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Flavonoids in Microheterogeneous Media, Relationship between Their Relative Location and Their Reactivity towards Singlet Oxygen.

Günther G, Berríos E, Pizarro N, Valdés K, Montero G, Arriagada F, Morales J - PLoS ONE (2015)

Bottom Line: In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer.The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin).Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile.

ABSTRACT
In this work, the relationship between the molecular structure of three flavonoids (kaempferol, quercetin and morin), their relative location in microheterogeneous media (liposomes and erythrocyte membranes) and their reactivity against singlet oxygen was studied. The changes observed in membrane fluidity induced by the presence of these flavonoids and the influence of their lipophilicity/hydrophilicity on the antioxidant activity in lipid membranes were evaluated by means of fluorescent probes such as Laurdan and diphenylhexatriene (DPH). The small differences observed for the value of generalized polarization of Laurdan (GP) curves in function of the concentration of flavonoids, indicate that these three compounds promote similar alterations in liposomes and erythrocyte membranes. In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer. The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin). Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium.

No MeSH data available.


Morin deprotonated.Panel A shows the optimized geometry for morin deprotonated at 2’-OH at the DFT B3LYP/6-311++G** level with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and highlights the hydrogen bond between 3OH and 2’-O- (1.438 Å, blue dashed line). White, cyan and red represent Hydrogen, Carbon and Oxygen atoms respectively. Panel B depicts the HOMO for the geometry in panel A (isovalue 0.02 a.u) showing large and localized electron density over the enol.
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pone.0129749.g006: Morin deprotonated.Panel A shows the optimized geometry for morin deprotonated at 2’-OH at the DFT B3LYP/6-311++G** level with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and highlights the hydrogen bond between 3OH and 2’-O- (1.438 Å, blue dashed line). White, cyan and red represent Hydrogen, Carbon and Oxygen atoms respectively. Panel B depicts the HOMO for the geometry in panel A (isovalue 0.02 a.u) showing large and localized electron density over the enol.

Mentions: Chemical deactivation of singlet oxygen by flavonols is known to involve carbon double bond C2-C3 in ring C (Fig 1) following a [2+2] cycloaddition mechanism [26]. Also, it has been reported that photooxidation reaction rate of enolic tautomers of dicarbonyl compounds is greatly enhanced by the presence of fluoride ion or tetrabutilammonium hydroxide [81]. This effect has been attributed to hydrogen bond formation between the fluoride ion and the enol hydrogen which enhances its nucleophilicity [82]. Fig 6A shows the optimized geometry for morin deprotonated at 2’-OH [74] calculated at the DFT B3LYP/6-311++G** level of theory. The structure is non planar with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and it possesses a 1.438 Å hydrogen bond between 3OH and 2’-O- (blue dashed line) in agreement with Musialik et al. proposal. The HOMO of morin shows localized electron density over the C2-C3 double bond (Fig 6B); therefore affecting the chemical reaction rate with singlet oxygen. On the other hand, kaempferol and quercetin neutral optimized geometry are planar (data not shown) and even though their HOMO also show electron density on the C2-C3 double bond, this is delocalized due to resonance. Furthermore, absence of an hydroxyl group in ring B avoids the formation of hydrogen bond with 3OH. The increased acidity besides the enhanced nucleophilicity of enolic bond could explain to the higher chemical reactivity observed for morin.


Flavonoids in Microheterogeneous Media, Relationship between Their Relative Location and Their Reactivity towards Singlet Oxygen.

Günther G, Berríos E, Pizarro N, Valdés K, Montero G, Arriagada F, Morales J - PLoS ONE (2015)

Morin deprotonated.Panel A shows the optimized geometry for morin deprotonated at 2’-OH at the DFT B3LYP/6-311++G** level with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and highlights the hydrogen bond between 3OH and 2’-O- (1.438 Å, blue dashed line). White, cyan and red represent Hydrogen, Carbon and Oxygen atoms respectively. Panel B depicts the HOMO for the geometry in panel A (isovalue 0.02 a.u) showing large and localized electron density over the enol.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4476713&req=5

pone.0129749.g006: Morin deprotonated.Panel A shows the optimized geometry for morin deprotonated at 2’-OH at the DFT B3LYP/6-311++G** level with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and highlights the hydrogen bond between 3OH and 2’-O- (1.438 Å, blue dashed line). White, cyan and red represent Hydrogen, Carbon and Oxygen atoms respectively. Panel B depicts the HOMO for the geometry in panel A (isovalue 0.02 a.u) showing large and localized electron density over the enol.
Mentions: Chemical deactivation of singlet oxygen by flavonols is known to involve carbon double bond C2-C3 in ring C (Fig 1) following a [2+2] cycloaddition mechanism [26]. Also, it has been reported that photooxidation reaction rate of enolic tautomers of dicarbonyl compounds is greatly enhanced by the presence of fluoride ion or tetrabutilammonium hydroxide [81]. This effect has been attributed to hydrogen bond formation between the fluoride ion and the enol hydrogen which enhances its nucleophilicity [82]. Fig 6A shows the optimized geometry for morin deprotonated at 2’-OH [74] calculated at the DFT B3LYP/6-311++G** level of theory. The structure is non planar with a dihedral angle C3-C2-C1’-C2’ equal to 27.6° and it possesses a 1.438 Å hydrogen bond between 3OH and 2’-O- (blue dashed line) in agreement with Musialik et al. proposal. The HOMO of morin shows localized electron density over the C2-C3 double bond (Fig 6B); therefore affecting the chemical reaction rate with singlet oxygen. On the other hand, kaempferol and quercetin neutral optimized geometry are planar (data not shown) and even though their HOMO also show electron density on the C2-C3 double bond, this is delocalized due to resonance. Furthermore, absence of an hydroxyl group in ring B avoids the formation of hydrogen bond with 3OH. The increased acidity besides the enhanced nucleophilicity of enolic bond could explain to the higher chemical reactivity observed for morin.

Bottom Line: In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer.The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin).Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago, Chile.

ABSTRACT
In this work, the relationship between the molecular structure of three flavonoids (kaempferol, quercetin and morin), their relative location in microheterogeneous media (liposomes and erythrocyte membranes) and their reactivity against singlet oxygen was studied. The changes observed in membrane fluidity induced by the presence of these flavonoids and the influence of their lipophilicity/hydrophilicity on the antioxidant activity in lipid membranes were evaluated by means of fluorescent probes such as Laurdan and diphenylhexatriene (DPH). The small differences observed for the value of generalized polarization of Laurdan (GP) curves in function of the concentration of flavonoids, indicate that these three compounds promote similar alterations in liposomes and erythrocyte membranes. In addition, these compounds do not produce changes in fluorescence anisotropy of DPH, discarding their location in deeper regions of the lipid bilayer. The determined chemical reactivity sequence is similar in all the studied media (kaempferol < quercetin < morin). Morin is approximately 10 times more reactive than quercetin and 20 to 30 times greater than kaempferol, depending on the medium.

No MeSH data available.