Synthesis and crystal structures of sterically tuned ether functionalized NHC-silver(I) complexes: Antibacterial and nucleic acid interaction studies

Article abstract of DOI:10.1080/00958972.2014.931575

A series of new imidazolium salts (1-4) as N-heterocyclic carbene (NHC) precursors have been synthesized by successive N-alkylation method. Reactions of these salts with Ag₂O by varying the metal to salt ratio forms a series of new Ag(I)-NHC co

Full text of DOI:10.1080/00958972.2014.931575

This article was downloaded by: [Pennsylvania State University]
On: 05 June 2014, At: 20:34
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Journal of Coordination Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gcoo20
Synthesis and crystal structures of sterically tuned
ether functionalized NHC-silver(I) complexes;
Antibacterial and nucleic acid interaction studies
Rosenani A. Haquea, Patrick O. Asekunowoa & Mohd. R. Razalia
a The School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
Accepted author version posted online: 05 Jun 2014.Published online: 05 Jun 2014.
Click for updates
To cite this article: Rosenani A. Haque, Patrick O. Asekunowo & Mohd. R. Razali (2014): Synthesis and crystal structures of
sterically tuned ether functionalized NHC-silver(I) complexes; Antibacterial and nucleic acid interaction studies, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2014.931575
To link to this article: http://dx.doi.org/10.1080/00958972.2014.931575
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service
to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting,
typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of
the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the
content, and all legal disclaimers that apply to the journal relate to this version also.
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://dx.doi.org/10.1080/00958972.2014.931575
Synthesis and crystal structures of sterically tuned ether functionalized
NHC-silver(I) complexes; Antibacterial and nucleic acid interaction studies
ROSENANI A. HAQUE*, PATRICK O. ASEKUNOWO and MOHD. R. RAZALI
The School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
A series of new imidazolium salts (1-4) as N-heterocyclic carbene (NHC) precursors have been
synthesized by successive N-alkylation method. Reactions of these salts with Ag2O by varying
the metal to salt ratio forms a series of new Ag(I)-NHC complexes (5-8). All compounds were
characterized by physico-chemical and spectroscopic techniques. The molecular structures of 1
and 5 were characterized by single crystal X-ray diffraction analysis. A comparative
investigation of the bacterial growth inhibition potential of the salts and respective complexes
indicates that 5-8 displayed good antibacterial activities on Staphylococcus aureus (ATCC
12600) and Escherichia coli (ATCC 11303) compared with the salts. Furthermore, it was
observed that with increase in chain length at N-positions the antibacterial activities also
increased. Nuclease activity of the reported salts and Ag(I)–NHC complexes with nucleic acids
(DNA and RNA) were also studied using agarose gel electrophoresis; the results show that the
compounds do not have any apparent interaction with nucleic acids in the absence of hydrogen
peroxide (H2O2). However, 5 and 8 were efficient in promoting the cleavage of nucleic acids in
the presence of H2O2.
Keywords: Ag(I)-NHC complexes; Antibacterial activity; DNA cleavage, N-Heterocyclic
carbene; X-ray diffraction
1. Introduction
Treatment of infectious diseases is becoming a global problem because of increasing numbers of
multi drug resistant pathogenic bacteria [1, 2]. This has underscored the need for new
antimicrobial compounds that will effectively treat resistant bacteria diseases [3, 4]. Silver has
*Corresponding author. Email: rosenani@usm.my
1

been known as a potent antimicrobial agent for centuries [5]. Silver salts are employed especially
in the treatment of extensive burns, chronic ulcers, and for prevention of conjunctivitis in
addition to bacterial infections [6]. Many NHC silver compounds have been synthesized; Youngs
and coworkers in 2004 reported the first Ag(1)-NHC complexes possessing antimicrobial
activity [7]. The search for more biologically active Ag(I)-NHC complexes led to synthesis of
modified caffeine silver acetate complex [8]. Ghosh and co-workers also synthesized Ag(I)-NHC
complexes of 1-benzyl-3-tert-butylimidazolium chloride and tested on analytically important
microorganisms [9]. The Ag(I)-NHC complexes derived from 4,5-dichloroimidazole have been
synthesized with having water stability for up to three days and this was attributed to the
presence of electron-withdrawing substituents present on the 4- and 5-positions of the imidazole
ring [10]. Varieties of functionalized NHC complexes with bidentate chelating NHCs, tripodal
NHCs and pincer type NHCs have also been investigated [11-15] especially in catalysis while
their antimicrobial properties are less explored. The effectiveness of the antimicrobial properties
of Ag(I) complexes may be influenced by the type of ligands that bind to Ag(I) [16]. Type of
substituents and chain length of alkyl chain have a significant effect on their antimicrobial
properties [17, 18]. Modification of NHCs can be easily achieved by introducing functional
groups at the nitrogens of the imidazole ring [11-13], thereby fine-tuning features like
lipophilicity, charge, solubility of the spacers (bridging groups) and substituents. This has
stimulated the design of complexes, reaching a compromise between biological activity and toxic
effects [19]. A very interesting characteristic of NHC chemistry is the ease with which a number
of complexes with similar structures and different lipophilicity can be prepared by changing the
substituents on the imidazolium salts [20, 21]. The lipophilicity of a substance is an influential
parameter in biological activity [11-13]. Increased lipophilicity of some compounds have been
found to have positive correlation with their antibacterial activity [22, 23]. Also found low
viscosity of a compound showed a higher antimicrobial activity [24, 25] and ether group with a
lipophilic property and electron donating ability into cations can help to reduce viscosities,
melting point and reducing degradation, thus retaining the antibacterial effect over a longer
period of time [26, 27]. In view of the above observations, the antibacterial and nuclease
activities of ether functionalized imidazolium salts and their respective Ag(I)-NHC complexes
are hereby investigated.
2

