Selection of entrainers in the 1-hexene/n-hexane system with a limited solubility

Vapor-liquid equilibria (VLE) have been measured for five 1-hexene/n-hexane/ionic liquid systems and 1-hexene/n-hexane/NMP (N-methyl-2-pyrrolidone) system with a headspace-gas chromatography (HSGC) apparatus at 333.15 K. The ionic liquids investigated were 1,3-dimethylimidazolium tetrafluoroborate [C₂MIM]⁺[BF₄]⁻, 1-butyl-3-methylimidazolium tetrafluoroborate [C₄MIM]⁺[BF₄]⁻, 1-methyl-3-octylimidazolium tetrafluoroborate [C₈MIM]⁺[BF₄]⁻, 1,3-dimethylimidazolium dicyanamide [C₂MIM]⁺[N(CN)₂]⁻ and 1-octylquinolinium bis(trifluoromethylsulfonyl)amide [C₈Chin]⁺[BTA]⁻. It was found that at low feeding concentration of 1-hexene and n-hexane, the separation ability of ionic liquids is in the order of [C₂MIM]⁺[BF₄]⁻ > [C₄MIM]⁺[BF₄]⁻ ≈ [C₂MIM]⁺[N(CN)₂]⁻ > [C₈MIM]⁺[BF₄]⁻ > [C₈Chin]⁺[BTA]⁻, which is consistent with the priori prediction of the COSMO-RS (conductor-like screening model for real solvents) model. But at high feeding concentration, the separation ability of ionic liquids is in the order of [C₂MIM]⁺[BF₄]⁻ < [C₄MIM]⁺[BF₄]⁻ ≈ [C₂MIM]⁺[N(CN)₂]⁻ < [C₈MIM]⁺[BF₄]⁻ < [C₈Chin]⁺[BTA]⁻. The liquid demixing effect should be taken into account. The activity coefficients of 1-hexene and n-hexane at infinite dilution calculated with the COSMO-RS model were correlated using the NRTL, Wilson and UNIQUAC model. In this work the predictive results from the COSMO-RS model and UNIFAC model for the 1-hexene/n-hexane and 1-hexene/n-hexane/NMP systems were compared. The UNIFAC model is one of the most important academic contributions by Prof. Jürgen Gmehling.     

Quantum chemical study of the bond orders in the ruthenium,diruthenium and dirhodium nitrosyl complexes

Density functional calculations with the B3LYP functional were carried out for the [Ru(NO)Cl₅]²⁻, [Ru(NO)(NH₃)₅]³⁺, [Ru(NO)(CN)₅]²⁻, [Ru(NO)(CN)₅]³⁻, [Ru(NO)(hedta)]^q (hedta = N-(hydroxyethyl)ethylenediaminetriacetate triple-charged anion; q = 0, −1, −2), Rh₂(O₂CR)₄, Rh₂(O₂CR)₄(NO)₂, Ru₂(O₂CR)₄, Ru₂(O₂CR)₄(NO)₂, Ru₂(dpf)₄, and Ru₂(dpf)₄(NO)₂ (dpf = N,N′-diphenylformamidinate ion; R = H, CH₃, CF₃) complexes. The electronic structure was analyzed in terms of Mayer and Wiberg bond order indices. The technique of bond order indices decomposition into σ-, π-, and δ-contributions was proposed.     

Syntheses of C-substituted icosahedral dicarbaboranes bearing the 8-dioxane-cobalt bisdicarbollide moiety

