Light insensitive silver(I) cyanoximates as antimicrobial agents for indwelling medical devices

Article abstract of DOI:10.1021/ic100830x

Ten silver(I) cyanoximates of AgL composition (L = NC-C(NO)-R, where R is electron withdrawing groups: -CN, -C(O)NR₂, -C(O)R′ (alkyl), -C(O)OEt, 2-heteroaryl fragments such as 2-pyridyl, 2-benzimidazolyl, 2-benzoxazolyl, 2-benzthiazolyl) were s

Full text of DOI:10.1021/ic100830x

Inorg. Chem. 2010, 49, 9863–9874 9863
DOI: 10.1021/ic100830x
Light Insensitive Silver(I) Cyanoximates As Antimicrobial Agents for Indwelling
Medical Devices
Nikolay Gerasimchuk,*,† Andrzej Gamian,‡ Garrett Glover,† and Bogumila Szponar‡
†Department of Chemistry, Temple Hall 456, Missouri State University, Springfield, Missouri 65897, and
‡Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Weigla 12,
53-114 Wroclaw, Poland
Received April 27, 2010
Ten silver(I) cyanoximates of AgL composition (L = NC-C(NO)-R, where R is electron withdrawing groups: -CN,
-C(O)NR2, -C(O)R0 (alkyl), -C(O)OEt, 2-heteroaryl fragments such as 2-pyridyl, 2-benzimidazolyl, 2-benzoxazolyl,
2-benzthiazolyl) were synthesized and characterized using spectroscopic methods and X-ray analysis. Crystal
structures of four complexes were determined and revealed the formation of two-dimensional (2D) coordination
polymers of different complexity in which anions exhibit bridging or combined chelate and bridging binding modes.
In these compounds, anions are in the nitroso form. All studied AgL complexes are sparingly soluble in water and
are thermally stable to 150 °C. Synthesized compounds demonstrated remarkable insensitivity toward visible light and
UV-radiation, which was explained based on their polymeric structures with multiple covalent bonds between bridging
cyanoxime ligands and Ag(I) centers. All 10 silver(I) cyanoximates were tested in vitro on the subject of their
antimicrobial activity against both Gram-positive and Gram-negative microorganisms such as Escherichia coli,
Klebsiella pneumoniae, Proteus sp., Pseudomonas aeruginosa, Enterococcus hirae, Streptococcus mutans,
Staphylococcus aureus, and Mycobacterium fortuitum as well as against Candida albicans in solutions, and in the
solid state as pressed pellets and dried filter paper disks presoaked with solutions of AgL in DMF. Results showed
pronounced antimicrobial activity for all investigated complexes. A combination of five factors: (1) light insensitivity,
(2) poor water solubility, (3) high thermal stability, (4) lack of toxicity of organic ligands, and (5) in vitro antimicrobial
activity allows development of silver(I) cyanoximates for medical applications. These include antimicrobial additives
to acrylate glue, cured by UV-radiation, used in introduction of prosthetic joints and dental implants, and prevention
of biofilm formation on several types of indwelling medical devices.
Introduction
are usually transient,6 allowing further infection development.
Even immediate device replacement and long-term administra-
tion of high-dose antibiotics are often ineffective.7,8 Streptococ-
cus mutans is considered an early colonizer of the tooth surface
and one of the major causes of caries development in humans.
The ability of these bacteria to produce biofilms on the surfaces
of biomaterials used during surgeries is one of the main causes
of developing stubborn infections.9 Biofilms10 have an increased
resistance to antibiotics11 and host defenses.12,13 As a result, they
The number of patients requiring an internal fixation device
or artificial joint has grown rapidly. In the United States alone,
more than 4.4 million people have at least one internal fixation
device and more than 1.3 million people have an artificial joint.1
Bacterial infection induced by an implant placement (Scheme 1A)
is a significant rising complication and is associated with con-
siderable morbidity and costs.2 These device-related infections
caused by Pseudomonas aeruginosa are usually acute and extre-
mely difficult to treat.3-5 Initial symptoms of these infections
(7) El-Khuffash, A. F.; Molloy, E. J.; Walsh, K. Neonatology 2008, 93,
113–116.
*To whom correspondence should be addressed. E-mail: NNGerasimchuk@
missouristate.edu; office: (417) 836-5165, laboratory: (417) 836-8564.
(1) Praemer, A.; Furner, S.; Rice, D. P.; Kelsey, J. L. American Academy
of Orthopaedic Surgeons; ETATS-UNIS: Park Ridge, IL, 1992; pp 27-41.
(2) Chen, W.; Oh, S.; Ong, A. P.; Oh, N.; Liu, Y.; Courtney, H. S.;
Appleford, M.; Ong, J. L. J. Biomed. Mater. Res. 2007, 82, 899–906.
(3) Bicanic, T. A.; Eykyn, S. J. J. Infect. 2002, 44, 137–139.
(4) Ishiwada, N.; Niwa, K.; Tateno, S.; Yoshinaga, M.; Terai, M.;
Nakazawa, M. Circ. J. 2005, 69, 1266–1270.
(5) Komshian, S. V.; Tablan, O. C.; Palutke, W.; Reyes, M. P. Rev. Infect.
Dis. 1990, 12, 93–702.
(6) Donlan, R. M.; Costerton, J. W. Clin. Microbiol. Rev. 2002, 15,
167–193.
(8) Gavin, P. J.; Suseno, M. T.; Cook, F. V.; Peterson, L. R.; Thomson,
R. B., Jr. Diagn. Microbiol. Infect. Dis. 2003, 47, 427–430.
(9) Potera, C. Science 1999, 283, 1837-1839.
(10) Hentzer, M.; Teitzel, G. M.; Balzer, G. J.; Heydorn, A.; Molin, S.;
Givskov, M.; Parsek, M. R. J. Bacteriol. 2001, 183, 5395-5401.
(11) Skjak-Braek, G.; Murano, G.; Paoletti, S. Biotechnol. Bioeng. 1989,
33, 90-94.
(12) Jesaitis, A.; Franklin, M. J.; Berglund, D.; Sasaki, M.; Lord, C. I.;
Bleazard, J. B.; Duffy, J. E.; Beyenal, H.; Lewandowski, Z. J. Immunol. 2003,
171, 4329-4339.
(13) Meluleni, G. J.; Grout, M.; Evans, D. J.; Pier, G. B. J. Immunol. 1995,
155, 2029-2038.
r
2010 American Chemical Society
Published on Web 09/27/2010
pubs.acs.org/IC

9864 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
Scheme 1
are notoriously difficult to eradicate, and are a source of many
recurrent infections.
such as bioglass16 and bone cement,17 and therefore, have
tremendous potential for implant therapies in the health care
industry.19-21 However, to the best of our knowledge, there
are no silver(I) compounds that combine light and thermal
stability, chemical inertness, water insolubility, and show
antimicrobial activity. The main problems appear to be poor
knowledge, insufficient development, and lack of subsequent
studies of organic ligands to provide such properties. However,
there is one particular class of low molecular weight organic
compounds that can act as ligands for binding silver(I) cations
and form complexes that will satisfy all the specific requirements
outlined above. These compounds are oximes, which represent
versatile organic molecules that were extensively used as
excellent ligands in analytical,22 inorganic,23-28 and bioinor-
ganic chemistry.29-31 Furthermore, among oximes one spe-
cific group of substances called cyanoximes - compounds with
the general formula HO-NdC(CN)-R - represents a new,
special class of biologically active molecules32 that are also
Clinical practice has shown that systemic antibiotics are
unable to provide effective treatment for implant-associated
infections. At the present time, only a high dose of antibiotics
applied locally at the bone-implant interface can prevent
such bacterial infections. However, this treatment causes a
number of side effects, such as increased bacterial resistance
to antibiotics, allergic reactions, and microbial flora deple-
tion. Thus, it is often the best solution to remove the device,
treat the infection, and repeat surgical introduction of a new
device. This kind of procedure is costly, both financially and
psychologically, as well as time-consuming.
Due to the rapid increase in use of artificial implants, it is
critical that new infection-preventing strategies are developed,
and in particular, antibacterial agents. One of the interesting
options is the introduction of a non-antibiotic antimicrobial
substance, for example, into the glue used during introduc-
tion of indwelling medical devices (Scheme 1) or surface
treatment of such devices to prevent pathogenic cell adhesion
and biofilm formation. There is a critical need for non-
antibiotic compounds that satisfy specific needs to be water
insoluble, light- and chemically stable, and yet could survive
sterilization at 100 °C without decomposition. Pure organic
compounds cannot meet these criteria, but some water-insoluble
metal complexes - for example silver(I) compounds - can
(Scheme 1B). Therefore, it is important to identify and study
new metal-based compounds that will meet these demands.
