Crescimento de cristais de L-aspargina monohidratada dopada com metais de transição e propriedades vibracionais a altas temperaturas

Abstract

In this work na investigation of monohydrated L-asparagine crystal doped with Ag, Cr, Cu, Fe, Mn, Ni and without doping is presented. Crystals were grown at controlled temperatures (both 300 K and 277 K) from aqueous solutions. The percentege of doping substances were 1%, 2%, 5% and 7%. The time for the first crystals begin to grow is about thee weeks and it depends on the solution pH. Changes in the color of the crystals as well as the morfology of some samples were very clear, indicating that doping has occurred. In order to quantify the doping, Atomic Emission Spectroscopy (ICP-AES) measurements were carried out. Also, Raman scattering measurements performed at room temperature in both pure and doped monohydrated L-asparagine are shown, in particular, with a discussion about the frequency changes due to the doping. The rising of a new peak in the medium frequency region due, possibly, to doping is discussed. For samples doped with Cr e Cu, different spectro were obtained. Additionally, temperature-dependent Raman experiments were performed for pure and Cr-doped crystals. A structural phase transition was observed in both materials and to confirm it thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were did for monohydrated L-asparagine. From these last measurements we realized that the phase transsition can be interpreted as the lost of the four water molecules of the unit cell.