Behavior Of Aqueous Solutions Research Articles

Alpha-beta transition induced by C18-conjugation of polyalanine and its implication in aqueous solution behavior of poly(ethylene glycol)-polyalanine block copolymers

BackgroundThe aqueous solution behavior of thermosensitive PEG-PA block copolymers as well as secondary structure of PA is expected to significantly change through modification of the hydrophobic PA by long chain alkyl (C18) groups with different configurations.MethodOleoyl and stearoyl (C18) groups were conjugated to poly(ethylene glycol)-poly(L-alanine) (PEG-PA; EG45A16) diblock copolymers to compare their conjugation effect on nano-assemblies and corresponding aqueous solution behavior of the polymers.ResultsDue to the nature of a hydrophilic PEG block and a hydrophobic PA or C18-modified PA, PEG-PA, oleoyl group-conjugated PEG-PA (PEG-PAO), and stearoyl group-conjugated PEG-PA (PEG-PAS) block copolymers form micelles in water. Compared with PEG-PA, the micelle size of PEG-PAO and PEG-PAS increased. Circular dichroism and FTIR spectra of aqueous polymer solutions showed that β sheet content increased, whereas α helix content decreased by C18 modification of PEG-PA. PEG-PAS showed better performance in ice crystallization inhibition than PEG-PAO. The sol-to-gel transition temperatures of aqueous PEG-PAO solutions were 25–37 °C higher than those of aqueous PEG-PA solutions, whereas aqueous PEG-PAS solutions remained as gels in the temperature range of 0–80 °C. 1H-NMR spectra indicated that the oleoyl groups increased core mobility, whereas stearoyl groups decreased the core mobility of the micelles in water. The difference in micromobility between PAO and PAS interfered or promoted gelation of the aqueous polymer solutions, respectively.ConclusionsThis study suggests that a hydrophobic C18-modification of polypeptide induces α helix-to-β sheet transition of the polypeptide; however, aqueous solution behaviors including ice recrystallization inhibition and gelation are significantly affected by the nature of the hydrophobic molecule.Graphical abstract

Thermodynamic Modeling of Aqueous LiCl, LiBr, LiI, and LiNO3 Solutions

Thermodynamic models are essential to facilitate the advancement of process design, optimization, and operation of electrolyte systems. In this work, a comprehensive thermodynamic framework based on the Electrolyte Nonrandom Two-Liquid model is developed to calculate phase equilibria behavior and salt solubility of aqueous LiCl, LiBr, LiI, and LiNO3 solutions. The model describes the non-ideality of the electrolyte solutions by using two binary interaction parameters for each molecule-electrolyte pair in the system. Each binary interaction parameter is further expressed with up to three temperature coefficients which are regressed from experimental data. To take into account the hydration of lithium ion, two separate chemistries for the dissociation of lithium salts are investigated. In the first case, the lithium ion is considered as a bare ion, Li+, while in the second case hydration of the lithium ion from Li+ to Li(H2O)+ is considered. The calculated thermodynamic properties compare adequately with the experimental data for both sets of chemistries for concentrations up to saturation and temperatures from 273.15 K up to 623.15 K. Moderate to significant improvements are observed with the incorporation of the hydration chemistry for aqueous LiCl, LiBr, and LiI solutions when compared to the non-hydrated lithium ion model results.

Investigation of the Localized Corrosion of Ni-Cr-Mo-W Alloy UNS N06022 in Aprotic Solvents at Room Temperature

