Protein Preferential Solvation in (Sucralose + Water) Mixtures.

Addition of sugars such as sucrose to aqueous protein solutions generally stabilizes proteins against thermal denaturation by preferential exclusion of sugars from proteins (preferential hydration of proteins). In this study, we investigated the effect of sucralose, a chlorinated sucrose derivative, on protein stability and preferential solvation. Circular dichroism and small-angle X-ray scattering measurements showed that sucrose increased the denaturation temperature of myoglobin and was preferentially excluded from the protein, whereas sucralose decreased the denaturation temperature of myoglobin and was preferentially adsorbed to the protein. No clear evidence was obtained for the indirect effects of sucralose on protein destabilization via the structure and properties of solvent water from the physicochemical properties (mass density, sound velocity, viscosity, and osmolality) of aqueous sucralose solutions; therefore, we concluded that a direct protein-sucralose interaction induced protein destabilization.

Anion specific conformational change in aqueous gellan gum solutions.

127I NMR is applied to investigate the motional state and the selective interaction of I- ions in tetramethylammonium form of gellan gum (TMA gellan), together with monitoring the conformational change by the optical rotation measurement. The experimental results indicate that I- ion promotes the conformational transition, and there exists the preferential affinity of I- ion for the ordered conformation of TMA gellan.

Editorial on Special Issue "New Era in the Volume Phase Transition of Gels".

The Special Issue of gels titled "Advancements in Gel Science" has been published from MDPI in 2019 [...].

Formation of Multi-Channel Collagen Gels Investigated Using Particle Tracking Microrheology.

Collagen is one of the most common materials used to form scaffolds for tissue engineering applications. The multi-channel collagen gel (MCCG) obtained by the dialysis of an acidic collagen solution in a neutral buffer solution has a unique structure, with many capillaries of diameters several tens to a few hundred micrometers, and could be a potential candidate as a biomimetic scaffold for three-dimensional tissue engineering. In the present study, the formation of MCCG was investigated by in situ rheological measurements based on a particle tracking method (particle tracking microrheology, PTM). PTM enabled us to measure changes in the rheological properties of collagen solutions under the continuous exchange of substances during dialysis. When an observation plane was set perpendicular to the direction of gel growth, we first observed convectional flow of the collagen solution, followed by phase separation and gelation. We showed that the structure of the MCCG originated from the transient structure formed during the initial stage of viscoelastic phase separation and was fixed by the subsequent gelation.

Necklace-like microstructure in shallow-quenched aqueous solutions of poly(n-isopropylacrylamide), detected by advanced small-angle neutron scattering methods.

The microstructure of aqueous poly(N-isopropyl acrylamide) (PNIPA) gel and solution was investigated by small-angle neutron scattering (SANS) in the vicinity of the gel volume phase transition at TV (= 34 °C). The SANS technique was reinforced by refractive neutron lenses and perfect single crystals in order to get access to µm length scales. At 31 °C SANS shows Ornstein-Zernike (OZ) type scattering in the swollen gel which at 32 °C starts to deviate from the OZ-formalism, exhibiting excess scattering and at the wave number qc≅ 5 × 10-3Å-1 a crossover to Porod's asymptotic q-4 power law. For shallow quenches of ΔT < 1.0 K above TV the excess scattering intensity is further increasing whereas qc is shifting toward lower values. Based on this observation and analysis of the SANS q-profiles, we propose a necklace-like microstructure consisting of PNIPA-rich globules of R≅ 100 Å size which are connected by swollen PNIPA chains and stabilized for more than a day by pinning of chain connectivity. The formation of PNIPA globules near TV is discussed in terms of partially cooperative dehydration which is crucial to explain the "miscibility square phase behavior" of aqueous PNIPA solutions. Globule-like structure was also found in aqueous PNIPA solution of size slightly larger than in gels. At deeper quenches of gels above TV (ΔT > 1.0 K) the globules are aggregating to larger objects of R≅ 0.24 µm size as determined from a strong intensity upturn in the small q-region of USANS.

Stretching PEO-PPO Type of Star Block Copolymer Gels: Rheology and Small-Angle Scattering.

Cross-linked Tetronic star block copolymer gels, based on poly(ethylene oxide) and poly(propylene oxide), behave quite regular with respect to mechanical properties, but exhibits unusual absence of structural response to strain. The elastic response is linear up to more than 100% strain, with a steady-state modulus of the order of 0.01 MPa after an initial stress relaxation. Neutron and X-ray scattering experiments show a consistent but unexpected response to uniaxial strain, with no changes in characteristic molecular dimensions. Upon strain beyond about 100%, that is, when the stress-strain curve is no longer linear, structural texture appears and becomes even more pronounced upon further strain, thus, indicating alignment of the self-assembled hexagonally ordered cylindrical micelles with the cylinder-axis perpendicular to the strain. It is proposed that the main structural response to large-amplitude strain is related to a layer-dominated structure of cross-linked star molecules.

