Seleno-nucleobases and their water-soluble ruthenium- Arene half-sandwich complexes: Chemistry and biological activity

Article abstract of DOI:10.1002/ejic.201402412

Half-sandwich organometallic ruthenium complexes of seleno- nucleobases, 3 and 4, were synthesized and characterized. The structures of both complexes were determined by X-ray crystallography and are the first crystal structures of ruthenium complexes with seleno-nucleobases. Interestingly, 3 self-assembles aided by adventitious water in DMF to give a tetranuclear square 3a.6H2O. Complex 4 is active against Jurkat and Molt-4 cell lines but inactive against the K562 cell line, whereas 3 is completely inactive against all three cell lines. The free ligand 6-selenopurine (1) and 6-selenoguanine (2) are highly active against these cell lines. Compound 2, like its thio analogue, is unstable under UVA light, whereas 4 is stable under similar conditions, which suggests that the ruthenium complex could reduce problems associated with the instability of the free ligand, 2, under irradiation.

Full text of DOI:10.1002/ejic.201402412

FULL PAPER
DOI:10.1002/ejic.201402412
Seleno-Nucleobases and Their Water-Soluble Ruthenium–
Arene Half-Sandwich Complexes: Chemistry and
Biological Activity
[
a]
[a]
[a]
Raja Mitra, Anup K. Pramanik, and Ashoka G. Samuelson*
Keywords: Bioorganic chemistry / Medicinal chemistry / Antitumor agents / Nucleobases / Half-sandwich complexes /
Ruthenium / Selenium
Half-sandwich organometallic ruthenium complexes of se-
K562 cell line, whereas 3 is completely inactive against all
leno-nucleobases, 3 and 4, were synthesized and charac- three cell lines. The free ligand 6-selenopurine (1) and 6-se-
terized. The structures of both complexes were determined
by X-ray crystallography and are the first crystal structures
of ruthenium complexes with seleno-nucleobases. Interest-
ingly, 3 self-assembles aided by adventitious water in DMF
to give a tetranuclear square 3a·6H O. Complex 4 is active
2
against Jurkat and Molt-4 cell lines but inactive against the
lenoguanine (2) are highly active against these cell lines.
Compound 2, like its thio analogue, is unstable under UVA
light, whereas 4 is stable under similar conditions, which
suggests that the ruthenium complex could reduce problems
associated with the instability of the free ligand, 2, under ir-
radiation.
Introduction
Derivatives of nucleobases have great potential for bioac-
tivity. Therefore, it is not surprising that they have been ex-
tensively explored as therapeutic agents. In particular, 6-
thioguanine (6-TG) has been used as an oral drug to treat
different types of leukemia.[ It has also been used as an
immunosuppressant to treat patients with transplanted or-
1]
[
1]
gans. Its therapeutic value is drastically marred by side
effects, which include skin cancer from exposure to ultravio-
let A (UVA) light as a result of a photoreaction in which 6-
SO3 [2]
TG is transformed to carcinogenic G
.
In this context,
it is interesting that antilymphoma activities of seleno deriv-
atives of natural nucleobases have been explored since the Figure 1. Structures of 6-selenoguanine-containing PtII complexes.
[
3]
1
960s. However, the instability and toxicity of 6-seleno-
purine (1) and 6-selenoguanine (2) as aqueous solutions
Side effects observed in platinum-based drugs are com-
pelling scientists to look elsewhere for anticancer agents.
have restricted their clinical applications.[
4]
[7]
One way of stabilizing a heterocyclic molecule is to coor-
Ruthenium-based complexes are receiving extensive atten-
tion over other metal complexes owing to transferrin-based
II
dinate it to a metal. Both 1 and 2 have been studied as Pt
complexes by Kanzawa et al. (Figure 1).[ Although [Pt(6-
5]
[8]
selective internalization into cancer cells. In 2001, Sadler
selenoguanine)(NH ) ] was found to be stable in aqueous
3
2
and co-workers showed that organometallic half-sandwich
ruthenium complexes with ethylenediamine as an ancillary
media relative to [Pt(6-selenoguanine) ], it decomposed
2
rapidly in mouse serum to give the active component de-
rived from cisplatin. However, the cytotoxicity of the [Pt(6-
[9]
ligand are potentially anticancer active. Since then many
other organometallic ruthenium complexes with various an-
selenoguanine)(NH ) ] was significantly less than that of
[10]
3
2
cillary ligands have been evaluated for anticancer as well
cisplatin or 6-selenoguanine.[
6]
[11]
as antimetastatic activities.