Syntheses of pharmaceuticals often require a series of intermediate steps involving reactions in aprotic organic solvents. Some of these solutions can be aggressive towards the metallic materials that constitute the reaction vessels used, so often corrosion-resistant alloys (CRA) such as the Ni-Cr-Mo-W UNS N06022 are employed. Such materials are expensive, but their use is required to prevent contamination of the product by metal ions. Ni-Cr-Mo-W alloys are known to exhibit outstanding corrosion resistance in reducing and oxidizing aqueous solutions as a result of their passive oxide film. However, the application of passive alloys in nonaqueous solvents raises additional concerns due to: i) limited availability of oxygen atoms for passivation; ii) different behavior of aggressive anions and acids as a result of the solvent’s physicochemical properties. Nevertheless, the literature on corrosion of CRA is focused on behavior in aqueous solutions and the literature on corrosion in organic solvents lacks information on the application of commercial alloys. The aim of this work is to investigate the corrosion of Ni-Cr-Mo-W alloys in aprotic organic solvents and to understand the influence of properties of the solvent on the susceptibility to pitting and to uniform corrosion, at room temperature.Preliminary work was carried out with anhydrous acetonitrile solutions containing HCl and the oxidant 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Mass loss and electrochemical tests have shown that alloy N06022 exhibits high-rate dissolution in such conditions. The corrosion rates observed after 24 h of immersion are greater than 10 mm/year, which is remarkably high when compared with the existing literature on corrosion of Ni-Cr-Mo alloys. Moreover, in neutral acetonitrile containing chloride, N06022 undergoes pitting at much lower Cl– concentrations and temperature than in aqueous solutions. In order to understand the enhanced susceptibility to pitting and uniform corrosion in aprotic solvents, potentiodynamic polarizations and electrochemical impedance spectroscopy were performed in various solution compositions, followed by surface characterization with scanning electron microscopy. The correlation of passivation and breakdown phenomena with variables of importance, namely water content, chloride concentration, and acidity will be investigated. Ultimately, this study will provide fundamental understanding of the passivity of Ni-based alloys in organic solvents, assisting the selection of materials for nonaqueous applications.

Oxygen-switchable thermo-responsive polymers with unprecedented UCST in water

Polysulfobetaine copolymers, poly[(ethylene glycol)-block-(3-((3-aminopropyl)dimethylammonio)propane-1-sulfonateacrylamide-co-benzylacrylamide-co-2,2,2-trifluoroethylacrylamide)], p(PEG-b-ADPSx-Bzy-Tfz), comprising hydrophobic components by varying their chemical compositions, are successfully synthesized by reversible addition–fragmentation chain-transfer polymerization (RAFT) and subsequent post-polymerization modification of an activated polymer scaffold. Owing to its amphiphilic nature p(PEG-b-ADPS0.58-Bz0.31-Tf0.11) copolymer can self-assemble into vesicles in aqueous solution and exhibits a dual-responsive behavior toward O2 and temperature stimuli. The O2 switchable temperature-dependent aqueous solution behavior of the derived species was assessed through turbidity measurements, NMR spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering, revealing that such vesicles can exhibit size change behavior via external stimuli due to their suitable chemical structure and stimuli responsiveness.

CO2 corrosion behavior of simulated heat-affected zones for X80 pipeline steel

The CO2 corrosion behavior of the simulated heat-affected zones (HAZs) of X80 pipeline steel in 3.5 wt% NaCl aqueous solutions was surveyed using electrochemical measurements and welding thermal simulation technology combined with microstructural analysis. The results revealed that changes in the corrosion resistance of the HAZ sub-regions were associated with variations in the microstructural sensitivity to the CO2 corrosion behavior in the NaCl aqueous solutions. The weakening of the corrosion resistance in the coarse-grained HAZ was attributed to the larger grain size and coarsening martensite/austenite constituents in the matrix. The corrosion products on the metal surface can lead to a minor reduction in the corrosion rate. In addition, increasing H+ concentration and higher residual stress can destroy the dynamic balance on the metal surface, thereby eventually damaging the corrosion product film.

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

Lignosulfonates are bio-based surfactants and specialty chemicals, which are generated by breaking the near-infinite lignin network during sulfite pulping of wood. Due to their amphiphilic nature, lignosulfonates are used in manifold applications such as plasticizer, dispersant, and stabilizer formulations. Function and performance are determined by their behavior in aqueous solution and at surfaces and interfaces, which is in turn imposed by the chemical make-up. This review hence summarizes the efforts made into delineating the physicochemical properties of lignosulfonates, while also relating to their composition and structure. Lignosulfonates are randomly branched polyelectrolytes with abundant sulfonate and carboxylic acid groups to ensure water-solubility. In aqueous solution, their conformation, colloidal state, and adsorption at surfaces or interfaces can be affected by a range of parameters, such as pH, concentration of other electrolytes, temperature, and the presence of organic solvents. These parameters may also affect the adsorption behavior, which reportedly follows Langmuir isotherm and pseudo second-order kinetics. The relative hydrophobicity, as determined by hydrophobic interaction chromatography, is an indicator that can help to relate composition and behavior of lignosulfonates. More hydrophobic materials have been found to exhibit a lower charge density. This may improve dispersion stabilization, but it can also be disadvantageous if an electrokinetic charge needs to be introduced at solid surfaces or if precipitation due to salting out is an issue. In addition, the monolignol composition, molecular weight distribution, and chemical modification may affect the physicochemical behavior of lignosulfonates. In conclusion, the properties of lignosulfonates can be tailored by controlling aspects such as the production parameters, fractionation, and by subsequent modification. Recent developments have spawned a magnitude of products and technologies, which is also reflected in the wide variety of possible application areas.

