Synthesis, Crystal Structure, and Thermal Stability of a Dibutyltin Complex {[4-Et2NC6H3(O)C=NC6H3(O)- 5-NO2](n-Bu2Sn)}2and Its Interaction with DNA①

ZHANG Zhi-Jian KUANG Dai-Zhi JIANG Wu-Jiu YU Jiang-Xi ZHU Xiao-Ming ZHANG Fu-Xing

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Synthesis, Crystal Structure, and Thermal Stability of a Dibutyltin Complex {[4-Et2NC6H3(O)C=NC6H3(O)- 5-NO2](-Bu2Sn)}2and Its Interaction with DNA①

ZHANG Zhi-Jiana②KUANG Dai-ZhibJIANG Wu-JiubYU Jiang-XibZHU Xiao-MingbZHANG Fu-Xingb

a(421008)b(421008)

The Schiff base organotin(IV) complex {[4-Et2NC6H3(O)C=NC6H3(O)-5-NO2](- Bu2Sn)}2has been synthesizedthe reaction between 4-(diethylamino) salicylaldehyde-2-amino- 4-nitrophenol Schiff base (H2L) and dibutyltin oxide. Complex C1has been characterized by IR,1H NMR,13C NMR spectra, and elemental analysis, and its crystal structure was determined by X-ray diffraction. It crystallizes in the monoclinic system, space group21/with=15.6559(8),= 9.1657(5),= 18.8351(10) ?,= 107.3440(10)°,= 4,= 2579.9(2) ?3,D= 1.442 Mg·m-3,(Mo) = 1.025 mm-1,(000) = 1152,= 0.0250 and= 0.0633. The central Sn atom is coordinated in a hexadentate manner to assume a distorted octahedral configuration.Complex C1 was studied by TGA analysis in air atmosphere. The interaction between complex C1 and the herring sperm DNA was realized through the intercalation of the complex based on the studies by EB fluorescent probe.

organotin complex, synthesis, crystal structure, thermal stability, DNA

1 INTRODUCTION

In recent years, organotin-Schiff base complexes have attracted wide attention because they possess various good biological activities such as antitumor, antiviral, bacteriocidal and fungicidal functions, and they may cut off DNA chains selectively[1-5]. As substituted salicylaldehyde Schiff bases contain two coordination atoms (N, O), this kind of ligands have good biocompatibility and their complexes possess various coordination modes, so they have become a research hotspot in the field of organometallic mate- rials[6-10]. We designed and synthesized 4-(diethyla- mino)salicylidene-2-amino-4-nitrophenol and its complex with dibutyltin. The thermal stability of this complex in air was determined, and preliminary researches were made on its interaction with herring sperm DNA by fluorescent spectrometry in tris buffer by using EB as the fluorescence probe.

2 EXPERIMENTAL

2. 1 Reagents and instruments

Infrared spectrum was recorded by an IR Pres- tige-21 infrared spectrometer (Japan Shimadzu, 4000～400 cm-1, KBr pellets).1H and13C NMR spectra were recorded by the Bruker Avance 400 NMR spectrometer (TMS as internal standard). Elemental analyses were performed on the PE-2400 (II) elemental analyzer. The crystal structure was solved by a Bruker SMART APEX II CCD single- crystal diffractometer; ultraviolet-visible spectrum was recorded by UV-2550 spectrometer (Japan Shi- madzu), and fluorescent spectrum on an F-7000 fluorescent spectrometer (Japan Hitachi); Melting point was measured on an XT-4 binocular micro- melting point apparatus without correction (Beijing Tektronix Instrument Co. Ltd.).

