Recent years have seen growing interest in the employment of small molecules for deoxyribonucleic acid (DNA) studies. [1][2][3][4][5][6] DNA might interact with small molecules according to three possible patterns: (1) The electrostatic interaction, which extends the external wall of DNA double helix and lacks selectivity; (2) Interaction with grooves of DNA; and (3) intercalation model. Some metal complexes such as Cuphenanthroline, Fe-EDTA, Mn-porphyrin and Ru-polypyridyl, can cleave or bind DNA in the presence of co-oxidants such as peroxides. 7-11 Schiff-bases are potential anticancer drugs, so they are currently studied extensively. [12][13][14][15][16] The anticancer activity of these complexes tends to increase when they complex with metal ions. 17,18 21 Gravert and his co-workers investigated DNA binding/cleaving properties of twenty-six salen complexes of Mn(III) in the presence of terminal oxidants using DNA affinity cleaving techniques, and found DNA cleaving efficiency varying with both the structure and stereochemistry of the bridge. 23 We reported metal complexes of salen interaction of DNA and found that Co-salen showed the strongest interaction of DNA and that the interactive model between Co-salen is an intercalative one. 24 This paper reports on the fluorescence spectra characteristics of water-soluble metal complexes of Schiff-base and their interactive effects on calf thymus DNA under physiological condition. The interactive pattern between metal complexes of Schiff-base and DNA was investigated by UV spectroscopy, KI quenching and competitive binding of ethidium bromide (EB) and Mn-Schiff-base with DNA.The effects of salt concentration and pH of medium on interaction of DNA and metal complexes of Schiff-base have also been investigated. Mn-Schiff-bases as a novel fluorescence probe have potential analytical applications for the determination of traces of DNA. Experimental ReagentsWater-soluble Metal-Schiff-base complexes ( The fluorescence spectral characteristics and the interaction of several water-soluble metal complexes of Schiff-base with DNA are described. Among the complexes tested, Mn-Schiff-base bound to DNA showed a marked decrease in the fluorescence intensity with a blue shift of the excitation and emission peaks. Some hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Mn-Schiff-base and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Mn-Schiff-base and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The linear relationship between F/F0 and the concentration of calf thymus DNA covers 3.0 × 10 -6 -2 × 10 -4 mol L -1 , which can be utilized for determining traces of calf thymus DNA with a detection limit of 8.0 × 10 -7 mol L -1 in base pairs.

Recent years have seen a growing interest in the studies of anticancer characteristics of complexes of organotin.1-8 Brown 1 firstly reported the restraint effect of Ph3-SnOOCCH3 for the growing of anticancer cells. Crown 2 et al. reported the anticancer characteristics of organotin complexes. Gielen 3-5 et al. synthesized a series of water-soluble organotin complexes and investigated their anticancer activities. The results indicate that the anticancer activities of these organotin complexes are 100 times higher than that of carboplatin and cisplatin used in clinical applications. Barbier 6 studied the interaction between water soluble organotin complexes and DNA using Mössbauer spectra, and found that no interaction occurred between CH3Sn and DNA under the physiological conditions, while low solubility organotin complexes, which are easily disassociated, interact with DNA through hydrophobe base. Mössbauer spectra, QSAR 7 and clinical experiments are often used to investigate the interaction mechanism of organotin complexes with DNA. Results show that R2Sn ++ plays important roles for the anticancer activities of organotin complexes. Crowe 8 et al. considered that the key of the interaction of organotin complexes with DNA is the disassociation of complexes, but they also found that some organotin complexes which have no R2Sn ++ group still have anticancer activities. So the interaction mechanism of the complexes of organotin with DNA has received much attention.In this research the interaction mechanism of the complexes of organotin with DNA was investigated with fluorescence spectra.The complex of organotin and Schiff-base, bis-(ethylene)tin(bis(salicylidene)ethylenediamine) [Et2Sn(salen)], was synthesized and the fluorescence spectra of the complex and interaction with DNA are described. The interactive pattern between Et2Sn(salen) and DNA was investigated by UV spectroscopy, KI quenching and competitive binding of ethidium bromide (EB) and Et2Sn(salen) with DNA. Studies on the interaction mechanism of anticancer drugs with DNA are interesting for the synthesis of new anticancer drugs or artificial nucleases. Et2Sn(salen) as a novel fluorescence probe has a potential analytical application for the determination of traces of DNA. Experimental Reagents and chemicalsEt2Sn(salen) was synthesized and purified as previously reported.10,11 Calf thymus DNA was purchased from Huamei Biotechnological Co. (Beijing) and used as received with the purity checked by the absorbance ratio, A260/A280, of DNA, which should not be less than 1.8 in a 0.2 mol L -1 phosphate buffer solution containing 60 mmol L -1 NaCl. The DNA concentration, expressed in base pairs, was estimated by spectrophotometry using a molar absorptivity value, ε260, of 1.31 × 10 4 mol L -1 cm -1 . Other chemicals were of analytical reagent grade. Doubly distilled water was used throughout. ApparatusAll fluorescence measurements were carried out with an M850 fluorescence spectrophotometer (Hitachi, Japan). Excitation and emission wavelengths of 277 nm and 4...

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