Luminescent properties of ruthenium(II) complexes with sterically expansive ligands bound to DNA defects

Article abstract of DOI:10.1021/ic3019524

A new family of ruthenium(II) complexes with sterically expansive ligands for targeting DNA defects was prepared, and their luminescent responses to base pair mismatches and/or abasic sites were investigated. Design of the complexes sought to combine the

Full text of DOI:10.1021/ic3019524

Article
pubs.acs.org/IC
Luminescent Properties of Ruthenium(II) Complexes with Sterically
Expansive Ligands Bound to DNA Defects
Anna J. McConnell, Mi Hee Lim,† Eric D. Olmon, Hang Song, Elizabeth E. Dervan,
and Jacqueline K. Barton*
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
S
* Supporting Information
ABSTRACT: A new family of ruthenium(II) complexes with sterically expansive ligands for
targeting DNA defects was prepared, and their luminescent responses to base pair mismatches
and/or abasic sites were investigated. Design of the complexes sought to combine the
mismatch specificity of sterically expansive metalloinsertors, such as [Rh(bpy)2(chrysi)]3+
(chrysi = chrysene-5,6-quinone diimine), and the light switch behavior of [Ru(bpy)2(dppz)]2+
(dppz = dipyrido[3,2-a:2′,3′-c]phenazine). In one approach, complexes bearing analogues of
chrysi incorporating hydrogen-bonding functionality similar to dppz were synthesized. While
the complexes show luminescence only at low temperatures (77 K), competition experiments
with [Ru(bpy)2(dppz)]2+ at ambient temperatures reveal that the chrysi derivatives
preferentially bind DNA mismatches. In another approach, various substituents were
introduced onto the dppz ligand to increase its steric bulk for mismatch binding while
maintaining planarity. Steady state luminescence and luminescence lifetime measurements
reveal that these dppz derivative complexes behave as DNA “light switches” but that the
selectivity in binding and luminescence with mismatched/abasic versus well-matched DNA is not high. In all cases, luminescence
depends sensitively upon structural perturbations to the dppz ligand.
reveal that it inserts into the destabilized mismatch site from
the minor groove with complete ejection of the mismatched
base pair into the major groove and no change in base pair
rise.9 Thus, the [Rh(bpy)2(chrysi)]3+ complex is a metal-
loinsertor rather than a classical metallointercalator. Further-
more, we demonstrated that abasic sites and single-base bulges
are also recognized by the [Rh(bpy)2(chrysi)]3+ complex.10
The source of defect-specific binding is the chrysi-inserting
ligand. Structural properties of the chrysi ligand (e.g., steric bulk
and planarity) make it too wide to intercalate into well-matched
duplex DNA, but it is well suited to bind to destabilized sites in
DNA. The binding affinity of this rhodium complex to each
mismatch is correlated with the thermodynamic stability of the
mismatch.
Another effort in our laboratory has been constructing metal
complexes as luminescent probes for DNA.8 Complex [Ru-
(bpy)2(dppz)]2+ (Figure 1, bpy = 2,2′-bipyridine) exhibits light
switch behavior in the presence of well-matched DNA.8 The
luminescence of this complex is quenched in aqueous solvents
due to formation of hydrogen-bonding interactions between
solvent molecules and the phenazine nitrogen atoms of the
dppz ligand.8,11,12 The Ru complex luminesces intensely in the
presence of DNA, however, because the phenazine moiety is
protected from the quenching environment upon intercalation
into the duplex.8,11,12 Steady state luminescence spectra, excited
state lifetime measurements, and NMR studies demonstrate
INTRODUCTION
■
Deficiencies in the DNA mismatch repair pathway, which
corrects DNA defects including base pair mismatches and
single-base bulges, are associated with several forms of human
cancer.1−3 Our laboratory has been interested in developing
octahedral metal complexes that target DNA defects.4−8 Since
deficiencies in mismatch repair necessarily lead to an increased
frequency of DNA defects within the cell, targeting these
defects with small metal complexes provides a new strategy in
designing new cancer diagnostics and chemotherapeutics.
We reported octahedral rhodium complexes that specifically
bind single-base mismatch sites in DNA and, upon photo-
activation, cleave the DNA backbone.4−6 The Rh complex
[Rh(bpy)2(chrysi)]3+ (Figure 1) recognizes 80% of mismatched
sites in all sequence contexts, and selectively targets a single-
base mismatch in a 2725 base pair DNA plasmid.5 Structural
studies of the rhodium complex bound to mismatched DNA
Figure 1. Chemical structures of [Rh(bpy)2(chrysi)]3+and [Ru-
Received: September 6, 2012
Published: October 31, 2012
(bpy)2(dppz)]2+.
© 2012 American Chemical Society
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Figure 2. Two strategies for designing new Ru complexes.
that the [Ru(bpy)2(dppz)]2+ complex intercalates into DNA by
one of two binding modes: side-on or perpendicular.8,11,13 In
the perpendicular mode, the Ru−dppz axis lies along the DNA
dyad axis, protecting the phenazine fragment from water. In the
side-on mode, the Ru−dppz axis lies along the long axis of the
base stack, partially exposing the ligand to solvent. Thus,
complexes bound in the better-protected perpendicular
intercalation mode show greater luminescent enhancement
upon binding to DNA and have longer excited state lifetimes
than those in the side-on mode. Recent crystal structures have
shown intercalation of dppz complexes into the DNA duplex
from the minor groove,14,15 though NMR studies have pointed
to intercalation from the major groove;13 the energetic
differences between major and minor groove orientations
must be small.
How might the luminescent properties of the [Ru-
(bpy)2(dppz)]2+ complex change in the presence of DNA
containing a defect? Previously, we have shown that [Ru-
(bpy)2(dppz)]2+, while showing luminescence bound to duplex
DNA, shows still greater luminescence in the presence of a
mismatch.16 More recent efforts to understand how mismatches
affect [Ru(bpy)2(dppz)]2+ binding have led to determination of
an atomic-resolution crystal structure of Δ-[Ru(bpy)2(dppz)]2+
bound to a mismatch-containing oligonucleotide.14 The
structure reveals that, like its rhodium counterpart, the
ruthenium complex also recognizes the destabilized mismatches
through metalloinsertion: the dppz ligand inserts into the base
stack from the minor groove, extruding the mispaired bases out
of the helix. Thus, it is conceivable that by combining the
structural features of [Rh(bpy)2(chrysi)]3+ (for mismatch-
specific recognition) and [Ru(bpy)2(dppz)]2+ (for lumines-
cence) it might be possible to develop an improved
luminescent reporter for DNA defects. Here, we investigated
two approaches for enhancing the mismatch specificity: (i)
replacement of the dppz ligand with sterically expansive
inserting ligands, such as chrysi, and (ii) incorporation of
various functionalities onto the dppz ligand to increase the
steric bulk. We report the preparation of a new family of
[Ru(bpy)2(L)]2+ derivatives (Figure 2) and the luminescent
behavior of each derivative in the presence of duplex DNA with
and without defects.
