КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 4, с. 246-256
УДК 541.49
SYNTHESIS, CRYSTAL STRUCTURES, LUMINESCENT PROPERTIES, THEORETICAL CALCULATION, AND DNA INTERACTION OF THE CADMIUM(II) AND LEAD(II) COMPLEXES WITH o-AMINOBENZOIC ACID AND 1,10-PHENANTHROLINE © 2015 Z. Y. Zhang, C. F. Bi, Y. H. Fan*, X. C. Yan, X. Zhang, P. F. Zhang, and G. M. Huang
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao, Shandong, 266100 P.R. China *E-mail: fyh1959@163.com; fanyh@ouc.edu.cn Received August 27, 2014
Two complexes, namely [Cd(Phen)(o-AB)2] (I) and [Pb(Phen)(o-AB)] (II) (Phen = 1,10-phenanthroline, o-AB = o-aminobenzoic acid), have been synthesized and characterized by elemental analysis and X-ray diffraction single-crystal analysis (CIF files CCDC nos. 910307 (I), 898292 (II)). Complex I is six coordinated by two nitrogen and four oxygen atoms from the Phen and o-AB to furnish a distorted octahedral geometry. Complex II is six coordinated by two nitrogen and four oxygen atoms from the Phen and o-AB to furnish an umbrella-like geometry. The complexes exhibit intense fluorescence at room temperature. The interaction between complex I and calf thymus DNA was also investigated by UV absorption spectra, fluorescence emission spectra and viscometry. The nature of the binding seems to be mainly an electrostatic interaction between DNA and complex I. Theoretical studies of the title complexes were carried out by density functional theory (DFT) B3LYP method.
DOI: 10.7868/S0132344X15030093
INTRODUCTION
Heterocyclic compounds are widely distributed in nature and essential to many biochemical processes. These compounds are worth attention for many reasons, chief among them are their biological activities; many drugs are heterocycles [1, 2]. 1,10-Phenanthro-line (Phen) and its substituted derivatives, both in the metal-free state and as ligands coordinated to transition metals, disturb the functioning of a wide variety of biological systems [3—5]. When the metal-free N,N-chelating bases are found to be bioactive, it is usually assumed that the sequestering of trace metals is involved, and that the resulting metal complexes are the actual active species [6—9]. Interests in aminobenzoic acids arise from both their biological importance and their chemical properties. o-Aminobenzoic acid, also named anthranilic acid, has been used as a convenient fluorescence probe in internally quenched fluorescent peptides due to its high quantum yield and small size. o-Aminobenzoic acid (o-AB) is also multifunctional hydrogen-bonding molecules [10—12].
In the viewpoint of constructing functional compounds, the title cadmium(II) and lead(II) complexes were synthesized in anhydrous solvent and their crystal structures were determined. The interaction between complex I and calf thymus DNA was also investigated by UV absorption spectra, fluorescence emission spectra and viscometry [13]. Based on crystal data,
density functional theory (DFT) studies of the title complexes were performed using the Gaussian 03 program suite. The natural atomic charges distribution, molecular total energy and frontier molecular orbital energies of the complexes were discussed [14].
EXPERIMENTAL
Materials and physical measurement. Calf thymus DNA (CT-DNA) were obtained from Sigma-Aldrich Co. (USA). The other reagents used in this work were of analytical grade. The experiments involving interaction of the complexes with CT-DNA were carried out in Milli-Q water buffer containing 5 mM Tris and 50 mM NaCl, and adjusted to pH 7.2 with hydrochloric acid. A solution of CT-DNA gave a ratio of UV ab-sorbance at 260 and 280 nm of about 1.8—1.9, indicating that the CT-DNA was sufficiently free of protein [15]. The CT-DNA concentration per nucleotide was determined spectrophotometrically by employing an extinction coefficient of6600 L mol-1 cm-1 at 260 nm [16].
Elemental analyses were carried out with a model 2400 PerkinElmer analyzer. The fluorescence spectra were recorded on an F-4500 fluorimeter. The X-ray diffraction data were collected on a Bruker Smart CCD X-ray single-crystal diffractometer. Viscosity measurements were conducted using an Ubbelodhe viscometer. Optimizations of geometrical structures
and Natural Bond Orbital (NBO) analyses of the title complexes were carried out by DFT B3LYP method. The 6—31 + G* basis set was used for C, N and O atoms, while the effective core potential (ECP) and valence double-Z LANL2DZ basis set was used for Pb and Cd atom [17, 18]. Atom coordinates used in the calculations were from crystallographic data, and a molecule in the unit cells was selected as the initial model. All calculations were conducted on a Pentium IV computer using Gaussian 03 program [19].
Synthesis of complexes. o-AB (2.0 mmol) was dissolved in 50 mL ofanhydrous methanol. M(OAc)2 • «H2O (M = Cd(II) and Pb(II)) (1.0 mmol) dissolved in 30 mL of anhydrous methanol was added dropwise to the above o-AB solution and stirred for 4 h at 55°C. Then Phen (1.0 mmol) dissolved in 10 mL ofanhydrous methanol was added dropwise to the above solution and stirred for 4 h at 55°C cooled and filtered. The filtrate was left for slow evaporation at room temperature. The wine prismatic crystals were formed 20 days later.
