Copper Coordination Sphere Research Articles

Polymeric dichlorido-bridged copper(II) offset stacked dimer coordination compounds and molecular spin stairs

A family of oxygen coordinated dichlorido-bridged n-X-2-pyridone (1, n = 3, X = Cl; 2, n = 3, X = Br; 3, n = 4, X = Cl; 4, n = 4, X = Br; 5, n = 5, X = Cl; 6, n = 5, X = Br) Cu(II) offset stacked dimer compounds, denoted molecular spin stairs, have been prepared and analyzed by single-crystal X-ray diffraction (1–4), powder X-ray diffraction (1–6), and variable temperature magnetic susceptibility measurements (1–6). Ferromagnetism is dominant in all compounds with a weaker antiferromagnetic exchange present in 1–4. The ferromagnetic exchange correlates to increased twist angles which are defined by the extent of the tetrahedral distortion of the copper coordination sphere and the identity of the halogen on the ring. The compounds were qualitatively fit to a ferromagnetic Heisenberg chain model with a Curie-Weiss interchain correction. The general Hamiltonian used is of the form H = − J ∑ S 1 S 2 . The ratio of exchange energies denoted α ( α = J FM | J AFM | ) ranges between 2.6 and 4.7. This family of compounds constitutes possible S = ½ Haldane-like materials.

Diborane Reductions of CO2 and CS2 Mediated by Dicopper μ-Boryl Complexes of a Robust Bis(phosphino)-1,8-naphthyridine Ligand.

A dinucleating 1,8-naphthyridine ligand featuring fluorene-9,9-diyl-linked phosphino side arms (PNNPFlu) was synthesized and used to obtain the cationic dicopper complexes 2, [(PNNPFlu)Cu2(μ-Ph)][NTf2]; [NTf2] = bis(trifluoromethane)sulfonimide, 6, [(PNNPFlu)Cu2(μ-CCPh)][NTf2], and 3, [(PNNPFlu)Cu2(μ-OtBu)][NTf2]. Complex 3 reacted with diboranes to afford dicopper μ-boryl species (4, with μ-Bcat; cat = catecholate and 5, with μ-Bpin; pin = pinacolate) that are more reactive in C(sp)-H bond activations and toward activations of CO2 and CS2, compared to dicopper μ-boryl complexes supported by a 1,8-naphthyridine-based ligand with di(pyridyl) side arms. The solid-state structures and DFT analysis indicate that the higher reactivities of 4 and 5 relate to changes in the coordination sphere of copper, rather than to perturbations on the Cu-B bonding interactions. Addition of xylyl isocyanide (CNXyl) to 4 gave 7, [(PNNPFlu)Cu2(μ-Bcat)(CNXyl)][NTf2], demonstrating that the lower coordination number at copper is chemically significant. Reactions of 4 and 5 with CO2 yielded the corresponding dicopper borate complexes (8, [(PNNPFlu)Cu2(μ-OBcat)][NTf2]; 9, [(PNNPFlu)Cu2(μ-OBpin)][NTf2]), with 4 demonstrating catalytic reduction in the presence of excess diborane. Related reactions of 4 and 5 with CS2 provided insertion products 10, {[(PNNPFlu)Cu2]2[μ-S2C(Bcat)2]}[NTf2]2, and 11, [(PNNPFlu)Cu2(μ,κ2-S2CBpin)][NTf2], respectively. These products feature Cu-S-C-B linkages analogous to those of proposed CO2 insertion intermediate.

