Hydro­gen bonding in N,N′‐bis­[(1S)‐2‐azido‐1‐(2‐methyl­propyl)­ethyl]­oxal­amide: twofold symmetry of R(10) hydrogen‐bonded dimers connected into an α‐network

The title compound, C₁₄H₂₆N₈O₂, belongs to a class of retropeptides with an oxal­amide unit (–NH–CO–CO–NH–), and is a precursor for the synthesis of an amine‐terminal gelator. The compound is a good synthon for one‐dimensional hydrogen bonding. The crystal structure reveals a hydrogen‐bonded cyclic dimer with unusual twofold rotation symmetry.     

Elucidating Sequence and Structural Determinants of Carbohydrate Esterases for Complete Deacetylation of Substituted Xylans

Acetylated glucuronoxylan is one of the most common types of hemicellulose in nature. The structure is formed by a β-(1→4)-linked D-xylopyranosyl (Xylp) backbone that can be substituted with an acetyl group at O-2 and O-3 positions, and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Acetyl xylan esterases (AcXE) that target mono- or doubly acetylated Xylp are well characterized; however, the previously studied AcXE from Flavobacterium johnsoniae (FjoAcXE) was the first to remove the acetyl group from 2-O-MeGlcpA-3-O-acetyl-substituted Xylp units, yet structural characteristics of these enzymes remain unspecified. Here, six homologs of FjoAcXE were produced and three crystal structures of the enzymes were solved. Two of them are complex structures, one with bound MeGlcpA and another with acetate. All homologs were confirmed to release acetate from 2-O-MeGlcpA-3-O-acetyl-substituted xylan, and the crystal structures point to key structural elements that might serve as defining features of this unclassified carbohydrate esterase family. Enzymes comprised two domains: N-terminal CBM domain and a C-terminal SGNH domain. In FjoAcXE and all studied homologs, the sequence motif around the catalytic serine is Gly-Asn-Ser-Ile (GNSI), which differs from other SGNH hydrolases. Binding by the MeGlcpA-Xylp ligand is directed by positively charged and highly conserved residues at the interface of the CBM and SGNH domains of the enzyme.     

Electrospun Polymer Materials with Fungicidal Activity: A Review

In recent years, there has been special interest in innovative technologies such as polymer melt or solution electrospinning, electrospraying, centrifugal electrospinning, coaxial electrospinning, and others. Applying these electrokinetic methods, micro- or nanofibrous materials with high specific surface area, high porosity, and various designs for diverse applications could be created. By using these techniques it is possible to obtain fibrous materials from both synthetic and natural biocompatible and biodegradable polymers, harmless to the environment. Incorporation of low-molecular substances with biological activity (e.g., antimicrobial, antifungal) is easily feasible. Moreover, biocontrol agents, able to suppress the development and growth of plant pathogens, have been embedded in the fibrous materials as well. The application of such nanotechnologies for the creation of plant protection products is an extremely promising new direction. This review emphasizes the recent progress in the development of electrospun fungicidal dressings and their potential to be applied in modern agriculture.     

Decoration of nitrogen vacancies by oxygen atoms in boron nitride nanotubes

Decoration of nitrogen vacancies by oxygen atoms has been studied by near-edge X-ray absorption fine structure (NEXAFS) around B K-edge in several boron nitride (BN) structures, including bamboo-like and multi-walled BN nanotubes. Breaking of B-N bonds and formation of nitrogen vacancies under low-energy ion bombardment reduces oxidation resistance of BN structures and promotes an efficient oxygen-healing mechanism, in full agreement with some recent theoretical predictions. The formation of mixed O-B-N and B-O bonds is clearly identified by well-resolved peaks in NEXAFS spectra of excited boron atoms.     

Small Time One-Sided LIL Behavior for Lévy Processes at Zero

We specify a function b ₀(t) in terms of the Lévy triplet such that lim sup  _t→0 X _t /b ₀(t)∈[1,1.8] a.s. iff ò₀¹[` \varPi ]⁽⁺⁾(b₀(t)) dt < ￥\int_{0}^{1}\overline{ \varPi }^{(+)}(b_{0}(t))\,dt<\infty for any Lévy process X with unbounded variation and a Brownian component σ=0. We show with an example that there are cases where lim sup  _t→0 X _t /b(t)=1 a.s. but b(t) is not asymptotically equivalent to b ₀(t) as t tends to 0. We achieve this by introducing an integral criterion which checks whether lim sup  _t→0 X _t /b(t) is 0, infinity, or a finite positive value for b(t) satisfying very mild conditions and any Lévy process.     

