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Acta Biomaterialia Mar 2022Energetic electrons have recently evolved as a powerful tool for crosslinking bio-derived hydrogels without the need for adding potentially hazardous reagents....
Energetic electrons have recently evolved as a powerful tool for crosslinking bio-derived hydrogels without the need for adding potentially hazardous reagents. Application of this approach allows for synthesis of biomimetic collagen-derived networks of highly tunable properties and functionalization. Yet, the underlying reaction kinetics are still not sufficiently established at this point. While hydroxyl radicals are generated by energetic electron-induced hydrolysis of water and play a key role in introducing covalent bonds between network fibers, a detailed mechanistic understanding would significantly increase applicability. We present a comprehensive analysis of central aspects of the reactivity between the hydroxyl radical (OH) and collagen, elastin, glycine (Gly) and l-lysine (Lys). Pulse radiolysis (PR), solid state nuclear magnetic resonance (NMR), ultraviolet-visible absorption spectroscopy (UV/VIS) and electron spray ionization mass spectrometry (ESI-MS) shine light on distinct features of the crosslinking process. These highlight retained protein backbone integrity in collagen and elastin whilst Lys's ability to form several imine bonded Lys-Lys-species suggests striking similarities to crosslinking via lysyl oxidase catalysis in vivo. Thus, energetic electron based crosslinking opens the venue for customized hybrid gels of outstanding biomimicry and -compatibility. STATEMENT OF SIGNIFICANCE: Energetic electron beam treatment constitutes a highly attractive approach to establish chemical bonds between (bio) molecules. Although a convincing number of publications showed the versatility regarding crosslinking of bioderived hydrogels, insights into the underlying chemistry are still unestablished at this point. The present work unravels the mechanistics of energetic electron induced processes in collagen and elastin hydrogels as well as several abundant amino acids in aqueous solution. As key finding we demonstrate, that i) the connection between polymer chains is dominated by amino acid side chain interaction and ii) two single l-lysine molecules form an imine bond between the terminal amino group of one molecule and the delta carbon of the second molecule. We also consider the formation of H-bonds as a second crosslinking pathway. These findings open up for advanced, optionally spatially resolved biomaterials design.
Topics: Biomimetics; Collagen; Cross-Linking Reagents; Electrons; Hydrogels; Lysine
PubMed: 34551331
DOI: 10.1016/j.actbio.2021.09.025 -
The Journal of Physical Chemistry. B Jan 2022The equilibrium between a solvent cavity-localized electron, e, and a dimeric solvent anion, (CHCN), which are the two lowest energy states of the solvated electron in...
The equilibrium between a solvent cavity-localized electron, e, and a dimeric solvent anion, (CHCN), which are the two lowest energy states of the solvated electron in acetonitrile, has been investigated by pulse radiolysis at 233-353 K. The enthalpy and entropy for the e to (CHCN) conversion amount to -11.2 ± 0.3 kcal/mol and -39.3 ± 1.2 cal/(mol K), corresponding to a 0.44 ± 0.35 equilibrium constant at 25 °C. The radiation yield of the solvated electron has been quantified using a Co(II) macrocycle that scavenges electrons with a 1.55 × 10 M s rate constant. The apparent yield increases without saturation over the attainable scavenger concentration range, reaching 2.8 per 100 eV; this value represents the lower limit for the acetonitrile ionization yield in pulse radiolysis. The apparent molar absorption coefficient of (20.8 ± 1.5) × 10 M cm at 1450 nm and 20 °C for the solvated electron and individual vis-near-infrared (NIR) absorption spectra of e and (CHCN) are derived from the data. Variances with previous reports are thoroughly discussed. Collectively, these results resolve several controversies concerning the solvated electron properties in acetonitrile and furnish requisite data for quantitative pulse radiolysis investigations in this commonly used solvent.
Topics: Acetonitriles; Electrons; Pulse Radiolysis; Solvents; Thermodynamics
PubMed: 34931828
DOI: 10.1021/acs.jpcb.1c08946 -
International Journal of Molecular... Jun 2022Hydroxyl radicals (HO) have long been regarded as a major source of cellular damage. The reaction of HO with methionine residues (Met) in peptides and proteins is a...
