Factors controlling the drop evaporation constant

In this paper, we discuss the factors affecting drop evaporation. We found that the droplet morphology at a specific temperature was controlled by the physical properties of the liquid itself, such as the molecular weight, density, diffusion coefficient in air, and heat of vaporization. Two processes are included in drop evaporation: diffusion of liquid molecules into the air (diffusion part) and flow of the liquid molecules from inside the drop to the free outer shell liquid layer within the liquid-vapor interface (evaporation part). The diffusion part remained steady during drying and was not sensitive to the variation of temperature. The evaporation part, however, was an active factor and determined the differences in drop evaporation behaviors.     

Molecular-dynamics studies of bending mechanical properties of empty and C60-filled carbon nanotubes under nanoindentation

This paper utilizes molecular-dynamics simulations to investigate the mechanical characteristics of a suspended (10, 10) single-walled carbon nanotube (SWCNT) during atomic force microscopy (AFM) nanoindentation at different temperatures. Spontaneous topological transition of the Stone-Wales (SW) defects is clearly observed in the indentation process. The present results indicate that under AFM-bending deformation, the mechanical properties of the SWCNT, e.g., the bending strength, are dependent on the wrapping angle. In addition, it is also found that the radial dependence of the reduced formation energy of the SW defects is reasonably insensitive only for the small tubes. However, for tube diameters greater than 2.4 nm [corresponding to the (18, 18) CNT], the SW defects tend to be more radius sensitive. The results indicate that the bending strength decreases significantly with increasing temperature. This study also investigates the variation in the mechanical properties of the nanotube with the density of C60 encapsulated within the nanotube at various temperatures. It is found that, at lower temperatures, the bending strength of the C60-filled nanotube increases with C60 density. However, the reverse tendency is observed at higher temperatures. Finally, the "sharpest tip" phenomena between the probe and the tube wall and the elastic recovery of the nanotube during the retraction process are also investigated.     

盐酸普拉克索关键中间体的合成

以1,4-二氧杂螺[4.5]癸-8-酮(2)为起始原料,经三甲基硅烯醚化、碘代反应、酸化后所得的产物,与硫脲发生环合、水解后制得2-氨基-6-氧代-4,5,6,7-氢苯并[1,2-d]噻唑(5,经氨化还原反应合成了2,6-二氨基-4,5,6,7-四氢苯并[1,2-d]噻唑(6)。5和6两种关键中间体的总收率分别为86%和71%,其结构经MS、¹H NMR和¹³C NMR确证,探索了合成盐酸普拉克索的两种关键中间体方法和工艺的影响因素。     

Asymmetric total synthesis of (+)-monocerin

A concise asymmetric total synthesis of (+)-monocerin has been accomplished. The cis-fused furobenzopyranone of monocerin was efficiently constructed via a Lewis acid-mediated stereoselective cyclization of 1,2,4-triols intermediate.     

Ag掺杂对n-ZnO纳米棒/p-GaN异质结结构和发光性能的影响

利用简单的水热合成法在p-GaN薄膜上制备了Ag掺杂的一维ZnO纳米棒（ZnO NRs）,并且研究了Ag掺杂对于ZnO NRs结构和形貌以及n-ZnO NRs/p-GaN异质结发光特性的影响。结果表明,不同Ag掺杂浓度的ZnO纳米棒截面均呈六边形的棒状结构,且纳米棒的取向垂直于衬底;XRD分析结果表明,随着Ag掺杂浓度的增加,ZnO纳米棒（0002）晶面的峰位向衍射角减小的方向移动,表明Ag⁺置换了ZnO晶格中的部分Zn²⁺后使其晶格常数略增加;随着Ag掺杂浓度的增加,ZnO纳米棒近带边发光峰发生一定的红移并且强度逐渐减弱,黄带发光峰逐渐增强,n-ZnO NRs/p-GaN异质结具有更好的传输效率。     

Comparative Analysis of Herbaceous and Woody Cell Wall Digestibility by Pathogenic Fungi

