Electrochemical C-H/C-C Bond Oxygenation: A Potential Technology for Plastic Depolymerization.

Herein, we provide eco-friendly and safely operated electrocatalytic methods for the selective oxidation directly or with water, air, light, metal catalyst or other mediators serving as the only oxygen supply. Heavy metals, stoichiometric chemical oxidants, or harsh conditions were drawbacks of earlier oxidative cleavage techniques. It has recently come to light that a crucial stage in the deconstruction of plastic waste and the utilization of biomass is the selective activation of inert C(sp3 )-C/H(sp3 ) bonds, which continues to be a significant obstacle in the chemical upcycling of resistant polyolefin waste. An appealing alternative to chemical oxidations using oxygen and catalysts is direct or indirect electrochemical conversion. An essential transition in the chemical and pharmaceutical industries is the electrochemical oxidation of C-H/C-C bonds. In this review, we discuss cutting-edge approaches to chemically recycle commercial plastics and feasible C-C/C-H bonds oxygenation routes for industrial scale-up.

A novel pH-responsive hydrogel system based on Prunus armeniaca gum and acrylic acid: Preparation and evaluation as a potential candidate for controlled drug delivery.

pH-responsive hydrogels have become effective and attractive materials for the controlled release of drugs at pre-determined destinations. In the present study, a novel hydrogel system based on Prunus armeniaca gum (PAG) and acrylic acid (AA) was prepared by a free radical mechanism using N, N-methylene bisacrylamide (MBA) as cross-linker and potassium persulfate (KPS) as initiator. A series of hydrogels varying PAG, AA, and MBA concentration was developed to determine the impact of these components. Formulated hydrogels were characterized for pH-responsive swelling, drug release, gel content, and porosity. Structural analysis was performed by FTIR, XRD, and SEM analysis. TGA study was applied to assess thermal stability. Oral acute toxicity and in vivo drug release were performed in rabbits. Hydrogels exhibited pH-dependent swelling and drug release. Swelling, drug loading and release, and porosity increased by increasing PAG and AA concentration while decreased by increasing MBA. The gel content of formulations was increased by increasing all three components. FTIR studies confirmed the development of copolymeric networks and the loading of drug. XRD studies revealed that hydrogels were amorphous, and the crystalline drug was changed into an amorphous form during loading. TGA results indicated that hydrogels were stable up to 600 °C. Acute oral toxicity results confirm that hydrogels were nontoxic up to a dose of 2 g/kg body weight in rabbits. The pharmacokinetic evaluation revealed that hydrogels prolonged the availability of the drug and the peak plasma concentration of the drug was obtained in 6 h as compared to the oral solution of the drug. Tramadol hydrochloride (THC) was used as a model drug. Hence, pH-responsive swelling and release, nontoxic nature and improved pharmacokinetics support that PAG-based hydrogels may be considered as potential controlled-release polymeric carriers.

Arenes and Heteroarenes C-H Functionalization Under Enabling Conditions: Electrochemistry, Photoelectrochemistry & Flow Technology.

C-H bond functionalization generates molecular complexity in single-step transformation. However, the activation of C-H bonds requires expensive metals or stoichiometric amounts of oxidizing/reducing species. In many cases, they often require pre-functionalization of starting molecules. Such pre-activating measures cause waste generation and their separation from the final product is also troublesome. In such a scenario, reactions activating elements generating from renewable energy resources such as electricity and light would be more efficient, green, and cost-effective. Further, incorporation of growing flow technology in chemical transformation processes will accelerate the safer accesses of valuable products. Arenes & heteroarenes are ubiquitous in pharmaceuticals, natural products, medicinal compounds, and other biologically important molecules. Herein, we discussed enabling tools and technologies used for the recent C-H bonds functionalization of arenes and heteroarenes.

Renewable Electricity Enables Green Routes to Fine Chemicals and Pharmaceuticals.

Syntheses of chemicals using renewable electricity and when generating high atom economies are considered green and sustainable processes. In the present state of affairs, electrochemical manufacturing of fine chemicals and pharmaceuticals is not as common place as it could be and therefore, merits more attention. There is also a need to turn attention toward the electrochemical synthesis of valuable chemicals from recyclable greenhouse gases that can accelerate the process of circular economy. CO2 emissions are the major contributor to human-induced global warming. CO2 conversion into chemicals is a valuable application of its utilisation and will contribute to circular economy while maintaining environmental sustainability. Herein, we present an overview of electro-carboxylation, including mechanistic aspects, which forms carboxylic acids using molecular carbon dioxide. We also discuss atom economies of electrochemical fluorination, methoxylation and amide formation reactions.

