Light activated patterning of dye-labeled molecules on surfaces

This Communication describes a novel method for patterning proteins, ligands, or other organic/inorganic species onto solid substrates. The process works by linking the moiety of interest to a fluorophore that can be subsequently photobleached and bound to the interface. The technique can be performed in aqueous solution and allows several species to be addressed onto the surface simultaneously by using different frequencies of light. Because the method can be used with fluorophores excited by visible light, shorter and more damaging wavelengths can be avoided.     

稀土氧化物对中高碳钢堆焊金属中夹杂物变质作用的热力学分析

采用热力学方法,研究了稀土氧化物对中高碳钢堆焊金属中夹杂物的变质作用。夹杂物生成的热力学分析表明,在堆焊熔池中,稀土氧化物可以被碳还原成稀土元素,稀土元素可以与氧、硫生成稀土氧化物、稀土硫化物和稀土硫氧化物,从而达到脱氧、脱硫、净化堆焊熔池的作用;稀土氧化物还可以直接与硫作用,生成稀土硫氧化物,起到脱硫的效果。     

Efficient computation of the first passage time distribution of the generalized master equation by steady-state relaxation

The generalized master equation or the equivalent continuous time random walk equations can be used to compute the macroscopic first passage time distribution (FPTD) of a complex stochastic system from short-term microscopic simulation data. The computation of the mean first passage time and additional low-order FPTD moments can be simplified by directly relating the FPTD moment generating function to the moments of the local FPTD matrix. This relationship can be physically interpreted in terms of steady-state relaxation, an extension of steady-state flow. Moreover, it is amenable to a statistical error analysis that can be used to significantly increase computational efficiency. The efficiency improvement can be extended to the FPTD itself by modelling it using a gamma distribution or rational function approximation to its Laplace transform.     

Isomeric characterization via ion neutralization and dissociation. Experimental variables

Major deficiencies of mass spectrometry for characterizing isomeric molecules, and of collisionally activated dissociation for characterizing isomeric ions, can be alleviated by complementary information from new techniques of neutraiization-reionization (NR) mass spectrometry. Mass data can be obtained from most fragments of the original species, irrespective of their ability to retain the charge; dissociation of fast neutrals prepared from isomeric ions can involve novel reaction pathways and can minimize competing isomerization reactions; isomeric neutrals undergoing similar dissociations can be differentiated by forming them with different internal energies; reionization of the neutral products to negative as well as positive ions can provide increased selectivity; and structural information on the resulting ions can be derived using MS/MS/MS, Dissociation by novel non-isomerization pathways can also be effected by a second addition (or subtraction) of an electron to produce an unstable ion of opposite charge. Special techniques can yield neutralized products in favorable dissociative states by collisional activation, by using neutralization targets of selected ionization energy, or through Franck-Condon factors. Optimum excitation of the neutral is important, as this should be high enough to minimize rearrangement, to maximize the differences in the dissociation pathways of isomers, and to minimize the further dissociation of the characteristic primary products of the neutral. NR experiments can, thus, also provide information on the energy surfaces for unimolecular dissociations of neutrals that are difficult to study by conventional techniques. Dissociations of the neutrals can be differentiated from those occurring after reionization by separate collisional activation of the neutrals, by changing the ionization energy of the neutralization agent, or by reionization to ions of opposite charge.     

SCTA and Adsorbents

Sample controlled thermal analysis (SCTA) can be used in several manners with respect to adsorbents. Almost 70% of adsorbent synthesis procedures involve a thermal step that can be adapted to a sample controlled method. In this respect, SCTA has been used for the preparation of activated alumina, calcination of zeolites and activation of carbons. The thermodesorption of adsorbed molecules can also be carried out using a sample controlled method. Here, both the surface area and pore volume of adsorbents can be assessed. Finally, SCTA can be highly beneficial in the thermal pretreatment of adsorbents prior to adsorption. This revised version was published online in July 2006 with corrections to the Cover Date.     

Controlling nanoparticle formation via sizable cages of supramolecular soft materials

We present a new generic strategy to fabricate nanoparticles in the "cages" within the fibrous networks of supramolecular soft materials. As the cages can be acquired by a design-and-production manner, the size of nanoparticles synthesized within the cages can be tuned accordingly. To implement this idea, both selenium and silver were chosen for the detailed investigation. It follows that the sizes of selenium and silver nanoparticles can be controlled by tuning the pore size of the fiber networks in the material. When the concentration of the gelator is high enough, monodisperse nanoparticles can be prepared. More interestingly, the morphology of the nanoparticles can be altered: silver disks can be formed when the concentrations of both the gelator and silver nitrate are sufficiently low. As the fiber network serves as a physical barrier and semisolid support for the nanoparticles, the stability in the aqueous media and the ease of application of these nanoparticles can be substantially enhanced. This robust surfactant-free approach will not only allow the controlled fabrication of nanoparticles, but also can be applied to the fabrication of composite materials for robust applications.     

