Showing papers by "Cesar A. Sierra published in 2018"

Heterogeneous Fenton oxidation of Orange II using iron nanoparticles supported on natural and functionalized fique fiber

Abstract: A detailed study of a catalyst, synthesized by impregnation of iron species on the surface of functionalized fique fiber was performed. Wet impregnation ranging from 1 to 5 days was evaluated in order to assess the amount of iron deposited as a function of time. Quantification of adsorbed iron species was done by atomic absorption spectroscopy (AAS), getting values of 10.9, 14.9, 13.2, 15.9 and 14.9 wt% from 1 to 5 days respectively. X-ray spectroscopy (XRF), X-ray diffraction (XRD) and Fourier Transformed Infrared spectroscopy (FTIR) were used to determine the identity and quantity of species present in the sample, providing evidence of Fe2O3 (hematite) species and showing that under the impregnating conditions there is not complete evolution of iron crystalline structures. SEM images of the iron-impregnated functionalized-fiber revealed areas with substantial nanoparticles aggregation and areas where they are finely dispersed. This nanostructured biomaterial was tested as catalyst in the degradation and mineralization of Orange II (OII) under reaction conditions that promotes a Fenton heterogeneous type reaction. The best experimental conditions obtained under a Box-Behnken experimental design yield up to 93.23% OII degradation.

Synthesis, characterization, X-ray crystal structure and DFT calculations of 4-([2,2':6',2''-terpyridin]- 4'-yl)phenol

Abstract: The synthesis of new terpyridine (Tpy) derivatives has been subject of extensive research due to its potential as functional materials for solar energy conversion, among other applications. In this contribution, the 4-([2,2':6',2''-terpyridin]-4'-yl)phenol (TpyOH) has been synthesized, characterized and studied through several methods, including X-ray crystallography and computational approaches. Single crystal X-ray structure analysis shows that TpyOH is essentially planar, with dihedral angles of about 5.03° between the central pyridinyl and the phenolic ring, and also 6.05 and 12.2° in the terpyridine moiety. In the crystal, molecules are linked by intermolecular hydrogen bonds and through π-π stacking interactions. Using a time-dependent density functional theory approach and taking into account bulk solvent effects, the absorption and fluorescence spectra of TpyOH were investigated and compared. The TD-DFT S0 → Sn and S1 → S0 transition energies are in good agreement with experimental results. The frontier molecular orbitals analysis showed that the low-energy absorption band has an intraligand charge transfer character (ICT), while the high-energy band is a common feature of π-π* transitions of the Tpy moiety. The S1→S0 emission transition also has an ICT character, with a 90% contribution from the HOMO→LUMO transitions.

Desarrollo de vectores génicos basados en polímeros sintéticos: PEI y PDMAEMA

Abstract: During recent years, the use of genetic therapies has taken relevance in the treatment of high-incidence diseases such as cancer. Usually, they are based on the release of genetic material, as plasmids, into the cell nucleus, which corrects a function or induces the production of a deficient protein at the physiological level. To carry out gene therapy, vectors capable of encapsulating the genetic material and guaranteeing its delivery in the target cell nucleus are required. Synthetic cationic polymers have attracted great attention as vectors due to their ability to condense nucleic acids to form particles that protect them from enzymatic degradation and facilitate their cellular uptake. Polyethylenimine and poly (N, N-dimethylaminoethyl methacrylate) are the most effective cationic polymers for gene delivery. However, these polymers require specific chemical modifications to either avoid or diminish their high cytotoxicity and low biodegradability. This review analyzes some of these modifications, focusing on recent advances in the development of amphiphilic copolymers as precursors of nanoparticles used as gene vectors.