F. Pina

Universidade NOVA de Lisboa | NOVA · Department of Chemistry

Iron‐gall inks, a vital part of our written cultural heritage, are at risk of complete loss due to degradation, a potential loss that we must urgently address. These inks are based on Fe³⁺‐complexes with phenolic compounds, which grow to form a complex network of iron oxyhydroxides. Over time, these black inks turn into brownish tones, with extensi...

In a recent Communication in this journal, Bandyopadhyay and co‐workers proposed a rational design of chalcone photoswitches that are claimed to convert into the respective flavylium cations upon irradiation with blue, green, and red light in aqueous media. Here we argue that the reported improvements on the optical/photochemical properties of the...

In a recent Communication in this journal, Bandyopadhyay and co‐workers proposed a rational design of chalcone photoswitches that are claimed to convert into the respective flavylium cations upon irradiation with blue, green, and red light in aqueous media. Here we argue that the reported improvements on the optical/photochemical properties of the...

The kinetics, thermodynamics, and degradation of malvidin mono- and diglucosides were studied following a holistic approach by extending to the basic medium. In acidic conditions, the reversible kinetics of the flavylium cation toward the equilibrium is controlled by the hydration and cis–trans isomerization steps, while in the basic medium, the OH...

Blue was the last color to be spread in Nature by the anthocyanins present in angiosperms, and the last color to be managed by Humans in Anthropocene. Blue also appears in a small number of algae, fungi, and bacteria, but these living beings have very little to do with the profusion of a natural blue hue. Humanity took many long years to figure out...

Iron-gall inks are an essential element of our written cultural heritage that is at risk of a total loss due to degradation. This degradation leads to the loss of the support, particularly the cellulose-based support. Intending to stabilize it, we have come a long way from the nineteenth-century cellulose nitrate laminations to the relatively recen...

Stopped flow corroborated by UV-vis measurements allowed for the calculation of the copigmentation constants of delphinidin 3-O-glucoside with the neutral (CP) and negatively charged CP(-) forms of chlorogenic acid. Solutions of delphinidin 3-O-glucoside in the absence and presence of the copigment were equilibrated at several pH values in the acid...

The thermodynamics and kinetics of compound 7-diethylamino-4'-dimethylaminoflavylium were studied in water : ethanol (1 : 1) and water in the presence of SDS and CTAB micelles. The blue flavylium cation is in equilibrium with the pink protonated flavylium cation defined by pKAH2+/AH+ and the yellow trans-chalcone, defined by pKAH+/Ct. The differenc...

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 th...

Flavylium compounds are a well-known family of pigments because they are prevalent in the plant kingdom, contributing to colors over a wide range from shades of yellow-red to blue in fruits, flowers, leaves, and other plant parts. Flavylium compounds include a large variety of natural compound classes, namely, anthocyanins, 3-deoxyanthocyanidins, a...

While identified by the respective flavylium cation, anthocyanins are much more than this molecule. The flavylium cation (generally appearing only at very acidic pH values) is one of the molecules of a complex sequence of pH dependent molecular species reversibly interconnected by different chemical reactions. These species include the red flavyliu...

A linear double pyridinium‐terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV‐Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensiti...

The concept of molecular metamorphosis is described. A molecule (flavylium cation) generates a sequence of other different molecules by means of external stimuli. The reversibility of the system allows for the flavylium cation to be recovered by other external stimuli, completing one cycle. Differently from supramolecular chemistry, molecular metam...

Flavylium-based compounds in their acidic and cationic form bring color to aqueous solutions, while under slightly acidic or neutral conditions they commonly bring discoloration. Selective host-guest complexation between water-soluble p-sulfonatocalix[n]arenes (SCn) macrocycles and the flavylium cationic species can increase the stability of the co...

Anthocyanins and related compounds are examples of the metamorphosis concept. Differently from supramolecular chemistry, the complexity is achieved at the bottom due to the formation of a pH and light dependent multistate of species. In this context, the flavylium cation functions as the generator molecule. The kinetics and thermodynamics of the fl...

The fact that many copigments such as cinnamic acids exhibit an acid-base equilibrium at moderately acidic pH values have not been taken in consideration in the copigmentation models and respective equations. In this work, the copigmentation constants of malvidin-3-O-glucoside and sinapic acid (pKa = 4.5) is reported. The flavylium cation (AH⁺) in...

