Coligand modulated oxidative O-demethylation of a methyl ether appended tetradentate N-ligand in Co(ii) complexes

Two Co(ii) complexes of the formula CoL^OMeX₂ (X = Cl^- (1a); X = I^- (1b)), where L^OMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl) aniline, were synthesized and their structure, spectra and reactivity were studied. Upon oxidation of 1a and 1b, the ligand L^OMe undergoes demethylation at the metal centre resulting in the formation of Co(iii) complexes with modified phenoxide ligands. This is the very first example of oxidative O-demethylation reported at a Co(ii) centre. The oxidative behaviour exhibits a striking dependence on the nature of coligands coordinated to the metal centre. The Co(ii) complex 1a with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the subsequent formation of a mononuclear Co(iii) complex with a demethylated ligand, CoL^O-Cl₂ (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O₂ to form a dihydroxo bridged binuclear Co(iii) complex [Co₂(L^O-)₂(OH)₂]²⁺ (3) with modified phenoxide ligands. The oxidation of 1b to 3 is monitored and the intermediate Co(ii) iodo aqua complex [CoL^OMeI(H₂O)]⁺ and Co(ii) diaqua complex [CoL^OMe(H₂O)₂]²⁺ are isolated and characterised.

Bite-Angle-Regulated Coordination Geometries: Tetrahedral and Trigonal Bipyramidal in Ni(II) with Biphenyl-Appended (2-Pyridyl)alkylamine N,N'-Bidentate Ligands

Two simple biphenyl-appended (2-pyridyl)alkylamine N-bidentate ligands, L^e and L^m, having ethylene and methylene spacers between donor groups, with bite angles L^e ≈ 100° and L^m ≈ 80°, dictate pseudotetrahedral and trigonal-bipyramidal geometries in six high-spin Ni(II)-halide complexes, [Ni(L^e)X₂] and [Ni(L^m)₂X](ClO₄) (where X = Cl^-, Br^-, I^-), respectively. The structures in the solid state, determined using X-ray crystallography, and in solution, determined using spectroscopic methods (UV-vis-NIR and paramagnetic ¹H NMR), which complement each other, are described.

Controlling the oxidation of bis-tridentate cobalt(ii) complexes having bis(2-pyridylalkyl)amines: ligand vs. metal oxidation

Two bis-tridentate chelated cobalt(ii) complexes, which differ in the ligand structure by a methylene group, activate molecular oxygen (O₂), and give different oxidation products.

Mononuclear [(BP)(2)MX](n+) (M = Cu(2+), Co(2+), Zn(2+); X = OH(2), Cl(-)) complexes with a new biphenyl appended N-bidentate ligand: structural, spectroscopic, solution equilibrium and ligand dynamic studies

A new series of five-coordinate [(BP)2MX]n+ complexes, (where X = OH2, M = Zn(II) (1), Cu(II) (2); X = Cl-, M = Cu(II) (3), Co(II) (4)) with a new bidentate chelating ligand [{N,N(1,1'-biphenyl-2,2'-dimethylene)-N(2-pyridyl methyl)} amine] with a biphenyl group (BP), have been synthesized and characterized by X-ray crystal structure and combined spectroscopic methods. They display unique trigonal bipyramidal (TBP) geometry, influenced by the bidentate ligand. The Zn(II) complex 1 reveals ligand dynamics due to an atropisomeric biphenyl moiety as indicated by variable temperature (VT) proton NMR spectroscopy. The calculated free energy for the inversion of the bridged biphenyl is approximately 13.08 kcal mol-1 (Tc = 273 K, Delta(nu) = 82.8 Hz, J = 8.7 Hz). The absorption spectra of Cu(II) complexes 2 and 3, in CH2Cl2 display greatly enhanced d-d bands (800-950 nm, epsilon>500 M-1 cm-1). On the other hand, complex 2 in N,N-dimethylformamide (DMF) showed almost 50% reduction in absorption intensity as DMF, a coordinating solvent, displaces the weakly-coordinated tertiary amine-nitrogens of the ligand and this competitive binding was studied by electronic absorption spectroscopy. When the mononuclear copper aqua complex 2 was treated with a base, a dicopper dihydroxide complex, [{(BP)Cu}2(mu-OH)2]2+, (2a) was obtained. The same phenomenon was also observed with chloro complex 3 when treated with a base. This mono-dicopper equilibrium and conversion of 2 --> 2a was monitored by UV-vis spectroscopy. Copper(II) complexes 2 and 3 displayed reverse EPR spectra consistent with the TBP geometry. Cyclic voltammetry of 2 and 3 in DMF showed an irreversible redox wave owing to Cu(II)/Cu(I) of five and four-coordinate species. The solution magnetic moment values of 1.76, 1.81 and 4.47 microB for 2, 3 and 4, respectively, are in agreement with Cu(II) (S = 1/2) and Co(II) (S = 3/2) high-spin configurations. The 1H NMR of 4 displays sharp but hyperfine shifted signals for the ligand protons between -30 to +220 ppm. The ESI-mass data complement the data obtained from X-ray structure.