Hydroxyl radicals (HO) have long been regarded as a major source of cellular damage. The reaction of HO with methionine residues (Met) in peptides and proteins is a complex multistep process. Although the reaction mechanism has been intensively studied, some essential parts remain unsolved. In the present study we examined the reaction of HO generated by ionizing radiation in aqueous solutions under anoxic conditions with two compounds representing the simplest model peptide backbone CHC(O)NHCHXC(O)NHCH, where X = CHCHSCH or CHSCH, i.e., the Met derivative in comparison with the cysteine-methylated derivative. We performed the identification and quantification of transient species by pulse radiolysis and final products by LC-MS and high-resolution MS/MS after γ-radiolysis. The results allowed us to draw for each compound a mechanistic scheme. The fate of the initial one-electron oxidation at the sulfur atom depends on its distance from the peptide backbone and involves transient species of five-membered and/or six-membered ring formations with different heteroatoms present in the backbone as well as quite different rates of deprotonation in forming α-(alkylthio)alkyl radicals.
Topics: Cysteine; Hydroxyl Radical; Methionine; Oxidation-Reduction; Peptides; Pulse Radiolysis; Sulfides; Tandem Mass Spectrometry
PubMed: 35742994
DOI: 10.3390/ijms23126550 -
Chemosphere May 2022The mechanism of high-energy radiation induced degradation of perfluorooctanoate anion (PFOA, CFCOO) was investigated in aqueous solutions. Identification and...
The mechanism of high-energy radiation induced degradation of perfluorooctanoate anion (PFOA, CFCOO) was investigated in aqueous solutions. Identification and quantification of transient species was performed by pulse radiolysis and of final products by gas and ion chromatography, electrochemical method using fluoride ion-selective electrode and ESI-MS after γ-radiolysis. Experimental data were further supported by kinetic simulations and quantum mechanical calculations. Radiation induced degradation of PFOA includes as a primary step one-electron reduction of PFOA by hydrated electrons (e) resulting in formation of [CFCOO]. The rate constants of this reaction were found to be in the range 7.7 × 10-1.3 × 10 Ms for ionic strength of the solutions in the range 0.01-0.1 M and were independent of pH of the solutions. At pH > 11 [CFCOO] tends to defluorination whereas at lower pH undergoes protonation forming [CFCOOH]. A sequence of consecutive reactions involving [CFCOOH] leads to PFOA regeneration what explains a high radiation resistance of PFOA at moderately acidic solutions. A simultaneous presence of oxidizing transient species (OH) in the irradiated system enhanced decomposition of (CF)·COO as well as [CFCOOH]. The key steps in this complex radical mechanism are the reactions of both these radical anions with OH leading to semi-stable products which further undergo consecutive thermal reactions. On the other hand, direct reactions of PFOA with OH and H were found to be relatively slow (7 × 10 and <4 × 10 Ms, respectively) and do not play relevant role in PFOA degradation. Collected for the first time results, such as dependence of selected reaction rate constants and selected products radiation chemical yields on pH as well as finding of several semi-stable products, missing in previous studies, indicate incompleteness of published earlier reaction pathways of PFOA degradation. The presented overall mechanism explains experimental results and verifies previously suggested mechanisms found in the literature.
Topics: Anions; Caprylates; Fluorocarbons; Kinetics; Oxidation-Reduction; Oxidative Stress
PubMed: 35143857
DOI: 10.1016/j.chemosphere.2022.133920 -
Physical Chemistry Chemical Physics :... Aug 2022Reactivity of transients involving Zn in high-temperature water radiolysis has been studied in the temperature range of 25-300 °C. The reduced monovalent zinc species...
Reactivity of transients involving Zn in high-temperature water radiolysis has been studied in the temperature range of 25-300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn ions using pulse radiolysis. The Zn species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, HO and ˙H. We find that the absorption of monovalent zinc is very sensitive to the pH of the medium. An absorption maximum at 306-311 nm is most pronounced at pH 7 and the signal then decreases in acidic media where the reducing electrons are competitively captured by protons. At pH values higher than 7, hydroxo-forms of Zn are created and the maximum of the absorption signal begins to shift to the red spectral region. We find that the optical spectrum of Zn cannot be fully explained in terms of a charge-transfer to solvent (CTTS) process, which was previously proposed. Reaction rates of most of the recombination reactions investigated follow the empirical Arrhenius relationship at temperatures up to 200 °C and have been determined at higher temperatures for the first time. A bimolecular disproportionation reaction of Zn is not observed under the conditions investigated.
PubMed: 35959849
DOI: 10.1039/d2cp02434a -
Science (New York, N.Y.) Oct 2021The radiolysis of water is ubiquitous in nature and plays a critical role in numerous biochemical and technological applications. Although the elementary reaction...
The radiolysis of water is ubiquitous in nature and plays a critical role in numerous biochemical and technological applications. Although the elementary reaction pathways for ionized water have been studied, the short-lived intermediate complex and structural dynamic response after the proton transfer reaction remain poorly understood. Using a liquid-phase ultrafast electron diffraction technique to measure the intermolecular oxygen···oxygen and oxygen···hydrogen bonds, we captured the short-lived radical-cation complex OH(HO) that was formed within 140 femtoseconds through a direct oxygen···oxygen bond contraction and proton transfer, followed by the radical-cation pair dissociation and the subsequent structural relaxation of water within 250 femtoseconds. These measurements provide direct evidence of capturing this metastable radical-cation complex before separation, thereby improving our fundamental understanding of elementary reaction dynamics in ionized liquid water.
PubMed: 34591617
DOI: 10.1126/science.abg3091 -
Proceedings of the National Academy of... May 2023Protonation reactions involving organometallic complexes are ubiquitous in redox chemistry and often result in the generation of reactive metal hydrides. However, some...
Protonation reactions involving organometallic complexes are ubiquitous in redox chemistry and often result in the generation of reactive metal hydrides. However, some organometallic species supported by η-pentamethylcyclopentadienyl (Cp*) ligands have recently been shown to undergo ligand-centered protonation by direct proton transfer from acids or tautomerization of metal hydrides, resulting in the generation of complexes bearing the uncommon η-pentamethylcyclopentadiene (Cp*H) ligand. Here, time-resolved pulse radiolysis (PR) and stopped-flow spectroscopic studies have been applied to examine the kinetics and atomistic details involved in the elementary electron- and proton-transfer steps leading to complexes ligated by Cp*H, using Cp*Rh(bpy) as a molecular model (where bpy is 2,2'-bipyridyl). Stopped-flow measurements coupled with infrared and UV-visible detection reveal that the sole product of initial protonation of Cp*Rh(bpy) is [Cp*Rh(H)(bpy)], an elusive hydride complex that has been spectroscopically and kinetically characterized here. Tautomerization of the hydride leads to the clean formation of [(Cp*H)Rh(bpy)]. Variable-temperature and isotopic labeling experiments further confirm this assignment, providing experimental activation parameters and mechanistic insight into metal-mediated hydride-to-proton tautomerism. Spectroscopic monitoring of the second proton transfer event reveals that both the hydride and related Cp*H complex can be involved in further reactivity, showing that [(Cp*H)Rh] is not necessarily an off-cycle intermediate, but, instead, depending on the strength of the acid used to drive catalysis, an active participant in hydrogen evolution. Identification of the mechanistic roles of the protonated intermediates in the catalysis studied here could inform design of optimized catalytic systems supported by noninnocent cyclopentadienyl-type ligands.
PubMed: 37186841
DOI: 10.1073/pnas.2217189120 -
Molecules (Basel, Switzerland) Dec 2021One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (OH) and azide (N) radicals leads to various primary reactive intermediates. Their optical absorption...
