Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j')

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j') are calculated using the time dependent channel packet method (CPM). The calculation employs 1 2A', 2 2A', and 1 2A" adiabatic electronic potential energy surfaces determined by numerical computation at the multireference configuration-interaction level [M. H. Alexander, J. Chem. Phys. 99, 6041 (1993)]. The 1 2A' and 2 2A', adiabatic electronic potential energy surfaces are transformed to yield diabatic electronic potential energy surfaces that, when combined with the total B+H2 rotational kinetic energy, yield a set of effective potential energy surfaces [M. H. Alexander et al., J. Chem. Phys. 103, 7956 (1995)]. Within the framework of the CPM, the number of effective potential energy surfaces used for the scattering matrix calculation is then determined by the size of the angular momentum basis used as a representation. Twenty basis vectors are employed for these calculations, and the corresponding effective potential energy surfaces are identified in the asymptotic limit by the H2 rotor quantum numbers j=0, 2, 4, 6 and B electronic states 2Pja, ja=1/2, 3/2. Scattering matrix elements are obtained from the Fourier transform of the correlation function between channel packets evolving in time on these effective potential energy surfaces. For these calculations the H2 bond length is constrained to a constant value of req=1.402 a.u. and state to state scattering matrix elements corresponding to a total angular momentum of J=1/2 are discussed for j=0<-->j'=0,2,4 and 2P1/2<-->2P1/2, 2P3/2 over a range of total energy between 0.0 and 0.01 a.u.     

A microfluidic device for whole-animal drug screening using electrophysiological measures in the nematode C. elegans

This paper describes the fabrication and use of a microfluidic device for performing whole-animal chemical screens using non-invasive electrophysiological readouts of neuromuscular function in the nematode worm, C. elegans. The device consists of an array of microchannels to which electrodes are attached to form recording modules capable of detecting the electrical activity of the pharynx, a heart-like neuromuscular organ involved in feeding. The array is coupled to a tree-like arrangement of distribution channels that automatically delivers one nematode to each recording module. The same channels are then used to perfuse the recording modules with test solutions while recording the electropharyngeogram (EPG) from each worm with sufficient sensitivity to detect each pharyngeal contraction. The device accurately reported the acute effects of known anthelmintics (anti-nematode drugs) and also correctly distinguished a specific drug-resistant mutant strain of C. elegans from wild type. The approach described here is readily adaptable to parasitic species for the identification of novel anthelmintics. It is also applicable in toxicology and drug discovery programs for human metabolic and degenerative diseases for which C. elegans is used as a model.     

Conformations of laulimalide in DMSO-d6

Laulimalide is one of the newest naturally occurring macrolides known to act as a microtubule stabilizing agent with properties similar to Taxol. It also stands as being one of the most flexible with 18 rotatable bonds. This large number of rotatable bonds allows for approximately 3(18) potential conformers. To examine the conformational energy surface of laulimalide, we have performed an NAMFIS deconvolution analysis for laulimalide in DMSO-d6. The latter has been supplemented with a post-NAMFIS energy analysis at the Becke3LYP/6-31G level that examines the opposing effects of internal hydrogen bonding and syn-pentane interactions. In this way, we have identified 15 laulimalide conformations that can be classified into 5 different families: Supine, Convex, Cobra, Stretch, and Concave motifs.     

Direct imaging of meniscus formation in atomic force microscopy using environmental scanning electron microscopy

Environmental scanning electron microscopy was used to image meniscus formation between an AFM tip and a surface. At high relative humidity, 70%-99%, the meniscus formed is 100 to 1200 nm in height, orders of magnitude larger than predicted by the Kelvin equation using spherical geometry. The height of the meniscus also demonstrates hysteresis associated with increasing or decreasing relative humidity.     

Methanol oxidation on unsupported and carbon supported Pt + Ru anodes

A novel Pt + Ru electrode material is shown to be highly active for the direct electro-oxidation of methanol in H₂SO₄ solutions and to show very little tendency to poison. X-ray photoelectron spectroscopy of this material before use as an anode showed that the ruthenium is oxidised and that there is an important surface concentration of oxidised platinum. After prolonged use as a methanol-oxidation anode, the concentration of oxidised platinum is somewhat increased and there is no evidence for any Pt-CO or Pt₂ = CO species; rather adsorbed formate is present. These data are consistent with Ru acting as a promoter of active surface oxygen. Dispersion of the Pt and Ru on a pure carbon support gives a much greater performance per gram of precious metal; however, the initial increase in overpotential is greater by over 100 mV. The differences in the catalytic behaviour of these two materials is discussed, and the importance of competing reactions is considered.     

Dinuclear chromium(V) amino acid complexes from the reduction of chromium(VI) in the presence of amino acid ligands: XAFS characterization of a chromium(V) amino acid complex

The first synthesis and characterization of Cr(V) complexes of non-sulfur-containing amino acids are reported. The reduction of Cr(VI) in methanol in the presence of amino acids glycine, alanine, and 2-amino-2-methylpropanoic acid (alpha-aminoisobutyric acid, Aib) yielded several Cr(V) EPR signals. For the reaction involving glycine, the only Cr(V) EPR signals detected were those of the Cr(V)-intermediate methanol complexes, which were also observed in the absence of amino acids. The reaction involving alanine yielded one Cr(V) signal with a g(iso) value of 1.9754 (a(iso) = 4.88 x 10(-4) cm(-1) and A(iso)(53Cr) = 17.89 x 10(-4) cm(-1)). However, a solid product isolated from the reaction solution was EPR silent and was characterized as a dioxo-bridged dimeric species, [Cr(V)2(mu-O)2(O)2(Ala)2(OCH3)2](2-), by multiple-scattering XAFS analysis and electrospray mass spectrometry. The EPR spectrum of the reduction reaction of Cr(VI) in the presence of Aib showed several different Cr(V) signals. Those observed at lower g(iso) values (1.9765, 1.9806) were assigned to Cr(V)-methanol intermediates, while the relatively broad six-line signal at g(iso) = 2.0058 was assigned as being due to a Cr(V) complex with coupling to a single deprotonated amine group of the amino acid. This was confirmed by simplification of the superhyperfine coupling lines from six to three when the deuterated ligand was substituted in the reaction. The reduction of Cr(VI) with excess alanine or Aib ligands resulted in the formation of tris-chelate Cr(III) complexes, which were analytically identical to complexes formed via Cr(III) synthesis methods. The fac-[Cr(Aib)3] complex was characterized by single-crystal X-ray diffraction.     

A Dynamic Systems Approach to Understanding Reaching Movements with a Prosthetic Arm

A case study was conducted on an experienced upper extremity prosthetic user that required him to perform a reaching and grasping task with both his prosthetic and normal anatomical hand. We used a scanning task (Wallace, Stevenson, Spear, & Weeks, 1994; Button, Bennett, & Davids, 1998) that required the participant to perform a wide range of coordination patterns defined by the relative phasing between the aperture of the fingers (or artificial prehensor) and the arm. Visual templates of the required finger trajectories in the various required phase conditions served as environmental information for the subject to follow. Based on previous work, we hypothesized that the participant would exhibit at least one stable reaching and grasping pattern in both his anatomical and prosthetic arm. In support of this hypothesis, the results showed a negative sloping relationship between the required relative phase and the mean delta relative phase (required relative phase minus the actual relative phase). The smallest delta relative phase occurred at approximately 80° and 115° relative phase for the anatomical and prosthetic arm, respectively during the scanning task. These results confirm our previous work of the presence of only one attractor in reaching and grasping movements using either the anatomical or prosthetic arm.     

Evidence of meniscus interface transport in dip-pen nanolithography: An annular diffusion model

Ring shaped dots were patterned with mercaptohexadecanoic acid ink by dip-pen nanolithography. These dots have an ink-free inner core surrounded by an inked annular region, making them different from the filled dots usually obtained. This suggests a different transport mechanism than the current hypothesis of bulk water meniscus transport. A meniscus interface ink transport model is proposed, and its general applicability is demonstrated by predicting the patterned dot radii of chemically diverse inks.