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The copolyesters and terpolyesters containing maleic or phthalic anhydride and 5,6,7,8,10,10-hexachloro-3a,4,4a,5,8,8a,9,9a-octahydro-5,8-methanonaphtho-[2,3-c]-furan-1,3-dione (‘hexolic anhydride’) with 2-butene-1,4-diol and 2,3-dichloro-2-butene-1,4-diol are synthesized by azeotropic condensation technique. The 1H- and 13C-NMR spectra of these polyesters are recorded and the chemical shifts for the corresponding nuclear magnetic atoms are assigned. A good correlation exists between the observed and theoretically calculated chemical shift values. The sequence distribution, the randomness factor, and the number-average sequence length of each anhydride monomer unit are calculated using 1H- and 13C-NMR spectra. It is found that both methods give identical results for the same copolyesters and terpolyesters. The results indicate that the copolyesters follow Bernoullian statistics and the terpolyesters correspond to alternative copolyesters. Copolyester und Terpolyester, die Malein- oder Phthalsaureanhydrid und 5,6,7,8,10,10-hexachlor-3a,4,4a,5,8,8a,9,9a-octahydro-5,8-methanonaphtho-[2,3-c]-furan- 1,3-dion (‘hexolic anhydride’) mit 2-Buten-1,4-diol und 2,4-Dichlor-2-buten-1,4-diol enthalten, wurden durch azeotope Kondensation synthetisiert. Die 1H- und 13C-NMR-Spektren dieser Polyester wurden aufgezeichnet und die chemischen Verschiebungen den entsprechenden Kernen zugeordnet. Es besteht eine gute Korrelation zwkclien den beobachteten und den theoretisch vorhergesagten chemischen Verschiebungen. Die Sequenzverteilung, der statistische Faktor und der Mittelwert der Sequenzlange jeder monomeren Anhydrid-Einheit wurden uber die 1H- und 13C-NMR-Spektren berechnet. Beide Methoden lieferten sowohl fur binare als auch fur ternare Copolyester identische Ergebnisse, die darauf hinweisen, das die Verteilung der Monomer-einheiten der binaren Copolyester mit einer Bernoulli-Statistik beschrieben werden kann, und das die ternaren Copolyester alternierende Sequenz haben.

The interaction of [CuL(H2O)](H2L = salicylideneglycine or salicylidene-α-alanine) with cytidine and cytosine has been investigated using UV–VIS, IR, EPR, 1H NMR line-broadening and electrochemical techniques. Adducts of the type [CuL(B)(H2O)n](B = cytosine or cytidine, n= 0 or 1) have been isolated. Infrared spectra of these adducts and a 1H NMR line-broadening study of the interaction of [Cu(salgly)(H2O)] with cytidine and deoxycytidine indicate the involvement of the N(3) and O(2) sites in co-ordination. EPR spectra and electrochemical studies show that the extra methyl group in the alanine complex leads to distortion of the co-ordination plane, thereby resulting in stronger interaction with bases. However, cytosine interacts with the glycine complex strongly as the planarity of the latter favours semi-chelation involving the O(2) site. The extent of interaction of the bases with the copper(II) complexes depends on the co-ordinative unsaturation and distortion from the co-ordination plane around CuII as well as the basicity and ortho effect of the former. On the other hand, steric effects of the ligands are important in binding to CuI.

The complexes [Cu(phen)(3)](ClO(4))(2) 1, [Cu(5,6-dmp)(3)](ClO(4))(2) 2, [Cu(dpq)(3)](ClO(4))(2) 3, [Zn(phen)(3)](ClO(4))(2) 4, [Zn(5,6-dmp)(3)](ClO(4))(2) 5 and [Zn(dpq)(3)](ClO(4))(2) 6, where phen = 1,10-phenanthroline, 5,6-dmp = 5,6-dimethyl-1,10-phenanthroline and dpq = dipyrido[3,2-d:2',3'-f]quinoxaline, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Cu(5,6-dmp)(3)](ClO(4))(2) and rac-[Zn(5,6-dmp)(3)](ClO(4))(2) have been determined. While 2 possesses a regular elongated octahedral coordination geometry (REO), 5 possesses a distorted octahedral geometry. Absorption spectral titrations of the Cu(II) complexes with CT DNA reveal that the red-shift (12 nm) and DNA binding affinity of 3 (K(b), 7.5 x 10(4) M(-1)) are higher than those of 1 (red-shift, 6 nm; K(b), 9.6 x 10(3) M(-1)) indicating that the partial insertion of the extended phen ring of dpq ligand in between the DNA base pairs is deeper than that of phen ring. Also, 2 with a fluxional Cu(II) geometry interacts with DNA (K(b), 3.8 x 10(4) M(-1)) more strongly than 1 suggesting that the hydrophobic forces of interaction of 5,6 methyl groups on the phen ring is more pronounced than the partial intercalation of phen ring in the latter with a static geometry. The DNA binding affinity of 1 is lower than that of its Zn(ii) analogue 4, and, interestingly, the DNA binding affinity 2 of with a fluxional geometry is higher than that of its Zn(II) analogue 5 with a spherical geometry. It is remarkable that upon binding to DNA 3 shows an increase in viscosity higher than that the intercalator EthBr does, which is consistent with the above DNA binding affinities. The CD spectra show only one induced CD band on the characteristic positive band of CT DNA upon interaction with the phen (1,4) and dpq (3,6) complexes. In contrast, the 5,6-dmp complexes 2 and 5 bound to CT DNA show exciton-coupled biphasic CD signals with 2 showing CD signals more intense than 5. The Delta-enantiomer of rac-[Cu(5,6-dmp)(3)](2+) 2 binds specifically to the right-handed B-form of CT DNA at lower ionic strength (0.05 M NaCl) while the Lambda-enantiomer binds specifically to the left-handed Z-form of CT DNA generated by treating the B-form with 5 M NaCl. The complex 2 is stabilized in the higher oxidation state of Cu(II) more than its phen analogue 1 upon binding to DNA suggesting the involvement of electrostatic forces in DNA interaction of the former. In contrast, 3 bound to DNA is stabilized as Cu(I) rather than the Cu(II) oxidation state due to partial intercalative interaction of the dpq ligand. The efficiencies of the complexes to oxidatively cleave pUC19 DNA vary in the order, 312 with 3 effecting 100% cleavage even at 10 microM complex concentration. However, interestingly, this order is reversed when the DNA cleavage is performed using H(2)O(2) as an activator and the highest cleavage efficiency of 2 is ascribed to its electrostatic interaction with the exterior phosphates of DNA.

The mixed-ligand copper(II) complex [Cu(tdp)(tmp)](ClO4), where H(tdp) is 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol and tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline, exhibits cleavage of the proteins bovine serum albumin and lysozyme, producing approximately 5 and 4 kDa protein fragments respectively within a few minutes at micromolar concentrations. The hydrophobic tmp ligand recognizes the hydrophobic site and enhances protein binding and cleavage even at physiological pH and temperature.

The copper(II) complex [Cu(tdp)(ClO4)].0.5H2O (1), where H(tdp) is the tetradentate ligand 2-[(2-(2-hydroxyethylamino)ethylimino)methyl]phenol, and the mixed ligand complexes [Cu(tdp)(diimine)]+ (2-5), where diimine is 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) (4), and dipyrido-[3,2-d:2',3'-f]-quinoxaline (dpq) (5), have been isolated and characterized by analytical and spectral methods. Complexes 1 and [Cu(tdp)(phen)]ClO4 (3) have been structurally characterized, and their coordination geometries around copper(II) are described as distorted octahedral. The equatorially coordinated ethanolic oxygen in 1 is displaced to an axial position upon incorporating the strongly chelating phen, as in 3. The solution structures of all the complexes have been assessed to be square-based using electronic absorption and electron paramagnetic resonance (EPR) spectroscopy. The interaction of the complexes with calf thymus DNA (CT DNA) has been explored by using absorption, emission, and circular dichroic spectral and viscometric studies, and modes of DNA binding for the complexes have been proposed. Absorption spectral (Kb = 0.071 +/- 0.005 (2), 0.90 +/- 0.03 (3), 7.0 +/- 0.2 (4), 9.0 +/- 0.1 x 10(5) M(-1) (5)), emission spectral (Kapp = 4.6 (1), 7.8 (2), 10.0 (3), 12.5 (4), 25.0 x 10(5) M(-1) (5)), and viscosity measurements reveal that 5 interacts with DNA more strongly than the other complexes through partial intercalation of the extended planar ring of the coordinated dpq with the DNA base stack. Interestingly, only complex 4 causes a B to A conformational change upon binding DNA. All the complexes hydrolytically cleave pBR322 supercoiled DNA in 10% DMF/5 mM Tris-HCl/50 mM NaCl buffer at pH 7.1 in the absence of an activating agent, and the cleavage efficiency varies in the order 5 > 3 > 2 > 4 > 1 with 5 displaying the highest Kcat value (5.47 +/- 0.10 h(-1)). The same order of cleavage is observed for the oxidative cleavage of DNA in the presence of ascorbic acid as a reducing agent. Interestingly, of all the complexes, only 5 displays efficient photonuclease activity through double-strand DNA breaks upon irradiation with 365 nm light through a mechanistic pathway involving hydroxyl radicals. The protein binding ability of 1-5 has been also monitored by using the plasma protein bovine serum albumin (BSA), and 4 exhibits a protein binding higher than that of the other complexes. Further, the anticancer activity of the complexes on human cervical epidermoid carcinoma cell line (ME180) has been examined. Interestingly, the observed IC50 values reveal that complex 4, which effects conformational change on DNA and binds to BSA more strongly, exhibits a cytotoxicity higher than the other complexes. It also exhibits approximately 100 and 6 times more potency than cisplatin and mitomycin C for 24 and 48 h incubation times, respectively, suggesting that 4 can be explored further as a potential anticancer drug. Complexes 4 and 5 mediate the arrest of S and G2/M phases in the cell cycle progression at 24 h harvesting time, which progress into apoptosis.

