Reversible thermochromic systems based on a new library of flavylium spirolactone leuco dyes

Funding Information: This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 814299 - CHARISMA. This work also received financial support from PT national funds ( FCT / MCTES , Fundação para a Ciência e Tecnologia and Ministério da Ciência, Tecnologia e Ensino Superior) through the project UIDB/50006/2020 (LAQV-REQUIMTE). Publisher Copyright: © 2023 The Author(s)The aim of this work was the design, synthesis, and characterization of new chromogenic spirolactone dyes based on a 2-phenyl-1-benzopyrylium (flavylium) backbone for further development of thermochromic smart labels. The influence of electron-donating and electron-withdrawing groups on the five synthesized dyes was studied in terms of color modification, acid-base behavior and thermochromic properties. By using UV–Vis absorption and emission spectroscopies, molar absorptivity, oscillator strength, Stokes shift, and fluorescence quantum yield were determined for each dye to evaluate the impact on color and excited state properties of the designed structures. The acid-base behavior and the ability to evolve towards leuco species was assessed by titrations with triethylamine and N,N-diisopropylethylamine in non-polar and polar aprotic solvents such as acetonitrile and octan-1-ol. In addition, the reversibility of the color was also evaluated by titrations with polar protic solvents (water and ethanol) and Lewis acids (gallic acid and iron(III) chloride). The number of equivalents of base/acid required to reach the leuco product and then to reverse the color were determined by representing the absorption maximum as a function of added base/acid in acetonitrile (water content less than 0.01-v/v). Finally, the thermochromic properties were evaluated in the presence of long-chain organic amines and water-insoluble solvents with melting points close to room temperature. The synthesized compounds can switch between two species if the appropriate conditions are used. Moreover, the tests carried out to assess their thermochromic behavior concluded that all dyes display thermochromism to some extent. The dyes that have electron-withdrawing groups attached, such as cyano, display stronger chromogenic effects useful for future applications.publishersversionpublishe

Flavylium dye as pH-tunable fluorescent and CD probe for double-stranded DNA and RNA

UIDB/50006/2020 ROTEIRO/0031/2013-PINFRA/22161/2016 HrZZ IP-2018-01-5475The interaction of 4′-(N,N-dimethylamino)-6-hydroxyflavylium cation with double stranded (ds-) DNA/RNA was studied by UV/Vis spectrophotometry, circular dichroism (CD), and also steady-state and time-resolved emission spectroscopies at neutral and weakly acidic conditions. At pH 5, the studied molecule, in its flavylium cationic form, showed considerable binding affinities (5 < logKs < 6) for all ds-DNA/RNA, contrary to chalcones forms (dominant at pH 7), which did not show binding to polynucleotides. Flavylium cation intercalated into ds-DNAs at variance to dominant groove aggregation within ds-RNA, which was reported by RNA-specific bisignate induced CD spectrum (ICD) bands. The intrinsically negligible fluorescence of flavylium was strongly increased upon the addition of DNA or RNA, whereby both the fluorescence intensity and emission lifetimes of complexes differed considerably: the strongest emission increase was observed for AU-RNA (detection limit estimated to 10 nM) followed by AT-DNAs and the much weaker effect of GC-DNAs. Both fluorescence sensitivity on the ds-DNA/RNA secondary structure and sequence-selective ICD bands make the flavylium–chalcones system an intriguing pH-switchable new probe for distinguishing between various polynucleotide sequences.publishersversionpublishe

Convenient Synthesis of 3-Vinyl and

A variety of 2-hydroxy aldehydes on reaction with 3-butenoic acid afford in a one-pot reaction the corresponding 3-vinylcoumarins. As expected, extension of the delocalized π-electron system accomplished by Heck coupling reactions with aryl halides results in an increased fluorescence of the compounds whose applicability is yet to be established

Contributions to the Characterization of Chromogenic Dyes in Color Slides

Funding: This research was supported by Fundação para a Ciência e Tecnologia, Ministério da Ciência, Tecnologia e Ensino Superior (FCT/MCTES), Portugal, through doctoral program CORES-PD/00253/2012, PhD grant SFRH/BD/52317/2013, and Associate Laboratory for Green Chemistry-LAQV financed by national funds (UIDB/50006/2020 and UIDP/50006/2020). This work was also funded through RNEM (Portuguese Mass Spectrometry Network) (LISBOA-01-0145-FEDER-022125–IST).Chromogenic reversal films (or color slides) are first-generation positive transparencies. These were used for various purposes, namely as an artistic medium, especially from the 1960s onwards. However, these materials are intrinsically vulnerable to chemical degradation and have poor long-term stability. Although over time significant improvements have been achieved in the stability of chromogenic products, chromogenic dyes are highly susceptible to oxidation and hydrolysis, both induced by light and/or relative humidity and temperature, leading to the fading and shift in the original color balance of the images. During the present investigation, a gap of knowledge regarding chromogenic materials in general, and chromogenic reversal films specifically, was detected. Today, there is still no methodology to identify the dyes present in a specific work and, therefore, to study their chemical mechanism of degradation. From this premise and focused on case studies from the Portuguese artist Ângelo de Sousa (1938–2011), a research study was carried out seeking the characterization of chromogenic dyes. Based on the isolation of the different dyes composing a chromogenic material, several procedures were tested to describe the dyes found in chromogenic reversal films, such as Raman spectroscopy, thin-layer chromatography (TLC), infrared spectroscopy, high-performance liquid chromatography with diode array detector (HPLC-DAD) and coupled with mass spectrometry (HPLC-HRMS). Promising results were achieved with this approach, opening new paths for the understanding of these materials.publishersversionpublishe

