Kinetics of dissociation of trivalent actinide chelates of trimethylenediamine-N,N,N',N'-tetraacetic acid [TMDTA]

Abstract. This study examined and compared the fixation and fixation kinetics of copper (Cu) in chelated (ethylene diamine tetraacetic acid, EDTA) and non-chelated mixed systems of micronutrients in the semiarid soils of the Southern High Plains, USA, using findings from Cu extraction studies and kinetic models. Approximately, 22 % more Cu was fixed in the non-chelated system compared to the chelated within the first 14 days with only 7 % difference between the two systems by day 90. Findings suggest a decrease in the effectiveness of chelated micronutrients over time, highlighting the significance of timing even when chelated micronutrients are used. The strengths of the relationship of change in available Cu with respect to other micronutrients (iron (Fe), manganese (Mn), and zinc (Zn)) were higher in the non-chelated system (R2: 0.68–0.94), compared to the chelated (R2: 0.42–0.81), with slopes of 0.40 (Cu–Fe), 0.31 (Cu–Mn), and 1.04 (Cu–Zn) in the non-chelated system and 0.26 (Cu–Fe), 0.22 (Cu–Mn), and 0.90 (Cu–Zn) in the chelated system. Reduction in the amount of available Cu was best described by the power function model (R2 =  0.91, SE  =  0.081) in the non-chelated system and second-order model (R2 =  0.95, SE  =  0.010) in the chelated system. The applications generated from this study could be used as tools for improved micronutrient management and also provide baseline data for future work in other semiarid/arid alkaline soils of the world. Findings are also more applicable to field settings, an improvement over related previous studies.

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Modulation of Na+-Ca2+ exchange in sarcolemmal vesicles by intravesicular Ca2+

AJP Cell Physiology ◽

10.1152/ajpcell.1987.252.1.c17 ◽

1987 ◽

Vol 252 (1) ◽

pp. C17-C23 ◽

Cited By ~ 31

Author(s):

J. P. Reeves ◽

P. Poronnik

Keyword(s):

Initial Rate ◽

Tetraacetic Acid ◽

Exchange System ◽

Threefold Increase ◽

Kinetics Of ◽

Sarcolemmal Vesicles ◽

Exchange Activity

When cardiac sarcolemmal vesicles were incubated at 37 degrees C in 160 mM NaCl containing 0.5 mM CaCl2 and subsequently assayed for Na-Ca exchange activity, they exhibited a threefold increase in the initial rate of 45Ca2+ uptake (at 20 microM 45Ca2+) compared with vesicles incubated without added CaCl2. Removal of endogenous Ca2+ by incubation of the vesicles with 0.1 mM ethylene-bis(beta-aminoethylether)N,N'-tetraacetic acid (EGTA) resulted in a 35% inhibition in exchange activity. The pretreatment with CaCl2 produced an acceleration of Na-Ca exchange activity rather than an increase in Ca2+ uptake due to Ca-Ca exchange. Pretreatment of the vesicles with CaCl2 lowered the apparent Km of the exchange system for Ca2+. The effects of the Ca treatment were reversed by subsequently incubating the vesicles with EGTA. In contrast to the effects of intravesicular Ca2+ on Nai-dependent Ca2+ uptake, external Ca2+ had no effect on Nao-dependent Ca2+ efflux. The results suggest that an understanding of the kinetics of the Na-Ca exchange system may be hampered by the autoacceleration of exchange activity that occurs during initial rate measurements as Ca2+ accumulates within the vesicles. This phenomenon may contribute to the variability that exists among different vesicle preparations in their apparent Km values for Ca2+.

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