The new iron(III) complex [Fe(L3)Cl(2)], where H(L3) is the tripodal monophenolate ligand N,N-dimethyl-N'-(pyrid-2-ylmethyl)-N'-(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine, has been isolated and studied as a structural and functional model for catechol dioxygenase enzymes. The complex possesses a distorted octahedral iron(III) coordination geometry constituted by the phenolate oxygen, pyridine nitrogen and two amine nitrogens of the tetradentate ligand, and two cis-coordinated chloride ions. The Fe-O-C bond angle (134.0 degrees) and Fe-O bond length (1.889 Angstrom) are very close to those (Fe-O-C, 133 degrees and 148 degrees, Fe-O(tyrosinate), 1.81 and 1.91 Angstrom) of protocatechuate 3,4-dioxygenase enzymes. When the complex is treated with AgNO(3), the ligand-to-metal charge transfer (LMCT) band around 650 nm (epsilon, 2390 M(-1) cm(-1)) is red shifted to 665 nm with an increase in absorptivity (epsilon, 2630 M(-1) cm(-1)) and the Fe(III)/Fe(II) redox couple is shifted to a slightly more positive potential (-0.329 to -0.276 V), suggesting an increase in the Lewis acidity of the iron(III) center upon the removal of coordinated chloride ions. Furthermore, when 3,5-di-tert-butylcatechol (H(2)DBC) pretreated with 2 mol of Et(3)N is added to the complex [Fe(L3)Cl(2)] treated with 2 equiv of AgNO(3), two intense catecholate-to-iron(III) LMCT bands (719 nm, epsilon, 3150 M(-1) cm(-1); 494 nm, epsilon, 3510 M(-1) cm(-1)) are observed. Similar observations are made when H(2)DBC pretreated with 2 mol of piperidine is added to [Fe(L3)Cl(2)], suggesting the formation of [Fe(L3)(DBC)] with bidentate coordination of DBC(2-). On the other hand, when H(2)DBC pretreated with 2 mol of Et(3)N is added to [Fe(L3)Cl(2)], only one catecholate-to-iron(III) LMCT band (617 nm; epsilon, 4380 M(-1) cm(-1)) is observed, revealing the formation of [Fe(L3)(HDBC)(Cl)] involving monodentate coordination of the catecholate. The appearance of the DBSQ/H(2)DBC couple for [Fe(L3)(DBC)] at a potential (-0.083 V) more positive than that (-0.125 V) for [Fe(L3)(HDBC)(Cl)] reveals that chelated DBC(2-) in the former is stabilized toward oxidation more than the coordinated HDBC(-). It is remarkable that the complex [Fe(L3)(HDBC)(Cl)] undergoes slow selective extradiol cleavage (17.3%) of H(2)DBC in the presence of O(2), unlike the iron(III)-phenolate complexes known to yield only intradiol products. It is probable that the weakly coordinated (2.310 Angstrom) -NMe(2) group rather than chloride in the substrate-bound complex is displaced, facilitating O(2) attack on the iron(III) center and, hence, the extradiol cleavage. In contrast, when the cleavage reaction was performed in the presence of a stronger base-like piperidine before and after the removal of the coordinated chloride ions, a faster intradiol cleavage was favored over extradiol cleavage, suggesting the importance of the bidentate coordination of the catecholate substrate in facilitating intradiol cleavage. Also, intradiol cleavage is favored in dimethylformamide and acetonitrile solvents, with enhanced intradiol cleavage yields of 94 and 40%, respectively.

The structure of the orthorhombic modification of an iron(III) chloride complex of bis(2-pyridylmethyl)amine, a potential tridentate N-donor ligand, has been determined, i.e. [bis(2-pyridylmethyl)amine-κ3N]trichloroiron(III), [FeCl3(C12H13N3)]. The iron(III) has a rhombically distorted octahedral coordination environment, made up of all the three N atoms of the capping tridentate ligand and three Cl− ions.

The X-ray crystal structure of the complex rac-[Ru(5,6-dmp)(3)]Cl(2) (5,6-dmp = 5,6-dimethyl-1,10-phenanthroline) reveals a distorted octahedral coordination geometry with the Ru-N bond distances shorter than in its phen analogue. Absorption spectral titrations with CT DNA reveal that rac-[Ru(5,6-dmp)(3)](2+) interacts (K(b), (8.0 +/- 0.2) x 10(4) M(-1)) much more strongly than its phen analogue. The emission intensity of the 5,6-dmp complex is dramatically enhanced on binding to DNA, which is higher than that of the phen analogue. Also, interestingly, time-resolved emission measurements on the DNA-bound complex shows biexponential decay of the excited states with the lifetimes of short- and long-lived components being higher than those for the phen analogue. The CD spectral studies of rac-[Ru(5,6-dmp)(3)](2+) bound to CT DNA provide a definite and elegant evidence for the enantiospecific interaction of the complex with B-form DNA. Competitive DNA binding studies using rac-[Ru(phen)(3)](2+) provide support for the strong binding of the complex with DNA. The Delta-enantiomer of rac-[Ru(5,6-dmp)(3)](2+) binds specifically to the right-handed B-form of poly d(GC)(12) at lower ionic strength (0.05 M NaCl), and the Lambda-enantiomer binds specifically to the left-handed Z-form of poly d(GC)(12) generated by treating the B-form with 5 M NaCl. The strong electronic coupling of the DNA-bound complex with the unbound complex facilitates the change in its enantiospecificity upon changing the conformation of DNA. The (1)H NMR spectra of rac-[Ru(5,6-dmp)(3)](2+) bound to poly d(GC)(12) reveal that the complex closely interacts most possibly in the major grooves of DNA. Electrochemical studies using ITO electrode show that the 5,6-dmp complex stabilizes CT DNA from electrocatalytic oxidation of its guanine base more than the phen analogue does.

The iron(III) complexes [Fe(pda)Cl(H(2)O)(2)] (1), [Fe(tpy)Cl(3)] (2), and [Fe(bbp)Cl(3)] (3), where H(2)pda is pyridine-2,6-dicarboxylic acid, tpy is 2,2':6,2''-terpyridine and bbp is 2,6-bis(benzimidazolyl)pyridine, have been isolated and studied as functional models for the intradiol-cleaving catechol dioxygenase enzymes. Mixed ligand complexes of H(2)pda with the bidentate ligands 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) have been also prepared and studied. All the complexes have been characterized using absorption spectral and electrochemical methods. The spectral changes in the catecholate adducts of the complexes generated in situ have been investigated. Upon interacting the complexes with catecholate anions a low energy catecholate to iron(III) charge transfer band appears, which is similar to that observed for enzyme-substrate complexes. All the complexes catalyze the oxidative intradiol cleavage of 3,5-di-tert-butylcatechol (H(2)dbc) in the presence of dioxygen. Interestingly, on replacing the pyridyl groups in 2 and the bulky benzimidazole groups in 3 by the carboxylate groups, the yields of the intradiol cleavage products of dioxygenation increases, 1 (50%)>2 (20%)>3 (10%). The higher intradiol yield for 1 has been ascribed to the meridional coordination of two carboxylate groups of pda(2-). In contrast to the trend in the intradiol cleavage yields, a tremendous decrease in the rate (200 times) is observed on replacing the two pyridyl moieties in 2 by two carboxylates as in 1 and a significant decrease in rate is observed on replacing the pyridyl moieties in 2 by strongly sigma-donating benzimidazole moieties as in 3. This is in conformity with the decrease in Lewis acidities of the iron(III) centers.

