Qualitative characterization of the diffusion of cationic-modified PVA into the cellulose fiber pores

In this work, the diffusion of cationic poly (vinyl alcohol) (CPVA) with well-defined structures into the pores of bleached kraft fibers was investigated at equilibrium level of adsorption by means of adsorption, solute exclusion technique (SET), and nuclear magnetic resonance (NMR) relaxation method. The results showed that the interaction between CPVA and dextran polymers was weak, which allowed us to use the SET method to investigate the variation in the pore size of fibers upon diffusing CPVAs. Both adsorption and SET methods confirmed the diffusion of CPVA polymers into the fiber pores. However, the NMR technique was unable to reflect the pore size changes. The main reason for such results was probably the error that occurred in removing water between fibers via applying the water retention value (WRV) test prior to the NMR analysis. In fact, not all of the water on the fiber surface, especially on the surface of CPVA-modified fibers, could be removed by the WRV, introducing some error in the NMR analysis.     

Cytochrome c embraced in sodium dodecyl sulfate nano-micelle as a homogeneous nanostructured peroxidase

A homogeneous nanostructured enzyme (artificial peroxidase, AP) with suitable catalytic efficiency was generated using bovine heart cytochrome c (Cyt c) and sodium dodecyl sulfate nano-micelles in 50?mM phosphate buffer pH 10.5 at 25?°C. The Michaelis?CMenten (K _m) and catalytic rate (k _cat) of the AP were determined to be 21.6?±?1.2???M and 0.474?±?0.013?s^?1, respectively. The catalytic efficiency of the AP was 0.0219?±?0.002???M^?1s^?1, which was 30?±?1.5?% as efficient as the native horseradish peroxidase (HRP). The mean diameter of AP was measured to be 6.4?nm using dynamic light scattering technique. The UV?CVis spectrometry, circular dichroism, surface tension, isothermal titration calorimetric and electrochemistry methods were utilized for additional characterization of the AP. Together our results suggest that the AP generated here can be used in place of HRP in industrial and commercial fields under some extreme conditions.     

Effect of resin staging on frontal polymerization of dicyclopentadiene

In thermal frontal polymerization (FP), ambient temperature and staging conditions highly affect the resin behavior and front properties. This study describes the effect of staging conditions and resin reactivity on frontal ring opening metathesis polymerization of dicyclopentadiene in presence of phosphite-inhibited second-generation Grubbs catalyst. An experimental setup is designed to characterize and understand the effect of inhibitor concentration, incubation time, and incubation temperature on front velocity, activation time, and front temperature of the FP reaction. The results reveal that front properties are influenced by various factors, including available energy density of resin, stability of catalyst-inhibitor complex, resin temperature, and resin viscosity. An increase in staging temperature results in lower pot lives but faster gelation process and activation of FP reaction. Additionally, increasing the inhibitor concentration leads to slower fronts, higher activation times, and longer pot lives. The results of this study can be extended to other FP systems and can be used in design of new manufacturing processes and applications using FP.     

An insight to the molecular interactions of the FDA approved HIV PR drugs against L38L↑N↑L PR mutant

The aspartate protease of the human immune deficiency type-1 virus (HIV-1) has become a crucial antiviral target in which many useful antiretroviral inhibitors have been developed. However, it seems the emergence of new HIV-1 PR mutations enhances drug resistance, hence, the available FDA approved drugs show less activity towards the protease. A mutation and insertion designated L38L↑N↑L PR was recently reported from subtype of C-SA HIV-1. An integrated two-layered ONIOM (QM:MM) method was employed in this study to examine the binding affinities of the nine HIV PR inhibitors against this mutant. The computed binding free energies as well as experimental data revealed a reduced inhibitory activity towards the L38L↑N↑L PR in comparison with subtype C-SA HIV-1 PR. This observation suggests that the insertion and mutations significantly affect the binding affinities or characteristics of the HIV PIs and/or parent PR. The same trend for the computational binding free energies was observed for eight of the nine inhibitors with respect to the experimental binding free energies. The outcome of this study shows that ONIOM method can be used as a reliable computational approach to rationalize lead compounds against specific targets. The nature of the intermolecular interactions in terms of the host–guest hydrogen bond interactions is discussed using the atoms in molecules (AIM) analysis. Natural bond orbital analysis was also used to determine the extent of charge transfer between the QM region of the L38L↑N↑L PR enzyme and FDA approved drugs. AIM analysis showed that the interaction between the QM region of the L38L↑N↑L PR and FDA approved drugs are electrostatic dominant, the bond stability computed from the NBO analysis supports the results from the AIM application. Future studies will focus on the improvement of the computational model by considering explicit water molecules in the active pocket. We believe that this approach has the potential to provide information that will aid in the design of much improved HIV-1 PR antiviral drugs.     

On a boundary value problem for a p‐Dirac equation

The p‐Laplace equation is a nonlinear generalization of the Laplace equation. This generalization is often used as a model problem for special types of nonlinearities. The p‐Laplace equation can be seen as a bridge between very general nonlinear equations and the linear Laplace equation. The aim of this paper is to solve the p‐Laplace equation for 1 < p < 2 and to find strong solutions. The idea is to apply a hypercomplex integral operator and spatial function theoretic methods to transform the p‐Laplace equation into the p‐Dirac equation. This equation will be solved iteratively by using a fixed‐point theorem. Applying operator‐theoretical methods for the p‐Dirac equation and p‐Laplace equation, the existence and uniqueness of solutions in certain Sobolev spaces will be proved. Copyright © 2016 John Wiley & Sons, Ltd.     

