A dinuclear copper(II) complex [Cu2(PD)(DPP-) 2](ClO4)2 (1) incorporating a constrained binucleating hexadenate ligand, PD (1,3-bis{bis[(2-pyridyl)ethyl]amino}benzene), and coligand, DPP- (diphenylphosphate) was synthesized and characterized, with a specific outlook towards evaluating spectroscopic and H2O2 reactivity relevant to the active-sites of noncoupled dinuclear copper enzymes, DβM and PHM. In solution, complex 1 exhibits a broad 1H NMR in the range -25 to +60 ppm and has a solution magnetic moment (μ) of ∼2.0 B.M./Cu(II), typical of a noninteracting dicopper(II) center. The room temperature H2O2 reactivity of 1 monitored by UV-Vis spectroscopy reveals the formation of a copper(II)-dioxygen intermediate 1a, which in turn leading to a arene ligand hydroxylation (PD-O-) and thus provide a new doubly-bridged dicopper(II) complex, [Cu2(PD-O-)(DPP-)](ClO4) 2 (2). The dioxygen intermediate produces OPPh3 on treatment with PPh3 revealing it is an electrophilic hydroperoxide oxidant. Solution magnetic moment of 1.61 B.M./Cu(II) indicates the product complex 2 is a moderately interacting dicopper(II) center and its 1H NMR spans between -20 and +180 ppm. A comparison of the optical absorption features of complex 1a with related dinuclear hydroperoxo-copper(II) complexes is discussed. © 2011 Elsevier B.V.

Narasimha N. Murthy

Department Of Chemistry

Gnana Sutha Siluvai

Babu Vargheese

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Inorganica Chimica Acta

Acta Crystallographica Section C: Crystal Structure Communications

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

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 2138 and 2174 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 Å and by the lengthening of the Cu-S(methionine) bond length by 0.06 Å. Similarly, FTIR studies on DIMPI binding to the M314I and H172A mutant forms of reduced PHMcc confirmed the assignment of the 2138-cm-1 IR band as a CuM-DIMPI complex, but surprisingly also showed DIMPI binding to CuH, as indicated by a band at 2148 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.

Journal of Biological Inorganic Chemistry

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

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-)(CH3 CN)]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 °C, producing the (μ-1,1-hydroperoxo)dicopper(II) complex [CuII2(UN2-O-)(OOH-)] 2+ (4) (λmax 390 nm (ε 4200 M-I 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.

Inorganic Chemistry

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

1H-NMR spectral properties of two paramagnetic binuclear copper(II) complexes 1 and 2, which are weakly antiferro- and ferromagnetically coupled, respectively, in the solid state, have been studied in solution; corresponding parameters are compared to a mononuclear copper(II) analogue 1a. Compound 1 exhibits unusually sharp and hyperfine shifted ligand signals (+230 to -14 ppm) that are about 100 times sharper than corresponding signals that could be detected for 1a (+20.4 to -13 ppm). Complex 2 also displays moderately sharp signals, shifted even to a greater magnitude (+272 to 0 ppm). These observations are in contrast with other moderately antiferromagnetically coupled binuclear copper(II) systems where much broader signals are observed in addition to reduced hyperfine chemical shifts. A complete assignment of signals for 1 and 2 was accomplished by a combination of proton relaxation data and two-dimensional correlated spectroscopy (COSY) measurements, while for 1a only partial analysis could be performed because of broadness of its signals. An analysis of the relaxation data and a quantitative comparison among 1a, 1, and 2 show that the unusual spectral features observed for the weakly coupled binuclear copper(II) (S = 1/4 ) centers is caused by a two orders of magnitude decrease in the electron relaxation (τ(s) = 10-11 s) as compared to τ(s) = 10-9 s for the mononuclear copper(II) species, 1a. Shortening of τ(s) for homobinuclear compounds is not otherwise predicted, and possible mechanisms for the results are discussed. The present findings are significant with respect to the factors determining electronic relaxation in magnetically coupled systems and to the understanding of proton NMR when applicable to binuclear copper(II) metalloproteins.

Journal	Inorganica Chimica Acta
ISSN	00201693
Open Access	No