The DNA-binding behavior and DFT calculation of ruthenium(II) complexes [Ru(phen)2L](ClO4)2 (L = HMOPIP and MOHPIP)

Article abstract of DOI:10.1080/00958972.2017.1411593

Two ruthenium(II) complexes, [Ru(phen)₂HMPIP]²⁺ (1) and [Ru(phen)₂MHPIP]²⁺ (2), have been synthesized and characterized by elemental analysis, ESI-MS, and ¹H NMR spectroscopy. The DNA-binding properti

Full text of DOI:10.1080/00958972.2017.1411593

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
The DNA-binding behavior and DFT calculation of
ruthenium(II) complexes [Ru(phen)2L](ClO4)2 (L =
HMOPIP and MOHPIP)
Shao-Yu Liang, Yu-Xin Chen, Yong-Chang Zeng, Qiong Wu, Fanghua Qiu, Xin-
Yu Wei, Li Li, Wen-Jie Mei & Wen-Jie Zheng
To cite this article: Shao-Yu Liang, Yu-Xin Chen, Yong-Chang Zeng, Qiong Wu, Fanghua Qiu,
Xin-Yu Wei, Li Li, Wen-Jie Mei & Wen-Jie Zheng (2017): The DNA-binding behavior and DFT
calculation of ruthenium(II) complexes [Ru(phen)2L](ClO4)2 (L = HMOPIP and MOHPIP), Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2017.1411593
To link to this article: https://doi.org/10.1080/00958972.2017.1411593
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Date: 18 December 2017, At: 19:23

Journal of Coordination Chemistry, 2017
https://doi.org/10.1080/00958972.2017.1411593
The DNA-binding behavior and DFT calculation of ruthenium(II)
complexes [Ru(phen)2L](ClO4)2 (L = HMOPIP and MOHPIP)
Shao-Yu Lianga,b#, Yu-Xin Chenc#, Yong-Chang Zenga, Qiong Wub, Fanghua Qiud,
Xin-Yu Weie, Li Lie, Wen-Jie Meie,f and Wen-Jie Zhengb
afirst affiliated hospital of shenzhen university, shenzhen, China; bschool of medicine, Jinan university,
Guangzhou, China; cdepartment of Clinical laboratory, school of medicine, shanghai tenth People’s
hospital, tongji university, shanghai, China; ddepartment of hospital infection control, Guangzhou hospital
of traditional Chinese medicine, Guangzhou, China; eschool of Pharmacy, Guangdong Pharmaceutical
university, Guangzhou, China; fGuangdong Province engineering technology Center for molecular Probes &
Biomedical imaging, Guangzhou, China
ARTICLE HISTORY
received 19 august 2017
accepted 18 november 2017
ABSTRACT
Two ruthenium(II) complexes, [Ru(phen)2HMPIP]2+ (1) and
[Ru(phen)2MHPIP]2+ (2), have been synthesized and characterized
by elemental analysis, ESI-MS, and H NMR spectroscopy. The DNA-
1
KEYWORDS
binding properties of 1 and 2 have been investigated by electronic
and emission spectra and viscosity experiments. The results show that
both 1 and 2 can bind to DNA in intercalating mode, with 1 exhibiting
stronger binding affinity. These were confirmed by the strong
hypochromism at IL and MLCT absorption bands in both complexes
when DNA was added into solution, and the increase in relative
viscosity of CT-DNA in the presence of both complexes. Moreover,
the calculated intrinsic binding constant for 1 and 2 from the decay of
electronic spectra is 3.82 × 105 and 2.06 × 105 M−1, respectively. Finally,
the effects of the substituent groups on the DNA-binding behavior
of ruthenium(II) complexes have also been rationally discussed by
computer calculation of density functional theory (DFT) methods.
ruthenium(ii) complex; dna-
binding properties; homo;
lumo
G
G
C
C
C
G
N
OH
H
N
N
N
N
N
Intercalating mode
Intercalating mode
Ru
OCH3
N
N
G
C
N
OCH3
H
N
N
N
N
G
C
Ru
N
OH
N
N
C
G
Duplex strand DNA
CONTACT fanghua Qiu
qiufanghua1976@163.com; Wen-Jie mei
wenjiemei@126.com
#these authors contributed equally to the work.
© 2017 informa uK limited, trading as taylor & francis Group