Silver has long been known to exhibit strong inhibitory and
bactericidal effects as well as a broad spectrum of antibacterial
properties. Since ancient times, people have known that water
can remain suitable for drinking for a long time if stored in
silver jars. Colloidal silver and silver nitrate have been used
safely in burn therapy, urinary tract infections, and central
venous catheter infections.14 The inhibitory effects of silver
and silver compounds on bacteria is believed to be associated
with silver reacting with microbial DNA or the sulfhydryl
groups found in the enzymes of bacterial electron transport
chains, causing its inactivation.15 One of the applications
of silver and its compounds is reduction of postoperative
infections caused by implants. Thus, intrinsically low toxicity
silver compounds were loaded into several implant materials18
(16) Kawashita, M.; Tsuneyama, S.; Miyaji, F.; Kokubo, T.; Kozuka, H.;
Yamamoto, K. Biomaterials 2000, 21, 393–398.
(17) Alt, V.; Bechert, T.; Steinrucke, P.;Wagener, M.; Seidel, P.; Dingeldein,
E.; Domann, E.; Schnettler, R. Biomaterials 2004, 25, 4383–4391.
(18) Toshikazu, T. Inorg. Mater. 1999, 6, 505–511.
(19) Rujitanaroj, P.; Pimpha, N.; Supaphol, P. Polymer 2008, 49(11),
4723–4732.
(20) Santoro, C. M.; Ducsherer, N. L.; Grainger, D. W. Nanobiotechno-
logy 2007, 3(2), 55–65.
(21) Valappil, S. P.; Pickup, D. M.; Carroll, D. L.; Hope, C. K.; Pratten,
J.; Newport, R. J.; Smith, M. E.; Wilson, M.; Knowles, J. C. Antimicrob.
Agents Chemother. 2007, 51(12), 4453–4461.
(22) (a) Chugaev, L. A. Chem. Ber. 1905, 38, 2520. (b) Chugaev, L. A.
J. Chem. Soc. London 1914, 125, 2187.
(23) Samus, N. M.; Ablov, A. V. Coord. Chem. Rev. 1979, 28, 177–196.
(24) Milios, S. J.; Samatatos, T. C.; Perlepes, S. P. Polyhedron 2006, 25(1),
134–194.
(25) Pavlischuk, V.; Birkelbach, F.; Weyhermuller, T.; Wieghardt, K.;
Choudhuri, P. Inorg. Chem. 2002, 41(17), 4405–4416.
(26) Bagai, R.; Abboud, K. A.; Christou, G. Inorg. Chem. 2007, 46(14),
5567–5575.
(27) Stamatatos, T. C.; Diamantopolou, E.; Raptopolou, C. P.;
Psycharis, V.; Esner, A.; Perlepes, S. P. Inorg. Chem. 2007, 46(7), 2350–2352.
(28) Gerasimchuk, N.; Barnes, C. L.; Boaz, D. J. Coord. Chem. 2010,
63(6), 943–952.
(29) Baffert, C.; Artero, V.; Fontecave, M. Inorg. Chem. 2007, 46(5),
1817–1824.
(30) Follert, A. D.; McNabb, K. A.; Peterson, A. A.; Scanlon, J. D.;
Cramer, C. J.; McNeill, K. Inorg. Chem. 2007, 46(5), 1645–1654.
(31) Ram, M. S.; Riordan, C. G.; Yap, G. P. A.; Liable-Sands, L.; Rheinhold,
A. L.; Marchaj, A.; Norton, J. R. J. Am. Chem. Soc. 1997, 119(7), 1648–1664.
(32) Palii G. K., Skopenko V. V., Gerasimchuk N. N., Makats E. F.,
Domashevskaya O. A., Rakovskaya R. V. Bis-(Nitrosothiocarbamylcyan-
methanide) copper(II) or nickel(II) which exhibit antimicrobial activity.
USSR patent, 1405282, 1988.
(14) Klasen, H. J. Burns 2000, 26, 131–138.
(15) Feng, Q. L.; Wu, J.; Chen, G. Q.; Cui, F. Z.; Kim, T. N.; Kim, J. O.
J. Biomed. Mater. Res. 2000, 52, 662–668.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9865
Scheme 2
capable of binding to different metal ions.33-35 The presence
of the CN-group significantly increases their acidity and
makes them better ligands for binding metal ions as compared
to conventional monoximes. Earlier data showed no intrinsic
in vitro cytotoxicity of free organic cyanoximes,36-38 and we
found that silver(I) cyanoximates are insoluble in water,
represent thermally and chemically stable compounds,39-42
and also exhibit antimicrobial activity.43 With the exception of
several publications and presentations,44-48 there were no
systematic studies regarding light-stable silver(I) antimicrobial
compounds targeting specific infections, and no oxime-based
compounds were tested on that matter at all.
In this work, we present results of the first part of our sys-
tematic investigation dealing with the synthesis, spectroscopic,
structural and photophysical characterization, as well as anti-
microbial activity studies for a new group of light-insensitive
silver(I) cyanoximates based on ligands shown in Scheme 2.
Experimental Section
Materials and Physical Measurements. Reagent or analyti-
cal grade materials were obtained from commercial suppliers
(Aldrich and Mallinckrodt) and were used without further puri-
fication. Elemental analyses on C, N, H content were performed
by a combustion method at the Atlantic Microlab (Norcross,
GA). Melting points for organic ligands were determined using
the UniMelt apparatus (by Thomas-Hoover) without correc-
tion. Identification of the obtained organic compounds was
(33) Gerasimchuk, N. N.; Simonov, Yu. A.; Dvorkin, A. A.; Rebrova,
O. N. Russ. J. Inorg. Chem. 1993, 38(2), 247–252.
(34) Mokhir, A. A.; Gerasimchuk, N. N.; Pol’shin, E. V.; Domasevitch,
K. V. Russ. J. Inorg. Chem. 1994, 39(2), 289–293.
(35) Kogan, V. A.; Burlov, A. S.; Popov, L. D.; Lukov, V. V.; Koschienko,
Yu.V.; Tsupak, E. B.; Barchan, G. P.; Chigarenko, G. G.; Bolotnikov., V. S.
Koord. Khim. 1987, 13(7), 879–885.
(36) Gerasimchuk, N.; Goeden, L.; Durham, P.; Barnes, C. L.; Cannon,
J. F.; Silchenko, S.; Hidalgo, I. Inorg. Chim. Acta 2008, 361, 1983–2001.
(37) Gerasimchuk, N.; Maher, T.; Durham, P.; Domasevitch, K.; Wilking,
J.; Mokhir, A. Inorg. Chem. 2007, 46(18), 7268–7284.
1
carried out using H, 13C NMR spectroscopy (Varian INova
400; T = 296 K; in DMSO-d6, with TMS as an internal standard
TMS, by Cambridge Laboratories), and mass-spectrometry
(positive FAB technique for the macrocyclic compound 14-
ane[N4]; m-nitrobenzylic alcohol, NBA, as a matrix using Autospec
Q and ZAB spectrometers from Manchester, UK). IR spectra
for synthesized organic cyanoxime ligands were recorded in KBr
pellets (400-4000 cm-1 region at 4 cm-1 resolution) using a
Nicolet Impact 410 spectrophotometer operating with OMNIC
software. At the same time, IR spectra of silver(I) complexes
were obtained from mulls in Nujol between two 2 cm KBr
disks. Visible spectra for the suspensions of several Ag(I)
cyanoximates in mineral oil between two quartz plates 4 ꢀ 1 cm
were recorded on an Agilent HP 8453E spectrophotometer in the
range of 300-1100 nm at 293 K. Room temperature solid-state
diffusion reflectance spectra of Ag(ACO) and Ag(PiCO) were
obtained on a Varian Bio-100 spectrophotometer with an integrating
sphere and MgO as a standard. Electrical conductivity of 1 mM
solutions of synthesized silver(I) cyanoximates in anhydrous DMSO
was measured at 296 K using a YSI Conductance-Resistance
meter model 34. Solutions of ammonium bromide, tetrabutyl-
ammonium bromide, and tetraphenyl-phosphonium bromide
(as 1:1 electrolytes), and hydrazinium dichloride (as 1:2 electrolyte)
were used for the electrode calibration.
