The influence of interunit carbon–carbon linkages during lignin upgrading

The cleavage of β-O-4 linkages in lignin can generate monomers with a phenyl propane structure that can easily be upgraded into valuable hydrocarbon biofuels and renewable aromatic chemicals. High-yield lignin monomer production from extracted (or technical) lignin that is produced in a practical way could facilitate the productivity and profitability of biomass conversion processes. However, interunit carbon–carbon (C–C) linkages present in native lignin or formed during lignin condensation in biomass pretreatments dramatically reduce lignin monomer yields. Here, we present a perspective on biological and chemical strategies that have been successfully used to reduce the formation of C–C linkages in native or technical lignin. We analyze the mechanisms involved in these strategies and offer our views on improving the quality of technical lignin resulting from biomass conversion in order to achieve high-yield lignin monomer production.     

Multi-walled carbon nanotube paste electrode for selective voltammetric detection of isoniazid

A multi-walled carbon nanotube paste electrode (MWCPE) is prepared as an electrochemical sensor with high sensitivity and selectivity in responding to isoniazid. The electrochemical oxidation of isoniazid is investigated in buffered solution by cyclic and differential pulse voltammetry. The electrode is shown to be very effective for the detection of isoniazid in the presence of other biological reductant compounds. The electrochemical oxidation of cysteine, due to the high overvoltage, is completely stopped at the surface of MWCPE. The electrode exhibits a very good resolution between the voltammetric peak of isoniazid and the peaks of ascorbic acid (AA) and dopamine (DA). A resolution of more than 450 mV between the anodic peak potentials makes the MWCPE suitable for simultaneous detection of isoniazid in the presence of AA or DA in clinical and pharmaceutical preparations. Differential pulse voltammetry (DPV) is applied as a sensitive method for the determination of isoniazid. The linear range in these determinations is 1 × 10⁻⁶–1 × 10⁻³ M for isoniazid and the detection limit is 5 × 10⁻⁷ M. The electrode was applied to the simultaneous determinations in isoniazid and AA mixtures and also, isoniazid and DA mixture over a wide concentration range. The slope variation for the calibration curves of isoniazid (RSD) was less than 4.5% (based on ten measurements over a period of three months).     

Heterogeneous oxidation of alcohols with hydrogen peroxide catalyzed by polyoxometalate metal–organic framework

HSiW-MOF, PMo-MOF, HPMo-MOF and PW-MOF were synthesized and characterized by elemental analysis, UV–Vis, FT-IR, cyclic voltammetry and XRD. These compounds were used as catalyst for the selective oxidation of alcohols by hydrogen peroxide. Within them, PW-MOF showed a higher catalytic activity compared to other catalysts in a similar reaction condition. Therefore, PW-MOF catalyst system was successfully used for the selective oxidation of the benzylic, linear and secondary alcohols to the corresponding aldehydes and ketones. Also, allylic alcohols were converted to the corresponding aldehydes with high conversion and significant selectivity. Moreover, PW-MOF was stable to leaching, behaved as true heterogeneous catalysts, easily recovered by filtration, and reused four times with the preserve of the catalytic performance.     

Solid-phase extraction, separation, and visible spectrophotometric determination of trace amounts of iron in water samples.

A simple and reliable method is presented for the rapid extraction, separation, preconcentration, and determination of iron as its bathophenanthroline complex by the use of octadecylsilica membrane disks and spectrophotometry. We evaluted extraction efficiency, the influence of sample matrix, type and optimum amount of extractant, flow rates of sample solution and eluent, pH, amounts of bathophenanthroline and hydroxylamine hydrochloride, breakthrough volume, and limit of detection. We also studied the effects of various cationic interferences on percent recovery of iron. Complete elution of the complex from disks was obtained with a minimal amount of solvent. The limit of detection of the proposed method is 0.080 ppb. The method was applied to the recovery and determination of iron in natural waters.     

A novel ternary GO@SiO2‐HPW nanocomposite as an efficient heterogeneous catalyst for the synthesis of benzazoles in aqueous media

A new solid acid catalyst, consisting of 12‐phosphotungstic heteropoly acid (HPW) supported on graphene oxide/silica nanocomposite (GO@SiO₂), has been developed via immobilizing HPW onto an amine‐functionalized GO/SiO₂ surface through coordination interaction (GO@SiO₂‐HPW). The GO@SiO₂‐HPW nanocomposite was characterized by Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and powder X‐ray diffraction (XRD). The prepared nanocomposite could be dispersed homogeneously in water and further used as a heterogeneous, reusable, and efficient catalyst for the synthesis of benzimidazoles and benzothiazoles by the reaction of 1,2‐phenelynediamine or 2‐aminothiophenol with different aldehydes.     