The treatment of 1,2-, 1,7- and 1,12-carbaborane lithiated isomers with [3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-(1′,2′-C₂B₉H₁₁)] (1) at molar ratios 1:1 or 1:2 at room temperature in THF leads generally to the formation of a series of orange double-cluster mono and dianions. These were characterized by NMR and MS methods as [1′′-X-1′′,2′′-closo-C₂B₁₀H₁₁]⁻, [2]⁻; [1′′-X-1′′,7′′-closo-C₂B₁₀H₁₁]⁻, [3]⁻ and [1′′-X-1′′,12′′-closo-C₂B₁₀H₁₁], [4]⁻ for the monoanions, whereas [1′′,2′′-X₂-1′′,2′′-closo-C₂B₁₀H₁₀]²⁻, [2]²⁻; [1′′,7′′-X₂-1′′,7′′-closo-C₂B₁₀H₁₀]²⁻, [3]²⁻; and [1′′,12′′-X₂-1′′,12′′-closo-C₂B₁₀H₁₀]²⁻, [4]²⁻ for the dianions (where X = 3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-1′,2′-(C₂B₉H₁₁)). Moreover, these borane-cage subunits can be easily modified via attaching variable substituents onto cage carbon and boron vertices, which makes these compounds structurally flexible potential candidates for BNCT of cancer and HIV-PR inhibition.     

Light induced magnetic properties of spiropyrane tris(oxalato)chromate (III) single crystals

The effect of UV light on Weiss temperature and ESR spectra in 1-isopropyl-3, 3, 5′, 6′-tetramethylspiro[indolin-2,2′-[2H]pyrano[3,2-b]pyridinium] tris(oxalato)chromate (III) (Sp₃Cr(C₂O₄)₃) has been found. Additional line has been observed in the ESR spectra of irradiated samples in “strong” magnetic fields of ~15 kOe. The analysis of angular dependences of the ESR spectra allowed a contribution of Cr³⁺ ions to magnetic properties of Sp₃Cr(C₂O₄)₃ to be determined. The zero-field splitting parameters D=0.619 cm⁻¹, E=0.024 cm⁻¹ were derived from the experimental data. The parameters were typical for Cr³⁺ in the chromium oxalate. Weiss temperature changed sign from 25 to −25 K under UV irradiation. The value of Weiss temperature and its changing cannot be explained by exchange interaction, dipole-dipole interaction or the effect of crystal field. The existence of Weiss temperature is explained by the changes in amount and spin of paramagnetic particles. The change is due to thermoactivated redistribution of electrons between chromium ions and spiropyrane molecules. Light-induced transfer of electrons is also explaining the change in sign of Weiss temperature under UV irradiation.     

Design and synthesis of fluorescent 6-aryl[1,2-c]quinazolines serving as selective and sensitive ‘on-off’ chemosensor for Hg in aqueous media

Three fluorescent quinazolines thiophen-2-yl-5,6-dihydrobenzo-[4,5]imidazo[1,2-c]quinazoline (1), pyridin-3-yl-5,6-dihydrobenzo-[4,5]imidazo-[1,2-c]quinazoline (2) and phenyl-5,5′,6,6′-dihydrobenzo-[4,4′,5,5′]imidazo-[1.1′,2-c,2′-c]quinazoline (3) have been synthesized. Structures of 1 and 3 have been authenticated crystallographically. Quinazolines 1-3 exhibit highly selective ‘on-off’ switching for Hg²⁺ ions. The fluorescence intensity displayed a linear relationship with respect to Hg²⁺ concentration (0.1-1.0 μM; R² = 0.99) with detection limit of 2.0 × 10⁻⁷ M.     

Chelating ionic versus bridged molecular structures of group 13 metal complexes with bidentate ligands

Complexes of aluminum and gallium trihalides with ethylenediamine (en) and N,N,N′,N′-tetramethylethylenediamine (tmen) of 2:1 composition have been synthesized and structurally characterized by single crystal X-ray diffraction analysis. In contrast to known molecular complexes of hydrido and methyl-substituted analogs, these solid complexes adopt ionic structures of the general type [M¹X₂LL]⁺[M²X₄]⁻ (X = Br, I; M¹, M² = Al or Ga; LL = en, tmen).     

A new family of pyrazolyl-based anionic bidentate ligands and crystal structure of bis(N-phenyl-2-pyrazolyl-1-carboximidothioato)copper(II)

Three new N,S-donor bidentate pyrazolyl-based ligands abbreviated as [PhNCSPz]⁻, 1, [PhNCSPz^Me2]⁻, 2, and [PhNCSPz^Ph2]⁻, 3, have been synthesized in THF by direct mixing of phenylisothiocyanide with suspension of appropriate sodium-pyrazolate salts and characterized by the common spectroscopic and analytical methods. The Cu(II) complexes of these anionic chelate ligands have been characterized and the crystal structure of Cu(PhNCSPz)₂, 4, has been determined. The space group of complex is P2₁c, with a = 5.9313(3), b = 21.206(1) Å, c = 8.0667(4) Å, β = 103.822(1)°.     

Two new coordination polymers of Robson-type macrocycle bridged by perchlorate anions: Structure,electrochemistry and magnetism

Two new coordination polymers of Robson-type macrocycles, [Cu₂L¹(μ-ClO₄)₂]_∞ (1) and [Cu₂L²(μ-ClO₄)₂]_∞ (2) (where H₂L¹and H₂L² are the [2+2] condensation products of 2,6-diformyl-4-flurophenol with 1,3-diaminopropane and 2-hydroxy-1,3-diaminopropane, respectively), have been synthesized and characterized. The intriguing feature is that intermolecular perchlorato bridges occur between adjacent copper(II) centers. The cyclic voltammograms of the complexes show that each complex undergoes two pseudo-reversible processes with the half wave potentials, −0.361 V and −0.729 V for 1, and −0.372 V and −0.744 V for 2, respectively. Magnetic susceptibility was measured for 1 and 2 over a temperature range of 2–300 K. The optimized magnetic data were J = −359.6 cm⁻¹, j′ = −30 cm⁻¹ and R = 6.8 × 10⁻⁸ for 1 and J = −411 cm⁻¹, j′ = −26 cm⁻¹ and R = 2.4 × 10⁻⁷ for 2, respectively. The data reveal antiferromagnetic couplings between the copper(II) ions of intra- and intermolecular units.     

New Cu(II)4 and Zn(II)4 complexes: Synthesis, characterization and magnetic and biological studies

Two new isomorphous tetranuclear complexes [Cu₄L₂(4,4′-bipy)₂]·(ClO₄)₄·2CH₃CN·2H₂O (1) and [Zn₄L₂(4,4′-bipy)₂]·(ClO₄)₃·CH₃O·4H₂O (2) have been obtained and fully characterized (where bipy = bipyridine, H₂L = macrocycle is the [2+2] condensation product of 2,6-diformyl-4-fluoro-phenol and 1,4-diaminobutane). They exhibit wheel-like configuration in which two 4,4′-bipy molecules connect two dinuclear [M₂L]²⁺ units. The interactions of the complexes with calf thymus DNA were studied by UV-Vis and CD spectroscopic techniques. The binding constants of 1 and 2 are 2.27 × 10⁶ and 3.89 × 10⁵ M⁻¹, respectively. The magnetic measurement of 1 reveals that there are strong antiferromagnetic coupling (J = -272.6 cm⁻¹) between two Cu(II) ions in the macrocyclic unit and ferromagnetic interaction (j′ = 41.7) between the Cu(II) ions in two adjacent macrocyclic units. Furthermore, the cyclic voltammogram of 1 shows that it undergoes two quasi-reversible processes with the half wave potentials -0.232 and -0.606 V, respectively.     

Multiple one-electron oxidation and reduction of trinuclear bis(2,4-pentanedionato)ruthenium complexes with substituted diquinoxalino[2,3-a:2′,3′-c]phenazine ligands

