Cyclodextrin encapsulation of the functional group diminishes an antioxidant's free radical scavenging rates

Abstract

Scavenging rates of cyclodextrin-solubilized lipophilic antioxidants, namely catechin, epicatechin, epigallocatechin gallate, and resveratrol, against alkoxyl (RO • ) radical were measured with the use of electron paramagnetic resonance (EPR) spin-trapping method. Results indicated that the scavenging rates of catechin and resveratrol were notably dependent on the solubilizer used, i.e., native β-cyclodextrin (β-CD) or heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD). But, epicatechin and epigallocatechin gallate showed almost no dependence on the cyclodextrin used. Catechin's scavenging rate in β-CD was 66% lower than in DM-β-CD; in contrast, resveratrol in β-CD showed 45% higher rate than in DM-β-CD. Based on the reported solution-NMR structure of the inclusion complex of these antioxidants, it was concluded that the scavenging rate is decreased when the cyclodextrin cavity preferentially encapsulates the antioxidant-function bearing group, i.e., o -and p-quinolinol group in catechin and resveratrol, respectively. The depth of inclusion of the functional group determines the extent of the scavenging rate difference, suggesting that the cavity wall of the cyclodextrin acts like a barrier that hinders the approach of attacking free radicals. C 2012 Wiley Periodicals, Inc. Int J Chem Kinet 1

Physico-chemical studies of resveratrol, methyl-jasmonate and cyclodextrin interactions: an approach to resveratrol bioproduction optimization

“…It should be noted that no interaction with H6 of DIMEB was observed whereas a correlation between the methoxy group in position 6 of DIMEB with all the RSV aromatic protons (H-1′, H-2′, H-5′, H-6′) was highlighted. Conversely to the 3D inclusion complex structures proposed by Lu et al 32 and Ishikawa et al , 33 no interaction with the ethylenic protons H-3′ and H-4′ in the central position of RSV was observed. As a 1 : 1 stoichiometry can be postulated on the basis of the RAMEB/RSV solubility study, these NMR observations probably indicate that DIMEB/RSV inclusion complex exists as two types of 1 : 1 complexes involving each aromatic moiety.…”

Scavenging rate constants of hydrophilic antioxidants against multiple reactive oxygen species

“…( 7 , 8 ) Thus, we have reported ORSC-ESR measurement of the scavenging rates in various lipophilic antioxidant compounds. ( 9 ) However, the ORSC method uses a single free radical species that is generated from the azo-initiator 2,2'-azobis(2-amidino-propane) dihydrochloride (AAPH). This free radical species has been identified as alkoxyl radical (RO • ).…”

Photoionization access to cyclodextrin-encapsulated resveratrol phenoxy radicals and their repair by ascorbate across the phase boundary

“…This antioxidative action of ResOH encapsulated by cyclodextrins has been addressed experimentally using activity assays [7,9,15,16] and kinetic measurements [17] . This unambiguous result contrasts markedly with the contradictory information about the influence of cyclodextrins on radical scavenging by complexed ResOH, which is the formal back reaction of Equation 2, hence strongly related to the ResO • repair.…”

“…This antioxidative action of ResOH encapsulated by cyclodextrins has been addressed experimentally using activity assays [7,9,15,16] and kinetic measurements [17] . [17] The obviously stronger cyclodextrin effects on ResO • scavenging by the co-antioxidant HAsc − compared to radical scavenging by the antioxidant ResOH prompted us to check whether the repair according to Equation 2 undergoes a mechanistic change when ResO • is complexed. However, the prolonged activity in the latter case might simply reflect the increased stability of complexed ResOH towards air and light [4,16] rather than a change of the rate constant of the scavenging proper, [45,46] that is, of the parameter characterizing the antioxidant activity on a molecular level.…”

“…To overcome the poor water solubility of this lipophilic "wonder molecule", which inhibits its oral uptake, cyclodextrins are receiving strong attention as its carriers. [14] Whereas several reports have addressed radical scavenging by cyclodextrin-complexed ResOH, [7,9,[15][16][17] nothing whatsoever is known about the repair of ResO • at the watercyclodextrin interface. Elucidating the kinetic and mechanistic aspects of these so-called repair reactions is essential for understanding radical-scavenging cascades as they occur in nature.…”