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IUCrData Jun 2023The study of the oxidation of various proteins necessitates scrutiny of the amino acid sequence. Since me-thio-nine (Met) and tyrosine (Tyr) are easily oxidized,...
The study of the oxidation of various proteins necessitates scrutiny of the amino acid sequence. Since me-thio-nine (Met) and tyrosine (Tyr) are easily oxidized, peptides that contain these amino acids are frequently studied using a variety of oxidation methods, including, but not limited to, pulse radiolysis, electrochemical oxidation, and laser flash photolysis. To date, the oxidation of the Met-Tyr dipeptide is not fully understood. Several investigators have proposed a mechanism of intra-molecular electron transfer between the sulfide radical of Met and the Tyr residue. Our elucidation of the structure and absolute configuration of l-Met-l-Tyr monohydrate, CHNOS·HO (systematic name: (2)-2-{[(2)-2-amino-4-methyl-sulfanyl-butano-yl]amino}-3-(4-hy-droxy-phen-yl)propanoic acid monohydrate) is presented herein and provides information about the zwitterionic nature of the dipeptide. We suspect that the zwitterionic state of the dipeptide and its inter-action within the solvent medium may play a major role in the oxidation of the dipeptide. In the crystal, all the potential donor atoms inter-act strong N-H⋯O, C-H⋯O, O-H⋯S, and O-H⋯O hydrogen bonds.
PubMed: 37936870
DOI: 10.1107/S2414314623005515 -
International Journal of Molecular... Oct 2019Among the radicals (hydroxyl radical (OH), hydrogen atom (H), and solvated electron (e)) that are generated via water radiolysis, OH has been shown to be the main... (Review)
Review
Among the radicals (hydroxyl radical (OH), hydrogen atom (H), and solvated electron (e)) that are generated via water radiolysis, OH has been shown to be the main transient species responsible for radiation damage to DNA via the indirect effect. Reactions of these radicals with DNA-model systems (bases, nucleosides, nucleotides, polynucleotides of defined sequences, single stranded (ss) and double stranded (ds) highly polymeric DNA, nucleohistones) were extensively investigated. The timescale of the reactions of these radicals with DNA-models range from nanoseconds (ns) to microseconds (µs) at ambient temperature and are controlled by diffusion or activation. However, those studies carried out in dilute solutions that model radiation damage to DNA via indirect action do not turn out to be valid in dense biological medium, where solute and water molecules are in close contact (e.g., in cellular environment). In that case, the initial species formed from water radiolysis are two radicals that are ultrashort-lived and charged: the water cation radical (HO) and prethermalized electron. These species are captured by target biomolecules (e.g., DNA, proteins, etc.) in competition with their inherent pathways of proton transfer and relaxation occurring in less than 1 picosecond. In addition, the direct-type effects of radiation, i.e., ionization of macromolecule plus excitations proximate to ionizations, become important. The holes (i.e., unpaired spin or cation radical sites) created by ionization undergo fast spin transfer across DNA subunits. The exploration of the above-mentioned ultrafast processes is crucial to elucidate our understanding of the mechanisms that are involved in causing DNA damage via direct-type effects of radiation. Only recently, investigations of these ultrafast processes have been attempted by studying concentrated solutions of nucleosides/tides under ambient conditions. Recent advancements of laser-driven picosecond electron accelerators have provided an opportunity to address some long-term puzzling questions in the context of direct-type and indirect effects of DNA damage. In this review, we have presented key findings that are important to elucidate mechanisms of complex processes including excess electron-mediated bond breakage and hole transfer, occurring at the single nucleoside/tide level.
Topics: Electrons; Nucleosides; Nucleotides; Phosphates; Pulse Radiolysis; Radiation, Ionizing; Solutions; Sugars; Water
PubMed: 31597345
DOI: 10.3390/ijms20194963 -
The Journal of Physical Chemistry. B May 2023The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and -element separation...
The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and -element separation technologies, two applications that require optimal performance in radiation environments. However, the radiation robustness of HOPO is currently unknown. Here, we employ a combination of time-resolved (electron pulse) and steady-state (alpha self-radiolysis) irradiation techniques to elucidate the basic chemistry of HOPO and its -element complexes in aqueous radiation environments. Chemical kinetics were measured for the reaction of HOPO and its Nd(III) ion complex ([Nd(HOPO)]) with key aqueous radiation-induced radical transients (e, H atom, and OH and NO radicals). The reaction of HOPO with the e is believed to proceed via reduction of the hydroxypyridinone moiety, while transient adduct spectra indicate that reactions with the H atom and OH and NO radicals proceeded by addition to HOPO's hydroxypyridinone rings, potentially allowing for the generation of an extensive suite of addition products. Complementary steady-state Am(III)-HOPO complex ([Am(HOPO)]) irradiations showed the gradual release of Am(III) ions with increasing alpha dose up to 100 kGy, although complete ligand destruction was not observed.
PubMed: 37084416
DOI: 10.1021/acs.jpcb.3c01469 -
Dalton Transactions (Cambridge, England... Jun 2024First-of-a-kind temperature-controlled electron pulse radiolysis experiments facilitated the radiation-induced formation of Am(IV) in concentrated (6.0 M) HNO, and...
First-of-a-kind temperature-controlled electron pulse radiolysis experiments facilitated the radiation-induced formation of Am(IV) in concentrated (6.0 M) HNO, and enabled the derivation of Arrhenius and Eyring activation parameters for instigating the radical reaction between NO˙ and Am(III).
PubMed: 38776119
DOI: 10.1039/d4dt00991f -
Molecules (Basel, Switzerland) Feb 2022Oxidation of methionine (Met) is an important reaction that plays a key role in protein modifications during oxidative stress and aging. The first steps of Met oxidation... (Review)
Review
Oxidation of methionine (Met) is an important reaction that plays a key role in protein modifications during oxidative stress and aging. The first steps of Met oxidation involve the creation of very reactive and short-lived transients. Application of complementary time-resolved radiation and photochemical techniques (pulse radiolysis and laser flash photolysis together with time-resolved CIDNP and ESR techniques) allowed comparing in detail the one-electron oxidation mechanisms initiated either by OH radicals and other one-electron oxidants or the excited triplet state of the sensitizers e.g., 4-,3-carboxybenzophenones. The main purpose of this review is to present various factors that influence the character of the forming intermediates. They are divided into two parts: those inextricably related to the structures of molecules containing Met and those related to external factors. The former include (i) the protection of terminal amine and carboxyl groups, (ii) the location of Met in the peptide molecule, (iii) the character of neighboring amino acid other than Met, (iv) the character of the peptide chain (open vs cyclic), (v) the number of Met residues in peptide and protein, and (vi) the optical isomerism of Met residues. External factors include the type of the oxidant, pH, and concentration of Met-containing compounds in the reaction environment. Particular attention is given to the neighboring group participation, which is an essential parameter controlling one-electron oxidation of Met. Mechanistic aspects of oxidation processes by various one-electron oxidants in various structural and pH environments are summarized and discussed. The importance of these studies for understanding oxidation of Met in real biological systems is also addressed.
Topics: Animals; Electrons; Humans; Methionine; Models, Molecular; Oxidation-Reduction; Peptides; Photochemical Processes; Proteins; Pulse Radiolysis
PubMed: 35164293
DOI: 10.3390/molecules27031028 -
Journal of the American Chemical Society Mar 2023High-energy radiation that is compatible with renewable energy sources enables direct H production from water for fuels; however, the challenge is to convert it as...
High-energy radiation that is compatible with renewable energy sources enables direct H production from water for fuels; however, the challenge is to convert it as efficiently as possible, and the existing strategies have limited success. Herein, we report the use of Zr/Hf-based nanoscale UiO-66 metal-organic frameworks as highly effective and stable radiation sensitizers for purified and natural water splitting under γ-ray irradiation. Scavenging and pulse radiolysis experiments with Monte Carlo simulations show that the combination of 3D arrays of ultrasmall metal-oxo clusters and high porosity affords unprecedented effective scattering between secondary electrons and confined water, generating increased precursors of solvated electrons and excited states of water, which are the main species responsible for H production enhancement. The use of a small quantity (<80 mmol/L) of UiO-66-Hf-OH can achieve a γ-rays-to-hydrogen conversion efficiency exceeding 10% that significantly outperforms Zr-/Hf-oxide nanoparticles and the existing radiolytic H promoters. Our work highlights the feasibility and merit of MOF-assisted radiolytic water splitting and promises a competitive method for creating a green H economy.
PubMed: 36812014
DOI: 10.1021/jacs.3c00547 -
Accounts of Chemical Research May 2022For more than a decade, photoredox catalysis has been demonstrating that when photoactive catalysts are irradiated with visible light, reactions occur under milder,... (Review)
Review
For more than a decade, photoredox catalysis has been demonstrating that when photoactive catalysts are irradiated with visible light, reactions occur under milder, cheaper, and environmentally friendlier conditions. Furthermore, this methodology allows for the activation of abundant chemicals into valuable products through novel mechanisms that are otherwise inaccessible. The photoredox approach, however, has been primarily used for pharmaceutical applications, where its implementation has been highly effective, but typically with a more rudimentary understanding of the mechanisms involved in these transformations. From a global perspective, the manufacture of everyday chemicals by the chemical industry as a whole currently accounts for 10% of total global energy consumption and generates 7% of the world's greenhouse gases annually. In this context, the Bio-Inspired Light-Escalated Chemistry (BioLEC) Energy Frontier Research Center (EFRC) was founded to supercharge the photoredox approach for applications in chemical manufacturing aimed at reducing its energy consumption and emissions burden, by using bioinspired schemes to harvest multiple electrons to drive endothermically uphill chemical reactions. The Center comprises a diverse group of researchers with expertise that includes synthetic chemistry, biophysics, physical chemistry, and engineering. The team works together to gain a deeper understanding of the mechanistic details of photoredox reactions while amplifying the applications of these light-driven methodologies.In this Account, we review some of the major advances in understanding, approach, and applicability made possible by this collaborative Center. Combining sophisticated spectroscopic tools and photophysics tactics with enhanced photoredox reactions has led to the development of novel techniques and reactivities that greatly expand the field and its capabilities. The Account is intended to highlight how the interplay between disciplines can have a major impact and facilitate the advance of the field. For example, techniques such as time-resolved dielectric loss (TRDL) and pulse radiolysis are providing mechanistic insights not previously available. Hypothesis-driven photocatalyst design thus led to broadening of the scope of several existing transformations. Moreover, bioconjugation approaches and the implementation of triplet-triplet annihilation mechanisms created new avenues for the exploration of reactivities. Lastly, our multidisciplinary approach to tackling real-world problems has inspired the development of efficient methods for the depolymerization of lignin and artificial polymers.
Topics: Catalysis; Electrons; Light; Oxidation-Reduction
PubMed: 35471814
DOI: 10.1021/acs.accounts.2c00083 -
ACS Omega Nov 2022Pulse radiolysis with a custom multichannel detection system has been used to measure the kinetics of the radiation chemistry reactions of aqueous solutions of...
Pulse radiolysis with a custom multichannel detection system has been used to measure the kinetics of the radiation chemistry reactions of aqueous solutions of chromium(VI) to 325 °C for the first time. Kinetic traces were measured simultaneously over a range of wavelengths and fit to obtain the associated high-temperature rate coefficients and Arrhenius parameters for the reactions of Cr(VI) + , Cr(VI) + H, and Cr(V) + OH. These kinetic parameters can be used to predict the behavior of toxic Cr(VI) in models of aqueous systems for applications in nuclear technology, industrial wastewater treatment, and chemical dosimetry.
PubMed: 36340103
DOI: 10.1021/acsomega.2c04807 -
The Journal of Chemical Physics Dec 2023Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted...
Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted acid/base, and a sacrificial electron donor (SED). Tertiary amines, in particular triethylamine (TEA) and triethanolamine (TEOA), are ubiquitously deployed in photocatalysis applications as SEDs and are capable of reductively quenching the PS's excited state. Upon oxidation, TEA and TEOA form TEA•+ and TEOA•+ radical cations, respectively, which decay by proton transfer to generate redox non-innocent transient radicals, TEA• and TEOA•, respectively, with redox potentials that allow them to participate in an additional electron transfer step, thus resulting in net one-photon/two-electron donation. However, the properties of the TEA• and TEOA• radicals are not well understood, including their reducing powers and kinetics of electron transfer to catalysts. Herein, we have used both pulse radiolysis and laser flash photolysis to generate TEA• and TEOA• radicals in CH3CN, and combined with UV/Vis transient absorption and time-resolved mid-infrared spectroscopies, we have probed the kinetics of reduction of the well-established CO2 reduction photocatalyst, fac-ReCl(bpy)(CO)3 (bpy = 2,2'-bipyridine), by these radicals [kTEA• = (4.4 ± 0.3) × 109 M-1 s-1 and kTEOA• = (9.3 ± 0.6) × 107 M-1 s-1]. The ∼50× smaller rate constant for TEOA• indicates, that in contrast to a previous assumption, TEA• is a more potent reductant than TEOA• (by ∼0.2 V, as estimated using the Marcus cross relation). This knowledge will aid in the design of photocatalytic systems involving SEDs. We also show that TEA can be a useful radiolytic solvent radical scavenger for pulse radiolysis experiments in CH3CN, effectively converting unwanted oxidizing radicals into useful reducing equivalents in the form of TEA• radicals.
PubMed: 38146832
DOI: 10.1063/5.0180065 -
FEBS Letters Apr 2022Flavohaemoglobins (FlavoHbs) function as nitric oxide dioxygenases, oxidizing nitric oxide with nitrite and shuttling electrons from NAD(P)H via FAD and O . Here, using...
Flavohaemoglobins (FlavoHbs) function as nitric oxide dioxygenases, oxidizing nitric oxide with nitrite and shuttling electrons from NAD(P)H via FAD and O . Here, using pulse radiolysis, we investigate intramolecular electron transfer between FAD and haem b in FlavoHbs. We found that reduction of FlavoHb with hydrated electrons proceeded via two phases: an initial fast phase and a second slower process. Absorbance measured at 600 nm revealed fast flavin reduction followed by a slower decrease corresponding to reoxidation of FAD. The slower process was partially lost in FlavoHbs lacking FAD. These results suggest that the slower phase is attributable to intramolecular electron transfer from FAD to the haem iron. The rate constant in the absence of azole compound (3.3 × 10 s ) was accelerated ~ 10-fold (2.7 × 10 s ) by the binding of econazole, reflecting a conformational change in the open-to-closed transition.
Topics: Anti-Bacterial Agents; Azoles; Candida; Electron Transport; Electrons; Flavin-Adenine Dinucleotide; Heme; Kinetics; NAD; Nitric Oxide; Oxidation-Reduction; Pichia
PubMed: 35253217
DOI: 10.1002/1873-3468.14327