Formation Of Hydrophobic Microdomains Research Articles

Fluorescence probe technique for determining the hydrophobic interactions and critical aggregation concentrations of Gleditsia microphylla gum, circular Gleditsia sinensis gum, and tara gum

Circular Gleditsia sinensis gum, Gleditsia microphylla gum, and tara gum are galactomannans (GMs) with similar mannose/galactose (M/G) molar ratios, which complicates the characterization of physicochemical properties using conventional methods. Herein, the hydrophobic interactions and critical aggregation concentrations (CACs) of the GMs were compared using a fluorescence probe technique, in which the I1/I3 ratio of pyrene indicated polarity changes. With increasing GM concentration, the I1/I3 ratio decreased slightly in dilute solutions below the CAC but decreased sharply in semidilute solutions above the CAC, indicating that the GMs formed hydrophobic domains. However, increases in temperature destroyed the hydrophobic microdomains and increased the CACs. Higher concentrations of salts (SO42−, Cl−, SCN−, and Al3+) promoted hydrophobic microdomain formation, and the CACs in Na2SO4 and NaSCN solutions were lower than those in pure water. Hydrophobic microdomain formation also occurred upon Cu2+ complexation. Although urea addition promoted hydrophobic microdomain formation in dilute solutions, the microdomains were destroyed in semidilute solutions and the CACs increased. The formation or destruction of hydrophobic microdomains depended on the molecular weight, M/G ratio and galactose distribution of GMs. Therefore, the fluorescent probe technique enables the characterization of hydrophobic interactions in GM solutions, which can provide valuable insight into molecular chain conformations.

Halloysite nanotubes as nanoreactors for heterogeneous micellar catalysis

HypothesisElectrostatic attractions between the anionic head group of sodium alkylsulphates and the positively charged inner surface of halloysite nanotubes (HNTs) drive to the formation of tubular inorganic micelles, which might be employed as nanoreactors for the confinement of non polar compounds in aqueous media. On this basis, sodium alkylsulphates/halloysite hybrids could be efficient nanocatalysts for organic reactions occurring in water. ExperimentsSodium decylsulphate (NaDeS) and sodium dodecylsulphate (NaDS) were selected for the functionalization of the halloysite cavity. The composition, the structure and the surface charge properties of the hybrid nanotubes were determined. The actual formation of inorganic micelles was explored by studying the microviscosity and polarity characteristics of the surfactant modified nanotubes through fluorescence spectroscopy experiments using DiPyme as probe. The performances of the sodium alkylsulphates/halloysite composites as micellar catalysts for the Belousov-Zhabotinsky (BZ) reaction were investigated. FindingsThe halloysite functionalization with sodium alkylsulphates generated the formation of hydrophobic microdomains with an enhanced microviscosity. Compared to the surfactant conventional micelles, the functionalized nanotubes induced larger enhancements on the rate constant of the BZ reaction. This is the first report on the surfactant/halloysite hybrids showing their efficiencies as reusable nanocatalysts, which are dependent on their peculiar microviscosity and polarity properties.

Conjugation reaction with ferulic acid boosts the antioxidant property of arabinogalactan-protein and enhances its ability to form complex with β-lactoglobulin

Ferulic acid was chemically grafted onto the arabinogalactan protein of Aegle marmelos fruit gum using 1,1′-carbonyldiimidazole as coupling reagent. Thus, grafted polysaccharides with different degrees of substitution were prepared and then characterized by gas chromatography/mass spectrometry, size exclusion chromatography, and ultraviolet-visible, infra-red, and nuclear magnetic resonance spectroscopic investigations. Fluorescence spectroscopic investigation showed hydrophobic microdomain formation in grafted polymers. The antioxidant activities of the derivatives, as determined by the 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl radical assay, were strong and increases with increasing the degree of feruloylation. Compared to parental arabinogalactan protein (K = 2.38 × 106 M−1), these grafted polymers bind more strongly with β-lactoglobulin (K = 11.4 × 106 M−1 and 8.19 × 106 M−1). Given that gum polysaccharides are valuable component in functional foods, synthesis of antioxidative graft polymer possessing good compatibility with β-lactoglobulin may have important implication.