The complexes (μ₃-L¹/L²)[Ru(acac)₂]₃, acac⁻ = 2,4-pentanedionato, L¹ = 2,3,8,9,14,15-hexachlorodiquinoxalino[2,3-a:2′,3′-c]phenazine and L² = 2,3,8,9,14,15- hexamethyldiquinoxalino[2,3-a:2′,3′-c]phenazine, undergo stepwise one-electron oxidation involving a total of three electrons and stepwise one-electron reduction with three (L²) or four electrons (L¹). All reversibly accessible states were characterized by UV–Vis–NIR spectroelectrochemistry. Oxidation leads to mixed-valent intermediates {(μ₃-L)[Ru(acac)₂]₃}⁺ and {(μ₃-L)[Ru(acac)₂]₃}²⁺ of which the Ru^IIIRu^IIRu^II combinations exhibit higher comproportionation constants K_c than the Ru^IIIRu^IIIRu^II states – in contrast to a previous report for the unsubstituted parent systems {(μ₃-L³)[Ru(acac)₂]₃}^+/2+, L³ = diquinoxalino[2,3-a:2′,3′-c]phenazine. No conspicuous inter-valence charge transfer absorptions were observed for the mixed-valent intermediates in the visible to near-infrared regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic ruthenium(III) type signals for the former. Electron addition produces ruthenium(II) complexes of the reduced forms of the ligands L, a high resolution EPR spectrum with ¹⁴N and ^35,37Cl hyperfine coupling and negligible g anisotropy was found for {(μ₃-L¹)[Ru(acac)₂]₃}⁻. DFT calculations of (μ₃-L¹)[Ru(acac)₂]₃ confirm several ligand-centered low-lying unoccupied MOs for reduction and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions.     

Structural characterization of [Fe(NO)(mnt)2] salts

The iron dithiolene compounds [Fe₂(mnt)₄]²⁻ [1]²⁻ and [Fe(NO)(mnt)₂]ⁿ (n = 1−, [2]¹⁻; n = 2−, [2]²⁻) ([mnt]²⁻ = maleonitriledithiolate = [(NC)₂C₂S₂]²⁻) have been characterized structurally by X-ray diffraction as their [Et₄N]⁺ salts at 100 K. Dianion [2]²⁻ is prepared from [2]¹⁻ by reduction with Na[Et₃BH] and is observed to have a bent Fe-NO angle at 149.9(5)° in contrast to the linear configuration of Fe-NO in [2]¹⁻ (180.0°). The change from linear to bent binding mode for NO, an increase of more than 0.1 Å in the Fe-N bond length, and the relative invariance of the Fe-S distances for [2]²⁻ versus [2]¹⁻ indicate that the NO ligand is the site of reduction. The [Et₃NH]⁺ complex of [2]¹⁻ was also identified by crystallography and found to have hydrogen bonding contacts between [Et₃NH]⁺ and the cyano nitrogen atom of an [mnt]²⁻ ligand. Furthermore, relatively close S?S contacts (3.602-3.615 Å) occur between [2]¹⁻ anions, which pack together in an offset, head-to-head fashion. These S?S contacts are absent in the structure of [Et₄N][2]. Infrared spectra show an energy decrease for, and a significant broadening of, the NO bond stretching absorption peak in [2]²⁻, which is consistent with a bent NO ligand sampling a range of conformations both by facile pivoting about the Fe-N axis and by a breathing of the Fe-NO angle.     

Complexes derived from the general copper(II)/maleamic acid/N,N′,N′′-chelate reaction systems: Synthetic,reactivity, structural and spectroscopic studies

The synthetic investigation of the Cu^II/maleamate(−1) ion (HL⁻)/N,N′,N′′-chelate general reaction system has allowed access to compounds [Cu₂(HL)₂(bppy)₂](ClO₄)₂·H₂O (1·H₂O), [Cu(HL)(bppy)(ClO₄)] (2) and [Cu(HL)(terpy)(H₂O)](ClO₄) (4) (bppy = 2,6-bis(pyrazol-1-yl)pyridine, terpy = 2,2′;6′,2′′-terpyridine). In the absence of externally added hydroxides, compound [Cu₂(L′)₂(bppy)₂](ClO₄)₂ (3) was obtained from MeOH solutions; L′⁻ is the monomethyl maleate(−1) ligand which is formed in situ via the Cu^II-assisted HL⁻ → L′⁻ transformation. In the case of tptz-containing (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) reaction systems, the Cu^II-assisted hydrolysis of tptz to pyridine-2-carboxamide (L1) afforded complex [Cu(L1)₂(NO₃)₂] (5). The crystal structures of 1–5 are stabilized by intermolecular hydrogen bonding and π–π stacking interactions. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Titanium(IV) terminal hydroxo complexes containing chelating bis(phosphine oxide) ligands