In the last few years, many
biologically active compounds have been used as ancillary
ligands to synthesize anticancer active ruthenium half-sand-
[
a] Department of Inorganic and Physical Chemistry,
Indian Institute of Science,
[
12]
Bangalore 560012, India
wich complexes. Multinuclear organometallic ruthenium
complexes have also shown potential anticancer activity
E-mail: ashoka@ipc.iisc.ernet.in
http://ipc.iisc.ernet.in/~ashoka/
[
13]
against cisplatin-resistant cell lines. It is evident that tun-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402412.
ing of ruthenium complexes can lead to better activity.[
14]
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We report here the synthesis and characterization of two
new ruthenium half-sandwich complexes, 3 and 4, which
bear 6-selenopurine (1) and 6-selenoguanine (2) as ancillary
ligands, their reactivity, and their anticancer activity against
three different leukemia cell lines. We have also explored the
effects of UVA light on the stability of 2 and 4.
Results and Discussion
6
Treatment of [{(η -cymene)RuCl } ] with two equiva-
2
2
lents of the seleno-nucleobase in dry dichloromethane re-
sulted in the formation of the expected half-sandwich com-
plex as a precipitate in reasonable yields (Scheme 1). All
1
13
1
ligands and complexes were characterized by H, C{ H},
7
7
and Se NMR spectroscopy, UV/Vis spectroscopy, HRMS,
and elemental analysis.
Figure 2. Comparison of 77Se NMR for 2 and 4 in [D
]DMSO.
6
served, which suggested that in acetonitrile solution both
complexes stay in the mononuclear form. The formation
and stabilization of multinuclear species, as discussed below,
is dependent on the solvent.
Scheme 1. Synthetic route used for the preparation of the com-
plexes.
1
Resonances in the H NMR spectra of the complexes
were downfield-shifted (δ = 0.5 to 1 ppm) relative to the
free ligand (Figure S1 in the Supporting Information). The
ratio of the ligand to the cymene in the complex was as
1
expected (1:1) on the basis of the H NMR spectra. In the
1
case of 4, a peak at δ = 14.19 ppm in the H NMR spectrum
suggests the presence of a NH proton. However, the NH
peak was absent in the case of 3, which suggested further
interactions of the ligand with another ruthenium center in
DMSO. The presence of a multinuclear species was also
1
3
indicated by the C NMR spectrum of 3, for which two
sets of CH , CH, and cymene peaks were present. Such a
3
1
3
doubling in the number of C signals often arises from the
presence of a multinuclear species (Figure S2). However, the
1
3
C NMR spectrum of 4 showed only fifteen resonances for
carbon atoms, which suggested a mononuclear species. 77Se
II
NMR spectroscopy revealed that on coordination to Ru
the Se peaks due to 1 (δ = 375.5 ppm) and 2 (δ =
84.5 ppm) are upfield-shifted to δ = 368.3 and 349.1 ppm,
7
7
3
respectively (Figure 2).
ESI-MS spectra of 3 and 4 in acetonitrile resulted in the
–
removal of HCl and Cl from the complex. In the positive-
ion mode, a singly charged species that corresponded to the
6
+
ion [(η -cym)Ru(seleno-nucleobase)–H] (cym = cymene)
was observed at m/z 434.9658 and 449.9772 in the ESI-MS
spectra for 3 and 4, respectively (Figure S3 in the Support-
ing Information). Insignificant amounts of multinuclear
2 2
Figure 3. ORTEP view of (a) 3a·6H O and (b) 4·DMF·H O at 40%
thermal ellipsoid. Solvents of crystallization and counteranions
have been omitted for clarity. Hydrogen atoms have also been omit-
ruthenium species (Ͻ2–5% of dinuclear species) were ob- ted in 3a·6H
2
O for clarity.
Eur. J. Inorg. Chem. 2014, 5733–5740
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The molecular structures of 3 and 4 were determined by Table 1. Selective bond lengths [Å] and angles [°] for 3a·6H
2
O and
4·DMF·H
2
O.
