O-donor Groups Research Articles

Amine-Imine Nickel Catalysts with Pendant O-Donor Groups for Ethylene (Co)Polymerization.

The introduction of a secondary interaction is an efficient strategy to modulate transition-metal-catalyzed ethylene (co)polymerization. In this contribution, O-donor groups were suspended on amine-imine ligands to synthesize a series of nickel complexes. By adjusting the interaction between the nickel metal center and the O-donor group on the ligands, these nickel complexes exhibited high activities for ethylene polymerization (up to 3.48 × 106 gPE·molNi-1·h-1) with high molecular weight up to 5.59 × 105 g·mol-1 and produced good polyethylene elastomers (strain recovery (SR) = 69-81%). In addition, these nickel complexes can catalyze the copolymerization of ethylene with vinyl acetic acid, 6-chloro-1-hexene, 10-undecylenic, 10-undecenoic acid, and 10-undecylenic alcohol to prepare the functionalized polyolefins.

Oligo- and polymerization of ethylene by pyrrolide-imine chromium catalysts bearing pendant O-, S- and N-donor groups. Synthesis, characterization and DFT studies

The synthesis and ethylene reactivity of a new set of chromium(III) complexes supported by pyrrolide-imine ligands bearing pendant O-, S- and N-donor groups [Cr{(C4H3N-2-CH=N)Z}(THF)Cl2] (Z = CH2Ph-2-OMe, Cr1; Z = Ph-2-OPh, Cr2; Z = Ph-2-OMe, Cr3; Z = Ph-2-SPh, Cr4; Z = Ph-2-SMe, Cr5; Z = CH2Py, Cr6; Z = C2H4Py, Cr7) are described. Activation of Cr1-Cr7 with MAO generates active systems affording a full range oligomerization of ethylene (C4-C12+) with turnover frequencies (TOFs) in the range of 13,900–94,200 mol(ethylene)·mol(Cr)–1·h–1 along with production of a varied amount of polymer (6.9 - 91.5 wt.%). The nature of the pendant group has a significant impact on the catalytic performances of these Cr complexes. Particularly, catalytic precursors containing pendant O-donor groups (Cr1-Cr3) produce mostly oligomers (up to 89.0 wt%) while those bearing sulfur-base donor groups (Cr4 and Cr5) are primarily polymerization systems. DFT calculations suggested the presence of two different CrIII catalytic species, the mononuclear species responsible for production of polymer and one dinuclear species that have been ascribed for production of oligomers. By tunning the reactional conditions, higher TOF and higher selectivities for production of α-olefins were achieved. Notably, the use of high MAO loading (1500 equiv.) enhanced the activity of Cr2 [TOF = 389,800 (mol ethylene)⋅(mol Cr)−1⋅h−1] producing mostly oligomers (97.7 wt% of total products) with high selectivity for α-olefins (>95.5 wt.%).

Chromium(III) complexes based on phenoxy-imine ligands with pendant N- and O-donor groups as precatalysts for ethylene oligomerization: synthesis, characterization, and DFT studies

Chromium complexes of general formula [Cr{ZNO}(THF)Cl2] [2a, ZNO = C9H6N-8-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2b, ZNO = Ph(NH)-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2c, ZNO = 2-MeO-Ph-CH2-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2d, ZNO = 2-PhO-Ph-(N=CH)-2,4-tert-butyl-2-(OC6H2); 2e, ZNO = PhO-C2H4-(N=CH)-2,4-tert-butyl-2-(OC6H2)] and the bis(ligand) complex [Cr{C9H6N-8-NH2}2Cl2]Cl (4) were synthetized and characterized by elemental analysis, IR spectroscopy, and by X-ray crystallography for 4. In the solid state, 4 is monomeric with two 8-amino-quinoline acting as bidentate ligands and two chloride ligands in cis position. The DFT calculations showed slightly higher HOMO energy for 2d. In addition, the energy levels of the LUMO are slightly influenced by pendant O- and N-donor group. Particularly, the LUMOs for complexes 2a and 2d show a small contribution from Cr and Cl atoms as compared to other chromium complexes (2b, 2c and 2e), and the orbitals are almost entirely delocalized over the phenoxy-imine unit. Upon activation with methylaluminoxane (MAO), chromium precatalysts 2a-2e showed good activity in ethylene oligomerization (TOF = 22.0 – 52.7 × 103 (mol ethylene)(mol Cr)−1⋅h−1 at 80°C) with Schultz-Flory distribution of oligomers (KC4-C10 ≈ 0.92), and production of polymer varying from 2.9 to 22.3 wt.%. The catalytic performance is mainly controlled by electronic effects at the phenoxy-imine ligands. The bis(ligand) chromium complex 4 showed good activity in ethylene oligomerization (TOF = 39,400 (mol ethylene)(mol Cr)−1 h−1), producing mostly oligomers (95.2 wt% of total products) with high selectivity for α-olefins. The highest activity among the six precatalysts screened was reached with 2c (TOF = 52,700 mol(ethylene)•mol(Cr)−1•h−1).