A non-aggregated zinc(II) phthalocyanine with hexadeca cations for antitumor and antibacterial photodynamic therapies

With a view to developing highly efficient photosensitizers for both antitumor and antimicrobial photodynamic therapies, herein, we reported a super cationic zinc(II) phthalocyanine (Pc4), which was prepared through the quaternization of the N, N-dimethyl-3-aminophenoxyl-hexadeca-substituted precursor Pc3. Meanwhile, two disubstituted analogues (Pc1 and Pc2) were also prepared as controls. The cationic Pc2 and Pc4 had higher photoactivities including fluorescence and singlet oxygen than the neutral counterparts Pc1 and Pc3, probably because of the inhibition of intramolecular charge transfer (ICT) effect of the amino groups. With the bulky steric effect and high hydrophilicity, Pc4 presented non-aggregated behavior in aqueous solutions. Therefore, it exhibited the highest in vitro photodynamic activity toward HepG2 cancer cells with an IC50 value as low as 0.04 μM. Furthermore, Pc4 showed a highly efficient in vivo PDT effect on H22 tumor-bearing mice with 98.7% tumor growth inhibition. In addition, Pc4 also exhibited an excellent in vitro and in vivo photodynamic inactivation against S. aureus. The results indicate that the non-aggregated hexadeca-cationic Pc4 could serve as a promising photosensitizer for both antitumor and antimicrobial photodynamic therapies.

Synthesis and interfacial properties of glyco-lipophosphoramidates

Lipophosphoramidates are a class of amphiphilic molecules that are tunable; and are heavily explored for a variety of industrial and medicinal applications. Self-assembled structures derived from such molecules enhance the bioavailability, selectivity and pharmacokinetic properties of drug molecules. Herein we report the synthesis of novel glyco-lipophosphoramidates (GLP-3, GLP-4, GLP-5, GLP-6) with varying linear and branched hydrocarbon tails via the Staudinger-phosphite reaction. The incorporation of the carbohydrate moiety as the head group region of the amphiphile promotes biocompatibility and biodegradability. Surface activity, adsorption, and aggregation behavior in aqueous solution were examined using surface tension, Langmuir monolayers, and atomic force microscopy (AFM). The critical aggregation concentrations (CAC) and Langmuir isotherms showed the typical dependence on acyl chain structure. Gibbs adsorption profiles provided limiting molecular areas in the range 55–85 Å2. AFM imaging revealed the formation of large spherical aggregates in aqueous solution above the CAC. Dye encapsulation studies support the self-assembly into vesicles by GLP-3, GLP-4 and GLP-5; demonstrating the potential for drug delivery or nanocarrier applications.

How Different Electrolytes Can Influence the Aqueous Solution Behavior of 1-Ethyl-3-Methylimidazolium Chloride: A Volumetric, Viscometric, and Infrared Spectroscopy Approach.

The density, sound velocity, and viscosity of 1-ethyl-3-methylimidazolium chloride [C2mim]Cl in pure water and aqueous solutions of some electrolytes such as potassium chloride, potassium carbonate, and potassium phosphate (weight fraction of salt fixed at ws = 0. 11) have been measured over a wide range of temperatures from 298.15 to 318.15 K. The obtained experimental data have been used to compute various volumetric, compressibility, and viscometric parameters, e.g., apparent molar properties, limiting apparent molar and transfer properties. The co-sphere overlap model was employed to describe the dominant intermolecular interactions in the ternary solutions. Additionally, the structure making/breaking nature of the [C2mim]Cl in the ternary solutions has been discussed in terms of Hepler's constant and the temperature derivative of viscosity B-coefficient (dB/dT). The activation free energy of solvent and solute, activation enthalpy, and activation entropy have been calculated by the application of transition state theory. The calculated parameters have been interpreted in the sense of solvent–solute and solute–solute interactions. The Fourier transform infrared (FTIR) studies also have been done for the studied systems. Volumetric, acoustic, viscometric, and spectroscopic studies can render some evidence and help to understand the aqueous solution behavior of ionic liquids.