The complex [CoL2](ClO4) • MeOH (1), where HL is the tridentate 3N ligand 1,3-bis(2-pyridylimino)isoindoline, has been isolated and its X-ray crystal structure successfully determined. It possesses a distorted octahedral structure in which both the ligands are coordinated meridionally to cobalt(III) via one deprotonated isoindoline (L−) and two pyridine nitrogen atoms. Interestingly, the average dihedral angle between pyridine and isoindoline rings is 25.9°, indicating that the ligand is twisted upon coordination to cobalt(III). The interaction of the complex with calf-thymus DNA has been studied using various spectral methods and viscosity and electrochemical measurements. For comparison, the DNA interaction of [Co(tacn)2]Cl3 (2), where tacn is facially coordinating 1,4,7-triazacyclononane, has been also studied. The ligand-based electronic spectral band of 1 and the N(σ) → Co(III) charge transfer band of 2 exhibit moderate hypochromism with small or no blue shift on interaction with DNA. The intrinsic binding constants calculated reveal that the monopositive complex ion [CoL2]+ exhibits a DNA-binding affinity lower than the tripositive complex ion [Co(tacn)2]3+. The steric clashes with DNA exterior caused by the second L− ligand bound to cobalt(III), apart from the lower overall positive charge on the [CoL2]+ complex, dictates its DNA-binding mode to be surface binding rather than partial intercalative interaction expected of the extended aromatic chromophore of deprotonated isoindoline anion. An enhancement in relative viscosity of CT DNA on binding to 1 is consistent with its DNA surface binding. On the other hand, a slight decrease in viscosity of CT DNA was observed on binding to 2 revealing that the smaller cation leads to bending (kinking) and hence shortening of DNA chain length. The electrochemical studies indicate that the DNA-bound complexes are stabilised in the higher Co(III) rather than the lower Co(II) oxidation state, suggesting the importance of electrostatic forces of DNA interaction.

The iron(III) complexes of the monophenolate ligands 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol [H(L1)], N,N-dimethyl-N'-(pyrid-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L2)], N,N-dimethyl-N'-(6-methyl-pyrid-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L3)], and N,N-dimethyl-N'-(1-methylimidazole-2-ylmethyl)-N'-(2-hydroxy-4-nitrobenzyl)ethylenediamine [H(L4)] have been obtained and studied as structural and functional models for the intradiol-cleaving catechol dioxygenase enzymes. The complexes [Fe(L1)Cl(2)].CH(3)CN (1), [Fe(L2)Cl(2)] (2), [Fe(L3)Cl(2)] (3), and [Fe(L4)Cl(2)] (4) have been characterized using absorption spectral and electrochemical methods. The single crystal X-ray crystal structures of 1 and 2 have been successfully determined. Both the complexes possess a rhombically distorted octahedral coordination geometry for the FeN(3)OCl(2) chromophore. In 2, the phenolate oxygen, the pyridine nitrogen, an amine nitrogen, and a chloride ion are located on the corners of a square plane with the nitrogen atom of a -NMe(2) group and the other chloride ion occupying the axial positions. In 1, also the equatorial plane is constituted by the phenolate oxygen, the pyridine nitrogen, an amine nitrogen atom, and a chloride ion; however, the axial positions are occupied by the second pyridine nitrogen and the second chloride ion. Interestingly, the Fe-O-C angle of 136.1 degrees observed for 2 is higher than that (128.5 degrees ) in 1; however, the Fe-O(phenolate) bond distances in both the complexes are the same (1.929 A). This illustrates the importance of the nearby sterically demanding coordinated -NMe(2) group and implies similar stereochemical constraints from the other ligated amino acid moieties in the 3,4-PCD enzymes, the enzyme activity of which is traced to the difference in the equatorial and axial Fe-O(tyrosinate) bonds (Fe-O-C, 133 degrees, 148 degrees ). The nature of heterocyclic rings of the ligands and the methyl substituents on them regulates the electronic spectral features, Fe(III)/Fe(II) redox potentials, and catechol cleavage activity of the complexes. Upon interacting the complexes with catecholate anions, two catecholate to iron(III) charge transfer bands appear, and the low energy band is similar to that of catechol dioxygenase-substrate complex. Complexes 1 and 3 fail to catalyze the oxidative intradiol cleavage of 3,5-di-tert-butylcatechol (H(2)DBC). However, interestingly, the replacement of pyridine pendant in 1 by the -NMe(2) group to obtain 2 restores the dioxygenase activity, which is consistent with its higher Fe-O-C bond angle. Remarkably, the more basic N-methylimidazole ring in 4 facilitates the rate-determining product releasing phase of the catalytic reaction, leading to enhancement in reaction rate and efficient conversion (77.1%) of the substrate to intradiol cleavage products as well. All these observations provide support to the novel substrate activation mechanism proposed for the intradiol-cleavage pathway.

The orientation of mono(1,10-phenanthroline)copper(II), [Cu(phen)]2+, and the ternary complexes with amino acids, [Cu(phen)X(aa)]n+, where X(aa) stands for an alpha-amino acid, has been investigated by electron paramagnetic resonance (EPR) spectra of the complexes on DNA fibers. It has been revealed that these complexes bind to DNA with several different binding modes. The observation of a species whose g axis is almost parallel to the DNA double helical axis has suggested that the phenanthroline moiety intercalates to DNA. An absence of the intercalated species for the corresponding 2,2'-bipyridine complex has shown that the three-fused aromatic rings in phenanthroline are critical for the intercalative binding of the complexes. The intercalative binding was promoted by 5,6-dimethyl groups on the phenanthroline ring, whereas it was disturbed by 2,9-dimethyl groups, indicating that the planarity of the coordination sphere is important for the intercalative binding. In all cases, the amount of the non-intercalated species was larger than that of the intercalated one. The amino acids in the ternary complexes of glycine, leucine, serine, threonine, cysteine, methionine, and asparagine were partly substituted with some coordinating groups in DNA, whereas the ternary complexes of lysine, arginine, and glutamine remained intact on DNA.

Four mononuclear iron(III) complexes of the type [Fe(L)Cl3] 1-4, where L is a tridentate 3N ligand such as (2-pyridin-2-ylethyl)(pyridin-2-ylmethyl)amine (L1), (methyl)(2-pyridin-2-ylethyl)(pyridin-2-ylmethyl)amine (L2), bis(pyridin-2-ylethyl)amine (L3), and (1-methyl-1H-imidazol-2-ylmethyl)(pyridin-2-ylethyl)amine (L4), have been isolated and studied as functional models for catechol dioxygenase enzymes. In [Fe(L2)Cl3] 2, the ligand L2 is coordinated facially to iron(III) whereas in [Fe(L1)Cl3] 1 and [Fe(L4)Cl3] 4 the ligands L1 and L4 are coordinated meridionally. In DCM, CH3CN and aqueous SDS, CTAB and TX-100 micellar media, the positions of both the low and high energy catecholate-to-iron(III) LMCT bands (465-530, 690-860 nm) observed for the 3,4-di-tert-butylcatecholate (DBC(2-)) adducts of the iron(III) complexes vary in the order 2134, which reflects the influence of the stereoelectronic factors, mode of coordination and the chelate ring size formed by the tridentate ligands. Spectral and electrochemical studies disclose the formation and location of the cationic adducts as solvated [Fe(L)(DBC)(H2O)](+) species mostly in the aqueous micellar pseudophases of SDS and TX-100 and in the aqueous phase of CTAB micellar solution. The [Fe(L)(DBC)Cl] adducts of 1, 3 and 4, generated in situ, afford major amounts of intradiol cleavage products (17.0-70.0%) and smaller amounts of extradiol (1.2-4.2%) products with varying extradiol to intradiol cleavage product selectivity (E/I: 1, 0.08 : 1; 3, 0.02 : 1; 4, 0.3 : 1). On the other hand, interestingly, the adduct [Fe(L2)(DBC)Cl] of 2 generated in DCM yields a major amount of extradiol (54.0%) and a lower amount (18.3%) of the intradiol cleavage products (E/I, 3 : 1). Remarkably, in aqueous SDS micellar media, it shows exclusive extradiol cleavage products (79.4%) while all the other complexes show very low selectivity (E/I: 1, 0.03 : 1; 2, 79.4 : 0, 3, 0.06 : 1, 4, 0.06 : 1), suggesting the suitability of SDS medium for 2 to elicit exclusive extradiol cleavage. The TX-100 micellar medium also provides a suitable hydrophobic environment for 2 to elicit extradiol cleavage. However, in CTAB micellar medium, 2 shows cleavage selectivity lower than others. Also, the rate of dioxygenation is higher in SDS micellar medium than in DCM, and is dependent upon the chelate ring size.

