Synthesis, crystal structure, and properties of the first Organomercury Dimer Derived from PMP

Article abstract of DOI:10.1002/zaac.201300208

The organomercury dimer [Hg₂(PMP)Cl₂] ₂·DMF (1) (PMP = 1-phenyl-3-methyl-2-pyrazolin-5-one) was prepared by the reaction of mercury chloride with PMP and characterized by elemental analysis, IR spectroscopy, TG, and single-crystal X-ray diffraction analysis. The title compound crystallizes in the triclinic space group P1, with a = 7.4298(6), b = 9.0313(8), c = 12.4145(13) A?, V = 760.50(12) A?3, Z = 1. Each mercury(II) atom is tricoordinated to one chlorine atom, one carbon atom of the pyrazole ring from one PMP, and one oxygen atom from another PMP. The coordination arrangement around the mercury atom is T-shaped. This is the first structural report on an organomercury derivative of PMP. The distance between the two HgII ions is 3.2735(8) A?, which indicates the presence of weak Hg Hg interactions. Meanwhile, 1 can be connected by intermolecular C-H Cl hydrogen bonding and weak Hg O/Cl/N interactions to form a three dimensional network. The thermal stability and antibacterial activity of 1 were studied. The binding of 1 with calf thymus DNA was investigated by absorption spectroscopy and viscometry.

Full text of DOI:10.1002/zaac.201300208

ARTICLE
DOI: 10.1002/zaac.201300208
Synthesis, Crystal Structure, and Properties of the First Organomercury
Dimer Derived from PMP
Rui-Bo Xu,*[a,b] Wei-Xing Ma,[a] Jia-Bin Qi,[a] Yi-Qiu Qin,[a] Jia-Wei Zhang,[a] Shu-
Ping Yang,[a] and Xing-You Xu[c]
Keywords: 1-Phenyl-3-methyl-2-pyrazolin-5-one; Organomercury chloride; Crystal structure; Thermal stability; Bioactivity
Abstract. The organomercury dimer [Hg2(PMP)Cl2]2·DMF (1) (PMP atom is T-shaped. This is the first structural report on an organomer-
= 1-phenyl-3-methyl-2-pyrazolin-5-one) was prepared by the reaction cury derivative of PMP. The distance between the two HgII ions is
of mercury chloride with PMP and characterized by elemental analysis, 3.2735(8) Å, which indicates the presence of weak Hg···Hg interac-
IR spectroscopy, TG, and single-crystal X-ray diffraction analysis. The tions. Meanwhile, 1 can be connected by intermolecular C–H···Cl hy-
¯
title compound crystallizes in the triclinic space group P1, with a =
drogen bonding and weak Hg···O/Cl/N interactions to form a three
7.4298(6), b = 9.0313(8), c = 12.4145(13) Å, V = 760.50(12) Å3, Z = dimensional network. The thermal stability and antibacterial activity
1. Each mercury(II) atom is tricoordinated to one chlorine atom, one of 1 were studied. The binding of 1 with calf thymus DNA was investi-
carbon atom of the pyrazole ring from one PMP, and one oxygen atom
from another PMP. The coordination arrangement around the mercury
gated by absorption spectroscopy and viscometry.
ested in the construction of metal complexes derived from
1 Introduction
PMP, and synthesized some PMP complexes such as
Mercury is well-known as a toxic element,[1] which has re-
ceived increasingly scientific attention.[1–3] Mercury metal,
mercury salts, and organomercury compounds are ubiquitous
and can be persistent environmental toxins. However, organ-
omercury compounds have become one of the most investi-
gated organometallic reagents for the introduction of a variety
of functional groups in predefined organic skeletons,[3,4] syn-
thesis of other organometallic compounds by transmet-
alation,[5,6] formation of various functional coordination com-
plex, and removement of mercury ions from aqueous solution
by coordination with suitable ligands.[7–9]
Pyrazolone derivatives, characterized as a five-membered
ring lactam, are important frameworks, which exhibit variety
of applications such as pharmaceutical candidates, biologically
important structural components.[10,11] Edaravone (1-phenyl-3-
methyl-2-pyrazolin-5-one; PMP) is an important intermediate
for dyes and pharmaceuticals, and had been used to treat the
acute stage cerebral infarction.[12–14] Just like other ligands
containing N and O donors, PMP can display several different
coordination modes[15–19]. For many years, we have been inter-
[17]
[Zn(PMP)2Cl]n,[15] [Cd(PMP)2]n,[16] and [Cd2(PMP)2Cl4]n
.
