Design and Photophysical Studies of Acridine-Based RuIIComplexes for Applications as DNA Photoprobes

Article abstract of DOI:10.1002/ejic.201600468

A series of new extended planar aromatic ligands based on an acridine core (dpac = dipyrido[3,2-a:2′,3′-c]acridine; dpacF₂= 7,8-difluorodipyrido[3,2-a:2′,3′-c]acridine; dpacF₄= 6,7,8,9-tetrafluorodipyrido[3,2-a:2′,3′-c]acridine) and their respective Ru^IIcomplexes were synthesized and extensively studied. The photophysical and theoretical studies revealed that Ru-DPAC and Ru-DPACF₂allow emission from a³MLCT_phen/dpacexcited state at 597 and 604 nm, respectively, whereas the lowest excited state for Ru-DPACF₄shifts from a bright³MLCT_phen/dpacstate towards a poorly luminescent³MLCT_dpacstate (λ_em= 609 nm) owing to the formation of hydrogen bonds with water molecules in the excited state. These complexes exhibit up to sevenfold luminescence enhancement in the presence of complementary and mismatched DNA, demonstrating a strong binding to polynucleotides. The results emphasize the interest in Ru^IIcomplexes bearing acridine derivatives as DNA interacting agents as a complement to the well-known phenazine-based derivatives.

Full text of DOI:10.1002/ejic.201600468

DOI: 10.1002/ejic.201600468
Full Paper
DNA Photoprobes
Design and Photophysical Studies of Acridine-Based RuII
Complexes for Applications as DNA Photoprobes
[
a]
[a]
[b]
[b]
Quentin Deraedt, Lionel Marcélis, Thomas Auvray, Garry S. Hanan,
[c]
[a]
Frédérique Loiseau, and Benjamin Elias*
Abstract: A series of new extended planar aromatic ligands bright 3MLCTphen/dpac state towards a poorly luminescent
3
based on an acridine core (dpac = dipyrido[3,2-a:2′,3′-c]-
MLCTdpac state (λem = 609 nm) owing to the formation of
acridine; dpacF2 = 7,8-difluorodipyrido[3,2-a:2′,3′-c]acridine; hydrogen bonds with water molecules in the excited state.
dpacF4 = 6,7,8,9-tetrafluorodipyrido[3,2-a:2′,3′-c]acridine) and These complexes exhibit up to sevenfold luminescence en-
II
their respective Ru complexes were synthesized and exten- hancement in the presence of complementary and mismatched
sively studied. The photophysical and theoretical studies re- DNA, demonstrating a strong binding to polynucleotides. The
II
vealed that Ru-DPAC and Ru-DPACF2 allow emission from a results emphasize the interest in Ru complexes bearing
3
MLCTphen/dpac excited state at 597 and 604 nm, respectively, acridine derivatives as DNA interacting agents as a complement
whereas the lowest excited state for Ru-DPACF shifts from a to the well-known phenazine-based derivatives.
4
Introduction
metal-to-ligand charge-transfer states (MLCT states) where the
electron located on the dppz ligand is either proximal or distal
from the metallic center. In water, a quenching occurs
Transition-metal complexes are of great interest in molecular
[7]
[
1]
biology and biochemistry. In addition to being present as co-
ordination sites in proteins or cofactors in Nature, these com-
pounds offer numerous advantages for their use as photo-
probes or photoreagents, such as DNA interacting agents. In-
deed, the great modularity of the properties of the transition-
metal complexes makes them ideal in this scope. Polypyridyl
through the formation of hydrogen bonds with the phenazine
core of the dppz, whereas upon intercalation into DNA, the
luminescence of the complex is restored, as observed in organic
[8]
media. In addition, studies with mismatch containing DNA
show correlation between the luminescence increase of
2+
[9]
[
Ru(bpy) dppz] and the mismatch thermodynamic stability.
2
II
Ru complexes have been the subject of considerable interest
These environment-sensitive optical properties render dppz-
for the past few decades. Even though numerous publications
II
based Ru complexes potent candidates as photoprobes for dif-
[
2]
describe their use as catalysts, or as energy conversion and
ferent DNA topologies.
[
3]
II
storage devices, these Ru complexes also appear to be rele-
Although complexes based on dppz derivatives and other
ligands incorporating a phenazine core have received a lot of
attention, fewer studies have been reported on complexes
based on ligands incorporating an acridine core. Studies on the
tpac ligand (tpac = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]acri-
[
4]
vant in the context of biological applications such as sensing
[
5]
II
and therapeutic agents. Among them, Ru complexes bearing
the intercalating dppz ligand (dppz = dipyrido[3,2-a:2′,3′-
c]phenazine) have been studied for the last twenty-five years.
2
+
2+
Indeed, [Ru(bpy) dppz] and [Ru(phen) dppz] (bpy = bipyr-
[10]
[11]
2
2
dine)
and the corresponding complexes
showed that the
idine, phen = phenanthroline) bind readily to DNA (K
≈
aff
acridine core induces notable modifications to the behavior of
the resulting complex compared with the phenazine-based
equivalent. Analogous to dppz, the dpac ligand (dpac = dipy-
6
–1
1
0 L mol ) and display intense luminescence in the presence
of DNA, whereas the luminescence of the complex alone is
switched off in aqueous media. This “light switch” behavior
has been ascribed to the population of a mixture of excited
[
6]
II
rido[3,2-a:2′,3′-c]acridine) and its Ru complex have been only
recently reported and the latter was shown to be a potent nico-
[
12]
tinamide (NAD) derivative for electron storage systems. How-
ever, its photophysical properties were not fully investigated
and its interaction with DNA was not studied. Furthermore, as
dpac bears one less non-chelating nitrogen atom than dppz,
only one hydrogen bond with solvent molecules in the excited
state would be possible, suggesting potential differences with
[
a] Institute of Condensed Matter and Nanosciences, Molecules, Solids and
Reactivity (IMCN/MOST), Université Catholique de Louvain,
Place Louis Pasteur 1/L4.01.02, 1348 Louvain-la-Neuve, Belgium
E-mail: Benjamin.Elias@uclouvain.be
http://www.uclouvain.be/en-237299.html
[
[
b] Département de Chimie, Université de Montréal,
2
900 Edouard-Montpetit, Montréal, Québec H3T-1J4, Canada
II
dppz-based Ru complexes.
c] Département de Chimie Moléculaire, Université Grenoble-Alpes,
CNRS UMR 5250, BP53 38041 Grenoble, France
In this context, our work focuses on the synthesis of a series
of extended planar aromatic ligands based on the acridine core
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600468.
{dpac (4); dpacF = 7,8-difluorodipyrido[3,2-a:2′,3′-c]acridine (5);
2
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II
Figure 1. Synthetic scheme of dpac ligands and their corresponding Ru complexes.