Dibutyltin oxide, ethidium bromide (EB), herring sperm DNA, and tris(hydroxymethyl) aminome- thane (Tris) were products of Sigma-Aldrich, and other regents were all analytically pure, and water was ultrapure water. The preparation of Tris-HCl (0.01 mol/L) buffer: Suitable quantity of Tris was weighed, and its pH value was adjusted to 7.40 by adding 0.1 mol/L HCl. The purity of herring sperm DNA was determined through comparing its absorbance at 260 and 280 nm (A260/A280= 1.8～1.9/1); it should be prepared using buffer at necessary pH, its concentration was determined based on the absorbance at 260 nm (260= 6600 L·mol-1·cm-1), and its stock should be kept at 4 ℃. The preparation of EB solution: Suitable quantity of solid EB was weighted, and dissolved in 0.01 mol/L Tris-HCl (pH = 7.40) buffer solution mentioned above.

2. 2 Synthesis

2. 2. 1 Synthesis of [4-Et2NC6H3(OH)C=N C6H3(OH)-5-NO2] (H2L)

A mixture of 4-(diethylamino)salicylaldehyde (1.93 g, 10 mmol) and 2-amino-4-nitrophenol (1.54 g, 10 mmol) was refluxed with stirring in absolute ethanol (50 mL) for 6 h. Most of the solvent was evaporated by vacuum. The reaction mixture was filtered, and the solid was recrystallized by absolute ethanol. The red needle-like crystals were collected in the yield of 2.04 g, 62%. m.p.: 298～300 ℃. Elemental analysis (C17H19N3O4): measured value (calculated value, %): C, 62.07 (62.00); H, 5.83 (5.81); N, 12.77 (12.76). IR (KBr, cm-1): 3530(O–H), 2970, 2928, 2870(C–H), 1627, 1607(C=N), 1522, 1329(C–NO2), 1238(C–O). UV-vis (DMSO),max(nm): 392.1H NMR (DMSO, 400 MHz),(ppm): 13.70 (s, 1H, 1-O), 11.37 (s, 1H, 13-O), 8.81 (s, 1H, H-7), 8.16 (d,= 2.4 Hz, 1H, H-9), 7.97 (dd,1= 8.8 Hz,2= 2.4 Hz, 1H, H-11), 7.37 (d,= 8.8 Hz, 1H, H-5), 7.05 (d,= 8.8 Hz, 1H, H-12), 6.33 (dd,1= 8.8 Hz,2= 1.8 Hz, 1H, H-4), 6.06 (d,= 1.8 Hz, 1H, H-2), 3.40 (q,= 6.7 Hz, 4H, -N(C2CH3)2), 1.13 (t,= 6.7 Hz, 6H, -N(CH2C3)2).

2. 2. 1 Synthesis of {[4-Et2NC6H3(O)C=N C6H3(O)-5-NO2](-Bu2Sn)}2(C1)

A mixture of 4-(diethylamino) salicylidene-2- amino-4-nitrophenol Schiff base (0.329 g, 1 mmol) and dibutyltin oxide (0.248 g, 1 mmol) was refluxed with stirring in absolute methanol (25 mL) for 8 h. Most of the solvent was evaporated by vacuum. The reaction mixture filtered, and the solid was recrys- tallized by absolute methanol. The red-brown crys- tals were collected. Yield: 0.376 g, 67%, m.p.: 265～267 ℃. Elemental analysis (C50H70N6O8Sn2): measured value (calculated value, %): C, 53.61 (53.59); H, 6.31 (6.30); N, 7.52 (7.50). IR (KBr, cm-1): 3067, 2955, 2866(C–H), 1611, 1578(C=N), 1520, 1352(C–NO2), 1246(C–O), 600(Sn–O–Sn), 505(Sn–O), 475(Sn–N), 417(Sn–C). UV-vis (DMSO),max(nm): 462, 340.1H NMR(CDCl3, 400MHz),(ppm): 8.36 (s, 1H, H-7), 8.18 (d,= 2.0 Hz, 1H, H-9), 8.02 (dd,1= 8.8 Hz,2= 2.0 Hz, 1H, H-11), 7.08 (d,= 9.2 Hz, 1H, H-5), 6.74 (d,= 8.8 Hz, 1H, H-12), 6.26 (dd,1= 9.2 Hz,2= 1.8 Hz, 1H, H-4), 5.92 (d,= 1.8 Hz, 1H, H-2), 3.44 (q,= 6.8 Hz, 4H, -N(C2CH3)2), 1.59～1.66 (m, 4H, H-), 1.47 (t,= 7.6 Hz, 4H, H-), 1.33 (sext,= 7.2 Hz, 4H, H-), 1.24 (t,= 6.8 Hz, 6H, -N(CH2C3)2), 0.85 (t,= 7.2 Hz, 6H, H-).13C NMR(CDCl3, 100 MHz),(ppm): 158.94 (C-7), 12.81 (-N(CH2H3)2), 13.52 (C-), 21.87 (C-), 26.49 (C-), 26.89 (C-), 44.83 (-N(H2CH3)2), 100.07, 105.59, 109.59, 110.08, 116.49, 123.97, 132.98, 136.73, 138.14, 155.75, 165.49, 171.48 (Ar-C).