EXPERIMENTAL PROCEDURES
■
Materials and Methods. All reagents and solvents were
purchased from commercial suppliers and used without further
purification. Chrysene-5,6-quinone and benzo[a]phenazine-5,6-qui-
none were synthesized according to literature procedures.17 Ru
complexes Ru(bpy)2Cl2, [Ru(bpy)2(dppz)](X)2 (15), and [Ru-
(bpy)2(tactp)](X)2 (18, X = PF6 or Cl) were prepared by previously
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described procedures.8,18,19 UV−vis spectra were recorded on a
Beckman DU 7400 UV−visible spectrophotometer (Beckman
Coulter). Oligonucleotides 5′-GAC CAG CTT ATC ACC CCT
AGA TAA GCG-3′ and 3′- CTG GTC GAA TAG TXG GGA TCT
ATT CGC-5′ [X = G (M), C (MM), or R (AB, R denotes a
tetrahydrofuranyl abasic site)] were synthesized on an ABI 3400 DNA
synthesizer (Applied Biosystems) or purchased from Integrated DNA
Technologies and purified as previously reported.20
The resulting solution was stirred for 10 min at 0 °C and allowed to
warm slowly to room temperature. The reaction was quenched by
addition of water after stirring for 4 h at room temperature, and the
solution was filtered. Filtrate was extracted with CH2Cl2 (three times).
After removal of CH2Cl2, the crude product was purified by SiO2
column chromatography with a solvent gradient (50%:50%
Hx:CH2Cl2 to 100% CH2Cl2) to obtain the desired product 7 (153
mg, 0.98 mmol, 89%). 1H NMR (CDCl3, 300 MHz, δ (ppm)): 6.82 (s,
2H), 3.98 (br, s, 4H), 3.44 (s, 2H). HREI (m/z) for M+ calcd
156.0687, found 156.0687.
Synthesis. 1,2-Dihydrobenz[c]acridine (1). This compound was
synthesized according to the literature procedure21 and purified by
1
SiO2 column chromatography (9:1 hexane/EtOAc). Yield: 57%. H
1,4-Dibromo-2,3-diaminonaphthalene (9). 9 was synthesized
NMR (CDCl3, 300 MHz, δ (ppm)): 8.60 (d, 3J = 7.4 Hz, 1H), 8.17 (d,
3J = 8.3 Hz, 1H), 7.95 (s, 1H), 7.77 (d, 3J = 8.1 Hz, 1H), 7.67 (t, 3J =
7.6 Hz, 1H), 7.59−7.33 (m, 3H), 7.33−7.25 (m, 1H), 3.15 (t, 3J = 6.5
according to reported procedures.25
Dppz Derivatives. Ligands were synthesized by refluxing 5−9 (0.63
mmol) with 1,10-phenanthroline-5,6-dione and 10 or 11 with 5,6-
diamino-1,10-phenanthroline26 (0.63 mmol) in ethanol (10 mL) for 8
h, as shown in Scheme 2.8d Yellow precipitates were collected, washed
with cold ethanol (three times, 20 mL), dried under vacuum, and used
for preparation of the Ru complexes without further purification.
3
Hz, 2H), 3.03 (t, J = 6.5 Hz, 2H). ESI(+)MS (m/z): [M+H]+ calcd
232.1, found, 232.4.
5,6-Dihydronaphtho[1,2-b][1,8]naphthyridine (2). A suspension
of α-tetralone (0.39 g, 2.7 mmol), (2-aminopyridin-3-yl)methanol22
(0.33 g, 2.6 mmol), benzophenone (0.48 g, 2.6 mmol), and potassium
tert-butoxide (0.30 g, 2.7 mmol) in dry dioxane (10 mL) was heated
under reflux under an Ar atmosphere for 2 h. The red suspension was
cooled to room temperature, filtered through Celite, and poured into a
saturated NH4Cl solution (20 mL). This was extracted with EtOAc (3
× 20 mL), and the combined organic layers were dried over Na2SO4
and filtered, and solvent was removed. Crude material was purified by
SiO2 column chromatography (1:1 hexane/EtOAc) to give 2 as a pale
+
Dppa. Yield: 86%. ESI(+)MS (m/z): [M + H] calcd 327.1,
found 327.2.
+
Dppae. Yield: 40%. ESI(+)MS (m/z): [M + H] calcd 331.1,
found 331.2.
+
Dppn. Yield: 83%. ESI(+)MS (m/z): [M + H] calcd 333.1,
found 333.1.
Br2dppn. Yield: 75%. ESI(+)MS (m/z): [M + H] + calcd 490.9,
found 491.0.
1
red solid (0.37 g, 61%). H NMR (CDCl3, 300 MHz, δ (ppm)): 9.06
+
(dd, 3J = 4.2 Hz, 4J = 1.8 Hz, 1H), 8.84−8.73 (m, 1H), 8.20−8.05 (m,
1H), 7.95 (s, 1H), 7.50−7.35 (m, 3H), 7.33−7.23 (m, 1H), 3.29−3.09
(m, 2H), 3.10−2.96 (m, 2H). ESI(+)MS (m/z): [M + H]+ calcd
233.1, found 233.4; [2M + Na]+ calcd 487.2, found 486.9.
Pyrene-phen. Yield: 90%. ESI(+)MS (m/z): [M + H] calcd
407.1, found 407.3.
[Ru(bpy)2(NH3)2](PF6)2. A solution of Ru(bpy)2Cl2 (0.47 g, 0.9
mmol) and NH4OH (10 mL) in MeOH (5 mL) was heated at 60 °C
for 4 h. The reaction mixture was cooled to room temperature, and the
solvent was removed in vacuo. Residue was redissolved in MeOH and
precipitated with Et2O. Solid was collected and redissolved in water
(10 mL), and excess NH4PF6 (s) was added. The suspension was
stirred in the absence of light for 1 h and filtered, and the red
precipitate was washed with cold water (15 mL) and Et2O (3 × 10
mL) and dried under vacuum to give [Ru(bpy)2(NH3)2](PF6)2 (0.58
g, 0.8 mmol, 88%). 1H NMR (CD3OD, 300 MHz, δ (ppm)): 9.18 (d,
3J = 5.6 Hz, 2H), 8.64 (d, 3J = 8.1 Hz, 2H), 8.46 (d, 3J = 8.1 Hz, 2H),
8.20 (t, 3J = 7.9 Hz, 2H), 7.82 (t, 3J = 7.7 Hz, 4H), 7.65 (d, 3J = 5.7 Hz,
2H), 7.27−7.08 (m, 2H), 2.89 (s, 6H).
