Engineering highly efficient Eu(iii)-based tri-ureasil hybrids toward luminescent solar concentrators.

Abstract

Following a computational-experimental approach, a highly luminescent beta-diketonate-europium(III) complex containing 2-thenoyltrifluoracetonate (tta(-)) and 5,6-epoxy-5,6-dihydro-[1,10] phenanthroline (ephen) ligands, Eu(tta)(3)ephen (II), was theoretically studied by DFT/TD-DFT calculations, synthesized from Eu(tta)(3)(H2O)(2)(I) and fully characterized by high resolution mass spectrometry, TGA analysis, vibrational, UV-Vis and photoluminescence spectroscopy. For intramolecular energy transfer analysis purpose, Ln(NO3)(3)(ephen)(2) [Ln = Eu (III), Gd (IV)] complexes were also synthesized and complexes I and III were theoretically studied. The organic-inorganic tri-ureasil matrix was used as a support for the immobilization of complex II and two hybrid samples were synthesized as a monolith (MtU5Eu-II) and as a thin film (FtU5Eu-II), characterized and its photoluminescence properties were compared with those of complex II. The photophysical properties of complex II benefit from the synergy between the excited-states of both ligands that create efficient energy transfer pathways to optimize the Eu3+ sensitization contributing to the large emission quantum yield (82 +/- 8%), which is one of the highest so far reported for solid lanthanide beta-diketonate complexes. Moreover, although the incorporation of complex II into the hybrid matrix is disadvantageous from the quantum yield point of view, MtU5Eu-II and FtU5Eu-II exhibit the highest emission quantum yields reported so far for Eu3+-containing hybrids (63 +/- 6% and 48 +/- 5%, respectively). Additionally, a significant improvement in the photostability under UV irradiation of the incorporated complex II is observed. The possibility of FtU5Eu-II to be used as a luminescent solar concentrator was evaluated and an optical conversion efficiency of similar to 9% as well as an ability to boost up the Si-photovoltaic cell output to 0.5% were verified.

Nolasco, M. M.; Vaz, P. M.; Freitas, V. T.; Lima, P. P.; Andre, P. S.; Ferreira, R. A. S.; Vaz, P. D. ; Ribeiro-Claro, P.; Carlos, L. D.


Full Article

Analysis by vibrational spectroscopy of seaweed polysaccharides with potential use in food, pharmaceutical and cosmetic industries

Abstract

Polysaccharides present in several seaweeds (Kappaphycus alvarezii, Calliblepharis jubata, and Chondrus crispus—Gigartinales, Rhodophyta; Gelidium corneum and Pterocladiella capillacea—Gelidiales, Rhodophyta; Laurencia obtusa—Ceramiales, Rhodophyta; Himanthalia elongata, Undaria pinnatifida, Saccorhiza polyschides, Sargassum vulgare, and Padina pavonica—Phaeophyceae, Ochrophyta) are analyzed by spectroscopic techniques. The nature of the polysaccharides (with extraction and without any type of extraction) present in these seaweeds was determined with FTIR-ATR and FT-Raman analysis of extracted phycocolloids and ground dry seaweed.

Leonel Pereira, Saly F. Gheda, Paulo J.A. Ribeiro-Claro.


Full Article

Chloramphenicol·cyclodextrin inclusion compounds: co-dissolution and mechanochemical preparations and antibacterial action.

Abstract

Beta-Cyclodextrin (beta CD) inclusion compounds of chloramphenicol in the solid-state were prepared via two different procedures, co-crystallisation from aqueous solution and the solvent-free method of co-grinding. Chloramphenicol inclusion into permethylated beta CD (TRIMEB) was also performed by co-dissolution in ethanol. The co-crystallisation procedure was the best for preparing chloramphenicol center dot beta CD in 1 : 1 stoichiometry in high purity, while with the co-grinding treatment and the same starting proportion, a complete inclusion was not achieved. Microcrystals of chloramphenicol center dot beta CD inclusion compound presented polymorphism, crystallising simultaneously in the triclinic P1 or monoclinic C2 space groups. Only crystals of the latter were suitable for single-crystal diffraction and data for the guest atoms was comprised of a smeared-out electron cloud, so theoretical calculations were used to propose their plausible geometry and location inside the host molecules. The co-grinding procedure curbed polymorphism and allowed the preparation of chloramphenicol center dot beta CD in the amorphous state; chloramphenicol center dot TRIMEB prepared by co-dissolution of the components in a 1 : 1 proportion was also an amorphous material. The influence of inclusion with beta CD and TRIMEB on the antimicrobial performance of chloramphenicol was evaluated, and both inclusion compounds demonstrated selective action against Enterococcus faecalis strains ATCC 29212 and A33562 and Listeria monocytogenes ATCC 7644. Chloramphenicol center dot TRIMEB also had higher activity against the E. faecalis strains A35906, 9308 and E4856 and against Listeria inocua.

Ramos, A. I.; Braga, T. M.; Silva, P.; Fernandes, J. A.; Ribeiro-Claro, P.; Lopes, M. D. S.; Paz, F. A. A.; Braga, S. S.


Full Article

On the Relevance of Considering the Intermolecular Interactions on the Prediction of the Vibrational Spectra of Isopropylamine

Abstract

The effects of implicitly considering the effects of hydrogen bonding on the molecular properties, such as vibrational frequencies, were inferred on the basis of DFT calculations. Several clusters of isopropylamine were assembled and theoretically characterized. The results showed that maximum H-bond cooperativity is achieved when the amine group acts simultaneously as donor and acceptor. The effect of H-bond cooperativity manifests itself in the relative cluster stability and on the structural and vibrational frequency predictions. Referring to the vibrational frequencies it was found that the NH2 stretching and torsion vibrational modes are the most affected by the amine involvement in hydrogen bonding. Both stretching modes were found to be significantly redshifted relative to themonomer.TheNH2 torsionalmode, on the other hand, was found to be blueshifted up to 350 cm−1. Finally, the comparative study between the theory levels performed allows to conclude that the small 6-31G∗ basis set is able to stabilize weak C–H⋅ ⋅ ⋅N interactions as long as the new dispersion corrected DFTmethods are considered. The impairments observed with conventionalDFTmethods for describing weak interactionsmay be overcome with the improvement of basis set, but the associated increase of computational costs may turn the calculations unfeasible.

A M Amado, S Fiuza, LAEB de Carvalho, Paulo J. A. Ribeiro-Claro.


Full Article

Effects of hydrogen-bond and cooperativity in the vibrational spectra of Luminol.

Abstract

Luminol, one of the most popular electrochemiluminescence systems used in forensic chemistry, proved to be a suitable system to study the importance of cooperativity in hydrogen-bond chains. The computational pairwise approach PiMM was applied to the system and a thorough band assignment was accomplished. Hydrogen-bond and hydrogen-bond cooperativity effects were assessed through a confrontation of energy, geometry and wavenumber changes from monomer and dimer on one hand and dimer and “full-cluster” trimer on the other. For the first time the PiMM method was also used to successfully predict changes in band relative intensities. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

Mendes, N.F. C.; Nolasco, M. M.; Ribeiro-Claro, P. J. A.


Full Article

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©Copyright 2024 - Computational Spectroscopy Lab - Department of Chemistry - University of Aveiro - 3810-193 Aveiro

©Copyright 2024 - Computational Spectroscopy Lab - Department of Chemistry - University of Aveiro - 3810-193 Aveiro