2
S.-Y. LIANG ET AL.
1. Introduction
For years, the DNA-binding properties of ruthenium(II) complexes have been investigated
for their potential utility on chemotherapy [1–5] and photodynamic therapy [6–9], because
DNA molecules have long been considered as a common target for anticancer agents. In
general, ruthenium(II) complexes have been reported to bind to DNA by three non-covalent
binding modes including intercalation [10], groove-binding [11], and electrostatic binding
mode [12–18]. In the last decade, a number of ruthenium(II) complexes have been designed
and synthesized, and the assembling of these complexes with DNA has been investigated
by all kinds of methods, such as UV and NMR spectroscopy and viscosity [19, 20]. These
in vitro studies indicate that the binding mode and the binding affinity of ruthenium(II)
complexes are dependent on the structure of DNA, as well as that of the structure of metal
complexes [21–23]. It is shown that ruthenium(II) complexes with enlarged aromatic inter-
calating ligands and intramolecular hydrogen bond will bind to DNA with high affinity [24].
More recently, studies on the electron effect have shown that the electron-withdrawing
group in intercalating ligand will improve the DNA-binding affinity of ruthenium(II) com-
plexes [25, 26]. Nevertheless, the interaction of ruthenium(II) complexes with biological
macromolecules is so complex, and to elucidate this is significant to design novel rutheni-
um(II) complexes with high biological activities.
Here, we report the synthesis of two ruthenium(II) complexes, [Ru(phen)2(HMPIP)]2+ (1)
and [Ru(phen)2(MHPIP)]2+ (2) (Scheme 1). The DNA-binding properties of 1 and 2 have been
investigated by spectroscopy and viscosity experiment. The results show that both com-
plexes can bind to DNA in intercalative mode, the steric hindrance between methoxy group
at intercalating ligand and the phosphor skeleton of DNA-helix play a key role to determine
the binding affinity of these complexes with DNA molecules.
2. Experimental
2.1. Chemicals
Microanalyses were carried out on an Elementar Vario EL elemental analyzer. Electrospray
experiments were carried out with a Thermo Finnigan LCQ DECA XP ion trap mass spectrom-
eter, equipped with an ESI source. UV–Vis spectra were recorded on a Shimadzu UVPC-3000
spectrophotometer.
1
2
Scheme 1. the molecular structure of ruthenium(ii) complexes [ru(phen)2(hmPiP)]2+ (1) and
[ru(phen)2(mhPiP)]2+ (2).

JOURNAL OF COORDINATION CHEMISTRY
3
2.2. Synthesis of (3-hydroxy-4-methoxy-phenyl)imidazo[4,5-f][1,10]
phenanthroline) (HMPIP)
The ligand HMPIP was prepared as described [27] with some modification. In general, a
solution of 1,10-phenanthraquinone (0.525 g, 2.5 mmol), ammonium acetate (3.88 g,
50 mmol), and 3-hydroxy-4-methoxyphenyl-aldehyde (532 mg, 3.5 mmol) in 10 mL glacial
acetic acid was refluxed for 2 h. The cooled deep-red solution was diluted with 25 mL water
and neutralized with ammonium hydroxide. Then, the mixture was filtered and the precip-
itates were washed with water and acetone, then dried and purified by chromatography
over 60–80 mesh SiO2 using absolute ethanol as eluent, and the obtained yield was 84%
(753 mg). Calcd for C27H14N4O4·H2O: C, 68.1; H, 3.38; N, 11.8. Found: C, 67.8; H, 4.41; N, 11.2%.
2.3. Synthesis of (3-methoxy-4-hydroxy-phenyl)imidazo[4,5-f][1,10]
phenanthroline) (MHPIP)
The ligand MHPIP was prepared by a similar method as above, but with 1,10-phenanthraqui-
none (525 mg, 2.5 mmol) and 3-methxoy-4-hydroxyphenyl-aldehyde (532 mg, 3.5 mmol);
yield: 76% (685 mg). Calcd for C27H14N4O4·H2O: C, 68.1; H, 3.38; N, 11.8. Found: C, 67.8; H, 4.41;
N, 11.2%.
2.4. Synthesis of [Ru(phen)2(HMPIP)](ClO4)2 (1)
Ruthenium(II) complex 1 was synthesized as in the literature [28] with some modifications.
[Ru(phen)2Cl2]·2H2O (0.106 g, 0.20 mmol) and HMPIP (0.095 g, 0.20 mmol) were added to
10 cm3 ethyleneglycol. The mixture was refluxed for 2 h under an argon atmosphere. The
cooled reaction mixture was diluted with water (20 cm3) and filtered to remove solid impu-
rities. The complex was then separated from soluble impurities by precipitation with NaClO4.
The precipitated complex was dried, dissolved in a small amount of MeOH, and purified by
chromatography over alumina oxide using MeOH-MeCN (10:1, v/v) as an eluent; yield: 67%
(112 mg, calculated from [Ru(phen)2Cl2]·2H2O). Calcd for C44H34Cl2N8O12Ru: C, 50.87; H, 3.30;
N, 10.79. Found: C, 50.64; H, 3.45; N, 10.51%. 1H NMR (DMSO-d6, δ/ppm): 9.69(s, 1H); 9.05(dd,
2H); 8.76(d, 4H); 8.37(s, 4H); 8.13(d, 1H); 8.06(d, 2H); 7.99(d, 2H); 7.819(m, 7H); 7.03(7.001 d,
1H); 3.94(s, 3H). 13C NMR (DMSO-d6, δ/ppm): 153.64−153.50 (m), 153.35−153.16 (m),
153.16−152.96 (m), 150.43−150.15 (m), 147.72 (s), 147.64 (s), 147.62−147.07 (m), 137.28 (s),
130.92 (s), 128.54 (s), 126.81 (s), 122.92−122.28 (m), 120.01−119.11 (m), 119.19−118.18 (m),
116.36−115.08 (m), 114.90−113.43 (m), 113.43−111.89 (m). ESI-MS (in water, m/z): 901.0(14%)
([M–ClO4]+); 803.3(100%) ([M–2ClO4–H]+); 402.3 (28%) ([M–2ClO4]2+).
2.5. Synthesis of [Ru(phen)2(MHPIP)](ClO4)2 (2)
Ruthenium(II) complex [Ru(phen)2(MHPIP)]2+ was synthesized as above, but with
[Ru(phen)2Cl2]·2H2O and MHPIP; yield: 72% (121 mg). Calcd for C44H34Cl2N8O12Ru: C, 50.87;
H, 3.30; N, 10.79. Found: C, 50.68; H, 3.51; N, 10.31%. 1H NMR (DMSO-d6, δ/ppm): 9.41(s, 1H);
9.05(t, 2H); 8.76(d, 4H); 8.37(s, 4H); 8.12(t, 1H); 8.06(d, 2H); 7.98(d, 2H); 7.76(m, 7H);
7.19(d, 1H); 3.88 (s, 3H); 13C NMR (DMSO-d6, δ/ppm): 154.09−153.72 (m), 153.31−153.20 (m),
153.15−153.05 (m), 150.78−150.24 (m), 149.79−149.33 (m), 148.77−148.32 (m), 147.68

