Synthesis, characterization and electrochemistry of 4′-functionalized 2,2′:6′,2″-terpyridine ruthenium(II) complexes and their biological activity

Article abstract of DOI:10.1039/b716011a

The synthesis and characterization of Ru(ii) terpyridine complexes derived from 4′-functionalized 2,2′:6′,2″-terpyridine ligands by a multi step procedure have been described. The complexes are redox-active, showing both metal-centred (oxidation) and ligand-centred (reduction) processes. The antibacterial and antifungal activity of the synthesized ruthenium(ii) complexes [Ru(attpy)₂](PF₆)₂ (attpy = 4′-(4-acryloyloxymethylphenyl)-2,2′:6′,2″-terpyridine); [Ru(mttpy)₂](PF₆)₂ (mttpy = 4′-(4-methacryloyloxymethylphenyl)-2,2′:6′,2″- terpyridine); [Ru(mttpy)(MeOPhttpy)](PF₆)₂ (MeOPhttpy = 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine); and [Ru(mttpy)(ttpy)](PF₆)₂ (ttpy = 4′-(4-methylphenyl)- 2,2′:6′,2″-terpyridine) were tested against four human pathogens (Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli) and five plant pathogens (Curvularia lunata, Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina and Rhizoctonia solani) by the well diffusion method and MIC values of the complexes are reported. A biological study of the complexes indicated that the complexes [Ru(mttpy) ₂](PF₆)₂ and [Ru(mttpy)(MeOPhttpy)](PF ₆)₂ exhibit very good activity against most of the test pathogens and their activity is better than those of some of the commercially available antibiotics like tetracycline and the fungicide carbendazim. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b716011a

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www.rsc.org/dalton | Dalton Transactions
Synthesis, characterization and electrochemistry of 4ꢀ-functionalized
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine ruthenium(II) complexes and their biological activity
Arockiam Anthonysamy,a Sengottuvelan Balasubramanian,*a Vellasamy Shanmugaiahb and
Narayanasamy Mathivananb
Received 17th October 2007, Accepted 28th January 2008
First published as an Advance Article on the web 28th February 2008
DOI: 10.1039/b716011a
The synthesis and characterization of Ru(II) terpyridine complexes derived from 4ꢀ-functionalized
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine ligands by a multi step procedure have been described. The complexes are
redox-active, showing both metal-centred (oxidation) and ligand-centred (reduction) processes. The
antibacterial and antifungal activity of the synthesized ruthenium(II) complexes [Ru(attpy)2](PF6)2
(attpy = 4ꢀ-(4-acryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine); [Ru(mttpy)2](PF6)2 (mttpy =
4ꢀ-(4-methacryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ- terpyridine); [Ru(mttpy)(MeOPhttpy)](PF6)2
(MeOPhttpy = 4ꢀ-(4-methoxyphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine); and [Ru(mttpy)(ttpy)](PF6)2 (ttpy =
4ꢀ-(4-methylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine) were tested against four human pathogens (Proteus vulgaris,
Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli) and five plant pathogens (Curvularia
lunata, Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina and Rhizoctonia solani) by the
well diffusion method and MIC values of the complexes are reported. A biological study of the
complexes indicated that the complexes [Ru(mttpy)2](PF6)2 and [Ru(mttpy)(MeOPhttpy)](PF6)2 exhibit
very good activity against most of the test pathogens and their activity is better than those of some of
the commercially available antibiotics like tetracycline and the fungicide carbendazim.
159mer fragment of the HIV gag gene messenger RNA.9 Another
approach in combining biochemistry with terpyridine supramolec-
Introduction
ular chemistry is the coupling of biotin to a 4ꢀ-aminopyridine,
applying the well-known isocyanate coupling reaction.10 Biotin
is known to bind strongly to the protein avidine via multiple
hydrogen bonding with a geometry comparable to a “lock and
key” system. Collectively these lend ruthenium complexes to redox
activation and photodynamic approaches to therapy as well as the
development of radiopharmaceuticals containing one of several
radionuclides of ruthenium.11,12 Ru(II) complexes are currently
used as antileukaemic and antiviral agents, and for treatment
against several types of other serious disorders such as Crohn’s
disease.13–16
The synthesis and characterization of symmetrical and unsym-
metrical Ru(II) terpyridine complexes and the antibacterial activity
of four terpyridine ruthenium(II) complexes against four human
and five plant pathogens under in vitro conditions are reported in
the present investigation.
Many metal complexes have been shown to possess bioactivity
and several drugs based on metal complexes have been developed.
These include platinum, gold, ruthenium and bismuth compounds
used in the treatment of certain types of cancer, arthritis and
stomach ailments.1,2 In clinical applications and biochemistry,
functionalized terpyridines have found a wide range of potential
uses, ranging from colorimetric metal determination to DNA
binding agents and anti-tumor research.3 Some of these metal
complexes have been reported to be potential anticancer drugs.4
There are three main properties that make ruthenium complexes
well suited for medicinal applications: (i) the rate of ligand
exchange, (ii) the range of accessible oxidation states and (iii) the
ability of ruthenium to mimic iron in binding to certain biological
molecules. There has been considerable interest in ruthenium
complexes, in recent years, because of their redox stability, excited
state reactivity and excited state lifetime.5 Owing to the octahedral
structure of Ru(II) and Ru(III) complexes as opposed to the square-
planar geometry of Pt(II) systems, ruthenium antitumor complexes
exhibit a behavior different from cisplatin, which appears to bind
DNA by cross-linking guanine, thereby causing a class of DNA-
binding proteins to adhere to the site.6–8 The useful incorporation
of terpyridine complexes into an oligonucleotide probe containing
a terpyridine attached to a serinol, which can also act as a building
block in DNA sequencing, was designed in order to target a
Results and discussion
Synthesis of 4ꢀ-functionalized terpyridine ligands and complexes
Several methods are available for the synthesis of terpyridine
ring systems.17–23 These methods suffer from some significant
drawbacks and limitations that can be overcome by using low
molecular weight PEG 300 (PEG = poly(ethylene glycol)) as a re-
action medium as developed by Smith et al.24 4ꢀ-(4-Methylphenyl)-
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (ttpy) was synthesized by the reaction of 2-
acetylpyridine with 4-methyl benzaldehyde in the molar ratio 2 : 1
at 0 ◦C (Scheme 1).
aDepartment of Inorganic Chemistry, School of Chemical Sciences, Uni-
versity of Madras, Guindy Campus, Chennai, 600 025, India. E-mail:
bala2010@yahoo.com; Fax: +91 44 22352870
bCentre for Advanced studies in Botany, University of Madras, Guindy
Campus, Chennai, 600 025, India
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Scheme 1
4ꢀ-(4-Bromomethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (Brttpy) was
synthesized according to the literature method.25 Brttpy was
converted into 4ꢀ-(4-hydroxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
in 54% yield.26 The hydroxy terpyridine was treated with acryloyl
chloride or methacryloyl chloride in 2-butanone at 0 ◦C to afford
4ꢀ-(4-acryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (attpy) or 4ꢀ-
(4-methacryloyloxy methylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ- terpyridine (mttpy)
in 80% yield (Scheme 2).
