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The transient species formed by oxidation of three dimers of 5,6-dihydroxyindole (1), a major building block of the natural biopolymer eumelanin, have been investigated. Pulse radiolytic oxidation of 5,5',6,6'-tetrahydroxy-2,4'-biindolyl (3) and 5,5',6,6'-tetrahydroxy-2,7'-biindolyl (4) led to semiquinones absorbing around 450 nm, which decayed with second-order kinetics (2k = 2.8 x 10(9) and 1.4 x 10(9) M-1 s(-1), respectively) to give the corresponding quinones (500-550 nm). 5,5', 6, 6'-Tetrahydroxy-2,2'-biindolyl (2), on the other hand, furnished a semiquinone (lambda(max) = 480 nm) which disproportionated at a comparable rate (2k = 3 x 10(9) M-1 s(-1)) to give a relatively stable quinone (lambda(max) = 570 nm). A quantum mechanical investigation of o-quinone, quinonimine, and quinone methide structures of 2-4 suggested that oxidized 2-4 exist mainly as 2-substituted extended quinone methide tautomers. Finally, an oxidation product of 3 was isolated for the first time and was formulated as the hydroxylated derivative 5 arising conceivably by the addition of water to the quinone methide intermediate predicted by theoretical analysis. Overall, these results suggest that the oxidation chemistry of biindolyls 2-4 differs significantly from that of the parent 1, whereby caution must be exercised before concepts that apply strictly to the mode of coupling of 1 are extended to higher oligomers.

Piceatannol (1) was found to be more effective than caffeic acid, an established antinitrosating agent, in inhibiting N-nitrosation of 2,3-diaminonaphthalene. Product analysis of the reaction mixture of 1 (20 microM) with nitrite ions (80 microM) at pH 3.0 and at 37 degrees C showed conversion to a single major nitration product, (E)-3,3',4,5'-tetrahydroxy-beta-nitrostilbene (2) (68% yield). This would result from an unexpected nitration at the double bond sector via the 4-phenoxyl radical, which was analyzed at the unrestricted DFT level.

Polymers of natural polyphenols have so far received little attention as bioavailable, biocompatible antioxidants for different applications e.g. in packaging and related technologies. Expected advantages with respect to the monomers would include lower volatility (with reduced adverse effects), greater chemical stability under processing conditions and lower tendency to be released from the polymer into the contact medium (food, water, etc.). Herein we report data on the synthesis, structural characterization and antioxidant properties of two novel bioinspired phenolic polymers prepared by horseradish/H2O2 oxidation of tyrosol (polyTYR) and caffeic acid methyl ester (polyCAME). The materials, obtained in 80-85% yields, were subjected to structural characterization by solid state CPMAS NMR, mass spectrometry and gel permeation chromatography (GPC). ESI(-)/MS and NMR analysis indicated that polyTYR was a mixture of regular oligomers up to the undecamer with heptamer as the most abundant, all featuring units linked through C-C bonds. GPC showed an average molecular weight of 1862 Da with a polydispersity index of 1.64. ESI(-)/MS of polyCAME showed oligomers up to at least the decamer stage, peaking at the tetramer. Analysis of the clusters of the pseudomolecular ion peaks and the presence of CH carbons due to O-substituted benzylic positions in NMR spectra suggested a structure including dihydrobenzofuran units. Both PolyTYR and polyCAME exhibited antioxidant properties in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays and proved to be efficient hydroxyl radical scavengers in a Fenton reaction assay. The potential of PolyCAME as stabilizer toward polyethylene (PE) thermal and photo-oxidative degradation was also evaluated. PolyCAME exhibited high stability toward decarboxylation and oxidative degradation during the thermal processes associated with PE film preparation. Characterization of PE films by thermal methods, photo-oxidative treatments combined with chemiluminescence and FTIR spectroscopy and mechanical tests indicated a significant effect of polyCAME on PE durability as shown for example by the increase of the Oxidative Induction Time (OIT).1The synthesized phenolic biopolymers are thus proposed as novel easily accessible, eco-friendly and biocompatible materials for a sustainable approach in packaging and other applications. 1) Ambrogi, V.; Panzella, L.; Persico, P.; Cerruti, P.; Lonz, C. A.; Carfagna, C.; Verotta, L.; Caneva, E.; Napolitano, A.; d'Ischia, M. Biomacromolecules 2014, 15, 302-310.