Ligand 3 and 4 Synthesis. A solution of 1 or 2 (2.0 mmol) in 1:1
acetic acid/acetic anhydride (10 mL) was cooled in an ice bath
(Scheme 1). A solution of Na2Cr2O7 (0.90 g, 3.0 mmol) in 1:1 acetic
Scheme 1
[Ru(bpy)2(L)]2+ Complexes. Method 1. A suspension of [Ru-
(bpy)2(NH3)2](PF6)2 (0.043 mmol) and NaH (0.8 mmol) in dry
MeCN (10 mL) was deoxygenated and stirred under an Ar
atmosphere for 30 min. Ligand (0.048 mmol) was added; the mixture
was deoxygenated and stirred at room temperature for 4 h before
quenching the reaction with a couple of drops of 1 M HCl. The
reaction mixture was diluted with water (10 mL), excess NH4PF6 (s)
was added, and the solution was concentrated in vacuo. Precipitates
were collected and washed with water (2 × 10 mL) and then
converted to the soluble chloride salt by anion exchange
chromatography (Sephadex QAE). Residues were purified on a
Waters C18 sep-pak cartridge and by preparative HPLC using a
gradient of H2O (with 0.1% TFA) to CH3CN over 60 min. Complex
was converted to the chloride salt by anion exchange chromatography
(Sephadex QAE).
acid/acetic anhydride (10 mL) was added dropwise, and the reaction
mixture was allowed to warm to room temperature. The reaction was
stirred at room temperature for 8 days, during which time a yellow
solid precipitated from the reaction mixture. Yellow precipitate was
filtered, washed with H2O, and dried.
Benz[c]acridine (acri) Quinone (3).23 Yield: 81%. 1H NMR
3
(CDCl3, 300 MHz, δ (ppm)): 9.07−8.87 (m, 2H), 8.25 (t, J = 8.1
Hz, 1H), 8.19 (d, 3J = 8.4 Hz, 1H), 7.98 (d, 3J = 8.1 Hz, 1H), 7.89 (dd,
[Ru(bpy)2(chrysi)](X)2 (12, X = TFA or Cl). Yield: 18%. H NMR
1
3
3J = 16.4, 8.1 Hz, 2H), 7.64 (t, J = 7.4 Hz, 2H). ESI(+)MS (m/z):
(CD3CN, 300 MHz, δ (ppm)): 12.91 (s, 1H), 12.42 (s, 1H), 8.58−
3
[2M + Na]+ calcd 541.1, found 540.8.
8.44 (m, 7H), 8.39−8.30 (m, 1H), 8.24 (d, J = 8.8 Hz, 1H), 8.19−
3
8.03 (m, 5H), 7.94 (d,3 J = 5.6 Hz, 2H), 7.82 (t, J = 8.3 Hz, 1H),
5,6-Naphtho[1,2-b][1,8]naphthyridine (naphthi) Quinone (4).
7.73−7.59 (m, 5H), 7.54−7.39 (m, 4H). ESI(+)MS (m/z): [M − H]+
calcd 669.1, found 669.1; [M]2+ calcd 335.1, found 334.6. UV−vis in
H2O, λabs/nm (ε × 104/M−1 cm−1): 255 (11.5), 282 (14.5), 550 (6.4).
[Ru(bpy)2(acri)](X)2 (13, X = TFA or Cl). Yield: 22%. 1H NMR
(CD3CN, 300 MHz, δ (ppm)): 14.06 (s, 1H), 13.07 (s, 1H), 9.75 (s,
1H), 9.12 (dd, 3J = 8.1 Hz, 4J = 1.4 Hz, 1H), 8.60−8.44 (m, 5H), 8.19
(d, 3J = 8.6 Hz, 1H), 8.13−8.00 (m, 7H), 7.97−7.84 (m, 1H), 7.83 (t,
3J = 7.6 Hz, 1H), 7.76−7.59 (m, 4H), 7.54−7.37 (m, 4H). ESI(+)MS
(m/z): [M − H]+ calcd 670.1, found 670.3; [M]2+ calcd 335.6, found
1
3
Yield: 69%. H NMR (CDCl3, 300 MHz, δ (ppm)): 9.29 (dd, J =
4.1 Hz, 4J = 1.8 Hz, 1H), 9.11 (d, 3J = 7.9 Hz, 1H), 9.06 (s, 1H), 8.38
(dd, 3J = 8.1 Hz, 4J = 1.7 Hz, 1H), 8.30 (d, 3J = 7.6 Hz, 1H), 7.91 (t, 3J
3
3
= 7.4 Hz, 1H), 7.69 (t, J = 7.5 Hz, 1H), 7.62 (dd, J = 8.1, 4.2 Hz,
1H). ESI(+)MS (m/z): [M + CH3OH + H]+ calcd 293.1, found 293.1.
3,6-Diethynylbenzene-1,2-diamine (7). A solution of 4,7-
diethynylbenzo[c][1,2,5]-thiadiazole24 (200 mg, 1.1 mmol) in 30
mL of THF was purged with Ar for 30 min and cooled to 0 °C. Eight
equivalents of LiAlH4 (in THF) were added dropwise over 10 min.
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Scheme 2
335.7. UV−vis in H2O, λabs/nm (ε × 104/M−1 cm−1): 238 (5.1), 285
Scheme 3
(8.2), 400 (1.1), 438 (1.2), 542 (3.7).
1
[Ru(bpy)2(naphthi)](X)2 (14, X = TFA or Cl). Yield: 4%. H NMR
(CD3CN, 300 MHz, δ (ppm)): 13.76 (s, 1H), 12.79 (s, 1H), 9.62 (s,
1H), 9.21 (dd, 3J = 4.1 Hz, 4J = 1.9 Hz, 1H), 9.08 (d, 3J = 7.4 Hz, 1H),
3
8.58−8.38 (m, 6H), 8.07 (dd, J = 16.0, 8.0 Hz, 6H), 7.89−7.58 (m,
5H), 7.54−7.31 (m, 4H). ESI(+)MS (m/z): [M − H]+ calcd 671.1,
found 671.2; [M]2+ calcd 336.1, found 335.4. UV−vis in H2O, λabs/nm
(ε × 104/M−1 cm−1): 241 (4.6), 288 (6.8), 425 (1.1), 540 (2.7).
Method 2. Ethylene glycol (7 mL) was added to a mixture of
Ru(bpy)2Cl2 (0.069 mmol) and the dppz derivatives (0.069 mmol),
and the solution was heated to 130 °C for 12 h (Scheme 3). After
cooling the reaction mixture to room temperature, the solution was
diluted with water (7 mL) followed by addition of excess NH4PF6 (s).
