Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of a novel ruthenium nitrosyl complex and studies on
photolability of coordinated NO
Kaushik Ghosh ⁎, Sushil Kumar, Rajan Kumar
Department of Chemistry, Indian Institute of Technology, Roorkee, Roorkee-247667, Uttarakhand, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present communication, we have reported the synthesis and characterization of a novel nitric oxide
Received 10 July 2010
Accepted 12 October 2010
Available online 19 October 2010
1
1
1
3 2 4 3 2 2
(NO) donating complex [Ru(L )(PPh ) (NO)](ClO ) (2) derived from [Ru(L )(PPh ) (Cl)] (1) (L H is
pyridine 2,6-dicarboxylic acid and H stands for dissociable proton). Characterization of 2 by UV–Vis, IR and
6
NMR spectral studies revealed the presence of {RuNO} species with S=0 ground state. ESI-MS data also
supported the formation of 2. Electrochemical studies on complex 2 were investigated. The coordinated NO
was found to be photolabile under visible as well as in UV light and photocleaved NO was transferred to
reduced myoglobin.
Keywords:
Ruthenium nitrosyl complex
Nitric oxide
Photolabile
© 2010 Elsevier B.V. All rights reserved.
Myoglobin trapping 1H and 31P NMR
Nitric oxide (NO) is highly reactive diatomic radical that is
physiologically generated by organisms ranging from bacteria to
humans [1]. This reactive radical has been found to be an important
signaling molecule and is involved in several physiological processes
namely blood pressure regulation, immune and endocrine response,
neurotransmission and cell death [1,2]. In the cellular level NO is
produced by the enzyme nitric oxide synthase (NOS) however,
production of NO below or above the physiological level initiates
different diseases like cardiovascular, neurologic and pulmonary
diseases, atherosclerosis and cancer [2]. In the recent years, there
has been considerable interest for the studies on interaction of NO
with metal complexes [3]. Interaction of metal complexes with NO
and synthesis of metal nitrosyl complexes are not only important for
the synthesis of new NO donors but are also important for NO
scavenging activity [4]. Metal complexes which could deliver NO upon
illumination of light are important in photodynamic therapy (PDT)
dissociable protons) derived from ligand pyridine 2,6-dicarboxylic
acid (shown in Scheme 1). The complex was characterized by UV–Vis
1
31
and IR spectral studies. NMR ( H and P) and ESI-MS spectral data
and redox property of the metal center will be scrutinized. Photol-
ability of the coordinated NO was determined by UV–Vis spectral
studies. To confirm the photolability, the liberated NO after photo-
cleavage was transferred to reduced myoglobin (Mb).
1
The precursor complex [Ru(L )(PPh
3
)
2
(Cl)] (1) was synthesized
Cl and pyridine 2,6-
by refluxing an ethanolic solution of Ru(PPh
3
)
3
2
dicarboxylic acid in 1:1 equivalent ratio. The brownish-red resultant
complex was eluted through an alumina column and was recrystal-
lized from benzene–ethanol mixture (1:1 v/v). Detail of the synthetic
procedure was reported in the supporting information. The resultant
complex was characterized by UV–Vis and IR spectral studies which
1
authenticated the formation of [Ru(L )(PPh
3
)
2
(Cl)] (1). These data
were consistent with the data reported by Natarajan and coworkers
[9] for the same resultant complex using Ru(PPh Cl as a starting
[3,5d].
3
)
3
3
This work stems from our interest in the synthesis of photolabile
material. Hence in our study during the reaction, aerial oxidation of
the metal center in presence of hard carboxylic acid donors [10] (vide
infra) and concomitant formation of 1 was observed.
Complex 1 was reacted with in situ generated NO by an acidified
2
NaNO solution [11]. The brownish-red color was turned to yellow
after 1 h of stirring. The resultant yellow compound 2 was isolated as
perchlorate salt (detail of the synthetic procedure was reported in
supplementary material). No change was observed when 1 was
ruthenium nitrosyl complexes [6]. Recently Mascharak and coworkers
reviewed [7] the research on photolabile ruthenium nitrosyl com-
plexes by different research groups and such type of complexes
derived from carboxylic acid and phosphine ligands are scarce [7,8].
We were interested to study the reactivity of ruthenium complexes
having ligands containing one or more than one carboxylic acid (–
COOH) donor(s) with nitric oxide. In the present study we report a
1
novel ruthenium nitrosyl complex [Ru(L )(PPh
3
)
2
(NO)](ClO
4
) (2)
2
treated with same acidic solution without NaNO .
1
(
where L H
2
is pyridine 2,6-dicarboxylic acid and H stands for
Complex 1 possesses a band near 400 nm in UV–Vis spectrum. This
band was disappeared in complex 2 and a peak near 320 nm was
observed. Molar extinction coefficients of the above two bands
indicated that the peaks were due to charge transfer transition. IR
⁎
–1
spectrum of 2 provided νNO at ~1890 cm and the presence of