On the structure of chemisorbed acetylene and ethylene on Ni,Pd and Pt surfaces

Filtered He II (hv = 40.8 eV) photoemission spectra for acetylene and ethylene molecularly chemisorbed at T ～ 100 K on Ni(111), Ni(110), Pd(111) and Pt(111) have been obtained. The resulting vertical ionization potentials are presented and used within the framework of an approximate model to obtain information of the geometric structure of these molecules. Two initial state effects are discussed which are found to be important in deducing the molecular structures. These include an initial state shift of the lowest lying carbon-2s derived orbital and a metal atom induced shift of the σ_CC valence orbital for strongly distorted species. The magnitudes of both effects are estimated — the latter using Hartree — Fock LCAO calculations of Be interacting with acetylene or ethylene. The deduced geometries of chemisorbed ethylene are found to differ only slightly from those determined without considering these effects, but for acetylene two classes of structures are found. One class of structures is weakly distorted while the other is strongly distorted (～sp^2.5 hybridization). The latter structure is consistent with recent vibrational loss studies of chemisorbed acetylene on Ni(111) and Pt(111). In contrast to chemisorbed acetylene, chemisorbed ethylene on Ni shows relatively weak distortions. More subtle crystallographic and structural effects for acetylene and ethylene on (111), (100) and (110) Ni surfaces are also discussed.     

Solvation of ethylmaltol and of its iron(III) complex

Summary Solubilities of tris(ethylmaltolato)iron(III) (ethylmaltol = 3-hydroxy-2-ethyl-4-pyrone) were measured in MeOH-H₂O, t-BuOH-H₂O and diol-H₂O mixtures, and in several primary alcohols. Solvation of the ethylmaltol ligand and of two 4-pyridinone analogues has been investigated through solubility measurements in MeOH- H₂O and in t-BuOH-H₂O mixtures, and in a series of primary alcohols. The solvation characteristics of these compounds are compared with those of the parent maltol, its iron(III) complex and a number of other nonelectrolytes.     

Resolvable and near-resolvable decompositions ofDK v into oriented 4-cycles

Summary A resolvableX-decomposition ofDK _v (the complete symmetric digraph onv vertices) is a partition of the arcs ofDK _v into isomorphic factors where each factor is a vertex-disjoint union of copies ofX and spans all vertices ofDK _v . There are four orientations ofC ₄ (the 4-cycle), only one of which has been considered: Bennett and Zhang, Aequationes Math.40 (1990), 248–260. We give necessary and sufficient conditions onv for resolvableX-decomposition ofDK _v , whereX is any one of the other three orientations ofC ₄. A near-resolvableX-decomposition ofDK _v is as above except that each factor spans all but one vertex ofDK _v . Again, one orientation ofC ₄ has been dealt with by Bennett and Zhang, and we provide necessary and sufficient conditions onv for the remaining three cases. The construction techniques used are both direct (for small values ofv) and recursive.The author thanks Simon Fraser University for its support during her graduate studies when the research for this paper was undertaken.The author acknowledges the Natural Sciences and Engineering Research Council of Canada for financial support under grant A-7829.     

Acoustic response from adherent targeted contrast agents

In ultrasonic molecular imaging, encapsulated micron-sized gas bubbles are tethered to a blood vessel wall by targeting ligands. A challenging problem is to detect the echoes from adherent microbubbles and distinguish them from echoes from nonadherent agents and tissue. Echoes from adherent contrast agents are observed to include a high amplitude at the fundamental frequency, and significantly different spectral shape compared with free agents (p <0.0003). Mechanisms for the observed acoustical difference and potential techniques to utilize these differences for molecular imaging are proposed.     