Radical Molecular Modulator for High-Performance Perovskite Solar Cells.

The long-term stability of perovskite solar cells (PSCs) remains an issue impeding their commercialization. Generally, polycrystalline perovskite thin films have many defects on the grain boundaries, which affect the optoelectronic performance and stability of the devices under moisture, heat, illumination, and the presence of an electric field condition. The O-donor Lewis base is often employed to regulate the performance of PSCs such as carbonyl and carboxyl compounds. Herein, we have developed a concept of radical molecular modulation using the O-donor group for high-performance perovskite photovoltaic devices. The judiciously designed radical modulators 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), which located at the perovskite grain boundary through interaction with the perovskite surface sites, effectively passivated the surface defects while templating the formation of large grain crystal and high-quality perovskite thin films. Accordingly, the optimized TEMPO-modulated PSCs achieved a power conversion efficiency of 20.73% with superior stability. This work makes an important contribution for exploring the effect of radical in perovskites to improve the performance of PSCs and other optoelectronic devices.

Promotional effect of macrocyclization in O2Nx naphtha-aza-crown macrocyclic ligands on fluorescence chemosensing of Al(III)

Two new macrocyclic ligands Ln (L and L′) bearing two fluorophore naphthalene moieties were synthesized and characterized by employing 1H and 13C NMR, IR, microanalysis as well as mass spectrometry. Comparative studies on the effect of assorted metal cations as Cr(III), Cu(II), Zn(II), Cd(II), Pb(II), Na(I), Ni(II), Co(II), Ba(II), Fe(II), Al(III), Mg(II), Cs(I), Ca(II), Hg(II), K(I), Mn(II), Ag(I), Fe(III) on fluorescence and UV–vis spectra of Ln in ethanol illustrated that both of the macrocycles were sensitive and selective fluorescence chemosensors for Al(III). Remarkable binding constant values as 1.36 × 105 M−1 and 1.15 × 105 M−1 alongside 1:1 stoichiometry for Al(III)/L and Al(III)/L′ were established by employing fluorescence spectrophotometry. Monitoring of probable coordination sites on Ln to Al(III) by 1H NMR spectroscopy indicated on the coordination of both N- and O-donor groups in DMSO-d6. In order to elucidate the effect of macrocyclic nature in this O2Nx naphtha-aza-crown family on the observed fluorescence chemosensing behavior of metal ion, two new O2Nx-donor macroacyclic ligands were also prepared and characterized by the abovementioned methods. The comparative experiments revealed that the macrocyclization had an escalating role on the fluorescence parameter of the macrocycle as a metal-ion chemosensor.

