Phase Transition In Aqueous Solution Research Articles

Synthesis and characterization of polysaccharide carbamates and mixed carbamates with tunable water solubility

Polysaccharide derivatives with two types of functionalities were synthesized; reactive groups for click-chemistry approaches and groups that can tune the water solubility of the products. Xylan phenylcarbonates (XPCs) and cellulose phenylcarbonates (CPCs) with degrees of substitution (DS) ranging from 0.6 to 3.0 were prepared as starting materials. In a modular synthesis approach, these carbonate derivatives were converted with different amines to obtain functional xylan carbamates (XCs) and cellulose carbamates (CCs) with (i) reactive alkynyl- or furfuryl groups and / or (ii) hydrophilic hydroxyalkyl or tertiary amino groups. Both types of functionalities were introduced separately or simultaneously in a convenient one-pot-approach. Mixed polysaccharide carbamates with low, intermediate, and high DS values (0.6 to 2.5) were successfully prepared and characterized. The water solubility of the carbamates and mixed carbamates was tuned by variation of the type and DS of the two hydrophilic substituents. Surprisingly, some of the products showed lower or upper critical solution temperatures (LCSTs, UCSTs). Thus, the thermoreversible phase transition in aqueous solutions was studied. The products obtained in this work are very promising for the preparation of hydrogels through selective covalent crosslinking as well as for the fabrication of thermoresponsive biomaterials.

Temperature response behavior of poly(1-vinyl-3-methylimidazole dimethyl phosphate-co-N-isopropylacrylamide) in aqueous and ester solutions driven by hydrogen bonding

A series of poly(1-vinyl-3-methylimidazole dimethyl phosphate-co-N-isopropylacrylamide) oligomers was synthesized by reversible addition-fragmentation chain transfer polymerization. The co-oligomers exhibited a pH-tunable lower critical solution temperature (LCST) phase transition in aqueous solutions. By changing the pH of the aqueous solution (HCI), the hydrogen bonding between the internal molecules of the co-oligomers and water molecules was weakened, which effectively reduced the cloud-point temperature. Poly(1-vinyl-3-methylimidazole dimethyl phosphate-co-N-isopropylacrylamide) oligomers exhibit an upper critical solution temperature (UCST) type of phase transition in an ester solution, which is associated with the formation and breaking of hydrogen bonds within the co-oligomers molecules. FT-IR analysis revealed the effect of temperature on hydrogen bonding between the functional groups. Energy decomposition, Electrostatic Potential (ESP), Atoms-in-Molecules (AIM), and Interaction region indicator (IRI) analyses demonstrated the presence of hydrogen bond donors N–H and imidazole ring C–H, and hydrogen bond acceptors C = O and P = O in the co-oligomers. The sites of hydrogen bonding between the co-oligomers and the solvent molecules as well as intermolecular forces were found to be the main factors contributing to the LCST/UCST-type phase transition.

Chlorophyllin-Containing Copolymers and Their Responsive Properties.

Copper-chlorophyllin is a water-soluble derivative of chlorophylls and shows low cytotoxicity and antimutagenic properties in cultured cells. It has multiple applications, including its use as a photosensitizer in photothermal therapy because of its green light-activated photothermal performance. In this work, it was copolymerized with a poly(ethylene glycol) methacrylic monomer to yield random copolymers by free radical polymerization, which showed dual temperature- and pH-dependent phase transitions in aqueous solutions. The cloud points of the copolymer solutions were raised by lowering the pH of the aqueous solutions due to the protonation of the carboxylic groups on the chlorophyllin moieties, which decreased the overall hydrophilicity of the polymers. At low pH values, complete protonation of the carboxylic acid groups of the chlorophyllin moieties led to an irreversible aggregation of the copolymers in water. The incorporation of chlorophyllin in the copolymer improved its stability over its single molecular form.

