Synthesis and Characterization of Manganese Dithiocarbamate Complexes: New Evidence of Dioxygen Activation

Abstract

(1) Background: Metal dithiocarbamate compounds have long been the subject of research due to their ease of formation, excellent properties and potential applications. However, manganese complexes with dithiocarbamates, to our knowledge, have never been used for medical imaging applications. With the aim of developing a new class of mononuclear manganese(II)-based agents for molecular imaging applications, we performed a specific investigation into the synthesis of mononuclear bis-substituted Mn(II) complexes with dithiocarbamate ligands. (2) Methods: Synthesis in either open or inert atmosphere at different Mn(II) to diethyldithiocarbamate molar ratios were performed and the products characterized by IR, EA, ESI-MS and XRD analysis. (3) Results: We found that only under oxygen-free atmospheric conditions the Mn(II) complex MnL2, where L = diethyldithiocarbamate ligand, is obtained, which was further observed to react with dioxygen in the solid state to form the intermediate superoxo Mn(III) complex [MnL2(η2-O2)]. The existence of the superoxo complex was revealed by mass spectroscopy, and this species was interpreted as an intermediate step in the reaction that led the bis-substituted Mn(II) complex, MnL2, to transform into the tris-substituted Mn(III) complex, MnL3. A similar result was found with the ligand L’ (= bis(N-ethoxyethyl)dithiocarbamate). (4) Conclusions: We found that in open atmosphere and in aqueous solution, only manganese(III) diethyldithiocarbamate complexes can be prepared. We report here a new example of a small-molecule Mn(II) complex that efficiently activates dioxygen in the solid state through the formation of an intermediate superoxide adduct.

Synthetic and Nanotechnological Approaches for a Diagnostic Use of Manganese

“…As for MDE2, a μ eff as low as ~3.4 BM was estimated. This is in agreement with the previous observations that Mn(II) compounds are oxidized over time to Mn(III) if not stored under controlled conditions in the absence of oxygen [ 11 ].…”

“…All complexes were characterized with elemental analysis, ESI(+)-MS, UV/Vis, and infrared (IR) analysis as previously reported [ 11 ]. In Figure 1 , the chemical structures of the selected Mn compounds are reported.…”

“…All other materials and solvents of high-purity grade were from Sigma-Aldrich (St Louis, MO, USA). The heterocyclic phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) and the Mn complexes MP, MDE2, MDE3, and MDB were prepared according to the procedure reported in the literature [ 11 , 17 ].…”

“…In the framework of the METRICS project (an acronym for multimodal PET/MRI imaging with cyclotron-produced 51/52 Mn isotopes), which aims to develop the technology needed to obtain a cyclotron-driven production of 52/51 Mn PET radionuclides and to achieve PET/MRI hybrid imaging by taking advantage of both paramagnetic and radio-active properties shown by manganese isotopes, we started an investigation into the class of dithiocarbamate ligands with the purpose of developing a new class of mononuclear manganese(II)-based agents for medical applications. These preliminary studies showed that Mn(II)(S 2 CNR 2 ) 2 complexes (R = Et or CH 2 CH 2 OEt) are poorly soluble in physiological conditions, and, if weathered or not properly stored in a controlled atmosphere, they convert into the tris-substituted complexes Mn(II)(S 2 CNR 2 ) 3 over time [ 11 ].…”

Chelation of Zn Cations as a Method for Their Replacement by Mn, Fe, Co in ZnSe Nanocrystals

“…Preparation of Precursor for Cation Exchange: Manganese (II) DDTC is known to oxidize immediately upon contact with air. [33] Thus, we chose to not isolate the compound and prepare the oleylamine solution according to ref. [20] First, oleylamine (4 mL, techn.…”