Synthesis Of 1,8‐dioxa‐dibenzo[e,h]azulenese

A novel synthetic route to 2‐methyl‐1,8‐dioxa‐dibenzo[e,h]azulenes [1] via cyclisation of the corresponding 1,4‐dicarbonyl compound is described. 1,4‐Dicarbonyl compounds were synthesized by the alkylation reaction of the 11H‐dibenzo[b,f]oxepine‐10‐one while analogous alkylation of 11H‐dibenzo[b,f]thiepine‐10‐one resulted in formation of O‐alkylated products. Selective oxidation of 2‐methyl group afforded 1,8‐dioxa‐dibenzo[e,h]azulenes with formyl and hydroxymethyl functionality at C(2) position.     

Hydrogen‐bonding and C—H⋯π interactions in 7‐hydroxy‐3‐methoxy‐4‐methyl‐5,6,7,8‐tetrahydro­pyrido­[1,2‐c]pyrimidin‐1(9H)‐one

In the title compound, C₁₀H₁₄N₂O₃, a pyrimidine ring is fused with a piperidine ring. The pyrimidine ring is planar, whereas the piperidine ring adopts a half‐chair conformation. The molecules of the title compound are connected via O—H⋯O intermolecular hydrogen bonds into infinite zigzag chains. The pyrimidine ring is involved in three C—H⋯π interactions, which link the hydrogen‐bonded chains into a three‐dimensional framework.     

Supramolecular Ionic‐Liquid Gels with High Ionic Conductivity

Supramolecular ionogels were prepared by the gelation of room‐temperature ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIm][BF₄]) with (S,S)‐bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF₄]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF₄]^? ions, which reduces the electrostatic attraction between [BMIm]⁺ and [BF₄]^? and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF₄], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.     

Benzylidene-bis-(4-hydroxycoumarin) and benzopyrano-coumarin derivatives: synthesis, ¹H/¹³C-NMR conformational and X-ray crystal structure studies and in vitro antiviral activity evaluations

We report on the synthesis of 4-hydroxycoumarin dimers 1-15 bearing an aryl substituent on the central linker and fused benzopyranocoumarin derivatives 16-20 and on their in vitro broad anti-DNA and RNA virus activity evaluations. The chemical identities and structure of compounds 1-20 were deduced from their homo- and heteronuclear NMR measurements whereas the conformational properties of 5, 14 and 20 were assessed by the use of 1D difference NOE enhancements. Unequivocal proof of the stereostructure of compounds 7, 9, 16 and 18 was obtained by single crystal X-ray diffraction method. The X-ray crystal structure analysis revealed that two 4-hydroxycoumarin moieties in the 4-trifluoromethylphenyl- and 2-nitrophenyl derivatives (compounds 7 and 9, respectively) are intramolecularly hydrogen-bonded between hydroxyl and carbonyl oxygen atoms. Consequently, the compounds 7 and 9 adopt conformations in which two 4-hydroxy-coumarin moieties are anti-disposed. Antiviral activity evaluation results indicated that the 4-bromobenzylidene derivative of bis-(4-hydroxycoumarin) (compound 3) possesses inhibitory activity against HSV-1 (KOS), HSV-2 (G), vaccinia virus and HSV-1 TK? KOS (ACVr) at a concentration of 9-12 μM and at a minimum cytotoxic concentration (MCC) greater than 20 μM. Compounds 4-6, 8, and 20 were active against feline herpes virus (50% effective concentration, EC?? = 5-8.1 μM), that is at a 4-7-fold lower concentration than the MCC.     

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li₄Ti₅O₁₂, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li₄Ti₅O₁₂ oxide composite as a positive electrode, and an organic electrolyte (LiPF₆–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m² g^?1) and texture parameters, as well as three types of organic electrolytes: Et₄NBF₄–propylene carbonate (PC), LiBF₄–PC and LiPF₆–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g^?1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g^?1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.