表面能与晶体生长/溶解动力学研究的新动向

界面现象使物质在结晶过程中出现了临界现象.但最近的研究指出在物质溶解过程中,在表面能量的控制下也存在着临界现象以及尺寸效应.实验发现,当晶体自身小到一 定的程度时(通常在纳米尺度上并和临界蚀坑的大小相近),在溶解过程中其速度会自发降 低,反应被抑制乃至停止.尽管在热力学上表面能的因素可以赋予小颗粒晶体较大的溶解度 ,但表面能却也能通过对临界条件的控制而使这些微粒在动力学上不被溶解.这个发现不仅 解决了纳米颗粒在水溶液中稳定性的问题,而且还从动力学的角度解释了生物矿物选择纳米 尺度作为其基本构成单元的原因.由于表面能和晶体生长/溶解的动力学有着密切的关系, 我们可以通过对表面能的调节来修改它们的动力学速度和晶体的形貌.反过来,也可以用动力学的方法来测定表面能及表面吸附/脱附常数等.相对于常规的界面研究手段,通过生 长和溶解动力学途径所得的数据有着很好的可靠性及重复性.我们认为,晶体生长和溶解的 动力学和表面能的研究相结合,不仅为界面研究提供了新的思路和方法,而且也会推动晶体生长和材料科学的发展.     

Bulk synthesis of polymer-inorganic colloidal clusters

We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry.     

电化学噪声测量分析系统设计与实现

根据电化学噪声原理,利用微机技术设计实现了电化学噪声测量分析系统。该系统具有高灵敏度,自动选择量程,多回路自动测量,可调整采样参数等功能,并在时／频域内对所测量的电化学噪声进行分析。     

Evaluating changes of writhe in computer simulations of supercoiled DNA

We compute changes in the writhe of a polygonal space curve when one of the vertices is displaced. The resulting expressions can be used in simulations of supercoiled DNA. For Brownian dynamics simulations, the expressions can be used to eliminate the explicit twisting degree of freedom. For Monte Carlo simulations, they can be used in fast local moves. Preliminary Monte Carlo simulations using only such fast local moves show that these can be used to efficiently simulate small DNA supercoils.     

Separation of different forms of transferrin by isoelectric focusing to detect effects on the liver caused by xenobiotics

Several genetic variants and also isoforms of transferrin differing in carbohydrate structure can be separated by polyacrylamide or agarose gel isoelectric focusing. Numerous blood plasma or serum samples can be analyzed in parallel in each gel. Studies of the heterogeneity of transferrin have already revealed many results of importance to different fields of human medicine. Gene typing can give important and useful information for paternity determination and in forensic medicine. The gene type C 2 seems to have increased frequency in certain malfunctions. Futhermore, functional abnormalities of liver cells can be revealed by determination of the concentrations of transferrin isoforms differing mainly in their carbohydrate parts. The isoforms can be quantified with zone immunoelectrophoresis assay. Thus valuable information can be obtained about important modulated regulations of cell and membrane functions, even when these are disturbed by disease and xenobiotics. The information may be useful e.g. in the detection of individuals suffering from toxic effects, to identify toxic agents and exposure conditions. Studies of house painters revealed that exposure to different types of paints had an effect on transferrin. Determination of the concentration of the isotransferrin with pI 5.7 in blood samples from alcoholics can be used as a marker for the detection of liver dysfunction and for the monitoring of therapy treatments. In addition, by analyzing the isotransferrins a rare genetic abnormality can be detected.     

Slow diffusion by singlet state NMR spectroscopy

Small diffusion coefficients can be measured by using populations of singlet states that have a relaxation time constant, T(s), which can be much longer than the longitudinal relaxation time, T1. Spatial information can be encoded with pulsed field gradients in the manner of stimulated echo sequences. Singlet states can be excited via double-quantum coherences to enhance the efficiency of phase encoding and decoding.     

A method for the determination of technetium in environmental waters

A method is described which can be used to determine technetium-99 levels in a range of water types. Ruthenium isotopes which may interfere in the analysis are removed from the sample by precipitation before concentration of pertechnetate onto an ion-exchange column. Other nuclides can be removed from the column using NaOH before elution of the technetium using NaSCN. The technetium in the NaSCN eluent can then be extracted into butan-2-one which can be evaporated onto a planchette. Technetium-99m is used as a yield tracer and after this has decayed away to negligible levles the amount of technetium on the planchette can be determined by measuring the rate of beta radiation emission from the final concentrate.     

Self-assembled cyclodextrin nanoparticles and drug delivery

Drug/cyclodextrin complexes self-assemble in aqueous solutions to form nanosized aggregates or nanoparticles. These complex aggregates are responsible for many of the physicochemical and biological properties of cyclodextrin complexes. Due to the aggregate formation aqueous drug/cyclodextrin solutions can behave more like dispersed nanoscale systems, such as nano-suspensions and liposomes, rather than true solutions. The aggregation can result in enhanced cyclodextrin solubilization of poorly soluble lipophilic drugs; they can serve as building blocks for ternary or higher order complexes; they can be developed into nano- and microparticulated drug carriers for targeted drug delivery to, for example, hair follicles; they can be developed into sustained drug delivery systems; and they can possible be used as mucus-penetrating drug delivery vectors. All of this can be obtained without chemical modifications of the cyclodextrin monomers.     