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...

Anthocyanins co-pigmentation models with application on 1:1 complexes were revisited, and their limitations were critically commented. The flavylium multistate of species is dramatically simplified to a single acid-base equilibrium between flavylium cation and its conjugated base CB, equal to the sum of quinoidal base, hemiketal, and cis and trans-...

[This corrects the article DOI: 10.1021/acsomega.9b01066.].

The pyranoanthocyanins present in red wine display great potential as photosensitizers in bio-inspired Dye-Sensitized Solar Cells (DSSCs). Following a biomimetic approach, a series of amino-π-bridge-pyranoanthocyanin derivatives were employed as dye sensitizers in DSSCs. The dimethylamine group was selected to take advantage of its electron-donor c...

The multistate of species originated by the compound 5-hydroxy-4'-dimethylaminoflavylium was studied in the presence of sodium dodecyl sulfate micelles 0.1 M. A series of pH jumps obtained by addition of base to the equilibrated solutions of the flavylium cation results in a metastable equilibrium between the flavylium cation and the quinoidal base...

The kinetics and thermodynamics (in acidic solutions) of the five chemical species reversibly interconnected by external stimuli (a multistate), such as pH and light, generated by the liverworts colorant riccionidin A were investigated. The degradation products of the multistate formed after 10 days at neutral pH were identified. The behaviour of r...

The aggregation of malvidin 3-O-(6-O-p-coumaroyl) glucoside flavylium cation (OeninCoum) in water is reported. Intra and intermolecular interactions of OeninCoum were characterized by UV–vis absorption, ¹H NMR and circular dichroism (CD). Theoretical calculations were also performed to describe the intramolecular interactions. At higher temperature...

In the present work, five 2-styryl-1-benzopyrylium salts and their relative self-assembly processes towards TiO2 nanocrystalline layers were evaluated as photosensitizers in dye-sensitized solar cells (DSSCs). Integration of these 2-styryl-1-benzopyrylium salts with the semiconductor allow for the performance of highly specific functions suitable f...

Anthocyanins and related flavylium derivatives exist in aqueous solution as a pH-dependent mole fraction distribution of species (a multistate system) with known biological activity. Introduction of nitrogen heterocycles in the flavylium core can lead to multistates with different constitution and increased activity. Compound 1, a diethylamino deri...

The similarity between 2,6-Bis(2-hydroxyarylidene)cyclohexanones and 2′-hydroxychalcones in generating respectively styrylflavylium and flavylium cations was explored. The complex pH and light dependent multistate of species of the asymmetric of 2,6-Bis(2-hydroxyarylidene)cyclohexanone bearing a diethyl amine in position 7 of the flavylium cation w...

Herein, a series of 3-O-glucosilated pyranoanthocyanin derivatives were synthesized following a bio-mimetic approach. The compounds were studied by means of UV–Vis spectroscopy in order to establish their chemical equilibria and determine the stability of the colored species over the pH range. The resistance of pyranoanthocyanins to hydration grant...

The comparison of the ground-state reactivity of anthocyanins and aurones model compounds (i.e. with and without the furano bridge) have shown that the kinetic paradigm does not depend on the bridge but only on the hydroxyl substituent pattern: Independently on the presence of the bridge: i) bell shaped kinetics for those with two hydroxyl substitu...

A new experimental procedure to calculate all equilibrium constants of the multistate of species of anthocyanins and related compounds, including those in basic medium, is reported. The procedure is based on a series of pH jumps monitored by stopped flow from an extended pH range of solutions at pseudo-equilibrium (when there is no significant form...

Anthocyanins are the main polyphenolic dyes found in young red wines, which are transformed into more stable structures such as pyranoanthocyanins, during wine ageing and maturation. While anthocyanins practically lose their red color between pH 1 and 5, as a result of the formation of colorless hemiketals, pyranoanthocyanins practically do not cha...

Two anthocyanins from purple-fleshed sweet potato were isolated and characterized by LC–MS and NMR analysis. They were identified as peonidin-3-(6′-hydroxybenzoyl)-sophoroside-5-glucoside and peonidin-3-(6′-hydroxybenzoyl-6″-caffeoyl)-sophoroside-5-glucoside. The acid–base dynamics of these acylated anthocyanins was evaluated by means of pH jump te...