Scheme 3
a carbonyl carbon peak in the region d 167.12–168.45. The
MeOPhttpy was dissolved in acetonitrile and allowed to evaporate
slowly to give golden yellow colored needle shaped crystals. An
ORTEP diagram30 of MeOPhttpy with atomic labeling scheme is
shown in Fig 1. The MeOPhttpy exhibits a transoid (trans–trans)
arrangement of pyridine rings about the interannular C–C bonds.
The transoid arrangement has been previously reported for similar
terpyridine ligands in the literature.31,32 The three pyridine rings
are approximately coplanar to each other and the two terminal
pyridine rings N2/C6–C10 and N3/C11–C5 make dihedral angles
of 1.66(7) and 3.30(7)◦ respectively with the central pyridine
ring (N1/C1–C5). The dihedral angle of the methoxyphenyl
substituent is 6.17(1)◦ with the N1/C1–C5 pyridine ring.
Scheme 2
Ruthenium(II)–bis(2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine) species are conve-
niently prepared by the stepwise addition of the two terpyridine
ligands to the ruthenium center.27,28 The reaction of mttpy or
attpy or ttpy or MeOPhttpy (MeOPhttpy = 4ꢀ-(4-methoxyphenyl)-
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine) with hydrated ruthenium(III) chloride in
refluxing ethanol afforded a dark brown insoluble ruthenium(III)
mono terpyridine complex in 70% yield. Subsequently the mono
complex was reacted with another equivalent of mttpy at reflux in
methanol under reductive conditions. The resulting ruthenium(II)
bis(terpyridine) complex was precipitated by the addition of
a large excess of ammonium hexaflurophosphate salt and the
[Ru(mttpy)2](PF6)2 or [Ru(attpy)2](PF6)2 was isolated as a red solid
(yield 65–70%) (Scheme 3).
Characterization of 4ꢀ-functionalized terpyridine ligands and
complexes
1
The terpyridine ligands were characterized by UV-VIS, IR, H
NMR, 13C NMR spectroscopy, EI mass spectrometry and elemen-
tal analysis. In the 1H NMR spectra of mttpy and attpy ligands, the
signals for aromatic protons of the terpyridine rings were observed
in the region d 7.30–8.72. The vinylic protons were observed as two
singlets in the region d 5.80–6.18. The benzylic protons appear as
a singlet at d 5.18 with an increase in downfield shift by d 0.7 for
both mttpy and attpy, which is attributed to the absence of the
strong electron withdrawing bromine group29 when compared to
the ligand Brttpy. The 13C NMR spectra of ttpy ligands show
Fig. 1 ORTEP diagram of MeOPhttpy at 30% probability level along
with its atom labeling scheme.
1
The H NMR spectra of [Ru(mttpy)2](PF6)2 and Ru(attpy)2]-
(PF6)2 complexes were recorded in DMSO-d6 solution and all
other unsymmetrical complexes were in CD3CN solution and the
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Fig. 2 1H spectrum of [Ru(mttpy)(MeOPhttpy)](PF6)2.
Table 1 Electronic spectral data for the ruthenium(II) terpyridine
representative spectrum is shown in Fig 2. The signals for aromatic
protons of the terpyridine rings of all the complexes appear in
the region d 7.13–9.51. An upfield shift for the 6,6ꢀꢀ-protons was
observed while comparing the spectrum of the free ligand with that
of the corresponding complex and all other terpyridine protons un-
dergo a downfield shift. The upfield and downfield shifts observed
in the case of the pyridine ring protons were in good agreement
with those previously reported in the literature.33–35 The positive
ion FAB mass spectra of ruthenium(II) terpyridine complexes,
provide compelling evidence for the formation of the complexes.
For example, the symmetrical complex [Ru(mttpy)2](PF6)2 shows
a molecular ion peak at m/z = 917, which is assignable to the
[Ru(mttpy)2 − 2PF6]+ fragment. The overall fragmentation pattern
in the FAB mass spectra of the respective complexes strongly
supports the proposed formulation of the complexes.36,37
complexes
kmax/nm (e/dm3 mol−1 cm−1
MLCT LMCT
)
Complexes
[Ru(mttpy)2](PF6)2
[Ru(attpy)2](PF6)2
[Ru(mttpy)(ttpy)](PF6)
492 (29 400) 312 (78 200), 289 (72 000)
490 (28 496) 309 (78 124), 284 (70 612)
491 (29 386) 312 (78 400), 289 (72 100)
[Ru(mttpy)(MeOPhttpy)](PF6)2 491 (28 436) 310 (78 100), 289 (71 800)
hibits the typical metal to ligand charge transfer (MLCT)
transition of the Ru(II)–terpyridine system at kmax= 492 nm
(e = 29 400 dm3 mol−1 cm−1) and the bands at 289 nm (e =
72 00 dm3 mol−1 cm−1) and 312 nm (e = 78 200 dm3 mol−1 cm−1)
are due to ligand centered (LC) transitions. A small red shift when
compared to that of the model ruthenium(II) terpyridine complex
[Ru(ttpy)2](PF6)2 (kmax= 490 nm; e = 28 000 dm3 mol−1 cm−1)
has been observed.27 The spin allowed metal to ligand charge
transfer (MLCT) band in the visible spectral region undergoes
an increase in intensity and a red shift, regardless of the
electron-donor or electron-acceptor nature of the substituents.
