There are colors that we naturally associate with the seasons: the colors of flowers in spring, brown in winter, the blue of the sky in summer… and this text is about the chemistry of autumn colors.
Paulo J. A. Ribeiro-Claro.
Montelukast (MLK), an oral antiasthmatic drug with growing use, requires special care in formulation and storage to avoid its degradation by action of light and water. This work investigates the increase in the stability of montelukast as the effect of molecular encapsulation with gamma-cyclodextrin (γ-CD) by means of a solvent-free method, cogrinding. As a first step, a 1:1 preferred stoichiometry is established for this hostguest system using a combination of molecular modeling and the continuous variation method. The solid 1:1 inclusion compound, γ-CD·MLK, is obtained by 2 comilling procedures. For comparison purposes, γ-CD·MLK is also prepared by a classical codissolution procedure and isolated by freeze-drying. Products were characterized by powder X-ray diffraction, 13C{1H} CP-MAS NMR, scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry, which confirm inclusion, demonstrate the formation of amorphous products by comilling, and highlight the importance of the amorphous nature of the starting materials for the stability of the comilled final product. The dissolution profile of montelukast when released from the comilled products shows equivalent concentrations to those obtained with the same mass of the pure drug, with the extra advantage of keeping the solution stability (unaltered concentration) for longer periods.
Jéssica S. Barbosa, Mariela M. Nolasco, Paulo Ribeiro-Claro, Filipe A. Almeida Paz, Susana S. Braga.
A thorough vibrational portrait of 4-fluorobenzaldehyde is presented, covering Infrared (Mid- and Far-), Raman and Inelastic Neutron Scattering (INS) spectra. Periodic DFT calculations (CASTEP) of a model 4FB crystal proved useful for vibrational assignment, yielding estimates of experimental spectra with near one-to-one correspondence – including the correct estimation of overtone and combination modes. A striking similarity among the Far-IR spectrum of liquid 4FB and that estimated based on a periodic structure indicates that the solid-liquid transition induces soft structural changes which leave most vibrational modes unaffected – except for those directly involved in Csingle bondH…O bonding, where crystal field splitting is observed.
Paulo J. A. Ribeiro-Claro, Pedro D. Vaz, Mariela M. Nolasco, Catarina F. Araujo, F.P.S.C. Gil, Ana M. Amado.
This work presents a comprehensive spectroscopic analysis of crystalline isoniazid, one of the main drugs in tuberculosis chemotherapy, using a blend of spectroscopic and computational methods. Mid-and far-infrared, Raman, and inelastic neutron scattering spectroscopies, with contribution of isotopic substitution are combined with discrete and periodic DFT quantum chemical calculations. This combined approach successfully reproduces the whole spectral range, allowing a sound assignment of all the vibrational bands. Previous misassignments have been corrected and several spectral features of isoniazid crystal are reported for the first time. Virtues and limitations of the computational approach (periodic and discrete) are also discussed in light of the present state-of-the-art in the field. (C) 2018 Elsevier B.V. All rights reserved.
Ribeiro-Claro, P.J.A.; Vaz, P.D.; Nolasco, M.M.; Amado, A.M.
A spectrum is a graphical representation of the magnitude of the radiation-matter interaction (intensity) as a function of the energy of that radiation. Thus, the ordinate axis in a spectrum is always indicative of the intensity of the signal recorded in the detector (often in arbitrary units and only with a relative value), but the abscissa axis represents any quantity proportional to energy.
Paulo Ribeiro-Claro.
Phone: +351 234-370-732
Research Themes
Policies
To provide the best experiences, we use technologies such as cookies to store and/or access information on your device. Consent to these technologies will allow us to process data such as browsing behavior or unique IDs on this website. Not consenting or withdrawing consent may negatively affect certain features and functions.