1
dpacF4 = 6,7,8,9-tetrafluorodipyrido[3,2-a:2′,3′-c]acridine (6)}, signals and/or lack of fine resolution for some peaks in the H
II
1
and the study of their respective Ru complexes {Ru-DPAC for NMR spectra. The H NMR spectra show unambiguously the
2
+
2+
[
Ru(phen) dpac] (1); Ru-DPACF for [Ru(phen) dpacF ] (2); absence of symmetry elements for all the complexes, which
2 2 2 2
2+
Ru-DPACF for [Ru(phen) dpacF ] (3)} (Figure 1). In this paper, induces the non-equivalence of (i) the protons on the extended
4
2
4
1
we report an extensive theoretical and experimental study on planar ligand and (ii) the ancillary ligands. The H NMR spectra
these complexes and analyze the influence of the acridine core are sensitive to concentration as some shifts occurred upon
on the photophysical properties and DNA interactions of the changes in the concentration. For solubility purposes, all the
II
resulting Ru complexes compared with dppz-based complexes. complexes were converted into the chloride salt for experi-
We also investigate the selectivity for Ru-DPAC to probe DNA ments conducted in water or buffer or to the hexafluorophos-
mismatches.
phate salt for studies in organic solvents.
Results and Discussion
Electrochemistry
The electrochemical data for the three complexes were ob-
tained by cyclic voltammetry in dry deoxygenated MeCN or
Synthesis
The acridine core can be obtained through numerous synthetic N,N-dimethylformamide (Table 1). Complexes 1–3 display a
[
24]
[10]
pathways, such as Skraup cyclization,
self-condensation,
one-electron reversible oxidation wave at a potential close to
0
0
II
[25]
2+
3+
2+ [28]
Cu , Pd , or Zn -based organometallic couplings,
and cyclo- that of the Ru /Ru oxidation of [Ru(phen) ] . This similar-
3
[
26]
additions.
In our case, a Tröger's base modified synthetic ity between the oxidation potentials of all these complexes con-
2
+/ 3+
scheme was found to be successful and allowed us to obtain firms the metal-based nature of the process (Ru Ru redox
dpac and its fluoro derivatives with high yields (Figure 1). The couple) irrespective of the substitution on the extended planar
synthetic methodology consisted of a cyclization between 5- ligand. Three reduction waves are monitored for each complex.
amino-1,10-phenanthroline and the appropriate o-aminobenzyl From the comparison with the reduction potentials of
[
10,27]
2+
[29]
2+
alcohols.
[Ru(phen)3] (–1.30 V vs. Ag/AgCl)
and [Ru(phen) dppz]
2
II
[29]
The corresponding Ru complexes were synthesized by the (Ru-DPPZ; –0.95 V vs. Ag/AgCl), the first reduction of the five
direct chelation of the extended ligand onto a Ru precursor complexes is attributed to the addition of one electron to the
II
(
Figure 1) by using methodologies previously described for sim- extended planar ligand. The anodic shift observed for Ru-
ilar compounds. All the intermediate and final compounds were DPACF (–0.97 V vs. Ag/AgCl) indicates greater stabilization of
4
protected from direct light during the synthesis and purification the π* orbital centered on the dpacF ligand with respect to
4
steps to prevent photochemical degradation. The reactions that of Ru-DPAC and Ru-DPACF . The next two reduction waves
2
were performed under argon to avoid any oxidation of the are attributed to successive reduction of the two ancillary phen
metal center.
ligands. The potentials in the excited state (namely, E * and
ox
The complexes were fully characterized by HRMS and 1H Ered*) for the three complexes have been estimated from the
NMR spectroscopy (see the Experimental Section and the Sup- ground-state redox potentials and the energy of the excited
porting Information). Not all the multiplicity and coupling con- state corresponds to the maximum of the emission spectrum
stants can be determined owing to the superposition of several at 298 K (see below). Not surprisingly, Ru-DPACF4 (Ered* =
Eur. J. Inorg. Chem. 2016, 3649–3658
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+1.07 V vs. Ag/AgCl) is the most oxidizing complex in the ex-
cited state.
Table 1. Potentials for the oxidation (E1/2 ox) and reduction (E1/2 red) of com-
plexes 1–3.
[
a]
[a,b]
1/2 red
[a]
ox*[c]
E
red*[d]
E
1/2 ox
E
λ
max em
E
[
V vs.
[V vs.
[nm]
[V vs.
[V vs.
Ag/AgCl]
Ag/AgCl]
Ag/AgCl]
Ag/AgCl]
[
Ru(phen)
3
]2+
1.32
–1.30
604
–0.73
0.70
–
–
1.47
1.68
Ru-DPPZ[30]
Ru-DPAC
1.35
1.35
–0.95
1.39
–1.22
618
597
–0.67
–0.73
1.02
0.86
–
–
–
1.35
1.66
Ru-DPACF
2
4
1.35
1.35
–1.15
604
609
–0.71
–0.69
0.91
1.07
–
–
1.34
1.62
Ru-DPACF
–0.97
–
–
1.30
1.52
[
a] Measured in dry acetonitrile. [b] The reversibility of the reduction proc-
esses being not able to be determined due to adsorption of the reduced
species on the electrode suface, E1/2 has been estimated from the reduction
peak. [c] The excited-state oxidation potential was estimated from the
ground-state oxidation potential and the energy of the emission maximum
with the equation Eox* = E1/2 ox – E0–0 ≈ E1/2 ox – ΔEλmax, em. [d] The excited-
state reduction potential was estimated from the ground-state reduction po-
tential and the energy of the emission maximum with the equation Ered* =
Figure 2. (a) Absorption and (b) emission spectra (λexc = 448 nm) of 1 (gray),
E1/2 red + E0–0 ≈ E1/2 red + ΔEλmax, em.
2
(orange), and 3 (blue) in acetonitrile under air at room temperature. Inset
of a: Absorption bands corresponding to MLCT transitions.
In the case of Ru-DPPZ, the absorption of a photon leads to
the formation of a charge-separated state, Ru /dppz , in which
Absorption Spectra and Computational Studies
3
+
·–
The absorption data at ambient temperature in water and an electron is transferred from the metal center towards either
acetonitrile, under air and under argon for the three complexes, the phen or phenazine part of the dppz ligand depending on
[
32]
as well as for other complexes for comparison purposes, are the environment of the complex. This accounts for the pecu-
listed in Table 2. Absorption spectra for all complexes in aceto- liar photophysical behavior of Ru-DPPZ. In our case, exchanging
II
nitrile are depicted in Figure 2, a. The absorption of Ru com- the phenazine core with an acridine, that is, replacing a nitro-
plexes generally corresponds to the superposition of different gen atom with a carbon atom, should influence the electronic
transitions involving either the ligands or both the metal and transitions involved in the formation of the excited state. Strik-
[
31]
the ligand.
and absorption spectra of the free ligands allowed us to assign band is observed for 1–3 compared with Ru-DPPZ.
In the present case, comparison with literature ingly, a sole small bathochromic shift (Δλ = 8 nm) of the MLCT
the intense absorption (ε ≥ 105
M
–1
cm ) bands in the UV re-
–1
To get more information on the photophysical scheme of
gion to ligand-centered (LC) transitions and the ones in the our complexes, 1–3 as well as Ru-DPPZ were studied computa-
visible region (ε ≈ 104
M
–1
cm around λ ≈ 400 nm) to metal- tionally. The ground- and vertical excited-state electronic struc-
–1
to-ligand charge-transfer (MLCT) transitions, where L = phen tures were investigated by means of DFT/time-dependent (TD)-
1
1
(
MLCTphen) and dpac ( MLCTdpac).
