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

Neira, Andrea C. ; Martínez-Alanis, Paulina R. ; Aullón, Gabriel ; Flores-Alamo, Marcos ; Zerón, Paulino ; Company, Anna ; Chen, Juan ; Kasper, Johann B. ; Browne, Wesley R. and Nordlander, Ebbe LU , et al. (2019) In ACS Omega 4(6). p.10729-10740
Abstract

The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine (2BB) was employed to prepare copper complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [(2BB)CuI]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)CuII(H2O)2](OTf)2 indicates that [(2BB)CuII(H2O)2]2+ is the main species from pH 4 to 7.5; above pH 7.5, the... (More)

The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine (2BB) was employed to prepare copper complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [(2BB)CuI]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)CuII(H2O)2](OTf)2 indicates that [(2BB)CuII(H2O)2]2+ is the main species from pH 4 to 7.5; above pH 7.5, the hydroxo-bridged species [{(2BB)CuII(H2O)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)CuI]OTf and [(2BB)CuII(H2O)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)CuI]OTf/O2 or [(2BB)CuII(H2O)2](OTf)2/H2O2/NEt3 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)CuII(H2O)2](OTf)2/H2O2/NEt3 results in more extensive cellobiose degradation. Likewise, the use of both [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 with KO2 afforded cellobiose oxidation products. In all cases, a common Cu(II) complex formulated as [(2BB)CuII(OH)(H2O)]+ was detected by mass spectrometry as the final form of the complex.

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ACS Omega
volume
4
issue
6
pages
12 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:85067701259
ISSN
2470-1343
DOI
10.1021/acsomega.9b00785
language
English
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yes
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8674d777-3b64-4dd6-b52a-9da44cf4e795
date added to LUP
2019-07-04 16:47:12
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2019-12-10 08:11:49
@article{8674d777-3b64-4dd6-b52a-9da44cf4e795,
  abstract     = {<p>The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine (2BB) was employed to prepare copper complexes [(2BB)Cu<sup>I</sup>]OTf and [(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub> as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [(2BB)Cu<sup>I</sup>]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<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub> indicates that [(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup> is the main species from pH 4 to 7.5; above pH 7.5, the hydroxo-bridged species [{(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>x</sub>}<sub>2</sub>(μ-OH)<sub>2</sub>]<sup>2+</sup> 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<sup>I</sup>]OTf and [(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub> 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<sup>I</sup>]OTf/O<sub>2</sub> or [(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub>/H<sub>2</sub>O<sub>2</sub>/NEt<sub>3</sub> 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<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub>/H<sub>2</sub>O<sub>2</sub>/NEt<sub>3</sub> results in more extensive cellobiose degradation. Likewise, the use of both [(2BB)Cu<sup>I</sup>]OTf and [(2BB)Cu<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>](OTf)<sub>2</sub> with KO<sub>2</sub> afforded cellobiose oxidation products. In all cases, a common Cu(II) complex formulated as [(2BB)Cu<sup>II</sup>(OH)(H<sub>2</sub>O)]<sup>+</sup> was detected by mass spectrometry as the final form of the complex.</p>},
  author       = {Neira, Andrea C. and Martínez-Alanis, Paulina R. and Aullón, Gabriel and Flores-Alamo, Marcos and Zerón, Paulino and Company, Anna and Chen, Juan and Kasper, Johann B. and Browne, Wesley R. and Nordlander, Ebbe and Castillo, Ivan},
  issn         = {2470-1343},
  language     = {eng},
  number       = {6},
  pages        = {10729--10740},
  publisher    = {The American Chemical Society (ACS)},
  series       = {ACS Omega},
  title        = {Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes},
  url          = {http://dx.doi.org/10.1021/acsomega.9b00785},
  doi          = {10.1021/acsomega.9b00785},
  volume       = {4},
  year         = {2019},
}