Abstract
Chlorogenic (CA) and rosmarinic (RA) acids are two natural bioactive hydroxycinnamic acids whose antioxidant properties can be modulated by the chelation of metal ions. In this work, the interactions of these two carboxylic phenols with calcium ions and the impact of such interactions on their antioxidant activity were investigated. UV-Vis absorbance, mass spectroscopy and 1H and 13C liquid NMR were used to identify complexes formed by CA and RA with calcium. Antioxidant activities were measured by the Bois method. Density functional theory (DFT) calculations were performed to evaluate the most stable configurations and correlated with NMR data. Taken together, these data suggest that calcium ions mainly interact with the carboxylate groups of both molecules but that this interaction modifies the reactivity of the catechol groups, especially for RA. These results highlight the complex interplay between metal chelation and antioxidant properties of natural carboxylic phenols.
Highlights
Phytopharmacology has attracted much scientific attention in the last decades because of its use in traditional medicine over three thousand years, mainly as herbal tea and in modern medicine since a large proportion of known drugs have been initially identified in plants and are currently used as such or as derivatives
It has been widely reported that polyphenols exhibit antioxidant and chelation properties that have industrial applications, such as therapeutic agents for the treatment of degenerative diseases or in antimicrobial food packaging [40,41,42,43,44]
In the case of chlorogenic acid, two binding sites for calcium are possible: a carboxylate group and a catechol group belonging to the caffeic acid unit
Summary
Phytopharmacology has attracted much scientific attention in the last decades because of its use in traditional medicine over three thousand years, mainly as herbal tea and in modern medicine since a large proportion of known drugs have been initially identified in plants and are currently used as such or as derivatives. IInn tthhiiss ccoonntteexxtt,, tthhiiss ssttuuddyy aaiimmeedd aatt aa ddeettaaiilleedd eevvaalluuaattiioonn ooff ccaallcciiuumm iioonnss iinntteerraaccttiioonnss wwiitthh cchhlloorrooggeenniicc aacciidd ((CCAA)) aanndd rroossmmaarriinniicc aacciidd ((RRAA)) ((FFiigguurree 11)). 8 signals were missing in the presence of calcium Such modifications could be induced by some relaxation issues and prevent any conclusion about the potential involvement of these positions in complexation. From both 1H and 13C NMR data, it could be hypothesized that calcium complexation could take place either with a carboxylic group or with catechol C19–C20. . ((aa)) 11HH,, aanndd ((bb)) 1133CC NNMMRR ssppeeccttrraa ooff rroossmmaarriinniicc aacciidd iinn tthhee aabbsseennccee ((rreedd lliinnee))aannddininththee ppreresseenncceeooffccaalclciuiumm, ,RRAA:C:Caa2+2+ == 11::110000 ((bblluuee lliinnee)) iinn DD22OO((ppHH77)). AgrtopuHps7., tAhet pcaHrb7o,xtyhleic cgarrobuopxysliocfgbroouthpscoomf bpootuhncdosmaproeudnedpsraorteodnaepterdotsoinnacteedthseinircepKthaesirapreK2as.9a2rean2.d923a.9n0df3o.r90RfAoraRnAd aCnAd, CurusAesisni,pngregecAstApiCveCcDeDtliyLvL.aeabTlbyhs. esoToffhftotwewrmfaaorrereemr. . veIInarnlvouoarerldduweeerrawtstoaorseeepnrneosspurutorererdetethtdbheyebnyDneDaeuunatratnrafaaleifltiteytytaolao.fl.f[t3[ht34he4]e]1aa1:n1n:d1dcoctthomhemepllplaaelttxettexewrrwooitnnihteehCwwCaa2aas+s2+,c,caaaallcscsueuecllacoaotntenedddd ddeepprroottoonnaattiioonn wwaass aassssuummeedd ttoossttaannddaattththeehhyyddrrooxxyyllggrroouuppsswwitihthththeelolowweessttppKKaass,, ii.e.e..,, CC2200 oorrCC33 hschayaymdfdfreeroioccxaxyffpylelsasircftfo,oprrtahRRretAA, hthwywedhhhroooyssxdeeyrplopKxgKyarasolsaugarrperoeu8o.pn83.63oC6na2na0Cdn2ids90.5ai9s6l.s5a,o6rlse,aosrspeassesupcsmtueicmvetdeievldyteol[ty3oh4[ha]3.va4Bve]ee.tchtBaheueesclloeaowuRwseAeesstaRtnppAdKKaaCanvAvdaalslCuuheAeariiennshtChCaeArAesaatanhmndede tthheerreefoforerewwaasscchhoosseennaasstthheemmoorreelliikkeelylyddeepprroottoonnaatitoionnssititeeiinntthhiisspphheennoolliiccccoommppoouunnddwwhhiilleehhyyddrrooxxyyll gbbgraarososuiisups,p,ststwlwoloococadadtietffiedfdefeirnireneninttisttssqsiqtiuetueisnisnwicwiceperpareaerhrthtyhyhpapavovoethetphepeKsKsiaziazerreededppfrofreoersrsetenhtnhteateactitcavialvecleciouioufmfmaalcilpciopohmhmaaptpitlcielcexaxaalcaltcoitooihohnonolvslvs,iai,tahtihnuinutsetseararbaabcocotvtivoieoen1ns10s0.ww.OOitinthnhttthhthhiesies ooxxyyggeennaattoommssoofftthheeccaarrbbooxxyylalatteeggrroouuppoorrooffththeeccaatetecchhoollggrroouupp. .OOppttiimmiizzeeddssttrruuccttuurreessaarreesshhoowwnninin FFigiguurree66aannddtototatal leenneergrgieiessaarererereppoortreteddininTTabalbele1.1
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