Fluorenone Schiff base derivative complexes of ruthenium, rhodium and iridium exhibiting efficient antibacterial activity and DNA-binding affinity

Article abstract of DOI:10.1016/j.jorganchem.2020.121246

Metal precursors [(arene)MCl₂]₂ (arene = p-cymene, Cp?; M = Ru, Rh and Ir) on reacting with 9-fluorenone derivative ligands L1, L2 and L3 resulted in the formation of mononuclear bidentate cationic N∩N bonded complexes. The biological studies of these complexes such as antibacterial activity studies (against Gram-positive and Gram-negative bacteria) revealed significant antibacterial activity with complexes 4, 7 and 9 having the highest activity potency (in-vitro). Whilst for DNA-binding studies, the results revealed that complexes 4 and 5 displayed significant changes in their spectral features upon addition of SM-DNA, thus, indicating that these complexes bind to DNA with a significant affinity.

Full text of DOI:10.1016/j.jorganchem.2020.121246

Journal Pre-proof
Fluorenone Schiff base derivative complexes of ruthenium, rhodium and iridium
exhibiting efficient antibacterial activity and DNA-binding affinity
Mohan Rao Kollipara, Lathewdeipor Shadap, Venkanna Banothu, Nipanshu Agarwal,
Krishna Mohan Poluri, Werner Kaminsky
PII:
S0022-328X(20)30148-0
DOI:
https://doi.org/10.1016/j.jorganchem.2020.121246
JOM 121246
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 7 February 2020
Revised Date: 16 March 2020
Accepted Date: 19 March 2020
Please cite this article as: M.R. Kollipara, L. Shadap, V. Banothu, N. Agarwal, K.M. Poluri, W. Kaminsky,
Fluorenone Schiff base derivative complexes of ruthenium, rhodium and iridium exhibiting efficient
antibacterial activity and DNA-binding affinity, Journal of Organometallic Chemistry (2020), doi: https://
doi.org/10.1016/j.jorganchem.2020.121246.
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Fluorenone Schiff base derivative complexes of ruthenium, rhodium and iridium exhibiting
efficient antibacterial activity and DNA-binding affinity
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Lathewdeipor Shadapa, Venkanna Banothub, Nipanshu Agarwalc, Krishna Mohan Poluric,
Werner Kaminskyd, Mohan Rao Kolliparaa*
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aCentre for Advanced Studies in Chemistry, North-Eastern Hill University, Shillong 793 022,
India. E-mail: mohanrao59@gmail.com
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bCentre for Biotechnology (CBT), Institute of Science & Technology (IST), Jawaharlal Nehru
Technological University Hyderabad (JNTUH), Kukatpally-500 085, Hyderabad, Telangana
State, India.
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cDepartment of Biotechnology and Centre for Nanotechnology, Indian Institute of Technology
Roorkee, Roorkee- 247 667, India.
dDepartment of Chemistry, University of Washington, Seattle, WA 98195, USA.
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Graphical abstract
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Mononuclear cationic complexes containing fluorenone Schiff base derivative ligands were
synthesized. Their coordination, biological activity against Gram-positive and Gram-negative
bacterial strains and their binding affinity towards SM-DNA were investigated.
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Abstract
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Metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) on reacting with
9-fluorenone derivative ligands L1
bidentate cationic N N bonded complexes. The biological studies of these complexes such as
antibacterial activity studies (against Gram-positive and Gram-negative bacteria) revealed
significant antibacterial activity with complexes and having the highest activity potency
in-vitro). Whilst for DNA-binding studies, the results revealed that complexes and displayed
, L2 and L3 resulted in the formation of mononuclear
∩
4,
7
9
(
4
5
significant changes in their spectral features upon addition of SM-DNA, thus, indicating that
these complexes bind to DNA with a significant affinity.
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Keywords: Ruthenium, rhodium, iridium, SM-DNA, in-vitro studies.
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1. Introduction
Schiff base metal complexes caught the attention of many chemists even today, due to
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high yield, mild reaction conditions and the wide applications they contributed to the field of
medicine and pharmaceuticals [1-4]. Many Schiff base ligands have shown good biological
activities such as antibacterial, anticancer, antimicrobial and so on by formation of complexes
with metal precursors, the activity may be enhanced or be suppressed which is a fascinating
research. The most common route in synthesizing new drugs is by designing the ligand moiety so
as to manipulate the solubility of the whole metal complex and their permeability in the
biological membrane [5, 6]. Previous reports have shown that the hydrazone nucleus of Schiff
base condensation serves to be of great interest synthetically as well as biologically [7-9].
Fluorenone based polycyclic aromatic hydrocarbons (PAHs) have been found to exhibit
exemplary biological activity such as antifungal, antitumor and antimicrobial activity [10, 11] as
well as owing to the efficient fluorescent property possessed by them, it has attracted the minds
of researchers working in sensors, displays and other photo electronic devices [12-16].
Metal precursors of ruthenium, rhodium and iridium have been reported to be versatile in
nature owing to their unique properties [17] and exhibit many properties like catalytic,
photochemical and biological activities [18]. The properties possessed by these metal precursors
sparked an interest to investigate the coordination and the biological activity such as antibacterial
study of fluorenone derivative ligands. Knowing that these ligands exhibit efficient fluorescent
property, we are also interested in studying their binding property towards DNA, which could
prove beneficial in medicinal and pharmaceutical fields in the future.
To the best of our knowledge, these complexes containing 9-fluorenone moiety have not
been reported elsewhere. The ligands used in this study have been prepared in two steps as
shown in Scheme 1.
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Scheme 1: Preparation of Ligands L1, L2 and L3.
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2. Experimental
2.1. Materials and Methods
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The reagents required for the synthesis of metal precursors such as α-phellandrene,
pentamethylcyclopentadiene were purchased from Sigma Aldrich. While the reagents in need for
the preparation of the ligands under study i.e., 9-fluorenone, hydrazine hydrate, 2-benzoyl
pyridine, acetyl pyridine and pyridine carbaldehyde were purchased from Spectrochem and Alfa
Aesar. The reagents obtained were of good commercial quality and were used without further
purification. [Cp*MCl2]2 (M = Rh/Ir) complexes were prepared using a synthesizer, Anton par
mono-wave 50 [19].
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To characterize the synthesized complexes, various spectroscopic techniques such as FT-
IR, H NMR, 13C NMR, ESI-mass spectroscopy, UV-Vis, and single-crystal X-ray diffraction
1
techniques were used. NMR spectra were recorded on a Bruker Advance II 400 MHz
spectrometer using CDCl3/DMSO or a mixture of both solvents in some complexes. Infrared
spectra (KBr pellets; 400-4000 cm-1) were recorded on a Perkin-Elmer 983 spectrophotometer.
Mass spectra were recorded with Micromass Quattro II instrument and Agilent 6540 UHD
