Related Concept Videos
02:37Disubstituted Cyclohexanes: cis-trans Isomerism
Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
01:26Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
01:20Radical Autoxidation
The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
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09:26
Cellular Lipid Extraction for Targeted Stable Isotope Dilution Liquid Chromatography-Mass Spectrometry Analysis
Published on: November 17, 2011
trans-10,cis-12-conjugated linoleic acid isomer exhibits stronger oxyradical scavenging capacity than
1Department of Food Science and Institute of Comparative and Environmental Toxicology, Stocking Hall, Cornell University, Ithaca, New York 14853, USA.
Journal of Agricultural and Food Chemistry
|November 23, 2000
Summary
High-purity trans-10,cis-12 conjugated linoleic acid (CLA) demonstrated significant antioxidant activity, outperforming cis-9,trans-11-CLA and alpha-tocopherol at low concentrations. The cis-9,trans-11 isomer showed pro-oxidant effects at high concentrations.
Area of Science:
- Lipid biochemistry
- Oxidative stress research
- Nutritional science
Background:
- Conjugated linoleic acid (CLA) has been investigated for antioxidant properties, but results are inconclusive.
- Previous studies used mixed CLA isomers, complicating interpretation of antioxidant effects.
Purpose of the Study:
- To evaluate the distinct antioxidant activities of high-purity cis-9,trans-11-CLA and trans-10,cis-12-CLA isomers.
- To clarify the contribution of individual CLA isomers to overall antioxidant or pro-oxidant effects.
Main Methods:
- Utilized high-purity (>98%) cis-9,trans-11-CLA and trans-10,cis-12-CLA isomers.
- Assessed antioxidant capacity using the total oxyradical scavenging capacity assay.
Main Results:
- Trans-10,cis-12-CLA exhibited antioxidant activity with a 15-min lag phase across all tested concentrations (2-200 microM).
- At low concentrations (2 and 20 microM), trans-10,cis-12-CLA was more effective than cis-9,trans-11-CLA and alpha-tocopherol.
- Cis-9,trans-11-CLA showed weak antioxidant activity at low concentrations but acted as a pro-oxidant at 200 microM.
Conclusions:
- The differing antioxidant and pro-oxidant properties of individual CLA isomers explain previous inconclusive findings.
- Trans-10,cis-12-CLA is a potent antioxidant, while cis-9,trans-11-CLA possesses pro-oxidant characteristics under specific conditions.