Electronic spectra of the complexes
The electronic spectra of the ruthenium complexes were recorded
in acetonitrile medium and the relevant data are summarized
in Table 1. The UV-VIS spectrum of Ru(mttpy)2(PF6)2 ex-
2138 | Dalton Trans., 2008, 2136–2143
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The [Ru(mttpy)(MeOPhttpy)](PF6)2 complex exhibits a typical
metal to ligand charge transfer (MLCT) transition of the Ru(II)–
terpyridine complex at kmax= 491 nm (e = 28 436 dm3 mol−1 cm−1)
and the ligand centred (LC) transitions at 289 nm (e =
71 800 dm3 mol−1 cm−1) and 310 nm (e = 78 100 dm3 mol−1 cm−1),
which shows that there is a small blue shift when compared to the
symmetrical [Ru(mttpy)2](PF6)2 complex.27,28,38
Electrochemistry of the ruthenium terpyridine complexes
The electrochemical properties of the monomer ruthenium com-
plexes were examined in acetonitrile medium and the relevant
data are shown in Tables 2 and 3. The ferrocene–ferrocenium
(+1) couple was used as an internal standard. The complexes
are redox-active, showing both metal-centered (oxidation) and
ligand-centered (reduction) processes. The metal based oxidation
potentials of the present complexes are significantly higher than
Fig. 3 Cyclic voltammograms of [Ru(attpy)](PF6)2 (scan rate: 100 mV s−1
(C oxidation and D reduction process).
)
substituent, in the unsymmetrical [Ru(mttpy)(MeOPhttpy)](PF6)2
complex allows the stabilization of the Ru(III) state and a shift of 50
mV (E1/2 +1.24 V, quasi-reversible processes) has been observed in
the oxidative processes when compared to [Ru(mttpy)](PF6)2 (E1/2
+1.29 V, quasi-reversible processes).
those observed for the model complexes [Ru(tpy)2](PF6)2 (E1/2
=
+ 0.92 V) and [Ru(ttpy)2](PF6)2 (E1/2 = +1.25 V). For example, the
cyclic voltammogram of the [Ru(mttpy)2](PF6)2 complex exhibits
a reversible oxidation peak at +1.29 V (E1/2) which can be
attributed to the RuII/RuIII process and the first and second ligand
reductions are observed at −1.19 V and −1.43 V (E1/2) respectively.
The oxidation potential increases by 40 mV and the reduction
potential decreases by 50 mV when compared to those of the
model complex27,38 [Ru(ttpy)2](PF6)2. The cyclic voltammogram
of the crylated [Ru(attpy)2(PF6)2] complex (Fig. 3) exhibits a
quasi-reversible oxidation peak at +1.27 V (E1/2) which can be
attributed to the RuII/RuIII process and the first and second
Biological activity of the ruthenium(II) terpyridine complexes
Escherichia coli is an important cause of gastroenteritis and
hemorrhagic colitis. Infection with E. coli O15:H7 can affect all
age groups and it causes more than 20 000 infections and as many
as 250 deaths each year in the USA alone.40 E. coli also produces
Vero toxins resulting in hemorrhagic colitis and hemolytic uremic
syndrome.41 Chronic colonization and infection of the lung
with Pseudomonas aeruginosa is a major cause of morbidity
and mortality in cystic fibrosis (CF) patients.43 Root emergence,
damping off of seedlings, crown and root of mature plants caused
by Rhizoctonia solani is a serious disease of sugar beet.42 Chronic
ulcers are constantly colonized or infected by bacteria such as
P. aeruginosa and Proteus mirabilis.44 P. mirabilis, a motile gram
negative enteric bacterium, is an important pathogen of the
urinary tract and is the primary infectious agent in patients with
indwelling urinary catheters.45 In people whose immune systems
are suppressed, Proteus vulgaris can be an opportunistic pathogen
causing urinary tract infection, pneumonia or septicemia. It is
not sensitive to ampicillin and cephalosporins. R. solani, a soil
borne fungus, causes seedling blight, root rot, fruit rot, or above
ground aerial blight. P. aeruginosa is a bacterium which is difficult
to control while R. solani causes banded leaf and sheath blight.46
The human pathogens namely Escherichia coli, Proteus vulgaris,
Proteus mirabilis and Pseudomonas aeruginosa were maintained on
nutrient agar (NA) consisting of the following (g L−1): beef extract
1.0; yeast extract 2.0, peptone 5.0, NaCl 5.0, agar 15.0; distilled
H2O 1 L; pH 7.2. The plant pathogens viz., Curvularia lunata,
Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina
ligand reductions are observed at −1.20 V and −1.41 V (E1/2
)
respectively. These redox processes are assigned to the successive
reduction of the two tpy ligands, assuming that each ligand can
be reduced within one cycle. Presumably, the first peak belongs to
terpyridine ligand, since the additional aromatic ring (tolyl) lowers
the lowest unoccupied molecular orbital p* due to an increased
conjugation.39 The presence of strongly electron-releasing OMe
Table 2 Electrochemical data for the ruthenium(II) terpyridine complexes
(oxidation process)
Oxidation
Complexes
E
pa/V
Epc/V
E
1/2/V
DE/mV
a
[Ru(tpy)2](PF6)2
+0.95
+1.28
+1.32
+1.30
+1.33
+0.89
+1.22
+1.26
+1.23
+1.23
+1.20
+0.92
+1.25
+1.29
+1.27
+1.28
+1.24
60
60
60
70
100
80
a
[Ru(ttpy)2](PF6)2
[Ru(mttpy)2](PF6)2
[Ru(attpy)2](PF6)2
[Ru(mttpy)(ttpy)](PF6)
[Ru(mttpy)(MeOPhttpy)](PF6)2 +1.28
a Model complexes.27,38
Table 3 Electrochemical data of ruthenium(II) terpyridine complexes (reduction process)
ttpy/ttpy−
ttpy/ttpy2−
Complexes
1Epa/V
1Epc/V
1E1/2/V
1DE/mV
2Epa/V
2Epc/V
2E1/2/V
2DE/mV
[Ru(mttpy)2](PF6)2
[Ru(attpy)2](PF6)2
[Ru(mttpy)(ttpy)](PF6)
[Ru(mttpy)(MeOPhttpy)](PF6)2
−1.22
−1.23
−1.20
−1.26
−1.16
−1.16
−1.16
−1.18
−1.19
−1.20
−1.18
−1.22
60
70
40
80
−1.48
−1.47
−1.46
−1.47
−1.38
−1.35
−1.37
−1.38
−1.43
−1.41
−1.42
−1.43
110
120
90
90
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Table 4 In vitro antibacterial activity against human pathogens (MICa/lg ml−1
)
Complexes
P. vulgaris
P. mirabilis
P. aeruginosa
E. coli
[Ru(attpy)2](PF6)2
20
20
12
25
15
NI
28
17
15
10
20
NI
25
17
14
13
20
NI
22
12
10
12
15
NI
[Ru(mttpy)2](PF6)2
[Ru(mttpy)(MeOPhttpy)](PF6)2
[Ru(mttpy)(ttpy)](PF6)2
Tetracycline
DMSO (control)
a MIC: Minimum inhibitory concentration; NI: no inhibition.