DFT calculations by using the hybrid PBE0 functional and the
3 2
Table 2. Absorption data for complexes 1–3 in CH CN and H O at 298 K in aerated or deaerated solution.
Absorbance λmax [nm] (ε [104
M
–1
cm–1])[a]
MeCN
2
H O
[
Ru(phen)
3
]2+
418, 447 (1.84)
221, 264, 370, 440 (2.34)
419, 447 (1.83)
220, 264, 368, 440
[
30]
Ru-DPPZ
Ru-DPAC (1)
224 (15.1), 264 (16.3), 280 (11.6), 448 (2.62)
223 (16.2), 264 (19.0), 278 (14.4), 448 (2.88)
221 (17.1), 264 (18.9), 279 (14.0), 448 (2.87)
224 (15.1), 264 (16.2), 280 (11.6), 448 (2.62)
223 (16.1), 264 (19.0), 278 (14.3), 448 (2.88)
221 (17.0), 264 (18.9), 279 (14.1), 448 (2.88)
Ru-DPACF
Ru-DPACF
2
(2)
(3)
4
[
a] Measurements made with solutions with 1 × 10–5 mol L–1 of the complex at room temperature.
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LanL2DZ basis set. The solvent (MeCN or H O) is included by a of fluoride atoms increases, the dpac contribution increases in
2
[
33]
conductor-like polarizable continuum model.
With this sys- the LUMO whereas the dpac contribution increases in the
tem, the first runs of calculations performed with water did LUMO + 1.
not account for the experimental differences when going from
The experimental absorption spectra matched well with the
acetonitrile to water. A similar observation was made by Daniel calculated transitions, allowing us to attribute the different tran-
[
34]
et al. who overcame the limitation of the continuum model, sitions by using natural transitions orbitals (NTOs)
which does not describe specific interactions, such as nitrogen– ures S19–S21). When comparing the absorption spectra of the
(see Fig-
[
23]
hydrogen bond interactions, by using a discrete model.
Wa- different complexes in acetonitrile, one can observe that there
ter molecules are thus added without any constraint on their are no major differences in the position and intensities of the
1
position before geometry optimization and calculations.
absorption maxima. Indeed, in all cases the MLCT
are the
phen
The energy diagram for the different compounds is pre- main transitions in the visible part of the spectra (400–550 nm);
1
1
sented in Figure 3 (further details on the electronic structures transitions involving the MLCTdpac and MLCT
of lower
dpac/dppz
can be found in Tables S2–S7 in the Supporting Information). intensities are redshifted as the number of fluoride atoms in-
For the sake of clarity, throughout the manuscript the electron- creases, but this does not affect the final absorption spectra. A
accepting portion of the extended ligands is underlined to dif- similar explanation can be used to account for the similarity
ferentiate the two moieties that are suggested to participate in between the absorption spectra in acetonitrile and water. As
the relaxation processes. The contributions of each moiety of the polarity of the solvent increases, the levels centered on the
the complexes are depicted in different colors; in particular, the metal and ancillary phen are equally destabilized, leaving the
1
phenanthroline part of the extended ligand (dpac, green) and
MLCTphen unchanged whereas the dpac/dppz orbitals are sta-
1
the terminal fragment (dpac/dppz, orange) are differentiated in bilized, leading to a redshift of the MLCTdpac/dppz and
1
order to discuss their respective contributions. Regardless of
MLCTdpac/dppz transitions. These shifts are, however, small, as
the solvent, the introduction of electron-withdrawing fluoride seen in Table 2.
modifies the electronic repartition in the ground state. Al-
though it has only a little effect on the Ru (red) and ancillary
Emission Spectra, Lifetimes, Quantum Yields, and
Computational Studies
phen (blue) centered orbitals, it strongly stabilizes the levels
centered on the dpac/dppz ligands. In addition, as the number
All our complexes display broad unstructured emission (Fig-
3
ure 2, b), typical of a MLCT-type excited state, both in organic
solvent and water. The luminescence lifetimes and the quantum
yields of luminescence for each complex were measured in wa-
ter and acetonitrile under an inert atmosphere (Table 3). The
4
–1
large k values (> 10 s , Table 3), the positive solvatochromic
r
effect (Δλ ≈ +20 nm when going from CH Cl to water, data
2
2
not shown) and the hypsochromic shift of the emission band
at 77 K (see Figure S3) confirm the charge-transfer character of
the excited state. It is worth mentioning that, in air-equilibrated
solvents, a decrease in the luminescence intensity with respect
to degassed solutions is systematically observed, indicating a
quenching by oxygen (see Table S1). We expect that, as for
II
3
other Ru complexes, an efficient photosensitization of O by
2
II
[35]
the excited Ru complexes is occurring.
Other quenching
mechanisms such as electron transfer to form superoxide
anions may also occur, but are beyond the scope of this study.
The emission maxima are almost identical for Ru-DPAC and
Figure 3. Energy diagram of the complexes 1–3 and Ru-DPPZ. Fragment con-
tributions are reported with different colors: Ru in red, ancillary phen in blue,
dpac/dppz in green, dpac/dppz in orange. Solvent used: left = MeCN, right =
H
2
O.
Ru-DPACF ; the addition of the two fluorine atoms onto the
2
Table 3. Emission data for complexes 1–3.
Emission λem max Emission λmax
[a,c,d]
em [ns][d]
3
–1 [d]
5
–1 [d]
Φ
em
τ
k
r
[10 s
]
k
r
[10 s
]
[
a,b]
[
nm]
at 77 K [nm]
MeCN
H
2
O
EtOH/MeOH, 4:1
MeCN
H
2
O
MeCN
H
2
O
MeCN
H
2
O
MeCN
H
2
O
[
Ru(phen)
3
]2+ 604
606
–*
604
607
611
564[36]
580
567
573
568
0.028
0.033
0.038
0.052
0.084
0.072
–*
0.066
0.189
0.050
460
663
710
875
915
920
–*
999
958
238
60.9
49.8
53.5
59.4
91.8
75.0
–*
66.1
197.3
210.1
21
15
14
11
10
9.7
–*
9.4
8.5
40
[
30]
[7d]
Ru-DPPZ
Ru-DPAC
Ru-DPACF
Ru-DPACF
618
597
604
609
2
4
–1
[
a] Measurements made with solutions with 1 × 10–5 mol L of the complex. [b] Measurements made under ambient air conditions. [c] The quantum yield of
2+
air
[28]
luminescence is calculated relative to that of [Ru(bpy)
3
]
in an aerated aqueous solution (Φem = 0.028). [d] Quantum yield of luminescence, luminescence
O.
lifetimes and radiative rate constants are determined under an argon atmosphere. Errors estimated to 10 %. * No luminescence was observed in H
2
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dpac ligand has thus only a small influence on the energy dif- the ancillary phen or the phen part of the planar ligand (dpac
3
3
ference between the MLCT and the ground state, whereas this or dppz). The similar energies of these emissive MLCT states
energy decreases for Ru-DPACF . This observation is in agree- explain the similarity of the luminescence maxima observed for
4
ment with the decrease in energy of the π* orbital centered on all complexes.
the extended planar ligand going to a more electron-withdraw-
In water, complexes 1–2 present a stronger emission and are
ing core. Interestingly, none of these complexes behave like Ru- longer lived (see Table 3). Calculations show that the relative
3
DPPZ, which is known to have light-switching behavior.
energy of each MLCT state is not significantly modified and
Numerous experimental and theoretical studies have been the fragment contributions to each triplet state remain similar
[
4b,7a,36]
devoted to understanding the light-switch effect.
