Chemical binding

About: Chemical binding is a research topic. Over the lifetime, 1822 publications have been published within this topic receiving 52516 citations.

Polymerization kinetics of polyurethane and vinyl ester resin interpenetrating polymer networks by using fourier transform infrared spectroscopy

Abstract: Fourier transform infrared spectroscopy (FTIR) was applied to the study of polymerization kinetics of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER), in which the pendent hydroxyl groups were capped with acetyl groups to minimize the possibility of chemical binding between the two networks. It was found that during the course of synthesis the two pairs of reactants interfere with each other in the SIN systems, giving rise to depressed reaction rates, although they follow different polymerization mechanisms. Increasing the reaction temperature could be more effective than increasing the free-radical initiator level with regard to the final conversions of both components. The reaction sequence could be varied through the amount of the step-growth polymerization catalyst and free-radical initiator as well as the reaction temperature adjustment. Using VER containing pendent hydroxyl groups could strongly affect the reaction kinetics of such SINs and lead to hybrid structures. The quick formation of one network would always depress the conversion of the other network in all SINs studied. © 1996 John Wiley & Sons, Inc.

Uptake of macro nutrients, barium, and strontium by vegetation from mineral soils on carbonatite and pyroxenite bedrock at the Lillebukt Alkaline Complex on Stjernøy, Northern Norway

Abstract: Carbonatite originating from the Lillebukt Alkaline Complex at Stjernoy in Northern Norway possesses favorable lime and potassium (K) fertilizer characteristics. However, enrichments of barium (Ba) and strontium (Sr) in carbonatite may cause an undesired uptake by plants when applied to agroecosystems. A field survey was carried out to compare concentrations of Ba, Sr, and macronutrients in indigenous plants growing in mineral soil developed on a bedrock of apatite–biotite–carbonatite (high in Ba and Sr) and of apatite–hornblende–pyroxenite (low in Ba and Sr) at Stjernoy. Samples of soil and vegetation were collected from three sites, two on carbonatite bedrock and one on pyroxenite bedrock. Ammonium lactate (AL)-extracted soil samples and nitric acid microwave-digested samples of soil, grasses, dwarf shrubs, and herbs were analyzed for element concentration using ICP-MS and ICP-OES. Concentrations of magnesium (Mg) and calcium (Ca) in both soil (AL) and plants were equal to or higher compared to values commonly reported. A high transfer of phosphorus (P) from soil to plants indicates that the apatite-P is available to plants, particularly in pyroxenite soil. The non-exchangeable K reservoir in the soil made a significant contribution to the elevated K transfer from soil to plant. Total concentrations of Ba and Sr in surface soil exhibited a high spatial variation ranging from 490 to 5,300 mg Ba kg−1 and from 320 to 1,300 mg Sr kg−1. The transfer of AL-extractable elements from soil to plants increased in the order Ba < Sr < Ca < Mg < K, hence reflecting the chemical binding strength of these elements. Concentrations of Ba and Sr were low in grasses (≈ 20 mg kg−1), intermediate in dwarf shrubs and highest in herbs. Plant species and their affinity for Ca seemed more important in explaining the uptake of Ba and Sr than the soil concentration of these elements. The leguminous plant species Vicia cracca acted as an accumulator of both Ba (1.800 mg kg−1) and Sr (2.300 mg kg−1).

Concentration dependence of in vitro biotransformation rates of hydrophobic organic sunscreen agents in rainbow trout S9 fractions: Implications for bioaccumulation assessment.

Abstract: In vitro biotransformation studies were performed to support the bioaccumulation assessment of 3 hydrophobic organic ultraviolet filters (UVFs), 4-methylbenzylidene camphor (4-MBC), 2-ethylhexyl-4-methoxycinnamate (EHMC), and octocrylene. In vitro depletion rate constants (kdep ) were determined for each UVF using rainbow trout liver S9 fractions. Incubations performed with and without added cofactors showed complete (4-MBC) or partial (EHMC and octocrylene) dependence of kdep on addition of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH), suggesting that hydrolysis of EHMC and octocrylene by NADPH-independent enzymes (e.g., carboxylesterases) is an important metabolic route. The concentration dependence of kdep was then evaluated to estimate Michaelis-Menten parameters (KM and Vmax ) for each UVF. Measured kdep values were then extrapolated to apparent whole-body biotransformation rate constants using an in vitro-in vivo extrapolation (IVIVE) model. Bioconcentration factors (BCFs) calculated from kdep values measured at concentrations well below KM were closer to empirical BCFs than those calculated from kdep measured at higher test concentrations. Modeled BCFs were sensitive to in vitro binding assumptions employed in the IVIVE model, highlighting the need for further characterization of chemical binding effects on hepatic clearance. The results suggest that the tested UVFs are unlikely to accumulate to levels exceeding the European Union Registration, Evaluation, Authorisation, and Restriction regulation criterion for bioaccumulative substances (BCF > 2000 L kg-1 ). However, consideration of appropriate in vitro test concentrations and binding correction factors are important when IVIVE methods are used to refine modeled BCFs. Environ Toxicol Chem 2019;38:548-560. © 2018 SETAC.