Table 5 In vitro antifungal activity against plant pathogens (MICa/lg ml−1
)
Complexes
R. solani
M. phaseolina
F. oxysporum
F. udum
C. lunata
[Ru(attpy)2](PF6)2
36
12
17
34
25
NI
14
15
9
7
18
NI
11
10
14
28
15
NI
30
29
19
11
12
NI
9
10
11
8
8
NI
[Ru(mttpy)2](PF6)2
[Ru(mttpy)(MeOPhttpy)](PF6)2
[Ru(mttpy)(ttpy)](PF6)2
Carbendazim
DMSO (control)
a MIC: Minimum inhibitory concentration; NI: no inhibition.
and Rhizoctonia solani were maintained on potato dextrose agar
(PDA) containing the following (g L−1): potato 200; dextrose 20;
agar 15; distilled H2O 1 L and the pH was maintained at 6.5. All
the above cultures were maintained in slants or Petri plates at room
temperature (28 2 ◦C). The minimum inhibitory concentration
(MIC) is defined as the lowest concentration of an antimicrobial
that will inhibit the visible growth of a microorganism after
overnight incubation. If there is nil growth of the organism, it
is indicated by a + sign and if there is no retardation in its growth,
it is indicated by a − sign.
pathogenic fungi compared to a DMSO control. The relevant
data are reproduced in Table 5. Further, the antifungal activity of
the test compounds was dose dependent and it was appreciable at
higher concentrations. Among the four complexes tested, the com-
plexes [Ru(mttpy)2](PF6)2 and [Ru(mttpy)(MeOPhttpy)](PF6)2
show remarkable antifungal activity against three economi-
cally important test pathogens viz. R. solani, M. phaseolina
and F. oxysporum compared to the rest of the complexes
and the commercial fungicide, carbendazim. The minimum in-
hibitory concentration of the complexes [Ru(mttpy)2](PF6)2 and
[Ru(mttpy)(MeOPhttpy)](PF6)2 against the above three plant
pathogens range from 10 to 15 lg ml−1 and 9 to 17 lg ml−1,
respectively compared to 15 and 25 lg ml−1 in carbendazim
(Table 5). These results are comparable with those of other
ruthenium complexes like [Ru(M)2(U)]2+, where M = 2,2ꢀ-
bipyridine/1,10-phenanthroline and U = tpl (Ru1), 4-Cl-tpl
(Ru2), 4-CH3-tpl (Ru3), 4-CH3O-tpl (Ru4), and 4-NO2-
Antibacterial activity
All four complexes exhibit different levels of inhibition against the
tested human pathogenic bacteria. The antibacterial activity of
the test compounds was dose dependent and it was pronounced at
higher concentrations. The complex [Ru(mttpy)(MeOPhttpy)]-
(PF6)2 shows remarkable antibacterial activity against all the test
pathogens compared to rest of the complexes and a commercial an-
tibiotic, viz. tetracycline. The minimum inhibitory concentration
of the complex [Ru(mttpy)(MeOPhttpy)](PF6)2 against human
pathogens was determined to be between 10 and 15 lg ml−1 as
compared to between 15 and 20 lg ml−1 in tetracycline. The
complexes [Ru(mttpy)(ttpy)](PF6)2 and [Ru(mttpy)2](PF6)2 exhibit
superior antibacterial activity towards four human pathogens
viz. P. vulgaris, P. mirabilis, P. aeruginosa and E. coli when
compared to the antibiotic tetracycline. The minimum inhibitory
concentration of the complexes [Ru(mttpy)(ttpy)](PF6)2 and
[Ru(mttpy)(MeOPhttpy)](PF6)2 against the above three bacterial
pathogens ranges from 10–25 lg ml−1 and 10–15 lg ml−1,
respectively compared to 15–20 lg ml−1 in tetracycline (Table 4).
However, the complex [Ru(attpy)2](PF6)2 was comparatively less
effective against all four human pathogens.
tpl (Ru5), -pai (Ru6), where tpl
=
thiopicolinanilide
6
and pai 2-phenyl-azo-imidazole as well as [Ru(g -p-
=
6
cymene)X2]2, [Ru(g -p-cymene)X2(pta)] (where pta= 1,3,5-triaza-
6
2+
7-phosphatricyclo[3.3.1.1.]decane), [H4 Ru4(g -p-benzene)4]
and [Ru(PPh3)2(LH)2]ClO4(where L= 4-phenyl/4-cyclohexyl
thiosemicarabazones of pyridine 2-aldehyde and thiophene-2-
aldehyde) previously reported in the literature.47–49
Conclusion
The synthesis of a Ru(II) complex with the 4ꢀ-(4- methacryloylo-
xymethylphenyl)-2,2ꢀ: 6ꢀ,2ꢀꢀ-terpyridine ligand has been achieved
by a multi step procedure. All four complexes investigated in the
present study exhibit antimicrobial activity against four human
and five plant pathogens. The biological study of the complexes
[Ru(mttpy)2](PF6)2 and [Ru(mttpy)(MeOPhttpy)](PF6)2 can be
investigated further as these systems exhibit very good activity
against most of the test pathogens and their activity is better than
some of the commercially available antibiotics and fungicide.
Antifungal activity
Similar to the antibacterial activity, all four complexes exhibit
different levels of antifungal activity against the five tested plant
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and the suspension was heated at 100 ◦C for 2 h. During this time,
the color of the mixture changed from red to dark green and was
accompaniedby the formationofa fine precipitate. Milliporewater
(200 mL) was added and the precipitate of substituted terpyridine
was isolated by filtration, washed with 100 mL of water, 20 mL of
cold ethanol and dried under vacuum.
Experimental methods
Materials
2-Acetylpyridine, p-methoxybenzaldehyde, p-tolualdehyde, tri-
ethylamine,
N-bromosuccinimide,
azobis(isobutyronitrile),
RuCl3·3H2O and N-ethylmorpholine were received from
E.Merck. Acryloylchloride and methacryloylchloride were
synthesized according to the literature method.50
4ꢀ-(4-Methylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (ttpy). Yield: 8.5 g
◦
1
(63%); mp: 167–170 C; IR (KBr disc m/cm−1): 3386, 1589; H
NMR (500 MHz, CDCl3) d: 2.42 (s, 3H, CH3), 7.30–7.34 (m,
2H), 7.82 (d, 2H, J = 8.0 Hz), 7.85–7.86 (m, 4H), 8.66 (d, 2H,
J = 7.5 Hz), 8.72–8.73 (m, 4H); 13C NMR (125 MHz, CDCl3)
d: 21.39, 118.72, 121.48, 123.88, 127.42, 129.75, 135.53, 136.98,
149.17, 150.26, 155.90, 156.39; mass (EI, 70 eV); m/z (%): 323
(100).
