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We present here 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 on the molecular structure of flavylium ions was investigated by combining electrochemical, spectroscopic and computational means. The computational investigation indicated that these molecules can interact strongly with the TiO2 surface by a single OH group of the dihydroxybenzene moiety, and can efficiently inject electrons into the TiO2 following the excitation of their lowest singlet states exhibiting charge transfer (CT) character. In general, all dyes within the explored series exhibited quite good regeneration efficiencies, often >= 70%, in the presence of an iodide electron donor, explaining the high IPCEs and photocurrents recorded in the presence of high lithium content electrolytes. The combination of molecular orbital calculations and electrochemical measurements has also revealed that the introduction of donor groups on the benzopyrylium ring has a generally positive effect resulting in an extended low energy light harvesting and in a potential improvement of the photoinduced charge separation at the semiconductor/dye/electrolyte interface. It also increases the reversibility of the oxidative redox processes of these bio-inspired species, a feature in favour of their long-term stability. At present the best dye within the explored series is 7-(N, N-diethylamino)-3', 4'-dihydroxyflavylium chloride based on a dialkylamine donor which is capable of delivering, under optimized conditions, a short-circuit current density of 15 mA cm(-2). This is the highest value so far obtained for synthetic analogues of anthocyanins.

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 obtained, with glass transition temperatures (between −6.9 and 6.0 °C) higher than those reported previously for salts of dication bipyridinium scaffolds (−17.5 to −30.0 °C). The prepared salt containing [(C10)bpy(C4O)bpy(C10)][NTf2] can form an ionic liquid crystal structure. The most promising salts were tested as efficient and reversible multicolored electrochromic devices through cyclic voltammetry studies and detailed characterizations of their electrochromic performances. In general, tetracations based on oxobis(bipyridinium) salts show higher chromatic contrast and lower coloration efficiency than similar dication salts. Exchange of the anion from iodide to [NTf2] increases the transition times and coloration efficiencies for all the prepared di- and tetracation salts. The electrochromic device stability of [(C3O)bpy(C4O)bpyC3O]I4 was tested by on/off cycling; this device loses around 23 % of the initial color after 8640 redox cycles and shows very good cycling stability compared with previously reported diiodide salts.

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 delocalization helps the protonation at the amino group. At very acidic pH condition (pH

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 for smart applications in material science. Spectroscopic and photoelectrochemical measurements conducted on these five bio-inspired dyes, in solution and upon adsorption onto titanium dioxide films, allowed detailed discussion of the anchoring ability of the different donor groups decorating the 2-styryl-1-benzopyrylium core and have demonstrated their ability as photosensitizers. Our results suggest that the introduction of a dimethylamino group in position 4&prime, of the 2-styryl-1-benzopyrylium skeleton can alter the conjugation of the molecule leading to larger absorption in the visible region and a stronger electron injection of the dye into the conduction band of TiO2. Moreover, our experimental data have been supported by theoretical calculations with the aim to study the energy of the excited states of the five compounds. In this specific case, the simulations reported contributed to better describe the properties of the compounds used and to help create the necessary basis for the design of new and targeted bio-inspired molecules.

The effect of β-cyclodextrin on the mole fraction distribution of the multistate species of the anthocyanin 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 dipole moments in a parallel orientation to the cyclodextrin n-fold axis, was unequivocally proved by means of the positive-induced circular dichroism signal. The discrimination of the two hemiketal enantiomers was achieved by the splitting of 1H NMR peaks in the presence β-cyclodextrin. The spectroscopic data shows that the β-cyclodextrin has only moderate enantioselectivity, slightly favoring one of the optical isomers. The observed binding affinity of β-cyclodextrin for the 3-methoxy-4′,7-dihydroxyflavylium multistate species increases in the order flavylium cation < quinoidal base < hemiketal < trans-chalcone < cis-chalcone. As a result of this selectivity and ...

