On-line rapid purification of [13N]N2 gas for visualization of nitrogen fixation and translocation in nodulated soybean.

Accurate analysis of N fixation in leguminous crops requires determination of N utilization within an intact plant; however, most approaches require tissue disassembly. We developed a simple and rapid technique to generate high-purity and high-yield [13N]N2 gas and obtained real-time images of N fixation in an intact soybean plant. The purification efficiency was ∼81.6% after decay correction. Our method provides accurate signals of N fixation and allows free changes to the tracer gas composition to suit different experimental designs.

Adsorption of humic acid from aqueous solution onto irradiation-crosslinked carboxymethylchitosan.

This paper presents the adsorption of humic acid from aqueous solution onto crosslinked chitosan derivative (carboxymethylchitosan), formed by additionless irradiation technique. The surface charge and swelling properties of crosslinked samples were investigated. The adsorption of humic acid onto crosslinked carboxymethylchitosan was carried out by the batch method at room temperature, and it was found to be strongly pH-dependent. Maximum amount of humic acid was adsorbed under acidic conditions at the optimum pH value of 3.5. Adsorption kinetic studies indicated the adsorption process was transport-limited at the same pH. The adsorption isotherm analysis data under various initial humic acid concentrations confirms that experimental data fitted well into the Langmuir equation. X-ray photoelectron spectroscopy (XPS) revealed that the amino groups of carboxymethylated chitosan were protonated, suggesting the formation of organic complex between the protonated amino groups and humic acid. From these preliminary evaluations, it was concluded that crosslinked carboxymethylated chitosan derivatives have a great potential in water treatment for the removal of humic acid and other polarized or electrically charged species.

Effect of Gamma Ray Irradiation on Friction Property of Poly(vinyl alcohol) Cast-Drying on Freeze-Thawed Hybrid Gel.

Poly(vinyl alcohol) (PVA) is a biocompatible polymer with low toxicity. It is possible to prepare physically cross-linked PVA gels having hydrogen bonds without using a cross-linking agent. The newly reported physically cross-linked PVA cast-drying (CD) on freeze-thawed (FT) hybrid gel has an excellent friction property, which is expected to be applied as a candidate material for artificial cartilage. Gamma ray sterilization for clinical applications usually causes additional chemical cross-linking and changes physical properties of gels. In this study, CD on FT hybrid gels were irradiated using gamma rays at a different dose rate and irradiance. The results showed the optimized irradiation conditions for gamma irradiated gels to retain excellent friction characteristics.

Radiation-induced enhancement of nitrite reducing activity of cytochrome c.

Commercial cytochrome c (Cyt c) was irradiated with Co-60 gamma-rays in the dose range of up to 3.0 kGy to investigate the enhancement of the nitrite reducing activity of Cyt c. The optimum irradiation dose to induce nitrite reducing activity for 30 muM Cyt c solution was 1.0 kGy under an O(2) atmosphere. The nitrite reducing activity of Cyt c irradiated at this dose was approximately 45-fold that of unirradiated Cyt c and ca. 1.2-fold that of nitrite reductase. The irradiation treatment resulted in unfolding of the peptide chain, exposure of the heme group, oxidation of methionine to methionine sulfoxide, dissociation of the sixth ligand (Met), and occurrence of autoxidation in Cyt c. Sepharose-immobilized irradiated Cyt c had a similar activity to that in solution. The resin retained the activity after five uses even after 1 year of storage. The irradiated Cyt c will be able to be used as a substitute for nitrite reductase.

Preparation and characterization of core-shell nanoparticles hardened by gamma-ray.

Core-shell nanoparticles have been prepared by irradiation of gamma-ray on block copolymer micelles consisting of hydrophilic polyacrylic acid and hydrophobic polyisoprene with each 40 monomer units. The structure was determined by means of dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The size distribution of the core-shell nanoparticles determined by DLS and AFM was very narrow. The average diameter of the particles decreased from 48 nm for the original micelles to 26 nm by the irradiation of 30 kGy. The core size determined by SAXS combined with DLS was roughly constant of 10 nm, irrespective of irradiation dose, whereas the shell thickness of the micelles was twice as large as the core size, and decreased with increasing irradiation dose.