Instrumentation
Infrared spectra of the precursor compounds, ligands and their
complexes were recorded in the range 4000–400 cm−1 using KBr
pellets on a Shimadzu FTIR 8000 spectrophotometer/Perkin
Elmer Spectrum RX1 FTIR spectrophotometer. 1H and 13C NMR
spectra of the ligands and complexes were obtained using a JEOL
GSX400 Fourier Transform NMR spectrophotometer operating
at 400 MHz and 100 MHz respectively. Electronic spectra of
the complexes were recorded on a Hitachi 320 double beam
spectrophotometer. Acetonitrile or DMF were used as the solvent
for all measurements. The FAB mass spectra of complexes were
obtained on a JEOL SX 102/DA-6000; m-nitrobenzylalcohol
(NBA) was used as the matrix. Electron impact mass spectra
of the ligands were obtained on a JNS-DX 303 HF mass
spectrometer. The C, H, N contents of the ligands and complexes
were carried out using Carlo Erba Elemental analyzer Model 1106
and Haereus CHN rapid analyser. The cyclic voltammograms of
10−3 M solutions of complexes were obtained on a CHI600A
electrochemical analyzer. The measurements were carried out
under oxygen free conditions using a three electrode cell in
which a glassy carbon electrode was the working electrode, a
saturated Ag/AgCl electrode was the reference electrode and a
platinum wire was used as an auxiliary electrode. The ferrocene–
ferrocenium (+1) couple was used as an internal standard and
4ꢀ-(4-Methoxyphenyl)-2,2ꢀ:6ꢀ,2ꢀ◦ꢀ-terpyridine
(MeOPhttpy).
Yield: 9.1 g (65%); mp: 161–163 C; IR (KBr disc m/cm−1): 3055,
1565; 1H NMR (400 MHz, CDCl3) d: 3.86 (s, 3H, CH3), 7.02 (d,
2H, J = 8.8 Hz), 7.31–7.34 (m, 2H), 7.83–7.88 (m, 4H), 8.64–8.72
(m, 6H); 13C NMR (100 MHz, CDCl3) d: 55.32, 114.29, 118.24,
121.34, 123.70, 128.49, 130.73, 136.79, 149.05, 149.10, 149.72,
155.35, 156.35, 160.50; mass (EI, 70 eV); m/z (%) : 339 (100).
4ꢀ-(4-Hydroxyphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (HOPhttpy). Yield:
8.6 g (64%); mp: 310–312 ◦C; IR (KBr disc m/cm−1): 3070, 1595,
1
1585; H NMR (400 MHz, CDCl3) d: 7.00 (d, 2H, J = 8.8 Hz),
7.33–7.36 (m, 2H), 7.83–7.87 (m, 4H), 8.64–8.78 (m, 6H), 9.85 (s,
br, 1H); 13C NMR (100 MHz, CDCl3) d: 114.22, 118.34, 121.39,
123.50, 128.42, 130.53, 136.79, 149.25, 149.18, 149.62, 155.45,
156.37, 160.57; mass (EI, 70 eV); m/z (%) : 325 (100).
Synthesis of 4ꢀ-(4-bromomethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
(Brttpy)
Brttpy was synthesized according to the literature method. Yield:
E
1/2 of the ferrocene–ferrocenium couple under these experimental
◦
3.46 g (70%).; mp: 176 C. IR (KBr disc m/cm−1): 1584, 790; H
NMR (500 MHz, CDCl3) d: 4.55 (s, 2H), 7.33–7.35 (m, 2H), 7.52
(d, 2H, J = 8.6 Hz), 7.85–7.89 (m, 4H), 8.65 (d, 2H, J = 8.1 Hz),
8.72–8.73 (m, 4H); 13C NMR (125 MHz, CDCl3) d: 33.09, 118.89,
121.48, 123.99, 127.71, 127.85, 137.03, 138.64, 138.71, 149.19,
149.56, 156.04, 156.16; anal. calcd for : C22H16BrN3 (402.29):
calculated (%); C, 65.68; H, 4.01; N, 10.44; found (%); C, 65.40;
H, 3.86; N, 10.50.
1
conditions was 470 mV in DMF medium and DEp for Fe/Fe+ is
70 mV. Tetra(n-butyl)ammonium perchlorate (TBAP) was used as
supporting electrolyte (CAUTION! TBAP is potentially explosive;
hence care should be taken in handling the compound) and the
concentration of TBAP was 10−1 M.
Test organisms
The cultures of human and plant pathogens used in this study
were obtained from the culture collections of Biocontrol and
Microbial Metabolites Lab, Centre for Advanced Studies in
Botany, University of Madras.
Synthesis of 4ꢀ-(4-hydroxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
(HOttpy)
Brttpy (0.95 g, 2.36 mmol) was converted into HOttpy in 54% yield
by using NaHCO3 (0.240 g, 2.85 mmol) in a water–acetonitrile
General synthetic procedure for 4ꢀ-functionalized terpyridines24
◦
solvent mixture. Yield: 0.482 g (60%); mp: 197–198 C; UV-VIS
2-Acetylpyridine (10.0 g, 82.5 mmol) was added to a suspen-
sion of crushed NaOH (3.3 g, 82.5 mmol) in poly(ethylene
glycol) (PEG 300) (70 mL) and stirred at 0 ◦C for 10 min.
p-Methoxybenzaldehyde (5.61 g, 41.2 mmol) or p-tolualdehyde
(4.96 g, 41.2 mmol) or p-hydroxybenzaldehyde (5.04 g, 41.2 mmol)
was added via asyringe and the suspension was kept at 0 ◦C for 2 h.
The suspension was manually stirred with spatula every 15 min
as the viscosity becomes too high for adequate mixing with a
magnetic stirrer. After 2 h, NH4OAc (20 g) was added in excess
(CH3CN); kmax nm (e/dm3 mol−1 cm−1): 286 (32 860), 227 (16 280);
1
IR (KBr disc m/cm−1): 3386, 1589; H NMR (500 MHz, CDCl3)
d: 1.71 (br s, 1H), 4.78 (s, 2H), 7.34–7.36 (m, 2H), 7.49 (d, 2H, J =
8.1 Hz), 7.86–7.90 (m, 4H), 8.66 (d, 2H, J = 8.0 Hz), 8.68–8.70 (m,
2H), 8.72 (s, 2H); 13C NMR (500 MHz, CDCl3) d: 64.94, 118.86,
121.51, 123.96, 127.50, 127.55, 137.03, 137.69, 142.03, 149.19,
150.01, 155.99, 156.32; mass (EI, 70 eV); m/z (%) : 339 (100);
anal. calcd for : C22H17N3O (339.39): calculated (%); C, 77.86; H,
5.05; N, 12.38; found (%); C, 77.49; H, 5.17; N, 12.26.
