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Wyświetlanie 1-2 z 2
Tytuł:
Jubileusz metody miareczkowania kulometrycznego
An anniversary of coulometric titration
Autorzy:
Małyszko, J.
Powiązania:
https://bibliotekanauki.pl/articles/171793.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
kulometria
miareczkowanie kulometryczne
miareczkowanie konwencjonalne
reakcje elektrodowe
titrants
coulometry
coulometric titration
conventional titrations
electrode processes
Opis:
In 1938, Szebellédy and Somogyi [1–7] have proposed an important methodological innovation in analytical chemistry. This methodology was termed coulometric titration. This paper presents an overview of the principles of operation and, in broad outline, applications of this methodology. Moreover, a short biography and scientific achievements of professor Laszlo Szebellédy are presented in the introduction. Chapter 1 of this review outlines the theoretical background and general description of coulometric titration. In this new technique, the electrical current generates a titrant that chemically reacts with an analyte. The amount of the analyte is determined from the quantity of the electrical charge passed until the point of chemical equivalence has been reached, according to the 2nd Faraday’s law of electrolysis. The new methodology offers several significant advantages over a conventional volumetric procedure, such as elimination of problems connected with the preparation, standardization and storage of standard solutions. In Chapter 2, an evolution of the method after the Second World War is presented. In these times, stable constant current sources became easy to construct [13–15]. Consequently, coulometric titrations started to use a constant current system. Under these conditions, the total number of coulombs consumed can be calculated readily from the intensity of current and the duration of electrolysis. Coulometric titrations have been developed for all types of volumetric titrations: oxidation–reduction [19–28], precipitation [17, 18], complex formation [37] and neutralization reactions [39, 40]. The generation of various titrants and possibilities of application are described. Special attention is devoted to the electrochemical generation of reagents which are not ordinarily utilized in conventional volumetric analysis owing to the instability of their solutions such as bromine, chlorine, silver(II) and titanium(III). Moreover, the coulometric titration procedure is significantly more sensitive than the volumetric titration, and it is particularly suited to automation, because complex mechanical devices such as an automatic burette are not required. The new method appeared to be an attractive alternative to all forms of the volumetric titration. Chapter 3 is dedicated to the contribution of Polish academic chemistry teachers to the development of the method discussed [57–89, 91–100]. Advantages and disadvantages of the method are listed in the last Chapter (Summary). Each Chapter includes selected works related to the history of the subject.
Źródło:
Wiadomości Chemiczne; 2011, 65, 5-6; 345-361
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Substancje biologicznie aktywne w winie
Bioactive compounds in wine
Autorzy:
Małyszko, J.
Karbarz, M.
Powiązania:
https://bibliotekanauki.pl/articles/172595.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
aktywność antyoksydacyjna
flawonoidy
kwas fenolowy
melatonina
resweratrol
wino czerwone
antioxidant activity
flavonoids
melatonin
phenolic acids
red wine
resveratrol
Opis:
Wines are the subject of an increasing number of investigations. The benefits of red wine became widely recognized after the observation of “French paradox” [8–10]. It has been found that there is a low mortality rate from ischemic heart disease among French people despite their high consumption of saturated fatty acids and the prevalence of other risk factors. The health-protective properties of wine are attributed to their antioxidant activity, i.e. the capability to scavenge reactive oxygen species, ROS . An imbalance between antioxidants and oxygen species results in oxidative stress leading to cellular damage. The phenolic compounds present in wine show beneficial physiological properties including protection against coronary heart disease, as well as anti-inflammatory and anti-carcinogenic activity. Most of the beneficial effects of wine are attributed to the presence of flavonoids, resveratrol, phenolic acids and other antioxidants. This paper reviews the significance of different compounds present in wine and their effect on human health. Chapter 1 focuses on flavonoids: flavonols, flavan-3-ols and anthocyanidins (Fig. 1) [14–29]. This class of compounds can exist both in a simple form, as aglycones, and bounded with sugars, as glycosides. The presence of phenolic hydroxyl group in these compounds is essential for their antioxidant activity and enables to scavenge free radicals in vivo. Chapter 2 describes chemical and physicochemical properties of resveratrol (Fig. 2) [30-41] which is the main antioxidant in wine. Moreover, this compound has been shown to inhibit the oxidation of low density lipoproteins and the aggregation of platelets [44-47]. Resveratrol also exhibits anti-inflammatory and anticancer properties [48, 49]. Chapter 3 reveals that wines are also a good source of other antioxidants [50–55] as phenolic acids (Fig. 3), tyrosol and hydroxytyrosol (Fig. 4), and also melatonin (Fig. 5). Unfortunately, some wines can include mycotoxins, mainly ochratoxin A [59, 60] (Fig. 6), which is produced by the phytopatogenic fungi, Aspergillus carbonarius. All types of red wine contain different amounts of ethanol and phenolic antioxidants, and therefore it is probable that the cardioprotective effect of red wine is caused by both these kinds of components [57–58]. Epidemiological observations, clinical and experimental in vitro research prove that regular and moderate intake of wine, particularly red wine, reduces cardiovascular morbidity and mortality [66–70].
Źródło:
Wiadomości Chemiczne; 2012, 66, 5-6; 563-579
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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