Photoactive ruthenium nitrosyls derived from quinoline- and pyridine-based ligands: Accelerated photorelease of NO due to quinoline ligation

Article abstract of DOI:10.1016/j.poly.2007.03.010

The ruthenium nitrosyl [(PaPy₂Q)Ru(NO)](BF₄)₂, derived from the quinoline-based ligand PaPy₂QH (PaPy₂QH = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinaldine-2-carboxamide; H = dissociable proton) has been synthesized and characterized by X-ray crystallography and spectroscopic techniques. This {Ru-NO}⁶ nitrosyl is soluble in aqueous media and stable under physiological conditions at pH 7. [(PaPy₂Q)Ru(NO)]²⁺ releases NO rapidly upon exposure to low-intensity UV light (5 mW/cm²). The NO donor capacity of this nitrosyl (quantum yield = 0.20, λ_irr = 365 nm) is considerably higher than that of analogous nitrosyl derived from a polypyridyl ligand without the quinoline moiety.

Full text of DOI:10.1016/j.poly.2007.03.010

Polyhedron 26 (2007) 4713–4718
www.elsevier.com/locate/poly
Photoactive ruthenium nitrosyls derived from quinoline- and
pyridine-based ligands: Accelerated photorelease of NO due to
quinoline ligation
a
b
a,
*
Michael J. Rose , Marilyn M. Olmstead , Pradip K. Mascharak
a
University of California, Santa Cruz, CA 95064, United States
b
University of California, Davis, CA 95616, United States
Received 1 February 2007; accepted 8 March 2007
Available online 15 March 2007
Abstract
The ruthenium nitrosyl [(PaPy
2 4 2 2 2
Q)Ru(NO)](BF ) , derived from the quinoline-based ligand PaPy QH (PaPy QH = N,N-bis(2-pyri-
dylmethyl)amine-N-ethyl-2-quinaldine-2-carboxamide; H = dissociable proton) has been synthesized and characterized by X-ray crystal-
6
lography and spectroscopic techniques. This {Ru–NO} nitrosyl is soluble in aqueous media and stable under physiological conditions at
2
+
2
2
pH 7. [(PaPy Q)Ru(NO)] releases NO rapidly upon exposure to low-intensity UV light (5 mW/cm ). The NO donor capacity of this
nitrosyl (quantum yield = 0.20, kirr = 365 nm) is considerably higher than that of analogous nitrosyl derived from a polypyridyl ligand
without the quinoline moiety.
ꢀ
2007 Elsevier Ltd. All rights reserved.
Keywords: Ruthenium nitrosyl; Polypyridine ligand; Carboxamide; Photoactivity; Quinoline
1
. Introduction
tion has been diverted to one emerging type of NO donors
that can be activated by light [12]. This class of photoche-
motherapeutics includes inorganic metal complexes of NO
(metal nitrosyls) that release NO upon exposure to light
[13]. These NO donors are of special interest because of
their potential use in photodynamic therapy (PDT) for can-
cer [14]. In previous work, we have described several
designed iron [15–17], manganese [18] and ruthenium [19]
nitrosyls that rapidly release NO upon illumination. For
Nitric oxide (NO) is an important signaling molecule
that participates in many biological processes including
blood pressure regulation, immune response, cell apopto-
sis, and tumor metastasis [1–8]. Consequently, there has
been much interest in developing novel NO donors as both
therapeutic agents and research tools in biology [9]. Over
the years, many NO donors have been synthesized and
characterized for such uses and several classes of NO
donors such as organic nitrites, nitrosothiols and
diazeniumdiolates (NONOates) have found therapeutic
use [9–11]. Most of these NO donors are activated by ubiq-
uitous stimuli like heat, changes in pH, or certain enzymes.
As a result, these drugs are mostly systemic and cannot be
employed for target-specific delivery. In recent years, atten-
2
+
example, the two nitrosyls [(PaPy )Fe(NO)]
and
3
2+
[(PaPy )Ru(NO)] , derived from the designed ligand N,N-
3
bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide
(PaPy H, H = dissociable proton) [20] exhibit excellent NO
3
photolability when exposed to low-energy visible and UV
light respectively. As shown below, the PaPy H ligand con-
3
tains a carboxamide group that binds the metal center
through the carboxamido-N following deprotonation.