Orange precipitates were collected, washed with water (3 × 5 mL),
and dried under vacuum. Complexes were recrystallized by addition of
Et2O into their CH3CN solutions at room temperature and afterward
converted to the soluble Cl salt by anion exchange chromatography
(Sephadex QAE). They were further purified by preparative HPLC
using a gradient of H2O (with 0.1% TFA) to CH3CN (with 0.1%
TFA) over 30 min.
1
[Ru(bpy)2(dppa)](X)2 (16, X = PF6 or Cl). Yield: 63%. H NMR
(CD3CN, 500 MHz, δ (ppm)): 9.76−9.68 (m, 2H), 9.06 (m, 1H),
8.70 (m, 1H), 8.59−8.54 (m, 4H), 8.49 (1H, m), 8.22 (s, br, 2H), 8.14
(m, 2H), 8.05 (m, 2H), 7.94 (m, 2H), 7.89 (m, 2H), 7.79 (2H, m),
7.49 (m, 2H), 7.30 (m, 2H). ESI(+)MS (m/z): [M − 2(PF6)]2+ calcd
370.1, found 370.0; [M − PF6]+ calcd 885.1, found 885.2. UV−vis in
H2O, λabs/nm (ε × 104/M−1 cm−1): 284 (10), 362 (1.9), 378 (1.9),
444 (1.6).
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[Ru(bpy)2(dppae)](X)2 (17). Ru complex was prepared as described
above. Crude product was purified via preparative TLC (silica, 4:4.5:1,
CH3CN:water:NH4Cl (satd, aq)) followed by preparative HPLC (a
gradient of H2O with 0.1% TFA to CH3CN with 0.1% TFA). Cl salt
was then obtained using anion exchange chromatography on Sephadex
QAE. Yield: 20%. ESI(+)MS (m/z): [M − 2(Cl)]2+ calcd 372.1, found
372.0. UV−vis in H2O, λabs/nm (ε × 104/M−1 cm−1): 244 (4.3), 272
(sh, 4.7), 288 (6.3), 306 (4.3), 364 (1.2), 380 (1.5), 426 (1.4), 440
(1.3).
was not expected to show “light-switch” behavior but specificity
in binding a mismatch was expected due to the ligand expanse.
In the second approach, simple substitutions (CO2H,
acetylene, Br, and phenyl) were incorporated onto the dppz
ligand in order to increase its width, length, or both (Figure 2).
For example, the wider ligand framework in pyrene-phen and
tactp is similar to that of the sterically bulky chrysi ligand. As
dppn is longer than dppz, [Ru(bpy)2(dppn)]2+ will likely bind
to well-matched sites from the major groove rather than the
minor groove leading to greater exposure of the phenazine
nitrogen atoms to solvent compared to dppz, thus reducing
luminescence. Therefore, because of the likelihood of low
luminescence when bound to well-matched DNA, complexes
with dppn (or dppa) might show a significant increase in
luminescence due only to selective intercalation or insertion
into destabilized lesion sites in DNA. Alternatively, increasing
the width of the dppz ligand to make dppae or tactp was
expected to discourage the binding of the complex to well-
matched DNA in a similar fashion to the sterically expansive
chrysi ligand. Increasing both the length and the width (to
make Br2dppn and pyrene-phen) would then combine the
effects.
[Ru(bpy)2(dppn)](X)2 (19). Yield: 72%. 1H NMR (CD3CN, 500
MHz, δ (ppm)): 9.71−9.681 (m, 2H), 9.17−9.16 (m, 2H), 8.57 (dd, J
= 8.0 Hz, 4H), 8.41−8.39 (m, 2H), 8.18−8.14 (m, 4H), 8.10−8.05 (m,
2H), 7.94−7.88 (m, 4H), 7.82−7.78 (m, 4H), 7.52−7.49 (m, 2H),
7.34−7.31 (m, 2H). ESI(+)MS (m/z): [M − 2(PF6)]2+ calcd 373.1,
found 373.1; [M − PF6]+ calcd 891.1, found 891.2. UV−vis in H2O,
λabs/nm (ε × 104/M−1 cm−1): 244 (5.3), 286 (7.0), 324 (7.4), 390
(1.6), 412 (2.2), 442 (2.0).
1
[Ru(bpy)2(Br2dppn)](X)2 (20). Yield: 69%. H NMR (CD3CN, 500
MHz, δ (ppm)): 8.43−8.41 (m, 2H), 7.49−7.46 (m, 2H), 7.43−7.39
(m, 4H), 6.96−6.94 (m, 2H), 6.87−6.84 (m, 2H), 6.79−6.76 (m, 2H),
6.66−6.55 (m, 8H), 6.23 (2H, m), 6.06 (2H, m). ESI(+)MS (m/z):
[M − 2(PF6)]2+ calcd 451.0, found 451.0; [M − PF6]+ calcd 1049.3,
found 1049.1. UV−vis in H2O, λabs/nm (ε × 104/M−1 cm−1): 254
(3.7), 286 (4.5), 324 (4.3), 396 (1.0), 420 (1.4), 446 (1.4).
1
[Ru(bpy)2(pyrene-phen)](X)2 (21). Yield: 76%. H NMR (CD3CN,
Synthesis of the Ru Complexes. Ligands 1 and 2 were
3
3
500 MHz, δ (ppm)): 9.71 (d, J = 7.5 Hz, 2H), 9.47 (d, J = 7.5 Hz,
3
synthesized in two steps from α-tetralone by a Friedlander
̈
2H), 8.59 (t, J = 9.3 Hz, 4H), 8.27−8.23 (m, 4H), 8.19−8.11 (m,
3
4
synthesis and subsequent oxidation with sodium dichromate
(Scheme 1).21,23 Ruthenium complexes 12−14 were synthe-
sized by reacting [Ru(bpy)2(NH3)2](PF6)2 with the appro-
priate quinone ligand in the presence of sodium hydride at
ambient temperature (Scheme 3). Complexes 12−14 were
isolated in 4−20% yield following purification and anion
exchange to the chloride salt. Unexpectedly, [Ru-
(bpy)2(phzi)]2+ (Figure 2) was not the major product from
the reaction with benzo[a]phenazine-5,6-quinone and was only
isolated in trace amounts, as characterized by HPLC and mass
spectrometry. We propose that [Ru(bpy)2(iqi)]2+ (22) (Figure
S1, Supporting Information) is the major product of the
reaction as the 1H NMR spectrum of the isolated complex only
contains one imine proton signal, and the mass spectrum is
consistent with loss of carbon monoxide. It has been reported
that a related ligand, 1,10-phenanthroline-5,6-dione, loses
carbon monoxide under basic conditions.27 Similar ligand
decomposition in the presence of sodium hydride during the
course of the reaction could account for the low yields of
complexes 12−1428 and formation of byproduct 22. Following
the loss of carbon monoxide from benzo[a]phenazine-5,6-
quinone, unlike the other ligands, it is still possible to
coordinate to the metal center in a bidentate fashion through
the phenazine nitrogen and imine formed from the remaining
quinone.
