This news item was adapted by students Kristin Thomas, Kim Hoke, Vineesha Arelli, and Justin Gerke as part of their Chemistry 212  Project in WS00 under the guidance of Prof. Rainer Glaser.

Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 25. Lipids.

For each of the following questions, please refer to the following article:

by Catherine Ann Rauch (CNN, 2000)

Editorial Comments

It’s the news chocolate fans long to hear, “Chocolate tastes great and is good for you, too!”  Chocolate has been enjoyed by numerous civilizations for hundreds of years, but only recently have its health benefits been examined.  The American Dietetic Association, American Academy for the Advancement of Science, and the Harvard School of Public Health have conducted studies on the health benefits of chocolate, with some surprising results.

Cholesterol is an important structural component in the lipid bilayer of cells.  In the body, cholesterol travels via lipoproteins.  There are several different types of lipoproteins, and they are classified according to their density.  Their density is directly related to their lipid (more lipids = less density).   High-density lipoproteins (HDL), low-density lipoproteins (LDL), and very low-density lipoproteins (VLDL) are important lipoproteins for cholesterol transport.  Very low density lipoproteins (VLDL) carry cholesterol and cholesteryl esters from the liver to body tissues.  LDL form from breakdown of VLDL.  HDL carries cholesterol and cholesteryl esters from the tissues to the liver, where they are metabolized and eventually excreted.  A schematic of this is shown here.

Research has shown that high HDL levels are correlated with lower rates of heart disease and high levels of LDL are correlated with increased rates of heart disease.  Therefore, HDL and LDL are known as “good” and “bad” cholesterol, respectively.  The exact reasons for the elevated heart disease with LDL and decreased heart disease with HDL is not known, but it appears that because HDL returns cholesterol to the liver (where it is metabolized, and eventually secreted), less cholesterol is available for oxidation.  The oxidation occurs through oxygen, which exists as a di-radical.

Peroxides and free radicals are formed when oxygen reacts with the double bonds in unsaturated fatty acids.  These peroxides and free radicals can damage cell components such as lipids, nucleic acids, and proteins.  In addition, oxidation of LDL cholesterol can lead to plaque deposits in the arteries, which are a risk factor for heart disease.  Thus anti-oxidants, compounds that take up or react with these free radicals, are extremely beneficial.

Chocolate contains many kinds of anti-oxidants, including polyphenols and flavonoids.  Some studies report that flavonoids inhibit LDL cholesterol oxidation. In addition to the reduction of LDL cholesterol, chocolate contains a fat called stearic acid that presents another health benefit.  Research published in the American Journal of Clinical Nutrition demonstrates that stearic acid can boost HDL levels.  Other research indicates that oleic acid may also be good for the heart.

This heart-healthy news about chocolate will come as good news to many people that claim to crave it.  While research on the health benefits of chocolate increases, chocolate “addiction” has been receiving some attention also.  There are over 400 chemicals in chocolate, many of which are known to affect mood. Studies published by the ADA indicate that the addiction is real, but there are arguments as to whether they are physiological or psychological in nature. For example, chocolate consumption can affect levels of endorphins, serotonin, and phenylethylamine.  It appears that women may be drawn to chocolate to boost certain hormonal levels that produce a desired mood.

Clearly, chocolate is a more complex delicacy than anyone realized and it seems that its benefits are only beginning to be uncovered.  As with anything, the saying “too much of a good thing” holds for chocolate as well.  One cannot ignore the disadvantages of eating too much fat in favor of the moderate advantages of lower cholesterol and anti-oxidants.

Pertinent Text References
Chapter 14
    - cholesterol:  pg 633-634
Chapter 19
    - phenylethylamine:  pg 819
Chapter 25:  Lipids
    - oleic acid:  pg 1166
    - cholesterol:  pg 1174 & 1180


Question 1:  What is the structure of oleic acid and stearic acid, and give the IUPAC name?

Answer 1

Question 2:  How is cholesterol oxidized?

Answer 2

Question 3:  Show a mechanism of how the O2 di-radical reacts with double bonds in unsaturated fatty acids.  (Hint:  Allyl stablized radicals)

Answer 3

Question 4:  Phenylethylamine is a hormone and is the component in chocolate that make one feel "in love."  Taken as a drug, it is regarded as highly addictive.  Synthesize phenylethylamine from benzene.  Use any reagents necessary.

Answer 4

Question 5:  If we advertise chocolate as a health benefit, will people ignore the other negative health effects?