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Accurate-Mass Q-TOF LC/MS using acetonitrile as the solvent. The absorption spectra for the
complexes were recorded on a Perkin-Elmer Lambda 25 UV-Vis spectrophotometer at room
temperature using acetonitrile as the solvent in the range of 200-600 nm.
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2.2. Structure determination by X-ray Crystallography
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Bruker AXS BV Nonius Kappa CCD diffractometer using graphite monochromatic Mo-
Kα radiation (λ = 0.71073 Å) was used for data collection. The approach for the data collection
was calculated using HKL 2008 software. The structure solution of the complexes was carried
using SIR-92 [20] and refined by a full-matrix least-squares method based on F2 against all
reflections using SHELXL-2014/7 [21]. All Hydrogen atoms were initially located in a
difference Fourier map and were refined with a riding model. Hydrogen atoms were placed in
geometrically idealized positions and constrained to ride on their parent atoms with C-H
distances in the range of 0.95-1.00 . Isotropic thermal parameters Ueq were fixed such that they
were 1.2 Ueq of their parent atom for CH's and 1.5 Ueq of their parent atom in case of methyl
groups. Metal atoms in the complexes were located from E-maps and all non-hydrogen atoms
were refined anisotropically by full-matrix least-squares. Crystallographic and structure
refinement parameters for the complexes and selected bond lengths and bond angles are
presented in Tables 1 and 2. The molecular structures were drawn using ORTEP-3 [22] and
packing pattern and interactions like π-π, H-bonding can be obtained using MERCURY [23].
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2.3. Antibacterial activity study
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All the bacterial strains used in the present study were obtained from the Department of
Microbiology, Osmania General Hospital, Hyderabad and tested for purity by standard
microbiological methods. The bacterial stock cultures used in this study were the Gram-positive
bacteria Staphylococcus aureus (E40) (isolated from exudate) and the Gram-negative bacteria
Escherichia coli (E72) (also isolated from exudate) and Klebsiella pneumoniae (U98) (isolated
from urine) maintained on Mueller-Hinton agar slants and stored at 4˚C. An agar-well diffusion
method [24] was employed for the evaluation of antibacterial activities of test compounds.
DMSO was used as a negative control. The bacterial strains were reactivated from stock cultures
by transferring into Mueller-Hinton broth and incubating at 37 ˚C for 18 h. A final inoculum
containing 106 colonies forming units (1 x 106 CFU/ml) was added aseptically to MHA medium
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and poured into sterile Petri dishes. Different test compounds at a concentration of 200 µg per
well were added to wells (8 mm in diameter). Plates were incubated overnight at 37 ºC and the
zone of inhibition was measured by considering the diameter around each well (mm).
Experiments were performed in triplicates.
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2.4. MIC and MBC
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The minimum inhibitory concentration (MIC) and minimum bactericidal concentration
(MBC) was determined by the micro-broth dilution method done in 96 well plates according to
the standard protocol [25]. A two-fold serial dilution of the compounds, with the appropriate
antibiotic, was prepared. Initially, 100 µL of MH broth was added to each well plate. Then 100
µL of compound or antibiotic was taken from the stock solution and dissolved in the first well
plate. Serial dilution was done to obtain different concentrations. The stock concentrations of
2.0 mg/mL. 24-hour culture turbidity was adjusted to match 0.5 McFarland standards which
correspond to 1×108 CFU/mL. The standardized suspension (100 µl) of bacteria was added to
all the wells except the antibiotic control well and the 96 well plates were incubated at 37 °C for
24 h. After 24-hour of incubation 40 µL of MTT {3-(4,5-dimethlthiazol-2-yl)-2,5-
diphenyltrazolium bromide} reagent (0.1 mg/ml in 1x PBS) was added to all the wells. MIC
was taken as the lowest concentration which did not show any growth which was visually noted
from the blue color developed by MTT. Subcultures were made from clear wells and the lowest
concentration that yielded no growth after subculturing was taken as the MBC.
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2.5. Fluorescence studies on DNA interaction
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DNA binding experiments of the ligand (L2) and complexes (4 and 5) were carried out
using a Fluorimetric assay. All experiments were done with fixed concentration (20 µM) of the
compounds under study while gradually increasing the Salmon melt (SM) DNA concentration
(5-100 ꢀM). For the acquisition of fluorescence emission spectrum at each concentration of
DNA, the parameters used were, λex= 260 nm; λem= 300-500 nm for ligand (L2), and λex= 311
nm; λem= 350-600 nm for complexes
4 and 5. The dissociation constant was quantitatively
analyzed using a ligand-binding model as described elsewhere [26].
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2.6.
General procedure for synthesis of metal complexes (1-9)
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Halide bridged metal precursors [(arene)MCl2]2 (0.1 mmol) and hydrazone derivative
ligands of fluorenone L1, L2 and L3 (0.2 mmol) were taken in dry methanol (10 ml) and initially
stirred at room temperature for 1 hour (Scheme 2) after which NH4PF6 was added where the
compound precipitated out and continued stirring for additional 1 hour. After 2 hours, the
compound was separated by filtration. The complex was washed with cold methanol to wash off
the NH4Cl salt and then with diethyl ether and air dried. All these complexes were of good yield,
air stable and most of the complexes were found to be fairly soluble in polar solvents but
insoluble in non-polar solvents.
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Scheme 2: Synthesis of complexes 1-9
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2.6.1. [(p-cymene)Ru(κ2N∩N-L1)Cl]PF6 (1)
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Yield: (89%); light orange; FT-IR (KBr, cm-1): 1623 (νC=C), 1599 (νC=N), 1442 (νC=C), 839 (νP-F);
1H NMR (400 MHz, CDCl3 + DMSO-d6, ppm) = 8.14 (d, JHH = 8 Hz, 2H), 8.04 (d, JHH = 8 Hz,
2H), 7.68 (d, JHH = 8 Hz, 4H), 7.49 (t, JHH = 8 Hz, 4H), 7.44 (d, JHH = 8 Hz, 3H), 7.26 (t, JHH = 8
Hz, 2H), 5.67 (d, JHH = 8 Hz, 2H, CH(p-cym)), 5.61 (d, JHH = 4 Hz, 2H, CH(p-cym)), 3.06-2.99 (sept,
1H, CH(p-cym)), 2.26 (s, 3H, CH(p-cym)), 1.30 (d, JHH = 8 Hz, 6H, CH(p-cym)); 13C NMR (100 MHz,
CDCl3, ppm) = 161.88, 154.84, 142.26, 141.26, 136.49, 131.42, 131.01, 129.83, 128.22, 122.89,
120.14, 101.19, 96.73, 81.30, 80.52, 30.62, 22.15, 18.95; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1
cm-1)}: 259 (4.05), 360 (1.20), 325 (1.12).
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2.6.2. [Cp*Rh(κ2N∩N-L1)Cl]PF6 (2)
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Yield: (90%); bright orange; FT-IR (KBr, cm-1): 1622 (νC=C), 1599 (νC=N), 1443 (νC=C), 843 (νP-
F); 1H NMR (400 MHz, CDCl3, ppm) = 8.14 (d, JHH = 8 Hz, 2H), 8.02 (d, JHH = 8 Hz, 2H), 7.70
(d, JHH = 8 Hz, 4H), 7.64 (s, 1H), 7.51 (t, JHH = 8 Hz, 2H), 7.44 (t, JHH = 8 Hz, 4H), 7.27 (t, JHH
=
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8 Hz, 2H), 1.73 (s, 15H, CH(Cp*)); 13C NMR (100 MHz, CDCl3 + DMSO, ppm) = 160.84, 153.60,
140.55, 139.50, 130.33, 129.92, 129.38, 128.18, 127.00, 126.91, 124.10, 121.23, 118.99, 118.89,
97.63, 97.55, 7.41; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 260 (2.66), 325 (0.69), 361