4H), 8.06 (td, J = 8.0 Hz, J = 1.2 Hz, 2H), 8.0−7.92 (m, 4H), 7.84
3
(d, J = 5.1 Hz, 2H), 7.74 (s, 2H), 7.52 (m, 2H), 7.34 (m, 2H).
ESI(+)MS (m/z): [M − 2(PF6)]2+ calcd 410.8, found 410.2; [M −
PF6]+ calcd 965.1, found 965.4. UV−vis in H2O, λabs/nm (ε × 104/
M−1 cm−1): 236 (3.7), 288 (5.0), 348 (1.1), 452 (1.3), 476 (1.3).
Luminescence Measurements. Steady State Fluorescence.
Luminescence spectra were recorded on an ISS-K2 spectrofluorometer
in 5 mM Tris, 50 mM NaCl, pH 7.5 at ambient temperature or in a 10
M LiCl glass at 77 K in aerated solutions. Samples were excited at 440
nm, and the emission intensity was integrated from 560 to 800 nm.
Excited State Lifetime Measurements. Samples were excited using
a Nd:YAG-pumped OPO (Spectra-Physics Quanta-Ray). Laser power
at 470 nm ranged from 3.0 to 4.5 mJ per pulse at 10 Hz. Emitted light
was collected and focused onto the entrance slit of an ISA double-
grating (100 mm) monochromator and detected by a PMT
(Hamamatsu R928). Each measurement is the average of 500 or
1000 shots of 8 ns duration. Emission decays were fit to mono- or
biexponential functions using nonlinear least-squares minimization.
RESULTS AND DISCUSSION
■
Design Considerations. Inspired by the activity of
[Rh(bpy)2(chrysi)]3+ and [Ru(bpy)2(dppz)]2+ (Figure 1)
toward DNA,4−10,13,14,16 we aimed to develop a new framework
for detecting DNA defects based on luminescence. The key
feature of the chrysi complex that enables it to specifically bind
to destabilized sites in DNA is the sterically expansive inserting
chrysi ligand.4−7,9,10 Meanwhile, the luminescence-based
detection of DNA by [Ru(bpy)2(dppz)]2+ is based on the
protection of the dppz ligand from water by the DNA
duplex.8,13 Thus, by combining the characteristics of chrysi and
dppz into a single ligand, it may be possible to create a Ru
complex that luminesces only when specifically bound to DNA
defects. Guided by these design considerations, a series of
ruthenium complexes, based on the structures of both
[Rh(bpy)2(chrysi)]3+ and [Ru(bpy)2(dppz)]2+ using two
strategies, was prepared as candidate luminescent reporters
for DNA defects (Figure 2). In one approach, sterically
expansive chrysi analogues with hydrogen-bonding function-
ality similar to the dppz ligand were investigated. The chrysi
parent complex was also studied as a comparison; this complex
Ru complexes [Ru(bpy)2(dppz)]2+ (15) and [Ru-
(bpy)2(tactp)]2+ (18) were prepared by previously published
methods.8,19 For the ligands dppa, dppae, dppn, and Br2dppn
(Scheme 2), the amine moieties were condensed with 1,10-
phenanthroline-5,6-dione in ethanol.8d,24,25 The pyrene-phen
ligand was obtained by condensation of pyrene-4,5-dione and
5,6-diamino-1,10-phenanthroline26 in ethanol.8d Complexes
(16, 17, and 19−21) were obtained by refluxing a solution
containing Ru(bpy)2Cl2 and 1 equiv of the corresponding dppz
derivative in ethylene glycol at 130 °C for 8 h, as depicted in
Scheme 3. Addition of excess NH4PF6 (s) into the reaction
solution of 1:1 ethylene glycol:water allowed isolation of the Ru
complexes as PF6 salts, followed by purification via recrystal-
lization or column chromatography. All complexes show the
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Figure 3. Emission spectra of [Ru(bpy)2(chrysi)]2+ (12) and [Ru(bpy)2(naphthi)]2+ (14) in the presence and absence of DNA at 77 K and room
temperature (10 M LiCl, λex = 440 nm). [Ru] = 5 μM, [DNA] = 0 or 5 μM. DNA sequences are shown at the top of the figure.
characteristic MLCT transition absorption in the visible region
at ∼440 nm.
Luminescent Characteristics of the Ru Complexes
with and without DNA. While complexes 12−14 (Scheme 3
and Figure 2) are not luminescent at ambient temperature in
(35%) > 14 (21%), in the presence of mismatched DNA than
for matched DNA (Figure 4). While it was not possible to
directly detect the luminescence of the complexes at room
temperature, competition studies provide evidence that the
various solvents (dry MeCN, Tris buffer, and 10 M LiCl),
2+
[Ru(bpy)2(chrysi)]2+ (12) and [Ru(bpy)2(naphthi)]
(14)
are luminescent in the absence of DNA at 77 K in a 10 M LiCl
glass (Figure 3). In the presence of DNA, there is no
luminescence differential between mismatched and matched
DNA for both complexes. [Ru(bpy)2(acri)]2+ (13) is not
luminescent at 77 K in dry MeCN nor in the presence or
absence of DNA in 10 M LiCl upon excitation at 440 nm. The
DNA “light switch” complex [Ru(bpy)2(dppz)]2+ (15) is also
luminescent at 77 K in the absence of DNA (Figure S2,
Supporting Information). Therefore, it is not possible to
determine the mismatch specificity or light switch behavior of
the complexes from low-temperature experiments.
At ambient temperature, [Ru(bpy)2(chrysi)]2+ (12), [Ru-
(bpy)2(acri)]2+ (13), and [Ru(bpy)2(naphthi)]2+ (14) are not
luminescent in the absence or presence of DNA. Therefore,
competition experiments were carried out with the “light
switch” complex [Ru(bpy)2(dppz)]2+ (15) in order to
investigate the room-temperature mismatch specificity of the
complexes. Control experiments reveal that complexes 12−14
do not quench the luminescence of 15 in the absence of DNA
in dry MeCN (Figure S3, Supporting Information). Lumines-
cence of 1:1 DNA/15 mixtures in aqueous buffer was measured
upon addition of up to 10 equiv of complexes 12−14. A
decrease in the luminescence is expected if the complex
displaces 15, as 15 is luminescent only when bound to DNA.
