scholarly journals THE RADICAL FORMATION DURING THE HYDROQUINONE AUTOOXIDATION IN THE STRONG ALKALINE MEDIUM

2021 ◽  
pp. 95-104
Author(s):  
Иван Дмитриевич Одарюк ◽  
Виктория Валентиновна Одарюк
Keyword(s):  
Ascorbic Acid ◽  
Alkaline Medium ◽  
Rate Constant ◽  
Direct Interaction ◽  
Radical Formation ◽  
Alkaline Media ◽  
Spectrophotometric Methods

При окислении гидрохинона в сильнощелочных средах основной вклад в процесс окисления вносит реакция прямого взаимодействия бианиона гидрохинона с кислородом. В результате исследования ингибированного аскорбиновой кислотой окисления гидрохинона в сильнощелочной среде хемилюминесцентным и спектрофотометрическим методами установлена константа скорости этой реакции, равная 241 ± 44 (М·с). The direct interaction between the dianion of hydroquinone and oxygen has made the major contribution in the process of hydroquinone oxidation in the strong alkaline media. As a result of the investigation of hydroquinone oxidation inhibited by ascorbic acid with chemiluminescence and spectrophotometric methods the rate constant of this reaction has been determined to be equal to 241 ± 44 (М·s).

scholarly journals Kinetics and Mechanistic Study of Hydrolysis of Adenosine Monophosphate Disodium Salt (AMPNa2) in Acidic and Alkaline Media

2019 ◽  
Vol 17 (1) ◽  
pp. 544-556
Author(s):  
Yoke-Leng Sim ◽  
Beljit Kaur
Keyword(s):  
Rate Constant ◽  
Adenosine Monophosphate ◽  
Disodium Salt ◽  
Second Order ◽  
Information Storage ◽  
Alkaline Media ◽  
Basic Medium ◽  
Mechanistic Study ◽  
Phosphate Ester ◽  
Hydrolysis Of

AbstractPhosphate ester hydrolysis is essential in signal transduction, energy storage and production, information storage and DNA repair. In this investigation, hydrolysis of adenosine monophosphate disodium salt (AMPNa2) was carried out in acidic, neutral and alkaline conditions of pH ranging between 0.30-12.71 at 60°C. The reaction was monitored spectrophotometrically. The rate ranged between (1.20 ± 0.10) × 10-7 s-1 to (4.44 ± 0.05) × 10-6 s-1 at [NaOH] from 0.0008 M to 1.00M recorded a second-order base-catalyzed rate constant, kOH as 4.32 × 10-6 M-1 s-1. In acidic conditions, the rate ranged between (1.32 ± 0.06) × 10-7 s-1 to (1.67 ± 0.10) × 10-6 s-1 at [HCl] from 0.01 M to 1.00 M. Second-order acid-catalyzed rate constant, kH obtained was 1.62 × 10-6 M-1 s-1. Rate of reaction for neutral region, k0 was obtained from graphical method to be 10-7 s-1. Mechanisms were proposed to involve P-O bond cleavage in basic medium while competition between P-O bond and N-glycosidic cleavage was observed in acidic medium. In conclusion, this study has provided comprehensive information on the kinetic parameters and mechanism of cleavage of AMPNa2 which mimicked natural AMP cleavage and the action of enzymes that facilitate its cleavage.

scholarly journals Complexes of Copper and Iron with Pyridoxamine, Ascorbic Acid, and a Model Amadori Compound: Exploring Pyridoxamine’s Secondary Antioxidant Activity

Antioxidants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 208
Author(s):  
Guillermo García-Díez ◽  
Roger Monreal-Corona ◽  
Nelaine Mora-Diez
Keyword(s):  
Antioxidant Activity ◽  
Ascorbic Acid ◽  
Rate Constant ◽  
Stable Complex ◽  
Aqueous Environment ◽  
Oh Radicals ◽  
Bidentate Ligands ◽  
Superoxide Radical Anion ◽  
Amadori Compound ◽  
The Stability

