Synthesis, characterization and DNA-binding properties of the Cu(II) complex with 7-methoxychromone-3-carbaldehyde-benzoylhydrazone

Article abstract of DOI:10.1248/cpb.57.69

A new chromone derivative (7-methoxychromone-3-carbaldehyde- benzoylhydrazone) ligand (HL) and its novel Cu(II) complex have been synthesized and characterized on the basis of elemental analyses, molar conductivities, proton nuclear magnetic resonance, in

Full text of DOI:10.1248/cpb.57.69

January 2009
Notes
Chem. Pharm. Bull. 57(1) 69—73 (2009)
69
Synthesis, Characterization and DNA-Binding Properties of the Cu(II)
Complex with 7-Methoxychromone-3-carbaldehyde-benzoylhydrazone
Gao-Fei QI, Zheng-Yin YANG,* and Dong-Dong QIN
College of Chemistry and Chemical Engineering and State Key Laboratory of Applied Organic Chemistry, Lanzhou
University; Lanzhou 730000, P. R. China.
Received May 27, 2008; accepted October 18, 2008; published online October 22, 2008
A new chromone derivative (7-methoxychromone-3-carbaldehyde-benzoylhydrazone) ligand (HL) and its
novel Cu(II) complex have been synthesized and characterized on the basis of elemental analyses, molar conduc-
tivities, proton nuclear magnetic resonance, infrared spectra and mass spectra analyses. The general formula of
the Cu(II) complex is [CuL(HB2BO)]Cl·2H2O. In addition, the interaction of the Cu(II) complex and its free lig-
and with calf-thymus DNA was investigated by electronic absorption spectroscopy, fluorescence spectroscopy and
viscosity measurement. Results suggest that both the two compounds can bind with calf-thymus DNA via an in-
tercalation mechanism. Furthermore, the Cu(II) complex can bind to DNA more strongly than the free ligand
due to the chelating effect of copper(II) ion to the free ligand.
Key words Cu(II) complex; chromone; interaction; calf thymus DNA; intercalation mechanism
The chromone moiety forms the important component of gated using a host of physical methods like spectrometric
pharmacophores of a number of biologically active mole- titrations, ethidium bromide displacement experiments and
cules of synthetic as well as natural origin and many of them viscosity measurements.
display a remarkable array of biological and pharmacologi-
Experimental
cal activities as antimicrobial, anticancer and pesticidal
Instrumentation Melting points were determined on a Beijing XT4-
100X microscopic melting point apparatus. Elemental analyses (C, H, N)
agents.1,2) Consequently, chromone chemistry continues to
were carried out on an Elemental Vario EL analyzer. The metal contents of
the complexes were determined by titration with EDTA (xylenol orange
tetrasodium salt used as an indicator and hexamethylidynetetraimine as
buffer). IR spectra were obtained in KBr discs on a Therrno Mattson FT-IR
spectrophotometer in the 4000—400 cmꢀ1 region. 1H-NMR spectra were
recorded on a 200 MHz on a Bruker DRX-200 spectrometer in DMSO-d6
(dimethyl sulfoxide) with TMS (tetramethyl silane) as internal standard.
Conductivity measurements were performed in DMF with a DDS-11A con-
ductometer at 25 °C. Electrospray ionization time-of-flight (ESI-TOF) mass
spectra were obtained on a Mariner ESI-TOF mass spectrometer. UV–visible
spectra were recorded on a Shimadzu UV-240 spectrophotometer. The fluo-
rescence spectra were recorded on a Hitachi RF-4500 spectrofluorophotome-
ter.
