http://dspace.mediu.edu.my:8181/xmlui/handle/123456789/4073 2026-04-24T04:40:17Z http://dspace.mediu.edu.my:8181/xmlui/handle/123456789/4357 Title: Moléculas em três dimensões: um estereoscópio para computador Description: In this paper we describe how to make a very simple stereoscope for observation of molecular models produced by several recent computer programmes. With this instrument, constructed essentially with four mirrors, the chemist can visualize molecular models in three dimensions directly from the personal computer monitor screen. 2013-05-30T00:00:00Z http://dspace.mediu.edu.my:8181/xmlui/handle/123456789/4352 Title: Aquisição de tempos de vida de fosforescência com resolução de fase e sua aplicação ao estudo de relaxações em polímeros Description: We describe in this work a simple experimental set up to perform time dependent luminescence experiments in time scales from mili-seconds to seconds, based on the phase resolution of the emission signal. This system is composed by modulation of a continuous light source with an external chopper controlled by a lock-in amplifier. We exemplified the utility of the system in studies of phosphorecence emission using benzophenone dissolved in polystyrene and since the phosphorescence intensity and lifetime are temperature-dependent processes, we also studied polymer relaxation processes in the temperature range from 20 to 400K. A software that drives the spectrofluorimeter and controls both the cryosystem and the lock-in amplifier was developed. 2013-05-30T00:00:00Z http://dspace.mediu.edu.my:8181/xmlui/handle/123456789/4347 Title: The chemistry of peroxynitrite, a biological toxin Description: Oxyradicals play a tole in several diseases. While for several decades the hydroxyl radical - produced via the Fenton reaction - has been considered the species that initiates oxyradical damage, new findings suggest that much of this damage can be ascribed to peroxynitrite, O=NOO-, formed from the reaction of the superoxide anion with nitrogen monoxide near activated macrophages. The rate constant for the reaction of this reaction has been investigated by flash photolysis and was found to be significantly higher than previously described in the literature, 1.9 x 10(10) M-1s-1. Studies of the isomerization to nitrate resulted in the discovery of a complex between peroxynitrite and its protonated form with a stability constant of 1 x 10(4) M-1. Some of the harmful reaction of peroxynitrous acid have been ascribed to the hydroxyl radical as a product of homolysis of the O-O bond during the conversion to nitrate. Kinetics of the isomerization reaction as a function of pressure show that the activation volume is only +1.5+1.0 ml mol-1, which is inconsistent with homolysis. Instead, an intermediate, possibly a distorted trans-isomer of O=NOOH could be responsible for the harmful reactions of peroxynitrite. 2013-05-30T00:00:00Z http://dspace.mediu.edu.my:8181/xmlui/handle/123456789/4342 Title: Mecanismo de fotodegradação de compostos orgânicos catalisada por TiO2 Description: Conventional technology used in the treatment of wastewater has been pointed as a major environmental problem for sustainable development, since minimization is not addressed accordingly. Advanced oxidation processes (AOP), based on the formation of hydroxyl radical (?OH), a powerful oxidant agent, have been considered to be a potential technology for the destruction of many toxic compounds. Photocatalysis using solar light, an AOP, has been studied for nearly 20 years and recently attracted great interest as a clean-up technology. However, solar detoxification processes have not yet achieved commercial success. This article presents an overview of reaction mechanisms at the surface of semiconductors used as photocatalysts (specially TiO2), when heterogeneous photocatalysis is used to remove hazardous compounds from contaminated sites. 2013-05-30T00:00:00Z