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Melanins, a group of dark insoluble pigments found widespread in nature, have become the focus of growing interest in materials science for various biomedical and technological applications, including opto‐bioelectronics, nanomedicine and mussel‐inspired surface coating. Recent progress in the understanding of melanin optical, paramagnetic redox, and conductivity properties, including photoconductivity, would point to a revision of the traditional concept of structural disorder in terms of more sophisticated and interrelated levels of chemical complexity which however have never been defined and codified. Herein, we bring to focus the various levels of structural disorder that emerged from spectral and chemical signatures over the past decade. A revised approach to structure–property relationships in terms of intermolecular interactions is also provided that may pave the way towards the rational design of next‐generation melanin‐based functional materials. [ABSTRACT FROM AUTHOR]

Melanins, a group of dark insoluble pigments found widespread in nature, have become the focus of growing interest in materials science for various biomedical and technological applications, including opto‐bioelectronics, nanomedicine and mussel‐inspired surface coating. Recent progress in the understanding of melanin optical, paramagnetic redox, and conductivity properties, including photoconductivity, would point to a revision of the traditional concept of structural disorder in terms of more sophisticated and interrelated levels of chemical complexity which however have never been defined and codified. Herein, we bring to focus the various levels of structural disorder that emerged from spectral and chemical signatures over the past decade. A revised approach to structure–property relationships in terms of intermolecular interactions is also provided that may pave the way towards the rational design of next‐generation melanin‐based functional materials. [ABSTRACT FROM AUTHOR]

Melanin biopolymers are currently the focus of growing interest for a broad range of applications at the cutting edge of biomedical research and technology. This Special Issue presents a collection of papers dealing with melanin-type materials, e.g., polydopamine, for classic and innovative applications, offering a stimulating perspective of current trends in the field. Besides basic scientists, the Special Issue is directed to researchers from industries and companies that are willing to invest in melanin research for innovative and inspiring solutions. [ABSTRACT FROM AUTHOR]

During the past decade, melanins and melanogenesis have attracted growing interest for a broad range of biomedical and technological applications. The burst of polydopamine-based multifunctional coatings in materials science is just one example, and the list may be expanded to include melanin thin films for organic electronics and bioelectronics, drug delivery systems, functional nanoparticles and biointerfaces, sunscreens, environmental remediation devices. Despite considerable advances, applied research on melanins and melanogenesis is still far from being mature. A closer intersectoral interaction between research centers is essential to raise the interests and increase the awareness of the biomedical, biomaterials science and hi-tech sectors of the manifold opportunities offered by pigment cells and related metabolic pathways. Starting from a survey of biological roles and functions, the present review aims at providing an interdisciplinary perspective of melanin pigments and related pathway with a view to showing how it is possible to translate current knowledge about physical and chemical properties and control mechanisms into new bioinspired solutions for biomedical, dermocosmetic, and technological applications. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA), a black insoluble biopolymerproduced by autoxidationof the catecholamine neurotransmitter dopamine (DA), and syntheticeumelanin polymers modeled to the black functional pigments of humanskin, hair, and eyes have burst into the scene of materials scienceas versatile bioinspired functional systems for a very broad rangeof applications. PDA is characterized by extraordinary adhesion propertiesproviding efficient and universal surface coating for diverse settingsthat include drug delivery, microfluidic systems, and water-treatmentdevices. Synthetic eumelanins from dopa or 5,6-dihydroxyindolesare the focus of increasing interest as UV-absorbing agents, antioxidants,free radical scavengers, and water-dependent hybrid electronic–ionicsemiconductors. Because of their peculiar physicochemical properties,eumelanins and PDA hold considerable promise in nanomedicine and bioelectronics,as they are biocompatible, biodegradable, and exhibit suitable mechanicalproperties for integration with biological tissues. Despite considerablesimilarities, very few attempts have so far been made to provide anintegrated unifying perspective of these two fields of technology-orientedchemical research, and progress toward application has been basedmore on empirical approaches than on a solid conceptual frameworkof structure–property relationships. The present Account isan attempt to fill this gap. Following a vis-à-vis of PDA andeumelanin chemistries, it provides an overall view of the variouslevels of chemical disorder in both systems and draws simple correlationswith physicochemical properties based on experimental and computationalapproaches. The potential of large-scale simulations to capture themacroproperties of eumelanin-like materials and their hierarchicalstructures, to predict the physicochemical properties of new melanin-inspiredmaterials, to understand the structure–property–functionrelationships of these materials from the bottom up, and to designand optimize materials to achieve desired properties is illustrated.The impact of synthetic conditions on melanin structure and physicochemicalproperties is systematically discussed for the first time. Rationaltailoring strategies directed to critical control points of the syntheticpathways, such as dopaquinone, DAquinone, and dopachrome, are thenproposed, with a view to translating basic chemical knowledge intopractical guidelines for material manipulation and tailoring. Thiskey concept is exemplified by the recent demonstration that varyingDA concentration, or using Tris instead of phosphate as the buffer,results in PDA materials with quite different structural properties.Realizing that PDA and synthetic eumelanins belong to the same familyof functional materials may foster unprecedented synergisms betweenresearch fields that have so far been apart in the pursuit of tailorableand marketable materials for energy, biomedical, and environmentalapplications. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA), a multifunctional biomaterial with strong adhesion and coating properties, exhibits melanin-like optoelectronic properties but is virtually devoid of intrinsic fluorescence. Herein we disclose the first PDA-based system that can develop fluorescence without chemical manipulation. The polymerization of dopamine in the presence of oil microdroplets results in the formation of smooth PDA-coated core-shell droplets, which develop a bright and persistent fluorescence upon UVA illumination. The fluorescence induction depends on the excitation wavelength, the nature of the oil, and oxidation and buffer conditions, suggesting photo-oxidation of PDA components within the oil matrix, which shields the developing fluorophores from water quenching. Peroxyl radical scavengers enhance the fluorescence, whereas hydrogen peroxide induces quenching. The new system holds potential interest for imaging and tocopherol sensing applications. [ABSTRACT FROM AUTHOR]

