Ekaterina Strounina

Water movement into dormant and non-dormant wheat (Triticum aestivum L.) grains

The movement of water into harvest-ripe grains of dormant and non-dormant genotypes of wheat (Triticum aestivum L.) was investigated using Magnetic Resonance Micro-Imaging (MRMI). Images of virtual sections, both longitudinal and transverse, throughout the grain were collected at intervals after the start of imbibition and used to reconstruct a picture of water location within the different grain tissues and changes over time. The observations were supplemented by the weighing measurements of water content and imbibition of grains in water containing I2/KI which stains starch and lipid, thereby acting as a marker for water. In closely related genotypes, with either a dormant or a non-dormant phenotype, neither the rate of increase in water content nor the pattern of water distribution within the grain was significantly different until 18 h, when germination became apparent in the non-dormant genotype. Water entered the embryo and scutellum during the very early stages of imbibition through the micropyle and by 2 h water was clearly evident in the micropyle channel. After 12 h of imbibition, embryo structures such as the coleoptile and radicle were clearly distinguished. Although water accumulated between the inner (seed coat) and outer (pericarp) layers of the coat surrounding the grain, there was no evidence for movement of water directly across the coat and into the underlying starchy endosperm.

Optically active sulfonated polyanilines

Abstract The water soluble sulfonated polyaniline, poly(2-methoxyaniline-5-sulfonic acid), has been prepared in optically active form via the electropolymerisation of 2-methoxyaniline-5-sulfonic acid in the presence of (R)-(+)- or (S)-(−)-1-phenylethylamine. The polymer films deposited on ITO-coated glass with the enantiomeric amines exhibited intense, mirror imaged circular dichroism spectra in the visible region. This enantioselectivity in the polymerisation/deposition is attributed to the respective chiral amines inducing a preferred one-handed helical structure to the sulfonated polyaniline chains via acid–base interactions. The optical activity and electroactivity of the chiral polymers are retained after their immobilisation on poly(4-vinylpyridine).

Synthesis and characterization of a POSS-PEG macromonomer and POSS-PEG-PLA hydrogels for periodontal applications.

A novel water-soluble macromonomer based on octavinyl silsesquioxane has been synthesized and contains vinyl-terminated PEG 400 in each of the eight arms to promote water solubility. The macromonomer was characterized by NMR and FTIR and its aqueous solution properties examined. In water it exhibits an LCST with a cloud point at 23 °C for a 10 wt % aqueous solution. It is surface active with a CMC of 1.5 × 10(-5) M in water and in 20:80 v/v acetone/water the CMC is 7.1 × 10(-5) M, and TEM images showed spherical 22 nm aggregates in aqueous solution above the CMC. The macromonomer was copolymerized in a 20:80 v/v acetone/water mixture with a vinyl-terminated, triblock copolymer of lactide-PEG-lactide to form a library of cross-linked hydrogels that were designed for use as scaffolds for alveolar bone repair. The cross-linked copolymer networks were shown to contain a range of nm-μm sized pores and their swelling properties in water and PBS at pH 7.4 were examined. At pH 7.4 the hydrogel networks undergo a slow hydrolysis with the release of principally PEG and lactic acid fragments. The hydrogels were shown to be noncytotoxic toward fibroblast cultures at pH 7.4, both initially (days 1-5) and after significant hydrolysis had taken place (days 23-28).

Conformational Changes in Sulfonated Polyaniline Caused By Metal Salts and OH

The fully sulfonated, water soluble polyaniline, poly(2-methoxyaniline-5-sulfonic acid), has been shown to be remarkably inert to alkaline dedoping, remaining in the conducting emeraldine salt form even in 2.0 M NaOH. Instead, its polyaniline chains undergo a conformational change from an extended coil to a compact coil structure. The same conformational change is caused, but more slowly, by the presence of added alkali and alkaline earth metal salts (1.0 M). These unprecedented rearrangements proceed via two steps, the speeds of which are sensitive to the nature of the metal ions and the associated anions. The processes are reversed by acid.

Blue hydrogenated lithium titanate as a high-rate anode material for lithium-ion batteries

Blue hydrogenated lithium titanate (LTO) was prepared by treating industrial grade white LTO at 500 °C under a 40 bar H2 atmosphere. This process improves the Li-ion diffusivity and electronic conductivity, leading to enhanced specific capacity and rate capability in lithium-ion batteries.

Structure and molecular mobility of soy glycinin in the solid state

We report a multitechnique study of structural organization and molecular mobility for soy glycinin at a low moisture content (<30% w/w) and relate these to its glass-to-rubber transition. Small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy are used to probe structure and mobility on different length and time scales. NMR (approximately 10(-6) to 10(-3) s) reveals transitions at a higher moisture content (>17%) than DSC or SAXS, which sample for much longer times (approximately 10 to 10(3) s) and where changes are detected at >13% water content at 20 degrees C. The mobility transitions are accompanied by small changes in unit-cell parameters and IR band intensities and are associated with the enhanced motion of the polypeptide backbone. This study shows how characteristic features of the ordered regions of the protein (probed by SAXS and FTIR) and mobile segments (probed by NMR and DSC) can be separately monitored and integrated within a mobility transformation framework.

