Oxidation and Antioxidants in Organic Chemistry and Biology

Денисов, Е. Т.; Afanas’ev, Igor B.

doi:10.1201/9781420030853

Cited by 574 publications

(573 citation statements)

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“…− using the hydroxylamine assay was between 9 and 30%. The mechanism and efficiency of the hydroxylamine assay being rather poorly understood (25), this fraction might indeed be higher. Disproportionation of O 2 − into H 2 O 2 in water at pH 7 is sufficiently fast (6 × 10 5 M −1 s −1 ) (26) that at micromolar concentrations most of the H 2 O 2 could originate from O 2 − if the latter is not intercepted by hydroxylamine.…”

Section: Assay Of Intermolecular Electron-transfer Kinetics Using Cytmentioning

confidence: 99%

How oxygen reacts with oxygen-tolerant respiratory [NiFe]-hydrogenases

Wulff

Day

Sargent

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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An oxygen-tolerant respiratory [NiFe]-hydrogenase is proven to be a four-electron hydrogen/oxygen oxidoreductase, catalyzing the reaction 2 H 2 + O 2 = 2 H 2 O, equivalent to hydrogen combustion, over a sustained period without inactivating. At least 86% of the H 2 O produced by Escherichia coli hydrogenase-1 exposed to a mixture of 90% H 2 and 10% O 2 is accounted for by a direct four-electron pathway, whereas up to 14% arises from slower side reactions proceeding via superoxide and hydrogen peroxide. The direct pathway is assigned to O 2 reduction at the [NiFe] active site, whereas the side reactions are an unavoidable consequence of the presence of low-potential relay centers that release electrons derived from H 2 oxidation. The oxidase activity is too slow to be useful in removing O 2 from the bacterial periplasm; instead, the four-electron reduction of molecular oxygen to harmless water ensures that the active site survives to catalyze sustained hydrogen oxidation.hydrogen | mass spectrometry | Fe-S cluster H ydrogenases are enzymes that catalyze the interconversion of H 2 and H + with great efficiency. Containing Fe or Fe and Ni as active metals, they are not only important in biohydrogen production (by fermentative and photosynthetic means) but also provide inspiration for detailed understanding and development of optimal molecular electrocatalysts. The minimal active site motif, common to all hydrogenases, is a low-spin Fe atom coordinated by CO, CN − , and thiolate ligands, a combination expected to be unstable under aerobic conditions. Indeed, most hydrogenases suffer long-term or permanent inactivation when exposed to even traces of O 2 . It is therefore of special interest that certain [NiFe]-hydrogenases have evolved to sustain H 2 oxidation in the continued presence of O 2 , without inactivation: these enzymes are known as O 2 -tolerant [NiFe]-hydrogenases.Most of our current insight into the mechanism of O 2 tolerance stems from studies on respiratory membrane-bound [NiFe]-hydrogenases that couple H 2 oxidation to reduction of quinones (1-3). These enzymes are localized at the cytoplasmic membrane and project into the periplasmic space. A model proposed for the O 2 -tolerance mechanism of these [NiFe]-hydrogenases ( Fig. 1) is based on the following evidence. Oxygen reacts with O 2 -tolerant membrane-bound [NiFe]-hydrogenases to form, exclusively, an inactive state known as Ni-B or "ready," formulated as a Ni(III)-OH species, which is rapidly reactivated by one-electron transfer to rejoin the catalytic cycle of H 2 oxidation. Provided Ni-B is the sole product of O 2 attack, the presence of O 2 merely attenuates the steady-state rate of H 2 oxidation. In contrast, standard (O 2 sensitive) [NiFe]-hydrogenases react with O 2 to give a mixture of states, including ones variously known as "unready" or Ni-A, in which O 2 is either only partially reduced (possibly trapped as a peroxide) or has oxygenated atoms of the active site (3-7). The unready states are only reactivated very slowly; consequently, t...

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Section: Assay Of Intermolecular Electron-transfer Kinetics Using Cytmentioning

confidence: 99%

How oxygen reacts with oxygen-tolerant respiratory [NiFe]-hydrogenases

Wulff

Day

Sargent

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…De acordo com a literatura, as moléculas mais utilizadas como antioxidantes são os fenois estericamente impedidos, as aminas aromáticas, alguns ésteres sulfitos, fosfitos e fosfatos, 27,95 e os principais tipos de aditivos antioxidantes, eficientes contra a degradação de substratos orgânicos, são os sequestradores de radicais, os desativadores de metais e os decompositores de hidroperóxidos. 27,95 Há exemplos recentes de sucesso na preparação de ftalocianinas, 96 porfirinas, 13,14,[16][17][18] fulereno 13,14,23 e derivados obtidos pelas reações de alilação e ciclocarbonilação do cardanol hidrogenado. 87 A determinação da atividade antioxidante dos derivados do LCC, funcionalizados na oxidação térmica de filmes de cis-1,4-poli-…”

Section: Avanços Oportunidades E Sustentabilidadeunclassified

Óleo da castanha de caju: oportunidades e desafios no contexto do desenvolvimento e sustentabilidade industrial

Mazzetto¹,

Lomonaco²,

Mele³

2009

Quím. Nova

135

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Recebido em 15/1/09; aceito em 20/3/09; publicado na web em 7/4/09 CASHEW NUT OIL: OPPORTUNITIES AND CHALLENGES IN THE CONTEXT OF SUSTAINABLE INDUSTRIAL DEVELOPMENT. The new millennium is marked by a growing search for renewable fuels and alternative raw materials from biomass in the petrochemicals industry. However, there are many challenges to overcome regarding technological and human resources aspects. In this scenario, cashew nut oil, which is rich in natural phenols, is considered to be very promising for the development of synthetic and functional products and as a feedstock for production of fine chemicals and a wide variety of new materials.Keywords: cashew nut shell liquid (CNSL); phenolic components; renewable source.Anacardium occidentale L. é o seu nome científico. Pertencente a família Anacardiaceae, 1 o cajueiro é uma árvore de aparência exótica, troncos tortuosos, folhas glabras, flores masculinas e hermafroditas e fruto reniforme. Seu pedúnculo superdesenvolvido e muito apreciado pela suculência é frequentemente confundido com o fruto, quando na verdade se trata do pseudofruto, cientificamente denominado de pedúnculo floral, com coloração variante entre o amarelo e o vermelho.O fruto do cajueiro, popularmente conhecido como castanha de caju, é um aquênio de comprimento e largura variável, casca coriácea lisa, mesocarpo alveolado, repleto de um líquido escuro quase preto, cáustico e inflamável, chamado de líquido da casca da castanha do caju (LCC) ou cashew nut shell liquid (CNSL) como é conhecido internacionalmente. Na parte mais interna da castanha está localizada a amêndoa, constituída de dois cotilédones carnosos e oleosos, que compõem a parte comestível do fruto, revestida por uma película em tons avermelhados (Figura 1).A origem do cajueiro fundamenta-se em provas circunstanciais que indicam, de forma convincente, o Brasil ou pelo menos o norte da América do Sul e parte da América Central como o centro de procedência da espécie cultivada. 2 O cajueiro adapta-se melhor às regiões costeiras do nordeste brasileiro, onde faz parte da vegetação de praias e dunas, além das formações de restingas, permitindo supor que a origem filogenética da espécie reside em limítrofes da Mata Amazônica ou cerrados com ecossistemas da região Nordeste, com base na maior diversidade e adaptação da planta nestas localidades.Um forte indício sobre a origem brasileira do caju está na mais antiga referência conhecida sobre a planta, a ilustração feita pelo monge naturalista francês André Thevet 2 (1502-1590) em seu livro intitulado Singularidades da França Antártica (Les singularitez de la France Antartique), em 1557, escrito após sua passagem pela costa do Nordeste e Norte do Brasil.Atualmente, a planta está disseminada em diversos países como Índia, Moçambique, Tanzânia, Quênia e mais recentemente Vietnã, Indonésia e Tailândia. No Brasil, de acordo com o Instituto Brasileiro de Geografia e Estatística -IBGE 3 e o Sindicato das Indústrias de Beneficiamento de Castanha de Caju e Amêndoas Vegetais do Estado do Ceará -S...

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“…If the GPx system is exhausted and becomes unable to purge the H 2 O 2 produced, the excess of this ROS may react with polyunsaturated fatty acids present in the sperm membrane, inducing lipid peroxidation (Morliere & Santus, 1998;Bansal & Bilaspuri, 2010). Furthermore, the remaining H 2 O 2 in the presence of transition metals, can be converted by the Fenton reaction in hydroxyl radical (Gutteridge, 1986;Denisov & Afanas'ev, 2005), considered an unstable ROS and thus mainly responsible for oxidative damage to biomolecules (i.e., proteins, lipids, DNA) (Aprioku, 2013;Meyerstein, 2013).…”

Section: (A) (B) (C)mentioning

confidence: 99%

Epididymal contraction and sperm parameters are affected by clonidine

et al. 2014

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SUMMARYThe use of clonidine, a selective agonist of a 2 -adrenoceptors, is related to the fertility impairment. Thus, it has been described that changes in the epididymal function are related to the loss of fertility. Therefore, this study was sought to further evaluate the effects of clonidine in the rat distal cauda epididymis contractions and its consequence in the sperm parameters. The in vitro effects of clonidine in the isolated distal cauda epididymis were evaluated by pharmacological experiments. The consecutive contractile responses for clonidine in distal cauda epididymis showed desensitization. The noradrenaline-induced contractions were desensitized after in vitro clonidine pre-treatment (10 À5 M for 10 min). Clonidine was unable to alter the noradrenaline contractions if the in vitro pre-treatment was made in the presence of idazoxan (a 2 -adrenoceptor antagonist), whereas prazosin (a 1 -adrenoceptor antagonist) was ineffective. Moreover, the in vitro clonidine pre-treatment increased frequency and amplitude of spontaneous contraction of distal cauda epididymis. In addition, to induce in vivo desensitization of a 2 -adrenoceptors, male Wistar rats were treated with crescent doses of clonidine and distal cauda of epididymis contraction and sperm parameters were analyzed. The in vivo treatment with clonidine diminished the potency of the contractions induced by adrenergic agonists and augmented the frequency and amplitude of spontaneous contraction of distal cauda epididymis. This treatment also altered the sperm transit time in epididymis, epididymal sperm reserves, sperm lipid peroxidation, and antioxidant enzymes activity. The results suggest that clonidine was able to affect the sperm quantity and quality by decreasing the transit time related to the increase in the frequency and amplitude of spontaneous contractions in epididymis, although the contractions induced by adrenergic agonists were desensitized.

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Oxidation and Antioxidants in Organic Chemistry and Biology

Cited by 574 publications

References 0 publications

How oxygen reacts with oxygen-tolerant respiratory [NiFe]-hydrogenases

How oxygen reacts with oxygen-tolerant respiratory [NiFe]-hydrogenases

Óleo da castanha de caju: oportunidades e desafios no contexto do desenvolvimento e sustentabilidade industrial

Epididymal contraction and sperm parameters are affected by clonidine

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