(38) Eddings, D.; Barnes, C.; Durham, P.; Gerasimchuk, N. N.; Domasevich,
K. V. Inorg. Chem. 2004, 43(13), 3894–3909.
(39) Gerasimchuk, N.; Glover, G. Visible light insensitive silver(I) cya-
noximates. Inorganic chemistry section, poster presentation (196). 237
Spring National ACS Meeting, March 22-26, 2009, Salt Lake City, UT.
(40) Glover, G.; Gerasimchuk, N.; Domasevitch, K. V. Heavy metals
(M = Cs, Ag(I), Tl(I)) nitrosodicyanmethanides M[ONC(CN)2]: synthesis,
crystal structures and properties. Proceedings of 43rd Midwest Regional
Meeting of the ACS, talk #49, p 64; Kearney, NE, October 8-11, 2008.
(41) Glower, G.; Gerasimchuk, N.; Biagioni, R.; Domasevitch, K. Inorg.
Chem. 2009, 48(6), 2371–2382.
(42) Gerasimchuk, N.; Esaulenko, A. N.; Dalley, N. K.; Moore, C. Dalton
Transact. 2010, 39, 749–764.
(43) Gerasimchuk, N.; Glover, G.; Gamian, A.; Domasevitch, K. V.
Further investigations of silver(I) cyanoximates. Proceedings of 43rd Mid-
west Regional Meeting of the ACS, talk #52, p 66; Kearney, NE, October
8-11, 2008.
(44) Fromm, K.M. P. Silver(I) coordination polymers, in Proceedings of
the ICCC-37 Oral Abstracts book; Cape Town, August 13-18, 2006, South
Africa, p 191.
(45) Fromm, K. M. Chains, rings, helices and polycatenanes in silver
coordination chemistry. Abstracts of Papers, 232nd ACS National Meeting,
San Francisco, CA, United States, September 10-14, 2006 (2006), INOR-
023.
(46) Fromm, K. M.; Brunetto, P.; Vig Slenters, T. Nanostructured
implant surface coating with antimicrobial properties. Abstracts of Papers,
237th ACS National Meeting, Salt Lake City, UT, USA, March 22-26,
2009, COLL-347.
(47) Slenters, T. V.; Hauser-Gerspach, I.; Daniels, A. U.; Fromm, K. M.
J. Mater. Chem. 2008, 18(44), 5359–5362.
X-ray Crystallography. Suitable crystals of compounds Ag-
(ACO), Ag(DCO), Ag(PiCO), and Ag(ECO) were mounted on a
thin glass fiber on the goniometer head of a Bruker APEX 2
diffractometer equipped with a SMART CCD area detector. All
data sets were collected at low temperature. The intensity data
for suitable crystals of these compounds (Supporting Informa-
tion, Figure S1) were collected in ω scan mode using Mo tube
(48) Kasuga, N. C.; Sato, M.; Amano, A.; Hara, A.; Tsuruta, S.; Sugie,
A.; Nomiya, K. Inorg. Chim. Acta 2008, 361(5), 1267–1273.

9866 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
Table 1. X-ray Analysis Experimental Data for Several Light Insensitive Ag(I) Cyanoximates
parameter
formula
Ag(ACO)
Ag(DCO)
Ag(PiCO)
Ag(ECO)
C3H2AgN3O2
219.95
C5H6AgN3O2
248.00
C7H9AgN2O2
261.03
C5H5AgN2O3
248.98
formula weight
crystal system
space group
monoclinic
P21/c, No. 14
11.735(3)
6.8313(15)
6.3756(15)
90.00
95.654(3)
90.00
508.6(2)
4
2.872
orthorhombic
Fdd2, No. 43
28.708(8)
29.606(9)
3.6835(11)
90.00
90.00
90.00
3130.7(16)
16
2.105
monoclinic
P21/c, No. 14
13.967(2)
5.9130(9)
10.2611(15)
90.00
104.4740(10)°
90.00
820.5(2)
4
2.113
triclinic
P1, No. 2
3.5875(9)
7.2743(18)
13.617(3)
82.497(3)°
84.531(3)°
81.968(3)°
347.78(15)
2
˚
a (A)
˚
b (A)
˚
c (A)
R (°)
β (°)
γ (°)
3
˚
V (A )
Z
Dcalc (g cm-3
)
2.378
240
2.85
3
F(000)
416
3.87
1920
2.52
512
2.41
μ (MoKR) (mm-1
Data Collection
radiation
)
MoKR
120(2)
0.71073
51.98
-14 > h > 14
0 > k > 8
0 > l > 7
1472
996
2σ
MoKR
120(2)
0.71073
60.94
-40 > h > 40
42 > k > -42
-5 > l > 5
11552
2376
2σ
MoKR
150(2)
0.71073
52.72
-17 > h > 17
-7 > k > 7
-12 > l > 12
7803
1673
2σ
MoKR
120(2)
0.71073
50.66
-4 > h > 4
-8 > k > 8
-16 > l > 16
3385
1275
2σ
temperature, K
wavelength
2θmax (o)
index ranges
reflections collected
unique data
discrimination
Structure Refinement
data used
928
83
2376
102
0.0193, 0.0392
0.0232, 0.0404
1.029
1673
145
0.0146, 0.0364
0.0170, 0.0377
1.116
1275
121
0.0279, 0.0677
0.0319, 0.0702
1.033
parameters refined
R (F), wR2 (F2) (obs.)
R (F), wR2 (F2) (all data)
GOF on F2
0.024, 0.0275
0.0609, 0.0699
1.209
-3
˚
largest peak/hole (e A
)
1.05/-0.74
0.443/-0.393
0.527/-0.294
1.034/-0.927
˚
(KR radiation; λ = 0.71073 A) with a highly oriented graphite
monochromator. Intensities were integrated from four series of
364 exposures, each covering 0.5° in ω within 20 to 60 s of
acquisition time and the total data set being a sphere.49 The
space group determination was done with the aid of XPREP
software.50 Absorption corrections were applied based on crys-
tal face indexing obtained using actual images recorded by
video camera. The following data processing was performed
using the SADABS program that was included in the Bruker
AXS software package.51 The structures were solved by direct
methods and refined by least-squares on weighted F2 values for
all reflections using the SHELXTL program.50All atoms re-
ceived assigned anisotropic displacement parameters and were
refined without positional constraints. All nine hydrogen atoms
in the structure of Ag(PiCO) were found on the difference map
and their positions were refined as well. Crystals of Ag(ACO)
turned out to be multidomain species and details of its structure
solution are shown in Supporting Information, Figure S2.
Complex Ag(DCO) contained a disordered solvent molecule with
partial occupancy. Details of structure solution for this com-
pound can be found in Supporting Information, Figure S2 as
well. Crystal data for all four studied compounds are presented
in Table 1, while bond lengths and valence angles are summa-
rized in Table 2. A complete set of bonds and angles around
metal centers is presented in Supporting Information, Figures
S3-S7. Figures for the crystal structures of these complexes
were drawn using Mercury 4.1.2 and ORTEP 32 software52 at a
50% thermal ellipsoids probability level. The PLATON checks
of crystallographic data and actual CIF files for reported
structures can be found in the Supporting Information section.
The X-ray powder diffraction studies of bulk samples of synthe-
sized AgL were carried out at 296 K on a Bruker Discover XRD
˚
system using Cu-radiation (KR radiation; λ = 1.5406 A).
Powdery samples of complexes were attached to 20 ꢀ 45 mm
cardboard rectangles (as sample holders) using a double-sided
12 mm Scotch tape from 3M followed by standard one-sided
19 mm tape.
Synthesis of Compounds. Preparation of cyanoximes37,53 and
their Ag(I) complexes is depicted in Scheme 3, while the typical
synthesis of silver(I) derivatives is shown as an example for only
one compound.
2-(Oximido)-2-benzoxazoleacetonitrile Silver(I), Ag(BOCO).
Brown H(BOCO) in the amount of 0.4605 g (2.46 mM) of brown
H(BOCO) was dissolved in a mixture of 10 mL of EtOH, diluted
with 10 mL of water, heated to þ50 °C, and then added dropwise
to a solution of 0.169 g (1.22 mM) of K2CO3 in 10 mL of H2O.
The reaction mixture turned immediately very dark brown and
was placed for 2 min into an ultrasound bath to accelerate the
evolution of CO2. A solution of 0.4183 g (2.46 mM) of AgNO3 in
10 mL of water was added dropwise under intensive stirring to a
solution of K(BOCO) above. Mixing resulted in a very fine orange-
brown precipitate, which after an additional 20 min of stirring was
filtered, washed with three portions of 10 mL of water, and then
dried in a vacuum desiccator charged with H2SO4 (c) for 3 days.