Application of gemini viscoelastic surfactant with high salt in brine-based fracturing fluid

In this study, a viscoelastic surfactant (VES), named VES-Q, with erucyl amide tails and cyclodextrin was successfully synthesized, and the phase behavior of aqueous VES solutions at different salt concentrations was observed. In addition, the size of the molecules under different salt types was measured using dynamic light scattering. The viscosity of VES-Q in salt solution corresponds to the molecular size of the surfactant was found. Due to the high salinity tolerance of VES-Q to common formation salts, we used formation water from West Sichuan and seawater the Gulf of Mexico to allocate VES-Q to two clean fracturing fluids, namely, fluid 1 and fluid 2, with a concentration of 2%. Rheological properties under high-temperature reservoir conditions were simulated. The clean fracturing fluid was prepared by the VES-Q method, and its performance met the requirements of hydraulic fracturing operations.

Red currant pectin: The physicochemical characteristic of pectin solutions in dilute and semi dilute regimes

In this study red currant was used as a source of pectin. The aim of this study was to investigate the physicochemical properties of obtained polysaccharide, with an emphasis on behaviour in aqueous solutions. Pectin was obtained using water extraction, then the basic characteristics of the obtained polysaccharide was performed (FT-IR-ATR, molar mass distribution, sugar composition, DE). An applied extraction method resulted in a water-soluble pectin fraction with Mw=1020 kg ⋅ mol-1 and DE=57.1%. To study the behaviour of pectins in aqueous solutions various methods were used: membrane osmometry, viscosity measurements, rheology, NMR and DLS. The obtained results allowed to describe pectin chains properties in both dilute and semi-dilute regimes, including c∗ value determination. Osmotic tests indicated low water affinity and strong intermolecular interactions for red currant pectin. Viscosity measurements revealed strong polyelectrolyte behaviour, initially the reduced viscosity of the solutions decreased, until the overlap concentration (c∗=0.78 g ⋅ dL-1) was reached and then increased sharply. Comprehensive interpretation of the results obtained by means of used methods allowed to conclude that red currant pectin takes the form of tightly wound coils in dilute solutions, with increasing concentration chains tending to expand and intermolecular interactions are being enhanced, which result in the formation of complex structures.

Surface Behavior of Aqueous Solutions of Sodium Lauryl Ether Sulfate, Additives and Their Mixtures: Experimental and Modeling Study

The surface tensions of aqueous solutions of sodium lauryl ether sulfate (SLES), ethanol, acetonitrile, 1-propanol and 2-propanol were individually measured using the pendant drop technique. Then, the surface tensions and critical micelle concentrations of the mixed aqueous solutions of (SLES + additives) were then measured at different concentrations of species for the first time. All measurements were conducted at the temperature of 298.15 K. In addition, a thermodynamic model was presented for accurately predicting of the surface tensions of the mixtures and the surface coverage of the surfactant in the mixture with the average absolute deviation of 1.45 %. Furthermore, an increase in the SLES concentration led to a higher surface coverage, although the presence of an additive caused a slight decrease in the surface coverage of SLES and an increase in the critical micelle concentration of the mixtures.

Diamine versus amines blend for CO2 chemical absorption

AbstractPresent work analyses the behavior of aqueous solutions of N,N‐dimethylethylenediamine as chemical solvent for carbon dioxide separation by gas–liquid absorption. The interest of this molecule is centered on the presence of different types of amino centers that confer it the capability to act as a solvent based on amines blend. For this reason, a comparison between diamine and amines blend solvent has been carried out in order to understand the differences between these solvents using absorption and nuclear magnetic resonance studies. This experimental work analyses the influence of amine type, concentration, and ratio between different amines. Also, the effect of gas flow rate used in the bubble column reactor upon the absorption kinetics has been analyzed.

Triapine Derivatives Act as Copper Delivery Vehicles to Induce Deadly Metal Overload in Cancer Cells