draw considerable interest of synthetic organic and medicinal
chemists.3—7) Recently, 3-formylchromone emerged as a
valuable synthon for incorporation of the chromone moiety
into a number of molecular frameworks has aroused our in-
terest. In previous work from our laboratory, we have pre-
sented a detailed investigation of the interactions of 6-substi-
tuted chromone-3-carbaldehyde hydrazone Ln(III) com-
plexes8,9) with calf-thymus DNA (CT-DNA) arised from the
fact that a great many hydrazones and their complexes have
diverse spectra of biological and pharmaceutical activities,
such as anticancer and antioxidative activities.10—12) How-
ever, up to now, the interactions with DNA of 7-substituted
chromone-3-carbaldehyde hydrazone and their complexes
have not been explored due to the difficulties in synthesis of
Materials and Methods CT-DNA and ethidium bromide (EB) were
purchased from Sigma Chemical Co. Saint Louis, MO (U.S.A.). EDTA and
CuCl2·2H2O were produced in China. All chemicals used were of analytical
grade. All the experiments involving the interaction of the complexes with
7-substituted chromone-3-carbaldehyde. In our first trials, we CT-DNA were carried out in doubly distilled water buffer containing 5 mM
Tris [tris(hydroxymethyl)aminomethane] and 50 mM NaCl and adjusted to
pH 7.1 with HCl. The solution of CT-DNA in the buffer gave a ratio of UV
absorbance of about 1.8—1.9 : 1 at 260 and 280 nm, indicating that the CT-
tried to yield the 7-substituted chromone-3-carbaldehyde
starting with 4-methoxy-2-hydroxyacetophenone and N,N-di-
methylformamide (DMF)-POCl3 according to the litera-
ture,13) but get a very low yield (5%). This result has also
been reported by the other literature.14) Later, difluorodioxa-
borin 1 (Fig. 1) overcome the low yield.15) Then, we intended
to continue the earlier studies of the chromone structure
and investigated the binding behaviors of 7-substituted
chromone-3-carbaldehyde hydrazone and its complexes with
CT-DNA. Considering that copper has an important biologi-
cal role in all living organisms as an essential trace element
and the copper(II) complexes have been used as probes of
DNA structure in solution.16,17) We mainly choose a new
chromone derivative (7-methoxychromone-3-carbaldehyde-
benzoylhydrazone) ligand (HL) and its a novel Cu(II) com-
plex in this paper as our object of research and investigated
the coordination of the chromone derivative ligand to cop-
per(II) and their DNA-binding properties. The interaction of
the two compounds with CT-DNA in our studies was investi-
DNA was sufficiently free of protein.18) The CT-DNA concentration per nu-
cleotide was determined spectrophotometrically by employing an extinction
coefficient of 6600 Mꢀ1 cmꢀ1 at 260 nm.19) The compounds were dissolved in
a mixture solvent of 1% CH3OH and 99% Tris–HCl buffer (5 mM Tris–HCl,
50 mM NaCl, pH 7.1) at the concentration 1.0ꢁ10ꢀ5 M. Absorption titration
experiments were performed with fixed concentrations drugs (10 mM) while
gradually increasing the concentration of CT-DNA. While measuring the ab-
sorption spectra, an equal amount of CT-DNA was added to both the com-
pounds solution and the reference solution to eliminate the absorbance of
CT-DNA itself. Viscosity experiments were conducted on an Ubbelodhe vis-
cometer, immersed in a thermostated water-bath maintained to 25 °C. Titra-
tions were performed for the Cu(II) complex and the ligand (0.5—3 mM),
and each compound was introduced into a CT-DNA solution (5 mM) present
in the viscometer. Data were presented as (h/h0)1/3 versus the ratio of the
concentration of the compound and CT-DNA, where h is the viscosity of
CT-DNA in the presence of the compound and h0 is the viscosity of CT-
DNA alone. Viscosity values were calculated from the observed flow time of
CT-DNA containing solution corrected from the flow time of buffer alone
(t0), hꢂtꢀt0.20,21)
To compare the binding affinity of the two compounds bound to DNA,
∗ To whom correspondence should be addressed. e-mail: yangzy@lzu.edu.cn
© 2009 Pharmaceutical Society of Japan

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Vol. 57, No. 1
Fig. 1. Scheme of the Synthesis of the Ligand (HL)
fluorescence titration method was used. Fixed amounts of compound were
titrated with increasing amounts of DNA, over a range of DNA concentra-
tions from 2.5 to 22.5 mM. An excitation wavelength of 353 nm was used.
Further support for the Cu(II) complex and the ligand binding to DNA via
intercalation is given through the emission quenching experiment. EB is a
common fluorescent probe for DNA structure and has been employed in ex-
aminations of the mode and process of metal complex binding to DNA.22)
A
2 ml solution of 10 mM DNA and 0.8 mM EB (at saturating binding levels)
was titrated by 10—100 mM the Cu(II) complex and ligand (lexꢂ525 nm,
Fig. 2. The Suggested Structure of the Complex
l
emꢂ520.0—650.0 nm). According to the classical Stern–Volmer equa-
tion23)
:
plex in Solution The stability of Cu(II) complex in an
aqueous solution has been studied by observing the UV–vis
spectra and estimating the molar conductivities at different
F0/FꢂKq[Q]ꢃ1
where F0 is the emission intensity in the absence of quencher, F is the emis-
sion intensity in the presence of quencher, Kq is the quenching constant, and time intervals for any possible change. The tested Cu(II)
[Q] is the quencher concentration. The shape of Stern–Volmer plots can be
used to characterize the quenching as being predominantly dynamic or
static. Plots of F0/F versus [Q] appear to be linear and Kq depends on tem-
perature.
complex was prepared in methanol and for experiments
freshly diluted in phosphate buffer system (at pH 7.4, 7.8).
Then, the UV–vis spectra and molar conductivities were re-
searched at different time intervals. The investigations re-
vealed that the UV–vis spectra have remained unaltered for
the solutions and its molar conductance values have no obvi-
ous change for very freshly prepared and for over the whole
experiment (12 h). It indicates that the Cu(II) complex is
quite stable in solution. The molar conductivity of the Cu(II)
complex is 71—71.5 (S cm2 molꢀ1) in DMF, showing that it
is 1 : 1 electrolytes.24)
IR Spectra The main stretching frequencies of the IR
spectra of the ligand and its Cu(II) complex are presented
in the experimental section. The n(CꢂO) of carbonyl band
of the ligand appears at 1670 cmꢀ1, while it becomes at
1646 cmꢀ1 in its Cu(II) complex, which makes a shift to-
wards lower frequency by 24 cmꢀ1. It shows that the carbonyl
oxygen of the free ligand takes part in the coordination. The
Preparations of the Free Ligand and Its Metal Complex. Synthesis of
the Ligand The compounds of 1 and 2 (Fig. 1) were prepared according to
the literature.15) Synthesis of the ligand HL was in accordance with the fol-
lowing method: an ethanol solution (20 ml) containing benzoyl hydrazine
(1.36 g, 10 mmol) was added dropwise to the compound 2 (2.04 g, 10 mmol)
of chloroform solution (10 ml) with stirring. After 10 min, a large amount of
light yellow precipitate appeared. Then continuing stirring for 6 h at room
temperature, the light yellow precipitate solid was collected by filtration and
washed with ethanol three times. Recrystallization from anhydrous ethanol
to give the ligand HL, which was dried in vacuo. Yield, 88%. mp 176—
178 °C. 1H-NMR (DMSO-d6, ppm) d: 11.91 (1H, s, NH), 8.75 (1H, s,
CHꢂN), 8.60 (1H, s, 2-H), 8.02 (1H, d, Jꢂ8.9 Hz, H-5), 7.09—7.14 (1H,
dd, Jꢂ2.4, 8.9 Hz, H-6), 7.21 (1H, d, Jꢂ2.4 Hz, 8-H), 7.90—7.93 (2H, d,
ph-H(1ꢄ 5ꢄ)), 7.48—7.59 (3H, m ph-H(2ꢄ 3ꢄ 4ꢄ)), 3.91 (3H, s, CH3). IR nmax
(cmꢀ1) 1670 (CꢂO of carbonyl), 1639 (CHꢂN), 1621 (CꢂO of hydra-
zonic).
Synthesis of the Cu(II) Complex The ligand (1 mmol, 0.32 g) was dis-
solved in chloroform (10 ml) and a solution of CuCl2·2H2O (1 mmol, 0.17 g)
in anhydrous ethanol (10 ml) was then added dropwise with stirring. Then Cu(II) complex exhibits band of the n(OH) vibration at
3405 cmꢀ1 which demonstrates that there is crystal water
the mixture solution was refluxed on an oil-bath at 80 °C for 4 h with stir-
ring. After cooling to room temperature, a large amount of green precipitate
appeared. It was separated from the solution by suction filtration, purified
by washing several times with ethanol, and dried for 24 h in vacuo.
in the complex.25) The band at 1639 cmꢀ1 assigned to the
n(CHꢂN) stretch for the free ligand was shifted to 1622
cmꢀ1 for its Cu(II) complex, indicating that the ligand coor-
[CuL(H2O)]Cl·2H2O. Yield: 81%. Analysis: Found (calculated) (%) for
dinate to metal ions via the azomethine nitrogen.26) The
C18H19N2O7ClCu (%): C, 45.58 (45.58); H, 3.56 (4.04); N, 5.79 (5.91); Cu,
13.45 (13.39). IR nmax (cmꢀ1) 3405 (OH of H2O), 1646 (CꢂO of carbonyl),
n(CꢂO) of hydrazonic band appears at 1621 cmꢀ1 in the free
1622 (CHꢂN). Lm (S cm2 molꢀ1): 71.
ligand, while the band disapears in its Cu(II) complex. This
change indicates that the n(CꢂO) of hydrazonic band may
lose its original characteristic and form coordinative bond by
Results and Discussion
Characterization of the Compounds. Properties of the an enolic format with metal. This point has been further con-
Compounds and Structure of the Cu(II) Complex The firmed followed by mass spectrometry.
ligand is soluble in chloroform, methanol and ethanol, while
ESI-TOF Mass Spectra of the Cu(II) Complex In
the Cu(II) complex is soluble in methanol, slightly soluble in order to further define the structure of Cu(II) complex, ESI-
ethanol. The two compounds are soluble in DMF; DMSO; TOF mass spectrometry has been taken. ESI-TOF mass spec-
insoluble in water; benzene and diethyl ether. But they are air tra demonstrates clearly the existence of molecular ion peak,
stable for extended periods. Since the crystal structure of the and the m/z of 402.8 can be assigned to fragment of
Cu(II) complex has not been obtained yet, we characterized [CuL(H2O)]ꢃ. This has further proved that infrared analysis
the complex and determined its possible structure by elemen- and been in accordance with the other means of characteriza-
tal analyses, molar conductivities, IR and mass (ESI-TOF) tion.
date. The likely structure of the Cu(II) complex is shown in
Fig. 2.
DNA-Binding Mode and Affinity. Electronic Absorp-
tion Titration Electronic absorption spectroscopy is an ef-
Stability and Molar Conductivity of the Cu(II) Com- fective method to examine the binding mode of DNA with

January 2009
71
metal complex.22,27,28) If the binding mode is intercalation, tected more efficiently than the ligand. This implies that both
the p* orbital of the intercalated ligand can couple with the p the compounds can be inserted between DNA base pairs and
orbital of the base pairs, thus, decreasing the p→p* transi- that the Cu(II) complex can bind to DNA more strongly than
tion energy and resulting in the bathochromism. On the other the ligand. In order to further illustrate this point clearly,
hand, the coupling p orbital is partially filled by electrons, changes in emission intensities for the ligand and the Cu(II)
thus, decreasing the transition probabilities and concomi- complex have been plotted against the added DNA concen-
tantly resulting in hypochromism.29) Figure 3 shows the ab- tration per mole compounds at about 433 nm in Fig. 5.
sorption spectra variations of the ligand and its Cu(II) com-
Steady-state emission quenching experiments are also
plex in the absence and presence of the CT-DNA (at a con- used to observe the binding mode of the compounds to DNA.
stant concentration of the compounds). The electronic spec- It is well known that EB can intercalate nonspecifically into
tra of ligand has a hypochromism band at 287 nm and an iso- DNA, which causes it to fluoresce strongly. Competitive
bathic point at 332 nm or so, while the Cu(II) complex ex- binding of other drugs to DNA and EB will result in dis-
hibits hypochromism band at 310 nm and 340 nm or so.
placement of bound EB and a decrease in the fluorescence
Fluorescence Spectra The ligand and its Cu(II) com- intensity. This fluorescence-based competition technique can
plex can emit weak luminescence in Tris-buffer with a max provide indirect evidence for the DNA-binding mode. Figure
wavelength of about 433 nm. The results of the emission 6 shows the emission spectra of the DNA–EB system with
titrations for the two compounds with DNA are illustrated in increasing amounts of the ligand and the Cu(II) complex.
the titration curves (Fig. 4). Upon addition of DNA, the The emission intensity of the DNA–EB system decreases as
emission intensities at about 433 nm of the two compounds the concentration of the two compounds increases, which
grow to around 1.52 and 1.54 times larger, respectively, than indicates that two compounds could displace EB from the
those in the absence of DNA. The results of the emission DNA–EB system. The resulting decrease in fluorescence is
titrations suggest that both the compounds are protected from caused by EB changing from a hydrophobic environment to
solvent water molecules by the hydrophobic environment in- an aqueous environment.30) The quenching plots illustrate
side the DNA helix, and that the Cu(II) complex can be pro- that the quenching of EB bound to DNA by the compounds
are in good agreement with the linear Stern–Volmer equa-
tion. The plots of F0/F versus [Q], Kq is given by the ratio of
the slope to the intercept. The Kq values for the ligand and its
Cu(II) complex are 1.92ꢁ104 and 3.05ꢁ104 Mꢀ1, respec-
tively. The data show that the interaction of the Cu(II) com-
plex with DNA is stronger than that of the ligand, which is
consistent with the above fluorescence spectra.
