Problem of the Week
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Garlic and the Role of Phytochemicals
Phytochemicals are biologically active plant molecules often produced by plants to protect it from being damaged by bacteria, fungi and parasites. These naturally
occurring plant chemicals are being demonstrated to help prevent chronic diseases, such as cancer and heart disease in humans. |
| Garlic, a perennial plant with white, starry flowers and bulb clusters of individual cloves, produces two important phytochemicals.
For thousands of years, garlic has been used throughout the world as a medicine. Sanskrit records, from approximately 5000 years ago, describe the use of garlic remedies. Chinese, Egyptian,
and Greek documents from Hippocrates, Aristotle and Pliny cite numerous therapeutic uses for garlic. In 1844 Theodor Wertheim, a German chemist, distilled a pungent substance from garlic
and called it allyl, the Latin name for garlic. Four years later, Louis Pasteur in Paris showed that allyl could inhibit the growth of bacteria. This was a great discovery because 150
years ago, doctors had nothing to kill bacteria. |
| Whole garlic cloves are intact bulbs that contain an odorless, sulfur-containing amino acid derivative called ALLIIN, a covalently
bonded compound with the chemical formula C6H11NO3S. When the bulb is crushed or cut, alliin is altered by the enzyme, alliinase and is converted into
allicin. Allicin (C6H10OS2) is an oily, yellow liquid that gives garlic its characteristic odor. Modern research has confirmed that the garlic plant can
be used to protect against infections, to lower blood cholesterol and fat levels, and to help with digestion. |
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List the covalent bonds present in one molecule of allicin. |
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Draw the Lewis structure for allicin. |
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Using the bond dissociation energy table, determine the total bond energy for one molecule of allicin. |
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Ajoene, C9H14OS3 an unsaturated sulfoxide disulfide, is the principal chemical
responsible for garlic's anticoagulant properties. It is a component of allicin and is currently being developed as a pharmaceutical for the treatment of blood clotting disorders. As a
naturally occurring "nutriceutical", this potent phytochemical might reduce the risk of stroke and heart disease. In addition, ajoene also has been found to have effective antimicrobial
properties, inhibiting the growth of both bacteria and fungi. |
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List the covalent bonds that are present in one molecule of ajoene. |
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Draw the Lewis structure for ajoene. |
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Using the bond dissociation energy table, determine the total bond energy of one molecule of ajoene. |
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Table: Bond dissociation energy (kJ/mol)
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Bond
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Energy
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Bond
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Energy
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H-H
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436
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C=O
|
745
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H-C
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416
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S=O
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522
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C-C
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345
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C=C
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614
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H-N
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391
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C-N
|
305
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N-N
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170
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C≡C
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839
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H-O
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464
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C-O
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358
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O-O
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138
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C-S
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259
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H-F
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569
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O-O
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145
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F-F
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159
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C-F
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488
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H-Cl
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431
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O=O
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494
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Cl-Cl
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243
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C-Cl
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330
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H-Br
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368
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C-Br
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288
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Br-Br
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192
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N-N
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170
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H-I
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297
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C-I
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238
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I-I
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151
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N≡N
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946
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S-S
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213
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N=N
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418
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Useful Web Sites:
Allicin - The Garlic Antibacterial
Allicin - The Smell of Health
Allicin in Garlic
Nova Online - Hot Science: Plant
Magic
Table 6: Common Bond Energies and Bond
Lengths |
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