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1.
Science ; 372(6540): 398-403, 2021 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-33888639

RESUMO

The "magic methyl" effect describes the change in potency, selectivity, and/or metabolic stability of a drug candidate associated with addition of a single methyl group. We report a synthetic method that enables direct methylation of C(sp3)-H bonds in diverse drug-like molecules and pharmaceutical building blocks. Visible light-initiated triplet energy transfer promotes homolysis of the O-O bond in di-tert-butyl or dicumyl peroxide under mild conditions. The resulting alkoxyl radicals undergo divergent reactivity, either hydrogen-atom transfer from a substrate C-H bond or generation of a methyl radical via ß-methyl scission. The relative rates of these steps may be tuned by varying the reaction conditions or peroxide substituents to optimize the yield of methylated product arising from nickel-mediated cross-coupling of substrate and methyl radicals.


Assuntos
Compostos de Benzil/química , Carbono/química , Radicais Livres/química , Hidrogênio/química , Níquel/química , Peróxidos/química , Transferência de Energia , Ligação de Hidrogênio , Luz , Metilação , Oxigênio/química
2.
Photochem Photobiol Sci ; 20(1): 183-188, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33721239

RESUMO

A hypothesis is proposed to explain the increased detrimental effect of COVID-19 for Black, Asian and Minority Ethnic (BAME) men and women compared to Caucasian individuals. This is based on the differing photochemistry of phaeomelanin in fair skin and eumelanin in dark/black skin. It is suggested that a range of reactive oxygen species, including, singlet oxygen and the superoxide radical anion, derived via direct photolysis of phaeomelanin, may escape the melanocyte and cause subsequent damage to the SARS-CoV-2 virus. It is further suggested that (large) carbon and sulphur peroxy radicals, from oxygen addition to radicals formed by carbon-sulphur bond cleavage, may assist via damage to the cell membranes. It is also speculated that light absorption by phaeomelanin and the subsequent C-S bond cleavage, leads to release of pre-absorbed reactive oxygen species, such as singlet oxygen and free radicals, which may also contribute to an enhanced protective effect for fair-skinned people.


Assuntos
/patologia , Grupos Étnicos , Processos Fotoquímicos , /etnologia , Carbono/química , Feminino , Radicais Livres/química , Humanos , Luz , Masculino , Melaninas/química , Fotólise , Oxigênio Singlete/química , Oxigênio Singlete/metabolismo , Pele/metabolismo , Enxofre/química , Superóxidos/química , Superóxidos/metabolismo
3.
Molecules ; 26(5)2021 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-33669016

RESUMO

The search for new biomedical applications of dendrimers has promoted the synthesis of new radical-based molecules. Specifically, obtaining radical dendrimers has opened the door to their use in various fields such as magnetic resonance imaging, as anti-tumor or antioxidant agents, or the possibility of developing new types of devices based on the paramagnetic properties of organic radicals. Herein, we present a mini review of radical dendrimers based on polyphosphorhydrazone, a new type of macromolecule with which, thanks to their versatility, new metal-free contrast agents are being obtained, among other possible applications.


Assuntos
Dendrímeros/química , Hidrazonas/química , Organofosfonatos/química , Polímeros/química , Dendrímeros/síntese química , Radicais Livres/síntese química , Radicais Livres/química , Humanos , Hidrazonas/síntese química , Estrutura Molecular , Organofosfonatos/síntese química , Polímeros/síntese química
4.
Molecules ; 26(5)2021 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-33673557

RESUMO

A theoretical approach is developed for the description of all possible recombination pathways in the ozone forming reaction, without neglecting any process a priori, and without decoupling the individual pathways one from another. These pathways become physically distinct when a rare isotope of oxygen is introduced, such as 18O, which represents a sensitive probe of the ozone forming reaction. Each isotopologue of O3 contains two types of physically distinct entrance channels and two types of physically distinct product wells, creating four recombination pathways. Calculations are done for singly and doubly substituted isotopologues of ozone, eight rate coefficients total. Two pathways for the formation of asymmetric ozone isotopomer exhibit rather different rate coefficients, indicating large isotope effect driven by ΔZPE-difference. Rate coefficient for the formation of symmetric isotopomer of ozone (third pathway) is found to be in between of those two, while the rate of insertion pathway is smaller by two orders of magnitude. These trends are in good agreement with experiments, for both singly and doubly substituted ozone. The total formation rates for asymmetric isotopomers are found to be somewhat larger than those for symmetric isotopomers, but not as much as in the experiment. Overall, the distribution of lifetimes is found to be very similar for the metastable states in symmetric and asymmetric ozone isotopomers.


Assuntos
Marcação por Isótopo/métodos , Isótopos de Oxigênio/química , Ozônio/química , Radicais Livres/química , Cinética , Modelos Químicos , Conformação Molecular
5.
Int J Mol Sci ; 22(4)2021 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-33546504

RESUMO

Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it.


Assuntos
Radicais Livres/química , Modelos Químicos , Espectroscopia de Ressonância de Spin Eletrônica , Halogênios/química , Estrutura Molecular , Dióxido de Nitrogênio/química
6.
Phys Chem Chem Phys ; 23(6): 3761-3770, 2021 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-33538741

RESUMO

Tetrazolium salts (TZs) are pervasively utilized as precursors in the dye industry, colorimetric probes in enzyme assays and for exploring nanomaterial toxicity, but its own toxicity is not investigated enough so far. Using femtosecond transient absorption spectroscopy, nanosecond pulse radiolysis (ns-PRL), western blotting and UV-vis absorption spectroscopy, here we characterized a neutral tetrazolinyl radical (with the same maximum absorption at 420 nm and different lifetimes of 5.0 and 9.0 µs for two selected TZs), the key intermediate of TZs reduction, and noticed TZs-formazan production under UV light irradiation accompanied by 41% increase in the cross-linking of lysozyme (Lyso, model protein) compared to TZs-free sample, which uncovered the photoenhanced oxidation of TZs towards Lyso. The ns-PRL in a reductive atmosphere simulated the electron/proton donors of amino acid residues in Lyso upon photoexcitation and revealed the reduction mechanism of TZs, as that first followed one-electron-transfer and then probably proton-coupled electron transfer. This is the first time to report on the photoenhanced oxidation mechanism of TZs, which would provide new insights into the applications of TZs in cell biology, "click" chemistry and nanotoxicology.


Assuntos
Aminoácidos/química , Muramidase/química , Sais de Tetrazólio/química , Aminoácidos/efeitos da radiação , Animais , Galinhas , Radicais Livres/química , Muramidase/efeitos da radiação , Oxirredução , Sais de Tetrazólio/efeitos da radiação , Raios Ultravioleta
7.
J Food Sci ; 86(3): 824-833, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33586780

RESUMO

A chickpea protein isolate (CPI) was oxidized using peroxyl radicals derived from 2,2'-azobis (2-amidopropane) dihydrochloride (AAPH), and the structural and foaming properties of the oxidized CPI were evaluated. The oxidation degree of protein was determined by measuring carbonyl content, dimer tyrosine content, free thiol content, and total thiol content. The structural changes of oxidized protein were evaluated by surface hydrophobicity, endogenous fluorescence intensity, Fourier transform infrared spectroscopy, SDS-PAGE, and amino acid content changes. Compared with the control group (0 mmol/L AAPH), moderate oxidation (0.04 mmol/L AAPH) led to the formation of a soluble protein with flexibility, which could improve the foaming properties of the protein (foaming capacity and stability increased by 25.50% and 6.38%, respectively). Over-oxidized (25 mmol/L AAPH) protein exhibited improved foaming capability, but its foam stability was reduced owing to the formation of insoluble aggregates. The results indicate that oxidation can change protein conformation, and the protein structure can affect the foamability of the CPI. PRACTICAL APPLICATION: CPI is a protein supplement food. Protein oxidation can occur during processing and storage, thereby affecting protein function. In this study, we evaluated how peroxy free radicals affect the structure, solubility and foaming properties of CPI, and clarified the mechanism between them. It has been found that peroxy free radicals can accelerate the oxidation of proteins and have a significant effect on foaming. Therefore, the degree of oxidation should be controlled to improve the quality of CPI.


Assuntos
Cicer/química , Peróxidos/química , Proteínas de Plantas/química , Radicais Livres/química , Interações Hidrofóbicas e Hidrofílicas , Estrutura Molecular , Oxirredução , Proteínas de Plantas/isolamento & purificação , Conformação Proteica , Solubilidade , Compostos de Sulfidrila/análise , Tirosina/análise
8.
Molecules ; 26(3)2021 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-33535612

RESUMO

Sonochemistry can be broadly defined as the science of chemical and physical transformations produced under the influence of sound. The use of sound energy is rather a young branch of chemistry and does not have the clear definitive rules of other, more established, divisions such as those in cycloaddition reactions or photochemistry. Nevertheless, there are a few guidelines which can help to predict what is going to happen when a reaction mixture is submitted to ultrasonic irradiation. Jean-Louis Luche, formulated some ideas of the mechanistic pathways involved in sonochemistry more than 30 years ago. He introduced the idea of "true" and "false" sonochemical reactions both of which are the result of acoustic cavitation. The difference was that the former involved a free radical component whereas only mechanical effects played a role the latter. The authors of this paper were scientific collaborators and friends of Jean-Louis Luche during those early years and had the chance to discuss and work with him on the mechanisms of sonochemistry. In this paper we will review the original rules (laws) as predicted by Jean-Louis Luche and how they have been further developed and extended in recent years.


Assuntos
Química/instrumentação , Radicais Livres/química , Radicais Livres/metabolismo , Marcadores de Spin , Ultrassom/instrumentação , Ultrassom/métodos , Humanos
9.
Food Chem ; 349: 129166, 2021 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-33550019

RESUMO

Grafting copolymerization of phenolic acids onto polysaccharides is an important strategy to improve their biological activities. In this study, ferulic acid (FA)-grafted carboxylic curdlan conjugates, namely, Cur-8-g-FA, Cur-24-g-FA, and Cur-48-g-FA, were synthesized by free radical-induced grafting. Results showed that FA was covalently grafted onto carboxylic curdlans via ester bonds. The grafting ratios of Cur-8-g-FA, Cur-24-g-FA, and Cur-48-g-FA were 223.03 ± 12.63, 115.63 ± 5.96, and 152.30 ± 4.57 mg FA/g, respectively, which were related with the carboxylate contents, molecular weights, and chain conformations of carboxylic curdlans. Compared with carboxylic curdlans, the FA-grafted carboxylic curdlan conjugates had lower thermal stability, molecular weight, and rheological property and looser surface morphology but had more prominent antioxidant benefits in vitro, which were proportional to their grafting ratios. Moreover, good storage stability against chemical degradation was exhibited by the ß-carotene in Pickering emulsions stabilized by Cur-8-g-FA with a high grafting ratio and molecular weight.


Assuntos
Antioxidantes/química , Ácidos Carboxílicos/química , Ácidos Cumáricos/química , beta Caroteno/química , beta-Glucanas/química , Emulsões/química , Radicais Livres/química , Hidroxibenzoatos , Peso Molecular
10.
Int J Mol Sci ; 22(2)2021 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-33435233

RESUMO

The azide radical (N3●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N3● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N3● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO4●-, CO3●-) and Tl2+ ions with the reduction potentials higher, and one radical (SCN)2●- with the reduction potential slightly lower than the reduction potential of N3● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N3● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N3● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N3● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N3● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)●+, radicals (7-R-3-MeQ)● and N3● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning's aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.


Assuntos
Quinoxalinas/química , Azidas/química , Elétrons , Radicais Livres/química , Água/química
11.
Carbohydr Polym ; 254: 117399, 2021 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-33357889

RESUMO

Starch based materials are attractive bio-based alternative to fully synthetic polymers. Native starch has however limited thermoprocessability and properties and must be modified. In order to improve the properties of starch-graft-poly(butyl-acrylate-co-styrene) copolymers via a process as green as possible, we report herein a new method for the dual functionalization of the polysaccharide via a one pot one step reaction in aqueous medium combining free radical polymerizations and ring-opening chemistry. Poly(butyl acrylate) or poly(butyl acrylate-co-styrene) (ca. 60 000 g/mol) and oligo(ε-caprolactone) were grafted on starch with a grafting percentage up to 75 %. The copolymers show two glass transition temperatures: one around 55-60 °C related to starch and a second attributed to the grafted vinyl polymers, from -46 °C to 20 °C depending on butyl acrylate/styrene ratio. The resulting dual functionalized materials exhibit excellent mechanical properties, with elongation at break in the range 20-210 %, while single functionalized starch shows less than 5 %.


Assuntos
Polimerização , Amido/química , Água/química , Acrilatos/química , Resinas Acrílicas/química , Caproatos/química , Radicais Livres/química , Lactonas/química , Poliestirenos/química , Temperatura de Transição , Compostos de Vinila/química
12.
Food Chem ; 339: 128047, 2021 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-32949916

RESUMO

The antioxidative activity of natural products has commonly been studied by free radical scavenging methods. However, the mechanisms by which antioxidation is explored by free radical scavenging methods remain largely unknown. This study analyzed the composition of walnut-derived pentapeptides PW5 with potential biological activity and its oxidation reaction products in 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) test by nuclear magnetic resonance (NMR) spectroscopy. The amino acid sequence of PW5 peptide successfully characterized as Proline-Proline-Lysine-Asparagine-Tryptophan exhibited significant antioxidant activity with lower IC50 value (0.2210 ± 0.0032 mM) compared to glutathione (GSH, 0.2567 ± 0.0023 mM, p < 0.001). Furthermore, we found that the tryptophan residue was the only residue in PW5 with obvious alteration after treatment with ABTS free radicals, which was linked to its potential antioxidant properties. These findings revealed how NMR-characterized structures and oxidation reaction products may be used to explore the antioxidative mechanisms of food-derived peptides as well as other natural products.


Assuntos
Antioxidantes/química , Juglans/química , Peptídeos/química , Sequência de Aminoácidos , Depuradores de Radicais Livres/química , Radicais Livres/química , Espectroscopia de Ressonância Magnética , Nozes/química , Oxirredução , Proteínas de Plantas/química
13.
Nat Chem ; 13(1): 24-32, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33349693

RESUMO

Oxidative cyclizations create many unique chemical structures that are characteristic of biologically active natural products. Many of these reactions are catalysed by 'non-canonical' or 'thwarted' iron oxygenases and appear to involve long-lived radicals. Mimicking these biosynthetic transformations with chemical equivalents has been a long-standing goal of synthetic chemists but the fleeting nature of radicals, particularly under oxidizing conditions, makes this challenging. Here we use redox-neutral photocatalysis to generate radicals that are likely to be involved in the biosynthesis of lignan natural products. We present the total syntheses of highly oxidized dibenzocyclooctadienes, which feature densely fused, polycyclic frameworks that originate from a common radical progenitor. We show that multiple factors control the fate of the proposed biosynthetic radicals, as they select between 5- or 11-membered ring cyclizations and a number of different terminating events. Our syntheses create new opportunities to explore the medicinal properties of these natural products, while shedding light on their biosynthetic origin.


Assuntos
Produtos Biológicos/química , Radicais Livres/química , Lignanas/biossíntese , Lignanas/química , Produtos Biológicos/síntese química , Materiais Biomiméticos/química , Materiais Biomiméticos/metabolismo , Catálise , Cristalografia por Raios X , Ciclização , Ciclo-Octanos/química , Ciclo-Octanos/metabolismo , Irídio/química , Luz , Conformação Molecular , Oxirredução , Rutênio/química , Schisandraceae/metabolismo , Estereoisomerismo
14.
Methods Mol Biol ; 2202: 137-148, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-32857353

RESUMO

Electron paramagnetic resonance (EPR) spectroscopy is an established method for the measurement of free radicals. Solar radiation is essential for human life as it stimulates vitamin D synthesis and well-being. However, an excessive dose of solar radiation leads to the formation of free radicals. Here, we describe an EPR method for measuring the amount of radicals induced by UVA irradiation in excised skin. For the first time, a wavelength stable UVA LED (365 nm) was used. The method allows the quantitative determination of radicals in skin before, during, and after UVA irradiation. A dose-dependent radical production could be demonstrated, independent of the yielded power.


Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Espécies Reativas de Oxigênio/análise , Pele/metabolismo , Óxidos N-Cíclicos/química , Radicais Livres/química , Humanos , Marcadores de Spin , Raios Ultravioleta
15.
Food Chem ; 334: 127578, 2021 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-32721836

RESUMO

Quality deterioration of mayonnaise is caused by lipid oxidation, mediated by radical reactions. Assessment of radicals would enable early lipid oxidation assessment and generate mechanistic insights. To monitor short-lived lipid-radicals, N-tert-butyl-α-phenylnitrone (PBN), a spin-trap, is commonly used. In this study, the fate of PBN-adducts and their impact on lipid oxidation mechanisms in mayonnaise were investigated. The main signals detected by Electron Spin Resonance (ESR) were attributed to L-radicals attached to 2-methyl-2-nitrosopropane (MNP), one of three degradation products of the PBN-peroxy-adduct. The second degradation product, benzaldehyde, was detected with Nuclear Magnetic Resonance (1H NMR), in line with MNP-L adduct generation. For the third class of degradation products, LO-radicals, their scission products were detected with 1H NMR and indicated that LO-radicals have a major impact on downstream oxidation pathways. This precludes mechanistical studies in presence of PBN. Degradation products of PBN-adducts can, however, be used for early assessment of antioxidants efficacy in oil-in-water emulsions.


Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Análise de Alimentos , Lipídeos/química , Detecção de Spin/métodos , Óxidos N-Cíclicos , Radicais Livres/análise , Radicais Livres/química , Compostos Nitrosos , Oxirredução
16.
Molecules ; 26(1)2020 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-33379397

RESUMO

Popular and readily available alkenes and alkynes are good substrates for the preparation of functionalized molecules through radical and/or ionic addition reactions. Difunctionalization is a topic of current interest due to its high efficiency, substrate versatility, and operational simplicity. Presented in this article are radical addition followed by oxidation and nucleophilic addition reactions for difunctionalization of alkenes or alkynes. The difunctionalization could be accomplished through 1,2-addition (vicinal) and 1,n-addition (distal or remote) if H-atom or group-transfer is involved in the reaction process. A wide range of moieties, such as alkyl (R), perfluoroalkyl (Rf), aryl (Ar), hydroxy (OH), alkoxy (OR), acetatic (O2CR), halogenic (X), amino (NR2), azido (N3), cyano (CN), as well as sulfur- and phosphorous-containing groups can be incorporated through the difunctionalization reactions. Radicals generated from peroxides or single electron transfer (SET) agents, under photoredox or electrochemical reactions are employed for the reactions.


Assuntos
Alcenos/química , Alquinos/química , Radicais Livres/química , Oxirredução , Peróxidos/química
17.
Nat Commun ; 11(1): 5599, 2020 11 05.
Artigo em Inglês | MEDLINE | ID: mdl-33154360

RESUMO

Synthetic polymers are indispensable in many different applications, but there is a growing need for green processes and natural surfactants for emulsion polymerization. The use of solid particles to stabilize Pickering emulsions is a particularly attractive avenue, but oxygen sensitivity has remained a formidable challenge in controlled polymerization reactions. Here we show that lignin nanoparticles (LNPs) coated with chitosan and glucose oxidase (GOx) enable efficient stabilization of Pickering emulsion and in situ enzymatic degassing of single electron transfer-living radical polymerization (SET-LRP) without extraneous hydrogen peroxide scavengers. The resulting latex dispersions can be purified by aqueous extraction or used to obtain polymer nanocomposites containing uniformly dispersed LNPs. The polymers exhibit high chain-end fidelity that allows for production of a series of well-defined block copolymers as a viable route to more complex architectures.


Assuntos
Elétrons , Radicais Livres/química , Nanopartículas/química , Polímeros/química , Biocatálise , Quitosana/química , Transporte de Elétrons , Emulsões , Enzimas Imobilizadas/química , Glucose Oxidase/química , Peróxido de Hidrogênio/química , Látex/química , Lignina/química , Nanocompostos/química , Polimerização
18.
PLoS One ; 15(9): e0239076, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32931505

