POLYETHOXYLATED NON-IONIC SURFACTANTS BASED MICROEMULSION

This study aimed to develop microemulsion through of ternary system composed of brine (aqueous phase), vegetable oil (oil phase), and non-ionic polyethoxylated surfactants, T20 and T80. From the ternary diagrams obtained, two systems were chosen in the regions of microemulsion (Winsor IV) and, subsequently, were conducted rheological study, at different temperatures, and cloud point studies of these systems. The results showed that the microemulsion of T20/brine/vegetable oil presented thermal stability up to 53° C and microemulsions of T80/brine/vegetable oil of 72o C, that could be due a change in micelle morphology and cloud point of each microemulsion system. The rheological results indicated non-Newtonian behavior, adjusted by Herschel - Bulkley model.

Effect of salts on micellization and clouding behavior of Pluronic F108 in aqueous solution using Trypan blue dye

Effect of Chloride, Nitrate, Bromide and Iodide anions of Potassium on the critical micellar concentration of a non-ionic surfactant Pluronic F108 was determined by using UV–visible spectroscopy. Dye-micellization method was adopted using the diazo dye, Trypan blue. The influence of the above mentioned salts on the surfactant structures, concentration and working experimental condition at the cmc were evaluated and discussed. The micellization was observed to occur at lower concentration in presence of the above salts. The influence of the above salts on cmc was characterized using UV- spectrophotometry, fluorimetry, dynamic light scattering, fluorescence lifetime and cloud point studies. It was noticed that the salts affect the aggregation process consistent with the Hofmeister series with the Chloride, the Nitrate, the Bromide and the Iodide ions coming in decreasing order. Trypan blue has been used, probably for first time as a probe for UV- spectroscopy and fluorimetry analysis in surfactant system.

The first kinetic hydrate inhibition investigation on fluorinated polymers: Poly(fluoroalkylacrylamide)s

Fluorohydrocarbons such as fluoromethane are capable of forming gas hydrates at temperatures higher than that of hydrocarbons. Based on this observation, we surmised that the interaction with hydrate cavities might be stronger with fluoroalkyl groups than with alkyl groups of similar size, and that therefore polymers with fluoroalkyl groups might show improved kinetic hydrate inhibition compared to polymers with alkyl groups. We have synthesized three fluorinated alkylacrylamide polymers, poly(N-fluoroethylacrylamide) (R-P1F), poly(N-difluoroethylacrylamide) (R-P2F), poly(N-trifluoroethylacrylamide) (R-P3F) by reversible addition-fragmentation chain transfer (RAFT) polymerization, followed by the removal of the chain end chain transfer agent (CTA) fragments. Poly(N-n-propylacrylamide) (R-PNPAM) and the previously investigated poly(N-isopropylacrylamide) (R-PNIPAM) with similar molecular weight (MW) and molecular weight distribution (MWD) were also synthesized. We have carried out high pressure slow constant cooling rocking cell experiments with a structure II forming natural gas mixture on all the polymers at varying concentrations. In addition, cloud point studies have been carried out. It was observed that R-P2F gave a better performance compared to R-P1F but a lower performance compared to the non-fluorinated polymers R-PNIPAM and R-PNPAM. Testing the KHI effect of increasing the fluorination to 3 fluorine atoms in an acrylamide homopolymer of this class was not possible due to lack of water-solubility of the polymer. Further isothermal tests were performed on R-P2F and R-PNIPAM to clarify the significance of the performance ranking of the KHIs. It was also observed that the induction time of R-P2F at 2500ppm is higher compared to 1000ppm of the same KHI polymer which is a typical performance-concentration effect seen with other polymer KHI classes.

PH-sensitive stearoyl-PEG-poly(methacryloyl sulfadimethoxine) decorated liposomes for the delivery of gemcitabine to cancer cells