Thermoresponsive behavior of graft copolymers based on poly(N,N‐dimethylacrylamide‐co‐diacetoneacrylamide) side chains

ABSTRACTA thermoresponsive graft copolymer was synthesized through free radical copolymerization and a “graft onto” method in aqueous solution. The primary structure of the graft copolymer is constituted of a partially hydrolyzed polyacrylamide (HPAM) backbone and thermosensitive side chains [amino‐terminated poly(N,N‐dimethylacrylamide‐co‐diacetone acrylamide) or P(DMA‐co‐DAAM)] with molecular weight around 105 g/mol. The 1H‐NMR spectra at various temperatures showed the temperature of thermoassociation (Tass) in the copolymer. At the same time, the pyrene fluorescence measurements demonstrated the formation of hydrophobic microdomains of P(DMA‐co‐DAAM) above Tass. The thermothickening behavior of the graft copolymers was studied by viscosity measurements, and the results suggested that in semidilute solutions, the Tass and the magnitude of thermothickening could be regulated by varying the hydrolysis degree of the backbone, the composition of side chains, and the addition of NaCl. The oscillatory shear experiments demonstrated that the copolymer can present a remarkable elasticity increase as the temerature increased to Tass. These thermoassociating copolymers with temperature‐tunable properties can have potential applications as smart materials in enhanced oil recovery. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 135, 47051.

Investigations of benzo[a]pyrene encapsulation and Fenton degradation by starch nanoparticles

Starch nanoparticles were produced by dialysis method from octenyl succinic anhydre (OSA) and 1,4-butane sultone (BS). The properties of the self-assembled nanoparticles were characterized by NMR spectroscopy (DOSY), fluorescence spectroscopy and dynamic light scattering (DLS). In order to investigate the formation of hydrophobic microdomains, the Nile Red dye was used as a fluorescent probe to evaluate the critical aggregation concentration (CAC) of modified starch in aqueous solution. The results show that the entrapment of the molecular guest was effective and only restricted by the solubility limit of the starch. Then, the modified starch was applied to solubilize benzo[a]pyrene (BaP) in view of degradation by Fenton process. Finally, it has been shown that 95% of BaP was degraded when it was encapsulated in OSA-BS-starch nanoparticles.

INTERMOLECULAR ASSOCIATION OF AMPHIPATHIC POLYELECTROLYTES IN AQUEOUS SOLUTIONS

The intermolecular association of amphipathic polyelectrolytes is studied using fluorescence and conductivity methods. This type of interaction is evidenced by the decrease in the average distances between charges as the polyelectrolyte side chain increases in length. This modify the dissociation degree and consequently, the linear charge density parameter. These distances were calculated with the Manning counterion condensation theory for the conductivity of polyelectrolyte solutions. The determination of the ratio I1/I3 of the fluorescence bands of pyrene with polymer content reveals the formation of hydrophobic microdomains at very low concentrations, smaller than the required concentration to produce a significant change in the average distances between charges. These distances and also the I1/I3 ratio vary with polymer concentration and their values were dependent on the size of the side chain in the polyelectrolyte. Finally, the experimental behavior of the solution viscosity and electrical conductivity of polyelectrolytes, which increase drastically with dilution, can be explained as a continuous change in the average distances between charges which produce conformational changes.

Influence of chemically modified alginate esters on the preparation of microparticles by transacylation with protein in W/O emulsions

Microencapsulation using the transacylation reaction in a W/O emulsion is based on the creation of amide bonds between the protein’s amine functions and the ester groups of a polysaccharide in the aqueous phase after alkalization. Commercial propylene glycol alginate (PGA) has been the only modified polysaccharide involved in the process up to now. In the present work, we describe the effect of substituting the commercial PGA by other chemically modified alginates in the formation of microparticles. Alkyl and hydroxyalkyl alginate esters, were synthesized and tested in the encapsulation process with human serum albumin (HSA). It was found that the hydroxyalkyl alginates were suitable polysaccharide substitutes for PGA in the transacylation reaction, whereas the alkyl alginates did not lead to microparticle formation in the same process. Hydroxyalkyl alginates with high esterification degree (DE) (>50) led to microparticles when involved in the preparation procedure. However with lower DE (<30), no microparticles could be obtained from 2% ester solution concentrations. This difference in reactivity was explained by the formation of hydrophobic microdomains with the alkyl esters that hindered the transacylation reaction, as opposed to hydroxyalkyl esters that bore hydrophilic ester groups.

