Structural and physicochemical characterization of the inclusion complexes of cyclomaltooligosaccharides (cyclodextrins) with melatonin.
The stoichiometry, geometry, stability, and solubility of the inclusion complexes of melatonin (MLT) with native cyclomaltooligosaccharides (alpha-, beta- or gamma-cyclodextrins, CDs) are determined experimentally by high-resolution NMR spectroscopy, calorimetric and solubility measurements, and mass spectrometry. The observed differences are discussed in terms of molecular recognition expression of the host-guest (h-g) interactions within the hydrophobic CDs cavities of different size. The 1:1 h-g stoichiometry in water solution prevails at low CD concentrations; the trend to form higher order associations is observed at increasing CD concentrations. The stability order beta-CD>gamma-CD>alpha-CD for the complexes in water solution and beta-CD>alpha-CD>gamma-CD for the protonated or alkali-cationated complexes in the gas phase are rationalized on the grounds of the structural data from NMR spectroscopy and of the thermodynamic parameters from calorimetric measurements.
Bongiorno
David
D
Dipartimento di Chimica e Tecnologie Farmaceutiche e Rete di Spettrometria di Massa del Mezzogiorno, Via Archirafi 32, I-90123 Palermo, Italy.
Ceraulo
Leopoldo
L
Mele
Andrea
A
Panzeri
Walter
W
Selva
Antonio
A
Turco Liveri
Vincenzo
V
D002151:Calorimetry; D003505:Cyclodextrins / Q000737:chemistry*; D005079:Excipients / Q000737:chemistry; D008550:Melatonin / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D012995:Solubility; D021241:Spectrometry, Mass, Electrospray Ionization; D013816:Thermodynamics
D003505:Cyclodextrins; D005079:Excipients; D008550:Melatonin