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 different kinetic pathways depending on if the flavylium is transformed into the trans-chalcone upon a direct pH jump or the protonated trans-chalcone if converted into flavylium upon a reverse pH-jump. Three aminoflavylium compounds were prepared and investigated in the presence of CTAB micelles. Two of the compounds bear bridges linking rings C and B of the flavylium core, and the third lacks this bridge. The bridge has the effect of destabilizing the chalcones and the hemiketal. Only in the presence of CTAB micelles does the system respond to light stimuli, a powerful tool that provides a small cis–trans isomerization barrier for the three compounds. The relatively slow response of the system to direct and reverse pH jumps is due to the small mole fractions of Cc available for isomerization (giving Ct) and B available for dehydration (giving AH+). The mathematical expression that accounts for the pH-dependent kinetic processes was revisited to account for the consequences of amine protonation in very acidic media. The crystal structures of the compounds possessing the bridge were obtained, and for one of the compounds, two polymorphic forms were isolated from different crystallization solutions.

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 flavylium cation (Φf = 0.004) is 2.5 times lower than the non-rigid analog. These results seem to exclude a Twisted Intramolecular Charge Transfer (TICT) model to explain the lack of photoisomerization of the chalcones and the small quantum yield of fluorescence emission in these compounds. The julolidine substituent is however slightly more efficient to prevent the hydration of the flavylium cation than the non-rigid amines. In both compounds hydration takes place only at basic pH values through the attack of the hydroxyl in position 2 of the quinoidal base. The chalcone forms of the julolidine derivative are unstable and decompose after several hours. The rate of flavylium formation from trans-chalcone is slow but increases directly with the mole fraction of protonated trans-chalcone for 1

Introduction 3D printing has wide application in medicine while it provides customizability and precision for anatomical model development. Our aims were to perform a systematic review and to explore the use of 3D printing applications on human reproduction and reproductive surgery. Evidence acquisition We have performed a systematic review in PubMed database to assess previous publications within 3D printing in human reproduction and gynecology. We have developed 3D models according to patients' magnetic resonance images (MRI). MRI were transformed into DICOM images that originated our 3D virtual models and PolyJet technology was applied for the printing process. We included two infertile patients in reproductive age with surgical indication for hysteroscopy septoplasty and myomectomy. Evidence synthesis Of 1965 studies searched, we excluded 1934 publications based on their titles. Abstracts of 31 remained studies were read, and 24 studies were selected for full-text analysis. We included 11 studies for the systematic review, based on our eligibility criteria. We have designed four 3D models (uterus, ovaries, uterine cervix and uterus with fibroids) that provided enriched information to improve pre-surgical planning, medical training, fertility-sparing surgery, patient comprehension of surgical procedures and assisted reproduction applications. Conclusions 3D models for human reproduction are feasible. They might improve assisted reproductive techniques, help in pre-surgical planning for reproductive surgeries, and provide accurate measures of ovarian reserve. Besides, we see future applications in endometrioma research and in the fabrication of devices, such as embryo transfer catheter and a 3D printed embryo.

In this chapter, the current state of knowledge regarding anthocyanin chemistry and the corresponding reversible multistate system of the chemical species is presented. Mathematical equations to account for the kinetics and thermodynamics of the multistate system of anthocyanins are presented in a simple form to allow their use by non-specialists. The calculation of all rate and equilibrium constants of malvidin-3-glucoside in diluted solutions has been carried out to illustrate the use of these expressions. The irreversible reactivity of anthocyanins in foodstuffs, particularly in wine, leading to pyranoanthocyanins of the first and second generation is discussed. The use of the relative energy level diagrams of the multistate species together with their pH-dependent mole fraction distribution is reported and their usefulness emphasized. Using the morning glory flower as an example, the expression of its blue colour is rationalized by considering the thermodynamics and kinetics of the multistate system.

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 was studied by pH jumps, monitored by UV–vis spectrophotometry, stopped flow, and NMR. The possible structural isomers corresponding to the migration of the amine substituent at the benzopyrylium to ring B of the flavylium cation via chalcone, or spiro species were not detected. However, cis and trans isomers from the pendent arm take place and a photochromic system involving flavylium cation switching from red to blue was characterized. In acidic medium the flavylium cation and the hemiketal protonated at the amine substituent are the equilibrium species. In moderately acidic solutions the spiro is the most stable species and in very basic medium the ionized trans-chalcone.