JR 400–NaAOT interaction: a detailed thermodynamic study of polymer–surfactant interaction bearing opposite charges

The present study entails interaction between the cationic polymer N,N-dimethylhydroxyethyl cellulose (JR 400) and the double-tailed anionic surfactant Na-bis-2-ethyhexylsulphosuccinate (NaAOT). This oppositely charged polymer and surfactant are expected to cause coacervation and precipitation; hence, we have observed formation of thick solution similar to diluted gel at [JR 400] ~ 0.01 and 0.10 % w/v in aqueous solution. Viscometry, conductometry, tensiometry, and microcalorimetry techniques are used to monitor the interaction process. The results are explained in the light of both intrachain and interchain linking by way of NaAOT reverse micelle formation. Adsorption of NaAOT monomers onto the charged side chains of the polymer shields interchain electrostatic repulsion, leading to the formation of hydrophobic microdomains and microscopic heterogeneity in the solution. The morphologies of the domains depend on the level of addition of NaAOT in the system. The different stages of physiochemical changes that arise in solution have been identified by the use of different techniques, and correlations of the results have been attempted in terms of pragmatic models.

The aggregation behavior of native collagen in dilute solution studied by intrinsic fluorescence and external probing

The aggregation behavior of type I collagen in acid solutions with the concentrations covering a range of 0.06–1.50mg/mL was studied utilizing both of the fluorescence resonance energy transfer (FRET) between the phenylalanine and tyrosine residues and the external probing of 1,8-anilinonaphthalene sulfonate (ANS). FRET at 0.30mg/mL showed the distance among collagen monomers was within 10nm without the obvious aggregates formed. The predominance of tyrosine fluorescence in FRET in the range of 0.45–0.75mg/mL identified the existence of collagen aggregates companied with the formation of hydrophobic microdomains revealed by the change of the fluorescence of ANS. The blue-shift of tyrosine fluorescence from 303 to 293nm for 0.90–1.50mg/mL dedicated the formation of high order aggregates. The results from the two-phase diagrams of the intrinsic fluorescence for the guanidine hydrochloride-induced unfolding of collagen confirmed these conclusions. By the two-dimensional correlation analysis for the intrinsic fluorescence of collagen solutions of 0.45, 0.75 and 1.05mg/mL, the probable characteristic fluorescence peaks for the interactions of proline-aromatic (CH∼π) among the collagen molecules were found at 298 and 316nm.

Temperature-responsive photoluminescence of quinoline-labeled poly(N-isopropylacrylamide) in aqueous solution

The pH- and temperature-responsive optical properties of a quinoline-labeled poly(N-isopropylacrylamide) copolymer are explored in aqueous solution and compared to the respective behavior of a similar quinoline-labeled poly(N,N-dimethylacrylamide) copolymer. These copolymers, P(NIPAM-co-SDPQ) and P(DMAM-co-SDPQ), were prepared through free radical copolymerization of 2,4-diphenyl-6-(4-vinylphenyl)quinoline (SDPQ) with the thermosensitive N-isopropylacrylamide (NIPAM) and the hydrophilic N,N-dimethylacrylamide (DMAM), respectively. Both copolymers exhibit the well-known pH-controlled optical response of quinoline unit in aqueous solution and the emitted color changes from blue to green upon decreasing pH. Nevertheless, a ∼20nm emission shift is observed upon heating the aqueous P(NIPAM-co-SDPQ) solution, regardless of pH, due to the formation of hydrophobic microdomains (Nile Red probing), as a consequence of the Lower Critical Solution Temperature (LCST) behavior of this copolymer in water. Interestingly, this LCST behavior also imposes the partial deprotonation of the otherwise protonated SDPQ unit at pH=2 and the emission of the basic form appears upon increasing temperature, suggesting that the acid/base equilibrium of the quinoline unit is significantly temperature-controlled, when introduced in the thermosensitive poly(N-isopropylacrylamide) chain.

