Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario.

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Bamboo-Based Biochar: A Still Too Little-Studied Black Gold and Its Current Applications.

Biochar (BC), also referred to as "black gold", is a carbon heterogeneous material rich in aromatic systems and minerals, preparable by the thermal decomposition of vegetable and animal biomasses in controlled conditions and with clean technology. Due to its adsorption ability and presence of persistent free radicals (PFRs), BC has demonstrated, among other uses, great potential in the removal of environmental organic and inorganic xenobiotics. Bamboo is an evergreen perennial flowering plant characterized by a short five-year growth period, fast harvesting, and large production in many tropical and subtropical countries worldwide, thus representing an attractive, low-cost, eco-friendly, and renewable bioresource for producing BC. Due to their large surface area and increased porosity, the pyrolyzed derivatives of bamboo, including bamboo biochar (BBC) or activated BBC (ABBC), are considered great bio-adsorbent materials for removing heavy metals, as well as organic and inorganic contaminants from wastewater and soil, thus improving plant growth and production yield. Nowadays, the increasing technological applications of BBC and ABBC also include their employment as energy sources, to catalyze chemical reactions, to develop thermoelectrical devices, as 3D solar vapor-generation devices for water desalination, and as efficient photothermal-conversion devices. Anyway, although it has great potential as an alternative biomass to wood to produce BC, thus paving the way for new bio- and circular economy solutions, the study of bamboo-derived biomasses is still in its infancy. In this context, the main scope of this review was to support an increasing production of BBC and ABBC and to stimulate further studies about their possible applications, thus enlarging the current knowledge about these materials and allowing their more rational, safer, and optimized application. To this end, after having provided background concerning BC, its production methods, and its main applications, we have reviewed and discussed the main studies on BBC and ABBC and their applications reported in recent years.

Antitrypanosomal Activity of 1,2,3-Triazole-Based Hybrids Evaluated Using In Vitro Preclinical Translational Models.

Chagas disease therapy still relies on two nitroderivatives, nifurtimox and benznidazole (Bz), which have important limitations and serious adverse effects. New therapeutic alternatives for this silent disease, which has become a worldwide public health problem, are essential for its control and elimination. In this study, 1,2,3-triazole analogues were evaluated for efficacy against T. cruzi. Three triazole derivatives, 1d (0.21 µM), 1f (1.23 µM), and 1g (2.28 µM), showed potent activity against trypomastigotes, reaching IC50 values 10 to 100 times greater than Bz (22.79 µM). Promising candidates are active against intracellular amastigotes (IC50 ≤ 6.20 µM). Treatment of 3D cardiac spheroids, a translational in vitro model, significantly reduced parasite load, indicating good drug diffusion and efficacy. Oral bioavailability was predicted for triazole derivatives. Although infection was significantly reduced without drug pressure in a washout assay, the triazole derivatives did not inhibit parasite resurgence. An isobologram analysis revealed an additive interaction when 1,2,3-triazole analogs and Bz were combined in vitro. These data indicate a strengthened potential of the triazole scaffold and encourage optimization based on an analysis of the structure-activity relationship aimed at identifying new compounds potentially active against T. cruzi.

Ecological Biosubstrates Obtained from Onion Pulp (Allium cepa L.) for Flexible Organic Light-Emitting Diodes.

A new biopolymer obtained from onion pulp (Allium cepa L.) was employed to produce a sustainable substrate for flexible organic light-emitting diodes (FOLEDs). Indium tin oxide (ITO) and SiO2 thin films were deposited by rf-magnetron sputtering onto these biosubstrates to obtain flexible, transparent, and conductive anodes, on top of which FOLEDs were produced. This new biomaterial exhibits an optical transparency of 63% at 550 nm. ITO films were optimized by varying rf power during deposition onto the biopolymers, and their electrical properties are comparable to the those of ITO grown on top of rigid substrates: a carrier concentration of -3.63 × 1021 cm-3 and carrier mobility of 7.72 cm2 V-1 s-1 for the optimized film. Consequently, the sheet resistance and resistivity of this ITO film were 8.92 Ω sq-1 and 2.23 × 10-4 Ω cm, respectively, hence allowing the production of FOLEDs. The A. cepa L. based FOLED was fabricated using CuPc, ß-NPB, and Alq3 as organic layers, and it exhibited a maximum luminance of about 2062 cd m-2 at 16.6 V. The current efficiency reached a maximum value of 2.1 cd A-1 at 85.3 mA cm-2. The obtained results suggest the possibility to use these substrates for innovative biocompatible applications in optoelectronics, such as photodynamic therapy.

Two-color surface plasmon resonance nanosizer for gold nanoparticles.

We study the potentialities of a two-color Surface Plasmon Resonance (SPR) spectroscopy nanosizer by monitoring the assembling of a colloidal dispersion of citrate stabilized gold nanoparticles (AuNPs) on SiO2 surface. When the AuNPs/water composite's optical density layer is negligible and the electron mean-free path limitation is taken into account in the AuNPs' dielectric constant;s formulation, the surface density σ of the nanoparticle array and the statistical mean size of the nanoparticles can be straightly determined by using two-color SPR spectroscopy in the context of Maxwell's Garnett theory. The optical method, demonstrated experimentally for AuNPs with a nominal mean diameter of 15 nm, can, theoretically, be extended to bigger nanoparticles, based on a simple scaling relation between the extinction cross section of the single nanoparticle σext and the surface density σ. The experimental results, comparable to those obtained by AFM, transmission electron microscopy and dynamic light scattering technique, establish a novel insight on the SPR spectroscopy's potential to accurately characterize nanomaterials.

Limits of the Effective Medium Theory in Particle Amplified Surface Plasmon Resonance Spectroscopy Biosensors.

The resonant wave modes in monomodal and multimodal planar Surface Plasmon Resonance (SPR) sensors and their response to a bidimensional array of gold nanoparticles (AuNPs) are analyzed both theoretically and experimentally, to investigate the parameters that rule the correct nanoparticle counting in the emerging metal nanoparticle-amplified surface plasmon resonance (PA-SPR) spectroscopy. With numerical simulations based on the Finite Element Method (FEM), we evaluate the error performed in the determination of the surface density of nanoparticles σ when the Maxwell-Garnett effective medium theory is used for fast data processing of the SPR reflectivity curves upon nanoparticle detection. The deviation increases directly with the manifestations of non-negligible scattering cross-section of the single nanoparticle, dipole-dipole interactions between adjacent AuNPs and dipolar interactions with the metal substrate. Near field simulations show clearly the set-up of dipolar interactions when the dielectric thickness is smaller than 10 nm and confirm that the anomalous dispersion usually observed experimentally is due to the failure of the effective medium theories. Using citrate stabilized AuNPs with a nominal diameter of about 15 nm, we demonstrate experimentally that Dielectric Loaded Waveguides (DLWGs) can be used as accurate nanocounters in the range of surface density between 20 and 200 NP/µm², opening the way to the use of PA-SPR spectroscopy on systems mimicking the physiological cell membranes on SiO2 supports.

Aerobic oxidation of 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid and its derivatives by heterogeneous NHC-catalysis.

The application of the oxidative system composed of a heterogeneous triazolium pre-catalyst, iron(ii) phthalocyanine and air is described for the selective conversion of 5-hydroxymethylfurfural (HMF) into the added-value 5-hydroxymethyl-2-furancarboxylic acid (HMFCA). The disclosed one-pot two-step procedure involved sequential oxidative esterifications of HMF to afford a polyester oligomer having hydroxyl and carboxyl terminal groups (Mw = 389-1258), which in turn was hydrolyzed by a supported base (Ambersep 900 OH) to yield HMFCA in 87% overall yield. The same strategy was adopted for the effective synthesis of ester and amide derivatives of HMFCA by nucleophilic depolymerization of the oligomeric intermediate with methanol and butylamine, respectively. The utilization of the disclosed oxidative system for the direct conversion of HMF and furfural into their corresponding ester, amide, and thioester derivatives is also reported.

Spherical gold nanoparticles and gold nanorods for the determination of gentamicin.

Gentamicin is an antibiotic indicated to treat mastitis in dairy cattle and for the treatment of bacterial resistance in the context of hospital infections. The effect caused by gentamicin on the optical properties of gold nanoparticles aqueous dispersions were used to develop quantitative methods to determine this antibiotic. Two different aqueous dispersions, one containing spherical Au nanoparticles (AuNPs) and the other containing Au nanorods (AuNRs), had their conditions adjusted to enable a stable and sensitive response towards gentamicin. The use of AuNPs, with measurement at 681nm of the rising coupling plasmon band, enabled a limit of detection (LOD) of 0.4ngmL-1 (0.02ng absolute LOD), ten times lower than the one achieved by measuring the decreasing of the longitudinal surface plasmon resonance band (at 662nm). The linear analytical response of AuNPs measured at 681nm did not require rationing of signal values to correct for linearity. Stability of the analytical response resulted in intermediary precision below 2%. No significant interference was imposed by excipients traditionally present in injectable solutions for veterinary use. Percent recoveries obtained in such formulations were between 94.5 and 98.2% regardless the existence of any difference in the proportion of the compounds known as gentamicin (C1, C1a and C2) in standard and in the samples. The method requires no derivatization with toxic reagents as usually is required in other spectroscopic approaches.

Circular dichroism and UV-Vis absorption spectroscopic monitoring of production of chiral silver nanoparticles templated by guanosine 5'-monophosphate.

Herein we report the chemical reduction of silver ions incorporated into chiral supramolecular nanostructures by NaBH(4) in buffered (basic) and unbuffered conditions. In situ self-assembly of guanosine 5'-monophosphate (5'-GMP) templated by Ag(I) and generation of silver nanoparticles (NPs) were continuously monitored by CD and UV-Vis spectroscopy measurements. 5'-GMP has been identified as an efficient chiral organic ligand to complex silver ions into a hierarchical helical nanostructure and is a useful capping agent for stabilizing silver NPs with a size diameter lower than 20 nm. The observation of opposite signed bands in the CD spectra of Ag(I)/5'-GMP complexes at different pH has suggested the existence of opposite-handed supramolecular helical structures depending on pH. Both helical supramolecular structures induce chirality in the silver NPs during their growth of the same handedness as shown by the CD signals in the plasmon resonance band.

Self-assembly of an alkylated guanosine derivative into ordered supramolecular nanoribbons in solution and on solid surfaces.

We report on the synthesis and self-assembly of a guanosine derivative bearing an alkyloxy side group under different environmental conditions. This derivative was found to spontaneously form ordered supramolecular nanoribbons in which the individual nucleobases are interacting through H-bonds. In toluene and chloroform solutions the formation of gel-like liquid-crystalline phases was observed. Sub-molecularly resolved scanning tunneling microscopic imaging of monolayers physisorbed at the graphite-solution interface revealed highly ordered two-dimensional networks. The recorded intramolecular contrast can be ascribed to the electronic properties of the different moieties composing the molecule, as proven by quantum-chemical calculations. This self-assembly behavior is in excellent agreement with that of 5'-O-acylated guanosines, which are also characterized by a self-assembled motif of guanosines that resembles parallel ribbons. Therefore, for guanosine derivatives (without sterically demanding groups on the guanine base) the formation of supramolecular nanoribbons in solution, in the solid state, and on flat surfaces is universal. This result is truly important in view of the electronic properties of these supramolecular anisotropic architectures and thus for potential applications in the fields of nano- and opto-electronics.

Reversible interconversion between a supramolecular polymer and a discrete octameric species from a guanosine derivative by dynamic cation binding and release.

[reaction: see text] The tunable interconversion between two highly ordered supramolecular motifs (G-quartet K(+)-templated column and G-ribbon) of a lipophilic guanosine derivative fueled by cation complexation and release in a cryptand [2.2.2] containing guanosine solution is reported. The process is controlled by the sequential addition of acid and base.

The control of the cholesteric pitch by some azo photochemical chiral switches.

A few chiral azo compounds, which undergo reversible photochemical switching, are presented. Of these, the most interesting contain the binaphthyl moiety and belong to the C2 (derivatives 1 and 2) or C1 symmetry group (derivatives 3 and 4). These binaphthyl compounds display intense CD and high beta values. Photochemical switching has profound effects on both the CD and beta values of these compounds; in the case of compound 3, the sign of beta changes upon isomerisation. Compound 2 has, to our knowledge, the highest beta of the switches reported in the literature and also seems the most interesting owing to its fast response to photochemical stimuli. Nematic phases can be transformed into cholesteric phases with reflection bands in the visible region by doping with reasonable amounts of 1 and 2. The reflection colours can be changed reversibly by photoisomerisation of the switches. Thermal reversion of the colourless UV photostationary state to the green isomeric EE state or to intermediate coloured states is temperature dependent. This can allow the thermal history of a sample to be traced.