Our work has established that coordination of the carbox-
amido-N conjugated to the pyridine ring is a major deter-
minant of the NO photolability of these nitrosyls.
*
Corresponding author. Fax: +1 831 459 2935.
E-mail address: pradip@chemistry.ucsc.edu (P.K. Mascharak).
0
277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.03.010

4714
M.J. Rose et al. / Polyhedron 26 (2007) 4713–4718
erate a dark orange solution. After 35 min of heating,
equiv. of solid NaNO (0.030 g, 0.42 mmol) was added
O
O
1
2
N
H
N
H
to the hot solution and the heating was continued for
5 min. A dilute solution of HBF in 3 ml of EtOH was
N
N
N
N
4
4
then added to the hot solution and the resulting precipitate
was collected by filtration through glass frit under N2
atmosphere. The reddish-orange solid was washed several
N
N
N
N
PaPy H
PaPy QH
2
3
times with cold EtOH, then Et O and dried under high vac-
2
uum. This crude complex was finally stirred in CH Cl con-
2
2
taining 5% MeOH for several hours. This step provided
pure [(PaPy Q)Ru(NO)](BF (not soluble in CH Cl
MeOH) as a yellow solid (170 mg) in 65% yield. Anal. Calc.
for C24 Ru: C, 41.11; H, 3.16; N, 11.99.
Found: C, 40.95; H, 3.26; N, 12.07%. Selected IR frequen-
6
The {Ru–NO} nitrosyl [(PaPy )Ru(NO)](BF ) exhib-
2
4
)
2
2
/
2
3
4 2
its great stability in aqueous solution over a wide range
of pH (3–11) for long periods of time. We have employed
this nitrosyl to successfully deliver NO to biological targets
such as myoglobin, cytochrome c oxidase and soluble
guanylate cyclase under controlled conditions of illumination
H B F N O
22 2 8 6 2
ꢀ1
cies (KBr disk, cm ): 1868 (s, mNO), 1633 (vs, mCO), 1457
(w), 1378 (m), 1083 (s), 1035 (s), 767 (m), 533 (w), 521
(w). Electronic spectrum in MeCN, kmax in nm (e in
[
18,21,22]. In order to further improve the NO donating
ꢀ
1
ꢀ1
1
capacity of this NO donor, we recently decided to increase
the extent of conjugation in the carboxamide arm of the
ligand. We hypothesized that the greater light-harvesting
properties of the quinoline moiety (versus pyridine) might
enhance the photolability of the Ru–NO unit. In such
attempt, we have now synthesized the ligand N,N-bis
M
cm ): 245 (19460), 308 (4280), 335 (sh, 3480), 420
(1040). H NMR (CD
CN) d: 9.07 d (1H), 8.38 m (2H),
3
8.23 t (2H), 8.17 m (2H), 8.03 t (1H), 7.90 d (2H), 7.55 d
(2H), 7.47 t (2H), 5.31 m (4H), 3.86 (2H), 3.42 t (2H).
2.2. Physical measurements
(
2-pyridylmethyl)amine-N-ethyl-2-quinaldine-2-carboxam-
ide (PaPy QH) that contains a quinoline group in place of
2.2.1. Spectroscopy
1
2
pyridine [23]. In this paper we report the synthesis, struc-
The H NMR spectra were recorded at 298 K on a Var-
6
ture and properties of the {Ru–NO} nitrosyl [(PaPy Q)Ru
ian 500 MHz instrument. A Perkin–Elmer Spectrum-One
FT-IR spectrometer was used to monitor the IR spectra.
The electronic absorption spectra were obtained with a
Carey 50 spectrophotometer (Varian).
2
(
NO)](BF ) . This nitrosyl indeed exhibits improved photo-
4 2
efficiency when exposed to low-intensity (mW) UV light.
