Evaluation of the oxygen reduction reaction electrocatalytic activity of postsynthetically modified covalent organic frameworks

The pyrolysis of organic precursors to produce heteroatomic-doped carbonaceous materials has emerged as a powerful tool to construct metal-free heterogeneous electrocatalysts due to their low cost and their environmental friendliness. However, the lack of control in the atomic positions or the location of the chemical functionalities makes it difficult to establish structure-property relationships. Herein, we report an easy strategy to compare the electrocatalytic oxygen reduction reaction (ORR) performance of metal-free and nonpyrolyzed materials by postsynthetic modification of covalent organic frameworks (COFs) via click-chemistry. This method facilitates the evaluation of different active centers using materials with the same morphology and prevents active site agglomeration by covalently anchoring these moieties inside of a porous and crystalline framework. In this study we developed a series of diimide-based materials (XDI0.17-COFs) with a loading of 7.65 × 10-4 mol of active site/mg of host COF. The bulk COFs have been delaminated to perform electrode modification by drop-casting. The electrocatalytic response toward the ORR has been studied in alkaline media obtaining the best results for the NDI0.17-COF with an onset potential of 0.77 V (vs reversible hydrogen electrode, RHE) and a limiting current of 4.2 mA/cm2 by a preferred pathway toward water electroreduction. Finally, an adequate combination of density functional theory with the thermochemical Gibbs free energy formalism has been used to theoretically rationalize the ORR mechanism in these metal-free and nonpyrolyzed materials. We have obtained theoretical ORR overpotentials for each COF system agreeing with the experimental observation, which correlate with the ability of the NDI, BzDI, and PDI molecular blocks to accommodate electrons. Our work provides a guideline on how to study the electrocatalytic performance of different organic moieties in metal-free and non-pyrolyzed COFs avoiding their de novo synthesis by using the click postsynthetic methodologyTED2021-129886B-C43, PID2019-106268GB-C32, RED2018-102412-T, PID2020-116728RB-I00, PID2020-113142RB-C21, PLEC2021-007906, 2018/NMT-4349TRANSNANOAVANSENS, S2018/NMT-4367, Y2020/NMT646

First advances of the archaeological excavation in the mausoleums of the southeastern gate of Baelo Claudia: the monument of Iunia Rufina

En este artículo se presenta la excavación arqueológica desarrollada en los mausoleos emplazados junto a la puerta sureste de la ciudad de Baelo Claudia (Bolonia, Tarifa, Cádiz). De estos dos monumentos apenas quedaba rastro en superficie. Dicha intervención trataba de aportar luz sobre su estructura, sobre su posición respecto al decumanus y sobre su cronología. Para ello se realizó una excavación en área abierta en la que se pudo constatar que habían padecido un expolio ya en época antigua y sufrido las consecuencias de un terremoto. Este evento sísmico había derrumbado los edificios cubriéndolos de escombros, sellando muchos de sus elementos decorativos. La excavación, por tanto, ha permitido recuperar estos elementos en buen estado de conservación, sobre todo de uno de los dos mausoleos. De los hallazgos destacan los órdenes arquitectónicos completos que fueron ejecutados en mármol, así como el epígrafe funerario, realizado con letras de bronce. Se trata de un importante hallazgo tanto por la calidad de la decoración arquitectónica, como por el hecho de que se trata de una de las escasas inscripciones realizadas en litterae aureae conservadas en el occidente del imperio.Recent archaeological works in the mausoleums near the South Eastern Gate of Roman Baelo Claudia (Bolonia, Tarifa, Cádiz) are presented in this paper. Both monuments were partly visible before the excavation and our aim was to throw light on their structure, spatial relation to the decumanus and their chronology. The open-area excavation allowed us to determine that they were looted in ancient times and that they even suffered an earthquake. Fortunately, the collapse of the mausoleums caused by that seismic episode covered –and hid- the different decorative elements with debris. Thus, the excavation has allowed recovering these valuable elements from one of the two mausoleums: the complete architectural order made in marble (base, column and capital), as well as the funerary inscription, made of bronze letters. This is an extraordinary find for the quality of the architectural elements and for being one of the few inscriptions made in litterae aureae that have been preserved

Green extracellular synthesis of silver nanoparticles by Pseudomonas alloputida, their growth and biofilm-formation inhibitory activities and synergic behavior with three classical antibiotics