The effectiveness of ion exchange resins in separating uranium and thorium from rare earth elements in acidic aqueous sulfate media. Part 2. Chelating resins

Chelating resins with different functional groups were evaluated for their potential application in separating uranium U(VI) and thorium Th(IV) from rare earth elements, RE(III). The candidate resins included a bis-picolylamine resin, aminophosphonic resins, iminodiacetic resins, and solvent-impregnated resins. The adsorption selectivity of these resins towards U(VI) and Th(IV) in the presence of selected RE(III) was examined in sulfuric acid media of varying concentrations. It was evident that the adsorption performance of the resins was acid concentration-dependent. Most candidate resins had potentially feasible selective adsorption at or below 0.1 mol/L H2SO4 (or pH ≥ 1). Depending on their functional groups, the chelating resins displayed varying selectivity towards U(VI), Th(IV) and RE(III). It was found that the iminodiacetic resins exhibited the highest affinity for U(VI) and Th(IV) over RE(III). At 0.005 mol/L H2SO4 (or pH 2), the adsorptions of U(VI) and Th(IV) were approximately 90% while adsorption of RE(III) was less than 20%. This can be explained by considering the coordination chemistry of the resins whereby molecular ligands with N- and O-donor atoms were demonstrated to adsorb both U(VI) and Th(IV) strongly. Comparing the different O-donor groups (i.e., sulfonyl, phosphoryl and carboxyl), the carboxyl group from the iminodiacetic resin gave the best separation of U(VI) and Th(IV) from RE(III). The performance of the solvent-impregnated resins has indicated the possibility of exploiting steric effects to obtain a highly selective chelating resin for U(VI) and Th(IV) over RE(III). In addition, the potential application of these resins in an integrated process for sequential 2-stage separation of U(VI) and Th(IV) from RE(III) in sulfuric acid media is also presented.

Group 4 metal compounds incorporating the amide ligand, [N(SiMe2{C6H4-2-OMe})2](-).

The anisole-substituted silyl-amide anion, [N(SiMe2{C6H4-2-OMe})2](-) (L), has been used as a pincer-type ligand in coordination chemistry. X-ray diffraction data for the lithium salt shows a trimetallic structure consisting of two equivalents of Li(L) that sequester a molecule of LiCl. The potassium salt K(L) is dimeric in the solid-state with bridging amide ligands. Each structure shows chelation of both O-donor groups to the electropositive metal. In contrast, the titanium compound Ti(L)Cl3 is four-coordinate with a monodentate amide. The zirconium compound Zr(L)2Cl2 is monometallic with a six-coordinate metal and two N,O-bidentate amides.

Recovery pattern of non-protein respiratory quotient and non-esterified fatty acids after liver resection

ObjectivePerioperative nutritional care is important to maintain preoperative and postoperative nutritional status. However, few reports have investigated energy metabolism after hepatectomy. The aim of this study was to determine differences in energy metabolism, blood biochemistry, and nutritional status before and after liver resection in patients with hepatocellular carcinoma (HCC) and healthy living donors for liver transplantation. MethodsEighteen hospitalized patients with HCC group and 13 living donors for liver transplantation (donor group) were enrolled in this study. The donor group was divided into two groups on the basis of age; Y-donor group (age < 40 y, n = 7), and O-donor group (age ≥ 40 y, n = 6). Energy metabolism was measured by indirect calorimetry at preoperative day and postoperative day (POD) 7 and 14, and blood biochemistry was also examined. ResultsRecovery of non-protein respiratory quotient (npRQ) and blood biochemical data such as total bilirubin, aspartate aminotransferase and alanine aminotransferase levels were observed in Y-donor group on POD 14. However, although biochemical data improved in the HCC and O-donor group, npRQ remained unchanged on POD 14. ConclusionsImprovement of npRQ took longer than blood biochemical data in patients with HCC and older donors. Because the recovery of npRQ is associated with donor age, careful nutritional management may be required for a longer time depending on the pathophysiological condition of each patient after hepatectomy.

Click synthesis of triazole-linked calix[4]arene ionophores. Potentiometric and ESI-MS screening of ion-selectivity

