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

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

The states, diffusion, and concentration distribution of water in radiation-formed PVA/PVP hydrogels

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 Co-60 sources at room temperature. The states of water in the hydrogels were characterized using DSC and NMR T-2 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 degrees 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 refer-red to as bound water, which is not freezable. The weight fraction of water at which only nonfreezable water is present in a hydrogel with F-VP = 0.19 has been estimated to be g(H2O)/g(Polymer) = 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 x 10(-11) m(2) s(-1) and 4.5 x 10(-11) m(2) 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 approximate to 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

Redox behavior of poly (2-methoxyamlme-5-sulfonic acid) and its remarkable thermochromism, solvatochromism, and ionochromism

A detailed investigation has been carried out of the redox behavior of poly(2-methoxyaniline-5-sulfonic acid) (PMAS) in aqueous solution. Oxidation of PMAS emeraldine salt with aqueous 0.10 M ammonium persulfate proceeded in an analogous fashion to that observed with unsubstituted polyaniline, generating a pale purple species with λmax at 330 and 540 nm, consistent with the fully oxidized pernigraniline base form of PMAS. Subsequent protonation with dilute acid yielded the blue PMAS pernigraniline salt (λmax 670 nm). In contrast to the behavior of previously studied polyanilines, the hydrazine reduction of PMAS emeraldine salt produced an equilibrium mixture of two leucoemeraldine base forms with λmax at 335 and 408 nm, respectively. These PMAS leucoemeraldine base species, believed to be conformers with differing degrees of planarity along their polymer chains, exhibit remarkable thermochromism, solvatochromism, and ionochromism that is unprecedented in polyaniline chemistry