Utilizing Experiment and Theory to Evaluate Rhodamine B ethylenediamine as a Fluorescent Sensor for G-type Nerve Agents.

Nerve gas mimic binding with Rhodamine B ethylenediamine (1) was studied in organic media. Binding of the nerve gas mimic, diethyl chlorophosphate (DCP), with the probe generated a non-fluorescent intermediate and a fluorescent product. Fluorescent and non-fluorescent products generated were identified using mass spectrometry and X-ray crystallography. Time-dependent density functional theory calculations were also used to investigate the electronic structure of the fluorescent probe in the ground and lowest lying π → π* singlet excited state. Though good agreement between theory and experiment can be obtained for the intense peak in the experimental spectrum using non-hybrid functionals, care must be taken when modelling these complexes due to the appearance of an n → π* transition that is too low in energy and appears to fall in the shoulders of the π → π* transitions.

Probing CO Generation through Metal-Assisted Alcohol Dehydrogenation in Metal-2-(arylazo)phenol Complexes Using Isotopic Labeling (Metal = Ru, Ir): Synthesis, Characterization, and Cytotoxicity Studies.

The reaction of 2-{2-(benzo[1,3]dioxol-5-yl)- diazo}-4-methylphenol (HL) with [Ru(PPh3)3Cl2] in ethanol resulted in the carbonylated ruthenium complex [RuL(PPh3)2(CO)] (1), wherein metal-assisted decarbonylation via in situ ethanol dehydrogenation is observed. When the reaction was performed in acetonitrile, however, the complex [RuL(PPh3)2(CH3CN)] (2) was obtained as the main product, probably by trapping of a common intermediate through coordination of CH3CN to the Ru(II) center. The analogous reaction of HL with [Ir(PPh3)3Cl] in ethanol did not result in ethanol decarbonylation and instead gave the organoiridium hydride complex [IrL(PPh3)2(H)] (3). Unambiguous evidence for the generation of CO via ruthenium-assisted ethanol oxidation is provided by the synthesis of the 13C-labeled complex, [Ru(PPh3)2L(13CO)] (1A) using isotopically labeled ethanol, CH313CH2OH. To summarize all the evidence, a ruthenium-assisted mechanistic pathway for the decarbonylation and generation of alkane via alcohol dehydrogenation is proposed. In addition, the in vitro antiproliferative activity of complexes 1-3 was tested against human cervical (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines. Complexes 1-3 showed impressive cytotoxicity against both HeLa (half-maximal inhibitory concentration (IC50) value of 3.84-4.22 µM) and HT-29 cancer cells (IC50 values between 3.3 and 4.5 µM). Moreover, the complexes were comparatively less toxic to noncancerous NIH-3T3 cells.

Rhodamine Based Turn-On Sensors for Ni(2+) and Cr(3+) in Organic Media: Detecting CN(-) via the Metal Displacement Approach.

Two novel sensors bearing rhodamine B and quinoline units have been synthesized. One of these, 1, allows sensitive and selective detection of Ni(2+) and Cr(3+) by forming non-fluorescent (1-Ni(2+)) and fluorescent (1-Cr(3+)) complexes respectively. Both metals trigger the formation of highly colored ring-open spirolactam. These form excellent probes for CN(-) which quenches the fluorescence of the 1-Cr(3+) complex by extracting the Cr(3+). Both Cr(3+) and Cu(2+) gave color changes with 2, but they are easily identified separately via the large fluorescence enhancement that occurs only with Cr(3+).

Synthesis and characterization of pyruvate-isoniazid analogs and their copper complexes as potential ICL inhibitors.

Currently used anti-tubercular drugs target actively growing Mycobacterium tuberculosis (Mtb) but there are no current therapies targeting persistent mycobacteria. Isocitrate lyase (ICL) is an important enzyme of the glyoxylate shunt pathway used by Mtb for sustaining intracellular infection in inflammatory macrophages under conditions of stress such as nutrient depletion and anaerobic metabolism. Since the humans do not possess this enzyme it constitutes an attractive target for selective drug design. Present work describes synthesis and structural characterization of pyruvate-isoniazid conjugates and their copper complexes with potent anti-tubercular activities against M. tuberculosis H37Rv.

Accessibility and selective stabilization of the principal spin states of iron by pyridyl versus phenolic ketimines: modulation of the 6A1 ↔ 2T2 ground-state transformation of the [FeN4O2]+ chromophore.

Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 Å) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and Mössbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and Mössbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ↔ (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the µ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(µ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).