2
2
2
. Experimental
2
.2.2. Photolysis experiments
Release of NO in solution under aerobic condition was
.1. Materials and methods
monitored with an in NO Nitric Oxide Measuring System
Innovative Instruments, Inc.) using the amiNO-2000 elec-
(
.1.1. General procedures
The starting Ru(II) salt [Ru(DMSO) Cl ] was prepared
trode. The rates of NO release upon exposure to UV light
were measured with a ꢁ0.1 mM solution of the complex
in 1 cm· 1 cm quartz cuvette. The light sources employed
in this study include (a) an UV Transilluminator (UVP,
4
2
from RuCl Æ 3H O as described elsewhere [24]. NO gas
3
2
was supplied by Spectra Gases, Inc. and purified as
described previously [16]. All other reagents were procured
from Aldrich Chemical Co. The solvents used in this work
were dried according to standard procedures: EtOH and
MeOH were distilled from Mg/I ; MeCN and CH Cl from
CaH ; Et O from Na; and DMF from BaO. The two
2
Inc.) with peak intensity of 5 mW/cm at 300 nm and
(b) monochromatic light generated from an Apex Illumi-
nator (150 W Xenon lamp) equipped with a Cornerstone
130 1/8M monochromator (measured intensity of
10 mW at 410 nm). The cuvettes (placed at a distance of
3 cm) were exposed to UV light for no more than 40 s
per interval to prevent heating the solution and the elec-
tronic spectra were recorded. The apparent rates of NO
release were followed at an appropriate wavelength for
each compound and the absorbance versus time plots gen-
erated in SigmaPlot, and fitted to the 3-parameter expo-
2
2
2
2
2
ligands PaPy H and PaPy QH were synthesized by follow-
ing published procedures [20,23]. [(PaPy )Ru(NO)](BF4)2
3
2
3
was synthesized according to procedures published by us
in a previous account [19].
2
.1.2. Synthesis of [(PaPy Q)Ru(NO)](BF )
2
4 2
A slurry of the yellow starting salt [Ru(DMSO) Cl ]
*
*
4
2
nential equation: y = y + a (1 ꢀ exp(ꢀk x)) as done
o
(
0.180 g, 0.38 mmol) in 15 ml of EtOH was heated to reflux
previously. For quantum yield (/) measurements, a
temperature to generate a clear orange solution. Sepa-
rately, 0.150 g (0.38 mmol) of the ligand PaPy QH was dis-
solved in 5 ml of EtOH and deprotonated with NaOEt
ꢁ
0.3 mM solution was used to ensure sufficient absor-
bance (P99%) at the incident wavelength; no more than
0% photolysis occurred in each measurement. Standard
2
2
(
generated in situ with 10 mg (0.42 mmol) of NaH). The
actinometry using ferrioxalate was employed to calibrate
the light source.
two solutions were then mixed at reflux temperature to gen-

M.J. Rose et al. / Polyhedron 26 (2007) 4713–4718
4715
Table 1
Table 1. A comparison of selected bond distances and bond
angles for [(PaPy Q)Ru(NO)](BF ) and [(PaPy )Ru-
Summary of crystal data for [(PaPy
2
Q)Ru(NO)](BF
4
)
2
Æ MeCN
2
4 2
3
Empirical formula
Formula weight
Crystal color and habit
Crystal size (mm)
Crystal system
C
742.22
dichroic yellow needle
0.45 · 0.06 · 0.05
triclinic
26
H
25
B
2
F
8
N
7
O
2
Ru
(NO)](BF ) are listed in Table 2.
