Lignin peroxidase-catalyzed oxidation of nonphenolic trimeric lignin model compounds: fragmentation reactions in the intermediate radical cations

The H(2)O(2)-promoted oxidations of the two nonphenolic beta-O-aryl lignin model trimers 1 and 2, catalyzed by lignin peroxidase (LiP) at pH = 3.5, have been studied. The results have been compared with those obtained in the oxidation of 1 and 2 with the genuine one-electron oxidant potassium 12-tungstocobalt(III)ate. These models present a different substitution pattern of the three aromatic rings, and by one-electron oxidation, they form radical cations with the positive charge, which is localized in the dialkoxylated ring as also evidenced by a pulse radiolysis study. Both the oxidations with the enzymatic and with the chemical systems lead to the formation of products deriving from the cleavage of C-C and C-H bonds in a beta position with respect to the radical cation with the charge residing in the dialkoxylated ring (3,4-dimethoxybenzaldehyde (5) and a trimeric ketone 6 in the oxidation of 1 and a dimeric aldehyde 8 and a trimeric ketone 9 in the oxidation of 2). These products are accompanied by a dimeric aldehyde 7 in the oxidation of 1 and 4-methoxybenzaldehyde (10) in the oxidation of 2. The unexpected formation of these two products has been explained by suggesting that 1.+ and 2.+ can also undergo an intramolecular electron transfer leading to the radical cations 1a.+ and 2a.+ with the charge residing in a monoalkoxylated ring. The fast cleavage of a C-C bond beta to this ring, leading to 7 from 1.+ and to 10 from 2.+, is the driving force of the endoergonic electron transfer. A kinetic steady-state investigation of the LiP-catalyzed oxidation of the trimer 2, the dimeric model 1-(3,4-dimethoxyphenyl)-2-phenoxy-1-ethanol (4), and 3,4-dimethoxybenzyl alcohol (3) has indicated that the turnover number (k(cat)) and the affinity for the enzyme decrease significantly by increasing the size of the model compound. In contrast, the three substrates exhibited a very similar reactivity toward a chemical oxidant [Co(III)W]. This suggests a size-dependent interaction of the enzyme with the substrate which may influence the efficiency of the electron transfer.     

Generation and reactivity of ketyl radicals with lignin related structures. On the importance of the ketyl pathway in the photoyellowing of lignin containing pulps and papers

[reaction: see text] Ketyl radicals with lignin related structures have been generated by means of radiation chemical and photochemical techniques. In the former studies ketyl radicals are produced by reaction of alpha-carbonyl-beta-aryl ether lignin models with the solvated electron produced by pulse radiolysis of an aqueous solution at pH 6.0. The UV-vis spectra of ketyl radicals are characterized by three main absorption bands. The shape and position of these bands slightly change when the spectra are recorded in alkaline solution (pH 11.0) being now assigned to the ketyl radical anions and a pKa = 9.5 is determined for the 1-(3,4,5-trimethoxyphenyl)-2-phenoxyethanol-1-yl radical. Decay rates of ketyl radicals are found to be dose dependent and, at low doses, lie in the range (1.7-2.7) x 10(3) s(-1). In the presence of oxygen a fast decay of the ketyl radicals is observed (k2 = 1.8-2.7 x 10(9) M(-1) s(-1)) that is accompanied by the formation of stable products, i.e., the starting ketones. In the photochemical studies ketyl radicals have been produced by charge-transfer (CT) photoactivation of the electron donor-acceptor salts of methyl viologen (MV2+) with alpha-hydroxy-alpha-phenoxymethyl-aryl acetates. This process leads to the instantaneous formation of the reduced acceptor (methyl viologen radical cation, MV+*), as is clearly shown in a laser flash photolysis experiment by the two absorption bands centered at 390 and 605 nm, and an acyloxyl radical [ArC(CO2*))(OH)CH2(OC6H5)], which undergoes a very fast decarboxylation with formation of the ketyl radicals. Steady-state photoirradiation of the CT ion pairs indicates that 1-aryl-2-phenoxyethanones are formed as primary photoproducts by oxidation of ketyl radicals by MV2+ (under argon) or by molecular oxygen. Small amounts of acetophenones are formed by further photolysis of 1-aryl-2-phenoxyethanones and not by beta-fragmentation of the ketyl radicals. The high reactivity of ketyl radicals with oxygen coupled with the low rates of beta-fragmentation of the same species have an important bearing in the context of the photoyellowing of lignin containing pulps and papers.     

Study of hadronic events inpp collisions at\sqrt s = 62GeV and comparison with hadronic events ine + e − collisions

We present an analysis of minimum bias events from proton-proton collisions at \(\sqrt s = 7GeV\) in the CERN ISR. We remove the effects of both the leading protons and compare theB=0 mesonic residue of the events to the hadronic events of similar energy produced ine ⁺ e ^? collisions. This comparison is presented in terms of the standard jet-type analyses involving quantities such as sphericity and aplanarity. We find significant differences between these data and the data frome ⁺ e ^? annihilations. The data of this experiment are consistent with the predictions of a longitudinal phase space model.     

