Kinetic Studies on Radical Scavenging Activity of Kaempferol Decreased by Sn(II) Binding

Abstract

Sn(II) binds to kaempferol (HKaem, 3,4 ,5,7-tetrahydroxy-2-(4-hydroxyphenyl)-4H-1benzopyran-4-one) at the 3,4-site forming [Sn(II)(Kaem) 2 ] complex in ethanol. DPPH • scavenging efficiency of HKaem is dramatically decreased by SnCl 2 coordination due to formation of acid inhibiting deprotonation of HKaem as ligands and thus reduces the radical scavenging activity of the complex via a sequential proton-loss electron transfer (SPLET) mechanism. Moderate decreases in the radical scavenging of HKaem are observed by Sn(CH 3 COO) 2 coordination and by contact between Sn and HKaem, in agreement with the increase in the oxidation potential of the complex compared to HKaem, leading to a decrease in antioxidant efficiency for fruits and vegetables with Sn as package materials. be increased by the presence of copper (II), iron (III), and zinc (II) by other authors and our recent studies [7,8,[23][24][25][26]. In the present study, HKaem was selected as a typical flavonoid with two possible chelation sites (3,4 and 4,5) for metal ions, and complex formation by Sn(II) coordination to HKaem was investigated together with the complex as a radical scavenger. The effect on radical scavenging efficiency of HKaem by Sn(II) coordination is of relevance as Sn is used for packaging of food, and accordingly deserves more attention.Molecules 2020, 25, x FOR PEER REVIEW

Antioxidant vs. Prooxidant Properties of the Flavonoid, Kaempferol, in the Presence of Cu(II) Ions: A ROS-Scavenging Activity, Fenton Reaction and DNA Damage Study

“…In the present study, we have evaluated the antioxidant/prooxidant properties of kaempferol ( Figure 1 ) in the presence of Cu(II) ions, under the conditions of a model Fenton type reaction system. The beneficial health effect of kaempferol has been demonstrated in the treatment of breast, esophageal, cervical, ovarian, and liver cancers and leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. In our recent work, we studied the interaction of Cu(II) ions with quercetin and determined how this impacted on the antioxidant and prooxidant properties of the flavonoid [ 4 ].…”

“…Sci. 2021, 22, x FOR PEER REVIEW 3 of 18 leukemia, which very likely arises from its prooxidant properties and the activation of pro-apoptotic pathways [14][15][16][17][18][19][20][21][22]. In our recent work, we studied the interaction of Cu(II) ions with quercetin and determined how this impacted on the antioxidant and prooxidant properties of the flavonoid [4].…”

Alkaline earth metal ion coordination increases the radical scavenging efficiency of kaempferol

“…[2][3][4] The complexation of avonoids with metal ions has been reported to signicantly enhance the antioxidant activities of most of these complexes, [5][6][7][8][9][10][11][12][13][14][15][16][17] while for some other combinations of metal ions and avonoids, their antioxidant activities are unchanged or even decrease. [18][19][20][21][22] The binding of metal ions with avonoids and the type of metal-avonoid complexes formed depend on solvent, pH, concentration and the nature of both the metal ions and avonoids, which complicates the understanding of the molecular mechanism behind the effect that the metal ions have on the activities of the avonoids. 5,6,18,19 A remarkable increase in the radical scavenging efficiency of avonoids by the coordination of the transition metal ions Zn (II) and Cu(II) has been demonstrated and quantitatively assigned to specic species in equilibrium in solution in our recent studies.…”

“…[18][19][20][21][22] The binding of metal ions with avonoids and the type of metal-avonoid complexes formed depend on solvent, pH, concentration and the nature of both the metal ions and avonoids, which complicates the understanding of the molecular mechanism behind the effect that the metal ions have on the activities of the avonoids. 5,6,18,19 A remarkable increase in the radical scavenging efficiency of avonoids by the coordination of the transition metal ions Zn (II) and Cu(II) has been demonstrated and quantitatively assigned to specic species in equilibrium in solution in our recent studies. 5,6 For both Zn(II) and Cu(II), 1 : 1 metal-avonoid complexes were found to have a higher radical scavenging ability than 1 : 2 complexes as a result of electron withdrawal from the phenolic group of the avonoid by metal ions.…”

Promotion effects of flavonoids on browning induced by enzymatic oxidation of tyrosinase: structure–activity relationship

“…3a, c, e and g) show that oxidation occurs aer addition of avonoids to tyrosinase, which are different from reaction of avonoids with Cu(II) or other metal ions forming relatively stable avonoid complexes as found in our previous studies. [38][39][40][41] In contrast, the autooxidation of avonoids alone are less complicated.…”