RESUMO

Dandelion (Taraxacum officinale), a common plant worldwide, is used as both a medicine and food. Fermentation is a food processing technology that has many advantages, such as low energy cost, changes in product characteristics, and enhanced product quality. The purpose of this study was to investigate the effect of solid-state fermentation (SSF) on the content, composition and antioxidant activity of dandelion flavonoids. Response surface methodology was used to optimize dandelion fermentation conditions. Under optimized conditions, the maximum flavone concentration was 66.05 ± 1.89 mg/g. The flavonoid content of the crude extract from fermented dandelion (FDF) was 183.72 ± 2.24 mg/g. The flavonoid compounds in the crude extracts were further identified by UPLC-ESI-MS/MS. A total of 229 flavonoid compounds were identified, and 57 differential flavonoids (including 27 upregulated and 30 downregulated flavonoids) between FDF and the crude extract of unfermented dandelion (DF) were observed, of which 25 were annotated to metabolic pathways. FDF displayed superior antioxidant activity to that of DF in in vitro DPPH radical-scavenging and reducing power assays. The favorable results of our investigation could provide a new way for the exploitation and utilization of dandelion, which could be promising for its application as an antioxidant and functional food additive with flavonoids as ingredients.


Assuntos
Antioxidantes/análise , Flavonoides/análise , Taraxacum/química , Antioxidantes/farmacologia , Compostos de Bifenilo/química , Fermentação , Flavonoides/farmacologia , Radicais Livres/química , Picratos/química , Extratos Vegetais/análise , Extratos Vegetais/farmacologia , Espectrometria de Massas por Ionização por Electrospray , Espectrometria de Massas em Tandem
19.
Free Radic Res ; 54(7): 517-524, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32781874

RESUMO

The present study reports radiation-chemical yields of 2.5-diaminoimidazolone (Iz) derivatives in X-irradiated phosphate-buffered solutions of guanosine and double-stranded DNA. Various gassing conditions (air, N20/O2 (4:1), N2O, vacuum) were employed to elucidate the contribution of several alternative pathways leading to Iz in reactions initiated by hydroxyl radical attack on guanine. In all systems, Iz was identified as the second by abundance guanine degradation product after 8-oxoguanine, formed in 1:5 (guanosine) and 1:3.3 (DNA) ratio to the latter in air-saturated solutions. Experimental data strongly suggest that the addition of molecular oxygen to the neutral guanine radical G(-H)• plays a major in Iz production in oxygenated solutions of double-stranded DNA while in other systems it may compete with recombination of G(-H)• with superoxide and/or alkyl peroxyl radicals. The production of Iz through hydroxyl radical attack on 8-oxoguanine was also shown to take place although the chemical yield of Iz (ca 6%) in this process is too low to compete with the other pathways. The linearity of Iz accumulation with dose also indicates a negligible contribution of this channel to its yield in all systems.


Assuntos
Dano ao DNA , DNA/química , Radicais Livres/química , Radical Hidroxila/química , Imidazóis/química , 8-Hidroxi-2'-Desoxiguanosina/química , Animais , DNA/efeitos da radiação , Diaminas/química , Guanosina/química , Masculino , Salmão
20.
Macromol Rapid Commun ; 41(15): e2000289, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32638497

RESUMO

Free radical polymerization upon near-infrared (NIR) light is still the subject of intense research efforts and remains a huge challenge particularly for long wavelengths (>1000 nm). In this study, a NIR sensitizer operating upon long wavelength (1064 nm) is proposed for an efficient polymerization of acrylate monomers. A new three-component photoinitiating system is developed comprising the NIR sensitizer in combination with an Iodonium salt (Iod) and an amine. Remarkably, the NIR sensitizer (IR 1064) absorbing strongly in all the near infrared region (700-1200 nm) offers the possibility to use a broad range of irradiation wavelengths, i.e., examples are provided at 785 and 1064 nm. Such long wavelengths are characterized by many advantages such as a deeper penetration of light and therefore a better curing of the monomer but it is also much safer than UV light. Excellent performance is observed for the three-component IR 1064/Iod/Amine system under air: high conversion of acrylate functions associated with a fast polymerization time. The use of IR 1064 as NIR sensitizer with a broad NIR absorption is-to the best of current knowledge-never proposed in the literature. The photoinitiating performances are studied using real-time Fourier transform infrared spectroscopy.


Assuntos
Acrilatos/efeitos da radiação , Radicais Livres/química , Processos Fotoquímicos , Acrilatos/química , Aminas/química , Cinética , Polimerização/efeitos da radiação , Radiação não Ionizante , Espectroscopia de Infravermelho com Transformada de Fourier/instrumentação , Raios Ultravioleta
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