4
S.-Y. LIANG ET AL.
(d, J = 9.0 Hz), 137.27 (s), 130.93 (s), 128.54 (s), 126.86−126.71 (m), 126.54−126.40 (m),
120.68−120.58 (m), 116.57−116.36 (m), 111.15−110.92 (m). ESI-MS (in water, m/z): 901.0(16%)
([M–ClO4]+); 803.3(100%) ([M–2ClO4–H]+); 402.2(59%) ([M–2ClO4]2+).
2.6. Theoretical section
Both octahedral complexes [Ru(phen)2(HMPIP)]2+ and [Ru(phen)2(MHPIP)]2+ forms from Ru(II)
and one main ligand or intercalating ligand L and two co-ligands (phen). There is no sym-
metry in these complexes. The full geometry optimization computations were performed
for these complexes applying the DFT-B3LYP method [29–34] and LanL2DZ basis set [35,
36]. The structural modes of the studied compounds are shown in Scheme 1 and the singlet
state was assumed [37]. All computations were performed with the G98 quantum chemistry
program package [38]. In order to vividly depict the detail of the frontier molecular orbital
interactions, the stereographs of some related frontier MO of the complexes were drawn
with the Molden v3.6 program [39] based on the obtained computational results.
2.7. Absorption titration experiments
The electronic absorption spectra were recorded at room temperature to determine the
binding affinity between DNA and polypyridyl ruthenium complexes. 3.0 mL solution of the
blank buffer and the ruthenium complex were placed in the reference and sample cuvettes,
respectively. During titration, an aliquot (2 μM) of buffered DNA solution was added to each
cuvette to eliminate the absorbance of DNA itself. The titration processes were repeated
until the spectra did not change for at least four titrations, indicating that binding saturation
was achieved.
2.8. Fluorescence emission titrations
Fluorescence spectroscopy measurements were performed on an RF-5301 fluorescence
spectrophotometer using a 1 cm path length quartz cell. Samples were excited at 340 nm
and emission spectrum was recorded between 500 and 700 nm. After the solutions were
mixed for 2 min, absorption spectra were recorded. The titration processes were repeated
until there was no apparent change in the spectra for at least three titrations, indicating the
achievement of the binding saturation [40].
2.9. Viscosity measurements
Viscosity measurements were carried out using an Ubbelodhe viscometer maintained at
32( 0.1) °C in a thermostatic bath. Fixed solutions of complexes and DNA in different con-
centrations were prepared in Tris-HCl buffer medium, the DNA samples containing approx-
imately 200 base pairs were used. The viscosity of DNA (η) was calculated by η = t−t0, where
t is flow times of DNA and t0 is the flow times of bank (the Tris buffer solution). Flow times
were measured by a digital stopwatch and each was measured three times. Viscosity of DNA
are presented as (η/η0)1/3 versus binding ratio [41, 42], where η is the viscosity of DNA in the
presence of complex and η0 is the viscosity of DNA in the absence of complex [43].

