Showing: 10 from total: 2477 publications
1991. Annulation of beta-aryl-alpha-nitro-alpha,beta-enals and 2,2-dimethyl-1,3-dioxan-5-one: a one-step assembly of nitrocyclitols. Application to a short practical synthesis of (+/-)-7-deoxy-2-epi-pancratistatin tetraacetate
Carlos Ortiz, JC ; Ozores, L ; Cagide Fagin, F ; Alonso, R
in CHEMICAL COMMUNICATIONS, 2006, ISSN: 1359-7345, 
Article,  Indexed in: crossref, scopus, wos 
DOI: 10.1039/b606277f P-00F-SJR
Abstract A novel, highly stereocontrotled formal [3 + 3] annulation of beta-aryl-alpha-nitro-alpha,beta-enals with the enamine derived from 2,2-dimethyl-1,3-dioxan-5-one and pyrrolidine afforded protected nitrocyclitols with five newly created stereocentres and constituted the key step in a short, gram-scale synthesis of a pancratistatin analogue.

1992. Water solubility in linear fluoroalkanes used in blood substitute formulations
Freire, MG ; Gomes, L ; Santos, LMNBF ; Marrucho, IM ; Coutinho, JAP
in JOURNAL OF PHYSICAL CHEMISTRY B, 2006, ISSN: 1520-6106,  Volume: 110, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The interactions between water and n-perfluoroalkanes or substituted alpha-(omega-) fluoroalkanes used in blood substitute formulations were investigated experimentally and using ab initio calculations. The solubility of water in C(6)-C(9) perfluoroalkanes and five C(8) analogues of substituted fluoroalkanes was measured in the temperature range between 288 and 318 K at atmospheric pressure, using a Karl Fischer coulometer. From these data, the thermodynamic functions and partial molar solvation quantities such as Gibbs energy, enthalpy, and entropy were determined and compared with the interaction energies in 1:1 water-fluoroalkane complexes in vacuum, obtained using B3LYP/6-311++G(d,p). The experimental solubility data indicates a significant specific interaction between the water and the alpha-(omega-)substitute atom (H, I, Br, or Cl) in the fluoroalkanes.

1993. Insights on the interactions between two cecropin-melittin peptides and model membranes: Calorimetric and spectroscopic results
Bai, G ; Gomes, P ; Seixas, R ; Hicks, M ; Prieto, M ; Bastos, M
in JOURNAL OF PEPTIDE SCIENCE, 2006, ISSN: 1075-2617,  Volume: 12, 
Abstract,  Indexed in: wos 

1994. Dynamics of an antibiotic oligopeptide
Middendorf, HD ; Alves, N ; Zanotti, JM ; Gomes, P ; Bastos, M
in PHYSICA B-CONDENSED MATTER, 2006, ISSN: 0921-4526,  Volume: 385-86, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Neutron time-of-flight spectra were measured for an HO-hydrated and a nominally dry sample of a 15-residue antibacterial oligopeptide from 99 to 271 K. Proton mobilities, quasielastic broadenings, and changes in low-frequency inelastic intensities characterise the evolution of the peptide energy landscape as a function of momentum transfer and temperature.

1995. Enthalpies of solution of paracetamol and sodium diclofenac in phosphate buffer and in DMSO at 298.15 K
Alves, N ; Bai, GY ; Bastos, M
in THERMOCHIMICA ACTA, 2006, ISSN: 0040-6031,  Volume: 441, 
Article,  Indexed in: crossref, scopus, wos 
Abstract We have been using a heat conduction microcalorimeter to measure enthalpies of dissolution of slightly soluble solids. Recently we did report the testing of the prototype and we are now extending the previous investigation to measurements with organic solvents. In the present work we use DMSO due to its importance in the pharmaceutical industry. The importance of the applications of enthalpies of solution in organic solvents calls for the need to find a substance that can be used in the future for chemical calibration in these solvents. Attempts for proposing such a substance have also been a goal for our research group. The enthalpies of solution of paracetamol and sodium diclofenac were measured in DMSO and in phosphate buffer (pH 6.91) at 298.15 K. We show that it is possible to obtain very good results with DMSO as solvent for these two drugs on our dissolution microcalorimeter. Nevertheless, due to their slow and low enthalpy of dissolution in this solvent, they cannot be seen as good candidates for test substances.