As a continuation of our work, we have prepared another novel
organomercury compound, [Hg2(PMP)Cl2]2·DMF (1). In 1,
each HgII is coordinated to O, C, and Cl atoms, adopting a T-
shaped arrangement. Compound 1 contains weak mercuro-
philic interactions [Hg···Hg distance of 3.2735(1) Å].[5,20,21] It
is well known that the mercury ion can easily attack alkanes
to form new metal–C(sp3) bonds or aromatic compounds to
form metal–C(sp2) bonds.[3,20,22] Moreover, regioselective
mono-metalation or di-metalation usually takes place at C-2,
C-4, C-6, or C-4,6 of the benzene ring.[3,19,20,23] Nevertheless,
the HgII ion of 1 is covalently bonded to the C2 of the pyrazo-
lone ring and not to the benzene ring. Regioselective met-
alation of pyrazolone ring has not yet been reported. Hence
this is the first case of mercuric-PMP. Herein, we report the
synthesis, crystal structure, thermal stability, antibacterial ac-
tivity, and DNA-bonding property of the novel organomercury
dimer 1.
2 Experimental Section
* Dr. R.-B. Xu
Fax: +86-581-85895085
2.1 Synthesis of [Hg2(PMP)Cl2]2·DMF (1)
E-Mail: xuruibo9125@163.com
[a] School of Chemical Engineering
Huaihai Institute of Technology
Lianyungang 222005, P.R. China
[b] State Key Laboratory of Analytical Chemistry for Life Science
School of Chemistry and Chemical Engineering
Nanjing University
A solution of HgCl2 (825 mg, 3 mmol in 15 mL anhydrous methanol)
was added dropwise with constant stirring to the solution of PMP
(523 mg, 3 mmol in 10 mL anhydrous methanol) at room temperature.
The resulting mixture was stirred under reflux at 60 °C for 3 h. After
cooling, no precipitate was found. On evaporation of the solution in
steam bath, yellow precipitate was obtained and dissolved in the mix-
ture of ethanol (10 mL), chloroform (5 mL), and DMF (5 mL). After
3 d, light yellow crystals suitable for X-ray analysis were obtained,
Nanjing 210093, P.R. China
[c] Huaiyin Institute of Technology
Huaian 223003, P.R. China
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R.-B. Xu et al.
ARTICLE
washed with small amounts of ethanol and dried in a vacuum
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
(Scheme 1). Yield: 77.3%. Mp.: 240–241 °C (dec.). Elem. analysis for Copies of the data can be obtained free of charge on quoting the
C23H23Cl4Hg4N5O3: calcd. C 20.29; H 1.70; N 5.14%; found: C 20.26; depository number CCDC-749487 (Fax: +44-1223-336-033; E-Mail:
H 1.73; N 5.18%. IR (KBr): ν˜ = 3435 w, 2935 m, 2858 m, 1715 m, deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
1614 s, 1593 s, 1498 s, 1456 w, 1363 m, 1319 m, 1294 s, 1195 w,
1117 w, 1073 w, 1003 w, 758 m, 692 m, 633m, 591 w, 504 w, 451 w
cm–1.