JOURNAL OF COORDINATION CHEMISTRY
5
3. Results
3.1. Synthesis and characterization
Ruthenium(II) complexes 1 and 2 were synthesized by refluxing the mixture of cis-
[Ru(phen)2Cl2] and corresponding ligands HMPIP and MHPIP, respectively. The complexes
were obtained as ClO4− salts.
The 1H NMR chemical shifts and their attribution of 1 and 2 are listed in Table 1. Compared
to [Ru(phen)2(MHPIP)](ClO4)2, the chemical shift at H4 and –OCH3 of [Ru(phen)2(HMPIP)](ClO4)2
transfer to low field, while the chemical shift at H5 transfer to high field.
3.2. DNA binding studies
Electronic spectra have been utilized to investigate the DNA-binding properties of 1 and 2.
At room temperature, both 1 and 2 exhibit an MLCT (metal-to-ligand charge-transfer) band
at 458 nm and a strong IL (intra-ligand) band at 264 nm in the electronic spectra. In tris-HCl
(pH = 7.2) buffer, the MLCT band of 1 shifts to 456 nm, while for 2 shifts to 453 nm. Upon
addition of calf thymus DNA, the MLCT transition and IL transition bands of both 1 and 2
undergo obvious hypochromic effect and red-shift (Figure 1); the hypochromism for 1 and
2 are listed in Table 2.
Table 1. the chemical shift δ (ppm) of 1 and 2 and their attribution.
1
2
δ (ppm)
Attribution
δ (ppm)
Attribution
9.692 (s, 1h)
9.048 (dd, 2h)
8.761 (d, 4h)
8.369 (s, 4h)
8.126 (d, 2h)
8.060 (d, 2h)
7.987 (d, 2h)
7.819 (m, 7h)
7.028 (d, 1h)
3.945 (s,3h)
h6
hb
hc
hd
hb
h1
h3
9.408 (s, 1h)
9.047 (t, 2h)
8.760 (d, 4h)
8.367 (s, 4h)
8.116 (t, 2h)
8.060 (d, 2h)
7.983 (d, 2h)
7.816 (m, 7h)
7.193 (d, 1h)
3.881 (s, 3h)
h6
hb
hc
hd
hb
h1
h3
ha, h2, h8
h7
h(oCh3)
ha, h2, h8
h7
oCh3
2.5
2.0
1.5
1.0
0.5
0.0
2.5
2.0
1.5
1.0
0.5
0.0
-2
-3
-4
-5
-6
-7
-8
-9
-4
-6
-8
-10
-12
0.0
0.2
0.4
0.6
0.0
0.1
0.2
0.3
0.4
0.5
0.6
[DNA] / [Ru]
[DNA] / [Ru]
300
400
Wavelength / nm
500
600
300
400
Wavelength / nm
500
600
Figure 1. the electronic spectra of ruthenium(ii) complexes 1 (left) and 2 (right) in the absence and
presence of calf thymus dna. [ru] = 20 μm.

