KOOPMHH^HOHHAS XHMH3, 2014, moM 40, № 6, c. 351-357
yffK 541.49
SYNTHESIS, CHARACTERIZATION, AND ANTIBACTERIAL ACTIVITY OF TWO ZINC(II) COMPLEXES WITH SCHIFF BASES DERIVED
FROM RIMANTADINE
© 2014 X. D. Jin1, *, C. Xu1, X. Y. Yin1, H. B. Wang1, Z. Y. Zou2, D. L. Liu1, C. H. Ge1,
X. H. Chang1, and Y. H. Jin3
1College of Chemistry, Liaoning University, Shenyang, 110036 P.R. China 2Department of Life Science, Liaoning University, Shenyang, 110036 P.R. China 3Liaoning Provincial Institute of Measurement, Shenyang, 110036 P.R. China *E-mail: jinxudong@yahoo.com Received September 6, 2013
The reactions of zinc(II) chloride and two Schiff base ligands derived from rimantadine and 5-chlorosalicylal-dehyde/4-methoxysalicylaldehydes, generated two novel complexes [Zn(L1)2Cl2] (I) and [Zn(L2)2Cl2] (II), where L1 = 2-((1-(1-adamantan-1-yl)ethyl)-iminomethyl)-4-chlorophenol, L2 = 2-((1-(1-adamantan-1-yl)ethyl)iminomethyl)-5-methoxyphenol. The complexes were characterized by the means of IR, 1H NMR, elemental analysis, molar conductance and thermal analysis. A single-crystal X-ray diffraction analysis reveals that both complexes crystallize in orthorhombic system, space group Fdd2 for I and Pbcn for II. In two complexes crystals, each asymmetric unit consists of one zinc(II) ion, two corresponding Schiff base ligands and two chlorine atoms; the central zinc atom lies on a twofold rotation axis and is four-coordinate via two chlorine atoms and two oxygen atoms from the Schiff base ligands, forming a distorted tetrahedral geometry.
DOI: 10.7868/S0132344X14050053
INTRODUCTION
The field of Schiff base complexes attracts interest mainly due to facile synthesis and biological activity [1—4]. The diverse structures for the ligands rest with the types of aldehydes and amines [5]. Although obtained ligands involve in a broad scope such as single, double, asymmetric and macrocyclic Schiff bases, etc., the biological activity study of rimantadine-sali-cylaldehyde (or substituted salicylaldehyde) Schiff bases and their corresponding complexes has not been reported in detail [6].
The clinic medical research indicated that both amantadine (Symmetrel™) and rimantadine (Flu-madineTM) could block the ion channel formed by the M2 protein of influenza A viruses, result in inhibiting the early stages of virus replication. Therefore in many countries, amantadine and rimantadine have been widely used to treat or prevent seasonal influenza as efficacious remedies [7—10]. However, the incidence of side effects to central-nervous-system was higher with amantadine [11]. Salicylaldehyde and its derivatives are with antibacterial and antiviral activity and they were used to produce efficient herbicides, insecticides and fungicides [12]. Zinc is a vital element in the life for its taking part in a particular metabolic process [13, 14]. The Zn(II) complexes with Schiff bases were also found to be with biological activity and they demon-
strated enhanced activities as compared to their parental ligands [15, 16]. In view of these points above, we designed and managed to synthesize a series of complexes containing both metal zinc(II) ion and the ligands derived from rimantadine and substituted salicylaldehyde. We hoped these zinc complexes could exhibit an extraordinary biological activity. In this work, two four-coordinate zinc(II) complexes [Zn(L1)2Cl2] (I) and [Zn(L2)2Cl2] (II), where L1 = 2-((1-(1-adaman-tan-1-yl)ethyl)-iminomethyl)-4-chlorophenol, L2 = = 2-((1-(1-adamantan-1-yl)ethyl)iminomethyl)-5-me-thoxyphenol, were reported. Their absolute structures were determined by a single-crystal X-ray diffraction analysis. The antibacterial activities of two Schiff base ligands and their complexes against two bacteria of Escherichia coli and Bacillus subtilis were synchronously investigated.
EXPERIMENTAL
Materials and methods. All chemicals and solvents were of analytical grade and used as received. Elemental analysis was carried out on PerkinElmer Flash EA 1112. Chemical shifts (5) for 1H NMR spectra were recorded at 300 MHz on a Varian Mercury-Vx300 spectrometer in CDCl3 solvent containing TMS as an internal standard. Infrared spectrum (IR) was scanned in the range 4000 to
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JIN et al.
400 cm-1 with KBr pellets on a Nicolet NEXUS FT-IR 5700 spectrophotometer. Melting points were measured on a WRS-1B micro melting point apparatus which were uncorrected. The molar conductance of the complexes in DMF (1.0 x 10-3 mol L-1) was measured on a DDS-11A conductormeter.
Synthesis of ligands. Two Schiffbase ligands, 2-((1-(1-adamantan-1-yl)ethyl)-imino-methyl)-4-chlorophenol (L1) and 2-((1-(1-adamantan-1-yl)ethyl)iminometh-yl)-5-methoxyphenol (L2), were prepared analogously to the literatures [17—20]. The synthetic route in this work was shown below:
OHC^^
I ITR
HO
Xjr
C2H5OH
h-O'
R
L1: R = 4-Cl; L2: R = 5-OCH3
Rimantadine hydrochloride (3.0 mmol) and KOH (3.0 mmol) in 50 mL anhydrous alcohol were stirred for 24 h. The produced white precipitates (KCl) were filtered out and the transparent liquid was added drop-wise to aldehyde (3.0 mmol) in 30 mL anhydrous alcohol under constant stirring. The resulting solution was refluxed for ~4 h, concentrated to about 20 mL through reduced pressure distillation and then stood at room temperature. A yellow solid appeared after 2—3 days with the solvent evaporation. The solid was filtered off and washed with anhydrous alcohol three times and air-dried.