2.3 Antibacterial Activity Determination
Compound 1 was evaluated for antibacterial activity against coli bacil-
lus, staphylococcus aureus, and bacillus subtilis by the modified agar
diffusion method.[25,26] The antibacterial activities of PMP and HgCl2
were also tested for comparison. The compounds were dissolved in
DMF. Nutrient agar thawed by heating in a water bath was transferred
to plates and frozen at 37 °C. After the test strains were spread
on the solid nutrient agar surface, stainless steel tubes
(7.8 mmϫ6 mmϫ10 mm) were spread vertically on the surface. Sam-
Scheme 1. Reaction scheme for the synthesis of 1.
ples (0.05 mL) with known concentration were injected into the steel
tubes and allowed to incubate at 37 °C for 24 h. Inhibition zone around
the disc was calculated as a zone diameter in millimeter. Blank tests
showed that DMF used in the preparation of the sample solutions does
2.2 X-ray Crystallography
Diffraction data for a crystal of dimensions 0.21ϫ0.17ϫ0.16 mm
were collected with a BRUKER SMART CCD diffractometer with the
graphite monochromated Mo-Kα (λ = 0.71073 Å) radiation by using
the ω-2θ scan technique (1.79 Յ θ Յ 25.01°) at 298(2) K. The crystal
structure was solved by direct methods and Fourier synthesis
not affect the test organisms.
2.4 DNA Binding Studies
Calf thymus DNA (CT-DNA) was dissolved in 5 mM Tris-HCl buffer
(SHELXS-97),[24] and refined by full-matrix least-squares techniques at pH 7.43. CT-DNA in the buffer gave a ratio of UV absorbance at
on F2 with the program SHELXL-97.[24] The carbon atoms (C11, C12, 260 nm and 280 nm and A260/ A280 of 1.85:1, which indicates that
and C13) and the oxygen atom (O2) of DMF in 1 are both disordered
over two positions, and all the site occupancy factors of C11, C12,
C13, and O2 are 0.50. The non-hydrogen atoms, except C and O atoms
in DMF, were refined anisotropically; and H atoms were added accord-
the DNA was free from protein.[27–28] The concentration of DNA was
measured by absorption spectroscopy using the molar absorption coef-
ficient (6600 mol–1·cm–1) at 260 nm.[27–28] Stock solutions were stored
at 4 °C and used after no more than 4 d. Absorption spectral titration
ing to theoretical models. A summary of crystallographic data and was performed by keeping the concentration of CT-DNA constant,
refinement parameters is given in Table 1.
while varying the title compound concentration. An equal volume of
the title compound was added to the CT-DNA solution and a reference
solution was added to eliminate the absorbance of the title compound
itself.
Table 1. Crystal data and structure refinement details for 1.
Expirical formula
C23H23Cl4Hg4N5O3
Formula weight
Color
Temperature /K
Wavelength /Å
Crystal system
Space group
a /Å
b /Å
1361.62
Light yellow
298(2)
0.71073
triclinic
¯
P1
7.4298(6)
9.0313(8)
12.4145(13)
108.949(2)
103.223(2)
92.5950(10)
760.50(12)
1
2.973
20.511
608
1.79–25.01
–8 Յ h Յ 6
–9 Յ k Յ 10
–14 Յ l Յ 14
4010
For viscosity measurements, flow time was determined with a man-
ually operated timer. Each sample was measured three-times to calcu-
late the average flow time. Relative viscosities for DNA in the pres-
ence and absence of the title compound were calculated from the equa-
tion, η = (t – t0) / t0, where t is the observed flow time of the DNA-
containing solution and t0 is that of Tris-HCl buffer. Data were pre-
sented as (η /η0)1/3 vs. binding ratio, where η is the viscosity of CT-
DNA in the presence of the title compound and η0 is the viscosity of
CT-DNA alone.[28–29]
c /Å
α /°
β /°
γ /°
Volume /Å3
2.5 Reagents and Instrumentation
Z
CT-DNA was purchased from the Sigma Corp. All other chemicals
were of reagent grade and used as received without further purification.
IR spectra were recorded with a Spectrum One BFT-IR spectrophotom-
eter as KBr pellets from 4000–450 cm–1. Thermal analyses were per-
formed on a NETZSCH STA 409PC differential thermal analyzer. The
absorption spectra were determined at room temperature with a Shim-
adzu Uv-2550 ultraviolet-visible spectrophotometer. Viscosity mea-
surements were carried out with an Ubbelodhe viscometer thermostat-
ted at 25Ϯ1 °C in a constant temperature bath.
Dcalcd. /Mg·m–3
Absorption coefficient /mm–1
F(000)
θ Range for data collection /°
Limiting indices
Reflections collected
Reflections independent, R(int)
2021, 0.0509
1.012
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ(I)]
R indices (all data)
0.0578, 0.1499
0.0733, 0.1632
3.312, –1.907
3 Results and Discussion
Largest diff. peak and hole /e·Å–3
3.1 Description of the Crystal Structure of 1
Single-crystal X-ray structural analysis indicates that 1 con-
Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic tains four Hg2+, four Cl–, two PMP2– and one disordered DMF.
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First Organomercury Dimer Derived from PMP
The ORTEP view of 1 with atomic labeling scheme is shown [Hg1–Cl2 2.306(4) Å and Hg2–Cl1 2.310(4) Å] are in the
in Figure 1. Selected bond lengths and angles are given in range of previously reported values [2.037(16)–
Table 2. In 1, each C2 atom of the pyrazolone ring from one 2.816(3) Å].[5,19,30] The Hg–O bond lengths [Hg1–O1A
PMP is bonded to two mercury ions, and the two mercury ions 2.7932(1) and Hg2–O1A 2.9095(1) Å, A: –x+2,–y+1, –z+2] are
are coordinated to O1 atom from another PMP, thus forming a longer than the reported usual lengths, but much shorter than
rare organomercury(II) dimer, [Hg2(PMP)Cl2]2 (Figure 1). the sum of the van der Waals radii (3.5 Å),[5,19,31] suggesting
Furthermore, the bond lengths [C2–Hg1, 2.095(15) Å and that the coordination interaction between mercury and oxygen
C2–Hg2, 2.091(15) Å] are in the range of C–Hg covalent atom is relatively weak. The local coordination arrangement
bond,[3,5,19,20,22] indicating the carbon and mercury atoms are of HgII is T-shaped with bond angles of 170.0(5)° for C2–
bonded covalently in 1. To the best of our knowledge, this is Hg1–Cl2 and 176.1(5)° for C2–Hg2–Cl1. The slight deviation
the first crystallographically characterized organomercury of the above-mentioned C–Hg–Cl bond angles from the linear-
compound derived from PMP, and no study on two HgII at- ity may be due to the coordination interaction of oxygen with
tached to one carbon atom has been reported.[3,5,19,20,22] HgII. Furthermore, two Hg–O bonds and two Hg–C bonds can
Furthermore, the mercury–mercury separation is 3.2735(8) Å, form a quadrilateral (for instance C2–Hg1–O2A–Hg2), in
which is much shorter than the van der Waals distance for two which the dihedral angle between C–Hg–Hg and O–Hg–Hg is
mercury atoms (4.1 Å) and longer than the Hg–Hg single bond 31.72(114)°. Two such quadrilaterals are connected by the C1
length (2.64 Å),[5,20,21] confirming the presence of a weak and C1A atoms of pyrazole rings from two different PMP mo-
Hg···Hg interaction.
lecules, consequently constructing a unique polynuclear struc-
ture (Figure 1). As for the pyrazole ring, the coplanarity is not
perfect (mean deviation from planarity is 0.0214 Å), and the
dihedral angle between the pyrazole ring composed of
C1C2C3N1N2 and the triangle of C2Hg1Hg2 is 87.61(49)°,
nearly 90°; i.e. the two planes are almost perpendicular to each
other.
