DFT and CASPT2 study on the mechanism of ethylene dimerization over Cr(II)OH+ cation

In this work, the ethylene coordination and dimerization mechanism over Cr(II)OH(+) cation were systematically investigated using density functional theory (DFT) and complete active space second-order perturbation theory (CASPT2). It was found that Cr(II)OH(+) cation can coordinate with up to four ethylene molecules which gives seven possible stable Cr(II)OH(+)·(C(2)H(4))(n) (n = 1-4) π-complexes. We investigated whether ethylene dimerization over Cr(II)OH(+) cation proceeds through either a carbene mechanism or a metallacycle mechanism. The potential energy surfaces were characterized using four different functionals (M06L, BLYP, B3LYP, and M06). It was found that the potential energy profiles calculated at the M06 level agreed well with the CASPT2 energy profiles. Since the intermediates involved in the proposed catalytic cycles showed different ground spin states, a reaction pathway involving a spin crossing between two potential energy surfaces was observed. The minimum-energy crossing points (MECPs) that connect the two potential energy surfaces were successfully located. The two-state metallacycle reaction pathway with the formation of chromacyclopentane as the rate-determining step was found to be energetically more favorable than the carbene reaction pathway. 1-Butene was formed from the chromacyclopentane by a two-step reductive elimination pathway through a chromium(IV) hydride intermediate.     

Semiconductor quantum dots photosensitizing release of anticancer drug

A new photo-controlled anticancer drug release system is reported based on the photo-induced electron transfer (PET) between semiconductor quantum dots (QDs) and N-methyl-4-picolinium (NAP) ester 1 under the excitation of visible light.     

Crystalline ZnO thin film by hydrothermal growth

In this work, we have successfully synthesised ZnO crystal thin film with a high quality from hydrothermal reaction on sapphire substrate. The growth mechanism is clarified based on an extensive XTEM study. In addition, electrical and optical properties of the crystal thin film, which can be controlled by impurities, are characterized. The synthesis technique provides fairly high quality and cost-effective substrates for optoelectronic and renewable energy applications.     

Selective supramolecular assembly of multifunctional ligands on a Cu(111) surface: metallacycles, propeller trimers and linear chains

We studied the supramolecular assembly of a multifunctional ligand, cis-bis-terpyridine tetraphenyl ethylene, on a Cu(111) surface by low-temperature scanning tunneling microscopy (STM). Three distinctive supramolecular structures, metallacycles, propeller-shaped clusters and extended linear chains, are formed under specific assembly conditions owing to different inter-molecular binding modes of Cu-coordination, van der Waals interaction and hydrogen bonding, respectively.     

Three-dimensional WO3 nanostructures on carbon paper: photoelectrochemical property and visible light driven photocatalysis

Three-dimensional (3D) WO(3) nanostructures were grown on carbon paper by a catalyst-free high temperature reactive vapor deposition process, which exhibit a good photoelectrochemical property and visible light driven photocatalytic performance.     

Wetting behavior of spherical nanoparticles at a vapor-liquid interface: a density functional theory study

The wetting behavior of spherical nanoparticles at a vapor-liquid interface is investigated by using density functional theory, and the line tension calculation method is modified by analyzing the total energy of the vapor-liquid-particle equilibrium. Compared with the direct measurement data from simulation, the results reveal that the thermodynamically consistent Young's equation for planar interfaces is still applicable for high curvature surfaces in predicting a wide range of contact angles. The effect of the line tension on the contact angle is further explored, showing that the contact angles given by the original and modified Young's equations are nearly the same within the region of 60° < θ < 120°. Whereas the effect is considerable when the contact angle deviates from the region. The wetting property of nanoparticles in terms of the fluid-particle interaction strength, particle size, and temperature is also discussed. It is found that, for a certain particle, a moderate fluid-particle interaction strength would keep the particle stable at the interface in a wide temperature range.     

Which mechanism operates in the electron-transfer process at liquid/liquid interfaces?

We present a more general expression for the relationship of potential dependence, which implies that a change in the interfacial drop across the interface has little effect on the free energy of the reaction, but mainly affects the surface concentration of reactant in each phase. Abundant experimental results from several well-known groups are analyzed in great detail to confirm our conclusion. At the same time, we define a new parameter named Frumkin correction factor to describe this relationship of potential dependence, which expresses the thermodynamic effect of double diffuse layers within both phases in contrast with the so often suggested kinetic electron-transfer (ET) coefficient; we also find that it depends on two intimately related aspects: the charges of reactive species and the ratio of the diffuse layer potential to the total potential within each phase, so it is quite arbitrary to ignore the diffuse layer effect in the aqueous phase just because of its relatively small values. In addition, a fascinating question on the inverted region at liquid/liquid interfaces has been successfully interpreted by an opposite surface concentration effect, which was often considered as a kinetic Marcus inverse by most groups.     

Multiplex digital PCR: breaking the one target per color barrier of quantitative PCR

Quantitative polymerase chain reactions (qPCR) based on real-time PCR constitute a powerful and sensitive method for the analysis of nucleic acids. However, in qPCR, the ability to multiplex targets using differently colored fluorescent probes is typically limited to 4-fold by the spectral overlap of the fluorophores. Furthermore, multiplexing qPCR assays requires expensive instrumentation and most often lengthy assay development cycles. Digital PCR (dPCR), which is based on the amplification of single target DNA molecules in many separate reactions, is an attractive alternative to qPCR. Here we report a novel and easy method for multiplexing dPCR in picolitre droplets within emulsions-generated and read out in microfluidic devices-that takes advantage of both the very high numbers of reactions possible within emulsions (>10(6)) as well as the high likelihood that the amplification of only a single target DNA molecule will initiate within each droplet. By varying the concentration of different fluorogenic probes of the same color, it is possible to identify the different probes on the basis of fluorescence intensity. Adding multiple colors increases the number of possible reactions geometrically, rather than linearly as with qPCR. Accurate and precise copy numbers of up to sixteen per cell were measured using a model system. A 5-plex assay for spinal muscular atrophy was demonstrated with just two fluorophores to simultaneously measure the copy number of two genes (SMN1 and SMN2) and to genotype a single nucleotide polymorphism (c.815A>G, SMN1). Results of a pilot study with SMA patients are presented.