A series of 1,2,3-triazole-linked calix[4]arene ionophores comprised of different O-donor groups (OH, COOEt, CONEt2) attached either to the lower rim of calix or to the triazole moieties were synthesized to explore their ion-selectivity for the first time in potentiometric transduction. Plasticized PVC membrane electrodes (ISEs) were fabricated, and their potentiometric selectivities were measured toward a series of mono- and divalent metal ions. Structure-ion-selectivity relationship and the structural requirements of the coordination sphere for selective binding were established. ISEs made of calix[4]arene-bis-triazoles were found generally to exhibit distinct Ag+ selectivity in the order 3 ≈ 4 > 2 > 1, indicating the beneficial effect of the carboxamide or ester groups in the complexing site. In contrast, calix[4]arene-tetratriazole 5 comprised only sp2 N-donor atoms displayed excellent Cu2+ selectivity over a series of alkali-, alkaline earth- and transition metal ions. A unique feature of the outstanding Ag+ selective electrodes made of 3 and 4 was recognized and suggested their potential application as Na+ ISEs in systems not containing silver ions. Further, the potential use of competitive ESI-MS experiments for screening the binding affinities of ionophores 3–6 to different metal ions was also demonstrated.

Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

Neutral trans-[Pd(C6F5)XL2] (X = Cl, Br) and cationic trans-[Pd(C6F5)L2(NCMe)]BF4 (L = SbPh3, AsPh3, As(C6Cl2F3)Ph2, AsCyPh2, AsMePh2, PPh3) complexes have been studied and tested for norbornene (NB) polymerization and copolymerization with 5-norbornene-2-carboxaldehyde (NB-CHO). The neutral complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated arsine AsPh2(C6Cl2F3) is the most active catalyst and allows for easy spectroscopic study of the reacting systems by 19F NMR. Calorimetry provides straightforward monitoring and detection of activation and deactivation processes in polymerization reactions that give insoluble products and cannot be followed by NMR spectroscopy.

Up to four phenoxyl radicals coordinated to two metal ions in copper and zinc complexes?

Neutral copper(II) and zinc(II) complexes of the mono- and dinucleating Schiff base ligands (2,4-di-tert-butyl-6-({2-[(3,5-di-tert-butyl-2-hydroxy-benzylidene)-amino]-phenylimino}-methyl)-phenol) and (2,4-di-tert-butyl-6-({2,4,5-tri-[(3,5-di-tert-butyl-2-hydroxy-benzylidene)-amino]-phenylimino}-methyl)-phenol) respectively were synthesized and characterized. The monometallic complex can be oxidized into a mono and a dication, while oxidation of the dimetallic one affords up to a tetracation. Whatever the ligand and metal are, oxidation takes place at the phenolate moieties, which were oxidized into coordinated phenoxyl radicals, i.e. the oxidation locus is not correlated to the ligand nuclearity. These results could be rationalized with previous ones by considering the hybridization of the coordinating nitrogens and the nature of the O-donor groups.

Cyclopalladation of the Indole Ring in Palladium(II) Complexes of 2N1O-Donor Ligands and Its Dependence on the O-Donor Properties

Synthetic, structural, spectroscopic, and kinetic studies have been carried out on the Pd(II) complexes of new 2N1O-donor ligands containing a pendent indole, 3-(N-2-pyridylmethyl-N-2-hydroxy-5-methoxybenzylamino)ethylindole (HMeO-iepp), 3-(N-2-pyridylmethyl-N-2-hydroxy-5-nitrobenzylamino)ethylindole (HNO2-iepp), and (N-2-pyridylmethyl-3-indolylethylamino)acetic acid (Hiepc) (H denotes a dissociable proton). [Pd(MeO-iepp)Cl] (2), [Pd(NO2-iepp)Cl] (3), and [Pd(iepc)Cl] (4) were prepared and revealed by X-ray analysis to have a pyridine nitrogen, an amine nitrogen, a phenolate or carboxylate oxygen, and a chloride ion in the coordination plane. UV absorption and 1H NMR spectral changes indicated that all the complexes could be converted to the indole-binding complexes where the O donor was replaced by the indole C2 atom by cyclopalladation in DMSO or DMF in the temperature range of 40-60 degrees C. Formation of the indole-binding complex species obeyed the first-order kinetics, from which the activation parameters were estimated. The formation rate was dependent on the properties of the O-donor group, a lower pKa value of its conjugate acid causing faster conversion to the indole-binding species in the order 2 (methoxyphenolate) < 3 (nitrophenolate) < 4 (carboxylate). On the other hand, the ratio of the indole-binding complex to the O-donor complex as a result of the conversion was greater for the complexes with a higher pKa value of the ligand OH group, the order being 2 > 3 > 4.