A Supramolecular Approach to Antimicrobial Surfaces

In this paper, we report on the preparation of Imidazole-functionalized glass surfaces, demonstrating the ability of a dinuclear Cu(II) complex of a macrocyclic ligand to give a “cascade” interaction with the deprotonated forms of grafted imidazole moieties. In this way, we realized a prototypal example of an antimicrobial surface based on a supramolecular approach, obtaining a neat microbicidal effect using low amounts of the described copper complex.     

K18- and CAG-hACE2 Transgenic Mouse Models and SARS-CoV-2: Implications for Neurodegeneration Research

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a global pandemic that might lead to very serious consequences. Notably, mental status change, brain confusion, and smell and taste disorders along with neurological complaints have been reported in patients infected with SARS-CoV-2. Furthermore, human brain tissue autopsies from COVID-19 patients show the presence of SARS-CoV-2 neuroinvasion, which correlates with the manifestation of meningitis, encephalitis, leukocyte infiltration, and neuronal damage. The olfactory mucosa has been suggested as a way of entry into the brain. SARS-CoV-2 infection is also known to provoke a hyper-inflammatory reaction with an exponential increase in the production of pro-inflammatory cytokines leading to systemic responses, even in the absence of direct infection of brain cells. Angiotensin-converting enzyme 2 (ACE2), the entry receptor of SARS-CoV-2, has been extensively demonstrated to be present in the periphery, neurons, and glial cells in different brain regions. To dissect the details of neurological complications and develop therapies helping COVID-19 survivors regain pre-infection quality of life, the development of robust clinical models is highly warranted. Several human angiotensin-converting enzyme 2 (hACE2) transgenic mouse models have been developed and used for antiviral drug screening and vaccine development, as well as for better understanding of the molecular pathogenetic mechanisms of SARS-CoV-2 infection. In this review, we summarize recent results from the studies involving two such mouse models, namely K18- and CAG-hACE2 transgenics, to evaluate the direct and indirect impact of SARS-CoV-2 infection on the central nervous system.     

Ultrastructural Damages to H1N1 Influenza Virus Caused by Vapor Essential Oils

Influenza viruses are transmitted from human to human via airborne droplets and can be transferred through contaminated environmental surfaces. Some works have demonstrated the efficacy of essential oils (EOs) as antimicrobial and antiviral agents, but most of them examined the liquid phases, which are generally toxic for oral applications. In our study, we describe the antiviral activity of Citrus bergamia, Melaleuca alternifolia, Illicium verum and Eucalyptus globulus vapor EOs against influenza virus type A. In the vapor phase, C. bergamia and M. alternifolia strongly reduced viral cytopathic effect without exerting any cytotoxicity. The E. globulus vapor EO reduced viral infection by 78% with no cytotoxicity, while I. verum was not effective. Furthermore, we characterized the EOs and their vapor phase by the head-space gas chromatography–mass spectrometry technique, observing that the major component found in each liquid EO is the same one of the corresponding vapor phases, with the exception of M. alternifolia. To deepen the mechanism of action, the morphological integrity of virus particles was checked by negative staining transmission electron microscopy, showing that they interfere with the lipid bilayer of the viral envelope, leading to the decomposition of membranes. We speculated that the most abundant components of the vapor EOs might directly interfere with influenza virus envelope structures or mask viral structures important for early steps of viral infection.     

Waste Cleaning Waste: Combining Alginate with Biowaste-Derived Substances in Hydrogels and Films for Water Cleanup

Biowaste-derived substances isolated from green compost (BBS-GC) are environmentally friendly reactants similar to humic substances, which contain multiple functionalities, that are suitable for adsorbing different kinds of pollutants in wastewater. Herein, sodium alginate (derived from brown algae) cross-linked with both Ca²⁺ ions and BBS-GC in the form of hydrogels and dried films are proposed as green, easy-to-form, and handleable materials for tertiary water treatments. The results show that both hydrogels and films are mechanically stable and can effectively remove differently charged dyes through an adsorption mechanism that can be described by the Freundlich model. BBS-GC-containing gels always performed better than samples prepared without BBS-GC, revealing that such unconventional materials can integrate waste valorization and water decontamination, potentially providing social and environmental benefits.     

Gadolinium‐Decorated Silica Microspheres as Redox‐Responsive MRI Probes for Applications in Cell Therapy Follow‐Up

The redox microenvironment within a cell graft can be considered as an indicator to assess whether the graft is metabolically active or hypoxic. We present a redox‐responsive MRI probe based on porous silica microparticles whose surface has been decorated with a Gd‐chelate through a disulphide bridge. Such microparticles are designed to be interspersed with therapeutic cells within a biocompatible hydrogel. The onset of reducing conditions within the hydrogel is paralleled by an increased clearance of Gd, that can be detected by MRI.     

Lanthanide Identity Governs Guest-Induced Dimerization in LnIII[15-MC N(L-pheHA)-5])3+ Metallacrowns

Series of lanthanide-containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (Ln^III[15-MC _N(L-pheHA)-5])³⁺ metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host-guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host-guest-host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides).