- Thermal and photochemical properties of 4′,7-dihydroxyflavylium in water-ionic liquid biphasic systems: A write-read-erase molecular switch
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Switching colors: 4′,7-Dihydroxyflavylium (AH+) in water-ionic liquid biphasic systems can be used as a write-read-erase system. In acid media, the chalcone (Ct) form is soluble in ionic liquids and is thermally metastable, but reacts photochemically (write) to give the yellow flavylium salt, which can be optically read without being erased. The system is prepared for a new cycle by two consecutive pH jumps .
- Pina, Fernando,Lima, Joao C.,Parola, A. Jorge,Afonso, Carlos A. M.
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- Hydroxychalcone inhibitors of Streptococcus mutans glucosyl transferases and biofilms as potential anticaries agents
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Streptococcus mutans has been implicated as the major etiological agent in the initiation and the development of dental caries due to its robust capacity to form tenacious biofilms. Ideal therapeutics for this disease will aim to selectively inhibit the biofilm formation process while preserving the natural bacterial flora of the mouth. Several studies have demonstrated the efficacies of flavonols on S. mutans biofilms and have suggested the mechanism of action through their effect on S. mutans glucosyltransferases (Gtfs). These enzymes metabolize sucrose into water insoluble and soluble glucans, which are an integral measure of the dental caries pathogenesis. Numerous studies have shown that flavonols and polyphenols can inhibit Gtf and biofilm formation at millimolar concentrations. We have screened a group of 14 hydroxychalcones, synthetic precursors of flavonols, in an S. mutans biofilm assay. Several of these compounds emerged to be biofilm inhibitors at low micro-molar concentrations. Chalcones that contained a 3-OH group on ring A exhibited selectivity for biofilm inhibition. Moreover, we synthesized 6 additional analogs of the lead compound and evaluated their potential activity and selectivity against S. mutans biofilms. The most active compound identified from these studies had an IC50value of 44?μM against biofilm and MIC50value of 468?μM against growth displaying >10-fold selectivity inhibition towards biofilm. The lead compound displayed a dose dependent inhibition of S. mutans Gtfs. The lead compound also did not affect the growth of two commensal species (Streptococcus sanguinis and Streptococcus gordonii) at least up to 200?μM, indicating that it can selectively inhibit cariogenic biofilms, while leaving commensal and/or beneficial microbes intact. Thus non-toxic compounds have the potential utility in public oral health regimes.
- Nijampatnam, Bhavitavya,Casals, Luke,Zheng, Ruowen,Wu, Hui,Velu, Sadanandan E.
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supporting information
p. 3508 - 3513
(2016/07/21)
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- Chalcones as positive allosteric modulators of α7 nicotinic acetylcholine receptors: A new target for a privileged structure
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The α7 acetylcholine nicotine receptor is a ligand-gated ion channel that is involved in cognition disorders, schizophrenia, pain and inflammation among other diseases. Therefore, the development of new agents that target this receptor has great significance. Positive allosteric modulators might be advantageous, since they facilitate receptor responses without directly interacting with the agonist binding site. Here we report the search for and further design of new positive allosteric modulators having the relatively simple chalcone structure. From the natural product isoliquiritigenin as starting point, chalcones substituted with hydroxyl groups at defined locations were identified as optimal and specific promoters of α77 nicotinic function. The most potent compound (2,4,2-2,5-2-tetrahydroxychalcone, 111) was further characterized showing its potential as neuroprotective, analgesic and cognitive enhancer, opening the way for future developments around the chalcone structure.
- Balsera, Beatriz,Mulet, José,Fernández-Carvajal, Asia,Torre-Martínez, Roberto De La,Ferrer-Montiel, Antonio,Hernández-Jiménez, José G.,Estévez-Herrera, Judith,Borges, Ricardo,Freitas, Andiara E.,López, Manuela G.,García-López, M. Teresa,González-Mu?iz, Rosario,Pérez De Vega, María Jesús,Valor, Luis M.,Svobodová, Lucie,Sala, Salvador,Sala, Francisco,Criado, Manuel
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p. 724 - 739
(2015/02/19)
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- Emptying the β-cyclodextrin cavity by light: Photochemical removal of the trans -chalcone of 4′,7-dihydroxyflavylium
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The interaction between the network of chemical reactions of the compound 4′,7-dihydroxyflavylium and β-cyclodextrin was studied by means of pH jumps, followed by UV-vis absorption, flash photolysis, stopped flow, and NMR. The trans-chalcone is the networ
- Petrov, Vesselin,Stanimirov, Stanislav,Petrov, Ivan K.,Fernandes, Ana,De Freitas, Victor,Pina, Fernando
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p. 10692 - 10701
(2013/11/06)
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- Structural transformations of the synthetic salt 4', 7-dihydroxyflavylium chloride in acid and basic aqueous solutions. Part 1 - Ground state
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A complete study of the structural pH dependent transformations of the synthetic flavylium salt 4',7-dihydroxyflavylium chloride (DHF). occurring in aqueous solutions, including the basic region, is described. The kinetic study of the transformations occuring in acidic media (quinoidal base (A) ? flavylium cation (AFT) ? hemiacetal (B) ? cis-chalcone (Ctrans) ? trans-chalcone (Ctrans)) allowed to conclude that the cis-trans isomerization is faster than the tautomerization and the hydration processes, which is unique in the anthocyanins family. Results obtained with the parent compound 4",7dimethoxyflavylium chloride (DMF) with relevance to this study are also presented. In equilibrated basic solutions the existence of acid-base equilibria involving the trans-Chalcone (Ctrans) and its conjugated bases. (C transand C2trans), was detected. Freshly prepared solutions at pH >7 show also the presence of a transient species identified as the ionized quinoidal base (A-), which is almost completely converted into C2-trans with a pH dependent rate constant. Springer-Verlag Iherica 1997.