Bis[2-(1H-imidazol-2-yl-κN)-1H-imidazol-3-ium]silver(I) trinitrate.

The synthesis of the title salt, [Ag(C(6)H(7)N(4))(2)](NO(3))(3), was carried out employing a 1:2 molar ratio of 2,2'-biimidazole and silver nitrate respectively. The cation has crystallographically-imposed C2 symmetry with the metal atom in an almost linear coordination environment [N-Ag-N = 177.01 (17)°]. The crystal structure displays N-H⋯O and C-H⋯O hydrogen-bonding inter-actions.

Polynuclear zinc(II) complexes of thiosemicarbazone: Synthesis, X-ray structure and biological evaluation.

Two new dimeric Zn(II) ([{ZnL1(DMSO2)}2]·DMSO (1), [{ZnL2Cl}2] (2)) and a novel tetrameric Zn(II) complex ([(Zn2L3)2(µ-OAc)2(µ3-O)2] (3)), where H2L1 = 4-(p-methoxyphenyl) thiosemicarbazone of o-hydroxynapthaldehyde, HL2 = 4-(p-methoxyphenyl)thiosemicarbazone of benzoyl pyridine and H2L3 = 4-(p-chlorophenyl)thiosemicarbazone of o-vanillin are reported. Ligands and their complexes were characterized by spectroscopic and single crystal X-ray diffraction techniques. In addition, the complexes exhibited good binding affinity towards HSA (1012 M-1), which is supported by their ability to quench the tryptophan fluorescence emission spectra of HSA. The complexes were also screened for their DNA binding propensity through UV-vis absorption titration, circular dichroism and fluorescence spectral studies. Results show that they effectively interact with CT-DNA through an intercalative mode of binding, with binding constants ranging from 103 to 104 M-1. Among the three complexes 1 has the highest binding affinity towards CT-DNA. Further, the phosphatase activity was evaluated using bis(2,4-dinitrophenyl)phosphate (BDNPP) as substrate, however, the complexes did not yield any measurable catalytic activity. Nevertheless the complexes showed significant cytotoxic potential against HeLa and HT-29 cancer cell lines that was assessed through MTT assay and DAPI staining. Remarkably, complex 1 showed better activity than cisplatin against HT-29 cell line.

Water-soluble Cobalt(II) & Cobalt(III) complexes supported by new triazine Schiff base ligands: Synthesis, structure and biological evaluation.

A new class of triazine ligands (E)-2-(2-(6-methyl-5-oxo-2,5-dihydro-1,2,4-triazin-3-yl)hydrazono)propanoic acid hydrate (HL1.H2O) and (Z)-2-(((E)-4-amino-6-methyl-5-oxo-4,5-dihydro-1,2,4-triazin-3(2H)ylidene)hydrazono)propanoic acid (H2L2) has been synthesized by the condensation reaction of pyruvic acid with diaminoguanidine and triaminoguanidine respectively. The corresponding Schiff base cobalt complexes [Co(L1)2].2H2O (1) and [Co(HL2)(L2)].H2O (2) have also been synthesized and characterized by analytical, thermal, spectroscopic and diffraction studies. Strong field ligand results low spin Co(III) centre in 2, which was evidenced by the shorter bond length of Co(III) complex. In H2L2 there is a choice of coordination modes based on distinct sets of donor atoms, both of which are seen in complex 2, involving either an -NH2 group on position 4 of the triazine ring, or via a ring nitrogen of the triazine itself. The deprotonation of one version of L2 allows the formation of the ligand field stabilized low spin Co(III) in 2. In complex 1, each ligand binds to the metal via pyruvate oxygen, azomethine nitrogen and triazine nitrogen forming two five-membered stable chelate rings. In complex 2, the coordination sphere assembled by two types of coordinating atoms from the same ligand with different conformation. Their binding ability and mode of binding with CT-DNA and BSA was studied by UV- absorption, fluorescence and CD spectroscopy. Density Functional Theory (DFT) studies provide further insights into the mode of binding, structure and mechanism. The HOMO and LUMO energy gap values indicate that both the complexes are prone to interact with CT-DNA and BSA. We have also performed molecular docking calculations to understand the mode of binding and the corresponding results confirm our experimental findings.

Copper conjugates of nimesulide Schiff bases targeting VEGF, COX and Bcl-2 in pancreatic cancer cells.