Physicochemical characterisation and hydrothermal stability investigation of cobalt-incorporated silica xerogels

The hydrothermal stability of the cobalt oxide silica xerogels was comprehensively investigated, including the effect of Co/Si molar ratio (0.00–0.50), vapour content (0–75 mol%), exposure time (0–100 h) and temperature (250–550 °C). Physicochemical properties of the xerogels were characterised by nitrogen sorption, FTIR, solid-state 29Si NMR (CP/MAS), micro-Raman, XRD and HR-TEM techniques. The structural characterisation indicated that increasing cobalt incorporation inhibited the degree of condensation in the silica network, and that the formation of tricobalt tetroxide (Co3O4) nanocrystals in the silica matrix was only observed in high cobalt loading samples (Co/Si ≥ 0.25). The hydrothermal stability of the xerogels assessed by N2 sorption was found to be strongly dependent on the cobalt loading; particularly when the presence of Co3O4 in the silica matrices was implicated. For the unstable xerogels (Co/Si < 0.25), the materials stability was significantly decreased by both vapour content and exposure time, resulting in an almost 90% surface area reduction. On the other hand, the high cobalt loading xerogels (Co/Si ≥ 0.25) were found to contain Co3O4 and were much more stable, losing less than 25% of surface area and maintaining microporous structure after exposing to a harsh condition of 75 mol% vapour at 550 °C for 40 h. A structural model is proposed whereby the cobalt oxide particles ‘shield’ the silica matrix and inhibit the hydrolysis and condensation of the silica in the pores walls. This effectively limits the structural rearrangement that hydrothermal treatment typically invokes and therefore confers improved hydrothermal stability.

Effects of thermal denaturation on the solid-state structure and molecular mobility of glycinin

The effects of moisture and thermal denaturation on the solid-state structure and molecular mobility of soy glycinin powder were investigated using multiple techniques that probe over a range of length and time scales. In native glycinin, increased moisture resulted in a decrease in both the glass transition temperature and the denaturation temperature. The sensitivity of the glass transition temperature to moisture is shown to follow the Gordon-Taylor equation, while the sensitivity of the denaturation temperature to moisture is modeled using Florys melting point depression theory. While denaturation resulted in a loss of long-range order, the principal conformational structures as detected by infrared are maintained. The temperature range over which the glass to rubber transition occurred was extended on the high temperature side, leading to an increase in the midpoint glass transition temperature and suggesting that the amorphous regions of the newly disordered protein are less mobile. (13)C NMR results supported this hypothesis.

The States, Diffusion, and Concentration Distribution of Water in Radiation‐Formed PVA/PVP Hydrogels

Abstract Hydrogels with various compositions of polyvinyl alcohol (PVA) and poly(1‐vinyl‐2‐ pyrrolidinone) (PVP) were prepared by irradiating mixtures of PVA and PVP in aqueous solutions with gamma‐rays from 60Co sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T2 relaxation measurements and the kinetics of water diffusion in the hydrogels were studied by sorption experiments and NMR imaging. The DSC endothermic peaks in the temperature range −10 to +10°C implied that there are at least two kinds of freezable water present in the matrix. The difference between the total water content and the freezable water content was referred to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with FVP=0.19 has been estimated to be gH2O/gPolymer=0.375. From water sorption experiments, it was demonstrated that the early stage of the diffusion of water into the hydrogels was Fickian. A curve‐fit of the early‐stage experimental data to the Fickian model allowed determination of the water diffusion coefficient, which was found to lie between 1.5×10−11 m2 s−1 and 4.5×10−11 m2 s−1, depending on the polymer composition, the cross‐link density, and the temperature. It was also found that the energy barrier for diffusion of water molecules into PVA/PVP hydrogels was ≈24 kJ mol−1. Additionally, the diffusion coefficients determined from NMR imaging of the volumetric swelling of the gels agreed well with the results obtained by the mass sorption method.

Tailoring mesoporous-silica nanoparticles for robust immobilization of lipase and biocatalysis

The rational design of nano-carriers is critical for modern enzyme immobilization for advanced biocatalysis. Herein, we report the synthesis of octadecylalkyl-modified mesoporous-silica nanoparticles (C18-MSNs) with a high C18 content (~19 wt.%) and tunable pore sizes (1.6–13 nm). It is demonstrated that the increased hydrophobic content and a tailored pore size (slightly larger than the size of lipase) are responsible for the high performance of immobilized lipase. The optimized C18-MSNs exhibit a loading capacity of 711 mg/g and a specific activity 5.23 times higher than that of the free enzyme. Additionally, 93% of the initial activity is retained after reuse five times, which is better than the best performance reported to date. Our findings pave the way for the robust immobilization of lipase for biocatalytic applications.