Fungal pathogens have evolved combinations of plant cell-wall-degrading enzymes (PCWDEs) to deconstruct host plant cell walls (PCWs). An understanding of this process is hoped to create a basis for improving plant biomass conversion efficiency into sustainable biofuels and bioproducts. Here, an approach integrating enzyme activity assay, biomass pretreatment, field emission scanning electron microscopy (FESEM), and genomic analysis of PCWDEs were applied to examine digestibility or degradability of selected woody and herbaceous biomass by pathogenic fungi. Preferred hydrolysis of apple tree branch, rapeseed straw, or wheat straw were observed by the apple-tree-specific pathogen Valsa mali, the rapeseed pathogen Sclerotinia sclerotiorum, and the wheat pathogen Rhizoctonia cerealis, respectively. Delignification by peracetic acid (PAA) pretreatment increased PCW digestibility, and the increase was generally more profound with non-host than host PCW substrates. Hemicellulase pretreatment slightly reduced or had no effect on hemicellulose content in the PCW substrates tested; however, the pretreatment significantly changed hydrolytic preferences of the selected pathogens, indicating a role of hemicellulose branching in PCW digestibility. Cellulose organization appears to also impact digestibility of host PCWs, as reflected by differences in cellulose microfibril organization in woody and herbaceous PCWs and variation in cellulose-binding domain organization in cellulases of pathogenic fungi, which is known to influence enzyme access to cellulose. Taken together, this study highlighted the importance of chemical structure of both hemicelluloses and cellulose in host PCW digestibility by fungal pathogens.     

极谱过程温度效应的研究(Ⅲ)——催化反应速率常数和反应活化能的测定

催化反应在极谱分析中的应用及反应速率常数的测定已有报道。通常根据Koutecky公式计算催化反应速率常数,而反应活化能则由不同温度下测定的速率常数,按照Arrhenius公式计算。我们根据前文提出的可逆、不可逆、准可逆、动力和催化过程各种极谱电流——温度关系的普遍方程式,测定了Ti(Ⅳ)-H_2SO_4H_2C_2O_4-KClO_3、Mo(Ⅳ)-H_2SO_4-NaNO_3、Mo(Ⅵ)-H_2SO_4-NH_4NO_3体系催化反应速率常数和反应活化能(或表观活化能),结果令人满意。     

Squadinorlignoside: A Novel 7,9′‐Dinorlignan from the Stems of Annona squamosa

Two new polar lignans, i.e., squadinorlignoside (= 4‐[(1E)‐1‐(hydroxymethyl)‐3‐(4‐hydroxyphenyl)prop‐1‐en‐1‐yl]phenyl β‐D ‐glucopyranoside; 1 ) and (6R,7R,8S)‐7a‐[(β‐D ‐glucopyranosyl)oxy]‐1‐methoxyisolariciresinol ( 2 ) were isolated from the stems of Annona squamosa, together with eight known lignans and five known neolignans (compounds 3 – 15 ; Fig. 1). All of these constituents are reported for the first time from the genus Annona. The structures, absolute configurations, and selected conformational aspects of the new compounds were elucidated spectroscopically. Compound 1 is the first example of a 7,9′‐dinorlignan natural product.     

Determination of lead in water samples by graphite furnace atomic absorption spectrometry after cloud point extraction

Cloud point extraction (CPE) has been used for the pre-concentration of lead, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and later analysis by graphite furnace atomic absorption spectrometry (GFAAS) using octylphenoxypolyethoxyethanol (TritonX-114) as surfactant. The chemical variables affecting the separation phase were optimized. Separation of the two phases was accomplished by centrifugation for 15 min at 4000 rpm. Under the optimum conditions i.e., pH 8.0, cloud point temperature 40 °C, [5-Br-PADAP] = 2.5 × 10⁻⁵ mol l⁻¹, [Triton X-114] = 0.05%, added methanol volume = 0.15 ml, pre-concentration of only 10 ml sample permitted an enhancement factor of 50-fold. The lower limit of detection (LOD) obtained under the optimal conditions was 0.08 μg l⁻¹. The precision for 10 replicate determinations at 5 μg l⁻¹ Pb was 2.8% relative standard deviation (R.S.D.). The calibration graph using the pre-concentration system for lead was linear with a correlation coefficient of 0.9984 at levels near the detection limits up to at least 30 μg l⁻¹. The method was successfully applied to the determination of lead in water samples.     

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H₂O/CCl₄ interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H₂O/CCl₄ interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10^–6 to 2.2×10^–6 mol L^–1, with limits of determination (3) of 5.0×10^–8 to 7.0×10^–8 mol L^–1. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.