2. 3 Structure determination

A crystal of complex C1 with dimensions of 0.21mm × 0.20mm × 0.20mm was chosen for data collection which was performed on a Bruker SMART APEX II CCD diffractometer equipped with a graphite-monochromatic Moradiation (= 0.71073 nm) using ascan mode. The crystal is of monoclinic system, space group21/with=15.6559(8),= 9.1657(5),= 18.8351(10) ?,= 107.3440(10)°,= 4,= 2579.9(2) ?3,D= 1.442 Mg·m-3,(Mo) = 1.025 mm-1,(000) = 1152,= 0.0250 and= 0.0633.A total of 12759 reflections were collected in the range of 1.49≤≤25.09, of which 4575were uniqueand 4023were observed with> 2() and used to solve the structure. The crystal structure was solved by direct methods. All non-hydrogen atoms were determined in successive difference Fourier synthesis, and the hydrogen atoms were placed theoretically. All hydrogen and non-hydrogen atoms were refined by their isotropic and anisotropic thermal parameters through full-matrix least-squares techniques. All calculations were completed by SHELX-97 pro- gram system[11].

2. 4 Interaction with DNA

A mixture of the herring sperm DNA, EB and complex solution of different concentration was placed in a 5 mL volumetric flask. After 3.5 h, the fluorescence spectra were scanned respectively, the emission wavelength was 258 nm, and the excita- tion wavelength was shown in the spectrum. The emission and excitation slit scanning width was 5.0 nm.

3 RESULTS AND DISCUSSION

3. 1 Spectral characteristics

The band at 3530 cm-1of the complex and ligands was attributed to the stretching vibration of O–H bond; the absorption peaks at 1578～1627 cm-1were assigned to the vibration of C=N bond, and those at 1238 and 1246 cm-1to that of the C–O bond. Complex C1 presents absorption peaks of medium intensity at 3067, 2955 and 2866 cm-1specific to the C–H bond of butyl group. The com- parison of spectra between the complex and ligands revealed vibration absorption peaks of Sn–C, Sn–N, Sn–O and Sn–O–Sn in low frequency (at 417, 475, 505, and 600 cm-1,respectively)[12-16], demons- trating the formation of organotin Schiff complex.

The1H NMR spectra show the expected integra- tion and peak varieties[17-19]. The ligand has two peaks resulting from the hydrogen protons of phenol hydroxyl group at 13.70 and 11.37 ppm, but they disappeared in the spectrum of the complex, showing the occurrence of absorption from the hydrogen protons of butyl group in high field; in addition, in the13C NMR spectra each peak conforms with the theoretical speculation of carbon atoms[17], indicating that organotin is coordinated with the Schiff base.