Solubility behavior of amphiphilic block and random copolymers based on 2‐ethyl‐2‐oxazoline and 2‐nonyl‐2‐oxazoline in binary water–ethanol mixtures

AbstractThe solution properties of random and block copolymers based on 2‐ethyl‐2‐oxazoline (EtOx) and 2‐nonyl‐2‐oxazoline (NonOx) were investigated in binary solvent mixtures ranging from pure water to pure ethanol. The solubility phase diagrams for the random and block copolymers revealed solubility (after heating), insolubility, dispersions, micellization as well as lower critical solution temperature (LCST) and upper critical solution temperature behavior. The random and block copolymers containing over 60 mol % pNonOx were found to be solubilized in ethanol upon heating, whereas the dissolution temperature of the block copolymers was found to be much higher than for the random copolymers due to the higher extent of crystallinity. Furthermore, the block copolymer containing 10 mol % pNonOx exhibited a LCST in aqueous solution at 68.7 °C, whereas the LCST for the random copolymer was found to be only 20.8 °C based on the formation of hydrophobic microdomains in the block copolymer. The random copolymer displayed a small increase in LCST up to a solvent mixture of 9 wt % EtOH, whereas further increase of ethanol led to a decrease in LCST, which is probably due to the “water‐breaking” effect causing an increased attraction between ethanol and the hydrophobic part of the copolymer. In addition, the EtOx‐NonOx block copolymers revealed the formation of micelles and dynamic light scattering demonstrated that the micellar size is increasing with increasing the ethanol content due to the enhanced solubility of EtOx. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 515–522, 2009

Characterization of the self-assembly process of hydrophobically modified dextrin

Hydrophobized dextrin, randomly substituted by long alkyl chain (C 16), forms stable hydrogel nanoparticles by self-assembling in water. Hydrophobic chains, distributed along the polymer backbone, promote the formation of hydrophobic microdomains within the nanoparticles. The influence of degree of substitution with hydrophobic chains (DS C16) on nanoparticles size, colloidal stability, density, aggregation number and nanoparticle weight was studied. Size distribution was also evaluated at different pH, urea concentration and ionic strength conditions. As shown by dynamic light scattering and transmission electron microscopy, the particles are spherical having a diameter of about 20 nm. The more substituted polymer forms more densely packed hydrophobic microdomains, such that the colloidal stability (in water and PBS buffer) of nanoparticles is increased. The knowledge of the aggregate building process and the characteristics of the nanoparticles are crucial for the design of drug delivery systems.

Phase behavior of temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) in dilute aqueous solution

AbstractSeveral different composition temperature‐ and pH‐sensitive poly(acrylic acid‐g‐N‐isopropylacrylamide) (P(AA‐g‐NIPAM)) graft copolymers were synthesized by free‐radical copolymerization utilizing macromonomer technique. The phase behavior and conformation change of P(AA‐g‐NIPAM) in aqueous solutions were investigated by UV–vis transmittance measurements, fluorescence probe, and fluorescence quenching techniques. The results demonstrate that the P(AA‐g‐NIPAM) copolymers have temperature‐ and pH‐sensitivities, and these different composition graft copolymers have different lower critical solution temperature (LCST) and critical phase transition pH values. The LCST of graft copolymer decreases with increasing PNIPAM content, and the critical phase transition pH value increases with increasing Poly(N‐isopropylacrylamide) (PNIPAM) content. At room temperature (20°C), different composition of P(AA‐g‐NIPAM) graft copolymers in dilute aqueous solutions (0.001 wt %) have a loose conformation, and there is no hydrophobic microdomain formation within researching pH range (pH 3 ∼ 10). In addition, for the P(AA‐g‐NIPAM) aqueous solutions, transition from coil to globular is an incomplete reversible process in heating and cooling cycles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Environmentally friendly photosensitizer: starch modified with chlorophyll-type chromophores

