Current Topics in Chemistry - Wade - Chapter 5
This news item was created by students Mark Beard, Joshua Botdorf, Andrew Felker, Derek Freund, Tim Michaelree, and Cary Sanders as part of their Chemistry 210 Semester Project in the WS99 under the guidance of Prof. Rainer Glaser.

Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 5. Stereochemistry.


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

POLARIZED LIFE
By David Schneider, American Scientific, 1998.


Editorial Comments

"Space...the final frontier." Or is it? Throughout history, many scientists and astronomers have theorized that perhaps life, or some form of life, existed in outer space or some far reaches of the galaxy. These theories, however, were in desperate need of proof of some type and scientists awaited some discovery that would give them a glimmer of hope with their theories. Recently, this glimmer has arisen with the discovery of celestial dust particles in star nebulas, which may be organic in nature. This discovery, outlined in David Schneider's article "Polarized Life", may be the beginning of an explanation which would not only show proof of life in space, but it would also give an explanation of the origin of the organic molecules that play a part in our everyday lives.

The genesis of stars and star formations reside in vast regions of gas and dust particles known as celestial dust clouds. It is here that stars and star formations are born, and these areas, known as nebulas, play an important role in the study of space. One such region of space, found in the Orion constellation, has played a very significant role in the previously mentioned studies of scientists. This region known as "Orion's OMC-1 star-formation region" has been studied extensively and seems to provide proof of life in space and evidence to the origins of organic molecules on earth.

This study, conducted by astronomers of the Anglo-Australian Observatory, first set out to attempt to understand the makeup of molecules found in these nebulas in space. The astronomers were measuring the polarization of these molecules that can come about when celestial dust grains scatter the light, which comes from nearby stars. This polarized light coming from the stars and nebulas allows the scientists to understand more, the properties of these celestial grains in outer space through observed rotations. The property of molecules which allows for this effect of light is known as chirality. Chirality is the right or left-handedness of molecules and it is this characteristic which turns the polarized light either to the left or right certain degrees or amounts. Throughout most of the researchers' studies, only minute amounts of optical rotation were observed. Orion's OMC-1 star-formation region, however, gave the researchers an optical rotation of almost 17 percent circular polarization. Only organic molecules in the grains of the celestial dust cloud could produce such dramatic results and scientists involved, saw a new discovery emerging.

Through all degrees of life, homochirality plays an important role in all biological mechanisms. This homochirality, or one-handedness, is important in amino acids and other organic molecules. The researchers of this discovery believe that this observed handedness in celestial dust clouds could explain the selectivity found in biological pathways, which accept either right or left-handed molecules. "The handedness of life could be explained if circularly polarized ultraviolet light bathed the dusty cloud that...preferentially destroyed the right-handed amino acids."

Although much of this is still hypothetical, it does give scientists and researchers some hard evidence which may lead to further understanding of the origins of life and proof that space is our primary frontier, rather that our final one.

For more information please see "The Sinister Cosmos" and "Murchison Meteorite"

 

Pertinent Text References
Chapter 5. Stereochemistry
Section 5-2. Chirality
Section 5-3. (R) and (S) Nomenclature of Chiral Carbon Atoms
Section 5-4. Optical Activity
Section 5-5. Biological Discrimination of Enantiomers


Questions

Question 1: In the editorial and in the article itself, the author tends to stress the importance of homochirality in biological systems. Why do you think it would be important for biological systems to accept only one-handedness of molecules and how does it add to the success of these systems?

Suggested Answer: Homochirality and one-handedness of biological systems allows for greater accuracy and stability through biological pathways and enzymatic reactions. The selectivity of certain forms of a chiral molecule in an enzymatic reaction, and the functionality of only certain chiral forms of a molecule is a biological system also contribute to the success of that biological

Question 2: According to the article, who was the first individual to understand the concept of chirality, and when did he discover it?

Suggested Answer:Louis Pasteur in 1848.

Question 3: In reference to topics of observed rotation and polarized light, why would researchers involved in this discovery be able to bring to light the makeup of organisms through their observed optical rotations?

Suggested Answer: The chirality of molecules of which the organism is composed. Because chiral structures rotate polarized light according to their degree of handedness.

Question 4: Do you personally believe that this evidence is significant in any way, and what do you feel should be the next step in this investigation? Is it important for science to prove our origins of existence?

Suggested Answer: Your opinion. Sorry. (Of course we believe this is important and that more research should be done. We want to know what you think.)

Question 5: In the article the main problem with the researchers argument is the fact that they discovered only circularly polarized infrared light instead of circularly polarized ultraviolet light. Why is it so important to their argument that the presence of circularly polarized ultraviolet light be discovered?

Suggested Answer: Because the energy per photon of ultraviolet light and not infrared light is great enough (70-140 kcal/mol for UV and only 1.1-11 kcal/mol for Infrared) to break typical bonds in organic molecules, which have bond dissociation energies between 36 and 136 kcal/mol.