2. Experimental
2.1. Materials and measurements
All chemicals were reagent grade and used as received. NMR spectra were recorded on a Bruker
500 MHz spectrometer at RT in DMSO-d6, using TMS as an internal standard. FTIR spectra
were recorded on a Perkin Elmer-2000 spectrometer from 4000–400 cm-1. Elemental analyses
were carried out on a Perkin-Elmer series II, 2400 microanalyzer. Melting points were measured
using a Stuart Scientific SMP-1 (UK) instrument. The instruments are available at The School of
Chemical Sciences, Universiti Sains Malaysia (USM). The X-ray single crystal structure analysis
was obtained using a Bruker Smart ApexII-2009 CCD area detector diffractometer.
2.2. Synthesis of 1,4-bis(3-methoxyethylimidazol-1-ylmethyl)benzene hexafluorophosphate (1)
A mixture of imidazole (2.00 g, 29.38 mmol) and KOH (2.47 g, 44.03 mmol) in DMSO (30 mL)
was stirred for 1 h at RT. 1-Bromo-2-methoxyethane (4.08 g, 29.38 mmol) was then added
dropwise to the reaction mixture. After 2 h the mixture was poured into 200-300 mL of water
and extracted with chloroform (3×30 mL). The extract was filtered twice through four plies of
Whatman filter papers in order to dry the extract. The process of filtration was repeated thrice to
collect a clear solution of the desired compound, and the solvent was removed under reduced
pressure to obtain thick colorless oil. The compound formed, N-methoxyethyl imidazole (0.5 g,
3.97 mmol) was added dropwise in a stirring solution of 1,4-bis(bromomethyl)benzene (0.52 g,
1.98 mmol) in acetonitrile (30 mL) and then refluxed for 24 h. The solvent was removed under
reduced pressure to give 1,4-bis(N-methoxyethylimidazol-1-ylmethyl)benzene dibromide which
was then reacted with a solution of KPF6 (0.73 g, 3.97 mmol) in methanol (20 mL). The mixture
was stirred at RT for 3 h and allowed to stand overnight. Then the solvent was removed under
reduced pressure and the resultant white powder was washed with distilled water (3×10 mL) to
remove unreacted KPF6, and air dried. The powder was recrystallized in a solution of
acetonitrile/methanol to obtain colorless crystals. Yield: 0.8 g (63%). Melting point: 168-170 °C;
1H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 3.28 (s, 6H, OCH3); 3.70 (t, J = 5.0 Hz, 4H,
CH2-OCH3); 4.37 (t, J = 5.0 Hz, 4H, 2 × N-CH2); 5.46 (s, 4H, 2 × N-CH2 –Benzylic); 7.48 (s,
4H, Ar-H); 7.75 (s, 4H, 2 × imidazolium H4΄, H5΄); 9.27 (s, 2H, 2 × imidazolium H2΄);
13C {1H} NMR (125 MHz, DMSO-d6, 298 K, δ ppm): 49.0 (N-CH2), 51.5 (CH2), 58.0 (CH3),
69.4 (CO), 122.3 (imidazolium C5΄), 123.2 (imidazolium C4΄), 128.8, 135.4 (Ar-C), 136.5
3

(imidazolium C2΄). FTIR (KBr disc) cm-1: 3405 (Caliph–Nimidazole), 3128 (C–Harom), 2960
(C−Haliph), 1127 (Carom–Nimidazole), 1357, 1165 cm-1 (C-O-C, C-O) Anal. Calc. for
C20H28N4F12O2P2: C, 37.2; H, 4.3; N, 8.1. Found: C, 37.3; H, 4.5; N, 8.3.
2.3. Synthesis of 1-methoxylethyl-3-propylimidazolium hexafluorophosphate (2)
A mixture of imidazole (1.70 g, 25.00 mmol) and KOH (1.96 g, 35.00 mmol) in DMSO (30 mL)
was stirred for 1 h at room temperature. 1-Bromo-2-methoxyethane (3.48 g, 25.00 mmol) was
added dropwise to the reaction mixture. After 2 h, the mixture was poured into 200-300 mL of
water and extracted with chloroform (3×30 mL). The extract was filtered thrice through four
plies of Whatman filter papers in order to dry the extract. The process of filtration was repeated
thrice to collect clear solution of the desired filtrate, and the solvent was removed under reduced
pressure to obtain thick colorless oil. The compound formed, N-methoxyethyl imidazole (0.90 g,
7.14 mmol) was added dropwise in a stirring solution of 1-bromopropane (0.88 g, 7.14 mmol) in
acetonitrile (30 mL) and refluxed for 20 h. The solvent was removed under reduced pressure to
give 1-methoxylethyl-3-propylimidazolium dibromide which was then reacted with a solution of
KPF6 (0.60 g, 3.26 mmol) in methanol (20 mL). The mixture was stirred at room temperature for
3 h and allowed to stand overnight. Then the solvent was removed under reduced pressure and
the resultant white powder was washed with distilled water (3×5 mL) to remove unreacted KPF6,
and air dried. The powder was purified by acetonitrile/dichloromethane and obtained as white
1
solid. Yield: 1.7 g (78%). Melting point: 115-117 °C; H NMR (500 MHz, DMSO-d6, 298 K,
δ ppm): 0.80 (t, J = 7.5 Hz, 3H, CH3), 1.78 (m, 2H, -CH2-CH3), 3.22 (s, 3H, OCH3), 3.68 (t, J =
5.0 Hz, 2H, CH2-OCH3), 4.15 (t, J = 7.0 Hz, 2H, N-CH2-CH2-CH3), 4.36 (t, J = 5.0 Hz, 2H,
N-CH2-CH2-OCH3), 7.71 (s, H, imidazolium H5΄), 7.74 (s, H, imidazolium H4΄), 9.17 (s, H,
13
imidazolium H2΄), C {1H} NMR (125 MHz, DMSO-d6, 298 K, δ ppm): 10.2 (CH3); 22.8
(CH2-CH3); 46.3 (OCH3); 48.6 (CH2-OCH3); 50.4 (N-CH2-CH2-CH3); 57.9 (N-CH2-CH2-
OCH3); 70.8 (CO); 122.2 (imidazolium C5΄); 122.6 (imidazolium C4΄); 135.9 (imidazolium
C2΄). FTIR (KBr disc): 3416 (Caliph–Nimidazole), 3148 (C–Harom), 2965 (C–Haliph), 1130
(Carom−Nimidazole), 1355, 1160 cm-1 (C-O-C, C-O) Anal. Calc. for C9H17N2OF6P: C, 34.4; H, 5.4;
N, 8.9. Found: C, 34.6; H, 5.6; N, 9.2.
4