It is to those in MeCN; hence, these compounds behave like
2
+
now commonly accepted that this quenching is caused by [Ru(phen)3] and exhibit an increased luminescence in water
hydrogen-bonding with water molecules, leading to the stabili- compared with organic solvent. Complexes 1–2 also follow the
3
3
zation of dark states, such as MLCT
and LC
, the latter same photophysical scheme in water as in MeCN (Figure 4, a).
dppz
dppz
[
37,38]
being the lowest triplet state (summarized in Figure 4, c).
In contrast to Ru-DPPZ, where the lowest excited states involve
Our calculations led to similar results with a change in the na- the phenazine core of the dppz, the acridine core in complexes
3
ture of the lowest metal-to-ligand charge-transfer state from a 1–2 seems not to be involved and MLCT remains localized on
3
bright MLCT
state in acetonitrile to a more stabilized dark the ancillary ligands or the phen moiety of the dpac ligands.
phen
3
MLCTdppz state in water.
We thus propose for these complexes that their lowest excited
3
3
In the case of our complexes, Ru-DPAC and Ru-DPACF do states are luminescent MLCTphen/dpac states. The MLCTdpac ex-
2
not present light-switching behavior whereas Ru-DPACF par- cited states are assumed to be higher in energy than the
4
3
tially does as its luminescence is notably reduced in water, as
indicated by its smaller quantum yield and larger knr value in
MLCTphen/dpac ones for these two complexes (in contrast to
MLCTdppz for Ru-DPPZ), suggesting the acridine core disfavors
3
water. Once again, computational studies were used to gain the charge-separation process in the excited state for 1–2. A
some information to explain this behavior and compare it with similar behavior has been previously observed for TPAC-based
II
Ru-DPPZ. The qualitative results obtained for the triplet TD-DFT mono- and dinuclear Ru complexes, for which the electro-
calculations were used to draw the photophysical schemes pre- chemical and spectroscopic data indicate that the lowest MLCT
3
sented in Figure 4 for each situation (for numeric values, see transition is a MLCTtpac one and that dinucleation affects very
3
Table S8). The computational studies show that LC states cen- slightly these properties. This suggests that the two metallic
3
II
tered on dpac/dppz ligands have a lower energy than MLCT centers of the dinuclear TPAC-based Ru complexes behave in-
3
states for all complexes. The presence of such LC states was dependently in spite of the conjugated TPAC bridging li-
[
11,41]
also reported in computational studies realized previ- gand.
[
23,35,39]
ously.
Nevertheless, the experimental characteristics of
In opposition to the former examples, Ru-DPACF displays a
4
emission clearly indicate that the luminescence of all Ru com- much shorter luminescence lifetime and lower quantum yield
plexes originates from the MLCT states and that low-lying LC in water than in acetonitrile (Table 3). For this complex, we
states are not likely to play a role in the deactivation of the assume that upon absorption of light, a MLCTphen state is
MLCT states generated upon light irradiation (see Table 3, formed, which rapidly undergoes an ISC to a luminescent
MLCTphen/dpac state. Further relaxation occurs on the acridine
MeCN compared with [Ru(phen) ] ). Therefore, we focus our moiety of the extended planar ligand, leading to the formation
II
3
3
1
1
3
larger quantum yield of luminescence for complexes 1–3 in
2+
3
3
3
discussion on the MLCT manifold, which accounts for the pho- of the MLCT
excited state. In water, there is an interconver-
dpac
tophysical behavior of our complexes.
sion between two excited states: one assigned to the non-
In acetonitrile, all compounds follow similar trends as in Fig- hydrogen-bonded excited state dpac, and the other one to a
[
40]
1
ure 4 (a). After an ultrafast ISC
from MLCT states generated mono-hydrogen-bonded excited state (depicted as dpac-H, in
3
upon absorption of photons, MLCT states are populated corre- Figure 4, b). The presence of the dpac-H excited state is sug-
sponding to charge transfer from the Ru center towards either gested by the shorter excited state lifetime of this complex in
II
3
Figure 4. Representation of the photophysical scheme for dpac-based complexes in water. The deactivation of the MLCT states is emphasized on the right
2 4
part of the figure for (a) Ru-DPAC and Ru-DPACF , (b) Ru-DPACF , and (c) Ru-DPPZ in water. The photophysical scheme for all complexes (1–3 and Ru-DPPZ)
in MeCN can be described as in (a). Solid arrows stand for radiative, wavy arrows stand for non-radiative transitions (intersystem crossing, internal conversion,
or vibrational relaxation).
Eur. J. Inorg. Chem. 2016, 3649–3658
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water. In a similar way as described for Ru-DPPZ,[7b] we propose we assume our complexes also intercalate into the DNA strands,
that the excited state localized on dpac, which is higher in en- which is consistent with the binding values obtained.
ergy in aprotic solvents, is stabilized when involved in a
hydrogen bond and thus becomes dominant in water. Indeed,
protic solvents would stabilize the charge-separated excited
state owing to the formation of a hydrogen bond with the free
nitrogen atom of the dpacF ligand. The partial quenching of
4
the luminescence of 3 is in agreement with the model pro-
posed by Lincoln and co-workers for which two hydrogen
bonds are required for the full luminescence quenching of the
excited state of Ru-DPPZ in water. The photophysical behavior
of Ru-DPACF thus contrasts with the photophysical properties
4
of Ru-DPAC and Ru-DPACF , which are similar to those of
2
2
+
[
Ru(phen) ] .
3
Figure 5. Steady-state luminescence titration (λexc = 448 nm) of 1 (green), 2
purple), and 3 (orange) with SS-DNA (full circles) and CT-DNA (empty dia-
monds). Measurements were performed by using 10 μ of complex in 50 m
Tris·HCl buffer, with 50 m NaCl at pH 7.4 under ambient air conditions. The
(
Photophysical Behavior in the Presence of DNA and
Polynucleotides
M
M
M
II
fitted curved were obtained by using a modified McGhee–von Hippel equa-
tion and drawn as solid and dashed curves for SS- and CT-DNA, respectively.
As mentioned in the Introduction, Ru complexes are relevant
tools to probe DNA. The influence of hydrogen bonds with wa-
ter on the photophysics of the complex is one of the key pa-
rameters in this context, but not the only one at stake. With the
notable exception of some photoreactive complexes, polypyr-
idyl Ru complexes are more luminescent in the presence of
Table 4. Binding affinity constants calculated for complexes 1–3 with SS-DNA
and CT-DNA.