Syntheses of the complexes. Zinc(II) chloride (1.0 mmol) in 20 mL anhydrous alcohol was added dropwise to a hot solution of a Schiff base ligand (1.0 mmol) in 20 mL anhydrous alcohol. Thereafter the mixture was refluxed for about 2 h and then kept at room temperature for overnight and complex precipitates were filtered off and dried. The yields were 58% for I and 62% for II.
For C38H48N2O2Cl4Zn (I) (M = 771.99)
anal. calcd., %: C, 59.12; H, 6.27; N, 3.63.
Found, %: C, 58.97; H, 6.16; N, 3.51.
For C40H54N2O4Cl2Zn (II) (M = 763.15)
anal. calcd., %: C, 62.95; H, 7.13; N, 3.67.
Found, %: C, 62.70; H, 6.89; N, 3.63.
The molar conductance values (AM) are 6.10 and 8.64 S cm2 mol-1 for I and II, respectively, which belong to the complex type of non-electrolytes molecular [17].
X-ray structure determination. Suitable crystals of I and II were grown by slow solvent evaporation of anhydrous alcohol. Diffraction data were collected on a Bruker Smart Apex II CCD with graphite mono-chromated MoZ„ radiation (X = 0.71073 A) at 298(2) K using the «-scan technique. The data were integrated by using the SAINT program, which also corrected the intensities for Lorentz and polarization
effect [18]. An empirical absorption correction was applied using the SADABS program [19]. The structures were solved by direct methods using the program SHELXS-97 and all non-hydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares technique using the SHELXL-97 crystallographic software package [20]. The hydrogen atoms were generated geometrically. All calculations were performed on a personal computer with the SHELXL-97 crystallographic software package. The details of the crystal parameters, data collection and refinement are summarized in Table 1. Selected bond lengths and angles with their estimated standard deviations are given in Table 2. The molecular structures, as shown in Fig. 1, were visualized by Diamond [21].
Supplementary material for complexes I and II has been deposited with the Cambridge Crystallographic Data Centre (nos. 886789 (I), 853684 (II); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
The main IR data for I and II are given in Table 3, wherein several main data for ligands are also provided for comparison. Broad and intensity absorptions at 3433-3449 cm-1 for ligands and complexes can be identified as v(O-H) indicating that phenolic hydrox-yls of ligands are not deprotonated when the complexes are formed. The strongest absorptions at 1632 and 1623 cm-1 for ligands as well as 1648 and 1643 cm-1 for the complexes are the characteristics of v(C=N); in metal complexes these bands undergo upward shift by 15 and 20 cm-1. The spectra of the ligands show strong bands at 1279 cm-1 for L1 and 1221 cm-1 for L2, which is fairly certain to v(C-O). In the complexes, this vibration band occurs at slight lower frequency with 1235 cm-1 for I and with 1214 cm-1 for II. The absorptions at 483 and 496 cm-1 for I and II are attributed to v(Zn-O), indicating that oxygens of the Schiff bases are coordinated to Zn.
1H NMR data for I and II in CDCl3 are given in Table 4, where the data for ligands are also provided for
Table 1. Crystal data and structure refinement information for compounds I and II
Parameter Value
I II
Formula weight 771.59 763.12
Crystal system Orthorhombic Orthorhombic
Space group Fdd2 Pbcn
a, A 15.5281(12) 13.2436(14)
b, A 43.024(15) 12.3110(13)
c, A 10.9346(13) 24.888(2)
Volume, A3 7305(3) 4057.8(7)
Z 8 4
Pcalcd mg/m3 1.403 1.249
Absorption coefficient, mm-1 1.001 0.777
/(000) 3232 1616
Crystal size, mm 0.40 x 0.30 x 0.20 0.40 x 0.37 x 0.24
9 Range for data collection, deg 2.37-23.08 3.35-23.12
Limiting indices -18 < h < 15 -15 < h < 14
-50 < k < 49 -14 < k < 11
-12 < l < 12 -29 < l < 29
Reflections collected 7027 19265
Independent reflections (Rint) 3096 (0.0269) 3584 (0.0497)
Data/restraints/parameters 3096/1/199 3584/0/224
Goodness-of-fit on F 2 1.070 1.020
Final R indices (I > 2a(I))* Rx = 0.0405, wR2 = 0.0839 R1 = = 0.0505, wR2 = 0.01190
R indices (all data)* R1 = 0.0490, wR2 = 0.0897 R1 = 0.0930, wR2 = 0.1491
Absorption correction Empirical
Refinement method Full-matrix least-squares on F 2
^ma^Pm™ « A~3 0.24/-0.19 0.49/-0.19
* R = S||F0| - |FC||/|F0|; wR2 = [Sw(F02 - Fc2)2/ Zw(F02)2]^2.
comparison. Singlet peaks at 14.46—12.74 ppm for ligands and complexes are assigned to the phenol
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