For all three complexes 12−14, there was a small decrease in
the luminescence of 15 in the presence of matched DNA with
the largest decrease observed with 12 (33% after 1 equiv). In
contrast, there was a much more significant luminescence
decrease, following the order 12 (55% after 1 equiv) > 13
Figure 4. Plots of the integrated emission intensity of 0.1 μM
[Ru(bpy)2(dppz)]2+ (15) and 0.1 μM matched (M) or mismatched
(MM) DNA with up to 10 equiv of [Ru(bpy)2(L)]2+, where L is chrysi
(12), acri (13), or naphthi (14) (5 mM Tris, pH 7.5, 50 mM NaCl, λex
= 440 nm). See Figure 3 for DNA sequences.
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Figure 5. Plots of the integrated emission intensity of 15−21 with matched (M), mismatched (MM), and abasic (AB) DNA (5 mM Tris, pH 7.5, 50
mM NaCl, λex = 440 nm). [Ru] = 0.1 (for 15, 18, and 21), 1 (for 16 and 17), 5 (for 19), and 10 μM (for 20). DNA sequences are depicted (top,
left).
complexes preferentially bind to DNA mismatches through
their sterically expansive inserting ligands.
Similar to 15, the [Ru(bpy)2(dppa)]2+ complex (16) exhibits
luminescence enhancement in the presence of MM and AB
DNA, relative to well-matched DNA, although its binding
affinity is lower than that of 15 (Figure 5 and Table S1,
Supporting Information). Attachment of a benzo group to the
end of the phenazine moiety increases the length of the dppz-
type ligand (dppn, Scheme 2). We assume binding to the
DNAs resembles that of the dppz complex. Significantly,
[Ru(bpy)2(dppn)]2+ (19) exhibits an increase in luminescence
with MM over M and AB DNA (Figure 5). This may be
because the extended dppn ligand of 19, when bound to well-
matched DNA from the major groove, offers less protection to
the phenazine nitrogens from solvent water molecules than
does dppz. However, for dppn, binding to mismatches likely
occurs from the minor groove as it does for dppz. The minor
groove is deep and narrow, allowing deeper intercalation of the
Ru complex and consequently better protection of the ligand
from solvent water.
Restoration of luminescence at low temperature for [Ru-
(bpy)2(chrysi)]2+ (12) and [Ru(bpy)2(naphthi)]2+ (14)
suggests that nonradiative solvent relaxation, most likely
through the exchangeable imino protons, is responsible for
the loss of luminescence at ambient temperature. Preliminary
studies have revealed that methylation of the imino protons of
12 restores luminescence at ambient temperature. However,
synthetic difficulties and decomposition of the methylated
complex limited further studies.
Unlike complexes 12−14, the [Ru(bpy)2(dppz)]2+ deriva-
tives (15−21, Figure 2) all show enhanced luminescence with
matched (M), mismatched (MM), and abasic (AB) DNA
versus in the absence of DNA in aqueous buffer, indicating that
the conserved phenazine portion retains some of the
photophysical properties of the parent complex 15 (Figure
5). However, complexes having extensively π-conjugated
ligands (18 −21) emit luminescence with detectable intensity
in the absence of DNA, possibly due to partial shielding of one
of the phenazine nitrogens from the solvent by the added steric
bulk.
Introduction of the expansive dppz derivatives dppae and
tactp, employing acetylene and chrysene functionalities,
respectively, to increase the width of the ligand, eliminates
the luminescence differential with DNA defects (Figure 5). In
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Table 1. Luminescence Decay Parameters for Ru(bpy)2(dppz)2+ in Competition Experiments with [Ru(bpy)2(chrysi)]2+ (12),
a
[Ru(bpy)2(acri)]2+ (13), and [Ru(bpy)2(naphthi)]2+ (14) in the Presence of Matched (M) and Mismatched (MM) DNA
M
MM
b
b
b
b
complex (ligand)
complex equiv
τ1, ns (%)
τ2, ns (%)
τ1, ns (%)
τ2, ns (%)
12 (chrysi)
0.0
0.5
1.0
1.5
2.0
0.0
0.5
1.0
1.5
2.0
0.0
0.5
1.0
1.5
2.0
32 (50)
36 (58)
36 (64)
34 (69)
30 (71)
37 (40)
36 (41)
35 (42)
36 (45)
34 (44)
37 (40)
37 (42)
38 (44)
36 (44)
36 (46)
120 (50)
120 (42)
120 (36)
120 (31)
110 (29)
120 (60)
120 (59)
120 (58)
120 (55)
120 (56)
120 (60)
130 (58)
130 (56)
120 (56)
120 (54)
54 (48)
45 (55)
36 (54)
33 (57)
32 (59)
48 (46)
46 (48)
42 (48)
41 (50)
40 (52)
46 (43)
44 (44)
44 (47)
45 (50)
41 (50)
200 (52)
180 (45)
140 (46)
130 (43)
120 (41)
190 (54)
180 (52)
170 (52)
170 (50)
170 (48)
180 (57)
180 (56)
180 (53)
180 (50)
170 (50)
13 (acri)
14 (naphthi)
a
λex = 470 nm, λem = 610 nm, 5 μM [Ru(bpy)2(dppz)]2+, and 5 μM [DNA] (5 mM Tris, pH 7.5, 50 mM NaCl). Matched (M) and mismatched
(MM) oligonucleotides shown in Figure 3 were used. Emission decays were fit to the biexponential function Y(t) = Y0 + A1·exp(−t/τ1) + A2·exp(−t/
b
τ2) to give the lifetimes τ1 and τ2. Relative contribution of each lifetime to the overall decay is indicated in parentheses. Error is estimated to be
10%.
the case of [Ru(bpy)2(tactp)]2+ (18), a previous study
demonstrated that luminescence increases not only through
interaction with DNA but also by dimerization or aggregation
of the complex itself with or without a DNA template.8d
Substituents were also incorporated onto dppn to widen this
ligand. These derivatives are Br2dppn and phen-pyrene
(Scheme 2), which are both wider and longer than dppz. Ru
complexes (20 and 21, Figure 2) bearing Br2dppn and phen-
pyrene do not show any differential luminescence between M,
MM, and AB DNA, however (Figure 5). The weak
luminescence of 20 may be due to heavy atom quenching by
bromine.29 The increased luminescence of 21 could occur in a
manner similar to that of the structural homologue 18, i.e.,
through DNA-templated dimerization.8d
In summary, the luminescence measurements of 15−21
(Figure 2) suggest that structural modification of dppz is not
sufficient to improve specific detection of DNA defects through
the luminescence response of dppz derivatives. The discrepancy
between the high specificity of [Rh(bpy)2(chrysi)]3+ complexes
binding to DNA mismatches and the lack of specificity
observed for these dppz derivatives might be due to differences
in the proximity of the steric bulk to the metal center in the
respective complexes. In the [Ru(bpy)2(dppz)]2+ derivatives
studied here, the bulky portions of the intercalating ligands are
well removed from the metal center, allowing considerable
conformational flexibility of binding. In the case of the Rh
complex, the chrysi ligand is much closer to the metal center, so
its binding geometry is constrained to that imposed by the
octahedral center. This notion echoes the conclusions from a
previous study comparing the binding of [Rh(bpy)2(chrysi)]3+
to mismatched DNA with that of [Ru(bpy)2(eilatin)]2+.30
However, unlike the weakly emissive eilatin complex, the dppz
derivatives preserve the “light switch” behavior in the presence
of DNA.
through competition experiments with [Ru(bpy)2(dppz)]2+
(15) in the presence of matched and mismatched DNA.