The multistate of chemical species generated by 4′-hydroxy-3,2′-furanoflavylium is similar to that of anthocyanins and related compounds. This furanoflavylium multistate system was fully characterized by UV-visible and NMR spectroscopy, allowing determination of the respective equilibrium and rate constants. In contrast to the multistate generated...

Multi‐colored intrinsically electrochromic based Deep Eutectic Solvents (IEDES) have been firstly developed. IEDES composed by the suitable mixing between viologen salt derivatives as HBA and ethylene glycol (EG), glycerol (Gly) and poly(ethylene glycol) (PEG) as HBD have been prepared and characterized by thermal and electrochemical studies. A det...

As in supramolecular chemistry, complexity could also be achieved through a bottom-up approach. Anthocyanins and related compounds such as the compound (E)-6-(dimethylamino)-4-(4-(dimethylamino)-2-hydroxybenzylidene)-1,2,3,4-tetrahydroxanthylium chloride (1), here reported, exhibit this type of complexity. The thermodynamics and kinetics of the com...

The thermodynamic and kinetic behavior of 4-(2,4-dihydroxybenzylidene)-6-hydroxy-1,2,3,4-tetrahydroxanthylium chloride was studied in detail. Similarly to anthocyanins, this compound generates a multistate of species that are reversibly interconverted by pH stimuli. The multistate system was studied by NMR and UV–visible (conventional spectroscopy...

O vinho pode ser considerado um laboratório onde estão a ter lugar diversas reações químicas. Por um lado, os polifenóis pré-existentes na uva (ou formados durante as fermentações), e muitos outros que vão aparecendo com o tempo, podem copigmentar com as antocianinas; por outro, estas vão reagir de um modo irreversível com alguns desses componentes...

The interaction of malvidin-3-O-glucoside (1) and a lignosulfonate was studied by UV-visible spectroscopy and the results obtained showed the formation of a complex between the negatively charged lignosulfonate and the flavylium cation form (AH+) of this anthocyanin at pH 1. The thermodynamic and kinetic parameters of 1 in the presence of a lignosu...

The design, synthesis and photoluminescence characterization of sulphide cluster-based zeolitic materials with the general formula Na8[SiAlO4]6SxCl2-2x is presented in this report. The employed experimental conditions, which included the thermal treatment of sodium Linde type A (Na-LTA) zeolites in presence of Na2SO4 and NaCl, yielded highly photol...

The multistate of species regarding 2′-hydroxyflavylium derivatives have a peculiar behavior due to the formation in moderately basic solutions of a flavanone from the mono-ionized trans-chalcone. The firmly established theory to account for the thermodynamics and kinetics of the flavylium based multistate of species in acidic medium was extended t...

All equilibrium and rate constants of heavenly blue anthocyanin (HBA 1) as well as the derivatives respectively with two (HBA 2) or none (HBA 3) acylated units were determined. The three acylated units of the sugar in position 3 of the peonidin chromophore of heavenly blue anthocyanin HBA 1 are essential to confer the peculiar stability of its purp...

The impact of a lignosulfonate (calcium) (L) on the chromatic features of two anthocyanin-derived bluish dyes (portisin, P and pyranoanthocyanin dimer, PD) was evaluated in aqueous solutions using UV–Visible spectroscopy. It was demonstrated that the interaction between each dye and this macromolecule at pH 1 occurs by two mechanisms, association a...

Anthocyanins lipophilization recently emerged as an efficient tool to deliver oil-soluble dyes aiming to expand their applications in lipophilic matrices such as cosmetics formulations. Sodium dodecyl sulfate (SDS) micelles were used to solubilize malvidin-3-glucoside derivatives bearing an ester chain derived from dodecanoic and hexanoic fatty aci...

Symmetrical and nonsymmetrical oxobis(bipyridinium) cations combined with iodide and bistriflimide anions were prepared. In the case of the bistriflimide-based bis(bipyridinium) salts, two room-temperature ionic liquids (RTILs) with a combination of linkers and terminal ethers, [(C3O)bpy(C4O)bpy(C3O)][NTf2]4 and [(C10)bpy(C4O)bpy(C3O)][NTf2]4, were...

Suzuki-Miyaura reaction of 8-iodochrysin, then, reduced by LiAlH4 to give the corresponding 3-deoxyanthocyanidins. At pH=1.0 the stable form is the 8-substituted flavylium cation in both compounds. At higher pH values the quinoidal bases are the stable species and some evidence for the 6,8-rearrangement was achieved, but the respective spectral var...

We present a complete study on four synthetic environmentally friendly flavylium salts employed as sensitizers for dye-sensitized solar cells (DSSCs). The effect of several donor groups in the flavylium molecular structure was investigated by combining electrochemical, spectroscopic and computational means. The computational investigation indicated...

Aminoflavylium compounds like anthocyanins are involved in multiple reversible, pH-dependent chemical reactions. In very acidic media, the thermodynamically stable species is the flavylium cation, while it is trans-chalcone in near-neutral media. Different from anthocyanins, aminoflavylium compounds achieve the thermodynamic reversibility through d...

The chemistry of 2,2’-spirobis[chromene] derivatives is intimately related to the one of anthocyanins and similar compounds. The 2,2’-spirobis[chromene] species plays a central role in the network of chemical reactions connecting two different flavylium-based multistate systems. In the present work, a new asymmetric 2,2’-spirobis[chromene] intermed...

The host-guest chemistry of the anthocyanin analog 7-β-D-glucopyranosyloxy-4′-hydroxyflavylium (GHF) was studied in the presence of the β-cyclodextrin derivative captisol by stopped flow, UV–visible spectroscopy, flash photolysis, circular dichroism and isothermal titration calorimetry. The equilibrium and rate constants of the multistate of chemic...

The equilibrium forms of three different families of dimethylamino-based pyranoanthocyanins (1, 2 and 3) were studied in aqueous solutions at different pH values from 1 to 12 using UV–Visible spectroscopy. The forms present under those conditions are strongly correlated to the pyranoanthocyanin structural features. The increase of the electronic de...

Cucurbit[7]uril inclusion complexes with guests bearing dimethylamino groups show the expected upward pK a shifts, whereas their diethylamino counterparts display a decrease in pK a due to the preferential stabilization of the unprotonated form. These results identify the diethylamino group as the substituent of choice to avoid receptor-assisted pr...

The effect of the β-cyclodextrin on the mole fraction distribution of the multistate species of the anthocyanins model compound, 3-methoxy-4',7-dihydroxyflavylium, was studied by NMR, stopped flow, circular dichroism and UV-Visible absorption spectroscopy. The formation of inclusion complexes with hemiketal and trans-chalcone, possessing transition...

Anthocyanins are identified by the respective flavylium cation, which is only one species of a multistate of different molecules reversibly interconverted by external inputs such as pH, light and temperature. The flavylium cation (acidic form) is involved in an apparent acid-base reaction, where the basic species is the sum of quinoidal base, hemik...

A structurally constrained derivative of 4',7-dihydroxyflavylium was studied in aqueous solution and in CTAB micelles by pH jumps, flash photolysis and continuous irradiation with spectroscopic details assessed as well by theoretical calculations. In water, up to pH = 8, the compound shows only acid base chemistry with deprotonation of the flavyliu...

3-Deoxyanthocyanidins and their O-β-D-glucosides are natural pigments abundant in black sorghum. O-glycosidation can perturb the acid-base properties of the chromophore and lower its electron density with a large impact on the distribution of colored and colorless forms in aqueous solution. In this work, the influence of O-glycosidation on color is...

In this study, stable and non-expensive aluminoborosilicate glasses with different photoluminescence colors were synthesized by doping with Pb(II) and sodium halides. While glasses with NaF and NaCl exhibit no (or very low) luminescence, glasses doped with NaBr and NaI display room temperature photoluminescence at 435 nm and 530 nm, respectively. T...

The effect of methyl, hydroxyl, and chloride substituents in position 3 of the 3',4',7-trihydroxyflavylium core structure was studied. The stability, relative energy of each of chemical species (thermodynamics), and their rates of interconversion (kinetics) are very dependent on these substituents. By comparing the mole fraction distribution at equ...

Two symmetric bis-flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown to be fully stochastic and behave like a single compound suggesting that the two flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid-base reaction bet...