Phase transitions of aqueous solutions of Pluronic F68 in the presence of Diclofenac Sodium

In recent years, advancements in bioengineering and materials science have witnessed increasing interest in synthetic polymers capable of fulfilling various applications. Owing to their distinctive properties, Pluronics can be used as nano-drug carriers, to deliver poorly water-soluble drugs, and as model systems to study colloidal science by tuning amphiphilic properties. In this work, we investigated the effect of diclofenac sodium on the self-assembly and thermoresponsive crystallization of Pluronic F68 in water solutions, by employing experimental rheology and Nuclear Magnetic Resonance (NMR). We built a complete phase diagram as a function of temperature and concentration for 45 wt% Pluronic F68 with various amounts of diclofenac sodium in water. The morphological transitions were followed as a function of temperature via linear rheology. We extrapolated the transition temperatures – identifying distinct phases – as a function of the drug concentration and proposed an empirical model for their prediction. NMR analysis provided further information on the structural characteristics of the systems, shedding light on the interactions between F68 and diclofenac sodium. Although dealing with a pharmaceutical salt, the study is focused on a colloidal system and its interaction with a binding molecule, that is of general interest for colloidal science.

Nanoscale Structural Phase Transitions in Aqueous Solutions of Organic Molecules

Adiabatic compressibility βS of the 4-methylpyridine + water solution is investigated in a wide concentration and temperature variation interval using Mandelstam–Brillouin scattering spectroscopy. The adiabatic compressibility minimum caused by the microinhomogeneous structure of the solution is experimentally established at the concentration of 0.06 molar fractions of 4-methylpyridine in the solution. The results of the investigations allow the construction of a diagram of possible states caused by a continuous three-dimensional hydrogen bond network of water. The results of experimental study of the excessive hypersound absorption in acetone + water and 3-methylpyridine + water solutions are discussed based on the conclusions of the theory of high-frequency sound scattering near the critical point (developed by Chaban) and the Landau theory. These results are described within the framework of the Landau and Chaban theories and explained by the existence of two different states with minimum thermodynamic stability in the solution.

Phase Transitions of Associative Biomacromolecules.

Multivalent proteins and nucleic acids, collectively referred to as multivalent associative biomacromolecules, provide the driving forces for the formation and compositional regulation of biomolecular condensates. Here, we review the key concepts of phase transitions of aqueous solutions of associative biomacromolecules, specifically proteins that include folded domains and intrinsically disordered regions. The phase transitions of these systems come under the rubric of coupled associative and segregative transitions. The concepts underlying these processes are presented, and their relevance to biomolecular condensates is discussed.

Supramolecular Surface Coatings with Acetylated Polyrotaxane-Based Triblock Copolymers for Thermal Regulation of Cell Adhesion and Fabrication of Cell Sheets.

Polyrotaxanes (PRXs) containing acetylated α-cyclodextrins exhibit a temperature-dependent phase transition in aqueous solutions across their lower critical solution temperature (LCST) of approximately 26.6 °C. To gain insights into the interactions of acetylated PRXs (Ac-PRXs) with biological components, thermoresponsive supramolecular surfaces were prepared by coating tissue culture polystyrene (TCPS) surfaces with Ac-PRX triblock copolymers, and their surface properties across the LCST were evaluated. The wettability and protein adsorption of Ac-PRX-coated surfaces changed significantly between 10 and 37 °C, whereas the uncoated TCPS and unmodified PRX-coated surfaces did not alter the wettability and protein adsorption at 10 and 37 °C. The adhesion, proliferation, morphology, and adhesion strength of NIH/3T3 cells on Ac-PRX-coated surfaces were found to be similar to those of the uncoated and unmodified PRX-coated surfaces. However, the adhesion strength of NIH/3T3 cells on Ac-PRX-coated surfaces decreased drastically at 10 °C. Consequently, the cells spontaneously detached from the Ac-PRX-coated surfaces without enzymatic treatment. Additionally, when incubating confluent cells at 10 °C, the cells detached from Ac-PRX-coated surfaces as cell sheets while retaining extracellular matrix proteins. The findings of this study provide new directions for the design of thermoresponsive supramolecular biointerfaces for applications in bioseparation and cell manipulation.

Thermoresponsive polymers in non-aqueous solutions

Polymers does not only show phase transition in aqueous solutions but they also do in organic solvents, which is the focus of this review article.

