Novel DNA binding agents: Hydrazone-based helical trinuclear Ag complexes

Article abstract of DOI:10.1002/jccs.200300027

Using the hydrazone linker and the self-assembly, functionalized Ag complexes with a helical structure showed a 2.96 A distance between metal-metal bonds, well-aligned aromatic rings, and the strong affinity toward DNA.

Full text of DOI:10.1002/jccs.200300027

Journal of the Chinese Chemical Society, 2003, 50, 189-192
189
Communication
Novel DNA Binding Agents: Hydrazone-based Helical Trinuclear Ag
Complexes
Chien-Chung Cheng* (
Chen-Shen Chang (
Department of Chemistry, Tamkang University, Taipei, Taiwan 251, R.O.C.
), Sue-Mei Hung (
), Chia-Yi Yeh (
),
) and Wen-Jwu Wang* (
)
Using the hydrazone linker and the self-assembly, functionalized Ag complexes with a helical structure
showed a 2.96 Å distance between metal-metal bonds, well-aligned aromatic rings, and the strong affinity to-
ward DNA.
Keywords: Helicate; Silver; DNA binding; Hydrazone; Bipyridine.
Metallo-supramolecules are getting more attention in
the development of nano-materials and biosciences.1 The
self-assembled metal complexes are found to be capable of
assisting the formation of metallic-nanoparticles2 in addition
to the array of metal-wires.3 As well, an inexpensive metallo-
supramolecular cylinder4 with a helical structure has been
demonstrated to bind DNA tightly on the major groove re-
gion. Accordingly, the property of coordination ligands of
these metallo-supramolecules is found to be an important fac-
tor in determining their molecular behaviors. In fact, a num-
ber of metallo-supramolecules have been prepared by using
poly-pyridine ligands and their analogs5 with metal ions to
form the helical structures in the last decade. Here, we re-
ported a novel type of hydrazone-based helical trinuclear Ag
complex. By way of the hydrazone linkers, the coordinated
ligands have been demonstrated to be prepared easily with
various functional groups. The corresponding Ag complex
displays a self-assembling helical structure with a shorter dis-
tance between Ag-Ag metal centers and the parallel aromatic
rings. In addition, these helical Ag complexes were found to
have a strong binding affinity toward DNA.
nated ligands with the Ag+ ion in CH3CN and/or CH2Cl2, fol-
lowed by the analysis with the SPECFIT program, the step-
wise formation constants of Ag complexes were obtained in
Fig. 2 suggesting the formation of multinuclear metal spe-
cies. Further, complex 2 was found to have a molecular
weight of approximately 1466.5 (M + 2CF3SO3) by the analy-
sis of FAB-mass spectroscopy. Therefore, the most likely
molecular formula of the multinuclear Ag complex is as-
3+
signed as Ag3L2
.
The X-ray crystal structure of complex 2 further sup-
ports the formation of Ag3L23+. The yellow needle crystal of
complex 2 was obtained by slowly diffusing ether into a
CH3CN solution of the Ag complex. The X-ray crystal struc-
ture displays the self-assembled helical structure containing
two sets of coordination ligands in association with three Ag+
ions in Fig. 1. These Ag ions have the four-coordination ge-
ometry with an average Ag-Ag bond distance of approxi-
mately 2.96 Å. The diameter of Ag3(L7)23+ complex is near
10 Å. The average distance between two parallel planar rings
indicated in Fig. 1 closes to 3.7-4.0 Å.
The DNA affinity of these trinuclear Ag complexes has
been examined in DNA melting temperature (Tm) studies.9
These hydrazone-based ligands are very insoluble in water
even in a DMSO solution. Once their corresponding Ag com-
plexes are formed, the solubility of metal complexes is solu-
ble in a 5% DMSO aqueous solution. Commercially available
sonicated calf thymus DNA (ct-DNA) was selected as the tar-
get DNA. The melting temperature of ct-DNA (100 mM) was
70 °C in 10 mM sodium phosphate buffer solution (pH 7.0).
Upon adding these complexes 1-3 (~ 0.3 mM) to a DNA solu-
tion, Tm was shifted to 77-78 °C that is 7-8 °C higher than Tm
These multi-dentate ligands, glyoxal bis (2,2¢-bipyr-
idyl-6-hydrazone) derivatives, are prepared sequentially by
selectively oxidizing and chlorinating bipyridine to give 6-
chloro-2,2¢-bipyridine6 as shown in Fig. 1. After substituted
by hydrazine,7 compound 5 was allowed to undergo Schiff-
base condensation with a proper dione to give target ligands
6-8, respectively. Their corresponding Ag complexes were
generally prepared by adding a CH3CN solution of AgClO4 or
AgCF3SO3 to a CH3CN suspension of ligands to yield a clear
yellow solution. Using the UV-Vis titration8 of the coordi-
* Corresponding author. Chien-Chung Cheng Fax: 886-2-26209924; e-mail: cccheng@mail.tku.edu.tw