Abstract: The spectacular variety of body coloration patterns in Sepia officinalis reflects the concerted activity of the skin chromatic elements, chromatophores, leucophores and iridophores. Recent studies have revealed that nitric oxide is an important messenger in the long term maintenance of the body coloration, inducing chromatophore expansion downstream glutamate activation. Herein we describe the presence of nitric oxide synthase and nitric oxide synthesis in isolated juvenile iridophores in Sepia. The possible roles of nitric oxide in the complex mechanisms leading to body coloration patterns in cephalopods are an important focus for ongoing and future studies. [Copyright &y& Elsevier]

Despite considerable advances in the past decade, melanin research still suffers from the lack of universally accepted and shared nomenclature, methodologies, and structural models. This paper stems from the joint efforts of chemists, biochemists, physicists, biologists, and physicians with recognized and consolidated expertise in the field of melanins and melanogenesis, who critically reviewed and experimentally revisited methods, standards, and protocols to provide for the first time a consensus set of recommended procedures to be adopted and shared by researchers involved in pigment cell research. The aim of the paper was to define an unprecedented frame of reference built on cutting-edge knowledge and state-of-the-art methodology, to enable reliable comparison of results among laboratories and new progress in the field based on standardized methods and shared information. [ABSTRACT FROM AUTHOR]

A series of 3-thioglycosylated 5,6-diacetoxyindole derivatives, which are important tools for eumelanin research and application, were prepared through a practical and efficient approach exploiting a dynamic mixture of thioglycoside agents. The strategy is feasible for installing both mono- and disaccharide units and relies on the facile in situ conversion of glycosyl disulfides into the corresponding, more reactive, phenylselenenyl sulfides in the presence of diphenyl diselenide, N-bromosuccinimide (NBS) and tetrabutylammonium bromide (TBAB). [ABSTRACT FROM AUTHOR]

Abstract: Wastewater sewage sludge was co-pyrolyzed with a well characterized clay sample, in order to evaluate possible advantages in the thermal disposal process of solid waste. Characterization of the co-pyrolysis process was carried out both by thermogravimetric–mass spectrometric (TG–MS) analysis, and by reactor tests, using a lab-scale batch reactor equipped with a gas chromatograph for analysis of the evolved gas phase (Py–GC). Due to the presence of clay, two main effects were observed in the instrumental characterization of the process. Firstly, the clay surface catalyzed the pyrolysis reaction of the sludge, and secondly, the release of water from the clay, at temperatures of approx. 450–500°C, enhanced gasification of part of carbon residue of the organic component of sludge following pyrolysis. Moreover, the solid residue remaining after pyrolysis process, composed of the inorganic component of sludge blended with clay, is characterized by good features for possible disposal by vitrification, yielding a vitreous matrix that immobilizes the hazardous heavy metals present in the sludge. [Copyright &y& Elsevier]

Elucidation of the relationships between structural features and UV–visible absorption properties of 5,6-dihydroxyindole oligomers is an essential step towards an understanding of the unique optical properties of eumelanins. Herein, we report the first combined experimental and density functional theory (DFT) investigation of the 5,6-dihydroxyindole oligomers so far isolated. 2,2′-Biindolyl 2 and the 2,4′-biindolyl 3 absorb at longer wavelengths relative to 2,7′-biindolyl 4 and their spectra were well predicted by DFT analysis. The absorption bands of 2,4′:2′,4′′- and 2,4′:2′,7′′-triindolyls 5 and 6 also fall at different wavelengths and can be interpreted by DFT simulations as being due to a combination of two main separate transitions. Tetramer 7, in which two 2,4′-biindolyl units are linked through a 2,3′-connection, exhibits a broad chromophore extending over the entire UV range without well defined absorption maxima. Within the dimer–tetramer range examined, three key points emerge: (1) an increase in oligomer chain length does not result in any regular and predictable bathochromic shift; (2) a marked broadening of the absorption bands occurs when going from the monomer to the tetramer structure; and (3) the mode of coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. It is concluded that use of experimentally characterized oligomeric scaffolds as a basis for DFT calculations is a most promising approach to building reliable structural models for studies of eumelanins optical properties. [ABSTRACT FROM AUTHOR]

Over the years, the role of biochemical, immunological, genetic, and other biological aspects in the pathogenesis of vitiligo has been studied. So far, no convincing model describing the interplay of these contributing factors has been formulated. Based on existing research, we propose that vitiligo has a multi-factorial etiology, characterized by multiple steps, but always involving an increase of external or internal phenol/catechol concentration, serving as a preferred surrogate substrate of tyrosinase, competing with its physiological substrate tyrosine. The conversion of these substrates into reactive quinones is reinforced by a disturbed redox balance (increasing hydrogen peroxide). Such reactive quinones can be covalently bound to the catalytic centre of tyrosinase (haptenation). This could give rise to a new antigen, carried by Langerhans cells to the regional lymph node, stimulating the proliferation of cytotoxic T cells. However, the activation of such cytotoxic cells is only a first step in skin melanocyte killing, which also depends on a shift in the balance between immune defence and tolerance, e.g. resulting from a decrease in properly functioning T-regulatory cells. With this new model, based on a synthesis of several of the existing theories, in mind, the external and internal factors involved in the etiopathogenesis of vitiligo are reviewed, against the background of reported clinical data, experimental studies and existing and potential new therapies. A similar complex mechanism may also lead to some other autoimmune diseases. [ABSTRACT FROM AUTHOR]