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 techniques. Equilibrium and kinetic constants were determined and, in general, these anthocyanins demonstrated a higher capacity in retaining the red and blue colors at acidic and basic pH values, suggesting a higher resistance to pH variations compared to the parent anthocyanin, peonidin-3-O-glucoside. The presence of acyl groups and additional glucoside moieties seems to determine this particular characteristic. The fluorescence properties of these anthocyanins were evaluated. Overall, the species present at higher pH values (7–9) showed higher fluorescence intensity for both anthocyanins, with an optimum λex/λem pair at λex 610 nm/λem 640 nm. The fluorescence characteristics of these anthocyanins were used to evaluate their location in gastric and intestinal cells by fluorescence microscopy.

SFRH/BPD/112465/2015 IF/00225/2015 PTDC/AGR-TEC/2789/2014 COMPETE POCI-01-0145-FEDER-016616 REDE/1517/RMN/2005 PT2020 and FEDER-Interreg Espana-Portugal Programme (Project ref. 0377_IBERPHENOL_6_E). 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 and copigmentation that are dependent on L concentration. For instance, at low concentrations of L (up to 0.27 μM) it is observed the association of dyes promoted by their complexation with lignin (different molecules of dye are bound to the same binding sites of L). At higher concentrations of L (25 μM), the aggregation of dyes decreases and each molecule is bound to a different site of L resulting in the formation of a charge-transfer complex (copigmentation). Moreover, the titration of both dyes (P and PD) in the presence of L (19 μM) showed a strong stabilization of their pyranoflavylium cation forms revealed by the considerably higher pKa1 (6.6 ± 0.1 and 6.2 ± 0.1 for P and PD, respectively) in the presence of this macromolecule when compared to the values obtained in the absence (pKa1 = 4.61 ± 0.03 and 4.93 ± 0.04). In addition, the water solubility of the dyes in the absence and presence of L was also evaluated by turbidimetry and the results showed that the water soluble lignosulfonate improved the solubility of the dyes over time. preprint published

PTDC/QEQ-QFI/1971/2014. POCI/01/0145/FEDER/00726 NORTE-01-0145-FEDER-000011. CONACYT (MEX/Ref. 288188). 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 acids. Detailed investigations on the kinetic and thermodynamic behavior of the pigments towards pH variations was carried out by means of UV-Vis spectroscopy. It was found that the pH domain of the red flavylium cation is extended in ca 0.3–0.4 pH units. The mole fraction of the quinoidal base at neutral conditions increased by 40% when compared with malvidin-3-glucoside in the same micellar media, which provides a great blue color stabilization. The results presented herein report for the first time the blue color stabilization of these lipophilic anthocyanin bioactives, opening new application fields as novel colorants for lipid-based foods and cosmetics. published

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 between flavylium cation and quinoidal base were calculated using a stopped flow technique. It was further demonstrated that the equilibrium between AH+–AH+ and indistinguishable flavylium-quinoidal base isomers AH+–A (A–AH+) can be calculated by subtracting 0.3 pH units from the observed acid–base constant. On the other hand, the equilibrium between both flavylium-quinoidal base isomers and the bis-quinoidal base A–A is obtained by adding 0.3 pH units. Moreover, both systems do not have a cis–trans isomerization barrier and the rate constants of interconversion between flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagram. It was also proved that the rate constant to form both isomers AH+–Ct from the bis-flavylium upon a pH jump from 1 to less acidic solutions is twice that of the observed value and the formation of the bis-trans-chalcone from both isomers AH+–Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.

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 kinetics after equilibrium perturbation by addition of base (direct pH jumps) or acid (reverse pH jumps). Except for the cis-chalcone, which is an elusive species, the relative energy levels of the other species could be calculated and a global energy level diagram constructed. The diagram explains that the stability of the diamino compound is due to the high energy level of the hemiketal species, which is difficult to access in acidic medium.

O II Encontro do Fórum Nacional de Cursos de Geologia, promovido pelo Centro de Geociências da Universidade Federal do Pará (UFPA), foi realizado entre os dias 14 e 17 de maio de 2003, em Belém, nas dependências do Campus Universitário do Guamá, da UFPA. O Fórum Nacional de Cursos de Geologia reuniu-se pela primeira vez, como entidade autônoma, em setembro de 2002 durante o 43º Congresso Brasileiro de Geologia, realizado em João Pessoa, PB. Nas discussões foram levantadas várias teses, relativas à estrutura e aos rumos da formação do geólogo nas universidades brasileiras, devidamente formalizadas perante as sessões plenárias do congresso.

O III Encontro do Fórum Nacional de Cursos de Geologia, promovido pelo Instituto de Geociências da Universidade Federal de Minas Gerais em colaboração com a Sociedade Brasileira de Geologia, realizou-se na cidade de Diamantina (MG), nas dependências do Centro de Geologia Eschwege, unidade do Instituto Casa da Glória da Universidade Federal de Minas Gerais, no intervalo dos dias 20 a 23 de junho de 2004. O III Encontro contou com o apoio do Instituto de Geociências da Unicamp, da Federação Nacional dos Geólogos (FEBRAGEO) e do Sindicato dos Geólogos no Estado de São Paulo (SIGESP). Não foi possível obter, nesta oportunidade, auxílio do Conselho Federal de Engenharia, Arquitetura e Agronomia (CONFEA), que apoiou financeiramente a realização do II Encontro do Fórum Nacional de Cursos de Geologia, realizado em Belém (PA), no ano de 2003, e do Conselho Regional de Engenharia, Arquitetura e Agronomia de Minas Gerais (CREA-MG).

Este trabalho apresenta os primeiros resultados concretos do Projeto Monitoria Proativa, implementado em 2009 no Curso de Geologia da Universidade Federal do Pará, como ferramenta pedagógica para otimização do aproveitamento estudantil nos conteúdos das geologias introdutórias, traduzidos em dois produtos didáticos: Roteiro de Atividades para Prática de Campo em Geologia Introdutória e Kits Didático-Metodológicos em Geologia Introdutória. Além disso o trabalho descreve, em linhas gerais, o processo pedagógico de sua elaboração.

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 the one of related compounds, such as vitisins, described in detail. The colour given by anthocyanins is function of their concentration due to self-aggregation as well as by the possibility of co-pigmentation with other wine components. These phenomena can only be fully understood if the thermodynamic and kinetics of anthocyanins and related compounds are known. In aged red wines, vitisins nicely illustrate the evolution of anthocyanins. These compounds result from the chemical reaction of anthocyanins with other wine components and are very resistant to the hydration lacking the colourless hemiketals formation. This indicates that less colorant is necessary to confer colour to the wine and also explains the colour change from the red-violet in young wines to the red-orange observed in aged wines.

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'-hydroxyflavylium described through this paper. In an optical memory, the metastable state could be the signal to be detected upon the write step. In that case the autoerase is prevented by the metastable state. Conversely, the metastable state may be the initial state and prevents the auto and unwanted write step. The compound 4'-hydroxyflavylium offers the possibility of achieving both of these two situations, depending on the sequence of the pH stimuli prior to light absorption. In this work the pH dependent distribution of the flavylium species of the network in the presence of β-cyclodextrin was calculated. Improvement of the performance of the photochromic system in the presence of β-cyclodextrin was observed.

Gel switchable electrochromic devices based on disubstituted bipyridinium derivatives have been developed. The type of substituent from the 4,4′-bipyridinium cation and counter-ions can influence the reversibility and switching of colours of these electrochromic systems. Three switching colours (yellow, blue and red or violet) can be obtained for iodide salts due to dimer formation. In the case of bistrifluoromethanesulfonylimide [NTf2] salts only two reversible colour switches (transparent and blue) were observed. Complementary electrochromic performance including chromatic contrast (ΔT%); transition times between the bleached and coloured states; colouration efficiencies (CE), colour coordinates (CIE L*a*b*) and preliminary cycling stability studies of the devices have been performed. The higher coloration efficiency is observed in the case of [(C10)2bpy][NTf2]2 (186.9 cm2 C−1), which is similar to other bipyridinium systems already reported in the literature.

We present here 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 on the molecular structure of flavylium ions was investigated by combining electrochemical, spectroscopic and computational means. The computational investigation indicated that these molecules can interact strongly with the TiO

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] intermediate possessing a constrained propylenic bridge between carbons 3 and 3′ was isolated and its role as a pivot in the anthocyanins-type multistate of chemical reactions was investigated by the conjugation of absorption spectroscopy, stopped-flow, NMR, and X-ray crystallography. It was confirmed that the propylenic bridge is essential to stabilize the spirobis[chromene] species. Furthermore, under acidic conditions, two cis–trans styrylflavylium isomers were identified, which could be interconverted directly into one another with light. This is the first report of styrylflavylium cations with photoisomerization on the styryl moiety.

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: pK(a) (acidity constant of the ground sate), pK(ap)* (apparent acidity constant of the excited state), and η(A*), the efficiency of excited base formation from the excited acid. β-Naphthol and 4-metyhl-7-hydroxyflavylium were studied in aqueous solution and upon incorporation in cucurbit[7]uril. For all the compounds studied the interaction with the host leads to 1:1 adducts and the ground-state pK(a) increases upon incorporation. Whereas the ESPT of 4-methyl-7-hydroxyflavylium practically does not change in the presence of the host, in the case of β-naphthol it is prevented and the fluorescence emission titration curves are coincident with those taken by absorption. The position of the guest inside the host was investigated by NMR experiments and seems to determine the efficiency of the ESPT. The ESPT decreases for the guest, exhibiting a great protection of the phenol to the bulk water interaction.

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 β-cyclodextrin. The system was characterized by 1H NMR, UV–Vis, continuous irradiation and circular dichroism. In the presence of β-cyclodextrin 4.8 mM the pK′a is reduced to 2.2. The association constants with β-cyclodextrin, follow the order trans-chalcone > quinoidal base > flavylium cation, respectively 1.7 × 103 M−1; 5.6 × 102 M−1; ≈0. The rate of inter-conversion of the network species increases in the presence of β-cyclodextrin circa 2.6 times. The appearance of an induced circular dichroism signal of trans-chalcone inside the β-cyclodextrin is described for the first time. It gives information about the position of the guest inside the host and allows the calculation of the respective association constant.

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 redox potential and evaluation of reversibility behaviour) analyses are performed. The most promising electrochromic oxo-bipyridinium ionic liquids in combination with transparent electrolytes are tested as reversible electrochromic devices. More efficient and sustainable electrochromic devices inspired by bipyridinium ionic liquids can be conceived for industrial applications such as electrochromic car rear-view mirrors and smart windows.

A photochromic system based on dracoflavylium, a natural pigment extracted from Dragon's blood, a resin appearing in the injury parts of the tree Dracaena draco, is studied in water. The photochromism arises from the irradiation of the trans-chalcone, giving a mixture of flavylium cation/quinoidal base as a photoproduct via cis-chalcone and hemiketal. The performance of the photochromic system can be improved in the presence of (2-hydroxypropyl)-β-cyclodextrin. A mathematical model to account for the details of the kinetics and thermodynamics of the system was deduced. The model is general for all the host-guest systems involving the flavylium network of chemical reactions with 1 : 1 stoichiometric association.

The kinetics and thermodynamics of the 2,6-bis(2-hydroxybenzilidene)cyclohexanone chemical reactions network was studied at different pH values using NMR, UV-vis, continuous irradiation, and flash photolysis. The chemical behavior of the system partially resembles anthocyanins and their analogue compounds. 2,6-Bis(2-hydroxybenzilidene)cyclohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 × 10(-5) s(-1)) is pH independent and controlled by the cis-trans isomerization barrier. However, the interesting feature is the appearance of the colorless compound, 7,8-dihydro-6H-chromeno[3,2-d]xanthene, isolated from solutions of acid to neutral range, characterized by (1)H NMR and single crystal X-ray diffraction. Light absorption by 2,6-bis(2-hydroxybenzilidene)cyclohexanone solutions immediately after preparation exclusively results in cis-isomer as photoproduct, which via hemiketal formation yields (i) red styrylflavylium by dehydration under extremely acidic solutions (pH1) and (ii) colorless 7,8-dihydro-6H-chromeno[3,2-d]xanthene by cyclization in solutions of acid to neutral range.

By using hyper-Rayleigh scattering experiments and quantum-chemical calculations, we demonstrate that nonlinear optics can be used to probe unequivocally, within a non-destructive process, the multiple electronic states that are activated upon pH- and light-triggered transformations of the 4a-hydroxyflavylium ion. These results open new perspectives in the design of molecular-scale high-density optical memory. Remember this: Hyper-Raleigh scattering measurements provide evidence for large variations of the quadratic nonlinear optical responses to pH-triggered transformations of the 4a-hydroxyflavylium ion. By exploiting the capability of nonlinear optics to probe the electronic states without triggering uncontrolled photoconversions, the network of interconverting processes in this system might be a basis for the development of high-density multiple-storage optical memory.

The network of chemical reactions involving anthocyanins and related compounds has been historically considered as the chemical transformations taking place when the flavylium cation (which is generally stable only in very acidic solutions) disappears upon a pH jump to higher pH values (direct pH jump). In this work profit is taken from the appearance of flavylium cation from equilibrated solutions at moderately acid pH values, (reverse pH jumps) as well as upon irradiation of trans-chalcone in the cases where photochemistry is available. Reverse pH jumps, flash photolysis and reaction quantum yields unequivocally show that at sufficiently acidic pH values the tautomerization becomes the rate determining step of flavylium cation formation. This is a lucky situation since gives kinetic information about tautomerization, the most difficult process to access in the anthocyanins and related compounds network of chemical reactions. The thermodynamic and kinetic details of flavylium base photochromic systems are described. Mathematical expressions for direct and reverse pH jumps, stopped flow and flash photolysis are presented as well as the procedure to obtain all of the rate and equilibrium constants of the system.

co-financed by the ERDF under the PT2020 Partnership Agreement (POCI-01-0145-FEDER - 007265). FCT/MCTES is acicnowledged for Project PTDC/QEQ-QFI/1971/2014, grants PD/BD/135087/2017 (ALP), SFRH/BD/136556/2018 (VG) and a research FCT contract (LC). 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 change their color intensity. For that they constitute a photosensitizer family with great potential for bio-inspired dye-sensitized solar cells (DSSCs). In this work, a series of pyranoanthocyanin derivatives were designed, synthesized and applied for the first time as dye sensitizers in DSSCs. A relation was established between dye structure and cell efficiency. Specifically, the influence of different linker units, carboxyl and catechol, was studied in terms of their influence in the various parameters related to DSSC efficiency. The presence of the catechol unit was shown to be essential for efficient electron injection of the dye into the TiO2 semiconductor, since carboxylic units showed a deleterious effect in electron injection due to their electron withdrawing character. An overall efficiency of 1.15% was obtained for the best performing compound, 10-catecholpyrano-3′,4’,5,7-tetrahydroxyflavylium, with no further optimization. authorsversion published

Novel mono and dialkylbipyridinium (viologens) cations combined with iodide, bromide, or bis(trifluoromethanesulfonyl)imide [NTf2] as anions were developed. Selective alkylation synthetic methodologies were optimized in order to obtain the desired salts in moderate to high yields and higher purities. All prepared mono- and dialkylbipyridinium salts were completely characterized by (1)H, (13)C, and (19)F NMR spectroscopy, Fourier-transform IR spectroscopy, and elemental analysis (in the case of NTf2 salts). Melting points, glass transition temperatures by differential scanning calorimetry (DSC) studies, and decomposition temperatures were also checked for different prepared organic salts. Viscosities at specific temperatures and activation energies were determined by rheological studies (including viscosity dependence with temperature in heating and cooling processes). Electrochemical studies based on cyclic voltammetry (CV), differential pulsed voltammetry (DPV), and square-wave voltammetry (SWV) were performed in order to determine the redox potential as well as evaluate reversibility behavior of the novel bipyridinium salts. As proof of concept, we developed a reversible liquid electrochromic device in the form of a U-tube system, the most promising dialkylbipyridinium-NTf2 ionic liquid being used as the electrochromic material and the room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide [EMIM][NTf2], as a stable and efficient electrolyte.

Selected metal complexes behaving as photochemical switches, mostly operating by light emission/absorption without the intervention of any added chemical species, are reviewed. First, the switching mechanisms are analyzed to offer readers an easier understanding of the described systems. Examples of photochemical switching based on complexation/decomplexation processes and photo-bistable systems, comprising metal complexes with azobenzene, azopyridine, diarylethene, spirocyclic and rhodamine ligands, make the central body of the review. These examples were chosen to provide an overview of the evolution of metal-ion based photochemical switches, collecting together historical cases and more recent systems mainly reported in the last 15 years.