The yield of orange-brown Ag(BOCO) was 98% (0.701 g). Anal.
Calc. for C9H4AgN3O2 (Found) %: C, 36.77 (37.12); H, 1.37
(1.58); N, 14.49 (14.33). Other silver(I) cyanoximates follow.
Silver(I) Nitrosodicyanomethanide, Ag(CCO). Bright-yellow
powder; yield 96%, complex decomposes in the range of
(49) SAINT: Data Integration Program; Bruker AXS: Madison, WI, 1998.
(50) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. (b) Sheldrick,
G. M. SADABS Area-Detector Absorption Correction, 2.03; University of
Gottingen, Gottingen, Germany, 1999.
(51) Software Package for Crystal Structure Solution, APEX 2; Bruker
AXS: Madison, WI, 2009.
€
€
(52) (a) Farrugia, L. J. Appl. Crystallogr. 1997, 30, 565. (b) Burnett, M. N.;
Johnson, C. K. ORTEP III: Report ORNL-6895; Oak Ridge National Laboratory:
Oak Ridge, TN, 1996.
(53) Ilkun, O. T.; Archibald, S.; Barnes, C. L.; Gerasimchuk, N.; Biagioni,
R.; Silchenko, S.; Gerasimchuk, O. A.; Nemykin, V. Dalton Transact. 2008,
5715.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9867
190-209 °C. Anal. Calc. for C3N3OAg (Found) %: C, 17.84
(17.98); N, 20.81 (20.69).
160-162 °C. Anal. Calc for C7H9AgN2O2 (Found): C, 32.21
(31.81); H, 3.48 (3.51); N, 10.73 (10.62).
Silver(I) r-Oximido-(acetamide)acetonitrile, Ag(ACO). Mi-
crocrystalline canary-yellow compound; yield 100%, decompo-
sition >229-232 °C. Anal. Calc for C3H2AgN3O2 (Found): C,
16.38 (16.47); H, 0.92 (0.99); N, 19.11(19.08).
Silver(I) r-Oximido-(2-benzoyl)acetonitrile, Ag(BCO). Pur-
ple fine powder obtained with yield 71%; decomposition at
180-182 °C. Anal. Calc for C9H5AgN2O2 (Found): C, 38.47
(38.29); H, 1.79 (1.92); N, 9.97 (9.86).
Silver(I) r-Oximido-([N,N-dimethylamine]acetamide)acetoni-
Silver(I) r-Oximido-(2-pyridyl)acetonitrile, Ag(2PCO). Yel-
low powder, yield 87%; decomposition at 178-187 °C. Anal.
Calc for C7H5N3O (Found): C, 33.10 (34.83); H, 1.59 (1.90); N,
16.54 (17.18).
trile, Ag(DCO) 0.5MeOH. Dark-yellow microcrystalline com-
3
pound obtained with 82% yield, decomposes at ∼158 °C. Anal.
Calc for C11H16Ag2N6O5 (Found): C, 25.02 (25.11); H, 3.05
(3.09); N, 15.92 (15.63).
Silver(I) r-Oximido-(2-[N-methyl]benzoimidazolyl)acetoni-
Silver(I) r-Oximido-(ethylacetoxy)acetonitrile, Ag(ECO).
Orange powder, 93% yield, decomposes at 202-207 °C. Anal.
Calc for C5H5AgN2O3 (Found): C, 24.12 (23.98); H, 2.02 (2.06);
N, 11.25 (11.11).
trile, Ag(BIMCO) 0.5H2O. The compound represents a very
3
fine yellow-green powder, decomposes at 160-180 °C; yield
96%. Anal. Calc for C10H8AgN4O1.5 (Found): C, 37.97 (37.60);
H, 3.16 (2.47); N, 17.72 (17.20).
Silver(I) r-Oximido-(2-pivaloyl)acetonitrile, Ag(PiCO). Very
fine pale yellow powder, yield 85%; rapid decomposition at
Silver(I) r-Oximido-(2-benzothiazolyl)acetonitrile, Ag(BTCO)
3
1.5H2O. Orange-brown fine powder; yield 100%; at ∼214-219 °C
complex decomposes. Anal. Calc for C9H7N3O2SAg, %: C,
32.03 (32.18); H, 2.08 (2.31), N, 12.46 (12.86).
All synthesized Ag(I) cyanoximates are sparingly soluble in
water, but dissolve in donor solvents such as pyridine, 2-pico-
line, and DMSO.
Table 2. Selected Bond Lengths and Valence Angles for Cyanoxime Anions in
Silver(I) Complexes
˚
bonds, A
complex
angles, o
Photophysical Measurements. Light sensitivity and stability
of synthesized Ag(I) cyanoximates was studied at 296 K using a
low-pressure Hg lamp with >85% output at λmax = 254 nm
where the intensity of light was measured with a UVX radio-
meter (UK). After 4 min warm-up time, this lamp generated a
steady flux of UV-radiation that was equal to the dose of 10.13 J/
cm2 within 30 min. Prior to these investigations, complexes were
thoroughly dried under high vacuum (<10-4 Torr) and ground
into a powder using an agate mortar. This made it easy to apply
these compounds to paper, adhesive tape, or cardboard. Samples
of complex were spread on white cardboard with an exposed
circular area (via a mask) of ∼3 cm. The radiation source was
positioned 1 cm from the sample. A pristine white silver chloride
prepared in the dark was used as a control substance to access
the light stability of silver(I) cyanoximates. Digital pictures
of irradiated samples were taken every 30 min using a statio-
nary digital camera (Kodak DX7630; 6.1 Mpx), and native
images were cropped to square shape without any contrast or
brightness editing using Samsung Digimax Viewer 2.0 software.
The experimental setup is shown in Figure S8, Supporting
Information.
Ag(ACO) C(1)-N(1) = 1.311(7)
C(1)-C(2) = 1.437(7)
C(1)-C(3) = 1.484(7)
C(2)-N(2) = 1.323(7)
C(3)-O(2) = 1.323(7)
C(3)-N(3) = 1.151(7)
N(1)-O(1) = 1.307(5)
N(1)-C(1)-C(2) = 117.1(4)
N(1)-C(1)-C(3) = 120.2(4)
C(2)-C(1)-C(3) = 122.7(4)
N(2)-C(2)-C(1) = 118.7(5)
O(2)-C(2)-N(2) = 122.0(5)
O(2)-C(2)-C(1) = 119.3(4)
N(3)-C(3)-C(1) = 179.7(6)
O(1)-N(1)-C(1) = 118.3(4)
N(1)-C(1)-C(2) = 119.82(19)
N(1)-C(1)-C(3) = 116.66(18)
C(2)-C(1)-C(3) = 122.93(18)
N(2)-C(2)-C(1) = 177.1(3)
O(1)-C(3)-N(3) = 121.67(18)
O(1)-C(3)-C(1) = 119.09(18)
N(3)-C(3)-C(1) = 119.23(17)
O(2)-N(1)-C(1) = 118.45(19)
C(5)-N(3)-C(4) = 116.69(16)
N(1)-C(1)-C(2) = 116.80(16)
N(1)-C(1)-C(3) = 117.52(15)
C(2)-C(1)-C(3) = 125.67(15)
N(2)-C(2)-C(1) = 170.85(19)
O(2)-C(3)-C(1) = 119.17(15)
O(2)-C(3)-C(4) = 121.45(16)
C(1)-C(3)-C(4) = 119.20(15)
Ag(DCO) C(1)-N(1) = 1.332(3)
C(1)-C(2) = 1.422(3)
C(1)-C(3) = 1.488(3)
C(2)-N(2) = 1.143(3)
C(3)-O(1) = 1.247(2)
C(3)-N(3) = 1.343(2)
C(4)-N(3) = 1.472(3)
C(5)-N(3) = 1.446(3)
N(1)-O(2) = 1.277(2)
Ag(PiCO) C(1)-N(1) = 1.320(2)
C(1)-C(2) = 1.430(2)
C(1)-C(3) = 1.487(2)
C(2)-N(2) = 1.150(2)
C(3)-O(2) = 1.217(2)
C(4)-C(5) = 1.528(3)
C(4)-C(7) = 1.537(3)
Antimicrobial Activity Studies. Bacterial Strains and Grow-
ing Conditions. The strains of bacteria were obtained from
Polish Collection of Microorganisms (PCM) of the Institute of
Immunology and Experimental Therapy of Polish Academy of
Sciences and were used throughout this study. Both Gram-
negative and Gram-positive bacteria, as well as yeasts, com-
monly isolated from patients suffering implant-related infec-
tions, were chosen for experiments. They included Escherichia
coli PCM 1144 (ATCC #10536), Klebsiella pneumoniae PCM 57,
Proteus sp. PCM 542 (ATCC# 13315), Pseudomonas aeruginosa
PCM 2563 (ATCC #15442), Streptococcus mutans PCM 2502,
Staphylococcus aureus PCM 2602 (ATCC #6538), Enterococ-
cus hirae PCM 2559 (ATCC #10541), Mycobacterium fortui-
tum PCM 672, Candida albicans PCM 2566 (ATCC #10231).
