A biophysical approach to phospholipase A2 activity and inhibition by anti-inflammatory drugs.

The present study describes the interaction of two nonsteroidal anti-inflammatory drugs (ibuprofen and piroxicam) with PLA(2) from Naja mossambica mossambica and seeks to deepen the knowledge about the influence of the biophysical properties of biomembranes, and the inhibitory effect of the drugs on the enzymatic activity. Fluorescent techniques with and without the use of probes, surface pressure/molecular area isotherms, surface pressure/time and molecular area/time measurements combined with circular dichroism spectroscopy and direct techniques of visualization of lipid membranes (Brewster angle microscopy), revealed that both drugs inhibit PLA(2). Additionally, the structure and characteristics of the lipid bilayer, as well as, the direct interaction of drugs with the enzyme seem to play an important role on the hydrolytic activity of PLA(2) towards membrane model systems. These results open a way of finding new and better strategies that can contribute to the development of suitable agents for relieving inflammatory conditions.

Electrochemical oxidation of bentazon at a glassy carbon electrode Application to the determination of a commercial herbicide.

The electrochemical methods cyclic, differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of the herbicide bentazon in a commercial product, containing bentazon as the active ingredient, used to treat rice and corn crops. The oxidation mechanism is complex, consisting of an electrochemical step followed by chemical dimerization reaction of the products, which causes severe adsorption problems and consequent poisoning of the electrode surface. The effect of adding Triton surfactant is to enable determinations with good reproducibility to be carried out; the analytical conditions were studied and optimized. The limit of detection obtained was 10(-5) M.

Development of a tubular periodate electrode for flow-injection determination of glycerol.

Periodate electrodes without inner reference solution based on tetraoctylammonium periodate plus solvent mediator (dibutyl phthalate or 2-nitrophenyl octylether) were constructed. Linear dynamic range, practical detection limit, slope, stability, selectivity coefficients, pH dependence, response time and lifetime were evaluated. A tubular version was further developed and coupled to a flow-injection system for glycerol determination in samples relevant to the industrial production of soaps, detergents and similar. The method involves glycerol oxidation by periodate with potentiometric evaluation of its consumption. The influence of oxidizing agent concentration (10(-5)-10(-2)M NalO(4)), ionic strength (0.0-1.0M Na(2)SO(4)) and mean resident time were investigated and the feasibility of using a single-fine manifold was discussed. The proposed system handles about 40 samples/hr, is very stable and suitable to industrial control. Results within the 1000 and 5000 mg/l range glycerol are precise (r.s.d. <0.005) and in fair agreement with conventional procedures. Baseline drift or noise is not observed and a thermostat water bath is not required. A noteworthy feature is the almost linear relationship between glycerol concentration and recorded peak height which is a consequence of combined effects of reaction kinetics and electrode Nernstian response.