[
5]
II
SS-DNA
K
CT-DNA
aff [L mol–
6
1 [a]
]
I/I
max
K
aff [L mol
–1 [a]
]
0
0
I/I max
DNA. This enhancement of luminescence is due to the associa-
tion of the complex with DNA, which protects the excited com-
plex from quenching or non-radiative deactivations. If com-
plexes possess one extended planar ligand, a specific interac-
tion is observed with DNA, where the complex is intercalated
inside the bases stack. This intercalation mode generally leads
5
Ru-DPAC
Ru-DPACF
Ru-DPACF
1.8×10
4.8×10
3.5×10
2.6
3.0
2.9
4.2×10
3.7×10
1.5×10
2.8
3.2
3.1
5
5
5
5
2
4
[
a] Binding constant were obtained by using a McGhee–von Hippel-type
equation; the binding site was fixed to two base pairs per complex (best fit).
Errors estimated to 5 %.
6
–1
to strong association (Kaff ≈ 10 L mol ) and an intense lumi-
nescence enhancement of the excited intercalated complex in
Even if these two natural DNAs contain nearly the same con-
comparison to the “free” complex left in aqueous me- tent of G–C base pairs (43 % for SS-DNA vs. 42 % for CT-
[
7c,8,29,42]
[44]
dia.
Interestingly, Ru-DPPZ is able to distinguish DNA),
the luminescence behavior is slightly different for the
matched and single-base mismatched sites in oligonucleotides. complexes 1–3 in the presence of each DNA. Such an observa-
This small sensitivity of the luminescence enhancement in the tion could arise from the different topologies of these two
presence of a mismatch can be correlated to its thermodynamic DNAs: CT-DNA features a long and well-defined scaffold
[
9]
[45]
stability. We thus investigated the ability of our new com- (> 10 000 base pairs),
whereas SS-DNA is made of shorter
and poorly defined sequences. The in-
teraction between the complexes and the DNA sequences de-
In the presence of increasing concentrations of DNA (CT-DNA pends on the local environment encountered by the interca-
[
46]
plexes to probe DNA and some particular topologies, such as (ca. 2000 base pairs)
different single-base mismatches.
[
47]
and SS-DNA), the luminescence of the dpac complexes 1–3 is lated complex;
the heterogeneity of these environments re-
enhanced (Figure 5). This increase in luminescence for the three sults in small but noticeable differences in the optical proper-
complexes is strong and occurs even at a very low ratio of DNA ties of the complexes. The binding curves obtained are thus
per complex, suggesting a high binding affinity of the com- affected by this heterogeneity, but overall the binding con-
plexes for these two DNA types. To determine the binding affin- stants calculated are in good agreement with an intercalation
ity for these equilibria, we used a modified McGhee–von Hippel mode of interaction between each of our complexes and DNA.
[
43]
equation
as an expression for the luminescence intensity as
In the case of SS-DNA, the emission intensity increases
II
a function of the ratio of Ru per DNA (I/I vs. [DNA]/[complex], quickly to reach a plateau value, between 2.6 and 2.9 for the
0
with I the intensity of luminescence in the absence of DNA three complexes, the fluorinated analogs 2 and 3 display
0
and [DNA] expressed in base-pair equivalents, see Table 4 and slightly higher I/I
values than the non-fluorinated complex 1.
0
Figure 5). The luminescence enhancement observed presuma- We also investigated the ability of Ru-DPAC to detect base
bly results from a decrease in the non-radiative deactivation mismatches in short oligonucleotides by using a series of hair-
3
processes of the MLCT excited states. This protection is in- pins oligonucleotide containing a mismatch near the center of
duced by the double helix microenvironment, which protects the duplex (see sequences in Figure 6). As shown in Figure 7,
the excited complexes from quenching by oxygen. As our ex- an attenuation of the luminescence is observed for the mis-
tended planar ligands are similar to dppz in terms of structure, matched hairpins with respect to the complementary one. No
Eur. J. Inorg. Chem. 2016, 3649–3658
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3654
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differential luminescence intensity occurs related to the nature exhibit increased luminescence in this solvent. However, the
3
of the mismatch. The absence of specificity for the nature of the lowest MLCT state for Ru-DPACF4 changes from a bright
3
3
mismatch sites, and, more surprisingly, the lower luminescence
MLCTphen/dpac state to a poorly luminescent MLCT
state.
dpac
3
enhancement of the complex in the presence of mismatched The stabilization of this state compared with the other MLCT
hairpins compared with the complementary one led us to the states occurs in water through the establishment of a hydrogen
conclusion that Ru-DPAC is less effectively intercalated between bond; the relative population of the excited state is then shifted
3
the mismatched base pair stack. This less effective intercalation to this state and the emissive MLCTphen/dpac states are less pop-
results in increased exposure to oxygen with respect to the ulated, yielding a reduction of the luminescence of Ru-DPACF4
complementary sites; a looser fit of the complex within the mis- in water compared with organic solvents.
match site favors non-radiative relaxation pathways of the ex-
Studies of these acridine-based complexes in the presence
cited state, leading to a decreased luminescence and/or a lower of DNA demonstrate that they strongly bind to polynucleotides
binding affinity for these sites compared with complementary and that this association, attributed to an intercalation within
sites. As saturation of the interaction between the complex and the base pair stacking, is accompanied by an enhancement in
the hairpins cannot be obtained, it is difficult to differentiate their luminescence. This enhancement is presumably due to a
the processes at stake in this case. The behavior observed for decrease in the non-radiative deactivation processes of the
[
9]
3
Ru-DPAC differs from the one reported for Ru-DPPZ under the
MLCT excited state of complexes intercalated in the double
same conditions. This fundamental difference underlines the helix, where the microenvironment protects them from quench-
complexity of designing complexes able to probe mismatched ing by oxygen. In the case of Ru-DPACF , an inhibition of
4
sites in DNA.
hydrogen bonds between the tetrafluoroacridine and water is
likely to be responsible for the luminescence enhancement
upon intercalation through DNA; this process is the same as the
one responsible for the light-switching behavior of the well-
known Ru-DPPZ complex. Ru-DPAC shows differential lumines-
cence intensity for matched and mismatched hairpins, but no
discrimination for the nature of the mismatch site. We suggest
that a looser fit to the mismatched containing hairpins lies at
the basis of the observed luminescence behavior of this com-
plex, resulting in an increased exposure to oxygen with respect
to the complementary sites. The design of extended planar li-
gands allowing better differential interactions between their
II
corresponding Ru complexes and polynucleotides is currently
under investigation in our group.
Figure 6. Hairpin oligonucleotide sequences used for titrations.
Experimental Section
[
13]
Materials and Instrumentation: [Ru(phen) Cl ] was synthesized
2
2
according to a previously described literature protocol. All solvents
and reagents for the synthesis were of reagent grade and were used
without any further purification. All solvents for the spectroscopic
and electrochemical measurements were of spectroscopic grade.
Water was purified with a Millipore Milli-Q system. Calf thymus DNA
type I (CT-DNA) and salmon sperm DNA (SS-DNA) were purchased
from Sigma–Aldrich. Hairpin oligonucleotides (ODNs) were pur-
chased from Eurogentec. DNA and ODN concentrations were deter-
–
1
–1
mined spectroscopically (λ
= 6600
260 000
M
cm /bp for CT-DNA
Figure 7. Oligonucleotides possessing (or not) a mismatched base pair. Meas-
260 nm
[
14]
–1
–1
and SS-DNA;
λ260
nm
=
M
cm
for ODN-AT,
urements were performed by using 1 μ
M
of complex in 5 m
M
Tris·HCl buffer,
–
1
–1
–1
cm–1 for ODN-CC,
with 1 m NaCl, at pH 7.5 under ambient air conditions.