3. 2 Crystal structure

The selected bond lengths and bond angles of complex C1 are shown in Table 1, and the mole- cular structure in Fig. 2. In the complex, there is a four-membered ring formed by Sn(1), O(2), Sn(1)iand O(2)iat the center of the Sn2O2plane, and this center is just the symmetrical center of the molecule. The bridging oxygen atom is coordinated with two tin atoms in a tridentate manner, and the bonds between it and two tin atoms are different in length: Sn(1)–O(2) in 2.1459(17)? belongs to a normal covalent Sn–O bond; and Sn(1)–O(2)iis 3.127(2) ? (symmetry code: i 1–, 1–, –), longer than the covalent Sn–O bondbut shorter than the sum of Van der Waals radii of the tin and oxygen atoms, and slightly longer than the Sn–O of similar complexes reported[20]. In the complex, the Sn(1) is coor- dinated with two oxygen atoms (O(1) and O(2)) from the phenol group of a Schiff ligand, one nitrogen atom N(1) from the imino group, two carbon atoms (C(18) and C(22)) from the butyl groups, and O(2)ifrom other Schiff ligand to con- stitute a hexadentate octahedral configuration. O(1), O(2), N(1), and O(2)ioccupy four positions in the equatorial plane, and C(18) and C(22) from butyl are located on the axis on both sides of this plane. The bond angle C(18)–Sn(1)–C(22) in the axial direction is 135.02(12)°, deviating from 180° by 44.98°. Therefore, in the molecular structure the central tin atom formed a distorted hexadentate octahedral configuration. Ligands are coordinated with the tin atom in a tridentate manner to form a five-membered ring in good planarity (O(2), C(13), C(8), N(1) and Sn(1) with mean deviation from their least-squares plane to be only 0.0096 ?) and a six-membered ring which consisting of O(1), C(1), C(6), C(7), N(1) and Sn(1) atoms is also well coplanar (the mean deviation from their least-squares plane being 0.0334 ?). The dihedral angle between the above two planes is 2.4°, showing that all atoms around the tin atom in the equatorial plane are basically coplanar.

Table 1. Selected Bond Lengths (?) and Bond Angles (°)

Symmetry code: i 1–, 1–, –

Fig. 1. Synthesis of the ligand and complex

Fig. 2. Molecular structure of C1 (Symmetry code: i 1–, 1–, –)

Fig. 3 shows C–H···O weak interaction existing between two oxygen atoms, O(3) and O(4), of nitro group in the benzene ring of a molecule with a hydrogen atom H(5)iiin the benzene ring of another molecule, forming a pair of hydrogen bonds (O(3)···H(5)ii: 2.716 ?, and O(4)···H(5)ii: 2.656 ?, symmetry code: ii –, 1–, –). Based on such hydrogen bonds, the molecules are connected with each other to form a 1D string-like structure.

Fig. 3. 1D string-like structure of complex C1 by C–H···O interaction (Symmetry codes: i 1–, 1–, –; ii –, 1–, –)

3. 3 Thermal stability

Model NETZSCH TG 209 F3 thermogravimeter was used to research the thermal stability of complex C1 in air at a heating rate of 20 ℃/min and a flow-rate of 20 mL/min within 40～700 ℃. As shown in Fig. 4, the weight loss may be divided into three steps. At the beginning stage of 40～240 ℃, almost no weight loss occurred; at the second stage from 240 to 600 ℃, a noticeable weight loss of 73.12% was observed, corresponding to the release of 4 butyl groups and 2 Schiff ligands; at the final stage of 600～700 ℃, no weight loss was found, with the final residue to be 26.88%. The residue may be SnO2because the measured value of 26.88% agreed with the theoretical value (26.86%). So, this complex is stable below 240 ℃.

Fig. 4. TG-DTG curve of complex C1

3. 4 Interaction with DNA

Ethidium bromide (EB) is a fluorescent dye, but its fluorescence is very weak. In DNA solution, EB may be inserted in parallel between the base pairs of DNA to intensify remarkably its fluorescence. In case the complex is added to the DNA solution containing EB, competition reaction would take place, thus the complex can squeeze EB out of the base pairs of DNA to quench the fluorescence, and therefore EB could be used as fluorescent probe to probe into the DNA structure[21].

