Bis(benzimidazolyl)amine copper complexes with a synthetic ‘histidine brace’ structural motif relevant to polysaccharide monooxygenases

Castillo, Iván; Neira, Andrea. C.; Nordlander, Ebbe; Zeglio, Erica

doi:10.1016/j.ica.2014.06.027

Cited by 9 publications

(14 citation statements)

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“…The species distribution was determined with MEDUSA software (ionic strength 0.1 M NaNO 3 ), where the dicationic species [( 2BB )Cu II ] 2+ clearly predominates in the pH range of 4–8; see Figure . One or two molecules of water are likely coordinated to the cupric ion in solution to form [( 2BB )Cu II (H 2 O) n ] 2+ ( n = 1, 2), as observed in the solid state . Interestingly, a monodeprotonated species is predicted to be present around pH 7.5 and above, which was assigned to a cupric–hydroxo complex [( 2BB )Cu II (OH)(H 2 O) n −1 ] + , likely in the form of a bridged dimer [{( 2BB )Cu II (H 2 O) n −1 } 2 (μ-OH) 2 ] 2+ , with log K = 15.88.…”

Section: Resultsmentioning

confidence: 97%

“…One or two molecules of water are likely coordinated to the cupric ion in solution to form [( 2BB )Cu II (H 2 O) n ] 2+ ( n = 1, 2), as observed in the solid state. 15 Interestingly, a monodeprotonated species is predicted to be present around pH 7.5 and above, which was assigned to a cupric–hydroxo complex [( 2BB )Cu II (OH)(H 2 O) n −1 ] + , likely in the form of a bridged dimer [{( 2BB )Cu II (H 2 O) n −1 } 2 (μ-OH) 2 ] 2+ , with log K = 15.88. This type of species would be favored over a complex with a deprotonated central amine, on the basis of the additional experimental evidence for a hydroxo-bridged dicopper complex (vide infra).…”

Section: Resultsmentioning

confidence: 99%

“…In this context, we recently reported the use of bis[(1-methyl-2-benzimidazolyl)ethyl]amine ( 2BB , , Chart ) as a simple structural model of the ligand environment in mononuclear active sites of LPMO. , Our interest was spurred by the presence of a methylated nitrogen atom in one of the histidinic imidazoles of fungal LPMO and the presence of a central secondary amine available for potential H-bonding with substrates. Additionally, the 2BB /Cu II system afforded complexes with bonding parameters in the range of those of LPMO active sites (Cu–N distances of ∼1.98 Å, N–Cu–N angles of ∼97 and ∼165°).…”

Section: Introductionmentioning

confidence: 99%

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Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes

et al. 2019

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The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine ( 2BB ) was employed to prepare copper complexes [( 2BB )Cu I ]OTf and [( 2BB )Cu II (H 2 O) 2 ](OTf) 2 as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [( 2BB )Cu I ]OTf revealed a Cu(I) center with a T-shaped coordination environment and metric parameters in the range of those observed in reduced LPMOs. Solution characterization of [( 2BB )Cu II (H 2 O) 2 ](OTf) 2 indicates that [( 2BB )Cu II (H 2 O) 2 ] 2+ is the main species from pH 4 to 7.5; above pH 7.5, the hydroxo-bridged species [{( 2BB )Cu II (H 2 O) x } 2 (μ-OH) 2 ] 2+ is also present, on the basis of cyclic voltammetry and mass spectrometry. These observations imply that deprotonation of the central amine of Cu(II)-coordinated 2BB is precluded, and by extension, amine deprotonation in the histidine brace of LPMOs appears unlikely at neutral pH. The complexes [( 2BB )Cu I ]OTf and [( 2BB )Cu II (H 2 O) 2 ](OTf) 2 act as precursors for the oxidative degradation of cellobiose as a cellulose model substrate. Spectroscopic and reactivity studies indicate that a dicopper(II) side-on peroxide complex generated from [( 2BB )Cu I ]OTf/O 2 or [( 2BB )Cu II (H 2 O) 2 ](OTf) 2 /H 2 O 2 /NEt 3 oxidizes cellobiose both in acetonitrile and aqueous phosphate buffer solutions, as evidenced from product analysis by high-performance liquid chromatography-mass spectrometry. The mixture of [( 2BB )Cu II (H 2 O) 2 ](OTf) 2 /H 2 O 2 /NEt 3 results in more extensive cellobiose degradation. Likewise, the use of both [( 2BB )Cu I ]OTf and [( 2BB )Cu II (H 2 O) 2 ...

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes

et al. 2019

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“…Recently, a copper(II) complex based on the bis(benzimidazole)amine ligand was prepared as a structural model for LPMOs, but no oxidative reactivity was reported. 7 We prepared two ligands (L AM and L IM ) providing a N 3 -coordination sphere for a copper ion and featuring an N-methylated imidazole moiety (Figure 1). 8 The corresponding complexes [(L AM )Cu(CH 3 CN)](ClO 4 ) 2 (1) and [(L IM )Cu(OH 2 )](ClO 4 ) 2 •H 2 O (2) were prepared.…”

mentioning

confidence: 99%

“…Several copper–oxygen intermediates have been characterized using biomimetic complexes, and much can be learned about the LPMO mechanism by using a small-model approach. Recently, a copper(II) complex based on the bis(benzimidazole)amine ligand was prepared as a structural model for LPMOs, but no oxidative reactivity was reported . We prepared two ligands (L AM and L IM ) providing a N 3 -coordination sphere for a copper ion and featuring an N-methylated imidazole moiety (Figure ).…”

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Copper Complexes as Bioinspired Models for Lytic Polysaccharide Monooxygenases

et al. 2017

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We report here two copper complexes as first functional models for lytic polysaccharide monooxygenases, mononuclear copper-containing enzymes involved in recalcitrant polysaccharide breakdown. These complexes feature structural and spectroscopic properties similar to those of the enzyme. In addition, they catalyze oxidative cleavage of the model substrate p-nitrophenyl-β-d-glucopyranoside. More importantly, a particularly stable copper(II) hydroperoxide intermediate is detected in the reaction conditions.

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LPMO‐like Activity of Bioinspired Copper Complexes: From Model Substrate to Extended Polysaccharides

Leblay,

Delgadillo‐Ruíz,

Decroos

et al. 2023

ChemCatChem

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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.

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Bis(benzimidazolyl)amine copper complexes with a synthetic ‘histidine brace’ structural motif relevant to polysaccharide monooxygenases

Cited by 9 publications

References 41 publications

Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes

Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes

Copper Complexes as Bioinspired Models for Lytic Polysaccharide Monooxygenases

LPMO‐like Activity of Bioinspired Copper Complexes: From Model Substrate to Extended Polysaccharides

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