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Synthesis of 4ꢀ-(4-methacryloyloxymethylphenyl)-
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (mttpy)
(76%); UV-VIS (CH3CN); kmax nm (e/dm3 mol−1 cm−1): 492
(29 400), 312 (78 200), 289 (72 000); IR (KBr disc m/cm−1): 1712,
1608, 1161, 840; 1H NMR (400 MHz, DMSO-d6) d: 1.98 (s, 6H),
5.40 (s, 4H), 5.80 (s, 2H), 6.18 (s, 2H), 7.28 (t, 4H, J = 6.3 Hz), 7.54
(d, 4H, J = 4.9 Hz), 7.77 (d, 4H, J = 7.8 Hz), 8.06 (t, 4H, J = 7.8
Hz), 8.43 (d, 4H, J = 8.3 Hz), 9.08 (d, 4H, J = 8.3 Hz), 9.48 (s, 4H);
13C NMR (100 MHz, DMSO-d6) d: 19.01, 65.98, 120.98, 124.05,
124.87, 125.65, 127.72, 129.56, 132.31, 135.23, 136.56, 137.90,
145.59, 152.29, 155.08, 157.79, 167.98; FAB+-MS (nitrobenzyl
alcohol matrix), m/z: 916 [M − 2PF6]+, 1061 [M − PF6]+; anal.
calcd for : C52H42F12N6O4P2Ru (1205.93): calculated (%); C, 51.79;
H, 3.51; N, 6.97; found (%); C, 51.70; H, 3.59; N, 6.84.
HOttpy (0.486 g, 1.43 mmol) and triethylamine (0.20 mL,
1.43 mmol) were dissolved in 2-butanone and methacryloyl
chloride (0.14 mL, 1.43 mmol) was added dropwise at 0 ◦C to the
solution. After the addition was over, the mixture was stirred for
another 6 h. The triethylamine hydrochloride salt formed during
this reaction was filtered off and the filtrate was concentrated
under reduced pressure. The crude product was recrystallized
from methanol. Yield: 0.47 g (80%). UV-VIS (CH3CN); kmax nm
(e/dm3 mol−1 cm−1): 287 (30 640), 227 (17 202); IR (KBr disc
1
m/cm−1): 2923, 1720, 1585, 1184; H NMR (400 MHz, CDCl3)
[Ru(attpy)2](PF6)2. Yield: 0.70 g (71%); UV-VIS (CH3CN);
kmax nm (e/dm3 mol−1 cm−1): 490 (28 496), 309 (78 124), 284
d: 1.92 (s, 3H), 5.19 (s, 2H), 5.54 (s, 1H), 6.12 (s, 1H), 7.34–7.45
(m, 4H), 7.87 (m, 4H), 8.64–8.68 (m, 4H), 8.72 (s, 2H); 13C NMR
(100 MHz, CDCl3) d: 18.33, 65.92, 119.39, 121.92, 124.12, 125.95,
127.58, 128.49, 136.17, 137.28, 137.91, 142.45, 148.28, 150.01,
155.02, 155.23, 167.18; mass (EI, 70 eV); m/z (%): 407.67 (100);
anal. calcd for C26H21N3O2 (407.46): calculated (%); C, 76.64; H,
5.19; N, 10.31; found (%); C, 76.69; H, 5.16; N, 10.26.
1
(70 612); IR (KBr disc m/cm−1) 1712, 1608, 1161, 840; H NMR
(400 MHz, DMSO-d6) d: 5.38 (s, 4H), 5.90 (dd, 2H, J = 11.5 Hz),
6.27 (dd, 2H, J = 11.2 Hz), 6.40 (dd, 2H, J = 17.5 Hz), 7.28 (t, 4H,
J = 6.5 Hz), 7.54 (d, 4H, J = 4.9 Hz), 7.77 (d, 4H, J = 7.8 Hz),
8.06 (t, 4H, J = 7.8 Hz), 8.43 (d, 4H, J = 8.3 Hz), 9.08 (d, 4H, J =
8.3 Hz), 9.48 (s, 4H); 13C NMR (100 MHz, DMSO-d6) d: 65.98,
120.98, 124.05, 124.87, 125.65, 127.72, 129.56, 132.31, 135.23,
136.56, 137.90,145.59, 152.29, 155.08, 157.79, 167.98; FAB+-MS
(nitrobenzyl alcohol matrix), m/z: 889 [M − 2PF6]+, 1033 [M −
Synthesis of 4ꢀ-(4-acryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
(attpy)
This compound was synthesized in a similar fashion to that of 4ꢀ-
(4-methacryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine by using
acryloyl chloride instead of methacryloylchloride. Yield: 0.46 g
(81%) UV-VIS (CH3CN); kmax nm (e/dm3 mol−1 cm−1): 287
(29 622), 228 (18 202); IR (KBr disc m/cm−1): 2928, 1732, 1580,
1184; 1H NMR (400 MHz, CDCl3) d: 5.18 (s, 2H), 5.58 (dd, 1H,
J = 2.0, 10.0 Hz), 6.18 (dd, 1H, J = 2.0, 10.6 Hz), 6.26 (dd,
1H, J = 2.0, 17.2 Hz), 7.34–7.45 (m, 4H), 7.87–7.89 (m, 4H),
8.64–8.68 (m, 4H), 8.73 (s, 2H).; 13C NMR (100 MHz, CDCl3)
d: 18.53, 64.92, 119.56, 122.02, 124.32, 126.05, 127.58, 128.79,
136.97, 137.88, 138.61, 142.85, 148.28, 150.50, 155.09, 155.28,
167.14; anal. calcd for C25H19N3O2 (393.44): calculated (%); C,
76.32; H, 4.87; N, 10.68; found (%); C, 76.67; H, 4.95; N, 10.25;
mass (EI, 70 eV); m/z (%): 394.12 (100).
PF6]+ anal. calcd for: C50H38F12N6O4P2Ru (1177.87): calculated
;
(%); C, 50.98; H, 3.25; N, 7.13; found (%); C, 51.60; H, 3.40; N,
6.62.
