QSAR Study of Antimicrobial 3-Hydroxypyridine-4-one and 3-Hydroxypyran-4-one Derivatives Using Different Chemometric Tools

A series of 3-hydroxypyridine-4-one and 3-hydroxypyran-4-one derivatives were subjected to quantitative structure-antimicrobial activity relationships (QSAR) analysis. A collection of chemometrics methods, including factor analysis-based multiple linear regression (FA-MLR), principal component regression (PCR) and partial least squares combined with genetic algorithm for variable selection (GA-PLS) were employed to make connections between structural parameters and antimicrobial activity. The results revealed the significant role of topological parameters in the antimicrobial activity of the studied compounds against S. aureus and C. albicans. The most significant QSAR model, obtained by GA-PLS, could explain and predict 96% and 91% of variances in the pIC₅₀ data (compounds tested against S. aureus) and predict 91% and 87% of variances in the pIC₅₀ data (compounds tested against C. albicans), respectively.     

Optimal design of a radial-flow membrane reactor as a novel configuration for continuous catalytic regenerative naphtha reforming process considering a detailed kinetic model

The significance of the catalytic naphtha reforming process in the petroleum refining and petrochemical industry generates continuous evolution of the technology. These improvements would be observed in presenting more efficient reactor setups in order to improve production yield and operating conditions, as well as elucidating better kinetic and deactivation models with higher predicting ability. Both of these items have been considered in this work. An optimized radial-flow moving bed membrane reactor has been proposed as a novel configuration for naphtha reforming process. Optimization has been carried out by differential evolution (DE) method considering 40 decision variables. A detailed kinetic model has also been presented. The proposed kinetic model consists of 32 lumped pseudo-components and 84 reactions. Deactivation rate of catalyst has also been taken into account by considering coke deposition on both acidic and metallic sites. Plant data have been used to validate the modeling results. In order to assess the performance of the proposed configuration, the obtained modeling results have been compared with those of conventional configuration, which shows the superiority of the presented one.     

Highly selective and sensitive voltammetric sensor based on modified multiwall carbon nanotube paste electrode for simultaneous determination of ascorbic acid,acetaminophen and tryptophan

A carbon-paste electrode modified with multiwall carbon nanotubes (MWCNTs) was used for the sensitive and selective voltammetric determination of ascorbic acid (AA) in the presence of 3,4-dihydroxycinnamic acid (3,4-DHCA) as mediator. The mediated oxidation of AA at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k), and diffusion coefficient (D) for AA were calculated. Using square wave voltammetry (SWV), a highly selective and simultaneous determination of AA, acetaminophen (AC) and tryptophan (Trp) has been explored at the modified electrode. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of AA, AC and Trp into three well-defined voltammetric peaks. In the mixture containing AA, AC and Trp, the three compounds can well separate from each other with potential differences of 200, 330 and 530 mV between AA and AC, AC and Trp and AA and Trp, respectively, which was large enough to determine AA, AC and Trp individually and simultaneously.     

Morphological and electrical characterization of conductive polylactic acid based nanocomposite before and after FDM 3D printing

Three dimensional (3D) printing holds strong potential for the formation of a new class of multifunctional nanocomposites. Therefore, both the nanocomposites and 3D printing communities need to make more collaborations and innovations for developing and processing of new polymers and composites to get benefit of functionalities of 3D printed nanocomposites. The contribution of this paper is the creation of 3D printable filaments from conductive polymer nanocomposites using a melt mixing process. Multi-walled carbon nanotubes (MWNTs) and high-structured carbon black (Ketjenblack) (KB) were incorporated into polylactic acid. The percolation threshold of MWNT composites is 0.54 wt % and of KB composites is 1.7 wt % by four-point resistance measurement method. In the similar melt mixing process, there was no dependence of diameter of produced 3D printer filaments on the MWNT loading, instead the diameter was dependent on the KB loading and increased with increasing the filler amount. The conductivity of extruded filaments from 3D printer in low filler contents decreases with increasing extruder temperature, yet in higher filler contents there is no effect of extruder temperature on conductivity. Finally, the resistance decreases exponentially with the increase of cross-sectional area of 3D printed tracks. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47040.     

Wet front penetration with unsteady state wicking in mortar studied by Magnetic Resonance Imaging (MRI)

The movement of water or water carrying aggressive ions is one of the leading causes of deterioration of concrete structures worldwide. Moisture profiles during unsteady state wicking were determined by one dimensional magnetic resonance imaging of 10 cm mortar specimens. Bulk free induction decay and T ₂ ^* lifetime mapping results show a bi-exponential behavior of the MR signal lifetime, T ₂ ^* , in all samples, indicating at least two different water populations. From T ₂ ^* mapping, the short T ₂ ^* lifetime, assigned to interlayer water (water between C–S–H layers), and its associated amplitude are constant along the sample. The long T ₂ ^* lifetime and its associated amplitude, related to water in the pore space (micro and macropores), change with local moisture content. To the best of our knowledge, this is the first time that interlayer water has been spatially resolved in MRI of cement-based materials. Gravimetric sorptivity measurements show two regimes of water absorption in the four samples studied. In the first regime, a capillary transport mechanism is dominant in filling the macropores. In the second regime, the interaction between water and solid matrix is postulated to cause swelling that results in a reduction of the water absorption rate. After swelling, diffusion controls pore filling. Water front penetration behavior observed with magnetic resonance imaging, and bulk free induction decay measurements showed changes in behavior that can be linked to sorptivity changes from an initial to a secondary regime. Inverse modelling was conducted to extract the transport properties, using the Hydrus program with the one-dimensional moisture content profiles. Modelling results showed a decrease in saturated hydraulic conductivity with water exposure time.     

Theoretical and experimental assessment of UV resistance of high-density polyethylene: Screening and optimization of hindered amine light stabilizers

Hindered amine light stabilizers (HALS) are widely used chemical stabilizers for preventing polymer degradation. In this study, the effects of type of HALS and its content in high-density polyethylene (HDPE) over the stabilization process are investigated employing density functional theory (DFT) and experimental approach. The electrophilicity index of four types of commercial HALS are compared by DFT to select the most effective one. Besides, the HDPE sample containing a phenolic antioxidant and different contents of the selected HALS are experimentally exposed to UV irradiation. The effect of HALS content on the changes in chain microstructure and molecular weight of HDPE are evaluated using gel permeation chromatography and frequency sweep rheometry. In the absence of HALS, HDPE suffers degradation and the phenolic antioxidant causes chain scission. However, by adding HALS, the chain branching and crosslinking mechanisms are predominant. The results of FTIR, DSC, and tensile analyses follow similar trends, revealing that the best stabilization performance corresponds to adding 600 ppm HALS to HDPE.