Effect of pH and α-, β- and γ-cyclodextrin on the spectral properties of etoricoxib: spectroscopic and molecular dynamics study

• Published in: Journal of inclusion phenomena and macrocyclic chemistry Vol. 88; no. 3-4; pp. 171 - 180
• Main Authors: Yousef, Fakhri O., Ghanem, Raed, Alshraa, Noura H., Al Omari, Nosayba M., Bodoor, Khaled, El-Barghouthi, Musa I.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.08.2017; Springer Nature B.V
• Subjects: Absorption spectra; Band spectra; Chemistry; Chemistry and Materials Science; Computer simulation; Crystallography and Scattering Methods; Cyclodextrins; Emission spectra; Fluorescence; Food Science; Holes; Molecular dynamics; Organic Chemistry; Original Article; Spectroscopic analysis; Stoichiometry; Cyclodextrins; Molecular dynamics simulations; Etoricoxib; Benesi–Hildebrand analysis
• ISSN: 1388-3127; 1573-1111
• DOI: 10.1007/s10847-017-0715-7

The spectral properties of etoricoxib (ETR) at pH 2.0, 6.0 and 10.0 in the presence of cyclodextrins (CDs) were investigated. The absorption spectrum of ETR in acidic medium exhibited two bands centered at 236 and 273 nm, while in basic medium it exhibited two bands centered at 236 and 285 nm. No change in the spectrum was observed in the presence of CDs. The fluorescence emission spectra of ETR in acidic and basic media exhibited one band at 380 nm and another one at 484 nm. The emission band at 484 nm was enhanced when ETR was complexed with β-CD and γ-CD at pH 2.0, 6.0 and 10.0, while the band at 380 nm was enhanced selectively when ETR was complexed with α-CD at pH 2.0. Molecular dynamics simulations computations revealed that at pH 2.0, the sulfonyl moiety of H 2 ETR 2+ is preferentially included within the α-CD cavity, which is believed to cause the enhancement of the band at 380 nm. Moreover, at pH 6.0 and 10.0, the enhancement of the band at 484 nm was related to the inclusion of the chloropyridinyl and methylpyridinyl groups of the bipyridine moiety of HETR + and ETR within β-CD and γ-CD cavities. Benesi–Hildebrand analysis showed that the ETR/β-CD complex adopts a 1:1 stoichiometry with association constant of K 11  = 64.8 at pH 2.0, K 11  = 105.4 at pH 6.0 and K 11  = 520.5 at pH 10.0.