title: Spectroscopic properties of neuroleptics: IR and Raman spectra of Risperidone (Risperdal) and of its mono- and di-protonated forms.
abstract: Structures and IR and Raman spectra of Risperidone in its neutral, mono- and di-protonated forms were calculated in gas phase by DFT-B3LYP/6-31G* level. Mono-protonation occurs at the nitrogen atom of the piperidine ring, while nitrogen atom of the pyrimidine ring is the preferred site for the second protonation. The lowest-energy structure of the mono-protonated Risperidone is characterized by formation of a strong seven-membered O(pyrimidine ring)⋯(+)H-N(piperidine ring) intramolecular hydrogen-bonded cycle. In the high-energy spectral region (3500-2500 cm(-1)), the bands of the N-H(+) stretches and the changes in wavenumbers and IR intensities of the C-H stretches near to the piperidine nitrogen atom (Bohlmann effect) are potentially useful to discriminate conformations and protonation states. Di-protonated structures can be identified by the presence of an isolated absorption peak located in the low-energy IR region (660-690 cm(-1)), attributed to the out-of-plane N-H(+)(pyrimidine ring) bending deformation. The most intense Raman band of neutral Risperidone placed at ca. 1500 cm(-1), assigned to C=C(pyrimidine ring) stretch + C=N(pyrimidine ring) stretch, can be a useful vibrational marker to distinguish the neutral from the protonated forms.
authors.affiliation: Department of Chemistry, University of Catania, viale A. Doria 6, Catania 95125, Italy. agalparone@unict.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Alparone
mesh_terms: D014150:Antipsychotic Agents / Q000737:chemistry*; D006860:Hydrogen Bonding; D008954:Models, Biological; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D018967:Risperidone / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013057:Spectrum Analysis / Q000379:methods; D013059:Spectrum Analysis, Raman; D013329:Structure-Activity Relationship
chemical_list: D014150:Antipsychotic Agents; D011522:Protons; D018967:Risperidone