X-ray crystallography and appear to be the first examples
of ruthenium complexes that contain seleno-nucleobases as
ligands. Single crystals suitable for crystal structure analysis
by X-ray diffraction were obtained in both cases by diffus-
3
a·6H
2
O
2
4·DMF·H O
Ru1–Se1
2.5574(9)
2.107(5)
2.095(5)
81.80(18)
Ru1–Se1
Ru2–Se2
Ru1–Cl1
Ru2–Cl2
Ru1–N1
Ru2–N6
2.5337(8)
2.5486(11)
2.3994(13)
2.3956(14)
2.102(3)
ing diethyl ether into a concentrated solution of the com- Ru1–N2
II
plex in DMF. In both complexes, Ru adopts the “three-
Ru1–N3
legged piano-stool” pseudo-octahedral geometry. Complex
formed small needle-shaped crystals and was shown to be
a mononuclear ruthenium complex on the basis of crystal-
2.109(3)
3
N2–Ru1–N3
N1–Ru1–Cl1
N6–Ru2–Cl2
N1–Ru1–Se1
N6–Ru2–Se2
Se1–Ru1–Cl1
Se2–Ru2–Cl2
83.13(10)
83.55(10)
84.50(7)
lographic analysis (Figure S4 in the Supporting Infor- N2–Ru1–Se1 89.07(14)
mation). However, the data quality of this needle-shaped
crystal was poor owing to its small size. Slow recrystalli-
zation from DMF/diethyl ether gave larger rectangular
crystals, which were shown by X-ray crystallography to be
84.13(9)
86.67(4)
86.89(4)
Se1–Ru1–N3
84.35(13)
a tetranuclear ruthenium complex 3a·6H O (Figure 3). It is
likely that mononuclear 3 as a solution in DMF undergoes
2
In all complexes, Ru1–Se1 distances range from
.5337(8) to 2.5574(9) Å and are longer than the previously
2
substitution of chloride by adventitious water, present in
reported ruthenium complexes bearing a Ru–Se bond
+
[15]
[
16]
the DMF, followed by the loss of H . The deprotonated
-selenopurine ligand replaces the water in an intermo-
lecular substitution to form a square tetranuclear species,
[
2.497(5) Å].
The double-bond character of the C=Se
6
unit is retained as the distances are found to be 1.868(6)
and 1.837(4) Å for 3a·6H O and 4·DMF·H O, respectively.
2
2
which crystallizes to give 3a·6H O (Scheme 2).
2
The complexes are capable of extensive intermolecular
hydrogen bonding, which is reflected in the crystal struc-
tures (Figure S5 in the Supporting Information).
Lipophilicity
It was very interesting to observe the contrasting solubil-
ity behavior of the ligands and their ruthenium complexes.
As the lipophilicity of a compound is an important param-
eter in determining its biodistribution, this contrasting be-
havior suggests a way by which the complex can reach a
site inaccessible to the ligand. Therefore the lipophilicity
(logP) of the complexes was measured using UV/Vis spec-
troscopy. Aqueous solutions of all complexes were parti-
tioned independently with n-octanol for 4 h at 37 °C. Con-
centrations of the complex in the aqueous phase before and
after partitioning with n-octanol were measured. Both com-
plexes have a negative logP value, –0.98Ϯ0.12 and
–0.75Ϯ0.27, respectively, for 3 and 4, which is consistent
with their high water-solubility.
Solution Chemistry
The stability of the metal complexes in aqueous media
plays an important role in biological activity. The stability
1
of both complexes was monitored by UV/Vis and H NMR
spectroscopy. The complex was dissolved in dry methanol
and was diluted further with water (95% v/v). A change in
absorbance with respect to time was monitored using UV/
Scheme 2. Formation of tetranuclear 3a from mononuclear 3.
Complex 4 showed a mononuclear structure with chlor- Vis spectroscopy. Both complexes showed small changes in
ide as the counteranion (4·DMF·H O) (Figure 3). The extra the UV/Vis spectra with time (Figure S6 in the Supporting
2
amine group present in 2 clearly has a role to play in pre- Information).
1
venting the formation of tetranuclear species in the case of
H NMR spectra were recorded in D O. Both complexes
2
4
. Key bond lengths are given in Table 1, and crystallo- showed no changes over short reaction times. Whereas com-
graphic parameters are given in the Supporting Information plex 4 showed no change even after 24 h, complex 3 indi-
Table S1). cated the formation of a new species, which presumably cor-
(
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responded to the tetranuclear species. Diffusion-ordered
spectroscopy (DOSY) experiments suggest that complex 4
has a hydrodynamic radius of 5.16 Å consistent with a mo-
nomeric structure. DOSY data could not be obtained from
complex 3 immediately after dissolving in D O as the inten-
2
sity of the peaks slowly changed with time. After incubation
for seven days, the presence of monomeric and tetrameric
species with the corresponding hydrodynamic radii of 5.26
and 7.83 Å could be inferred. NMR spectra and DOSY
data are given in the Supporting Information (Figure S7).