Fig. 5 reflects the fluorescence quenching of EB- DNA system caused by the complex of different concentration. The fluorescence of EB-DNA system is quenched along with increasing the concentration of the complex, suggesting that the coordination of this complex with the base pairs of DNA squeezed EB out of the base pairs of DNA. In order to research quantitatively the ability of this complex to bind DNA, we calculated the quenching constant to substitute for EB to interact with DNA using the Stern-Volmer equation[22, 23]:0/= 1 +sq. Thesqwas calculated as 0.60, indicating that a certain intercalation took place between this complex and DNA, as reported in literature[24].

Fig. 5. Effects of complex C1 on the fluorescent spectra of EB-DNA systemDNA= 30mol/L;EB= 3mol/L; from 1 to 10,= 0, 5, 15, 25, 35, 45, 55, 65, 75, 85mol/L,respectively;inset: plot of0/(=/DNA);em= 258 nm

(1) Assunta Girasolo, M.; Rubino, S.; Portanova, P.; Calvaruso, G.; Ruisi, G.; Stocco, G. New organotin(IV) complexes with L-arginine,α--Boc-L-arginine and L-alanyl-L-arginine: synthesis, structural investigations and cytotoxic activity.2010, 695, 609–618.

(2) Molter, A.; Kalu?erovi?, G. N.; Kommera, H.; Paschke, R.; Langer, T.; P?ttgen, R.; Mohr, F. Synthesis, structures, 119Sn M?ssbauer spectroscopic studies and biological activity of some tin(IV) complexes containing pyridyl functionalised selenosemicarbazonato ligands.2012, 701, 80–86.

(3) Dang, Y. Q.; Yang, H. J.; Tian, L. J. Syntheses and structural characterization of dimethyltin complexes of-(3-Methoxysalicylidene)--amino acid.2012, 31, 479–484.

(4) Shujah, S.; Ziaur, R.; Muhammad, N.; Ali, S.; Khalid, N.; Tahir, M. N. New dimeric and supramolecular organotin(IV) complexes with a tridentate Schiff base as potential biocidal agents.2011, 696, 2772–2781.

(5) Yin, H. D.; Liu, H.; Hong, M. Synthesis, structural characterization and DNA-binding properties of organotin(IV) complexes based on Schiff base ligands derived from 2-hydroxy-1-naphthaldy and 3- or 4-aminobenzoic acid.2012, 713, 11–19.

(6) Kobakhidze, N.; Farfán, N.; Romero, M.; Méndez-Stivalet, J. M.; Gabriela Ballinas-López, M.; García-Ortega, H.; Domínguez, O.; Santillan, R.; Sánchez-Bartéz, F.; Gracia-Mora, I. New pentacoordinated Schiff-base diorganotin(IV) complexes derived from nonpolar side chain-amino acids.2010, 695, 1189–1199.

(7) Hong, M.; Yin, H. D.; Chen, S. W.; Wang, D. Q. Synthesis and structural characterization of organotin(IV) compounds derived from the self-assembly of hydrazone Schiff base series and various alkyltin salts.2010, 695, 653–662.

(8) Cui, J. C.;Qiao, Y. L.; Ding, L. H.; Yin, H. D. Synthesis, characterization and crystal structure of a trinucleardiorganotin(IV) complex with-acetylsalicylhydrazide.2010, 1, 1784–1787.

(9) Yin, H. D.; Cui, J. C.; Qiao, Y. L. Synthesis, characterization and crystal structure of binuclear diorganotin(IV) complexes derived from hexadentate diacylhydrazone ligands.2008, 27, 2157–2166.

(10) Yin, H. D.; Hong, M.; Li, G.; Wang, D. Q. Synthesis, characterization and structural studies of diorganotin(IV) complexes with Schiff base ligand salicylaldehyde isonicotinylhydrazone.2005, 690, 3714–3719.

(11) Sheldrick, G. M.University of G?ttingen: G?ttingin, Germany 1998.

(12) Jiang, W. J.; Yang, N. F.; Kuang, D. Z.; Feng, Y. L.; Zhang, F. X.; Wang, J. Q.; Liu, M. Q.; Yu, J. X. Synthesis, crystal Structure and luminescent property of the one-dimensional chain chlorodibenzyltin 2-quininate.2011, 30, 1327–1331.