Phase diagrams of temperature-responsive copolymers p(MEO2MA-co-OEGMA) in water

Random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) have a temperature-induced phase transition in aqueous solutions, which can be tuned for different temperatures from ca. 20 °C to 90 °C, by changing their monomer ratio. Here, we explore a novel approach combining UV–Vis measurements (light scattering) with standard and modulated-temperature differential scanning calorimetry (DSC), to obtain the phase diagrams of copolymers with different compositions over an unprecedented wide concentration range (0.7–800 mg/mL). We used three copolymers synthesized by RAFT polymerization with very low size dispersity, and containing 6, 8 and 11 mol% of OEGMA. The change in their phase transition temperature with concentration show that they reach different lower critical solution temperature (LCST) in the concentration interval 20–30 mg/mL. Our results offer new insights on the influence of concentration, in particular for high concentrations, on the temperature, the reversibility and the kinetics of the phase transition. This information can be used to assist the design of copolymers with predetermined temperature response.

Searching for Aquamelt Behavior among Silklike Biomimetics during Fibrillation under Flow.

In this paper, we elucidate a generic mechanism behind strain-induced phase transition in aqueous solutions of silk-inspired biomimetics by atomistic molecular dynamics simulations. We show the results of modeling of homopeptides polyglycine Gly30 and polyalanine Ala30 and a heteropeptide (Gly-Ala-Gly-Ala-Gly-Ser)5, i.e., the simplest and yet relevant sequences that could mimic the behavior of natural silk under stress conditions. First, we analyze hydrophobicities of the sequences by calculating the Gibbs free energy of hydration and inspecting the interchain hydrogen bonding and hydration by water. Second, the force-extension profiles are scanned and compared with the results for poly(ethylene oxide), the synthetic polymer for which the aquamelt behavior has been proved recently. Additionally, the conformational transitions of oligopeptides from coiled to extended states are characterized by a generalized order parameter and by the dependence of the solvent-accessible surface area of the chains on applied stretching. Fibrillation itself is surveyed using both the two-dimensional interchain pair correlation function and the SAXS/WAXS patterns for the aggregates formed under stress. These are compared with experimental data found in the literature on fibril structure of silk composite materials doped with oligoalanine peptides. Our results show that tensile stress introduced into aqueous oligopeptide solutions facilitates interchain interactions. The oligopeptides display both a greater resistance to extension as compared to poly(ethylene oxide) and a reduced ability for hydrogen bonding of the stretched chains between oligomers and with water. Fiber formation is proved for all simulated objects, but the most structured one is made of a heteropeptide (Gly-Ala-Gly-Ala-Gly-Ser)5: For this sequence, we obtain the highest degree of the secondary structure motifs in the fiber. We conclude that this is the most promising candidate among considered sequences to find the aquamelt behavior in further experimental studies.

The solution-gel phase transition in aqueous solutions of agarose

Thermal hysteresis and stability of agarose–water gelling systems were studied by the spectrophotometer for different concentrations at different temperatures. Gelation temperature depends on the concentration of agarose. With the increase in the concentration of agarose gelation temperature, strength of agarose increases too. With the increase in the concentration of polymer solvent–gel phase transition, gel melting happens at higher temperatures. The price of enthalpy was determined (150.0127 KC/mol). In gelation process, the phase separation is completed and in this process, the value of this [Formula: see text] equally increases.

Molecular Weight-Dependent, Flexible Phase Behaviors of Amphiphilic Block Copolymer/Additive Complexes in Aqueous Solution.