Traditionally, the positive correlation between red hair and melanoma has been attributed to both the poor antioxidant and photoprotective properties of pheomelanins compared to the dark eumelanins, and the capacity of pheomelanin to act as photosensitizer inducing generation of reactive oxygen species upon UV irradiation. Recently, the occurrence of UV-independent pathways of carcinogenesis was provided by a series of experiments showing that induction of an activating mutation of BRAF into red mice resulted in a high incidence of invasive melanomas in the absence of UV stimulation . In addition, the skin of pheomelanic mice contained higher levels of oxidative DNA and lipid damage with respect to albino-Mc1re/e mice (Mitra et al, Nature 2012, 491, 449-453). These data clearly showed that the pheomelanin pathway could mediate oxidative stress and melanomagenesis ; however the mechanisms have not so far addressed at molecular level. To get an insight into these processes we investigated the reactivity of pheomelanin pigment isolated from human red hair (RHP) and synthetic pheomelanins from cysteinyldopa (CD-Mel) toward critical cellular antioxidants such as GSH and NAD(P)H. Data showed a remarkable increase in the oxidation rate of both compounds in the presence of RHP compared to the controls, whereas much less marked variations were noticed with the eumelanin extracted from black hair. HPLC analysis consistently indicated a rise in GSH disulfide (GSSG) levels with GSH decrease, confirming a redox reaction. Formation of NAD(P)+ was similarly observed in the reaction mixture of NAD(P)H with RHP. In the absence of oxygen, GSH and NAD(P)H depletion was not observed while the presence of enzymes as superoxide dismutase and catalase did not modify the effect of pheomelanin suggesting a ROS independent mechanism. Similar effects were obtained with CD-Mel confirming that the prooxidant effects are due to the pheomelanic component. The mechanism of GSH oxidation by RHP was investigated by EPR spectroscopy. Besides inducing antioxidant depletion, RHP, like CD-Mel, proved also capable of promoting autoxidation of melanin precursors, such as 5-S-cysteinyldopa and dopa, under conditions of exclusion of light, with formation of pheomelanin or eumelanin pigments. This effect is oxidative in character, since it depends on oxygen, revealing a remarkable prooxidant capacity of the pigment serving as a biocatalyst for non-enzymatic melanogenesis (Panzella et al., PCMR 2014, 27,244-252; Greco et al. Chem Comm. 2011,47, 10308-10310). A mechanism has been proposed to account for the observed effects in which GSH, NAD(P)H and melanin precursors oxidation is not mediated by ROS, but is the result of a direct redox exchange with oxidized 1,4-benzothiazine units within the pigment scaffold. Re-oxidation of reduced pheomelanin by oxygen with formation of ROS would ensure shuttling of pheomelanin between the redox states. Overall these results provide a unifying chemical framework into which to explain the mechanisms underlying the relationships between pheomelanin pigmentation and oxidative stress.

Herein, we wish to report new data that DHICA possesses efficient hydrogen donor properties, Fe(III) reducing power and OH radical-scavenging efficiency in Fenton processes and show for the first time that the main circulating DHICA metabolite, 6H5MICA, exhibits an antioxidant activity comparable to that of DHICA. We propose that DHICA and 6H5MICA may provide a missing key toward an understanding of the physiological signifi- cance of Dct and melanogenesis beyond the mere provision of a pigment.

Synthetic eumelanin produced using 5,6-dihydroxyindole-2-carboxylic acid as precursor and H2O2/horseradish peroxidase as oxidative reagent, in form of dry powder, has been investigated under photoexcitation by TR-EPR spectroscopy. The formation of spin polarized radical pairs from triplet excited states of melanin has been obsd. both in absence and in presence of oxygen and has been followed as a function of the temp. in the range 140-290 K. The triplet mechanism explains the obsd. polarization pattern in net emission. In the presence of oxygen new radical pairs are formed by interaction of melanin with mol. oxygen.