Carcinogen adsorbent prepared from DNA complex by gamma-ray irradiation.

The effects of gamma-ray irradiation on aqueous solutions of chub mackerel chromatin, salmon milt DNA with CoCl(2), mixtures of DNA with Type A gelatin, bovine serum albumin (BSA), CM-chitosan, carboxymethyl cellulose (CMC) and Catinal (hydroxyethyl-cellulose, O-[2-hydroxy-3-(trimethyl ammonio)-propyl], chloride) and DNA in the presence of polyfunctional monomers with the aim to insolubilize DNA for preparing a novel carcinogen adsorbent have been studied. Among those, precipitates or inhomogeneous gel consisting of cross-linked DNA were prepared from the samples of aqueous DNA in the presence of CoCl(2) at low irradiation dose, around 10 Gy, and bulk homogeneous gels were successfully prepared from aqueous mixtures of DNA with gelatin, BSA, CMC and Catinal in a limited range of irradiation doses. Gel fraction and swelling ratio of the gels were measured. Adsorption of a carcinogen, acridine orange, was also examined for the gels. From the experimental results, the optimum conditions for preparing insolubilized homogeneous DNA gels were determined.

Biological effect of irradiated chitosan on plants in vitro.

For degradation of chitosan, chitosan with an 80% degree of deacetylation and a weight-average molecular mass (Mw) of approx. 48 kDa was irradiated with gamma-rays at doses up to 200 kGy in a 10% (w/v) solution. The Mw of chitosan was reduced from 48 to 9.1 kDa by irradiation. The characteristics of irradiated chitosan were analysed by using Fourier-transform IR spectroscopy and an elemental analyser. The amino group was found to be stable, whereas the C-O-C group decreased with increase in the dose. The product of chitosan irradiated at 100 kGy with an Mw of approx. 16 kDa showed the strongest growth promotion effect on plants in vitro. For shoot culture, supplementation with irradiated chitosan increased the fresh biomass of shoot clusters (7.2-17.0%) as well as the shoot multiplication rate (17.9-69.0%) for Chrysanthemum morifolium (florist's chrysanthemum), Limonium latifolium (limonium or sea-lavender), Eustoma grandiflorum (lisianthus, tulip gentian or Texas bluebell) and Fragaria ananassa (modern garden strawberry). The optimum concentrations of irradiated chitosan were found to be approx. 70-100 mg/l for chrysanthemum, 50-100 mg/l for lisianthus and 30-100 mg/l for limonium. For the plantlet culture, the optimum concentrations were found to be approx. 100 mg/l for chrysanthemum, 30 mg/l for lisianthus, 40 mg/l for limonium and 50 mg/l for strawberry. Supplementation with optimum concentrations of irradiated chitosan resulted in a significant increase in the fresh biomass (68.1% for chrysanthemum, 48.5% for lisianthus, 53.6% for limonium and 26.4% for strawberry), shoot height (19.4% for chrysanthemum, 16.5% for lisianthus, 33.9% for limonium and 25.9% for strawberry) and root length (40.6% for chrysanthemum, 66.9% for lisianthus, 23.4% for limonium and 22.6% for strawberry). In addition, treatment with irradiated chitosan enhanced the activity of chitosanase in treated plants and also improved the survival ratio and growth of the transferred plantlets acclimatized for 10-30 days under greenhouse conditions.

Reagent-free crosslinking of aqueous gelatin: manufacture and characteristics of gelatin gels irradiated with gamma-ray and electron beam.