Pluronic amphiphilic block copolymers, well known to have a phase behavior can be controlled by external conditions, have a wide range of potential for applications such as nanotemplates or nanobuilding blocks. However, the phase behaviors of Pluronic block copolymer/additive complexes with highly ordered phases have not been fully investigated. Here, we report the unusual molecular weight-dependent self-assembly of Pluronic block copolymer/additive complexes. Depending on the temperature and additive, Pluronic P65 block copolymer with a lower molecular weight showed the closed loop-like (CLL) phase behavior with the disorder-order-disorder-order phase transition in aqueous solution, whereas Pluronic P105 and P85 block copolymers with higher molecular weights underwent highly ordered continuous phase transitions with face centered cubic (FCC), hexagonal, and lamellar phases. It is expected that the specific phase behavior of the block copolymer/additive complex can be applied in optical devices such as nanotemplates or optical sensors for a highly ordered superlattice. Furthermore, this study provides a new route to control the phase behavior of the block copolymers without a complicated process.

Protoporphyrin IX copolymer with poly(ethylene glycol) methacrylate and its thermoresponsive properties

Porphyrins and their derivatives have been widely used in catalysis, energy conversion, photonics, and biomedicine; however, their use in biological applications is restricted by their limited solubility in aqueous systems. We have prepared a water-soluble copolymer containing moieties of naturally occurring protoporphyrin IX using direct copolymerization of a poly(ethylene glycol) (PEG) methacrylate monomer with protoporphyrin IX via free-radical polymerization. The content of protoporphyrin IX in the copolymer was determined by 1H NMR and UV–vis absorption spectroscopies. Their solution properties and the photostability of the protoporphyrin IX moiety in the copolymer provide direct evidence of the covalent incorporation of protoporphyrin IX within the copolymer. The copolymer showed a reversible phase transition in aqueous solution due to the lower critical solution temperature (LCST). The phase transition temperature varies with the pH of the solutions because of the protonation of the carboxylic acid groups. This copolymer may be useful as an alternative thermoresponsive material for biomedical applications.

Concentration Dependences of Macromolecular Sizes in Aqueous Solutions of Albumins

On the basis of experimental data for the shear viscosity in the aqueous solutions of ovine serum albumin and using the cellular model describing the viscosity in aqueous solutions, the concentration dependences of the effective radius of ovine serum albumin macromolecules in the aqueous solutions within a concentration interval of 3.65–25.8 wt% and a temperature interval of 278–318 K at the constant pH = 7.05 are calculated. The concentration and temperature dependences of the effective radii of ovine, bovine, and human serum albumin macromolecules are compared. It is shown that they are partially similar for the solutions of ovine and human serum albumins within concentration intervals of 0.12–0.49 vol% and 0.18–0.48 vol%, respectively, provided an identical acid-base balance (pH) in those solutions. The following conclusions are drawn: (i) the concentration dependences of the effective radii of structurally similar macromolecules of various albumins are similar, but provided an identical pH, and (ii) the dependence of the volume concentration of aqueous albumin solutions on the temperature at the constant radius of a macromolecule confirms the hypothesis about the existence of a dynamic phase transition in aqueous solutions at a temperature of 42 ∘C, at which the thermal motion of water molecules significantly changes.

Synthesis and phase behavior of double sensitive linear amphiphilic prepolymers before gelation

A series of amphiphilic linear prepolymers for gelation, poly(poly(ethylene glycol) diglycidyl ether—monoethanolamine—poly(propylene glycol) diglycidyl ether), i.e. polyPEMPPs, were designed and synthesized by using poly(ethylene glycol) diglycidyl ether (PEGDGE), Poly(propylene glycol) diglycidyl ether (PPGDGE), and monoethanolamine (MEA) as main raw materials through nucleophilic addition/ring-opening reaction. The amphiphilic structure in the backbone of the prepolymers polyPEMPPs causes a phase transition in aqueous solution and has multiple stimuli responsiveness. The effects of hydrogen bonding and electrostatic interactions on phase transition behavior were discussed and analyzed structural reasons in detail. This has important guiding significance for further research on control sol–gel transition. The effects of polyPEMPPs concentration, content of PEGDGE and solution pH values on the phase transition temperature were examined. The experimental results show that increasing polyPEMPPs concentration promotes the phase transition, the transition temperature decreasing with increasing PEGDGE content. In the pH experiment, intra- and intermolecular association became difficult and the phase behavior will be inhibited, whether hydrochloric acid system or sodium hydroxide system. Moreover, we also experimented oscillatory phase transition, and the result exhibited a stably reversible phenomenon transition.

