Catecholate Complexes Research Articles

Quantitative proteomic analysis reveals Ga(III) polypyridyl catecholate complexes disrupt Aspergillus fumigatus mitochondrial function.

Infections caused by the airborne fungal pathogen, Aspergillus fumigatus, are increasing in severity due to growing numbers of immunocompromised individuals and the increasing incidence of antifungal drug resistance, exacerbating treatment challenges. Gallium has proven to be a strong candidate in the fight against microbial pathogens due to its iron-mimicking capability and substitution of Ga(III) in place of Fe(III), disrupting iron-dependent pathways. Since the antimicrobial properties of 2,2'-bipyridine and derivatives have been previously reported, we assessed the in vitro activity and proteomic effects of a recently reported heteroleptic Ga(III) polypyridyl catecholate compound against A. fumigatus. This compound has demonstrated promising growth-inhibition and impact on the A. fumigatus proteome compared to untreated controls. Proteins associated with DNA replication and repair mechanisms along with lipid metabolism and the oxidative stress responses were elevated in abundance compared to control. Crucially, a large number of mitochondrial proteins were reduced in abundance. Respiration is an important source of energy to fuel metabolic processes required for growth, survival and virulence, the disruption of which may be a viable strategy for the treatment of microbial infections.

Synthesis, Structure, Electrochemical Properties, and Antioxidant Activity of Organogermanium(IV) Catecholate Complexes.

A series of novel organogermanium(IV) catecholates 1-9 of the general formula R'2Ge(Cat), where R' = Ph, Et, have been synthesized. Compounds were characterized by 1H, 13C NMR, IR spectroscopy, and elemental analysis. The molecular structures of 1-3, 6, and 8 in crystal state were established using single-crystal X-ray analysis. The complexes are tetracoordinate germanium(IV) compounds containing a dioxolene ligand in a dianion (catecholato) form. Electrochemical transformations of target germanium(IV) complexes have been studied by cyclic voltammetry. The electro-oxidation mechanism of complexes 1-5, 7, and 10 (the related complex Ph2Ge(3,5-Cat) where 3,5-Cat is 3,5-di-tert-butylcatecholate) involves the consecutive formation of mono- and dicationic derivatives containing the oxidized forms of redox-active ligands. The stability of the generated monocations depends both on the hydrocarbon groups at the germanium atom and on the substituents in the catecholate ring. Compounds 6, 8, and 9 are oxidized irreversibly under the electrochemical conditions with the formation of unstable complexes. The radical scavenging activity and antioxidant properties of new complexes were estimated in the reaction with DPPH radical, ABTS radical cation, and CUPRACTEAC assay. It has been found that compounds 8 and 9 with benzothiazole or phenol fragments are more active in DPPH test. The presence of electron-rich moieties in the catecholate ligand makes complexes 5 and 7-9 more reactive to ABTS radical cation. The value of CUPRACTEAC for organogermanium(IV) catecholates varies from 0.23 to 1.45. The effect of compounds 1-9 in the process of lipid peroxidation of rat liver (Wistar) homogenate was determined in vitro. It was found that most compounds are characterized by pronounced antioxidant activity. A feature of complexes 1, 3, and 5-9 is the intensification of the antioxidant action with the incubation time. In the presence of additives of complexes 3, 5, 6, and 8, an induction period was observed during the process of lipid peroxidation.

Redox-Active Tin(IV) Complexes Based on Sterically Hindered Catecholate Ligands

The oxidative addition of sterically hindered 3,6-dicyclohexyl-o-benzoquinone (L1), 3,5-di-tert-octyl-o-benzoquinone (L2), 4-tert-octyl-o-benzoquinone (L3), and 3,5-bis(2-phenylpropyl)-o-benzoqui-none (L4) to tin(II) chloride in THF affords the corresponding tin(IV) catecholate complexes with the generalformula RCatSnCl2 · 2THF, where Cat is the catecholate fragment; and R is 3,6-с-Hex (I), 3,5-tert-Oct (II), 4-tert-Oct (III), and 3,5-C(Me)2 Ph (IV), regardless of the molar ratio of the starting reactants. The molecu-lar structures of substituted o-benzoquinone L4 and complexes I and III in the crystalline form are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2259370 (L4), 2259371 (I), and 2259372 (III)). The oxidation-reduction properties of synthesized compounds I–IV are studied by cyclic voltammetry.