2.4. Synthesis of 1-methoxylethyl-3-butylimidazolium hexafluorophosphate (3)
Salt 3 was prepared in an analogous fashion to 2 but instead of 1-bromopropane, 1-bromobutane
(0.88 g, 7.14 mmol) was added. Salt 3 was isolated as a white solid. Yield: 0.8 g (63%). Melting
point: 120-122 °C. 1H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 0.80 (t, J = 7.5 Hz, 3H, CH3);
1.30 (m, 2H, -CH2-CH3); 1.78 (m, 2H, N-CH2-CH2); 3.22 (s, 3H, OCH3); 3.68 (t, 2H, J =
5.0 Hz, CH2-OCH3); 4.15 (t, 2H, J = 7.0 Hz, N-CH2-CH2-CH3); 4.36 (t, J = 5.0 Hz, 2H, N-CH2-
CH2-OCH3); 7.71 (s, H, imidazolium H5΄); 7.74 (s, H, imidazolium H4΄); 9.17 (s, H,
imidazolium H2΄). 13C {1H} NMR (125 MHz, DMSO-d6, 298 K, δ ppm): 10.2 (CH3), 22.8 (CH2-
CH3), 46.3 (OCH3), 48.6 (CH2-OCH3), 50.4 (N-CH2-CH2-CH3), 57.9 (N-CH2-CH2-OCH3), 70.8
(CO), 122.2 (imidazolium C5΄), 122.6 (imidazolium C4΄), 135.5 (imidazolium C2΄). FTIR (KBr
disc): 3406 (Caliph–Nimidazole), 3188 (C–Harom), 2995 (C–Haliph), 1125 (Carom–Nimidazole), 1307,
1170 cm-1 (C-O-C, C-O) cm-1. Anal. Calc. for C10H19N2OF6P: C, 36.6; H, 5.8; N, 8.5. Found: C,
36.9; H, 6.0; N, 8.8.
2.5. Synthesis of 1-methoxylethyl-3-pentylimidazolium hexafluorophosphate (4)
Salt 4 was prepared in an analogous fashion to 2 but instead of 1-bromopropane,
1-bromopentane (0.97 g, 6.40 mmol) was added. Salt 4 was isolated as a white solid. Yield:
1
0.85 g (65%). Melting point: 125-127 °C. H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 0.90
(t, J = 7.5 Hz, 3H, CH3); 1.25 (m, 2H, -CH2-CH3); 1.35 (m, 2H, -CH2-CH2-CH3); 1.85 (m, 2H,
N-CH2-CH2); 3.30 (s, 3H, OCH3), 3.80 (t, J = 5.0 Hz, 2H, CH2-OCH3), 4.25 (t, J = 7.0 Hz, 2H,
N-CH2), 4.45 (t, J = 5.0 Hz, 2H, N-CH2-CH2-OCH3), 7.85 (s, H, imidazolium H5΄), 7.90 (s, H,
13
imidazolium H4΄), 9.37 (s, H, imidazolium H2΄), C {1H} NMR (125 MHz, DMSO-d6, 298 K,
δ ppm): 10.2 (CH3), 22.8 (CH2-CH3), 46.3 (OCH3), 48.6 (CH2-OCH3), 50.4 (N-CH2-CH2-CH3),
57.9 (N-CH2-CH2-OCH3), 70.8 (CO), 122.2 (imidazolium C5΄), 122.6 (imidazolium C4΄), 135.9
(imidazolium C2΄), FTIR (KBr disc): 3416 (Caliph–Nimidazole), 3178 (C–Harom), 2999 (C–Haliph),
1129 (Carom–Nimidazole), 1327, 1170 cm-1 (C-O-C, C-O). Anal. Calc. for C11H21N2OF6P: C, 40.5;
H, 6.4; N, 8.6. Found: C, 40.8; H, 6.7; N, 8.9.
5

2.6.
Synthesis
of
1,4-bis(3-methoxyethylimidazol-1-ylmethyl)benzenesilver(I)
bis(hexafluorophosphate) (5)
Ag2O (0.35 g, 1.5 mmol) was added to a solution of 1 (0.48 g, 0.75 mmol) in acetonitrile
(35 mL) and the mixture was kept stirring at 50-60 °C for 18 h, covered from light. The mixture
was then filtered through a pad of celite and the resulting colorless solution was evaporated to
give a white solid which was redissolved in acetonitrile, followed by reduction of solvent to
about 3 mL. Addition of diethyl ether reprecipitated 5 as a white solid. Yield: 0.5 g (56%).
Single crystals of 5 suitable for X-ray were obtained by slow diffusion of diethyl ether into
1
acetonitrile solution containing the complex. Melting point: 216-218 °C; H NMR (500 MHz,
DMSO-d6, 298 K, δ ppm): 3.17 (s, 12H, 4 × OCH3); 3.69 (t, J = 5.5 Hz, 8H, 4 × CH2-OCH3);
4.35 (t, J = 5.0 Hz, 8H, 4 × N-CH2); 5.31 (s, 8H, 4 ×N-CH2 –Benzylic); 7.15 (s, 8H, Ar-H); 7.49
13
(s, 4H, 2 × imidazolium H5΄); 7.55 (s, 4H, 2 × imidazolium H4΄); C {1H} NMR (125 MHz,
DMSO-d6, 298 K, δ ppm): 50.8 (N-CH2), 53.6 (CH2); 58.1 (CH3); 71.4 (CO); 122.1
(imidazolium C5΄); 122.8 (imidazolium C4΄); 127.6, 137.1 (Ar-C); 179.9 (imidazolium C2΄-Ag).
FTIR (KBr disc) cm-1: 3440 (Caliph–Nimidazole), 3198 (C–Harom), 2985 (C–Haliph), 1327
(Carom−Nimidazole), 1357, 1165 cm-1 (C-O-C, C-O), Anal. Calc. for C40H52N8Ag2O4F12P2: C, 39.5;
H, 4.3; N, 9.2. Found: C, 39.7; H, 4.4; N, 9.3.
2.7. Synthesis of 1-methoxylethyl-3-propylimidazoliumsilver(I) hexafluorophosphate (6)
Ag2O (0.37 g, 1.60 mmol) was added to a solution of 2 (0.5 g, 1.60 mmol) in acetonitrile
(35 mL) and the mixture was stirred at 50-60 °C for 12 h, covered from light. The mixture was
then filtered through celite and the resulting colorless solution was evaporated to give a white
solid which was redissolved in acetonitrile, followed by reduction of solvent to about 3 mL.
Addition of diethyl ether re-precipitated the product as white solid. Single crystals of 6 suitable
for X-ray were obtained by ether diffusion. Yield: 0.85 g (88%). Melting point: 172-174 °C;
1H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 0.88 (t, J = 7.5 Hz, 6H, 2 × CH3); 1.82 (m, 4H,
2 × -CH2-CH3); 3.25 (s, 6H, 2 × OCH3); 3.69 (t, J = 5.0 Hz, 4H, 2 × CH2-OCH3); 4.11 (t, J =
7.0 Hz, 4H, 2 × N-CH2-CH2-CH3); 4.32 (t, J = 5.0 Hz, 4H, 2 × N-CH2-CH2-OCH3); 7.48 (s, H,
13
imidazolium H5΄); 7.50 (s, H, imidazolium H4΄). C {1H} NMR (125 MHz, DMSO-d6, 298 K,
δ ppm): 10.8 (CH3), 24.5 (CH2-CH3), 46.3 (OCH3), 50.7 (CH2-OCH3), 52.5 (N-CH2-CH2-CH3),
58.1 (N-CH2-CH2-OCH3); 71.4 (CO), 121.7 (imidazolium C5΄); 122.2 (imidazolium C4΄); 179.3
6