4
2
3
. Results and discussion
3.1. Synthesis
The nitrosyl [(PaPy Q)Ru(NO)](BF ) was synthesized
ꢀ
Space group
P1
Temperature (K)
90(2)
˚
a (A)
7.5961(8)
12.4837(13)
15.7711(17)
72.844(2)
85.539(2)
80.816(2)
1409.9(3)
2
2
4 2
˚
b (A)
via acidification of the corresponding Ru(II)–NO precur-
sor in a one-pot reaction (Eq. (1)) [25–27]. The reaction
˚
2
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
ꢀ
of the deprotonated ligand PaPy Q with the Ru(II) start-
2
ing salt [Ru(DMSO) Cl ] followed by the addition of
4
2
˚
3
Volume (A )
NaNO leads to the formation of the Ru(II)–NO precur-
2
2
Z
3
sor (not yet successfully isolated). Acidification of this spe-
D
calc (Mg/m )
1.748
0.650
ꢀ1
cies, generated in situ, with HBF finally affords the nitrosyl
Absorbance coefficient, l (mm
)
4
Reflections collected
Independent reflections [Rint
Observed reflections (I > 2r(I))
Maximum and minimum transmission
Goodness-of-fit on F
Final R indices [I > 2r(I)]
R indices (all data)
18500
8121 [0.0441]
6629
in good yield. Coordination of the deprotonated carbox-
amido nitrogen to the ruthenium center is not affected in
this acidification step. Although addition of dilute HClO4
]
0.968 and 0.759
1.017
2
II
þ
6
Ru –NO
2
þ 2H ! fRu–NOg þ H
2
O
ð1Þ
a
1
b
2
R
R
= 0.0425, wR
= 0.0580, wR
= 0.1045
= 0.1129
in place of HBF results in formation of the perchlorate
1
2
4
P
P
a
salt of the nitrosyl, acids like HCl afford an intractable mix-
ture of species. [(PaPy Q)Ru(NO)](BF ) is soluble in a
R
1
=
iF
o
j ꢀ jF
c
i/ jF
o
j.
P
P
b
2
2
2
2
o
2
1=2
2
2
o
2
wR2 ¼ f ½wðF ꢀ F Þ ꢂ= ½wðF Þ ꢂg
and w ¼ 1=½r ðF Þ þ ðaPÞ þ
2
4 2
o
c
2
c
2
o
ðbPÞꢂ, where P ¼ ð2F þ F Þ=3.
wide variety of polar solvents including H O, MeCN,
2
DMF and MeOH.
Table 2
3
.2. Structure of [(PaPy Q)Ru(NO)](BF ) Æ MeCN
2 4 2
˚
Selected bond lengths (A) and bond angles (ꢁ) for [(PaPy
2
Q)Ru-
(
NO)](BF
4
)
2
and [(PaPy
3
)Ru(NO)](BF
4 2
)
2
+
The structure of the cation [(PaPy Q)Ru(NO)]
is
2
[
(PaPy
2
Q)Ru(NO)](BF
4
)
2
[(PaPy
3
)Ru(NO)](BF
4
)
2
ꢀ
shown in Fig. 1. The pentadentate PaPy Q ligand is coor-
2
Ru–N(6)
1.779(2)
1.147(3)
2.133(2)
1.988(2)
2.062(2)
2.084(2)
2.078(2)
1.344(3)
1.231(3)
1.779(2)
1.142(3)
2.097(2)
1.997(2)
2.073(3)
2.074(2)
2.086(2)
1.340(4)
1.230(4)
dinated to the ruthenium center via three ring nitrogens,
the tertiary amine nitrogen and the carboxamido nitrogen.
The sixth coordination site, trans to the carboxamido nitro-
gen, is occupied by NO and the overall geometry is pseudo
octahedral. Similar binding by the analogous ligand
PaPy3 to ruthenium has been observed in [(PaPy )-
N(6)–O(2)
Ru–N(1)
Ru–N(2)
Ru–N(3)
Ru–N(4)
Ru–N(5)
N(2)–CCO
ꢀ
3
C
CO–O(1)
Ru–N(6)–O(2)
N(6)–Ru–N(1)
N(6)–Ru–N(2)
N(6)–Ru–N(3)
N(6)–Ru–N(4)
N(6)–Ru–N(5)
168.8(2)
105.43(9)
171.29(9)
94.21(9)
88.34(9)
95.67(9)
170.9(2)
98.63(10)
172.23(11)
101.97(10)
89.91(10)
94.06(10)
2
.2.3. X-ray crystallography
Long yellow needles of [(PaPy Q)Ru(NO)](BF ) Æ
2
4 2
MeCN were grown via vapor diffusion of Et O into an
2
MeCN solution of the complex at room temperature. Dif-
fraction data were collected at 90 K on a Bruker SMART
˚
ApexII instrument using Mo Ka radiation (k = 0.71073 A)
and the data were corrected for absorption. The structures
were solved using the standard SHELXS-97 package. Addi-
tional refinement details are contained in the CIF files
2
Fig. 1. Thermal ellipsoid (probability level 50%) plot of [(PaPy Q)-
Ru(NO)] with the atom-labeling scheme. H atoms are not shown for the
sake of clarity.