Catechol/o-benzoquinone exchange at gold(iii).

Although gold(iii) chemistry has tremendously progressed in the past 2 decades, gold(iii) catecholate complexes remain extremely scarce and underdeveloped. Upon preparation and full characterization of P^C-cyclometalated gold(iii) complexes, we serendipitously uncovered an intriguing catechol exchange process at gold(iii). Electron-rich catecholates turned out to be readily displaced by electron-poor o-benzoquinones. DFT calculations revealed an original path for this transformation involving two consecutive Single Electron Transfer events between the catecholate and o-benzoquinone moieties while gold maintains its +III oxidation state. This catechol/o-benzoquinone exchange at gold(iii) represents a new path for the exchange of X-type ligands at transition metals.

Cover Feature: Vanadium(V) Pyridine‐Containing Schiff Base Catecholate Complexes are Lipophilic, Redox‐Active and Selectively Cytotoxic in Glioblastoma (T98G) Cells (Chem. Eur. J. 68/2023)

Cover Feature: Vanadium(V) Pyridine‐Containing Schiff Base Catecholate Complexes are Lipophilic, Redox‐Active and Selectively Cytotoxic in Glioblastoma (T98G) Cells (Chem. Eur. J. 68/2023)

Synthesis, structure and electrochemical properties of tris(3-phenylpyrazolyl)borato zinc(II) adducts with o-semiquinonate ligands

The structure and electrochemical properties of zinc(II) complexes bearing the face-capping, hydrotris-(3-phenylpyrazol-1-yl)borate, [TpPh]–, ligand are reported while investigating the effect of the [TpPh]– ligand on bound, o-semiquinonate(SQ) radicals. The o-SQ complexes were synthesized by in situ oxidation of parent catecholate complexes with the fate of the bound, SQ radical dependent on the substitution pattern of the SQ ring. A stable SQ radical was isolated using 3,5-di-tert-butylsemiquinonate, (3,5-DBSQ)–; however, the unsubstituted, [TpPh]ZnII(SQ) radical complex decomposed through oxidative coupling forming a dimer complex bridged by a fused bis-SQ ring system. The protective pocket formed by the phenyl substituents on [TpPh]– is not able to prevent decomposition of bound, SQ radicals bearing minimal steric bulk, implying SQ ring substitution is the major contributor towards stabilization of SQ radicals in this system. The redox properties of the {[TpPh]Zn}2(bis-SQ) determined through cyclic voltammetry are consistent with a bis-SQ assignment having inefficient π-delocalization while those of [TpPh]Zn(3,5-DBSQ) are consistent with the presence of a bound SQ radical ligand.

Vanadium(V) Pyridine-Containing Schiff Base Catecholate Complexes are Lipophilic, Redox-Active and Selectively Cytotoxic in Glioblastoma (T98G) Cells.