Novel, acid-sensitive liposomes that respond to physiopathological pH for tumour targeting applications were obtained by surface decoration with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (mPEG-DSPE) and stearoyl-poly(ethylene glycol)-poly(methacryloyl sulfadimethoxine) copolymer (stearoyl-PEG-polySDM). The pH-sensitive stearoyl-PEG-polySDM copolymer contained an average of seven methacryloyl sulfadimethoxines per molecule and was found to possess an apparent pKa of 7.2. Preliminary cloud point studies showed that the hydrophilic/hydrophobic copolymer conversion occurred at pH 7.0. The copolymer was soluble above pH 7.0 and underwent aggregation at lower pH. Liposome formulations were prepared with 0.2:0.6:100, 0.5:1.5:100 and 1:3:100 mPEG-DSPE/stearoyl-PEG-polySDM/lipids molar ratios. All of the liposome formulations were stable at pH 7.4, even in the presence of foetal bovine serum, but they underwent rapid size increase at pH 6.5. TEM analysis showed that, at pH 6.5, the formulations coated with a stearoyl-PEG-polySDM/lipids molar ratio greater than 1:100 underwent aggregation. At pH 7.4, the liposomes showed negative zeta potential that significantly decreased after incubation at pH 6.5. Cell-culture studies indicated that the liposomes were not toxic up to 10mg/mL. Fluorescence spectroscopy, cytofluorimetry and confocal microscopy showed that at pH 6.5, the incubation of MCF-7 tumour cells with fluorescein-labelled 1:3:100 mPEG-DSPE/stearoyl-PEG-polySDM/lipids molar ratio liposomes resulted in time-dependent cell association, while at pH 7.4 the cell interaction was significantly lower. The same pH-responsive liposome formulation loaded with gemcitabine (98.2±4.7nmol gemcitabine/lipid μmol loading capacity) was stable at pH 7.4 for several hours, while at pH 6.5 it rapidly aggregated. At pH 6.5, these liposomes displayed higher cytotoxicity than at pH 7.4 or compared to non-responsive control liposomes at both incubation pH. Notably, treatment with free gemcitabine did not yield cytotoxic effects, indicating that the carrier can efficiently deliver the anticancer drug to the cytosolic compartment.

Disassembly and reassembly improves morphology and thermal stability of human papillomavirus type 16 virus-like particles

Recombinant human papillomavirus (HPV) 16 L1 protein self-assembles into virus-like particles (VLPs) with diameters of 40 to 60 nm, which are key components in prophylactic HPV vaccines. Marked improvement in morphology and thermal stability on VLP disassembly and reassembly was demonstrated at production scale. Differential scanning calorimetry showed enhanced conformational stability as indicated by the unfolding temperatures and peak heights/areas. Cloud point studies indicated (1) a much lower propensity for post-reassembly VLPs to aggregate during a time course study and (2) much higher cloud point temperatures. In-solution atomic force microscopy showed more uniform size distribution and fully closed particles, with evidence of virion-like assembly revealed by the structural details from a single particle image. Similar approaches for the reassembly of other recombinant VLPs with intrinsic conformational switches would be expected to improve the particle properties and render nanoparticles more suitable for use as vaccines or therapeutics. From the Clinical EditorThe authors of this study demonstrated that recombinant human papillomavirus 16 L1 protein self-assembles into virus-like particles (VLPs) with marked improvement in morphology and thermal stability on VLP disassembly and reassembly at production scale. This is expected to render these nanoparticles more suitable for use as vaccines or therapeutics.

Allylic monomers as reactive plasticizers of polyphenylene oxide. Part I: Uncured systems

The effect of various diallyl (diallyl ortho phthalate, diallyl terephthalate and diethylene glycol diallyl carbonate) and triallyl monomers (triallyl cyanurate and triallyl isocyanurate) on the processability of polyphenylene oxide (PPO) was studied. The solubility parameters of the monomers indicated that diallyl orthophalate, dially terephthalate and triallyl cyanurate should be miscible with PPO suggesting their applicability as reactive plasticizers to improve the processability of PPO. Rheological studies of 60:40 wt:wt PPO:allylic blends indicate that the addition of 40 wt% of allylic monomers significantly improved processability – blends of 60PPO:40DEGDAC indicates the highest viscosity and the highest T g. Rheological studies and dynamic mechanical analysis on various PPO/DAOP blends show that the increasing amounts of DAOP progressively decreases the viscosity and T g of the blends. Phase separation at room temperature was observed by visual opacity, cloud point studies and DMTA in PPO:DAOP blends with less than 60 wt% PPO but at elevated temperatures the blends were miscible.

Cloud Point Studies of Tween and Glycol in the Presence of Salts

This article deals with the cloud point studies of ethoxylated sorbitan ester, Tween in the presence of glycols, and salts. Cloud point temperature of Tween 20 (5 mol dm−3) and Tween 80 (1 mol dm−3) has been determined in the presence of various salts in addition to glycols. The glycols chosen for these studies were triethylene glycol (TEG), and ethylene glycol mono butylether (EGMBE). At concentration below 0.02 M these salts have no significant effect on cloud point temperature in all cases. The cloud point temperature of Tween+TEG and Tween+EGMBE found to decrease in the presence of sodium chloride (NaCl) and potassium chloride (KCl). The cloud point temperature of Tween 20 + TEG and Tween 20 + EGMBE found to increase in the presence of urea and nicotinamide. The change in cloud point was found to be more in case of nicotinamide as compare to urea. The influence of an additive on the cloud point depends on how it affects the intermicellar interactions. An effort has been made to understand the interaction between solvent and additives leading to a change in solubility of Tween.

