Organic chemistry for medicine and biology students

Chem 2311

Chapter 15Lipids and Detergents

By Prof. Dr.Adel M. Awadallah

Islamic University of Gaza

The lipids are a large and diverse group of naturally occuring organic compounds that are related by their solubility in nonpolar organic solvents (e.g. ether, chloroform,

acetone & benzene) and general insolubility in water .

There is great structural variety among the lipids ,

Fatty AcidsSoaps and DetergentsFats and OilsWaxesPhospholipidsEicosonoidsTerpenesSteroidsLipid Soluble Vitamins

Fats and Oils are made from two kinds of molecules: glycerol and three fatty acids.

Since there are three fatty acids attached, these are known as triglycerides.

• Most fatty acids are unbranched and contain an even number of carbon atoms.

Unsaturated acids usually have the Cis (Z) configuration. They have lower boiling points than the corresponding saturated ones.

• Saturated triglycerides are usually solids because they can back together fairly regularly, as in a crystal.

• Space filling and schematic models of glyceryl tripalmitate

• Oils, however, are liquids because they contain higher percentage of unsaturated fatty acids

• Space filling and schematic models of glyceryl dipalmitooeleate

Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds. If oil is used only once like when you fry an egg, only a few of the bonds do this so it’s not too bad. However, if oil is constantly reused, like in fast food French fry machines, more and more of the cis bonds are changed to trans until significant numbers of fatty acids with trans bonds build up. The reason this is of concern is that fatty acids with trans bonds are carcinogenic, or cancer-causing. The levels of trans fatty acids in highly-processed, lipid-containing products such as margarine are quite high, and I have heard that the government is considering requiring that the amounts of trans fatty acids in such products be listed on the labels.

Since fats are valued over oils by some Northern European and North American populations, vegetable oils are extensively converted to solid triglycerides (e.g. Crisco) by partial hydrogenation of their unsaturated components. Some of the remaining double bonds are isomerized (to trans) in this operation. These saturated and trans-fatty acid glycerides in the diet have been linked to long-term health issues such as atherosclerosis.

• Hydrogenation of Vegetable Oils

Simple and mixed triglycerides

Fats and Oils composition

• Saponification of Fats and Oils

Synthetic detergents (Syndets)

Phospholipids

40 % of cell membrane (60 % proteins)Phospholipids are the main constituents of cell membranes. They

resemble the triglycerides in being ester or amide derivatives of glycerol or sphingosine with fatty acids and phosphoric acid. The phosphate moiety of the resulting phosphatidic acid is further esterified with ethanolamine, choline or serine in the phospholipid itself.

This bilayer membrane structure is also found in aggregate structures called liposomes. Liposomes are microscopic vesicles consisting of an aqueous core enclosed in one or more phospholipid layers. They are formed when phospholipids are vigorously mixed with water. Unlike micelles, liposomes have both aqueous interiors and exteriors.

• 4. Waxes• Waxes are esters of fatty acids with long chain monohydric alcohols

(one hydroxyl group). Natural waxes are often mixtures of such esters, and may also contain hydrocarbons.

•

• Waxes are widely distributed in nature. The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators. The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent. Carnuba wax is valued for its toughness and water resistance.

Terpenes and Steroids

Terpenes constitute the largest and most diverse class of natural products.

A majority of these compounds are found only in plants, but some of the larger and more complex terpenes ( e.g. squalene & lanosterol ) occur in animals.

Terpenes incorporating most of the common functional groups are known, so this does not provide a useful means of classification. Instead, the number and structural organization of carbons is a definitive characteristic.

Terpenes may be considered to be made up of isoprene ( more accurately isopentane ) units, an empirical feature known as the isoprene rule. Because of this, terpenes usually have 5n carbon atoms ( n is an integer ), and are subdivided as follows:

Isoprene unit(isopentane)

ClassificationIsoprene UnitsCarbon Atoms

monoterpenes2C10

sesquiterpenes3C15

diterpenes4C20

sesterterpenes5C25

triterpenes6C30

tetraterpens8C40

Examples of Terpenes

Isoprene itself, a C5H8 gaseous hydrocarbon, is emitted by the leaves of various plants as a natural byproduct of plant metabolism. Next to methane it is the most common volatile organic compound found in the armosphere.

SteroidsThe important class of lipids called steroids are actually metabolic derivatives

of terpenes, but they are customarily treated as a separate group. Steroids may be recognized by their tetracyclic skeleton, consisting of three fused six-membered and one five-membered ring, as shown in the diagram to the right. The four rings are designated A, B, C & D as noted, and the peculiar numbering of the ring carbon atoms (shown in red) is the result of an earlier misassignment of the structure. The substituents designated by R are often alkyl groups, but may also have functionality. The R group at the A:B ring fusion is most commonly methyl or hydrogen, that at the C:D fusion is usually methyl. The substituent at C-17 varies considerably, and is usually larger than methyl if it is not a functional group. The most common locations of functional groups are C-3, C-4, C-7, C-11, C-12 & C-17. Ring A is sometimes aromatic. Since a number of tetracyclic triterpenes also have this tetracyclic structure, it cannot be considered a unique identifier.

Cholesterol

27 carbon atoms

Biosynthesized from Lanosterol

Present in all animal cells

Concentrated in the brain and spinal cord

The chief constituent of gallstones

Total amount in the average human body = ½ bound

< 200 mg / dl (desirable)

> 280 mg / dl ((coronary heart disease

Sex Hormones: compounds produced in the ovaries and testes (pl of. testis) that control reproductive physiology and secondary sex characteristics

Sex Hormones

estrogens androgens

estradiol progesterone testosterone androsterone

* initiating changes during mesnstrual cycle* development of sec. sex characteristics

* prepares uterus for implementation of the ferilized egg* prevent ovulation

regulate the development of male reproductiveorgans and sec. sex characteristics

anabolic(muscle-building)

drugs to prevent muscle withering