ChemInform Abstract: MELANIN. 2. ELECTROCHEMICAL STUDY OF THE OXIDATION OF α‐METHYLDOPA AND 5,6‐DIHYDROXY‐2‐METHYLINDOLE

Young, Thomas E.; Babbitt, Brion W.; WOLFE, L. A.

doi:10.1002/chin.198051078

Cited by 2 publications

(2 citation statements)

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“…According to the literature, experimental barriers (at 298 K) for the intramolecular cyclization of dopaquinone (ΔG ‡ = 62.3 kJ/mol) and dopamine quinone (ΔG ‡ = 64.8 kJ/mol) are very similar. 55,56 These experimental data are reproduced at the SMD-M06L/ 6-31+G(d,p)/LANL2DZ level of theory (ΔG ‡ = 63.3 and 58.9 kJ/mol, respectively; see Scheme 4), which confirms that intrinsic cyclization rates are comparable and relatively rapid in both cases. The rate-determining step of cyclization involves the unprotonated form of the amino group, and therefore the reaction rate is strongly pH dependent.…”

Section: ■ Introductionsupporting

confidence: 58%

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

et al. 2022

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Gold nanoparticles (AuNPs) have found applications in biomedicine as diagnostic tools, but extensive research efforts have been also directed toward their development as more efficient drug delivery agents. The high specific surface area of AuNPs may provide dense loading of molecules like catechols (L-DOPA and dopamine) on nanosurfaces, enabling functionalization strategies for advancing conventional therapy and diagnostic approaches of neurodegenerative diseases. Despite numerous well-described procedures in the literature for preparation of different AuNPs, possible transformation and structural changes of surface functionalization agents have not been considered thoroughly. As a case in point, the catechols L-DOPA and dopamine were selected because of their susceptibility to oxidation, cyclization, and polymerization. To assess the fate of coating and functionalization agents during the preparation of AuNPs or interaction at the nano–bio interface, a combination of spectroscopy, light scattering, and microscopy techniques was used while structural information and reaction mechanism were obtained by NMR in combination with computational tools. The results revealed that the final form of catechol on the AuNP nanosurface depends on the molar ratio of Au used for AuNP preparation. A large molar excess of L-DOPA or dopamine is needed to prepare AuNPs funtionalized with fully reduced catechols. In the case of molar excess of Au, the oxidation of catechols to dopamine quinone and dopaquinone was promoted, and dopaquinone underwent intramolecular cyclization in which additional oxidation products, leukodopachrome, dopachrome, or its tautomer, were formed because of the larger intrinsic acidity of the more nucleophilic amino group in dopaquinone. MD simulations showed that, of the oxidation products, dopachrome had the highest affinity for binding to the AuNPs surface. The results highlight how a more versatile methodological approach, combining experimental and in silico techniques, allows more reliable characterization of binding events at the surface of AuNPs for possible applications in biomedicine.

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Section: ■ Introductionsupporting

confidence: 58%

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

et al. 2022

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“…49 Or they also did by using an authentic sample of 5. 53 Hawley et al observed the oxidation peak due to 5,6-dihydroxy-N-methylindole from the adrenaline pathway. 48 In our case, barely discernible peaks due to 5 ⇀ 6 at −0.026 V were observed at pH 7.7 and 8.0 in DPV.…”

Section: Ece Study Of Dopamine At Long-length Cnt Electrodementioning

confidence: 99%

Electrochemical Study of Dopamine at Electrode Fabricated by Cellulose-Assisted Aqueous Dispersion of Long-Length Carbon Nanotube

Muguruma

Inoue

Inoue³

et al. 2016

J. Phys. Chem. C

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A long-length (hundred micrometers) carbon nanotube is successfully dispersed in aqueous solution with surfactant cellulose while maintaining its length. An electrochemical study of the synthetic pathway of dopamine (DA), dopamine-o-quinone (DAQ), leucodopaminechrome (LDAC), and dopaminechrome (DAC) at the electrode fabricated by the long-length carbon nanotube dispersed solution is presented. The sequence DA ⇌ DAQ ⇀ LDAC ⇌ DAC for the reaction is electron transfer-chemical reaction-electron transfer (ECE)-type, which is a chemical reaction (DAQ ⇀ LDAC, C) interposed between two electron transfer reactions (DA ⇌ DAQ and LDAC ⇌ DAC, E). The salient electrochemical signals due to both DA ⇌ DAQ and LDAC ⇌ DAC can be obtained at the long-length carbon nanotube electrode, unlike other carbon electrodes such as carbon paste, graphene, fullerene, nanofiber, and graphite. The overall reaction is dominated by step DAQ ⇀ LDAC and is sensitive to pH. With cyclic voltammetry in acidic media, the peak current due to LDAC ⇀ DAC disappeared at a higher scan rate because the reaction rate for DAQ ⇀ LDAC was so slow that DAQ was completely consumed in the electron transfer of DAQ ⇀ DA before the chemical reaction of DAQ ⇀ LDAC could go forward. In alkaline media, the peak height due to DAC ⇀ LDAC became as high as that due to DA ⇀ DAQ because the DAQ ⇀ LDAC rate became fast enough that a sufficient amount of LDAC was generated for the subsequent reaction of LDAC ⇀ DAC. Concomitantly, the reaction DAQ + LDAC ⇌ DA + DAC was generated. Quantitative and selective detection of dopamine based on the signal due to LDAC ⇀ DAC is possible just as in the conventional strategy of direct oxidation of dopamine (DA ⇀ DAQ).

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ChemInform Abstract: MELANIN. 2. ELECTROCHEMICAL STUDY OF THE OXIDATION OF α‐METHYLDOPA AND 5,6‐DIHYDROXY‐2‐METHYLINDOLE

Abstract: α‐Methyldopa (Ia) und Dopa (Ib) werden der elektrochemischen Oxidation unterworfen und über zahlreiche diskutierte Zwischenstufen wie (II) und (III) in die Dihydroxy‐indole (IV) sowie melanoide Pigmente übergeführt.

Cited by 2 publications

References 1 publication

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

Transformation of L-DOPA and Dopamine on the Surface of Gold Nanoparticles: An NMR and Computational Study

Electrochemical Study of Dopamine at Electrode Fabricated by Cellulose-Assisted Aqueous Dispersion of Long-Length Carbon Nanotube

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