Syntheses and structures of some adducts of silver(I) oxyanion salts with some 2- N, O-donor-substituted pyridine bases

Syntheses and room-temperature single crystal X-ray structural characterizations are recorded for a variety of silver(I) oxyanion (perchlorate, nitrate and trifluoroacetate (‘tfa’) (increasing basicity)) adducts, AgX, with a number of pyridine (‘py’) bases, L, functionalized in the 2-position with N- or O-donor groups, namely 2-amino-, 2-amino-6-methyl-, 2-aminomethyl-, 2-hydroxy-, 2-methoxy- and 2-acetyl- pyridines, ‘2np’, ‘nmp’, ‘amp’, ‘ohp’, ‘mop’, and ‘acp’. A variety of stoichiometries and associated structural types are defined: [Ag(chelate) 2]X, L/X = amp,acp/ClO 4, [XAg(chelate) 2], L/X = acp/tfa, of 1:2 AgX:L stoichiometry; for 1:1 stoichiometry, although a discrete mononuclear complex [(chelate)Ag(O 2NO)] is defined for AgNO 3: acp (1:1), all others are polymers, successive silver atoms being linked by N, N′-bridging ligands singly (L/X = 2np/ClO 4 (⋯HAgHTAgTHAgH⋯), amp/ClO 4, NO 3 (⋯HTAgHTAg⋯) (‘H’ ≡ head, ‘T’ = tail)) or pairwise, ⋯L 2AgX 2AgL 2Ag⋯ (L/X = 2np/tfa, nmp/NO 3). More complex polymeric arrays are found with L/X = ohp/NO 3, tfa, where interaction with the metal takes place via the O-donor only, the py functionality being protonated, and in adducts of more complex stoichiometry AgNO 3:mop (2:3) and AgNO 3:2np (3:4).

Self-assembly of palladium(II) and platinum(II) complexes of 2-hydroxypyrimidine to novel metallacalix[4]arenes. Receptor properties through multiple H-bonding interactions.

Reaction of [enM(H2O)2](NO3)2 (en = ethylenediamine, M = PdII, PtII) with 2-hydroxypyrimidine (Hpymo) in water results in self-assembly to cyclic complexes of type [enM(pymo-N1,N3)]4(NO3)4 (1, M = PdII; 2, M = PtII) which are structurally analogous to calix[4]arenes. The tetranuclear cations in compounds 1 and 2 adopt, in the solid state, a 1,3-alternate orientation of the pymo residues. Attempts to coordinate either soft (PdII, PtII), borderline (CuII, ZnII), or hard (LaIII, BeII, NaI) metal ions to the oxo surface of the metallacalix[4]arene lower rim were fruitless. In fact, X-ray studies performed on [[enPt(pymo-N1,N3)]4(ClO4)4]2.[Cu(H2O)6](ClO4)2.9H2O (4) showed that multiple H-bonding interactions between the water coordination sphere of the copper center and the oxo surface of two tetranuclear cations take place instead of a direct interaction between the heterometal and the oxo surface of the metallacalix[4]arene. Encapsulation of [Cu(H2O)6]2+ is also responsible for the stabilization of the pinched-cone conformation of the tetranuclear cations in 4. pH* dependent 1H NMR spectra of compounds 1 and 2 indicate a very low basicity of the O-donor group of the pymo residues, revealing no protonation of this position down to pH* 0. Moreover, recrystallization of 2 from strongly acidic aqueous solution (approximately 1 M HClO4) affords the adduct [[enPt(pymo-N1,N3)]4(ClO4)4]2.[H20O8](ClO4)4 (6). Analogously to 4, the cationic [H20O8]4+ species is sandwiched between two tetranuclear cations as a result of multiple H-bonding interactions with the oxo surface of two metallacalix[4]arenes. Again a pinched-cone orientation of the pymo residues is realized.