N(1)-O(1) = 1.3026(19) O(1)-N(1)-C(1) = 118.10(15)
Ag(ECO)a C(1)-N(1) = 1.322(5)
N(1)-C(1)-C(2) = 119.4(4)
N(1)-C(1)-C(3) = 120.5(4)
C(2)-C(1)-C(3) = 120.1(4)
N(2)-C(2)-C(1) = 179.4(5)
O(2)-C(3)-O(3) = 124.0(4)
O(2)-C(3)-C(1) = 118.5(4)
O(3)-C(3)-C(1) = 117.6(4)
C(1)-C(2) = 1.423(6)
C(1)-C(3) = 1.468(6)
C(2)-N(2) = 1.140(5)
C(3)-O(2) = 1.271(5)
C(3)-O(3) = 1.272(5)
C(4)-O(2) = 1.451(8)
C(4)-C(5) = 1.501(11) O(2)-C(4)-C(5) = 106.3(6)
N(1)-O(1) = 1.287(4)
O(1)-N(1)-C(1) = 116.8(3)
C(3)-O(2)-C(4) = 114.2(4)
a Data for disordered mirrored ethoxy group are not present; for
complete details on disorder see CIF file in Supporting Information.
Scheme 3

9868 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
In addition, several multidrug-resistant bacterial strains iso-
lated from patients with nosocomial infections K. pneumoniae
244, P. aeruginosa 2314, AMA, Enterococcus faecium VRE
(vancomycin-resistant), Streptococcus pneumoniae PCI, S. aureus
MRSA (methicillin-resistant), S. aureus MRSC (coagulase-
negative methicillin-resistant), were also included in the in vitro
testing. Bacteria were cultivated on sugar broth at 37 °C for 24 h
in aerobic conditions, and prior to use in tests, cells were diluted
with the same medium to obtain suspensions of about 2 ꢀ 105
cfu/mL.
R-CH2-CN compounds are mostly commercially available
pure substances which can be converted in a one-step
procedure to respective cyanoximes (Scheme 3). These are
three different routes of the Meyer reaction,57 which
depending on the reactivity of the methylene group of
starting acetonitrile were applicable for the preparation
of different cyanoximes. Room temperature nitrosation 1
using gaseous methylnitrite CH3-ONO is the most con-
venient reaction that has been successfully used for syn-
thesis of a variety of cyanoximes.56,58,59 These com-
pounds represent nice crystalline substances60 that can
be easily purified by recrystallization in the presence of
activated carbon, or by flash column chromatography on
silica.
Antibacterial Tests in Solutions. The antibacterial activities of
synthesized Ag(I) cyanoximates were determined against bac-
terial strains by the microplate Alamar Blue assay.54 Stock
solutions of AgL compounds were prepared in DMSO (1 mg/
mL) and then were diluted with appropriate media in the range
from 0.03 to 1000 μg/mL on the cell culture microtitration plate.
Aliquots of 100 μL of the studied AgL compound at different
concentrations and 100 μL of the diluted suspension of the
bacterial cells were added to wells. Control wells contained
either bacteria only or medium only, and plates were incubated
at 37 °C for 48 h. After that, solutions of 20 μL of Alamar Blue
reagent (AbD Serotec) (10ꢀ diluted) and 12.5 μL of 20% Tween
80 were added to wells and incubation was continued at 37 °C
for 2 more hours. The fluorescence was measured using Victor2
apparatus (Wallac, Perkin-Elmer), and the experiment was
repeated three times. The minimal inhibitory concentration
(MIC) was defined as the lowest drug concentration which pre-
vented a color change from blue to pink, inhibiting the bacterial
growth for g90%. Means and standard error values were
determined using the Microsoft Excel.
Identification and characterization of the obtained and
purified organic molecules were carried out using ele-
mental analyses, thin-layer chromatography (TLC), and
1
spectroscopic methods such as UV-visible, IR, H, 13C
NMR spectroscopy (including 2D COSY, HMQC, and
HSQC experiments). Ligands shown in Scheme 2 have
the ability to form chelate complexes and also act as
bridging ligands. They possess interesting features -
electronic and structural - that are reflected in their
hydrophilic/hydrophobic character and acidity (ligands
1-6, Scheme 2), the ability to form layered structures in
the solid state due to π-π stacking interactions between
heterocyclic groups (ligands 7-10, Scheme 2), and, fin-
ally, multiple donor centers capable of tightly binding
silver(I) atoms to form coordination polymers of different
complexity. Coordination compounds of the latter metal
are particularly interesting: they have unusual struc-
tures,61 show properties of gas-sensing materials,41,42 and
lately demonstrate antimicrobial activity.43 These afore-
mentioned electronic and structural factors allow the
fine-tuning of properties of the obtained Ag(I) complexes
and possibility for study of structure-activity relation-
ships during investigations of their in vitro biological
activity.
Antibacterial Tests in Solid State: Soaked Dried Paper Disks
and Pellets. Solutions (or suspensions if the compound was
not completely solubilized) of studied Ag(I) cyanoximates in
DMF at 10 mg/mL concentration were prepared and 20 μL of it
was placed on filter paper discs (diameter 12 mm). These discs
were dried for ∼2 h in the dark prior to testing where each filter
was placed on agar plates with inoculated microorganisms,
which were then incubated at 37 °C for 24 h. Thereafter, micro-
organisms’ growth inhibition zone (if present) was measured
(in mm).
Also, Ag(I) cyanoximates were pressed into 12 mm in diameter
pellets using a Carver 20 tons hydraulic press. The method of
testing pellets was similar to the one described above. Solid
pellets of AgL were carefully placed on agar plates with inocu-
lated bacteria. The exposition time was 24 h at 37 °C, after which
inhibition zones were measured and results were documented by
digital photography.
Silver(I) cyanoximates with ligands shown in Scheme 2
have 1:1 stiochiometry and are poorly soluble in aqueous/
alcohol solutions and thus can be conveniently separated
from the reaction mixture. These AgL complexes are also
insoluble in hydrocarbons, acetone, but are sparingly
soluble in CH3CN. Dry, solid Ag(I) cyanoximates have
shown significant thermal stability and do not decompose
upon heating to 150 °C.
Visible spectra of fine suspensions of studied Ag(I)
cyanoximates in mineral oil revealed broad ligand-
based single band in the range of 400-500 nm that
corresponds to n f π* transition in the nitroso chromo-
phore. Obtained data of electron spectroscopy allowed
estimation of the band gap in AgL, which turned out to
be in the range of 3.00-3.55 eV (Figure S10, Supporting
Results and Discussion
Ten light insensitive silver(I) cyanoxime complexes with
ligands shown in Scheme 2 were synthesized and character-
izedusing spectroscopic methods, X-ray analysis, and invitro
antimicrobial studies. Below we present a description of prop-
erties of the obtained compounds in a systematic way starting
from the chemical part of this work, continued by photo-
physical studies, and then followed by biological investiga-
tions.
Chemical Part: Synthesis and Characterization of
Ligands and Metal Complexes. Recently, we successfully
developed a methodology for a high-yield preparation
of cyanoximes from substituted acetonitriles.55,56 These
(57) Meyer, V. Ber. Deutsch. Chem. Ges. 1873, 6, s.1492.
(58) Robertson, D.; Cannon, J. F.; Gerasimchuk, N. Inorg. Chem. 2005,
44, 23, 8326-8342.
(59) Goeden, L. The Synthesis, Characterization and Bilogical Activity
Studies of Pt(II) and Pd(II) Disubstituted Arylcyanoximates. MS Thesis;
Southwest Missouri State University: Springfield, April 2005.
(60) Mokhir, A. A.; Domasevich, K. V.; Kent Dalley, N.; Kou, X.;
Gerasimchuk, N. N.; Gerasimchuk., O. A. Inorg. Chim. Acta 1999, 284,
85–98.
(54) Ahmed, S. A.; Gogal, R. M.; Walsh, J. E. J. Immunol. Methodol.