Soil contamination of heavy metals in the Katedan Industrial Development Area, Hyderabad, India

Studies on quantitative soil contamination due to heavy metals were carried out in Katedan Industrial Development Area (KIDA), south of Hyderabad, Andhra Pradesh, India under the Indo-Norwegian Institutional Cooperation Programme. The study area falls under a semi-arid type of climate and consists of granites and pegmatite of igneous origin belonging to the Archaean age. There are about 300 industries dealing with dyeing, edible oil production, battery manufacturing, metal plating, chemicals, etc. Most of the industries discharge their untreated effluents either on open land or into ditches. Solid waste from industries is randomly dumped along roads and open grounds. Soil samples were collected throughout the industrial area and from downstream residential areas and were analysed by X-ray Fluorescence Spectrometer for fourteen trace metals and ten major oxides. The analytical data shows very high concentrations of lead, chromium, nickel, zinc, arsenic and cadmium through out the industrial area. The random dumping of hazardous waste in the industrial area could be the main cause of the soil contamination spreading by rainwater and wind. In the residential areas the local dumping is expected to be the main source as it is difficult to foresee that rain and wind can transport the contaminants from the industrial area. If emission to air by the smokestacks is significant, this may contribute to considerable spreading of contaminants like As, Cd and Pb throughout the area. A comparison of the results with the Canadian Soil Quality Guidelines (SQGL) show that most of the industrial area is heavily contaminated by As, Pb and Zn and local areas by Cr, Cu and Ni. The residential area is also contaminated by As and some small areas by Cr, Cu, Pb and Zn. The Cd contamination is detected over large area but it is not exceeding the SQGL value. Natural background values of As and Cr exceed the SQGL values and contribute significantly to the contamination in the residential area. However, the availability is considerably less than anthropogenic contaminants and must therefore be assessed differently. The pre- and post-monsoon sampling over two hydrological cycles in 2002 and 2003 indicate that the As, Cd and Pb contaminants are more mobile and may expect to reach the groundwater. The other contaminants seem to be much more stable. The contamination is especially serious in the industrial area as it is housing a large permanent residing population. The study not only aims at determining the natural background levels of trace elements as a guide for future pollution monitoring but also focuses on the pollution vulnerability of the watershed. A plan of action for remediation is recommended.

Targeted Guanine Oxidation by a Dinuclear Copper(II) Complex at Single Stranded/Double Stranded DNA Junctions