Copper conjugates of Schiff base derivatives of nimesulide (1), a well-known cyclooxygenase-2 (COX-2) inhibitor, were synthesized, structurally characterized and evaluated for their COX selectivity indices and cytotoxicities on pancreatic tumor, BxPC-3 (COX-2 positive) and MiaPaCa (COX-2 negative) cell lines. Copper conjugates exhibit distorted square planar geometries as revealed by the single crystal X-ray structure determination of Cu(L1)(2) and show significant growth inhibition in both cell lines (IC50 values 3-26 microM for COX-2 positive and 5-9 microM for COX-2 negative cell line) than the parent nimesulide (35 microM for COX-2 positive and >100 microM for COX-2 negative cell line). The mechanistic pathway for the biological activity involves inhibition of vascular endothelial growth factor (VEGF) and COX inhibition, as well as down regulation of antiapoptotic Bcl-2 and Bcl-(XL) proteins.

Synthesis, structure and cytotoxicity of a series of Dioxidomolybdenum(VI) complexes featuring Salan ligands.

Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes [MoO2L1-7] (1-7) derived from various tetradentate diamino bis(phenolato) "salan" ligands, N,N'-dimethyl-N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminoethane {(X=Br, Y=Me, Z=H (H2L1); X=Me, YCl, Z=H (H2L2); X=iPr, Y=Cl, Z=Me (H2L3)} and N,N'-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)-1,2-diaminopropane {(X=Y=tBu, Z=H (H2L4); X=Y=Me, Z=H (H2L5); X=iPr, YCl, Z=Me (H2L6); X=Y=Br, Z=H (H2L7)} containing O-N donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV-vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. The complexes (1-7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell line. IC50 values of the complexes in HT-29 follow the order 6<7<<1<2<5<<3<4 while the order was 6<7<5<1<<3<4<2 in HeLa cells. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 (IC50 values of 6 are 2.62 and 10.74µM and that of 7 is 11.79 and 30.48µM in HT-29 and HeLa cells, respectively) may be dependent on the substituents in the salan ligand environment coordinated to the metal.

Biomolecules linked to transition metal complexes--new chances for chemotherapy.

From the synthetic point of view the fast developing fields of medicine and biology offer new opportunities for the design of very effective drugs with high selectivity. Especially in the field of anticancer therapy many efforts have been made to deliver drugs to specific tissues. Sugar substituted porphyrin compounds, bile acid conjugates, and pH-sensitive immunoliposomes are only some examples. Although there are many different approaches to exploit biomolecules as shuttles only a start has been made. Since the targeting of a drug is a very complex process, a successful design of a new compound has to consider chemical as well as biological aspects and requires a multidisciplinary cooperation with physicians and biologists. Three interesting concepts are evaluated exemplarily: antibodies, molecules with binding affinity to hormone receptors, and bile acids. The main issues are: selection of the drug and the carrier, ways of linking the pharmacological active compound to the biomolecule, the optimal way of linking the drug to the spacer, and cytotoxicity, apoptosis, and drug resistance.

Cholic acid-carboplatin compounds (CarboChAPt) as models for specific drug delivery: synthesis of novel carboplatin analogous derivatives and comparison of the cytotoxic properties with corresponding cisplatin compounds.

This report continues our work on new compounds which consist of three functional parts--a transport fragment, a spacer and a biologically active 'drug' component. Here cholic acid functions as the transport fragment, linked via an alkyl spacer to a carboplatin analog, representing the drug (carbo-ChAPt-Fig. 1). We describe the synthesis and characterization of the series of complexes [Pt(Cyclobutane-1,1-dicarboxylato)(diamine)], [diamine=CholCOO(CH(2))(n)CH(CH(2)NH(2))(2) and THP(CH(2))(n)CH-(CH(2)NH(2))(2), n=4, 6, 8, 11]. The compounds were characterized by elemental analysis and NMR-measurements. Cytostatic activity data are given. In general, the cytostatic activity is similar to that of the parent compound and is strongly influenced by the length of the alkyl chain spacer separating the drug and transport fragments, the ones with long chain spacers being more toxic than the parent complexes. Preliminary investigations indicate the ability of the ChAPt to break resistance of tumor cells against common platinum tumor drugs, e.g. cisplatin. They are effective even on cell lines that have developed resistance to other drugs such as cis- and carboplatin. They are more cytotoxic so they are potentially effective at lower dose concentrations. The mode of cell death was examined by trypan-blue exclusion test and DNA gelelectrophoresis. Typical fragmentation of DNA was observed and the cells were still able to exclude trypan-blue.

Single- and multiphoton turn-on fluorescent Fe(3+) sensors based on bis(rhodamine).