On the other hand, the bond lengths of C1–O1 and C11–O2
are 1.23(2) and 1.23(8) Å, close to the typical C=O double
bond of 1.210 Å.[32] The C3–N2 bond length [1.32(2) Å] be-
longs to C=N double bond (1.329 Å) in pyrazole,[32] whereas
the C11–N3 distance [1.36(9) Å] falls into the range of conju-
gated C=N bond length (1.34–1.38 Å). The above-mentioned
analyses of bond lengths indicate that the pyrazolone ring of
PMP is present in the keto form.
In 1, each ligand PMP bears two negative charges, because
the C2 atom forms two covalent bonds with C1 and C3. And
each C2 links to two Hg2+ ions, which are coordinated to one
Cl–, respectively. Consequently, the whole molecule is electro-
neutral.
Figure 1. ORTEP view of 1 with the atom labeling scheme. The ellip-
soids enclose 50% of the electronic density. Symmetry operator for
equivalent position: A = –x+2, –y+1, –z+2.
Secondary bonds play an important role in the construction
of mercury complexes or organomercury compounds.[19] Com-
pound 1 exhibits three types of weak secondary interactions
between the HgII and O atoms of DMF [intermolecular Hg1/
Hg2···O2 interactions; contact distance of 3.128(4)/3.048(4) Å]
or N of PMP [intermolecular Hg2···N2C interaction; contact
distance of 3.115(2) Å, C: x, 1+y, z] or Cl [intermolecular
Hg1D···Cl2/Cl1A interactions; contact distance of 3.307(4) /
3.314(4) Å, D: –1+x, y, z and A: 1–x, –y, 1–z, and intermo-
lecular Hg2···Cl2A interactions; contact distance of
3.754(5) Å]. The above-mentioned Hg···O/N/Cl distances are
close to the sum of the van der Waals radii of mercury (1.73–
2.05 Å) and oxygen (1.52 Å) or nitrogen (1.55 Å) or chlorine
(1.8 Å),[5,19,30] indicating that these secondary interactions in
1 are weak. Furthermore, there are two types of intermolecular
C–H···Cl hydrogen bonds in 1. Two hydrogen atoms of one
methyl group of PMP from one organomercury dimer are hy-
drogen-bonded to two chlorine atoms from two other organ-
Table 2. Selected bond lengths /Å and bond angles /° for 1.
Bond lengths
Hg(1)–C(2)
Hg(1)–Cl(2)
Hg(1)–Hg(2)
Hg(2)–C(2)
Hg(2)–Cl(1)
Hg(1)–O(2)
Hg(2)–O(2)
O(1)–C(1)
2.095(15)
2.064(4)
3.2735(8)
2.091(15)
2.310(4)
3.13(4)
O(2)–C(11)
O(2)–C(12)#1
N(2)–C(3)
N(3)–C(11)
N(3)–C(11)#1
C(1)–C(2)
1.23(8)
1.31(9)
1.32(2)
1.36(9)
1.36(9)
1.46(2)
1.41(2)
3.05(4)
1.23(2)
N(1)–N(2)
Bond angles
C(2)–Hg(1)–Cl(2)
Cl(2)–Hg(1)–O(2)
C(2)–Hg(2)–O(2)
170.0(5)
107.2(8)
82.5(9)
C(2)–Hg(1)–O(2)
C(2)–Hg(2)–Cl(1)
Cl(1)–Hg(2)–O(2)
80.4(9)
176.1(5)
98.9(8)
Cl(1)–Hg(2)–Hg(1) 139.44(12) O(2)–Hg(2)–Hg(1) 59.2(7)
Symmetry transformations used to generate equivalent atoms: #1: –x
+ 2, –y + 1, –z + 2.
In the structure of 1, each HgII is three-coordinate to one
carbon atom from one PMP, one oxygen atom from another omercury dimers; and one hydrogen atom of phenyl ring from
PMP and one terminal chlorine atom. The Hg–Cl bond lengths the same PMP is hydrogen-bonded to the Cl1#1 atom from the
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R.-B. Xu et al.