To gain insight into the nature of molecular structures
in aqueous solution, high-resolution ESI-MS studies were
carried out with solutions of 3 and 4. Peaks that correspond
6
6
+
to [(η -cym)RuSeNBX] or [(η -cym)RuSeNB(OH )] (NB
2
=
nucleobase) were not observed for any of the complexes,
which suggests a weak Ru–X/O bond that readily dissoci-
ates under the ESI-MS conditions. Complex 3 showed
peaks that correspond to a mononuclear species (m/z
434.9669) and a dinuclear ruthenium species (m/z 866.9276)
with equal relative intensities (Table 2). Peaks that corre-
spond to a trinuclear (m/z 1297.8807) and a tetranuclear
Figure 4. Theoretical (red) and observed (blue) isotopic distribu-
tion of (a) mononuclear, (b) dinuclear, (c) trinuclear, and (d) tetra-
nuclear ruthenium species observed in the HR ESI-MS spectra of
(m/z 1730.8606) species were also observed in ESI-MS spec-
tra with a relative abundance around 5%. Isotopic distribu-
tion of all peaks matched exactly with the expected natural
abundance values. A representative comparison between
theoretical and experimental isotopic distribution is shown
in Figure 4. Complex 4 shows two peaks that correspond
to a mononuclear (m/z 449.9776) and a dinuclear (m/z
3
in water.
spectroscopic splitting patterns recorded in DMSO that
contained water. However, under the ESI-MS conditions, it
becomes fragmented, thereby resulting in the formation of
mononuclear, dinuclear, and trinuclear ruthenium species.
Complex 4 stays mostly in the mononuclear form with a
small amount of the dinuclear ruthenium species (Table S2
in the Supporting Information) as observed in the ESI-MS
spectrum.
897.0039) species (Figure S8 in the Supporting Infor-
mation). No trinuclear and tetranuclear ruthenium species
were observed.
Table 2. Values of m/z of Ru complexes in aqueous solution ob-
tained in ESI-MS.
Observed peak
Empiriical formula
(calcd. m/z)
Found m/z
+
[M]
6
SeRu]+
3
4
[(η -cym)Ru
[C15
H
17
N
4
434.9669
866.9276
1298.8837
1730.8606
Growth Inhibition by Sulforhodamine B (SRB) Assay
+
(
[
1-H)]
{(η -cym)Ru
1-H)}
{(η -cym)Ru
1-H)}
{(η -cym)Ru
1-H)}
(434.9670)
6
33 8 2 2
[C30H N Se Ru
]+
We have recently identified ruthenium complexes of 6-
TG that are anticancer-active against several leukemia cell
(
[
(
[
2
+ H]+
(866.9270)
[C45
(1298.8880)
[C60
6
]+
]+
H
49
N
12Se
3
4
Ru
Ru
3
4
[
17]
+ H]+
lines.
It would be interesting to see if the selenium ana-
3
6
H
65
N
16Se
logue of 6-TG and their corresponding ruthenium com-
plexes can also exhibit antileukemic activity. Growth inhibi-
(
4
+ H]+
(1730.8490)
6
SeRu]+
tion (GI ) of ligands and their corresponding ruthenium
[(η -cym)Ru
[C15
H
18
N
5
449.9776
897.0039
50
+
(
[
2-H)]
{(η -cym)Ru
2-H)}
(449.9779)
complexes were checked against K562 (chronic myeloge-
nous leukemia), Jurkat (leukemic T cell lymphoblast), and
Molt-4 (leukemic T cell lymphoblast) cell lines by means of
6
35 2 2
[C30H N10Se Ru
]+
(
2
+ H]+
(896.9490)
[
18]
the sulforhodamine B assay.