A dinuclear copper(II) complex [Cu(II)2(PD'O-)(H2O)2](ClO4)3 (5) with terminal Cu(II)-H(2)O moieties and a Cu...Cu distance of 4.13 A (X-ray structure) has been synthesized and characterized by EPR spectroscopy (ferromagnetic coupling observed) and cyclic voltammetry. Dizinc(II) and mononuclear copper(II) analogues [Zn(II)2(PD'O-)(H2O)2]3+ (7) and [Cu(II)(mPD'OH)(H2O)]2+ (6), respectively, have also been synthesized and structurally characterized. Reacting 5/MPA/O(2) (MPA = 3-mercaptopropionic acid) with DNA leads to a highly specific oxidation of guanine (G) at a junction between single- and double-stranded DNA. Mass spectrometric analysis of the major products indicates a gain of +18 and +34 amu relative to initial DNA strands. The most efficient reaction requires G at the first and second unpaired positions of each strand extending from the junction. Less reaction is observed for analogous targets in which the G cluster is farther from the junction or contains less than four Gs. Consistent with our previous systems, the multinuclear copper center is required for selective reaction; mononuclear complex 6 is not effective. Hydrogen peroxide as a substitute for MPA/O2 also does not lead to activity. Structural analysis of a [Cu(II)2(PD'O-)(G)]3+ complex (8) and dizinc analogue [Zn(II)(2)(PD'O-)(G)](ClO4)3 (9) (G = guanosine) reveals coordination of the G O6 and N7 atoms with the two copper (or zinc) centers and suggests that copper-G coordination likely plays a role in recognition of the DNA target. The Cu2-O2 intermediate responsible for guanine oxidation appears to be different from that responsible for direct-strand scission induced by other multinuclear copper complexes; the likely course of reaction is discussed.

The perchlorate salt of the novel diprotonated dinucleating ligand 1,3-bis{[2-(2-pyridinio)ethyl][2-(2-pyridyl)ethyl]amino}benzene

In the title salt, 1,3-bis{[2-(2-pyridinio)ethyl][2-(2-pyridyl)ethyl]amino}benzene diperchlorate dihydrate, C34H38N(6)2+.2ClO4-.2H2O, the cation contains two ethylpyridyl and two ethylpyridinium pendant pairs anchored to the two N atoms of 1,3-phenylenediamine. The pyridyl and pyridinium N atoms are flanked by a molecule of water through strong hydrogen-bonding interactions [N-H...O = 2.762 (6) and 2.758 (6) A, and O-H...N = 2.834 (6) and 2.839 (6) A]. The water molecules have weak hydrogen-bonding interactions with the perchlorate anions as well. One of the perchlorate anions is severely disordered.

Isocyanide binding to the copper(I) centers of the catalytic core of peptidylglycine monooxygenase (PHMcc)

Binding of the Cu(I)-specific ligands 2,6-dimethylphenyl isocyanide (DIMPI) and isopropyl isocyanide (IPI) to the reduced form of peptidylglycine monooxygenase (PHM) is reported. Both ligands bind to the methionine-containing CuM center, eliciting FTIR bands at 2,138 and 2,174 cm(-1), respectively, but appear unable to coordinate at the histidine-containing CuH center in the wild-type enzyme. This chemistry parallels that previously observed for CO binding to the reduced PHM catalytic core (PHMcc). However, in contrast to the CO chemistry, peptide substrate binding did not induce binding of the isocyanide at CuH. XAS confirmed the binding of DIMPI at CuM via the observation of a short Cu-C interaction at 1.87 A and by the lengthening of the Cu-S(methionine) bond length by 0.06 A. Similarly, FTIR studies on DIMPI binding to the M314I and H172A mutant forms of reduced PHMcc confirmed the assignment of the 2,138-cm(-1) IR band as a CuM-DIMPI complex, but surprisingly also showed DIMPI binding to CuH, as indicated by a band at 2,148 cm(-1). An inorganic complex, [Cu(1,2-Me2Im)2(DIMPI)](PF6), was synthesized and its crystal structure was determined as a model for the interaction of isocyanides with imidazole-containing Cu(I) complexes. Comparison of EXAFS data for the protein and model suggests that DIMPI probably binds to CuM in a tilted fashion, similar to that of ethyl isocyanide binding to myoglobin.

Copper(I) complexes, copper(I)/O(2) reactivity, and copper(II) complex adducts, with a series of tetradentate tripyridylalkylamine tripodal ligands

