Cross-linking mechanisms of arginine and lysine with α,β-dicarbonyl compounds in aqueous solution

Cross-linking in proteins by α,β-dicarbonyl compounds is one of the most damaging consequences of reactive carbonyl species in vivo and in foodstuffs. In this article we investigate computationally the cross-linking of glyoxal and methylglyoxal with lysine and arginine residues using density functional theory and the wB97XD dispersion-corrected functional. Five pathways, A-E, have been characterized. In pathways A and B, the reaction proceeds via formation of the Schiff base, aldimine, followed by addition of arginine. In contrast, in pathways C-E, direct addition of arginine to the dicarbonyl compounds occurs first, leading to a dihydroxyimidazolidine intermediate, which then reacts with lysine after dehydration and proton transfer reactions. The results reveal that pathways A, C, and E are competitive whereas reactions via pathways B and D are much less favorable. Inclusion of up to five explicit water molecules in the proton transfer and dehydration steps is found to lower the energy barriers in the feasible pathways by about 5-20 kcal/mol. Comparison of the mechanisms of methylglyoxal-derived imidazolium cross-linking (MODIC) and glyoxal-derived imidazolium cross-linking (GODIC) shows that the activation barriers are lower for GODIC than MODIC, in agreement with experimental observations.     

Synthesis and characterization of cadmium selenide nanoparticles loaded on activated carbon and its efficient application for removal of muroxide from aqueous solution

In the first, Cadmium selenide Nanoparticle loaded on activated carbon (CdSe-NP-AC) has been synthesized and characterized by different techniques including XRD and SEM. Then, this new adsorbent successfully has been applied for the removal of muroxide (MO) from aqueous solution in batch studies, while the effect of various experimental parameters like initial pH (pH(0)), contact time, amount of (CdSe-NP-AC) and initial MO concentration (C(0)) on its removal percentage was examined by one at a time optimization method. It was found following optimization of variable, the adsorption of MO onto (CdSe-NP-AC) followed pseudo-second-order kinetics and show Tempkin and Langmuir models for interpretation of experimental data. It was observed that by increasing the temperature the removal percentage was improved and the positive change in entropy (ΔS°) and heat of adsorption (ΔH°) show the endothermic nature of process, while the high negative value in Gibbs free energy change (ΔG°) indicates the feasible nature of adsorption process.     

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT?GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, ??, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4?±?0.5?s^?1 and 0.51, respectively at pH?=?7.0. The obtained results indicate that hydrazine peak potential at OMWCNT?GCE shifted for 14, 109, and 136?mV to negative values as compared with oxadiazole-modified GCE, MWCNT?GCE, and activated GCE surface, respectively. The electron transfer coefficient, ??, and the heterogeneous rate constant, k??, for the oxidation of hydrazine at OMWCNT?GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0???M and 10.0 to 400.0???M and detection limit of 0.17???M for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT?GCE was shown to be successfully applied to determine hydrazine in various water samples.     

Reaction between alkyl isocyanides and dimethyl acetylenedicarboxylate in the presence of polyhydroxybenzenes. Synthesis of 4H-chromene derivatives

The reactive intermediate generated by the addition of alkyl isocyanides to dimethyl acetylenedicarboxylate was trapped by phenols such as resorcinol, catechol, hydroquinone, pyrogallol, 2,4-dihydroxybenzaldehyde, or 8-hydroxyquinoline to produce highly functionalized 4H-chromenes in fairly good yields.     

硅衬底上纳米晶金刚石生长

研究了蚀刻气体对生长在硅衬底上纳米晶金刚石合成的影响.合成方法为热丝化学气相沉积法,衬底温度为550 oC,反应压力为4 kPa. 其中甲烷和氢气分别作为源气体和稀释气体. 氮气、氢气和氨气用作蚀刻气体. 结果表明,仅氢气作为蚀刻气体可获得最佳工艺条件.     

Self-assembly of boehmite nanopetals to form 3D high surface area nanoarchitectures

A flower-like boehmite nanostructure was prepared through a template-free chemical route by the self-assembly process of nanosize petals 800–1000 nm long, 200–250 nm wide, 20–50 nm thick and having an average crystallite size of about 2.21 nm. X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), DTA/TGA analyses and Brunauer–Emmet–Teller (BET-N₂) analyses were used in order to characterize the product obtained. XRD results exhibited that the obtained nanostructures composed of pure orthorhombic AlOOH phase. The effects of Cl⁻ ions and TEA on the growth of boehmite three-dimensional nanoarchitectures in the presence of NO₃^-\mathrm{NO}_{3}^{-} ions were investigated. BET analyses of as-prepared material demonstrate that this nanostructure material has a high specific surface area, as high as 123 m² g⁻¹.     

Compact formulations of the Steiner Traveling Salesman Problem and related problems

The Steiner Traveling Salesman Problem (STSP) is a variant of the TSP that is particularly suitable when routing on real-life road networks. The standard integer programming formulations of both the TSP and STSP have an exponential number of constraints. On the other hand, several compact formulations of the TSP, i.e., formulations of polynomial size, are known. In this paper, we adapt some of them to the STSP, and compare them both theoretically and computationally. It turns out that, just by putting the best of the formulations into the CPLEX branch-and-bound solver, one can solve instances with over 200 nodes. We also briefly discuss the adaptation of our formulations to some related problems.     

Assessment of thermo-hydraulic performance of MXene-based nanofluid as coolant in a dimpled channel: a numerical approach

Journal of Thermal Analysis and Calorimetry - The present study numerically investigates the optimization of thermal performance in a dimpled channel using a promising genre of nanofluid which is...