Autoxidation and Antioxidants. Basic Principles and New Developments

1974 ◽  
Vol 47 (4) ◽  
pp. 976-990 ◽  
Author(s):  
J. A. Howard
Keyword(s):  
Transition Metal Complexes ◽  
Radical Scavenging ◽  
Oxygen Radical ◽  
Basic Principles ◽  
New Developments ◽  
Chain Initiation ◽  
Elementary Reactions ◽  
Reasonable Degree ◽  
The Stability ◽  
Solid System

Abstract There is no doubt that liquid-phase hydrocarbon autoxidation is one of the most thoroughly understood reactions in organic chemistry. Our knowledge of the elementary reactions involved in this process is so complete that it should be possible to calculate, with a reasonable degree of precision, the overall rate of autoxidation of a hydrocarbon or mixture of hydrocarbons, provided, of course, that the rate of chain initiation can be estimated. It should also be possible to make a reasonable intelligent guess at the stability of a solid system, with the reservations appropriate to the change of phase. With regard to inhibition, there is probably not a great deal of room for further improvement in the inherent efficiency of H-atom donating antioxidants. This is because a decrease in the strength of the X—H bond makes the hydrogen more susceptible to abstraction by molecular oxygen. Radical scavenging transition metal complexes also suffer from the limitation that the more reactive the complex is to ROO the more reactive it will be to O2. There may, of course, be further improvements in the efficiency of preventative antioxidants, particularly multi-functional antioxidants with the ability to decompose hydroperoxides and peroxides by several non-radical mechanisms and also scavenge free-radicals.

scholarly journals Synthesis of Biobased Phloretin Analogues: An Access to Antioxidant and Anti-Tyrosinase Compounds for Cosmetic Applications

Antioxidants ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 512
Author(s):  
Laurène Minsat ◽  
Cédric Peyrot ◽  
Fanny Brunissen ◽  
Jean-Hugues Renault ◽  
Florent Allais
Keyword(s):  
Natural Products ◽  
Consumer Demand ◽  
Radical Scavenging ◽  
Green Process ◽  
Direct Extraction ◽  
Low Concentration ◽  
Cosmetic Formulations ◽  
Valuable Compounds ◽  
The Stability

The current cosmetic and nutraceutical markets are characterized by a strong consumer demand for a return to natural products that are less harmful to both the consumers and the environment than current petrosourced products. Phloretin, a natural dihydrochalcone (DHC) found in apple, has been widely studied for many years and identified as a strong antioxidant and anti-tyrosinase ingredient for cosmetic formulations. Its low concentration in apples does not allow it to be obtained by direct extraction from biomass in large quantities to meet market volumes and prices. Moreover, its remarkable structure prevents its synthesis through a green process. To overcome these issues, the synthesis of phloretin analogs appears as an alternative to access valuable compounds that are potentially more active than phloretin itself. Under such considerations, 12 chalcones (CHs) and 12 dihydrochalcones (DHCs) were synthesized through a green Claisen–Schmidt condensation using bio-based reagents. In order to evaluate the potential of these molecules, radical scavenging DPPH and anti-tyrosinase tests have been conducted. Moreover, the UV filtering properties and the stability of these analogs towards UV-radiations have been evaluated. Some molecules showed competitive antioxidant and anti-tyrosinase activities regarding phloretin. Two compounds in particular showed EC50 lower than phloretin, one chalcone and one dihydrochalcone.

scholarly journals Computational Studies of 4-Formylpyridinethiosemicarbazone and Structural and Biological Studies of Its Ni(II) and Cu(II) Complexes

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Mydhili P. Sripathi ◽  
Sireesha Berely ◽  
Chittireddy Venkata Ramana Reddy
Keyword(s):  
Elemental Analysis ◽  
Radical Scavenging ◽  
Molar Conductance ◽  
Computational Studies ◽  
Hydrolytic Cleavage ◽  
Bacterial Strains ◽  
Intercalative Mode ◽  
Biological Studies ◽  
Calf Thymus ◽  
The Stability