M
264 900
M
cm for ODN-AA, 253 300 M
–
1
–1
–1
cm–1 for ODN-CT, and
259 100
57 500
M
cm for ODN-AC, 254 200 M
–
1
–1
2
M
cm for ODN-TT). The molar extinction coefficients of
the hairpin oligonucleotides were calculated based on the base
content of each sequence. H NMR experiments were performed in
Conclusions
1
II
CDCl , CD OD, or CD CN with a Bruker AC-300 Avance II (300 MHz)
3 3 3
We successfully synthesized and characterized new Ru com-
plexes with extended planar ligands based on an acridine core.
Their spectroscopic and electrochemical data revealed that 1–
or a Bruker AM-500 (500 MHz) at 20 °C. The chemical shifts (given
in ppm) are measured versus the residual peak of the solvent as
the internal standard. High-resolution mass spectrometry (HRMS)
spectra were recorded with a Q-Extractive orbitrap from Thermo-
Fisher by using reserpine as the internal standard. Samples were
3
2
allow emission from an MLCT
excited state, which
phen/dpac
explain the similarity of the luminescence maxima. As only mi-
nor reorganizations of the different triplet excited states of 1–2 ionized by electrospray ionization (ESI; capillary temperature =
occur in water, these compounds behave like [Ru(phen)3] and 320 °C, vaporizer temperature = 320 °C, sheath gas flow rate = 5 mL
2
+
Eur. J. Inorg. Chem. 2016, 3649–3658
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Full Paper
–
1
min ). UV/Vis absorption spectra were recorded with a Shimadzu EtOAc (25 mL) was added, followed by a solution of NaOH 2
M until
UV-1700. Room temperature fluorescence spectra were recorded effervescence stops, and MilliQ water (40 mL). The organic phase
with a Varian Cary Eclipse instrument. Luminescence intensity at was separated and the aqueous phase was extracted with Et O (3 ×
2
7
7 K was recorded with a FluoroLog3 FL3–22 from Jobin Yvon 30 mL). The combined organic phases were dried with MgSO4,
equipped with an 18 V 450 W Xenon Short Arc lamp and an R928P
photomultiplier, using an Oxford Instrument Optistat DN nitrogen
evaporated, and dried under vacuum. The desired compound was
1
obtained as a beige solid, yield 93 %. H NMR (300 MHz, CDCl ): δ =
3
cryostat controlled by an Oxford Intelligent Temperature Controller 7.15 (ddd, Jc-d = 8.0, Jc-b = 8.0, Jc-a = 1.6 Hz, 1 H, H ), 7.07 (dd,
c
(ITC503S) instrument. For the luminescence lifetime measurements
Ja-b = 7.6, Ja-c = 1.6 Hz, 1 H, H ), 6.70–6.75 (m, 2 H, H and H ), 4.70
a
b
d
as a function of temperature, the pulsed excitation source was a
pulsed laser Nd:YAG Q-switched laser (Continuum Inc.) frequency-
tripled (355 nm) coupled with an optical parametric oscillator (Con-
tinuum Inc.) covering the wavelength region 410–2300 nm with
a maximum pulse energy from 10 to 120 mJ depending on the
wavelength. The emission was detected perpendicularly by a pho-
tomultiplier (R928, Hamamatsu). The signal was recorded with a
digital oscilloscope (HP 54200A), connected through the IEEE488
interface to a personal computer, and was averaged over at least
(s, 2 H, CH ), 3.19 (br., 2 H, NH ) ppm.
2
2
dpac (4): 5-Amino-1,10-phenanthroline (183.0 mg, 0.938 mmol) and
2-aminobenzyl alcohol (115.6 mg, 0.938 mmol) were suspended in
6
N
HCl (3.0 mL). The reaction mixture was stirred at reflux (65 °C)
for 20 h and, after cooling to room temperature, the reaction was
quenched by addition of NH ·H O until reaching pH 9. The orange
3
2
precipitate was filtered and purified by using a neutral alumina col-
umn for chromatography (eluent: acetone/methanol gradient, from
1
00:0 to 90:10), yielding the targeted compound as a dark-orange
16 shots. The emission wavelength was selected by a grating
1
solid, yield 93 %. H NMR (500 MHz, CD OD): δ = 9.77 (dd, J
=
=
3
c-b
Czerny–Turner monochromator (Spectra Pro 2300i, Acton Research
Corp.). Cyclic voltammetry was carried out in a one-compartment
cell, using a glassy carbon disk working electrode (approximate
8
1
.3, Jc-a = 1.8 Hz, 1 H, H ), 9.68 (s, 1 H, H ), 9.30 (dd, J = 8.3, Ji-k
c d i-j
.5 Hz, 1 H, H ), 9.14 (dd, J = 4.5, Ja-c = 1.8 Hz, 1 H, H ), 9.08 (dd,
i
a-b
a
Jk-j = 4.5, Jk-i = 1.6 Hz, 1 H, H ), 8.34 (d, J = 8.7 Hz, 1 H, H ), 8.26
k
e-f
e
2
area = 0.03 cm ), a platinum wire counter electrode, and an Ag/AgCl
(
d,Jh-g =7.6Hz,1H,H ),7.95(dd,Jf-e=8.5,Jf-g=6.9Hz,1H,H ),7.89(2dd,
h
f
–
1
reference electrode (salt bridge: 3 mol L NaCl/saturated AgCl). The
potential of the working electrode was controlled by an Autolab
PGSTAT 100 potentiostat through a PC interface. The cyclic voltam-
Jb-c = Jj-I = 8.0, Jb-a = Jj-k = 4.5 Hz, 2 H, H and H ), 7.76 (t, J =
b
j
g-h
7
.2 Hz, 1 H, H ) ppm. MS (APCI, +c): calcd. 282.10 for C H N ,
g 19 12 3
+
found 282.27 [M + H ].
2-Amino-4,5-difluorophenyl)methanol: A solution of LiAlH4 in
dry Et O (78.5 mg in 2.0 mL) was added dropwise to a solution of
–
1
mograms were recorded with a sweep rate of 300 mV s , in dried
(
acetonitrile or N,N-dimethylformamide (Sigma–Aldrich, HPLC
–
4
–1
grade). The concentration of the complexes was 8 × 10 mol L ,
with 0.1 mol L–1 tetrabutylammonium perchlorate as supporting
electrolyte. Before each measurement, the samples were purged
with nitrogen. The molar absorption coefficients were determined
2
4,5-difluoroanthranilic acid (200.0 mg, 1.155 mmol) in dry Et O
2
(
1
8.0 mL). The mixture was then stirred at reflux (35 °C) for 1 h
5 min. After cooling to room temperature, EtOAc (10 mL) was
added, followed by a solution of NaOH (2 ) until effervescence
stopped, and MilliQ water (15 mL). The organic phase was separated
and the aqueous phase was extracted with Et O (3 × 10 mL). The
1
M
by H NMR spectroscopy by using 2,2′-[(perfluoroethane-1,2-
diyl)bis(oxy)]bis(2,2-difluoroethan-1-ol) as a reference. DFT calcula-
[
15]
tions were performed by using Gaussian 09.