Synthesis, structural and computational study, DNA binding and cytotoxic activity of Cu(II) complexes of 6- and 7-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazones

Three new coordination complexes of Cu(II) ions made from two hydrazone ligands, 7-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL1) and 6-chloro-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-2-furoyl-hydrazone (HL2) have been synthesized and fully characterized by spectroscopic techniques. Their crystal and molecular structures revealed distorted square pyramidal mononuclear complexes: [(L1)Cu(H2O)2](NO3)·3H2O, 1(NO3), [(L2)Cu(H2O)2](NO3)·2H2O·CH3OH, 2(NO3), and [(L2)Cu(NO3)(CH3OH)]·2CH3OH, 3, comprising the ligand (L1 and L2) in tridentate fashion (ONO) with two water molecules in 1+ and 2+, and a single methanol molecule and a nitrate ion in 3 in their respective copper coordination spheres. EPR spectra in frozen methanol revealed the occurrence of several species arising from different coordination environments. A detailed DFT investigation on the energetics of solvents exchange (H2O, MeOH, and DMSO) and simulation of the EPR parameters showed that the exchange processes occur easily in solution. The value gz indicated the occurrence of a dimeric aggregate for 2+. The new copper complexes exhibited a noticeable antiproliferative activity with IC50 values in the micromolar range against HCT-15, H157, BxPC3, PNS-1, and A431 cell lines and they were found to be 3-fold more effective than cisplatin against pancreatic PSN-1 cell lines. Cross-resistance tests on A2780 and LoVo cancer cell lines and the corresponding multidrug or oxaliplatin resistant sublines showed that complexes 1(NO3) and 2(NO3) were equally cytotoxic to sensitive and resistant cells, thus overcoming multidrug and oxaliplatin resistance.

A systematic look at structural diversity of metal phosphonates

AbstractHerein, we report the synthesis of three new copper phosphonate frameworks using a tetrahedral‐shaped organic building block, methane tetra‐p‐phenylphosphonic acid (H8‐MTPPA), and three different N‐ancillary ligands terpyridine (terpy), 2,2’‐bipyridine (2,2’‐bpy), phenanthroline (phen) to optimize the ligand binding modes on copper coordination sphere to generate molecular secondary building units (SBUs) in metal organophosphonates. We report the crystal structures of rod‐shaped one‐dimensional zig‐zag chain structure, [{Cu(terpy)}(H6‐MTPPA)(H2O)]⋅2H2O, three‐dimensional framework, [{Cu5(2,2’‐bpy)2}(H2‐MTPPA)(H4‐MTPPA)], and one‐dimensional structure [{Cu2(phen)2}(H4‐MTPPA)]⋅4H2O. Magnetic analysis of three‐dimensional copper phosphonate framework, namely [{Cu5(2,2’‐bpy)2}(H2‐MTPPA)(H4‐MTPPA)], showed paramagnetic behavior. Crystal structures were characterized by single crystal X‐ray diffraction, FT‐IR, and thermogravimetric analysis (TGA).

Нитрат 4,4’-дипиридил меди(II) – 2D металл-органический каркас

The crystal structure of the organometallic framework, namely, 4,4’-dipyridylcopper(II) nitrate with the DMSO molecule in the copper coordination sphere, has been described, the structural features have been established by the X-ray method. Crystallographic data: C55H93Cu2N12O23S7, М 1641.91; monoclinic syngony, space group P 1 21/n 1; cell parameters: a = 15.490(3), b = 14.760(3), c = 15.980(3); a = 90, β = 90.10(3), g = 90 deg.; V = 3653.5(13) Å3, Z = 2, ρcalc = 1.493 g/cm3. The bidental ligand in the organometallic framework is 4,4’-bipyridyl; copper, being a complexing ion, forms a coordination octahedron, the nitrogen atoms of bipyridine fragments are in four equatorial positions, the oxygen atoms of nitrate ion and dimethyl sulfoxide are in two axial positions. The Cu–N bond lengths in the equatorial position are in the range of 2.014–2.031 Å, and the Cu–O bond lengths are 2.297 Å and 2.515 Å. The occupation of the equatorial positions by 4,4’-dipyridyl leads to formation of a layered structure, which distinguishes the resulting compound from another MOF based on copper(II), nitrate ions and 4,4’-dipyridyl, in which all the equatorial positions are occupied by NO3-groups. The individual layers in the obtained 4,4’-dipyridylcopper(II) nitrate are not crosslinked; they are shifted relative to neighboring layers. The pyridyl rings of 4,4’-dipyridyl are rotated at an angle of 5.77(2) degrees. relative to each other.