Zinc levels in human hair are relatively high (up to 200 g/g) suggesting a role in melanogenesis. We report herein a systematic investigation of the effects of zinc on the properties of synthetic pheomelanins prepared by oxidation of 5-S-cysteinyldopa (CD) with peroxidase/H2O2. For comparison a red hair pheomelanin obtained by a mild hydrolytic procedure was also investigated. The pigments were characterized by: a) EPR spectroscopy at X-band; b) alkaline hydrogen peroxide degradation followed by HPLC determination of benzothiazole-2-carboxylic acid (BTCA); and c) reverse phase HPLC coupled with UV or ESI(+)-MS detection. Pheomelanins prepared in the presence of Zn2+ (zinc pheomelanins) exhibited more distinct chromatographic patterns with some differences in product distribution depending on the amounts of oxidant used. The main components were identified by ESI-MS as benzothiazine dimers and trichochrome-related species. EPR spectra of pheomelanins showed a distinct three-line spectral feature characteristic for the pheomelanin semiquinonimine subunits. Saturation of pheomelanins with zinc ions at pH 5, or in situ irradiation in the resonant cavity with visible light, resulted in an enhancement of the intensity of the melanin EPR signals. Aerobic photoreactivity of the pheomelanins was also investigated by EPR-oximetry and EPR-spin trapping using DMPO as a spin trap. The highest photoinduced oxygen consumption was found for zinc pheomelanins, which was accompanied by the fastest photogeneration of superoxide anion. Our data indicate that zinc pheomelanin is significantly more photoreactive and when irradiated with visible light becomes substantially more reducing than pheomelanin synthesized in the absence of zinc. All these data will be comparatively presented and the role of zinc ions in directing CD oxidation and affecting the structure of the final pigment will be discussed.

Synthetic eumelanin produced using 5,6-dihydroxyindole-2-carboxylic acid as precursor and H2O2/horseradish peroxidase as oxidative reagent, in form of dry powder, has been investigated under photoexcitation by TR-EPR spectroscopy. The formation of spin polarized radical pairs from triplet excited states of melanin has been observed both in absence and in presence of oxygen and has been followed as a function of the temperature in the range 140–290 K. The triplet mechanism explains the observed polarization pattern in net emission. In the presence of oxygen new radical pairs are formed by interaction of melanin with molecular oxygen.

Solar ultraviolet rays (UVR) play an important role in melanoma and non-melanoma skin cancer development while melanins, produced by melanocytes, are involved in photoprotection, control of oxidative stress, regulation of skin homeostasis and immunity. The ratio between the two main groups of melanin, eumelanins and pheomelanins, is regulated by the mc1r gene encoding for melanocortin-1-receptor (MC1R), whose inactivation causes a switch from eumelanin to pheomelanin production. While eumelanins are considered to be photoprotective, pheomelanins are known to be (photo)toxic as they lead to the production of reactive oxygen species in the presence and in the absence of UV radiation. It seems that not only eumelanins but even their precursors can contribute to the (photo)protective action. In particular, 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and its main metabolite 6-hydroxy-5- methoxyindole-2-carboxylic acid (6H5MICA) have antioxidant properties so they could play a critical role in the responses of the melanocyte to oxidative stress and inflammation. Moreover, it has been showed that DHICA is able to act as a chemical messenger inducing antioxidant defense systems and cell differentiation in keratinocytes. On these basis, DHICA and its methylated metabolite could play an important role in chemopreventive strategies of melanoma skin cancer.

The addition of thiol compounds to o-quinones, as exemplified by the biologically relevant conjugation of cysteine to dopaquinone, displays an anomalous 1,6-type regiochemistry compared to the usual 1,4-nucleophilic addition, for example, by amines, which has so far eluded intensive investigations. By means of an integrated experimental and computational approach, herein, we provide evidence that the addition of glutathione, cysteine, or benzenethiol to 4-methyl-o-benzoquinone, modeling dopaquinone, proceeds by a free radical chain mechanism triggered by the addition of thiyl radicals to the o-quinone. In support of this conclusion, DFT calculations consistently predicted the correct regiochemistry only for the proposed thiyl radical-quinone addition pathway. These results would prompt a revision of the commonly accepted mechanisms for thiol-o-quinone conjugation and stimulate further work aimed at assessing the impact of the free radical processes in biologically relevant thiol-quinone interactions.