Abstract: Objective: : To evaluate an in vivo pro-oxidant state in patients with ataxia telangiectasia (AT). Methods: : A set of oxidative stress endpoints were measured in 9 AT homozygotes, 16 AT heterozygotes (parents) and 83 controls (grouped in age ranges as for patients and parents, respectively). The following analytes were measured: (a) leukocyte 8-hydroxy-2′-deoxyguanosine (8-OHdG); (b) blood glutathione (GSSG and GSH); and (c) plasma levels of glyoxal (Glx) and methylglyoxal (MGlx). Results: : AT patients displayed a significant decrease in blood GSSG (p =0.012) and in MGlx plasma concentrations (p =0.012). A non-significant decrease in the GSSG:GSH ratio (p =0.1) and a non-significant increase in 8-OHdG and Glx levels were observed in AT patients vs. young controls (age range 4–35 years). AT heterozygotes failed to display any significant changes vs. adult controls (age range 36–68 years). Conclusion: : No significant increase in oxidative stress biomarkers was detected in blood from AT patients. The decrease in GSSG and MGlx levels in AT patients may suggest an adaptive response to a pro-oxidant state in AT-related target organs. [Copyright &y& Elsevier]

Abstract: Traditionally raised by the toxicological implications of excess exposure to nitrogen oxides and nitrite ions, interest in the chemistry of biological nitrosations and nitrations has gained new impetus in the past decade following the discovery of nitric oxide (NO) as an endogenous physiological regulator and an amplifier of oxidative stress-dependent toxic processes. This account is concerned with an overview of the reactions of nitrosating and nitrating agents of pathophysiological relevance with two potential biochemical targets, namely polyunsaturated fatty acids and catecholamines. The results of model studies on the mechanism of the antinitrosating activity of caffeic acid and chlorogenic acid are also presented. To cite this article: M. D''Ischia, C. R. Chimie 8 (2005) . [Copyright &y& Elsevier]

Provides insights into acid-promoted reaction of caffeic acid and esters with nitrite. Decarboxylation on chain nitrozation pathway to oxime derivatives; Isomerization of nitrous group to stable aldoxime functionality; Exhibition of mutual reactivity to hydrogen-concentration ion.

Investigates the Maillard reaction of L-3,4-Dihydroxyphenylalanine (L-DOPA) and dopamine with D-glucose under physiologically relevant conditions to specifically elucidate the nature of competing pathways. Reaction of L-DOPA with D-glucose; Reactions of Dopamine and L-tyrosine with D-glucose; Effects of transition metal cations on the reaction of L-DOPA with D-glucose.

Describes a novel octahydropyridobenzothiazepine metabolite in human urine. Details on a biomimetic formation from the melanogen 5-S-cysteinyldopa and formaldehyde; Relevance of the Pictet-Spengler condensation in forming the compound; Critical role of sulfur substituents in subverting regiochemistry of Schiff bases cyclization.

Studies the oxidation of 5,6 dihydroxyindole in acidic aqueous media. Characterization of the products formed by acid promoted oxidation of 1a; Experimental procedures utilized; Formation of diindolocarbazoles; Description of the oxidation of indolic compounds in acidic media.

Astrochemistry and astrobiology, the fascinating disciplines that strive to unravel the origin of life, have opened unprecedented and unpredicted vistas into exotic compounds as well as extreme or complex reaction conditions of potential relevance for a broad variety of applications. Representative, and so far little explored sources of inspiration include complex organic systems, such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives; hydrogen cyanide (HCN) and formamide (HCONH2) oligomers and polymers, like aminomalononitrile (AMN)-derived species; and exotic processes, such as solid-state photoreactions on mineral surfaces, phosphorylation by minerals, cold ice irradiation and proton bombardment, and thermal transformations in fumaroles. In addition, meteorites and minerals like forsterite, which dominate dust chemistry in the interstellar medium, may open new avenues for the discovery of innovative catalytic processes and unconventional methodologies. The aim of this review was to offer concise and inspiring, rather than comprehensive, examples of astrochemistry-related materials and systems that may be of relevance in areas such as surface functionalization, nanostructures, and hybrid material design, and for innovative technological solutions. The potential of computational methods to predict new properties from spectroscopic data and to assess plausible reaction pathways on both kinetic and thermodynamic grounds has also been highlighted. [ABSTRACT FROM AUTHOR]