2
+
(
Supplementary material). Instrument parameters, crystal
data, and data collection parameters are summarized in

4716
M.J. Rose et al. / Polyhedron 26 (2007) 4713–4718
2
+
Ru(NO)]
[19]. Although the metric parameters of
2
+
[
(PaPy Q)Ru(NO)] are very similar to those of [(PaPy )-
4000
2
3
2
+
Ru(NO)] , there are some differences. For example, the
2
+
Ru–N(O) bond length of [(PaPy Q)Ru(NO)] is identical
to that of [(PaPy )Ru(NO)] (both 1.779(2) A long). Sim-
2
3000
2
+
˚
3
ilarly, the N(6)–O(2) bond distances are very close to each
˚
˚
other (1.142(3) A and 1.147(3) A). In both cases, the short-
2000
ꢀ
ꢀ
est bond between the ligand (PaPy3 or PaPy Q ) and the
ruthenium center is the Ru–Namido bond (1.997(2) A and
.988(2) A, respectively). However, the Ru–N
of [(PaPy Q)Ru(NO)] is longer (2.133(2) A) than the cor-
responding Ru–Npy distance of [(PaPy )Ru(NO)]
2.097(2) A). In addition, the quinoline moiety is slightly
2
˚
1000
˚
1
distance
quin
2+
˚
2
2
+
3
0
˚
(
300
400
500
600
700
Wavelength (nm)
tilted away from the coordinated NO (Table 2). The latter
difference most possibly arises from the steric bulk of the
quinoline unit. The larger quinoline moiety also causes
Fig. 3. Electronic absorption spectra of [(PaPy
2
Q)Ru(NO)](BF
4
)
2
(solid
line) and [(PaPy )Ru(NO)](BF ) (dashed line) in MeCN.
3
4 2
2
+
more bending of the Ru–N–O unit in [(PaPy Q)Ru(NO)]
2
2
+
(
168.8(2)ꢁ) compared to 170.9(2)ꢁ in [(PaPy )Ru(NO)] .
3
No p–p stacking has been noted in the structure of
3
80 nm to a significant extent. As discussed below, this
additional absorption due to quinoline has a strong effect
[
(PaPy Q)Ru(NO)](BF ) Æ MeCN.
2 4 2
2
+
on the photoreactivity of [(PaPy Q)Ru(NO)] compared
3
.3. Spectroscopic characterization
2
2
+
to [(PaPy )Ru(NO)]
.
3
2
+
1
[
(PaPy Q)Ru(NO)] exhibits sharp H NMR spectrum
2
3
.4. Photolability of NO
in CD CN solution at 298 K (Fig. 2), typical of low-spin
3
6
diamagnetic {Ru–NO} complexes. The N–O stretching
2
+
ꢀ1
In recent years, we and others have reported a number
frequency (mNO) of [(PaPy Q)Ru(NO)] (1868 cm ) also
2
6
of {Ru–NO} nitrosyls that exhibit photolability of the
bound NO ligand [19,28–31]. Most of these nitrosyls afford
Ru(III) species as the photoproduct (Eq. (2)) in solvents
like water. For example, photorelease of NO from
falls within the generally accepted range (1800–
ꢀ
1
1
950 cm ) for such nitrosyls. Coordination of the depro-
tonated carboxamido nitrogen to the metal center is evi-
dent in the red-shift of the mCO value of the complex
2
+
2+
ꢀ
1
[
(PaPy )Ru(NO)]
generates [(PaPy )Ru(H O)]
that
compared to that of the free ligand (1633 cm
1
versus
3
3
2
ꢀ
1
has been characterized by EPR spectroscopy. In the pres-
ent work, we have studied the photorelease of NO from
667 cm ).
