Introduction and characterization of fatty acids.

1. FATTY ACIDS – INTRODUCTION, & PROPERTIES

2. FATTY ACIDS – INTRODUCTION
Fatty acids which occur in natural fats are usually monocarboxylic
and contain an even number of C atoms as these are synthesized
from two carbon units .These range from 4 to 30 carbon atoms
and are straight chain derivatives. The chain may be saturated
(containing no double bonds) or unsaturated (containing one or
more double bonds) . Some fatty acids may have hydroxyl
group(s) in the chain ( hydroxy fatty acids) and still others may
possess ring structure (cyclic fatty acids). They are generally
present in the esterified form as glycerides and phospholipids. If
free, a carboxyl group of a fatty acid will be ionized.
Fatty acids differ from each other in
a) length of hydrocarbon tail,
b) degree of unsaturation,
c) position of of double bonds in the chain.
Short-chain fatty acids like acetic , propionic and butyric acids are
intermediates in metabolism.

3. FATTY ACIDS - FUNCTIONS
Functions of Fatty Acids:
1) Source of energy in stored forms
2) Solubilize vitamins like A, D, E, and K.
3) Building units of majority of lipids
4) Constituent of phospholipids

4. FATTY ACIDS - NOMENCLATURE
b)The omega-reference system indicates the number of
carbons , the number of double bonds and the position
of the double bond closest to the omega carbon,
counting from the omega carbon (which is numbered 1
for this purpose). This system is useful in physiological
considerations because of the important physiological
differences between omega - 3 and omega - 6 fatty
acids, and the impossibility to interconvert them in the
human body.

5. FATTY ACIDS - NOMENCLATURE
Greek Letters are Used in Two Ways

6. FATTY ACIDS - NOMENCLATURE
Summary of the Four Common Systems
Here are the four commonly used ways of designating fatty acids.

7. FATTY ACIDS - NOMENCLATURE
5) Δx (or delta-x) nomenclature-
•Each double bond is indicated by Δx, where the
double bond is located on the xth carbon–carbon
bond, counting from the carboxylic acid end.
• Each double bond is preceded by a cis- or trans-
prefix, indicating the conformation of the molecule
around the bond. For example, linoleic acid is
designated "cis-Δ9, cis-Δ12 octadecadienoic acid".
•This nomenclature has the advantage of being less
verbose than systematic nomenclature, but is no
more technically clear or descriptive.

8. FATTY ACIDS - NOMENCLATYRE
6) Lipid numbers- take the form C:D, where C is the
number of carbon atoms in the fatty acid and D is the
number of double bonds in the fatty acid (if more
than one, the double bonds are assumed to be
interrupted by CH2 units, i.e., at intervals of 3 carbon
atoms along the chain).
•This notation can be ambiguous, as some different
fatty acids can have the same numbers.
Consequently, when ambiguity exists this notation is
usually paired with either a Δx or n−x term.

9. FATTY ACIDS-CLASSIFICATION
Classification of fatty acids:-
1) Saturated Fatty Acid: Contain no double bond, chain is
saturated. The molecular formula of a saturated fatty
acid is CnH2n+1COOH e.g. palmitic acid is
C15H31COOH.
e.g. Butyric acid (4), Caproic acid (6) Caprylic acid (8)
Capric acid (10), Laurie acid (12), Myristic acid (14),
Palmitic acid, (16) Stearic acid (18), Arachidic acid (20)
Behenic acid (22) Lignoceric acid (24), Cerotic acid (26)
Montanic acid (28) [Figures in the bracket is number of
carbons].

10. CLASSIFICATION OF SATURATED FATTY ACIDS
Common Name Systematic Name Structural Formula Lipid Numbers
Propionic acid Propanoic acid CH3CH2COOH C3:0
Butyric acid Butanoic acid CH3(CH2)2COOH C4:0
Valeric acid Pentanoic acid CH3(CH2)3COOH C5:0
Caproic acid Hexanoic acid CH3(CH2)4COOH C6:0
Caprylic acid Octanoic acid CH3(CH2)6COOH C8:0
Capric acid Decanoic acid CH3(CH2)8COOH C10:0
Lauric acid Dodecanoic acid CH3(CH2)10COOH C12:0
Myristic acid Tetradecanoic acid CH3(CH2)12COOH C14:0
Palmitic acid Hexadecanoic acid CH3(CH2)14COOH C16:0
Stearic acid Octadecanoic acid CH3(CH2)16COOH C18:0
Arachidic acid Eicosanoic acid CH3(CH2)18COOH C20:0

11. CLASSIFICATION OF UNSATURATED FATTY ACIDS
2) Unsaturated Fatty Acids: Contain one to six double bonds in
chain and degree of unsaturation depends on the no. of double
bonds present in it. These are sub classified on the basis of
degree of unsaturation.
•Monoethenoid Acids [ monounsaturated fatty acids] (MUFAs):
Contain one double bond e.g. oleic acid, palmitoleic acid .
•Polyunsaturated fatty acids(PUFAs)- The double bonds
alternate with –CH2 groups (nonconjugated double- bond system)
in polyenoic fatty acids and are usually of the ‘cis’ type. These are
divided as follows-
a) Diethenoid Acids: Contain two double bonds e.g. Linoleic acid.
b) Triethenoid Acids: Contain three double bonds e.g. Linolenic
acid, Eleostearic acid
c) Tetraethenoid Acids: Contain four double bonds e.g.
Arachidonic acid.

12. CLASSIFICATION OF UNSATURATED FATTY ACIDS
ω−n
Common
Name
Lipid
Numbers
Δn Structural
Formula
Trans or
Cis
Naturally Occurring in
ω−3
α-Linolenic
acid
C18:3 Δ9,12,15
CH3CH2CH=
CHCH2CH=
CHCH2CH=
CH(CH2)7C
OOH
cis Flaxseeds, chiaseeds, walnuts
ω−3
Eicosapent
aenoic acid
C20:5 Δ5,8,11,14,17
CH3CH2CH=
CHCH2CH=
CHCH2CH=
CHCH2CH=
CHCH2CH=
CH(CH2)3C
OOH
cis
cod liver, herring, mackerel, salmon,
menhaden and sardine
ω−6
Linoleic
acid
C18:2 Δ9,12
CH3(CH2)4C
H=CHCH2C
H=CH(CH2)
7COOH
cis Peanut oil, chicken fat, olive oil

13. CLASSIFICATION OF FATTY ACIDS
Essential Fatty Acids:
Fatty acids which cannot be synthesized by the cells
of the body must be obtained from other source.
Mammals lack the enzymes to introduce double bonds
at carbon atoms beyond C9.Hence, all fatty acids
containing a double bond at positions beyond C9 have
to be supplied in the diet. These are called Essential
fatty acids (EFA) . Important essential fatty acids are
•Linoleic(18:2 ∆ 9,12)
•Linolenic (18:3 ∆ 9,12,15)
•Arachidonic acid (20:4 ∆ 5,8,11,14)

14. PROPERTIES OF FATTY ACIDS-
The length and degree of unsaturation of the
hydrocarbon chain determines many of the properties
of the fatty acids. Properties may be studied under
following headings :-
1.SOLUBILITY IN WATER-Solubility in water decreases
with increase in chain length and degree of
unsaturation of the fatty acids. Short chains are
soluble in water owing to the polar nature of the –
COOH group , which ionizes at neutral lpH. Higher
fatty acids are insoluble in water but soluble in organic
solvents. Except acetic acid , all other fatty acids are
lighter than water.

15. PROPERTIES OF FATTY ACIDS-

16. PROPERTIES OF FATTY ACIDS-
2. MELTING (BOILING)POINT-
Melting and boiling points increase with increasing
chain length but decrease drastically with increase in
the number of double bonds. Fatty acids of chain length
<8C are liquid at room temperature(R.T.).Saturated
fatty acids12:0 to 24:0 have a waxy consistency at R.T.
while unsaturated fatty acids of the same chain length
are oily liquids . Fats containing fatty acids 18:2 are
liquid below 0oC.Saturated chains have an extended, zig-
zag configuration at low temperatures, but shorten at
higher temperatures owing to rotation of the -C-C-
bonds. This explains why biomembranes get thinner
with increasing temperatures.

17. PROPERTIES OF FATTY ACIDS-
3. ISOMERISM-
The presence of double bonds in the fatty acid
chain results in the existence of isomers. Cis
isomers are common in nature but unstable,
while trans isomers are less common but more
stable. Most fatty acids in our body are of the
cis type. Trans fatty acids are common in the
triglycerides of dairy and meat products, and in
partially hydrogenated oils. Saturated fatty
acids like stearic acid, and unsaturated fatty
acids with trans bonds, have linear shapes but
the presence of a cis double bond bends the
shape of the molecule.

18. PROPERTIES OF FATTY ACIDS-
AMPHIPATHIC NATURE-
The carboxylic ends of fatty acid molecules
are hydrophilic and react with the cellular
environment, while the ‘R’ chains are hydrophobic
and interact with each other. This amphipathic
nature is important in the formation and function of
micelles and membranes.
OXIDATION.- Oxidation of the double bonds in
unsaturated fatty acids yield hydroxy, aldehydic and
ketonic derivatives that undergo polymerization
into resins. While this is a cause of rancidity in fats,
oxidation of oils like linseed oil, produces water
proof films.

19. PROPERTIES OF FATTY ACIDS-
HALOGENATION –
Halogenation of the double bonds is useful
analytically . e.g. the Iodine Number is the number of
gms of Iodine required to saturate 100 gms of a fat.
Absorption of UV light by the double bonds is a basis for
characterizing fats.
FORMATION OF ESTERS WITH ALCOHOLS – The
esters of fatty acids with the trihydric alcohol , glycerol
, are called neutral fats or triglycerides . Esters with
some higher monohydroxy alcohols are called waxes.

20. PROPERTIES OF FATTY ACIDS-
FORMATION OF SOAPS WITH ALKALIES – Fatty acids make
soap with alkali.
Sodium soaps are hard. Potassium soaps are soft but costly . To
make sodium soaps usable as toilet soaps, sodium carbonate or
silicate is added in small amounts .This makes soaps lather with
even hard water.
Soaps used for shaving are usually potassium soaps using
coconut oil or palm oil as the source of fatty acids. To make a soap
less alkaline and more smooth to the skin, excess of fatty acids are
added.
Zinc stearate is a soft powder which is non- irritant to the skin and
water repellent. It is commonly used in dusting powders . Calcium
and magnesium soaps are insoluble in water and do not lather .
hard water which contains salts of calcium and
magnesium is hence unsuitable for washing purposes.

21. PROPERTIES OF FATTY ACIDS-
9-HYDROLYTIC RANCIDITY- On storage fats become rancid.
This is caused by the growth of lipase secreting microbes.
Lipase splits fats into glycerol and free fatty acids. Fatty acids
impart unpleasant odour and flavor to the fat. Fats should
not be mixed with water and kept in cold to avoid rancidity.
10-OXIDATIVE RANCIDITY- Oils containing highly unsaturated
fatty acids are spontaneously oxidized by atmospheric
oxygen at ordinary temperatures. The autoxidation takes
place slowly and forms short chain fatty acids(C4-C10) and
aldehydes which give rancid taste and odour to the fats. This
is observed more frequently in animal fats than in vegetable
fats. Vegetable fats contain natural antioxidants which check
autoxidation.

22. PROPERTIES OF FATTY ACIDS-
11- HYDROGENATION- Unsaturated fatty acids, either free or
combined in lipids, react with gaseous hydrogen to yield the
saturated fatty acids. The reaction is of great commercial
importance since it permits transformation of inexpensive
and unsaturated liquid vegetable fats into solid fats. The
latter are used in the manufacture of candles, vegetable
shortenings and of oleomargarine.
Pt, Pd or Ni are used as catalyst in the above reaction.

23. PROPERTIES OF FATTY ACIDS-
Acrolein test- Fats when heated in the presence of a
dehydrating agent NaHSO4 produce an unsaturated
aldehyde called Acrolein from the glycerol moiety. Acrolein
is easily recognized by its pungent odour and thus forms the
basis of the test for the presence of glycerol in Fat molecule.

24. CHARACTERISATION OF FATS-
Fats are characterized (purity check) or otherwise assessed
by determining certain chemical constants for individual fats-
• Saponification number –
Number of mgs of KOH required to neutralize the free and
combined fatty acids in a gm of a given fat is its
saponification number. A high saponification number
indicates that the fat is made up of low molecular weight
fatty acids and vice versa.
• Iodine Number-
is the number of gms of Iodine required to saturate 100
gms of a fat. Since Iodine is taken up by the double bonds, a
high iodine number indicates a high degree of unsaturation
of the fatty acids of the fat.

25. CHARACTERISATION OF FATS-
•Acid number –
Number of mgs of KOH required to neutralize the free
fatty acids in a gm of fat is known as acid number . The
acid number indicates the degree of rancidity of the
given fat.
•Reichert – Meissl (R. M.) number –
The number of mls of 0.1 N alkali required to neutralize
the volatile fatty acids ( separated by saponification ,
acidification and steam distillation of the fat ) contained
in 5 gms of the fat is the R.M. number

26. CHARACTERISATION OF FATS-
Polenske number-It is the number of milliliters of
0.1N KOH required to neutralize the insoluble fatty
acids(those which are not volatile with steam
distillation) obtained from 5 gm. of fat.
Acetyl number-It is the number of milligrams of
KOH required to neutralize the acetic acid obtained
by saponification of 1 gm of fat after it has been
acetylated.(the treatment of fat or fatty acid
mixture with acetic anhydride results in acetylation
of all alcoholic OH groups.) The acetyl number is
thus a measure of the number of OH groups in the
fat. For eg. the caster oil has high acetyl number
(146)because it has high content of a hydroxy acid,
ricinoleic acid.

27. • http://en.wikipedia.org/wiki/Fatty_acid
References:-
• http://library.med.utah.edu/NetBiochem/FattyAcids/4_1a.h
tml
• en.wikipedia.org/wiki/Fattyacid
• http://en.wikipedia.org/wiki/List_of_saturated_fatty_acids
• https://www.rpi.eddeu/pt/bcbp/molbiochem/MBWeb/
mb2/part1/fasynthesis.htm#malcoa
• Bioc 460 Spring 2008 - Lecture 36 (Miesfeld)
• http://www.powershow.com/view/3d84e5-
ZmVkM/LIPID_BIOSYNTHESIS_powerpoint_ppt_presentation
• www.learningace.com/doc/4760431/.../lect-22-fasynthesis
• http://en.wikipedia.org/wiki/Fatty_acid_synthesis