New mono- and polyazafulleroids C 60(NR) n ( n=1, 2, 4, 6) derived from a chiral azide containing N- and O-donor groups, and reactivity with [RhCl(CO) 2] 2

Reactions in a 1:1 molar ratio of the chiral azide (2 S,4 S)-4-azido-1-benzyloxycarbonyl-2-( t butylaminocarbonyl)pyrrolidine (N 3R, R=C 17H 23N 2O 3, 1) with C 60 in ClPh, in the temperature range 100–132°C, lead to mixtures of mono- and polyazafulleroid species of general formula C 60(NR) n ( n=1, 2, 4), with a composition depending on the reaction conditions, and with a yield in the most substituted polyazafulleroids that increases with the concentration of reactants. However the reaction in a 1:6 molar ratio (fullerene–azide 1) leads only to hexaazafulleroids C 60(NR) 6. All mono- and polyazafulleroids C 60(NR) n react with [Rh(CO) 2Cl] 2 to give complexes of composition C 60(NR) n [Rh(CO) 2Cl] n , which could be used as catalysts in asymmetric hydrogenation of prochiral olefins.

TEMPLATE SYNTHESES AND PROPERTIES OF COPPER(II)-LANTHANIDE(III) COMPLEXES OF PHENOL-BASED SYMMETRIC AND UNSYMMETRIC DINUCLEATING MACROCYCLES

Cu(II)-Ln(III) complexes of H2(fsal-n,m) ((n,m = (2,3), (3,2) (3,3); Ln = Lanthanide), fsal-n,m-Cu.Ln, have been synthesized by a template reaction, where fsal-n,m 2- denotes inculcating macrocycles with two 2,6-bis(iminomethyl)-4-methylphenolate entities combined through two lateral chains, -(CH2)n- and -(CH2)m-, at the iminonitrogens. Temperature dependences of magnetic susceptibilities for the Cu(II)-Gd(III) complexes showed that an intermolecular ferromagnetic interaction operates between Cu(II) and Gd(III) ions in fsal-2,3-Cu,Gd and fsal-3,2-Cu,Gd. Absorption spectra suggested that substrates possessing N- and O-donor groups such alcohols are specifically bound at the Cu-Ln center of fsal-2,3-Cu,Ln. through the nitrogen to the copper site and through the oxygen to the lanthanide site. The fluorescence intensity of Eu(III) decreased drastically on forming the Cu-Eu complex.

Copper(II)–Lanthanide(III) Complexes of Symmetric Dinucleating Macrocycle with Two Phenolate Bridges

Abstract The first heteronuclear copper(II)–lanthanide(III) complexes, CuLn(fsal-2,2)(NO3)3(H2O)n (n = 2 for Ln = Nd and n = 1 for Ln = Eu and Gd), of a symmetric macrocyclic dinucleating Schiff base ligand, H2fsal-2,2, which is a condensation product of two molecules of 2,6-diformyl-4-methylphenol and two molecules of ethylenediamine, were synthesized by the reaction of [N,N′-bis(3-formyl-5-methylsalicylidene)ethylenediaminato]copper(II) and ethylenediamine in the presence of lanthanide(III) ion as a template, where fsal-2,2 denotes the dianion formed by the deprotonation of two phenolic hydroxyl groups in H2fsal-2,2. The absorption spectra suggested that substrates possessing N- and O-donor groups, such as amino alcohols, are specifically bound at the Cu–Ln center through nitrogen-coordination to the copper site and through oxygen-coordination to the lanthanide site. The fluorescence intensity of Eu(III) decreased drastically upon forming the Cu–Eu complex. A cryomagnetic susceptibility measurement indicated a ferromagnetic spin-spin interaction between Cu(II) and Gd(III) ions.