Independently of the natural or synthetic origin, flavylium derivatives follow the same network of chemical reactions. Actually, the flavylium cation is stable only at low pH values. Increasing the pH gives rise to the formation of several species: quinoidal bases, hemiketal, cis- and trans-chalcones, and their deprotonated forms. A deep knowledge of the thermodynamics and kinetics of these species is an essential tool to practical applications of these compounds, in particular, in the domain of food chemistry. In this work the network of chemical reactions involving flavylium derivatives is presented, and the respective thermodynamics and kinetics are discussed in detail, including the mathematical expressions and a step-by-step procedure to calculate all of the rate and equilibrium constants of the system. Examples of systems possessing a high or low cis-trans isomerization barrier are shown. Recent practical applications of anthocyanins and related compounds illustrate the potentialities of the flavylium-based family of compounds.

The color properties and stability of three types of 3-deoxyvitisins derived from peonidin (deoxyvitisin A, B and methyldeoxyvitisin) were studied using UV-Visible spectroscopy. Similarly to pyranoanthocyanins, the conjugated double bonds among pyranic rings C and D provide a higher electronic delocalization that prevents the nucleophilic attack of water at position 2 and the subsequent formation of the hemiketal and chalcone species. Consequently, besides the flavylium cation (AH+), neutral (A) and ionized bases (An−) have been identified by increasing pH, and the respective acidity constants were determined. The acidity constant values for the formation of the neutral quinoidal base (pKa2(deoxyvit A) = 4.8, pKa1(deoxyvit B) = 4.7 and pKa1(methyldeoxyvitisin) = 5.2) are slightly higher than the ones reported in the literature for their corresponding 3-glucosyl derivatives (vitisins). Given their higher stability, these pigments may be regarded as potential food colorants.

Calculation of the quantum yields from the photostationary state, in the cases where the thermal back reaction competes efficiently with the photoproducts formation is described. The system can be mathematically treated as a single equilibrium involving two opposite reactions, one driven by light of constant intensity and the other due to the thermal back reaction. By analogy with excited state redox potential calculations, the photostationary state can be defined by a constant, which is function of the number of absorbed photons by the cis and trans forms, the respective reaction quantum yields, the light intensity, irradiated volume, as well the rates of the thermal forward and backward thermal reactions (in the absence of light). Application of this concept to the flavylium network of chemical reactions is presented. The model compound 4′,7-dihydroxyflavylium was used to test the model.

Endometriosis is an inflammatory disease defined by the presence of ectopic endometrial tissue outside the uterine cavity and is associated with infertility. An aberrant molecular phenotype of the eutopic endometrium in women with endometriosis is thought to affect endometrial receptivity. For successful maternal-embryonic dialog, an appropriate expression of growth factors, cytokines and hormones and their regulation of cell adhesion molecules is necessary. Many articles have found that certain biomarkers such as leukemia inhibiting factor (LIF) from the IL-6 family, glycodelin A (GdA) and αvβ3 integrin are abnormally downregulated in women with endometriosis. The altered expression of progesterone receptor expression also decreased expression of HOX genes in the eutopic endometrium, leading to an abnormal activation or repression of the downstream genes regulated by the HOX genes that produce biomarkers of endometrial receptivity. Understanding the molecular and cellular mechanisms of endometriosis-rela...

The bio-inspired compound 7,8-dihydroxy-2-(4-dimethylaminostyryl)-1-benzopyrylium (styrylflavylium) was synthesized through the insertion of a double bond between rings B and C of the flavylium cation. The pH dependent network of chemical reactions of the new compound is similar to the one of anthocyanins and related compounds. The styrylflavylium is the dominant species at very low pH values. At moderately acidic pH values the respective quinoidal base is formed by deprotonation of the styrylflavylium in competition with the hydration reaction to give an analogous of the anthocyanins hemiketal. The cis -chalcone is formed through the hemiketal (ring C opening) and the trans -chalcone by the cis–trans isomerization of the former. All the rate and equilibrium constants of these reactions have been calculated, permitting to completely characterize the styrylflavylium network. While in water no photochromism could be observed in the presence of CTAB micelles, formation of the flavylium cation upon irradiation of the trans -chalcone takes place. Complexation of the quinoidal base with Al 3+ was clearly identified.

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 chemical species derived from the flavylium ion were calculated and compared with those in the absence of the host. A new procedure to obtain the host-guest association constants of the multistate (including the transient species) by superimposing the two energy level diagrams, in the presence and absence of the cyclodextrin, was developed. The results indicate that the magnitude of the association constants follows the order, trans-chalcone ≈ cis-chalcone ≈ hemiketal > quinoidal base > flavylium cation. The hydration equilibrium constant increases ca. 42 times in the presence of captisol as the hydration and dehydration rate constants respectively increases and decreases. The other equilibrium constants are modestly affected: the rate constants of ring closure and opening are significantly decreased in the complex and the isomerization rate constants increase in both directions. The quantum yield of the photochromic system in the presence of captisol is 0.3, i.e. 3 times higher than in the absence of the host.

