Lab 2: Lipid Characterization Flashcards
What are the three primary functions of fat?
1) Storage
2) Cushion to vital organs (ex: kidneys)
3) Insulation
What elements compose fatty acids?
Carbon, hydrogen, and oxygen
What group is at the end of a fatty acid chain?
Carboxyl
What are triglycerides compose of? How are they joined?
- Glycerol and three fatty acids
- Joined by dehydration synthesis
What is glycerol?
A type of alcohol with a hydroxyl group on each of its three carbons
What are lipids soluble in? What are they insoluble in?
- Soluble in solvents (hexane, acetone)
- Insoluble in water
What is saponification? What are the products produced?
- Hydrolysis of a triglyceride with an alkali, such as NaOH
- Sodium salts of the fatty acids and a glycerol
Are fats typically saturated or unsaturated? Why are they solid?
- Saturated (animal sources)
- Straight chains are easier to pack closely together
Do saturated or unsaturated fatty acids have more hydrogens?
Saturated fatty acids are SATURATED with hydrogen (more)
Are oils typically saturated or unsaturated? Why are they liquid?
- Unsaturated (plant sources)
- Double bonds induce kinks in the structure, inhibiting close packing
How can we analyze the degree of bond saturation?
- Iodine Value
- Utilize a halogen solution, such as iodine or bromide
- Analyze the degree of decolourization of these solutions after it comes into contact with the lipid
What is the basis of the Iodine Value test?
- The more double bonds a fat contains, the more halogen is required
- A high iodine number means a high degree of unsaturation
How can we analyze differences in chain length?
By the differences in intensity of colour due to the absorption of a chemical known as Sudan III
What compound is used to analyze chain length?
Sudan III
What compound is used to analyze the degree of bond saturation?
Halogen solution (iodine or bromide)
How do water and lipids differ in terms of polarity?
- Water is polar due to differences in electronegativity between O and H
- Lipids are nonpolar
What happens when a lipid is dissolved in water?
- Water molecules form a cage around lipids, increasing the order and reducing the entropy of the system (thermodynamically unfavourable)
- Water (polar) and lipids (nonpolar) form two phases in solution
Why is acetone amphiphatic?
- Acetone is hydrophilic due to its polarity
- Acetone may dissolve lipids in water since it can interact with them due to its two methyl side chains
What is needed for saponification?
Water since it is a hydrolysis reaction
How many molecules of base are needed in saponification? What do they cleave?
- 3 molecules (NaOH or KOH)
- Cleave 3 ester bonds of one TG
How does the base break ester bonds in saponification? In between which atoms?
OH- nucleophiles of the base break C=O pi bonds in each fatty acid
In saponification, how is a carboxylate anion formed?
- Following hydrolysis of the C=O bi bond
- Intermediate reforms the pi bond, forming an alkoxide leaving group
- Alkoxide leaving group depronotates the carboxylic acid, resulting in a carboxylate anion
What do Na+ cations react with in saponification?
React with the anions to form sodium salts of the fatty acids (soaps)
What are the products of a saponification reaction of one triglyceride?
- 3 soap molecules
- 1 glycerol
What kind of soap molecules does KOH form? Why?
- Liquid soap
- Since it is more water-soluble
What kind of soap molecules does NaOH form? Why?
- Solid soap
- Since it is less water-soluble
What happens when soap is dissolved in water? What compounds are formed?
- Na+ ions dissolve since charged particles are water-soluble
- Hydrophilic carboxylate anion is attached to a hydrophobic hydrocarbon chain (amphipathic)
How do amphipathic molecules reorient themselves in water?
Into micelles, where the anions point outside (thermodynamically favorable)
How does the hydrophilic domain of soap interact with hydrophilic compounds?
Through hydrogen bonds and ion-dipole interactions
How does the hydrophobic domain of soap interact with hydrophobic compounds?
- Trap non-polar compounds in their center
- They are rinsed away with water
Why do soap micelles stay dispersed in water?
Since the carboxylate anions are charged negatively, which makes them repel one another
What is RO-?
Alkoxide leaving group
What is the role of RO-?
Acts as a base by deprotonating the carboxylic acid, resulting in the formation of a carboxylate anion
What is the saponification value?
The amount of KOH (mg) needed to neutralize the fatty acids from the hydrolysis of 1- gram of oil
What do the K+ cations neutralize?
The carboxylate anions
What is phenolphthalein?
Weak acid indicator that is pink in basic solutions, and colourless in acidic solutions
What is the role of HCl in the determination of the iodine value?
HCl was the titrant, which allowed the determination of the endpoint through the phenolphthalein indicator
What does the saponification value indicate?
Indicates the average weight of the FAs in a TG
Do long-chain fatty acids have lower or higher SV? Why?
- Lower
- Due to fewer carboxylate anions per unit of mass, requiring less KOH for neutralization
Is the saponification value of jojoba oil lower or higher than coconut oil?
Lower
Are lipids soluble in NaOH? Ethanol? Acetone? Chloroform?
- NaOH: no
- Ethanol: no
- Acetone: yes
- Chloroform: yes
Does jojoba oil react positively or negatively to the acrolein test? What about coconut oil?
- Jojoba: positive (smelly)
- Coconut: negative (no smell)
Did coconut oil produce a hard or soft soap? Why?
- Hard soap
- Since it mostly contains lauric acid, which is highly saturated –> contributes to the hardness of the soap
- Saturated fatty acids pack better due to their straight conformation
Did jojoba oil produce a hard or soft soap? Why?
- Soft soap
- Since jojoba oil is a liquid wax
- Contains little triglycerides, although the ones that it does contain, are all unsaturated
What is the reaction in the acrolein test?
- Glycerol reacts with KHSO4
- Produces acrolein (unsaturated aldehyde) and 2 water molecules
Did jojoba oil or coconut oil smell from the acrolein test?
Coconut oil did, since it contains glycerol
Jojoba oil only contains 3% TG, so very little glycerol (no smell)
