complexation

Question 1

What is a complex?

Answer 1

Complexes are coordination compounds resulting for a lewis acid-base reaction or a donor-acceptor mechanism between 2+ chemical constituents.

Question 2

What is lewis theory?

Answer 2

Bases are electron donors and acids are electron acceptors

Question 3

How are host-guest complexes help together?

Answer 3

h bonding
ion pairing
vdW forces

Question 4

What is an inclusion complex? what are the 4 types?

Answer 4

An inclusion complex is where one constituent is trapped in a open-lattice or cage-like structure of the other consitutient. 
Types are:
- channel lattice
- layer
- clathrate
- monomolecular complex.

Question 5

Describe channel lattice complexes. Give an example.

Answer 5

Compounds can crystallise into a channel-like structure, permitting enclosure on non-branched compounds.
Example: urea; used to seperate impurities in drug analysis

Question 6

Describe layer type complexes. Give examples

Answer 6

Clay minerals can trap a range of compounds between layers of their lattice.

• minerals trapped in layers can cause incompatibilities of bentonite with drugs.
• bentonite-salicylate complexes can be used for gradual release.

Question 7

Describe clathrate complexes and important aspects

Answer 7

Compounds crystallize into cage-like structures with a hollow cavity inside where guest molecules can be trapped.

• chemical bonds are not important
• only guest size is important.

Question 8

Describe monomolecular complexes and give an example

Answer 8

The entrapment of a single guest molecule in the cavity of one host molecule
example: cyclodextrin

Question 9

Describe the structure of cyclodextrin

Answer 9

A family of compounds composed of sugar molecules bound in a ring. This is cylindrical and represents a truncated cone. The large interior cavity holds guest molecules.
- outer surface is hydrophilic and inner surface is hydrophobic

Question 10

How do cyclodextrins interact with molecules?

Answer 10

Able to form complexes with hydrophobic molecules

• those of appropriate size can be partially or wholly accommodated by the complex.
• reversible non-covalent interactions occur between molecules.
• drug is released from cyclodextrin during absorption due to the dilution effect.

Question 11

What are applications of cyclodextrin

Answer 11

• enhances solubility
• improves organoleptic characteristics (e.g. masking taste)
• stabiliser and protector
• dissolution and bioavailability enhancement

Question 12

How does cyclodextrin enhance dissolution and hence bioavailability of molecules?

Answer 12

By speeding up solubilisation of lipophilic compounds (wetting) and hence improving solubility of lipophilic drugs.
(enhances dissolution rate)

Question 13

What is a metal ion complex?

Answer 13

Simplest type, where ligands donate a pair of electrons to the metal ion (acceptor), forming a complex.

Question 14

What is a coordination number?

Answer 14

how many ligands are donating their electrons to form that metal-ion complex

Question 15

What is a chelate?

Answer 15

Chelates are organic substance containing 2 or more donor groups, combining with a metal ion to form a chelate

Question 16

how are chelates applied?

Answer 16

• heavy metal detoxification to bind out excess ions

- drug stabilisation to sequester heavy metals responsible for stimulating oxidative degradation

Question 17

What are some incompatibilites of chelation?

Answer 17

Can be responsible for incompatibilities affecting absorption of drugs e.g. tetracycline forms calcium ion complex which is insoluble and reduces absorption of tetracyclines.

Question 18

what are organic molecular complexes?

Answer 18

• polymer complexes

- drug complexes

Question 19

Give examples of drug-polymer complexes, incompatibilities and uses

Answer 19

Polyethalene glycols (PEGs) and similar polymers containing nucleophilic oxygen.
- incompatibilities can manifest precipitate, delayed biological activites or loss of preservative action. 

Used to modifty biopharmaceutical parameters of drugs
e.g. tincture of iodine modified to povidine iodine allowing topical application with less staining and irritation.

Question 20

Why is drug complexation used? Give examples.

Answer 20

Drug complexation improves drug release and absorption, or can be used to impair drug release.

e. g.
- caffiene improves F of ergotamine.
- complex with gentisic acid is less soluble than caffeine and masks bitter taste.