Evolution of Flavylium-Based Color Systems in Plants: What Physical Chemistry Can Tell Us

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.info:eu-repo/semantics/publishedVersio

The Use of Flavylium Salts as Dynamic Inhibitor Moieties for Human Cb5R

Authors would like to acknowledge the Biochemistry Department in the Faculty of Medicine at the Universidad Autónoma de Madrid for the equipment and support for some of the required reagent purchases. FCT/MCTES is also acknowledged for supporting the National Portuguese NMR Network (ROTEIRO/0031/2013-PINFRA/22161/2016, co-financed by FEDER through COMPETE 2020, POCI, PORL. We thank José Paulo da Silva for the HRMS-ESI analysis. Publisher Copyright: © 2022 by the authors.Cytochrome b5 reductase (Cb5R) is a flavoprotein that participates in the reduction of multiple biological redox partners. Co-localization of this protein with nitric oxide sources has been observed in neurons. In addition, the generation of superoxide anion radical by Cb5R has been observed. A search for specific inhibitors of Cb5R to understand the role of this protein in these new functions has been initiated. Previous studies have shown the ability of different flavonoids to inhibit Cb5R. Anthocyanins are a subgroup of flavonoids responsible for most red and blue colors found in flowers and fruits. Although usually represented by the flavylium cation form, these species are only stable at rather acidic pH values (pH ≤ 1). At higher pH values, the flavylium cation is involved in a dynamic reaction network comprising different neutral species with the potential ability to inhibit the activities of Cb5R. This study aims to provide insights into the molecular mechanism of interaction between flavonoids and Cb5R using flavylium salts as dynamic inhibitors. The outcome of this study might lead to the design of improved specific enzyme inhibitors in the future.publishersversionpublishe

The Use of Flavylium Salts as Dynamic Inhibitor Moieties for Human Cb5R

Cytochrome b5 reductase (Cb5R) is a flavoprotein that participates in the reduction of multiple biological redox partners. Co-localization of this protein with nitric oxide sources has been observed in neurons. In addition, the generation of superoxide anion radical by Cb5R has been observed. A search for specific inhibitors of Cb5R to understand the role of this protein in these new functions has been initiated. Previous studies have shown the ability of different flavonoids to inhibit Cb5R. Anthocyanins are a subgroup of flavonoids responsible for most red and blue colors found in flowers and fruits. Although usually represented by the flavylium cation form, these species are only stable at rather acidic pH values (pH &le; 1). At higher pH values, the flavylium cation is involved in a dynamic reaction network comprising different neutral species with the potential ability to inhibit the activities of Cb5R. This study aims to provide insights into the molecular mechanism of interaction between flavonoids and Cb5R using flavylium salts as dynamic inhibitors. The outcome of this study might lead to the design of improved specific enzyme inhibitors in the future

The Use of Flavylium Salts as Dynamic Inhibitor Moieties for Human Cb5R

Cytochrome b5 reductase (Cb5R) is a flavoprotein that participates in the reduction of multiple biological redox partners. Co-localization of this protein with nitric oxide sources has been observed in neurons. In addition, the generation of superoxide anion radical by Cb5R has been observed. A search for specific inhibitors of Cb5R to understand the role of this protein in these new functions has been initiated. Previous studies have shown the ability of different flavonoids to inhibit Cb5R. Anthocyanins are a subgroup of flavonoids responsible for most red and blue colors found in flowers and fruits. Although usually represented by the flavylium cation form, these species are only stable at rather acidic pH values (pH ≤ 1). At higher pH values, the flavylium cation is involved in a dynamic reaction network comprising different neutral species with the potential ability to inhibit the activities of Cb5R. This study aims to provide insights into the molecular mechanism of interaction between flavonoids and Cb5R using flavylium salts as dynamic inhibitors. The outcome of this study might lead to the design of improved specific enzyme inhibitors in the future.Peer reviewe