Copper-dependent lytic polysaccharide monooxygenases (LPMOs) are key enzymes in the oxidative depolymerization of recalcitrant polysaccharides and have inspired the development of biomimetic copper complexes capable of running the cleavage of O-glycosidic bonds. In this work, two mononuclear copper(II) complexes, bearing asymmetric pyridine–imidazole ligands containing either an imine or amine donors, were synthesized and investigated as structural and functional models of the LPMO active site. Electrochemical, UV-vis and EPR studies revealed the properties of both complexes fall in the range reported for the enzymes and previously reported synthetic systems. Density functional theory calculations supported the experimental redox and spectroscopic properties, providing insights into the coordination changes occurring upon reduction. The interaction of the complexes with hydrogen peroxide was studied by UV–vis and EPR spectroscopy at low temperature, revealing the transient formation of copper–oxygen intermediates consistent with Cu(II)-hydroperoxo species. The oxidative reactivity of the complexes was evaluated using p-nitrophenyl-β-D-glucopyranoside, coumarin-3-carboxylic acid, and cellobiose as model substrates. Kinetic analysis demonstrated a strong dependence of the catalytic activity on hydrogen peroxide concentration, indicating that oxidant activation constitutes a key step in the catalytic cycle. Reactive oxygen species generation studies further showed that peroxide activation proceeds mainly through metal-centered pathways rather than uncontrolled Fenton-type chemistry. The two complexes reported in this work thus reproduce several structural, electronic, and functional features of LPMOs and provide valuable insight into copper-mediated oxidative cleavage of carbohydrates.

An aminodithiophenolate scaffold with an NS2 donor set supports diiron complex formation. The diferrous precursor activates O2, giving rise to a diferric mu-oxido species, which acts as a proton-reduction electrocatalyst for H2 production at diiron sites relevant to hydrogenase enzymes.

Synthesis, characterization, and electrocatalytic water oxidation studies of the cubane-type complexes [(μ 3 - L 1 O )CoCl(MeOH)] 4 (1) and [(μ 3 - L 2 O )CoCl(MeOH)] 4 (2) are herein reported.

Synthesis, characterization, and electrocatalytic water oxidation studies of the cubane-type complexes [(mu 3-L1O)CoCl(MeOH)]4 (1) and [(mu 3-L2O)CoCl(MeOH)]4 (2) are herein reported. Cubanes 1 and 2 were obtained in high yields under mild conditions by self-assembly of the ligands L1OH = 1-H-2-benzimidazolylmethanol and L2OH = 1-methyl-2-benzimidazolylmethanol with CoCl26H2O in basic methanolic solution. Both compounds feature a cubane-type structure in which the central {Co4O4} units are built by four CoII centers coordinated by alkoxide-bridged oxygen and nitrogen atoms from the deprotonated LnOH ligands and stabilized by MeOH molecules and chloride ions. Magnetic studies allowed the determination of g = 2.42 and g = 2.57 values for 1 and 2, respectively. At low temperatures, 1 shows antiferromagnetic behavior, while 2 shows ferromagnetic coupling. DFT analyses support the antiferromagnetic behavior of 1. Unfortunately, the same method was not effective at explaining the ferromagnetic character of 2. Such inconsistency was explained through an exhaustive ac-susceptibility study by considering the single molecular magnet (SMM) behavior of 2. Cyclic voltammetry of 1 and 2 in phosphate buffer solution (pH = 7.4) displayed catalytic currents at 1.65 and 1.68 V vs. Standard Hydrogen Electrode (SHE), corresponding to water oxidation, with TOF values of 1.04 and 1.99 s-1, overpotentials of 710 and 680 mV, faradaic efficiencies of 88% and 90%, and TON values of 2.8 and 3.5 for 1 and 2, respectively. Electrochemical Quartz Microbalance (EQCM) analysis showed the robustness of 1 and 2 since only around 0.05% of their mass was deposited on the electrode surface. Subsequent SEM-EDX microanalysis demonstrated that although 1 converts to CoOx during electrolysis, it also changes into an undetermined form of the original catalyst, containing C, O, and Co. In the case of 2, analysis of the electrode after WOC did not allow the detection of Co, C, or O, establishing 2 as a more stable catalyst than 1.