Structural Study of Four-Armed Amphiphilic Star-Block Copolymers: Pristine and End-Linked Tetronic T1307.

We present a comparative structural study of 30 wt % aqueous suspensions of two related systems based on 4-arm PEO-PPO type of macromolecules (Tetronic T1307, BASF) with the PPO block near the star center. One system concerns the pristine 4-arm PEO-PPO star block copolymer T1307. The second system is a 1:1 blend consisting of, respectively, tetra-amine (TAT) and tetra-N-hydroxysuccinimide (TNT) terminated T1307. The two systems show common characteristics which are also known from linear PEO-PPO type of copolymers (Pluronic, BASF): at low temperatures the measured structure is dominated by the characteristics of individual molecules, while at higher temperatures hydrophobic effects of the PPO domains cause self-assembly into spherical or rodlike micelles. These micelles form in both systems ordered mesophases. The pristine T1307 copolymer suspension behaves generally very similarly to linear PEO-PPO type of di- and triblock copolymers: unimers at low temperatures associating into micelles at higher temperatures, forming subsequently cubic and hexagonal phases upon further increase in temperatures. The cubic phase of the 30 wt % Tetronic T1307 has FCC symmetry. The structure of the cross-linked 30 wt % 1:1 TAT-TNT system is basically organized into two-dimensional network sheets. At low temperatures the system is rather disordered but still with a sharp correlation peak which is associated with the distance between neighboring network sheets. Upon raising temperatures, PPO self-assembly causes organization across neighboring sheets, resulting in cylinder-like assemblies perpendicular to the sheets. These cylinders form hexagonal structure.

Nonsolvents-induced swelling of poly(methyl methacrylate) nanoparticles.

Polymer nanoparticles have been used in a wide variety of applications. In most of these applications, they are generally dispersed in a non-solvent. However, the effect of the non-solvent on the structure, physical properties and function of the nanoparticles has not yet ever taken into account. In this study, monodispersed poly(methyl methacrylate) (PMMA) nanoparticles were prepared by a surfactant-free emulsion polymerization. The PMMA nanoparticles were dispersed in water and in methanol, both typical non-solvents for PMMA, so that we could discuss the effect of the non-solvent on the nanoparticles. Dynamic light scattering measurements revealed that the hydrodynamic radius of the PMMA nanoparticles in methanol was larger than the same PMMA dispersed in water. Their DLS values were also larger than the radius of the nanoparticles measured by atomic force microscopy. When pyrene was dispersed in methanol with the PMMA nanoparticles, it was incorporated into the nanoparticles. These results clearly indicate that non-solvent molecules can be sorbed into polymer nanoparticles because the area of the interface, where polymer segments might be dissolved into liquid phases, as the total volume is quite larger for such nanoparticles. Therefore, based on our findings, it can be arguably established that the present assumption for a polymer not to be swollen in its non-solvent is not necessarily true.

Liquid crystalline inorganic nanosheets for facile synthesis of polymer hydrogels with anisotropies in structure, optical property, swelling/deswelling, and ion transport/fixation.

Macroscopically anisotropic hydrogels were synthesized by hybridization of poly(N-isopropylacrylamide) with liquid crystalline inorganic nanosheets; their anisotropies in the structure and properties are demonstrated.

Visible light-induced water oxidation catalyzed by molybdenum-based polyoxometalates with mono- and dicobalt(III) cores as oxygen-evolving centers.

The Mo-based polyoxometalates containing mono- and dicobalt(III) catalyst cores, [CoMo(6)O(24)H(6)](3-) and [Co(2)Mo(10)O(38)H(4)](6-), were found to serve as O(2)-evolving catalysts in a system consisting of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)) and sodium persulfate (S(2)O) in an aqueous borate buffer solution at pH 8.0. Kinetics of O(2) evolution reveals that the higher cobalt nuclearity is not necessary to attain the highly active nature of the catalyst.

Salt effect on microscopic structure and stability of colloidal complex obtained from neutral/polyelectrolyte block copolymer and oppositely charged surfactant.