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•−) or ascorbate (ASC−). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of −35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of −58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•− and ASC−. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 103 and 4.09 × 1013 times, respectively. With iron, the rates become 1.78 × 103 and 4.45 × 1015 times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

scholarly journals Spectrophotometric Estimation of Sulfadoxine in Pharmaceutical Preparations

2010 ◽  
Vol 7 (4) ◽  
pp. 1246-1253 ◽  
Author(s):  
Sangita Sharma ◽  
Madhurjya Neog ◽  
Vipul Prajapati ◽  
Hiren Patel ◽  
Dipti Dabhi
Keyword(s):  
Hydrochloric Acid ◽  
Alkaline Medium ◽  
Sodium Nitrite ◽  
Pharmaceutical Preparations ◽  
Chromotropic Acid ◽  
Spectrophotometric Methods ◽  
Ethylenediamine Dihydrochloride ◽  
Beer’S Law ◽  
Medium Method ◽  
Light Orange

Four simple, sensitive, accurate and rapid visible spectrophotometric methods (A, B, C and D) have been developed for the estimation of sulfadoxine in pharmaceutical preparations. They are based on the diazotization of sulfadoxine with sodium nitrite and hydrochloric acid followed by coupling withN-(1-naphthyl) ethylenediamine dihydrochloride (Method A) to form pink coloured chromogen, diphenylamine (Method B) to form light pink coloured chromogen, chromotropic acid (in alkaline medium) (Method C) to form orange coloured chromogen, Resorcinol (in alkaline medium) (Method D) to form light orange coloured chromogen and exhibiting absorption maxima (λmax) at 536 nm, 524 nm, 520 nm and 496 nm respectively. The coloured chromogens formed are stable for more than 2 h. Beer’s law was obeyed in the concentration range of 1.0 - 5.0 μg/mL in Method A , 5.0 - 25.0 μg/mL in Method B, 5.0 - 25.0 μg/mL in Method C and 4.0 - 8.0 μg/mL in Method D respectively. The results of the three analysis have been validated statistically and by recovery studies. The results obtained in the proposed methods are in good agreements with labeled amounts, when marketed pharmaceutical preparations are analyzed.

Ascorbic acid enhances hydroxyl radical formation in iron-fortified infant cereals and infant formulas

1997 ◽  
Vol 156 (6) ◽  
pp. 488-492 ◽  
Author(s):  
R. Almaas ◽  
T. Rootwelt ◽  
S. Øyasæter ◽  
O. D. Saugstad
Keyword(s):  
Ascorbic Acid ◽  
Hydroxyl Radical ◽  
Radical Formation ◽  
Infant Formulas

New insights into the formation mechanism of Ag, Au and AgAu nanoparticles in aqueous alkaline media: alkoxides from alcohols, aldehydes and ketones as universal reducing agents

2015 ◽  
Vol 17 (33) ◽  
pp. 21683-21693 ◽  
Author(s):  
Janaina F. Gomes ◽  
Amanda C. Garcia ◽  
Eduardo B. Ferreira ◽  
Cleiton Pires ◽  
Vanessa L. Oliveira ◽  
...  
Keyword(s):  
Alkaline Medium ◽  
Formation Mechanism ◽  
Reducing Agents ◽  
Reducing Agent ◽  
Alkaline Media ◽  
Aldehydes And Ketones

Alkoxide from alcohols, aldehydes and ketones in alkaline medium is the actual and universal reducing agent of silver and gold ions.

scholarly journals Sensitive Spectrophotometric Methods for the Determination of Ascorbic Acid

2008 ◽  
Vol 5 (1) ◽  
pp. 10-15 ◽  
Author(s):  
H. D. Revanasiddappa ◽  
M. A. Veena
Keyword(s):  
Ascorbic Acid ◽  
Acid Medium ◽  
Pharmaceutical Formulations ◽  
Molar Absorptivity ◽  
Spectrophotometric Methods ◽  
Maximum Absorbance ◽  
Hydrochloric Acid Medium ◽  
Subsequent Determination ◽  
Sulphuric Acid Medium

Two simple and sensitive spectrophotometric methods (A and B) have been described for the determination of ascorbic acid. Method A is based on the oxidation of ascorbic acid (AA) by known excess of Se(IV) in hydrochloric acid medium and subsequent determination of unreacted Se(IV) by reacting it with iodide in the same acid medium to liberate iodine, which react with starch to form a stable blue coloured iodine-starch complex, which shows maximum absorbance at 590 nm. Method B is based on the oxidation of ascorbic acid (AA) by known excess of Cr(VI) in sulphuric acid medium and the determination of unreacted Cr(VI) with diphenyl carbazide (DPC) under the same acidic medium to produce a stable red-violet coloured species, which shows a maximum absorbance at 550 nm. The reacted oxidants (in methods A and B) correspond to the AA content. The apparent molar absorptivity values are found to be 1.627×104and 1.641×104L mol-1cm-1for methods A and B, respectively. The proposed methods are simple, sensitive and suitable for the routine analysis of AA in pharmaceutical formulations and in real samples.

Investigation of the mechanism of ascorbic acid radical formation and destruction

1977 ◽  
Vol 26 (1) ◽  
pp. 49-54
Author(s):  
A. P. Moravskii ◽  
Yu. N. Skurlatov ◽  
E. V. Shtamm ◽  
V. F. Shuvalov
Keyword(s):  
Ascorbic Acid ◽  
Radical Formation ◽  
Acid Radical

Ascorbic Acid Catalyzes Nitric Oxide Production from Nitrite Ions.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1574-1574 ◽  
Author(s):  
Nathawut Sibmooh ◽  
Barbora Piknova ◽  
Alan N. Schechter
Keyword(s):  
Nitric Oxide ◽  
Ascorbic Acid ◽  
Rate Constant ◽  
Dehydroascorbic Acid ◽  
Nitrite Reduction ◽  
Erythrocyte Membranes ◽  
No Production ◽  
Ferrous Ions ◽  
Physiological Conditions ◽  
Ferrous Heme

Abstract We have previously shown that nitrite ions can be reduced by hemoglobin to nitric oxide (NO), a ubiquitous signaling molecule and potent vasodilator. Nitrite serves as a stable tissue and vascular source for NO production; the reduction reaction is maximal at about 50% oxygen saturation values and is enhanced at low pH but little is known about other effectors of this reaction. In the current work, we studied the effect of ascorbic acid on nitrite reduction under physiological conditions using chemiluminescence to quantify NO production. In physiological buffer, this reaction has a rate constant of about 1×10−5 M−1.s−1. Thus, a significant production of NO would likely occur in plasma only at pharmacological levels of ascorbic acid (> 1 mM) although lowering pH below 7.0 markedly enhances this reaction. Loading human erythrocytes with 0.5 mM dehydroascorbic acid, which is in redox equilibrium with ascorbic acid and which can significantly raise intracellular ascorbic acid levels, increased basal levels of nitrite ions from 42±9.0 nM to 98±56 nM. Uptake of nitrite ions into erythrocytes by incubation in 10 μM nitrite was increased about 1.5 fold by dehydroascorbic acid and the half-time of nitrite loss was slowed to the same extent. Ascorbic acid also reduced free ferric heme in erythrocytes and plasma to ferrous heme which catalyzed the reduction of nitrite to NO with a rate constant of 2.3×103 M−1.s−1 under physiological conditions. However, free ferrous ions did not significantly produce NO in physiological buffer (rate constant = 1.8×10−2 M−1.s−1). The reaction of ferrous heme with nitrite was not affected by heme binding to proteins such as hemopexin and albumin, or erythrocyte membranes. These results suggest that physiological levels of ascorbic acid (20–80 μM in plasma and erythrocytes) may act to catalyze NO production in the blood by promoting the reduction of nitrite ions by free ferrous heme and by increasing intra-erythrocytic levels of nitrite ions which can be reduced to NO by deoxyhemoglobin.

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