Supramolecular transition-metal catalysts with tailored reaction environments allow for the usage of abundant 3d metals as catalytic centres, leading to more sustainable chemical processes. However, such catalysts are large and flexible systems with intricate interactions, resulting in complex reaction coordinates. To capture their dynamic nature, we developed a broadly applicable, high-throughput workflow, leveraging quantum mechanics/molecular mechanics molecular dynamics (QM/MM MD) in explicit solvent, to investigate a Cu(I)-calix[8]arene catalysed C-N coupling reaction. The system complexity and high amount of data generated from sampling the reaction require automated analyses. To identify and quantify the reaction coordinate from noisy simulation trajectories, we applied interpretable machine learning techniques (Lasso, Random Forest, Logistic Regression) in a consensus model, alongside dimensionality reduction methods (PCA, LDA, tICA). Leveraging a Granger Causality model, we go beyond the traditional view of a reaction coordinate, by defining it as a sequence of molecular motions that led up to the reaction.

Base metal complexes were obtained with phenanthroline-functionalized calix[8]arenes as scaffolds in good yields. All complexes were characterized by spectroscopic and mass spectrometry techniques, and their electrochemical properties determined by cyclic voltammetry (CV). Electrocatalytic tests for CO2 and proton reduction reactions (CO2RR and HER, respectively) were carried out with all systems, with trifluoroethanol as proton source. The complex with general formulae [M(1,5-(2,9-dimethyl-1,10-phenanthro)-p-tert-butylcalix[8] arene)Cl2] (M = Co, Ni, Cu) presented a significant current increase around E =-2.2 to-2.5 V (relative to the ferricenium/ferrocene couple) under CO2 atmosphere, indicative of an electrocatalytic process; this was not the case for the Zn derivative. This behavior was compared to that of the analogous 2,9-dimethyl-1,10-phenanthroline derivatives, with the phenol-containing calix[8]arene complexes that feature -OH groups as intramolecular proton relays acting as more stable and efficient electrocatalysts for CO2RR.

A bidentate NHC-thiolate ligand based on the imidazo[1,5-a]pyridine scaffold and featuring an extended π-system is described. It is derived from a readily available zwitterionic precursor and the chemistry of the corresponding homoleptic Ni(II) complex is investigated.

Discrepancies regarding the coordination environment, donor atoms, nuclearity, and oxidation state of the active site of particulate methane monooxygenase (pMMO), a copper-dependent enzyme capable of activating the strong C-H bond of methane, persist despite numerous structural and spectroscopic studies. To address the proposed mono- (Cu-II) or bimetallic (2Cu(I)) nature of the so-called Cu-B site, we report the bis(benzimidazole)-based NMe-N,N'-(1-Me-2-CH2C7H4N2)(2)C6H4 ligand (N4) and its copper complexes. In the solid state [Cu(N4)(ClO4)]ClO4 features tetragonal geometry defined by the chelating ligand and an axial perchlorate; geometric and EPR parameters are very close to those reported for the Cu-B site. Attempts to obtain a dicopper(I) analog resulted in [Cu(N4)][CuCl2], based on spectroscopic, electrochemical, and ESI-MS data. Although these results support the assignment of Cu-B as a monometallic site, air exposure of [Cu(N4)][CuCl2] leads to ligand oxidation in the structurally characterized [Cu(N4=O)Cl], raising the possibility of distorted tetragonal Cu(I) centers activating O-2 and oxidizing substrates, in C-H activation chemistry that may take place at Cu-B.

Copper complexes supported by benzimidazole-based tetradentate neutral ligands featuring thio- and selenoether donors, resemble the coordination environment of the active site in copper dependent monooxygenases Dopamine-beta-monooxygenase (D beta M) and peptidylglycine-alpha-hydroxylating monooxygenase (PHM). The cuprous complexes react with O2 at low temperature generating a reactive copper-oxygen species assigned to a side-on cupric-superoxo complex, which activates the C & horbar;H bond of dihydroanthracene. Based on structural, 1H and 77Se NMR, and EPR spectroscopic characterization, together with DFT computations, the selenoether moiety likely acts as a hemilabile ligand in these scaffolds, which results in an electrophilic cupric-superoxide intermediate poised for H-atom transfer, as has been proposed for related bis(benzimidazole)-thioether analogues and selenoether-modified enzymatic systems. Copper complexes supported by thio- and selenoether ligands provide a coordination environment similar to the active sites of methionine-containing copper monooxygenases. Spectroscopic data, supported by theoretical studies, suggest that the chalcogenoethers act as hemilabile ligands, providing access to electrophilic side-on cupric-superoxo intermediates capable of H-abstraction from dihydroanthracene. These results point at potential hemilability in methionine and selenomethionine-containing metalloenzymes. image