Treatment of [L_OEtTi(OTf)₃] (, OTf⁻ = triflate) with S-binapO₂ (binap = 2,2′-bis(diphenylphosphinoyl)-1,1′-binaphthyl) afforded the terminal hydroxo complex [L_OEtTi(S-binapO₂)(OH)][OTf]₂ (1). Treatment of [L_OEtTi(OTf)₃] with K(tpip) (tpip⁻ = [N(Ph₂PO)₂]⁻) afforded [L_OEtTi(tpip)(OTf)][OTf] (2) that reacted with CsOH to give [L_OEtTi(tpip)(OH)][OTf] (3). The structures of 1 and 2 have been determined.     

Two tri-spin complexes based on gadolinium and nitronyl nitroxide radicals: Structure and ferromagnetic interactions

Three Radical-Ln(III)-Radical complexes based on nitronyl nitroxide radicals have been synthesized, structurally and magnetically characterized: [Gd(hfac)₃(NITPhOEt)₂] (1) (hfac=hexafluoroacetylacetonate, and NITPhOEt=4′-ethoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), [Gd(hfac)₃(NITPhOCH₂Ph)₂] (2) (NITPhOCH₂Ph=4′-benzyloxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Lu(hfac)₃(NITPhOCH₂Ph)₂] (3). The X-ray crystal structure analyses show that the structures of the three compounds are similar and all consist of the isolated molecules, in which central ions Gd^III or Lu^III are coordinated by six oxygen atoms from three hfac and two oxygen atoms from nitronyl radicals. The magnetic studies show that in both of the two Gd^III complexes, there are ferromagnetic Gd^III-Rad interactions and antiferro-magnetic Rad-Rad interactions in the molecules (with J_Rad−Gd=0.27 cm⁻¹, j_Rad-Rad=−2.97 cm⁻¹ for 1: and J_Rad−Gd=0.62 cm⁻¹, j_Rad-Rad=−7.01 cm⁻¹ for 2). An analogous complex of [Lu(hfac)₃ (NITPhOCH₂Ph)₂] (3) containing diamagnetic Lu^III ions has also been introduced for further demonstrating the nature of magnetic coupling between radicals.     

Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.     

Synthesis and metal-binding studies of a novel pyrene discotic

The synthesis of a novel bis-crown quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine discotic and its binding properties to a series of alkali and alkaline-earth metals is reported. A schematic representation of the binding equilibrium of the sensor to the metal is proposed. The binding constant of the sensor to barium(II) was estimated to be 1.4 × 10⁴ M⁻¹ based on ¹H NMR studies.     

A novel 1D organic-inorganic hybrid based on alternating heteropolyanions [GeMo12O40] and isopolyanions [Mo6O22]

A novel one-dimensional (1D) coordination polymer [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)][GeMo₁₂O₄₀]·H₂O (2,2′-bpy=2,2′-bipyridine), which represents the first example of 1D organic-inorganic hybrid based on a Keggin-type heteropolyanion [GeMo₁₂O₄₀]⁴⁻ and an unprecedented isopolyanion [Mo₆O₂₂]⁸⁻, has been hydrothermally synthesized and characterized by single crystal X-ray diffraction. Crystal data: C₆₀H₅₀Cu₆GeMo₁₈N₁₂O₆₃, monoclinic, P2₁/c, a=13.9344(3), b=20.0329(3), c=17.2151(3) Å; β=94.0220(10)°, V=4793.70(15) Å³, T=293(2) K; Z=2.     