Two new series of complexes with pyridine-containing Schiff bases, [VV O(SALIEP)L] and [VV O(Cl-SALIEP)L] (SALIEP=N-(salicylideneaminato)-2-(2-aminoethylpyridine; Cl-SALIEP=N-(5-chlorosalicylideneaminato)-2-(2-aminoethyl)pyridine, L=catecholato(2-) ligand) have been synthesized. Characterization by 1 H and 51 V NMR and UV-Vis spectroscopies confirmed that: 1) most complexes form two major geometric isomers in solution, and [VV O(SALIEP)(DTB)] (DTB=3,5-di-tert-butylcatecholato(2-)) forms two isomers that equilibrate in solution; and 2) tert-butyl substituents were necessary to stabilize the reduced VIV species (EPR spectroscopy and cyclic voltammetry). The pyridine moiety within the Schiff base ligands significantly changed their chemical properties with unsubstituted catecholate ligands compared with the parent HSHED (N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine) Schiff base complexes. Immediate reduction to VIV occurred for the unsubstituted-catecholato VV complexes on dissolution in DMSO. By contrast, the pyridine moiety within the Schiff base significantly improved the hydrolytic stability of [VV O(SALIEP)(DTB)] compared with [VV O(HSHED)(DTB)]. [VV O(SALIEP)(DTB)] had moderate stability in cell culture media. There was significant cellular uptake of the intact complex by T98G (human glioblastoma) cells and very good anti-proliferative activity (IC50 6.7±0.9 μM, 72 h), which was approximately five times higher than for the non-cancerous human cell line, HFF-1 (IC50 34±10 μM). This made [VV O(SALIEP)(DTB)] a potential drug candidate for the treatment of advanced gliomas by intracranial injection.

Copper(II) Catecholate Complexes with Polypyridyl Ligands

Copper(II) catecholate complexes based on 3,6-di-tert-butyl-o-benzoquinone with N-donor ligands of the phenanthroline series have been synthesized: (3,6-Cat)Cu(Phen) (I), (3,6-Cat)Cu(DPQ) (II), and (3,6-Cat)Cu(DPPZ) (III), where 3,6-Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, Phen is phenanthroline, DPQ is dipyrido[3,2-d:2',3'-f]quinoxaline, and DPPZ is dipyrido[3,2-a:2',3'-c]phenazine. The synthesized copper(II) complexes demonstrate intramolecular ligand-to-ligand charge transfer responsible for their intense violet color. The electronic structure of the synthesized chromophores was studied by electronic spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The molecular and crystal structures of the synthesized compounds were determined by X-ray diffraction analysis (CIF files CCDC 2 250 975 (I⋅THF), 2 250 976 ([(II⋅THF)(II)]⋅3THF), 2250977 (II)).

Copper(II) Catecholate Complexes with Polypyridyl Ligands

Copper(II) Catecholate Complexes with Polypyridyl Ligands

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands

New heteroleptic zinc catecholate complexes based on 3,6-di-tert-butyl-o-benzoquinone and containing metal-coordinated N-donor ligands (2,2'-bipyridine and phenanthroline) were prepared by ligand exchange. According to X-ray diffraction data, both complexes were dimers with multiple intermolecular π–π interactions between the aromatic moieties of neighboring molecules (CCDC nos. 2222704 (I), 2222705 (II)). The electronic transmission spectra of crystalline samples of I and II and their solutions show broad absorption bands in the visible region with a maximum at about 500 nm.

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands

Not So Similar: Different Ways of Nb(V) and Ta(V) Catecholate Complexation.

The reactions between catechol (H2cat) and niobium(V) or tantalum(V) precursors in basic aqueous solutions lead to the formation of catecholate complexes of different natures. The following complexes were isolated and characterized by single-crystal X-ray diffraction (SCXRD): (1) (NH4)3[NbO(cat)3]∙4H2O; (2) K2[Nb(cat)3(Hcat)]·2H2cat·2H2O; (3) Cs3[NbO(cat)3]·H2O; (4) (NH4)4[Ta2O(cat)6]·3H2O; (5) Cs2[Ta(cat)3(Hcat)]·H2cat; (6) Cs4[Ta2O(cat)6]·7H2O. The isolated crystalline products were characterized by elemental analysis, X-ray powder diffraction (XRPD), FTIR, and TGA. The structural features of these complexes, such as {Ta2O} unit geometry, Cs-π interactions, and crystal packing effects, are discussed.