[Display omitted] Halloysite nanotubes (HNTs) represent a versatile core structure for the design of functional nanosystems of biomedical interest. However, the development of selective methodologies for the site-controlled functionalization of the nanotubes at specific sites is not an easy task. This study aims to accomplish a procedure for the site-selective/specific, "pin-point", functionalization of HNTs with polydopamine (HNTs@PDA). This goal was achieved, at pH 6.5, by exploiting the basicity of ZnO nanoparticles anchored on the HNTs external surface (HNTs@ZnO) to induce a punctual polydopamine polymerization and coating. The morphology and the chemical composition of the nanomaterial was demonstrated by several techniques. Turbidimetric analysis showed that PDA coating affected the aqueous stability of HNTs@PDA compared to both HNTs@ZnO and HNTs. Notably, hyperthermia studies revealed that the nanomaterial induced a local thermic rise, up to 50 °C, under near-infrared (NIR) irradiation. Furthermore, secondary functionalization of HNTs@PDA by selective grafting of biotin onto the PDA coating followed by avidin binding was also accomplished. [ABSTRACT FROM AUTHOR]

The article focuses on synthetic eumelanintype biopolymers such as mussel-inspired polydopamine and optical, electronic, and free-radical properties that make them attractive for materials and biomedicine applications. It mentions biopolymers show that tyrosine containing tripeptides can serve as tunable precursors for polymeric eumelanin-like pigments, with properties that depend on the peptide sequence and oxidative polymerization.

The author offers information on photoprotective role of melanin pigments in the skin. Topics discussed include two types of silver-reduction based staining methods, argentaffinic or argyrophilic, the melanin dust dogma of skin pigmentation and factors affecting deceptive melanin dust-like response to Fontana-Masson (FM) in the stratum corneum.

Pays tribute to science professor Giuseppe Prota, who died on January 10, 2003. Academic background; Contributions to the field of pigment cell research; Awards and achievements.

Review: 84 refs. [ABSTRACT FROM AUTHOR]

Herein is delineated a first systematic framework for the definition of structure‐antioxidant property relationships in the dihydroxynaphthalene (DHN) series. The results obtained by a combined experimental and theoretical approach revealed that 1,8‐DHN is the best performing antioxidant platform, with its unique hydrogen‐bonded peri‐hydroxylation pattern contributing to a fast H atom transfer process. Moreover, the comparative analysis of the antioxidant properties of DHNs carried out by performing DPPH and FRAP assays and laser flash photolysis experiments, revealed the higher antioxidant power associated with an α‐substitution pattern (i. e. in 1,8‐ and 1,6‐DHN) with respect to DHNs exhibiting a β‐substitution pattern (i. e. in 2,6‐ and 2,7‐DHN). DFT calculations and isolation and characterization of the main oligomer intermediates formed during the oxidative polymerization of DHNs supported this evidence by providing unprecedented insight into the generation and fate of the intermediate naphthoxyl radicals, which emerged as the main factor governing the antioxidant activity of DHNs. [ABSTRACT FROM AUTHOR]

Introduces a series of papers regarding aspects of pigment cell research related to the works of late professor Giuseppe Prota who died on January 10, 2003. Melanogenesis in the ink gland of Sepia officinalis; Study on melanocortin 1 receptor signaling; Melanogenesis and melanoma.

[Display omitted] The possibility to use hexamethylenediamine (HMDA) to impart film forming ability to natural polymers including eumelanins and plant polyphenols endowed with biological activity and functional properties has been recently explored with the aim to broaden the potential of polydopamine (PDA)-based films overcoming their inherent limitations. 5,6-dihydroxyindole-2-carboxylic acid, its methyl ester (MeDHICA) and eumelanins thereof were shown to exhibit potent reducing activity. MeDHICA and HMDA were reacted in aqueous buffer, pH 9.0 in the presence of different substrates to assess the film forming ability. The effect of different reaction parameters (pH, diamine chain length) on film formation was investigated. Voltammetric and AFM /SEM methods were applied for analysis of the film redox activity and morphology. HPLC, MALDI-MS and 1HNMR were used for chemical characterization. The film reducing activity was evaluated in comparison with PDA by chemical assays and using UV stressed human immortalized keratinocytes (HaCat) cells model. Regular and homogeneous yellowish films were obtained with moderately hydrophobic properties. Film deposition was optimal at pH 9, and specifically induced by HMDA. The film consisted of HMDA and monomeric MeDHICA accompanied by dimers/small oligomers, but no detectable MeDHICA/HMDA covalent conjugation products. Spontaneous assembly of self-organized networks held together mainly by electrostatic interactions of MeDHICA in the anion form and HMDA as the dication is proposed as film deposition mechanism. The film displayed potent reducing properties and exerted significant protective effects from oxidative stress on HaCaT. [ABSTRACT FROM AUTHOR]

The design of modern devices that can fulfil the requirements for sustainability and renewable energy applications calls for both new materials and a better understanding of the mixing of existing materials. Among those, surely organic–inorganic hybrids are gaining increasing attention due to the wide possibility to tailor their properties by accurate structural design and materials choice. In this work, we'll describe the tight interplay between porous Si and two melanic polymers permeating the pores. Melanins are a class of biopolymers, known to cause pigmentation in many living species, that shows very interesting potential applications in a wide variety of fields. Given the complexity of the polymerization process beyond the formation and structure, the full understanding of the melanins' properties remains a challenging task. In this study, the use of a melanin/porous Si hybrid as a tool to characterize the polymer's properties within mesopores gives new insights into the conduction mechanisms of melanins. We demonstrate the dramatic effect induced on these mechanisms in a confined environment by the presence of a thick interface. In previous studies, we already showed that the interactions at the interface between porous Si and eumelanin play a key role in determining the final properties of composite materials. Here, thanks to a careful monitoring of the photoconductivity properties of porous Si filled with melanins obtained by ammonia-induced solid-state polymerization (AISSP) of 5,6-dihydroxyindole (DHI) or 1,8-dihydroxynaphthalene (DHN), we investigate the effect of wet, dry, and vacuum cycles of storage from the freshly prepared samples to months-old samples. A computational study on the mobility of water molecules within a melanin polymer is also presented to complete the understanding of the experimental data. Our results demonstrate that: (a) the hydration-dependent behavior of melanins is recovered in large pores (≈ 60 nm diameter) while is almost absent in thinner pores (≈ 20 nm diameter); (b) DHN-melanin materials can generate higher photocurrents and proved to be stable for several weeks and more sensitive to the wet/dry variations. [ABSTRACT FROM AUTHOR]