A dinuclear iron(III) complex containing an asymmetric Fe2(μ-OCH3)2 structural unit has been structurally characterized. Its novel EPR and electronic spectral and electrochemical properties are discussed.

Nickel(II) bis-complexes of bis(pyrid-2-ylmethyl)amine (bpma) and bis(benzimidazol-2-ylmethyl)amine (bbma) have been isolated. The complexes have been characterised using IR, UV-VIS and 1H NMR spectral techniques. The pink complex [Ni(bpma)2](ClO4)2 crystallises in the orthorhombic space group Fdd2, with a=22.12(2), b=28.087(2), c=8.857(3) �, �=?=?=90� and Z=8. The nickel(II) atom has a slightly distorted octahedral structure in which the ligands are cis-facially coordinated. The M-Npy bond length in [M(bpma)2]2+ [M=Mn(II), Fe(II), Ni(II), Cu(II), Zn(II)] complexes decrease and then increase with increase in d-orbital population. The ligand field parameters of the new complexes are compared with those of other complexes with NiN6 chromophore. ? 1998 Elsevier Science Ltd. All rights reserved.

Bright blue Cu(Dipica)(2)(BF(4))(2) crystallizes in the monoclinic space group P2(1)/n, with unit cell parameters a = 23.406(6) Å, b = 9.338(2) Å, c = 25.573(7) Å, beta = 95.39(2) degrees, and Z = 8. The structure was solved by conventional Patterson and Fourier methods. The R and R(w) values for 5282 observed reflections were 7.06% and 9.10% respectively. Two structurally different complex cations are present in the same unit cell, one hexacoordinate and the other pentacoordinate. In the hexacoordinate cation, the two tridentate bis(2'-picolyl)amine ligands are trans-facially coordinated with two pyridine nitrogens and the two secondary amine nitrogens situated on four positions in a plane [Cu-N(pyr) = 2.189(6), 2.146(6) Å; Cu-N(sat) = 2.207(6), 2.201(5) Å]. The remaining two pyridine nitrogens constitute the axis [Cu-N(pyr) = 2.035(5), 2.038(5) Å] in an equatorially expanded pseudooctahedral geometry. The pentacoordinate cation possesses a square-pyramidal configuration, the two secondary nitrogens being mutually cis, with one Dipica equatorially tridentate [Cu-N(pyr) = 2.044(5), 2.027(5) Å, Cu-N(sat) = 1.995(5) Å]. The other Dipica functions as a bidentate ligand, with one of the pyridine nitrogens occupying the equator [Cu-N(pyr) = 1.986(5) Å] and the aliphatic nitrogen defining the axial copper position [Cu-N(sat) = 2.344(5) Å]. Its second pyridine is uncoordinated but hydrogen-bonded to the coordinated NH of the other ligand. Solution properties offer no clear distinction between the two cation stereochemistries. The ternary chelates [Cu(Dipica)(Acac)]ClO(4) and [Cu(Dipica)(Bipy)](ClO(4))(2) are also described.

The binding of delta-, lambda-, and rac-[Ru(phen)3]2+ (phen = 1,10-phenanthroline) and delta-, lambda-, and rac-[Ru-(bpy)3]2+ (bpy = 2,2'-bipyridyl) with calf thymus DNA has been examined by cyclic and differential pulse voltammetric techniques to obtain structural insight into the noncovalent binding of the enantiomers to DNA. The insignificant shift in RuII/RuIII peak potentials on the addition of DNA suggests that both the oxidized and reduced forms bind to DNA to the same extent. Interestingly, DNA selectively decreases the peak currents of delta-[Ru(phen)3]2+ but not those of the lambda-enantiomer; rac-[Ru(phen)3]2+ exhibits an intermediate behavior, thus suggesting that the delta-form exhibits significant selectivity for B-DNA. The binding constants (K2+) and binding site sizes (s) have been determined from the decrease in the peak currents. The binding constant (K2+) of delta-[Ru(phen)3]2+ is on the order of 10(4) M-1 which is less than that for proven intercalators. In contrast, the electrochemical behavior of all three forms of [Ru(bpy)3]2+ remains almost unaffected in the presence of DNA, suggesting that the complexes might reside on the hydrophilic coat of the DNA helix.

The interaction of copper(II) salts with the imidazole-containing disulphide 5-(1,2,5-dithiazaepan-5-ylmethylene)-4-methyl-2-ethyl imidazole (MAMI) in MeOH have been investigated. The 1∶1 Cu(ClO4)2∶MAMI system exhibited a single ligand field band at ca. 12200cm-1, an intense shoulder at ca. 31500 cm-1 and a less intense split feature at 24400 and 25300cm-1 assignable to S(σ) → CuII and S(π) → CuII charge transfer (CT) transitions, respectively. The e.p.r. parameters suggested the presence of a CuN2SO chromophore, however; the 1∶1 Cu(NO3)2∶MAMI system did not exhibit a S → CuII CT band and the g∥ value was comparatively high. An electrochemical study of the 1∶1 Cu(ClO4)2∶MAMI system in MeOH revealed that the copper-disulphide interaction, though weaker, would confer a high redox potential as well as reversibility, similar to the copper-thioether interaction.

The complexes [Co(diimine)(3)](ClO(4))(2)1-3 and [Ni(diimine)(3)](ClO(4))(2)4-6, where diimine = 1,10-phenanthroline (phen) (1,4), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) (2,5) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (3,6), have been isolated, characterized and their interaction with CT DNA studied by using a host of physical methods. The X-ray crystal structures of rac-[Co(5,6-dmp)(3)](ClO(4))(2)2 and rac-[Ni(5,6-dmp)(3)](ClO(4))(2)5 have been determined and the isostructural and also isomorphous complex cations possess distorted octahedral coordination geometries. The absorption spectral titrations of the complexes with DNA reveal that the CT DNA binding affinity (K(b)) of the complexes varies as 321; 654. The Ni(II) complexes display DNA binding stronger than the corresponding Co(II) analogues, which is expected of their bigger sizes. The higher DNA binding affinity of 3 and 6 is due to the involvement in partial insertion of the extended phen ring in between the DNA base pairs. In contrast, 2 and 5 interact with DNA in the major groove through hydrophobic forces involving the methyl groups on the 5,6 positions of phen ring. An enhancement in relative viscosities of DNA upon binding to 1-6 is consistent with the DNA binding affinities. The CD spectral studies show only an induced CD band on the characteristic positive band of CT DNA for both the phen (1,4) complexes. In contrast, the 5,6-dmp (2,5) and dpq (3,6) complexes bound to CT DNA exhibit biphasic CD signals in place of the positive CD band and the negative helicity band disappears. This reveals that the complexes bind to DNA enantiopreferentially and effect changes in secondary structure of DNA. The CV and DPV responses indicate that the DNA-bound dpq complexes are stabilized in the lower oxidation state of Co(II) more than in the Co(III) oxidation state. The prominent DNA cleavage abilities of 1-3 observed in the presence of H(2)O(2) (200 μM) follows the order 213 with efficiencies of more than 90% even at 10 μM complex concentration. Interestingly, Ni(II) complexes 4-6 exhibit higher cytotoxicity (IC(50): 1, 28.0; 2, 15.0; 3, 20.0; 4, 8.0; 5, 2.0; 6, 2.0 μM at 48 h; IC(50): 1, 30.0; 2, 20.0; 3, 25.0; 4, 10.0; 5, 3.0; 6, 3.0 μM at 24 h) against human breast cancer (MCF 7) cell lines than the Co(II) complexes 1-3 as well as cisplatin in spite of their inability to cleave DNA. Also, the 5,6-dmp complex 5 shows cytotoxicity higher than the dpq complex 6 at 24 h incubation time and both 5 and 6 display apoptotic and necrotic modes of cell death.