Heterogeneous Local Dynamics in Mussel-Inspired Elastomers

Materials with increased mechanical strength and toughness bearing mussel-inspired iron–catechol complexes and network architectures exhibit several dynamic features, e.g., high and broad glass-“transition” temperature, not explored so far. By combining differential scanning calorimetry and dielectric spectroscopy, the latter as a function of temperature and pressure, we have explored the increase in the glass temperature, Tg, and the concomitant increase in the breath of Tg in bioinspired networks bearing one (covalent) or two (covalent and coordination) types of cross-links. Cross-linked networks experience heterogeneous segmental dynamics that are responsible for the broad Tg range observed in the thermal measurements. The two distinct dynamics reflect the relaxation of segments in the vicinity versus more distant cross-linked units. The various topologies are shown to have different fragilities and tend to form stronger glasses with increasing network topology. In addition, the ionic conductivity is influenced by the segmental dynamics and the increased Tg in the networks. These features (reduced specific heat step, Δcp, at Tg and “strong” dynamic behavior) are also found in permanently cross-linked polymers with dynamic network topology known as vitrimers. The similarities in the two network systems are discussed.

Alkyl Chain Appended Fe(III) Catecholate Complex as a Dual-Modal T1 MRI-NIR Fluorescence Imaging Agent via Second Sphere Water Interactions.

The C12-alkyl chain-conjugated Fe(III) catecholate complex [Fe(C12CAT)3]3-, Fe(C12CAT)3 [C12CAT = N-(3,4-dihydroxyphenethyl)dodecanamide], was synthesized and characterized, reported as a dual-modal T1-MRI and an optical imaging probe. The DFT-optimized structure of Fe(C12CAT)3 reveals a distorted octahedral coordination geometry around the high spin Fe(III) center. The formation constant (-log K) of Fe(C12CAT)3 was calculated as 45.4. The complex exhibited r1-relaxivity values of 2.31 ± 0.12 and 1.52 ± 0.06 mM-1 s-1 at 25 and 37 °C, respectively, on 1.41 T at pH 7.3 via second-sphere water interactions. The interaction of Fe(C12CAT)3 with human serum albumin showed concomitant enhancement of r1-relaxivity to 6.44 ± 0.15 mM-1 s-1. The MR phantom images are significantly brighter and directly correlate to the concentration of Fe(C12CAT)3. Adding an external fluorescent marker IR780 dye to Fe(C12CAT)3 leads to the formation of self-assembly by C12-alkyl chains. It resulted in the fluorescence quenching of the dye, and its critical aggregation concentration was calculated as 70 μM. The aggregated matrix of Fe(C12CAT)3 and IR780 dye is spherical, with an average hydrodynamic diameter of 189.5 nm. This self-assembled supramolecular system is found to be non-fluorescent and was "turn-on" under acidic pH via dissociation of aggregates. The r1-relaxivity is found to be unchanged during the matrix aggregation and disaggregation. The probe showed MRI ON and fluorescent OFF under physiological conditions and MRI ON and fluorescent ON under acidic pH. The cell viability experiments showed that the cells are 80% viable at 1 mM probe concentration. Fluorescence experiments and MR phantom images showed that Fe(C12CAT)3 is a potential dual model imaging probe to visualize the acidic pH environment of the cells.

A New Type of Valence Tautomerism in Cobalt Dioxolene Complexes - Temperature-Induced Transition from a Cobalt(III) Catecholate to a Low-Spin Cobalt(II) Semiquinonate State.

