A poly(amido-amine), PAA, bearing b-CD units in the side chain was synthesized by a polyaddition reaction of 1,4-bis-acryloyl-piperazine with 6-monodeoxy-6-monoamino-b-cyclodextrin (b-CD-NH2). Unlike the simple b-CD-NH2 with greater basicity constant (logK = 8.60), the polymer revealed an unusual polyelectrolyte behaviour with lower basicity constant (logK° = 6.29) of the tertiary nitrogen atom that is strongly dependent on the degree of protonation a of the whole macromolecule. It follows the modified Henderson-Hasselbalch equation with n = 1.75, in a wide a-range. The greater (46.9 kJ/mol) and the lower (28.9 kJ/mol) enthalpy (-DH°) changes of the compounds were in line with the protonation of a primary or a tertiary nitrogen atom. Calorimetric data suggested that the PAA protonation destroyed a packing structure formed by two rigid b-CD side chain interacting heat-to-head. UV spectrophotometric data showed that the PAA exhibits affinity with the L-ascorbic acid at low pH (pH 2.46) with an isosbestic point at 241 nm and a slight blue shift of the maximum absorption of the ascorbic acid (244 nm) on PAA additions.
The protonation thermodynamics of cyclodextrin-containing polymers for drug inclusion
Mendichi R;
2010
Abstract
A poly(amido-amine), PAA, bearing b-CD units in the side chain was synthesized by a polyaddition reaction of 1,4-bis-acryloyl-piperazine with 6-monodeoxy-6-monoamino-b-cyclodextrin (b-CD-NH2). Unlike the simple b-CD-NH2 with greater basicity constant (logK = 8.60), the polymer revealed an unusual polyelectrolyte behaviour with lower basicity constant (logK° = 6.29) of the tertiary nitrogen atom that is strongly dependent on the degree of protonation a of the whole macromolecule. It follows the modified Henderson-Hasselbalch equation with n = 1.75, in a wide a-range. The greater (46.9 kJ/mol) and the lower (28.9 kJ/mol) enthalpy (-DH°) changes of the compounds were in line with the protonation of a primary or a tertiary nitrogen atom. Calorimetric data suggested that the PAA protonation destroyed a packing structure formed by two rigid b-CD side chain interacting heat-to-head. UV spectrophotometric data showed that the PAA exhibits affinity with the L-ascorbic acid at low pH (pH 2.46) with an isosbestic point at 241 nm and a slight blue shift of the maximum absorption of the ascorbic acid (244 nm) on PAA additions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