Copper(I) and copper(II) complexes possessing a series of related ligands with pyridyl-containing donors have been investigated. The ligands are tris(2-pyridylmethyl)amine (tmpa), bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine (pmea), bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine (pmap), and tris[2-(2-pyridyl)ethyl]amine (tepa). The crystal structures of the protonated ligand H(tepa)ClO(4), the copper(I) complexes [Cu(pmea)]PF(6) (1b-PF(6)), [Cu(pmap)]PF(6) (1c-PF(6)), and copper(II) complexes [Cu(pmea)Cl]ClO(4).H(2)O (2b-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4).H(2)O (2c-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4) (2c-ClO(4)), and [Cu(pmea)F](2)(PF(6))(2) (3b-PF(6)) were determined. Crystal data: H(tepa)ClO(4), formula C(21)H(25)ClN(4)O(4), triclinic space group P1, Z = 2, a = 10.386(2) A, b = 10.723(2) A, c = 11.663(2) A, alpha = 108.77(3) degrees, beta = 113.81(3) degrees, gamma = 90.39(3) degrees; 1b-PF(6), formula C(19)H(20)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 14.413(3) A, b = 16.043(3) A, c = 18.288(4) A, alpha = beta = gamma = 90 degrees; (1c-PF(6)), formula C(20)H(22)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 13.306(3) A, b = 16.936(3) A, c = 19.163(4) A, alpha = beta = gamma = 90 degrees; 2b-ClO(4).H(2)O, formula C(19)H(22)Cl(2)CuN(4)O(5), triclinic space group P1, Z = 4, a = 11.967(2) A, b = 12.445(3) A, c = 15.668(3) A, alpha = 84.65(3) degrees, beta = 68.57(3) degrees, gamma = 87.33(3) degrees; 2c-ClO(4).H(2)O, formula C(20)H(24)Cl(2)CuN(4)O(5), monoclinic space group P2(1)/c, Z = 4, a = 11.2927(5) A, b = 13.2389(4) A, c = 15.0939(8) A, alpha = gamma = 90 degrees, beta = 97.397(2) degrees; 2c-ClO(4), formula C(20)H(22)Cl(2)CuN(4)O(4), monoclinic space group P2(1)/c, Z = 4, a = 8.7682(4) A, b = 18.4968(10) A, c = 13.2575(8) A, alpha = gamma = 90 degrees, beta = 94.219(4) degrees; 3b-PF(6), formula [C(19)H(20)CuF(7)N(4)P](2), monoclinic space group P2(1)/n, Z = 2, a = 11.620(5) A, b = 12.752(5) A, c = 15.424(6) A, alpha = gamma = 90 degrees, beta = 109.56(3) degrees. The oxidation of the copper(I) complexes with dioxygen was studied. [Cu(tmpa)(CH(3)CN)](+) (1a) reacts with dioxygen to form a dinuclear peroxo complex that is stable at low temperatures. In contrast, only a very labile peroxo complex was observed spectroscopically when 1b was reacted with dioxygen at low temperatures using stopped-flow kinetic techniques. No dioxygen adduct was detected spectroscopically during the oxidation of 1c, and 1d was found to be unreactive toward dioxygen. Reaction of dioxygen with 1a-PF(6), 1b-PF(6), and 1c-PF(6) at ambient temperatures leads to fluoride-bridged dinuclear copper(II) complexes as products. All copper(II) complexes were characterized by UV-vis, EPR, and electrochemical measurements. The results manifest the dramatic effects of ligand variations and particularly chelate ring size on structure and reactivity.

Dicopper(I) complexes of unsymmetrical binucleating ligands and their dioxygen reactivities