1996. A new calorimetric system to measure heat capacities of solids by the drop method
Bernardes, CES ; Santos, LMNBF ; Da Piedade, MEM
in Measurement Science and Technology, 2006, ISSN: 0957-0233,  Volume: 17, 
Proceedings Paper,  Indexed in: crossref, scopus 
Abstract A new electrically calibrated calorimetric system to measure heat capacities of solids has been designed and tested by determining the heat capacity of sapphire and benzoic acid in the temperature range 298-393 K. Comparison of the obtained results with recommended adiabatic calorimetry data showed that the maximum and average absolute deviations were 3.3% and 1.6%, respectively. The technique provides a convenient alternative to routine heat capacity determinations by DSC, since the experiments are faster and, in general, the results have better accuracy. In addition, the sample cells can be kept under argon or nitrogen atmosphere thus enabling the study of air sensitive compounds. © 2006 IOP Publishing Ltd.

1997. Voltammetric quantification of fluoxetine: Application to quality control and quality assurance processes
Lencastre, RP ; Matos, CD ; Garrido, J ; Borges, F ; Garrido, EM
in JOURNAL OF FOOD AND DRUG ANALYSIS, 2006, ISSN: 1021-9498,  Volume: 14, 
Article,  Indexed in: scopus, wos 
P-004-HKK
Abstract The oxidative behaviour of fluoxetine was studied at a glassy carbon electrode in various buffer systems and at different pH using cyclic, differential pulse and square wave voltammetry. A new square wave voltammetric method suitable for the quality control of fluoxetine in commercial formulations has been developed using a borate pH 9 buffer solution as supporting electrolyte. Under optimized conditions, a linear response was obtained in the range 10 to 16 mu M with a detection limit of 1.0 mu M. Validation parameters such as sensitivity, precision and accuracy were evaluated. The proposed method was successfully applied to the determination of fluoxetine in pharmaceutical formulations. The results were statistically compared with those obtained by the reference high-performance liquid chromatographic method. No significant differences were found between the methods.

1998. Standard molar enthalpies of formation of copper(II) beta-diketonates and monothio-beta-diketonates
Ribeiro da Silva, MAVR ; Santos, LMNBF
in JOURNAL OF CHEMICAL THERMODYNAMICS, 2006, ISSN: 0021-9614,  Volume: 38, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation of the crystalline complexes of dibenzoylmethane (HDBM), thenoyltrifluoroacetone (HTTFA), monothiodibenzoylmethane (HDBMS), and monothiothenoyltrifluoroacetone (HTTFAS) of copper(II) were determined, at T = 298.15 K, by high precision solution-reaction calorimetry. The standard molar enthalpies of sublimation of the copper(II) beta-diketonate complexes were measured by high-temperature Calvet microcalorimetry. From the standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar dissociation enthalpies copper(II)-ligand, (D-m)(Cu-L), were derived. [GRAPHICS]

1999. Computer Simulations of Salt Solubility
Gil, VMS ; Paiva, JCM
in Journal of Chemical Education, 2006, ISSN: 0021-9584,  Volume: 83, 
Article,  Indexed in: crossref 

2000. The design, construction, and testing of a new Knudsen effusion apparatus
da Silva, MAVR ; Monte, MJS ; Santos, LMNBF
in JOURNAL OF CHEMICAL THERMODYNAMICS, 2006, ISSN: 0021-9614,  Volume: 38, 
Article,  Indexed in: crossref, scopus, wos 
Abstract A new Knudsen effusion apparatus, enabling the simultaneous operation of nine effusion cells at three different temperatures, is fully described. The performance of the new apparatus was checked by measuring the vapour pressures, between 0.1 Pa and 1 Pa, over ca. 20 K temperature intervals of benzoic acid, phenanthrene, anthracene, benzanthrone, and 1,3,5-triphenylbenzene. The derived standard molar enthalpies of sublimation are in excellent agreement with the mean of the literature values available for these five compounds and with the recommended values for four of them.