Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto

About: Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto is a based out in . It is known for research contribution in the topics: Population & Genus. The organization has 2143 authors who have published 3674 publications receiving 71071 citations. The organization is also known as: FFCLRP & FFCLRP-USP.

Structural and Spectroscopic Properties of Luminescent Er3+-Doped SiO2–Ta2O5 Nanocomposites

Abstract: This paper reports on the preparation and structural, morphological, and luminescence properties of Er3+-doped nanocomposites based on SiO2–Ta2O5 prepared by the sol–gel method. The influence of the tantalum oxide content on the structural and spectroscopic properties was analyzed for Si/Ta molar ratios of 90:10, 80:20, 70:30, 60:40, and 50:50. The sols were kept at 60°C for formation of the xerogel, followed by annealing at 900°, 1000°, and 1100°C for 2 h for production of the nanocomposites. The densification, phase separation, and crystallization processes were monitored through vibrational spectroscopy (FTIR), X-ray diffraction, and high-resolution transmission electron microscopy. Er3+ emission in the infrared region, assigned to the 4I13/2→4I15/2 transition, was observed for all the nanocomposites. Evolution from a vitreous-like environment to a crystalline one was identified upon increasing the annealing temperature and tantalum content. According to the results obtained, the Er3+ ions are preferentially localized close to the region rich in Ta2O5 nanoparticles. The localization of Er3+ ions was shown to be dependent on the amount of tantalum. Moreover, the fact that the Er3+ ions are located close to Ta2O5 nanoparticles promotes a broadband emission with full-width at half-maximum of 90 nm around 1550 nm.

Fragmentation of diketopiperazines from Aspergillus fumigatus by electrospray ionization tandem mass spectrometry (ESI-MS/MS).

Abstract: Diketopiperazines (DKPs) corresponding to cyclic dipeptides have been reported to exhibit antimicrobial, antitumor, antimutagenic and antiviral properties. These compounds are commonly isolated from microorganisms and sponges and from a variety of tissues and body fluids. In this work, we used electrospray ionization tandem mass spectrometry (ESI-MS/MS) to investigate the fragmentation of a series of DKPs previously isolated from Aspergillus fumigatus, which exhibit the same structural core. Loss of CO directly from the protonated molecule was found to be a fragmentation process common to all the compounds analyzed. However, our results revealed a series of ions that are diagnostic for the substituents at C(4) and C(9). In order to rationalize the differences in the fragmentation pathways of substituted and nonsubstituted DKPs, the relative Gibbs energies (1G) of the product ions and intermediate ions were estimated using the B3LYP/6‐31++G(d,p) model. The data reported here can be used for the structural elucidation of DKPs from low sample amounts, as an alternative to NMR. Copyright  2007 John Wiley & Sons, Ltd.