Influence of ethanol on aspirin release from hypromellose matrices

Release profiles of aspirin from hypromellose matrices in hydro-ethanolic media were studied. Percent aspirin released increased with increasing levels of ethanol in the dissolution media, correlating with the drug's solubility, however, dose dumping of aspirin did not occur. An initial rapid release was observed in media comprising 40% ethanol. Release in these conditions was considered to be both erosion and diffusion-mediated, in contrast to the release in 0, 10, 20 and 30% ethanol media, where erosion-controlled release dominated. Image analysis of matrix swelling indicated a slower initial interaction between ethanol and hypromellose accounting for the initial rapid release. Cloud point studies suggested that ethanol retarded hydration of the polymer.

Water in Supercritical Carbon Dioxide Microemulsions: Spectroscopic Investigation of a New Environment for Aqueous Inorganic Chemistry

In this paper, we present spectroscopic evidence for the formation of water in supercritical carbon dioxide (scCO2) microemulsions stabilized by an ammonium carboxylate perfluoro polyether (PFPE) surfactant. FTIR spectroscopy has been employed to determine the existence of “bulk” (hydrogen-bonded) water (H2O and D2O) at the core of the microemulsions, and to distinguish between this and the presence of “free” (monomeric) water dissolved in the scCO2 and builds on preliminary results described elsewhere (Johnston, K. P.; Harrison, K. L.; Clarke, M. J.; Howdle, S. M.; Heitz, M. P.; Bright, F. V.; Carlier, C.; Randolph, T. W. Science 1996, 271, 624). Cloud point studies confirm that optically transparent and thermodynamically stable microemulsion solutions are formed. We have investigated the utility of these microemulsions as novel environments for reaction chemistry. In particular, we have shown that, using the PFPE surfactant, an aqueous solution of potassium permanganate (KMnO4) may be dispersed in scCO2, leading to a purple-colored solution with concentration on the order of 5 × 10-4 M, as detected by UV−vis absorption spectroscopy. Moreover, aqueous sodium nitroprusside (Na2[Fe(CN)5(NO)]) and potassium dichromate (K2Cr2O7) are also shown to be soluble in the water/PFPE/scCO2 microemulsions and to undergo simple aqueous inorganic reactions with gaseous reactants such as H2S and SO2. Methyl orange has been used to investigate the presence of a carbonic acid microenvironment in the water/PFPE/scCO2 microemulsions.

Phase Separation Dynamics of Blends of Telechelic Epoxy Terminated Polybutadiene and Maltene

Abstract Thermally induced phase separation in a mixture of telechelic epoxy terminated polybutadiene (ETPB) and maltene has been studied by means of time-resolved light scattering and optical microscopy. Maltene, consisting of various hydrocarbon derivatives, was extracted from asphalt with n-heptane and isolated by centrifugation. The cloud point studies of the ETPB/maltene mixture showed an upper critical solution temperature (UCST) which is thermally reversible. Several deep temperature quench experiments were conducted at an off-critical composition (27/73 ETPB/maltene) from a single phase (80°C) to a two-phase region (27, 29, 31 and 33 °C). The time-evolution of the structure factor for the late stage of spinodal decomposition (SD) was analyzed in the framework of nonlinear and dynamical scaling laws. The reverse quench experiments were also undertaken to elucidate the phase dissolution process.

Complexation between polyoxyethylene and polymethacrylic acid—the importance of the molar mass of polyoxyethylene

The effect of the molar mass of polyoxyethylene, POE, upon the mechanism of complexation with polymethacrylic acid, PMAA, has been examined, using pH, density, calorimetric and cloud point studies. Complexation has been found to occur, even for POE of molar mass as low as 200, further, the mechanism appears to be more complex than a simple 1:1 base mole pairing of oxyethylene units (OE) with methacrylic acid units (MAA) by a hydrogen bond mechanism. When the molar mass of POE is < 2000 complexation arises between already pre-existing OE dimers and MAA via hydrogen bonding. For POE molar mass of 2000 and above, hydrophobic pairing of OE and MAA units occurs, followed by hydrogen bonding of another OE or MAA, depending upon the relative concentrations of POE and PMAA.

Miscibility and phase diagrams for poly(vinyl methyl ether) and polyacrylate blend systems

The miscibility of binary polymer blend systems consisting of poly(vinyl methyl ether) (PVME) and polyacrylates has been studied. Based on film clarity, glass transition temperature and cloud-point studies, PVME is found to be miscible with poly(ethyl acrylate), poly(n-propyl acrylate) and poly(n-butyl acrylate) but not with poly(methyl acrylate). The phase diagrams of some of these blends are reported.