(imidazolium Ag-C2΄). FT-IR (KBr disc) cm-1: 3458 (Caliph–Nimidazole), 3187 (C–Harom), 2995
(C−Haliph), 1336 (Carom–Nimidazole), 1355, 1160 cm-1 (C-O-C, C-O). Anal. Calc. for
C18H32N4AgO2F6P: C, 36.7; H, 5.4; N, 9.5. Found: C, 36.8; H, 5.5; N, 9.7.
2.8. Synthesis of 1-methoxylethyl-3-butylimidazoliumsilver(I) hexafluorophosphate (7)
Complex 7 was prepared in an analogous fashion to 6 except that 2 was replaced with 3 (1.00 g,
3.20 mmol) and Ag2O (0.72 g, 3.20 mmol). Yield: 0.95 g (53%). Single crystals suitable for
X-ray were obtained by slow diffusion of diethyl ether into acetonitrile solution containing the
complex. Melting point: 178-180 °C; 1H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 0.88 (t, J =
7.5 Hz, 6H, 2 × CH3); 1.30 (m, 4H, 2 × -CH2-CH3); 1.82 (m, 4H, 2 ×N-CH2-CH2); 3.25 (s, 6H,
2 × OCH3); 3.69 (t, J = 5.0 Hz, 4H, 2 × CH2-OCH3,); 4.11 (t, J = 7.0 Hz, 4H, 2 × N-CH2-CH2-
CH3); 4.32 (t, J = 5.0 Hz, 4H, 2 × N-CH2-CH2-OCH3); 7.48 (s, H, imidazolium H5΄); 7.50 (s, H,
13
imidazolium H4΄); C {1H} NMR (125 MHz, DMSO-d6, 298 K, δ ppm): δ 10.8 (CH3); 24.5
(CH2-CH3); 46.3 (OCH3); 50.7 (CH2-OCH3); 52.5 (N-CH2-CH2-CH3); 58.1 (N-CH2-CH2-
OCH3); 71.4 (CO); 121.7 (imidazolium C5΄); 122.2 (imidazolium C4΄); 177.97 & 179.56 [(d,
1
1J(C-109Ag) = 198.5 Hz and d, J(C-107Ag) = 185.0 Hz]. 3406 (Caliph–Nimidazole); 3188 (C–Harom);
2995 (C–Haliph); 1275 (Carom-Nimidazole); 1307, 1170 cm-1 (C-O-C, C-O). Anal. Calc. for
C20H36N4AgO2F6P: C, 38.8; H, 5.8; N, 9.1. Found: C, 39.0; H, 6.0; N, 9.2.
2.9. Synthesis of 1-methoxylethyl-3-pentylimidazoliumsilver(I) hexafluorophosphate (8)
Complex 8 was prepared according to the same procedure for 7 except that 2 was replaced with 4
(0.80 g, 2.90 mmol) and AgO2 (0.67 g, 2.90 mmol). White solid. Yield: 0.55 g (51%). Melting
1
point: 184-186 °C. H NMR (500 MHz, DMSO-d6, 298 K, δ ppm): 0.90 (t, J = 7.5 Hz, 6H,
2 × CH3); 1.25 (m, 4H, 2 × -CH2-CH3); 1.35 (m, 4H, 2 × -CH2-CH3) 1.85 (m, 4H, 2 ×
CH2-CH2); 3.30 (s, 6H, 2 × OCH3), 4.15 (t, J = 5.0 Hz, 4H, 2 × CH2-OCH3,); 4.30 (t, J = 7.0 Hz,
4H, 2 × N-CH2-CH2-CH3); 4.72 (t, J = 5.0 Hz, 4H, 2 × N-CH2-CH2-OCH3); 7.90 (s, H,
13
imidazolium H5΄); 7.95 (s, H, imidazolium H4΄). C {1H} NMR (125 MHz, DMSO-d6, 298 K,
δ ppm): 10.2 (CH3); 22.8 (CH2-CH3); 46.3 (OCH3); 48.6 (CH2-OCH3); 50.4 (N-CH2-CH2-CH3);
57.9 (N-CH2-CH2-OCH3) 70.8 (CO), 122.2 (imidazolium C5΄), 122.6 (imidazolium C4΄), 180.0
(imidazolium Ag-C2΄). FTIR (KBr disc): 3456 (Caliph–Nimidazole), 3198 (C–Harom), 2999
7

(C−Haliph), 1349 (Carom–Nimidazole), 1327, 1170 cm-1 (C-O-C, C-O) Anal. Calc. for
C20H36N4AgO2F6P: C, 38.9; H, 5.8; N, 9.1. Found: C, 40.3; H, 6.1; N, 9.3.
2.10. Antibacterial studies
Stock solutions of all compounds were prepared by using DMSO. Antibacterial tests were
performed using the Kirby Beur disc diffusion method [28]. Single colonies of Escherichia coli
(ATCC 11303) and Staphylococcus aureus (ATCC 12600) from fresh culture agar plates were
respectively cultured in two bottles containing 5 mL nutrient broth solution and incubated
overnight at 37 °C. The turbidity of each culture was adjusted by comparing it to 0.5 McFarland
standard, which is equal to 1.58 × 108 CFU/mL or 0.5 (O.D600 reading). Using sterile cotton
buds, each bacterial lawn culture was spread uniformly on different agar plates before placing
the antimicrobial assay discs on the plate. Four discs were placed on each agar plate and 5 µL
volumes of the test compounds were loaded on the discs with concentrations at 100 and
50 µg/mL. The plates were incubated at 37 °C for 24 h and the diameters of inhibition zones
were measured in mm. The antibacterial test was calculated as the mean of three replicates. The
effectiveness of these compounds in relation to inhibition zone was compared with silver nitrate,
based on its established antimicrobial properties [29] and streptomycin was used as positive
control. The minimum inhibitory concentration (MIC) of each compound was determined based
on the lowest concentration of the compound that inhibited the growth of bacteria using the broth
dilution method [30]. Single colonies of S. aureus and E. coli were isolated from agar plates and
were grown in 5.0 mL LB broth. The solutions were incubated at 37 °C and shaken at 180 rpm
overnight to yield bacteria solutions. Stock solutions of the compounds were prepared by
dissolving each in DMSO to give stock concentrations of 50 mg/mL. Respectively from each
stock solution, 2 μL of the compounds (salts and complexes), AgNO3 and streptomycin were
dissolved in 2 mL of the broth culture and used to prepare four serial dilutions of 100, 50, 25 and
12.5 μg/mL. Serial dilutions were done for each compound by transferring 1 mL (100 μg/mL) of
the compound solution from the first tube to the second tube already containing 1 mL of nutrient
broth. Next, 1 mL from tube 2 was again transferred into tube 3 and another 1 mL from tube 4 to
give the concentration of 50, 25 and 12.5 μg/ml, respectively. Prepared bacteria solution (5 μL)
was added to each tube, and the tubes were incubated at 37 °C for 16 h in a shaking incubator at
8

