Cyclodextrins are cyclic sugars commonly composed of 6,7,or 8 glucose units called α, β, γ–cyclodext — Analytical Chemistry Chemistry Question
Cyclodextrine
Cyclodextrins are cyclic sugars commonly composed of 6,7,or 8 glucose units called α, β, γ–cyclodextrins respectively.
β–cyclodextrin (O atoms are shown in red and C atoms in black)
Their shape resembles a truncated cone with a hydrophobic cavity and a hydrophilic exterior lined with hydroxyl groups.
(OH)14 HO OH HO OH OH HO OH
A plethora of hydrophobic molecules can be encapsulated in the cavity forming inclusion complexes
Structure of a cyclodextrin with the pheromone of Dacus Oleae
This property in combination with the fact that they are natural, water soluble compounds makes them suitable candidates for many applications, especially as carriers for pharmaceutical compounds.
Cyclodextrin inclusion complexes form crystals the molecular structure of which can be determined by X–ray crystallography. Consider a crystal of such an inclusion complex of β–cyclodextrin with the empirical formula C42H70O35×C12H12N2×12 H2O. It crystallizes in space group P21. Its unit cell dimensions (with uncertainties) are a = 15.394(7) Å, b = 31.995(12) Å, c = 15.621(7) Å, β = 103.738(15)°, (α = γ = 90°).
In this unit cell there are four molecules of the inclusion complex (2 molecules in the asymmetric unit).
a) What is the molecular volume in Å 3 of the inclusion complex?
b) What is the density of the crystal?
Model Answer
a) V = a b c sin(β) = 7474 Å 3 , Vm= 7474 Å 3 / 4 = 1868 Å 3
b) FW = 1535.4 g mol –1 , ρ = FW 4/(V NA), hence ρ = 1.3646 g cm –3