190 J. Chin. Chem. Soc., Vol. 50, No. 2, 2003
Cheng et al.
of ct-DNA itself alone. Under similar conditions, ethidium
bromide (EtBr), a well-known DNA intercalator, needs the
concentration up to 1 mM to reach the same extent of tempera-
ture shifting, which is at least three times concentration of
that of helical Ag complexes. No precipitate was observed at
the high temperature. However, the absorption spectra of the
single-stranded DNA area in the melting temperature study
showed the lower absorption intensity at 260 nm compared to
that of ct-DNA itself. It suggests the occurrence of the stack-
ing effect between helical Ag complexes and nucleobases of
Fig. 1. Synthesis of hydrazone-based ligands and their corresponding Ag complexes. ORTEP of Ag3(L7)23+ (R = CH3).
Fig. 2. (Left) Spectrophotometric titration spectrum of L7 by Ag(I) salt in CH2Cl2/CH3CN (1:1). (Right) After the spectrum
analysis of the component by SPECFIT/32TM program, the stepwise stability constants (Log K) of Ag complex were
3+
obtained for individual steps in the assembly of Ag3L2
.

Novel DNA Binding Agents
J. Chin. Chem. Soc., Vol. 50, No. 2, 2003 191
single-stranded DNA. Furthermore, the binding constant of
complex 2 was estimated by the UV titration method with
ct-DNA10 giving a value of > 106 M at 10 mM sodium phos-
phate buffer (pH 7.0). It indicates that the helical Ag com-
plexes have a strong affinity toward DNA.
helical Ag complex solution rises at 415 nm along with an in-
creasing ct-DNA concentration (0-100 mM) at ambient tem-
perature in a freshly prepared CH3CN/water solution. Since
the nucleobase pairs regions of DNA are environmentally
more hydrophobic compared to other regions of DNA, the in-
teraction of fluorophores and nucleobases prevents the atten-
uation of the fluorescence intensity from the quenching reac-
tion by water. Thus, it suggests that the helical Ag complexes
bind to DNA in the hydrophobic environment. A similar en-
hancement was observed in the DNA binding with metallo-
intercalators12 such as Os(phen)2dppz2+.11 Intercalators are
known to be crucial for the biological system to provide much
stronger anchors and a slow dissociation rate toward DNA.13
Unlike other metallo-supramolecules, the hydrazone-based
Ag complexes show a good alignment of the parallel aro-
matic rings with a distance close to 3.7-4.0 Å which may have
interaction with DNA base-pairs.
One possibility for the strong DNA affinity is due to the
positive charge interaction with DNA. However, the melting
temperature of Ag2L22+ complexes containing two Ag+ ions is
higher than that of Ag3L23+ with three Ag+ ions. Under similar
concentration, the DNA melting reaction with LaCl3 with
3+
three positive charges did not give the same shift of Ag3L2