(0.77).
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2.6.3. [Cp*Ir(κ2N∩N-L1)Cl]PF6 (3)
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Yield: (81%); yellowish orange; FT-IR (KBr, cm-1): 1622 (νC=C), 1599 (νC=N), 1441 (νC=C), 844
(νP-F); 1H NMR (400 MHz, CDCl3 + DMSO-d6, ppm) = 8.14 (d, JHH = 8 Hz, 2H), 8.05 (d, JHH
=
8 Hz, 2H), 7.66 (d, JHH = 8 Hz, 4H), 7.48 (t, JHH = 8 Hz, 3H), 7.41 (t, JHH = 8 Hz, 4H), 7.25 (t,
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JHH = 8 Hz, 2H), 1.74 (s, 15H, CH(Cp*)); C NMR (100 MHz, CDCl3, ppm) = 166.34, 162.60,
161.03, 154.96, 153.78, 153.26, 149.07, 146.03, 139.86, 128.37, 131.16, 130.31, 129.96, 129.09,
128.28, 127.19, 123.71, 123.37, 122.21, 112.09, 98.73, 98.65, 97.01, 96.94, 9.22; ESI-MS (m/z):
calculated: 687.2, found: 687.4 [M-PF6-Cl]2+; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 260
(3.79), 326 (1.11), 361 (1.13).
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2.6.4. [(p-cymene)Ru(κ2N∩N-L2)Cl]PF6 (4)
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Yield: (85%); dark yellow; FT-IR (KBr, cm-1): 1611 (νC=C), 1587 (νC=N), 1448 (νC=C), 842 (νP-F);
1H NMR (400 MHz, CDCl3 + DMSO-d6, ppm) = 9.74 (d, J = 4 Hz, 1H), 8.33 (t, J = 8 Hz, 1H),
8.26 (d, JHH = 8 Hz, 1H), 7.93 (d, JHH = 8 Hz, 2H), 7.87 (d, JHH = 8 Hz, 2H), 7.64-7.62 (m, 2H),
7.48 (t, JHH = 8 Hz, 1H), 7.31-7.24 (m, 2H), 6.08 (d, JHH = 8 Hz, 1H, CH(p-cym)), 5.80 (d, JHH = 8
Hz, 1H, CH(p-cym)), 5.50 (d, JHH = 4 Hz, 1H, CH(p-cym)), 5.36 (d, JHH = 8 Hz, 1H, CH(p-cym)), 2.97-
2.90 (sept, 1H, CH(p-cym)), 2.45 (s, 3H), 2.14 (s, 3H, CH(p-cym)), 1.29 (d, JHH = 8 Hz, 3H, CH(p
-
cym)), 1.17 (d, JHH = 8 Hz, 3H, CH(p-cym)); 13C NMR (100 MHz, CDCl3 + DMSO, ppm) = 160.40,
156.84, 154.54, 152.44, 142.01, 139.54, 138.17, 133.06, 132.48, 131.79, 127.57, 127.46, 126.34,
126.03, 125.48, 121.94, 120.37, 119.36, 104.75, 96.86, 86.60, 84.95, 82.59, 28.92, 21.46, 18.37,
16.09, 13.20; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 259 (3.92), 312 (1.10).
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2.6.5. [Cp*Rh(κ2N∩N-L2)Cl]PF6 (5)
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Yield: (88%); orange; FT-IR (KBr, cm-1): 1618 (νC=C), 1586 (νC=N), 1450 (νC=C), 841 (νP-F); H
NMR (400 MHz, CDCl3, ppm) = 8.82 (d, JHH = 4 Hz, 1H), 8.22 (t, JHH = 8 Hz, 1H), 8.01 (d, JHH
= 8 Hz, 1H), 7.91 (d, JHH = 8 Hz, 1H), 7.85 (t, JHH = 8 Hz, 1H), 7.72 (d, JHH = 8 Hz, 1H), 7.63 (d,
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JHH = 8 Hz, 1H), 7.56 (t, JHH = 8 Hz, 2H), 7.41 (t, JHH = 8 Hz, 2H), 7.04 (t, JHH = 8 Hz, 1H), 2.47
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(s, 3H), 1.76 (s, 15H, CH(Cp*)); C NMR (100 MHz, CDCl3 + DMSO, ppm) = 159.07, 156.73,
151.65, 151.24, 142.18, 140.31, 139.54, 133.19, 132.94, 132.16, 128.09, 127.83, 127.49, 125.56,
122.05, 119.60, 119.53, 96.96, 96.88, 14.15, 7.88; ESI-MS (m/z): calculated: 570.1, found: 570.3
[M-PF6]+; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 260 (3.29), 317 (1.02).
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2.6.6. [Cp*Ir(κ2N∩N-L2)Cl]PF6 (6)
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Yield: (77%); dark yellow; FT-IR (KBr, cm-1): 1622 (νC=C), 1586 (νC=N), 1446 (νC=C), 843 (νP-F);
1H NMR (400 MHz, CDCl3, ppm) = 9.00 (d, JHH = 8 Hz, 1H), 8.31-8.25 (m, 2H), 8.19-8.15 (m,
1H), 8.03 (d, JHH = 4 Hz, 1H), 7.90-7.87 (m, 2H), 7.75-7.66 (m, 2H), 7.61-7.53 (m, 2H), 7.22 (s,
1H), 2.54 (s, 3H), 1.62 (s, 15H, CH(Cp*)); 13C NMR (100 MHz, CDCl3 + DMSO, ppm) = 161.66,
158.69, 158.09, 157.62, 153.87, 151.28, 151.02, 147.97, 142.74, 142.59, 141.14, 140.24, 139.76,
139.47, 135.62, 135.40, 133.86, 133.48, 132.80, 132.72, 130.39, 129.91, 128.64, 128.49, 128.28,
128.05, 127.81, 127.20, 123.52, 122.89, 121.53, 121.00, 120.15, 119.99, 119.84, 119.23, 119.00,
90.14, 89.76, 12.93, 8.28; ESI-MS (m/z): calculated: 660.2, found: 660.2 [M-PF6]+; UV-Vis
{CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 261 (3.43), 311 (1.00).
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2.6.7. [(p-cymene)Ru(κ2N∩N-L3)Cl]PF6 (7)
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Yield: (87%); brownish yellow; FT-IR (KBr, cm-1): 1617 (νC=C), 1589 (νC=N), 1449 (νC=C), 842
(νP-F); 1H NMR (400 MHz, CDCl3, ppm) = 9.38 (d, JHH = 4 Hz, 1H), 8.22 (s, 1H), 8.06 (t, JHH
=
8 Hz, 1H), 7.92 (t, JHH = 8 Hz, 2H), 7.74 (t, JHH = 8 Hz, 2H), 7.59-7.51 (m, 2H), 7.41-7.30 (m,
3H), 6.96 (t, JHH = 8 Hz, 1H), 5.97 (d, JHH = 8 Hz, 1H, CH(p-cym)), 5.94 (d, JHH = 4 Hz, 1H, CH(p
-
cym)), 5.80 (d, JHH = 8 Hz, 1H, CH(p-cym)), 5.65 (d, JHH = 4 Hz, 1H, CH(p-cym)), 2.97-2.89 (sept, 1H,
CH(p-cym)), 2.24 (s, 3H, CH(p-cym)), 1.23 (t, JHH = 8 Hz, 6H, CH(p-cym)); 13C NMR (100 MHz,
CDCl3, ppm) = 157.68, 157.23, 155.31, 153.47, 153.07, 151.85, 151.42, 143.21, 143.05, 140.57,
138.93, 138.72, 134.09, 134.01, 133.25, 132.76, 132.55, 128.54, 128.33, 128.01, 127.78, 127.30,
127.02, 126.66, 125.56, 123.16, 122.94, 121.04, 119.92, 119.77, 119.45, 106.34, 105.90, 102.54,
99.84, 88.24, 86.40, 85.15, 83.97, 83.32, 30.17, 22.32, 21.28, 20.54, 19.44, 17.50, 17.11; ESI-
MS (m/z): calculated: 554.1, found: 554.3 [M-PF6]+; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-
1)}: 261 (3.46), 321 (1.05).
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2.6.8. [Cp*Rh(κ2N∩N-L3)Cl]PF6 (8)
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Yield: (87%); orange; FT-IR (KBr, cm-1): 1618 (νC=C), 1589 (νC=N), 14450 (νC=C), 842 (νP-F); H
NMR (400 MHz, CDCl3, ppm) = 8.83 (d, JHH = 4 Hz, 1H), 8.27 (s, 1H), 8.14 (t, JHH = 8 Hz, 1H),
7.95 (d, JHH = 8 Hz, 1H), 7.84 (t, JHH = 8 Hz, 2H), 7.61-7.56 (m, 2H), 7.51 (t, JHH = 8 Hz, 1H),
7.40-7.36 (m, 2H), 7.27 (s, 1H), 7.01 (t, JHH = 8 Hz, 1H), 1.76 (s, 15H, CH(Cp*)); 13C NMR (100
MHz, CDCl3 + DMSO, ppm) = 157.27, 155.92, 153.40, 151.21, 150.45, 148.55, 142.26, 139.89,
139.08, 135.51, 133.17, 132.47, 131.97, 130.52, 130.19, 128.90, 128.25, 127.96, 127.59, 126.99,
126.77, 126.29, 123.86, 121.86, 121.48, 120.46, 119.54, 119.31, 118.88, 118.74, 97.70, 97.63,
96.70, 96.62, 7.58; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 260 (3.76), 323 (1.27).
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2.6.9. [Cp*Ir(κ2N∩N-L3)Cl]PF6 (9)
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Yield: (81%); yellow; FT-IR (KBr, cm-1): 1628 (νC=C), 1595 (νC=N), 1451 (νC=C), 840 (νP-F); H
NMR (400 MHz, CDCl3 + DMSO-d6, ppm) = 8.73 (s, 1H), 8.65 (d, JHH = 8 Hz, 1H), 8.00 (d, JHH
= 4 Hz, 3H), 7.80 (d, JHH = 8 Hz, 1H), 7.70-7.63 (m, 2H), 7.47-7.41 (m, 2H), 7.35 (t, JHH = 8 Hz,
13
1H), 7.03-6.98 (m, 1H), 6.85 (t, JHH = 8 Hz, 1H), 1.58 (s, 15H, CH(Cp*)); C NMR (100 MHz,
CDCl3 + DMSO, ppm) = 158.43, 157.36, 156.80, 155.03, 152.58, 151.71, 150.89, 148.78,
142.79, 141.17, 140.21, 139.48, 135.78, 135.10, 133.40, 133.06, 132.49, 130.73, 130.40, 129.94,
129.20, 128.49, 127.91, 127.19, 127.10, 124.07, 122.25, 121.81, 120.75, 119.91, 119.57, 119.07,
118.93, 91.40, 90.06, 89.66, 7.72; UV-Vis {CH3CN, λmax, nm (ε, 104 M-1 cm-1)}: 261 (2.91), 315
(0.91).
230
231
3. Results and discussion
3.1. Synthesis of metal complexes
232
233
234
235
236
237
238
Halide bridged metal precursors on reaction with the respective fluorenone hydrazone
ligands L1, L2 and L3 in dry methanol for 2 hours in the ratio of 1:2, resulted in the formation of
cationic metal complexes 1-9 (Scheme 2). These complexes upon stirring for 1 hour
instantaneously precipitated on the addition of NH4PF6 and stirred further for an additional 1
hour. All these complexes have been isolated as mononuclear cationic bidentate complexes with
ꢁ
PF6 as the counter ion. The ligands coordinated to the metal centers through the imine nitrogen
and the pyridyl nitrogen forming a five-membered ring. All these complexes were isolated in
11

