Regiochemistry of nucleophilic substitution of 4-phenylsulfonyl tetrafluoropyridine with unequal bidentate nucleophiles

The regiochemistry of nucleophilic substitution of 4-phenylsulfonyl tetrafluoropyridine with unequal bidentate nucleophiles was investigated. The first nucleophilic substitution occurs at the 2-position of the pyridine ring by nitrogen nucleophile site (secondary or primary amine) followed by intermolecular ring closure at the geometrically accessible 3-position of the pyridine ring (by S, O and N nucleophiles). From this investigation, difluorinated tetrahydropyrido[3,4-b][1,4]oxazine, thiazine and pyrazine scaffolds were synthesized very readily by a one-pot annelation reaction of 4-phenylsulfonyl tetrafluoropyridine with appropriate unequal bidentate nucleophiles.     

Comparison of Volatile Organic Compounds of Thymus Vulgaris Using Hydrodistillation and Headspace Solid Phase Microextraction Gas Chromatography Mass Spectrometry

Essential oil of aerial parts of Tymus vulgaris L. from Babaaman montains of Iran were isolated by hydrodistillation with an average oil yield 1.9 w/w%. The components of the oil were identified by gas chromatography mass spectrometry. On a separate experiments the compositions of volatile emission of the plant were studied by headspace solid phase microextraction and gas chromatography mass spectrometry. The tempratures used during the sample preparation were 25°C and 50°C. In order to determine the effect of solvent (water) on the separation, the experiments were done in the presence and absence of distilled water in the extraction vial at the tempratures mentioned above. Ten majour components were obtained in four different experimental headspace solid phase microextraction conditions and the hydrodistillation methods from the plant. Thymol was found to be the most abundant costituent (27.2–73.09%), follwoed by p‐cymene (6.86–31.76%), γ‐terpinene (1.02–9.26%), myrcene (0.05–8.84%), α‐pinene (0.25–6.63%), caryophyllene (3.09–5.56%), thymol methyl ether (0.99–2.97%), thymolacetate (0.11–2.05%), carvacrol (0.49–1.70%) and α‐cadinol (0.38–1.10%).     

Determination of Hg in water and wastewater samples by CV-AAS following on-line preconcentration with silver trap

An online mercury preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS) coupled to a flow injection (FI) method was studied. The method was developed involving the determination of ng/L levels of mercury retained on the silver wool solid sorbent. Experimental conditions such as sample volume, flow rate, stability of the column and effect of foreign ions on the determination of trace amounts of mercury were optimized. The detection limit is 3 ng/L and dynamic range 10–250 ng/L require only 50 mL of sample. The relative standard deviations (RSD) of the determinations are below 4%. The presence of common metal ions, such as K+, Na⁺, Cu²⁺, Pb²⁺, Fe³⁺, Ni²⁺, and Mn²⁺, does not interfere with the measurement of mercury by this method. The method was successfully applied to the determination of mercury in water and wastewater samples.     

Functional Mutations in and Characterization of VHH Against Helicobacter pylori Urease

Manipulation of clinically significant antibodies can effectively improve the processes of diagnosis and treatment. Affinity maturation process has a significant role in improvement of antibodies efficiency. Error-prone PCR technique is one of the proposed methods for improvement of the affinity of antibodies. In the present research, a method was applied to camel heavy-chain antibody (VHH, nanobody) raised against UreC subunit of urease enzyme from Helicobacter pylori. This VHH was used as a starting molecule to construct a highly diversified phage displayed VHH library. The constructed library of nanobody mutants was subjected to several rounds of panning against UreC antigen. High-affinity mutant was selected. Our VHH (HMR23) showed 1.5-fold higher binding activity than the parental VHH. In addition, the mutant VHH presented a better performance in inhibition of urease activity at low concentrations retaining its specificity and thermal stability.     

Walnut Oil Nanoemulsion: Optimization of the Emulsion Capacity,Cloudiness, Density,and Surface Tension

Response surface methodology (RSM) in conjunction with central composite rotatable design (CCRD) was employed to find out the influence of preparation properties of walnut oil/water nanoemulsion namely ultrasonic time (5–15 minutes), walnut oil content (4–10% w/w) and concentration ratio of Span 80 to Tween 80 (K ₀, 0.55–0.80) on response variables including emulsion capacity, cloudiness, density and surface tension. The calculated regression models with high value of coefficient of determination (0.910–0.973) and insignificant lack of fit test indicated satisfactory agreement of empirical models with experimental observations. The results revealed linear term of walnut oil concentration was the most significant (p < 0.05) parameter on the all responses. The overall optimum region to achieve the ideal characteristics was ultrasonic time of 11.74 minutes, walnut oil content of 4.00% (w/w) and K ₀ of 0.80.     