6
S.-Y. LIANG ET AL.
Table 2. the change of electronic spectra of ruthenium(ii) complexes 1 (20 μm) and 2 (20 μm) in the
absence and presence of calf thymus dna.
MLCT
IL
Comp.
λ0/nm
λb/nm
Δλ/nm
H/%
λ0/nm
λb/nm
Δλ/nm
H/%
1
2
456
453
465
458
9
5
17
11
263
263
265
264
2
1
38
34
notes: mlCt: metal to ligand charge transfer; il: intra ligand charge transfer; h: hypochromism.
The intrinsic DNA-binding constants of ruthenium(II) complexes were calculated accord-
ing to Equation (1):
[DNA]
ꢀ − ꢀ
[DNA]
ꢀ − ꢀ
1
=
+
(1)
kb(ꢀ − ꢀ )
a
f
b
f
b
f
where [DNA] is the concentration of DNA in base pairs, ε , ε , and ε are the apparent extinc-
(
)
a
f
b
Aobsd
tion coefficient
, the extinction coefficient for free complex, and the extinction coeffi-
[M]
cient for the complex in the fully bound form, respectively. In plots of [DNA] versus [DNA], Kb
ꢀ −ꢀ
a
f
is given by the ratio of slope to intercept. The calculated binding constant for 1 and 2 is
3.82 × 105 and 2.06 × 105 M−1, respectively, and are higher than those reported for polypyri-
dine ruthenium(II) complexes in literature, with binding constants of 1.52 × 105–1.81 × 105 M−1
[44–48] and suggest that the increase of aromatic ring can improve the DNA-binding affinity.
The calculated binding constants for [Ru(phen)2(o-TFPIP)]2+ (1) and [Ru(phen)2(p-CPIP)]2+ (2)
are 5.81 × 104 and 8.55 × 104 M−1, respectively.
3.3. Emission spectra
To further clarify the DNA-binding of 1 and 2, the emission spectra of 1 and 2 were studied
in the absence and presence of calf thymus DNA, as shown in Figure 2.
At room temperature, when excited at 470 nm, both 1 and 2 exhibit a strong emission
band in range of 500–700 nm, with the maximum at 589 and 590 nm, respectively. When
calf thymus DNA was added into solution, the emission observed decreased. At the [DNA]/
[Ru] = 1.2, the I/I0 for 1 and 2 is about 0.52 and 0.81, respectively (Figure 2(C)). These data
are in agreement with that of electronic spectra, indicating that 1 binds more strongly than
2 to DNA due to the space hindrance when bound to DNA molecules.
3.4. Viscosity experiment
In order to elucidate the way ruthenium complex interacts with DNA, viscosity experiments
give the strongest evidence to determine the binding mode of ruthenium(II) complexes to
DNA in lacking of crystal data. In general, the relative viscosity of DNA will increase if a com-
pound binds to DNA in an intercalative mode, while the groove-binding mode will decrease
the relative viscosity of DNA resulting from the kink of double-strand helix of DNA. The
relative viscosity of calf thymus DNA in the presence of 1 and 2 is shown in Figure 3.
Compared to [Ru(bpy)3]2+, which bind to DNA in electrostatic mode, the relative viscosity
of calf thymus DNA increased in the presence of 1 and 2 because the space between base

JOURNAL OF COORDINATION CHEMISTRY
7
(A)
(B)
400
500
350
300
250
200
150
100
50
400
300
200
100
0
0
500
550
600
650
700
500
550
600
650
700
Wavelength / nm
Wavelength / nm
(C)
1.0
0.8
0.6
0.0
0.4
0.8
1.2
1.6
[DNA]/[Ru]
Figure 2. the emission spectra of ruthenium(ii) complexes 1 (a) and 2 (B) in the absence and presence
of calf thymus dna. [ru] = 20 μm. (C). the changes of emission of ruthenium(ii) complexes 1 (■) and 2
(●) upon increasing amounts of calf thymus dna.
1.12
1.10
1.08
1.06
1.04
1.02
1.00
0.98
0.00
0.02
0.04
0.06
0.08
0.10
[Ru] / [DNA]
Figure3.effectsofincreasingamountsofru(ii)complexes:[ru(phen)2(hmPiP)]2+ 1(■),[ru(phen)2(mhPiP)]2+
2 (●) and [ru(bpy)3]2+ (▼) on the relative viscosity of Ct-dna in 5 mmtris-hCl buffer (ph 7.2), 50 mm naCl
at 32( 0.1) °C. [dna] = 5.0 × 104 m.
pairs of double-stranded DNA helix is enlarged when the ligand of ruthenium(II) complex
intercalates into base pairs. These data indicate that both 1 and 2 bind to DNA in intercalative
mode.