The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine (bpy) 1, 1,10-phenanthroline (phen) 2, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) 3 and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) 4, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structure of rac-[Fe(5,6-dmp)(3)](ClO(4))(2)3 has been determined and the packing diagram shows the presence of two enantiomeric forms of the complex cations in the same unit cell. The structures of 1-4 in solution have also been studied using UV-Visible, Cyclic Voltammetry and ESI-MS data and all data available suggests that they retain their solid state structures even in solution. The absorption spectral titrations of the iron(ii) complexes with CT DNA reveal that the DNA binding affinities of the complexes vary in the order, 4 (K(b): 9.0 × 10(3))2 (6.8 × 10(3))3 (4. 8 × 10(3))1 (2.9 × 10(3) M(-1)). The DNA interaction of dpq complex (4) involves partial insertion of the extended phen ring in between the DNA base pairs, which is deeper than that of phen (2). The 5,6-dmp (3) complex is involved in groove binding in the major groove of DNA. The lower DNA binding affinity of 1 is due to electrostatic interaction of the cationic complexes with exterior phosphates of DNA. The EthBr displacement assay and DNA viscosity study support these DNA binding modes and the above trend in DNA binding affinities. The complexes of 1 and 2 show induced CD (ICD) upon interaction with CT DNA while 3 and 4 bound to DNA exhibit inversion in the positive band with the helicity band showing very small changes, which implies that 3 and 4 bind enantiopreferentially to DNA. The DNA cleavage abilities of 1-4 have been observed at 10 μM concentration of complexes in the presence of 100 μM H(2)O(2) and the DNA cleavage efficiency (90%) follows the order 3124. The anticancer activity of 1-4 against human breast cancer cell line (MCF-7) has also been studied. The IC(50) values of the complexes at different incubation time intervals of 24 and 48 h follow the order, 3 (0.8, 0.6)4 (20.0, 17.0)2 (28.0, 22.0)1 (32.0, 29.0 μM). Interestingly, 3 exhibits anticancer activity more potent than 1, 2 and 4 and cisplatin for both 24 and 48 h. It induces cell death both through apoptosis and necrosis mechanisms, as revealed by morphological assessment data obtained by using AO/EB and Hoechst 33258 fluorescence staining methods.

Several mononuclear Ni(II) complexes of the type [Ni(L)(CH(3)CN)(2)](BPh(4))(2) 1-7, where L is a tetradentate tripodal 4N ligand such as N,N-dimethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L1), N,N-diethyl-N',N'-bis(pyrid-2-ylmethyl)ethane-1,2-diamine (L2), N,N-dimethyl-N'-(1-methyl-1H-imidazol-2-ylmethyl)-N'-(pyrid-2-ylmethyl)ethane-1,2-diamine (L3), N,N-dimethyl-N',N'-bis(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L4), N,N-dimethyl-N',N'-bis(quinolin-2-ylmethyl)ethane-1,2-diamine (L5), tris(benzimidazol-2-ylmethyl)amine (L6) and tris(pyrid-2-ylmethyl)amine (L7), have been isolated and characterized using CHN analysis, UV-Visible spectroscopy and mass spectrometry. The single-crystal X-ray structures of the complexes [Ni(L1)(CH(3)CN)(H(2)O)](ClO(4))(2) 1a, [Ni(L2)(CH(3)CN)(2)](BPh(4))(2) 2, [Ni(L3)(CH(3)CN)(2)](BPh(4))(2) 3 and [Ni(L4)(CH(3)CN)(2)](BPh(4))(2) 4 have been determined. All these complexes possess a distorted octahedral coordination geometry in which Ni(II) is coordinated to four nitrogen atoms of the tetradentate ligands and two CH(3)CN (2, 3, 4) or one H(2)O and one CH(3)CN (1a) are located in cis positions. The Ni-N(py) bond distances (2.054(2)-2.078(3) Å) in 1a, 2 and 3 are shorter than the Ni-N(amine) bonds (2.127(2)-2.196(3) Å) because of sp(2) and sp(3) hybridizations of the pyridyl and tertiary amine nitrogens respectively. In 3 the Ni-N(im) bond (2.040(5) Å) is shorter than the Ni-N(py) bond (2.074(4) Å) due to the stronger coordination of imidazole compared with the pyridine donor. In dichloromethane/acetonitrile solvent mixture, all the Ni(ii) complexes possess an octahedral coordination geometry, as revealed by the characteristic ligand field bands in the visible region. They efficiently catalyze the hydroxylation of alkanes when m-CPBA is used as oxidant with turnover number (TON) in the range of 340-620 and good alcohol selectivity for cyclohexane (A/K, 5-9). By replacing one of the pyridyl donors in TPA by a weakly coordinating -NMe(2) or -NEt(2) donor nitrogen atom the catalytic activity decreases slightly with no change in the selectivity. In contrast, upon replacing the pyridyl nitrogen donor by the strongly σ-bonding imidazolyl or sterically demanding quinolyl/benzimidazolyl nitrogen donor, both the catalytic activity and selectivity decrease, possibly due to destabilization of the intermediate [(4N)(CH(3)CN)Ni-O˙](+) radical species. Adamantane is selectively (3°/2°, 12-17) oxidized to 1-adamantanol, 2-adamantanol and 2-adamantanone while cumene is selectively oxidized to 2-phenyl-2-propanol. In contrast to cyclohexane oxidation, the incorporation of sterically hindering quinolyl/benzimidazolyl donors around Ni(ii) leads to a high 3°/2° bond selectivity for adamantane oxidation. A linear correlation between the metal-ligand covalency parameter (β) and the turnover number has been observed.

Copper(II) complexes of Schiff base ligands formed by the condensation of cystamine (cys) or 2,2′-diaminodiphenyl-disulphide (ddds) with salicylaldehyde (sal) or pyridine-2-carboxaldehyde (pal), and also their C=N reduced analogues, have been isolated and characterised. The e.p.r. spectra of the complexes reveal a dx2-y2 ground state and exhibit low A∥ and g∥ values. The spectral results suggest equatorial coordination of disulphide in a square-based geometry. The π-delocalisation, unsaturation and flexibility in the ligands affect the ligand field, charge transfer and e.p.r. spectral parameters as well as the redox behaviour.

The iron(iii) complexes of the bis(phenolate) ligands 1,4-bis(2-hydroxy-4-methyl-benzyl)-1,4-diazepane H(2)(L1), 1,4-bis(2-hydroxy-4-nitrobenzyl)-1,4-diazepane H(2)(L2), 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane H(2)(L3) and 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane H(2)(L4) have been isolated and studied as structural and functional models for 3,4-PCD enzymes. The complexes [Fe(L1)Cl] 1, [Fe(L2)(H(2)O)Cl] 2, [Fe(L3)Cl] 3 and [Fe(L4)Cl] 4 have been characterized using ESI-MS, elemental analysis, and absorption spectral and electrochemical methods. The single crystal X-ray structure of 3 contains the FeN(2)O(2)Cl chromophore with a novel square pyramidal (τ, 0.20) coordination geometry. The Fe-O-C bond angle (135.5°) and Fe-O bond length (1.855 Å) are very close to the Fe-O-C bond angles (133, 148°) and Fe-O(tyrosinate) bond distances (1.81, 1.91 Å) in 3,4-PCD enzyme. All the complexes exhibit two intense absorption bands in the ranges 335-383 and 493-541 nm, which are assigned respectively to phenolate (pπ) → Fe(iii) (dσ*) and phenolate (pπ) → Fe(iii) (dπ*) LMCT transitions. The Fe(iii)/Fe(ii) redox potentials of 1, 3 and 4 (E(1/2), -0.882--1.010 V) are more negative than that of 2 (E(1/2), -0.577 V) due to the presence of two electron-withdrawing p-nitrophenolate moieties in the latter enhancing the Lewis acidity of the iron(iii) center. Upon adding H(2)DBC pretreated with two equivalents of Et(3)N to the iron(iii) complexes, two catecholate-to-iron(iii) LMCT bands (656, ε, 1030; 515 nm, ε, 1330 M(-1) cm(-1)) are observed for 2; however, interestingly, an intense catecholate-to-iron(iii) LMCT band (530-541 nm) is observed for 1, 3 and 4 apart from a high intensity band in the range 451-462 nm. The adducts [Fe(L)(DBC)](-) generated from 1-4in situ in DMF/Et(3)N solution react with dioxygen to afford almost exclusively the simple two-electron oxidation product 3,5-di-tert-butylbenzoquinone (DBQ), which is discerned from the appearance and increase in intensity of the electronic spectral band around 400 nm, and smaller amounts of cleavage products. Interestingly, in DMF/piperidine the amount of quinone product decreases and those of the cleavage products increase illustrating that the stronger base piperidine enhances the concentration of the catecholate adduct. The rates of both dioxygenation and quinone formation observed in DMF/Et(3)N solution vary in the order 1342 suggesting that the ligand steric hindrance to molecular oxygen attack, the Lewis acidity of the iron(iii) center and the ability of the complexes to rearrange the Fe-O phenolate bonds to accommodate the catecholate substrate dictate the extent of interaction of the complexes with substrate and hence determine the rates of reactions. This is in line with the observation of DBSQ/H(2)DBC reduction wave for the adduct [Fe(L2)(DBC)](-) at a potential (E(1/2): -0.285 V) more positive than those for the adducts of 1, 3 and 4 (E(1/2): -0.522 to -0.645 V).