Two oaklins guaiacylcatechinpyrylium (GCP) and syringylcatechinpyrylium (SCP) and a model compound deoxypeonidin (DOP) were synthesized, and the rate and equilibrium constants of the respective pH dependent network of chemical reactions were calculated. In contrast to anthocyanins, the three compounds possess a small cis-trans isomerization barrier and hence the rate of the trans-chalcone formation follows a bell-shaped curve as a function of pH. The three compounds exhibit photochromism obtained by irradiation of the trans-chalcone, which, depending on pH, leads to the colored species flavylium cation and quinoidal base. The flash photolysis together with pH jumps followed by UV-vis absorption and stopped flow is a very useful tool to achieve the rate and equilibrium constants of the network of chemical reactions followed by these molecules. Oaklin compounds which are formed in wine aged in oak barrels present physical-chemical properties more similar to simpler deoxyanthocyanidins rather than anthocyanins and may play a significant role in color changes observed in wine aging. Given their higher stability, they may be regarded as potential food colorants.

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 flavylium cation to form a quinoidal base that further deprotonates with pKas of 4.8 and 7.4. In the basic region, unprotonated trans-chalcones are formed. No neutral trans-chalcone (Ct) is formed in water preventing the establishment of the well-known photochromism involving photoisomerization of this species with subsequent formation of the flavylium cation. Addition of 0.02 M CTAB drastically changes the mole fraction distribution of species, leading to the formation of Ct (χCt = 1 at pH = 5) and unveiling a photochromic behavior with a pH-tunable colour contrast in a large pH range (2 < pH < 8). The Ct species can be hidden again (irreversibly) upon addition of α-cyclodextrin that disrupts the CTAB micelles, reverting the system to its initial mole fraction distribution of species. These supramolecular inputs work atop the molecular reaction networks by modifying their species’ mole fraction distribution.

Fundacao para a Ciencia e a Tecnologia (FCT) (SFRH/BPD/72652/2010; SFRH/BPD/84805/2012) FCT Fundo Europeu de Desenvolvimento Regional (FEDER) (007265 UID/QUI/50006/2013) he rearrangement between isomers 6- and 8-bromo-apigeninidin (6 and 8) was studied by pH jumps using stopped flow, UV/Vis, NMR, and HPLC analysis. The system constitutes a pH-dependent network of chemical reactions involving up to 18 different species. The dynamic network is equivalent to a single diprotic acid exhibiting two pK(a)s, 2.55 and 5.4. Similar to other flavylium derivatives, the mole fraction of the species hemiketal and cis-chalcone in both multistate isomers are negligible at the equilibrium. At pH 1, the pure isomers are slowly converted in a mixture containing about 50% of isomers 6 and 8, while at pH 4, the system evolves to mixture of 10% trans-chalcone and 90% of quinoidal bases. A series of pH jumps from pure isomer 6 at pH 1 to pH 6 and back to pH 1 leads to the same initial absorption spectra of the pure isomer 6. The same occurs for pure isomer 8, showing the lack of communication between the cis-chalcones, at least in the time scale of few minutes. A pH jump from the equilibrated mixture of the isomers at pH 1.0 to 5.8 permits to follow a very slow isomerization. publishersversion published

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 equilibrium of the three multistate systems with the parent 3′,4′,7-trihydroxyflavylium, introduction of a methyl substituent in position 3 increases the mole fraction of hemiketal at the expense of the trans-chalcone and increases the hydration rate very significantly; a hydroxyl substituent in position 3 gives rise to a degradation process, as observed in anthocyanidins. In the case of 3-chloro-3′,4′,7-trihydroxyflavylium, a dramatic increase of the flavylium cation acidity was observed and a photochromic system can be operated upon irradiation of the respective trans-chalcone in 1 m HCl. According to the photochromic response of 3,3′,4′,7-tetrahydroxyflavylium and 3′,4′,7-trihydroxyflavylium, some requirements for a good photochromic performance are discussed.