Spectroscopic,Thermal, and Structural Studies of Two New Co‐Crystals of [4,4′‐Bithiazole]‐2,2′‐diamine

Two new 2 : 1 co‐crystals based on [4,4′‐bithiazole]‐2,2′‐diamine (=2,2′‐diamino‐4,4′‐bithiazole (DABTZ)) with 2,2′‐bipyridine (bipy) and benzo‐18‐crown‐6 (bk) were synthesized by slow‐evaporation method in MeOH. These co‐crystals were characterized by means of elemental analysis, and IR, and ¹H‐ and ¹³C‐NMR spectroscopy. Also, thermal analyses under air atmosphere and X‐ray crystallography have been performed on these structures. X‐Ray single‐crystal analyses revealed that these networks contain large vacant voids. These structures, [(DABTZ)₂(bipy)] and [(DABTZ)₂(bk)(MeOH)], crystallized in monoclinic and triclinic forms with space groups of P2₁/c and P , respectively. The self‐assembly of these compounds in the solid state is likely caused by both H‐bonding and π? π stacking.     

Hydrophobization and characterization of internally crosslink-reinforced cellulose fibers

Transforming hydrophilic cellulose fibers into hydrophobic, non-hygroscopic fibers could potentially lead to a variety of new products, such as flexible packaging, self-cleaning films and strength-enhancing agents in polymer composites. To achieve this, softwood cellulose pulp was chemically modified with successive chemical treatments. First the C2 and C3 hydroxyl groups of the glucose units were selectively oxidized by periodate oxidation to reactive dialdehyde units on the cellulose chain, followed by a Schiff base reaction with 1,12-diaminododecane to crosslink the microfibrils within the fiber wall. This was done, because introducing high levels of alkylation resulted in fiber disintegration, which could be prevented by crosslinking. After internal crosslinking a second Schiff base reaction was performed with butylamine. This procedure yielded highly hydrophobic and low-hygroscopic cellulosic materials. The modified cellulose fibers were investigated by a variety of techniques, including Fourier transform infrared spectroscopy, nuclear magnetic resonance, field-emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, moisture sorption and water contact angle measurements. The water uptake of the fibers after being modified reduced from 4 to around 1 %. Various reaction conditions were studied for optimum performance.     

An electrochemical sensor based on octahedral composite modified glassy carbon electrode for voltammetric detection of cocaine

The current work aimed to fabricate a new cocaine sensor of octahedral palladium-doped cobaltite composite (Oh-Pd²⁺ : Co₃O₄-C) using a simple hydrothermal protocol. As-fabricated cocaine sensing approach was validated by various methods. Energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy were recruited to characterize our charged modified composite. The electrode could sensitively detect cocaine, with a lengthy linear range (0.01 μM–900.0 μM) and a limit of detection (1.3 nM). The quantitative cocaine determination was achieved in the biological specimens using our modified electrode, the results of which displayed admirable outcomes.     

Hydroxonium hydrate tris(2,4,6‐triamino‐1,3,5‐triazin‐1‐ium) bis[bis(pyridine‐2,6‐dicarboxylato)manganate(II/III)] hydroxide pyridine‐2,6‐dicarboxylic acid solvate pentahydrate

For charge balance in the title compound, (H₅O₂)(C₃H₇N₆)₃[Mn(C₇H₃NO₄)₂]₂(OH)·C₇H₅NO₄·5H₂O, it is assumed that the metal atom site is disordered Mn^II/Mn^III, probably due to partial air oxidation of the starting Mn^II species. The formula unit of the complex contains a hydroxonium hydrate cation, H₅O₂⁺, also known as the Zundel cation, with twofold symmetry. The O...O [2.445 (10) Å] and O...H distances [1.24 (2) Å] in the H₅O₂⁺ cation indicate a strong hydrogen bond. In addition, there is a hydroxide ion that is disordered with respect to a twofold rotation axis. One of the melaminium groups and the pyridine‐2,6‐dicarboxylate (pydc) ligand also reside on crystallographic twofold axes. The coordination environment of the Mn ion is distorted octahedral. Three intermolecular C=O...π interactions are observed, with distances of 3.536 (4), 3.262 (4) and 3.750 (4) Å between carboxylate C=O groups and the centroids of the aromatic rings of pydc and melaminium. There are numerous O—H...O, O—H...N, N—H...O, N—H...N and C—H...O hydrogen bonds. Most of the components of the structure are organized into one plane.     

