Biocompatible hybrids based on nanographene oxide covalently linked to glycolporphyrins: synthesis, characterization and biological evaluation

The major limitation in the development of hybrids based on graphene oxide (GO) and porphyrins is their dispersibility and stability in aqueous systems due to the hydrophobic character induced by porphyrins. Most of the previous approaches reported the direct functionalization of GO with polyethylene glycol (PEG) chains followed by the self-assembly of porphyrins by π-π interactions. Here, new hybrids were prepared using porphyrins previously functionalized with different number/types of glycol branches to be covalently attached through esterification to the carboxyl groups of GO sheets of nanometric dimensions. The number of the glycol chains and its relative position in the porphyrin core showed to be fundamental to improve the hybrids dispersion and stability in aqueous solutions. The best performing hybrids were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, UV-Vis absorption and fluorescence spectroscopy. The in vitro biocompatibility assessment of these hybrids was conducted using human Saos-2 cells. Their effects on cell proliferation and viability, the generation of reactive oxygen species as well as the cell morphology after cell uptake were analysed. The results demonstrate the biocompatibility of these hybrid nanomaterials with human Saos-2 cells, which is very promising for future application in biomedicine namely in cancer therapy.publishe

Mechanistic insights on the site selectivity in successive 1,3-dipolar cycloadditions to meso-tetraarylporphyrins

A DFT study on site selectivity in successive 1,3-dipolar cycloadditions of meso-tetraarylporphyrins with azomethine ylide and N-methylnitrone has been carried out. The calculation of the thermodynamic stability of both ylide and nitrone-derived adducts reveals that bacteriochlorins are more stable and have stronger aromatic character than isobacteriochlorins. Calculations of whole reaction pathways show that cycloadditions of azomethine ylide on porphyrin and its derived chlorin are irreversible and hence kinetically controlled. Solvent influence on the site selectivity of this reaction has also been considered, and appears to be decisive in controlling the site selectivity. In contrast, cycloadditions of nitrone over porphyrin and chlorin are clearly reversible, pointing to a thermodynamic control of these reactions.This work was supported by the Ministerio de Ciencia y Tecnología (projects CTQ2005-08016 and Consolider Ingenio 2010 CSD2006-00), the University of Aveiro, the Fundação para a Ciência e a Tecnologia (grant SFRH/BPD/8374/2002 of A.M.G.S.) and FEDER for funding the Organic Chemistry Research Unit.Peer reviewe

Screening of wild type Streptomyces isolates able to overproduce clavulanic acid

The selection of new microorganisms able to produce antimicrobial compounds is hoped for to reduce their production costs and the side effects caused by synthetic drugs. Clavulanic acid is a \u3b2-lactam antibiotic produced by submerged culture, which is widely used in medicine as a powerful inhibitor of \u3b2-lactamases, enzymes produced by bacteria resistant to antibiotics such penicillin and cephalosporin. The purpose of this work was to select the best clavulanic acid producer among strains of Streptomyces belonging to the Microorganism Collection of the Department of Antibiotics of the Federal University of Pernambuco (DAUFPE). Initially, the strains were studied for their capacity to inhibit the action of \u3b2-lactamases produced by Klebsiella aerogenes ATCC 15380. From these results, five strains were selected to investigate the batch kinetics of growth and clavulanic acid production in submerged culture carried out in flasks. The results were compared with the ones obtained by Streptomyces clavuligerus ATCC 27064 selected as a control strain. The best clavulanic acid producer was Streptomyces DAUFPE 3060, molecularly identified as Streptomyces variabilis, which increased the clavulanic acid production by 28% compared to the control strain. This work contributes to the enlargement of knowledge on new Streptomyces wild strains able to produce clavulanic acid by submerged culture

Mapping wood volume in seasonally dry vegetation of Caatinga in Bahia State, Brazil

The Caatinga biome in Brazil comprises the largest and most continuous expanse of the seasonally dry tropical forest (SDTF) worldwide; nevertheless, it is among the most threatened and least studied, despite its ecological and biogeographical importance. The spatial distribution of volumetric wood stocks in the Caatinga and the relationship with environmental factors remain unknown. Therefore, this study intends to quantify and analyze the spatial distribution of wood volume as a function of environmental variables in Caatinga vegetation in Bahia State, Brazil. Volumetric estimates were obtained at the plot and fragment level. The multiple linear regression techniques were adopted, using environmental variables in the area as predictors. Spatial modeling was performed using the geostatistical kriging approach with the model residuals. The model developed presented a reasonable fit for the volume m3 ha with r2 of 0.54 and Root Mean Square Error (RMSE) of 10.9 m3 ha–1. The kriging of ordinary residuals suggested low error estimates in unsampled locations and balance in the under and overestimates of the model. The regression kriging approach provided greater detailing of the global wood volume stock map, yielding volume estimates that ranged from 0.01 to 109 m3 ha–1. Elevation, mean annual temperature, and precipitation of the driest month are strong environmental predictors for volume estimation. This information is necessary to development action plans for sustainable management and use of the Caatinga SDTF in Bahia State, Brazil

