REV.CHIM.(Bucharest)♦68♦No. 10 ♦2017 http://www.revistadechimie.ro 2265 Spectral Study of Some Lanthanides Complexes with Quaternary Pyridinium Ligands ANDREEA CARAC 1 , , RICA BOSCENCU 1 *, GETA CARAC 2 , SIMONA GABRIELA BUNGAU 3 1 Carol Davila University of Medicine and Pharmacy, Faculty of Pharmacy, 6 Traian Vuia Str., 020956 Bucharest, Romania 2 Dunarea de Jos University, Faculty of Sciences and Environment, Department of Chemistry, Physics and Environment, 47 Domneasca Str., 800008, Galati, Romania 3 University of Oradea, Faculty of Medicine and Pharmacy, 29 Nicolae Jiga Str., 410028, Oradea, Romania Some lanthanides complexes with two N-heterocyclic ligands derived from 4,4'-bipyridinium and 1,2-bis- (4-pyridinium) ethane (noted BP and BPE) were studied in presence of triethylamine and methanol in view of their application as cytotoxic agents. Absorption spectra have been recorded by UV-Vis spectroscopy during the complexation process in solution. The ligands demonstrate preferential arrangements in lanthanide’s electronic structure which is identified much clearly in ultraviolet range. La(III)-BP solution indicates absorption at λ max = 206 nm while La(III)-BPE at λ max of 208 nm. The solution from the Nd(III)-BPE complex synthesis shows the highest absorbance at λ max = 220 nm, compared with Nd(III)-BP at λ max = 212 nm. The bathochromic shifts of the spectral bands can be assigned to the physical interaction of Ln(III) ions with ligands. No major changes were observed in the absorption, hypsochromic and hyperchromic effects when varying the ligand. The complexes spectral properties were performed by dissolving them in methanol in three phases until a complete dissolution of the precipitates was achieved. Keywords: pyridinium ligands, lanthanide complexes, UV-Vis, conductivity The lanthanide complexes have received a progressive attention in the last decades, mainly because of their biomedical applications [1, 2]. Lanthanide (III) ions can form complexes with a wide variety of ligands and the new compounds synthesis is influenced by the ionic radii of the metallic ions. Being electropositive, reactive metals and hard Lewis acids due to their high charge density lanthanides ions prefer to bind to oxygen, nitrogen and sulfur [3]. The exquisite lanthanide properties are based on their electrons from the 4f orbital. Due to their shielding in the 5s 2 5p 6 subshells the electronic transition 4f-4f is ligand independent and is Laporte forbidden [4]. Their luminescence is in millisecond range in comparison with the organic dyes which is in the nanosecond range [5]. Typically, lanthanides form trivalent ions with an electronic structure consisting of a Xenon core and 4f valence electrons [Xe]4f n , except cerium, terbium, praseodymium with oxidation number + 4 and samarium, europium and terbium with oxidation number + 2. The 4f electrons are responsible for the easy separation from the rest of the elements but difficult in the series because their energy level is close to the 5d layer. An important aspect of their electronic configuration is the decrease of the ionic radii in the lanthanide series which is referred as the lanthanide contraction. This phenomenon is the result of a high nuclear charge [6]. It was noticed that lanthanides can be mediators in a wide range of degenerative disease based on their antioxidant properties and their role as ROS (reactive oxygen species) scavenger. It is also interesting that they lose this property when they bond to the cellular membrane and they can’t create free radicals [1]. New experimental methods regarding lanthanides ions role in the biochemical process have been developed. Based on the physical and spectral properties, lanthanides have numerous applications, such as fluorescent probes in biological assays [7, 8]. The physiological effects of lanthanides ions observed at the cellular level are mainly explained by the similarity * email: rboscencu@yahoo.com of their ionic radii to the calcium ionic radii [1, 2]. In rat organs, cerium and praseodymium ions have shown hepatotoxic effects such as jaundice, steatosis and increased aminotransferases. The toxic effects of gadolinium include mineral deposits in capillary, liver and spleen necrosis, gastric mucosa demineralization and thrombocytopenia. Cerium is responsible for magnesium deficit, which may be a cause of cardiac fibrosis that could lead to cardiomyopathy. Other lanthanides ions have a protective liver effect [9]. However, the toxic effect of lanthanides ions may be a combination of hepatotoxic action of the active metabolite generated by the microsomal metabolism and the effects of lanthanum ions, which is the selective blocking of the cells by the calcium channels. A study of the thyroid cells has determined that lanthanide ions are calcium antagonists [1]. Ions that have short ionic radii are the most potent inhibitors and the blocking potential varies inversely as the ionic radii. Lanthanides ions inhibit the Ca 2+ from the sarcoplasmic reticulum of the skeletal muscle fibers [10-12]. Lanthanide complexes exhibit special magnetic, optical and catalytic properties [13-18]. To create a new generation of metal complexes and understand their biological behavior we must evaluate the complexes and their ligands for their physicochemical and optical properties. Studies were initiated for obtaining lanthanides complexes using quaternary pyridinium salts in methanol as solvent. We chose quaternary pyridinium salts derived from 4,4'-bipyridinium and 1,2-bis-(4-pyridinium) ethane because their structure recommends them as important organic ligands and so far, no data has been published concerning their complexation with lanthanum ions like La (III) and Nd(III). Several key factors which influence the stability of lanthanide (III) complexes with organic ligands were highlighted through successive extraction in methanol.