Reactivity of lignin subunits: the influence of dehydrogenation and formation of dimeric structures

Maia, Rosangela Almeida; Ventorim, Gustavo; Batagin‐Neto, Augusto

doi:10.1007/s00894-019-4130-4

Cited by 34 publications

(20 citation statements)

References 42 publications

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“…There are few studies that investigate the reactivity of different types of lignin phenolic –OH groups towards isocyanates using macromolecular models. Most works reported in literature employ models with low molecular weight compounds, as p -coumarol, coniferol and sinapol (lignin precursors), and other compounds similar to lignin building blocks, such as guaycol and syringol [ 22 , 34 , 36 , 37 , 38 ].…”

Section: Resultsmentioning

confidence: 99%

Reactivity of Aliphatic and Phenolic Hydroxyl Groups in Kraft Lignin towards 4,4′ MDI

et al. 2021

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Several efforts have been dedicated to the development of lignin-based polyurethanes (PU) in recent years. The low and heterogeneous reactivity of lignin hydroxyl groups towards diisocyanates, arising from their highly complex chemical structure, limits the application of this biopolymer in PU synthesis. Besides the well-known differences in the reactivity of aliphatic and aromatic hydroxyl groups, experimental work in which the reactivity of both types of hydroxyl, especially the aromatic ones present in syringyl (S-unit), guaiacyl (G-unit), and p-hydroxyphenyl (H-unit) building units are considered and compared, is still lacking in the literature. In this work, the hydroxyl reactivity of two kraft lignin grades towards 4,4′-diphenylmethane diisocyanate (MDI) was investigated. 31P NMR allowed the monitoring of the reactivity of each hydroxyl group in the lignin structure. FTIR spectra revealed the evolution of peaks related to hydroxyl consumption and urethane formation. These results might support new PU developments, including the use of unmodified lignin and the synthesis of MDI-functionalized biopolymers or prepolymers.

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Section: Resultsmentioning

confidence: 99%

Reactivity of Aliphatic and Phenolic Hydroxyl Groups in Kraft Lignin towards 4,4′ MDI

et al. 2021

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“…Glutathione and Trolox geometries were directly optimized in a KS-DFT/B3LYP/6-31G(d,p) considering the 3D geometries available in the PubChem database as input [34]. For a finite system, such as a molecule, once the number of electrons is a discrete variable, there is a dependence of the electronic density (and chemical reactivity) with the removal/inclusion of the electrons in the system that can be understood in terms of how the atomic charge reorganizes, which is defined as the condensed-to-atom Fukui indexes (CAFI) [35,36]. These descriptors define three different types of reactions, towards nucleophiles (f k + ), electrophiles (f k − ), and free radicals (f k 0 ), and are expressed in the following equations:…”

Section: In Silico Antioxidant Studiesmentioning

confidence: 99%

“…The Hirshfeld partition charge method was employed to avoid negative CAFI values [37,38]. The local softness (s k + , s k − , and s k 0 ) was estimated from the CAFI values by multiplying them by the global softness of the compounds [35,36]. DFT-based calculations were conducted with the aid of the Gaussian 09 computational package [39].…”

Section: In Silico Antioxidant Studiesmentioning

confidence: 99%

“…This information is summarized in Figure 4E, which highlights the interesting trend between donor/acceptor properties of samalandrin-I compared to the other compounds (good acceptor and moderate donator). Figure 5 illustrates the CAFI representation (structures in the inset) and local softness of salamandrin-I, glutathione, Trolox, and common reactive oxygen species (ROS) [35,36]. The colored structures in the inset represent the distribution of the CAFI values on the molecules, where red and blue colors represent, respectively, reactive to non-reactive sites (intermediate values are given using an RGB scale).…”

Section: In Silico Antioxidant Studiesmentioning

confidence: 99%

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The Antioxidant Peptide Salamandrin-I: First Bioactive Peptide Identified from Skin Secretion of Salamandra Genus (Salamandra salamandra)

et al. 2020

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Amphibian skin is a multifunctional organ that plays key roles in defense, breathing, and water balance. In this study, skin secretion samples of the fire salamander (Salamandra salamandra) were separated using RP-HPLC and de novo sequenced using MALDI-TOF MS/MS. Next, we used an in silico platform to screen antioxidant molecules in the framework of density functional theory. One of the identified peptides, salamandrin-I, [M + H]+ = 1406.6 Da, was selected for solid-phase synthesis; it showed free radical scavenging activity against DPPH and ABTS radicals. Salamandrin-I did not show antimicrobial activity against Gram-positive and -negative bacteria. In vitro assays using human microglia and red blood cells showed that salamandrin-I has no cytotoxicity up to the concentration of 100 µM. In addition, in vivo toxicity tests on Galleria mellonella larvae resulted in no mortality at 20 and 40 mg/kg. Antioxidant peptides derived from natural sources are increasingly attracting interest. Among several applications, these peptides, such as salamandrin-I, can be used as templates in the design of novel antioxidant molecules that may contribute to devising strategies for more effective control of neurological disease.

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“…A considerable number of DFT studies of lignin model systems have been published, involving aromatic molecules both in the gas-phase (see, for example, Refs. [8][9][10]) and on model metal catalysts (see, for example, Refs. [11][12][13]).…”

Section: Introductionmentioning

confidence: 99%

Lignin Intermediates on Palladium: Insights into Keto‐Enol Tautomerization from Theoretical Modelling

et al. 2020

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It has been suggested in the literature that keto‐to‐enol tautomerization plays a vital role for lignin fragmentation under mild conditions. On the other hand, previous modelling has shown that the adsorbed keto form is more stable than enol on the Pd(111) catalyst. The current density functional theory study of lignin model molecules shows that, in the gas‐phase, keto is more stable than enol, but on the Pd surface, we find enol conformers that are at least as stable as keto. This supports the experimental result that the favourable reaction pathway for lignin depolymerization involves keto‐enol tautomerization. An energy decomposition analysis gives insights concerning the origin of the fine energy balance between the keto and enol forms, where the molecule–surface interaction (−7 eV) and the molecular strain energy (+3 eV) are the main contributors to the adsorption energy.

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Reactivity of lignin subunits: the influence of dehydrogenation and formation of dimeric structures

Cited by 34 publications

References 42 publications

Reactivity of Aliphatic and Phenolic Hydroxyl Groups in Kraft Lignin towards 4,4′ MDI

Reactivity of Aliphatic and Phenolic Hydroxyl Groups in Kraft Lignin towards 4,4′ MDI

The Antioxidant Peptide Salamandrin-I: First Bioactive Peptide Identified from Skin Secretion of Salamandra Genus (Salamandra salamandra)

Lignin Intermediates on Palladium: Insights into Keto‐Enol Tautomerization from Theoretical Modelling

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