Energies, stability and structure properties of radicals derived from organic sulfides containing an acetyl group after the *OH attack: ab initio and DFT calculations vs experiment

The mutual location of the sulfur atom and the acetyl group was found to affect significantly the (*)OH-induced oxidation mechanism of the organic sulfides containing either an alpha- or beta-positioned acetyl group. This phenomenon was reflected in formation of different intermediate products observed in pulse radiolysis experiments (Varmenot et al. J. Phys. Chem. A. 2004, 108, 6331-6346). In order to obtain a better support for the earlier interpretation of the experimental data, quantum mechanical calculations were performed using a density functional theory method (DFT-B3LYP) and the ab initio method (M?ller-Plesset perturbation theory MP2) for optimizations and energy calculations of the parent molecules and radicals and radical cations derived from them. In accordance with experiments, it was found that the alpha-positioned acetyl group in S-ethylthioacetate (SETAc) destabilizes hydroxysulfuranyl radicals and monomeric sulfur radical cations. Instead, formation of stable C-centered radicals of the alpha-(alkylthio)alkyl-type was found energetically favorable, the H3C-(*)CH-S-C(=O)CH3 radical, in particular. On the other hand, the beta-positioned acetyl group in S-ethylthioacetone (SETA) does not destabilize hydroxysulfuranyl radicals, monomeric sulfur radical cations, and dimeric sulfur radical cations. Moreover, the alpha-(alkylthio)alkyl radicals of the type -S-(*)CH-C(=O)- were found to be particularly stabilized. The calculated transition states pointed toward the efficient direct conversion of the hydroxysulfuranyl radicals derived from SETAC and SETA radicals into the respective C-centered radicals. This reaction pathway, important in neutral solutions, is responsible for the absence of the dimeric radical cations of SETAc at low and high concentrations and of the dimeric radical cations of SETA at relatively low concentrations of the solute.     

Essential oil from aerial parts of of Betonica grandiflora Willd. from Iran

The chemical composition of the essential oil obtained from the aerial parts of Betonica grandiflora Willd., growing wild in Iran, was analysed by gas chromatography-mass spectrometry for the first time. Overall, 40 volatile components were identified on the basis of their mass spectra characteristics and retention indices in which ledol (21.8%), myrtenyl acetate (21.7%), eudesm-7(11)-en-4-ol (6.5%), trans-caryophyllene (5.5%), α-bisabolol (4.9%) and isolongifolol (4.5%) were the major constituents. Oxygenated sesquiterpenes, monoterpene hydrocarbons and sesquiterpene hydrocarbons were the main groups of compounds with 45.6%, 23.1% and 18.4%, respectively. The oil was moderately active against Bacillus subtilis and Staphylococcus aureus and inactive against Enterococcus faecalis and Klebsiella pneumoniae.     

Optimal standby activation in m-out-of-n systems: A preventive approach

This article investigates an optimal preventive standby activation policy for an $m$-out-of-$n$ redundant system. We assume that for such a system, which starts operating at time $t=0$, a standby component will be activated at either the failure time of the system or at a predetermined time $\tau$, whichever occurs first. We first obtain the system reliability function under this switching policy as a function of $\tau$. Then, we investigate the optimal switching time $\tau$ so that the mean time to failure of the system is maximized. The results indicate that the existence of an optimal value of $\tau$ depends on the lifetime of the standby redundancy and its virtual age in the standby state. Some illustrative examples are presented to examine the theoretical outcomes.