Coil-Globule Transition Thermodynamics of Poly(N-isopropylacrylamide).

Thermosensitive polymers such as poly(N-isopropylacrylamide) (PNIPAM) undergo a phase transition in aqueous solution from a random-coil structural ensemble to a globule structural ensemble at the lower critical solution temperature (LCST). Above this temperature, PNIPAM agglomerates and becomes insoluble, whereas it is soluble below the temperature. Thus, thermosensitive polymers represent essential targets for several applications, e.g., in drug delivery. Although their ability to change structure in response to a temperature alteration is highly relevant for industrial processes, their thermodynamic properties are mostly qualitatively understood, and the quantitative thermodynamic picture is still elusive. In this study, we used a combined atomistic molecular dynamics and well-tempered metadynamics simulation approach to estimate coil-globule transition thermodynamics. An isotactic 30-mer of PNIPAM was investigated over a broad temperature range between 200 and 360 K. The transition from the globule to the random-coil structure was observed with well-tempered metadynamics. For the first time, the free energy surface of PNIPAM was estimated and it is shown that the simulation results are in line with the experimentally observed thermosensitive behavior. Below the LCST, the random-coil ensemble represents the global energy minimum and is thermodynamically favored by 21 ± 9 kJ/mol compared to the globule ensemble; both are separated by a barrier of 49 ± 14 kJ/mol. In contrast, above the LCST, the globule ensemble is thermodynamically favored by 21 ± 8 kJ/mol over the random-coil ensemble. The barrier from random-coil to globule is 17 ± 10 kJ/mol.

On the use of aqueous solutions of polyvinyl methyl ether for the embolization of blood vessels

Aqueous solutions of polyvinyl methyl ether were investigated in order to test whether it is possible to utilize them as bases for embolic agents used to deliberately block blood vessels. This may be necessary in the course of treatment of vascular abnormalities, tumors, as well as during the preparation of patients for surgery. The right branch of the binodal curve for the binary system “polyvinyl methyl ether–water” was drawn using the cloud point method and the lower critical mixing temperature (35.5 °C) was calculated. Furthermore, the exact concentration of polyvinyl methyl ether in aqueous solutions at which phase transition occurs (given the temperature of 35.5 °C) was found to be 30 wt %. The viscosity–velocity curves for the 30% solution of polyvinyl methyl ether, obtained by rheoviscometry in the temperature range of 5 to 36 °C, indicate that this aqueous solution has a low viscosity and behaves like a Newtonian fluid. However, at the temperature of 35 °C and higher, close to the phase transition, a significant deviation from its Newtonian behavior is observed due to precipitation of polyvinyl methyl ether as it forms a solid white mass. Through the use of the Arrhenius–Frenkel–Eyring equation, the activation energy of the viscous flow for polyvinyl methyl ether solutions was found to be 31 kJ/mol. Based on refractometry data, it was demonstrated that phase transition in aqueous solutions of polyvinyl methyl ether is reversible. This feature can facilitate medical equipment cleaning before introducing the embolic agent into a patient’s bloodstream. Finally, the investigation determined some parameters, in which the formation of embolic agents from a 30% polyvinyl methyl ether aqueous solution occurs (in situ in a blood vessel at a temperature of 35.5 °C).

Amorphous carbon inhibited TiO2 phase transition in aqueous solution and its application in photocatalytic degradation of organic dye

Compared with anatase phase TiO2, rutile phase TiO2 is not suitable to be used as high-performance catalyst due to its disadvantages such as low carrier mobility and few active sites. However, rutile phase TiO2 can be easily generated in the chlorine-containing solution during hydrothermal process, which is a major problem for the preparation of high-performance TiO2 based photoelectrochemical and photocatalytic devices. In this study, we demonstrate a suppression phenomenon of anatase-to-rutile phase transition in aqueous solution induced by amorphous carbon. Amorphous carbon formed by the carbonization of glucose adhered on the primary TiO2 grains, inhibiting the generation of rutile phase TiO2 nanostructures in a certain degree. During subsequent calcination process, anatase phase TiO2 formed gradually. And TiO2 phase junction was obtained. The TiO2 phase junction exhibits enhanced photocatalytic degradation performance of organic dyes due to the effective separation of carriers and abundant active sites. This study provides a new and feasible way for controllable fabrication of high performance anatase phase TiO2 based photoelectrochemical and photocatalytic devices.