The synthesis and characterization of the monocationic cobalt(III) catecholate complex [Co(L-N4 t Bu2 )(Cl2 cat)]+ (L-N4 t Bu2 =N,N'-Di-tert.-butyl-2,11-diaza[3.3](2,6)pyridinophane, Cl2 cat2- =4,5-dichlorocatecholate) are presented. The complex exhibits valence tautomeric properties in solution; but, in contrast to the usually observed conversion from a cobalt(III) catecholate to a high-spin cobalt(II) semiquinonate state, valence tautomerism of [Co(L-N4 t Bu2 )(Cl2 cat)]+ leads to the formation of a low-spin cobalt(II) semiquinonate complex upon raising the temperature. This new type of valence tautomerism for a cobalt dioxolene complex has been unambiguously established by a detailed spectroscopic investigation using variable-temperature NMR, IR and UV-Vis-NIR spectroscopy. Determination of the enthalpies and entropies characterizing the valence tautomeric equilibria in various solutions shows that the influence of the solvent is almost exclusively entropic.

Cooperativity and intermolecular hydrogen bonding in donor‐acceptor complexes of phenol and polyhydroxybenzenes

AbstractCooperativity between intermolecular and intramolecular hydrogen bonds is an important factor determining the strength of donor‐acceptor complexes. Its impact in poly‐1,2‐diols, notably polyhydroxybenzenes, is subject to debate. Density functional theory calculations have been performed on complexes of phenol, catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene with pyridine, trimethylamine and trimethylphosphine oxide. Binding energies, proton NMR shifts, Quantum Theory of Atoms in Molecules analysis and Interacting Quantum Atoms (IQA) interaction energies reveal a positive cooperative effect of a topological intramolecular hydrogen bond (IMHB) in catechol relative to phenol, with insignificant or small negative effects of further HO groups. Except for catechol complexes, there are no topological IMHBs in any donors or their complexes, although all show Non‐Covalent Interaction isosurfaces. The absence of a topological IMBH in catechol itself is explained by electron density contour plots. Complexes of Me3N and Me3PO with catechol, pyrogallol and 1,2,3,4‐tetrahydroxybenzene display additional intermolecular hydrogen bonds, C‐H…H‐C and C‐H…O=P, respectively, with the hydrogen atom ortho to the bound HO group. The predominantly covalent or electrostatic character of the various hydrogen bond types is discussed in terms of the IQA energy partition scheme, which is also useful for characterising IMHBs in the absence of a bond critical point. These results further our understanding of the nature and the limits of cooperative hydrogen bonding in donor‐acceptor complexes.

Modular Synthesis and Patterning of High-Stiffness Networks by Postpolymerization Functionalization with Iron-Catechol Complexes.

Bioinspired iron-catechol cross-links have shown remarkable success in increasing the mechanical properties of polymer networks, in part due to clustering of Fe3+-catechol domains which act as secondary network reinforcing sites. We report a versatile synthetic procedure to prepare modular PEG-acrylate networks with independently tunable covalent bis(acrylate) and supramolecular Fe3+-catechol cross-linking. Initial control of network structure is achieved through radical polymerization and cross-linking, followed by postpolymerization incorporation of catechol units via quantitative active ester chemistry and subsequent complexation with iron salts. By tuning the ratio of each building block, dual cross-linked networks reinforced by clustered iron-catechol domains are prepared and exhibit a wide range of properties (Young's moduli up to ∼245 MPa), well beyond the values achieved through purely covalent cross-linking. This stepwise approach to mixed covalent and metal-ligand cross-linked networks also permits local patterning of PEG-based films through masking techniques forming distinct hard, soft, and gradient regions.

Charge-Transfer Benzoquinone:Catechol Complexes, Their Aging Reactions, High-Pressure Polymorphs and Skew Pancake Bonds

