Complexation Flashcards Preview

Pharm202 > Complexation > Flashcards

Flashcards in Complexation Deck (16):

What are complexes?

Coordination compounds resulting from donor acceptor mechanisms or lewis base reactions between two or more chemical constituents


How does lewis theory relate to complexation?

An acid will accept electrons, forming a covalent bond and a base will provide a pair of electrons by which the base coordinates with the acid


What kind of structural relationships hold complexes together?

Hydrogen bonding
Ion pairing
Van der waals forces other than those of full covalent blnds


What is host guest chemistry also known as?

Inclusion complex which involves the entrapment of one compound in the molecular framework of another


How are complexes largely classified?

On the structure and the nature of the acceptor

1) inclusion complex
2) metal ion complex
3) organic molecular complex


What is an inclusion complex?

One constituent of the complex is trapped in the open lattice or cage like crystal structure of the other

Formation depends on the architecture of molecules as opposed to chemical affinity
This is also known as host guest inclusion


What are the different types of inclusion complexes?

channel lattice type
layer type
Monomolecular complex- cyclodextrins


What is a channel lattice type complex?

A type of inclusion complex

Compounds can crystallise in a channel like structure which permits enclosure of non branched compounds.

Urea can form this structure, can be used in the separation of interfering compounds in drug analysis.


What is layer type complex?

A form of inclusion complex where the constituent is trapped between the layers of their lattice

E.g. Clay minerals like betonite can trap a wide range of compounds like alcohols and glycols.

Probably responsible for many incompatibilities of betonite with
However betonite salicylate complex could be used for gradual release


What are clathrates?

A type of inclusion complex where the compound crystallises in the form of a cage like lattice to trap guest molecules.

Chemical bonds are not important, only the molecular size of the guest molecule is important

E.g. Hydroquinone has a suitable cage size to trap CO2 or HCl


What is a monomolecular complex?

Form of inclusion complex which involves the entrapment of a single guest molecule in the cavity of one host molecule

The classic example is cyclodextrins,
This type of complex is used in air freshners and cosmetics


What are cyclodextrins?

A form of monomolecular, inclusion complex.

These are a family of compounds made up of sugar molecules bound together in a ring (cyclic oligosaccharides)

They typically contain 6-8 sugar units


What does a CD look like?

The ring is cylindrical and like a truncated cone

Has a large interior cavity that can hold guest molecules
The outer surface is hydrophilic, the internal surface of the cavity is non polar.


Why are cyclodextrins modified?

Natural ones are toxic to the kidney and are poorly water soluble.
Modification generates a wide range of molecular hosts which can tailor a CD host to a particular guest and meet specific requirements

Sulfobutylether-β-CD and hydroxypropyl-β-CD are well tolerated in humans and have no adverse effects


Why do cyclodextrins make good inclusion complexes.

They are able to form host guest complexes with lipophilic molecules given the nature imparted by their structure
Lipophilic molecules with appropriate size can be accommodated wholly or partially in the complex
It exhibits Reversible non covalent interactions between molecules


What are pharmaceutical applications of cyclodextrins?

Solubility enhancement, also in injectable formulations, avoids hemolysis and cytotoxicity, reduces tissue irritating effects, inhibits drug precipitation

Dissolution bioavailability enhancement by speeding up solubilisation of lipophilic drugs by wetting, and improving the solubility of lipophilic drugs

Taste masking e,g, femoxetin, bitter taste

Stabilisation of drugs e.g. Mitomycin C from acidic degradation

Fixation of volatile compound, conversion of liquids to solids,
Creating mixtures from otherwise incompatible compounds