The results are listed in
In contrast to the aqueous solutions, solutions of both Table 3, and the experimental details are given in the Sup-
complexes in acetonitrile show mononuclear species as the porting Information. Both ligands were found to be active
major peak in the ESI-MS spectra. It suggests that water against K562 and Jurkat cell lines. However, against the
plays an important role in the formation of multinuclear Molt-4 cell line only 2 was found to be active (Ͻ0.1 μm)
species. As the synthesis of complexes is carried out in dry relative to 1 (15.6 μm). Surprisingly, complex 3 was inactive
CH Cl , under an inert atmosphere, it is likely that the com- against all the leukemia cell lines we tested including those
2
2
plexes are formed as mononuclear species.
cell lines for which ligand 1 is active (K562 and Jurkat).
We propose that 3 attains a stable tetranuclear structure Interestingly, 4 was active against Jurkat and Molt-4 cell
aided by water in DMF as seen from the X-ray structure lines, whereas against the K562 cell line it is completely in-
1
determination. This is also consistent with the H NMR active (58.5 μm).
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Table 3. In vitro growth inhibition of human cancer cell lines after ratio of seleno-nucleobase to cymene, on the basis of the
6
II
exposure to ligands or [(η -cymene)Ru Cl(seleno-nucleobases)]
complexes for 48 h.
MS analysis, it is inactive and is shown to be a tetranuclear
species on the basis of DOSY-NMR spectroscopy and crys-
tallography. Anticancer activities of seleno-nucleobases are
reduced upon coordination to the ruthenium center. Al-
though 4 showed less cytotoxicity, its stability in aqueous
media under UVA light makes it worthy of further study as
an alternative to the unstable 2. Further studies are
underway to confirm the potential application of these
ruthenium complexes as anticancer agents.
GI50 [μm]
Compound
K562
chronic
Jurkat
Molt-4
(
(leukemic T cell (leukemic T cell
lymphoblast)
myelogenous
leukemia)
lymphoblast)
1
Ͻ0.1
Ͻ0.1
79.9
58.5
Ͻ0.1
Ͻ0.1
Ͻ0.1
54.2
Ͻ0.1
Ͻ0.1
15.6
Ͻ0.1
53.4
7.4
2
3
4
Adriamycin
Ͻ0.1
Experimental Section
Photochemistry
Despite the comparable anticancer activity of 2 with 6-
3 2
Materials and Methods: RuCl ·xH O and selenourea were obtained
from Sigma–Aldrich (India). α-Phellandrene was purchased from
Merck, India. 6-Chloropurine and 6-chloroguanine were purchased
TG, extensive studies with the former have not been carried from SRL, India. Precursors for ruthenium complexes were pre-
out as it offers no advantages over 6-TG.[ We have re- pared according to the literature procedures. All reactions were
4b]
[19]
cently shown that the ruthenium half-sandwich framework carried out in an atmosphere of dry nitrogen using standard
stabilizes 6-TG against UVA light.[
17b]
Schlenk and vacuum-line techniques, and the solvents were dried
H, C{H}, and Se NMR spectra were
recorded with a Bruker AMX 400 NMR spectrometer operating at
00 MHz for H, 100 MHz for C, and 76.3 MHz for Se in [D
DMSO or D O. Elemental analyses were performed with a Thermo
Scientific Flash EA 1200 CHNS analyzer. HRMS of all samples
were recorded with an Agilent 6538 Ultra-High Definition (UHD)
Accurate-Mass Q-TOF. UV/Vis and fluorescence spectra were re-
corded with a Perkin–Elmer Lamda 35 UV/visible spectrophotom-
We wished to check
by standard methods.[
20] 1
13
77
to see if 2 and 4 suffered from any of the problems reported
in the case of 6-TG in the presence of UVA light in aqueous
solutions. UV/Vis spectra before and after photoirradiation
10 and 30 min) suggest that 2 is unstable under UVA irra-
diation. A decrease in the 360 nm band was observed with
an increase in the 317 nm band (Figure 5). Photoirradiation
1
13
77
4
6
]-
2
(
also caused an increase in the fluorescence at 390 nm (λem
)
when excited at 317 nm (λ ) (Figure S10 in the Supporting eter and a Perkin–Elmer Lamda 50B spectrofluorometer, respec-
ex
Information). However, 4 was found to be quite stable (Fig- tively. Growth inhibition (GI50) by sulforhodamine B (SRB) assays
were carried out by the Advanced Centre for Treatment, Research,
ure 5) under similar conditions. Although 4 is less potent
than 2, it is possible that the photostability of 4 would be
an advantage during long-term usage and in its selective
and Education in Cancer (ACTREC), Mumbai, by following the
literature procedure.[
18]
delivery through transferrin.