Thiosemicarbazones continue to attract the interest of researchers as potential anticancer drugs. For example, 3-aminopyridine-2-carboxaldehyde thiosemicarbazone, or triapine, is the most well-known representative of this class of compounds that has entered multiple phase I and II clinical trials. Two new triapine derivatives HL1 and HL2 were prepared by condensation reactions of 2-pyridinamidrazone and S-methylisothiosemicarbazidium chloride with 3-N-(tert-butyloxycarbonyl) amino-pyridine-2-carboxaldehyde, followed by a Boc-deprotection procedure. Subsequent reaction of HL1 and HL2 with CuCl2·2H2O in 1:1 molar ratio in methanol produced the complexes [CuII(HL1)Cl2]·H2O (1·H2O) and [CuII(HL2)Cl2] (2). The reaction of HL2 with Fe(NO3)3∙9H2O in 2:1 molar ratio in the presence of triethylamine afforded the complex [FeIII(L2)2]NO3∙0.75H2O (3∙0.75H2O), in which the isothiosemicarbazone acts as a tridentate monoanionic ligand. The crystal structures of HL1, HL2 and metal complexes 1 and 2 were determined by single crystal X-ray diffraction. The UV-Vis and EPR spectroelectrochemical measurements revealed that complexes 1 and 2 underwent irreversible reduction of Cu(II) with subsequent ligand release, while 3 showed an almost reversible electrochemical reduction in dimethyl sulfoxide (DMSO). Aqueous solution behaviour of HL1 and 1, as well as of HL2 and its complex 2, was monitored as well. Complexes 1−3 were tested against ovarian carcinoma cells, as well as noncancerous embryonic kidney cells, in comparison to respective free ligands, triapine and cisplatin. While the free ligands HL1 and HL2 were devoid of antiproliferative activity, their respective metal complexes showed remarkable antiproliferative activity in a micromolar concentration range. The activity was not related to the inhibition of ribonucleotide reductase (RNR) R2 protein, but rather to cancer cell homeostasis disturbance—leading to the disruption of cancer cell signalling.

Solvent-Resistant and Nonswellable Hydrogel Conductor toward Mechanical Perception in Diverse Liquid Media.

Wet-resistant flexible electronics have gained impressive attention as underwater wearable sensors, all-weather electronic skins, and implantable bioelectrodes. However, fabricating a stable and nonswelling hydrogel-based electronic device used in diverse liquid media is challenging and promising for the progress of wet-resistance electronics. Herein, a solvent-resistant and tough hydrogel conductor is successfully prepared and exhibits fatigue resistance, antifreezing behavior, and nonswelling and wet-adhesion performances in organic and aqueous solutions. Moreover, the hydrogels are utilized as all-weather wearable sensors featuring high sensitivity, reliability, and wide sensing ranges for monitoring and distinguishing various physiological signals and human motions. Furthermore, the hydrogel sensors can even achieve accurate and stable mechanical sensing of pressure, bending, and stretching in diverse solvents consisting of water, chloroform, hexane, and dodecane. It is envisioned that the solvent-resistant and antifreezing hydrogel conductor can present promising feasibility as all-weather electronic skins, intelligent sensors in solvents, and soft robots in various harsh liquid environments.

Proton-coupled redox properties and water oxidation catalysis of an aqua-coordinated (µ-oxo)diruthenium(III) complex

The electronic absorption and redox properties as well as the catalysis for water oxidation reaction (WOR) of an aqua-coordinated oxo-bridged diruthenium(III) complex trans(µ-O,OH2)-[Ru2(µ-O)(µ-CH3COO)2(bpy)2(H2O)2](PF6)2·3H2O ([1](PF6)2·3H2O; bpy = 2,2′-bipyridine) in aqueous media are reported. [1]2+ displays a visible absorption band at 566 nm ascribed to metal-to-metal charge transition (MMCT) within the Ru2O core. This visible band redshifts due to the deprotonation of the terminal aqua ligands of [1]2+ in alkaline solutions. [1]2+ shows proton-coupled electron transfer behaviors in aqueous solutions at pH 0–14. The oxidation of RuIIIRuIII in [1]2+ has successfully reached the higher oxidation states including RuIVRuIV and RuVRuV which are stabilized by the deprotonation of the terminal aqua ligands and are important for catalytic water oxidation. WOR catalyzed by [1]2+ in acidic solutions was studied using electrochemical and chemical oxidation. In the solution of [1]2+ at pH 1.0, the overpotential for WOR was ~0.38 V. A turnover number of 23 was obtained by using (NH4)2Ce(NO3)6 as the oxidant. A nucleophilic-attack catalytic mechanism was proposed.

Structural Diversity in Galactans From Red Seaweeds and Its Influence on Rheological Properties.

