Encontrados 13 documentos, a visualizar página 1 de 2
VIBRATIONAL SPECTROSCOPY (FTIR-ATR AND FT-RAMAN) - A Rapid and Useful Tool for ...
Pereira, Leonel; Amado, Ana M.; Ribeiro-Claro, Paulo J. A.; van de Velde, FredThe wide industrial application of phycocolloids (e.g. alginates, agar and carrageenans) is based on their particular properties to form gels in aqueous solution. Recently, new spectroscopic techniques have provided more accurate identification of the natural composition of the polysaccharides produced by these seaweeds. With the combination of two spectroscopic techniques (FTIR-ATR and FT-Raman) it is possible...
Identification of selected seaweed polysaccharides (phycocolloids) by vibration...
Pereira, Leonel; Amado, Ana M.; Critchley, Alan T.; Velde, Fred van de; Ribeiro-Claro, Paulo J. A.http://www.sciencedirect.com/science/article/B6VP9-4V2NKJR-7/2/a0aa172e4a0e00ab9e24983d8609f77f
Pseudopolymorphic transitions of niclosamide monitored by Raman spectroscopy
Sardo, Mariana; Amado, Ana M.; Ribeiro-Claro, Paulo J. A.Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient conditions, which can lead to changes in its bioavailability. In this study, the kinetics of the pseudopolymorphic transitions of niclosamide crystals are characterized. FT-Raman spectroscopy is used to quantify the anhydrate and hydrate forms of niclosamide crystals, mostly because of its high sensitivity to the strong inte...
Probing pseudopolymorphic transitions in pharmaceutical solids using Raman spec...
Amado, Ana M.; Nolasco, Mariela M.; Ribeiro-Claro, Paulo J. A.Theophylline is known to undergo vapor phase induced hydrate-anhydrate pseudopolymorphic transformations, which can affect its bioavailability. In this work, the kinetics of the pseudopolymorphic transitions of theophylline crystals in different storage conditions is studied using a vibrational spectroscopic technique. While the hydration is a single-step process with a half-life time of ca. 5 h, the dehydratio...
Análise comparativa dos ficocolóides produzidos por algas carragenófitas usadas...
Pereira, Leonel; Critchley, Alan T.; Amado, Ana M.; Ribeiro-Claro, Paulo J. A.As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, como agentes gelificantes, emulsionantes, estabilizantes e espessantes. São ingredientes naturais, usados há várias décadas na área alimentar e são considerados como seguros, tendo obtido a classificação GRAS (Generally Recognised As Safe). Neste trabalho foram analisadas a percentagem de peso seco e a composição quím...
Para-halogenated benzaldehyde molecules included in cyclodextrins: a combined s...
Ribeiro-Claro, Paulo J. A.; Costa, António M. Amorim da; Vueba, Manuel L.; Pina, M. Eugénia; Amado, Ana M.The inclusion complexes of 4-X-benzaldehyde guests (X = F, Cl, Br) in alpha-, beta-and gamma-cyclodextrins (alphaCD, betaCD and gammaCD) were prepared and characterized by means of thermogravimetry, differential scanning calorimetry (DSC) and vibrational spectroscopy. The stoichiometry of the inclusion complexes ranges from 2:1 to 1:2, depending on the cavity size of the host. Sensitive vibrational modes such a...
Computationally-Assisted Approach to the Vibrational Spectra of Molecular Cryst...
Nolasco, Mariela M.; Amado, Ana M.; Ribeiro-Claro, Paulo J. A.A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suita...
Coordination properties of 2-aminocyclopentene-1-dithiocarboxylic acid to trans...
Amado, Ana M.; Ribeiro-Claro, Paulo J. A.The question of the (N,S) vs. (S,S) coordination mode on M · (ACDA)2 complexes (ACDA=2-aminocyclopentene-1-dithiocarboxylic acid, M=Ni2+, Pd2+, Pt2+) was assessed through an extensive ab initio study, using the hybrid B3LYP density functional approach. The (S,S) coordination was found to be the most stable one, with an energy difference of ca. 50 kJ mol-1 relative to the (N,S) coordination mode. Detailed analys...
Use of FTIR, FT-Raman and 13C-NMR spectroscopy for identification of some seawe...
Pereira, Leonel; Sousa, Ana; Coelho, Helena; Amado, Ana M.; Ribeiro-Claro, Paulo J. A.Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans)--agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosif...
Evidence of C−H···O Hydrogen Bonds in Liquid 4-Ethoxybenzaldehyde by NMR and Vi...
Marques, M. P. M.; Costa, A. M. Amorim da; Ribeiro-Claro, Paulo J. A.Raman, FTIR, and NMR (both 13C and 17O) spectroscopies are used in a complementary way in order to study the occurrence of C−H···O intermolecular hydrogen bonds in liquid 4-ethoxybenzaldehyde (4EtOB). Additional information concerning the structure of the possible dimers is obtained through ab initio calculations, at the B3LYP/6-31G* level. The strongest evidences of the presence of C−H···O hydrogen bonds in th...
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