A Thiazole-linked Covalent Organic Framework for Lithium-Sulphur Batteries

Lithium-sulphur (Li−S) batteries are a promising alternative power source, as they can provide a higher energy density than current lithium-ion batteries. Porous materials are often used as cathode materials as they can act as a host for sulphur in such batteries. Recently, covalent organic frameworks (COFs) have also been used, however they typically suffer from stability issues, resulting in limited and thus insufficient durability under practical conditions and applications. Herein, we report the synthesis of a crystalline and porous imine-linked triazine-based dimethoxybenzo-dithiophene functionalized COF (TTT-DMTD) incorporating high-density redox sites. The imine linkages were further post-synthetically transformed to yield a robust thiazole-linked COF (THZ-DMTD) by utilizing a sulphur-assisted chemical conversion method, while maintaining the crystallinity. As a synergistic effect of its high crystallinity, porosity and the presence of redox-active moieties, the thiazole-linked THZ-DMTD exhibited a high capacity and long-term stability (642 mAh g⁻¹ at 1.0 C; 78.9 % capacity retention after 200 cycles) when applied as a cathode material in a Li−S battery.     

Stereoselectivity in the epoxidation of carbohydrate-based oxepines

The facial selectivity in the DMDO epoxidation of carbohydrate-based oxepines derived from glucose, galactose, and mannose has been determined by product analysis and density functional theory (DFT, B3LYP/6-31+G**//B3LYP/6-31G*) calculations. Oxepines 3 and 4, derived from d-galactose and d-mannose, largely favor alpha- over beta-epoxidation. The results reported here, along with selectivities in the DMDO-mediated epoxidation of d-xylose-based oxepine 1 and d-glucose-based oxepines 2 and 5 reported earlier, support a model in which electronic effects, guided by the stereochemistry of the oxygens on the oxepine ring, largely determine the stereoselectivity of epoxidation. Other contributing factors included conformational issues in the oxepine's transition state relative to the reactant, the asynchronicity in bond formation of the epoxide, and the overall steric bulk on the alpha- and beta-faces of the oxepine. Considered together, these factors should generally predict facial selectivity in the DMDO-epoxidation of cyclic enol ethers.     

Complex Cascade Reaction Networks via Cross β Amyloid Nanotubes

Biocatalytic reaction networks integrate complex cascade transformations via spatial localization of multiple enzymes confined within the cellular milieu. Inspired by nature's ingenuity, we demonstrate that short peptide‐based cross‐β amyloid nanotubular hybrids can promote different kinds of cascade reactions, from simple two‐step, to multistep, to complex convergent cascades. The compartmentalizing ability of paracrystalline cross‐β phases was utilized to colocalize sarcosine oxidase (SOX) and hemin as an artificial peroxidase. Further, the catalytic potential of the amyloid nanotubes with ordered arrays of imidazoles were used as hydrolase mimic. The SOX‐hemin amyloid nanohybrids featuring a single extant enzyme could integrate different logic networks to access complex digital designs with the help of three concatenated AND gates and biologically relevant stimuli as inputs.     

Zwitterionic imidazolium salt: An efficient organocatalyst for tetrahydropyranylation of alcohols

An aprotic imidazole based zwitterionic-salt, 4-(3-methylimidazolium)-butane sulfonate has been found to be an efficient organocatalyst for tetrahydropyranylation by the reaction of 3,4-dihydro-2H-pyran (DHP) and different aliphatic alcohols as well as various phenolic compounds. The notable advantages of the present method are general applicability to various alcohols, clean reaction, production of no hazardous waste, open air reaction conditions and high yields. The catalyst can be reused without the loss of significant catalytic activity.     

13C-1H HSQC experiment of probe molecules aligned in thermotropic liquid crystals: sensitivity and resolution enhancement in the indirect dimension

The spectra of molecules oriented in liquid crystalline media are dominated by partially averaged dipolar couplings. In the 13C-1H HSQC, due to the inefficient hetero-nuclear dipolar decoupling in the indirect dimension, normally carried out by using a pi pulse, there is a considerable loss of resolution. Furthermore, in such strongly orienting media the 1H-1H and 13C-1H dipolar couplings leads to fast dephasing of transverse magnetization causing inefficient polarization transfer and hence the loss of sensitivity in the indirect dimension. In this study we have carried out 13C-1H HSQC experiment with efficient polarization transfer from 1H to 13C for molecules aligned in liquid crystalline media. The homonuclear dipolar decoupling using FFLG during the INEPT transfer delays and also during evolution period combined with the pi pulse heteronuclear decoupling in the t1 period has been applied. The studies showed a significant reduction in partially averaged dipolar couplings and thereby enhancement in the resolution and sensitivity in the indirect dimension. This has been demonstrated on pyridazine and pyrimidine oriented in the liquid crystal. The two closely resonating carbons in pyrimidine are better resolved in the present study compared to the earlier work [H.S. Vinay Deepak, Anu Joy, N. Suryaprakash, Determination of natural abundance 15N-1H and 13C-1H dipolar couplings of molecules in a strongly orienting media using two-dimensional inverse experiments, Magn. Reson. Chem. 44 (2006) 553-565].     

