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Kwas α-liponowy – antyutleniacz antyutleniaczy : właściwości i metody oznaczania

Skorupa A., Michałkiewicz S.

Wiadomości Chemiczne

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2017

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[Z] 71, 11-12

817--842

EN

Attention has been paid to healthy lifestyle in recent years. This is possible through increased physical activity and proper nutrition. This involves a significant increase in the interest in natural ingredients in a human daily diet. They come from both vegetable and animal products. This group of substances includes, for example, ascorbic acid (vitamin C), tocopherol (vitamin E), vitamin D, coenzyme Q10 and others. The important role of many compounds provided with food is their antioxidant action, which protects the body against the harmful effects of reactive oxygen species. They also exhibit therapeutic effects in diseases caused by oxidative stress. α-Lipoic acid (LA) also fits well into this group of substances and even gains the title of an “universal antioxidant” and an “antioxidant of antioxidants”. LA is produced in the human body in small amounts, and its biosynthesis occurs in the mitochondria. It is a compound with a very broad spectrum of therapeutic and biological activity. The amounts produced in the body are not sufficient and should therefore be supplied to the body from external sources. Food is the second, except de novo synthesis, the source of this compound. LA is a great antioxidant that can counteract the effects of aging. It is used mainly in the treatment of diabetic neuropathy and cardiovascular diseases, multiple sclerosis and Alzheimer’s disease. Such a wide action and occurrence causes the development of determination methods. Literature data indicate that free LA is primarily determined by liquid and gas chromatography, capillary electrophoresis, spectrophotometric and electrochemical techniques. In plant and animal cells it is mainly in the form of lipoyllysine. Determination of such a bound LA requires the proper preparation of the sample. This is usually acid, alkaline or enzymatic hydrolysis. This review summarizes the basic physicochemical and biochemical properties of α-lipoic acid and the methods of its determination.

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Elektroanaliza parabenów w kosmetykach

Michałkiewicz S., Jakubczyk M.

Przemysł Chemiczny

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2017

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T. 96, nr 6

1394--1397

PL

Opracowano nową, prostą oraz szybką woltamperometryczną metodę oznaczania parabenów w kosmetykach z zastosowaniem techniki pulsowej różnicowej DPV (differential pulse voltammetry) na mikroelektrodzie z włókna węglowego o średnicy 35,4 μm. Środowiskiem do badań była mieszanina lodowatego kwasu octowego i acetonitrylu (20% obj.) zawierająca 0,1 M octan sodu jako elektrolit podstawowy. Taki skład roztworu umożliwia oznaczanie tych konserwantów nawet w obecności matryc. Uzyskano zadowalające co do precyzji oraz dokładności wyniki oznaczania. Opracowana metoda może być skutecznym narzędziem do kontroli zawartości parabenów w analizach laboratoryjnych przemysłu kosmetycznego.

EN

Total content of parabens was detd. by differential pulse voltammetry (DPV) with C fiber microelectrode. The measurements were carried out in a mixt. of glacial AcOH and MeCN (20% by vol.) contg. 0.1 M AcONa. A good accuracy of the DPV method was achieved and its usefulness in routine anal. under industrial conditions was confirmed.

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Woltamperometryczna identyfikacja i oznaczanie antyutleniaczy w olejach roślinnych w rozpuszczalniku mieszanym kwas octowy - octan etylu

Michałkiewicz S.

Aparatura Badawcza i Dydaktyczna

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2012

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T. 17, nr 3

57-64

PL

Zastosowano woltamperometrię pulsową różnicową (DPV) na mikroelektrodzie do identyfikacji i oznaczania antyutleniaczy: witaminy E (tokoferoli), sezamolu i BHT (2,6-di-te/t-butylohydroksytoluen) w olejach roślinnych. Metoda jest prosta i szybka, a przygotowanie roztworów ogranicza się do rozpuszczenia oleju w rozpuszczalniku mieszanym kwas octowy - octan etylu (3:2, v/v), zawierającym 0,1 M Na-CI04 jako elektrolit podstawowy. Uzyskane wyniki są zgodne z danymi literaturowymi dla sezamolu oraz całkowitej zawartości witaminy E w przeliczeniu na alfa-tokoferol. Ze względu na niewystarczające różnice pomiędzy potencjałami utleniania alfa-, gamma- i delta-tokoferoli, składniki witaminy E nie mogą być analizowane oddzielnie. Zawartość BHT w niektórych olejach przekraczała dopuszczalny poziom 0,01%.

EN

Differential pulse voltammetry (DPV) at a microelectrode has been applied to the identification and quantification of antioxidants: vitamin E (tocopherols), sesamol and BHT (2,6-di-tert-butylhydroksytoluene) in plant oils. The method is simple, fast and the preparation of the solutions is limited just to the dissolution of the oils in a mixed solvent acetic acid - ethyl acetate (3:2, v/v) containing 0.1 M NaCI04 as the supporting electrolyte. The obtained results are in a good accordance with the literature data for sesamol and the total amount of vitamin E expressed as a-tocopherol content. Because of small differences between the oxidation potentials for alpha-, gamma- anddelta6-tocopherol, the components of vitamin E cannot be analyzed separately. The content of BHT in some oils exceeds the permitted level of 0.01%.

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Substancje biologicznie aktywne w olejach jadalnych

Małyszko J., Michałkiewicz S.

Wiadomości Chemiczne

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2010

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[Z] 64, 5-6

467-491

EN

Recently, the food industry, the agricultural community and consumers have shown a growing interest in the so-called functional food [1–3]. Natural bioactive compounds in some dietary products are claimed to prevent various diseases such as inflammation, degenerative diseases and cancer [5]. This paper reviews molecular structures, nutritional importance and availability of natural bioactive compounds present in vegetable and fish oils. Chapter 1 includes general description of polyunsaturated fatty acids (PUFA's), their physiological role and metabolism in mammalian organisms ([7–20], Schemes 1 and 2, Figs. 1 and 2). There is a link between dietary PUFA intake, inflammation and immunity. A composition of fatty acids in mammalian cells is sensitive to change in the fatty acids diet. The n-6 PUFA’s are the precursors of prostaglandines and related compounds, which play an important role in inflammation and in regulation of immunity. On the contrary, the n-3 PUFA's abundant in fish oils and also present in some plant seed oils have antiinflammatory properties and are therapeutically useful in several diseases. DHA from this family may also exert beneficial effects on development of the nervous system. Irrespective of PUFA's, vegetable oils contain a variety of bioactive compounds, mainly lipid-soluble antioxidants. This class of antioxidants includes vitamin E ([21–37], Figs. 3 and 4), which is a generic term that constitutes a group of structurally related compounds comprising of tocopherols and tocotrienols. A presence of the phenolic hydroxyl group in these compounds is critical for their antioxidant activity and enables to scavenge freeradical species both in vitro and in vivo. Other bioactive compounds present in vegetable oils are plant lignans ( [38–64], Fig. 5). In a human body, the plant lignans are converted to the mammalian lignans enterodiol and enterolactone. In the literature cited, lignans are discussed as anticancer agents, especially against breast and prostate cancer. Apart from a weak estrogenic properties, their anticancer activity may be supported on the antioxidation capacity. Vegetable oils are also a good source of phytosterols ([65–80], Figs. 6 and 7). Despite their similar chemical structures, phytosterols and cholesterol differ markedly from each other in regard to their pharmacological characteristics including intestinal absorption and further metabolism. Phytosterols produce a wide spectrum of therapeutic effects in the human organism including anti-tumor properties. In addition, another compounds present in edible oils are described, e.g. carotens and coenzyme Q10, all of which have potent biological activity, and exert beneficial effects in regard to cardiovascular and cancer diseases ([81–101], Fig. 8). The majority of the bibliography included in the present review is selected from that published since 2000 by the year 2009.

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Potential windows accessible to platinum and carbon electrodes in acetic acid and its mixtures with ethyl acetate

Michałkiewicz S., Kaczor M.

Chemia Analityczna

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2004

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Vol. 49, No. 1

121-128

EN

Linear scan voltammetry (LSV) has been applied in order to determine potential windows accessible to platinum and carbon microelectrodes in icy acetic acid. Sodium perchlorate and sodium acetate served as supporting electrolytes. Acetic acid exhibited very positive decomposition potential and small residual current at platinum, in particular when sodium perchlorate is used as an electrolyte. Electrochemical properties of carbon electrodes (CE) in the same medium were much worse. A decrease of sodium perchlorate concentration below 0.1 mol L-1 negligibly affected the potential window, yet led to undesirable shape distortions in the recorded voltammograms due to the considerable ohmic drop of the electrode potential. This effect was reflected during the anodic oxidation of alfa-tocopherol acetate. Moreover, potential windows for both: platinum and carbon electrodes were estimated in a mixed medium containing acetic acid and ethyl acetate (3:1, v/v).

PL

Wyznaczono użyteczny zakres potencjałów na mikroelekrrodzie platynowej oraz węglowej w roztworach nadchloranu sodowego i octanu sodowego w lodowatym kwasic octowym. Badania przeprowadzono stosując woltamperometrię z liniowo zmieniającym się potencjałem. Najbardziej dodatni potencjał rozkładowy i bardzo mały prąd szczątkowy występują na platynie w roztworach nadchloranu sodowego. W tych samych warunkach węgiel wykazuje znacznie gorsze wJaściwości elektrochemiczne. Obniżenie stężenia nadchloranu sodowego poniżej 0.1 mol L'1 tylko nieznacznie zmienia potencjałowy zakres trwałości kwasu octowego, ale wywiera niekorzystny wpływ na rejestrowane krzywe wóltamperometryczne z powodu znacznych spadków omowych potencjału. Wykazano to na przykładzie anodowego