Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: C. Aragão x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

This work proposes thermal characterization as analytical methodology for the identification and purity assay of warifteine, an alkaloid in Cissampelos sympodialis Eichl. Thermal and kinetic parameters were determined by means of TG and DSC photovisual studies. The TG results showed that the decomposition of warifteine in air and nitrogen atmospheres proceeds in three and four steps, respectively. The TG data allowed calculation of the kinetic parameters of warifteine. The activation energy values obtained by different methods displayed a good correlation. With the DSC photovisual system applied it is possible to detect the impurity level in warifteine after its purification.

Restricted access

Abstract  

The present work reports studies of the thermal behaviour of some anti-hypertensive drugs. Their purities were determined by DSC and specialized pharmacopeial methods. The activation energy values suggest the following sequence of satability: nifedipine>propanolol hydrochloride>captoril. Analysis of the DSC data indicated that the degrees of purity of nifedipine, captopril and propanolol hydrochloride were similar to those found by pharmacopeial methods BP 93 and USP 23. The simplicity, speed and low operational costs of thermal analysis justify its application in the quality control of pharmaceutical drugs.

Restricted access

Abstract  

Chlorpropamide ((4-chloro-N-(propylamino)-carbonyl)-benzenesulfonamide) belongs to compounds having sulfonylurea group and is widely used as an oral antidiabetic agent. In this work differential scanning calorimetry (DSC) was used during pre-formulation of chlorpropamide tablets to determine the drug-excipients compatibility. The DSC curves of chlorpropamide and binary mixtures with excipients (sodium croscarmellose, sodium lauryl sulfate, microcrystalline cellulose, magnesium stearate and calcium carbonate) showed that chlorpropamide exhibited interaction with magnesium stearate and sodium lauryl sulfate. The binary mixtures of chlorpropamide–magnesium stearate presented a single endothermic process at 96–108 °C and chlorpropamide–sodium lauryl sulfate showed a wide endotherm at 99–120 °C.

Restricted access
Community Ecology
Authors: C. Calderón del Cid, R. S. Rezende, A. R. Calor, J. S. Dahora, L. N. de Aragão, M. L. Guedes, A. N. Caiafa, and A. O. Medeiros

Abstract

Leaf litter breakdown is an important process in riparian ecosystems, regulated by the concomitant fluctuations of allochthonous organic matter input (quality and quantity), the environmental conditions, and the decomposer community. Our objective was to assess the effects of temporal variability of litter quantity and quality over the stream's decomposer community. We hypothesized that the litter effects over the decomposer community would be overruled by Cerrado's harsh environmental conditions. Precipitation fluctuations, especially during dry and rain seasons, did modify the litterfall periodicity, but not the average organic matter entering the system or the litterfall triggers. Fifteen riparian species were identified contributing with organic matter into the stream, however, Richeria grandis contributed with 48% of litter biomass, helping explain the nutritional intra-annual balance given by the litter chemistry, that would be determinant for ecosystem stability. Higher aquatic hyphomycetes sporulation rates and invertebrate density during the dry season suggest that the decomposer community required a more stable environment (consistent low current) in order to colonize and exploit leaf litter. Our results point out that physical fragmentation was the predominant driver of litter breakdown for our system, due to high decomposition rates, litter remaining mass correlated negatively with precipitation, and low decomposer abundance and activity. Invertebrate collectors' abundance was negatively correlated with litter remaining mass and showed no temporal variation, suggesting that this functional group may have benefited from the particulate organic matter produced by physical fragmentation. Therefore, annual temporal variations on Brazilian savanna stream systems may drive the functioning of the ecosystem.

Restricted access