The Stereoselective Total Synthesis of the Elusive Cephalosporolide F.

Here we report a seven-step protecting-group-free stereoselective total synthesis of the elusive (+)-cephalosporolide F from d-glucose. A microwave-assisted reaction between the Meldrum's acid and the d-glucose to the respective octono-1,4-lactone derivative, and a low temperature visible-light photoredox spirocyclization of a chiral N-alkoxyphthalimide to ceph F, are the two key chemical reactions that allowed the accomplishment of this unprecedented feat under an environmentally friendly processes.

Electrochemical and Spectroscopic (FTIR) Evidence of Conducting Polymer-Cu Ions Interaction.

In this work, we provide electrochemical and spectroscopic evidence of the conducting polymer-heavy metal ion interaction by comparing the electrochemical and spectroscopic behavior (FTIR) of two different conducting polymer-modified electrodes based on 3,4-alkoxythiophenes: 3,4-ethylenedioxythiophene (EDOT) and ortho-xylen-3,4-dioxythiophene (XDOT) during the potentiodynamic stripping of copper. By analyzing the electrochemical and spectroscopic results, it is possible to propose two different copper dissolution processes during the electrochemical stripping process, which depend on the conducting polymer used. With PEDOT matrix, stripping occurs in a two-step pathway, observed as two anodic peaks, involving the formation of the Cu+-PEDOT complex and the subsequent oxidation step of the Cu+ complex to release Cu2+ ions. On the other side, the experiments carried out let us propose the formation of a poorly stable Cu2+-PXDOT complex or a superficial mechanism for the Cu2+ release, characterized by a single stripping signal for this process. Thus, the incorporation of Cu ions into the matrix and the stripping release are intimately related to the chemical structure of the polymer used.

Beyond 1,2,3-Triazoles: Formation and Applications of Ketenimines Derived from Copper Catalyzed Azide Alkyne Cycloaddition.

The ketenimines represent an interesting class of organic intermediates which has undergone a regrowth as a consequence of recent extensions of copper catalyzed azide alkyne cycloaddition (CuAAC) to other synthetic fields. This review summarizes the most recent generation methods of ketinimines from CuAAC reaction, highlighting chemical properties focused to the synthesis of cyclic compounds among others, affording a general outlook towards the development of new biologically active compounds.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells.

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC's advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

Electrochemical Generation and Use in Organic Synthesis of C-, O-, and N-Centered Radicals.

During the last decade several research groups have been developing electrochemical procedures to access highly functionalized organic molecules. Among the most exciting advances, the possibility of using free radical chemistry has attracted the attention of the most important synthetic groups. Nowadays, electrochemical strategies based on these species with a synthetic purpose are published continuously in scientific journals, increasing the alternatives for the synthetic organic chemistry laboratories. Free radicals can be obtained in organic electrochemical reactions; thus, this review reassembles the last decade's (2010-2020) efforts of the electrosynthetic community to generate and take advantage of the C-, O-, and N-centered radicals' reactivity. The electrochemical reactions that occur, as well as the proposed mechanism, are discussed, trying to give clear information about the used conditions and reactivity of these reactive intermediate species.

Electro-Oxidation-Plasma Treatment for Azo Dye Carmoisine (Acid Red 14) in an Aqueous Solution.

Currently, azo dye Carmoisine is an additive that is widely used in the food processing industry sector. However, limited biodegradability in the environment has become a major concern regarding the removal of azo dye. In this study, the degradation of azo dye Carmoisine (acid red 14) in an aqueous solution was studied by using a sequenced process of electro-oxidation-plasma at atmospheric pressure (EO-PAP). Both the efficiency and effectiveness of the process were compared individually. To ascertain the behavior of azo dye Carmoisine over the degradation process, the variations in its physical characteristics were analyzed with a voltage-current relationship, optical emission spectra (OES) and temperature. On the other hand, chemical variables were analyzed by finding out pH, electrical conductivity, absorbance (UV/VIS Spectrophotometry), chemical oxygen demand (COD), cyclic voltammetry (CV), energy consumption and cost. The sequenced process (EO-PAP) increased degradation efficiency, reaching 100% for azo dye Carmoisine (acid red 14) in 60 min. It was observed that the introduction of small quantities of iron metal ions (Fe2+/Fe3+) as catalysts into the plasma process and the hydrogen peroxide formed in plasma electrical discharge led to the formation of larger amounts of hydroxyl radicals, thus promoting a better performance in the degradation of azo dye. This sequenced process increased the decolorization process.

Ascorbic Acid as an Aryl Radical Inducer in the Gold-Mediated Arylation of Indoles with Aryldiazonium Chlorides.

In recent years interest in the development of protocols that facilitate the oxidative addition of gold to access mild cross-coupling processes mediated by this metal has increased. In this context, we report herein that ascorbic acid, a natural and readily accessible antioxidant, can be used to accelerate the oxidative addition of aryldiazonium chlorides onto AuI . The aryl-AuIII species generated in this way, has been used to prepare 3-arylindoles in a one-pot protocol starting from anilines and para-, meta-, and ortho- substituted aryldiazonium chlorides. The mechanism underlying the oxidative addition has been examined in detail based on EPR analyses, cyclic voltammetry, and DFT calculations. Interestingly, we have found that in this protocol, the chloride atom induces the AuII /AuIII oxidation step.

Highly Ordered Macroporous Poly-3,4- ortho-xylendioxythiophene Electrodes as a Sensitive Analytical Tool for Heavy Metal Quantification.

Highly ordered macroporous electrodes of the conducting polymer poly-3,4- ortho-xylendioxythiophene (PXDOT) are presented as a sensitive analytical tool for heavy metal ion quantification due to a controlled gain in electroactive area. They were designed by using colloidal crystal templates. A direct correlation between the final number of porous layers and the deposition charge ( Qd) employed for electropolymerization is observed. All the electrodes exhibit a surface-templated structure due to an interaction between the radical cation, formed during the electropolymerization, and the surface groups of the silica beads. The voltamperometric response of the macroporous PXDOT electrodes shows a rather fast electron transfer with Δ Ep values between 70 mV and 110 mV. Square wave anodic stripping voltammetric (SWASV) analysis of Cu2+ as a representative heavy metal ion shows a linear response in the subppm range. As a model application, the efficient quantification of Cu2+ in a commercial mezcal sample is validated by the standard addition method and the results correlate adequately with the values obtained by atomic absorption spectroscopy.

Conducting Polymers in the Fields of Energy, Environmental Remediation, and Chemical-Chiral Sensors.

Conducting polymers (CPs), thanks to their unique properties, structures made on-demand, new composite mixtures, and possibility of deposit on a surface by chemical, physical, or electrochemical methodologies, have shown in the last years a renaissance and have been widely used in important fields of chemistry and materials science. Due to the extent of the literature on CPs, this review, after a concise introduction about the interrelationship between electrochemistry and conducting polymers, is focused exclusively on the following applications: energy (energy storage devices and solar cells), use in environmental remediation (anion and cation trapping, electrocatalytic reduction/oxidation of pollutants on CP based electrodes, and adsorption of pollutants) and finally electroanalysis as chemical sensors in solution, gas phase, and chiral molecules. This review is expected to be comprehensive, authoritative, and useful to the chemical community interested in CPs and their applications.

Electrochemical Corey-Winter reaction. Reduction of thiocarbonates in aqueous methanol media and application to the synthesis of a naturally occurring α-pyrone.

An electrochemical version of the Corey-Winter reaction was developed giving excellent results in aqueous methanol media (MeOH/H2O (80:20) with AcOH/AcONa buffer 0.5 M as supporting electrolyte), using a reticulated vitreous carbon as cathode in a divided cell. The electrochemical version is much more environmentally friendly than the classical reaction, where a large excess of trialkyl phosphite as reducing agent and high temperatures are required. Thus, cathodic reduction at room temperature of two cyclic thiocarbonates (-1.2 to -1.4 V vs Ag/AgCl) afforded the corresponding alkenes, trans-6-(pent-1-enyl)-α-pyrone and trans-6-(pent-1,4-dienyl)-α-pyrone, which are naturally occurring metabolites isolated from Trichoderma viride and Penicillium, in high chemical yield and with excellent stereo selectivity.

Reduction of pollutants and disinfection of industrial wastewater by an integrated system of copper electrocoagulation and electrochemically generated hydrogen peroxide.

The objective of this study was to evaluate the effect of copper electrocoagulation and hydrogen peroxide on COD, color, turbidity, and bacterial activity in a mixed industry wastewater. The integrated system of copper electrocoagulation and hydrogen peroxide is effective at reducing the organic and bacterial content of industrial wastewater. The copper electrocoagulation alone reduces COD by 56% in 30 min at pH 2.8, but the combined system reduces COD by 78%, biochemical oxygen demand (BOD5) by 81%, and color by 97% under the same conditions. Colloidal particles are flocculated effectively, as shown by the reduction of zeta potential and the 84% reduction in turbidity and 99% reduction in total solids. Additionally, the total coliforms, fecal coliforms, and bacteria are all reduced by 99%. The integrated system is effective and practical for the reduction of both organic and bacterial content in industrial wastewater.

Investigations on the use of graphite electrodes using a Hull-type growth cell for the electrochemically-assisted protein crystallization.

This paper describes the use of an electrochemical Hull type cell adapted for protein crystallization evaluating three inclination angles (45°, 60° and 90°). For optimization experiments, classical platinum wire electrodes were used and once the best geometry was known, they were replaced with 0.5 mm diameter low-cost graphite automatic pencil leads. Using Pt and graphite, the cell with electrodes fitted at 90° showed the most favorable geometry for promoting the growth of lysozyme crystals with enough size for protein crystallography (between 200-250 µm in solution, and between 500-650 µm in gel). The crystalline quality (mosaicity and I/σ(I) ratio) of crystals obtained at different current values, was studied using these graphite electrodes and was compared with those protein crystals grown using platinum wire electrodes in solution as well as in gel experiments. These studies showed that it is possible to efficiently substitute the platinum electrodes by the low-cost graphite electrodes. This cell could be a first approach to a disposable cell for a large-scale use of electrochemically-assisted crystal growth method.

A ferrous oxalate mediated photo-Fenton system: toward an increased biodegradability of indigo dyed wastewaters.

This study assessed the applicability of a ferrous oxalate mediated photo-Fenton pretreatment for indigo-dyed wastewaters as to produce a biodegradable enough effluent, likely of being derived to conventional biological processes. The photochemical treatment was performed with ferrous oxalate and hydrogen peroxide in a Compound Parabolic Concentrator (CPC) under batch operation conditions. The reaction was studied at natural pH conditions (5-6) with indigo concentrations in the range of 6.67-33.33 mg L(-1), using a fixed oxalate-to-iron mass ratio (C(2)O(4)(2-)/Fe(2+)=35) and assessing the system's biodegradability at low (257 mg L(-1)) and high (1280 mg L(-1)) H(2)O(2) concentrations. In order to seek the optimal conditions for the treatment of indigo dyed wastewaters, an experimental design consisting in a statistical surface response approach was carried out. This analysis revealed that the best removal efficiencies for Total Organic Carbon (TOC) were obtained for low peroxide doses. In general it was observed that after 20 kJ L(-1), almost every treated effluent increased its biodegradability from a BOD(5)/COD value of 0.4. This increase in the biodegradability was confirmed by the presence of short chain carboxylic acids as intermediate products and by the mineralization of organic nitrogen into nitrate. Finally, an overall decrease in the LC(50) for Artemia salina indicated a successful detoxification of the effluent.

Tacticity influence on the electrochemical reactivity of group transfer polymerization-synthesized PTMA.

Spectroscopic, thermal, and electrochemical characterization results are presented for the redox active polymer poly(2,2,6,6-tetramethyl-1-piperinidyloxy-4-yl methacrylate) or PTMA, synthesized by group transfer polymerization (GTP), and its precursors 4-hydroxy-tetramethylpiperidine-N-oxyl (HO-TEMPO) and 4-methacryloyloxy-tetramethylpiperidine-N-oxyl (MO-TEMPO). DSC analysis of synthesized PTMA showed that the glass transition temperature (T(g)) of the polymer structure occurs at 155 °C, corroborated by dynamic mechanical analysis (DMA), which is higher when compared with T(g) data for PTMA synthesized by other methods. Also, the amount of radical species present in PTMA synthesized by GTP reactions (100%) is higher than the values typically upon synthesizing PTMA by radical polymerization. Electrochemical and spectroelectrochemical-electron spin resonance studies in acetonitrile revealed two redox events in the PTMA polymer, one of which is reversible, accounting for ca. 80% of the spins in the polymer and giving rise to the battery behavior. The other redox event is irreversible, accounting for the remaining ca. 20% of spins, which has not previously been reported. These two redox events are linked to a structural property associated with the tacticity of the polymer, where the reversible feature (responsible for cathode behavior) is the dominant species. This corresponds to a number of isotactic domains of the polymer (determined by high temperature (1)H NMR). The second feature accounts for the three-line impurity observed in the ESR, which has been reported previously but poorly explained, associated to the number of heterotactic/syndiotactic triads.

Characterization and detoxification of a mature landfill leachate using a combined coagulation-flocculation/photo Fenton treatment.

The aim of the present work was to characterize and treat a mature landfill leachate using a coagulation/flocculation process followed by a photo-Fenton oxidation treatment. The leachate was obtained from a landfill in Tetlama, Morelos (Mexico) during the drought season and was characterized in terms of its major pollutants. Considerable levels of chemical oxygen demand (COD), total carbon (TC) and NH4+ were identified, as well as high concentrations of Hg, Pb, and As. Other heavy metals such as Ni, Co, Zn, Cd, and Mn were detected at trace levels. The lethal concentration (LC50) of the leachate, evaluated on Artemia salina, was 12,161±11 mg/L of COD, demonstrating an antagonistic interaction among the leachate's components. The treatment of this effluent consisted of a coagulation-flocculation process using an optimal dose of FeCl3 · 6H2O of 300 mg/L. The supernatant was treated using a photo-Fenton process mediated with FeCl2 · 4H2O and H2O2 in a compound parabolic concentrator (CPC) photo-reactor operating in batch mode using an R ratio (R=[H2O2]/[Fe2+]) of 114. The global removal efficiencies after treatment were 56% for the COD, 95% for TC, and 64% for NH4+. The removal efficiencies for As, Hg, and Pb were 46%, 9%, and 85%, respectively.

Experimental and theoretical evidence of a persistent radical-cation dimer generated during the electrooxidation of an N-glucosamine-pyrrole derivative.

The results of the electrochemical characterization by cyclic voltammetry of 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-2-(pyrro-1-yl)-ß-d-glucopyranose (Py-GSATA) are presented. This compound was analyzed in acetonitrile containing 0.1 M tetrabutylammonium perchlorate, using a platinum disk electrode as the working electrode. Py-GSATA showed two irreversible oxidation signals, the first at 1.24 and the second at 1.54 V vs Fc(+)/Fc. After successive cyclic voltammetry, under different experimental conditions, it was shown that it is not possible to electropolymerize this pyrrole derivative. Surprisingly, the bulk anodic electrolysis of Py-GSATA generated a single electroactive soluble product with an electrochemical cathodic signal located at -0.35 V vs Fc(+)/Fc. Mass spectrometry of the solution showed the presence of a dimeric species of the parent compound. ESR spectroscopy of the electrolysis solution showed a persistent radical species stable at least for 6 months (4 °C). UV-vis spectroscopy was consistent with low chain cation-radical oligomers. In order to propose an explanation to the dimer cation stability in solution, molecular modeling using a B3LYP/6-31+G** level of theory was used to analyze the stability and feasibility of the electrogenerated species.

Electro-oxidation of hispanolone and anti-inflammatory properties of the obtained derivatives.

The electrochemical oxidation ((+)Pt-Ni(-)/NH(4)Br/MeOH) of the natural product hispanolone (1a) produced, in high yield (>95%), spiro-tetracyclic compounds 7a-7d as a result of the intramolecular addition of the C-9 hydroxyl group into the C-16 position with the simultaneous addition of a CH(3)O group at the C-15 position of the hispanolone furan moiety. After the electrochemical oxidation, an acid-catalyzed slow secondary reaction occurred producing the previously undescribed alpha-butenolide derivative, iso-Leopersin G (9). An anti-inflammatory study with the electro-synthesized compounds showed that 1a has higher anti-inflammatory properties with very low cytotoxicity (e.g., the inhibition of TPA-induced ear edema assay IC(50) = 1.05 microM/ear, positive control indomethacin IC(50) = 0.27 microM/ear).

Polyisoprenylated benzophenones in cuban propolis; biological activity of nemorosone.

The Copey tree (Clusia rosea) has a large distribution in Cuba and its floral resin is a rich source of polyisoprenylated benzophenones. To determine the presence of these natural products, we carried out a study by HPLC of 21 propolis samples produced by honey bees (Apis mellifera) from different provinces of Cuba. Nemorosone resulted to be the most abundant polyisoprenylated benzophenone and the mixture of xanthochymol and guttiferone E was also observed, but in minor proportion. We studied the biological activity of the pure natural product nemorosone and its methyl derivatives. We found that nemorosone has cytotoxic activity against epitheloid carcinoma (HeLa), epidermoid carcinoma (Hep-2), prostate cancer (PC-3) and central nervous system cancer (U251). It also exhibited antioxidant capacity. Methylated nemorosone exhibited less biological activity than the natural product.