N. Pravin et al. / Journal of Molecular Structure 1123 (2016) 162e170
163
transition metal complexes were reported owing to their fasci-
nating ability to interact with nucleic acids fabricating them to be
DNA intercalative binders as well as DNA cleavers [8]. These
effective abilities of the metal complexes enthralled the researchers
and fuelled them to research upon such binding interactions with
DNA [9] and proteins [10e12] with the promise of varied applica-
tions that might be helpful in developing a successful probe or
anticancer drug. Moreover, the interaction of complex with DNA
causes an agitation due to the localized MLCT (metal to ligand
charge transfer transition) which makes the complexes colored.
This particular alteration is important which is ideal in providing a
spectroscopic probe.
Throughout the literature, among the reported metal com-
plexes, Schiff base transition metal complexes and their design and
characterization of biological activity are prominent. Many Schiff
base metal complexes having interesting traits in the medicinal and
biological activity were previously reported [13e15]. The present
work is designed based on the nature of co-ligands used and the
geometrical orientation of the complex formed, as they play a vital
role in enhancing the DNA-metal complex interactions [16] as an
improvement from our previously reported works [17]. Thus,
conveying the importance of the ligands in a metal complex, the
same has been proved by experimental data reported in this work.
Throwing light on the above facts, we herein report the syn-
thesis, characterization, DNA binding, DNA cleavage (in the pres-
ence of H2O2) and antimicrobial studies of a series of novel
octahedral complexes containing 1,10-phenanthroline and 2,20-
bipyridyine as ancillary ligands. The compounds are Knoevenagel
condensate Schiff base complexes with Cu(II), Co(II), Ni(II) and
Zn(II) as central metal ions. The obtained results are valuable for
further research in crafting and developing effective antimicrobial
agents and novel DNA probes so as to meet the demands of the
researchers in search of an effective drug.
67.8; H, 4.9; N, 8.5; Ni, 8.9%; Found C, 67.5; H, 4.7; N, 8.2; Ni, 8.8%. IR
data (KBr, cmꢁ1); 1584
n(C]N); 1527 n(eHC]C); 440 (MeN), 524
n
(MeO). MS m/z (%): 654 [Mþ]. LM 10ꢁ3 (ohmꢁ1 cm2 molꢁ1) ¼ 20.4.
lmax (nm) in DMF, 683, 582, 427. meff (BM):3.15.
[ZnL(MA)(bpy)] (4) Yield: 75%, Anal. Calc. for C37H32N4O4Zn: C,
67.1; H, 4.8; N, 8.4; Zn, 9.8%; Found C, 66.8; H, 4.3; N, 8.2; Zn, 9.6%. IR
data (KBr, cmꢁ1); 1608
n
n
(C]N); 1519
(MeO). MS m/z (%): 660 [Mþ]. 1H NMR (
(m); 2.07 (CH3, 6H) (s), 3.17 (CH2) (s), 7.1e9.3 (bpy) (m). 13C NMR (
n
(eHC]C); 451 (MeN), 531
d): 6.9e7.45 (aromatic)
d
,
ppm): 127.8e128.6 (C1 to C3), 132.9 (C4), 136.8 (C5), 110.4 (C6), 175.4
(C7), 136.0 (C8), 127.2e130.0 (C9eC12), 20.4 (C13), 121e155.3
(C14eC18),
174.2
(C19),
38.1
(C20).
LM
10ꢁ3
(ohmꢁ1 cm2 molꢁ1) ¼ 11.8. lmax (nm) in DMF, 302, 339. meff (BM):
diamagnetic.
[CuL(MA)(phen)] (5), Yield: 78%, Anal. Calc. for C39H32CuN4O4:
C, 68.4; H, 4.7; Cu, 9.2; N, 8.1%; Found C, 68.2; H, 4.4; Cu, 9.0; N, 7.9%.
IR data (KBr, cmꢁ1); 1592
n
(C]N); 1517
n
(eHC]C); 448 (MeN),
533
n
(MeO).
MS
m/z (%):683
[Mþ]. 10ꢁ3
LM
(ohmꢁ1 cm2 molꢁ1) ¼ 23.5. lmax (nm) in DMF, 736, 364, 323. meff
(BM): 1.87.
[CoL(MA)(phen)] (6) Yield: 75%, Anal. Calc. for C39H32CoN4O4: C,
68.9; H, 4.7; Co, 8.6; N, 8.2%; Found C, 68.6; H, 4.5; Co, 8.3; N, 8.0%.
IR data (KBr, cmꢁ1); 1609
n
(C]N); 1529
n
(eHC]C); 439 (MeN),
521
n
(MeO).
MS
m/z (%):679
[Mþ]. 10ꢁ3
LM
(ohmꢁ1 cm2 molꢁ1) ¼ 17.5. lmax (nm) in DMF, 656, 567, 461. meff
(BM): 4.89.
[NiL(MA)(phen)] (7)Yield: 76%, Anal. Calc. for C39H32N4NiO4: C,
68.9; H, 4.7; N, 8.2; Ni, 8.6%; Found C, 68.5; H, 4.4; N, 8.1; Ni, 8.3%. IR
data (KBr, cmꢁ1); 1604
n(C]N); 1522 n(eHC]C); 445 (MeN), 516
n
(MeO). MS m/z (%):678 [Mþ]. LM 10ꢁ3 (ohmꢁ1 cm2 molꢁ1) ¼ 13.6.
lmax (nm) in DMF, 678,563,446. meff (BM): 3.18.
[ZnL(MA)(phen)] (8)Yield: 73%, Anal. Calc. for C39H32N4O4Zn: C,
68.2; H, 4.7; N, 8.1; Zn, 9.5%; Found C, 68.1; H, 4.3; N, 7.9; Zn, 9.3%. IR
data (KBr, cmꢁ1); 1598
n
n
(C]N); 1510
(MeO). MS m/z (%):684 [Mþ]. 1H NMR (
(m); 1.7 (CH3, 6H) (s), 3.17 (CH2) (s), 8.4e9.1 (phen) (m). 13C NMR (
n
(eHC]C); 452 (MeN), 526
2. Experimental protocols
d
, ppm): 7.3e9.0 (aromatic)
d
,
The materials and methods, DNA binding, cleavage and anti-
microbial procedures are included in the Supplementary file (S1).
ppm): 127.8e128.6 (C1 to C3), 132.9 (C4), 143.9 (C5), 108.8 (C6), 169.3
(C7), 136.0 (C8), 127.2e130.0 (C9eC12), 11.7 (C13), 126e146.7
(C14eC18),
174.2
(C19),
38.1
(C20).
LM
10ꢁ3
2.1. Synthesis of metal complexes
(ohmꢁ1 cm2 molꢁ1) ¼ 22.3. lmax (nm) in DMF, 312, 351. meff (BM):
diamagnetic.
The Schiff base ligand L was synthesized using a method pre-
viously reported by us [18]. The Schiff base L (5 mmol) was dis-
solved in ethanol and to this solution, a solution of M(II) chloride
(5 mmol) (M ¼ Cu, Co, Ni, Zn) in ethanol was added dropwise while
stirring continuously. After the reaction for 1 h at 60 ꢀC, a solution
of malonic acid (5 mmol) in ethanol was added. The reaction so-
lution was then refluxed for 2 h. To the resultant mixture, 1,10-
phenanthroline/2,20-bipyridine (5 mmol) was added slowly and
the reaction solution was magnetically stirred and refluxed in a
rotamantle for 3 h. The reaction mixture was then cooled to an
ambient temperature and the obtained solid was filtered, washed
with diethyl ether and finally dried in vacuum. The outline of the
synthesis of the metal complexes is given in Scheme 1.
3. Results and discussion
Scheme 1 portrays the synthetic pathway in the formation of
Schiff base and its corresponding complexes. The ligand and its
complexes are found to be air stable. The ligand is soluble in
common organic solvents but the complexes are soluble only in
DMF and DMSO.
3.1. Elemental analysis and molar conductivity measurements
The data obtained from elemental analysis for the metal com-
plexes 1e8 agree well with the assigned formulae of the proposed
structure showing that all the complexes are in equimolar ratios
(Primary ligand: metal: Malonic acid: co-ligand). These mixed
ligand complexes are of the type [ML(MA)(bpy)] and [ML(MA)(-
phen)] wherein L is the Knoevenagel Schiff base; MA is malonic
acid; bpy is 2,20-bipyridine; phen is 1,10-phenanthroline. The metal
complexes were dissolved in DMSO, and the molar conductivities of
10ꢁ3 mol dmꢁ3 of the solution at 25 ꢀC were measured. The molar
conductance data of the mixed ligand complexes fall within the
range (11.8e23.5 Uꢁ1 cm2 molꢁ1) that signifies the nature of the
complexes to be non-electrolytic [19]. The chloride ion is absent in
the ionization sphere of the complexes and is confirmed by the
[CuL(MA)(bpy)] (1) Yield: 77%, Anal. Calc. for C37H32CuN4O4: C,
67.3; H, 4.8; Cu, 9.6; N, 8.4%; Found C, 67.1; H, 4.6; Cu, 9.4; N, 8.2%. IR
data (KBr, cmꢁ1); 1602
n(C]N); 1521 n(eHC]C); 443 (MeN), 528
n
(MeO). MS m/z (%): 659 [Mþ]. LM 10ꢁ3 (ohmꢁ1 cm2 molꢁ1) ¼ 19.1.
lmax (nm) in DMF, 720, 380, 316. meff (BM): 1.83.
[CoL(MA)(bpy)] (2) Yield: 72%, Anal. Calc. for C37H32CoN4O4: C,
67.7; H, 4.9; Co, 8.9; N, 8.5%; Found C, 67.4; H, 4.5; Co, 8.7; N, 8.2%. IR
data (KBr, cmꢁ1); 1597
n(C]N); 1515 n(eHC]C); 437 (MeN), 518
n
(MeO). MS m/z (%): 655 [Mþ]. LM 10ꢁ3 (ohmꢁ1 cm2 molꢁ1) ¼ 14.2.
lmax (nm) in DMF, 667, 578, 441. meff (BM): 4.85.
[NiL(MA)(bpy)] (3) Yield: 79%, Anal. Calc. for C37H32N4NiO4: C,