11,292 research outputs found
Vibrational properties of inclusion complexes: the case of indomethacin-cyclodextrin
Vibrational properties of inclusion complexes with cyclodextrins are studied
by means of Raman spectroscopy and numerical simulation. In particular, Raman
spectra of the non-steroidal, anti-inflammatory drug indomethacin undergo
notable changes in the energy range between 1600 and 1700 cm when
inclusion complexes with cyclodextrins are formed. By using both \emph{ab
initio} quantum chemical calculations and molecular dynamics, we studied how to
relate such changes to the geometry of the inclusion process, disentangling
single-molecule effects, from changes in the solid state structure or
dimerization processes.Comment: 14 file figure
Mid-infrared signatures of hydroxyl containing water clusters: Infrared laser Stark spectroscopy of OHâH2O and OH(D2O)n (n = 1-3)
Small water clusters containing a single hydroxyl radical are synthesized in liquid helium droplets. The OHâH2O and OH(D2O)n clusters (n = 1-3) are probed with infrared laser spectroscopy in the vicinity of the hydroxyl radical OH stretch vibration. Experimental band origins are qualitatively consistent with ab initio calculations of the global minimum structures; however, frequency shifts from isolated OH are significantly over-predicted by both B3LYP and MP2 methods. An effective Hamiltonian that accounts for partial quenching of electronic angular momentum is used to analyze Stark spectra of the OHâH2O and OHâD2O binary complexes, revealing a 3.70(5) D permanent electric dipole moment. Computations of the dipole moment are in good agreement with experiment when large-amplitude vibrational averaging is taken into account. Polarization spectroscopy is employed to characterize two vibrational bands assigned to OH(D2O)2, revealing two nearly isoenergetic cyclic isomers that differ in the orientation of the non-hydrogen-bonded deuterium atoms relative to the plane of the three oxygen atoms. The dipole moments for these clusters are determined to be approximately 2.5 and 1.8 D for âup-upâ and âup-downâ structures, respectively. Hydroxyl stretching bands of larger clusters containing three or more D2O molecules are observed shifted approximately 300 cmâ1 to the red of the isolated OH radical. Pressure dependence studies and ab initio calculations imply the presence of multiple cyclic isomers of OH(D2O)3.Fil: HernĂĄndez, Federico Javier. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; Argentina. University of Georgia; Estados UnidosFil: Brice, Joseph T.. University of Georgia; Estados UnidosFil: Leavitt, Christopher M.. University of Georgia; Estados UnidosFil: Liang, Tao. University of Georgia; Estados UnidosFil: Raston, Paul L.. James Madison University. Department of Chemistry and Biochemistry; Estados UnidosFil: Pino, Gustavo Ariel. Consejo Nacional de Investigaciones CientĂficas y TĂŠcnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂmicas. Instituto de Investigaciones en FĂsico-quĂmica de CĂłrdoba; ArgentinaFil: Douberly, Gary E.. University of Georgia; Estados Unido
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