A few diiron(III) complexes [Fe2(O)(OAc)2(L1)2](ClO4)2, [Fe2(O)(OBz)2(L1)2](ClO4)2, [Fe2(O)(OAc)2(L2)2](ClO4)2 and [Fe2(O)(OBz)2(L2)2](ClO4)2, where L1=N,N-bis(pyrid-2-ylmethyl)-iso-butylamine, L2=N,N-bis(pyrid-2-ylmethyl)benzylamine, AcO=acetate and BzO=benzoate, have been isolated and characterized by means of elemental analysis and spectral and electrochemical methods. The molecular structures of the complexes and have been determined by single-crystal X-ray diffraction analysis and they possess a distorted bioctahedral geometry in which each iron atom is coordinated to the oxygen atom of the micro-oxo bridge, two oxygen atoms of the micro-benzoato bridges and three nitrogen atoms of L1 and L2 ligands capping the two ends of the diiron(III) cluster. The ESI-MS spectral data of the complexes reveal that the complexes remain intact in dichloromethane (DCM) solution. Upon adding one equivalent of Et3N to a mixture of one equivalent of the diiron(III) complexes and excess of m-chloroperbenzoic acid (m-CPBA) in DCM, an intense absorption band (lambdamax, 670-700 nm) appears, which corresponds to the species [Fe2(O)(OAc)(m-CPBA)(L)2]2+ (ESI-MS, m/z 466) suggested as the intermediate involved in the oxygenation reactions. All the present complexes show efficient alkane hydroxylation with 300-400 turn over numbers and good selectivities for cyclohexane (A/K, 10-14) and adamantane (3 degrees/2 degrees, 9-11). Interestingly, the formation of monoiron(III) species has been discerned in the alkane hydroxylation reactions beyond approximately 50 turnovers. The mononuclear 1:1 iron(III) complexes of L1 and L2 ligands generated in situ are also found to catalyze the oxygenation reactions with high selectivity and efficiency for cyclohexane (A/K, 10-14). Upon their reaction with m-CPBA in DCM, a characteristic absorption band (lambdamax, 600 nm, epsilonmax, 355 M(-1) cm(-1)) appears and decays at room temperature. This spectral feature is consistent with the mononuclear high-valent iron-oxo species suggested as an intermediate in the oxygenation reactions.

Three novel non-heme micro-oxo-bridged diiron(III) complexes [Fe2(micro-O)(L1)2] 2, where H2(L1) is N,N'-o-phenylenebis(salicylideneimine), [Fe2(micro-O)(L2)2].2H2O 4, where H2(L2) is N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), and [Fe2(micro-O)(L3)2] 6, where H2(L3)=1,4-bis(2-hydroxybenzyl)-1,4-diazepane, have been isolated and studied as catalysts for the selective oxidative transformation of alkanes into alcohols using m-choloroperbenzoic acid (m-CPBA) as co-oxidant. The mononuclear iron(III) complexes [Fe(L1)Cl] 1 and [Fe(L4)Cl] 7, where H2(L4)=1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane, have been also isolated and those corresponding to the dimeric complexes 4 and 6 have been generated in CH3CN solution and characterized as [Fe(L2)Cl] 3 and [Fe(L3)Cl] 5 by using ESI-MS, absorption and EPR spectral and electrochemical methods. The molecular structures of 4 and 6 have been successfully determined by single crystal X-ray diffraction. Both 4 and 6 possess the Fe-O-Fe structural motif with each iron atom possessing a distorted square pyramidal coordination geometry. The steric constraint at the iron(III) center in 6 is higher than that in 4 as understood from the values of the trigonality structural index (tau: 4, 0.226, 0.273; 6, 0.449) due to the higher steric congestion built by the diazapane back bone. The micro-oxo-to-Fe(III) LMCT band for 4 is observed around 622 nm (epsilon, 1830 M(-1) cm(-1)) in methanol but is not observed in CH3CN solution and it is blue-shifted to around 485 nm (epsilon, 5760 M(-1) cm(-1)) in 6, possibly due to the higher Fe-O-Fe bond angle in the latter (4, 177.4; 6, 180 degrees). The Fe(III)/Fe(II) redox potentials of the dinuclear complexes (E1/2: 2, -0.606; 4, -0.329; 6, -0.889 V) are more negative than those for their corresponding mononuclear complexes (E1/2: 1, -0.300 V; 3, -0.269; 5, -0.289 V) due to O2- coordination. Interestingly, upon addition of peroxides (H2O2, t-BuOOH) and the peracid m-CPBA, the intensity of the phenolate-to-Fe(III) LMCT band for 2 and 6 decreases but does not exhibit any appreciable change for 4. In the presence of m-CPBA cyclohexane is selectively (A/K, 12.2) oxidized by the dimeric complex to cyclohexanol (A, CyOH) and a small amount of the further oxidized product cyclohexanone (K, CyO). However, interestingly, the corresponding monomeric complex affords enhanced yields of both CyOH and CyO but with a lower selectivity (A/K=1.7) and also 1-chlorocyclohexane via oxidative ligand transfer (OLT). The oxidation of adamantane by 4 affords exclusively 1-adamantanol (50.5%) and 2-adamantanol (9.5%) with enhanced yields over 12 h. In contrast, 3 provides 1-adamantanol (32.4%) and 2-adamantanol (14.8%) and adamantanone (14.6%) in addition to 1-chloroadamantane (14.1%) as the OLT product. The secondary C-H bond of ethylbenzene is randomly activated by both 3 and 4 to give 1-phenylethanol and acetophenone. Also, oxidation of cumene with tertiary C-H bonds to give 2-phenyl-2-propanol and the further oxidized product acetophenone is illustrated by invoking the iron-phenoxyl radical species as invoked for metalloporphyrin-catalyzed systems. The strong chemoselectivity in C-H bond activation of alkanes by 4has been illustrated by invoking the involvement of a high-valent iron-oxo intermediate generated by using m-CPBA rather than the conventional oxidants H2O2 and t-BuOOH. In contrast to 4, the complexes 2 and 6 fail to effect the oxidation of hydrocarbons in the presence of H2O2, t-BuOOH and m-CPBA as the co-oxidant.

A series of new 1:1 iron(III) complexes of the type [Fe(L)Cl3], where L is a tridentate 3N donor ligand, has been isolated and studied as functional models for catechol dioxygenases. The ligands (1-methyl-1H-imidazol-2-ylmethyl)pyrid-2-ylmethyl-amine (L1), N,N-dimethyl-N′-(1-methyl-1H-imidazol-2-ylmethyl)ethane-1,2-diamine (L2) and N-(1-methyl-1H-imidazol-2-ylmethyl)-N′-phenylethane-1,2-diamine (L3) are linear while the ligands tris(1-pyrazolyl)methane (L4), tris(3,5-dimethyl-1-pyrazolyl)methane (L5) and tris(3-iso-propylpyrazolyl)methane (L6) are tripodal ones. All the complexes have been characterized by spectral and electrochemical methods. The X-ray crystal structure of the dinuclear catecholate adduct [Fe(L2)(TCC)]2O, where TCC2− is a tetrachlorocatecholate dianion, has been successfully determined. In this complex both the iron(III) atoms are bridged by a μ-oxo group and each iron(III) center possesses a distorted octahedral coordination geometry in which the ligand L2 is facially coordinated and the remaining coordination sites are occupied by the TCC2− dianion. Spectral studies suggest that addition of a base like Et3N induces the mononuclear complex species [Fe(L2)(TCC)Cl] to dimerize forming a μ-oxo-bridged complex. The spectral and electrochemical properties of the catecholate adducts of the complexes generated in situ reveal that a systematic variation in the ligand donor atom type significantly influences the Lewis acidity of the iron(III) center and hence the interaction of the complexes with simple and substituted catechols. The 3,5-di-tert-butylcatecholate (DBC2−) adducts of the type [Fe(L)(DBC)Cl], where L is a linear tridentate ligand (L1–L3), undergo mainly oxidative intradiol cleavage of the catechol in the presence of dioxygen. Also, the extradiol-to-intradiol product selectivity (E:I) is enhanced upon removal of the coordinated chloride ion in these adducts to obtain [Fe(L)(DBC)(Sol)]+ and upon incorporating coordinated N-methylimidazolyl nitrogen in them. In contrast to the iron(III) complexes of imidazole-based ligands, those of the tripodal pyrazole-based ligands L4–L6 yield major amounts of the oxidized product benzoquinone and small amounts of both intra- and extradiol products. One of the pyrazole arms coordinated in the equatorial plane of these sterically constrained complexes is substituted by a solvent molecule upon adduct formation with DBC2−, which encourages molecular oxygen to attack this site leading to benzoquinone formation. The DBSQ/DBC2− redox potentials of both the imidazole- and pyrazole-based complexes fall in the narrow range of −0.186 to −0.214 V supporting this proposal.