Among bioactive phytochemicals, ellagic acid (EA) is one of the most controversial because its high antioxidant and cancer-preventing effects are strongly inhibited by low gastrointestinal absorption and rapid excretion. Strategies toward an increase of solubility in water and bioavailability, while preserving its structural integrity and warranting its controlled release at the physiological targets, are therefore largely pursued. In this work, EA lysine salt at 1:4 molar ratio (EALYS), exhibiting a more than 400 times increase of water solubility with respect to literature reports, was incorporated at 10% in low methoxylated (LM) and high methoxylated (HM) pectin films. The release of EA in PBS at pH 7.4 from both film preparations was comparable and reached 15% of the loaded compound over 2 h. Under simulated gastric conditions, release of EA from HM and LM pectin films was minimal at gastric pH, whereas higher concentrations&mdash, up to 300 &mu, M, corresponding to ca. 50% of the overall content&mdash, were obtained in the case of the HM pectin film after 2 h incubation at the slightly alkaline pH of small intestine environment, with the enzyme and bile salt components enhancing the release. EALYS pectin films showed a good prebiotic activity as evaluated by determination of short chain fatty acids (SCFAs) levels following microbial fermentation, with a low but significant increase of the effects produced by the pectins themselves. Overall, these results highlight pectin films loaded with EALYS salt as a promising formulation to improve administration and controlled release of the compound.

The ability of gelatin-based hydrogels of incorporating and releasing under controlled conditions 5,6-dihydroxyindole-2-carboxylic acid (DHICA), a melanin-related metabolite endowed with marked antioxidant properties was investigated. The methyl ester of DHICA, MeDHICA, was also tested in view of its higher stability, and different solubility profile. Three types of gelatin-based hydrogels were prepared: pristine porcine skin type A gelatin (HGel-A), a pristine gelatin cross-linked by amide coupling of lysines and glutamic/aspartic acids (HGel-B), and a gelatin/chitosan blend (HGel-C). HGel-B and HGel-C differed in the swelling behavior, showed satisfactorily high mechanical strength at physiological temperatures and well-defined morphology. The extent of incorporation into all the gelatins tested using a 10% w/w indole to gelatin ratio was very satisfactory ranging from 60 to 90% for either indoles. The kinetics of indole release under conditions of physiological relevance was evaluated up to 72 h. The highest values were obtained with HGel-B and HGel-C for MeDHICA (90% after 6 h), and an appreciable release was observed for DHICA reaching 30% and 40% at 6 h for HGel-B and HGel-C, respectively. At 72 h, DHICA and MeDHICA were released at around 30% from HGel-A at pH 7.4, with an increase up to 40% at pH 5.5 in the case of DHICA. DHICA incorporated into HGel-B proved fairly stable over 6 h whereas the free compound at the same concentration was almost completely oxidized. The antioxidant power of the indole loaded gelatins was monitored by chemical assays and proved unaltered even after prolonged storage in air, suggesting that the materials could be prepared in advance with respect to their use without alteration of their efficacy.

We report herein an optimized procedure for preparation of carboxamides of 5,6-dihydroxyindole-2-carboxylic acid (DHICA), the main biosynthetic precursor of the skin photoprotective agents melanins, to get access to pigments with more favorable solubility properties with respect to the natural ones. The developed procedure was based on the use of a coupling agent (HATU/DIPEA) and required protection of the catechol function by easily removable acetyl groups. The O-acetylated compounds could be safely stored and taken to the reactive o-diphenol form just before use. Satisfactorily high yields (>85%) were obtained for all amides. The oxidative polymerization of the synthesized amides carried out in air in aqueous buffer at pH 9 afforded melanin-like pigmented materials that showed chromophores resembling those of DHICA-derived pigments, with a good covering of the UVA and the visible region, and additionally exhibited a good solubility in alcoholic solvents, a feature of great interest for the exploitation of these materials as ingredients of dermocosmetic formulations. © 2022 by the authors.

Condensed tannins (CT) have been the focus of increasing interest in the last years as a result of their potent biological properties, which have prompted their use in the food and feed sector as functional ingredients. The possible exploitation of these compounds as multifunctional additives for the implementation of active food packaging has also been recently appreciated. In this perspective, an overview of the structural features, accessible sources, methods of analysis, and functional properties of CT is provided, with the aim of critically emphasizing the opportunities offered by this widespread class of natural phenolic compounds for the rational design of multifunctional and sustainable food packaging materials.

Conocephalum conicum L. is a cosmopolitan liverwort species able to respond to local environmental pollution by changing its biological features. In the present study, we assessed the different biological responses in C. conicum to heavy metal contamination of Regi Lagni channels, a highly polluted freshwater body. As for the in field experiment, we set up moss bags containing collected samples of the local wild growing C. conicum, from the upstream site (non-polluted area), and we exposed them in the three selected sites characterized by different and extreme conditions of heavy metal pollution. In addition, to better understand the contribution of heavy metals to the alterations and response of the liverwort, we performed in vitro tests, using the same concentration of heavy metals measured in the sites at the moment of the exposition. In both experimental settings, bioaccumulation, ultrastructural damage, reactive oxygen species production and localization, antioxidant enzymes activity (superoxide dismutase, catalase and glutathione S-transferases), glutathione (reduced and oxidized) levels, localization of compounds presenting thiol groups and phenolic content were investigated. The results showed that the samples from different sites and conditions (for in vitro tests) showed significant differences. In particular, the ultrastructural alterations show a trend correlated to the different exposure situations; ROS contents, glutathione, antioxidant enzyme activities, and phenolic contents were increased showing an enhancement of the antioxidant defense both by the enzymatic way and by using the synthesis of antioxidant phenolic compounds. This study confirms the ability of C. conicum to respond to heavy metal pollution and the responses studied are, at least partially, correlated to the presence of heavy metals. All the responses considered respond consistently with the pollution trend and they can be proposed as pollution biomarkers. Therefore, we suggest the use of C. conicum to identify local hot spots of pollution in further investigation.

Δ2,2’-bi-(2H-1,4-benzothiazine) chromophore of trichochrome pigments occurring in red hair and feathers has been recognized as a source of inspiration for the design of functional chromophores given its excellent photochromic, solvatochromic, and acidichromic properties. Here we report the synthesis of a symmetric homolog of the bibenzothiazine system produced by condensation of 3-phenyl-2H-1,4-benzothiazine with glyoxal that was assigned the cyanine-type 2Z,2′Z-(1,2-ethanediylidene)bis(3-phenyl-2H-1,4-benzothiazine) (1) structure by spectral analysis and DFT calculations. The cyanine showed an intense absorption maximum at ca. 480 nm (e = 16.070 ± 60 M−1cm−1) in 3:1 methanol/water at pH ≥ 4.0 undergoing a marked bathochromic shift in acid to 610 nm (e = 22.330 ± 40 M−1cm−1), and further shift to 637 nm in 2.5 M HCl accompanied by a distinct color change from red to deep blue. The bathochromic shift upon exposure to acids was observed on fabrics, paper, polylactic acid films or alginate hydrogels as well as on thin films of the cyanine exposed to acid/basic vapors and proved reversible over several cycles. The acidichromic behaviour was associated to a remarkable hydrophobic-to-hydrophilic switch, that was probed in a filter permeability experiment. Other applications that are presented for the cyanine include the use as pH sensor paper for visual assessment of pHs below 0 and devices for monitoring food freshness, e.g detection of volatile amines generated by fish spoilage or pH changes associated to milk deterioration.