For C26H20N4O4Cd (I)
anal. calcd., %: C, 55.28; H, 3.56; N, 9.92. Found, %: C, 55.35; H, 3.68; N, 9.83.
DNA-binding studies were carried out by ultraviolet (a) and fluorescence (b) spectra and viscosity measurements (c). a. Complex I was dissolved in a mixture of DMSO and Tris—HCl buffer. Absorption titration experiments were carried out by gradually increasing the DNA concentration and maintaining the complexes concentration at 5.75 x 10-7 M. Absor-bances were recorded after each successive addition of DNA solution and equilibration.
b. For complex I, spectral measurements was carried out by successive additions ofDNA (0.0—3.78 x 10-5 mol/L) to the complex I (1.51 x 10-5 mol/L) in Tris-HCl buffer. The sample was excited at 319 nm. The scanner speed was 240 nm min-1 and the slit width was 2.5 nm.
c. Viscosity measurements were conducted using an Ubbelodhe viscometer, which was immersed in a ther-mostated water bath maintained to 298 (±0.1) K. Titrations were performed for the complex which can be introduced into a DNA solution in the viscometer. Data were presented as (n/n0)1/3 versus the ratio of the concentration of the complex and DNA, where n is the viscosity of DNA in the presence of the complex and n0 is the viscosity of DNA alone.
For C26H20N4O4Pb (II)
anal. calcd., %: C, 47.34; H, 3.06; N, 8.49. Found, %: C, 47.30; H, 3.12; N, 8.50.
X-ray structure determination. All data were collected on a Bruker Smart CCD X-raysingle-crystal dif-fractometer at 298(2) K with a graphite-monochro-mated Mo^a radiation (X = 0.71073 A) by using an ®—29 scan mode. The structure was solved by direct methods using SHELXS-97 [20]. The non-hydrogen atoms were defined with Fourier synthesis method. Positional and thermal parameters were refined by fullmatrix least-squares method to convergence. A summary of the key crystallographic information is given in Table 1. Selected bond lengths and bond angles of complexes I and II are listed in Table 2. Hydrogen bond geometry of the complexes is listed in Table 3. Crystal structure of the title complexes are depicted in Fig. 1. Packing diagrams of the title complexes are depicted in Fig. 2.
Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 910307 (I), 898292 (II); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
Fluorescence properties. The fluorescence spectra of the complexes and the ligands were carried out in methanol solution. For complex I, the sample was excited at 319 nm. The scanner speed was 240 nm min—1 and the slit width was 2.5 nm. For complex II, the sample was excited at 314 nm. The scanner speed was 240 nm min—1 and the slit width was 2.5 nm.
RESULTS AND DISCUSSION
As shown in Fig. 1a, in complex I, Cd(II) atom is located in a very distorted octahedral coordination with six bonds to two N atoms from one Phen and four carboxy-late O atoms from two o-AB ligands. There are two four-membered chelate rings (Cd(1)-O(1)-C(1)-O(2), Cd(1)-O(3)-C(8)-O(4)) and one five-membered chelate ring (Cd(1)-N(3)-C(19)-C(20)-N(4)). As shown in Fig. 1b, in complex II, Pb(II) atom is located in a very distorted octahedral coordination with six bonds to two N atoms from one Phen and four carbox-ylate O atoms from two o-AB ligands. There are two four-membered chelate rings (Pb(1)-O(1)-C(1)-O(2), Pb(1)-O(3)-C(8)-O(4)) and one five-membered chelate ring (Pb(1)-N(3)-C(19)-C(20)-N(4)). But the geometry of complex II is different from the complex I, which forms an umbrella-like geometry in which Pb(1)—O(1) bond serves as the umbrella handle.
As shown in Fig. 2a and Table 3, complex I forms two intermolecular hydrogen bonds N(1)—H(1^)-O(1) and N(2)—H(2$)-"O(3) between the exocyclic amine group and the oxygen atom of the carboxyl group. The molecules are linked into extended chains parallel to the y axis and the z axis through the involving intermolecular N—H-O hydrogen bonds. A three-dimensional network is assembled through van der Waals' forces and intermolecular n—n interactions [21, 22].
As shown in Fig. 2b and Table 3, complex II forms two intermolecular hydrogen bonds N(1)—H(L5)-O(2) and N(2)—H(2$)-"O(3) between the exocyclic amine group and the oxygen atom of the carboxyl group. The molecules are linked into extended chains parallel to
Table 1. Crystallographic data and structure refinement for complexes I and II
Parameter Value
I II
Fw 564.86 659.65
Crystal system Monoclinic Triclinic
Space group P2i/c P1
a, A 7.6462(6) 7.8127(6)
b, A 17.1758(17) 12.9880(11)
c, A 17.7436(18) 13.4150(12)
a, deg 90 63.4960(10)
P, deg 100.1000(10) 84.243(2)
Y, deg 90 77.5180(10)
V
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