Kinetics and mechanistic studies of the interaction of thiosulfate with cis-diaqua-bis[1-alkyl-2-(arylazo)imidazole]ruthenium(II) complexes

The nucleophilic substitution reaction of S₂O₃²⁻ with [Ru(HaaiR′)₂(OH₂)₂](ClO₄)₂ (1) [HaaiR′ = 1-alkyl-2-(phenylazo)imidazole] and [Ru(ClaaiR′)₂(OH₂)₂](ClO₄)₂ (2) [ClaaiR′ = 1-alkyl-2-(chlorophenylazo)imidazole] [where R′ = Me(a), Et(b) or Bz(c)] in acetonitrile–water (50% v/v) medium to yield Na₂[Ru(HaaiR′)₂(S₂O₃)₂] (3a, 3b or 3c) and Na₂[Ru(ClaaiR′)₂(S₂O₃)₂] (4a, 4b or 4c) has been studied. The products were characterized by microanalytical data and spectroscopic techniques (UV–Vis, NMR and mass spectroscopy). The reaction proceeds in two consecutive steps (A → B → C); each step follows first order kinetics with respect to each complex and S₂O₃²⁻, and the first step second order rate constant (k′₂) is greater than the second step one (k″₂). An increase in the π-acidity of the ligand increases the rate. Thermodynamic parameters, the standard enthalpy of activation (Δ^‡H⁰) and the standard entropy of activation (Δ^‡S⁰), have been calculated for both steps using the Eyring equation from variable temperature kinetic studies. The low Δ^‡H⁰ and large negative Δ^‡S⁰ values indicate an associative mode of activation for both aqua ligand substitution processes.     

Hetero-metallic frameworks of [Pd(CN)4] and Cu(II) with triamines: A rare example of a tetracyanometallate bridged 2D coordination polymer

Four cyano bridged Cu(II)–Pd(II) heterometallic complexes, [Cu(dpt)Pd(CN)₄]_n (1), {[Cu₂(medpt)₂Pd(CN)₄](ClO₄)₂ · 3H₂O}_n (2), {[Cu₂(dien)₂Pd(CN)₄](ClO₄)₂ · 2CH₃OH}_n (3) and {[Cu₂(iPrdien)₂Pd(CN)₄](ClO₄)₂ · 2H₂O}_n (4) [dpt = 3,3′-iminobispropylamine; medpt = 3,3′-diamino-N-methyldipropylamine; dien = diethylenetriamine and iprdien = N′-isopropyldiethylenetriamine] have been synthesized and characterized by single crystal X-ray diffraction analysis, magnetic measurement and thermal study. Complexes 1, 2 and 3 are 1D coordination polymers, while 4 presents a 2D network. In 1, the cis-directed cyanide ligands of [Pd(CN)₄]²⁻ anions link two Cu(dpt) units to form a neutral coordination polymer, whereas in 2, 3 and 4, all the cyanide groups of [Pd(CN)₄]²⁻ take part in bonding with four adjacent Cu(II) ions, resulting in cationic coordination polymers counterbalanced by perchlorate anions. The structures are compared with those of analogous [Ni(CN)₄]²⁻ derivatives. The magnetic behavior shows antiferromagnetic interactions in all the complexes.     

Copper(II) complexes of N4 tetradentate ligands with flexible alkyl spacers: Crystal structure,DNA binding and cleavage studies

Mononuclear copper(II) complexes, [Cu L1] (ClO₄)₂ (1), [Cu L2] (ClO₄)₂ (2) and [Cu L3] (ClO₄)₂ (3) with quadridentate Schiff base ligands L1 (N,N′-bis-pyridin-2-ylmethyl-butane-1,4-diimine), L2 (N,N′-bis-pyridin-2-ylmethyl-pentane-1,5-diimine) and L3 (N,N′-bis-pyridin-2-ylmethyl-hexane-1,6-diimine) have been synthesized and characterized. The crystal structure data of 1 reveals the existence of the complex in two different geometries, namely a square pyramid and a distorted octahedron, which eventually leads to the packing of the molecule into helical and anti-parallel structures respectively. Absorption titration studies with calf thymus DNA for all three complexes are suggestive of groove binding with binding constant values for 1, 2 and 3 being 2.6 ± 0.2 × 10⁴ M⁻¹, 11.5 ± 0.2 × 10⁴ M⁻¹ and 1.83 ± 0.2 × 10⁴ M⁻¹ respectively. Control cleavage experiments using pBR 322 plasmid DNA and distamycin suggest minor groove binding for these complexes. In the presence of ascorbic acid, the complexes show efficient DNA cleavage, the order of efficiency being 1 > 2 ≅ 3.