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241
good yield, air-stable and soluble in polar solvents but insoluble in hexane, pet ether and diethyl
ether. Characterization for these complexes was done by various spectroscopic techniques
including X-ray analysis.
242
3.2. FT-IR study
243
244
245
246
247
248
249
250
251
252
The presence of the prominent functional groups in a compound can be easily detected
using FT-IR spectroscopy. In our synthesized complexes, the stretching frequency of C=N was
found to be in the range of 1586-1599 cm-1 while in the case of the free ligands, the stretching
frequency of C=N was found to be in the range of 1601-1608 cm-1. This small decrease in the
stretching frequency of C=N group can be due to the coordination of the ligand via the nitrogen
atom to the metal center which could be the delocalization of electrons. The aromatic carbons
could be well observed in the range 1442-1451 cm-1 and 1610-1628 cm-1. Since the isolated
complexes consist of PF6ꢁ as the counter, its stretching frequency could be observed in the range
at 839-844 cm-1. The presence of the signals of the expected prominent groups, supported the
formation of the complexes.
253
3.3. 1H NMR spectroscopy
1
254
255
256
257
258
259
260
261
262
263
264
265
266
267
The H NMR spectra of the complexes have been provided in the supplementary
information (Figures S1-S9). The signal peaks displayed by this spectroscopic study supported
the coordination of the ligands to the metal centers. The number of proton signals observed,
matched with that of the expected number of proton peaks showing the appearance of the ligand
proton signals as well as p-cymene and Cp* ring protons. All the aromatic protons of the ligands
were observed in the downfield region in the range 8.14-8.65 ppm. In the case of complexes 4-6
,
we observed a very downfield peak in the range 8.82-9.74 ppm, which could be the proton
adjacent to the pyridyl nitrogen. Whilst in the case of complexes 7-9, again the downfield peak in
the range 8.73-9.38 ppm is the signal peak of the imine proton. In complexes 4-6, the presence of
the methyl group could be clearly observed at 2.45 ppm, 2.47 ppm and 2.54 ppm respectively.
The aromatic proton signals of the p-cymene ring of ruthenium complex
splitting i.e, two doublets bearing two protons each at 5.67 ppm and 5.61 ppm while, ruthenium
complexes and , displayed an unusual splitting pattern where we observed four doublets
1, displayed a typical
4
7
containing one proton each in the range 5.36-6.08 ppm. With Regards to the six protons of the
12