ARTICLE
dimer, in which Cl#1 and Cl#3 coexist. Detailed data for the
hydrogen bonds are given in Table 3. All the above-mentioned
weak secondary Hg···N/O/Cl interactions and the intermo-
lecular hydrogen bonds at the supramolecular level lead to a
three-dimensional network (Figure 2). The hydrogen bonds
and the Hg···N/O/Cl interactions in 1 are shown in Figure 3.
Table 3. Hydrogen bonding data /Å,° for 1.
D–H···A
d(D–H) d(H···A) d(D···A)
(DHA)
C(6)–H(6)···Cl(1)#1
C(4)–H(4A···Cl(2)#2 0.96
C(4)–H(4C)···Cl(1)#3 0.96
0.93
2.80
2.87
2.83
3.62(2)
3.693(17)
3.744(18)
147.6
144.9
158.8
Symmetry transformations used to generate equivalent atoms: #1: –x
+ 2, –y + 1, –z + 1; #2: x, y + 1, z; #3: x–1, y, z;
Figure 3. Intermolecular hydrogen bonds and the weak secondary
Hg···N/O/Cl interactions of 1. The hydrogen atoms not involved in
hydrogen bonds are omitted for clarity.
3.3 Thermal Investigations
The thermal stability of 1 powder was studied by thermo-
gravimetric (TG) analysis from 25–900 °C. The TG curve
(Figure 4) showed two continuous weight loss steps during
heating. 1 is stable up to 149 °C, at which point it begins to
decompose. The weight loss of the first step in the range of
149–292 °C is 67.58%, attributed to lose two HgCl2 and two
ligands PMP absence of carbonyl oxygen atoms (calcd.
66.49%). In addition, the TG curves often clearly show indi-
vidual steps of weight loss resulted from loss of absorbed or
coordinated solvent molecules under 200 °C. In this case, such
a step can’t be found, indicating there is no DMF in 1 powder.
Upon further heating, the second weight loss occurs and almost
no residue remains over 659 °C.[35] The weight loss (31.03%)
at 292–900 °C can be assigned to loss of 2HgO (calcd.
33.51%).
Figure 2. Ball and polyhedral representation of the packing diagram
of 1 viewed along the z axis. The DMF molecules and hydrogen atoms
not involved in the hydrogen bonds are omitted for clarity.
3.2 IR Spectroscopy
On comparing the infrared spectrum of the free PMP ligand,
it is found that the strong band at 1599 cm–1 in PMP is split
into two strong bands at 1614 cm–1 and 1593 cm–1 in 1, which
may be caused by the coordination of the carbonyl group to
the mercury atom. Consequently, the band at 1614 cm–1 is as-
signed to the ν(C=O) vibration of the pyrazolone ring and the
strong bands at 1593 cm–1 and 1498 cm–1 to the ν(C=C) vi-
bration of the phenyl ring skeleton.[11,15,33] The absorption
band at 633 cm–1 is the characteristic IV peak of amide caused
by the bending vibration of O=C–N.[34] Furthermore, the broad
medium band at 1715 cm–1 is ascribed to the tertiary amide
ν(C=O) vibration of DMF.[34] The above assignments are in
accordance with the crystal structure of 1.
Figure 4. TG curve of 1.
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First Organomercury Dimer Derived from PMP
Table 4. Antibacterial activities of 1, PMP, and mercury salt.
Compounds
Concentration /mg·mL–1
Diameter of inhibition zone /mm
Escherichia coli
Staphylococcus aureus
Bacillus subtilis
HgCl2
10
5
1
0.1
10
5
23.55
17.35
13.55
9.10
15.21
13.18
11.43
11.00
15.35
14.10
12.23
11.68
7.82
26.65
23.85
18.94
10.85
16.13
14.75
13.32
11.25
17.80
17.65
15.26
11.71
7.82
25.95
24.25
19.55
10.50
15.35
14.83
11.57
11.13
18.13
17.58
14.12
13.51
7.81
PMP
1
1
0.1
10
5
1
0.1
DMF
3.4 Antibacterial Tests
is neutral, the electrostatic interaction between 1 and CT-DNA
is also ruled out. Consequently, it is suggested that 1, the or-
ganomercury dimer, binds to DNA in a groove-binding mode.
