3131-52-0Relevant articles and documents
In situ insights into the nanoscale deposition of 5,6-dihydroxyindole-based coatings and the implications on the underwater adhesion mechanism of polydopamine coatings
Lyu, Qinghua,Song, Hongyan,Yakovlev, Nikolai L.,Tan, Wui Siew,Chai, Christina L. L.
, p. 27695 - 27702 (2018)
The biomimetic coating polydopamine (PDA) has emerged as a promising coating material for various applications. However, the mechanism of PDA deposition onto surfaces is not fully understood, and the coating components of PDA and its relation to the putative intermediate 5,6-dihydroxyindole (DHI) are still controversial. This investigation discloses the deposition mechanisms of dopamine (DA)-based coatings and DHI-based coatings onto silicon surfaces by monitoring the nanoscale deposition of both coatings in situ using high-precision ellipsometry. We posit that the rapid and instantaneous nano-deposition of PDA coatings onto silicon surface in the initial stages critically involves the oxidation of DHI and/or its related oligomers. Our studies also show that the slow conversion of DA to DHI in PDA solution and the coupling between DA and DHI-derived precursors could be crucial for subsequent PDA coating growth. These findings elucidate the critical role of DHI, acting as an 'initiator' and a 'cross linker', in the PDA coating formation. Overall, our study provides important information on the early stage nano-deposition behavior in the construction of PDA coatings and DHI-based coatings.
Short-lived quinonoid species from 5,6-dihydroxyindole dimers en route to eumelanin polymers: Integrated chemical, pulse radiolytic, and quantum mechanical investigation
Pezzella, Alessandro,Panzella, Lucia,Crescenzi, Orlando,Napolitano, Alessandra,Navaratman, Suppiah,Edge, Ruth,Land, Edward J.,Barone, Vincenzo,D'Ischia, Marco
, p. 15490 - 15498 (2006)
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 × 109 and 1.4 × 109 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 (λmax = 480 nm) which disproportionated at a comparable rate (2k = 3 × 109 M -1 s-1) to give a relatively stable quinone (λmax = 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.
MECHANISM OF THE REARRANGEMENT OF DOPACHROME TO 5,6-DIHYDROXYINDOLE
Costantini, C.,Crescenzi, O.,Prota, G.
, p. 3849 - 3850 (1991)
Kinetic and isotopic labelling studies provide for the first time evidence that at physiological pH the rearrangement of dopachrome (1) to 5,6-dihydroxyindole (2) involves abstraction of the proton at position 3 and formation of the intermediate quinone-methide 4.
Effect of aluminum (III) on the conversion of dopachrome in the melanin synthesis pathway
Di, Junwei,Bi, Shuping
, p. 1689 - 1696 (2003)
The effect of aluminum ions on the kinetics and mode of the conversion of dopachrome (DC) in acidic environment has been studied using UV-Vis spectrophotometric and cyclic voltammetric methods. The DC conversion step is an important reaction in melanogenesis. Aluminum ions catalyze greatly the decarboxylative transformation of DC to give 5,6-dihydroxyindole (DHI) rather than 5,6-dihydroxyindole-2-carboxylic acid (DHICA) at pH 5.5, which enhance the ratio of formation DHI/DHICA in melanin synthesis pathway. The kinetics of DC conversion catalyzed by aluminum ions is dependent on the concentration of DC and aluminum ions. These results provide evidence that aluminum ions could play a role in the synthesis of melanin pathway in acidic condition through catalyzing the DC decarboxylative transformation to yield DHI and influence the melanin structure and properties.
Effect of stacking and redox state on optical absorption spectra of melanins-comparison of theoretical and experimental results
Stark, Klaus B.,Gallas, James M.,Zajac, Gerry W.,Golab, Joseph T.,Gidanian, Shirley,McIntire, Theresa,Farmer, Patrick J.
, p. 1970 - 1977 (2005)
In this work the effect of aggregation and oxidation on the optical absorption of eumelanin oligomeric sheets is investigated by applying quantum mechanics and atomistic simulation studies to a simplified eumelanin structural model that includes 1 -3 sheets of hexameric oligomer sheets. The oligomeric hypothesis is supported by AFM characterizations of synthetic eumelanins, formed by auto-oxidation or electrochemical oxidation of dihydroxyindole (DHI). Comparison of calculated absorption spectra to experimental spectra demonstrates a red shift in absorption with oxidation and stacking of the eumelanin and validates the theoretical results.
Ultra-low temperature oxidation of 5,6-dihydroxyindole: A novel approach to study synthetic melanogenesis
Hatcher, Lanying Q.,Simon, John D.
, p. 608 - 612 (2008)
The detailed structure of melanin remains elusive due to the complexity and insolubility of the pigment. Herein we describe a novel oxidation of 5,6-dihydroxyindole (DHI) as a means to characterize soluble intermediates formed prior to oligomerization. The approach entails the use of a biomimetic copper-peroxo oxidant, at ultra-low temperature (-78°C). DHI oxidized by [LCuII(O2)CuIIL]B(C6F 5)4 (L = 2,6,10-trimethyl-2,6,10-triazaundecane) under argon produces the one electron oxidation product, semiquinone radical, which is spectroscopically observed at -78°C. MS analysis of the reaction mixture reveals the DHI dimer as well as other extensively oxidized DHI units.
Detection of melanochromes by MALDI-TOF mass spectrometry
Kroesche, Christoph,Peter, Martin G.
, p. 3947 - 3952 (1996)
Melanin formation from dopamine, DOPA, DHI, or DHICA, was analyzed by means of matrix-assisted laser desorption mass spectrometry. Oligomers of dihydroxyindoles, i.e. melanochromes, up to DP11 were detected. Increments of 16 mass units provide evidence for the presence of trihydroxyindole units. The results indicate that polymerization of dihydroxyindoles towards melanins occurs by sequential coupling of monomers with concomitant oxygenation.
Evidence for the intermediacy of quinone-methides in the rearrangement of aminochromes to 5,6-dihydroxyindoles
Crescenzi,Costantini,Prota
, p. 6095 - 6096 (1990)
Oxidation of α-methyldopa methyl ester leads to the aminochrome 4, which, at neutral pH, spontaneously rearranges to give a relatively stable quinone-methide identified as 5. This provides the first evidence for the postulated intermediacy of quinone-methides in the conversion of aminochromes to 5,6-dihydroxyindoles.
Chemical, pulse radiolysis and density functional studies of a new, labile 5,6-indolequinone and its semiquinone
Pezzella, Alessandro,Crescenzi, Orlando,Natangelo, Anna,Panzella, Lucia,Napolitano, Alessandra,Navaratnam, Suppiah,Edge, Ruth,Land, Edward J.,Barone, Vincenzo,D'Ischia, Marco
, p. 1595 - 1603 (2007)
The chemical and spectroscopic characterization of 5,6-indolequinones and their semiquinones, key transient intermediates in the oxidative conversion of 5,6-dihydroxyindoles to eumelanin biopolymers, is a most challenging task. In the present paper, we report the characterization of a novel, relatively long-lived 5,6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach. The quinone was obtained by oxidation of 5,6-dihydroxy-3-iodoindole (1a) with o-chloranil in cold ethyl acetate or aqueous buffer: it displayed electronic absorption bands around 400 and 600 nm, was reduced to 1a with Na2S2O4, and reacted with o-phenylenediamine to give small amounts of 3-iodo-1H-pyrrolo[2,3- b]phenazine (2). The semiquinone exhibited absorption maxima at 380 nm (sh) and 520 nm and was detected as the initial species produced by pulse radiolytic oxidation of 1a at pH 7.0. DFT investigations indicated the 6-phenoxyl radical and the N-protonated radical anion as the most stable tautomers for the neutral and anion forms of the semiquinone, respectively. Calculated absorption spectra in water gave bands at 350 (sh) and 500 nm for the neutral form and at 310 and 360 (sh) nm for the anion. Disproportionation of the semiquinone with fast second-order kinetics (2k = 1.1 × 1010 M-1 s -1) gave a chromophore with absorption bands resembling those of chemically generated 1a quinone. Computational analysis predicted 1a quinone to exist in vacuo as the quinone-methide tautomer, displaying low energy transitions at 380 and 710 nm, and in water as the o-quinone, with calculated absorption bands around 400 and 820 nm. A strong participation of a p orbital on the iodine atom in the 360-380 nm electronic transitions of the o-quinone and quinone-methide was highlighted. The satisfactory agreement between computational and experimental electronic absorption data would suggest partitioning of 1a quinone between the o-quinone and quinone-methide tautomers depending on the medium.
Method for preparing 5, 6-dihydroxyindole by using modified ordered mesoporous carbon supported metal catalyst
-
Paragraph 0032; 0039-0041; 0048-0049, (2021/05/01)
The invention belongs to the technical field of organic synthesis, and discloses a method for preparing 5, 6-dihydroxyindole by using a modified ordered mesoporous carbon supported metal catalyst. According to the invention, phenolic resin is taken as a carbon source, polyether F127 is taken as a soft template, an ordered mesoporous carbon loaded metal material is prepared as a catalyst, and high catalytic activity and good stability are shown in the reaction of 3, 4-dimethoxyaniline and ethylene glycol. The catalyst prepared by the method has remarkable effects of avoiding agglomeration and stripping of active components, improving the reaction catalytic activity and prolonging the service life. The raw materials are easy to obtain, the cost is low, the product is white powder, the product purity reaches 98.3%, the ethylene glycol conversion rate in the reaction is close to 60%, the selectivity of the 5, 6-dimethoxy indole reaches 85% or above, and the final yield of the 5, 6-dihydroxy indole can reach 81% or above.