[Ru(mttpy)(ttpy)](PF6)2. Yield: 0.75
g
(82%); UV-VIS
(CH3CN); kmax nm (e/dm3 mol−1 cm−1): 491 (29 386), 312 (78 400),
289 (72 100); IR (KBr disc m/cm−1): 1713, 1614, 1161, 830; H
1
NMR (400 MHz, CD3CN) d: 1.93 (s, 3H), 2.01 (s, 3H), 5.36 (s,
2H), 5.72 (s, 1H), 6.18 (s, 1H), 7.19 (t, 4H, J = 6.1 Hz), 7.45 (d,
4H, J = 5.9 Hz), 7.77 (d, 4H, J = 8.2 Hz), 7.97 (t, 4H, J = 8.0
Hz), 8.23 (d, 4H, J = 8.2 Hz), 8.66 (d, 4H, J = 7.8 Hz), 9.02
(s, 4H);13C NMR (100 MHz, CD3CN) d: 18.34, 21.39, 65.43,
118.20, 124.52, 125.39, 126.39, 127.34, 128.83, 129.76, 136.34,
137.41, 138.84, 139.86, 153.37, 156.54, 159.23, 168.12; FAB+-MS
(nitrobenzyl alcohol matrix), m/z: 832 [M − 2PF6]+, 976 [M −
PF6]+; anal. calcd for: C48H38F12N6O2P2Ru (1121.85): calculated
(%); C, 51.39; H, 3.41; N, 7.49; found (%);C, 51.50; H, 3.82; N,
7.66.
General method of synthesis of ruthenium(III) complexes
4ꢀ-(4-Methacryloyloxymethylphenyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine
(mttpy) (0.50 g, 1.23 mmol) or 4ꢀ-(4-acryloyloxymethylphenyl)-
2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (attpy) was added to RuCl3·3H2O (322 mg,
1.23 mmol) in ethanol and refluxed for 8 h under an inert
atmosphere. The mixture was cooled and the dark brown
precipitate was collected by filtration, washed thoroughly with
methanol, water and diethyl ether and dried under vacuum. Yield:
(0.530 g, 70%).
[Ru(mttpy)(MeOPhttpy)](PF6)2. Yield: 0.73 g (78%); UV-VIS
(CH3CN); kmax nm (e/dm3 mol−1 cm−1): 491 (28 436), 310 (78 100),
1
289 (71 800); IR (KBr disc m/cm−1): 1713, 1614, 1161, 839; H
NMR (500 MHz, CD3CN) d: 1.92 (s, 3H), 3.94 (s, 3H), 5.36 (s,
2H), 5.77 (s, 1H), 6.19 (s, 1H), 7.15 (t, 4H, J = 4.8 Hz), 7.28 (d,
2H, J = 5.9 Hz), 7.42 (d, 4H, J = 5.6 Hz), 7.74 (d, 2H, J = 5.3
Hz), 7.92 (t, 4H, J = 7.6 Hz), 8.07 (d, 2H, J = 8.3 Hz), 8.15 (d, 2H,
J = 8.3 Hz), 8.62 (d, 4H, J = 7.8 Hz), 8.91 (s, 2H), 8.93 (s, 2H);
FAB+-MS (nitrobenzyl alcohol matrix), m/z: 848 [M − 2PF6]+,
993 [M − PF6]+; anal. calcd for: C48H38F12N6O3P2Ru (1137.85):
calculated (%); C, 50.67; H, 3.37; N, 7.39; found (%); C, 51.99; H,
3.60; N, 7.56.
General method of synthesis of ruthenium(II) complexes
[Ru(mttpy)2](PF6)2. mttpy (0.331 g, 0.812 mmol) was added
to [Ru(mttpy)]Cl3 (0.50 g, 0.813 mmol) in methanol along with
N-ethylmorpholine (5 drops). The mixture was refluxed for 6 h
under an inert atmosphere. The resulting deep red solution
was filtered and a three-fold excess of methanolic ammonium
hexafluorophosphate was added to the filtrate. The resulting
red precipitate was filtered off and recrystallized from acetone–
acetonitrile solution and dried under vacuum.28 Yield: 0.750 g
Antibacterial activity of compounds against human pathogens
The antibacterial activity of the synthesized ruthenium(II)
complexes [Ru(attpy)2](PF6)2; [Ru(mttpy)2](PF6)2; [Ru(mttpy)-
(MeOPhttpy)](PF6)2; and [Ru(mttpy)(ttpy)](PF6)2 was tested
2142 | Dalton Trans., 2008, 2136–2143
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against human pathogens by the well diffusion method.51,52
One mL inoculum of each test pathogen was added to the molten
nutrient agar (NA) medium and poured into a sterile Petri dish
under aseptic conditions. After solidification, a 5 mm well was
made in the center of each plate using a sterile cork borer. Different
concentrations of the complex were made from the stock solution
which was filter sterilized using 0.25 lm filter paper. Each well
received 50 lL solution of each compound and the Petri dishes
were incubated at room temperature. 100 lL dimethyl sulfoxide
(DMSO) 99% was used as a test control. After 48 h, the appearance
of an inhibition zone around the well was observed.
17 M. Heller and U. S. Schubert, Eur. J. Org. Chem., 2003, 947.
18 F. Kro¨hnke, Synthesis, 1976, 1.
19 K. T. Potts, M. J. Cipullo, P. Ralli and G. Theodoridis, J. Org. Chem.,
1982, 47, 3027.
20 U. S. Schubert and C. Eschbaumer, J. Org. Chem., 1999, 64, 1027.
21 M. Heller and U. S. Schubert, J. Org. Chem., 2002, 67, 947.
22 M. Heller and U. S. Schubert, Synlett, 2002, 5, 751.
23 G. W. V. Cave and C. L. Raston, Chem. Commun., 2000, 2199.
24 C. B. Smith, C. L. Raston and A. N. Sobolev, Green Chem., 2005, 7,
650.
25 A. K. Mohanakrishnan and P. C. Srinivasan, Synth. Commun., 1995,
25, 2407.
26 I. Eryazici, C. N. Moorefield, S. Durmus and G. R. Newkome, J. Org.
Chem., 2006, 71, 1009.
27 J.-P. Collin, S. Guillerez, J. P. Sauvage, F. Barigelletti, L. De Cola, L.
Flamigni and V. Balzani, Inorg. Chem., 1991, 30, 4230.
28 A. Anthonysamy, S. Balasubramanian, B. Muthuraaman and P.
Maruthamuthu, Nanotechnology, 2007, 18, 095701.
29 R.-A. Fallahpour, M. Neuburger and M. Zehnder, Polyhedron, 1999,
18, 2445.
30 A. Anthonysamy, S. Balasubramanian, K. Chinnakali and H. -K. Fun,
Acta Crystallogr., Sect. E, 2007, 63, o1148.
31 G. D. Storrier, S. B. Colbran and D. L. Craig, J. Chem. Soc., Dalton
Trans., 1997, 3011.