Recent developments of advanced numerical heat transfer in porous media

Journal of Thermal Analysis and Calorimetry -     

Multiplexed Discrimination of Single Amino Acid Residues in Polypeptides in a Single SERS Hot Spot

The SERS-based detection of protein sequences with single-residue sensitivity suffers from signal dominance of aromatic amino acid residues and backbones, impeding detection of non-aromatic amino acid residues. Herein, we trap a gold nanoparticle in a plasmonic nanohole to generate a single SERS hot spot for single-molecule detection of 2 similar polypeptides (vasopressin and oxytocin) and 10 distinct amino acids that constitute the 2 polypeptides. Significantly, both aromatic and non-aromatic amino acids are detected and discriminated at the single-molecule level either at individual amino acid molecules or within the polypeptide chains. Correlated with molecular dynamics simulations, our results suggest that the signal dominance due to large spatial occupancy of aromatic rings of the polypeptide sidechains on gold surfaces can be overcome by the high localization of the single hot spot. The superior spectral and spatial discriminative power of our approach can be applied to single-protein analysis, fingerprinting, and sequencing.     

利用MOF-253衍生氮掺杂碳限域效应促进Pt纳米单晶电催化剂的氧析出反应

目前,为了有效解决电化学能量转化反应动力学过程缓慢和商业化应用等问题,需要大力提高催化剂的电催化活性和稳定性,并大幅降低贵金属催化剂的用量.通常,铂(Pt)基催化剂对燃料电池的氧还原反应(ORR)和水电解过程的氢析出反应(HER)表现出很高的活性.然而,对于高效的金属-空气电池和水电解装置,其中的氧析出反应(OER)则需要高活性的非Pt电催化剂来降低电化学过电位及提高其对高电位的耐受性.虽然相较于Pt催化剂,IrO2和RuO2等贵金属催化剂表现出了更高的OER活性,然而,它们的稳定性差,难以满足实际应用需求,严重阻碍了其在金属-空气电池和水电解中的应用.通常,Pt对OER的低效催化主要归因于在OER电催化过程中Pt与电解液直接接触,导致Pt表面快速被氧化,形成Pt氧化物(Pt^+4O2和Pt^+2O)层.形成的Pt氧化物对OER不起催化作用,从而降低了Pt的利用率和总的水电解效率.为了避免Pt表面的快速氧化,实现高的OER性能,我们将Pt金属纳米粒子有效地限域在超薄功能多孔碳层内.前期,已有大量的有关金属基ORR和HER催化剂研究证明,这种策略对于稳定金属纳米颗粒非常有效,可有效避免金属催化剂的快速氧化,而且还可抑制金属颗粒迁移和团聚;此外,还有利于增强催化剂的导电性和离子物种的扩散能力,从而提高催化剂的电催化性能.然而,要达到提高金属催化剂OER电催化性能的目的,还需要设计一种具有优良结构的功能化异质原子掺杂多孔碳基限域材料.金属有机框架(MOF),特别是MOF-253,由于具有较高的柔韧性、丰富的孔、可控的几何结构和高比表面积,被认为是制备功能多孔碳基限域材料的理想前驱体.为此,通过结合功能多孔碳基材料的限域作用及MOF-253和超细Pt纳米单晶的优势,本文合成了MOF-253衍生氮掺杂碳(N/C)限域的Pt纳米单晶(Pt@N/C)核壳型电催化剂.制备的Pt-N-C框架不仅具有超薄的氮掺杂活性多孔碳保护层壳体(平均厚度为0.51 nm),还有具高度分散和稳定化的Pt纳米单晶核体;值得指出的是,因受到碳层的限域作用,即使经900℃的高温处理,Pt纳米单晶仍保持了较小的晶体尺寸(平均粒径仅为6.7 nm);此外,该催化剂的Pt载量较低,仅为6.1wt%(Pt@N/C-10).将其作为OER电催化剂,表现出优异的OER性能:在10 mA cm^-2电流密度下,其过电位仅为298 mV,低于商业IrO2催化剂(353 mV);而且,经2000周加速电位扫描后,其电位仅降低19.4 mV,也低于IrO2(23.3 mV).本文很好地证明了通过构建空间限域结构可以有效解决Pt等金属催化剂因表面氧化而导致OER动力学活性和稳定性低的问题.     

Extraction of Arsenic(V) from Water Using Emulsion Liquid Membrane

In this article, the extraction of arsenic(V) from water by means of emulsion liquid membrane is investigated. The influence of operating factors such as stirring speed, concentration of sulfuric acid in the external aqueous phase, concentration of sodium sulfate in internal stripping phase, and concentration of carrier in the membrane phase on the extraction efficiency are investigated and their optimum values, which provide the maximum recovery of arsenic, are determined. Taguchi experimental design is used in order to reduce the number of experiments. The optimum amounts for the extraction of arsenic from water, based on the results, are: stirring speed, 500 rpm; concentration of sulfuric acid in the feed, 1.5 g mol/lit; concentration of reagent in internal phase, 1.5 g mol/lit; and concentration of carrier in 3 ml kerosene which is added to the membrane phase, 0.1 g mol/lit.     

{\Re} -parts in (semi)hypergroups

In this article, first we generalize the concept of complete parts and γ-parts in semi-hypergroups and then we study ${\Re}$ -closures in semi-hypergroups. Finally, we investigate strongly regular relations and the quotient-induced structures.