in DNA Tm study suggesting that charge-charge interaction
is not the only controlling factor for such DNA binding affin-
ity.
An alternative approach to examine DNA binding af-
finity of these helical Ag complexes is to use agarose gel
electrophoresis. As a result shown in Fig. 3, the reaction of
3+
helical Ag3L2 with supercoiled plasmid DNA gives the
Overall, by means of the hydrazone linker and the self-
assembly, various helical Ag complexes can be accomplished
with different functional groups and parallel aromatic rings.
The details of the DNA binding mode and their sequence
preference are under investigation. Therefore, the prepara-
tion of these helical Ag complexes provides an alternative
strategy in the design of functionalized metallo-supramole-
cules for the development of nanoparticles and metallo-
pharmaceuticals.
smear high-molecular-weight bands in agarose gel studies.
The reactivity of the helical Ag complexes in binding with
DNA is along the order of complexes 2 > 3 > 1. The methyl
groups in complex 2 may have the methyl-methyl interaction
with thymine nucleobase to increase the binding affinity.
When the concentration of the helical complexes 2 was in-
creased up to 30 mM, the Ag3L23+-DNA adducts were precipi-
tated out from the solution resulting in the diminishing of the
DNA intensity.
The study of the fluorescent emission intensity11,12 in
association with DNA reveals the possible binding mode of
these helical Ag complexes. When the excitation wavelength
is fixed at 330 nm, the fluorescence emission intensity of the
This work was supported by Tamkang University, Aca-
demia Sinica, and the National Science Council of Taiwan,
R.O.C.
Received December 4, 2002.
NOTES AND REFERENCES
Crystal data for complex 2, Ag3L2·3SO3CF3:
Ag3C51H44N16Cl2F9O9S3; Mr = 1686.71, crystal dimension 0.02
´ 0.08 ´ 0.04 mm3, triclinic, space group P1, a = 16.0093(8), b =
16.6374(8), c = 24.3136(12) Å, a = 80.72(10), b = 82.33(10), g
= 70.99(10)°, V = 6019.9(5) Å3, Z = 4, F(000) = 3352, rcalcd
=
1.861 g-cm-3, Rf = 0.1052, Rw = 0.2086, GOF = 1.093, 2.01 < q <
25.05o, T = 298 K, Moka (l = 0.71073 Å), 27835 measure of re-
flection, Siemens Smart CCD diffractometer. Refinement used
SHELXL-97 (G. M. Sheldrick, SHELXL-97, Program for the
Refinement of Crystal Structures, Gottingen, 1997).
Fig. 3. DNA binding assay of helical Ag complexes,
3+
Ag3L2 in the binding study of supercoiled
FX-174 DNA (36 mM per nucleotide) in 10 mM
sodium phosphate buffer (pH 7.1) for 10 min at
25 °C. Lane 1, DNA control; lanes 2 to 4,
Ag3(L8)23+; lanes 5-7, Ag3(L7)23+; lanes 8-10,
Ag3(L6)23+ (1-30 mM).
1. Albrecht, M. Chem. Rev. 2001, 101, 3457-3497; Kaes, C.;
Katz, A.; Hosseini, M. W. Chem. Rev. 2000, 100, 3553-3590;
Niemeyer, C. M. Angew. Chem. Int. Ed. 2001, 40, 4128-