The hybrid func-
2
[16]
[17]
combined organic phases were dried with MgSO , evaporated, and
tional PBE0 was used to carry out the DFT and TD-DFT calcula-
4
tions in combination with the LanL2DZ[
18]
dried under vacuum. The desired compound was obtained as a
basis set for all atoms.
flaky yellowish-brownish solid, yield 91 %. 1H NMR (300 MHz,
Geometry optimizations were conducted without symmetry con-
straints. Frequency calculations on each optimized structure con-
firmed that the energy minima was reached. The energy, oscillator
strength, and related MO contributions for the 100 lowest singlet–
CDCl ):δ=6.92(dd,J =10.5,Ja-c =8.6Hz,1H,H ),6.50(dd,J =11.8,
3
a-b
a
d-c
Jd-b = 6.8 Hz, 1 H, H ), 4.61 (s, 2 H, CH ), 4.12 (br., 2 H, NH ) ppm.
d
2
2
dpacF2 (5): 5-Amino-1,10-phenanthroline (50.0 mg, 0.256 mmol)
and (2-amino-4,5-difluorophenyl)methanol (40.8 mg, 0.256 mmol)
singlet and ten lowest singlet–triplet excitations for the S -opti-
0
mized geometry were obtained, respectively, from the TD-DFT/sin-
glets and the TD-DFT/triplets output files. One should note that the
PBE0 functional, although providing the correct excitation energies,
is not able to fully reproduce their relative intensities. This behavior
has already been noticed in the literature in the case of even sim-
pler compounds and different functionals and more elaborated ap-
proaches have been used in cases where the band shape is of inter-
were suspended in 6
stirred at reflux (65 °C) for 20 h and, after cooling to room tempera-
ture, the reaction was quenched by addition of NH ·H O until
reaching pH 9. The orange-red precipitate was filtered and purified
by using a neutral alumina column for chromatography (eluent:
acetone/methanol gradient, from 100:0 to 90:10), yielding the tar-
N HCl (1.0 mL). The reaction mixture was
3
2
1
geted compound as an orange solid, yield 98 %. H NMR (300 MHz,
[19]
est, which was actually not the case in the present study. Gauss-
CDCl ): δ = 9.70 (dd, J = 8.2, Jc-a = 1.9 Hz, 1 H, H ), 9.27 (dd, J = 4.5,
3
c-b
c
a-b
View 3.0.9,[ GaussSum 3.0,
20]
[21]
and Chemissian 4.38
[22]
software
Ja-c = 1.8 Hz, 1 H, H ), 9.25 (s, 1 H, H ), 9.23 (dd, J = 4.4, Jk-i
=
a
d
k-j
were used for data analysis, visualization, and surface plots. Calcula-
1
.5 Hz, 1 H, H ), 8.96 (dd, J = 8.3, Ji-k = 1.6 Hz, 1 H, H ), 8.10 (dd,
k i-j i
tions were performed in MeCN or H O solution by use of the con-
2
Je-f = 10.9, Je-g = 7.6 Hz, 1 H, H ), 7.78 (m, 3 H, H , H , and H ) ppm.
MS (APCI, +c): calcd. 318.08 for C H F N , found 318.55 [M + H ].
e b j h
ductor-like polarized continuum (CPCM) solvation model as imple-
mented in Gaussian 09.[ Because the continuum model could
not describe specific interactions such as nitrogen–hydrogen-bond
interactions, a discrete model is also used in an approach similar to
+
19 10 2 3
15]
(2-Amino-3,4,5,6-tetrafluorophenyl)methanol: A solution of Li-
AlH4 in dry Et O (76.5 mg in 2.0 mL) was added dropwise to a
2
[23]
solution of 2-amino-3,4,5,6-tetrafluorobenzoic acid (200.0 mg,
that reported by Daniel et al. recently.
0.9565 mmol) in dry Et O (8.0 mL). The mixture was then stirred at
2
Synthetic Procedures and Characterization of dpac Ligands and
reflux (35 °C) for 2 h 10 min. After cooling to room temperature,
EtOAc (10 mL) was added, followed by a solution of NaOH (2
II
Respective Ru Complexes
M)
2
-Aminobenzyl Alcohol: A solution of LiAlH in dry Et O (300.0 mg
until effervescence stopped, and MilliQ water (15 mL). The organic
phase was separated and the aqueous phase was extracted with
4
2
in 7.5 mL) was added dropwise to a solution of anthranilic acid
(
617.3 mg, 4.50 mmol) in dry Et O (30 mL). The mixture was then
Et O (3 × 10 mL). The combined organic phases were dried with
2
2
stirred at reflux (35 °C) for 1 h. After cooling to room temperature,
MgSO , evaporated, and dried under vacuum. The desired com-
4
Eur. J. Inorg. Chem. 2016, 3649–3658
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3656
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
1
+
– +
pound was obtained as a beige solid, yield 93 %. H NMR (300 MHz,
924.08193 for [C H N F PRu] , found 924.08240 ([M – PF ] )
43 25 7 8 6
2+
CDCl ): δ = 4.78 (d, J
= 1.95 Hz, 2 H, CH ), 3.63 (br., 2 H, NH ) and calcd. 389.55860 for [C H N F Ru] , found 389.55897
3
CH2-F
2 2 43 25 7 2
–
2+
ppm.
([M – 2 PF ] ).
6
dpacF (6): 5-Amino-1,10-phenanthroline (167.1 mg, 0.8568 mmol)
and (2-amino-3,4,5,6-tetrafluorophenyl)methanol (167.1 mg,
Ru-DPACF
4
(3): One equivalent of dichloro precursor Ru(phen)
2
Cl
(6)
2
4
(11.6 mg, 0.0218 mmol) was mixed with 1.3 equiv. of dpacF
4
0
.8568 mmol) were suspended in 6
N
HCl (2.0 mL). The reaction
(10.0 mg, 0.0283 mmol) in a mixture of absolute ethanol/water
(50:50, 2.0 mL). The reaction mixture was stirred under an argon
atmosphere at reflux (80 °C) and the reaction was followed by ab-
sorption spectroscopy. After 2 h 30 min, the medium was concen-
mixture was stirred at reflux (65 °C) for 20 h and, after cooling to
room temperature, the reaction was quenched by addition of
NH ·H O until reaching pH 9. The orange-red precipitate was fil-
3
2
tered and purified by using a neutral alumina column for chroma-
tography (eluent: acetone/methanol gradient, from 100:0 to 90:10). yielded a red precipitate. After centrifugation, the solid was washed
trated and addition of small portions of NH PF and drops of water
4 6
After evaporation of the solvents, the residue was washed with
chloroform. The precipitate was filtered and the filtrate was evapo-
with excess water. After drying under vacuum, the orange-red resi-
due was purified by HPLC (XBridge C18 10 × 100 mm, 5 μ , gradi-
ent from H O/CH CN, 90:10 + 0.1 % TFA to CH CN + 0.1 % TFA,
elution time: 3.07 min). The counter-anion exchange from PF to Cl
was performed by eluting a solution of the complex in a mixture
M
rated, yielding the targeted compound as an orange-yellow solid,
2
3
3
1
yield 94 %. H NMR (300 MHz, CDCl ): δ = 9.77 (dd, J = 8.1, Jc-a
=
6
3
c-b
1
.7 Hz, 1 H, H ), 9.55 (s, 1 H, H ), 9.31 (dd, J = 4.5, Ja-c = 1.7 Hz, 1
c d a-b
1
H, H ), 9.27 (dd, J = 4.4, Jk-i = 1.5 Hz, 1 H, H ), 9.05 (dd, J = 8.2,
of CH
CD CN): δ = 9.97 (s, 1 H, H
), 9.33 (dd, Jc-b = 7.5, Jc-a = 1.0 Hz, 1 H, H
3
CN/H
2
O on Sephadex DEAE A25. H NMR (PF
), 9.68 (dd, Ji-j = 8.3, Ji-k = 1.3 Hz, 1 H,
), 8.61 (2dd, J4-3 = J7-8 =
6
salt, 500 MHz,
a
k-j
k
i-j
Ji-k = 1.5 Hz, 1 H, H ), 7.83 (m, 2 H, H and H ) ppm. MS (APCI, +c):
3
d
i
b
j
+
calcd. 354.07 for C H F N , found 354.31 [M + H ].