The abnormal susceptibility of red-haired individuals to UV-induced inflammation and skin cancers is commonly attributed to the marked photoreactivity of pheomelanin pigments, which would be responsible for the sustained generation of reactive oxygen species in the skin following sun exposure. The structural factors determining pheomelanin photolability remain mostly unknown. Here, we describe the effects of zinc ions, typically found at high levels in red hair, in enhancing both oxygen consumption and superoxide production in model pheomelanin pigments following irradiation with UVA and visible light. Electron paramagnetic resonance (EPR) oximetry and EPR-spin trapping experiments with synthetic pheomelanins, prepared by oxidation of dopa and cysteine or isomeric cysteinyldopas under different conditions, indicate a higher photoreactivity of the pigments prepared in the presence of zinc ions compared with those obtained in the absence of the metal. Quantitative analysis of thiazole-containing structural markers of the synthetic pheomelanins provides evidence that the effect of zinc ions is due to modification of the formation pathway and structural features of the pigments. Overall, these results point to a hitherto unrecognized critical role of zinc ions in pheomelanogenesis, which may affect the intrinsic photoreactivity of the pigment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interacting NH 4 + and catechol groups play a fundamental role in self-assembly. • IPESs herein sampled at QM level can be employed in tuning lower-level methods. • The present findings indicate σ-type as the most important contributor to binding. • The σ -type/cation- π ratio is strongly dependent on the number of hydroxyl groups. • The present findings call for a reassessment of the importance of the two conformers. Cation- π interactions between ammonium and catechol groups provide a commonly held paradigm in the complex interplay of noncovalent forces that govern both biological phenomena, such as underwater adhesion in mussel byssus and other marine organisms, and aggregation processes in self-assembly of catecholamine-derived polymers. However, closer consideration of the peculiar properties of the catechol functionality, that features two adjacent phenoxyl groups endowed with chelating properties, would suggest operation of alternate interaction geometries besides typical cation- π. Following previous studies on various alkali metal cations, we report herein compelling computational evidence in favor of a so far overlooked σ -type interaction between the ammonium cation and the catechol system, as the most important contributor to binding, far exceeding the cation- π component. The present findings would hence prompt an experimental and theoretical reassessment of the actual importance of cation- π against σ -type interaction between ammonium and catechol groups in underwater adhesive patterns. In this framework, the catechol-ammonium interaction energy potential surfaces herein reported may provide an improved reference to approach more realistic natural and synthetic adhesion models encompassing other participating molecules/ions and the role of the solvent. [ABSTRACT FROM AUTHOR]

Abstract: SnO2 and SnO2 +Co-porphyrin solids were prepared from SnCl4 in propanol and hydrolyzed to sol. Thermal behavior of samples obtained at 110°C was studied in the 20–600°C interval by thermal analysis coupled with mass spectrometry for identification of released species. The original samples maintain residual Sn–OR, Sn–OH and Sn–Cl groups up to 350°C. The sample doped with 1% Co-porphyrin differs for a significant presence of residual Sn–Cl species, accounting for SnCl4 release in the 300–340°C range. 119Sn solid state NMR analysis reveals disordered SnO2 species in the sample heated at 250°C and non-uniform SnO6 units in the SnO2 +Co-porphyrin sample at 110°C, due to persistence of Sn–OR and Sn–OH groups. This complexity is lost at 250°C. X-ray diffraction analysis confirms all these data. The sensing efficiency of these materials versus alcohols is ascribed to the presence of an open, incomplete SnO2 structure, which is more pronounced in the Co-porphyrin-doped sample. [Copyright &y& Elsevier]

Abstract: The reactions of 5-S-cysteinyldopa (1), l-α-methyldopa (2) and dl-m-tyrosine (3) with d-glucose were investigated at 90°C in phosphate buffer at pH ranging from 5.0 to 9.0. Whereas 1 gave mainly the double Maillard condensation product N,N′-bis(1″-deoxy-d-fructos-1″-yl)-5-S-cysteinyldopa, as an inseparable mixture of β-d-fructopyranosyl and α,β-d-fructofuranosyl derivatives, 2 and 3 gave both Maillard and Pictet–Spengler products, although to different extents and with different regio- and stereochemistry. A peculiar pattern of reactivity was displayed by 2 which gave, besides the Maillard product and the expected 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline C-1 diastereoisomeric pairs, the unprecedented 7,8-dihydroxy-1,2,3,4-tetrahydroisoquinoline derivative via the ortho cyclization pathway. Pictet–Spengler cyclization of 2 and 3 proceeded with Felkin–Anh-type asymmetric induction, favouring the 1R isomer throughout the pH range 5.0–9.0. These results, which highlight the first example of carbohydrate-derived 7,8-dihydroxytetrahydroisoquinoline, provide new insights into the factors governing competition between Maillard and Pictet–Spengler condensation pathways. [Copyright &y& Elsevier]