1994, 170, 211.
(55) Domasevitch, K. V.; Gerasimchuk, N. N.; Mokhir, A. A. 2000, 39
(6), 1227-1237.
(56) Robertson, D.; Barnes, C.; Gerasimchuk, N. N. J. Coord. Chem.
2004, 57(14), 1205–1216.
(61) Skopenko, V. V.; Ponomareva, V. V.; Simonov, Yu. A.; Domasevitch,
K. V.; Dvorkin, A. A. Russ. J. Inorg. Chem. 1994, 39(8), 1332–1339.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9869
Figure 1. Numbering schemes in crystal structures of silver(I) cyanoximates. Displayedare one anion and its closest Ag(I) environments in Ag(ACO) - A,
Ag(DCO) - B, Ag(PiCO) - C, Ag(ECO) - D. An ORTEP drawing at 50% thermal ellipsoids probability level. Disordered methanol molecules in the
structure of Ag(DCO) and mirror image of the disordered ethoxy-group in the structure of Ag(ECO) are not shown for clarity.
Information). What is the most important for current
studies is that all synthesized AgL are light insensitive
as was shown after many years of their exposure to
daylight without change (Figure 4), and also to the
short wavelength (254 nm) UV radiation (Figure 5).
At that point it was clear that the explanation for a
remarkable light insensitivity of these complexes rests in
their solid-state structures. Despite the poor solubility
of compounds in water, alcohols, acetone, and other
common organic solvents, we were able to grow single
crystals of Ag(I) cyanoximates suitable for the X-ray
analysis. A thermostat with slow cooling of hot satu-
rated AgL solutions within 5-6 days was used for crystal
growth.
Crystal Structures. Details of determined crystal struc-
tures of Ag(ACO), Ag(DCO), Ag(PiCO), and Ag(ECO)
are shown in Figures 1, 2, and 3 below in a way rather
traditional for inorganic chemistry: the one cyanoxime
ligand and closest metal centers, coordination polyhe-
dron of silver(I) cation, and organization of the crystal
lattice, respectively. All these compounds represent co-
ordination polymers of different complexity in which the
metal center is covalently bound to ligands since Ag-O
and Ag-N distances are significantly shorter than the
sum of van der Waals radii of involved atoms equal to
70
˚
˚
3.24 and 3.27 A, and even ionic radii of 2.58 and 2.97 A,
respectively.62 The only basic description of crystal struc-
tures is given below, while the complete set of bond
lengths and valence angles - especially around metal
centers - can be found in CIF files and Supporting
Information (Figures S3-S7).
Ag(ACO). This complex represents layered 2D coordi-
nation polymer in which cyanoxime anion acts as both a
chelating ligand and a bridging group utilizing oxygen
atoms of the amide and nitroso groups (Figure 1A). Bond
lengths in a planar five-membered chelate ring are Ag(1)-
˚
N(1) = 2.352 and Ag(1)-O(2) = 2.455 A with the
“bite angle” N(1)-Ag(1)-O(1) = 68.11°. The anion in
the structure of Ag(ACO) is planar, in the nitroso form
and adopts cis-anti configuration. This configuration
of the oxime anion is contrary to the trans-anti found in
organotin(IV),37 organotellurium(IV),63 and organoanti-
mony(V)55 complexes, but similar to that observed in
(62) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; John Wiley &
Sons: New York, 1972.
(63) Domasevitch, K. V.; Skopenko, V. V.; Rusanov, E. B. Z. Natur-
forsch. 1996, 51b, 832.

9870 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
Figure 2. Geometries of coordination polyhedrons in silver(I) cyanoximates: A - Ag(ACO), B - Ag(DCO), C - Ag(PiCO), D - Ag(ECO).
Ni(II) complexes,64 where the ligand is in the nitroso form
as well. The peculiarity of this structure is rather short
The anion is not planar, and there are two planes in its
structure in the complex: O(2)-N(1)-C(1)-C(2)-N(2)
and C(5)-N(3)-C(4)-C(3) with a dihedral angle of
40.05° between them. The oxygen atom O(1) is off the
˚
“argentophilic” interactions at 3.1934(8) A between Ag(I)
centers in the 2D polymer propagating along the c axis
(Figure 3). For comparison, the Ag-Ag single bond is
2.889 A, while the Ag---Ag distance in metallic silver
-
˚
latter plane by 0.245 A. The DCO anion forms a con-
65
˚
ditional chelate ring with Ag atom: there is no planarity in
the Ag(1)-N(1)-C(1)-C(3)-O(1) ring, and the distance
(Fm3m; f.c.c.) is 4.086 A.66 With consideration of argen-
˚
˚
tophilic interaction the coordination number of silver(I)
center in Ag(ACO) is eight (Figure 2A). The H-bonding
in the amide group is important for the stabilization of the
structure since the only one hydrogen atom of the amide
group in the anion is engaged ininterlayer H-bonding, while
the second hydrogen is involved in intralayer H-bonding
with the oxygen atom of the nitroso group of neighboring
anion.
Ag(DCO). This complex also represents a 2D layered
coordination polymer (Figure 3B) but differently orga-
nized than that in the structure of Ag(ACO). Thus, the
anion acts as a bridge between two silver(I) centers rather
than a chelator (Figure 1B). Contrary to the structure of
Ag(ACO), the CN-group of the anion in the structure of
Ag(DCO) is involved in coordination to the metal center.
Ag(1)-O(1) (2.582 A, Figure 1) represents a long inter-
action between these atoms. Moreover, the oxygen atom
O(1) acts as a bridge between two silver(I) atoms, and its
˚
other contact to the metal center is in 2.697 A in length.
Also, O(1) atom is off the plane Ag(1)-N(1)-O(2)-
˚
C(1)-C(3) by 0.596 A, which is another indication of its
electrostatic involvement into coordination to the silver
atom. Thus, the coordination number of Ag(I) in the
complex is two, with two long electrostatic contacts from
the oxygen atom of the amide group (Figure 2B). The
anion is in the nitroso form and adopts cis-anti config-
uration similar to that in its Cu(II) complex,67 which is
opposite to the trans-anti configuration found in struc-
tures of HDCO68 and Ph4Sb(DCO).55 The bond length
˚
Ag(1)-N(2) is a record short - 2.128 A, and followed by
˚
bond Ag(1)-N(1) = 2.217 A (Figure 2B). The almost
(64) Gerasimchuk, N. N.; Dalley, K. N. J. Coord. Chem. 2004, 57(16),
1431–1445.
(65) Handbook of Chemistry and Physics, 81st ed.; Lide, D. R., Ed.; CRC
Press: Boca Raton, FL, 2000-2001.
(66) Emsley, J. The Elements; Clarendon Press: Oxford, 1991.
(67) Domasevitch, K. V.; Lindeman, S. V.; Struchkov, Yu. T.; Gerasimchuk,
N. N.; Zhmurko, O. A. Russ. J. Inorg. Chem. 1993, 38(1), 98–103.
(68) Simonov, Yu. A.; Dvorkin, A. A.; Gerasimchuk, N. N.; Domasevitch,
K. V.; Malinovskii, T. I. Kristallografiya 1990, 35(3), 766–768.

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9871
Figure 3. Organization of covalent 2D-polymers in the structures of Ag(ACO) (A), Ag(DCO) (B), Ag(PiCO) (C), and Ag(ECO) (D). H-atoms of the
amide group in the structure of Ag(ACO) are omitted for clarity. Coloring scheme: magenta - Ag, gray - C, red - O, blue -N.
linear arrangement between them at the angle N(1)-
Ag(1)-N(2) = 166.11° is responsible for the formation
of polymeric chains which run along the c direction and
joined together by bridging O(1) atom (with long contacts
Ag(1)-O(1) and the angle O(1)-Ag-O(1)0 = 88.48°
between chains) into an elegant 2D layered structure
(Figure 3B). In the crystal, there are also van der Waals
interactions between methyl groups of adjacent layers.
Silver(I) atoms form linear arrays parallel to the c direc-
reflects its unusual bridging role between two metal cen-
ters: the angle Ag(1)-N(2)-Ag(1)0 = 84.95° (Figure 1C).
The nitrogen atom N(2) is not coordinated to these silver
atoms due to geometrical restrictions imposed by its lone
pair situated further along the C(2)-N(2) bond. Thus,
angles Ag(1)-N(2)-C(2), Ag(1)0-N(2)-C(2),andAg(1)-
N(2)-Ag(1)0 are 90.65°, 118.38°, and 84.95 respec-
tively, and are highly improper in value to be considered
for binding of the cyano group. For comparison, the
angle Ag-N(5)-C(5) in the linearly coordinated CN-
group in the structure of Ag(DCO) is 164.65°, while a
similar angle Ag(1)-N(2)-C(2) is 171.26° in the structure
of Ag(ECO) (Figure 2D). Therefore, coordination poly-
hedron of the Ag(I) center in Ag(PiCO) has a slightly dis-
torted and practically planar trigonal geometry (Figure 2C).
2D layers in the structure of the complex are run along the
c direction. Van der Waals interactions between t-butyl
groups of anions exist between layers (Figure 3C). The
˚
tion with intermetallic separation of 3.684 A - longer
than any reasonable metallophilic interactions.
Ag(PiCO). The crystal structure of this compound is a
layered 2D coordination polymer as well (Figure 3C). The
anion performs bridging function between four different
silver(I) atoms (Figure 1C). Similar to the structure of
Ag(ACO), the oxygen atom of the nitroso-group acts as a
bridge between two metal centers (Figure 1C). There are
three short covalent bonds in the coordination polyhe-
dron: two bonds between Ag(I) and oxygen atoms O(1)
and O(1)0 of this bridging nitroso-group and the nitrogen
atom of this group (Figures 1C and 2C). The distance
˚
shortest Ag---Ag distance in this complex is 3.591 A.
Ag(ECO). This is the first known structure containing
this cyanoxime ligand. The crystal structure of this com-
plex follows already described Ag(DCO) and Ag(PiCO)
and also represents layered 2D coordination polymer
(Figure 3D). The ethoxy group in this complex is disordered
by two positions with almost equal occupancies: 0.497
and 0.503. Ag(ECO) structures presented in Figures 1-3
structures contain only a major domain with its mirror image
along C(1)-C(3) direction omitted for clarity. The ECO-
anion in this complex also acts as a bridging ligand between
four different silver(I) centers (Figure 1D). All four bonds bet-
ween the Ag(I) center and surrounding anions are cova-
lent with those to nitrogen atoms N(1) and N(2) being
especially short (Figure 2D). Coordination polyhedron of
˚
Ag(1)-O(2) = 2.614 A is even longer than that in the
structure of Ag(DCO) discussed above. Again, there is
long interaction between these two atoms in Ag(1)-
N(1)-C(1)-C(3)-O(2) arrangement, which is no-planar
with the dihedral angle between mean planes Ag(1)-
O(2)-C(3) and Ag(1)-N(1)-C(1) equal to 21.25°. This
situation is similar to the structure of Ag(DCO), and it
should be mentioned that in chelate complexes, five-mem-
bered rings are typically planar. The anion is in the nitroso-
form (bond length N(1)-O(1) is shorter than C(1)-N(1),
Table 2) and adopts cis-anti configuration. The cyano
group is bent (angle C(1)-C(2)-N(2) = 170.85°) and

9872 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
Figure 4. Vials with silver(I) cyanoximates showing the time of exposure to daylight.
the metal center in this complex is well described as a seesaw.
The anion is in the nitroso-form (Table 2) and adopts a
surprisingly planar trans-anti configuration of its cyano-
˚
xime core. The shortest Ag---Ag distance here is 3.587 A.
Determined single crystal structures of silver(I) cyanoxi-
mates described here silver(I) cyanoximates truly reflect
structures of bulk materials since their calculated and
experimental powder XRD patterns are in a good agree-
ment (Figures S22 and S23, Supporting Information).
Photophysical Part: UV-Light Stability Studies. Silver(I)
cyanoximates with chelating ligands shown in Scheme 2
exhibited a remarkable visible light insensitivity for years
of direct exposure to daylight (Figure 4). This convenient
property coupled with antimicrobial activity makes syn-
thesized complexes potentially valuable materials for
their investigations as additives to acrylate glues during
introduction of indwelling medical devices such as pros-
thetic joints and dental implants (Figure S9, Supporting
Information). These polymeric composites are cured
within several minutes with UV-light that causes cross-
linking and solidifying of the mass into a hard material.
Therefore, studies of stability of Ag(I) cyanoximates
toward short wavelength UV-radiation validated their
choice for further practical considerations. Results of
testing are shown in Figure 5 and indicate great stability
of examined silver(I) cyanoximates for a prolonged per-
iod of time to doses of UV-radiation that completely
darken ionic AgCl used as control photosensitive sub-
stance. That means that fine powders of AgL survive
intact during UV-irradiation sufficient for polymeriza-
tion of the acrylate composite material, which opens
the possibility for their further development for in vivo
experiments and preclinical and clinical studies. The
origin for such significant resistance toward visible and
UV-light is in the structures of complexes. In order to
show light insensitivity a compound should: (a) form a
coordination polymer organized in a manner of zigzag
chains or 2D sheets; (b) contain at least two short covalent
bonds between silver(I) and nitrogen atoms of the ligand;
(c) contain a bridging oxime/nitroso group. Therefore,
based on six established up-to-date crystal structures
of light stable Ag-cyanoximates (four in this work and
the other two are Ag(BCO)61 and Ag(CCO),41 the light-
insensitive motif can be deduced in oxime-based silver(I)
complexes to one in Figure 6.
Figure 5. Resistance of synthesized solid silver(I) cyanoximates Ag-
(CCO), Ag(ACO), Ag(DCO), and Ag(PiCO) toward high-energy UV-
radiation at 254 nm in comparison to conventional light-sensitive silver
chloride.
Figure 6. “Light insensitive motif” in Ag(I) cyanoximates. Solid red
lines - absolutely necessary to have bridging nitroso-group: 6 out of 6
cases; dashed red line - binding of silver atom via the cyano-group, and
formation of a second bridge via the oxygen atom of the nitroso group:
both present in 4 out of 6 cases.
compounds - as antimicrobial light-insensitive additives
to adhesives for indwelling medical devices - only min-
utes of light stability are required. The source of a dark
color in final products of degradation is metallic silver
that is in the colloidal state. This conclusion is based on
comparative analysis of the XRD patterns of fine metallic
silver powder (obtained from substitution reaction be-
tween Al wire and AgNO3 aqueous solution at 293 K,
pH = 6.0) and those for the initial Ag-cyanoximates, and
same complexes darkened after UV-light exposure. Thus,
After many hours of intense short-wavelength UV
radiation powdery samples of Ag-cyanoximates even-
tually become darkened. It should be noted that for
the purpose of intended application of synthesized

Article
Inorganic Chemistry, Vol. 49, No. 21, 2010 9873
Table 3. MIC of Silver(I) Cyanoximates in Solutionsa
MIC
AgL
E. coli
K. pneumoniae
P. aeruginosa
S. mutans
S. aureus
M. fortuitum
C. albicans
Ag(ACO)
Ag(BCO)
0.031
0.031
0.25
1
0.125
0.125
0.5
0.125
0.125
0.25
0.125
0.063
0.125
0.063
1
0.5
0.5
1
0.063
0.063
0.5
0.031
0.016
0.125
0.063
0.016
0.063
0.031
0.016
0.016
0.016
1
0.031
0.031
0.25
0.063
1
Ag(BIHCO)
Ag(BIMCO)
Ag(BOCO)
Ag(BTCO)
Ag(CCO)
Ag(DCO)
Ag(ECO)
Ag(PICO)
erythromycinb
0.031
0.063
0.031
0.031
0.016
0.031
0.016
nec
0.031
0.031
0.031
0.031
0.031
0.031
0.016
ne
1
0.25
0.031
0.063
0.063
0.063
0.063
0.063
0.063
0.25
0.063
d
0.063
0.125
0.063
0.031
0.031
0.063
0.063
0.031
0.031
0.031
0.004
a The lowest MICs are shown in bold. b Erythromycin (antibiotic acting against Gram-positive bacteria). c ne - not examined. d No inhibition effect
was detected.
no lines corresponding to metal Ag were observed in the
Θ-2Θ XRD scans (Figures S13 and S14, Supporting
Information). This is attributed to two factors: (1) to
the small size of silver particles estimated to be less than
˚
∼100 A, and (2) small physical quantity of produced
metallic silver. A typical sample mass of initial AgL spread
over the cardboard used in the UV-irradiation studies
did not exceed 40-50 mg (Figure S8, Supporting Infor-
mation). However, characteristic peaks of “plasmon”
bands69 of colloidal silver at 380-450 nm were detected
in UV-visible spectra of exposed Ag-cyanoximates in
DMSO or Py (Figures S15-S20, Supporting Information)
in addition to the Tyndall effect (Figure S21, Supporting
Information). Both these features showed colloidal state
of metal present in UV-light exposed samples. Studies on the
origin of darkening of exposed to UV-light exposed samples
and physical properties turned out to be very interesting
itself and have developed into a separate investigation,
which is out of scope of this paper. Together with data of
thermal analysis, it will be published separately elsewhere.