Robustness and stability of the L-carnosine copper(II) dimer. Changes in the copper coordination sphere upon heating/solvent substitution

Coordination compounds of L-carnosine (H2car) have been the subject of much research, as they have potential therapeutic applications due to their antioxidant and anti-inflammatory properties. This paper analyzes the coordination...

Bromine versus chlorine substituent in breathing crystals of a copper(I) coordination compound with a triazolamine Schiff base.

It is known that N-[4-(chlorobenzylidene)-4H-1,2,4-triazol-4-amine in reaction with copper(I) perchlorate(VII) forms metastable breathing crystals built up of X-shaped binuclear units containing copper(I) ions in a trigonal coordination sphere. Using trifluoromethanesulfonate instead of perchlorate(VII) affects the self-assembly of the X-shaped units and the breathing function of the resulting crystals. The latter are not breathing crystals. Copper(I) trifluoromethanesulfonate with N-[4-(bromobenzylidene)-4H-1,2,4-triazol-4-amine crystallizes in two forms: open (with the presence of 1D channels) and closed (without 1D channels). Both are characterized by the presence of X-shaped binuclear cationic units and the trigonal coordination sphere of copper(I) ions. The open form has the ability to engage in reversible sorption. The desorption process is associated with the large reorientation of the binuclear units and the reorganization of the intermolecular interactions leading to the closure of the channels. The post-synthetically obtained channel-less form differs from the channel-less form obtained by direct crystallization, the latter being incapable of sorption. The mechanism of the desorption process of the open form is governed by the general principle of dense packing, and the main reason for the sorption process is the formation of directional halogen-halogen interactions. The halogen atom in the para position of the ligands influences the formation of different crystalline forms and also a different mechanism for the desorption process.

Chalcogen Bonding in the Decoration of the Secondary Coordination Sphere of Copper(II) Complexes: Activation of Nitriles, the Auxiliary Ligand Substituent Effect

Chalcogen Bonding in the Decoration of the Secondary Coordination Sphere of Copper(II) Complexes: Activation of Nitriles, the Auxiliary Ligand Substituent Effect

Asymmetric Sulfoxidation by a Tyrosinase Biomimetic Dicopper Complex with a Benzimidazolyl Derivative of L-Phenylalanine.

A challenge in mimicking tyrosinase activity using model compounds is to reproduce its enantioselectivity. Good enantioselection requires rigidity and a chiral center close to the active site. In this study, the synthesis of a new chiral copper complex, [Cu2(mXPhI)]4+/2+, based on an m-xylyl-bis(imidazole)-bis(benzimidazole) ligand containing a stereocenter with a benzyl residue directly bound on the copper chelating ring, is reported. Binding experiments show that the cooperation between the two metal centers is weak, probably due to steric hindrance given by the benzyl group. The dicopper(II) complex [Cu2(mXPhI)]4+ has catalytic activity in the oxidations of enantiomeric couples of chiral catechols, with an excellent discrimination capability for Dopa-OMe enantiomers and a different substrate dependence, hyperbolic or with substrate inhibition, for the L- or D- enantiomers, respectively. [Cu2(mXPhI)]4+ is active in a tyrosinase-like sulfoxidation of organic sulfides. The monooxygenase reaction requires a reducing co-substrate (NH2OH) and yields sulfoxide with significant enantiomeric excess (e.e.). Experiments with 18O2 and thioanisole yielded sulfoxide with 77% incorporation of 18O, indicating a reaction occurring mostly through direct oxygen transfer from the copper active intermediate to the sulfide. This mechanism and the presence of the chiral center of the ligand in the immediate copper coordination sphere are responsible for the good enantioselectivity observed.