Three different deep eutectic solvent (DES)-based extraction procedures were rationally designed and optimized for the recovery of antioxidants from chestnut wood fiber (CWF), a clean and largely available solid waste of the tannin industry. First, a mild protocol was developed using a choline chloride (ChCl)/tartaric acid DES at 50 °C, for 90 min. Ellagic acid (EA) was identified as the only low molecular weight phenolic component of the extract. In other experiments, harsher conditions were explored involving treatment of CWF with ChCl-based DESs at 120 °C for 8 h, which afforded a solid sample characterized by high phenolic content (up to 1.0 mg of gallic acid equivalents/mg of sample) and antioxidant properties (EC50

Herein, the antioxidant and food stabilizing properties of a pecan nut shell (PNS) hydroalcoholic extract (PNSE) are reported. Chemical degradation of PNSE demonstrated the presence of condensed tannins as the main phenolic components. PNSE showed remarkable antioxidant properties in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (EC50 = 0.004 mg/mL). PNSE was initially tested as an inhibitor of mushroom tyrosinase, exhibiting a quite low IC50 value (0.055 mg/mL) against the enzyme diphenolase activity, suggesting its use in enzymatic browning inhibition. The anthocyanin stabilization properties were evaluated under accelerated aging conditions of both pure pigments and commercial fruit juices, and PNSE was found to be effective at concentrations (0.05 mg/mL) at which well-known stabilizers such as chlorogenic and ferulic acids proved to fail. PNSE also performed well in the stabilization of spray-dried anthocyanins for use as a food colorant, increasing the half-life of blackberry anthocyanins up to 20%. In order to explore the possibility of using PNSE as a functional additive for active packaging, polylactic acid (PLA) films containing PNSE were prepared by solvent casting, and no substantial alteration of the mechanical properties was found on addition of the extract up to 10% w/w. The films showed remarkable antioxidant properties (DDPH reduction >60% with a 3% w/w loading, at a dose of 1 mg/mL in the DPPH solution) and delayed the onset of browning of apple smoothies (ca. 30% inhibition with a 10% w/w loading). These results highlight the exploitation of PNS as a low-cost polyphenol source for food industry applications., Pecan nut shell represents an easily accessible and sustainable source of functional additives for food industry applications.

Reported herein is the purification of the pigment of black sturgeon caviar and its unambiguous identification as a typical eumelanin by means of chemical degradation coupled with electron paramagnetic resonance (EPR) evidence. HPLC and LC-MS analysis of oxidative degradation mixtures revealed the formation of pyrrole-2,3,5-tricarboxylic acid (PTCA), a specific marker of eumelanin pigments, in yields compatible with a 6.5% w/w pigment content. EPR spectral features and parameters were in close agreement with those reported for a typical natural eumelanin such as Sepia melanin from squid ink. The identification for the first time of eumelanin in a fish roe is expected to provide a novel molecular basis for the valorization of black caviar and production wastes thereof in food chemistry and diet.

Biology is well known for its ability to communicate through molecularly specific signaling modalities and a globally acting electrical modality associated with ion flow across biological membranes. Emerging research suggests that biology uses a third type of communication modality associated with a “flow” of electrons through reduction/oxidation (redox) reactions. This redox signaling modality appears to act globally and has features of both molecular and electrical modalities: since free electrons do not exist in aqueous solution, the electrons must “flow” through molecular intermediates that can be switched between two states-with electrons (reduced) or without electrons (oxidized). Importantly, this global redox modality is easily accessible through its electrical features using convenient electrochemical instrumentation. In this review, we explain this redox modality, describe our electrochemical measurements, and provide four examples demonstrating that redox enables communication between biology and electronics. The first two examples illustrate how redox probing can acquire biologically relevant information. The last two examples illustrate how redox inputs can transduce biologically relevant transitions for patterning and the induction of a synthetic biology (synbio) “transceiver” for two-hop molecular communication. In summary, we believe redox provides a unique ability to bridge biodevice communication because simple electrochemical methods enable global access to biologically meaningful information. Furthermore, we envision that redox may facilitate the application of information theory to the biological sciences.