A novel water-soluble polymeric photosensitizer (SPheo) based on starch and containing pheophorbide (Pheo), a chlorophyll-derived chromophore, was synthesized and its photophysical and photochemical properties were studied. Pheo chromophores attached to the polymeric chains of starch absorb light of the UV-visible spectral region. The clustering of hydrophobic Pheo chromophores results in the formation of hydrophobic microdomains in aqueous solution where organic molecules can be solubilized. SPheo polymer efficiently photosensitizes reactions mediated by energy and/or electron transfer from the electronically excited chromophores to the molecules of organic compounds solubilized in polymeric microdomains or residing in water. Copyright © 2007 Society of Chemical Industry

Synthesis and association properties in water solution of random copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid and isodecyl methacrylate—potential application as surfactants in micellar-enhanced ultrafiltration processes

Hydrophobically modified water-soluble polymers have been prepared by copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and isodecyl methacrylate (iDMA) in N,N-dimethylformamide under nitrogen atmosphere, varying the composition feed. Fluorescence spectroscopy was used to further confirm the copolymers self-aggregate in water. Critical concentration of the self-aggregate formation (CAC) decreased by increasing the molar fraction of iDMA in the AMPSco copolymers and varied between 1.20 and 0.04 g/L depending on the degree of hydrophobic modification. Hence, copolymer composition and charge density allowed tuning the pseudomicellar characteristics of these new amphiphilic copolymers. The addition of a salt or a low-molecular-weight surfactant was studied. Binding of CTAB to the AMPSco copolymers leads to a high decrease of CAC, i.e., 0.006 g/L. Effect of the composition in the viscosimetric behavior of the hydrophobically modified copolymers AMPSco was investigated. The removal of single metal ions, Cu2+, and m-cresol from aqueous solutions by ultrafiltration with the help of the copolymers was investigated. Equilibrium dialysis experiments demonstrate that the formation of hydrophobic microdomains can be used to control the sequestration of foulants, and thus these novel copolymers have potential application as polymeric surfactants in micellar-enhanced ultrafiltration processes for water purification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Temperature-Sensitive Water-Soluble Polyelectrolyte/Surfactant Complexes Formed between Dodecyltrimethylammonium Bromide and a Comb-Type Copolymer Consisting of an Anionic Backbone and Poly(N-isopropylacrylamide) Side Chains

The properties of the complexes formed in water between the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and the comb-type anionic polyelectrolyte poly(sodium acrylate-co-sodium 2-acrylamido-2-methylpropanesulfonate)-g-poly(N-isopropylacrylamide) (P(NaA-co-NaAMPS)-g-PNIPAM) were investigated in dilute aqueous solutions and compared to the properties of the complexes formed between DTAB and poly(sodium acrylate-co-sodium 2-acrylamido-2-methylpropanesulfonate)-g-poly(N,N-dimethylacrylamide) (P(NaA-co-NaAMPS)-g-PDMAM). It was found that, contrary to the water-insoluble complexes formed between the linear polyelectrolyte P(NaA-co-NaAMPS) and the oppositely charged DTAB, the complexes formed between DTAB and the comb-type copolymers, either P(NaA-co-NaAMPS)-g-PNIPAM or P(NaA-co-NaAMPS)-g-PDMAM, maintain water solubility at room temperature. In both cases, complexation is accompanied by charge neutralization, formation of hydrophobic microdomains, and a substantial decrease of the reduced viscosity of the aqueous solution. Contrary to the P(NaA-co-NaAMPS)-g-PDMAM/DTAB complexes, the P(NaA-co-NaAMPS)-g-PNIPAM/DTAB complexes separate out from water upon heating, due to the lower critical solution temperature behavior of the PNIPAM side chains. At high DTAB concentrations, mixed aggregates between the PNIPAM side chains and DTAB cations are formed, leading to the indirect introduction of positive charges in the complex and to the elevation of the phase separation temperature.