Unexpected coordination mode for a phenol/pyridine-containing tripodal ligand towards copper(II) ions: Solid state, solution and DFT Studies

Reaction between the tripodal ligand HBPAMFF, namely, 3-[N,N-(2-pyridylmethyl)(2-hydroxybenzyl)aminomethyl]-5-methylsalicylaldehyde, and stoichiometric amounts of CuCl2·2H2O afforded a turquoise mononuclear complex (1), which crystallizes in the monoclinic system, space group P 21/c. The pentacoordinated copper site adopts a slightly distorted square pyramidal geometry with the apical position occupied by a phenolic oxygen. A combined experimental-theoretical analysis of the mid-infrared absorptions of 1 confirmed that both phenol groups present in HBPAMFF remain fully protonated upon complexation. Still in the solid state, X-band EPR spectroscopy showed a three g-values rhombic spectrum without a hyperfine unfolding. Solution studies were performed in acetonitrile (MeCN), in which the chloride ions remain mostly coordinated to copper, and dimethylsulfoxide (DMSO), with the replacement of a chloride ion by a solvent molecule in the coordination sphere of copper. Electronic spectroscopy and frozen solution EPR also confirm the different nature of the species present in MeCN and DMSO. This work shines a light on some structural aspects regarding metal compounds of phenol-containing ligands, such as HBPAMFF, and their mono- and binucleating derivatives.

Roles of the Zinc Ion and Water Molecule in the Active Site of the Copper-Zinc SOD Catalyst

In this work, we study the effect of a water molecule and a zinc ion on the catalytic activity of copper-zinc superoxide dismutase by computer simulation at the level of density functional theory using the PBE functional and the def2-SVPD and def2-TZVPD basis sets. Assessment is carried out in two directions. The first is a comparison of the main characteristics of electron transfer according to Marcus in the presence and absence of a water molecule in the active site. The second is the topological analysis of the electron density of the ligand environment of the copper ion according to Bader. It has been found that the presence of a water molecule and a zinc ion next to a copper ion has little effect on the primary stage of catalysis, the reduction of the copper ion. However, their presence significantly affects the course of the second stage of the catalytic cycle in the oxidation of copper. The water molecule is involved as a proton carrier. It may be present next to the copper ion during primary electron transfer. The water molecule leaves the first coordination sphere of copper after the initial electron transfer; otherwise, it forms a strong bond with the nitrogen atom, interrupting the electron transfer, according to the topological analysis. The presence of a water molecule near copper significantly impairs the secondary electron transfer, and the catalytic cycle is generally blocked.

Rational engineering of AA5_2 copper radical oxidases to probe the molecular determinants governing their substrate selectivity.

Fungal copper radical oxidases (CROs) from the Auxiliary Activity family 5 (AA5) constitute a group of metalloenzymes that oxidize a wide panel of natural compounds, such as galactose-containing saccharides or primary alcohols, into product derivatives exhibiting promising biotechnological interests. Despite a well-conserved first copper-coordination sphere and overall fold, some members of the AA5_2 subfamily are incapable of oxidizing galactose and galactosides but conversely efficiently catalyse the oxidation of diverse aliphatic alcohols. The objective of this study was to understand which residues dictate the substrate preferences between alcohol oxidases and galactose oxidases within the AA5_2 subfamily. Based on structural differences and molecular modelling predictions between the alcohol oxidase from Colletotrichum graminicola (CgrAlcOx) and the archetypal galactose oxidase from Fusarium graminearum (FgrGalOx), a rational mutagenesis approach was developed to target regions or residues potentially driving the substrate specificity of these enzymes. A set of 21 single and multiple CgrAlcOx variants was produced and characterized leading to the identification of six residues (W39, F138, M173, F174, T246, L302), in the vicinity of the active site, crucial for substrate recognition. Two multiple CgrAlcOx variants, i.e. M4F (W39F, F138W, M173R and T246Q) and M6 (W39F, F138W, M173R, F174Y, T246Q and L302P), exhibited a similar affinity for carbohydrate substrates when compared to FgrGalOx. In conclusion, using a rational site-directed mutagenesis approach, we identified key residues involved in the substrate selectivity of AA5_2 enzymes towards galactose-containing saccharides.