Bacterial resistance to antibiotics is on the rise and hinders the fight against bacterial infections, which are expected to cause millions of deaths by 2050. New antibiotics are difficult to find, so alternatives are needed. One could be metal-based drugs, such as silver nanoparticles (AgNPs). In general, chemical methods for AgNPs’ production are potentially toxic, and the physical ones expensive, while green approaches are not. In this paper, we present the green synthesis of AgNPs using two Pseudomonas alloputida B003 UAM culture broths, sampled from their exponential and stationary growth phases. AgNPs were physicochemically characterized by transmission electron microscopy (TEM), total reflection X-ray fluorescence (TXRF), infrared spectroscopy (FTIR), dynamic light scattering (DLS), and X-ray diffraction (XRD), showing differential characteristics depending on the synthesis method used. Antibacterial activity was tested in three assays, and we compared the growth and biofilm-formation inhibition of six test bacteria: Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis. We also monitored nanoparticles’ synergic behavior through the growth inhibition of E. coli and S. aureus by three classical antibiotics: ampicillin, nalidixic acid, and streptomycin. The results indicate that very good AgNP activity was obtained with particularly low MICs for the three tested strains of P. aeruginosa. A good synergistic effect on streptomycin activity was observed for all the nanoparticles. For ampicillin, a synergic effect was detected only against S. aureus. ROS production was found to be related to the AgNPs’ antibacterial activit

Intra-varietal diversity for agronomic traits in 'Garnacha Blanca'

'Garnacha Blanca' is a somatic variant derived from 'Garnacha Tinta', an old variety with large genetic and phenotypic variability. In this work we have studied for two years the phenotypic variation existing in 'Garnacha Blanca' for yield and quality related traits in accessions from 14 sampling locations of ancient vineyards in the Ebro Valley, Spain. The results showed high variability among the accessions in many of the traits studied in 'Garnacha Blanca'. Different accessions could be distinguished both years using several traits, including two important traits in terms of quality and yield: bunch compactness and yield per plant. A large environment effect, intrinsic to the 'Garnacha' group, enhances phenotypic variation among years, what requires increasing the number of bunches and years for clonal characterization in this variety. The dimensions of the berry showed the least variability, while traits related to bunch architecture like bunch length were discriminant and also stable

Oxygen reduction using a metal-free naphthalene diimide-based covalent organic framework electrocatalyst

A novel naphthalene diimide-based covalent organic framework (NDI-COF) has been synthesized and successfully exfoliated into COF nanosheets (CONs). Electrochemical measurements reveal that the naphthalene diimide units incorporated into NDI-CONs act as efficient electrocatalyst for oxygen reduction in alkaline media, showing its potential for the development of metal-free fuel cellsFinancial support from the Spanish Government (projects MAT2016-77608-C3-1-P, MAT2016-77608-C3-2-P, CTQ2017-84309-C2-1-R, MAT2017-85089-C2-1-R, FJCI-2017-33536 and RYC-2015-17730), the UCM (INV.GR.00.1819.10759) and the Madrid Regional Government (TRANSNANOAVANSENS-CM (S2018/NMT-4349)) is acknowledge

Study, preparation and characterization of thiosemicarbazone ligands and their compounds

The 20th International Electronic Conference on Synthetic Organic Chemistry session General Organic SynthesisThiosemicarbazones are formed by the condensation of an aldehyde or ketone with a thiosemicarbazide. They have high coordinative capacity given that they have several potential donor atoms through which they can bind to transition metals. This coordinative capacity can be increased if the R1 and R2 substituents include additional donor atoms. In addition, thiosemicarbazones as well as their semicarbazones analogues have considerable biological and pharmacological interest because of their antibacterial, antiviral and antitumor activity. This communication includes the preparation and characterization of a series of thiosemicarcarbazones and their applications in the synthesis of palladium organometallic compoundsWe wish to thank the financial support received from the Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia Competitiva Programme Projects GRC2015/00

Functionalized thiosemicarbazone ligands and their complexes

The 20th International Electronic Conference on Synthetic Organic Chemistry session General Organic SynthesisThe purpose of this work is the design, synthesis and characterization of thiosemicarbazone ligands bearing a phenyl boronic acid functionality. The main interest is the synthesis of organopalladium compounds with the boronic acid included within the corresponding molecule. These could lead to further modification of the properties of the organometallic species applicable to the Suzuki-Miyaura reaction. The ligands were prepared by reaction of acetylphenylboronic acid with several thiosemicarbazides. The compounds were characterized by IR, 1H and 31P NMR spectroscopyWe wish to thank the financial support received from the Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia Competitiva Programme Projects GRC2015/009

Synthesis of iminophosphoranes as ligands for organometallic compounds

Iminophosphoranes are organic compounds of general composition R3P=NR and can be considered as nitrogen analogues to phophorus ylides. They can be obtained by the Staudinger and Kirsanov reactions. This compounds have multiple applications: they can be used as intermediates in reactions such as the Aza-Wittig, as a protecting group for amines or as a ligands for coordinated or cyclometallated compounds. The P=N bond is highly polarized, so that the nitrogen bears a partial negative charge. This feature makes them act as σ-donors with only minor π-acceptor properties, so when forming coordination compounds they can be displaced by other ligandsWe wish to thank the financial support received from the Xunta de Galicia (Galicia, Spain) under the Grupos de Referencia Competitiva Programme Projects GRC2015/00

Azure A embedded in carbon dots as NADH electrocatalyst: Development of a glutamate electrochemical biosensor

Carbon nanodots modified with azure A (AA-CDs) have been synthesized and applied as redox mediator of bioelectrocatalytic reactions. A deep characterization of AA-CDs nanomaterial has been carried out, proving the covalent attachment of azure A molecules into the carbon dots nanostructure. Disposable screen-printed carbon electrodes (SPCE) have been modified with AA-CDs, through the action of chitosan polymer (Chit-AA-CDs/SPCE). The Chit-AA-CDs/SPCE electrocatalytic activity towards the oxidation of NADH has been proved, obtaining excellent results regarding the low oxidation potential achieved (−0.15 V vs. Ag) and low detection and quantification limits (LOD and LOQ) for NADH, 16 and 53 µM, respectively. The developed electrochemical platform has been applied for the construction of a glutamate biosensor by immobilizing L-glutamic dehydrogenase (GLDH/Chit-AA-CDs/SPCE). The morphology of GLDH/Chit-AA-CDs/SPCE platform was analysed by AFM at each different step of the electrode modification process. The resulting biosensing platform is capable of detect NADH enzymatically generated by GLDH in the presence of glutamate and NAD+. Good analytical parameters were obtained for glutamate analysis using GLDH/Chit-AA-CDs/SPCE, as LOD and LOQ of 3.3 and 11 µM, respectively. The biosensor has been successfully applied to the analysis of food and biological samplesThis work has been supported by the Spanish Ministerio de Ciencia e Innovacion (PID2020–116728RB-I00) and Comunidad Autonoma de Madrid (SI3/PJI/2021–00341, P2018/NMT-4349 TRANSNANOAVANSENS Program

Carbon nanodots modified-electrode for peroxide-free cholesterol biosensing and biofuel cell design

The determination of cholesterol is greatly important because high concentrations of this biomarker are associated to heart disease. Moreover, cholesterol can be used as a fuel in enzymatic fuel cells operating under physiological conditions. Here, we present a cholesterol biosensor and a peroxide-free biofuel cell based on the electrocatalytic oxidation of the NADH generated during the enzymatic reaction of cholesterol dehydrogenase (ChDH) as an alternative to the H2O2 biosensing strategies used with cholesterol oxidase-bioelectrodes. Azure A functionalized-carbon nanodots were used as NADH oxidation electrocatalysts and for ChDH covalent immobilization. The biosensor responded linearly to cholesterol concentrations up to 1.7 mM with good sensitivity (4.50 mA cm−2 M−1) and at a low potential. The ChDH bioelectrode was combined with an O2-reducing bilirubin oxidase cathode to produce electrical energy using cholesterol as fuel and O2 as oxidant. Furthermore, the resulting enzymatic fuel cell was tested in human serum naturally containing free cholesterolA.L.DL. and M.P. thank MCIU/AEI/FEDER, EU for funding project RTI2018–095090-B-I00. M.B. acknowledges funding from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement No. 713366. This work was also supported by Talent Attraction Project from CAM (SI3/PJI/ 2021–00341 and 2021–5A/BIO-20943), Spanish Ministerio de Ciencia e Innovacion (PID2020–116728RB-I00) and TRANSNANOAVANSENSCAM Program (S2018/NMT-4349