Nano TiO2/SO4 as a heterogeneous solid acid catalyst for the synthesis of 5-substited-1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted-1H-tetrazoles from various nitriles and sodium azide is reported using nano TiO₂/SO₄²⁻ as an effective heterogeneous catalyst. A wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in good to excellent yields.     

An evaluation of british columbian beetle-killed hybrid spruce for bioethanol production

The development of bioconversion technologies for production of fuels, chemicals, and power from renewable resources is currently a high priority for developed nations such as the United States, Canada, and the European Union as a way to improve national energy security and reduce greenhouse gas emissions. The widespread implementation of such technologies will require a sustainable supply of biomass from forestry and agriculture. Forests are a major source of feedstocks for biofuels production in Canada. Woody biomass includes residues from logging and forest thinning, and from wood processing and pulp production. More recently, damaged wood caused by beetle infestations has become available on a large scale in Western Canada. This study evaluates beetle-killed British Columbian hybrid spruce (HS) (Picea glauca x P. engelmannii) as a feedstock for the production of bioethanol. In the past 30 yr, attack by the beetle Dendroctonus rufipennis and associated fungi has resulted in estimated losses of more than three billion board feet in British Columbia alone. Here we describe the chemical and some physical characteristics of both healthy (HHS) and beetle-killed (BKHS) British Columbian HS and evaluate the technical feasibility of using these feedstocks as a source of biomass for bioethanol production. Untreated HHS and BKHS did not differ significantly in chemical composition except for the moisture content, which was significantly lower in BKHS (approx 10%) compared with HHS (approx 18%). However, the yields of carbohydrates in hydrolyzable and fermentable forms were higher at mild pretreatment conditions (H-Factor <1000) for BKHS compared with HHS. At medium (H-Factor 1000-2000) and severe (H-Factor >2000) pretreatment conditions HHS and BKHS behaved similarly. Organosolv pretreated HHS and BKHS demonstrated good ethanol theoretical yields, approx 70 and 80%, respectively.     

Probing differences in binding of methylbenzylamine enantiomers to chiral cobalt(II) salen complexes

In this work, we investigate the mode of chiral interactions between the asymmetric Co(II) salen complex, (S,S)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamine-Co(II) ([Co(1)]), and single enantiomers of methylbenzylamine (MBA) using different continuous-wave and pulsed electron paramagnetic resonance techniques combined with density functional theory computations. While [Co(1)] displays a large affinity for binding a single MBA molecule, it has a much weaker affinity for binding a second MBA molecule. Subtle differences are detected in the EPR spectra of the homochiral (S,S-[Co(1)](S-MBA)) and heterochiral (S,S-[Co(1)](R-MBA)) adducts using low [Co(1)] : MBA ratios. Moreover at high concentrations of racemic MBA, a strong preference (80%) is observed for the formation of the bis-ligated heterochiral adduct (S,S-[Co(1)](R-MBA)(2)) compared to the homochiral analogue (20% of S,S-[Co(1)](S-MBA)(2)). Differences in the (14)N hyperfine coupling from the diamine backbone in [Co(1)] were also evidenced by hyperfine sublevel correlation (HYSCORE), revealing magnetically equivalent N nuclei for the homochiral adducts and inequivalent N nuclei for the heterochiral adducts. Using DFT, these slight differences were reproduced, and explained based upon the different modes of alignment of the MBA molecule in the adduct. The current findings therefore reveal the appreciable enantiodiscrimination that occurs during the binding of MBA enantiomers to the chiral Co(II) salen complex.     

Optical Toffoli and Feynman reversible gates designing using DNA transmission lines

Optical gates based on switchable material have become a focus of investigation. The present study designs an optical gate that uses DNA transmission lines and developed for Feynman and Toffoli reversible gates. It is shown that the implementation of a transmission line such as Ag/DNA/Ag produces a structure with high-quality switching. The switching characteristics of DNA were considered when designing the basic transmission line. The “On” mode is assumed for DNA with low conductivity. As conductivity increases, the line switches to the “Off” mode. A conceptual design is proposed in the present study for Feynman and Toffoli reversible gates for an optical regime at 300 THz based on DNA switching. A conceptual model is developed with an Ag/DNA/Ag transmission line controlled by changing the DNA bias. This transmission line provides a “Yes” gate, which is necessary for a reversible gate. The full wave time domain method was used to model the optical gates. The current work discusses how a DNA memristor can be used to design a compact reversible gate having a simple structure and high switching quality for use in optical systems.     

A study on dissociation of sII krypton hydrate and the effect of hydrocarbon guest molecules as stabilizer by molecular dynamics simulation

In this paper, the characteristics of structure II krypton hydrate are studied by molecular dynamics simulation under isobaric-isothermal (NPT) ensemble condition. The dissociation process of the hydrate is simulated and the effect of krypton (Kr) and various types of hydrocarbon guest molecules (HGMs) on the stability of the hydrate structure is investigated during the simulation time of 1 ns. The studied HGMs are propane, isobutane, neopentane, cyclopropane, cyclobutane, cyclopentane and cyclopentene. The structural change of the Kr-hydrate is analyzed with the radial distribution function, mean square displacement and diffusion coefficient. As temperature increases, the obtained results indicate a gradual increase in the Kr-hydrate cell size, which leads to distortion of the hydrate lattice and escaping of the encapsulated Kr molecules from the hydrate structure to form small bubbles of Kr aggregated in the aqueous solution.     

