Mn(II), Co(II), Zn(II), Fe(III) and U (VI) complexes of 2-acetylpyridine 4 N-(2-pyridyl) thiosemicarbazone (HAPT); structural, spectroscopic and biological studies Usama El-Ayaan a,b, * , Magdy M. Youssef a,b , Shar Al-Shihry b a Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt b Department of Chemistry, College of Science, King Faisal University, P.O. Box 380, Hofuf 31982, Saudi Arabia article info Article history: Received 14 May 2009 Received in revised form 28 July 2009 Accepted 29 July 2009 Available online 3 August 2009 Keywords: 2-Acetylpyridine Thiosemicarbazone complexes Spectroscopy Antibacterial abstract The present work carried out a study on transition metal ion complexes which have been synthesized from 2-acetylpyridine 4 N-(2-pyridyl) thiosemicarbazone (HAPT) 1. These complexes namely [Zn(HAPT)Cl 2 ] 2, [Mn (HAPT)Cl 2 ] 3, [Co (HAPT)Cl 2 ] 4, [Fe(APT)Cl 2 (H 2 O)] 5 and [UO 2 (HAPT)(OAc) 2 ] 6, were characterized by elemental analysis, spectral (IR, 1 H NMR and UV–vis) and magnetic moment measure- ments. Thermal properties and decomposition kinetics of all compounds are investigated. The interpre- tation, mathematical analysis and evaluation of kinetic parameters (E, A, DH, DS and DG) of all thermal decomposition stages have been evaluated using Coats–Redfern equation. The biochemical studies showed that, complexes 3 and 6 have powerful and complete degradation effect on the both DNA and protein. The SOD-like activity exhibited that complex 3 has a strong antioxidative properties. The anti- bacterial screening demonstrated that, the free ligand (HAPT), complexes 2, 3 and 6 have the maximum and broad activities against Gram-positive and Gram-negative bacterial strains. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Thiosemicarbazones and their metal complexes have been subject of interest because of their chemical and biological proper- ties [1,2]. The well documented biological activities of several het- erocyclic thiosemicarbazones have been often attributed to their ability to form chelates with transition metal ions [3,4]. 2-Acetyl- pyridine thiosemicarbazones were the first thiosemicarbazones in which antimalarial activity was detected, and the highest activ- ity is reported when the N(4) position is either disubstituted or part of a ring system [5]. N,N,S-tridentate thiosemicarbazones de- rived from 2-acetylpyridine form an important class of compounds possessing biological activity [6,7]. Metal complexes of 4 N-alkyl [8], 4 N-dialkyl-thiosemicarbazone [9] derived from 2-acetylpyri- dine have been spectrally characterized; with tridentate coordina- tion of neutral and anionic ligands being reported. In this paper we prepared the new ligand 2-acetylpyridine 4 N- (2-pyridyl) thiosemicarbazone (HAPT) (Fig. 1) and studied its ligan- tional behavior towards some transition metal ions namely, Mn 2+ , Co 2+ , Zn 2+ , Fe 3+ and U 6+ . This class of ligands are very versatile compounds; structural iso- mers (E-, E’-and Z-forms) are reported [10,11]. We apply geometry optimization and conformational analysis to the free ligand and studied all possible structural isomers and have got the minimum energy with E-isomer. 1 H NMR measurements confirm the presence of one tautomers (E-form) for the HAPT free ligand. Other studies shows only one isomer in the solid state but three isomers are ex- isted in solution [12] which confirmed by our calculations (Fig. 2). Spectroscopic and thermal degradation kinetics of the resulting complexes in addition to its antibacterial activities against Gram- positive and Gram-negative bacteria are discussed. 2. Experimental 2.1. Instrumentation and materials All starting materials were purchased from Fluka, Riedel and Merck and used as received. Elemental analyses (C, H and N) were performed on a Perkin–Elmer 2400 Series II Analyzer. Electronic spectra were recorded on a UV-UNICAM 2001 spectrophotometer using 10 mm pass length quartz cells at room temperature. Mag- netic susceptibility was measured with a Sherwood Scientific mag- netic susceptibility balance at 297 K. Infrared spectra were recorded on a Perkin–Elmer FTIR spectrometer 2000 as KBr pellets and as Nujol mulls in the 4000–200 cm 1 spectral range. 1 H and 13 C NMR measurements at room temperature were obtained on a Jeol JNM LA 300 WB spectrometer at 250 MHz, using a 5 mm probe head in CDCl 3 . Thermogravimetric (TG) and differential (DTG) 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.07.042 * Corresponding author. Present address: Department of Chemistry, College of Science, King Faisal University, P.O. Box 380, Hofuf 31982, Saudi Arabia. Tel.: +966 553901011; fax: +966 35886437. E-mail address: uelayaan@kfu.edu.sa (U. El-Ayaan). Journal of Molecular Structure 936 (2009) 213–219 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc