Imaging the pair-correlated excitation function: The F+CH4-->HF(v')+CH3(nu=0) reaction

The velocity map ion imaging technique was applied to measure the reaction excitation function for the first time. It was found that the "raw" excitation function was significantly distorted by the density-to-flux transformation of the title reaction. Through a systematic investigation, possible reasons for such a dramatic effect are outlined. In addition, the state-resolved, pair-correlated excitation functions and branching ratios are presented. Effects of imperfect time slicing in the time-sliced velocity imaging technique in general are also discussed.     

Organotransition-Metal Complexes of Multidentates 1. Synthesis and Characterization of N,N-Bis(Pyrazol-1-Ylmethyl)Aminomethane and N,N-Bis(3, 5-Dimethylpyrazol-1-Ylmethyl)-Aminomethane Derivatives of the Group VI Metal Carbonyls

N, N-bis(pyrazol-1-ylmethyl)aminomethane (bpam) and N, N-bis(3, 5-dimethylpyrazol-1-ylmethyl)aminomethane (bdmpam) reacted with M(CO)₆ or M(CO)₃(CH₃CN)₃ in acetonitrile to give respectively fac-(bpam)M(CO)₃ and fac-(bdmpam)M(CO)₃ in good yields (M=Cr, Mo, W). These complexes are characterized by elemental analysis, IR, and NMR and compared with the related polypyrazolylborate complexes of the group VI metal carbonyls.     

Effects on the normalized Laplacian spectral radius of non-bipartite graphs under perturbation and their applications

The normalized Laplacian eigenvalues of a network play an important role in its structural and dynamical aspects associated with the network. In this paper, we consider how the normalized Laplacian spectral radius of a non-bipartite graph behaves by several graph operations. As an example of the application, the smallest normalized Laplacian spectral radius of non-bipartite unicyclic graphs with fixed order is determined.     

Organotransition-Metal Complexes of Multidentates 2. Synthesis and Allyl Bromination of N,N-Bis(3,5-Dimethylpyrazol-1-YL)Methane Derivatives of the Group VI Metal Carbonyls

N,N-Bis(3,5-dimethylpyrazol-1-yl)methane (H₂CPz'₂) reacts with the hexacarbonyls of chromium, molybdenum, and tungsten to give cis-(H₂CPz'₂)M(CO)₄ derivatives with M=Cr, Mo, W. The direct allyl bromination of these complexes is also investigated and only the molybdenum complex is converted into (H₂CPz'₂)Mo(CO)₂(π-C₃H₃)(Br).     

Microfluidic chip for fast nucleic acid hybridization

The design and experimental verification of a fast nucleic acid hybridization microchip using the fluidic velocity and strain rate effects was conducted. This hybridization chip was able to increase the hybridization signal 6-fold, reduce non-specific target-probe binding and background noise within 30 min, as compared to conventional hybridization methods, which may take from 4 h to overnight. Excellent correlation between experimental results and simulation analysis was obtained in this study. A detailed study of a newly designed microfluidic chip for enhancing hybridization was conducted. Three different designs of devices were fabricated and tested. Two different lengths of targets, 25-mer oligonucleotide and 1.4 kb ssDNA, were tested in this study. The hybridization efficiency can be improved by introducing velocity and extensional strain rate to the sample. This study demonstrates that the signal in the proposed method exhibits intensities 6-fold higher than those in static conditions. The necessary time for the hybridization process can be reduced from overnight to 30 min using the methods developed in this study. Experimental results also show that the strain rate provides stronger effect on hybridization than that of velocity. Combining hybridization with microfluidic concepts of velocity and strain rate effects may provide additional specificity and efficiency in nucleic acid detection and genomic study. This microfluidic hybridization chip can provide potential application in genomic study.     

Actively controlled self-assembly of colloidal crystals in microfluidic networks by electrocapillary forces

We report a simple approach to actively control the formation of the self-assembled colloidal crystals in the microfluidic networks using a combination of electrocapillary forces and evaporation-induced self-assembly. Using this scheme, we can not only selectively fabricate the colloidal crystals in the desired channels, but we can also build colloidal crystals with different optical properties in different channels or in the same channel.     

Vacuum sampling in the landscape during inflation

We consider the phenomenological consequences of sampling multiple vacua during inflation motivated by an enormous landscape. A generic consequence of this sampling is the formation of domain walls, characterized by the scale mu of the barriers that partition the accessed vacua. We find that the success of big bang nucleosynthesis (BBN) implies mu > or = 10 TeV, as long as the sampled vacua have a nondegeneracy larger than O(MeV4). Otherwise, the walls will dominate and eventually form black holes that must reheat the universe sufficiently for BBN to take place; in this case, we obtain mu > or = 10(-5)MP. These black holes are not allowed to survive and contribute to cosmic dark matter density.     

A solution study on the local and global structure changes of cytochrome c: an unfolding process induced by urea

The local and global structural changes of cytochrome c induced by urea in aqueous solution have been studied using X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS). According to the XAS result, both the native (folded) protein and the unfolded protein exhibit the same preedge features taken at Fe K-edge, indicating that the Fe(III) in the heme group of the protein maintains a six-coordinated local structure in both the folded and unfolded states. Furthermore, the discernible differences in the X-ray absorption near-edge structure (XANES) of these two states are attributed to a possible spin transition of the Fe(III) from a low-spin state to a high-spin state during the unfolding process. The perseverance of six-coordination and the spin transition of the iron are reconciled by a proposed ligand exchange, with urea and water molecules replacing the methionine-80 and histidine-18 axial ligands, respectively. The SAXS result reveals a significant morphology change of cytochrome c from a globular shape of a radius of gyration R(g) = 12.8 A of the native protein to an elongated ellipsoid shape of R(g) = 29.7 A for the unfolded protein in the presence of concentrated urea. The extended X-ray absorption fine structure (EXAFS) data unveil the coordination geometries of Fe(III) in both the folded and unfolded state of cytochrome c. An initial spin transition of Fe(III) followed by an axial ligand exchange, accompanied by the change in the global envelope, is proposed for what happened in the protein unfolding process of cytochrome c.     

A Novel Inorganic Clathrate Generated through Arene‐Arene Interactions

The direct mixing of CoCl₂, sodium 2,6‐pyridinedicarboxylate (Na₂(2,6‐pda)), KSCN, and 1,2‐bis(4‐pyridyl)ethane (bpye) in water at the ambient temperature afforded purple crystals readily. The crystal structure, as determined by X‐ray diffraction crystallography, consists of discrete inorganic [Co₂(η³‐2,6‐pda)₂(μ‐SCN)₂(H₂O)₂] and organic bpye molecules. Adjacent dicobalt molecules are connected via intermolecular hydrogen bonds, to form one‐dimensional hydrophobic channels in the solid state, which serve as a host framework to incarcerate bpye guests inside. Every organic molecule attaches to four adjacent inorganic species via arene‐arene interactions. The facile approach in assembling the dicobalt and bpye molecules together into an inorganic clathrate is demonstrated.     

On Theoretical Study of a Molecular Dimer System

In this paper, the vibronic structure of a dimer system is studied both theoretically and numerically. To construct adiabatic potential surfaces and electronic and vibrational wave functions for a dimer system, the adiabatic approximation is applied to two identical molecules, each of which has two electronic states with one vibrational mode. In this scheme, the excitonic splitting results not only from the electronic coupling of two molecules, but also from the vibronic coupling in each molecule. By using the resulting wavefunctions and the corresponding energies, the absorption and fluorescence spectra are studied. The effect of temperature on these spectra is also studied.