Synthesis and Characterization
6
-Selenopurine (1): 6-Selenopurine was synthesized according to the
[3a]
literature procedure.
chloropurine). H NMR (400 MHz, [D
Yield 219 mg (56%, from 171 mg of 6-
]DMSO, 20 °C): δ = 8.25
1
6
(
1
2
2
d, J = 2.4 Hz, 1 H, CH), 8.54 (s, 1 H, CH), 13.8 (br. s, 1 H, NH),
7
7
4.27 ppm (br. s, 1 H, NH) ppm. Se (76 MHz, [D
0 °C): δ = 375.5 ppm. C Se·H O: calcd. C 27.66, H 2.79, N
5.81; found C 27.56, H 3.23, N 25.06. Q-TOF HRMS (CH CN):
Se : 200.9675 [M + H ], found 200.9674 (100%);
6
]DMSO,
5
H
4
N
4
2
3
+
+
5 5 4
calcd. for C H N
calcd. 222.9493 [M + Na ], found 222.9499 (19%).
+
6-Selenoguanine (2): 6-Selenogunaine was synthesized by adopting
the procedure used for 6-selenopurine preparation. Briefly, 6-
chloroguanine (200 mg, 1.18 mmol) and selenourea (148 mg,
1.2 mmol) were dissolved in ethanol (5 mL). The orange solution
was heated under reflux conditions for 2 h to obtain an orange-
yellow precipitate. The precipitate was filtered, washed with water,
% DMSO before and after irradiation (10 and 30 min) with UVA and dried in air. On the basis of thermogravimetric analysis (TGA)
Figure 5. UV/Vis spectra of 2 and 4 in aqueous solution containing
1
light.
data, it was observed that three molecules of water were present,
yield 320 mg (quantitative, considering three molecules of water).
1
H NMR (400 MHz, [D
.70 ppm (s, 1 H, CH) ppm. C NMR (100 MHz, [D
6
]DMSO, 20 °C): δ = 7.12 (br. s, 2 H, NH
2
),
]DMSO,
20 °C): δ = 126.2, 143.3, 149.7, 155.2, 168.7 ppm. Se (76 MHz,
]DMSO, 20 °C): δ = 384.5 ppm. C Se·2H O·0.2C OH:
1
3
8
6
7
7
Conclusion
[D
6
5
H
5
N
5
2
2 5
H
We have successfully synthesized and characterized the
first bioorganometallic half-sandwich ruthenium complexes
of seleno-nucleobases. Of the two water-soluble complexes H ], found 215.9783 (100%); calcd. 237.9602 [M + Na ], found
calcd. C 24.90, H 3.95, N 26.91; found C 25.11, H 3.21, N 27.07.
+
Q-TOF HRMS (CH
3
CN): calcd. for C
5
H
6
N
5
Se : 215.9784 [M +
+
+
3
and 4, only 4 is active. Although complex 3 retains the 237.9606 (23%).
5737
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6
–1
[
0
(
Ru(η -cymene)Cl(6-selenopurine)]Cl (3): 6-Selenopurine (48 mg,
mately 3 mg (1 mgmL ) of each of the complexes was dissolved in
MilliQ water (3 mL). The stock solution was divided into two parts
(1 and 2 mL) in glass vials. One part of the solution (1 mL) was
6
.24 mmol) was added to a solution of [{(η -cymene)RuCl
75 mg, 0.12 mmol) in dry CH Cl (5 mL). Within 30 min of stir-
2 2
2
}
2
]
ring at room temperature, an orange-yellow precipitate was formed.
The heterogeneous mixture was stirred for another 4.5 h. After
0
taken and the absorbance recorded to obtain the value of A after
incubating at 37 °C for 4 h. Octanol was added (2 mL) to another
part of the solution and stirred at 37 °C for 4 h. The water layer
that, it was filtered, washed with CH
ether, and dried in air to obtain a free-flowing bright orange-yellow
powder, yield 72 mg (58%). 1H NMR (400 MHz, [D
]DMSO,
0 °C): δ = 1.08 [dd, J = 22.8, J = 6.8 Hz, 6 H, (CH CH], 2.10 equation.