180 rpm. Bacteria growth was noted by turbidity of the solution in the tubes and MIC was
determined by the lowest concentration lacking turbidity.
2.11. Gel electrophoresis
The electrophoresis method was employed to study the interaction of the test compounds with
nucleic acids [31]. The extracted plasmid DNA and RNA, pTS414 (10 μg/mL), and 1 μL of the
test sample (50 μg/mL) were mixed in 50 mM Tris-HCl buffer (pH 8.00). The contents were
incubated for 8 h at 37 °C. Plasmid extraction was done using a plasmid purification kit (Intron
Biotechnology, Korea) without the addition of RNase in order to extract both RNA and DNA.
The electrophoresis was performed using 0.8 % Agarose gel. For each sample 5 μL of the
mixture was loaded into the well. The voltage used was 90 V running on 0.5 × Tris-Acetate
EDTA (TAE) buffer and the gel was stained with ethidium bromide solution (10 μg/mL) for
15 min. The gel was subsequently exposed to uv light and captured by a gel documentation
system (FluorChem HD2; Cell Bioscience). The nucleating abilities of the synthesized
imidazolium salts/Ag-NHC complexes (1-8) were determined by its efficiency in
cleaving/degrading the plasmid DNA and RNA. The same procedure was used in the presence of
H2O2 oxidant.
3. Results and discussion
3.1. Synthesis and characterization
The NHC precursors (1-4) were synthesized from reactions between bis(bromomethyl)benzene,
1-bromopropane, 1-bromobutane, 1-bromopentane and N-methoxyethylimidazole in refluxing
acetonitrile for 20-24 h to yield the desired products 1-4, respectively. The obtained bromide
salts were converted to hexafluorophosphate salts (in order to enhance their solubility, stability
and easier handling) by metathesis with KPF6 in methanol to obtain 1-4 as a white solid in
moderate yield. Elemental analyses of the salts agree with the proposed composition and their
1H NMR spectra showed the expected signals for the imidazolium salts. Complex 5 was prepared
in 1:2 molar ratio of 1 to Ag2O, while 6-8 were prepared in equimolar reactions of 2-4 with
Ag2O in acetonitrile at 50-60 °C for 12-18 h, covered from light. All the NHC complexes (5-8)
were purified by repeated precipitation in acetonitrile by the addition of diethyl ether. The
complexes are soluble in acetonitrile, acetone and DMSO but are insoluble in water, ethyl
9

acetate, hexane, diethyl ether and toluene. The synthetic route to the formation of NHC
precursors (1-4) and their respective Ag(I)-NHC complexes (5-8) are outlined in schemes 1
and 2.
OCH3
N
N
N
N
N
+
N
N
+
N
N
+
N
N
+
N
Br
KPF6
2Br
Methanol,
stir, 3h
2PF6
CH3CN, reflux,
24 h
H3CO
H3CO
OCH3
OCH3
1
OCH3
OCH3
OCH3
H
a)
b)
DMSO, KOH
STIR, RT
N
+
N
N
+
N
R
N
N
N
KPF6
Br-R
Br
PF6
Methanol,
stir, 3h
OCH3
N
CH3CN, reflux,
20 h
Br
R
2- 4
2: R = CH2CH2CH3
3: R = CH2CH2CH2CH3
4: R = CH2CH2CH2CH2CH3
Scheme 1. Synthesis of bis and mono-imidazolium salts (1-4).
3.2. Hydrolysis test
Solution studies of these complexes were essential in order to identify the bioactive species
resulting from dissolution of the solid complex, and so understand the underlying biochemical
mechanism involved in the antibacterial activity. This study is also relevant to the antibacterial
studies since the complexes have to be maintained in culture medium for at least 24 h. Therefore,
we have determined the stabilities of the Ag-NHC complexes 3 and 4 in both 10% and 100%
DMSO-d6 aqueous solution. Both complexes are stable in aqueous solution for 24 h, since their
1H NMR spectra remained unchanged after 48 h. The representative 1H and 13C NMR spectra of
6 after 48 h in 10% aqueous DMSO is shown in figure 1 and is identical to the spectra obtained
after 15 min (see supplementary data figure S8).
In order to further assess the stability of the complexes in the broth mixture, 10 mg/mL
stock solutions of the complexes in DMSO were prepared and added in a 1:1 ratio to LB broth
10

prepared in DMSO. This was done to imitate the conditions of the MIC evaluation experiments.
1
The H NMR and 13C NMR spectra were taken after 15 min and 48 h. The complexes
demonstrated stability in the LB/DMSO broth mixture at 37 °C, as shown by the unchanged
13
1H and C NMR spectra after 48 h. However the circumstances under physiological conditions
may vary, but these preliminary results are noteworthy.
2+
CH3CN, 50oC
18 h
H3CO
H3CO
N
N
N
OCH3
2PF6
OCH3
N
N
N
N
+
N
N
+
N
Ag
Ag
2PF6
Ag2O
N
N
H3CO
OCH3
5
1
OCH3
OCH3
H3CO
+
CH3CN, 50oC
12 h
N
+
N
N
N
N
N
PF6
Ag
PF6
Ag2O
R
R
R
2- 4
6 - 8
2, 6: R = CH2CH2CH3
3, 7: R = CH2CH2CH2CH3
4, 8: R = CH2CH2CH2CH2CH3
Scheme 2. Synthetic pathway to Ag(I)-mono/bis-NHC complexes (5-8) from NHC
precursors (1-4).
3.3. FTIR spectra
FTIR data can be used as a preliminary confirmation for synthesis of Ag(I)-NHC complexes
because they usually show some characteristic peaks comparable to the respective ligands [32].
For all analyzed salts, sharp stretching vibrations were observed at 1170-1357 cm-1 ascribed to
the C-O and C-O-C modules and remained unchanged in the spectra of Ag(I)-NHC complex.
This suggests the presence of ether functionality outside the coordination sphere (oxygen
functionalities are not coordinated), which is further confirmed by X-ray diffraction analysis.
The NHC carbon, upon complexation with silver, alters the vibration bands. This is evident at
11

1125-1130 cm-1 for the salts and 1275-1349 cm-1 for the Ag(I)-NHC complexes, assignable to
imidazole ring ν(Carom-Nimidazole) vibrations [33] and this pattern appears for all the complexes.
However metal-to-carbene carbon vibrations are normally observed in far-IR region and,
therefore, could not be assigned in the available IR spectral data.
3.4. NMR spectra
1
The H NMR spectra of imidazolium salts 1-4 in DMSO-d6 exhibit a characteristic NCHN
proton resonance at ca. 9.17-9.37 ppm, suggesting formation of the desired salts. Two doublets at
ca. 7.8 ppm were observed for imidazolium C4H and C5H resonances, respectively. Further,
methoxy protons and ethylene protons of ether-functionality resonated as a singlet and two
triplets in the range ca. 3.22-3.28 and 3.68-4.37 ppm, respectively. Finally, alkyl proton
resonances were found in the range ca. 0.8-4.4 ppm, which is in agreement with the similar
13
structures [34]. The C NMR spectra of the salts displayed prominent peaks in the downfield
region at ca. 135.94-136.51 ppm, attributed to imadazole ring carbene carbon [35-37]. The
signals for benzylic (N-CH2-benzylic) and alkyl chain (-CH2-) were observed at ca. 51.22-52.27
and 10.00-49.87 ppm, respectively. As expected, in the 1H NMR spectra, the peak corresponding
to the NCHN proton resonance completely disappeared, suggesting complex formation which is
further confirmed by the downfield shift of carbene carbon nuclei to ca. 179-180 ppm in the
13
13C NMR spectra. Surprisingly, for 7, C NMR spectrum displayed a downfield resonance for
the C2-carbon nuclei as two doublets centered at 178 and 180 ppm. This is due to the presence of
1
1
13C–109Ag and 13C–107Ag with the coupling constants of J(C–109Ag) 198.5 and J(C–107Ag)
185.0 Hz, respectively. This observation is in accord with the similar reported compounds
[34, 38]. Apart from these major changes, there are no observable changes observed in both
spectra.
3.5. Single-crystal X-ray diffraction studies
The crystal data of 1 and 5 are shown in table 1, while the selected bond lengths and angles are
given in tables 2 and 3. Compound 1 crystallizes in the triclinic, space group P-1, containing one
paraxylyl bridged bis-carbene cation and two hexafluorophosphate anions in the asymmetric unit
(figure 2). The internal ring angles of imidazole (N–C–N) are 108.66(15) for N3-C14-N4 and
108.56(15) for N1-C1-N2, respectively. The central benzene ring (C1-C6) makes dihedral angles
12