Luminescence from the dppz complex decays biexponentially,
with each lifetime corresponding to one binding geometry:
perpendicular (longer lifetime) or side-on (shorter lifetime).8,16
Greater protection of the phenazine moiety from water via
intercalation leads to longer emission lifetimes for the two
binding modes (side-on and perpendicular), a higher relative
population of the longer-lived species, or both.
The lifetimes do not change within experimental error in the
presence of matched DNA upon addition of up to 2 equiv of
complexes 12−14, although the relative population of the
longer-lived species decreases (Table 1). This is consistent with
a change in binding mode from perpendicular to side-on and
suggests that the small luminescence decrease observed in the
luminescence competition experiments is largely due to a
binding mode change rather than displacement of [Ru-
(bpy)2(dppz)]2+ (15) from matched DNA.
In the absence of a competing complex, both lifetimes are
greater for a 1:1 mixture of [Ru(bpy)2(dppz)]2+ (15) and
mismatched DNA compared to well-matched DNA due to
greater protection of the phenazine moiety at the mismatch
(Table 1). After addition of 2 equiv of complexes 12−14, both
excited state lifetimes decrease and approach each of the
lifetimes of 15 observed in the presence of matched DNA. The
magnitude of the decrease agrees with the steady state
luminescence competition experiments where the largest
decrease is observed with 12 followed by 13 and 14. In
addition to the lifetime changes, the relative population of the
perpendicular state decreases. These results contrast those from
analogous experiments with matched DNA, suggesting that the
changes are due to displacement of 15 from the mismatch
rather than a binding mode change. This is further evidence
that the complexes bind preferentially to mismatched DNA
over matched DNA.
Excited State Lifetimes. The excited state lifetimes also
reveal the binding preferences of the complexes. Given that
complexes 12−14 (Figure 2) are not luminescent at ambient
temperature, their mismatch specificity was investigated
For the [Ru(bpy)2(dppz)]2+ derivatives (15−21, Figure 2),
the binding preferences of the complexes in 2:1 DNA/Ru
mixtures could be probed directly at ambient temperature. As
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shown in Table 2, 15 displays a higher relative abundance
bound in the perpendicular mode in the presence of DNA
decays in emission. Lifetime measurements show a lower
relative yield of long-lived species for 17 and shorter lifetimes
for 20 in the presence of DNA-containing defects. These results
are consistent with the slight decrease in steady state
luminescence observed for 17 and 20 when combined with
DNA-containing defects (Figure 5).
Table 2. Luminescence Decay Parameters for the
[Ru(bpy)2(dppz)]2+ Complexes in the Presence of Matched
a
(M), Mismatched (MM), and Abasic (AB) DNA
no DNA
in the presence of DNA
SUMMARY AND IMPLICATIONS
■
b,
c
c
c
complex (ligand)
τ (ns)
DNA
τ1, ns (%)
τ2, ns (%)
Taking inspiration from the mismatch specificity of the
sterically expansive chrysi ligand and light switch behavior of
[Ru(bpy)2(dppz)]2+, a family of Ru(II) complexes was
prepared in an attempt to specifically target DNA defects and
indicate their presence by the appearance of luminescence. In
one design strategy, complexes containing sterically expansive
ligands, such as chrysi and analogues with hydrogen-bonding
functionality similar to dppz, were synthesized. Incorporation of
the sterically expansive ligand appears to improve the mismatch
specificity; however, the complexes are nonluminescent at
room temperature. The exchangeable imino protons most likely
quench luminescence at room temperature through solvent
relaxation as luminescence is restored at 77 K for [Ru-
(bpy)2(chrysi)]2+ (12) and [Ru(bpy)2(naphthi)]2+ (14).
Despite their mismatch specificity, the lack of luminescence
signals at room temperature limits the use of these complexes
as probes. Light switch behavior cannot be exploited at low
temperature to improve mismatch discrimination, as the known
“light switch” complex [Ru(bpy)2(dppz)]2+ (15) shows
luminescence at 77 K even in the absence of DNA.
Ru complexes containing dppz derivatives (15−21) were
also synthesized with the goal of increasing their steric bulk
through incorporation of various functionalities on the ligand
framework. Their luminescence responses, however, were not
substantially enhanced compared with the parent complex 15 in
the presence of DNA with a mismatched or abasic site.
Nevertheless, the narrow ligands (dppa and dppn) show
differential luminescence behavior in the presence of a DNA
defect. Widening the dppz ligand using a simple group such as
acetylene or Br does not enhance targeting to destabilized
regions of DNA. Furthermore, Ru complexes with the
extensively π-conjugated ligands (tactp and pyrene-phen) are
likely to aggregate and are therefore unable to report
mismatches via luminescence output.
These observations are consistent with a recent crystal
structure in which the dppz ligand of Δ-[Ru(bpy)2(dppz)]2+
inserts deeply from the minor groove at mismatched sites.14 In
the crystal structure, the central ring of the phenazine portion
of dppz stacks with the DNA bases, affording the nitrogen
atoms of the phenazine moiety maximum protection from
solvent water. Considering the structural resemblance between
dppa and dppz, complexes of the two ligands are likely to bind
DNA in the same manner. The similarity in mismatch
discrimination between [Ru(bpy)2(dppa)]2+ (16) and [Ru-
(bpy)2(dppz)]2+ (15) is therefore not surprising. Extension of
dppz to form dppn alters the equilibrium binding geometry of
the complex. The relatively high mismatch discrimination of the
dppn complex may therefore indicate stronger binding and
more effective protection from solvent at mismatched sites.