To understand the stability, chelation behaviour, and biological activity of 4-Formylpyridinethiosemicarbazone (H4FPT), it is important to recognize its interactive geometry. Hence, computational studies on geometrically optimized structures of thione and thiol forms of H4FPT were performed. Binary metal complexes of the ligand, H4FPT (L) with the Ni(II) and Cu(II) metal ions (M), were synthesized and characterized by various spectroanalytical techniques as elemental analysis, molar conductance, magnetic susceptibility measurements, LC-MS, TGA, IR, UV-Visible, ESR, and powder XRD. Elemental analysis, LC-MS, and TGA studies indicate 1:2 (ML2) composition for mononuclear Ni(II) complex and 1:1 (ML) composition for dinuclear Cu(II) complex. Electronic absorption titrations, fluorescence quenching studies, and viscosity measurements suggest intercalative mode of binding of the complexes with calf thymus DNA (CT-DNA). These complexes also promote hydrolytic cleavage of plasmid pBR322. The ligand (H4FPT) and its complexes showed moderate-to-good activity against Gram-positive and Gram-negative bacterial strains. The DPPH radical scavenging studies showed antioxidant nature of both complexes.

A review of solid phase extraction: Basic principles and new developments

1995 ◽  
Vol 40 (7-8) ◽  
pp. 474-483 ◽  
Author(s):  
L. A. Berrueta ◽  
B. Gallo ◽  
F. Vicente
Keyword(s):  
Solid Phase Extraction ◽  
Solid Phase ◽  
Phase Extraction ◽  
Basic Principles ◽  
New Developments

scholarly journals Emphasized Mechanistic Antimicrobial Study of Biofunctionalized Silver Nanoparticles on Model Proteus mirabilis

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Asra Parveen ◽  
Manjunath S. Yalagatti ◽  
Venkataraman Abbaraju ◽  
Raghunandan Deshpande
Keyword(s):  
Silver Nanoparticles ◽  
Antibacterial Activity ◽  
Proteus Mirabilis ◽  
Reducing Sugars ◽  
Radical Scavenging ◽  
Human Pathogens ◽  
Antimicrobial Study ◽  
Synthetic Procedure ◽  
Dpph Method ◽  
The Stability

Antimicrobial study of biofunctionalized silver nanoparticles has been done with the emphasis on its mechanism on both gram positive and negative bacteria. The biofunctionalized silver nanoparticles are employed considering their importance in green chemistry with respect to easy synthesis, usefulness, and economic synthetic procedure involved. The stability of these nanoparticles was determined by zeta potential analyzer. The probable mechanism of antibacterial activity was performed on Proteus mirabilis by field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDAX) study which does not show the presence of silver. The free radicals generated by silver nanoparticles were responsible for lethal antibacterial activity by rupturing the cell surface which causes improper nutrient and signal supply. Free radical scavenging efficacy of silver nanoparticles was confirmed by 1,1-Diphenyl-2-picrylhydrazyl (DPPH) method. AgNP enhanced the membrane leakage of reducing sugars by destroying the proteins existing on the cell wall. These nanoparticles are found to be toxic against human pathogens and are highly effective on Staphylococcus aureus. The effect of silver nanoparticles is concentration dependent and independent of the type of strains used.

Transition Metal Complex Catalysed Photo- and Electrochemical (De)hydrogenations Involving C=O- and C=N-Bonds

Synthesis ◽  
2021 ◽  
Author(s):  
Igor Fokin ◽  
Kai-Thorben Kuessner ◽  
Inke Siewert
Keyword(s):  
Transition Metal ◽  
Metal Complex ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Transition Metal Complex ◽  
Basic Principles

Herein, we summarize the photo- and electrochemical protocols for dehydrogenation and hydrogenations involving carbonyl and imine functions. The three basic principles that have been explored to interconvert such moieties with transition metal complexes are discussed in detail and the substrate scope is evaluated. Furthermore, we describe some general thermodynamic and kinetic aspects of such electro- and photochemically driven reactions.

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