Development of beta-keto 1,3-dithianes as versatile intermediates for organic synthesis

beta-Keto 1,3-dithianes can be generated by the double conjugate addition of dithiols to propargylic ketones, esters and aldehydes in excellent yields. As masked 1,3-dicarbonyl systems these substrates can be converted to a range of functionalised oxygen-containing heterocycles that can be used in natural product synthesis.     

Enhancing the information content of vibrational spectra through sample perturbation

Infrared and Raman band frequencies, intensities and line shapes are often sensitive to the local molecular environment determined by molecular conformation, surrounding matrix, temperature, pressure, etc. The variety of local environments experienced by a condensed-phase molecule can lead to vibrational spectra with broad bands containing many overlapped spectral features. The spectral resolution of these overlapped features can be enhanced by making perturbations to the sample environment. Examples of perturbations which can be applied to the sample to enhance the information content of infrared spectra are changes in temperature, concentration and mechanical strain. In each instance, the spectra obtained as a function of the perturbation can be cross-correlated to produce a two-dimensional correlation map defined by two independent wavenumber axes. in this representation, infrared bands which respond to the perturbation in a similar or different manner can be clearly identified. This information can be used to help resolve overlapped bands and make unambiguous band assignments.     

A simple, user-friendly process for the homologation of aldehydes using tosylhydrazone salts

Aldehydes can be homologated to ketones in moderate to good yields using aryldiazomethanes generated in situ from tosylhydrazones. Chiral aldehydes can be employed with almost complete retention of configuration. The tosylhydrazones can also be generated in situ from the corresponding aldehyde leading to a one-pot process for coupling two different carbonyl compounds to give ketones.     

From the one-bead-one-compound concept to one-bead-one-reactor

The one-bead-one-compound method gives access to millions of compounds that can be screened directly on the bead. Although characterization techniques are increasingly potent and reliable, problems can still be encountered in deciphering the sequence of the active compound because of sensitiveness or manipulation of the bead. ChemMatrix, a totally PEG-based resin, has resolved the synthesis of peptides of outstanding difficulty. Like other PEG-based resins, it permits on-bead screening because of its compatibility in aqueous media and has the further advantage of having a high loading, comparable to polystyrene resins. ChemMatrix beads previously swelled in water can be nicely divided into four parts that can be characterized using different analytical techniques or just stored for safety or for further testing. The four bead parts show high homogeneity and can thus be considered to be replicas.     

Microcapillary electrophoresis chips utilizing controllable micro-lens structures and buried optical fibers for on-line optical detection

In this study, a new design of a controllable micro-lens structure capable of the enhancement of LIF detection system has been demonstrated, which can be further integrated with buried optical fibers on a micro-CE chip for sample separation and detection. Two pneumatic side-chambers were placed between a micro-CE channel and an optical fiber channel. The intervals between the side-chamber and the microchannel were used to form two surfaces of the controllable micro-lens structure. Deformations of the two surfaces can be generated after pressurized index-matching fluid was injected into the pneumatic side-chambers. The side-chambers can be deflected as a double convex lens to focus both the excitation light source and the fluorescent emission signal. The profile and the focal length of the micro-lens structure can be actively adjusted by applying different liquid pressures so that biosamples with a low concentration can be detected. Using low-cost polymeric materials such as polydimethylsiloxane, rapid and reliable fabrication techniques involving standard lithography and replication process was employed for the formation of the proposed chip device. Experimental results revealed the controllable micro-lens structure can be successfully deformed as a convex lens to focus the laser light source and the collected fluorescence signal can be enhanced accordingly. The power amplitude of excitation laser light can be enhanced by 5.4-fold. FITC dye and DNA markers were then utilized for micro-CE testing. The results indicated that the signal amplitude could be enhanced 2.5-fold when compared to the case without the activation of the micro-lens. According to the experimental results, the developed device has a great potential to be integrated with other microfluidic devices for further biomedical applications.     

Results of computerization and automation of a Perkin-Elmer 240 carbon-hydrogen-nitrogen analyzer

These results indicate that a C, H, and N system can be automated and computerized for increased flexibility while maintaining a high degree of accuracy and precision. There are a number of significant advantages which can be realized in terms of hard-copy summaries, report formats that can be torn off and sent out, and tube files that can be used to summarize which samples are currently being run. There are some drawbacks in the fact that specialty runs must be made for high nitrogen-containing compounds, liquids, and hydroscopic materials. However, the time saving is substantial, and the analyst has blocks of time to run other determinations. Satisfactory turn-around times can be maintained. This indicates that the automation and computerization are well worth the efforts.