Structure of the molecule e.g. degree of unsaturation of the heterocyclic ring. Unsaturation decreases the basicity - e.g. piperidine alkaloids are more basic than pyridine alkaloids.
Presence & position of other substituents & functional groups:
- Electron releasing groups, e.g. alkyl groups increase the basicity.
- Electron withdrawal groups, e.g. carbonyl groups decrease the basicity.
- Alkaloids are neutral or slightly acidic when the electron availability on the amino nitrogen atom decreases e.g. Ricinine is acidic.
- Some are amphoteric due to the presence of acidic groups in their molecule. e.g.
- Phenolic alkaloids: morphine, psychotrine & cephaline.
- Alkaloids containing a carboxylic group: narceine.
Physical Properties- Condition & Color
1.Condition:
- Crystalline solids.
•Volatile e.g. nicotine & nornicotine, anabasine, arecoline, coniine.
•Non-volatile e.g. pilocarpine & hyoscine, pelletierine.
•Volatile e.g. nicotine & nornicotine, anabasine, arecoline, coniine.
•Non-volatile e.g. pilocarpine & hyoscine, pelletierine.
2.Color:
- colorless.
- colorless.
- Some : colored e.g.:
•Colchicine & berberine (yellow).
•Canadine (orange).
•Salts of sanguinarine (copper-red).
Physical properties:
Condition, Color, Solubility, Optical isomers
•Colchicine & berberine (yellow).
•Canadine (orange).
•Salts of sanguinarine (copper-red).
Physical properties:
Condition, Color, Solubility, Optical isomers
3. Solubility in water, alcohol & other organic solvents:
- Alkaloidal bases & salts & soluble in alcohol.
- Bases, generally & soluble in organic solvents & insoluble in water.
- Salts , generally & soluble in water & insoluble or sparingly soluble in organic solvents.
- Salts of weak bases decompose in aqueous solution without alkalinization bases extracted with organic solvents.
Exceptions:
- Bases soluble in water: caffeine, ephedrine, nicotine, arecoline, codeine, colchicine, pelletierine, pilocarpine & quaternary ammonium bases.
- Bases insoluble or sparingly soluble in certain organic solvents: morphine & psychotrine in ether, theobromine & theophylline in benzene.
- Salts insoluble in water: quinine sulphate.
- Salts soluble in organic solvents: lobeline & apoatropine hydrochlorides soluble in chloroform.
4.Optical activity
•Many alkaloids are optically active due to presence of one or more chiral C atoms.
•Optical isomers may have different physiological activities.
•Usually l (-) isomers > active than d (+) isomers:
l-ephedrine is 3.5 times > active than d-ephedrine.
l-ergotamine is 3-4 times > active than d-ergotamine.
Exceptions:
•d-Tubocurarine > active than l-Tubocurarine
•Quinine (l-form) & quinidine (its d-isomer) are both active
•The racemic dl-atropine is active.
•Many alkaloids are optically active due to presence of one or more chiral C atoms.
•Optical isomers may have different physiological activities.
•Usually l (-) isomers > active than d (+) isomers:
l-ephedrine is 3.5 times > active than d-ephedrine.
l-ergotamine is 3-4 times > active than d-ergotamine.
Exceptions:
•d-Tubocurarine > active than l-Tubocurarine
•Quinine (l-form) & quinidine (its d-isomer) are both active
•The racemic dl-atropine is active.