Isomerization between 2-(2,4-Dihydroxystyryl)-1-benzopyrylium and 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium

Abstract

2-Phenyl-1-benzopyrylium (flavylium) and 2-styryl-1-benzopyrylium (styrylflavylium) cations establish in aqueous solution a series of equilibria defining chemical reaction networks responsive to several stimuli (pH, light, redox potential). Control over the mole fraction distribution of species by applying the appropiate stimuli defines a horizontal approach to supramolecular chemistry, in agreement with the customary bottom-up approach toward complex systems. In this work, we designed an asymmetric styrylchalcone able to cyclize in two different ways, producing two isomeric styrylflavylium cations whose chemical reaction networks are thus interconnected. The chemical reaction networks of 2-(2,4-dihydroxystyryl)-1-benzopyrylium (AH(+)) and 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium (AH(+)(iso)) comprise the usual species observed in flavylium-derived networks, in this case, the styryl derivatives of quinoidal bases, hemiketals, and chalcones. The thermodynamics and kinetics of the crossed networks were characterized by the use of UV-vis absorption and NMR spectroscopy as well as time-resolved pH jumps followed by stopped-flow. The two styrylflavylium cations are connected (isomerize) through two alternative intermediates, the asymmetric trans-styrylchalcone (Ct) and a spiropyran-type intermediate (SP). At pH = 1, AH(+) slowly evolves (k(obs) ≈ 10(-5) s(-1)) to a mixture containing 62% AH(+)(iso) through the Ct intermediate, while at pH = 5, the SP intermediate is involved. The observed rate constants for the conversion of the styrylflavylim cations into equilibrium mixtures containing essentially Ct follow a pH-dependent bell-shaped curve in both networks. While at pH = 1 in the dark, AH(+) evolves to an equilibrium mixture containing predominantly AH(+)(iso), irradiation at λ > 435 nm induces the opposite conversion.

Achieving Complexity at the Bottom. 2,6-Bis(arylidene)cyclohexanones and Anthocyanins: The Same General Multistate of Species

“…Synthesis of 6-(Dimethylamino)-4-(4-(dimethylamino)-2-hydroxybenylidene)-1,2,3,4-tetrahydroxanthylium (1). The compounds 4-dimethylamino-2-hydroxybenzaldehyde (0.39 g, 2.36 mmol) and cyclohexanone (0.116 g, 1.18 mmol) were dissolved in 10 mL of ethanol and heated to 50 °C.…”

“…We coined this last concept as molecular metamorphosis. 1 While in supramolecular chemistry the complexity results from the higher dimension and diversity of the building blocks, in metamorphosis it is the number of species that gives the complexity. Anthocyanins and related compounds are a paradigm of metamorphosis.…”

“…Complexity can be achieved through a bottom-up approach, as in supramolecular chemistry, or by a multistate of chemical species reversibly interconverted by external stimuli, such as pH and light. We coined this last concept as molecular metamorphosis . While in supramolecular chemistry the complexity results from the higher dimension and diversity of the building blocks, in metamorphosis it is the number of species that gives the complexity.…”

2,2′-Spirobis[chromene] Derivatives Chemistry and Their Relation with the Multistate System of Anthocyanins

“…2 In theory, each of the species could have a cis−trans isomerization in the pendent styryl arm (that includes ring B) although, to our knowledge, no experimental evidence for this possibility has been found so far. 6 Introduction of a hydroxyl group in position 2′ of ring B of a styrylflavylium, as shown in Scheme 2, increases the number of species since there are two possibilities of forming cis-chalcone and closing the ring, leading to different styrylflavylium isomers. A particularly interesting mechanistic aspect was the previously reported kinetic evidence for a transient intermediate, the 2,2′spirobis[chromene] species, that links both flavylium systems, as represented in Scheme 2.…”

Synthesis and Structural Characterization of a Novel Symmetrical 2,10-Bis-Styryl-1-Benzopyrylium Dye

“…More recently, Pina and coworkers described a series of these 2-styryl-1-benzopyrylium salts and studied their reaction network and photochromic properties in the absence and presence of CTAB micelles. 6,9,10 Over the last years, our research group has been dedicated to the isolation and identification of new families of anthocyanin derivatives, essentially from red wine, named as pyranoanthocyanins. 11,12 The hemisynthesis of these pigments have been also reported in winelike conditions and their formation mechanism normally involves cycloaddition reactions between the C-4 and hydroxyl substituent of C-5 from anthocyanins and a double bond from another…”