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270
271
272
273
274
275
276
277
278
two methyl groups of p-cymene, complexes
1
and
7
showed a doublet and a triplet at 1.30 ppm
showed two doublets at
and 1.23 ppm respectively with six protons each. Whereas, complex
4
1.29 ppm and 1.17 ppm respectively with three protons each. This infrequent pattern is due to the
diastereotopic nature of the metal center when the ligands coordinated to the metal centers [27].
A septet of the isopropyl proton for all the ruthenium complexes 1, 4, 7 was observed around
2.99-3.06 ppm, 2.90-2.97 ppm and 2.89-2.97 ppm respectively and the methyl proton at the
para-position of the p-cymene ring displayed a singlet at 2.26 ppm, 2.14 ppm and 2.24 ppm
respectively. Similarly, for the rhodium and iridium complexes, in addition to the proton peaks
of the ligands, a sharp singlet around 1.58-1.76 ppm was observed corresponding to the methyl
protons of Cp*. Therefore, by observing and studying these expected peaks, NMR data
substantiated the formation of the complexes.
279
3.4. 13C NMR spectroscopy
280
281
282
283
284
285
286
287
288
The spectra of the representative complexes have been given in the supplementary data
(Figures S10-S18). The ligands displayed their aromatic carbon peaks around 112.09-166.34
ppm. A singlet peak of the C=N carbon appeared in the range 157.27-166.34 ppm. The signal
peak of methyl carbon of the complexes of ligand L2 was observed around 14.15-16.09 ppm.
The p-cymene ring carbons were observed in the range 80.52-106.34 ppm while that of the
methyl, methine and isopropyl carbons were observed around 13.20-30.17 ppm respectively. The
methyl carbons of the Cp* ring were observed around 7.41-9.22 ppm and the ring carbons were
observed at 96.62-98.73 ppm. From these results, we can confirm the formation of the complexes
as the significant peaks expected could be detected and observed.
289
3.5. Mass studies of the complexes
290
291
292
293
294
295
296
Mass data of the representative complexes have been provided in the supplementary data
(Figures S19-S22). The molecular masses of the complexes under study were found to be in
accordance with the expected calculated masses. We found that some of the complexes, in
addition to the molecular ion peaks, also showed isotopic peaks too by addition/loss of protons.
The found molecular ion peaks of the analyzed complexes were displayed at m/z: 687.4 (
3), m/z:
570.3 ( ), m/z: 660.2 ( ) and m/z: 554.3 ( 3
5
6
7
) corresponding to [M-PF6]+ except for complex
which corresponded to [M-PF6-Cl]+. These molecular ion peaks observed, indicated the
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297
298
formation of the complexes and showed that the arene rings bonded to the metal center very
strongly as no other fragments were observed corresponding to the fragmented arene rings.
299
3.6. UV-Visible description of metal complexes
300
301
302
303
304
305
306
307
308
309
310
311
312
313
The electronic spectra of the metal complexes give us the knowledge about the electronic
transitions which could be π- π*/ n- π* or charge transfer transitions like LMCT/MLCT. This
study was carried out using acetonitrile as the solvent with 10-4 M concentrations at room
temperature and spectra recorded were provided in the supplementary data (Figure S23). The
metal atoms under study are d6 low spin metals and are at their most reduced oxidation state,
their orbitals of proper geometry are filled which can interact with the empty low-lying π*
orbitals of the ligands which results in metal-to-ligand charge transfer (MLCT) transitions. The
metal-to-ligand charge transfer (MLCT) dπ(M) to π*(L) transitions showing low energy
absorption bands were observed in the range 311-361 nm while the ligand-centered π- π*/ n- π*
transfer corresponding to high energy absorption bands were observed in the range 259-261 nm
[28]. Upon analyzing the spectra, we observed that complexes 1-3 displayed two low energy
absorption bands in the range 325-326 nm and 360-361 nm where the second absorption band
which was not observed in the other complexes could be the contribution from the conjugated
benzene ring of the benzoyl pyridine.
314
3.7. Description of molecular structures of metal complexes
315
316
317
318
319
320
321
322
323
324
325
Though the various spectroscopic techniques give us the information of the desired
complexes, yet, a crystallographic study proves to be a strong ratification giving in-depth
information about the coordination and various bonding bonds in metal complexes. Few of the
complexes have been studied using this study which supported the expected N∩N bonding
modes. The ORTEP diagram of the representative complexes 4, 5, 8 and 9 with atom numbering
are presented in Figures 1-2. The significant crystallographic parameters are listed in Table 1 and
the bond lengths and bond angles of these complexes are given in Table 2. X-ray analysis studies
ꢁ
confirmed the complexes are cationic in nature with PF6 as the counter ion bearing the general
formula [(arene)M(κ2 N-L1)Cl]PF6. The molecular structures obtained, highlighted a typical
N
∩
three-legged “piano stool” geometry where the ligands bonded to the metal centers in a chelating
fashion N∩N forming a five-membered ring and a terminal chloride. In terms of geometry, the d6
14