The salt effect on complex formation of poly(acrylamide)-block-poly(acrylic acid) (PAM-b-PAA) and dodecyltrimethylammonium bromide (DTAB) at different NaBr concentrations, C(NaBr), was investigated by laser light scattering (LLS) and small angle neutron scattering (SANS). LLS and SANS clearly indicates that the aqueous solution of PAM-b-PAA and DTAB associate into colloidal complexes. For low surfactant-to-polymer charge ratio Z lower than the critical value Z(C), the colloidal complexes are single DTAB micelles dressed by a few PAM-b-PAA. Above Z(C), the colloidal complexes form a core-shell microstructure. The complex formation in the PAM-b-PAA/DTAB is enhanced by addition of salt: Z(C) decreases with increasing C(NaBr). This is considered to similar to the cmc behavior for the pure surfactant system. The core of the complex consists of densely packed surfactant micelles (DTA(+)), and PAA block chains bind to these micelles, displace their counteranions (Br-) and bridge them. The corona of the complex is constituted from the PAM. Since the interaction between polyelectrolyte and oppositely charged surfactant is primarily electrostatic in nature, the core radius and the intermicellar distance of the DTA(+) micelles inside the core depend on C(NaBr). The addition of salt screens the electrostatic attraction between oppositely charged PAA block and DTAB, which weakens the interaction. With increasing C(NaBr), therefore, the core of the colloidal complex is considered to swell, which leads to the increases in the core radius R(C) and the intermicellar distance of the DTA(+) micelles inside the core. The aggregation number expressed in terms of DTA(+) micelles per complex is also evaluated using the analogy with the homopolyelectrolyte/surfactant system.

Design of an injectable in situ gelation biomaterials for vitreous substitute.

To adapt the physical properties of living materials to their biological function, nature developed various types of polymers with outstanding physical behavior. One example is the vitreous body, which is important intraocular elements not only because of its optical and mechanical performances, but also due to its important role in the pathogenesis and treatment of conditions affecting adjacent tissues and eventually the whole eye. Here, we report a novel biocompatible material for injectable vitreous substitute, composed of thermosensitive amphiphilic polymer, which is capable of forming a transparent gel in the vitreous cavity. It is nontoxic, provides adequate support for the retina, and allows light to reach the sensory elements at the back of the eye. The amphiphilic polymer exhibits mechanical stability by assembling to form highly interconnected hydrophobic domains, which leads to the constitution of a network structure.

Changing the volume of a giant macrocycle: the swelling of the macrocycle with organic solvents.

The novel tetrahedral macrocycles 1a-1c have been synthesized. Macrocycles 1a and 1c were revealed to have the property to increase in volume in solution by complexation between the macrocycle and the solvent molecules.

Stereoregulation of thermoresponsive polymer brushes by surface-initiated living radical polymerization and the effect of tacticity on surface wettability.

In this study, stereocontrolled poly(N-isopropylacrylamide) (PIPAAm) brushes were grafted from surfaces by atom transfer radical polymerization (ATRP) in the presence of a Lewis acid, and the effect of PIPAAm brush tacticity on the thermoresponsive wettabiliy was investigated. PIPAAm grafted by ATRP in the presence of Y(OTf)(3) showed high isotacticity, while the control brush polymerized in the absence of Y(OTf)(3) was clearly atactic. The isotacticity and molecular weight of PIPAAm brushes were controlled by polymerization conditions. The wettability of isotactic PIPAAm-grafted surfaces decreased slightly below 10 °C, although the phase transition temperature of atactic surface was 30 °C, and the bulk isotactic polymer was water-insoluble between 5 and 45 °C.

Photochemical and thermal hydrogen production from water catalyzed by carboxylate-bridged dirhodium(II) complexes.

A series of dinuclear Rh(II) complexes, [Rh(2)(µ-OAc)(4)(H(2)O)(2)] (HOAc = acetic acid) (1), [Rh(2)(µ-gly)(4)(H(2)O)(2)] (Hgly = glycolic acid) (2), [Rh(2)(µ-CF(3)CO(2))(4)(acetone)(2)] (3), and [Rh(2)(bpy)(2)(µ-OAc)(2)(OAc)(2)] (4), were found to serve as H(2)-evolving catalysts in a three-component system consisting of tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)), methylviologen (MV(2+)), and ethylenediaminetetraacetic acid disodium salt (EDTA). It was also confirmed that thermal reduction of water into H(2) by MV(+)˙, in situ generated by the bulk electrolysis of MV(2+), is effectively promoted by 1 as a H(2)-evolving catalyst. The absorption spectra of the photolysis solution during the photocatalysis were monitored up to 6 h to reveal that the formation of photochemical or thermal byproducts of MV(+)˙ is dramatically retarded in the presence of the Rh(II)(2) catalysts, for the H(2) formation rather than the decomposition of MV(+)˙ becomes predominant in the presence of the Rh(II)(2) catalysts. The stability of the Rh(II)(2) dimers was confirmed by absorption spectroscopy, (1)H NMR, and ESI-TOF mass spectroscopy. The results indicated that neither elimination nor replacement of the equatorial ligands take place during the photolysis, revealing that one of the axial sites of the Rh(2) core is responsible for the hydrogenic activation. The quenching of Ru*(bpy)(3)(2+) by 1 was also investigated by luminescence spectroscopy. The rate of H(2) evolution was found to decrease upon increasing the concentration of 1, indicating that the quenching of Ru*(bpy)(3)(2+) by the Rh(ii)(2) species rather than by MV(2+) becomes predominant at the higher concentrations of 1. The DFT calculations were carried out for several possible reaction paths proposed (e.g., [Rh(II)(2)(µ-OAc)(4)(H(2)O)] + H(+) and [Rh(II)(2)(µ-OAc)(4)(H(2)O)] + H(+) + e(-)). It is suggested that the initial step is a proton-coupled electron transfer (PCET) to the Rh(II)(2) dimer leading to the formation of a Rh(II)Rh(III)-H intermediate. The H(2) evolution step is suggested to proceed either via the transfer of another set of H(+) and e(-) to the Rh(II)Rh(III)-H intermediate or via the homolytic radical coupling through the interaction of two Rh(II)Rh(III)-H intermediates.