- Pina, Fernando,Benedito, Lina,Melo, Maria Joao,Parola,Lima, Joao C.,Macanita, Antonio L.
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p. 111 - 118
(2007/10/03)
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- Photochromism of the synthetic 4′,7-dihydroxyflavylium chloride
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The synthetic compound 4′,7-dihydroxyflavylium chloride shows an interesting photochromic effect at moderately acidic pH values. Pale yellow solutions of this compound, equilibrated in the dark at pH 3.4, become bright yellow upon irradiation with 313-nm light. Switching off the light, gives back the initial pale yellow solution. Photochemical methods, 1H NMR, and molecular orbital calculations were used to elucidate this photochromic behavior. In solutions equilibrated in the dark (pH 5.7), the existence of two main species in equilibrium is demonstrated: the colored flavylium cation and the colorless trans-chalcone. Freshly prepared solutions of this compound at pH 6.2 reveal the existence of another colored form, the quinonoidal base, which reacts thermally to yield trans-chalcone. An analogous reaction takes place in freshly prepared solutions at pH 3.4: the flavylium cation is partially converted into trans-chalcone. The extent of such conversion is pH dependent and nearly complete at pH 6.2. Irradiation of transchalcone at the wavelength of 313 nm partially gives back the initial colored form, with concomitant formation of small amounts of photodegradation products. The turnover of the photochromic reaction is greater at pH 3.4 than at pH 6.2. The photochromism is explained on the basis of a trans-cis photoisomerization. In fact the relative stability of the two chalcone isomers is reversed in the excited state, as predicted from molecular orbital calculations.
- Figueiredo, Paulo,Lima, Jo?o C.,Santos, Helena,Wigand, Marie-Claude,Brouillard, Raymond,Ma?anita, António L.,Pina, Fernando
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p. 1249 - 1254
(2007/10/02)
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- Chemistryl of Anthocyanin Pigments. 9. UV-Visible Spectrophotometric determination of the Acidity Constants of Apigeninidin and Three Related 3-Deoxyflavinium Salts
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The equilibrium constants for the structural transformations of some 3-deoxyanthocyanidins in water at 25 deg C have been measured by using the pH-jump method.This method have been described previously.According to their particular substitution patterns, hydroxylated flavinium salts can exist in slightly acidic media in several neutral forms: the quinoidal bases A, the carbinol pseudobase B, and the chalcone pseudobase C.Two of the conpounds investigated, namely 4',5,7-trihydroxyflavinium (apigeninidin) and 4'-methoxy-4-methyl-5,7-dihydroxyflavinium chlorides, exist essentially as a mixture of the three neutral forms A, B, and C, the colored species A being the most abundant.As expected, 4',7-dihydroxyflavinium chloride is stable in the open chalcone structiure C.This result is in a good agreement with the catalytic light effect generally observed for the ring-closure reaction of this species leading to the flavinium cation AH+.Only the monohydroxylated pigment 4'-methoxy-4-methyl-7-hydroxyflavinium chloride is the quinoidal base A perfectly stable, whatever the pH.In contrast to natural anthocyanins, the hydration of the pyrilium ring is less efficient and occurs, therefore, at much higher pH values (pH 5-6).Proton loss from the phenolic acidic hydroxyl groups of the flavinium cation takes place in the usual acidity range (pH 4-5), indicating that these groups are strongly hydrogen bonded to the surrounding water molecules.The chalcone content is much higher than for the anthocyanins, and for 4',7-dihydroxyflavinium chloride for instance, the value for the equilibrium ratio of the chalcone to the carbinol is as high as 20.6.
- Brouillard, R.,Iacobucci, G. A.,Sweeny, J. G.
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p. 7585 - 7590
(2007/10/02)
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