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The characterization of a novel, relatively long-lived 5, 6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach is described. Pulse radiolytic investigations have revealed the generation of one or more transient radical or radical-anion forms of the semiquinone which rapidly disproportionates to give the o-indolequinone.

The isolation and structural characterization of the main products formed by acid-promoted reaction of ((E)-3,4',5-trihydroxystilbene) with N[[O.sub.2].sup-] under mild conditions is described. The oxygen-independent N[[O.sub.2].sup-] -mediated oxidative fission of the double bond under mild, physiologically relevant conditions is unprecendented in stilbene chemistry and is proposed to involve breakdown of hydroxynitro(so) intermediates.

The results of detailed investigation into the nature of the oligomer products formed by phenolic oxidation of 17beta-estradiol are presented. The results provide the first systematic inventory of oxidative coupling products of 17beta-estradiol and lay the foundation for future studies aimed to develop novel estrogen derivatives based on oligomeric scaffolds.

Research has been conducted on the antipyretic drug paracetamol. The oxidation chemistry of this drug with UV/H (sub)2 O (sub)2 system has been examined via various techniques including (super)15 N NMR analysis and the details are reported.

Research has been conducted on the polysaturated fatty acids and their methyl esters. The isolation, spectral characterization and biological screening of the nitration products of the reaction of these acids and their esters with NO (sub)2 (super)- in acidic media are reported.

Research has been conducted on the reaction of L-3,4-dihydroxyphenylalanine and dopamine with D-glucose. The nature of the competing pathways, the role of the transition metal cations and the chemical viability of the nonenzymatic glycation processes have been investigated.

The reaction between a polyunsaturated fatty acid derivative ethyl linoleate with nitrite in acidic media provides a direct route for preparing nitrated lipid products on a small scale. The methodology yields nitration products of unsaturated fatty acids, such as nitroalkanes, nitro alcohols, and dienes.

Research describes the urinary melanogen 5-S-cysteinyldopa exhibiting an octahydropyridobenzothazepine skeleton and examines the origin of the heterocyclic ring system from double condensation reaction between 5-S-cysteinyldopa and formaldehyde. Data discuss the reaction of 5-alkylthiocatecholamines with formaldehyde under biomimetic Pictet-Spengler conditions.

The water-soluble 5,6-dihydroxyindole (DHI) polymer produced by oxidation of ad hoc designed 5,6-dihydroxy-3-indolyl-1-thio-[beta]-D-galactopyranoside is described. The studies have shown that eumelanin black color is not only defined by the overlap of [pi]-electron conjugated chromophores within the individual polymer components, but also by oxidation state- and aggregation-dependent interchromophoric interactions causing perturbations of the heterogeneous ensemble of [pi]-electron systems and overall spectral broadening.

An efficient nitroselenenylation/oxidation pathway to 9-nitrolinoleic acid and 10-nitrolinoleic acid which facilitated comparative product studies under physiologically relevant conditions is reported. The studies on the position-dependent influence of the nitro group on the oxidation behavior of the 1,4-pentadienyl moiety is also reported.

The article explains the nitration, as well as the nitrosation chemistry of menthofuran, a toxic furan obtained from various mint oils. It also demonstrates the synthetic and biomedical significance of menthofuran-derived scaffolds.

Chemical or enzymatic oxidation of 5,6-dihydrocyindole has led to the rapid deposition of a black solid by using a complex oligomerization/polymerization process that has proceeded in the early stages via dimers and trimers characterized by 2,4'- and 2,7'-couplings. Three additional tetramers are obtained by the oxidation of 5,5',6,6'-tetrahydroxy-2,7biindolyl with the peroxidase/[H.sub.2][O.sub.2] system.

The transient species formed by oxidation of three dimers of 5,6-dihydroxyindole, a major building block of the natural biopolymer eumelanin are examined. Pulse radiolytic oxidation of 5.5',6.6'-tetrahydroxy-2.4'-biindolyl and 5.5',6.6'-tetrahydroxy-2.7'-biindoyl led to semiquinones absorbing about 450 nm, which decayed with second-order kinetics (2k=2.8 x [10.sup.9] and 1.4 x [10.sup.9] [M.sup.-1][s.sup.-1], respectively) to give the corresponding quinines (500-550 nm).

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]

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.

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.

The mechanism of the acid-dependent interring dehydrogenation in the conversion of the single-bonded 3-phenyl-2 H -1,4-benzothiazine dimer 2 to the Δ 2,2 ' -bi(2 H -1,4-benzothiazine) scaffold of red hair pigments is disclosed herein. Integrated chemical oxidation and oxygen consumption experiments, coupled with electron paramagnetic resonance (EPR) analyses and DFT calculations, allowed the identification of a key diprotonated free-radical intermediate, which was implicated in a remarkable oxygen-dependent chain process via peroxyl radical formation and evolution to give the Δ 2,2 ' -bi(2 H -1,4-benzothiazine) dimer 3 by interring dehydrogenation. The critical requirement for strongly acidic conditions was rationalized for the first time by the differential evolution channels of isomeric peroxyl radical intermediates at the 2- versus 3-positions. These results offer for the first time a rationale to expand the synthetic scope of the double interring dehydrogenation pathway for the preparation of novel symmetric double-bond bridged captodative heterocycles.

The reliability of several density functional theory (DFT) functionals and of the Möller-Plesset second-order perturbation theory calculations with modified basis sets (mp2 mod ) approach in describing cation-π interactions is systematically investigated by benchmarking their performances with respect to high quality reference CCSD(T) calculations of the binding energies between alkaline cations of varying radius (Na + , K + , Rb + , and Cs + ) and three aromatic species (benzene, phenol, and catechol). For this class of noncovalent interaction, mp2 mod delivers, on average, results in very good agreement with the reference CCSD(T) data, yet at a very small computational cost, exploiting the reduced dimensions of the modified basis set. Conversely, the tested DFT functionals show a more erratic behavior, with different performances depending on both the investigated system and the combination of the employed functional and basis set. The mp2 mod computational convenience is further exploited to extensively sample two-dimensional interaction energy surfaces of all investigated cation-π systems, which allow for a deeper insight on the effect of the increasing number of hydroxyl substituents, revealing the insurgence, upon substitution, of alternative minima, evident in particular for the smaller cations. The present results strongly support for further applications of the mp2 mod method to study a larger variety of aromatic/metal cation species, relevant both in biological processes and in technological applications.

In the last few years, the development of versatile coating chemistries has become a hot topic in surface science after the discovery that catecholamines can lead to conformal coatings upon oxidation from aqueous solutions. Recently, it was found that aminomalononitrile (AMN), a molecule implicated in the appearance of life on earth, is an excellent prototype of novel material-independent surface functionalizing agents leading to conformal and biocompatible coatings in a simple and direct chemical process from aqueous solutions. So far, very little insight has been gained regarding the mechanisms underlying coating deposition. In this paper, we show that the chemical evolution of AMN film deposition under slightly basic conditions is different in solution and on silica. Thereon, the coating proceeds via a nucleation process followed by further deposition of islands which evolve to produce nitrogen-rich superhydrophilic fibrillar structures. Additionally, we show that AMN-based material can form films at the air-solution interface from unshaken solutions. These results open new vistas into the chemistry of HCN-derived species of potential relevance in materials science.

1,8-Naphthalenediol (dihydroxynaphthalene, 1,8-DHN) has been shown to be a potent hydrogen atom transfer (HAT) antioxidant compound because of the strong stabilization of the resulting free radical by intramolecular hydrogen bonding. However, the properties, reactivity, and fate of the 1,8-DHN phenoxyl radical have remained so far uncharted. Herein, we report an integrated experimental and computational characterization of the early intermediates and dimer products that arise by the oxidation of 1,8-DHN. Laser flash photolysis (LFP) studies of HAT from 1,8-DHN to the cumyloxyl and aminoxyl radicals showed the generation of a transient species absorbing at 350, 400, and >600 nm attributable to the 1,8-DHN phenoxyl radical. Peroxidase/H 2 O 2 oxidation of 1,8-DHN was found to proceed via an intense blue intermediate (λ max 654 nm) preceding precipitation of a black melanin-like polymer. By halting the reaction in the early stages, three main dimers featuring 2,2'-, 2,4'-, and 4,4'-bondings could be isolated and characterized in pure form. Density functional theory calculations supported the generation of the 1,8-DHN phenoxyl radical and its subsequent coupling via the 2- and 4-positions giving extended quinone dimers with intense transitions in the visible range, consistent with UV-vis and LFP data. Overall, these results allowed to elucidate the mechanism of oxidative polymerization of 1,8-DHN of possible relevance to melanogenesis in fungi and other processes of environmental and astrochemical relevance., Competing Interests: The authors declare no competing financial interest.

The role of 5,6-dihydroxyindole (DHI)-based oligomers, including porphyrin-like tetramers, in polydopamine (PDA) film formation was addressed by a comparative structural investigation against model polymers from DHI and its 2,7'-dimer. MALDI-MS data showed that (a) PDA is structurally different from DHI melanin and does not contain species compatible with DHI-based oligomers as primary building blocks; (b) PDA films and precipitate display a single main peak at m/ z 402 in common; (c) no species matching the range of m/ z values expected for cyclic porphyrin-type tetramers was detected in DHI melanin produced in the presence or in the absence of folic acid (FA) as templating agent, nor by oxidation of the 2,7'-dimer of DHI as putative precursor. 15 N NMR resonances and Raman spectra predicted by extensive DFT calculations on porphyrin-type structures at various oxidation levels did not match spectral data for PDA or DHI melanin. Notably, unlike PDA, which gave structurally homogeneous films on quartz on atomic force microscopy (AFM) and micro-Raman spectroscopy, DHI melanin did not form any adhesive deposit after as long as 24 h. It is concluded that PDA film deposition involves structural components unrelated to DHI-based oligomers or porphyrin-type tetramers, which, on mechanism-based analysis, may arise by quinone-amine conjugation leading to polycyclic systems with extensive chain breakdown.

The deposition of polydopamine (PDA) films on surfaces, a versatile deposition method with respect to the nature of the used substrate, is unfortunately accompanied by deposition of insoluble precipitates in solution after a prolonged oxidation time of dopamine solutions. Therefore, there is evident interest to find methods able to stop the deposition of PDA on surfaces and to simultaneously control the self-assembly of PDA in solution to get stable colloidal aggregates. In addition to proposed methods relying on the use of polymers like poly(vinyl alcohol) and proteins like human serum albumin, we show herein that boric acid is an efficient adjuvant that is simultaneously able to stop the self-assembly of PDA in solution as well as on surfaces and to change the adhesive properties of the resulting PDA coatings.