8
S.-Y. LIANG ET AL.
4. Discussion
It is shown from spectroscopy and viscosity studies that both 1 and 2 can bind to DNA in
intercalative mode, and 1 binds tighter than 2 to DNA. The theoretical computations by the
DFT method were utilized to explain the fact, and the calculated bond lengths, bond angles,
and dihedral angles of 1 and 2 are listed in Table 3.
According to Table 3, the dihedral angle (N9-C4-C5-C6) of 1 and 2 is 1.0 and 0.2°, respec-
tively, indicating that 2 may bind to DNA more tightly than 1, since the binding affinity of
ruthenium(II) complexes depends on the planarity of intercalating ligands; this is in conflict
with the results from the spectroscopy studies.
Based on the computation results, some frontier molecular orbital energies and total
energies, the schematic diagram of the energies and related MLCT transitions, and the molec-
ular orbital stereographs of [Ru(phen)2L]2+ are given in Table 4, Figure 4(B) and Figure 5,
respectively.
As it is well established, there are π–π interactions in the DNA-binding of these complexes
by intercalation mode. Kurita and Kobayashi [49] reported a simple calculation mode by the
DFT method for stacked DNA base-pairs with backbones, and the computed HOMO and
NHOMO (NH) energies of the DNA section mode with base pairs are much higher (−1.27 and
−1.33 eV) than our computed LUMO and NLUMO (NL) energies (∼ −7.0 eV) of complexes
[Ru(phen)2L]2+ (L=HMPIP and MHPIP). We believe that such a trend in the relative energies
will be retained in our DNA system, since the attraction of metal complex cations with high
positive charges for electrons in MOs is much stronger than that of DNA, and thus the elec-
tron must easily be transferred from the HOMO of base pairs of DNA to the LUMO of the
complexes intercalating to DNA [50, 51]. The LUMO energy of 1 and 2 is −0.2664 and −0.2667
a.u., respectively. Although the lower LUMO energy of 1 contributes to more binding affinity
of this complex to DNA, the difference between 1 and 2 is so subtle to explain the difference
in DNA-binding affinity of 1 and 2.
There are other factors affecting the binding of these complexes with DNA. The calculated
geometric structures of 1 and 2 are shown in Figure 4(A). From Figure 4(A), it is obviously
different than the orientation of methoxy group in intercalating ligand. For 1, the methoxy
group is forward, which is apart from the phosphor skeleton when 1 approaches DNA mol-
ecules. At the same time, hydroxyl group at 3-position in HMPIP will form intramolecular
hydrogen bond with the base pair of DNA helix to increase the DNA-binding affinity. As for
Table 3. the main bond lengths, bond angles, and dihedral angles of complexes 1 and 2.
Bond length/nm
Bond/ °
Dihedral angle/ °
a
b
c
Comp.
Ru–Nm
Ru–Nco
C–C(N)m
C–C(N)co
Am
Aco
N9–C4–C5–C8 N9–C4–C5–C6
1
2
0.2105
0.2104
0.2106
0.2106
0.1405
0.1405
0.1406
0.1406
79.3
79.3
79.4
79.5
−179.0
−179.8
1.0
0.2
aru–nm expresses the mean coordination bond length between ru and n atoms of the main ligand and ru-nco expresses
that between ru and n atoms of the coligand (phen).
bC–C(n)m expresses the mean bond length of the ring skeleton of the main ligand.
cAm expresses the coordination bond angle between ru and two n atoms of the main ligand.
Table 4. some frontier molecular orbits energies (εi/a.u) for ruthenium(ii) complexes 1 and 2.
Comp.
H–3
H–2
H–1
HOMO
LUMO
L+1
L+2
ΔεL–H
ΔεL–NH
1
2
−0.3945
−0.3951
−0.3915
−0.3919
−0.3715
−0.3746
−0.3371
−0.3416
−0.2664
−0.2667
−0.2630
−0.2633
−0.2597
−0.2600
0.0707
0.0749
0.1051
0.1079

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 4. (a) Calculated geometric structures of ruthenium(ii) complexes 1 and 2. (B) schematic diagrams
of some frontier mo energies and the related mlCt transitions of complexes 1 and 2.
1-HOMO-2
1-HOMO-1
1-HOMO
1-LUMO
1-LUMO+1
1-LUMO+2
2-HOMO-2
2-HOMO-1
2-HOMO
2-LUMO
2-LUMO+1
2-LUMO+2
Figure 5. some related frontier mo stereographs of ruthenium(ii) complexes 1 and 2.
2, although the hydroxyl group is at 4-position in intercalating ligand to improve the binding
affinity of this complex with DNA, the repulsion force between the methoxy group at 3-posi-
tion in MHPIP and the phosphor skeleton of double-stand DNA will distort MHPIP to destroy
the planarity of this ligand when 2 interacts with DNA. As a result, the steric hindrance
between the intercalating ligand and DNA will decrease the binding affinity of 2.
5. Conclusion
Two ruthenium(II) complexes, [Ru(phen)2(HMPIP)]2+ (1) and [Ru(phen)2(MHPIP)]2+ (2), have
been synthesized by refluxing cis-[Ru(phen)2Cl2] and corresponding ligands HMPIP and

