Prediction of the structural and spectral properties for L,L-ethylenedicysteine diethylester (EC) and its complex with Technetium-99m radionuclide

The technetium-99m complex of the L,L-ethylenedicysteine diethylester (EC), of the brain imaging agent, was reported as a good choice for replacement of the renal nuclear medicines like OIH radiopharmaceutical. This present research work studies the structural, electronic and spectral properties of the EC compound and its complex with technetium-99m radionuclide from theoretical insight. All computations were done by Gaussian 03 package at B3LYP/6-31+G(d,p) level of theory. The frontier molecular orbital (FMO) computations show the stability of 99mTc-EC structure is lower than the EC molecule. In contrast, the highest reactivity is related to the 99mTc-EC complex. From the nuclear magnetic resonance (NMR) calculations, the comparison between chemical shifts of carbon atoms of 99mTc-EC to EC molecule shows the carbon atoms of technetium-99m-EC complex are more shielded. Also, the natural bond orbital (NBO) analysis shows more d orbitals of technetium atom and more p orbitals of sulfur, nitrogen and oxygen atoms are used for Tc-S, Tc-N and Tc-O molecular orbital hybrids.