The influence of ancillary NCS− ions on structural, spectroscopic, magnetic and biological properties of copper(II) l-argininato complex

The anions are one of the factors that govern the self-organization of the crystal structure involving [Cu(l−Arg)]2+ cation complex. Therefore, the crystals of hexa−coordinated l−argininato copper(II) complex with coordinated isothiocyanato ions, trans−[Cu(l−Arg)2(NCS)2]⋅2H2O (1), were synthesized and studied by X−ray structural analysis, spectroscopic techniques (FT−IR, Raman, X− and Q−band EPR, NIR−Vis−UV), magnetic and thermal methods. The distortion of elongated octahedron (T = 0.757) shows the static character. The complex presents a monomeric nature but the [Cu(l−Arg)2(NCS)2] units are bound via O‒H∙∙∙O, N‒H∙∙∙O and N‒H∙∙∙N hydrogen bonds forming two dimensional layers. One broad band with three well−marked maxima at 15,850 cm−1, 16,630 cm−1 and 17,500 cm−1 are generated by 2B1g(dx2-y2) → A1g(dz2), 2B2g(dxy) and 2Eg(dxz ≈ dyz) transitions. The values of g tensor components g⊥=gx=gy 2.056 (77 K) / 2.057 (298 K) agree well with the g⊥ found for other trans−N2O2 chromophore with two chelating l−Arg-ligands in copper(II) xy plane. The relation of gz (g||=2.245) >>gx=gy (g⊥= 2.056) > 2.0023 is characteristic for dx2-y2 orbital of unpaired electron ground state in the axial symmetry of copper(II) environment. The field induced slow magnetic relaxation is observed, despite the lack of the zero-field splitting of Cu(II) monomeric complex 1. Due to the labile character and the preference for distorted coordination geometries leading to plasticity of copper(II) coordination sphere, the comprehensive spectroscopic studies of the complexes arising in aqueous solutions when complex 1 was in aqueous solutions, were conducted (NIR−Vis−UV, EPR). The antimicrobial activity of 1 was evaluated against the yeast, dermatophyte and bacteria. Microsporum gypseum was the most sensitive strain, with a 4-time lower MIC comparing to the reference drug - Fluconazole.

Refining details of the structural and electronic properties of the CuB site in pMMO enzyme through sequential molecular dynamics/CPKS-EPR calculations.

This work investigated the structural and electronic properties of the copper mononuclear site of the PmoB part of the pMMO enzyme at the molecular level. We propose that the CuB catalytic site in the soluble portion of pMMO at room temperature and under physiological conditions is a mononuclear copper complex in a distorted octahedral arrangement with the residues His33, His137, and His139 on the equatorial base and two water molecules on the axial axis. Our view was based on the molecular dynamics results and DFT calculations of the electronic paramagnetic resonance parameters and comparisons with experimental EPR data. This new proposed model for the CuB site brings additional support concerning the recent experimental evidence, which pointed out that a saturated coordination sphere of the copper ion in the CuB center is an essential factor that makes it less efficient than the CuC site in the methane oxidation. Therefore, according to the CuB site model proposed here, an additional step involving a displacement of at least one water molecule of the copper coordination sphere by the O2 molecule prior to its activation must be necessary. This scenario is less likely to occur in the CuC center once this one is buried in the alpha-helices, which are part of the pMMO structure bound to the membrane wall, and consequently located in a less solvent-exposed region. In addition, we also present a simple and efficient sequential S-MD/CPKS protocol to compute EPR parameters that can, in principle, be expanded for the study of other copper-containing proteins.