10
S.-Y. LIANG ET AL.
MHPIP under Ar atmosphere. These complexes have been characterized by elemental anal-
ysis, ESI-MS, and 1H NMR spectroscopy. The investigation on the DNA-binding properties of
1 and 2 by spectroscopy and viscosity techniques show that both complexes bind to DNA
in intercalative mode. The intrinsic DNA-binding constants calculated for 1 and 2 are
3.82 × 105 and 2.06 × 105 M−1, respectively. The emission spectra increased in the presence
of CT-DNA, and the relative emission strength for 1 and 2 at ratio of [DNA]/[Ru] = 1.2 is ca.
0.52 and 0.81, respectively. These data, together with the results of electronic spectra, show
that 1 binds more strongly than 2 to DNA.
In general, there are three factors determining the binding affinity of ruthenium(II) com-
plexes and DNA; that is the planarity of intercalating ligand, the frontier molecular orbits
energies, and the steric hindrance between the substituent group at intercalating ligand
and the phosphor skeleton of double-stranded DNA-helix. The studies on the calculation
by DFT methods show that the steric hindrance play a key role in the interaction of ruthe-
nium(II) complexes [Ru(phen)2(HMPIP)]2+ and [Ru(phen)2(MHPIP)]2+, and the detailed mech-
anism is under further investigation.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Nature Science Foundation of China [grant number 81572926],
[grant number 81603669]; the Provincial Major Scientific Research Projects in Universities of Guangdong
Province [grant number 2014KZDXM053]; the Science and Technology Project of Guangdong Province
[grant number 2014A020212312]; Natural Science Fund of Guangdong [grant number 408182136045];
the Science Foundation for China Postdoctor [grant number 2016M592604].
References
[1] S.M. Guichard, R. Else, E. Reid, B. Zeitlin, R. Aird, M. Muir, M. Dodds, H. Fiebig, P.J. Sadler, D.I. Jodrell.
Biochem. Pharmacol., 71, 408 (2006).
[2] F. Pierard, A. Kirsch-De Mesmaeker. Inorg. Chem. Commun., 9, 111 (2006).
[3] F. Schmitt, P. Govindaswamy, G. Süss-Fink, W.H. Ang, P.J. Dyson, L. Juillerat-Jeanneret, B. Therrien.
J. Med. Chem., 51, 1811 (2008).
[4] E. Wachter, D.K. Heidary, B.S. Howerton. Chem. Commun., 48, 9649 (2012).
[5] M. Brindell, E. Kuliś, S.K. Elmroth, K. Urbańska, G. Stochel. J. Med. Chem., 48, 7298 (2005).
[6] W.J. Mei, J. Liu, K.C. Zheng, L.J. Lin, H. Chao, A.X. Li, F.C. Yun, L.N. Ji. Dalton Trans., 1352 (2003).
[7] H. Chao, W.J. Mei, Q.W. Huang, L.N. Ji. J. Inorg. Biochem., 92, 165 (2002).
[8] K. Qiu, J. Wang, C. Song, L. Wang, H. Zhu, H. Huang, J. Huang, H. Wang, L. Ji, H. Chao. ACS Appl.
Mater. Inter., 9, 18482 (2017).
[9] W. Sun, S. Li, B. Häupler, J. Liu, S. Jin, W. Steffen, U.S. Schubert, H.-J. Butt, X.-J. Liang, S. Wu. Adv.
Mater., 29, 1603702 (2017).
[10] C.J. Cardin, J.M. Kelly, S.J. Quinn. Chem. Sci., 8, 4705 (2017).
[11] J.P. Hall, P.M. Keane, H. Beer, K. Buchner, G. Winter, T.L. Sorensen, D.J. Cardin, J.A. Brazier, C.J. Cardin.
Nucleic Acids Res., 44, 9472 (2016).
[12] X.H. Zou, B.H. Ye, H. Li, J.G. Liu, Y. Xiong, L.N. Ji. Dalton Trans., 1423 (1999).
[13] L. Ji, Q. Zhang, C. Hui, L. Ji, Q. Zhang, C. Hui. Sci. China, 46, 1332 (2001).
[14] P.L. And, B. Nordén. J. Phys. Chem. B, 102, 9583 (1998).
[15] Y. Xiong, L.N. Ji. Coord. Chem. Rev., 185, 711 (1999).