The equilibrium between 6-bromo and 8-bromo-apigeninidin is quantitatively displaced towards the formation of the former in the presence of cucurbit[7]uril due to the selective recognition of the 6-bromo isomer by the host. This phenomenon permits to conceive a unidirectional multistate switch addressed with host-guest inputs and enables the revers...

A 4′-hydroxyflavylium bearing a julolidine (2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizine) substituent in position 7 to minimize the amine rotation was characterized. Similarly to the 7-(N,N-diethylamino)-4′-hydroxyflavylium, the compound does not show trans-cis chalcone photoisomerization in water and the fluorescence emission quantum yield of its...

The introduction of two amine substituents in 4’ and 7 positions, leads to the formation of a blue flavylium cation, 7-(N,N’-diethylamino)-2-(9-julolidine)-1-benzopyrilium, which is extremely stable across a wide acidic pH range. The kinetic and thermodynamic constants of the multistate system have been calculated by studying the relaxation kinetic...

The host–guest complexes formed from six differently substituted flavylium cations and cucurbit[7]uril (CB7) have been characterized by UV/Vis absorption, fluorescence emission and 1H NMR spectroscopy. It was observed that all flavylium cations form 1:1 inclusion complexes with association constants that depend on the nature and position of the sub...

A multistate molecular dyad containing flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The flavylium cation is only stable at acidic pH values. Above pH≈5 the hydration of the flavylium leads to the...

The copigmentation and the anti-copigmentation effects can be mimicked by the interaction of anthocyanin's model compounds respectively with cucurbit[7]uril (CB7) and β-cyclodextrin (β-CD). The complex network of chemical reactions displayed by this family of compounds includes the colored flavylium cation, AH+, and quinoidal base, A, along with th...

The multistate system of 4’,7-dihydroxy-3-methoxyflavylium is constituted by a multiequilibrium involving trans-chalcone, cis-chalcone, hemiketal, flavylium cation and quinoidal base. This system possesses two independently addressable inter-connected photochromic systems based on the cis-trans isomerization and ring opening-closure of the hemiketa...

Gel switchable electrochromic devices based on disubstituted bipyridinium derivatives have been developed. The type of substituent from 4,4´-bipyridinium cation and counter-ions can influence the reversibility and switch of colours of these electrochromic systems. Three switching colours (yellow, blue and red or violet) can be obtained for iodide s...

Metastable states regarding the network of chemical reactions involving flavylium compounds were investigated as well as the role they may play in models for optical memories capable of write-read-erase. A necessary requirement to achieve metastable states in flavylium systems is the existence of a high cis-trans isomerization barrier, as in 4'-hyd...

The determination of rate and equilibrium constants of anthocyanin metabolites with in vivo occurrence, cyanidin-4'-O-methyl-3-glucoside (Cy4'Me3glc) and cyanidin-7-O-glucuronyl-3-glucoside (Cy7Gluc3glc), was carried out for the first time by means of direct and reverse pH jumps. The thermodynamics and kinetics of these compounds are similar to the...

Excited-state proton transfer (ESPT) was studied by fluorescent emission using a mathematical model recast from the Weller theory. The titration curves can be fitted with three parameters: pKa (acidity constant of the ground sate), pKap* (apparent acidity constant of the excited state), and ηA*, the efficiency of excited base formation from the exc...

The network of chemical reactions of the compound 4'-(2-hydroxyethoxy)-7-hydroxyflavylium and its photochromic properties were studied in the absence and presence of beta-cyclodextrin. The system was characterized by H-1 NMR, UV-Vis, continuous irradiation and circular dichroism. In the presence of beta-cyclodextrin 4.8 mM the pK(a)' is reduced to...

Electrochromic symmetric and non-symmetric disubstituted oxo-bipyridinium ionic liquids are developed in high purities and yields. Detailed spectroscopic (NMR, FTIR and elemental analysis), thermal (DSC for melting point and glass transition temperatures, Tg determination) and electrochemical (cyclic and square wave voltammetry for determination of...

Anthocyanins are much more than flavylium cation. At least four other species in moderately acidic solutions are formed constituting a pH reversible network of chemical reactions. The study of this network is an indispensable tool to rationalize the colour as well as the reactivity of these molecules. The network of anthocyanins was revisited and t...