Aim of this study was the development of an active packaging based on whey proteins (WP) functionalized with Pecan nut shell extract (PNSE). To this purpose, aqueous solutions of WP, PNSE and glycerol were mixed and characterized, whereas corresponding films were prepared by casting. Zeta-potential measurement revealed that the film forming solutions were stable, and the particle size was reduced further to the incorporation of PNSE, as a result of tannins-WP interactions. Films were handleable and homogeneous, and PNSE was able to improve their mechanical and barrier properties. PNSE-containing films inhibited the growth of the foodborne bacteria Enterococcus faecalis and Salmonella enterica subsp. enterica ser. Typhimurium. Ferric reducing/antioxidant power assay clearly highlighted the ability of PNSE to impart antioxidant properties to the films. Finally, simulated digestion experiments showed a significant lowering of the proteolysis rate in the presence of PNSE, although 40 % of the protein was still digested after 60 min incubation. Overall, these results put the basis for a possible use of PNSE functionalized WP-based films as new environmentally friendly candidates for increasing the shelf-life of foods.

A red pigment was prepared by reaction of chlorogenic acid (CGA) with tryptophan (TRP) in air at pH 9 (37% w/w yield) and evaluated as food dye. The main component of pigment was formulated as an unusual benzochromeno[2,3-b]indole linked to a TRP unit, featuring a cyanine type chromophore (λmax 542, 546 nm, 1% extinction coefficient of the sodium salt = 244 ± 2). The chromophore showed a minimal pH dependence and proved stable for at least 3 h at 90 °C, both at pH 3.6 or 7.0, whereas red wine anthocyanins showed a substantial (30%) and betanin a complete abatement after 1 h at the acidic pHs. An intense coloring of different food matrices was obtained with the pigment at 0.01 % w/w. No toxicity was observed up to 0.2 mg/mL on hepatic and colonic cell lines. These data make this dye a promising alternative for red coloring of food., This work was supported by the grant AGL2015-67087-R (MINECO/FEDER, UE) from the Spanish Ministry of Science and Innovation (MINECO). The authors also thank the European Union (FSE, PON Ricerca e Innovazione 2014-2020, Azione I.1 “Dottorati Innovativi con caratterizzazione Industriale”) for funding a PhD grant to Federica Moccia. Authors thank Dr Ermelinda Falletta (Department of Chemistry, Univeristy of Milan) for UPLC-MS equipment support.

A new red hair-inspired 1,4-benzothiazine-based scaffold is disclosed herein, built upon a modular D-&pi, A architecture via condensation of the easily accessible 3-phenyl-2H-1,4-benzothiazine with indole-3-carboxaldehyde. The compound was obtained in around 50% yields and was characterized by complete spectroscopic analysis. The new benzothiazine-based cyanine displayed a characteristic reversible acidichromic behavior with a marked bathochromic shift upon acidification. The chromophore resisted at least fifteen hydrochloric acid/sodium hydroxide cycles without appreciable alterations. The expedient and scalable synthetic procedure together with the pH sensitive chromophoric properties would make the new compound an attractive prototype for novel modular chromophore for pH-sensing and other applications.

Tannins have always been the subject of great interest for their countless properties, first of all their ability to produce functional coatings on a variety of materials. We report herein a comparative evaluation of the antioxidant properties of wood tannin-based coated substrates. In particular, nylon membrane filters were functionalized with chestnut (hydrolyzable) or quebracho (condensed) tannins by dip coating under different conditions. The efficiency of functionalization was evaluated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays, which invariably highlighted the superior ability of condensed tannins to induce the formation of a functional and robust coating. The results of the antioxidant assays revealed also the deleterious effects of aerial or enzymatic oxidation conditions on substrate functionalization, being more significant in the case of hydrolyzable tannins. On the other hand, the use of oxidizing conditions allowed to obtain more stable coatings, still exhibiting good antioxidant properties, in the case of condensed tannins. The presence of iron ions did not lead to a significant improvement of the coating efficiency for either tannins. The systematic approach used in this work provides novel and useful information for the optimal exploitation of tannins in antioxidant functional coatings.

