Ethylenediaminetetraacetic Acid Molecules Research Articles

Effect of surface tension of the matrix on fast-atom bombardment mass spectral determination of ethylenediaminetetraacetic acid

The importance of the influence of surface activity on the mass spectra obtained from particle bombardment of liquid surfaces has long been known. In this work the fast-atom bombardment (FAB) mass spectral determination of ethylenediaminetetraacetic acid (EDTA) in several liquid matrices is investigated. Differences in the relative molar response observed for glycerol, thioglycerol and triethanolamine are discussed in terms of the surface tension of these liquids. The surface tensions of the pure liquid matrices and the EDTA solutions have been determined at 25 and 70 °C using the axisymmetric drop-shape analysis profile (ADSAP) technique. EDTA solutions have a higher surface tension than the corresponding pure liquid matrices, indicating that EDTA molecules are concentrated mainly in the bulk. Furthermore, the order observed for the intensity of the ion signal obtained with the three matrices, glycerol > thioglycerol > triethanolamine, follows the order of the surface tension which is maximum for glycerol and minimum for triethanolamine. We conclude that the surface concentration of EDTA is at a maximum in the liquid matrix with the highest surface tension, yielding an optimized mass spectrum.

Insulin aggregation in aqueous media and its effect on alpha-chymotrypsin-mediated proteolytic degradation.

Self-association of zinc-insulin monomers into dimers and hexamers may lead to enhanced protection of the peptide from proteolytic degradation. The present study has been undertaken to investigate the relationship, if any, between the rate of enzymatic degradation of insulin by a protease, alpha-chymotrypsin, and the extent of insulin aggregation in aqueous solutions. Insulin solutions (0.6 mg/ml) containing varying proportions of dimer and hexamer were obtained by adding ethylene diamine tetraacetic acid (EDTA) within a concentration range of 0.005 to 0.040 mM. As the EDTA concentration was increased above 0.040 mM, a complete dissociation of hexamers to dimers occurred and the rate of enzymatic degradation reached its maximum. The overall first-order rate constants appeared to be linearly related to the square of EDTA concentrations. The apparent first-order rate constants for dimer and hexamer degradation obtained from a linear plot of rate constant versus EDTA squared concentration were found to be 0.02800 +/- 0.00065 and 0.00798 +/- 0.00075 min-1, respectively. Two major insulin degradation products were also detected and the kinetics of product appearance agreed well with the disappearance kinetics of insulin. The results indicated that the degradation of insulin dimers by alpha-chymotrypsin is about 3.5 times faster than the degradation of the hexamer. The second-order dependency of degradation rate on EDTA concentration might be due to the fact that insulin hexamers contain two zinc ions which are sequestered by two EDTA molecules. Chelation of zinc ions by EDTA lead to hexamer deaggregation to dimers as was evidenced from a circular dichroism study.(ABSTRACT TRUNCATED AT 250 WORDS)