Preparation of thermo-responsive polymer brushes on hydrophilic polymeric beads by surface-initiated atom transfer radical polymerization for a highly resolutive separation of peptides.

Poly(N-isopropylacrylamide-co-N-tert-butylacrylamide) [P(IPAAm-co-tBAAm)] brushes were prepared on poly(hydroxy methacrylate) (PHMA) [hydrolyzed poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)] beads having large pores by surface-initiated atom transfer radical polymerization (ATRP) and applied to the stationary phases of thermo-responsive chromatography. Optimized amount of copolymer brushes grafted PHMA beads were able to separate peptides and proteins with narrow peaks and a high resolution. The beads were found to have a specific surface area of 43.0 m(2)/g by nitrogen gas adsorption method. Copolymer brush of P(IPAAm-co-tBAAm) grafted PHMA beads improved the stationary phase of thermo-responsive chromatography for the all-aqueous separation of peptides and proteins.

Effective separation of peptides using highly dense thermo-responsive polymer brush-grafted porous polystyrene beads.

For the development of well-defined highly dense thermo-responsive polymer grafted surface as an improved stationary phase for thermo-responsive chromatography, poly(N-isopropylacrylamide) (PIPAAm) brush-grafted porous polystyrene beads were prepared by surface-initiated atom transfer radical polymerization (ATRP). The PIPAAm grafted region of polystyrene beads was adjusted by the addition of isooctane as a poor solvent for polystyrene upon the reaction of ATRP initiator immobilization. Using a thermo-responsive HPLC column containing the prepared beads with PIPAAm brush grafted on the inside pores nearby the outer surfaces, angiotensin subtypes were effectively separated with aqueous mobile phase, because the densely grafted PIPAAm on nearby the outer surface effectively interacted with the peptides hydrophobically. Retention of basic peptide was achieved by the beads with basic mobile phase. These results indicated that the prepared beads with grafted PIPAAm nearby the outer surface became an effective chromatographic stationary phase for retaining basic peptides using wide pH range of mobile phase.

Thermoresponsive polymer brush surfaces with hydrophobic groups for all-aqueous chromatography.

For developing thermoresponsive chromatographic matrices with a strong hydrophobicity, poly(N-isopropylacrylamide-co-n-butyl methacrylate) (poly(IPAAm-co-BMA)) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with a CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 16 h. The prepared beads were characterized by chromatographic analysis. Chromatograms of the benzoic-acid family and phenol as model analytes were obtained with high-resolution peaks because of their strong hydrophobic interactions to the densely grafted hydrophobized copolymers on the beads. Retention times of the analytes increased with the increase in BMA composition ratio. Dehydration of grafted copolymer with large BMA composition was performed at low temperature. These results indicated that the copolymer-brush-grafted surface prepared by ATRP was an effective tool for separating hydrophilic analytes at low temperature through modulating the strong hydrophobic interaction.

Preparation of thermoresponsive anionic copolymer brush surfaces for separating basic biomolecules.

Poly(N-isopropylacrylamide-co-acrylic acid-co-N-tert-butylacrylamide) (poly(IPAAm-co-AAc-co-tBAAm) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 4 h. The prepared beads were characterized by chromatographic analysis. Basic analytes, catecholamine derivatives, and angiotensin peptides could be separated by a short column length containing the beads because of its high densely grafted copolymer structure. Chromatograms for catecholamine derivatives were obtained with high resolution peaks due to their electrostatic and hydrophobic interactions to the densely grafted anionic copolymers on the beads. Effective separation of angiotensin peptides was performed near the lower critical solution temperature of copolymers, because the total electrostatic and hydrophobic interactions between the copolymer and the analytes become strong at the temperature. These results indicated that the copolymer brush grafted surfaces prepared by ATRP was an effective tool for separating basic biomolecules by modulating the electrostatic and hydrophobic interactions.