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Complexation:- Short note for GPAT

Complexation

1. Playing an important role in plasma protein binding, ES complex, affinity chromatography, chiral chromatography, antigen-antibody interactions applied to isolate antibiotics.
2. Toxicity of heavy metals Fe (Deferoxamine), Pb, Hg, As. Standard chelating agents are Dimercaprol, D-
penicillamine, EDTA.
3. Numerous antimicrobial/antineoplastic agents exhibit their action by complex formation with DNA base pairs like Quinacrine, actinomycin D, Daunorubicin, ethidium bromine. These drug molecules are larger planar aromatic rings & they easily inserted between planar base pair in DNA double helix.

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4. Chiral chromatography: uses stationary phase cyclodextrins which form transient reversible diasteromers
with enantiomers in the sample with minimum 3 point interactions like π-π, hydrophobic, H bonding etc.

Charge –transfer complex: Or electron-donor acceptor complex. E.g. Iodine in organic solvents hydrocarbon
solvent like CCl4 has violet colour of iodine while in aromatic hydrocarbons, alcohols, ester it is brown due to charge transfer complex.
Sequestration: When chelating agent & metal ion form a water soluble complex.
Quinhydrone complex: 1:1 ratio of hydroquinone & benzoquinone & this complex settles at green complex.
Picric acid complex: Butesin picrate used in 1% ointment for burns & painful skin abrasions.
Cyclodextrins: They are macrocyclic host formed from bacterial enzyme Bacillus macerans amylase on starch. They are composed of α-D-glucose units joined with glycosidic (other linkage). There interior is hydrophobic and exterior is hydrophilic (due to large number of –OH group on surface) forming a truncated cone.

β Cyclodextrins is mostly used in pharmaceuticals while γ-cyclodextrins have largest cavity size.

Relative low aqueous solubility of the cyclodextrins may be due to formation of intramuscular H-bonding between hydroxyl group which prevent their interaction with water molecules. So a low degree of methylation of some –OH group in CD reduces intramolecular H bonding leaving some –OH group free to interact with water & thus increasing aqueous solubility.
Clathrates: Host molecule form a crystal lattice containing spaces into which guest molecules can fit.

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