In order to obtain a gelatin hydrogel crosslinked by a reagent-free method, gamma-ray and electron beam radiation was applied to porcine, bovine and fish gelatin gels and the products were characterized by measuring the gel fraction, the swelling ratio and the enzymatic degradability. On increasing the radiation dose, the gel fraction increased and both the swelling ratio and the enzymatic degradability decreased. The transition temperature from gel to sol of the hydrogel containing more than 5% mammal gelatins increased up to more than 90 degrees C when gamma-ray or electron beam were irradiated by more than 10 kGy. The results show that the degree of crosslinking of irradiated gelatin hydrogels increases with increasing irradiation dose and with decreasing concentration. It is suggested that the radiation crosslinking occurs around the physical crosslinking point or multiple helix structure of gelatin gel.

Biological effect of radiation-degraded alginate on flower plants in tissue culture.

Alginate with a weight-average molecular mass (Mw) of approx. 9.04 x 10(5) Da was irradiated at 10-200 kGy in 4% (w/v) aqueous solution. The degraded alginate product was used to study its effectiveness as a growth promoter for plants in tissue culture. Alginate irradiated at 75 kGy with an Mw of approx. 1.43 x 10(4) Da had the highest positive effect in the growth of flower plants, namely limonium, lisianthus and chrysanthemum. Treatment of plants with irradiated alginate at concentrations of 30-200 mg/l increased the shoot multiplication rate from 17.5 to 40.5% compared with control. In plantlet culture, 100 mg/l irradiated alginate supplementation enhanced shoot height (9.7-23.2%), root length (9.7-39.4%) and fresh biomass (8.1-19.4%) of chrysanthemum, lisianthus and limonium compared with that of the untreated control. The survival ratios of the transferred flower plantlets treated with irradiated alginate were almost the same as the control value under greenhouse conditions. However, better growth was attained for the treated plantlets.

Laser photolysis of carboxymethylated chitin derivatives in aqueous solution. Part 2. Reaction of OH* and SO4*- radicals with carboxymethylated chitin derivatives.

The reactions of OH* or SO4*- radicals with carboxymethyl chitin (CM-chitin) and its deacetylated product, carboxymethyl chitosan (CM-chitosan), were investigated in aqueous solutions using a laser photolysis technique. The rate constants of the reactions of OH* and SO4*- radicals with CM-chitosan are always higher than those for CM-chitin, indicating that the amino-group could increase the reactivity of carboxymethylated chitin derivatives. The rate of the reactions of CM-chitin and CM-chitosan with OH* radical was found to decrease at lower pH when polymers chains tend to the coiled conformation. In comparison, the rate constant of the reaction of SO4*- radicals with CM-chitin or CM-chitosan decreased with pH, indicating that CM-chitin or CM-chitosan has a higher reactivity with the SO4*- radical at low pH due to the protonation of the amino group.

Laser photolysis of carboxymethylated chitin derivatives in aqueous solution. Part 1. Formation of hydrated electron and a long-lived radical.

Laser photolysis experiments on carboxymethylated chitin derivatives, such as carboxymethyl chitin (CM-chitin) and carboxymethyl chitosan (CM-chitosan), in aqueous solution by a 248 nm excimer laser were carried out for the first time. The transient absorption spectra of photolyzed CM-chitin or CM-chitosan solutions revealed a strong band with the maximum at 720 nm, which was assigned to the hydrated electron (eaq-). In the presence of argon, the eaq- decays by reacting with CM-chitin or CM-chitosan, and the rate constants are (6.1 +/- 0.1) x 10(7) M(-1) s(-1) and (3.7 +/- 0.1) x 10(7) M(-1) s(-1), respectively. Long-lived radicals with relatively weak absorption intensity were detected in the near-UV region. The absorption band was not notably characteristic and showed only an increasing absorption toward shorter wavelengths. It is similar to the signal of *CM-chitin or *CM-chitosan macroradicals formed by the reaction of CM-chitin or CM-chitosan with an OH* radical. It was assigned to *CM-chitin- or *CM-chitosan- macroradicals formed by eaq- + CM-chitin or CM-chitosan reaction. CM-chitin aqueous solutions were further examined by pulse radiolysis in order to confirm the site of the long-lived radical.