Self-Assembly and Aggregation-Induced Emission in Aqueous Media of Responsive Luminescent Copper(I) Coordination Polymer Nanoparticles.

Luminescent copper(I)-based compounds have recently attracted much attention since they can reach very high emission quantum yields. Interestingly, Cu(I) clusters can also be emissive, and the extension from small molecules to larger architecture could represent the first step towards novel materials that could be obtained by programming the units to undergo self-assembly. However, for Cu(I) compounds the formation of supramolecular systems is challenging due to the coordinative diversity of copper centers. This works shows that this diversity can be exploited in the construction of responsive systems. In detail, the changes in the emissive profile of different aggregates formed in water by phosphine-thioether copper(I) derivatives were followed. Our results demonstrate that the self-assembly and disassembly of Cu(I)-based coordination polymeric nanoparticles (CPNs) is sensitive to solvent composition. The solvent-induced changes are related to modifications in the coordination sphere of copper at the molecular level, which alters not only the emission profile but also the morphology of the aggregates. Our findings are expected to inspire the construction of smart supramolecular systems based on dynamic coordinative metal centers.

Possible coordination modes of copper(II) atom in model silsesquioxanes complexes at various pH conditions: DFT study

The functionalized cage-like silsesquioxanes (POSSs) have enticed scientific community's continuous interest. In this work, we try to supplement empirical expertises and answer questions concerning the coordination modes of copper(II) cation in the POSS-1 ligand neighborhood through the DFT calculations. It is postulated that ethanol solvent molecules take an active part in the coordination to the metallic center in the acidic environment. At the alkaline solution, the square planar shape of two POSS-1 ligands surrounded the copper(II) cation, including two oxygen and two nitrogen atoms in the first coordination sphere of copper, is recommended.

Linear Metal-Organic Frameworks Based on Bis(1-Benzotriazolyl)methane and Zinc and Copper Nitrates

Complexes {[(Zn(Bbtm)(H2O)4](NO3)2}n (I) and [Cu(Вbtm)(NO3)2]n (II) are formed due to the reactions of solutions of zinc and copper(II) nitrates with the bis(1,1'-1,2,3-benzotriazolyl)methane ligand (Bbtm). Their crystal structures are determined by X-ray diffraction analysis (CIF files ССDС nos. 1963126 (I) and 1963127 (II)). Complex I is a linear metal-organic framework (1D-MOF) in which the octahedral coordination of the central atom is provided by four water molecules and two nitrogen atoms of two Bbtm molecules in the trans position. In the structure of complex II, the coordination sphere of copper contains two nitrogen atoms of the Вbtm ligands and four oxygen atoms of two nitrate anions, one of which is bridging like the Вbtm ligand. This makes it possible to describe the structure of complex II as 3D-MOF. The luminescence spectra are recorded for earlier undescribed compound I. The emission maximum is observed at 363 nm. Compound I is also tested as a catalyst for the cycloaddition of СО2 to epoxides. The synthesized MOF efficiently catalyzes the cycloaddition reactions for both monosubstituted and disubstituted epoxides.

Coordination behavior of succinylsulfathiazole – Crystal structure of [Cu(SST).(Pyridine)3.H2O]n, DNA interaction and cytotoxic studies

