Lipids are fatty substances and similar which are found in plants and animals. Like carbohydrates and proteins constitute an important group of organic molecules with pharmacological use and form a heterogeneous range of chemical functions. Initially, lipids are grouped based on its solubility characteristics, in general, are soluble in organic solvents such as ether and chloroform and are insoluble in water. Classification of lipids Lipids can be classified into five groups according to their chemical structure.

1. What are lipids?
Lipidsare fattysubstancesandsimilarwhichare foundinplantsand animals.Like carbohydratesand
proteinsconstitute animportantgroupof organicmoleculeswithpharmacological use andforma
heterogeneousrange of chemical functions.
Initially,lipidsare groupedbasedonitssolubilitycharacteristics,ingeneral,are solubleinorganic
solventssuchasetherand chloroformandare insoluble inwater.
Classificationof lipids
Lipidscan be classifiedintofive groupsaccordingtotheirchemical structure.
FixedOilsandFats:Estersof glycerinwithfattyacids.E.g.:The olive oil.The fixedoilswhichare solidsat
room temperature are commonlycalledgreases.E.g.:lard.
Waxes:estersof monohydricalcoholsof high molecularweightwithfattyacidsof highmolecular
weight.E.g.the fatobtainedfromspermaceti.
Sterols:Alcoholswiththe typicalstructure of cyclopentanephenanthrene (steroid).E.g.cholesterol and
ergosterol.
Phospholipids:Estersconsistingof glycerin,fattyacids,phosphoricacidandsome nitrogenous
compounds.The mostimportantof thisgroup are the lecithins.
Glycolipids:are substancesisolatedfrombrainandothersourceswhichare basedon the hydrolysisof
fattyacids,galactose and nitrogenouscompounds.Due tothe mostcommonsugar presentinthese
compoundsisgalactose theyare alsocalledgalactolipids.Thesecompoundshave nopharmaceutical
application.
Fixedoilsandfats
Definitionof fixedoilsandfats.Obtainingmethods.
Theyare estersof glycerinwithfattyacidsof highmolecularweightbyaliphaticlongchain,particularly
palmitic,stearicandoleicacids.Simpleestersof glycerinare oftencalledglycerides.

2. The difference inconsistencybetweenthe fixedoilsandfatsiscausedbythe relative proportionof
liquidorsolidesterof glycerin,whichdependsonthe extensionof the aliphaticchainanditsdegree of
saturation.
The fixedoilscontainagreaterproportionof liquidglycerides(polyunsaturated) suchasglycerinoleate,
while fatsare rich insolidglyceridessuchasglycerinstearate.The glyceridesof unsaturatedfattyacids
have a lowermeltingpointthansaturatedoneswiththe same carbonnumber.
Amongfixedoilsmustbe made aspecial distinctiontothe volatileoils,because althoughtheirchemical
structure belongtothisclassification,physicallyasthe name suggests,are volatile.
The difference liesinthatthe volatileoilsdon’tcontainglycerinesters,theyare alsoknownasessential
oils.
Obtainingmethods
Both fixedoilsandfatsare obtainedbyexpressionextractionof the plantoranimal tissue.Inthis
processthe material issubjectedtohydraulicpressureandheatisusedif necessary.
The oilsobtainedinthe firstexpression extraction(coldpressed) have ahighcommercial value suchas
olive oil where the firstexpressionisknownbyvirginoliveoil,butforsubsequentexpressionsis
necessarytosubjectthemtoa processof purification.
The fixedoilsare frequentlytreatedforitsclarificationandfinallyare filtered.Some technologies
obtainedoil byvolatilesolventsthatare recoveredlater.Fatsandoilsanimalsare usuallyobtainedby
the methodof tissue heatingtoitsmeltingandsubsequentmechanical separation.
What are the waxes?
Waxesare similartothe fixedoilsandfatssince theyare estersof fattyacids,butwiththe difference
that the alcohol isnot glycerin.

3. Insteadof trihydricalcohol the bondingisformedwithasterol ormonoalcohol long-chainfrom16to 36
carbons andfatty acidsof 24 to 36 carbon atoms,alsosome of these waxesobtainedfromplantsare
composedof paraffinchains.
The estersthat constitute the waxesare generallymore resistanttosaponificationof glyceridesof fats
and fixedoils.
What are sterols?
Sterolsare steroidrelatedstructuresfoundnaturallyinplantsandanimalsandwhose structuresinclude
partiallyorfullyahydrogenatedcore of 17H-cyclopentane-α-phenanthrene.
Besidesthe sterols,the steroidsconstitute partof othersubstancessuchascompoundsof adrenal
origin,certainalkaloids,antirachiticvitamins,bile acids,cardiacglycosides,saponinsandsex hormones.
Steroidstructure
The general structure of the steroidis:
Steroidstructure
The rings are properlynumberedandletteredasindicated.The fusionof the ringspreventsthe free
rotationof the structure causingtwodifferentprojectionsinthe plane of symmetrywhichare
designatedasalphaandbeta,whichare alsoidentifiedasstereochemical structurescisandtrans
respectively.
The hydrocarbonseriesof sterolsgivesrise tovariousactive ingredientspresentinplantsandanimals.
Thus,for example,the ergosterol presentinabundance inyeastandergotwhichbecomesergocalciferol
(vitaminD2).
Definitionof phospholipids

4. Phospholipidsare essential componentsof manyanimal andplantcellsandhave beencategorizedas
lecithin,cephalinandsphingomyelin,beingthe lecithinsthose withpharmaceutical application.These
include the lipoidal structurescontainingphosphorusintheirmolecules.
Whenlecithinsare fullyhydrolyzedcanproduce twomoleculesof fattyacid,a molecule of glycerin,a
phosphoricacidmolecule andabasicnitrogencompoundwhichisusuallycholine.
The fatty acidsobtainedbyhydrolysisfromlecithinsare oleic,palmiticandstearic.Choline isamember
of the vitaminBcomplex,itsfunctioninthe bodyistopreventthe accumulationof fatinthe liverandits
acetylatedderivative(acetylcholine)isreleasedatthe parasympatheticnerveendingswhenstimulated
to control the transmissionof pulsesthroughcholinergicsynapses.
Commercial lecithinisobtainedfromeggs,braintissue andsoybeans