Fanconi anaemia (FA) is a genetic disease characterised by bone marrow failure with excess risk of myelogenous leukaemia and solid tumours. A widely accepted notion in FA research invokes a deficiency of response to DNA damage as the fundamental basis of the 'crosslinker sensitivity' observed in this disorder. However, such an isolated defect cannot readily account for the full cellular and clinical phenotype, which includes a number of other abnormalities, such as malformations, endocrinopathies, and typical skin spots. An extensive body of evidence pointing toward an involvement of oxidative stress in the FA phenotype includes the following: (i) In vitro and ex vivo abnormalities in a number of redox status endpoints; (ii) the functions of several FA proteins in protecting cells from oxidative stress; (iii) redox-related toxicity mechanisms of the xenobiotics evoking excess toxicity in FA cells. The clinical features in FA and the in vivo abnormalities of redox parameters are here reconsidered in view of the pleiotropic clinical phenotype and known biochemical and molecular links to an in vivo prooxidant state, which causes oxidative damage to biomolecules, resulting in an excessive number of acquired abnormalities that may overwhelm the cellular repair capacity rather than a primary deficiency in DNA repair. FA may thus represent a unique model disease in testing the integration between the acquisition of macromolecular damage as a result of oxidative stress and the ability of the mammalian cell to respond effectively to such damage. [ABSTRACT FROM AUTHOR]

Chlorogenic acid (1), a cancer chemopreventive agent widely found in fruits, tea and coffee, undergoes efficient conjugation with glutathione (GSH), in the presence of horseradish peroxidase/H2O2 or tyrosinase at pH 7.4, to yield three main adducts that have been isolated and identified as 2-S-glutathionylchlorogenic acid (3), 2,5-di-S-glutathionylchlorogenic acid (4) and 2,5,6-tri-S-glutathionylchlorogenic acid (5) by extensive NMR analysis. The same pattern of products could be obtained by reaction of 1 with GSH in the presence of nitrite ions in acetate buffer at pH 4. Mechanistic experiments suggested that oxidative conjugation reactions proceed by sequential nucleophilic attack of GSH on ortho-quinone intermediates. Overall, these results provide the first complete spectral characterization of the adducts generated by biomimetic oxidation of 1 in the presence of GSH, and disclose a new possible nitrite-mediated conjugation pathway of 1 with GSH at acidic pH of physiological relevance. [Copyright &y& Elsevier]

In acetate buffer, pH 4, at room temperature, nitrite ions can mediate an unusual decarboxylative conjugation of caffeic acid with glutathione leading to novel isomeric 2-(3,4-dihydroxyphenyl)-2-S-glutathionylacetaldehyde oximes. These results hint at a possible role of endogenous and/or dietary glutathione in the mechanisms by which caffeic acid can affect the burden of carcinogenic N-nitroso compounds in the digestive tract. [Copyright &y& Elsevier]

A concise highlight of the main types of chromophoric systems obtained in the authors' and other laboratories through biomimetic chemistry or synthetic manipulation of nature-inspired o-quinones is the primary focus of this Minireview. Following oxidative conversion of a variety of natural catechol substrates like DOPA, dopamine, 5-S-cysteinyldopa and caffeic acid, in the presence of suitable additives, a remarkable variety of chromophoric systems can be produced, which display specific optical and electronic properties, e. g. acidichromism, solvatochromism or strong emission upon excitation. Such properties can be tailored for specific applications through rational synthetic manipulations and/or fine-tuning through non-covalent and supramolecular interactions. Practical access routes to the reported o-quinone-derived chromophoric systems are illustrated along with the main prospective applications. [ABSTRACT FROM AUTHOR]

Formation and structural modification of oxygenated polycyclic aromatic hydrocarbons (oxyPAHs) by UV irradiation on minerals have recently been proposed as a possible channel of PAH transformation in astrochemical and prebiotic scenarios of possible relevance for the origin of life. Herein, it is demonstrated that high‐energy proton‐beam irradiation in the presence of various meteorites, including stony iron, achondrite, and chondrite types, promotes the conversion of two representative oxyPAH compounds, 1‐naphthol and 1,8‐dihydroxynaphthalene, to complex mixtures of oxygenated and oligomeric derivatives. The main identified products include polyhydroxy derivatives, isomeric dimers encompassing benzofuran and benzopyran scaffolds, and, notably, a range of quinones and perylene derivatives. Addition of urea, a prebiotically relevant chemical precursor, expanded the range of identified species to include, among others, quinone diimines. Proton‐beam irradiation of oxyPAH modulated by nitrogen‐containing compounds such as urea is proposed as a possible contributory mechanism for the formation and processing of insoluble organic matter in meteorites and in prebiotic processes. [ABSTRACT FROM AUTHOR]

A new red hair-inspired 1,4-benzothiazine-based scaffold is disclosed herein, built upon a modular D-π-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. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA) is widely used as hydrophilic coating for several applications. However, most of the methods studied to improve or manipulate PDA properties are multistep and time-consuming, and there is a need for versatile strategies aimed at controlling and modifying the properties of PDA. PDA-halloysite nanocomposites were produced under different oxidation conditions in alkaline and acidic media and were characterized by UV–visible and attenuated total refraction- Fourier Transform Infrared spectroscopies, thermogravimetric analysis, porosimetry, scanning electron microscopy, X-ray diffraction and contact angle measurements against the reference PDA polymer. Inclusion of the inorganic halloysite nanofiller in the PDA component was found to affect the thermal properties of the nanocomposite as well as its structure, depending on the experimental conditions. The ability of the nanocomposites to adsorb organic dyes as possible membrane coatings for environmental remediation was also investigated by different models, suggesting promising applications as adsorbents for the treatment of wastewaters. [ABSTRACT FROM AUTHOR]

Developing effective strategies to increase the chemical stability and to fine‐tune the physico‐chemical properties of melanin biopolymers by rational control of π‐electron conjugation is an important goal in materials science for biomedical and technological applications. Herein we report that poly‐1,8‐dihydroxynaphthalene (pDHN), a non‐nitrogenous, catechol‐free fungal melanin mimic, displays a high degree of structural integrity (from MALDI‐MS and CP/MAS 13C NMR analysis), a strong radical scavenging capacity (DPPH and FRAP assays), and an unusually intense EPR signal (g=2.0030). Morphological and spectral characterization of pDHN, along with deassembly experiments in ionic liquids, indicated amorphous aggregates of small globular structures with an estimated stacking distance of 3.9 Å and broadband absorption throughout the visible range. These results indicate that DHN‐based melanins exhibit a high structural integrity and enhanced antioxidant and free‐radical properties of potentially greater biomedical and technological relevance than for typical indole‐based eumelanins. [ABSTRACT FROM AUTHOR]

Developing safe and high efficiency contrast tools is an urgent need to allow in vivo applications of photoacoustics (PA), an emerging biomolecular imaging methodology, with poor invasiveness, deep penetration, high spatial resolution and excellent endogenous contrast. Eumelanins hold huge promise as biocompatible, endogenous photoacoustic contrast agents. However, their huge potential is still unexplored due to the difficulty to achieve at the same time poor aggregation in physiologic environment and high PA contrast. This study addresses both issues through the design of a biocompatible photoacoustic nanoprobe, named MelaSil_Ag-NPs, relying on silica-templated eumelanin formation as well as eumelanins redox and metal chelating properties to reduce Ag+ ions and control the growth of generated metal nanoparticles. This strategy allowed self-structuring of the system into a core-shell architecture, where the Ag core was found to boost PA signal, despite the poor eumelanin content. Obtained hybrid nanoplatforms, showed stable photoacoustic properties even under long irradiation. Furthermore, conjugation with rhodamine isothiocyanate allowed particles detection through fluorescent imaging proving their multifunctional potentialities. In addition, they were stable towards aggregation and efficiently endocytosed by human pancreatic cancer cells (BxPC3 and Panc-1) displaying no significant cytotoxicity. Such numerous features prove huge potential of those nanoparticles as a multifunctional platform for biomedical applications. Self-structuring of Silica-Eumelanin-Ag nanoparticles into a hybrid SiO 2 -Mel shell@Ag core architecture led to a huge improvement of photoacoustic signal. Unlabelled Image • Eumelanin photoacoustic properties are exploited to produce bioinspired photoacoustic nanoprobes. • In situ formation of silica-melanin‑silver leads to a self-structured hybrid nanoprobe. • Silver nanoparticles enhance intrinsic melanin photooacoustic signal. • Hybrid silica-eumelanin‑silver nanoprobes combine enhanced photoacoustic signal and high stability in biological media. [ABSTRACT FROM AUTHOR]

Excellent and selective correlations between the electron-transfer (ET) or hydrogen atom transfer (HAT) capacity (DPPH and lipid peroxidation inhibition assays) and EPR indices of π-electron spin delocalization delineate specific structural determinants of antioxidant activity in biomimetic phenolic polymers. [ABSTRACT FROM AUTHOR]

Summary: To inquire into the role of the carboxyl group as determinant of the properties of 5,6‐dihydroxyindole melanins, melanins from aerial oxidation of 5,6‐dihydroxyindole‐2‐carboxylic acid (DHICA) and its DHICA methyl ester (MeDHICA) were comparatively tested for their antioxidant activity. MALDI MS spectrometry analysis of MeDHICA melanin provided evidence for a collection of intact oligomers. EPR analysis showed g‐values almost identical and signal amplitudes (ΔB) comparable to those of DHICA melanin, but spin density was one order of magnitude higher, with a different response to pH changes. Antioxidant assays were performed, and a model of lipid peroxidation was used to compare the protective effects of the melanins. In all cases, MeDHICA melanin performed better than DHICA melanin. This capacity was substantially maintained following exposure to air in aqueous buffer over 1 week or to solar simulator over 3 hr. Different from DHICA melanin, MeDHICA melanin was proved to be fairly soluble in different water‐miscible organic solvents, suggesting its use in dermocosmetic applications. [ABSTRACT FROM AUTHOR]

The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level. Quite unexpectedly, nuclear magnetic resonance (NMR) analysis of the early oligomer fractions indicated linear, 4-, and 7-linked structures in marked contrast with DHI, which gives highly complex mixtures of partially degraded oligomers. Density functional theory (DFT) calculations supported the tendency of DHBT to couple via the 4- and 7-positions. These results uncover the role of nitrogen as a major determinant of the structural diversity generated by the polymerization of DHI, and point to replacement by sulfur as a viable entry to regioregular eumelanin-type materials for potential applications for surface functionalization by dip coating. [ABSTRACT FROM AUTHOR]