Self-Aggregation of Amphiphilic Cationic Polyelectrolytes Based on Polysaccharides

The self-aggregation of polyelectrolytes having N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride pendant groups (alkyl = octyl, dodecyl, or cetyl) randomly distributed along a polysaccharide backbone (dextran) was studied by steady-state fluorescence techniques using several free fluorescent probes or pyrene-labeled polymers and by viscometry. The onset, offset, and highest values of the fluorescence response of N-phenylnaphthylamine (NPN), pyrene (Py), and 1,6-diphenyl-3,5,6-hexatriene (DPH) were corroborated with NPN and DPH anisotropy and quenching experiments to describe the dynamic of hydrophobic microdomain formation and microdomain characteristics. The start of the aggregation process (critical aggregation concentration, cac) and the microdomain characteristics such as polarity, microviscosity, size, and number strongly depend on the alkyl chain length and the degree of substitution with cationic pendant groups. Fluorescence experiments with pyrene-labeled polymers and viscosity data sugge...

Novel Water-Soluble Photosensitizers from Dextrans

Novel water-soluble polymeric photosensitizers based on the natural polymer dextran were synthesized and studied. The modified dextran contained photoactive anthracene (An) chromophores. They were soluble in water with the solubility decreasing with an increase in the number of An moieties bound to the polymeric chain. In aqueous solutions, the macromolecules adopted a compact conformation which resulted in the formation of hydrophobic microdomains. The properties of these domains were characterized with molecular probes such as perylene and pyrazolo-quinoline derivative. The polymer absorbed in the UV/vis region and photosensitized reactions mediated by energy and/or electron transfer from electronically excited An to the molecules of organic compounds solubilized in polymeric microdomains or resided in water.

Rigid Interior of Styrene−Maleic Anhydride Copolymer Aggregates Probed by Fluorescence Spectroscopy

Several fluorescence techniques have been applied to characterize the aggregates of styrene−maleic anhydride copolymers (SMA). The formation of hydrophobic microdomains was confirmed by monitoring the I1/I3 ratios of pyrene dissolved in SMA solutions. Fluorescence quenching experiments indicate that protective quenching is occurring. The excimer-to-monomer ratio of di(1-pyrenylmethyl) ether and stopped-flow fluorescence measurements show that the interior of these SMA aggregates is extremely rigid, much more than that of typical surfactant micelles. Fluorescence anisotropy was applied to determine the hydrodynamic radius of these aggregates which was found to equal 1.7 ± 0.2 nm, in qualitative agreement with earlier measurements by small-angle X-ray scattering and small-angle neutron scattering. SMA aggregates have sizes similar to that of typical surfactant micelles, but their interior is frozen.

Synthesis of Amphiphilic Random Copolymers and Fluorescence Study of Their Association Behavior in Water

A series of different copolymers of 2-acrylamido-2-methylpropanesulfonic acid, AMPS, and butyl methacrylate, BuMA, were prepared by free radical polymerization at 70°C in N,N ′-dimethylformamide under nitrogen atmosphere varying the composition feed. The polyamphiphiles isolation was carried out by passing the polymeric solutions through a sodium cation exchange resin. The stabilities of the obtained homopolymers and copolymers were characterized by thermal analysis (TGA, DSC). Fluorescent probes were used to study the hydrophobic microdomain formation due to the association phenomena observed in water solution when the amphiphilic copolymer concentration was increased. The fluorescence emission of amino derivatives of 7-nitrobenz-2-oxa-1,3-diazole (NBD) showed sensitivity to detect polarity and microviscosity changes in the microenvironment of the copolymers. The minimum concentration for the hydrophobic microdomains formation, Cm , decreased by increasing the molar fraction of BuMA in the AMPSCo copolymers. Hence, copolymer composition and charge density allowed tuning the pseudo-micellar characteristics of these new polyamphiphilic copolymers.