Selecting informative rules with parallel genetic algorithm in classification problem

The classification system is very important for making decision and it has been attracted much attention of many researchers. Usually, the traditional classifiers are either domain specific or produce unsatisfactory results over classification problems with larger size and imbalanced data. Hence, genetic algorithms (GA) are recently being combined with traditional classifiers to find useful knowledge for making decision. Although, the main concerns of such GA-based system are the coverage of less search space and increase of computational cost with the growth of population. In this paper, a rule-based knowledge discovery model, combining C4.5 (a Decision Tree based rule inductive algorithm) and a new parallel genetic algorithm based on the idea of massive parallelism, is introduced. The prime goal of the model is to produce a compact set of informative rules from any kind of classification problem. More specifically, the proposed model receives a base method C4.5 to generate rules which are then refined by our proposed parallel GA. The strength of the developed system has been compared with pure C4.5 as well as the hybrid system (C4.5 + sequential genetic algorithm) on six real world benchmark data sets collected from UCI (University of California at Irvine) machine learning repository. Experiments on data sets validate the effectiveness of the new model. The presented results especially indicate that the model is powerful for volumetric data set.     

Silicon nano crystal filled ellipse core based quasi photonic crystal fiber with birefringence and very high nonlinearity

In this paper, we have proposed a new type of quasi photonic crystal fiber (PCF) with a silicon nano crystal core. This structure can be used to sense aqueous analysis over a wavelength range of 1.00?µm to 3.00?µm. The properties of this structure are simulated using the vector-finite element method (VFEM) employing a boundary condition. The proposed model provides a significant effect of birefringence and a very high nonlinear coefficient for two different fundamental modes, which are obtained by adjusting the size of the silicon nano crystal filled ellipse core. This provides a high nonlinearity of 4.2?×?10⁵ W^?1Km^?1 and a birefringence of ? 3.2?×?10^?1 at the wavelengths 1.00?µm and 3.00?µm, respectively. Some others properties, such as the effective area, scattering loss, confinement loss, numerical aperture (NA)and power fraction are also analyzed to measure the performance of this structure. The proposed model is useful for sensing and biomedical imaging applications. The proposed structure may also find extensive applications in optical communication and sensor systems.     

Effects of slip,viscous dissipation and Joule heating on the MHD flow and heat transfer of a second grade fluid past a radially stretching sheet

The flow and heat transfer of an electrically conducting non-Newtonian second grade fluid due to a radially stretching surface with partial slip is considered. The partial slip is controlled by a dimensionless slip factor, which varies between zero （total adhesion） and infinity （full slip）. Suitable similarity transformations are used to reduce the resulting highly nonlinear partial differential equations into ordinary differential equations. The issue of paucity of boundary conditions is addressed and an effective numerical scheme is adopted to solve the obtained differential equations even without augmenting any extra boundary conditions. The important findings in this communication are the combined effects of the partial slip, magnetic interaction parameter and the second grade fluid parameter on the velocity and temperature fields. It is interesting to find that the slip increases the momentum and thermal boundary layer thickness. As the slip increases in magnitude, permitting more fluid to slip past the sheet, the skin friction coefficient decreases in magnitude and approaches zero for higher values of the slip parameter, i.e., the fluid behaves as though it were inviscid. The presence of a magnetic field has also substantial effects on velocity and temperature fields.     

Crystal Structure of a Metallohybrid Acid of 1,3,5-Benzenetricarboxylic Acid of Copper(II)

Abstract The crystal structure of a metallohybrid carboxylic acid obtained from the reaction of 1,3,5-benzenetricarboxylic acid (TCAH3) with copper(II)acetate monohydrate in the presence of pyridine (py) having composition Cu(py)₂(TCAH2)₂(H₂O)₂ [1] is reported. It crystallizes in triclinic space group P-1 and with a = 7.0110(3)?, b = 8.9523(5)?, c = 11.5370(5) ?, α = 79.776(3) °, β = 82.881(3)°, γ = 83.628(3)°, and V = 704.18(6)?³. The hydrogen bond in 1 is compared with the hydrogen bond pattern in the structure of 1,3-dicarbomethoxy 4,6-benzenedicarboxylic acid, which crystallizes in mononclinic space group P21/c and has unit cell parameters of a = 6.9549(16)?, b = 8.7676(15)?, c = 20.111(4)?; β = 92.585(17) ° and V = 1225.1(4) ?³. Index Abstract Crystal structure of a metallohybrid carboxylic acid obtained from the reaction of 1,3,5-benzenetricarboxylic acid with copper(II)acetate monohydrate in the presence of pyridine is determined and compared with hydrogen bond pattern present in the structure of 1,3-dicarbomethoxy 4,6-benzenedicarboxylic acid. Crystal structure of a metallohybrid acid of 1,3,5-benzenetricarboxylic acid of copper(II). Kusum Bania, Nilotpal Barooah, Rupam Sarma, Jubaraj B. Baruah