Critical Reviews: Spectroscopic Studies on Palladium (ii)–complexes with Xanthine and Its Derivatives at Normal and High External Pressure

A critical reviews on molecular spectroscopic work on the palladium (II) complexes with xanthine, caffeine, theobromine, and theophyline at normal and high external pressure is presented. The methods for high external pressure measurement with the aid of Diamond Anvil Cell and Raman Measurements are also reported. *Corresponding author: [email protected] Part –I: SPECTROSCOPIC STUDIES ON PALLADIUM (II) COMPLEXES WITH XANTHINE AND ITS DERIVATIVES AT NORMAL PRESSURE Xanthines are a group of purine alkaloids including caffeine, theophylline and theobromine [1]. Xanthine is a product on the pathway of purine degradation and an important component of DNA, RNA and coenzymes [2}. Xanthine and its derivatives are used in the treatment of asthama, chronic bronchitis and emphysema. Caffeine is a strong stimulant and effects on the central nervous system, heart and kidney. Theobromine is a major constituent of cocoa. It has little stimulatory action on the central nervous system and it is used as a diuretic drug. Theophylline is an active constituent of tea and it is used in medicine as antiasthmatic and diuretic. Natural and synthetic xanthine derivatives have a number of bio-medical applications [3-11]. Metal ions play an important role for the transfer of ATP in biological systems [12]. The binding of metal ions to the biomolecules is of interest because of its importance in DNA replication and the inhibition of neoplastic growth [13, 14]. Recently much attention has been paid to palladiumcontaining complexes, due to their potent antitumor activities [15, 16]. Metal complexes of xanthine and its derivatives are also of interest because these ligands can serve as models for biologically important analogues [17, 18]. Xanthine generally bound to the metal at N-1, N-3, N-7, N-9, C-8, O-2 and O-6 positions. Xanthine coordinate to the metals through carbon adjacent to the imidazole nitrogen when the nitrogen sites are blocked with substituents [19]. The presence of an alkyl group at N-3 sterically hindered coordinates at N-9 large metal ions [20]. Caffeine is coordinated with ruthenium through C-8 [21]. The most likely binding site in caffeine and theophylline were thought to be N-9 and N-7 imidazole nitrogens, while theobromine possessed N-1 and N-9 binding sites. Coordination of neutral theophylline ligand through N-9 was reported in some Rh and Pt complexes [22,23] and N-7, O-6 chelation was also demonstrated [24,25]. The structure of xanthine and its derivatives is shown in Figure below: