Omega Fatty Acids

"Health Food" companies are always trying to sell us something new.
Instead of eating tasty fish they recommend we consume fish oil wrapped in plastic as a pill. Apparently this is because we are suddenly deficient in "omega-3 fatty acids".
So what are omega-3 fatty acids?
Where do they come from?
Do we really need them?

AUS-e-TUTE Members should log-in to access the new omega fatty acid resources (tutorial, game, test, exam).

If you are not an AUS-e-TUTE Member you can access a free-to-view tutorial at
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Short Chain Fatty Acids?

I came across this story in the Sydney Morning Herald this morning, "A make-or-break moment for what may be a new molecule". Sounds exciting doesn't it. A hint of uncertainty, is it or isn't it a new molecule? What will it "make or break"?

It appears that Charles Mackay, a Professor of Microbiology at Monash Biomedicine Discovery Institute has, "demonstrated that dietary fibre and its breakdown fermented products, the short chain fatty acids (SCFAs) influence gut homeostasis, the composition of the gut microbiota, immune tolerance, and inflammatory responses."  I must apologize, I've never been particularly interested in biology, so I actually have no idea what any of that means, but from the story in the newspaper it appears that Professor Mackay thinks we should be eating more "short chain fatty acids" as are present in fermented foods such as vinegars and hence vegetables pickled in vinegars, and this will help regulate our blood pressure and immune system, keeping us healthy. Good news for me, I love pickled onions and gherkins, and have been known to indulge in sauerkraut and kimchi.

But what on earth is a "short chain fatty acid"?

Now, a fatty acid is a long chain carboxylic acid.
A carboxylic acid is a molecule with a carboxylic acid functional group (COOH) at the end of a hydrocarbon chain.
For example, formic acid is the carboxylic acid which is present in an ant's sting. It has only one carbon atom in the chain, its formula is HCOOH (CH₂O₂)
Acetic acid is the carboxylic acid that gives vinegar it's tang. It has 2 carbon atoms in its chain,

CH₃-COOH (C₂H₄O₂)

But fatty acids have lots of carbon atoms in the chain, common fatty acids have 12 or 14 or 16, or 18 carbon atoms in the chain. These fatty acids (long chain carboxylic acids) are found naturally in the oils and fats of plants and animals. If the long hydrocarbon chain is saturated (contains only single bonds between the carbon atoms in the chain) it is called a saturated fatty acid. If there is one, or more, double bonds between carbon atoms in the long chain then it is referred to as an unsaturated fatty acid.

So a "short chain fatty acid" would be what? A short long chain carboxylic acid? Sounds like nonsense doesn't it? Maybe it's a medium length chain carboxylic acid?

According to wikipedia (which may or may not be a reliable source of information),  a "short chain fatty acid" is a fatty acid with 2 to 6 carbon atoms. Included in wikipedia's list of "short chain fatty acids" are the two carboxylic acids we used as examples above, formic acid (which has only 1 carbon atom in its chain and hence does not actually fit within wikipedia's own definition and hence my concern about the reliability of the information it provides), and, acetic acid. So, a "short chain fatty acid" is in fact NOT a short chain "fatty acid", it is simply a short chain carboxylic acid!

Is the "molecule" new, as claimed by the headline? Most unlikely because:

• "short chain fatty acids" is just a poor description of a group of molecules sharing a carboxylic acid functional group, not just 1 molecule
• we've known about these short chain carboxylic acids for a very, very long time

References:
http://www.smh.com.au/national/a-make-or-break-moment-for-what-may-be-a-new-miracle-molecule-20180216-p4z0ky.html
https://research.monash.edu/en/persons/charles-mackay 
https://en.wikipedia.org/wiki/Short-chain_fatty_acid 

Suggested Study Questions:

1.  Draw the 2-dimensional structure formula for each of the following carboxylic acids:
   • formic acid
   • acetic acid
   • propanoic acid
   • butanoic acid
   • pentanoic acid
   • hexanoic acid
2. Draw a condensed structural formula for each of the carboxylic acids in question 1.
3. Draw a skeletal structural formula for each of the carboxylic acids in question 1.
4. Give the molecular formula for each of the carboxylic acids in question 1.
5. Give the empirical formula for each of the carboxylic acids in question 1
6. Are the carboxylic acids in question best described as saturated or unsaturated? Explain your answer.
7. On each 2-dimensional structural formula, identify, circle and name the functional group common to all the molecules.
8. Draw at least 2 structural isomers with the molecular formula C₅H₁₀O₂
9. Circle the functional groups in the molecules you draw in question 8. Name these functional groups.
10. Choose 2 of the structural isomers drawn in question 8. Would you expect these 2 molecules to have very similar, or very different, physical and chemical properties. Explain your answer.

Omega-3 Acids Fight Cancer

Scientists at the University of Guelph have found that omega-3s from fish are better at preventing cancer than omega-3s from plants.

"Omega-3s" refer to omega-3 fatty acids which are a type of long-chain, polyunsaturated carboxylic  acid. Long-chain carboxylic acids are referred to as "fatty acids".
The three omega-3 fatty acids studied were: 

• α-linolenic acid (ALA) which is found in plant seeds and oils

• eicosapentaenoic acid (EPA) which is found in fish, algae and phytoplankton

• docosahexaenoic acid (DHA) which is found in fish, algae and phytoplankton

 The skeletal structural formula for α-linolenic acid is shown below:

 The IUPAC name of α-linolenic acid is (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid. 
The carbon atom of the carboxyl functional group (COOH) is labelled as 1, the next carbon atom in the chain is 2, then 3, etc, up until we reach the last carbon in the chain, carbon 18. The parent hydrocarbon for this molecule is therefore octadecane, with a suffix added for the carboxyl functional group, so we have octadecanoic acid. 
Along the way we find 3 (tri) double bonds (en) at carbons numbered 9, 12 and 15, so we modify the name of the carboxylic acid in one of two ways:

• 9,12,15-octadecatrienoic acid

• octadeca-9,12,15-trienoic acid

The "Z" indicates the 3-dimensional geometry,  in this case the "Z" geometry equates to a "cis" geometry.
So why would  (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid be called an omega-3 acid?
There is an alternative naming "system" (not IUPAC)  in which the first carbon atom is not labelled 1, but instead it is called "alpha" (α), and, the carbon atom at the end of the long hydrocarbon chain is called "omega" (ω). Then, the last carbon atom in the chain (omega) is labelled 1, and you start counting back towards the carboxyl functional group. If you do this, you will find that carbon 3 has a double on it, hence, (9Z,12Z,15Z)-9,12,15-octadecatrienoic acid is called an omega-3 fatty acid. The 3 indicates the position of the first double bond from the omega carbon atom.

The skeletal structural formula of eicosapentaenoic acid is shown below:

The IUPAC name for this molecule is (5Z,8Z,11Z,14Z,17Z)-5,8,11,14,17-Icosapentaenoic acid. 
There are 20 carbon atoms in the chain so the parent hydrocarbon chain is icosane, which is modified with a suffix because there is a carboxyl functional group, icosanoic acid.
There are 5 (pent) double bonds (en) located on carbons 5, 8, 11, 14 and 17, so the name of this molecule is either:

• 5,8,11,14,17-icosapentenoic acid

• icosa-5,8,11,14,17-pentenoic acid

Once again, the Zs in the name refer to the geometry (same as a "cis" geometry in this case).
Notice that, in the alternative naming "system" in which the last carbon atom in the chain is labelled "omega" and then you count backwards from this, we see that the first double bond encountered is on carbon 3, so this molecule is also referred to as an omega-3 fatty acid.

The skeletal structural formula below is that of docosahexaenoic acid:

This molecule has the IUPAC name (4Z,7Z,10Z,13Z,16Z,19Z)-4,7,10,13,16,19-Docosahexaenoic acid. 22 carbon atoms in the chain (docosa), 6 (hexa) double bonds on carbons 4, 7, 10, 13, 16, 19 and a carboxyl functional group: 4,7,10,13,16,19-docosahexaenoic acid or docosa-4,7,10,13,16,19-hexenoic acid. Zs indicate geometry (same as "cis" in this case).
Using the alternative numbering system, the first double bond occurs of the third carbon atom from the omega carbon atom (last carbon in the chain) so it is also classified as an omega-3 fatty acid.

While all three of these omega-3 fatty acids were shown to be effective in reducing the size of tumours in mice, however, higher doses of the plant-based α-linolenic acid was required to deliver the same impact as the omega-3 fatty acids found in fish (icosapentaenoic acid and docosahexaenoic acid)



Reference:

Jiajie Liu, Salma A. Abdelmagid, Christopher J. Pinelli, Jennifer M. Monk, Danyelle M. Liddle, Lyn M. Hillyer, Barbora Hucik, Anjali Silva, Sanjeena Subedi, Geoffrey A. Wood, Lindsay E. Robinson, William J. Muller, David W.L. Ma. Marine fish oil is more potent than plant based n-3 polyunsaturated fatty acids in the prevention of mammary tumours. The Journal of Nutritional Biochemistry, 2017; DOI: 10.1016/j.jnutbio.2017.12.011

Further Reading:
Introduction to naming organic molecules: http://www.ausetute.com.au/namctut1.html
Introduction to functional groups: http://www.ausetute.com.au/fungroup.html
Fatty acids: http://www.ausetute.com.au/fattyacid.html 
Structure and properties of carboxylic acids: http://www.ausetute.com.au/carboxyl.html
Molecular formula: http://www.ausetute.com.au/molecularformula.html
2-Dimensional structural formula: http://www.ausetute.com.au/structural2D.html
Condensed structural formula: http://www.ausetute.com.au/condensedsf.html
Skeletal structural formula: http://www.ausetute.com.au/skeletal.html
Cis-trans isomers: http://www.ausetute.com.au/cistranso.html 


Suggested Study Questions:

1. What functional group is common to all fatty acids? 
2. Define the following terms as they are used in chemistry:
   • saturated
   • unsaturated
   • monounsaturated
   • polyunsaturated
3.  Give the molecular formula for each of the three omega-3 acids in the article
4. The structural formula given in the article are referred to as "skeletal". What does this mean in chemistry?
5. Draw a 2-dimensional (full display) structural formula for each of the omega-3 acids in the article.
6. On the structural formula of each of the three omega-3 acids circle the:
   
   • carboxyl functional group in red
   • double bonds in blue
7. What features are common to three omega-3 acids in the article?
8.  In what ways do the the three omega-3 acids in the article differ?
9. You have probable heard about omega-6 acids. How do you think an omega-6 acid will be similar to an omega-3 acid?
10. How will an omega-6 acid be different from an omega-3 acid?
11. What is meant by a cis isomer and a trans isomer?
12. All the omega-3 fatty acids in the article are the cis isomers. Build a model, and draw, a trans isomer of one of the fatty acids.

Betaines

Betaines are found in plants, animals and microorganisms. Rich sources of betaines in the human diet are seafood, spinach and wheat germ or bran. Research is beginning to indicate that betaines are important nutrients for the prevention of chronic disease. Researchers are also interested in incorporating betaines into polymer brushes used for antifouling and lubrication.

Betaines are compounds with a positively charged functional group linked to a negatively charged functional group with an alkyl chain in between. The alkyl chain is often referred to as an alkyl chain spacer.  The general structure of an N-alkyl betaine is shown below:

The first betaine discovered was found in sugar beets in the nineteenth century. This betaine is (trimethylammonio)acetate, also known as trimethylglycine, and its skeletal structure is shown below:

Another example of a betaine is 2-(trimethylammonio)octadecanoate (also known as hexadecylbetaine) with the skeletal structure shown below:

2-(Trimethylammonio)tetradecanoate, or dodecylbutaine or laurylbutaine, is also a butaine and its skeletal structure is shown below:

Betaines are strongly attracted to water molecules because of these two charged functional groups.
The solubility of betaines in water is dependent on the length of the carbon chain, as well as on temperature and pH. 
In acidic solution, betaines acquire a net positive charge and act like a cationic surfactant. In anionic solutions, betaines acquire a net negative charge and act like an anionic surfactant.

Betaines can also be used in polymer brushes which are polymers bound to a surface. Polymer brushes can be used for antifouling and lubrication because the hydration of the ionic groups reduces the ability of other materials to adhere to the surface. 

Researchers at Kyushu University recently investigated a series of alkly chain spacers of different lengths bound to a silicon surface. They found that the polymer brushes swelled in humid air and water. It is believed that this is due to electrostatic repulsion between charged groups, and not dependent on the length of the alkyl chain.
In deionised water, net positive cations and net negative anions are repelled because of the  electrostatic force which causes the chain dimension to expand, whereas they shrink under high ionic strength by a charge screening effect of the bound ions.

