A carregar...
Projeto de investigação
Functional Soft Materials Based on Supra-Amphiphilic Molecular Switches
Financiador
Autores
Publicações
Intermolecular Copigmentation of Malvidin-3- O-glucoside with Caffeine in Water
Publication . Camuenho, Ambrósio; Seco, André; Parola, A. Jorge; Basílio, Nuno; Pina, Fernando; LAQV@REQUIMTE; DQ - Departamento de Química; ACS - American Chemical Society
Intermolecular copigmentation of malvidin-3-O-glucoside with caffeine was studied using a holistic procedure that includes the extension to basic pH values. In moderately basic solutions (7.5 < pH < 9.5) and independently of the copigment presence, there is a pH region where degradation of the quinoidal base and anionic quinoidal bases is faster than hydration and OH-nucleophilic addition, preventing the system from reaching the equilibrium. Intermolecular copigmentation with caffeine reduces significantly the degradation rate of quinoidal bases. In a more basic medium, the equilibrium is reached and degradation occurs from the anionic chalcones. In this case, the addition of caffeine also reduces the degradation rate in the interval 10 < pH < 11.5.
Evolution of flavylium‐based color systems in plants
Publication . Pina, Fernando; Alejo‐armijo, Alfonso; Clemente, Adelaide; Mendoza, Johan; Seco, André; Basílio, Nuno; Parola, António Jorge; LAQV@REQUIMTE; DQ - Departamento de Química; MDPI - Multidisciplinary Digital Publishing Institute
Anthocyanins are the basis of the color of angiosperms, 3‐deoxyanthocyanins and sphagnorubin play the same role in mosses and ferns, and auronidins are responsible for the color in liverworts. In this study, the color system of cyanidin‐3‐O‐glucoside (kuromanin) as a representative compound of simpler anthocyanins was fully characterized by stopped flow. This type of anthocyanin cannot confer significant color to plants without intra‐ or intermolecular interactions, complexation with metals or supramolecular structures as in Commelina communis. The anthocyanin’s color system was compared with those of 3‐deoxyanthocyanins and riccionidin A, the aglycone of auronidins. The three systems follow the same sequence of chemical reactions, but the respective thermodynamics and kinetics are dramatically different.
Flavylium Compounds. From nature’s colour palette to a versatile component in supramolecular devices
Publication . Seco, André Miguel Lopes; Basílio, Nuno; Parola, António
This thesis explores the chemistry of anthocyanins and flavylium-based supramolecular
systems, focusing on their structural dynamics, responsiveness to external stimuli, and
applications. The first part investigates colour stability in anthocyanins. A comprehensive
study of the mono- and di-glycosylated forms of malvidin identifies a pH range where
equilibrium is never attained. A novel transient species (B42−) is detected in the diglycosylated malvidin, altering the equilibrium distribution and affecting colour stability. The
study of delphinidin 3-O-glucoside with chlorogenic acid reveals a stronger affinity for
the coloured forms of the anthocyanin, thus explaining how copigmentation is used to
stabilise colour in plants.
The second part explores the versatility of flavylium systems beyond colour chemistry.
Flavylium compounds complexed with cucurbit[7]uril (CB7) act as photobase generators,
capable of modulating the pH of the medium through light stimuli, achieving pH shifts
up to ΔpH = 1.5. Quaternary supramolecular complexes are formed through cooperative
interactions between CB7, flavylium guests, and a tetracationic cyclophane (blue box), overcoming electrostatic repulsion and resulting in highly fluorescent nanotubular assemblies
(Φfl = 0.78). Furthermore, the incorporation of flavylium units in pseudorotaxane axles
enables control over the motion of a macrocycle such as CB7 along the thread through light
and pH stimuli. In these systems, flavylium acts as a reversible photoswitch, allowing for
the development of stimuli-responsive supramolecular materials.
By studying anthocyanin chemistry alongside supramolecular chemistry based on the
flavylium cation, this thesis demonstrates how molecular interactions govern colour stability, fluorescence, and (supra)molecular dynamics. The results contribute to deepening
the understanding of colour stability in anthocyanins while providing supramolecular
chemistry with new tools for designing more efficient and functional systems.
The impressive colors of the bis-aminostyrylbenzopyrylium system. Evidence by stopped-flow for the B4 formation at pH>13
Publication . Araújo, Paula; Borges, Alexandra; Oliveira, Joana; Seco, André; Outis, Mani; Lima, João C.; Basílio, Nuno; de Freitas, Victor; Pina, Fernando; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier
The kinetics and thermodynamics of the compound 7-diethylamino-2-(4′-dimethylaminostyryl)-1-benzopyrylium was studied in ethanol:water (1:1) and in microheterogenous media (SDS and CTAB micelles) and compared with its corresponding flavylium (7-diethylamino-4′-dimethylaminoflavylium) also known as 7-diethylamino-2-(4′-dimethylaminophenyl)-1-benzopyrylium. The introduction of a double bond between the benzopyrylium system and the phenyl group gives rise to vivid color changes resulting from the formation of violet protonated styrylbenzopyrylium cation (AH22+), green styrylbenzopyrylium cation (AH+), orange trans-chalcone (Ct) and magenta anionic trans-chalcone (Ct−). All species except protonated styrylbenzopyrylium cation are stable for long periods. In ethanol:water the pH domain of the styrylbenzopyrylium cation and trans-chalcone are respectively ΔpH = 4.5 and 4.4 and the anionic trans-chalcone for pH > 10.5. In the presence of SDS micelles, there is an increase of the pH domain of the styrylbenzopyrylium cation ΔpH = 5.9 at the expense of the trans-chalcones, ΔpH = 2.95, while in CTAB it is the trans-chalcone the dominant species, ΔpH = 6.2, with concomitant decreasing of the styrylbenzopyrylium cation pH range ΔpH = 1. This can be due to the electric charge present on the surface of each micelle, for instance the negative charge surface of SDS micelles stabilizes the positive charge of styrylbenzopyrylium cation and its protonated form, while the positive charge surface of CTAB micelles stabilizes the negative and neutral charge of the trans-chalcones species. The peculiar behavior of the kinetics in basic medium was investigated by stopped-flow. It was verified that in ethanol:water, SDS and CTAB micelles a transient species resulting from the OH− attack to position 4 of the styrylbenzopyrylium cation (B4) behaves as a kinetic product delaying the kinetic toward the equilibrium.
Unidades organizacionais
Descrição
Palavras-chave
Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Número da atribuição
2020.07313.BD