Crystallographic and first-principles density functional theory study on the structure,noncovalent interactions,and chemical reactivity of 1,5-benzodiazepin-2-ones derivatives

The present work arose out of a desire to fundamentally understand the molecular geometry, weak interactions, electron density delocalization, and chemical reactivity features of 1,5-benzodiazepines-containing family. Herein, a complete X-ray crystallographic study, supported by trustworthy sets of computational approaches, has been reported for two organic crystals. Quantifying intramolecular and intermolecular interactions by Hirshfeld-Becke surfaces analysis conjointly with noncovalent interaction-reduced density gradient topological study revealed that supramolecular assemblies are stabilized by N-H ^… O (inter) and O-H ^… N (intra) hydrogen bonds, Cg ^… Cg (π ^… π) and C-H(O) ^… π intercontacts, as well as Van der Waals interactions and steric effects. The long-range-corrected functional wB97XD, which uses Grimme's D2 dispersion model, seems to be just right for our systems. The quantum theory of atoms in molecules analysis confirms that both significant O1-H1…N1 and N2-H2A…O2 H-bonds are weak and electrostatic in nature. Furthermore, global reactivity indices computed via the conceptual density functional theory framework allows these molecules to be classified as moderate electrophiles and marginal nucleophiles. The active sites favorable for nucleophilic/electrophilic attacks were also predicted based on local Parr functions. Finally, a comparative evaluation on the aromaticity character and π-π stacking ability has been done for different (pseudo) rings.     

The Specific Heat Capacity,Effective Thermal Conductivity,Density, and Viscosity of Coolants Containing Carboxylic Acid Functionalized Multi-Walled Carbon Nanotubes

Obviously, the behavior of thermophysical properties of covalently functionalized CNT-based water and -based ethylene glycol (EG) nanofluids cannot be predicted from the predicted models. We present a study of the specific heat capacity, effective thermal conductivity, density, and viscosity of coolants containing functionalized multi-walled carbon nanotubes (CNT-COOH) with carboxylic acid groups at different temperatures. After synthesizing of CNT-COOH-based water and CNT-COOH-based EG nanofluids, measurements on the prepared coolant were made at various concentrations by different experimental methods. While the thermal conductivity of both nanofluids illustrated a significant increase, the specific heat capacity of both samples showed a downward behavior with increasing temperature. Although the thermal conductivity of CNT-COOH-based water nanofluids is bigger than CNT-COOH-based EG nanofluids, CNT-COOH-based water has weaker temperature dependence than that of the CNT-COOH-based EG nanofluids. The viscosity was investigated in different shear rates and temperatures. It is noteworthy that CNT-COOH-based EG nanofluids show relatively a non-Newtonian behavior. Interestingly, specific heat capacities of both prepared nanofluids were decreased with increasing concentration. Also, the density of the CNT-COOH-based water and -based EG nanofluids increased and decreased smoothly with increasing CNT-COOH concentration and temperature, respectively.     

Constraints on neutron skin thickness and symmetry energy of ~(208)Pb through Skyrme forces and cluster model

We used the cluster structure properties of the 212Po to estimate the neutron skin thickness of 208Pb.For this purpose,we considered two important components:(a)alpha decay is a low energy phenomenon;therefore,one can expect that the mean-field,which can explain the ground state properties of 212Po,does not change during the alpha decay process.(b)212Po has a high alpha cluster-like structure,two protons and two neutrons outside its core nucleus with a double magic closed-shell,and the cluster model is a powerful formalism for the estimation of alpha decay preformation factor of such nuclei.The slope of the symmetry energy of 208Pb is estimated to be 75±25 MeV within the selected same mean-fields and Skyrme forces,which can simultaneously satisfy the ground-state properties of parent and daughter nuclei,as their neutron skin thicknesses are consistent with experimental data.     

Tests of perfect judgment ranking using pseudo-samples

Ranked set sampling (RSS) is a sampling approach that can produce improved statistical inference when the ranking process is perfect. While some inferential RSS methods are robust to imperfect rankings, other methods may fail entirely or provide less efficiency. We develop a nonparametric procedure to assess whether the rankings of a given RSS are perfect. We generate pseudo-samples with a known ranking and use them to compare with the ranking of the given RSS sample. This is a general approach that can accommodate any type of raking, including perfect ranking. To generate pseudo-samples, we consider the given sample as the population and generate a perfect RSS. The test statistics can easily be implemented for balanced and unbalanced RSS. The proposed tests are compared using Monte Carlo simulation under different distributions and applied to a real data set.