Insight into on-wafer crystallization of pure-silica-zeolite films through nutrient replenishment

Tetraethylorthosilicate (TEOS) is added to a pure-silica-zeolite MEL nanoparticle suspension and the mixture is subsequently used for preparing spin-on low-dielectric constant (low-k) films. The films are then characterized by ellipsometric porosimetry, transmission electron microscopy (TEM), and nanoindentation. Investigation into the film microstructure indicates that the addition of TEOS significantly increases the fraction of the crystalline domains, decreases the inter-crystal mesopore size, and narrows the pore size distribution. Films with 12% TEOS loading have a mean pore size distribution centered at 3.5 nm (diameter) with a full width at half maximum (fwhm) of 0.8 nm, while those with no TEOS have a distribution at 11.1 nm and fwhm of 7.9 nm. At 12% TEOS loading, the reduced modulus and hardness are 11.0 and 1.12 GPa, respectively; without TEOS, the values are 6.4 and 0.57 GPa.     

New opportunities in crystal engineering - the role of atomic force microscopy in studies of molecular crystals

Here, we highlight recent research involving atomic force microscopy investigations of molecular crystals, and focus particularly on the latest relevant advances in our knowledge of crystal-growth mechanisms and structure-property relationships in organic crystals. This brief survey features the importance of incorporating AFM into solid-state research as an essential tool for the informed design and construction of crystalline materials.     

2.2]Paracyclophane as a bridging unit in the design of organic dyes for sensitized solar cells

Organic dyes consisting of a [2.2]paracyclophane unit along the main chromophore are examined for their application in sensitized solar cells. These materials exhibit considerably high values of open-circuit voltage (V(oc)) ranging 0.69-0.72 V, and an overall efficiency up to 3.8%.     

Luminescent organogold(III) complexes with long-lived triplet excited states for light-induced oxidative C-H bond functionalization and hydrogen production

All that glitters is gold: highly phosphorescent gold(III) complexes with extended π-conjugated cyclometalating ligands exhibit rich photophysical and photochemical properties. They act as efficient photocatalysts/photosensitizers for oxidative functionalizations of secondary and tertiary benzylic amines and homogeneous hydrogen production from a water/acetonitrile mixture.     

Aminoglycosides modified by resistance enzymes display diminished binding to the bacterial ribosomal aminoacyl-tRNA site

Understanding the basic principles that govern RNA binding by aminoglycosides is important for the design of new generations of antibiotics that do not suffer from the known mechanisms of drug resistance. With this goal in mind, we examined the binding of kanamycin A and four derivatives (the products of enzymic turnovers of kanamycin A by aminoglycoside-modifying enzymes) to a 27 nucleotide RNA representing the bacterial ribosomal A site. Modification of kanamycin A functional groups that have been directly implicated in the maintenance of specific interactions with RNA led to a decrease in affinity for the target RNA. Overall, the products of reactions catalyzed by aminoglycoside resistance enzymes exhibit diminished binding to the A site of bacterial 16S rRNA, which correlates well with a loss of antibacterial ability in resistant organisms that harbor these enzymes.     

Two-channel microelectrochemical bipolar electrode sensor array

We report a two-channel microelectrochemical sensor that communicates between separate sensing and reporting microchannels via one or more bipolar electrodes (BPEs). Depending on the contents of each microchannel and the voltage applied across the BPE, faradaic reactions may be activated simultaneously in both channels. As presently configured, one end of the BPE is designated as the sensing pole and the other as the reporting pole. When the sensing pole is activated by a target, electrogenerated chemiluminescence (ECL) is emitted at the reporting pole. Compared to previously reported single-channel BPE sensors, the key advantage of the multichannel architecture reported here is physical separation of the ECL reporting cocktail and the solution containing the target. This prevents chemical interference between the two channels.     

A Bidirectional S(E)' Strategy for 1,5-syn and 1,5-anti Stereocontrol toward the Synthesis of Complex Polyols

Studies report a bidirectional S(E)' strategy applicable for the stereocontrolled synthesis of nonracemic 1,5-syn and 1,5-anti diols and their derivatives. Nonracemic 1,3,2-diazaborolidine auxiliaries are incorporated by chemoselective tin-boron exchange to provide reactive allylic boranes. The convergent pathway utilizes sequential reactions with two aldehydes producing stereochemical outcomes from cyclic, closed, and open transition state preferences, respectively. Synthesis of fragment 16 of peloruside A is accomplished in four steps from readily available aldehydes 9 and 13.     

Source apportionment of atmospheric particulate carbon in Las Vegas,Nevada,USA

A study was conducted to quantify wintertime contributions of source types to carbonaceous PM_2.5 at four urban sites in the Las Vegas Valley,one of the most rapidly growing urban areas in the southwestern United States.Twenty-four hour average ambient samples were collected for mass,ions,elements,organic carbon（OC）,elemental carbon（EC）,and trace organic markers analysis.Additional measurements were made to determine diurnal patterns in light-absorbing black carbon（BC） as a marker for combustion sources.Carbonaceous PM sources of on-road gasoline vehicles,on-road diesel vehicles,and off-road diesel engines were characterized with their chemical profiles,as well as fuel-based emission factors, using an In-Plume Sampling System.The Effective Variance Chemical Mass Balance（EV-CMB） source apportionment model was applied to the ambient samples collected,using source profiles developed in this study as well as profiles from other relevant studies.Four main sources contributed to PM_2.5 carbon within the Las Vegas Valley:（1） paved road dust,（2） on-road gasoline vehicles,（3） residential wood combustion,and（4） on-road diesel vehicles.CMB estimated that on-road mixed fleet gasoline vehicles are the largest source for OC and EC at all the sites.The contribution of paved road dust to both OC and EC was 5-10%at the four sites.On-road diesel vehicles contribute 22%of the OC and 34%of the EC at a site near the city center,which is located immediately downwind of a major freeway.Residential wood combustion is a more important source than on-road diesel vehicles for two residential neighborhood sites.These results are consistent with our conceptual model,and the research methodology may be applied to studying other urban areas.     

基于单一分光棱镜干涉仪的双通路定量相位显微术

仅仅使用一个单独的分光棱镜(BS),实现了一种用于生物细胞三维成像的双通路定量相位显微术.不同于传统的使用方法,将BS倾斜放置,使中央半反射层与入射光光轴之间存在一个非常小的角度.这样基于BS的分光特性,经过BS后的透射光束和反射光束将会叠加在一起并形成干涉.调节样品位置,利用相机拍摄同时获得了存在π相移的双通路干涉图.这种离轴干涉模式,只需要记录单幅干涉图就可以获得真实的相位信息,方法结构简单,易于操作,适用于微小透明样品的三维形貌测量.