One-electron oxidation of 2-selenouracil (2-SeU) by hydroxyl (OH) and azide (N) radicals leads to various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by the density functional theory (DFT) method. The transient absorption spectra recorded in the reactions of OH with 2-SeU are dominated by an absorption band with an λ = 440 nm, the intensity of which depends on the concentration of 2-SeU and pH. Based on the combination of conductometric and DFT studies, the transient absorption band observed both at low and high concentrations of 2-SeU was assigned to the dimeric 2c-3e Se-Se-bonded radical in neutral form (2). The dimeric radical (2) is formed in the reaction of a selenyl-type radical (6) with 2-SeU, and both radicals are in equilibrium with K = 1.3 × 10 M at pH 4 (below the pK of 2-SeU). Similar equilibrium with K = 4.4 × 10 M was determined for pH 10 (above the pK of 2-SeU), which admittedly involves the same radical (6) but with a dimeric 2c-3e Se-Se bonded radical in anionic form (2). In turn, at the lowest concentration of 2-SeU (0.05 mM) and pH 10, the transient absorption spectrum is dominated by an absorption band with an λ = 390 nm, which was assigned to the OH adduct to the double bond at C5 carbon atom (3) based on DFT calculations. Similar spectral and kinetic features were also observed during the N-induced oxidation of 2-SeU. In principle, our results mostly revealed similarities in one-electron oxidation pathways of 2-SeU and 2-thiouracil (2-TU). The major difference concerns the stability of dimeric radicals with a 2c-3e chalcogen-chalcogen bond in favor of 2-SeU.
Topics: Oxidation-Reduction; Pulse Radiolysis; Sulfur Compounds; Uracil; Water
PubMed: 35011366
DOI: 10.3390/molecules27010133 -
Biomolecules Jun 2023Numerous chemical probes have been used to measure or image oxidative, nitrosative and related stress induced by free radicals in biology and biochemistry. In many... (Review)
Review
Numerous chemical probes have been used to measure or image oxidative, nitrosative and related stress induced by free radicals in biology and biochemistry. In many instances, the chemical pathways involved are reasonably well understood. However, the rate constants for key reactions involved are often not yet characterized, and thus it is difficult to ensure the measurements reflect the flux of oxidant/radical species and are not influenced by competing factors. Key questions frequently unanswered are whether the reagents are used under 'saturating' conditions, how specific probes are for particular radicals or oxidants and the extent of the involvement of competing reactions (e.g., with thiols, ascorbate and other antioxidants). The commonest-used probe for 'reactive oxygen species' in biology actually generates superoxide radicals in producing the measured product in aerobic systems. This review emphasizes the need to understand reaction pathways and in particular to quantify the kinetic parameters of key reactions, as well as measure the intracellular levels and localization of probes, if such reagents are to be used with confidence.
Topics: Reactive Oxygen Species; Oxidation-Reduction; Free Radicals; Superoxides; Oxidants; Antioxidants; Coloring Agents; Oxidative Stress
PubMed: 37509077
DOI: 10.3390/biom13071041 -
Chemosphere Jan 2022The chemical changes caused by electron beam and γ irradiations and the biochemical characteristics of degradation products of a frequently used antibiotic oxacillin...
The chemical changes caused by electron beam and γ irradiations and the biochemical characteristics of degradation products of a frequently used antibiotic oxacillin were investigated and compared with those of cloxacillin by applying pulse radiolysis, chemical and biochemical oxygen demand, total organic carbon content, oxygen uptake rate, toxicity and antibacterial activity measurements. Oxacillin was found to be non-toxic, but poorly biodegradable by the mixed microbial population of the activated sludge of a wastewater treatment plant. Therefore, it can significantly contribute to the spread of β-lactam antibiotic resistant bacteria. However, the products formed by γ-irradiation were more easily biodegradable as they were utilized as nutrient source by the microbes of the activated sludge and the products did not show antibacterial activity. During irradiation treatment of aerated aqueous solutions mainly hydroxyl radicals induce the elimination of antimicrobial activity by making alterations at the bicyclic β-lactam part of these antibiotics. Since the β-lactam part is the same in oxacillin and cloxacillin, the biochemical characteristics of products of the two antibiotics are similar. The attack of hydrated electron takes place on the carbonyl groups. When the irradiation is made under anoxic conditions these reactions may also contribute considerably to alterations at the β-lactam part and thereby to the loss of antibacterial activity.
Topics: Anti-Bacterial Agents; Oxacillin; Radiation, Ionizing; Water Purification; beta-Lactams
PubMed: 34346325
DOI: 10.1016/j.chemosphere.2021.131467