192 J. Chin. Chem. Soc., Vol. 50, No. 2, 2003
Cheng et al.
4158; Lehn, J.-M. Supramolecular Chemistry, VCH,
Weinheim, 1995, 139-195.
D.; Fisher, J. Angew. Chem. Int. Ed. 1997, 36, 2509-2511;
Garrett, T. M.; Koert, U.; Lehn, J.-M. J. Phy. Org. Chem.
1992, 5, 529-532; Marquisrigault, A.; Dupontgervais, A.;
Baxter, P. N. W.; Dorsselaer, A. V.; Lehn, J.-M. Inorg.
Chem. 1996, 35, 2307-2310.
2. Shenton, W.; Davis, S. A.; Mann, S. Adv. Mater. 1999, 11,
449-52; Mann, S.; Shenton, W.; Li, M.; Connolly, S.;
Fitzmaurice, D. Adv. Mater. 2000, 12, 147-150; Mirkin, C.
A.; Lestinger, R. L.; Mucic, R. C.; Storhoff, J. J. Nature
1996, 382, 607; Alivisatos, A. P. Nature 1996, 382, 609.
3. Chou, M. Y.; Chan, M. C. W.; Peng, S. M.; Cheung, K. K.;
Che, C. M. Chem. Commun. 2000, 1259-1260; Wong, K. T.;
Lehn, J.-M.; Peng, S. M.; Lee, G. H. Chem. Commun. 2000,
2259-2260.
4. Hannon, M. J.; Moreno, V.; Prieto, M. J.; Moldrheim, E.;
Sletten, E.; Meistermann, I.; Isaac, C. J.; Sanders, K. J.;
Rodger, A. Angew. Chem. Int. Ed. 2001, 40, 880-884;
Hannon, M. J.; Painting, C. L.; Jackson, A.; Hamblin, J.;
Errington, W. Chem. Commun. 1997, 1807-8.
5. Fujita, M. Self-assembled Macrocycles, Cages, and Cate-
nanes Containing Transition Metals in their Backbones;
Sauvage, J.-P.; Hosseini, M. W. Eds. Comprehensive Supra-
molecular Chemistry; Pergamon, 1996, 9, 253-282; Atwood,
J. L.; Davies, J. E. D.; MacNicol, D. D.; Vogtle, F. Compre-
hensive Supramolecular Chemistry; Elsevier: Oxford, 1996.
6. Chang, T. H.; Ong, C. W.; Chou, Y. M.; Chuang, K.-S.;
Wang, W. J. J. Chin. Chem. Soc. 1996, 43, 73-75.
9. Cory, M.; McKee, D. D.; Kagan, J.; Henry, D. W.; Miller, J.
A. J. Am. Chem. Soc. 1985, 107, 2528-2536; Waring, M. J.
J. Mol. Boil. 1965, 13, 269-282; Kelly, J. M.; Tossi, A. B.;
McConnell, D. J.; OhUigin, C. Nucleic Acids Res. 1985, 13,
6017-6034.
10. Smith, S. R.; Neyhart, G. A.; Kalsbeck, W. A.; Thorp, H. H.
New J. Chem. 1994, 18, 397-406.
11. Holmlin, R. E.; Barton, J. K. Inorg. Chem. 1995, 34, 7-8;
Aroinaguiri, S.; Maiya, B. G. Inorg. Chem. 1999, 38, 842-
843.
12. Johnson, D. S.; Boger, D. L. DNA Binding Agents;
Murakami, Y., Ed., Comprehensive Supramolecular Chem-
istry; Pergamon, 1996, 4, 73-160.
13. Foye, W. O. Cancer Chemotherapeutic Agents; ACS: Wash-
ington, D. C. 1995; Propst, C. L.; Perun, T. L. Eds. Nucleic
Acid Targeted Drug Design; Marcel Dekker: New York,
1992; Neidle, S.; Waring, M. Eds. Molecular Aspects of
Anticancer Drug-DNAIinteraction; CRC press Inc., Boca
Raton, 1993; Barton, J. K. Metal-nucleic Acid Interactions;
Bertini, I.; Gray, H. B.; Lippard, S. J.; Valentine, J. S. Eds.,
Bioinorganic Chemistry; University Science Books: Mill
Valley, 1994, 455-504.
7. Zoltewicz, J. A.; Cruskie, M. P.; Dill, Jr., C. D. Tetrahedron
1996, 52, 4239-4244.
8. Ziessel, R.; Arriman, A.; Suffert, J.; Youinou, M. T.; Cian, A.