326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
metal atoms show pseudo octahedral geometry with the arene rings (p-cymene, Cp*) occupying
the three facial coordination while the other three coordination sites are occupied by the two
nitrogen donor atoms of the respective ligands (i.e, the pyridyl nitrogen and the imine nitrogen)
and from the terminal chloride. Complex
4
crystallized in a triclinic system with space group
crystallized in monoclinic systems with space group ‘P21/c’
crystallized along with one dichloromethane solvent molecule. In the
and , the distance between the metal (M) to centroid of the p-
‘P1¯ ’ while complexes
5
,
8
and
9
respectively. Complex
5
representative complexes
4
,
5
,
8
9
cymene/Cp* ring was found to be 1.690 Å, 1.778 Å, 1.771 Å and 1.776 Å respectively. The
metal to pyridyl nitrogen [M(1)-N(1)] bond distances were found to be 2.0751(19) Å, 2.102(3)
Å, 2.1093(18) Å and 2.096(2) Å respectively while the metal to imine nitrogen [M(1)-N(2)]
bond distances of the complexes were found to be 2.0771(18) Å, 2.105(3) Å, 2.1135(18) Å and
2.082(2) Å respectively. The metal to chloride [M(1)-Cl(1)] bond lengths in these complexes
were found to be 2.3896(6) Å, 2.3919(9) Å, 2.3779(6) Å and 2.3792(7) Å respectively. The
measured bond lengths and bond angles for these complexes were found to be analogous to the
previously reported values [29]. The bite angle N(1)-M(1)-N(2) of the respective complexes
4, 5,
8
and was found to be 76.02(7)°, 75.18(10)°, 75.68(7)° and 75.61(8)° while angle N(1)-M(1)-
9
Cl(1) was found to be 84.28(5)°, 85.88(8)°, 86.93(5)° and 84.87(6)° and angle N(2)-M(1)-Cl(1)
was found to be 84.66(5)°, 92.77(8)°, 93.38(5)° and 91.60(6)°. From these molecular data, these
complexes displayed pseudo octahedral geometry.
345
346
347
348
349
350
351
352
The stability of the complexes can be attributed to the interactions within the crystal
lattice between units. These complexes showed intermolecular interactions like hydrogen
interactions and π---π interactions aiding stability. Complex
C28 and C24---C27 at 3.308 and 3.345 respectively) and inter-hydrogen interaction (H6---
Cl1 at 2.669 ), complex showed two inter-hydrogen interactions (H23---Cl1 and H26---Cl1 at
2.896 and 2.778 respectively), complex showed hydrogen interaction (H8C---Cl1 at 2.627
) and complex showed π-π interaction (C21---C22 at 3.387 ) and inter-hydrogen interaction
4 showed π-π interaction (C23----
5
8
9
(H8A---Cl1 at 2.635 ). These interactions have been shown in Figures 3-4.
353
3.8. In-vitro antibacterial assay
354
355
Heterocyclic metal complexes of transition metals have been widely reported to show
potent antibacterial activity and their mechanisms are diversified [30]. In this study, ligands (L1
,
15

356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
L2 and L3) and complexes (1-9) were evaluated for their in-vitro antibacterial activity against
Gram-positive {Staphylococcus aureus(E40)} and Gram-negative {Escherichia coli (E72) and
Klebsiella pneumoniae (U98)} strains. The zone of inhibition (mm) in comparison with
ciprofloxacin (positive control) was given in Figure 5, Table 3 and Figure S24. All the
compounds exhibited potent antibacterial activity against the tested organisms. In-vitro assay
results, revealed that complex
activity against Gram-positive (Staphylococcus aureus). Complex
complex (23 ± 1.19 mm) also showed the highest activity against Gram-negative (Escherichia
coli) while complex (25 ± 1.36 mm) and complex (22 ± 1.06 mm) showed more activity
7
(23 ± 1.16 mm), and complex
9
(21 ± 1.02 mm) displayed
7
(24 ± 1.25 mm) and
4
7
9
against Gram-negative (Klebsiella pneumoniae). Form these results these compounds could be
class and antibacterial agents.
As previously reported by Perez [31], the activity of a compound can be reasoned as
when the cationic metal complexes are diffused to the bacteria, there is an ionic interaction
between the anionic membrane with the cationic complexes which is responsible to the activity
of the complexes. Another factor contributing to the potency of the ligands as well as the
complexes is due to the chelation property of the ligands which reduces the permeability barriers
of the cells. This effect could also increase the penetration of the metal complexes, thereby
disrupts the protein needed for the growth of the bacteria [30]. However, the activity of the tested
compounds has not superseded the activity of the standard Ciprofloxacin for which the actual
mechanism of inhibition can be studied in the future.
The MIC and MBC results were listed in Figure 6 and Table 4. The MIC & MBC values
of the compounds ranged from 0.062 to 1.0 mg/ml against all the three organisms. The MIC &
MBC values of complex
and Klebsiella pneumoniae and 0.125 to 0.25 mg/ml for E. coli the values of complex
complex
4 and complex 5 values ranged from 0.062 to 0.125 mg/ml for S. aureus
4
and
7
. The MIC and MBC values of ciprofloxacin ranging from 0.031 to 0.062 mg/mL and
0.062 to 0.0125 mg/mL against the tested organisms were taken as standard.
Tough, not much explanation can be drawn from this study as to why complexes
4, 7
and
9
showed better antibacterial activity results as compared to others but this could serve to be a
potential research for antibacterial drugs in the future.
385
3.9. DNA binding study
16