Electrochemical Phosphorylation of Organic Molecules.

Organophosphorus chemistry is a broad field with multi-dimensional applications in research area of organic, biology, drug design and agrochemicals. Conventional methods have been adopted extensively to access phosphorylated compounds that rely on the use of toxic, moisture sensitive phosphorylating agents and occur in the presence of oxidants, catalysts, as well as high temperatures and harsh conditions are required for complete transformations. However, recent progress has been made for phosphorylation reactions using electricity to introduce green and sustainable synthetic procedures. These reactions can be performed at mild conditions and proceed with excellent atom economy. Herein, we targeted electrochemical phosphorylation reactions with generation of new bonds such as C(sp3 ) -P, C(sp2 ) -P, O-P, N-P, S-P and Se-P. This review is aimed to offer an overview of recent developments in the synthetic methodology to easy access of organophosphorus compounds using electrochemistry.

Interfacial Photoelectrochemical Catalysis: Solar-Induced Green Synthesis of Organic Molecules.

Many oxidation and reduction reactions in conventional organic synthesis rely on harsh conditions, toxic or corrosive substances, and environmentally damaging chemicals. In addition, competing reactions may take place, some of which produce hazardous waste products and, therefore, reaction selectivity suffers. To overcome such synthetic drawbacks, an enormous effort is being devoted to find alternative processes that operate much more efficiently, requiring milder conditions to contribute to a greener economy and provide urgently needed new pathways with enhanced selectivity. Fortunately, there is a strategy that has attracted global interest from multiple disciplines that involves the use of sunlight to perform artificial photosynthesis, in which a photoelectrochemical cell splits water into hydrogen fuel, reduces CO2 into "solar" fuels, and more recently, convert organic chemicals into higher value products. Recently, photoanode and photocathode materials have emerged as useful tools to perform organic oxidations and reductions for the synthesis of important molecules, other than just hydrogen or oxygen. Whereas many studies have focused on the degradation of unwanted and dangerous chemicals, solar-induced organic transformations have attracted much less attention. This Minireview summarizes some of latest research efforts in using photoelectrochemical cells to facilitate organic oxidation and reduction reactions to avoid valuable substances while avoiding toxic reagents and expensive precious metal catalysts. Future developments that will enable such technologies to broaden their scope are also considered.

Diabetes Treatment: Selective Synthetic Receptor for Glucose.

A new synthetic receptor has selective and strong interactions with glucose, directing towards future diabetes management. These studies pave the way to design future selective receptors that can potentially be modified with combinations of urea walls having multiple H-binding sites to generate hydrophilic affinities, and the incorporation of promising aromatic systems for hydrophobic π-interactions with glucose CH.

Synthesis, design and sensing applications of nanostructured ceria-based materials.

Cerium-based materials possess redox properties due to the presence of dual valence states of Ce3+ and Ce4+. In the last few years, the scientific community has paid much attention to designing and synthesizing cerium-based materials through advantageous routes for widespread catalytic and sensing applications in many fields. Cerium materials have been synthesized in many different forms, shapes and sizes. The catalytic and sensing capabilities of cerium nanostructures are highly dependent on their morphologies and can be improved significantly by modifying the sizes and shapes of the nanostructures to develop sensing scaffolds with improved sensing performance. These nanostructures provide a basis for applications in many fields. From a literature survey (2010 to 2015), it can be concluded that the fundamental morphologies, ratios, and capping of cerium nanostructures (CeNSs) constructively affect their properties and applications. Designed sensors utilizing CeNSs exhibit outstanding stability, high selectivity and eminent reproducibility in relation to time and temperature. This review will provide a perspective insight on the future trends in the design of different morphologies of CeNSs and their promising applications.

Charged probes: turn-on selective fluorescence for RNA.

RNA controls many biological processes. The selective detection and imaging of RNA molecules can provide information about their location, kinetics, and functions at the cellular level. The imidazolium-based positively charged probes would play a significant role in the deep investigation of RNA biomolecules to check their therapeutic potential and aid in the future rational molecular and drug design.

Facile Synthesis of a Selective Biomolecule Chemosensor and Fabrication of Its Highly Fluorescent Graphene Complex.

A novel hydrophilic imidazolium fluorescent chemosensor has been utilized to prepare water-soluble fluorescent graphene complex via a facile ion-exchange strategy, which gives a very high quantum yield (0.87). The highly fluorescent graphene complex displays a close resemblance to the water-soluble fluorescent chemosensor, as the chemisorbed imidazolium hinders the electron transfer between the naphthalene moiety and the graphene. If the imidazolium is simply physisorbed on graphene by physical mixing, it does not show a high quantum yield because the π-π stacking between the naphthalene moiety and graphene leads to fluorescence quenching. The fluorescent chemosensor selectively detects RNA by turn-on fluorescence at physiological pH in aqueous solution. The fluorescent chemosensor as well as the fluorescent graphene complex would find potential applications as photoresponsive materials and biomedical probes.

Halides with Fifteen Aliphatic C-H···Anion Interaction Sites.

Since the aliphatic C-H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C-H (Cali-H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali-H groups. An X-ray structure of imidazolium-based scaffolds using Cali-H···A(-) interactions (A(-) = anion) shows that a halide anion is directly interacting with fifteen Cali-H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali-H···A(-) interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms.

Precise tuning of cationic cyclophanes toward highly selective fluorogenic recognition of specific biophosphate anions.

Cationic cyclophanes with bridging and spacer groups possess well-organized semirigid cavities and are able to encapsulate and stabilize anionic species through diverse molecular interactions. We highlight the precise tuning of functionalized cyclophanes toward selective recognition of AMP, GTP, and pyrophosphate (PPi) using fluorescence, NMR spectroscopy, and density functional theory (DFT).

Selective detection of guanosine-5'-triphosphate and iodide by fluorescent benzimidazolium-based cyclophanes.

New fluorescent benzimidazolium-based receptors selectively display the effective fluorescence quenching effect for biologically important anions, GTP and I(-), in aqueous solution of physiological pH 7.4. These affinities can be attributed to the strong ionic H-bonding along with additional interactions of fluorophore moieties with the nucleic base of GTP and I(-).

Selective fluorescent detection of RNA in living cells by using imidazolium-based cyclophane.

A water-soluble imidazolium-based fluorescent chemosensor senses RNA selectively through fluorescence enhancement over other biologically relevant biomolecules in aqueous solution at physiological pH 7.4. Fluorescence image detection of RNA in living cells such as onion cells, HeLa cells, and animal model cells was successfully demonstrated which displays a chelation-enhanced fluorescence effect. These affinities can be attributed to the strong electrostatic (C-H)(+)···A(-) ionic H-bonding and the aromatic moiety driven π-stacking of imidazolium-based cyclophane with the size-complementary major groove of RNA.

Fluorogenic sensing of CH3CO2- and H2PO4- by ditopic receptor through conformational change.

Cyclo-bis-(urea-3,6-dichlorocarbazole) (1) forms a 1 : 2 complex with CH(3)CO(2)(-) and H(2)PO(4)(-) through hydrogen bonding with the two urea moieties, resulting in fluorescence enhancement via a combined photoinduced electron transfer (PET) and energy transfer mechanism. The binding mechanism involves a conformational change of the two urea receptors to a trans orientation after binding of the first anion, which facilitates the second interaction.

A highly selective fluorescent chemosensor for guanosine-5'-triphosphate via excimer formation in aqueous solution of physiological pH.

A new water-soluble and fluorescent imidazolium-anthracene cyclophane 1 effectively recognizes and differentiates the biologically important GTP and ATP in 100% aqueous solution of physiological pH 7.4. Fluorescence, (1)H-NMR spectra and ab initio calculations demonstrate that excimer formation and fluorescence enhancement occur upon GTP and ATP binding, respectively, through (C-H)(+)···A(-) hydrogen bond interactions.

Fluorescent imidazolium-based cyclophane for detection of guanosine-5'-triphosphate and I(-) in aqueous solution of physiological pH.

A new water-soluble and fluorescent imidazolium-anthracene cyclophane (1) effectively recognizes the biologically important GTP and I(-) over other anions in a 100% aqueous solution of physiological pH 7.4. Fluorescence and (1)H NMR spectra and ab initio calculations demonstrate that emission arises from the formation of an excimer state and quenching occurs upon GTP/I(-) binding through (C-H)(+)···A(-) hydrogen bond interactions.