Intermolecular vibrational coherence in bacteriochlorophyll a with clustered polar solvent molecules

We show that resonant impulsive excitation of the Qy absorption band of bacteriochlorophyll a (BChl) launches a rapidly damped (gamma < 200 fs) ground-state coherent wave-packet motion that arises from intermolecular modes with clustered solvent molecules. Femtosecond pump-probe, dynamic-absorption signals were obtained at room temperature with BChl solutions in pyridine, acetone, and 1-propanol. The vibrational coherence observed in the 0-800-fs regime is modeled in the time domain by two (or three, in the case of 1-propanol) modulation components with asymmetric, inhomogeneously broadened line shapes and frequencies in the 100-200-cm(-1) range. The mean frequency of the vibrational coherence exhibits at least a quadratic dependence on the dipole moment of the solvent molecules and a y-intercept in the 100-cm(-1) regime. This trend is modeled by an expression for the natural frequency of a "6-12" potential composed of attractive terms from van der Waals forces and a repulsive term from the exchange (Pauli exclusion) force. The model suggests that comparable contributions to the potential are provided by the dipole-dipole and London dispersion interactions. These results support the hypothesis that the low-frequency vibrational modes in the 100-cm(-1) regime that are coupled to the light-driven charge-separation reactions in the reaction center from purple bacteria are derived from intermolecular vibrational modes between the chromophores and the surrounding protein medium.     

The preparation of a phosphorus doped silicon film from phosphorus containing silicon nanoparticles

Phosphorus containing and octyl-terminated silicon nanoparticles (NPs) are generated by a solution reduction route under room temperature conditions for the first time and characterized by TEM, HRTEM, EDX, 1H/13C/31P NMR, EPR, and PL spectroscopy, then annealed to form a thin film with phosphorus doping confirmed by microprobe elemental analyses.     

Design and characterization of a functional library for NMR screening against novel protein targets

In the past few years, NMR has been extensively utilized as a screening tool for drug discovery using various types of compound libraries. The designs of NMR specific chemical libraries that utilize a fragment-based approach based on drug-like characteristics have been previously reported. In this article, a new type of compound library will be described that focuses on aiding in the functional annotation of novel proteins that have been identified from various ongoing genomics efforts. The NMR functional chemical library is comprised of small molecules with known biological activity such as: co-factors, inhibitors, metabolites and substrates. This functional library was developed through an extensive manual effort of mining several databases based on known ligand interactions with protein systems. In order to increase the efficiency of screening the NMR functional library, the compounds are screened as mixtures of 3-4 compounds that avoids the need to deconvolute positive hits by maintaining a unique NMR resonance and function for each compound in the mixture. The functional library has been used in the identification of general biological function of hypothetical proteins identified from the Protein Structure Initiative.     

High spatial and angular resolution diffusion-weighted imaging reveals forniceal damage related to memory impairment

Introduction

Diffusion tensor imaging (DTI) measures in patients with multiple sclerosis (MS), particularly those measures associated with a specific white matter pathway, have consistently shown correlations with function. This study sought to investigate correlations between DTI measures in the fornix and common cognitive deficits in MS patients, including episodic memory, working memory and attention.

Materials and Methods

Patients with MS and group age- and sex-matched controls underwent high-resolution diffusion scanning (1-mm isotropic voxels) and cognitive testing. Manually drawn forniceal regions of interest were applied to individual maps of tensor-derived measures, and mean values of transverse diffusivity (TD), mean diffusivity (MD), longitudinal diffusivity (LD) and fractional anisotropy (FA) were calculated.

Results

In 40 patients with MS [mean age±S.D.= 42.55±9.1 years; Expanded Disability Status Scale (EDSS)=2.0±1.2; Multiple Sclerosis Functional Composite (MSFC) score=0.38±0.46] and 20 healthy controls (mean age±S.D.= 41.35±9.7 years; EDSS=0.0±0; MSFC score=0.74±0.24), we found that FA, MD and TD values in the fornix were significantly different between groups (P< .03), and patient performance on the Brief Visuospatial Memory Test-Revised (BVMT-R) was correlated with DTI measures (P< .03).

Discussion

These results are consistent with findings of axonal degeneration in MS and support the use of DTI as an indicator of disease progression.