Biological Part: In Vitro Assessment of Antibacterial
Activity of Silver(I)-cyanoximates. Studies in Solutions.
All 10 cyanoximates exhibited antimicrobial activity
against the tested infection agents. The lowest MIC
value was detected for Ag(DCO) and Ag(PICO), which
indicated their highest activity (Table 3). These data
suggested that hydrophobic methylated cyanoximes
(Scheme 2) showed stronger inhibitory effect possibly
due to their interactions with cell membranes which
may help in complexes’ intracellular uptake. However,
the solubility of silver(I) cyanoximates in DMSO and
DMF is limited, and, therefore, there was a need in
conducting experiments with solid samples of synthesized
AgL. This was achieved by using dried paper disks
presoaked with AgL solution. Seven out of 10 compounds
were studied in this manner. Investigated compounds
soluble in DMF were remarkably more effective against
clinical isolates from nosocomial infections than to
strains from the Collection of Microorganisms.
Figure 7. Photographs of agar plates showing zones of inhibition by
AgL pellets in two cultures on solid media: in Pseudomonas aeruginosa
(A - bottom view, B - top view) and in Mycobacterium fortuitum
(C - bottom view, D - top view) growth on solid media.
Solid State Studies. Seven cyanoximates (Ag(BCO),
Ag(CCO), Ag(DCO), Ag(ECO), Ag(BIMCO), Ag(BOCO),
and Ag(PiCO)) were deposited on filter papers and tested
for their effect on bacterial growth on solid media. The
inhibition zones of microbial growth was examined and
presented in Figure S11, Supporting Information. The
results demonstrated that studied Ag(I) cyanoximates
exhibit antimicrobial activity in the solid state as well,
but their efficiency was strain dependent. Furthermore,
we tested the antimicrobial effect of the silver(I) cyanoxi-
mates deposited as pressed pellets (12 mm in diameter)
against five strains of microorganisms grown on agar
plates. Figure 7 shows two examples of growth inhibition
experiments and demonstrated clear inhibition zones in
Pseudomonas aeruginosa growth and Mycobacterium for-
tuitum in the presence of Ag(BOCO), Ag(CCO), Ag-
(DCO), and Ag(ECO) pellets. The quantitative data are
summarized in Figure S12 (Supporting Information), and
further confirm that all seven tested silver(I) cyanoxi-
mates inhibit bacterial growth and can be used as agents
to prevent infections and biofilm formations.
(69) (a) Brus, L. Acc. Chem. Res. 2008, 41(12), 1742–1749. (b) Guo, L.; Yu,
J.; Li, Y.; Gu, Y.; Huang, Y.; Mo, Y. Chinese Sci. Bull. 2000, 45(16), 1464–1467.
(c) Malynych, S.; Moroz, I.; Kurlyak, V. Ukr. J. Phys. Opt. 2007, 8(1), 54–59.
(d) Kottmann, J. P.; Martin, O. J. F.; Smith, D. R.; Schultz, S. Phys. Rev. B 2001,
64, 235402. Link, S.; Wang, Z. L.; El-Sayed, M. A. J. Phys. Chem. 1999, 103
(18), 3529–3533. Cardenas-Trivino, G.; Vera, V. L.; Munoz, C. Mater. Res. Bull.
1998, 33(4), 645–653.
Conclusions
Ten silver(I) cyanoximates were synthesized and charac-
terized using elemental analyses, spectroscopic methods, and
(70) Bondi, A. J. Phys. Chem. 1964, 68(3), 441–451.

9874 Inorganic Chemistry, Vol. 49, No. 21, 2010
Gerasimchuk et al.
X-ray analysis. Five complexes were obtained and character-
ized for the first time, while crystal structures were determined
for four compounds. All synthesized Ag(I) complexes have
demonstrated thermal stability upon heating up to 150 °C and
a remarkable light insensitivity. That includes years of ex-
posure to daylight or hours of direct exposure to the short
wavelength (254 nm) UV-radiation. The antimicrobial acti-
vity of all obtained silver(I) cyanoximates was tested both in
solutions and in the solid state against Escherichia coli,
Klebsiella pneumoniae, Proteus sp., Pseudomonas aeruginosa,
Enterococcus hirae, Streptococcus mutans, Staphylococcus
aureus, Mycobacterium fortuitum, Candida albicans, and in
addition on several multidrug-resistant bacterial strains iso-
lated from patients with nosocomial infections K. pneumoniae
244, P. aeruginosa, Streprococcus pneumoniae PCI, AMA,
Enterococcus faecium VRE (vancomycin-resistant), S. aureus
MRSA (methicillin-resistant). Examination of fresh clinical
isolates from nosocomial infections revealed the data valuable
for application purposes of the investigated compounds.
Results have indicated pronounced antimicrobial activity of
studied complexes. A combination of four properties includ-
ing (1) thermal stability, (2) light insensitivity, (3) poor water
solubility, and (4) antimicrobial activity is important for their
intended potential applications in indwelling medical devices.
Thus, visible light insensitive silver(I) complexes with anti-
microbial activity will offer benefits as an adjunct or alternative
material compared to current materials used for implants.
Inertness of these metal compounds toward intense UV-light
allows their application as additives to UV-radiation curable
polymeric glues in joint replacement therapy and dental
implant insertions. Because bacterial adhesion and biofilm
formation are important predisposing factors in the develop-
ment of clinical implant infection, it is crucial that silver(I)
cyanoximates showed an effect on their development. A
significant thermal resistance of these complexes is essential
for equipment sterilization, while poor water solubility will
prevent compounds from leaching out from solidified poly-
meric composites, or from the surface of indwelling devises.
Silver(I) complexes introduced in polymeric acrylate glue
composites will prevent infection from occurring.
medical practice during introduction of indwelling devices
and conduct light-induced bulk polymerization. Samples for
these studies will be in the form of disks or small cylinders in
order to model conditions and shapes for indwelling medical
devices. Mixtures of silver(I) cyanoximates could also be also
tested to ensure broader microbicidal activity. Since preli-
minary experiments demonstrated that Ag(I) cyanoximates
inhibit microbial growth in liquid and solid media, these
complexes may prevent or inhibit bacterial adhesion and
biofilm formation. Thus, the effect of Ag (I) complexes on
adhesion of P. aeruginosa, S. aureus, and S. mutans will be
tested, and then the ability of bacteria to develop biofilm on
the coated surfaces will be investigated as well.
Acknowledgment. N.G. is very grateful to Dr. Marianna
Patrauchan (OSU) and Ms. Janice Young (MSU) for
helpful discussion of the microbiological part of this
work, to Mrs. Jennifer Snyder for patient growing of
suitable crystals of Ag(DCO), to Dr. Bruce Noll (Bruker
AXS) for help with resolution of a two-positional dis-
order in Ag(ECO), and to Mrs. Alex Corbett for technical
help.
Supporting Information Available: Actual photographs of
crystals of AgL (S1); details of crystal structure determination
for Ag(ACO) (S2); table of bonds and angles around silver(I)
atom in the structure of Ag(ACO) (S3-4); table of bonds and
angles around silver(I) atom in the structure of Ag(DCO) (S5);
table of bonds and angles around silver(I) atom in the structure
of Ag(PiCO) (S6); table of bonds and angles around metal center
in the structure of Ag(ECO) (S7); experimental setup for the
photodegradation studies (S8); schematic representation of
application of light-stable antimicrobial Ag(I) complexes as
glue additive during prosthetic joints introduction (S9); visible
spectra of suspensions of two compounds (S10); tables of paper
disks and solid pellets studies antimicrobial studies of synthe-
sized AgL (S11, S12); XRD patterns for several studied com-
plexes and metallic silver as a control (S13, S14); UV-visible
spectra of some AgL samples in DMSO and Py prior and after
their exposure to UV-light (S15, S18); full line shape analysis for
the Ag(ACO) (S16, S17) and Ag(ECO) (S19, S20) systems
selected as examples; the Tyndall effect in those solutions
(S21); calculated from single crystal data and experimental
powder XRD patterns from some bulk AgL (S22, S23). This
material is available free of charge via the Internet at http://
pubs.acs.org.
Future Plans
We will investigate mixtures of silver(I) cyanoximates
with conventional acrylate-based light-curable glues used in