Kinetics and mechanism of imazosulfuron hydrolysis.

Knowledge of the kinetics and pathways of hydrolytic degradation is crucial to the prediction of the fate and transport mechanism of chemicals. This work first describes the kinetics of the chemical hydrolysis of imazosulfuron, a new sulfonylurea herbicide, and evaluates the results to propose a degradation pathway. The hydrolysis of imazosulfuron has been studied in aqueous buffers both within the pH range 1.9-12.3 at ambient temperature (thermostated at 25 +/- 2 degrees C) and at pH 3.6 within the temperature range of 15-55 degrees C. The hydrolysis rate of imazosulfuron was characterized by a first-order kinetics, pH- and temperature-dependent, and accelerated by acidic conditions and higher temperatures. The calculated half-lives at pH 4.5 and 5.9 were 36.5 and 578 days, respectively. At pH 6.6, 7.4, 9.2, and 12.3 no significant change in imazosulfuron concentration was observed after 150 days. Half-lives were much lower at pH <4 (= imazosulfuron pK(a)), at which they ranged from 3.3 to 6.3 days. Moreover, a change in temperature from 15 to 25 degrees C in acidic conditions (pH 3.6) decreased the half-life of imazosulfuron by a factor of approximately 4.0; in any case, a 3-5-fold increase in the rate of hydrolysis was found for each 10 degrees C increase in temperature. In acidic conditions the only hydrolysis products were the two molecules resulting from the cleavage of the sulfonylurea bridge.

Degradation of imazosulfuron in soil.

Imazosulfuron, 1-(2-chloroimidazo[1,2-alpha]pyridin-3-ylsulfonyl)-3- (4,6-dimethoxypyrimidin-2-yl)urea, is a new post-emergence sulfonylurea herbicide applied once per growing season, highly active at low application levels, used to control most annual and perennial broad-leaf weeds and sedges in paddy rice (75-95 g AI ha-1) and turf (500-1000 g AI ha-1), and characterised by low mammalian toxicity. The degradation of imazosulfuron in a sandy loam soil (10-15 cm depth) has been investigated under aerobic and anaerobic laboratory conditions to evaluate its likely environmental fate. Test soils were treated with imazosulfuron in acetonitrile to give a final concentration of 0.2 mg kg-1 (100 g ha-1). The treated soils were extracted with methylene chloride + acetonitrile + 1 M ammonium hydroxide (4 + 15 + 1 by volume) and analysed by HPLC. Recoveries from spiked soils ranged from 80% to 95% (RSD 0.5-2.5%; n = 3) for imazosulfuron and its metabolites 2-chloroimidazo[1,2-alpha]pyridin-3-sulfonamide (IPSN), 1-(2-chloroimidazo[1,2-alpha]pyridin-3-ylsulfonyl)-3-(4-hydroxy-6- methoxypyrimidin-2-yl)urea (HMS) and 2-amino-4,6-dimethoxypyrimidine (ADPM). The limits of quantitation ranged from 0.001 mg kg-1 to 0.005 mg kg-1. Chemical cleavage of the sulfonylurea bond to give ADPM and IPSN was the main degradation pathway in aerobic conditions, whereas a remarkable production of HMS under anaerobic conditions suggested that degradation was due to micro-organisms which had the ability to demethylate imazosulfuron. In aerobic and anaerobic conditions, imazosulfuron disappeared from the soil with a half-life of approximately 70 (90% CL 62-75; r2 = 0.98) and 4 (90% CL 3.2-4.2; r2 = 0.97) days, respectively.

Adsorption and desorption of imazosulfuron by soil.

Understanding and quantifying the adsorption and desorption of herbicides by soil is important for predicting their fate and transport in the environment. Here we report a study concerning the adsorption and desorption, by four different soils, of imazosulfuron, 1-(2-chloroimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4, 6-dimethoxypyrimidin-2-yl)urea, a new sulfonylurea herbicide. Both phenomena are well-described by the Freundlich equation, which shows this herbicide to be little adsorbed by each of the four soils investigated. The Freundlich adsorption constants, K(f-ads), ranged from 1.46 to 3.02. Distribution coefficients between soil and water, Kd, measured on soils of different organic matter contents and pH values showed an important effect of these two parameters on imazosulfuron retention. The Freundlich desorption data indicated that a significant amount of the imazosulfuron sorbed is not easily desorbed. The desorption process showed an evident hysteresis phenomenon, which may contribute to the persistence of imazosulfuron in soil.

Calcium bioavailability and parathyroid hormone acute changes after oral intake of dairy and nondairy products in healthy volunteers.

This study was designed to compare calcium bioavailability and serum parathyroid hormone acute changes after oral intake of 500 mg of elemental calcium from liquid milk, yogurt, calcium-citrate-enriched powdered milk or a calcium carbonate pill; or after intake of soybean imitation-milk. After a 12-h fast, blood samples were drawn both at baseline and 1, 2, 3 and 4 h after an oral intake of the above-mentioned products, which were ingested together with a light neutral breakfast. The administration order of the study products was randomly assigned to each of 19 healthy young volunteers (11 females, 8 males). The baseline serum concentrations of ionized calcium, phosphorus and intact parathyroid hormone (iPTH) were normal. Calcium-citrate-enriched powdered milk induced a significant increase in serum ionized calcium (p<0.001) and a significant and continuous decrease in serum iPTH concentration (p<0. 001). Yogurt and the calcium carbonate pill induced a similar but less significant effect, increasing serum ionized calcium (p<0.05) and decreasing serum iPTH (p<0.01). Liquid milk only induced a significant change in serum ionized calcium and iPTH concentration during the first 2 h; this effect was lost during the following 2 h. In conclusion, our study suggests the possibility that the addition of calcium citrate to powered milk may improve calcium bioavailability and enhance the inhibitory effect on serum iPTH in the assayed conditions.

High performance liquid chromatographic analysis of quinolone antibacterial agents.

Eleven quinolone antibacterials have been analyzed by HPLC. The effects of different pH values and organic modifiers on chromatographic behaviour are discussed. Moreover the influence on separation mechanism of different counter-ions at various concentrations in the eluent has been investigated. Two different chromatographic methods have been selected, that allow the simultaneous analysis of quinolones containing or not a piperazinyl moiety, respectively.

Analytical profile of zolpidem.

The paper present an analytical profile of Zolpidem. The applications of chromatographic methods (HPLC and HPTLC) and non-aqueous titrimetry in the analysis of this drug are described. Partition coefficients at pH 2.0 and 7.4 and absorptivity values have been determined. Reversed phase HPLC and HPTLC systems have been successfully performed utilizing methanol/water mixtures as eluent and octadecylsilane as stationary phase. Acidimetric and alkalimetric methods in non aqueous titrimetry have been applied for quantitative analysis. The suggested procedures are proposed as an effective tool for quality control on pure compound and pharmaceutical formulations.