Theoretical Study of the Interactions between Isolated DNA Bases and Various Groups IA and IIA Metal Ions by Ab Initio Calculations

Interactions of the DNA bases adenine (A), guanine (G), cytosine (C), and thymine (T) with various metal ions (M) of groups IA and IIA of the periodic table of the elements were studied at the HF, MP2, and DFT levels of theory. The structures and thermodynamic stabilities of these species were studied at the gas phase. The calculations uphold that there exist two active sites in G and one in A, C, and T. The calculations also show that the O² atom in T is a more active site for metal ion bindings than that in C. The stability energies for G … M complexes are larger than those for A … M complexes and the stability energies for T … M complexes are larger than those for C … M complexes. As z/r ratio for the metal ion increases, the interaction energy for the complex increases systematically. Thermodynamic quantities such as ΔH, ΔG, ΔS, and ln K were determined for each complexation reaction, [Base+M ⁿ⁺ →(Base … M) ⁿ⁺]. A, G, and C complexation reactions except for C … Rb⁺ are exothermic. The situation is quite different for T complexation reactions and all except for T … Be²⁺ and T … Mg²⁺ are endothermic.     

Chelation of a proton by an aliphatic tertiary diamine

A series of monoprotonated aliphatic diamines has been examined, which crystallize in three general motifs: salt-bridged, cyclic, or clustered. The monoprotonated triflic acid salt of Me2N(CH2)4NMe2 forms a proton-bridged cyclic cation. The internal N-N distance is 2.66 A, with the bridging proton in the middle, having an NHN angle >/=172 degrees. The triflate oxygens lie more than 4 A away from the midpoint between the nitrogen atoms, indicating that a salt bridge does not form. The average NH distance in a solid sample was determined by measuring the 15N-H dipolar coupling in the triflic acid salt of the completely deuterated diamine (CD3)2N(CD2)4N(CD3)2. The value of the dipolar coupling constant, 5250 +/- 90 Hz, corresponds to an average NH distance of 1.32 A, nearly half-the NN distance. That result agrees with DFT calculations, which give a double-well potential minimum for proton transit between the two amino groups, having a zero-point vibrational level close to the barrier top. Theory predicts that the maximum value of the zero point vibrational wave function is almost coincident with a local potential energy maximum, consistent with the experimental findings.     

Irreversible replacement of sodium with thallium in sodium coordination polymer nanostructures by solid-state mechanochemical cation exchange process

Solid-state conversion of Na^I coordination polymer nanostructure, synthesized by sonochemical procedure, to Tl^I coordination polymer has been observed upon liquid-assisted mechanochemical reaction of [Na₂TP] _n (1) (H₂TP = terephthalic acid), with TlNO₃. During this conversion, ion exchange process of Na(I) with Tl(I) was occurred and [Tl₂TP] _n (2) was synthesized. The X-ray diffraction (XRD) pattern of 2 after mechanochemical reaction of it with NaNO₃ indicated that this transformation is irreversible. Compounds 1 and 2 were characterized by IR spectroscopy, X-ray powder diffraction (XRD), elemental analysis, thermogravimetric and differential thermal analyses and scanning electron microscopy.     

Magnetite nanoparticles surface-modified with a zinc(II)-carboxylate Schiff base ligand as a sorbent for solid-phase extraction of organochlorine pesticides from seawater

Magnetite nanoparticles were surface-modified with mercaptoacetic acid (MAA), complexed with Zn(II), and then treated with the dual Schiff base (referred to as imine-based ligand; IBL; obtained by reaction of p-aminobenzoic acid and 2,3-butanedione) to give particles with an architecture of type Fe₃O₄@MAA@IBL. These are shown to be viable sorbents for magnetic solid phase extraction of organochlorine pesticides (OCPs) from seawater samples. Efficient extraction of the OCPs probably is due to lone pair-π, π-complexation and π-interactions. The sorbent was characterized by transmission electron microscopy, scanning electron microscopy, FT-IR and energy-dispersive X-ray spectroscopy. The effects of the volumes of sample, sorbent dosage and eluent, adsorption and desorption times, and the salinity of the sample on the extraction efficiencies were optimized. The OCPs (heptachlor, aldrin, dieldrin, p,p’-DDE and p,p’-DDT) were quantified by gas chromatography with microelectron capture detection. Under optimal conditions, the limit of detections range was between 1.0 and 1.9 ng L^?1. The enrichment factors are between 84.1 and 99.9 %. The sorbent was applied to the rapid extraction of trace quantities of OCPs from seawater samples and gave good relative recoveries (78 to 108 %) and relative standard deviations (<8.3 %).

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Graphical Abstract Fe₃O₄ nanoparticles were functionalized with mercaptoacetic acid. The carboxylate was coordinated with Zn(II) and the ligands were immobilized via coordination with Zn(II). The lone pair-π, π-complexation and π-interaction of modified magnetite nanoparticles made this sorbent effective for extraction of organochlorine pesticides.