The electronic absorption spectrum of [(PaPy Q)-
(Fig. 3) consists of a prominent band at
20 nm (e = 1040 M cm ) arising from the d(Ru)
p (NO) transition. Similar bands are also observed
in other {Ru–NO} nitrosyls such as [(salen)Ru-
2
2
+
2
+
[
(PaPy Q)Ru(NO)] in both protic and aprotic solvents.
2
Ru(NO)]
ꢀ
1
ꢀ1
As shown in Fig. 4, exposure of a solution of [(PaPy Q)-
Ru(NO)](BF ) in MeCN to low-intensity UV light
4 2
4
!
2
*
6
6
III
fRu–NOg þ hm þ solv ! Ru –ðsolvÞ þ NO
ð2Þ
(
NO)(Cl)] (kmax = 376 nm) and [(bpb)Ru(NO)(Cl)] (kmax
=
3
80 nm) [28,29]. The small red-shift of the absorption band
results in changes in its electronic spectrum consistent with
the photorelease of NO. Upon illumination, new peaks are
generated at 385 nm and 470 nm and isosbestic points at
360 nm and 305 nm clearly indicate clean conversion of
2
+
of [(PaPy Q)Ru(NO)]
Ru(NO)] (kmax = 410 nm, Fig. 3) most possibly arises
from the extended conjugation of the quinoline moiety
compared to that of [(PaPy )-
2
+
3
2
2
+
[
[
29]. Close inspection of the absorption spectra of
(PaPy Q)Ru(NO)] and [(PaPy )Ru(NO)] reveals that
[(PaPy Q)Ru(NO)]
to the solvato species. Release of
2
2
+
2+
NO upon illumination can be detected easily by the use
of NO-electrode. The resulting NO amperogram (Fig. 4,
inset) indicates that NO is released rapidly upon illumina-
2
3
introduction of the quinoline moiety in the ligand frame
enhances the overall absorption in the UV range of 350–
1
Fig. 2. H NMR spectrum (500 MHz) of [(PaPy
2
Q)Ru(NO)](BF
4
)
2
in CD
3
CN at 298 K.

M.J. Rose et al. / Polyhedron 26 (2007) 4713–4718
4717
2
+
5
4
3
2
1
000
000
000
000
000
0
Ru(NO)] retains its high level of photoactivity at this
6
0s
4
3
2
000
000
000
60s
wavelength (/410 = 0.17) compared to [(PaPy )Ru-
(NO)] (/410 = 0.05). It is therefore evident that the coor-
dinated quinoline moiety not only increases absorption in
the 350–380 nm region (thus acting as a light harvestor)
3
3
0s
2+
30s
30s
2
0s
10s
1000
*
but also enhances the d(Ru) ! p (NO) transition and
0
5
10 15 20 25 30
Time (min)
increases the photoactivity at ꢁ400 nm.
Measurements on the time-dependent release of NO
2
+
2+
from [(PaPy )Ru(NO)] and [(PaPy Q)Ru(NO)] (under
3
2
2
3
00 nm UV light, 5 mW/cm ) indicate that [(PaPy Q)-
2
2
+
Ru(NO)]
releases NO faster (t1/2 ꢃ 0.6 min) than
2+
[(PaPy )Ru(NO)] (t1/2 ꢃ 1.4 min). This fact in conjunc-
3
3
00
400
500
600
700
800
tion with high / value and greater stability in water makes
2
+
Wavelength (nm)
[(PaPy Q)Ru(NO)] a very good candidate for the deliv-
2
ery of NO to biological targets.