H
i
c
7′
1
9 8 4 3
4
4′
7
8
.6, J = J = 1.2 Hz, 4 H, H , H , H , H ), 8.26 (AB system, 4 H,
4
-2
7-9
6′
2
Ru-DPAC (1): One equivalent of dichloro precursor Ru(phen) Cl2
5
5′
6
2/2′
H , H , H , H ), 8.19 (dd, J = 5.2, J = 1.2 Hz, 1 H, H ), 8.16
2-3
2-4
/9′
(
(
10.0 mg, 0.0188 mmol) was mixed with 1.2 equiv. of dpac (4)
6.9 mg, 0.024 mmol) in a mixture of absolute ethanol/water (50:50,
9
(dd, J9-8 = 5.3, J9-7 = 1.2 Hz, 1 H, H ), 8.10 (dd, Jk-j = 5.3, Jk-i =
1
2
.3 Hz, 1 H, H ), 8.04 (dd, J = 5.4, Ja-c = 1.0 Hz, 1 H, H ), 8.00 (m,
k
a-b
a
2
.0 mL). The reaction mixture was stirred under an argon atmos-
H, H2 , H ), 7.73 (2dd, J = J = 5.4, Jb-c = Jj-i = 8.3 Hz, 2 H,
/2′
9/9′
b-a
3′
j-k
8′
phere at reflux (80 °C) and the reaction was followed by absorption
spectroscopy. After 3 h, the medium was concentrated and addition
of small portions of NH PF and drops of water yielded a red precip-
3
8
H , H ), 7.65 (m, 4 H, H , H , H , H ) ppm. HRMS (ESI, +p): calcd.
b
j
+
– +
960.06309 for [C H N F PRu] , found 960.06347 ([M – PF ] ) and
43 23 7 10 6
4
6
2+
calcd. 407.54918 for [C H N F Ru] , found 407.54953
43 23 7 4
itate. After centrifugation, the solid was washed with excess water.
After drying under vacuum, the orange-red residue was purified by
preparative plate chromatography (silica, eluent: CH CN/H O/satu-
–
2+
([M – 2 PF ] ).
6
3
2
rated aqueous NH Cl 4:3:1, R = 0.30). The counter-anion exchange Acknowledgments
4
f
from PF to Cl was performed by eluting a solution of the complex
6
1
Q. D. and B. E. gratefully acknowledge the Université Catholique
de Louvain, the Fonds National pour la Recherche Scientifique
in a mixture of CH CN/H O on Sephadex DEAE A25. H NMR (PF
3
2
6
salt, 500 MHz, CD CN): δ = 9.80 (s, 1 H, H ), 9.73 (dd, J = 8.2, Ji-k
=
3
d
i-j
1
.3 Hz, 1 H, H ), 9.25 (dd, Jc-b = 8.4, Jc-a = 1.2 Hz, 1 H, H ), 8.61 (2dd, (FRS-FNRS), the Région Wallonne, and the Fondation Louvain
J4-3 = J7-8 = 8.7, J4-2 = J7-9 = 1.2 Hz, 4 H, H , H , H , H ), 8.41 (d, (Prix Pierre et Colette Bauchau) for financial support. This re-
i
c
4
4′
7
7′
Jf-e = 8.6 Hz, 1 H, H ), 8.35 (d, J = 8.2 Hz, 1 H, H ), 8.25 (AB system,
H, H , H , H , H ), 8.20 (dd, J = 5.3, Ja-c = 1.2 Hz, 1 H, H ), 8.19
a-b a
f
6′
g-h
g
search was enabled in part by support provided by WestGrid
5
5′
6
4
(
(
(
www.westgrid.ca) and Compute Canada Calcul Canada
www.computecanada.ca). L. M. thanks the Belgian American
2
2′
9
9′
dd, Jk-j = 5.3, Jk-i = 1.3 Hz, 1 H, H ), 8.03 (m, 5 H, H , H , H , H ,
k
3
3′
8
8′
H ), 7.87 (d, J = 8.6 Hz, 1 H, H ), 7.64 (m, 6 H, H , H , H , H , H , H )
h
e-f
e
b
j
Educational Foundation (BAEF) for the Cabeaux–Jacobs Fellow-
ship. F. L. thanks the Labex Arcane, France (ANR-11-LABX-0003-
01) and the chemistry platform NanoBio campus in Grenoble
for luminescence lifetime measurement facilities. Q. D. also
warmly thanks Laurent Collard, Cédric Lentz, Christophe Rubay,
and Stéphanie Wautier for their scientific help.
+
ppm. HRMS (ESI, +p): calcd. 888.10078 for [C H N F PRu] , found
4
3 27 7 6
–
+
2+
8
88.10167 ([M – PF ] ) and calcd. 371.56802 for [C H N Ru] ,
6 43 27 7
–
2+
found 371.56835 ([M – 2 PF ] ).
6
Ru-DPACF (2): One equivalent of dichloro precursor Ru(phen) Cl
2
2
2
(
(
10.0 mg, 0.0188 mmol) was mixed with 1.5 equiv. of dpacF (5)
2
8.9 mg, 0.028 mmol) in a mixture of absolute ethanol/water (50:50,
2
.0 mL). The reaction mixture was stirred under an argon atmos-
phere at reflux (80 °C) and the reaction was followed by absorption
spectroscopy. After 3 h, the medium was concentrated and addition
of small portions of NH PF and drops of water yielded a red precip-
Keywords: Photophysics · DNA · DNA recognition ·
Ruthenium · Acridine
4
6
itate. After centrifugation, the solid was washed with excess water.
After drying under vacuum, the orange-red residue was purified by
preparative plate chromatography (silica, eluent: CH CN/H O/satu-
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Eur. J. Inorg. Chem. 2016, 3649–3658
www.eurjic.org
3657
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Received: April 22, 2016
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9, 839–845.
Published Online: July 14, 2016
Eur. J. Inorg. Chem. 2016, 3649–3658
www.eurjic.org
3658
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim