Introduction

Kutty, Prameela Kannan; Kutty, Methil Kannan

doi:10.1007/978-981-33-6408-0_1

Cited by 1 publication

(2 citation statements)

References 57 publications

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“…[8] , for the Gibbs translational free energy correction T•Str, the translational entropy is calculated using the free solvent volume of water with an intermediate value of 7 for the Cfree constant. For the dimers and water we assume standard conditions (aX = 1), while for oxygen we assume an activity of 2.5e-4, which corresponds to the solubility of oxygen in water at 298 K (8 mg•L -1 ) [9] . The latter term is included as RT•ln(aX) in G(O2).…”

Section: Si22 Calculation Of Free Energymentioning

confidence: 99%

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Stability and Optical Absorption of a Comprehensive Virtual Library of Minimal Eumelanin Oligomer Models

Wang¹,

Blancafort

2021

Preprint

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Eumelanin is the black biopolymer responsible for photoprotection in living organisms. Lack of knowledge of the atomic-level structure limits understanding of its function and exploitation of its potential in material science. To overcome these limitations, we present a systematic density functional theory study of the stability and optical properties of a library of 830 dimers of 5,6-dihydroxyindole (DHI), which are minimal models of eumelanin oligomers. Our aim is to understand the principles that govern the formation of DHI oligomers, relate the optical properties of the dimers with their stability, and establish their possible role in the photophysics of the biopolymer. From the structural point of view, we find a preference for oxidized over reduced and cyclic over linear structures, which speaks in favor of polycyclic graphite-like structures for the larger oligomers. We present an electrocyclization mechanism leading to the cyclic structures. We also find that besides the widely considered quinone and quinone methide oxidation patterns where two heteroatoms per DHI fragment are oxidized, dimers with one or three oxidized sites per fragment and an interfragment double bond are also stable and may be present in eumelanin. As far as the optical properties are concerned, some oxidized dimers combine relative stability with absorption energies as low as 1.3 eV. Such fragments may be present as substructures in the naturally found oligomers and might have a relevant contribution to the absorption spectrum of the biopolymer. In addition to these insights into the struc-tural and optical properties of the oligomers, we introduce a new classification scheme and a representative set of 53 dimers combining thermodynamic stability with chemical diversity.<br>

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Section: Si22 Calculation Of Free Energymentioning

confidence: 99%

“…[8] Melanin oligomers contain 4 to 8 DHI/DHICA units. [9] DHI and DHICA are prone to oxidation, ie elimination of the pyrrolic or phenolic hydrogen atoms. Therefore, the DHI/DHICA fragments can also be present in quinone or quinone methide form, where two sites are oxidized on the same fragment (see Scheme 1a).…”

Section: Introductionmentioning

confidence: 99%

Stability and Optical Absorption of a Comprehensive Virtual Library of Minimal Eumelanin Oligomer Models

Wang¹,

Blancafort

2021

Preprint

View full text Add to dashboard Cite

show abstract

Introduction

Cited by 1 publication

References 57 publications

Stability and Optical Absorption of a Comprehensive Virtual Library of Minimal Eumelanin Oligomer Models

Stability and Optical Absorption of a Comprehensive Virtual Library of Minimal Eumelanin Oligomer Models

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