A series of mixed ligand ruthenium(II) complexes [Ru(Hdpa)2(diimine)](ClO4)2, 1-5 where Hdpa is 2,2'-dipyridylamine and diimine is 1,10-phenanthroline (phen) and a modified/extended 1,10-phenanthroline such as, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), 5-methyldipyrido[3,2-d:2',3'-f]quinoxaline (mdpq) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) have been isolated and characterized by analytical and spectral methods. The complex [Ru(Hdpa)2(phen)](PF6)2 1 has been structurally characterized and the coordination geometry around Ru(II) in it is described as distorted octahedral. 1H NMR spectral data reveal that 1-5 should have a C2 symmetry lying on the diimine plane due to the rapid flapping of the coordinated Hdpa ligands. The interaction of the complexes with calf thymus (CT) DNA has been explored by using absorption and emission spectral and viscometry and electrochemical techniques and the mode of DNA binding of the complexes has been proposed. The DNA binding affinity of the complexes decreases with decrease in number of planar aromatic rings in the co-ligand supporting the intercalation of the diimine co-ligands in between the DNA base pairs. Circular dichroic spectral studies reveal that the complexes 3-5 exhibit induced circular dichroism upon binding to CT DNA. Interestingly, upon interaction with CT DNA all the complexes show an increase in anodic current in the cyclic voltammograms suggesting that they are involved in electrocatalytic guanine oxidation. Interestingly, of all the complexes, only 5 alters the DNA superhelicity upon binding with supercoiled pBR322 DNA, which is consistent with its higher DNA binding affinity. Further, the cytotoxicities of the complexes against human cervical epidermoid carcinoma cell line (ME180) have been examined. Interestingly, 5 exhibits a cytotoxicity against ME180 higher than other complexes with potency approximately 8 times more than cisplatin for 24 h incubation but 4 times lower than cisplatin for 48 h incubation.

A series of 1 : 1 iron(III) complexes of sterically hindered and systematically modified tridentate 3N donor ligands have been isolated and studied as functional models for extradiol-cleaving catechol dioxygenases. All of them are of the type [Fe(L)Cl(3)], where L is N-methyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L1), N-ethyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L2), N-benzyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L3), N,N-dimethyl-N'-(pyrid-2-ylmethyl)ethylenediamine (L4), N'-methyl-N'-(pyrid-2-ylmethyl)-N,N-dimethylethylenediamine (L5), N'-ethyl-N'-(pyrid-2-ylmethyl)-N,N-dimethylethylenediamine (L6) and N'-benzyl-N'-(pyrid-2-ylmethyl)-N,N-dimethylethylenediamine (L7). They have been characterized by elemental analysis and spectral and electrochemical methods. The X-ray crystal structures of the complexes [Fe(L2)Cl(3)] 2, [Fe(L3)Cl(3)] 3 and [Fe(L7)Cl(3)] 7 have been successfully determined. All the three complexes possess a distorted octahedral coordination geometry in which the ligand is facially coordinated to iron(III) and the chloride ions occupy the remaining coordination sites. Upon replacing the N-ethyl group on the terminal nitrogen donor in 2 by the bulky N-benzyl group as in 3, the terminal Fe-N bond distance increases slightly from 2.229(5) A to 2.244(5) A. Upon incorporating the sterically demanding N-benzyl group on the central nitrogen donor in 4 to obtain 7, the central Fe-N(amine) bond distance increases from 2.181(5) A to 2.299(2) A. The catecholate adducts [Fe(L)(DBC)(Cl)] and [Fe(L)(DBC)(Sol)](+), where H(2)DBC is 3,5-di-tert-butylcatechol and Sol = solvent (H(2)O/DMF), have been generated in situ and their spectral and redox properties and dioxygenase activities have been studied in N,N-dimethylformamide and dichloromethane solutions. The adducts [Fe(L)(DBC)(Sol)](+) undergo cleavage of DBC(2-) in the presence of molecular oxygen to afford both intra- and extradiol cleavage products. The extradiol products are higher in dichloromethane than in DMF solution and the extradiol to intradiol product selectivity (E/I, 7.2 : 1-18.5 : 1) observed decreases upon increasing the steric bulk of N-alkyl substituent on the terminal nitrogen atom and upon incorporating an N-alkyl substituent on the central nitrogen atom. The plot of log(k(O(2))) vs. energy of the low energy catecholate-iron(III) LMCT band is linear, which is consistent with the proposal that the LMCT band energy corresponds to the energy needed for a spin-inversion process at the iron center upon dioxygen attack. Also, the rate of oxygenation is dictated by the solvent as well as the Lewis acidity of the iron(III) center, as shown by the linear plot of log(k(O(2))) vs.E(1/2) of the Fe(III)/Fe(II) redox potentials of the [Fe(L)(Sol)(3)](3+) complexes.

Solutions of [CuCl2LOH], and other reaction mixtures containing LOH and Cu(II) or Cu(I) salts, degrade to yield dark green or brown residues containing the LH ligand. In contrast, [MCl2LOH] (M = Zn, Ni, Co) are indefinitely stable in solution and the solid state.

The interaction of copper(II/I) complexes of a few 2,9-dimethyl-1,10-phenanthrolines with calf thymus DNA has been investigated using absorption and circular dichroic spectral and electrochemical techniques and viscometry. The observation of the usual hypochromism and the novel hyperchromism in the absorption spectra of [CuI(bcp)2]+ [bcp = 2,9-dimethyl-4,7-diphenyl-1,10- phenanthroline] and [CuI(dpsmp)2]3- [dpsmp2- = 2,9-dimethyl-4,7-bis(sulfonatophenyl)-1,10-phenanthroline] respectively in the presence of DNA and the increase in viscosity of DNA at low loadings of both these complexes have been interpreted in terms of bridging of a pair of DNA duplexes by the complex species. These tetrahedral copper(I) complexes, which lack minor groove binding because of substituents at the 4- and 7-positions of phen ring, are efficient in bridging the duplexes. The electrochemical behaviors of [CuI(dmp)2]+ [dmp = 2,9-dimethyl-1,10-phenanthroline] and [CuI(bcp)2]+ bound to DNA have been compared with that of the analog...

A series of high-spin octahedral 1 : 2 iron(III) complexes of Schiff bases derived from salicylaldehyde and aromatic amines and the 1 : 1 and 1 : 2 complexes of bis(pyridin-2-yl)-aza and bis(benzimidazol-2-yl)-aza and -thioether ligands have been isolated. The crystal structure of trichloro[bis(pyridin-2-ylmethyl)amine]iron(III) has been determined. It contains two crystallographically independent molecules in the asymmetric unit cell. In each molecule iron(III) possesses a rhombically distorted octahedral co-ordination, constituted by all the three nitrogens of the facial ligand and three chloride ions. The effects of stereochemical and/or donor atom variations on the UV/VIS and EPR spectra and FeIII–FeII redox potentials and hence on the Lewis acidity of the iron(III) centre are discussed. The phenolate-to-iron(III) charge-transfer band energy of [FeL12]Cl [HL1=N-(pyridin-2-ylmethyl)salicylideneamine] is higher and its FeIII–FeII redox potential more negative than those of the corresponding 1 : 1 complex.

The crystal structure of tetrakis(cytosine)copper(II) perchlorate dihydrate has been determined. All the hydrogen atoms were obtained from Fourier-difference synthesis. The geometry around copper is a bicapped octahedron (4 + 2 + 2*). The adjacent cytosine rings are oriented head-to-tail with respect to each other and are roughly at right angles to the co-ordination plane. The exocyclic oxo groups form an interligand, intracomplex hydrogen-bonding network above and below the co-ordination plane with the exocyclic amino groups of alternate cytosine bases. The EPR and electronic spectra are consistent with the retention of the solid-state structure in solution. The steric effect of the C(2)O group of cytosine is offset by the presence of the intracomplex hydrogen-bonding network. The trend in E½ values of CuII–CuI couples for 1 : 4 complexes of cytosine, cytodine, pyridine, 2-methylpyridine and N-methylimidazole suggests that both steric effects and π-delocalization in imidazole and pyridine ligands and the steric effect of C(2)O in pyrimidine ligands are important in stablising CuI relative to CuII.