Selective and sensitive turn-on fluorescent Fe(3+) sensors based on novel bis(rhodamine) dye molecules are reported. The compounds are synthesized with very high yields and characterized with NMR, ESI mass spectrometry, and elemental analysis. Single- and two-photon fluorescence enhancement is observed for both molecules in the presence of Fe(3+). High selectivity and sensitivity is observed over other metal ions and is shown to be due mainly to the spirolactam ring-opening power of Fe(3+). All measurements are made in buffer environments simulating biological conditions to facilitate single- and multiphoton fluorescence imaging of Fe(3+) in vivo and in vitro. Larger enhancement of fluorescence for both one- and two-photon excitation makes them suitable candidates for fluorescent labeling of biological systems. Two photon cross-section and time-resolved fluorescence measurements are utilized to understand the selectivity of the present sensors for Fe(3+)-sensing.

A novel copper(II) complex of a tripodal ligand with phenolate-phenol interligand, intramolecular hydrogen bonding.

A novel tripodal ligand with three different arms, viz., pyridine, phenol and an oxime and its copper(II) complex were synthesised. The X-ray crystal structure of the compound reveals that it is a dinuclear complex consisting of two copper(II) ions doubly bridged by two oximato groups in a trans arrangement. The complex contains unusual cis-axially coordinated phenolates as well as a novel interligand, intramolecular phenolate-phenol hydrogen bond. Variable-temperature magnetic susceptibility measurements revealed that the two copper(II) centers are strongly antiferromagnetically coupled, with the exchange coupling constant -2J = 800(42) cm(-1) (H = -2J S(1) x S(2)) for the two interacting S = 1/2 centres. The complex yields an (1)H NMR spectrum in CD(3)CN solution at room temperature, with relatively sharp signals and rather small hyperfine shifts, evidencing that the antiferromagnetically coupled dinuclear core is maintained in solution.

Synthesis, characterization, and reactivity of iron trisamidoamine complexes that undergo both metal- and ligand-centered oxidative transformations.

Functional systems that combine redox-active metals and noninnocent ligands are no longer rare chemical oddities; they are instead emerging as significant components of catalytic and enzymatic reactions. The present work examines the synthetic and functional aspects of iron compounds ligated by a family of new trisamidoamine ligands of the type [(RNC6H4)3N]3- (L1). When R is the electron-rich 4-t-Bu-Ph moiety, the ligand can undergo oxidative rearrangement and store oxidizing equivalents under specific conditions. Starting ferrous complexes of the general formula [(L1)FeIIsolv]- (solv=CH3CN, dimethylformamide) can be easily oxidized (a) by dioxygen to afford the corresponding [(L1)FeIIIOH]- complexes, featuring several cases of terminal hydroxo units, and (b) by organochlorides (R-Cl) to provide [(L1)FeIIIsolv] congeners and coupled R-R products. Efforts to synthesize [(L1)FeIII-O-FeIII(L1)]2- by using [Cl3FeIII-O-FeIIICl3]2- indicate that intrinsic FeIIICl units can oxidatively rearrange the ligand to afford [(L1re)(Cl)FeII][Et4N]2, although the oxidizing equivalent is not retained. Compound [(L1re)(Cl)FeII][Et4N]2 can be further oxidized to [(L1re-2)(Cl)FeIII][Et4N] by CH2Cl2. Finally, oxidation of [(L1)FeIIIsolv] by FeCl3 affords [(L1reH)(Cl)FeII(micro-Cl)2FeII(Cl)(L1re-2H)], which features a similar ligand rearrangement that also gives rise to a diamagnetic, doubly oxidized moiety. These results underscore the complexity of chemical transformations available to systems in which both the metal and the ligand are redox-active entities.

Synthesis and mesogenic properties of binuclear copper(II) complexes derived from salicylaldimine Schiff bases.