Mononuclear copper complex of succinylsulfathiazole has been synthesized and characterized using relevant spectroscopic and X-ray diffraction techniques. EPR data and X-ray structural analysis confirmed that Cu(II) ion exhibits an intermediate geometry between trigonal and square bipyramid. Succinylsulfathiazole (SST) ligand behaves as a head-to-tail bridging moiety linking two metal (Cu) cations via carbonyl oxygen and thiazolate nitrogen atom, resulting one dimensional polymeric chain running along [010] direction. In the mononuclear copper complex formulated as [Cu(SST).(Pyridine)3.H2O]n, three nitrogen atoms of three secondary ligand pyridines coordinated to copper at the equatorial plane, the fourth coordination of distorted pentadentate copper is due to thiazolate nitrogen (N3) occupying the apical position and carbonyl oxygen (O1) of SST ligand at -x + 1/2, y-1/2, -z-1/2 remaining at fifth coordination site completes the coordination sphere of copper. The inversely related Cu-SST molecular complexes are held together by pair of NH…O dimer forming R22(14) graph set motif which are further connected by water oxygen (O6) via OH…O interactions. Quantitative contributions of intermolecular interactions are worked out using Hirshfeld surface (HS) and 2D fingerprint plots. Lipophilicity index (Log P), correlates well with the% contribution of CH…π interaction. To evaluate the binding capabilities and binding mode of molecular complex with CT-DNA, absorption study and viscosity measurement are carried out, confirming the intercalation mode of binding which is further supported by molecular docking studies. In vitro cytotoxicity screening of the complex have been performed on zoological species Artemia cyst.

Mechanistic basis of substrate–O2 coupling within a chitin-active lytic polysaccharide monooxygenase: An integrated NMR/EPR study

Lytic polysaccharide monooxygenases (LPMOs) have a unique ability to activate molecular oxygen for subsequent oxidative cleavage of glycosidic bonds. To provide insight into the mode of action of these industrially important enzymes, we have performed an integrated NMR/electron paramagnetic resonance (EPR) study into the detailed aspects of an AA10 LPMO-substrate interaction. Using NMR spectroscopy, we have elucidated the solution-phase structure of apo-BlLPMO10A from Bacillus licheniformis, along with solution-phase structural characterization of the Cu(I)-LPMO, showing that the presence of the metal has minimal effects on the overall protein structure. We have, moreover, used paramagnetic relaxation enhancement (PRE) to characterize Cu(II)-LPMO by NMR spectroscopy. In addition, a multifrequency continuous-wave (CW)-EPR and 15N-HYSCORE spectroscopy study on the uniformly isotope-labeled 63Cu(II)-bound 15N-BlLPMO10A along with its natural abundance isotopologue determined copper spin-Hamiltonian parameters for LPMOs to markedly improved accuracy. The data demonstrate that large changes in the Cu(II) spin-Hamiltonian parameters are induced upon binding of the substrate. These changes arise from a rearrangement of the copper coordination sphere from a five-coordinate distorted square pyramid to one which is four-coordinate near-square planar. There is also a small reduction in metal-ligand covalency and an attendant increase in the d(x2-y2) character/energy of the singly occupied molecular orbital (SOMO), which we propose from density functional theory (DFT) calculations predisposes the copper active site for the formation of a stable Cu-O2 intermediate. This switch in orbital character upon addition of chitin provides a basis for understanding the coupling of substrate binding with O2 activation in chitin-active AA10 LPMOs.

Tuning the thermal stability of copper(II) hexacyanoferrate(II) nanoparticles

It is well known that the physical properties of nanoparticles can be tuned by controlling synthetic factors such as pH, temperature, reactant ratio or type of stabiliser used. In this work, the reactant ratio is varied to produce batches of copper(II) hexacyanoferrate(II) (Cu-HCF) with different cyano decomposition temperatures. This is accomplished by controlling the number of Fe(CN) 4−6 site vacancies throughout the structure. By reducing the number of vacancies and consequently the need for water to complete the structure, the thermal decomposition temperature of Cu-HCF can be increased. In addition to this, we also note that the guest ion similarly contributes to the decomposition temperature. By exchanging K+ with Cs+, an increased resistance to thermal decomposition is realised. As the incorporation of Cs+ ions into the structure does not alter the number of Fe(CN) 4−6 site vacancies, this enhancement is attributed to a change in the geometry of the copper coordination sphere.