Viscosity Measurements As optical photophysical
probes generally provide necessary, but not sufficient, clues
to further clarify the interactions between the study complex
and DNA, viscosity measurements were carried out. Hydro-
dynamic measurements that are sensitive to length change
(i.e. viscosity and sedimentation) are regarded as the least
ambiguous and the most critical tests of binding in solution
Fig. 3. (a) Electronic Spectra of the Ligand (10 mM) in the Presence of In-
creasing Amounts of CT-DNA
[CT-DNA]ꢂ0—40 mM. Arrow shows the absorbance changes upon increasing CT- in absence of crystallographic structural data. A classical in-
DNA concentration.
tercalation model demands that the DNA helix lengthen as
(b) Electronic Spectra of the Cu(II) Complex (10 mM) in the Presence of In-
base pairs are separated to accommodate the binding ligand,
creasing Amounts of CT-DNA
leading to an increase in DNA viscosity. In contrast, a partial,
[CT-DNA]ꢂ0—40 mM. Arrow shows the absorbance changes upon increasing CT-
DNA concentration.
non-classical intercalation of compound could bend (or kink)
the DNA helix, reducing its effective length and, concomi-
tantly, its viscosity.21,31) Viscosity experimental results clearly
show that both the compounds can intercalate between adja-
cent DNA base pairs, causing an extension in the helix, and
Fig. 4. (a) The Emission Enhancement Spectra of the Ligand (10 mM) in
the Presence of 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5 mM CT-DNA
Arrow shows the emission intensity changes upon increasing DNA concentration.
(b) The Emission Enhancement Spectra of the Cu(II) Complex (10 mM) in
the Presence of 0, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5 mM CT-DNA
Fig. 5. Changes in Emission Intensities (at About 433 nm) for the Ligand
(10 mM) and its Cu(II) Complex (10 mM) in the Presence of Calf Thymus
DNA (0—22.5 mM) in Buffer Solutions
Arrow shows the emission intensities upon increasing DNA concentration.

72
Vol. 57, No. 1
Fig. 6. (a) The Emission Spectra of DNA-EB System (10 mM, 0.8 mM EB), lexꢂ525 nm, lemꢂ520—650 nm, in the Presence of 5, 10, 15, 20, 25, 30, 35,
40, 45 and 50 mM Ligand
ꢀ1
Arrow shows the emission intensity changes upon increasing ligand concentration. Inset: Stern–Volmer plot of the fluorescence titration data of ligand, Kqꢂ1.92ꢁ104
M
.
(b) The Emission Spectra of DNA–EB System (10 mM, 0.8 mM EB), lexꢂ525 nm, lemꢂ520—650 nm, in the Presence of 5, 10, 15, 20, 25, 30, 35, 40, 45 and
50 mM Cu(II) Complex
Arrow shows the emission intensity changes upon increasing Cu(II) complex concentration. Inset: Stern–Volmer plot of the fluorescence titration data of Cu (II) complex,
ꢀ1
Kqꢂ3.05ꢁ104
M
.
the free ligand.32) The information obtained from the present
work would ultimately be helpful to the understanding of the
mechanism of metal complexes with nucleic acids, and use-
ful in the development of potential probes of DNA structure
and conformation.
Acknowledgments This work is supported by the National Natural Sci-
ence Foundation of China (20475023) and Gansu NSF (0710RJZA012).
References
1) Wiley P. F., J. Am. Chem. Soc., 74, 4326—4329 (1952).
2) Koo J., J. Org. Chem., 26, 635—636 (1961).
3) Drewe J. A., Groundwater P. W., J. Chem. Soc., Perkin Trans. 1, 1997,
601—605 (1997).
4) Tanaka H., Stohlmeyer M. M., Wandless T. J., Taylor L. P., Tetrahe-
dron Lett., 41, 9735—9739 (2000).
Fig. 7. Effect of Increasing Amounts of the Ligand and the Cu(II) Com-
plex on the Relative Viscosity of CT-DNA at 25 °C
5) Bandyopadhayay C., Sur K. R., Patra R., Sen A., Tetrahedron, 56,
3583—3587 (2000).