Effect of Peptide Sequence on the LCST-Like Transition of Elastin-Like Peptides and Elastin-Like Peptide-Collagen-Like Peptide Conjugates: Simulations and Experiments.

Elastin-like polypeptides (ELPs) are thermoresponsive biopolymers that undergo an LCST-like phase transition in aqueous solutions. The temperature of this LCST-like transition, Tt , can be tuned by varying the number of repeat units in the ELP, sequence and composition of the repeat units, the solution conditions, and via conjugation to other biomacromolecules. In this study, we show how and why the choice of guest (X) residue in the VPGXG pentad repeat tunes the Tt of short ELPs, (VPGXG)4, in the free state and when conjugated to collagen-like peptides (CLPs). In experiments, the (VPGWG)4 chain (in short, WWWW) has a Tt < 278 K, while (VPGFG)4 or FFFF has a Tt > 353 K in both free ELP and ELP-CLP systems. The Tt for the FWWF ELP sequence decreases from being >353 K for free ELP to <278 K for the corresponding ELP-CLP system. The decrease in Tt upon conjugation to CLP has been shown to be due to the crowding of ELP chains that decreases the entropic loss upon ELP aggregation. Even though the net hydrophobicity of ELP has been reasoned to drive the Tt , the origins of lower Tt of WWWW compared to FFFF are unclear, as there is disagreement in hydrophobicity scales in how phenylalanine (F) compares to tryptophan (W). Motivated by these experimental observations, we use a combination of atomistic and coarse-grained (CG) molecular dynamics simulations. Atomistic simulations of free and tethered ELPs show that WWWW are more prone to acquire β-turn structures than FFFF at lower temperatures. Also, the atomistically informed CG simulations show that the increased local stiffness in W than F due to the bulkier side chain in W compared to F, alone does not cause the shift in the transition of WWWW versus FFFF. The experimentally observed lower Tt of WWWW than FFFF is achieved in CG simulations only when the CG model incorporates both the atomistically informed local stiffness and stronger effective attractions localized at the W position versus the F position. The effective interactions localized at the guest residue in the CG model is guided by our atomistically observed increased propensity for β-turn structure in WWWW versus FFFF and by past experimental work of Urry et al. quantifying hydrophobic differences through enthalpy of association for W versus F.

Glass polymorphism and liquid-liquid phase transition in aqueous solutions: experiments and computer simulations.

One of the most intriguing anomalies of water is its ability to exist as distinct amorphous ice forms (glass polymorphism or polyamorphism). This resonates well with the possible first-order liquid-liquid phase transition (LLPT) in the supercooled state, where ice is the stable phase. In this Perspective, we review experiments and computer simulations that search for LLPT and polyamorphism in aqueous solutions containing salts and alcohols. Most studies on ionic solutes are devoted to NaCl and LiCl; studies on alcohols have mainly focused on glycerol. Less attention has been paid to protein solutions and hydrophobic solutes, even though they reveal promising avenues. While all solutions show polyamorphism and an LLPT only in dilute, sub-eutectic mixtures, there are differences regarding the nature of the transition. Isocompositional transitions for varying mole fractions are observed in alcohol but not in ionic solutions. This is because water can surround alcohol molecules either in a low- or high-density configuration whereas for ionic solutes, the water ion hydration shell is forced into high-density structures. Consequently, the polyamorphic transition and the LLPT are prevented near the ions, but take place in patches of water within the solutions. We highlight discrepancies and different interpretations within the experimental community as well as the key challenges that need consideration when comparing experiments and simulations. We point out where reinterpretation of past studies helps to draw a unified, consistent picture. In addition to the literature review, we provide original experimental results. A list of eleven open questions that need further consideration is identified.