Fig. 4. Changes in electronic spectrum of [(PaPy
2
4 2
Q)Ru(NO)](BF ) in
Ford and co-workers have synthesized several chro-
mium-nitro complexes that include peripheral ‘‘UV anten-
nae’’, like pyrene, to increase the overall photochemical
efficiency of NO generation [34]. In this work, a directly
coordinated light-harvesting quinoline unit (Fig. 3)
enhances the photoefficiency of [(PaPy Q)Ru(NO)](BF )
4 2
MeCN observed upon photolysis with low-intensity UV light
2
(
kirr = 300 nm, 5 mW/cm ). Inset: NO amperogram indicating release of
NO in aqueous solution (pH 7) upon exposure to short pulses of UV light.
2
+
tion of an aqueous solution (pH 7) of [(PaPy Q)Ru(NO)]
2
2
with low-intensity UV light.
compared to its pyridine analogue [(PaPy )Ru(NO)](BF ) .
3 4 2
In order to explore the effect(s) of the quinoline moiety
We believe that other photoactive ruthenium nitrosyls
could be similarly modified to improve (a) their photoeffi-
ciencies and (b) their potential as NO donors in PDT.
2
+
on the capacity of NO release by [(PaPy Q)Ru(NO)] , we
2
have compared its photochemical efficiency with that of
2
+
[
(
(PaPy )Ru(NO)] . The quantum yield value at 300 nm
3
2
+
/300) of [(PaPy Q)Ru(NO)] in MeCN solution (0.14) is
2
Acknowledgement
2
+
significantly higher than that of [(PaPy )Ru(NO)]
3
(
0.06). Under physiological conditions (H O, pH 7),
2
This research was supported by a grant from the Na-
tional Science Foundation (CHE-0553405).
2
+
[
(PaPy Q)Ru(NO)] also exhibits a higher quantum effi-
2
ciency (/355 = 0.20) compared to its pyridine congener
2
+
[
[
(PaPy )Ru(NO)] +(/355 = 0.12). When the / value of
3
2
(PaPy Q)Ru(NO)] is compared with the / values of
Appendix A. Supplementary material
2
other photoactive ruthenium nitrosyls (Table 3), it becomes
2
+
evident that [(PaPy Q)Ru(NO)] exhibits sufficient photo-
CCDC 634946 contains the supplementary crystallo-
2
activity for biological purposes.
graphic data for [(PaPy Q)Ru(NO)](BF ) Æ MeCN. These
2
4 2
Close examination of Fig. 3 reveals that ligation of
data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2007.03.010.
2
+
the quinoline-based ligand in [(PaPy Q)Ru(NO)] shifts
2
*
the d(Ru) ! p (NO) transition (photoactive band) to
2
+
4
20 nm. [(PaPy )Ru(NO)] exhibits its k
at 410 nm.
max
3
In order to examine the effect(s) of irradiation at
400 nm, we have also determined the quantum yields
ꢁ
of both nitrosyls at 410 nm. Interestingly, [(PaPy Q)-
2
Table 3
6
Quantum Yield (/) values for {Ru–NO} nitrosyls
Complex
Quantum Yield, / (kirr in nm)
MeCN
H
2
O
DMF
a
a
[
[
[
[
[
[
(PaPy
(PaPy
(bpb)Ru(NO)(Cl)]
(salen)Ru(NO)(Cl)]
3
2
)Ru(NO)](BF
4 2
Q)Ru(NO)](BF )
4
)
2
0.060 (300), 0.050 (410)
0.14 (300), 0.17 (410)
0.062 (300)
0.12 (355)
0.20 (355)
0.042 (300)
0.075 (300)
this work
this work
ref. [29]
ref. [28]
ref. [32]
ref. [33]
0.13 (365)
3
+
b
b
(NH
(NH
a
3
)
)
4
Ru(NO)(py)]
Ru(NO)(P(OEt)
0.11 (330)
0.30 (310)
3+
3
4
3
)]
pH 7, phosphate buffer.
Measurements made 6pH 4.
b

4
718
M.J. Rose et al. / Polyhedron 26 (2007) 4713–4718
[19] A.K. Patra, M.M. Olmstead, P.K. Mascharak, Inorg. Chem. 42
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