6) Majumdar K. C., Bhattacharya T., Tetrahedron Lett., 42, 4231—4233
(2001).
7) Wang Y., Tan W., Li W. Z., Li Y., J. Nat. Prod., 64, 196—199 (2001).
8) Wang B. D., Yang Z. Y., Li T. R., Bioorg. Med. Chem., 14, 6012—
6021 (2006).
thus increase the viscosity of DNA. The effects of both com-
pounds on the viscosity of DNA are shown in Fig. 7.
Conclusion
Taken together, a new chromone derivative (7-methoxy-
chromone-3-carbaldehyde-benzoylhydrazone) ligand and its
novel Cu(II) complex have been prepared and characterized.
DNA-binding studies indicate that the Cu(II) complex and its
free ligand can interact with calf-thymus DNA by intercala-
tion mechanism. Furthermore, various comparative experi-
9) Wang B. D., Yang Z. Y., Crewdson P., Wang D. Q., J. Inorg. Biochem.,
101, 1492— 1504 (2007).
10) Wang L., Zhu Y., Yang Z., Wu J., Wang Q., Polyhedron, 10, 2477—
2481 (1991).
11) Yu S., Wang S., Luo Q., Wang L., Peng Z., Gao X., Polyhedron, 12,
1093—1096 (1993).
12) Padhye S., Kauffman G. B., Coord. Chem. Rev., 63, 127—160 (1985).
ments show that the Cu(II) complex can bind to DNA more 13) Nohara A., Umetani T., Sanno Y., Tetrahedron Lett., 22, 1995—1998
(1973).
strongly than the free ligand, which attribute to chelating ef-
fect of the copper(II) ion to the free ligand. Chelating effect
(metal ion to free ligand) can enhance the planar functional-
14) Nohara A., Umetani T., Sanno Y., Tetrahedron, 30, 3553—3561
(1974).
15) Hogberg T., Vora M., Drake S., Mitscher L. A., Chu D. T. W., Acta
ity of metal complex, so the complex can insert and stack be-
tween the base pairs of double helical DNA more easily than
Chem. Scand., B38, 359—366 (1984).
16) Barton J. K., Science, 223, 727—734 (1986).

January 2009
73
17) Hudson B. P., Barton J. K., J. Am. Chem. Soc., 120, 6877—6888
26) Narang K. K., Singh V. P., Transition Met. Chem., 18, 287—290
(1993).
(1998).
18) Satyanarayana S., Dabrowiak J. C., Chaires J. B., Biochemistry, 31,
27) Kelly J. M., Tossi A. B., McConnell D. J., OhUigin C., Nucleic Acids
Res., 13, 6017—6034 (1985).
9319—9324 (1992).
19) Kumar C. V., Asuncion E. H., J. Am. Chem. Soc., 115, 8547—8553 28) Tysoe S. A., Morgan R. J., Baker A. D., Strekas T. C., J. Phys. Chem.,
(1993). 97, 1707—1711 (1993).
20) Eriksson M., Leijon M., Hiort C., Norden B., Gradsland A., Biochem- 29) Pyle A. M., Rehmann J. P., Meshoyrer R., Kumar C. V., Turro N. J.,
istry, 33, 5031—5040 (1994). Barton J. K., J. Am. Chem. Soc., 111, 3051—3058 (1989).
21) Xiong Y., He X. F., Zou X. H., Wu J. Z., Chen X. M., Ji L. N., Li R. 30) Zeng Y. B., Yang N., Liu W. S., J. Inorg. Biochem., 97, 258—264
H., Zhou J. Y., Yu K. B., Dalton Trans., 1, 19—24 (1999). (2003).
22) Barton J. K., Danishefsky A., Golderg J., J. Am. Chem. Soc., 106, 31) Satyanarayana S., Dabrowiak J. C., Chaires J. B., Biochemistry, 32,
2172—2176 (1984).
2573—2584 (1993).
23) Efink M. R., Ghiron C. A., Anal. Biochem., 114, 199—227 (1981).
24) Geary W. J., Coord. Chem. Rev., 7, 81—122 (1971).
25) Wang Y., Yang Z. Y., Transition Met. Chem., 30, 902—906 (2005).
32) Xu H., Zheng K. C., Lin L. J., Li H., Gao Y., Ji L. N., J. Inorg.
Biochem., 98, 87—97 (2004).