386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
The phosphate backbone and the nucleotide bases of a double-stranded DNA is one of the
most preferential sites for metallodrugs. In order to assess the binding characteristics of the
synthesized organometallic complexes, the binding affinities for the synthesized complexes
towards DNA were tested through a fluorescence titration assay by measuring the fluorescence
property of the ligand/complexes. SM-DNA was titrated into a solution containing
ligand/complex(s). Upon addition of DNA to ligand L2, no significant change was observed in
the intensities of its fluorescence spectrum indicating that inherently it does not bind to DNA
with high affinity (Figure 7 (A)). However, the ruthenium complex
4 and the rhodium complex 5
showed significant changes in their spectral features upon the addition of DNA, thus indicating
that these complexes bind to DNA with a significant affinity {Figure 7 (B) and (C)}. It is worth
noting that although the intensities are varied upon the addition of DNA, no significant spectral
shifts are observed. This suggests that the binding mode is probably a grove binding and
electrostatic interactions [32]. Using the hyperbolic equation for ligand binding [25], the
dissociation constants were calculated for both complexes
4
and
5
. The obtained dissociation
suggested that
constants are found to be 54 ± 4 ꢀM for complex and 52 ± 6 ꢀM for complex
4
5
both these complexes bind to SM-DNA with moderate affinity.
402
4. Conclusion
403
404
405
406
407
408
409
410
411
412
413
414
415
We have successfully synthesized complexes of ruthenium, rhodium and iridium
containing 9-fluorenone derivative ligands and characterized by various spectroscopic techniques
as well as studied their biological activity such as antibacterial agents and their affinity to bind to
ꢁ
SM-DNA. Structurally, these complexes were found to be cationic in nature with PF6 as the
counter ion, where the ligands bind to the metal center in a bidentate N∩N chelating manner.
The biological studies demonstrated that these complexes and fluorenone derivative ligands
displayed significant biological activities with complexes
antibacterial activity amongst the tested compounds. Also, the fluorenone derivatives being
florescent, DNA-binding study was studied in which complexes and showed efficient binding
4, 7 and 9 showing the highest
4
5
affinity to SM-DNA which could in future be studied for anticancer as well. The synthesis of
these complexes of 9-fluorenone derivatives proves to be a pioneering mark to the development
of various metallodrugs with this ligand moiety as it can be studied for various biological
inhibition activities and can be further studied at the molecular level.
17

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418
419
Acknowledgments
Lathewdeipor Shadap thanks CSIR, New Delhi, India for providing financial assistance in the
form of JRF, CDRI-Lucknow and Dr. Sanjay Adhikari for Mass analysis, NEHU-SAIF,
Shillong, India for spectral studies.
420
421
422
423
424
425
Appendix A. Supplementary data
CCDC 1982597 (4), 1982596 (5), 1982599 (8) and 1982598 (9) contains the
supplementary crystallographic data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK; Fax: +44 1223 336033.
426
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486
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488
489
Figure 1: ORTEP diagram of complexes
4 and 5 with 50% probability thermal ellipsoids.
Hydrogen atoms (except methyl protons) and counter ions have been omitted for clarity.
490
491
492
493
494
Figure 2: ORTEP diagram of complexes 8 and 9 with 50% probability thermal ellipsoids.
Hydrogen atoms and counter ions have been omitted for clarity.
495
21

496
497
498
499
500
501
Figure 3: Inter-molecular interactions of complexes
(C23----C28 and C24---C27 at 3.308 and 3.345 respectively) and inter-hydrogen interaction
(H6---Cl1 at 2.669 ). Complex shows two inter-hydrogen interactions (H23---Cl1 and H26---
4 and 5. Complex 4 shows π-π interactions
5
Cl1 at 2.896 and 2.778 respectively).
502
503
504
505
506
507
Figure 4: Inter-hydrogen interactions of complexes 8 and 9. Complex 8 shows hydrogen
interaction (H8C---Cl1 at 2.627 ). Complex
9
shows π-π interaction (C21---C22 at 3.387
)
and inter-hydrogen interaction (H8A---Cl1 at 2.635 ).
508
22

509
510
511
Figure 5: Antibacterial studies of ligands and complexes against Gram-positive and Gram-
negative bacteria with Ciprofloxacin as the reference.
512
513
514
515
Figure 6: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration
(MBC) of the ligands and complexes.
23

516
517
518
519
520
Figure 7: The emission profile of ligand (L2) (A), complex 4 (B) and complex 5 (C) at 20 µM
in the presence of increasing concentrations of SM-DNA. The arrows represent the changes in
emission intensity upon addition of SM-DNA.
521
24