The redox chemistry of [CuL]2+[L = pdto = 1,8-bis(pyridin-2-yl)-3,6-dithiaoctane, bbdo = 1,8-bis(benzimidazol-2-yl)-3,6-dithiaoctane, pttn = 1,9-bis(pyridin-2-yl)-2,5,8-trithianonane or pttu = 1,11-bis(pyridin-2-yl)-3,6,9-trithiaundecane] in the presence of α-, β- and γ-cyclodextrins (cd) in aqueous solution has been extensively investigated by cyclic and differential pulse voltammetric techniques. The addition of cyclodextrins to the complexes results in a substantial decrease in peak currents rather than in peak potentials. The ipa rather than ipc or ΔEp or E½ is very sensitive to the variation in the cyclodextrin concentration. The couple CuII–CuI of [Cu(pdto)]2+ tends to become reversible, as shown by the decrease in ΔEp and that of ipa/ipc towards unity. Plots of ipa, ipc, Epa and ΔEpvs. the number of moles of cyclodextrin show sharp inflections, interestingly at 5, 4 and 3 mol of α-, β- and γ-cd respectively. These limiting values do not correspond to the usual inclusion complex formation by cyclodextrins but to the formation of novel and regular arrays around the complex, the number of molecules in the array being dictated by the size of the cyclodextrin. This also illustrates the prevention of adsorption of [Cu(pdto)]+ on the glassy carbon electrode. For the other complexes the changes in redox properties in the presence of cyclodextrins are not as regular and significant. Plots of changes in ipa and ipcvs. cyclodextrin concentration give Hill's coefficients greater than unity (1.3–2.1). The values of K+/K2+ for all the complexes and Ka(K2+) for the complex formation of [Cu(pdto)]2+ with cyclodextrins have been determined and discussed. Significant reduction or enhancement in Iµmax values has been observed both for the ligand-field and charge-transfer bands in the presence of all three cyclodextrins.

Circular dichroism spectral studies reveal that [Cu(5,6-dmp)2]2+(5,6-dimethyl-1,10-phenanthroline) selectively and reversibly induces the conversion of calf thymus DNA from the right-handed B to the left-handed surface-bound Z conformation.

Copper(II) complexes of 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (dppt) with ClO4–, BF4–, NO3–, Cl– and Br– as counter ions have been prepared. The crystal structure of the complex [Cu(dppt)2(H2O)2][ClO4]2 has been determined. The co-ordination geometry of the copper ion is elongated octahedral, the equatorial plane being formed by the N(2) nitrogens of both the triazine units and two pyridyl nitrogens and the axial positions being occupied by water molecules. The copper ion can be best described as centrosymmetric with the two dppt ligands being strictly coplanar to each other. The electronic and EPR spectral properties illustrate the strong axial interaction by solvent molecules with the weakly ligated CuN4 plane. The markedly positive redox potential (0.57–0.34 V vs. NHE) of these complexes is ascribed to the π-acceptor properties of the ligand rather than to steric effects of the phenyl substituents. The E½ and ΔEp values are significantly dependent on the solvent and the anions. The spectral and electrochemical behaviour of the copper(II) complex of 3-(2-pyridyl)-5,6-bis(p-sulfonatophenyl)-1,2,4-triazine, the sulfonato derivative of dppt, in aqueous solution at various pH revealed that it could not act as an effcient catalytically active redox agent.

The 1 : 1 and 1 : 2 copper(II) complexes with the tridentate compound bis(benzimidazol-2-ylmethyl)amine (L1) and its benzimidazole (L2) and amine (L3)N-methyl-substituted derivatives have been prepared and their spectroscopic properties studied. While the 1 : 1 complexes are of the type CuLX2·nH2O (X = ClO4–, NO3–, Cl– or Br–), the 1 : 2 complexes are of the type CuL2(ClO4)2·nH2O (L = L1 or L3, n= 0–4). In all these complexes L acts as a tridentate ligand with the amine nitrogen and both the benzimidazole nitrogens co-ordinating to CuII. The complex [CuL12][ClO4]2·2H2O crystallises in the monoclinic space group P21/c with a= 9.828(2), b= 9.546(2) and c= 19.906(2)A and β= 95.71(1)°, for Z= 2. The R value is 0.0635 for 2180 significant reflections. The copper(II) ion has an elongated octahedral geometry with four equatorial benzimidazole and two long-distance axial amine N donors. The Cu–Nbzim and Cu–Namine distances are 2.011(4) and 2.597(6)A respectively. Factors favouring facial co-ordination of tridentate ligands are discussed. The 1 : 1 complexes involve meridional co-ordination of the ligands, with square-based geometry as revealed by ligand-field and EPR spectral properties. The NMe substitution as in CuL3(ClO4)2 confers low max and high E½ for the CuII–CuI couple. Most of the 1 : 1 complexes are less reversible but exhibit E½ values more positive than those of the corresponding 1 : 2 complexes.

A series of iron(III) complexes of the type [FeLCl2]·H2O [HL =N-(pyridin-2-ylmethyl)salicylideneamine, (2-hydroxy-5-nitrobenzyl)(pyridin-2-ylmethyl)amine, (2-hydroxy-5-nitrobenzyl)(2-pyridin-2-ylethyl)amine, N-(2-imidazol-4-ylethyl)salicylideamine, N-(benzimidazole-2-ylmethyl)salicylaldimine, (benzimidazol-2-ylmethyl)(2-hydroxybenzyl)amine, or (benzimidazol-2-ylmethyl)(2-hydroxy-5-nitrobenzyl)amine] have been prepared. Also [FeLCl3]·H2O [L = bis(benzimidazol-2-ylmethyl)amine] has been isolated. These complexes have been characterised using IR, UV/VIS and EPR spectral and electrochemical techniques. Their interaction with a variety of mono- and bi-dentate heterocyclic bases as well as phenols has been investigated using electronic and EPR spectroscopy. Their interaction with 3,5-di-tert-butylcatechol (H2dbcat) and its anions reveals changes in the phenolate-to-iron(III) chargetransfer (c.t.) band similar to those for catechol dioxygenase–substrate complexes. The redox behaviour of the iron(III) complexes and their 1 : 1 adducts with dbcat anions generated in situ has been investigated in methanol. There is a linear correlation between the FeIII–FeII redox potential and the c.t. band energy of the complexes. All the complexes catalyse the oxidative cleavage of H2dbcat by molecular oxygen to yield cis,cis-muconic anhydride. The catalytic activity has been correlated with the FeIII–FeII as well as dbsq˙–H2dbcat (dbsq = 3,5-di-tert-butyl-1,2-benzosemiquinone) redox potentials of the dbcat adducts.

The linear quadridentate R(CH2)mSCH2CH2S(CH2)nSCH2CH2S(CH2)mR, where m= 1, n= 2 (L1), or 3 (L2), m= 2 n= 2 (L3) or 3 (L4), and the pentadentate RCH2(SCH2CH2)4SCH2R (L5)(R = benzimidazol-2-yl) compounds formed 1 : 1 copper(II) perchlorate complexes. Some of the quadridentate compounds also formed complexes of the type CuLX2(X = Cl–, NO3– or BF4–). All the complexes exhibited an absorption band around 30 000 cm–1 originating from a S(σ)→ CuII charge-transfer transition. In solution the ClO4– and BF4– salts of [CuL1]2+ exhibit only one ligand-field band (14 800 cm–1) while the other complexes show two bands (≈ 11 000, 15 000–16 000 cm–1). The polycrystalline EPR spectra of the former complexes are axial while those of the other complexes are rhombic. The cryogenic solution EPR spectra of the former complexes differ from those of the other complexes by exhibiting comparatively low g‖ values and well resolved nitrogen superhyperfine structures. All these spectral features suggest a unique ‘folded’ geometry for the [CuL1]2+ complex. Among the tetrathioether complexes, the CuII–CuI redox potential increases with increase in the number of six-membered chelate rings, implying an increase in preference for the copper(I) over the copper(II) state. For copper(II) complexes of bis(benzimidazolyl) thioether ligands with all-five-membered chelate rings the potential increases with increase in the number of thioether donors.

Mononuclear copper(II) complexes of tri- and tetra-dentate tripodal ligands containing phenolic hydroxyl and benzimidazole or pyridine groups have been isolated. They are of the type [CuL(X)]·nH2O, [CuL(H2O)]X·nH2O or [CuL]·nH2O where X = Cl–, ClO4–, N3– or NCS– and n= 0–4. The electronic spectra of all the complexes exhibit a broad absorption band around 14 000 cm–1 and the polycrystalline as well as the frozen-solution EPR spectra are axial, indicating square-based geometries. The crystal structure of [CuL(Cl)][HL =(2-hydroxy-5-nitrobenzyl)bis(2-pyridylmethyl)amine] revealed a square-pyramidal geometry around CuII. The mononuclear complex crystallises in the triclinic space group P with a= 6.938(1), b= 11.782(6), c= 12.678(3)A and α= 114.56(3), β= 92.70(2), γ= 95.36(2)°. The co-ordination plane is comprised of one tertiary amine and two pyridine nitrogens and a chloride ion. The phenolate ion unusually occupies the axial site, possibly due to the electron-withdrawing p-nitro group. The enhanced π delocalisation involving the p-nitrophenolate donor elevates the E½ values. The spectral and electrochemical results suggest the order of donor strength as nitrophenolate < pyridine < benzimidazole in the tridentate and nitrophenolate < benzimidazole < pyridine in the tetradentate ligand complexes.