Selective two-photon absorption in carbon dots: a piece of the photoluminescence emission puzzle

Carbon nanodots (Cdots) are now emerging as promising nonlinear fluorophores for applications in biological environments. A thorough and systematic approach to the two-photon induced emission of Cdots that could provide design guidelines to control their nonlinear emission properties is still missing. In this work, we address the nonlinear optical spectroscopy of Cdots prepared by controlled chemical cutting of graphene oxide (GO). The two-photon absorption in the 700–1000 nm region and the corresponding emission spectrum are carefully investigated. The highest two-photon absorption cross-section estimated was 130 GM at 720 nm. This value is comparable with the one reported for graphene nanoribbons with push–pull architecture. The emission spectrum depends on the excitation mode. At the same excitation energy, nonlinear excitation results in excitation-wavelength independent emission, while upon linear excitation the emission is excitation-wavelength dependent. The biphotonic interaction seems to be selective towards sp2 clusters bearing electron donor and acceptor groups found in push–pull architectures. Both linear and nonlinear emission can be understood based on the existence of isolated sp2 clusters involved in π–π stacking interactions with clusters in adjacent layers.The authors are grateful to Fundação para a Ciência e Tecnologia (FCT, Portugal), European Union, QREN, FEDER and COMPETE for funding the QOPNA, TEMA, and CQFM research unit (project Pest-C/QUI/UI0062/2013, UID/EMS/ 00481/2013 and UID/NAN/50024/2013). FCT is acknowledged for the Post-Doctoral grants of C. I. M. S., S. N. P and I. F. A. M., and for supporting the individual work contract of E. M., I. B. and P. A. A. P. M. within the Investigador FCT program (SFRH/BPD/105478/2014, SFRH/BPD/92409/2013, SFRH/BPD/ 75782/2011, IF/00759/2013, IF/00582/2015 and IF/00917/ 2013). G. G. gratefully acknowledges the funding by European Commission under individual fellowship Marie SklodowskaCurie (NANOTER, Grant Agreement 708351).Peer reviewe

New fluorescent probes based on gallium(III) corrole complexes for the recognition of hydrogen sulfide: a journey from solution to intracellular site

In this work, three fluorescent probes for detection of hydrogen sulfide (H2S) where prepared based on gallium (III) corrole complexes bearing nitro groups at beta-pyrrolic positions. Two of the compounds selected, the 3-nitro5,10,15- tris(pentafluorophenyl)corrolatogallium(III)(pyridine) (CGa-NO2) and the 3,17-dinitro-5,10,15-tris (pentafluorophenyl)corrolatogallium(III)(pyridine) (CGa-2NO2) present one and two nitro groups directly linked to the beta-pyrrolic position. The third compound, the (E)-3-(2-nitroprop-1-en-1-yl)-5,10,15-tris(pentafluorophenyl)corrolatogallium(III)(pyridine) (CGa-EtNO2), has a carbon-carbon double bond spacer between the corrole unit and the nitro group. All these derivatives were obtained from 5,10,15-tris(pentafluorophenyl)corrolatogallium(III)(pyridine) (CGa). The precursor CGa and the derivative CGa-EtNO2 behaved as turn-OFF probes, while compound CGa-NO2 responded as a turn-ON probe in the presence of H2S in the pH range of 5-9. Mechanistic studies show that the interaction of H2S with the probes involves its coordination with gallium(III) and in some cases the reduction of the nitro group to a new aminated corrole. While the formation of the coordination complex with H2S is almost immediate, the kinetics of the reduction is slow. Interestingly, for CGaNO2 the two processes can be explored in a ratiometric sensing of H2S in a non-aqueous solution showing a good linearity over an extended concentration range (5-200 mu M). The response of the corroles to H2S in intracellular medium was studied in 2D cultured cells (HeLa).LISBOA-01-0145-FEDER-029319; LA/P/0056/2020info:eu-repo/semantics/publishedVersio

An insight into the gas-phase fragmentations of potential molecular sensors with porphyrin-chalcone structures

Porphyrin-chalcone derivatives with potential cation sensing ability have been studied by ESI-MS and multistage ESI-MS. The presence of conjugated C=C and C=O double bonds in the chalcone moiety is responsible for the formation of diagnostic fragment ions common to all the studied meta and para chalcones. The ortho isomers show different fragmentation patterns that can be explained by different electronic charge distributions. (C) 2015 Elsevier B.V. All rights reserved