Galactans are important components of many plant cell walls. Besides, they are the major polysaccharides in extracellular matrixes from different seaweeds, and other marine organisms, which have an acidic character due to the presence of sulfate groups in their structures. In particular, most of the red seaweeds biosynthesize sulfated galactans with very special linear backbones, constituted by alternating (1→3)-β-d-galactopyranose units (A-unit) and (1→4)-α-galactopyranose residues (B-unit). In the industrially significant seaweeds as source of hydrocolloids, B-units belong either to the d-series and they produce carrageenans (as in the order Gigartinales), or to the l-series, and they are sources of agarose and/or structurally related polymers (i.e., Gelidiales, Gracilariales). In both cases, the latter units appear as cyclized 3,6-anhydro-α-galactose in certain amounts, which can be increased by alkaline cyclization of α-galactose 6-sulfate units. Besides, it has been clearly shown that some red algae produce different amounts of both galactan structures, known as d/l-hybrids. It is not yet clear if they comprise both diasteromeric types of units in the same molecule, or if they are mixtures of carrageenans and agarans that are very difficult to separate. It has been reported that the biosynthesis of these galactans, showing that the nucleotide transport for d-galactopyranose units is UDP-d-Gal, while for l-galactose, it is GDP-l-Gal, so, there is a different pathway in the biosynthesis of agarans. However, at least in those seaweeds that produce carrageenans as major galactans, but also agarans, both synthetic pathways should coexist. Another interesting characteristic of these galactans is the important variation in the sulfation patterns, which modulate their physical behavior in aqueous solutions. Although the most common carrageenans are of the κ/ι- and λ-types (with A-units sulfated at the 4- and 2-positions, respectively) and usually in agarans, when sulfated, is at the 6-position, many other sulfate arrangements have been reported, greatly influencing the functional properties of the corresponding galactans. Other substituents can modify their structures, as methyl ethers, pyruvic acid ketals, acetates, and single stubs of xylose or other monosaccharides. It has been shown that structural heterogeneity at some extent is essential for the proper functional performance of red algal galactans.

Ideal thermodynamic behaviors of aqueous electrolyte solutions at very high concentrations

All physical chemistry textbooks state that solutions of strong electrolytes behave in a non-ideal fashion, except at very high dilution. Examples are provided here for ideal behaviors to very high concentrations, as demonstrated by excellent adherence to Raoult’s law: for NaNO2 solutions up to 12 molal (827.9 g per kilogram of water) and for CsNO2 solutions up to 35 molal (6821.9 g/kg). Improved adherence is reported for previously published almost-ideal RbNO2 solutions up to 62 molal (8151.1 g/kg).

Crucial Role of Water in the Formation of Basic Properties of Living Matter

A relation between the water properties and the behavior of aqueous solutions of albumin, the main protein component of human blood plasma, has been analyzed. The dependence of the pH index of acid-base balance in aqueous albumin solutions on the albumin concentration is experimentally studied. It is shown that the temperature dependences of pH in biological solutions are determined by the properties of water, and the concentration ones by the concentration of a protein component. It is albumin that makes the main contribution to the pHs of blood and blood plasma, and it should be considered as a factor that maintains the equilibrium pH value. It is shown that the most characteristic changes in the concentration dependences of the density and shear viscosity of human plasma occur at a protein concentration corresponding to the percolation threshold. A characteristic dimerization of albumin macromolecules is assumed to take place at the percolation threshold, which corresponds to the superposition on one another of heart-shaped medallions representing the spatial forms of albumin. The dependences of the effective radii of polyvinyl alcohol and albumin macromolecules on the solution temperature and concentration are demonstrated to be an indicator that water plays a decisive role in the formation of basic properties of biosolutions. In particular, it is responsible for the presence of an upper temperature limit of 42 ∘C for the existence of living matter. The universal nature of the water influence manifests itself in that the water properties affect the behavior of both the classic PVA polymer and protein biomolecules.

Temperature Behavior of Aqueous Solutions of Poly(2-oxazoline) Homopolymer and Block Copolymers Investigated by NMR Spectroscopy and Dynamic Light Scattering.

1H NMR methods in combination with dynamic light scattering were applied to study temperature behavior of poly(2-isopropyl-2-oxazoline) (PIPOx) homopolymer as well as PIPOx-b-poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx)-b-PMeOx diblock copolymers in aqueous solutions. 1H NMR spectra showed a different way of phase transition for the main and side chains in PIPOx-based solutions. Additionally, the phase transition is irreversible for PIPOx homopolymer and partially reversible for PIPOx-b-PMeOx copolymer. As revealed by NMR, the phase transition in PEtOx-based copolymers solutions exists despite the absence of solution turbidity. It is very broad, virtually independent of the copolymer composition and reversible with some hysteresis. Two types of water molecules were detected in solutions of the diblock copolymers above the phase transition—“free” with long and “bound” with short spin–spin relaxation times T2. NOESY spectra revealed information about conformational changes observed already in the pre-transition region of PIPOx-b-PMeOx copolymer solution.