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Biomimetic modeling of copper complexes: a study of enantioselective catalytic oxidation on d-(+)-catechin and L-( - )-epicatechin with copper complexes.

Mutti FG, Pievo R, Sgobba M, Gullotti M, Santagostini L - Bioinorg Chem Appl (2008)

Bottom Line: The unstable quinones were trapped by the nucleophilic reagent, 3-methyl-2-benzothiazolinone hydrazone (MBTH), and have been calculated the molar absorptivities of the different quinones.The catalytic efficiency is moderate, as inferred by kinetic constants, but the complexes exhibit significant enantio-differentiating ability towards the catechols, albeit for the dinuclear complexes, this enantio-differentiating ability is lower.In all cases, the preferred enantiomeric substrate is D-(+)-catechin to respect the other catechol, because of the spatial disposition of this substrate.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Chimica Inorganica, Metallorganica e Analitica "Lamberto Malatesta", Università di Milano, Istituto ISTM-CNR, Via Venezian 21, 20133 Milano, Italy.

ABSTRACT
The biomimetic catalytic oxidations of the dinuclear and trinuclear copper(II) complexes versus two catechols, namely, D-(+)-catechin and L-( - )-epicatechin to give the corresponding quinones are reported. The unstable quinones were trapped by the nucleophilic reagent, 3-methyl-2-benzothiazolinone hydrazone (MBTH), and have been calculated the molar absorptivities of the different quinones. The catalytic efficiency is moderate, as inferred by kinetic constants, but the complexes exhibit significant enantio-differentiating ability towards the catechols, albeit for the dinuclear complexes, this enantio-differentiating ability is lower. In all cases, the preferred enantiomeric substrate is D-(+)-catechin to respect the other catechol, because of the spatial disposition of this substrate.

No MeSH data available.


Nucleophilic attach of thereagent MBTH to the catechols.
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sch1: Nucleophilic attach of thereagent MBTH to the catechols.

Mentions: Thecatalytic oxidation of polyphenolic substrates, including catechins, was wellstudied by many authors [38–41]. These reactions take place in the presence ofatmospheric oxygen when polyphenol oxidase (PPO) and the correspondingsubstrates are mixed at the same time. The fundamental first step is thetransformation of o-diphenolsto the corresponding o-quinones.The fate and stability of o-quinonesvary widely, depending both on the phenolic precursor and on environmentalfactors. In particular, the o-quinonesof D-(+)-catechin and L-(–)-epicatechinwere seen to be much less stable than those of other o-quinones. The prolonged autoxidation, either chemical orenzymic, led to the formation of polymers resulting from repeated condensationreactions between an aromatic ring of one molecule with an aromatic ring ofanother (“head to tail” polymerization mechanism). Depending on how phenoliccompounds are oxidized, the condensation products formed from catechins maydiffer. In fact, the pH of the solution influences considerably the obtainedproducts [42, 43], because at low pH values is favored the formation ofcolorless condensation products, whereas yellow compounds tended to be formedat higher pH values. To avoid any effect due to pH-dependence of oxidation productsand to stop the reaction at quinones formation, a nucleophilic reagent MBTH, that traps thequinones and generates chromophoric adducts, was used (Scheme 1).


Biomimetic modeling of copper complexes: a study of enantioselective catalytic oxidation on d-(+)-catechin and L-( - )-epicatechin with copper complexes.

Mutti FG, Pievo R, Sgobba M, Gullotti M, Santagostini L - Bioinorg Chem Appl (2008)

Nucleophilic attach of thereagent MBTH to the catechols.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2553160&req=5

sch1: Nucleophilic attach of thereagent MBTH to the catechols.
Mentions: Thecatalytic oxidation of polyphenolic substrates, including catechins, was wellstudied by many authors [38–41]. These reactions take place in the presence ofatmospheric oxygen when polyphenol oxidase (PPO) and the correspondingsubstrates are mixed at the same time. The fundamental first step is thetransformation of o-diphenolsto the corresponding o-quinones.The fate and stability of o-quinonesvary widely, depending both on the phenolic precursor and on environmentalfactors. In particular, the o-quinonesof D-(+)-catechin and L-(–)-epicatechinwere seen to be much less stable than those of other o-quinones. The prolonged autoxidation, either chemical orenzymic, led to the formation of polymers resulting from repeated condensationreactions between an aromatic ring of one molecule with an aromatic ring ofanother (“head to tail” polymerization mechanism). Depending on how phenoliccompounds are oxidized, the condensation products formed from catechins maydiffer. In fact, the pH of the solution influences considerably the obtainedproducts [42, 43], because at low pH values is favored the formation ofcolorless condensation products, whereas yellow compounds tended to be formedat higher pH values. To avoid any effect due to pH-dependence of oxidation productsand to stop the reaction at quinones formation, a nucleophilic reagent MBTH, that traps thequinones and generates chromophoric adducts, was used (Scheme 1).

Bottom Line: The unstable quinones were trapped by the nucleophilic reagent, 3-methyl-2-benzothiazolinone hydrazone (MBTH), and have been calculated the molar absorptivities of the different quinones.The catalytic efficiency is moderate, as inferred by kinetic constants, but the complexes exhibit significant enantio-differentiating ability towards the catechols, albeit for the dinuclear complexes, this enantio-differentiating ability is lower.In all cases, the preferred enantiomeric substrate is D-(+)-catechin to respect the other catechol, because of the spatial disposition of this substrate.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Chimica Inorganica, Metallorganica e Analitica "Lamberto Malatesta", Università di Milano, Istituto ISTM-CNR, Via Venezian 21, 20133 Milano, Italy.

ABSTRACT
The biomimetic catalytic oxidations of the dinuclear and trinuclear copper(II) complexes versus two catechols, namely, D-(+)-catechin and L-( - )-epicatechin to give the corresponding quinones are reported. The unstable quinones were trapped by the nucleophilic reagent, 3-methyl-2-benzothiazolinone hydrazone (MBTH), and have been calculated the molar absorptivities of the different quinones. The catalytic efficiency is moderate, as inferred by kinetic constants, but the complexes exhibit significant enantio-differentiating ability towards the catechols, albeit for the dinuclear complexes, this enantio-differentiating ability is lower. In all cases, the preferred enantiomeric substrate is D-(+)-catechin to respect the other catechol, because of the spatial disposition of this substrate.

No MeSH data available.