JOURNAL OF COORDINATION CHEMISTRY
11
[16] J.G. Liu, B.H. Ye, H. Li, L.N. Ji, R.H. Li, J.Y. Zhou. J. Inorg. Biochem., 73, 117 (1999).
[17] W.J. Mei, Y.Z. Ma, J. Liu, J.C. Chen, K.C. Zheng, L.N. Ji, J.H. Yao. Transition Met. Chem., 31, 277 (2006).
[18] N.M. Gabra, B. Mustafa, Y.P. Kumar, C.S. Devi, A. Srishailam, P.V. Reddy, K.L. Reddy, S. Satyanarayana.
J. Fluoresc., 24, 169 (2014).
[19] Y. Sun, J. Li, H. Zhao, L. Tan. J. Inorg. Biochem., 163, 88 (2016).
[20] D. Lazić, A. Arsenijević, R. Puchta, Ž.D. Bugarčić, A. Rilak. Dalton Trans., 45, 4633 (2016).
[21] S. Fukuzumi, M. Tanaka, M. Nishimine, K. Ohkubo. J. .Photochem. Photobiol. A: Chem., 175, 79 (2005).
[22] K.K. Naresh, R. Ramesh, Y. Liu. J. Inorg. Biochem., 100, 18 (2006).
[23] E. Ioachim, E.A. Medlycott, G.S. Hanan, F. Loiseau, S. Campagna. Inorg. Chim. Acta, 359, 766 (2006).
[24] R.P. Paitandi, R.S. Singh, S. Mukhopadhyay. Inorg. Chim. Acta, 454, 117 (2016).
[25] J. Liu, W.J. Mei, L.J. Lin, K.C. Zheng, H. Chao, F.C. Yun, L.N. Ji. Inorg. Chim. Acta, 357, 285 (2004).
[26] H. Luo, J. Xiao, J. Chen, H. Xu, J. Lu, Z. Liu, S. Chen, M. Tong, K. Zheng, L. Ji. Chin. J. Chem., 28, 1317
(2010).
[27] E.A. Steck, A.R. Day. J. Am. Chem. Soc., 65, 121 (1943).
[28] R. Hage, J.G. Haasnoot, J. Reedijk, R. Wang, E.M. Ryan, J.G. Vos, A.L. Spek, A.J.M. Duisenberg. Inorg.
Chim. Acta, 174, 77 (1990).
[29] P. Hohenberg, W. Kohn. Phys. Rev. B, 136, B864 (1964).
[30] A.D. Becke. J. Chem. Phys., 98, 1372 (1993).
[31] A. Görling. Phys. Rev. A, 46, 3753 (1992).
[32] R. Behjatmanesh-Ardakani, F. Pourroustaei-Ardakani, M. Taghdiri. J. Mol. Model., 22, 3 (2016).
[33] V. Dixit, R.A. Yadav. Int. J. Pharm., 491, 277 (2015).
[34] R. Behjatmanesh-Ardakani. Struct. Chem., 25, 919 (2014).
[35] P.J. Hay, W.R. Wadt. J. Chem. Phys., 82, 270 (1985).
[36] M. Khajehzadeh, M. Moghadam. Spectrochim. Acta, Part A, 180, 51 (2017).
[37] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A.V. von Zelewsky. Coord. Chem. Rev., 84,
85 (1988).
[38] M. Frisch. J. Am. Chem. Soc., 24, 235 (1998).
[39] J. Wang, X. Hou, Z. Zhao, H. Bo, Q. Chen. Inorg. Chem. Commun., 67, 40 (2016).
[40] W.J. Mei, Y.X. Liu, J. Liu, J. Li, K.C. Zheng, L.N. Ji. Transition Met. Chem., 30, 82 (2005).
[41] Q. Wu, J. Wu, W.-J. Mei, Q. Wang, Z. Zhang, X.-H. Wu, F.-Y. Sun, W.-L. Wu, Y.-H. Chen, X.-Y. Hu, Y.-Y.
Tao. Aust. J. Chem., 66, 1422 (2013).
[42] G. Cohen, H. Eisenberg. Biopolymers, 8, 45 (1969).
[43] H. Fritzsche, H. Triebel, J.B. Chaires, N. Dattagupta, D.M. Crothers. Biochem., 21, 3940 (1982).
[44] C. Wang, Q. Wu, Y. Zeng, D. Huang, C. Yu, X. Wang, W. Mei. J. Coord. Chem., 68, 1489 (2015).
[45] S. Sathiyaraj, R.J. Butcher, C. Jayabalakrishnan. J. Coord. Chem., 66, 580 (2013).
[46] P. Čanović. J. Biol. Inorg. Chem., 43, 1 (2017).
[47] R.R. Mallepally. J. Fluoresc., 27, 1 (2017).
[48] P.V. Reddy. Anal. Biochem., 485, 49 (2015).
[49] N. Kurita, K. Kobayashi. Comput. Chem., 24, 351 (2000).
[50] K. Fukui, T. Yonezawa, H. Shingu. J. Chem. Phys., 20, 722 (2004).
[51] R. Misra, P. Gautam. Org. Biomol. Chem., 12, 5448 (2017).