The results (Table 4) show that 1, free ligand PMP, and mer-
cury chloride exhibit strong antibacterial activities against
Staphylococcus aureus, Bacillus subtilis, and Escherichia coli,
indicating the broad-spectrum properties of the compounds
tested. Moreover, these compounds increase in activity with
concentration for all the test strains.
Mercury chloride shows the highest activity against all the
tested bacteria, when the concentration is greater than
0.1 mg·mL–1, whereas 1 exhibits slightly higher activity than
PMP. In general, compared to inorganic species, the corre-
sponding organometallic compounds have a higher solubility
in lipids, which makes it easier to diffuse through the lipidic
matrix of the cellular membrane and hence increase the toxic-
ity potential.[36,37] The fact that 1 with concentrations in the
range of 1–10 mg·mL–1 exhibits lower antibacterial activity
than the mercury salt may be a result of the high stability of
1. It is difficult for 1 to release toxic mercury ions because of
its high stability,[37–39] i.e. the existence of Hg–C covalent
bonds, Hg–O coordinate bonds, and intermolecular Hg···N/Cl/
O secondary interactions. In fact, the antibacterial activity of
any compound is a complex combination of steric, electronic,
and pharmacokinetic factors,[40] which makes it difficult to
predict biological activity.
Figure 5. Absorption spectra of CT-DNA in the absence and presence
of 1. [DNA] = 132 μmol·L–1, [1] = 0–140 μmol·L–1 from the top to
bottom. The arrow indicates the change in absorbance upon increasing
amounts of 1.
3.5.2 Viscosity Measurements
3.5 DNA Binding Experiments
To further explore the binding mode of 1 to CT-DNA, vis-
cosity measurements were carried out. Under appropriate con-
3.5.1 Absorption Spectroscopy
The application of electronic absorption spectroscopy in ditions, intercalation causes a significant increase in the vis-
DNA-binding studies is a useful technique.[41] The absorption cosity of DNA solutions due to an increase in the separation
spectra of CT-DNA in the presence and absence of 1 are given of the base pairs at the intercalation sites. An increase in the
in Figure 5. Upon addition of increasing amounts of 1 to the overall DNA contour length can be observed.[43] In contrast,
solution of CT-DNA, a slight red shift (ca. 3 nm) and decrease compounds that bind exclusively in DNA grooves, under the
in intensity of the absorption band (i.e. hypochromism is ca. same conditions, typically cause less pronounced change (posi-
6.3%) was observed, indicating weak binding of 1 to DNA. tive or negative) or no change in DNA solution viscosity.[43]
The changes of absorbance and wavelength may be ascribed The effect of 1 on the viscosity of DNA is depicted in Figure 6.
to the intercalative binding with DNA. However, the decrease With increasing amounts of 1, the relative viscosity of DNA
in the absorption intensity (hypochromism) is very much less increases very slowly. In other words, the addition of 1 to CT-
than that observed for an intercalator like ethidium bromide.[42] DNA does not lead to significant change in relative specific
Therefore, classical intercalation is ruled out for 1. Because 1 viscosity, which indicates that 1 binds CT-DNA by groove
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R.-B. Xu et al.
ARTICLE
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4 Conclusions
The organomercury dimer [Hg2(PMP)Cl2]2·DMF (1) was
synthesized and characterized by elemental analysis, IR spec-
troscopy, TG, and single-crystal X-ray diffraction analysis. The
DNA binding properties of 1 were investigated by absorption
spectroscopy and viscosity measurements. Experimental re-
sults indicate that 1 can bind to DNA by groove binding mode.
In addition, antibacterial tests showed that 1 features strong
and broad-spectrum antibacterial activities against tested bac-
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Received: April 17, 2013
Published Online: July 2, 2013
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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