Porous Si/eumelanin hybrids are a novel class of organic-inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation of the eumelanin-silicon interface. Herein we report an integrated experimental and computational study aimed at probing interface stability via surface modification and eumelanin manipulation, and at modeling the organic-inorganic interface via formation of a 5,6-dihydroxyindole (DHI) tetramer and its adhesion to silicon. The results indicated that mild silicon oxidation increases photocurrent stability via enhancement of the DHI-surface interaction, and that higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of growing eumelanin. [ABSTRACT FROM AUTHOR]

Due to the emerging biomedical relevance and technological potential of fungal melanins, and prompted by the virtual lack of information about their structural arrangement, an optimized synthetic protocol has been devised for a potential structural model of Ascomyces allomelanin through enzyme-catalyzed oxidative polymerization of 1,8-dihydroxynaphthalene (1,8-DHN). Electrospray ionization mass spectrometry (ESI-MS) measurements of freshly synthesized DHN-polymer recorded in the negative ion mode allowed detection of oligomers up to m/ z 4000, separated by 158 Da, corresponding to the in-chain DHN-unit. The dominant peaks were assigned to singly-charged distribution, up to 23 repeating units, whereas a doubly charged polymer distribution was also detectable. Chemical derivatization, ultra-performance liquid chromatography (UPLC)-ESI MS, and MS/MS data confirmed that oxidative polymerization of 1,8-DHN proceeds through C−C coupling of the naphthalene rings. The new insights reported here into synthetic 1,8-DHN oligomers/polymers as a mimic of fungal melanins may guide novel interesting advances and applications in the field of biomimetic functional materials. [ABSTRACT FROM AUTHOR]

The exploitation of easily accessible and nontoxic natural catechol compounds for surface functionalization and coating is attracting growing interest for biomedical applications. We report herein the deposition on different substrates of chemically stable thin films by autoxidation of 1 mM caffeic acid (CA) solutions at pH 9 in the presence of equimolar amounts of hexamethylenediamine (HMDA). UV-visible, mass spectrometric, and solid state 13C and 15N NMR analysis indicated covalent incorporation of the amine during CA polymerization to produce insoluble trioxybenzacridinium scaffolds decorated with carboxyl and amine functionalities. Similar coatings are obtained by replacing CA with 4-methylcatechol (MC) in the presence of HMDA. No significant film deposition was detected in the absence of HMDA nor by replacing it with shorter chain ethylenediamine, or with monoamines. The CA/HMDA-based films resisted oxidative and reductive treatments, displayed efficient Fe(II) and Cu(II) binding capacity and organic dyes adsorption, and provided an excellent cytocompatible platform for growing embryonic stem cells. These results pointed to HMDA as an efficient cross-linking mediator of film deposition from natural catechols for surface functionalization and coatings. [ABSTRACT FROM AUTHOR]

Despite the growing scientific and technological relevance of polydopamine (PDA), a eumelanin-like adhesive material widely used for surface functionalization and coating, knowledge of its structural and physicochemical properties, including in particular the origin of paramagnetic behavior, is still far from being complete. Herein, we disclose the unique ability of ionic liquids (ILs) to disassemble PDA, either as a suspension or as a thin film, up to the nanoscale, and to establish specific interactions with the free radical centers exposed by deaggregation of potential investigative value. Immersion of PDA-coated glasses into four different ILs ([C1C1im][(CH3O)HPO2], [C1C1im][(CH3O)CH3PO2], [C1C1im][(CH3O)2PO2], [N1888][C18:1]) at room temperature caused the fast and virtually complete removal of the coating as determined by UV-visible spectroscopy and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) analysis of the colored supernatants from PDA suspensions in ILs revealed the presence of nanostructures not exceeding 50 nm in diameter. Electron paramagnetic resonance (EPR) analysis indicated profound IL-dependent modifications in signal intensity, line-width, and g-factor values of PDA. These differences were interpreted in terms of a partial conversion of C-centered radicals into O-centered semiquinone-type components following destacking and interaction with the anion component in ILs. The discovery of ILs as a powerful tool to disassemble PDA under mild conditions provides a new entry both to detailed investigations of this biopolymer on the nanoscale and to mild removal of coatings from functionalized surfaces, greatly expanding the scope of PDA-based surface functionalization strategies. [ABSTRACT FROM AUTHOR]

A letter to the editor about a study which investigated whether 5,6-dihydroxyindole-2-carboxylic acid (DHICA) is the key to dopachrome tautomerase and melanocyte functions is presented.

Efficient surface functionalization with polydopamine (PDA) films can be easily achieved on virtually any object via single immersion in slightly basic dopamine solutions. In such conditions, however, poor homogeneity, low thickness, and long time of reaction are usually the major limitations. Herein, we report a rational entry to the control of PDA deposition via chemical oxidation under slightly acidic conditions (pH 5.0) ensuring inhibition of uncontrolled autoxidation processes to gain insight about the reaction mechanism and the impact of oxidation conditions on PDA structure. Comparative chemical analysis of dopamine oxidation with three different oxidants (ammonium peroxodisulfate, sodium periodate, and copper sulfate) revealed significant differences in the reaction course and allowed selection of periodate for the fast and homogeneous deposition of PDA films with thickness never before reported. Notably, PDA coatings with unprecedented superhydrophilic/superoleophobic properties were obtained under conditions of high periodate concentration due to degradation of quinone units to yield carboxyl functions. Moreover, these films still present biocompatibility and metal cation reduction properties. Overall, these results provide a novel rational methodology to tailor PDA coatings for technological applications based on periodate control over dopamine polymerization and postsynthetic functional group modification. [ABSTRACT FROM AUTHOR]