Reference:
https://www.sciencedaily.com/releases/2017/08/170821094302.htm

Further Reading
Introduction to Functional Groups
2-Dimensional Structural Formula
Condensed Structural Formula
Molecular Formula
Amino Acids
Surfactants ( as found in synthetic detergents)
Intermolecular Forces and Solubility

Suggested Study Questions

1. Locate and identify each functional group on the skeletal structural formula of
• general formula N-alkyl betaine 
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
2. Draw a 2-dimensional structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
3. Write the condensed structural formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
4. Write the molecular formula for each of the following molecules:
• (trimethylammonio)acetate
• 2-(trimethylammonio)octadecanoate
• 2-(trimethylammonio)tetradecanoate
5. Compare the structure of betaines to that of 2-amino acids. Can N-alkyl betaines be classified as alpha amino acids (2-amino acids) ? Justify your answer.
6. Write chemical equations to describe what happens to an N-alkyl betaine in:
• acidic aqueous solution
• basic aqueous solution
7. Compare the structure of N-alkyl betaines to the surfactants found in synthetic detergents. In what ways are surfactant molecules 
• similar to N-alkyl betaines
• different from N-alkyl betaines
8. Explain how N-alkyl betaines act like 
• a cationic surfactant in acidic aqueous solution
• an anionic surfactant in basic aqueous solution
9. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in water? Justify your answer.
10. Consider the structure of (trimethylammonio)acetate and 2-(trimethylammonio)octadecanoate. Which molecule do you expect to be more soluble in paraffin oil? Justify your answer.

Fatty Acids

Do you want to answer any of the questions listed below:

• What is a fatty acid?
• What are the structures and formulae of common fatty acids?
• What is a saturated fatty acid?
• What is an unsaturated fatty acid?
• What is a monounsaturated fatty acid?
• What is a polyunsaturated fatty acid?
• What determines the melting point and solubility of a fatty acid?
• What is an essential fatty acid?
• What is an omega-3 fatty acid?
• What is an omega-6 fatty acid?

AUS-e-TUTE has new resources to help you answer these questions!
AUS-e-TUTE Members should log-in to use the new tutorial, game, test and exam.

If you are not an AUS-e-TUTE Member, a "free-to-view" Fatty Acids tutorial is currently available at http://www.ausetute.com.au/fattyacid.html for evaluation purposes.

Polylactic Acid

The London Organizing Committee of the Olympic and Paralympic Games (LOCOG) was committed to making 2012 the very first "zero-waste" Olympic and Paralympic Games.

11 million attendees produced 8,500 tons of solid waste, mostly in the form of plastic packaging.

8,000 tons of this plastic waste was transported to a site where it was composted within 9 weeks and subsequently used to fertilize local crops.

That's right!

There are plastics that can be composted, and the plastic used at the London Olympic Games was the most common compostable plastic which is known as polylactic acid or PLA.

And the chemistry of polylactic acid (PLA) is the subject of this edition of AUS-e-NEWS, AUS-e-TUTE's free quarterly newsletter.

You can subscribe to our newsletter by contacting us at http://www.ausetute.com.au/contact.html

Carboxylic Acid Nomenclature

Learning to name alkanoic acids (simple carboxylic acids) has never been easier thanks to AUS-e-TUTE's latest resources.
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A free tutorial is currently available for evaluation purposes at
http://ausetute.com.au/namalkacid.html

For membership information  go to http://ausetute.com.au/membership.html

To join AUS-e-TUTE go to http://ausetute.com.au/register.html

AUS-e-TUTE Update

The following resources have been added to AUS-e-TUTE:

• Neutralisation Reactions (tutorial, game, test)
• Acidic, Basic, Neutral Solutions (tutorial, game, test)
• Properties of Alkanes (tutorial, game, test, exam)
• Properties of Alkanols (alcohols) (tutorial, game, test, exam)
• Properties of Alkanoic (carboxylic) acids (tutorial, game, test, exam)
• Properties of Amines (tutorial, game, test, exam)

Syllabus Study Guides have also been updated.