The design, synthesis, and characterization of binuclear copper(I) complexes and investigations of their dioxygen reactivities are of interest in understanding fundamental aspects of copper/O2 reactivity and in modeling copper enzyme active-site chemistry. In the latter regard, unsymmetrical binuclear systems are of interest. Here, we describe the chemistry of new unsymmetrical binuclear copper complexes, starting with the binucleating ligand UN2-H, possessing a m-xylyl moiety linking a bis[2-(2-pyridyl)ethyl]amine (PY2) tridentate chelator and a 2-[2-(methylamino)ethyl]pyridine bidentate group. Dicopper(I) complexes of UN2-H, [Cu2(UN2-H)]2+ (1), as PF6- and ClO4- salts, are synthesized. These react with O2 (Cu:O2 = 2:1, manometry) resulting in the hydroxylation of the xylyl moiety, producing the phenoxohydroxodicopper(II) complex [Cu2(UN2-O-)(OH-)(CH3CN)]2+ (2). Compound 2(PF6)2 is characterized by X-ray crystallography, which reveals features similar to those of a structure described previously (Karlin, K. D.; et al. J. Am. Chem. Soc. 1984, 106, 2121-2128) for a symmetrical binucleating analogue having two tridentate PY2 moieties; here a CH3CN ligand replaces one pyridylethyl arm. Isotope labeling from a reaction of 1 using 18O2 shows that the ligand UN2-OH, extracted from 2, possesses an 18O-labeled phenol oxygen atom. Thus, the transformation 1 + O2-->2 represents a monooxygenase model system. [CuI2(UN2-OH)(CH3CN)]2+ (3), a new binuclear dicopper(I) complex with an unsymmetrical coordination environment is generated either by reduction of 2 with diphenylhydrazine or in reactions of cuprous salts with UN2-OH. Complex 3 reacts with O2 at -80 degrees C, producing the (mu-1,1-hydroperoxo)dicopper(II) complex [CuII2(UN2-O-)(OOH-)]2+ (4) (lambda max 390 nm (epsilon 4200 M-1 cm-1), formulated on the basis of the stoichiometry of O2 uptake by 3 (Cu:O2 = 2:1, manometry), its reaction with PPh3 giving O=PPh3 (85%), and comparison to previously studied close analogues. Discussions include the relevance and comparison to other copper bioinorganic chemistry.

Synthesis, Structure, and Solution NMR Studies of Cyanide-Copper(II) and Cyanide-Bridged Iron(III)-Copper(II) Complexes

A range of small molecules, such as cyanide, are known to bind and/or inhibit the active site of the heme-copper oxidase enzymes. As such, model studies are aimed at elucidating ligand binding modes and their subsequent impact on spectroscopic properties of derived complexes. We describe here the isolation and characterization of two compounds containing the Fe-CN-Cu moiety, [(py)(F(8)-TPP)Fe(III)-CN-Cu(II)(TMPA)](2+) (5) and [(F(8)-TPP)Fe(III)-(CN)(2)-{Cu(II)(TMPA)}(2)](3+) (6) [py = pyridine, TMPA = tris(2-pyridylmethyl)amine, and (F(8)-TPP) = tetrakis(2,6-difluorophenyl)porphyrinate(2-)]. [Cu(II)(TMPA)(CH(3)CN)](ClO(4))(2) and [(py)(F(8)-TPP)Fe(III)(CN)] (3) react to yield 5, while 6 is formed by combination of [Cu(II)(TMPA)(CN)]PF(6) (2-(PF(6))) and [(F(8)-TPP)Fe(III)(PF(6))] (4). Complex 2-(PF(6)) crystallizes in the orthorhombic space group Iba2 with a = 17.2269(5) Å, b = 17.3143(4) Å, and c = 14.4971(4) Å, Z = 8, complex (5-(Sb/P)F(6))(1.5)(ClO(4))(0.5) was obtained in the orthorhombic space group P222 with a = 17.9541(2) Å, b = 20.5359(1) Å, and c = 21.2023(2) Å, Z = 4, and 6-(PF(6))(3) crystallized in the monoclinic space group P2(1)/c with a = 15.318(4) Å, b = 33.921(2) Å, and c = 19.649(6) Å, beta = 109.69(2) degrees, and Z = 4. Compound 5 possesses a low-spin iron(III) center, bridged via cyanide to copper. The iron-cyanide vector deviates slightly from linearity (174.6(5) degrees ). The copper(II) ion is five-coordinated by the TMPA N-donor atoms and the cyanide carbon atom. The Cu(TMPA) moiety is bent with an angle of 163.8(5) degrees around the cyanide-copper vector. Compound 6 possesses a low-spin iron(III) atom axially coordinated by two cyanide ligands capped on either side by trigonally coordinated [Cu(TMPA)] moieties. The [Cu(1)(TMPA)] unit is twisted somewhat ( angleCu1-N&tbd1;C = 168 degrees ), whereas the [Cu(2)(TMPA)] unit is coordinated in a nearly linear fashion with respect to the cyanide-iron vector ( angleCu2-N&tbd1;C4 = 175 degrees ). (1)H and (2)H NMR spectroscopy on 5 and 6 confirmed the low-spin nature of these iron complexes (pyrrole resonance found at -11.1 and -8 ppm, respectively). The NMR data as well as observed solution magnetic moment (&mgr;(B) = 2.7 for 5; &mgr;(B) = 3.4 for 6) suggest ferromagnetic coupling between the paramagnetic metal ions. This gives rise to an enhancement of the electronic relaxation rate for Cu(II) in both 5 and 6 allowing for the observation of the sharp and downfield shifted TMPA ligand proton signals.