32 R.-A. Fallahpour, M. Neuburger and M. Zehnder, New J. Chem., 1999,
23, 53.
33 U. S. Schubert, C. Eschbaumer, O. Hien and P. R. Andres, Tetrahedron
Lett., 2001, 42, 4705.
34 A. El-ghayoury, H. Hofmeier, A. P. H. J. Schenning and U. S. Schubert,
Tetrahedron Lett., 2004, 45, 261.
Antifungal activity of compounds against plant pathogens
The antifungal activity of
ruthenium(II)
complexes
[Ru(attpy)2](PF6)2; [Ru(mttpy)2](PF6)2; [Ru(mttpy)(MeOPhttpy)]-
(PF6)2; [Ru(mttpy)(ttpy)](PF6)2 was tested on the mycelial growth
of test fungi using the well diffusion technique. The DMSO
solution of each compound mixed with molten potato dextrose
agar (PDA) was poured into a 9 cm Petri dish and allowed to
solidify. The plates were inoculated with 5 mm mycelial discs of
the test fungi. The PDA with 10% DMSO was taken as control.
The plates were incubated at room temperature for 6 d and the
mycelial growth was measured.
35 P. R. Andres, R. Lunkwitz, G. R. Pabst, K. Bo¨hn, D. Wouters, S.
Schmatloch and U. S. Schubert, Eur. J. Org. Chem., 2003, 3769.
36 F. Barigelletti, B. Ventura, J.-P. Collin, L. Flamigni and J. P. Sauvage,
Eur. J. Inorg. Chem., 2000, 113.
37 E. C. Constable, R. W. Handel, C. E. Housecroft, A. F. Morales, B.
Ventura, L. Flamigni and F. Barigelletti, Chem.–Eur. J., 2005, 11,
4024.
Acknowledgements
Financial support from the DST, New Delhi is gratefully acknowl-
edged.
38 J. P. Sauvage, J. P. Collin, J. C. Chambron, S. Guillerez, C. Coudret, V.
Balzani, F. Barigelletti, L. De Cola and L. Flamigni, Chem. Rev., 1994,
94, 993.
References
1 E. Alessio, Y. Xuu, S. Cauci, G. Mestroni, F. Quadrifoglio, P. Viglino
and L. G. Marzilli, J. Am. Chem. Soc., 1989, 111, 7068.
2 A. S. Gaballa, M. S. Asker, A. S. Barakat and S. M. Teleb, Spectrochim.
Acta, Part A, 2007, 67, 114.
3 M. J. Maclachlan, M. Ginzburg, N. Coombs, T. W. Coyle, N. P. Raju,
J. E. Greedan, G. A. Ozin and I. Manners, Science, 2000, 287, 1460.
4 M. J. Clarke, F. Zhu and D. R. Frasca, Chem. Rev., 1999, 99, 2511.
5 V. Balzani, A. Juris, M. Venturi, S. Campagna and S. Serroni, Chem.
Rev., 1996, 96, 759.
6 A. Gelasco and S. J. Lippard, Top. Biol. Inorg. Chem., 1999, 1, 1.
7 E. R. Jamieson and S. J. Lippard, Chem. Rev., 1999, 99, 2467.
8 N. Farrell, Y. Qu and J. D. Roberts, Top. Biol. Inorg. Chem., 1999, 1,
99.
9 A. T. Daniher and J. K. Bashkin, Chem. Commun., 1998, 1077.
10 H. Hofmeier, J. Pahnke, C. H. Weidl and U. S. Schubert, Biomacro-
molecules, 2004, 5, 2055.
11 M. Hartmann and B. K. Kepler, Inorg. Chem., 1995, 16, 339.
12 N. Farrell, Transition Metal Complexes as Drugs and Chemotherapeutic
Agents, Kluwer Academic, Boston, 1989.
13 O. H. Nielsen, B. Vainer and J. Rask-Madsen, Aliment. Pharmacol.
Ther., 2001, 15, 1699.
14 R. A. De Abreu, J. P. Bokkerink, C. W. Keuzenkamp-Jansen, E. H. Stet
and J. F. Trijbels, Adv. Exp. Med. Biol., 1998, 431, 687.
15 J. F. Markowitz, Rev. Gastroenterol. Disord., 2003, 3, 23.
16 M. C. Dubinsky, P. V. Hassard, E. G. Seidman, L. Y. Kam, M. T. Abreu,
S. R. Targan and E. A. Vasiliauskas, Inflammatory Bowel Dis., 2001, 7,
181.
39 E. Figgemeier, L. Merz, B. A. Hermann, Y. C. Zimmermann, C. E.
Housecroft, H.-J. Gu¨ntherodt and E. C. Constable, J. Phys. Chem. B,
2003, 107, 1157.
40 P. A. Wright, D. Bell, A. Johnson and E. J. Bolton, Lancet, 1999, 346,
514.
41 M. A. Karmali, Clin. Microbiol. Rev., 1989, 2, 15.
42 L. Imundo, J. Barasch, A. Prince and Q. Al-Awqati, Proc. Natl. Acad.
Sci. U. S. A., 1995, 92, 3019.
43 K. A. El-Tarabily, J. Appl. Microbiol., 2004, 96, 69.
44 J. Antimorto, Chemotherapy (Tokyo), 2004, 54, 772.
45 J. W. Warren, J. H. Terney, J. M. Hoopes, H. L. Murcie and W. C.
Anthony, J. Infect. Dis., 1982, 146, 719.
46 A. Muis and A. J. Quimido, Indones. J. Agri. Sci., 2006, 7, 1.
47 U. K. Mazumder, M. Gupta, S. S. Karki, S. Bhattacharya, S.
Rathinasamy and T. Sivakumar, Bioorg. Med. Chem., 2005, 13,
5766.
48 P. Sengupta, R. Dinda, S. Ghosh and W. S. Sheldrick, Polyhedron, 2003,
22, 447.
49 C. S. Allardyce, P. J. Dyson, D. J. Ellis, P. A. Salter and R. Scopelliti,
J. Organomet. Chem., 2003, 35, 668.
50 G. H. Stempel, Jr., R. P. Cross and R. P. Mariella, J. Am. Chem. Soc.,
1950, 72, 2299.
51 A. Pandurangan, N. Mathivanan, V. R. Prabavathy, V. Kabilan,
V. Murugesan and K. Murugesan, Indian J. Exp. Biol., 1995, 33,
357.
52 S. Magaldi, S. Mata-Essayag, C. Hartung de Capriles, C. Perez, M. T.
Colella, C. Olaizola and Y. Ontiveros, Int. J. Infect. Dis., 2004, 8, 39.
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