of 112.1(1)° and 111.42(2)° with the imidazole rings, (N3-C11-C8) and (N2-C4–C5),
respectively, almost perpendicular to the plane of the xylyl group.
Complex 5 crystallizes in the triclinic space group P-1 with half of the molecule
contained in the asymmetric unit. The structure consists of ligands 1, each of them displays the
1
1
μ -κ (C)Ag:κ (C′)Ag′ bridging mode, facilitating the formation of dinuclear complex (figure 3a).
2
In this dinuclear complex, each silver ion displays a linear coordination geometry with the
Ag1-C1 and Ag1i-C15 distances 2.105(3) Å and 2.101(3) Å, respectively, while the angle of
C1-Ag1-C15i (and its symmetry equivalent) is 177.59(10)°. The Ag-C bond distances for both
sets of imidazolium rings at Ag1 and Ag1i are in accord with comparable imidazolium
complexes of Ag(I) [39]. The internal ring angles between the planes of the two imidazolin-2-
ylidene rings for Ag1 and Ag1i are 123.7(3)-131.1(3)° and are oriented at the dihedral angles of
12.6(6)°. Each dinuclear complex interdigitates with each other in which the methoxy group is
directed into the cavities of the adjacent molecule, facilitating the formation of a 1D network
(figure 3b).
3.6. Antibacterial activity
Stock solutions of all the compounds were prepared in DMSO. All dilutions were carried out
with distilled water. The concentrations of the test compounds were 12.5, 25, 50 and
100 μg mL-1 using silver nitrate for positive control and streptomycin as the standard drug.
Compounds were screened for their antibacterial activity against E. coli and S. aureus using the
disc diffusion method. The MIC was determined based on the lowest concentration that inhibited
growth of the bacteria. The antibacterial activities of all complexes showed good inhibition
against both the Gram negative (E. coli) and Gram positive (S. aureus) bacteria. However, no
inhibition was observed for all salt samples (table 4 and figure 4). From these results, the
antibacterial activity of 5 (MIC, 12.5 μg mL-1) was the highest. The MIC values for the
complexes against both Gram positive and Gram negative bacteria are 12.5-100 μg mL-1
(table 5). These values are comparable to the MIC for silver nitrate (50 μg/mL) and some other
related results in the literature [5b, 41-43], showing that these new Ag-NHC complexes are
potent. Salts (1-4) do not show any activity. The complexes (5-8) showed bactericidal activities
against both Gram positive and Gram negative bacteria, which is in agreement with the literature
[44]. Complexes 5 and 8 showed significant bactericidal effect against Gram positive bacteria at
13

12.5 μg mL-1 and 25 μg mL-1, respectively, while for 6 the activity was 100 μg mL-1 (table 5).
The present results showed that 5 (dinuclear silver complex) and mononuclear 8, which is
bearing the N-pentyl substituent, are the most sensitive against both Gram negative and Gram
positive bacteria compared to mononuclear 6 and 7. This further underscores the existing
literature that, the number of silver centers within the complex molecule determines their
biological activities [45]. It is quite obvious that 8 showed better antibacterial activity
(MIC 25 μg mL-1) for the Gram positive bacteria than 6 and 7 (MIC, 100 and 50 μg mL-1),
respectively. Although 6, 7 and 8 are mononuclear, they possess different N-alkyl substitution;
complex 8 bearing N-pentyl substituent has better antibacterial activity in comparison with
others bearing N-propyl and butyl substituents. The order of activity in this work as it relates to
chain length seems to be in agreement with previous work carried out by our research group and
other researchers, where it was found that the biological activity increased with increase in chain
length for complexes [46-49]. Therefore, the antibacterial activity could be due to lipophilicity of
the complexes which may enhance the transport of NHCs into the cell and subsequently into the
cell organs where silver may inhibit cellular respiration and metabolism of biomolecules. All the
complexes exhibited moderate to good bacteriostatic effect against Gram negative and Gram
positive bacteria, when compared with streptomycin, while 5 and 8 show better activity than
AgNO3 (table 5). However, the NHC precursors showed poor reaction against Gram positive and
Gram negative bacteria. Such increased activity of the metal complexes relative to their
corresponding NHC precursors can be explained on the basis of chelation theory [50].
3.7. Nuclease activity
Gel electrophoresis was used to evaluate the nuclease properties of the reported compounds.
Plasmid extraction was done using a plasmid purification kit (Intron Biotechnology, Korea)
without the addition of RNase in order to extract both RNA and DNA. This method is intended
to further investigate the interaction of these synthesized compounds with DNA and/or RNA as a
preliminary study for predicting likely mode of action(s) of the reported compounds; DNA and
also RNA are part of the possible targets of most current bactericidal antimicrobials [51].
Agarose gel image showing the effects of compounds on nucleic acids is shown in figure 5.
Compounds 1-8 were studied for their interactions with nucleic acids by agarose gel
electrophoresis against plasmid, pTS414 DNA/RNA in the presence and absence of H2O2 as an
14

oxidizing agent. The electrophoresis analysis showed that the imidazolium salts 1-4 displayed no
visible activity towards nucleic acids (DNA and RNA) in the presence and absence of H2O2
(lanes 1, 2, 3 and 4). Also there was no observed activity for the complexes in the absence of
H2O2; however, 5 and 8 displayed activity in the presence of the oxidant; in lane 8 for 8 there
was no observed interaction with DNA but the RNA is degraded. There is disappearance of
supercoiled DNA strand (absence of the marker band), indicating that 5 displayed complete
DNA cleavage and also RNA degradation appearing (lane 5). Possible reaction mechanisms for
DNA cleavage in the presence of H2O2 have been reported [52, 53]. This study has shown that
the control DNA/RNA alone (lane 2) does not show any apparent cleavage both in the absence
and presence of H2O2, whereas 5 and 8 do show activity (lanes 5 and 8), respectively. Perhaps 5
and 8 have different pathway of action, as they have shown variation in the activity against DNA
and RNA. However, further studies need to be carried out in this respect.
4. Conclusion
We report the synthesis, crystal structures, nucleic acid interaction study and investigation of
antibacterial properties of a new series of NHC precursors (1-4) and respective Ag-NHC
complexes (5-8) in anticipation of discovering new compounds that will serve as antibacterial
and nucleic acids cleaving agents. From the antibacterial results we can conclude that the NHC
precursors showed no antibacterial activity when compared with the silver complexes, which
have promising results, with good activity against Escherichia coli (Gram negative bacteria) and
Staphylococcus aureus (Gram positive bacteria). The nuclease studies revealed that 5 and 8
possess nuclease activity.
Supplementary material
Crystallographic data for the structure in this work has been deposited at the Cambridge
Crystallographic Data Centre, CCDC 941464, 939882 and 941102. Copies of these materials can
be obtained from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-
1223-336033; E-mail: deposit@ccdc.cam.ac.uk/deposit).
15

Acknowledgement
The authors thank Universiti Sains Malaysia (USM) for the Research University (RU) Grant
1001/PKIMIA/811217. The authors are grateful to Prof. A.A. Amirul of the School of Biological
Sciences, Universiti Sains Malaysia for his useful technical assistance.
References
[1]
S. Saha, D. Dhanasekaran, S. Chandraleka, N. Thajuddin, A. Panneerselvam. Adv.
Biomed. Res., 4, 224 (2010).
[2]
[3]
[4]
[5]
M.E. Mulligan, K. Murray-Leisure. Am. J. Med., 94, 313 (1993).
R. Bax, R. Bywater, G. Cornaglia. Clin. Microbiol. Infect., 7, 316 (2001).
D.M. Livermore. Clin. Microbiol. Infect., 10, 1 (2004).
(a) I. Özdemir, N. Gürbüz, O. Doğan, S. Günal, I. Özdemir. Appl. Organomet. Chem., 24,
758 (2010). (b) B. Yığıt, Y.Gök, I. Özdemır, S. Günal. J. Coord. Chem., 65, 371 (2012).
(c) Y. Li, X. Dong, Y. Gou, Z. Jiang, H-L. Zhu. J. Coord. Chem., 64, 1663 (2011). (d) I.
Özdemir, S. Demir, S. Günal, C. Arıcı, D. Ülkü. Inorg. Chim. Acta, 363, 3803 (2010).
T.A. Bell, J.T. Grayston, M.A. Krohn, R.A. Kronmal. Pediatrics, 92, 755 (1993).
A. Melaiye, R.S. Simons, A. Milsted, F. Pingitore, C. Wesdemiotis, C.A. Tessier, W.J.
Youngs. J. Med. Chem., 47, 973 (2004).
[6]
[7]
[8]
[9]
A. Kascatan-Nebioglu, A. Melaiye, K. Hindi, S. Durmus, M. Panzner, L. Hogue, R.
Mallett, C. Hovis, M. Coughenour, S. Crosby, A. Milsted, D. Ely, C. Tessier, C. Cannon,
W.J. Youngs. Med. Chem., 49, 6811 (2006).
S. Ray, R. Mohan, J.K. Singh, M.K. Samantaray, M.M. Shaikh, D. Panda, P.J. Ghosh.
J. Am. Chem. Soc., 129, 15042 (2007).
[10] K. Hindi, T. Siciliano, S. Durmus, M. Panzner, D. Medvetz, V. Reddy, L. Hogue, C.
Hovis, J. Hilliard, R. Mallett, C. Tessier, C. Cannon, W.J. Youngs. Med. Chem., 51, 1577
(2008).
[11] O. Kühl. Chem. Soc. Rev., 36, 592 (2007).
[12] A.T. Normand, K.J. Cavell. Eur. J. Inorg. Chem., 14, 2781 (2008).
[13] A. John, P. Ghosh. Dalton Trans., 39, 7183 (2010).
[14] (a) P.L. Arnold, M. Rodden, K.M. Davis, A.C. Scarisbrick, A.J. Blake, C. Wilson. Chem.
Commun., 14, 1612 (2004). (b) S.T. Liddle, P.L. Arnold. Chem. Commun., 1, 3559
16

(2006). (c) D. Pugh, A.A. Danopoulos. Coord. Chem. Rev., 251, 610 (2007). (d) Y. Zhou,
W. Chen. Organometallics, 26, 2742 (2007).
[15] C. Bocchino, M. Napoli, C. Costabile, P. Longo. J. Polym. Sci., 49, 862 (2011).
[16] K. Nomiya, S. Takahashi, R. Noguchi, S. Nemoto, T. Takayama, M. Oda. Inorg. Chem.,
39, 3301 (2000).
[17] A. Busetti, D.E. Crawford, M.J. Earle, M.A. Gilea, B.F. Gilmore, S.P. Gorman, G.
Laverty, M. McLaughlin, K.R. Seddon. Green Chem., 12, 420 (2010).
[18] J. Pernak, P. Chwala. Eur. J. Med. Chem., 38, 1035 (2003).
[19] H.T. Chifotides, K.R. Dunbar. Acc. Chem. Res., 38, 146 (2005).
[20] D. Bourissou, O. Guerret, F.P. Gabbaï, G. Bertrand. Chem. Rev., 100, 39 (2000).
[21] W.A. Herrmann, C. Kocher. Angew. Chem., 36, 2162 (1997).
[22] C.G. de Almeida, G.D. Garbois, L.M. Amaral, C.C. Diniz, M. Le Hyaric. Biomed.
Pharmacother., 64, 287 (2010).
[23] K. Subramani, Margabandu. Int. J. Chem. Tech. Res., 2, 3 (2010).
[24] M. Jumaa, F.H. Furkert, B.W. Muller. Eur. J. Biopharm., 53, 115 (2002).
[25] R. Margabandu, K. Subramani. Int. J. Chem. Tech. Res., 3, 2 (2010).
[26] S. Fang, Y. Jin, L. Yang, S.I. Hirano, K. Tachibana, S. Katayama. Electrochim. Acta, 56,
4663 (2011).
[27] M.J. Monteiro, F.F. Camilo, M.C.C. Ribeiro, R.M. Torresi. J. Phys. Chem., 114, 12488
(2010).
[28] W.L. Drew, A.L. Barry, R. O'Toole, J.C. Sherris. Appl. Microbiol., 24, 240 (1972).
[29] A.B. Lansdown, A. Williams, S. Chandler, S. Benfield. J. Wound Care, 14, 155 (2005).
[30] I. Wiegand, K. Hilpert, R.E.W. Hancock. Nature Protocols, 3, 163 (2008).
[31] N. Raman, R. Jeyamurugan, A. Sakthivel, L. Mitu. Spectrochim. Acta, Part A, 75, 88
(2010).
[32] M.A. Iqbal, R.A. Haque, M.B.K. Ahamed, A.M.S. Abdul Majid, S.S. Al-Rawi. Med.
Chem. Res., 22, 2455 (2013).
[33] S. Budagumpi, V.K. Revankar. Transition Met. Chem., 35, 649 (2010).
[34] R.A. Haque, M.A. Iqbal, S. Budagumpi, M.B.K. Ahamed, A.M.S. Abdul Majid, N.
Hasanudin. Appl. Organomet. Chem., 27, 214 (2013).
[35] F.E. Hahn, M.C. Jahnke, T. Pape. Organometallics, 26, 150 (2007).
17