Binuclear Copper Complexes Based on the 6,6'-Bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine Ligand

The tripodal tetradentate ligand TMPA (tris(2-pyridylmethyl)amine) has provided a wealth of valuable new Cu(I) and Cu(II) chemistry, in particular associated with copper(I)/dioxygen reactivity studies (Karlin, K. D.; Kaderli, S.; Zuberbühler, A. D. Acc. Chem. Res. 1997, 30, 139-147). Dinucleating analogues have also been recently investigated, and here we describe new copper complexes of the 6,6'-bis[[bis(2-pyridylmethyl)amino]methyl]-2,2'-bipyridine ligand (bTMPA). The synthesis and X-ray crystallographic characterization of [(bTMPA)Cu(II)(2)(CH(3)CN)(2)(ClO(4))(2)](2+) (1, as ClO(4)(-) salt) and [(bTMPA)Cu(II)(2)(N(3))(2)(ClO(4))(2)] (2) are provided. [1: space group C2/c; a = 15.907(4) Å, b = 29.268(7) Å, c = 13.941(2) Å; beta = 97.79(2) degrees; Z = 4; volume = 6431(2) Å(3). 2: space group P2(1)/c; a = 8.118(5) Å, b = 29.743(8) Å, c = 9.120(6) Å; beta = 114.00(5) degrees; Z = 2; volume = 2012(2) Å(3).] Both solid state structures possess six-coordinate copper(II) ions, and in neither case does the 2,2'-bipyridine (bipy) moiety within bTMPA chelate to a single metal ion. Dissociation of bound perchlorate and the presence of pentacoordinate solution structures are suggested by spectroscopic (UV-vis with two d-d absorptions; axial EPR spectra) along with conductivity data (1, 1:4 electrolyte; 2, 1:2 electrolyte). Electrochemical measurements by cyclic volammetry have been carried out, and for a dicopper(I) analogue, [(bTMPA)Cu(I)(2)](ClO(4))(2) (3(ClO(4))(2)), a single quasireversible redox wave is observed; E(1/2) = +199 mV (versus Ag/AgCl in dimethylformamide), which is approximately 280 mV more positive than that observed for the simple "parent" compound [Cu(I)(TMPA)(CH(3)CN)](ClO(4)). Unlike [Cu(I)(TMPA)(CH(3)CN)](ClO(4)), 3 does not readily form dioxygen adducts.

Gynaecomastia in leprosy in three districts of Tamil Nadu

The prevalence of Gynaecomastia (GM), a well known complication of leprosy in adult male patients was studied in 790 cases of whom 641 were the inmates of five leprosy hospitals and the remaining 149 mostly from the clinics of field area attached to the Central Leprosy Teaching and Research Institute, Chengalpattu during 1982-83. The overall prevalence rate was found to be 19.24%. Among the hospitalised patients, it was 22.15% against 6.71% among the patients attending the clinics in the field area. The youngest and the oldest patient in this study was 16 years and 83 years respectively. The highest rate of 32.89% was in the 36-45 age group. Only 152 GM cases were detected; the rates in the lepromatous, borderline lepromatous, borderline tuberculoid were 29.21%, 9.64% and 3.68% respectively. Those who gave a history of frequent ENL reactions had a higher rate of GM i.e. 34.55 as against 21.52 without or with very infrequent ENL reaction. Early treatment had a remarkable effect in the reduction of GM. Only 14% developed GM when the treatment was started within 2 years after the onset of leprosy as against 46.9% when the same was started after 16 years. In the latter group, the longer duration of the disease could also play a contributory role. Sterility rate was more than double in those with GM i.e. 34.14% against 14% without it.