The tyrosinase-catalyzed oxidation of tyramine, leading to the deposition of pseudo-polydopamine (&psi, PDA) thin films, is disclosed herein as a superior technology for surface functionalization and coating at a neutral pH and at a low substrate concentration, compared to the standard autoxidative PDA coating protocols. Smooth &psi, PDA thin films of variable thickness up to 87 nm were obtained from 1 mM tyramine by varying tyrosinase concentrations (5&ndash, 100 U/mL). Compared to the PDA films obtained by the similar enzymatic oxidation of 1 mM dopamine with tyrosinase (T-PDA), &psi, PDA displayed slower deposition kinetics, lower water contact angles in the range of 11&deg, &ndash, 28&deg, denoting higher hydrophilicity but similar UV-vis absorption profiles, as well as electrochemical properties and antioxidant activity. MALDI-MS analysis indicated for &psi, PDA a well defined pattern of peaks compatible with dopamine tetrameric structures degraded to a variable extent. The exposure to a tyramine solution of tyrosinase-loaded alginate spheres, or films deposited on glass or polyethylene, resulted in a rapid gel-confined &psi, PDA formation with no leakage or darkening of the solution, allowing the complete recovery and re-utilization of the unreacted tyramine. In contrast, an abundant PDA precipitation outside the gel was observed with dopamine under the same conditions. The &psi, PDA deposition by tyrosinase-catalyzed tyramine oxidation is thus proposed as a controllable and low-waste technology for selective surface functionalization and coating or for clean eumelanin particle production.

Phenolic compounds are broadly represented in plant kingdom, and their occurrence in easily accessible low-cost sources like wastes from agri-food processing have led in the last decade to an increase of interest in their recovery and further exploitation. Indeed, most of these compounds are endowed with beneficial properties to human health (e.g., in the prevention of cancer and cardiovascular diseases), that may be largely ascribed to their potent antioxidant and scavenging activity against reactive oxygen species generated in settings of oxidative stress and responsible for the onset of several inflammatory and degenerative diseases. Apart from their use as food supplements or as additives in functional foods, natural phenolic compounds have become increasingly attractive also from a technological point of view, due to their possible exploitation in materials science. Several extraction methodologies have been reported for the recovery of phenolic compounds from agri-food wastes mostly based on the use of organic solvents such as methanol, ethanol, or acetone. However, there is an increasing need for green and sustainable approaches leading to phenolic-rich extracts with low environmental impact. This review addresses the most promising and innovative methodologies for the recovery of functional phenolic compounds from waste materials that have appeared in the recent literature. In particular, extraction procedures based on the use of green technologies (supercritical fluid, microwaves, ultrasounds) as well as of green solvents such as deep eutectic solvents (DES) are surveyed.

Based on their potent antioxidant properties, natural phenolic compounds have gained more and more attention for their possible exploitation as food supplements, as well as functional ingredients in food and in the cosmetic industry [...]

Eumelanins, the dark variant of skin pigments, are endowed with a remarkable antioxidant activity and well-recognized photoprotective properties that have been ascribed to pigment components derived from the biosynthetic precursor 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Herein, we report the protective effect of a polymer obtained starting from the methyl ester of DHICA (MeDHICA-melanin) against Ultraviolet A (UVA)-induced oxidative stress in immortalized human keratinocytes (HaCaT). MeDHICA-melanin was prepared by aerial oxidation of MeDHICA. At concentrations as low as 10 µg/mL, MeDHICA-melanin prevented reactive oxygen species accumulation and partially reduced glutathione oxidation in UVA-irradiated keratinocytes. Western blot experiments revealed that the polymer is able to induce the translocation of nuclear factor erythroid 2–related factor 2 (Nrf-2) to the nucleus with the activation of the transcription of antioxidant enzymes, such as heme-oxygenase 1. Spectrophotometric and HPLC analysis of cell lysate allowed to conclude that a significant fraction (ca. 7%), consisting mainly of the 4,4′-dimer of MeDHICA (ca. 2 μM), was internalized in the cells. Overall these data point to the potential use of MeDHICA-melanin as an antioxidant for the treatment of skin damage, photoaging and skin cancers.