Multivariate statistical design optimization for ultrasonic-assisted restricted access supramolecular solvent-based liquid phase microextraction of quercetin in food samples

In this method, quercetin as a flavonoid has been extracted, preconcentrated and determined by using ultrasonic-assisted restricted access supramolecular solvent-based liquid phase microextraction method in food samples. The quercetin concentration in extraction phase was determinated by UV–visible spectrophotometer which has microsampling cuvette. Multivariate statistical design approach was used to optimize the analytical variables including the pH, ratio of restricted access solvent components, volume of restricted access solvent, ultrasonication and centrifugation times. The analytical performance values of the developed method including limit of detection, limit of quantification, preconcentration factor and relative standard deviation (10 replicates of 10–5 M of quercetin solution) were found as 2.98, 9.93 μg L^?1, 30 and 6.3%, respectively. The method provides important advantages such as use of minimum volume of organic solvents, simple and economical operation and easy optimization via multivariate statistical design approach. The developed procedure was validated with four food samples, and acceptable recoveries (87–104%) were achieved.     

Preparation and characterization of cationic poly vinyl alcohol with a low degree of substitution

The cationization of polymers has been regarded as an effective method to improve their performance for various applications. In this work, the cationization of poly vinyl alcohol (PVA) was investigated under different conditions, i.e., various glycidyl-trimethylammonium chloride (GTMAC) to PVA ratios, reaction temperatures, times, PVA and NaOH concentrations and solvent compositions. The results showed that the overall efficiency of the cationic modification was rather low, which was due to the hydrolysis of both GTMAC and cationic-modified PVA (CPVA) under the strong alkaline conditions employed. The results also showed that the optimum GTMAC/PVA ratio depended on the solvent composition. The cationization was confirmed by means of ¹H NMR and FTIR analyses. The maximum efficiency in water was obtained under the conditions of 95 °C, 1 h, 0.5 (mol) GTMAC/PVA ratio, and 5% (mol) NaOH concentration, while that in the ethanol/DMSO mixture (1.25 v/v) was obtained under the conditions of 70 °C, 1 h, 0.5 (mol) GTMAC/PVA ratio, and 5% (mol) NaOH concentration. Additionally, the interaction of CPVAs with a silicon wafer (as a substrate) was determined by employing an atomic force microscope (AFM) in water and air.     

Microperoxidase-11/NH2-FSM16 as a H2O2-resistant heterogeneous nanobiocatalyst: a suicide-inactivation study

The catalytic activity of heme peptides is an area of intense investigation. They are utilized for exploring the fine details of structural and functional properties of an active site, and to create minimized and industrial catalysts. The peroxidase activity and kinetics of suicide-inactivation of microperoxidase-11/FSM16 as a heterogeneous nanobiocatalyst in oxidation reaction of guaiacol were studied in the presence of high concentration of hydrogen peroxide (2?mM), as its natural suicide-substrate. The substrate concentration was first-order in relation to aromatic substrate (AH), and the ratio of suicide-substrate (H₂O₂) was kept much higher than the benign substrate (guaiacol). The results of kinetic analysis confirmed a similar mechanism for suicide-peroxide inactivation of horseradish peroxidase (HRP), microperoxidase (MP-11) and MP-11/NH₂-FSM16. Inactivation kinetic parameters, including intact activity of MP-11/NH₂-FSM16, ??_i, and the apparent inactivation rate constant (k _i) were obtained as 0.229?±?0.009?min^?1 and 0.651?±?0.041?min^?1 at [H₂O₂]?=?2.0?mM, respectively, in 5.0?mM phosphate buffer solution (PBS; pH 7.0) at 27?°C. Our results indicated that covalent immobilization of microperoxidase onto NH₂-FSM16 protected the heme group against peroxide inactivation resulting in generation of an efficient peroxide-resistant heterogeneous nanobiocatalyst.     

Rendering cellulose fibers antimicrobial using cationic β-cyclodextrin-based polymers included with antibiotics

Cationic β-cyclodextrin polymer (CPβCD) and its complexes with butylparaben and triclosan were reported in this paper. 2D NMR confirmed that the host-guest complexes were formed by including antibiotics inside the cavities of CPβCDs, which significantly improved the water solubility of the antibiotics. Results of inhibition zones and shaking flask methods of antimicrobial-modified cellulose fibres showed that both antibiotics/CPβCD complexes had excellent antimicrobial activities when applying on the cellulose fibers whereas triclosan appeared to more effective. Morphology of untreated and treated bacteria revealed by AFM suggested that the antibiotics/CPβCD complexes inhibited bacteria through affecting the metabolism of the bacteria instead of damaging the cell membrane. Due to the strong electrostatic association, CPβCD polymers adsorbed on the surface of cellulose fibres almost completely within the range of dosages investigated.     

Microdetermination of collagenase and collagen

A method for the microdetermination of bacterial collagenase activity and different types of collagen is described. The assay can be used in the range of 2–60 μg for type I and from 10 to 60 μg for other types. Interference of other proteins was eliminated, even those that binds the Sirius red dye. The method is sensitive, rapid, and inexpensive in determination of collagen type I in its pure and fibril form and bacterial collagenase activity and its kinetic parameter.