[36] F.E. Hahn. Angew. Chem., 45, 1348 (2006).
[37] M. Poyatos, J.A. Mata, E. Falomir, R.H. Crabtree, E. Peris. Organometallics, 22, 1110
(2003).
[38] M.V. Baker, D.H. Brown, R.A. Haque, B.W. Skelton, A.H. White. Dalton Trans., 21,
3756 (2004).
[39] Cambridge Structural Database, Version 5, 33 (2011).
[40] R.A. Haque, S.A. Ahmed, Z.H. Zetty, M. Hermamalini. Acta Cryst., 68, 489 (2012).
[41] R.A. Haque, P.O. Asekunowo, M.R. Razali. Transition Met. Chem. (2014); DOI:
10.1007/s11243-014-9801-5.
[42] I. Ozdemir, E.O Ozcan, S. Giinal, N. Gurbus. Molecules, 15, 2499 (2010).
[43] A.R. Knapp, M.J. Panzner, A.D. Medvetz, B.D. Wright, C.A Tessier, W.J Youngs. Inorg.
Chim. Acta, 364, 125 (2010).
[44] M.O. Agwara, P.T. Ndifon, M.K. Ndikontan, M.A. Atamba. Res. J. Chem. Environ., 12,
87 (2008).
[45] H. Mahboobi, A. Viarengo, D. Colangelo, D. Osella. Biometals, 16, 403 (2003).
[46] R.A. Haque, N. Hasanudin, M.A. Iqbal, A. Ahmad, S. Hashim, A. Abdul Majid, M.B.K.
Ahamed. J. Coord. Chem., 66, 3211 (2013).
[47] M.A. Iqbal, R.A. Haque, M.B. Khadeer Ahamed, A.M.S. Abdul Majid, S. Sawsan
Al-ravi. Med. Chem. Res., 22, 2455 (2013).
[48] K.M. Hindi, M.J. Panzner, C.A. Tessier, C.L. Cannon, W.J. Youngs. Chem. Rev., 109,
3859 (2009).
[49] J. Pernak, P. Chwala. Eur. J. Med. Chem., 38, 1035 (2003).
[50] J.W. Searl, R.C. Smith, S. Wyard. J. Proc. Phys. Soc., 78, 1174 (1961).
[51] C. Walsh, Antibiotics: Actions, Origins, Resistance, ASM Press: Washington, D.C.
(2003).
[52] K. Yamamoto, S. Kawanishi. J. Biol. Chem., 264, 15435 (1989).
[53] I.P. Dominique, M.J. Belousoff, L.B.G. Spiccia. Coord. Chem. Rev., 256, 897 (2012).
18

(a)
(b)
1
13
Figure 1. Representative (a) H NMR and (b) C NMR spectra of 6 after 48 h in 10% aqueous
DMSO.
19

Figure 2. Structure of 1 with the ellipsoids shown at 50% probability. Two hexafluorophosphate
anions in the lattice were omitted for clarity.
20

(a)
(b)
Figure 3. (a) Structure of 5 with ellipsoids shown at 50% probability. Hydrogens and
i
hexafluorophosphate have been omitted for clarity. Symmetry element used: 1-x, 2-y, -z.
(b) Interdigitate interactions between dinuclear complex in 5.
21

(a)
35
30
25
20
15
10
5
100 μg/mL
50 μg/mL
0
Compounds
(b)
35
30
25
20
15
10
5
100 μg/mL
50 μg/mL
0
Compounds
Figure 4. Antimicrobial activity of investigated compounds against (a) E.coli and (b) S.aureus
after being treated with samples solution.
22

(a)
DNA
RNA
(b)
DNA
RNA
Figure 5. (a) Nuclease activity in the absence of H2O2 and (b) in the presence of H2O2 at
50 μg/mL. M: Marker; C: DNA/RNA alone; Lane 1: DNA/RNA + 1; Lane 2: DNA/RNA + 2;
Lane 3: DNA/RNA + 3; Lane 4: DNA/RNA + 4; Lane 5: DNA/RNA + 5; Lane 6: DNA/RNA +
6; Lane 7: DNA/RNA+ 7; Lane 8: DNA/RNA + 8.
23

Table 1. Crystal data and structure refinement details for 1 and 5.
Formula
Formula wt
Crystal system
Space group
a (Å)
C20H28N4F12O2P2
646.40
C40H52N8Ag2O4F12P2
1214.58
Triclinic
P-1
Triclinic
P-1
9.0505(2)
10.1646(2)
15.8288(3)
81.4000(10)
74.6060(10)
69.3910(10)
1311.54(5)
2
11.1859(2)
11.5922(2)
11.8396(2)
61.428(1)
63.427(1)
87.524(1)
1177.61(4)
1
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcal/g cm-3
Temperature
Λ (MoKα)
μ (mm-1)
Crystal size (mm)
Rint
1.637
1.713
100 K
100 K
0.71073
0.71073
0.279
0.997
0.50×0.38×0.22
0.0230
0.37×0.30×0.22
0.027
F(000)
660
612
R1, wR2
0.0443, 0.1147
0.0431, 0.1305
24

Table 2. Selected bond lengths (Å) and angles (°) for 1.
N1-C1
N2-C1
N3-C15
N4-C15
1.331(2)
1.385(2)
1.329(2)
1.333(2)
N1-C1-N2
108.56(15)
108.66(15)
N3-C15-N4
25

Table 3. Selected bond lengths (Å) and angles (°) of 5.
Ag1-C1
N1-C1
2.105(3)
1.329(4)
1.368(4)
2.101(3)
1.370(4)
1.321(4)
N2-C1
Ag1i-C15
N3-C15
N4-C15
N1-C1-N2
105.4(3)
105.0(3)
177.59(10)
N3-C15-N4
C1-Ag1-C15i
i
Symmetry element used: 1-x, 2-y, -z
26

Table 4(a). Antibacterial activities of the compoundsa against E.coli and S.aureus obtained by
the disc diffusion methodb (zone of inhibition).
Inhibition zone (mm)
Strain
Test compound (100 μg/mL)
5
6
7
8
AgNO3
23 3
Streptomycin
32.0 0.5
E.coli
27 1
10.0 0.7
20 1
24 1
S.aureus
28 1
14.0 0.4
22.0 0.5
28 2
23.7 0.5
32.5 0.5
a Compounds 1-4 showed no activity.
b Test compound volume = 5 μL; Test compound concentrations = 100 μg/mL.
Table 4(b). Antibacterial activities of the compoundsa against E.coli and S.aureus obtained by
the disc diffusion methodb (zone of inhibition).
Inhibition zone (mm)
Strain
Test compound (50 μg/mL)
5
7
8
AgNO3
17.0 0.5
18.5 0.7
Streptomycin
23.0 0.5
E.coli
20 1
15.0 0.8
18 2
S.aureus
20.2 0.5
16 3
21.0 0.7
23.5 0.5
a Compounds 1-4 and 6 showed no activity.
b Test compound volume = 5 μL; Test compound concentrations = 50 μg/mL.
27

Table 5. Minimum inhibition concentration (MIC) against E.coli (Gram
negative bacteria) and S.aureus (Gram positive bacteria).
E.coli (μg/mL)
S.aureus (μg/mL)
Test compound
MIC
25
MIC
12.5
100
50
5
6
100
50
7
8
25
25
AgNO3
50
50
Streptomycin
1-4 did not show activity
12.5
12.5
28

29