522
Table 1: Crystal structure data and refinement of complexes 4, 5, 8 and 9
[4]PF6
[5]PF6
[8]PF6
[9]PF6
Complexes
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C30H29ClF6N3PRu
713.05
100 (2)
0.71073
triclinic
C31H32Cl3F6N3PRh
800.82
100 (2)
0.71073
monoclinic
P 21/c
C29H28ClF6N3PRh
701.87
100 (2)
0.71073
monoclinic
P 21/c
C29H28ClF6IrN3P
791.16
100 (2)
0.71073
monoclinic
P 21/c
P1¯
a (Å)/α (°)
b (Å)/β (°)
11.4358(3)/70.394(2)
11.7250(3)/67.839(2)
14.4559(3)/90.00(3)
13.7703(3)/94.7570(10) 14.1966(2)/98.7490(10) 14.2576(2)/98.7890
(10)
11.6117(2)/90
11.5419(2)/90
c (Å)/γ (°)
12.1334(3)/84.6380(1 16.4670(4)/90.00(3)
0)
17.5295(3)/90
17.6082(2)/90
Volume (Å3)
Z
1418.34(7)
2
3266.66(13)
4
2856.06(8)
4
1.632
2863.58(7)
4
1.835
Density (calc) (Mg/m- 1.67
1.628
3
)
Absorption coefficient 0.77
0.879
0.812
4.876
F(000)
720
1616
0.60 x 0.40 x 0.30
2 to 20°
1416
0.60 x 0.30 x 0.25
2 to 20°
1544
0.25 x 0.22 x0.20
2 to 20°
Crystal size (mm3)
Theta range for data
collection
0.50 x 0.48 x 0.15
2 to 20°
Index ranges
-15<=h<=13,-
15<=k<=15, -
16<=l<=14
11607
6986 [R(int) =
0.0465]
-19<=h<=19, -
18<=k<=16, -
21<=l<=21
13847
8061 [R(int) = 0.0491]
-15<=h<=15, -
17<=k<=18, -
23<=l<=23
12939
7033 [R(int) = 0.0328]
-15<=h<=15, -
19<=k<=17, -
23<=l<=23
12722
7062 [R(int) =
12722]
Reflections collected
Independent
reflections
Completeness to theta 99.9 %
= 25.00°
99.6%
99.8 %
99.9 %
Refinement method
Full-matrix least-
Full-matrix least-
Full-matrix least-
Full-matrix least-
2
2
2
2
squares on F
6986/0/383
squares on F
8061/1/412
squares on F
7033/0/375
squares on F
7062/7/375
Data/restraints/param
eters
Goodness-of-fit on F2
Final R indices
[I>2sigma(I)]
1.005
R1 = 0.0343, wR2 =
0.0818
1.012
R1 = 0.0451, wR2 =
0.1062
1.043
R1 = 0.0337, wR2 =
0.0337
1.054
R1 = 0.0241, wR2 =
0.0533
R indices (all data)
R1 = 0.0435, wR2 =
0.0864
R1 = 0.0735, wR2 =
0.1166
R1= 0.0448, wR2 =
0.0870
R1 = 0.0329, wR2 =
0.0556
Largest diff. peak and 0.759 and -1.425
1.277 and -1.092
1.208 and -1.072
1.420 and -1.786
hole (e.Å-3)
CCDC No.
1982597
1982596
1982599
1982598
2
2
2 2 1/2
523
524
Structures were refined on F0 : wR2 = [Σ[w(F0 - Fc2)2] / Σw(F0 ) ] , where w-1
=
2
2
[Σ(F0 )+(aP)2+bP] and P = [max(F0 , 0) + 2Fc2]/3
25

525
526
Table 2: Selected bond lengths (Å) and bond angles (°) of complexes 4, 5, 8 and 9
Complexes
4
5
8
9
M(1)-CNT
1.690
1.778
1.771
1.776
M(1)-N(1)
2.0751(19) 2.102(3) 2.1093(18) 2.096(2)
2.0771(18) 2.105(3) 2.1135(18) 2.082(2)
M(1)-N(2)
M(1)-Cl(1)
2.3896(6)
84.28(5)
84.66(5)
76.02(7)
2.3919(9) 2.3779(6)
85.88(8) 86.93(5)
92.77(8) 93.38(5)
75.18(10) 75.68(7)
2.3792(7)
N(1)-M(1)-Cl(1)
N(2)-M(1)-Cl(1)
N(1)-M(1)-N(2)
84.87(6)
91.60(6)
75.61(8)
527
528
529
CNT represents the centroid of the arene/Cp* ring and (M = Ru, Rh and Ir).
Table 3: Antibacterial activity (Agar well) of the tested compounds
Compound
Ligand (L1
S. aureus a
15 ± 0.36
16 ± 0.42
20 ± 0.99
17 ± 0.44
16 ± 0.28
18 ± 0.52
14 ± 0.36
17 ± 0.48
15 ± 0.32
23 ± 1.16
20 ± 0.86
21 ± 1.02
32 ± 0.40
E. coli b
K. pneumoniae c
14 ± 0.27
15 ± 0.58
14 ± 0.19
12 ± 0.18
13 ± 0.25
19 ± 0.69
13 ± 0.26
16 ± 0.43
17 ± 0.67
25 ± 1.36
16 ± 0.67
22 ± 1.06
31 ± 0.20
1
)
16 ± 0.48
22 ± 1.16
18 ± 0.76
19 ± 0.82
14 ± 0.19
23 ± 1.19
18 ± 0.55
15 ± 0.39
23 ± 1.08
24 ± 1.25
22 ± 1.12
21 ± 0.97
29 ± 0.15
2
Complex
Complex
Complex
1
2
3
3
4
5
Ligand (L2
)
6
Complex
Complex
Complex
4
5
6
7
8
9
Ligand (L3
)
10
11
Complex
Complex
Complex
7
8
9
12
13
Ciprofloxacin
b
530
531
532
aS. aureus = Staphylococcus aureus (E40); E. coli = Escherichia coli (E72); K. pneumoniae =
cKlebsiella pneumoniae (U98), and Data are means (n = 3) ± Standard deviation of three
replicates.

533
534
Table 4: MIC and MBC of tested compounds
Stock concentration in 2.0 mg/ml
Compound
Names
S. No.
S. aureus a
E. coli b
K. pneumoniae c
MIC
0.5
MBC
1.0
MIC
0.25
MBC
0.5
MIC
0.5
MBC
1.0
1
Ligand (L1)
2
Complex
Complex
Complex
1
2
3
0.25
0.25
0.25
0.25
0.125
0.062
0.125
0.125
0.25
0.25
0.25
0.031
0.5
0.25
0.5
0.25
0.25
0.25
0.25
0.125
0.062
0.125
0.125
0.25
0.5
0.5
3
0.5
0.125
0.125
0.125
0.125
0.25
0.25
0.25
0.25
0.25
0.5
0.5
4
0.5
0.5
5
Ligand (L2
)
)
0.5
0.5
6
Complex
Complex
Complex
4
5
6
0.25
0.125
0.25
0.25
0.5
0.25
0.125
0.25
0.25
0.5
7
8
0.125
0.25
0.25
0.5
9
Ligand (L3
10
11
12
13
Complex
Complex
Complex
7
8
9
0.125
0.25
0.25
0.5
0.5
1.0
0.5
0.25
0.5
0.25
0.062
0.5
Ciprofloxacin
0.062
0.031
0.062
0.125
b
535
536
aS. aureus = Staphylococcus aureus (E40); E. coli = Escherichia coli (E72); K. pneumoniae =
cKlebsiella pneumoniae (U98).
27

Highlights
ꢀ Complexes of fluorenone derivative ligands formed cationic mononuclear coordination.
ꢀ 4, 7 and 9 showed highest antibacterial activity amongst the tested compounds.
ꢀ
Complexes 4 and 5 showed efficient binding affinity to SM-DNA.

Professor K. Mohan Rao
Department of Chemistry
North Eastern Hill University
Shillong 793022
e mail: mohanrao59@gmail.com
mobile: 9436166937 (M)
tel. no. 0364 272 2620
The Editor
JOMC
Declaration of interest statement
'Declarations of interest: none'
Yours truly,
Mohan Rao Kollipara