Kinetic study of ligand exchange reaction between 99mTc-glucoheptonate and N-benzyl- N-methyl-piperazinyl-bis-(aminoethanethiol) (BPA-BAT)

Abstract

In order to explore the exchange reaction between the 99mTc-GH (glucoheptonate) and N 2S 2 (BAT) ligands, as a common method for the preparation of 99mTc complexes, detailed kinetic studies were evaluated. This paper presents our preliminary results on kinetic studies of the exchange reaction at different ligand concentrations, as well as the determination of the overall formation rate constants and the fractional rate constants for each stereoisomer. The ligand exchange reaction between 99mTc-GH and a stronger N 2S 2 ligand, BPA-BAT—( N′-benzyl- N-methyl-piperazinyl derivative of bis-(aminoethanethiol), racemic mixture) is a second order reaction. The average rate constant (formation constant, k) of this ligand exchange reaction was determined: k = 3.71 × 10 3 M −1 min −1. Based on the ratio of 99mTc syn- vs the anti-isomer at equilibrium (1.229 ± 0.026), the same rate constant for the formation of individual isomers was calculated: k syn = 2.045 × 10 3 M −1 min −1; k anti = 1.664 × 10 3 M −1 min −1.