The aim to access linked tetravanadate [V 4 O 12 ] 4− anion with mixed copper(II) complexes, using α -amino acids and phenanthroline-derived ligands, resulted in the formation of four copper(II) complexes [Cu(dmb)(Gly)(OH 2 )] 2 [Cu(dmb)(Gly)] 2 [V 4 O 12 ]·9H 2 O ( 1 ) [Cu(dmb)(Lys)] 2 [V 4 O 12 ]·8H 2 O ( 2 ), [Cu(dmp) 2 ][V 4 O 12 ]·C 2 H 5 OH·11H 2 O ( 3 ), and [Cu(dmp)(Gly)Cl]·2H 2 O ( 4 ), where dmb = 4,4′-dimethioxy-2,2′-bipyridine; Gly = glycine; Lys = lysine; and dmp = 2,9-dimethyl-1,10-phenanthroline. The [V 4 O 12 ] 4− anion is functionalized with mixed copper(II) units in 1 and 2 ; while in 3 , it acts as a counterion of two [Cu(dmp)] 2+ units. Compound 4 crystallized as a unit that did not incorporate the vanadium cluster. All compounds present magnetic couplings arising from Cu⋯O/Cu⋯Cu bridges. Stability studies of water-soluble 3 and 4 by UV–Vis spectroscopy in cell culture medium confirmed the robustness of 3 , while 4 appears to undergo ligand scrambling over time, resulting partially in the stable species [Cu(dmp) 2 ] + that was also identified by electrospray ionization mass spectrometry at m / z = 479. The in vitro cytotoxicity activity of 3 and 4 was determined in six cancer cell lines; the healthy cell line COS-7 was also included for comparative purposes. MCF-7 cells were more sensitive to compound 3 with an IC 50 value of 12 ± 1.2 nmol. The tested compounds did not show lipid peroxidation in the TBARS assay, ruling out a mechanism of action via reactive oxygen species formation. Both compounds inhibited cell migration at 5 µM in wound-healing assays using MCF-7, PC-3, and SKLU-1 cell lines, opening a new window to study the anti-metastatic effect of mixed vanadium–copper(II) systems. Graphical abstract

The design of molecular systems with capabilities to carry out the water oxidation reaction and thereby overcome the bottleneck of artificial photosynthesis is one of the scientific fields of most significant interest and urgency due to its potential to address energy demand and climate change. Nevertheless, the search for efficient and robust catalysts has been limited by the degradation of carbon-based ligands under oxidative conditions, leading to the search for fully inorganic catalysts. Polyoxometalates (POMs), an emerging class of carbon-free ligands with oxygen-enriched surfaces, offer a unique alternative as inorganic scaffolds to self-assemble and stabilize transition-metal clusters with unique redox properties. Under catalytic working conditions, POMs can undergo electron transfer reactions coupled to O 2 formation without modifying their parental structure. As a result, these materials have recently entered the scene as catalytic players in designing new artificial photosynthetic platforms for water oxidation. We focus on the methods used to create these compounds, their unique structural characteristics, and how effectively they function as catalysts. We also explore the proposed mechanisms behind their ability to produce O 2 and their potential use in designing photosynthetic devices.

Transition metal catalysts with modified second-coordination sphere employed in the electrocatalytic CO2 can result in increased activity or directed product selectivity. Calixarenes can form metal complexes and potentially catalyze reactions within its cavity, taking advantage of the surrounding phenols groups to tune the reactivity by second-coordination sphere effects. Here, we present a Mn(I) bromotricarbonyl complex with phenanthroline-functionalized calix[8]arene ligands capable of electrocatalytically reducing CO(2 )into different products with 2,2,2-trifluoroethanol as proton donor. The selectivity of the reaction seems to be affected by the calixarene cavity: two calixarene-free analogous complexes reduce CO(2 )to CO almost exclusively, while the calixarene complexes produce primarily CO, H-2. Interestingly, in some cases the less frequently observed CH4 was also detected, albeit with low Faradaic efficiency. Thus, the manganese center placed within the calixarene cavity promotes the formation of reduced CO2 products by more than two electrons and two protons, affording CH(4 )in some cases.

Copper Bioinorganic Chemistry, pp. 187-209 (2023) No Access6: Inorganic Models of Lytic Polysaccharide MonooxygenasesIvan CastilloIvan CastilloInstituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, CU, 04510, Ciudad de México, Méxicohttps://doi.org/10.1142/9789811269493_0006Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: The following sections are included: Introduction Lytic Polysaccharide Monooxygenases Copper Complexes as Hydrolase Mimics Polysaccharide Hydrolysis Copper Complexes Copper Complexes as LPMO Mimics Copper(II)/Bis(Benzimidazolyl)Amine System Copper(III)/Bis(Carboxamido)Pyridine System Copper(II)/Copper(I)/(Pyridyl,Imidazolyl)Amine System Copper(II)/(Pyridyl)Diazepane Complexes Copper(II)/Bis(Imidazolyl)Amine System Copper(II)/Bis(Picolyl)Amine System Concluding Remarks References FiguresReferencesRelatedDetails Recommended Copper Bioinorganic ChemistryMetrics History PDF download