Charge-transfer complexes are the key elements of optoelectronic devices. Quinhydrone (Qh) was the first discovered charge-transfer complex, and for its structure, the π-stacking and pancake bonds were identified. Later, the atom-over-atom criterion was added to the pancake-bond definition. However, this feature is absent in the structures of both Qh polymorphs. Here, we report new charge-transfer complexes of para-benzoquinone (pBq) and catechol (Ct), the only unknown isomers of Qh. Compounds pBq and Ct preferentially co-crystallize to a 1:1 brown complex, α-pBq:Ct, with the molecules alternatively stacked into columns. We have revealed the accelerated aging reaction of α-pBq:Ct, leading to an orange pBq:2Ct complex, the only representative of the 1:2 stoichiometry for the complexes of pBq with isomeric hydroquinone (Hq), resorcinol (Rs), and Ct. On compression to 1.5 GPa, α-pBq:Ct undergoes a transition converting the catechol conformers syn into anti in a markedly darker new phase β-pBq:Ct. This conversion extensively extends the transition hysteresis between phases α- and β-pBq:Ct. At about 2.5 GPa, a radical complex γ-pBq:Ct is formed, which starting from 3.0 GPa gradually transforms into the black amorphous phase δ-pBq:Ct. In phase α-pBq:2Ct, both Ct-conformers syn and anti are present, but high pressure induces a phase transition, eliminating conformers syn in a much darker new phase, β-pBq:2Ct. High pressure reduces the energy band gap of all pBq:Ct and pBq:2Ct phases. The skew geometry of pancake bonds associated with p–p interactions is common for all Qh, pBq:Rs, pBq:Ct, and pBq:2Ct complexes.

Mussel-inspired ferric ion-polydopamine complex as a facile, green and efficient platform to functionalize carbon fiber for improving interfacial adhesion of composites

A mussel inspired co-deposition of ferric ion-polydopamine (PDA) is explored and constructed on carbon fiber via facile dip-coating strategy for the first time to realize the enhancement in interfacial adhesion of epoxy composites. Varied contents of ferric ion are designed to allow comparison how the contents of formed complexes affect the surface characteristics of fiber and interfacial adhesion of composites. Compared with pure PDA modified fiber, the size and number of PDA nanospheres attached on fiber first declines distinctly and then increases as the addition level of ferric ions raises, but the coordination product of both bis-and tris-Fe3+-catechol complexes exist, only the yield of complexes varies with the addition amount of FeCl3. This indicates that the level of Fe3+ ions obviously impact DA oxidation, not the complex product. Increments in interfacial shear strength across all ferric ion-PDA complex modified fibers are noticed, associating with the stronger Fe3+…O coordination bonds that could enhance the interfacial crosslinking density. However, the optimal IFSS is attainable when appropriate amount of Fe3+ ions were added, which endows the fiber with good resin wettability. The ferric ion-PDA complex assisted surface modification demonstrated to be an effective and feasible avenue in interphase tuning of fiber reinforced composites, which could be also anticipated to extend to other metallic ion-PDA complexes.

Synthesis, characterisation and antibacterial activity of novel Ga(III) polypyridyl catecholate complexes.

Ga(III) polypyridyl catecholate complexes of type [Ga(bipy)2(O,O)](NO3) or [Ga(phen)2(O,O)](NO3) respectively were readily synthesised on reaction of Ga(NO3)3 in methanol with 1 equivalent of catecholate ligand (2,3-DHBA, 3,4-DHBA, 2,3,4-THBA or CafA) and then 2 equivalents of either bipy or phen. The complexes were characterised in full including by X-ray crystallography, which established that the catecholate ligands coordinate the Ga(III) centres in a bidentate manner via the two deprotonated hydroxy groups. All Ga(III) complexes exhibited good in vitro antibacterial activity against the Gram-negative pathogenic bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. The complexes were inactive against the Gram-positive pathogenic bacteria Staphylococcus aureus including against a methicillin-resistant Staphylococcus aureus strain (MRSA). [Ga(bipy)2(2,3-DHBA-2H)](NO3)·1.5H2O (1) was shown to be non toxic in vivo in larvae of Galleria mellonella at doses up to 2000 μg mL-1 and to offer protection at doses of 100 and 250 μg mL-1 at 48 and 96 h to larvae infected with P. aeruginosa.