Kinetic and high-pressure mechanistic investigation of the aqua substitution in the trans-aquaoxotetracyano complexes of re(v) and tc(v): some implications for nuclear medicine.

J Mattheus Botha,Andreas Roodt

doi:10.1155/2008/745989

Abstract

A kinetic study of the aqua substitution in the [TcO(OH2)(CN)4]− complex by different thiourea ligands (TU = thiourea, NMTU = N-methyl thiourea, NNDMTU = N, N′-dimethylthiourea) yielded second-order formation rate constants (25°C) as follows [NNDMTU, NMTU, TU, respectively]: kf = 11.5 ± 0.1, 11.38 ± 0.04, and 7.4 ± 0.1 M−1s−1, with activation parameters: Δ H#kf : 55 ± 2, 42 ± 3, 35 ± 5 kJ mol−1; ΔS#kf : − 40 ± 8, − 84 ± 11, − 110 ± 17 J K−1mol−1. A subsequent high-pressure investigation of the aqua substitution in the [ReO(OH2)(CN)4]− and [TcO(OH2)(CN)4]− complexes by selected entering ligands yielded ΔV#kf values as follows: Re(V): −1.7 ± 0.3(NCS−), −22.1 ± 0.9 (TU) and for Tc(V): −3.5 ± 0.3(NCS−), −14 ± 1 (NNDMTU), and −6.0 ± 0.5 (TU) cm3mol −1, respectively. These results point to an interchange associative mechanism for the negative NCS− as entering group but even a pure associative mechanism for the neutral thiourea ligands.

Highlights

Technetium-99m is widely used in over 90% of all current diagnostic nuclear medicinal applications [1,2,3,4,5] due to its favourable nuclear properties (t1/2 = 6.02 hours, y = 140 keV 100%) and availability from a generator
The development of technetium myocardial imaging agents commenced with work by Deutsch [9,10,11,12], who investigated the [99mTcCl2(dmpe)2]+ [dmpe = bis(1,2-dimethylphosphino)ethane] and [99mTcX2(diars)2]+ complexes (diars = o-phenylenebis(dimethylarsine), X = Cl, Br) [12]
Studies on animal models indicated that the reduction of TcIII is biologically accessible for the cationic [99mTcIII− Cl2(dmpe)2]+ complex, yielding neutral [99mTcIICl2(dmpe)2]

Summary

Introduction

Recommended by Jannie Swarts A kinetic study of the aqua substitution in the [TcO(OH2)(CN)4]− complex by different thiourea ligands (TU = thiourea, NMTU = N-methyl thiourea, NNDMTU = N,N -dimethylthiourea) yielded second-order formation rate constants (25◦C) as follows [NNDMTU, NMTU, TU, respectively]: k f = 11.5 ± 0.1, 11.38 ± 0.04, and 7.4 ± 0.1 M−1s−1, with activation parameters: ΔHk#f : 55 ± 2, 42 ± 3, 35 ± 5 kJ mol−1; ΔS#kf : −40 ± 8, −84 ± 11, −110 ± 17 J K−1mol−1. A subsequent high-pressure investigation of the aqua substitution in the [ReO(OH2)(CN)4]− and [TcO(OH2)(CN4)]− complexes by selected entering ligands yielded ΔVk#f values as follows: Re(V): −1.7 ± 0.3(NCS−), −22.1 ± 0.9 (TU) and for Tc(V): −3.5 ± 0.3(NCS−), −14 ± 1 (NNDMTU), and−6.0 ± 0.5 (TU) cm3mol−1, respectively.

Results

Conclusion