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Two novel Iron (II) complexes featuring tetrapodal bis(benzimidazole)amino thio- and selenoether ligands (LS and LSe) were synthesized, characterized, and tested as electrocatalysts for the hydrogen evolution reaction. The bromide complexes [Fe(LS,LSe)Br2] (1-2) are highly insoluble, but their DMSO solvates were characterized by single crystal X-ray diffraction, revealing an octahedral coordination environment that does not feature coordination of the chalcogen atoms. The corresponding triflate derivatives [Fe(LS,LSe)(MeCN)3]OTf2 (1c-2c) were employed for electrocatalytic proton reduction, with 1c exhibiting higher activity, thus suggesting that the thioether may participate as a more competent pendant ligand for proton transfer.

The Front Cover shows the open conformer of the 1,4-phenanthroyl derivatized calix[8]arene/Cu(I) system that allows for C−S coupling to occur on the right hand side. On the left, a collapsed conformer of the same system does not allow for efficient catalysis to occur, since no macrocyclic cavity that may host the reactants is present. In the article, experimental and computational mechanistic studies are combined to unveil the origins for the poor catalytic performance in flexible macrocyclic systems with a vast conformational space. Thanks to @MESHICOLOR for the graphic design. More information can be found in the Research Article by M. Podewitz, I. Castillo and co-workers.

Polysaccharide oxidative depolymerization is highly desirable to achieve recalcitrant biomass valorization. Inspired by recently discovered Lytic Polysaccharide Monooxygenases, mononuclear copper complexes have been prepared and studied in the literature. However, the activities were evaluated on different substrates and under various conditions. In this work we intended to establish a robust and reproducible activity assay, in aqueous solution at a pH close from neutrality and under mild conditions. We have evaluated several complexes on substrates of increasing complexity: the model substrate para‐nitrophenyl‐β‐D‐glucopyranoside ( p ‐NPG), cellobiose (glucose dimer), as well as on extended substrates (chitin, cellulose and bagasse from agave). The different assays were compared and proof‐of‐concept that bioinspired complexes can oxidatively promote polysaccharide depolymerization was obtained. Finally, we measured level of hydroxyl radicals released by the complexes under comparable experimental conditions and mechanistic pathways are discussed.

Functionalization of the phenolic rim of p-tert-butylcalix[8]arene with phenanthroline to create a cavity leads to formation of two regioisomers. Substitution of positions 1 and 5 produces the known C-2v-symmetric regioisomer 1,5-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene (L-1,L-5), while substitution of positions 1 and 4 produces the C-s-symmetric regioisomer 1,4-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene (L-1,L-4) described herein. [Cu(L-1,L-4)I] was synthesized from L-1,L-4 and CuI in good yield and characterized spectroscopically. To evaluate the effect of its cavity on catalysis, Ullmann-type C-S coupling was chosen as proof-of-concept. Selected aryl halides were used, and the results compared with the previously reported Cu(I)/L-1,L-5 system. Only highly activated aryl halides generate the C-S coupling product in moderate yields with the Cu(I)/L-1,L-4 system. To shed light on these observations, detailed computational investigations were carried out, revealing the influence of the calix[8]arene macrocyclic morphology on the accessible conformations. The L-1,L-4 regioisomer undergoes a deformation that does not occur with L-1,L-5, resulting in an exposed catalytic center, presumably the cause of the low activity of the former system. The 1,4-connectivity was confirmed in the solid-state structure of the byproduct [Cu(L-1,L-4-H)(CH3CN)(2)] that features Cu(I) coordinated inside a cleft defined by the macrocyclic framework.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The Cover Feature illustrates the C−N coupling of aniline and aryl bromide in the cavity of a supramolecular copper phenanthroline calix[8]arene catalyst. In their Research Article, R. A. Talmazan, J. Refugio Monroy and co-workers showed how encapsulation of an otherwise poor Cu(I) phenanthroline catalyst by calix[8]arene enhances the catalytic activity for C−N coupling between aryl amines and aryl halides. Yields up to 92% were achieved with low catalyst loadings (2.5% mol). A multiscale computational protocol based on DFT and MD simulations revealed the origins of the drastically improved catalytic performance. More information can be found in the Research Article by R. A. Talmazan, J. Refugio Monroy and co-workers.