Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

Novel epimerization of aromatic C-nucleosides with electron-withdrawing substituents with trifluoroacetic acid-benzenesulfonic acid using mild conditions

Trifluoroacetic acid and benzenesulfonic acid in dichloromethane at ambient temperature have been found to be efficient co-catalysts for the epimerization of C-nucleosides with electron-withdrawing substituents. This approach provides a convenient route to the β anomer of the nucleosides with high yields in the range 54-78%. Synthesis of the 3′-phosphoramidite of 2,4-difluorophenyl C-nucleoside suitable for solid-phase DNA synthesis is described.     

JT-60U装置温度分布剖面不变性的实验研究

在一系列H模放电条件下，建立了一个旨在研究等离子体温度分布剖面不变性的数据库。介绍了数据库建立过程中要解决的关键问题和所用软件，对等离子体温度分布剖面不变性及芯部约束与边缘参数的关系进行了研究。     

Physangulidines A, B, and C: three new antiproliferative withanolides from Physalis angulata L

Bioassay-directed fractionation of the whole plant of Physalis angulata L. afforded three new antiproliferative withanolides with an unusual carbon framework: physangulidines A (1), B (2), and C (3). Structures of the three isomeric withanolides were determined by a combination of HRMS, NMR spectroscopic, and X-ray crystallographic methods. Each has shown significant antiproliferative activity against DU145 prostate cancer cells. Physangulidine A (1) was further tested against a wide range of additional cancer cell lines and found to exhibit significant antiproliferative activity.     

Efficient epimerization of pyrene and other aromatic C-nucleosides with trifluoroacetic acid in dichloromethane

Trifluoroacetic acid has been found to be an efficient and non-oxidative catalyst for the epimerization of pyrene and other C-nucleosides in dichloromethane at ambient temperature. Aspects of the epimerization mechanism are also elucidated.     

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology.Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1-3.5) and their orientation on oil droplet formation.Increasing the membrane rotation speed decreased the droplet size,and the oil droplets produced were more uniform using slotted pores as compared to circular geometry.At a given rotation speed,the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity).The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity.At a given pore fluid velocity and rotation speed,pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores.This work indicates practical benefits in the use of slotted membranes over conventional methods.     

The catalytic power of uracil DNA glycosylase in the opening of thymine base pairs

Uracil DNA glycosylase (UNG) locates uracil and its structural congener thymine in the context of duplex DNA using a base flipping mechanism. NMR imino proton exchange measurements were performed on free and UNG-bound DNA duplexes in which a single thymine (T) was paired with a series of adenine analogues (X) capable of forming one, two, or three hydrogen bonds. The base pair opening equilibrium for the free DNA increased 55-fold as the number of hydrogen bonds decreased, but the opening rate constants were nearly the same in the absence and presence of UNG. In contrast, UNG was found to slow the base pair closing rate constants (kcl) compared to each free duplex by a factor of 3- to 23-fold. These findings indicate that regardless of the inherent thermodynamic stability of the TX pair, UNG does not alter the spontaneous opening rate. Instead, the enzyme holds the spontaneously expelled thymine (or uracil) in a transient extrahelical sieving site where it may partition forward into the enzyme active site (uracil) or back into the DNA base stack (thymine).     

Predicting thermal conductivity of liquid suspensions of nanoparticles (nanofluids) based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles (nanofluids) based on rheology.The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively,which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids.The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol.And the modified Hamilton-Crosser equation successfully predicted the effective thermal conductivity of the nanofluids.     

Uracil-directed ligand tethering: an efficient strategy for uracil DNA glycosylase (UNG) inhibitor development

Uracil DNA glycosylase (UNG) is an important DNA repair enzyme that recognizes and excises uracil bases in DNA using an extrahelical recognition mechanism. It is emerging as a desirable target for small-molecule inhibitors given its key role in a wide range of biological processes including the generation of antibody diversity, DNA replication in a number of viruses, and the formation of DNA strand breaks during anticancer drug therapy. To accelerate the discovery of inhibitors of UNG we have developed a uracil-directed ligand tethering strategy. In this efficient approach, a uracil aldehyde ligand is tethered via alkyloxyamine linker chemistry to a diverse array of aldehyde binding elements. Thus, the mechanism of extrahelical recognition of the uracil ligand is exploited to target the UNG active site, and alkyloxyamine linker tethering is used to randomly explore peripheral binding pockets. Since no compound purification is required, this approach rapidly identified the first small-molecule inhibitors of human UNG with micromolar to submicromolar binding affinities. In a surprising result, these uracil-based ligands are found not only to bind to the active site but also to bind to a second uncompetitive site. The weaker uncompetitive site suggests the existence of a transient binding site for uracil during the multistep extrahelical recognition mechanism. This very general inhibitor design strategy can be easily adapted to target other enzymes that recognize nucleobases, including other DNA repair enzymes that recognize other types of extrahelical DNA bases.