(13) Yu, J. X.; Feng, Y. L.; Kuang, D. Z.; Yin D. L.; Zhang F. X.; Wang, J. Q. Synthesis, crystal structure and quantum chemistry of two tricyclohexyltin pyridinecarboxylate complexes..2012, 28, 279–284.

(14) Barba, V.; Zaragoza, J.; H?pfl, H.; Farfán, N.; Beltrán, H. I.; Zamudio-Rivera, L. S. Use of bis-aminoalcohol benzoquinones and dihydroxybenzoquinones in the formation of mono and polymeric structures of diorganotin(IV) derivatives.2011, 696, 1949–1956.

(15) Jiang, W. J.; Kuang, D. Z.;Yu, J. X.;Feng, Y. L.; Zhang, F. X.; Wang, J. Q. Synthesis, crystal structure, quantum chemistry and thermal stability of the bis-oxygen-bridged tetranuclear dibutyltin (2,4,6-trimethyl)benzoate.2012, 28, 2363–2368.

(16) Yin, H. D.; Dong, L.; Hong, M.; Cui, J. C. Structural diversity of organotin(IV) complexes self-assembled from hydroxamic acid and mono- or dialkyltin salts.2011, 696, 1824–1833.

(17) Pretsch, E.; Philippe, B.; Martin, B.Springer-Verlag Berlin and Heidelberg GmbH & Co. K 2009.

(18) Clark, H. C.; Jain, V. K.; Mehrotra, R. C.; Singh, B. P.; Srivastava, G.; Birchall, T. Tin-119, phosphorus-31, carbon-13 and proton nuclear magnetic resonance and M?ssbauer studies of mono-, di- and tri-organotin(IV) dialkyldithiophosphates.1985, 279, 385–394.

(19) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. NMR chemical shifts of trace impurities: common laboratory solvents, organics, and gases in deuterated solvents relevant to the organallic chemist.2010, 29, 2176–2179.

(20) Jiang, W. J.; Kuang, D. Z.;Yu, J. X.; Feng, Y. L.; Zhang, F. X.; Wang, J. Q. Synthesis, crystal structure, quantum chemistry and thermal stability of the bis-oxygen-bridged tetranuclear dibutyltin (2,4,6-trimethyl)benzoate {[-Bu2Sn(2,4,6-TMBA)]2O}2..2012, 28, 2363–2368.

(21) Wu, X. Y.; Liu, J. F.; Zhao, G. L. Synthesis, crystal structures and DNA-binding of Cu(II), Zn(II) coordination polymer constructed from 4-hydroxyphenylacetic acid..2012, 28, 1661–1667.

(22) Zhao, G. L.; Shi, X.; Zhang, J. P.; Liu, J. F.; Xian, H. D.; Shao, L. X. Synthesis, crystal structures and biological activity of transition metal complexes of 2-phenyl-4-selenazole carboxylic acid.2010, 40,1525–1535.

(23) Wolfe, A.; Shimer, G. H.; Meehan, T. Polycyclic aromatic hydrocarbons physically intercalate into duplex regions of denatured DNA.1987, 26, 6392–6396.

(24) Zhao, G. L.; Shen, J. B.; Shi, X.; Chen, J. F.; Lü, X.; Zhou, Y. F.; Chen, Y. Synthesis, crystal structure and biological activity of nickel(II) complex of 2-phenyl-4-selenazole carboxylic acid..2012, 28,959–964.

① This research was supported by the Natural Science Foundation of Hunan Province (No. 13JJ3112), Scientific & Technological Projects of Hunan Province (No. 2013TZ2025, 2014FJ3060), Scientific Research Fund of Hunan Provincial Education Department of China (14C0171), the Foundation of Key Laboratory of Functional Organometallic Materials, University of Hunan Province (No. 13K03, 13K04, 13K05), and the Science Foundation of Hengyang Normal University (No. 12C45, 13A21)

. E-mail: 17339551@qq.com

2 December 2013;

24 June 2014 (CCDC 965797)