CHAPTER 17: Unit 4. Lipids Physical Properties

The general physical properties of ALL lipids is being insoluble in water. Examples of physical properties are given below:

1.  Fatty Acids

Prostaglandins (PG) general structures:

The different types of prostaglandins can be processed and decomposed easily. Some of the prostaglandins can cause higher blood pressure and others can cause lower blood pressure. Furthermore, some prostaglandins can cause contraction and relaxation in human muscles.In case of injury, the arachidonic acid is converted into prostaglandins. In this process, inflammation and pain are appearing in the area of the injury where such conversion had taken place.Some drugs and anti-inflammatory medicine can be used to fight such inflammation and injury. In this process the prostaglandins are converted back into arachidonic acid. Such drugs are called NASID which are none steroidal based. NASID stands for N = Nonsteroidal, A = Anti, I = Inflammatory and D = Drugs).Examples of such NASID are:Naproxen such as Aleve and NaprosynKetoprofen such as ActronNabumetone such as RelafanLong term usage of such NASID may have very strong side effects which cause to kidney failure and gastro-intestinal destruction and damage.

2. Lipids Based on Fatty Acids:

The melting and the boiling points of fatty acids and lipids based on fatty acids will depend on the length of the hydrocarbon long chain. The higher the long chain hydrocarbon, the higher the molar mass the higher is the melting and boiling points.As mentioned above, the “kink” or the “curved shape” of the cis unsaturated fatty acid will lead to irregular shape and unpacked shape resulting in lower melting and boiling points of such unsaturated fatty acids compared to their trans isomers which have very linear packed shape.The boiling points as well as the melting points of oils (liquid unsaturated triglycerides) and fats (solid saturated triglycerides) will depend on their structures. While monounsaturated as well as polyunsaturated triglycerides tend to be liquids and the saturated glycerides tend to solids in general. The long chain hydrocarbon (generally in glycerides solids or liquids) as well as the number of double bonds (in monounsaturated and polyunsaturated glycerides) will determine the melting and the boiling points being higher or lower when looking at the comparison between them.Generally, saturated fatty acids and their corresponding triglycerides exhibit higher melting and boiling points than the monounsaturated and polyunsaturated fatty acids and their corresponding triglycerides and tend to be solids at room temperature. The monounsaturated and the polyunsaturated fatty acids and their corresponding triglycerides will have lower melting and boiling points in general. The higher the number of double bonds is, the lower the melting and boiling points is in the monounsaturated and the polyunsaturated fatty acids and their corresponds triglycerides.

3. Steroids