s, 3 H, CH ), 2.68 [sept, 1 H, (CH CH], 5.72 (d, J = 5.6 Hz, 1
H, H–Arcymene), 5.94 (m, 2 H, H–Arcymene), 6.07 (d, J = 6.0 Hz, 1
H, H–Arcymene), 8.70 (s, 1 H, CHligand), 9.63 ppm (s, 1 H, CHligand
ppm. 13C NMR (100 MHz, [D
]DMSO, 20 °C): δ = 18.8, 19.3,
2.4, 22.6, 23.2, 30.9, 31.5, 81.3, 82.1, 83.0, 83.6, 86.4, 87.3, 100.5,
2 2
Cl and then with diethyl
was separated and the absorbance was recorded to obtain A
0
–
6
A (Aoctanol). Values of logP were calculated using the following
2
3 2
)
(
3
3 2
)
)
6
2
1
Solution Chemistry: Ruthenium complexes were dissolved in dry
methanol to make a stock solution with a concentration of 1 mm.
From this stock solution, 50 μL was added to water (950 μL) in a
7
7
01.0, 103.6, 107.4, 139.9, 144.9, 148.8, 150.2, 167.8 ppm. Se
]DMSO, 20 °C): δ = 369.5 ppm. UV/Vis (MeOH):
(76 MHz, [D
6
–1
λ
C
max (ε) = 358 (6100 m–1 cm ) nm; elemental analysis calcd. (%) for
RuSeCl ·H O: calcd. C 34.43, H 3.85, N 10.71; found
C 34.16, H 3.98, N 10.12. Q-TOF HRMS (CH CN): calcd. for
RuSe : 434.9658 [M – 2Cl – H ] ; found 434.9670.
1
mL cuvette to obtain a final concentration of 50 μm of the com-
15
H
18
N
4
2
2
plex in 5% MeOH/water. The change in the absorption spectra was
monitored by UV/Vis spectroscopy.
3
+
–
+ +
15 17 4
C H N
1
To monitor the hydrolysis by H NMR spectroscopy, the complex
6
[
(
Ru(η -cymene)Cl(6-selenoguanine)]Cl (4): 6-Selenoguanine·3H
2
O
was taken in a NMR spectroscopy tube. After dissolving the com-
6
1
65 mg, 0.24 mmol) was added to a solution of [{(η -cymene)
RuCl ] (75 mg, 0.12 mmol) in dry CH Cl
stirring at room temperature, an orange-yellow precipitate was
formed. The heterogeneous mixture was stirred for another 12 h. acquisition time was 1 s and the relaxation delay was 1.5 s (D1).
After that, it was filtered, washed with CH Cl and then with di-
The diffusion time was between 0.11 and 0.125 s (D O) and the
plex in D
2
O, the H NMR spectrum was recorded immediately and
1
2
}
2
2
2
(5 mL). Within 2 h of after 24 h. H DOSY data was acquired with the standard Bruker
ledbpgp2s program using 32 t increments of 32 transients. The
1
2
2
2
ethyl ether, and dried in air to obtain a free-flowing bright yellow
powder. A needle-shaped single crystal suitable for X-ray diffrac-
rectangular gradient pulse duration was between 1.2 and 1.4 ms
(P30). Gradient recovery delays of 200 μs followed the application
of each gradient pulse. Data was accumulated by linearly varying
the diffusion encoding gradients over a range from 5 to 95 % for
32 gradient increment values.
tion was obtained from diffusion of diethyl ether into a solution
1
ofthecomplexinDMF,yield96 mg(75%). HNMR(400 MHz,[D
6
]-
DMSO, 20 °C): δ = 1.10 [dd, J = 18.4, J = 7.2 Hz, 6 H, (CH
CH], 2.11 (s, 3 H, CH ), 2.65 [sept, 1 H, (CH CH], 5.66 (d, J =
.0 Hz, 1 H, H–Arcymene), 5.80 (dd, J = 10.8, J = 6.0 Hz, 2 H,
H–Arcymene), 6.01 (d, J = 6.0 Hz, 1 H, H–Arcymene), 7.72 (br. s, 2
H, NH ), 9.19 (s, 1 H, CHligand), 14.12 ppm (br. s, 1 H, NH) ppm.
C NMR (100 MHz, [D ]DMSO, 20 °C): δ = 19.3, 22.6, 23.1, 31.5,
1.0, 82.2, 82.9, 83.4, 100.5, 103.2, 133.5, 146.6, 147.9, 157.4,
65.3 ppm. 77Se (76 MHz, [D
]DMSO, 20 °C): δ = 349.1 ppm.