The synthesis and mesomorphic (liquid crystal) properties of new binuclear dihalocopper(II) complexes derived from N- and ring-substituted salicylaldimine Schiff bases are reported, together with the mesomorphic properties of their monomeric precursor complexes. With just N-substituents both the dichlorodicopper(II) binuclear complexes and their mononuclear analogues are waxy solids with melting points that increase with their N-chain length. However, with both N- and ring-substituents in the 4-positions, the mononuclear and binuclear complexes are each liquid crystalline or mesogenic, except in case of the mononuclear complexes where the N-substituent is straight chain alkyl. The other mononuclear complexes exhibit a variety of liquid crystal phases: smectic A, C, and E (SA, SC, and SE, respectively). The liquid crystal phase SA is observed in the binuclears with shorter chain N-substituents p-R-O-C6H4- and shorter chain ring-substituents. The chain lengths were increased until the phase behavior expanded to a further form SC in the case of an N-substituent p-C14H29O-C6H4- and a -OC12H25 ring substituent. This points the way toward achieving multiphase behavior with these binuclear systems. The Cu-Br analogues of the binuclear complexes behave similarly but with significant qualitative differences, specifically lower mesophase stability and higher melting temperatures. The structures of the nonmesogenic binuclears ([Cu(N-dodecylSal)X]2, X=Cl, Br) were determined with the aid of X-ray crystallography. These are prototypes for the structures of the binuclear complexes and especially for the shape of the central Cu2O2 X2 core in the binuclears: distorted planar coordination about the copper with distortion toward tetrahedral measured by a characteristic twist angle tau (0 degrees planar; 90 degrees tetrahedral). The binuclear complexes also show magnetic coupling which can be used to estimate the geometry. For [Cu(N-dodecylSal)X]2 tau>36 degrees, which corresponds to weaker coupling than observed in the mesogenic binuclears where a stronger magnetic coupling indicates a geometry closer to planar (tau=25 degrees). The mesophases were characterized by differential scanning calorimetry (DSC) analysis and optical polarized microscopy.

Criteria for liquid crystal formation in 5-alkoxy-, 5-alkylamino-, and 5-alkanoyl-tropolone complexes of transition metals (Cu(II), Zn(II), Ni(II), Co(II), UO(2)(VI), VO(IV)). The first uranium metallomesogen. Crystal structure of bis(5-hexadecyloxytropolonato)copper(II).

The mesophase properties of bis(5-alkoxytropolonato)copper(II) complexes are reported and interpreted in terms of d-layer spacings, which indicate considerable intertwining of the alkyl chains. The mesogenic properties depend on the nature of the 5-substituent: to be mesogenic, it must be alkoxy with n > 8, and may not be 5-alkanoyl or 5-alkylamino. The nature of the metal is also important: to be mesogenic, it may be Cu(II) or UO(2)(VI) but not Ni(II), Zn(II), Co(II), or VO(IV). The crystal structure of bis(5-hexadecyloxytropolonato)copper(II) shows how, even in the crystalline state, molecular packing is dominated by the interactions between alkyl chains, together with copper-oxygen interactions. In the Cu(II) complexes, strong interactions occur between Cu atoms and O atoms of neighboring molecules. These are stronger than alkyl-alkyl interactions and therefore dominate alkyl-alkyl interactions between neighbors which otherwise govern the possibility and nature of mesogenic properties. The Cu.O interactions disrupt alkyl-alkyl chain interactions enough to produce a mesophase; such interactions do not obtain in the T(d)() Zn(II) and Co(II) complexes, and indeed, these complexes are not mesogenic. Likewise, alkyl chain interactions by the oxygens of the UO(2)(VI) lead to a mesophase, and U constitutes the heaviest metal ever placed into a mesogenic molecule. In the case of VO(IV), analogous synthetic steps from VOSO(4) led to a new series of binuclear complexes [(VO)(2)(SO(4))(5-alkoxytropoloato)(2)].

The cytotoxicity and mechanisms of 1,2-naphthoquinone thiosemicarbazone and its metal derivatives against MCF-7 human breast cancer cells.

We have investigated the antitumor functions and mechanisms of 1,2-naphthoquinone-2-thiosemicarbazone (NQTS) and its metal complexes (Cu(2+), Pd(2+), and Ni(2+)) against MCF-7 human breast cancer cells. The cells were dosed with these complexes at varying concentrations, and cell viability was measured by a sulforhodamine B (SRB) method. To study mechanisms of action, the complexes were incubated with topoisomerase II (topo II) and supercoiled DNA, linear DNA, nicked open DNA, and relaxed DNA were detected by agarose gel electrophoresis. The results revealed that these complexes are effective antitumor chemicals in inhibiting MCF-7 cell growth, with Ni-NQTS being the most effective among the complexes studied. Our data also indicated that Ni-NQTS is more effective than the commercial antitumor drug, etoposide, based on IC(50) values. The mechanistic study of action showed that metal complexes of NQTS, NQ, and NQTS can only stabilize the single-strand nicked DNA, but not double-strand breakage intermediates. In addition, metal derivatives of these ligands, but not the parent NQ and NQTS, exerted an antagonizing effect on topoisomerase II activity. In summary, chemicals with or without metal derivatives might possess different chemical-topoisomerase II-DNA interactions.