Similarly, widening the terminal phenazine ring of dppz to form
tactp or pyrene-phen may result in stacking between the DNA
bases and these wider, extended structures, decreasing the
degree of protection experienced by the nitrogen atoms of the
phenazine ring. Presumably, these modifications are also
responsible for aggregation of the complexes. Consequently,
d
15 (dppz)
180
190
190
210
170
200
190
M
72 (83)
210 (17)
210 (23)
190 (31)
190 (5)
250 (4)
540 (7)
MM
AB
M
74 (77)
86 (69)
16 (dppa)
32 (95)
MM
AB
M
32 (96)
26 (93)
e
17 (dppae)
280 (60)
390 (67)
500 (62)
1210 (100)
1180 (100)
1120 (100)
62 (51)
3900 (40)
4280 (33)
4640 (38)
MM
AB
M
18 (tactp)
MM
AB
M
19 (dppn)
840 (49)
1010 (51)
710 (42)
1060 (37)
880 (34)
800 (46)
MM
AB
M
200 (49)
35 (58)
20 (Br2dppn)
21 (pyrene-phen)
99 (63)
MM
AB
M
130 (66)
82 (54)
930 (100)
880 (100)
810 (100)
MM
AB
a
λex = 470 nm, λem = 610 nm, 10 μM [Ru], and 20 μM [DNA] (5 mM
Tris, pH 7.5, 50 mM NaCl). Matched (M), mismatched (MM), and
abasic (AB) oligonucleotides in Figure 5 were used. Emission decays
were fit to the monoexponential function Y(t) = Y0 + A1·exp(−t/τ1) or
biexponential function Y(t) = Y0 + A1·exp(−t/τ1) + A2·exp(−t/τ2) to
give the lifetimes τ1 and τ2. Relative contribution of each lifetime to the
b
overall decay is indicated in parentheses. [Ru] = 10 μM, CH3CN.
Error is estimated to be 10%. Reference 8. 20 μM [Ru] and 40
c
d
e
μM [DNA].
following the order AB > MM > M. This supports the
observation from steady state measurements that the
luminescence intensity of 15 is present in the following
order: AB > MM > M (Figure 5).16 Likewise, in the case of
[Ru(bpy)2(dppa)]2+ (16), longer lifetimes corresponding to
the perpendicular mode (AB > MM > M) are observed, which
can explain the trend in the steady state luminescence
measurements of 16, as shown in Figure 5. Furthermore,
[Ru(bpy)2(dppn)]2+ (19), which shows differential lumines-
cence turn-on with MM over M and AB, indicates longer
lifetimes in both binding modes only with MM. Overall, excited
state lifetime measurements indicate that 15, 16, and 19 display
longer lifetimes or a higher population in the perpendicular
mode in the presence of DNA containing a lesion, suggesting
greater protection of the phenazine nitrogen atoms upon
binding to DNA defects.
Ru complexes 18 and 21, which can aggregate in the
presence of a DNA template, exhibit single-exponential
luminescent decays with DNA (Table 2), suggesting that
their luminescence enhancement originates mainly from
nonspecific binding to DNA. Ru complexes 17 and 20, which
have increased steric bulk on the phenazine fragment but utilize
different substituents than 18 and 21, present biexponential
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(9) (a) Pierre, V. C.; Kaiser, J. T.; Barton, J. K. Proc. Natl. Acad. Sci.
U.S.A. 2007, 104, 429−434. (b) Cordier, C.; Pierre, V. C.; Barton, J. K.
J. Am. Chem. Soc. 2007, 129, 12287−12295. (c) Zeglis, B. M.; Pierre,
V. C.; Kaiser, J. T.; Barton, J. K. Biochemistry 2009, 48, 4247−4253.
(10) Zeglis, B. M.; Boland, J. A.; Barton, J. K. J. Am. Chem. Soc. 2008,
130, 7530−7531.
the phenazine nitrogens in tactp and pyrene-phen may be
similarly accessible to solvent whether the complex is
dimerized, intercalated, or inserted; hence, the tactp and
pyrene-phen complexes exhibit similar luminescence profiles
with all three types of DNA.
Of the two approaches investigated here, increasing the steric
bulk of the dppz framework appeared to be more successful, as
all of the derivative complexes retained “light switch” behavior.
Although the structural modifications investigated here are not
sufficient by themselves to enhance the luminescence differ-
ential between matched and defective DNA, future efforts to
improve the mismatch specificity of [Ru(bpy)2(dppz)]2+ should
perhaps shift away from appending steric bulk to the distal
portion of the dppz ligand. The [Ru(bpy)2(dppz)]2+ scaffold,
thus, may be able to withstand the even bolder modifications
necessary to achieve mismatch-specific luminescence.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Chemical structure and characterization information of [Ru-
(bpy)2(iqi)]2+ (22), Tables S1 and S2, and Figures S1−S3. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(20) Brunner, J.; Barton, J. K. Biochemistry 2006, 45, 12295−12302.
(21) Martinez, R.; Ramon, D. J.; Yus, M. J. Org. Chem. 2008, 73,
9778−9780.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jkbarton@caltech.edu.
■
(22) Thomas, A. A.; Le Huerou, Y.; De Meese, J.; Gunawardana, I.;
Kaplan, T.; Romoff, T. T.; Gonzales, S. S.; Condroski, K.; Boyd, S. A.;
Ballard, J.; Bernat, B.; DeWolf, W.; Han, M.; Lee, P.; Lemieux, C.;
Pedersen, R.; Pheneger, J.; Poch, G.; Smith, D.; Sullivan, F.; Weiler, S.;
Wright, S. K.; Lin, J.; Brandhuber, B.; Vigers, G. Bioorg. Med. Chem.
Lett. 2008, 18, 2206−2210.
Present Address
†Life Sciences Institute and Department of Chemistry,
University of Michigan, Ann Arbor, MI 48109, United States.
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(24) DaSilveira Neto, B. A.; Sant’Ana Lopes, A.; Ebeling, G.;
Notes
The authors declare no competing financial interest.
Gonca̧ lves, R. S.; Costa, V. E. U.; Quina, F. H.; Dupont, J. Tetrahedron
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ACKNOWLEDGMENTS
(25) Yang, J.; Jiang, C.; Zhang, Y.; Yang, R.; Yang, W.; Hou, Q.; Cao,
Y. Macromolecules 2004, 37, 1211−1218.
■
We thank the NIH (GM33309 to J.K.B.) for their financial
support, the Lindemann Trust for a postdoctoral fellowship to
A.J.M., the Tobacco-Related Disease Research Program
(TRDRP) for a postdoctoral fellowship to M.H.L., and a
Dissertation Research Award to H.S. We also thank Dr. Eva
(26) Bodige, S.; MacDonnell, F. M. Tetrahedron Lett. 1997, 38,
8159−8160.
(27) Inglett, G. E.; Smith, G. F. J. Am. Chem. Soc. 1950, 72, 842−844.
(28) Sodium hydride is necessary for the condensation reaction to
proceed; however, similar yields were obtained, reducing the number
of equivalents of sodium hydride.
Ruba for developing the synthesis of [Ru(bpy) (chrysi)]2+ and
̈
2
Jessica Yeung for carrying out preliminary studies. We are
grateful to the Beckman Institute Laser Resource Center
(BILRC) at Caltech for facilities.
(29) Dreeskamp, H.; Koch, E.; Zander, M. Chem. Phys. Lett. 1975, 31,
251−253.
(30) Zeglis, B. M.; Barton, J. K. Inorg. Chem. 2008, 47, 6452−6457.
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