Electron Transfer. 130. Reductions with Indium(I)1

Aqueous solutions of the hypovalent state indium(I) have been prepared by treatment of In(Hg) with silver triflate in acetonitrile, followed by dilution with oxygen-free water. These solutions are stable for over 5 h at 25 degrees C. In(I)(aq) reacts with oxidants of the type [(NH(3))(5)Co(III)(Lig)](2+) (In(I) + 2Co(III) --> In(III) + 2Co(II)), and kinetic profiles are consistent with a two-step sequence proceeding with formation of the metastable state In(II), which reacts rapidly with Co(III). Rate ratios for reductions of halogeno-substituted oxidants point to predominance of halide-bridged paths for the chloro, bromo and iodo complexes. Reductions of carboxylato-substituted derivatives are slow but appear to entail inner-sphere precursors if aided by an O-donor group in a position favorable for chelation. In no case is there evidence for reaction via initial reduction of the ligand (the radical-cation mechanism) although the potential of the In(I,II) couple (-0.40 V) allows this path for carbonyl-substituted oxidants. Reductions by In(I), like those by Eu(II), make no significant use of bridging by heterocyclic donor nitrogen centers in pyridine and pyrazine complexes.

Copper K-extended x-ray absorption fine structure studies of oxidized and reduced dopamine beta-hydroxylase. Confirmation of a sulfur ligand to copper(I) in the reduced enzyme.

The structure of the copper sites in oxidized and reduced dopamine beta-hydroxylase has been studied by extended x-ray absorption fine structure spectroscopy using a restrained refinement approach to data analysis. An histidine-rich active site has been found to be present with an average histidine coordination of between two and three histidine ligands per copper. In the oxidized protein, the data support four-coordination, involving two to three imidazole groups at 1.99 A with additional ligands derived from water or exogenous O-donor groups at an average distance of 1.94 A. Studies on the reduced enzyme have focused on resolving the controversy in the literature (Scott, R. A., Sullivan, R. J., De Wolfe, W. E., Dolle, R. E., and Kruse, L. I. (1988) Biochemistry 27, 5411-5417; Blumberg, W. E., Desai, P. R., Powers, L., Freedman, J. H., and Villafranca, J. J. (1989) J. Biol. Chem. 264, 6029-6032) as to whether a S/Cl scatterer is a ligand to Cu(I). Five independent samples of reduced enzyme prepared under conditions designed to probe the Cu(I) ligand environment have been measured and analyzed. All five samples gave identical spectra and could be simulated by two to three imidazoles (1.93 A) and 0.5 S/Cl (2.25 A) per Cu(I). The spectra were insensitive to the presence of added bromide or to exclusion of chloride during preparation. The results establish that the heavy atom scatterer is derived from a sulfur donor. Some evidence was found for an additional O/N scatterer at 2.6 A in the reduced enzyme. A hypothesis for the structure of the copper sites has been proposed involving inequivalent CuA(His)3(H2O)...CuB-(His)2X(H2O) coordination in the oxidized enzyme, which upon reduction loses coordinated water and coordinates a sulfur probably from a methionine.

Cobalt(II)–lanthanoid(III)(Ln = La, Nd, or Gd) complexes of N,N′-ethylenebis(3-carboxysalicylideneimine). Interaction of ligating groups on the Co–Ln centre

Cobalt(II)–lanthanoid(III) complexes of N,N′-ethylenebis(3-carboxysalicylideneimine)(H4csalen), [CoLa(csalen)(CH3OH)(NO3)], [CoNd(csalen)(H2O)2(NO3)], and [CoGd(csalen)(H2O)(NO3)], have been prepared and characterized, where the cobalt ion is bound at the N2O2 site and the lanthanoid ion at the O4 site of the binucleating ligand. Based on electronic and e.s.r. spectra the configuration around the cobalt ion was shown to be planar at room temperature in dimethylformamide (dmf) or dimethyl sulphoxide (dmso) while square pyramidal at liquid-nitrogen temperature with a solvent molecule at the axial site. When a nitrogen-containing base such as pyridine or n-propylamine was added to dmf solutions of the Co–Ln complexes the base was co-ordinated to the cobalt ion to afford five-co-ordination around the metal at room temperature. At liquid-nitrogen temperature the configuration around the cobalt was dependent upon the nature of the added base: six-co-ordination for pyridine or its derivatives and five-co-ordination for aliphatic amines. It is suggested that substrates possessing N- and O-donor groups such as 2-aminoethanol are specifically bound at the Co–Ln centre, via N to the cobalt and O to the lanthanoid ion.