3 2
) -
3
3 2
)
To detect the actual hydrolyzed products of ruthenium complexes,
they were dissolved in LC-MS grade water to obtain a concentra-
tion of 2 mm. From this stock solution, 10 μL was added to MilliQ
water (990 μL). This solution was infused into the ESI-MS instru-
ment using an auto-injection module (Agilent 1290 infinity) at-
tached to the ESI-MS [Agilent 6538 Ultra-High Definition (UHD)
Accurate-Mass Q-TOF]. The same solution was infused after incu-
bation at 298 K for 6 and 24 h. Mobile phase: 50% acetonitrile
6
2
13
6
8
1
6
–1
UV/Vis (MeOH):
RuSeCl ·H
C 34.17, H 3.95, N 12.70. Q-TOF HRMS (CH
λ
max (ε)
=
378 (6600 m–1 cm ) nm.
O: calcd. C 33.47, H 3.93, N 13.01; found
CN): calcd. for
RuSe : 449.9772 [M – 2Cl – H ] ; found 449.9780.
C
15
H
19
N
5
2
2
(
LC-MS grade, Fluka)/50% water (purified using a Millipore sys-
3
tem) that contained 0.1% formic acid (LC-MS grade, Agilent) with
+
–
+ +
C
15
H
18
N
5
–1
a flow rate of 0.3 mLmin . The capillary voltage and the frag-
mentor voltage were kept at 4.0 kV and 200 V, respectively. The
Single-Crystal X-ray Crystallography: Single crystals of the com-
plexes were separately mounted on a loop in Paratone oil along the
largest dimension. Data were collected with a Bruker AXS single-
crystal diffractometer controlled by the SMART (Version 5.05;
Madison, WI, 1998) software package with a D8 Quest CMOS
–
1
capillary temperature was 350 °C with a 10 Lh flow of nitrogen
drying gas. ESI-MS data were processed using the MassHunter
software.
Photochemistry: Standard ferrioxalate actinometry was performed
photon detector and a sealed Mo-K
at 2.2 kW and 50/35 [kV/mA]. Intensity data were collected at room
temperature for 3, 3a·6H O, and at 100 K for 4·DMF·H O. Crys-
tallographic computations were performed using the WinGX
α
(λ = 0.71073) source working
to standardize the UV radiation of the home-built photoreac-
tor.[
17b,25]
The ruthenium complexes 4 and 2 (0.1 mm concentration
in 8 mL of MilliQ water that contained 1% DMSO) were irradiated
in a round-bottomed flask with continuous stirring. An aliquot
2
2
1.63.02) package.[ The data were corrected for Lorentz and po-
larization effects. The structures were solved by direct methods
using the module SIR-92) followed by the full-matrix least square
21]
–2
(
(2 mL) was taken out after 10 min [(7Ϯ1) kJm ] and 30 min
–
2
[(20Ϯ1) kJm ]. After irradiation, UV/Vis and fluorescence spectra
(
of the solution were recorded.
2
[22]
procedure of F for all reflections (SHELXL-97).
All non-
CCDC-1000363 (for 3a·6H
2 2
O), -967546 (for 4·DMF·H O), and
hydrogen atoms were refined by anisotropic displacement param-
eters and hydrogen atoms were located or fixed at idealized posi-
tions. Structures were drawn using ORTEP-3.[
-
1000364 (for 3) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
23]
Lipophilicity (logP) Measurements: The lipophilicity of the com-
plexes was measured by the standard “shake flask technique”.[
Experiments were carried out at (37Ϯ1) °C in triplicate. Approxi-
24]
Supporting Information (see footnote on the first page of this arti-
1
77
13
cle): Contains H, Se, C NMR and high-resolution ESI-MS
Eur. J. Inorg. Chem. 2014, 5733–5740
5738 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
spectra of all complexes, crystal structure of mononuclear complex
, crystallographic data and refinement parameters, various weak
interactions in crystal, H NMR spectra, UV/Vis and ESI-MS data
of aqueous solutions for all complexes, and fluorescence spectra of
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Technology (DST), New Delhi, for generous funding. R. M. thanks
the Council of Scientific and Industrial Research (CSIR), New
Delhi, for a Senior Research Fellowship. The authors would like to
thank Dr. A. Juvekar of the Advanced Centre for Treatment, Re-
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5740
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