Abstract
The purpose of this work was to synthesize and characterize the thiatetraaza macrocycle 1-thia-4,7,10,13-tetraazacyclopentadecane ([15]aneN4S). Its acid-base behaviour was studied by potentiometry at 25 °C and ionic strength 0.10 M in KNO3. The protonation sequence of this ligand was investigated by 1H-NMR titration that also allowed the determination of protonation constants in D2O. Binding studies of [15]aneN4S with Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ metal ions were further performed under the same experimental conditions. The results demonstrated that this compound has a higher selectivity and thermodynamic stability for Hg2+ and Cu2+, followed by Ni2+. The UV-visible-near IR spectroscopies and magnetic moment data for the Co(II) and Ni(II) complexes indicated a tetragonal distorted coordination geometry for both metal centres. The value of magnetic moment and the X-band EPR spectra of the Cu(II) complex are consistent with a distorted square pyramidal geometry.
Highlights
Exposure to toxic metals is associated with the potential development of numerous health effects, including different types of cancer [1,2]
The first step involved the synthesis of the precursor diamide, 1-thia-4,7,10,13-tetraazacyclopentadecane-3,14-dione by reaction of the dimethyl ester of thiodiglycolic acid, prepared according to a reported procedure [22], with triethylenetetramine in dry methanol at 40 °C, under N2 for nine days
Some modifications were introduced in the present work, such as controlled reaction temperature, dried solvent in a larger volume and nitrogen atmosphere, which led to the highly improved yield of 74% on dioxo-[15]aneN4S synthesis
Summary
Exposure to toxic metals is associated with the potential development of numerous health effects, including different types of cancer [1,2]. Despite the available chelators, the search for new effective chelating compounds is still needed, since the ones currently used in clinic present a number of toxic side effects, low metal specificity and controversial efficacy [5,9,10]. We have explored the possible use of macrocyclic compounds for medical applications, namely in chelation therapy [7,11]. These compounds may exhibit important properties such as less toxicity, high kinetic and thermodynamic stabilities [12], rendering them very promising agents in this context. Macrocycles are advantageous in terms of selectivity, since they have more rigid structures and can inflict specific coordination geometry to the metal ion, while open chain chelators can adapt more to the geometric requirements of the metal centre [7,13]
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