Finite element approximation of nonlocal parabolic problem

In this article, we present a finite element scheme combined with backward Euler method to solve a nonlocal parabolic problem. An important issue in the numerical solution of nonlocal problems while using Newton's method is related to its structure. In fact differently from the local case where the Jacobian matrix is sparse and banded, in the nonlocal case the Jacobian matrix is dense and computations are much more onerous compared to that for differential equations. In order to avoid this difficulty, we use the technique given by Gudi (SIAM J Numer Anal 50 (2012), 657–668) for elliptic nonlocal problem of Kirchhoff type. We discuss the well‐posedness of the weak formulation at continuous as well as at discrete levels. We also derive a priori error estimates for semidiscrete and fully discrete formulations in L² and H¹ norms. Results based on the usual finite element method are provided to confirm the theoretical estimates. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 786–813, 2017     

A Convenient Approach to Stereoisomeric Iminocyclitols: Generation of Potent Brain‐Permeable OGA Inhibitors

Pyrrolidine‐based iminocyclitols are a promising class of glycosidase inhibitors. Reported herein is a convenient epimerization strategy that provides direct access to a range of stereoisomeric iminocyclitol inhibitors of O‐GlcNAcase (OGA), the enzyme responsible for catalyzing removal of O‐GlcNAc from nucleocytoplasmic proteins. Structural details regarding the binding of these inhibitors to a bacterial homologue of OGA reveal the basis for potency. These compounds are orally available and permeate into rodent brain to increase O‐GlcNAc, and should prove useful tools for studying the role of OGA in health and disease.     

Electrochemically Deposited Porous Graphene−Polypyrrole−Polyphenol Oxidase for Dopamine Biosensor

We report a method for the fabrication of glassy carbon electrode modified porous graphene-polypyrrole-polyphenol oxidase (GCE−PG−PPy−PPO) modified electrode for the determination dopamine. The optimization of pH, concentration and detection limit of dopamine was employed by amperomatric technique. The detection limit of dopamine was found to be in a linear range of 2×10⁻⁸ to 4.6×10⁻⁵ M and lower limit detection is 4×10⁻⁹ M. Michealis – Menten constant (Km) and the activation energy were calculated as 31.32 μM and 37.4−Kj mol⁻¹, respectively. The developed biosensor was used to quantify the dopamine in human urine sample.     

Layer-by-layer nanoassembly of polyelectrolytes using formamide as the working medium

Formamide, in its pure state, has been used as a working solvent for layer-by-layer (LbL) polyelectrolyte self-assembly. Polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH) polyelectrolyte films were deposited onto planar substrates and colloidal particles. Film deposition was confirmed using quartz crystal microbalance and zeta potential measurements. Formamide was used as an alternative to the water-based working solvents commonly used for LbL self-assembly. Few LbL self-assembly studies using nonaqueous solvents have been reported. Most studies performed with nonaqueous solvents have required the addition of small volumes of water to dissolve the polyelectrolytes. Conversely, the high dielectric constant of pure formamide led to the dissolution and transport of PSS and PAH. Using formamide, it is possible to deposit nanometer thick polyelectrolyte films onto water-sensitive surfaces. Formamide can be thus be used for encapsulating water sensitive hydrogen storage materials within polyelectrolyte films.     

New LMI-based criteria for global robust stability of delayed neural networks

Some novel, linear matrix inequality based, criteria for the uniqueness and global robust stability of the equilibrium point of Hopfield-type neural networks with delay are presented. A comparison of the present criteria with the previous criteria is made.     

Poly l-lactide-layered double hydroxide nanocomposites via in situ polymerization of l-lactide

The use of clay nanofillers offers a potential route to improved barrier properties in polylactide films. Magnesium-aluminium layered double hydroxides (LDHs) are interesting in this respect and we therefore explored synthesis of PLA-LDH nanocomposites by ring-opening polymerization. This method is attractive because it should ensure good dispersion of LDH in the polymer. The effect of adding either LDH carbonate (LDH-CO₃) or laurate-modified LDH (LDH-C₁₂) was investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that exfoliated nanocomposites were obtained when using LDH-C₁₂ but that LDH-CO₃ gave a partly phase-separated morphology. Thermogravimetric analysis showed that PLA-LDH combinations exhibited higher degradation onset temperatures and differential scanning calorimetry confirmed that LDHs can act as nucleating agents. However, PLA molecular weight was significantly reduced when in-situ polymerization was conducted in the presence of the LDHs and we suggest that chain termination via LDH surface hydroxyl groups and/or metal-catalyzed degradation could be responsible.     

Palladium(II) and platinum(II) complexes of β-functionalized ethyl selenolates: Effect of substitution on synthesis, reactivity, spectroscopy, structures and thermal behavior

Sodium ethylselenolates with functional groups X (where X = -OH, -COOH, -COOMe and -COOEt) at β-carbon were prepared in situ by reductive cleavage of corresponding diselenide with NaBH₄ either in methanol or aqueous ammonia. Treatment of these selenolates with [M₂Cl₂(μ-Cl)₂()₂] (M = Pd or Pt;  = PMePh₂, PnPr₃) in different stoichiometry yielded various bi- and tri-nuclear complexes. The homoleptic hexanuclear complexes [Pd(μ-SeCH₂CH₂X)₂]₆ (X = OH, COOH, COOEt), were obtained by reacting Na₂PdCl₄ with NaSeCH₂CH₂X. All these complexes have been fully characterized. Molecular structures of ethylselenolates containing hydroxyl and carboxylic acid groups revealed solid state associated structures through inter-molecular hydrogen bond interactions. Trinuclear complex, [Pd₃Cl₂(μ-SeCH₂CH₂COOH)₄(PnPr₃)₂] (3a), was disposed in a boat form unlike chair conformation observed for the corresponding methylester complex. The effect of β-functionality in ethylselenolate ligands towards reactivity, structures and thermal properties of palladium and platinum complexes has been extensively studied.     

Degradation of the pesticide fenitrothion as mediated by cationic surfactants and alpha-nucleophilic reagents

The reaction of fenitrothion with a series of alpha-nucleophile oximates having pK(a) values in the range of 7.7-11.8 was studied both in the absence and presence of cetyltrimethylammonium (CTA(+)) surfactants. Reaction with CTA-oximates was found to proceed through two pathways: S(N)2(P) and S(N)2(C); an S(N)Ar pathway was not observed. Accordingly, the observed rate constants were dissected into the two corresponding S(N)2(P) and S(N)2(C) pathways. Use of the pseudophase ion exchange (PPIE) model for micellar catalysis in the CTA(+) system allowed evaluation of micellar second-order rate constant (k(2m)) parameters and binding constants, (K(S)). K(S) values for CTA-oximates were found to vary with the counterion, and the rate enhancement depended on a combination of K(S) and k(2m) values. k(2m)/k(2w) values ranged from 0.0025 to 0.64, suggesting that a concentration effect is mainly responsible for the rate enhancement. In the absence of surfactant, an alpha-effect (i.e., k(alpha)/k(normal)) varying from 8 to 450 was observed for the oximate reaction, decreasing with increasing pK(a). It is proposed that differential solvation (transition-state imbalance) is a cause of the alpha-effect in this system.