Exploring skeletal diversity via ring contraction of glycal-derived scaffolds

Aryl ether C-glycoside scaffolds have been prepared from tri-O-acetyl-D-glucal by C-glycosylation followed by allylic substitution with phenols mediated by Pd(0). The aryl ethers were subjected to either [3,3]-sigmatropic rearrangement to produce 3-pyranyl-phenols or Au(III)-mediated ring contraction to create highly substituted tetrahydrofurans. [structure: see text]     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Bonding energy of Sylgard on fused quartz: an experimental investigation

The bonding energy between the polymer Sylgard and fused quartz is determined experimentally using a miniature bulge test combined with three-dimensional digital image correlation (3D-DIC). Based on the experimental observation, Mindlin plate theory is used to compute the bonding energy (adhesive energy or surface energy) between the Sylgard and the fused quartz. The experimental results demonstrate that the combination of the miniature bulge test and the 3D-DIC provides a viable tool to directly measure interfacial and bonding properties.     

π0 Multiplicities in π+;p interactions at 10.5 GeVc

Measurement of the π⁰ multiplicity cross sections are reported for n₀ ? 6, where n⁰ is the number of produced π⁰ particles, and for N ? 8, where N is the number of charged particles. The inclusive π⁰ cross section is 29 ± 3 mb. Values for the correlation parameters, 〈n₀〉 and 〈n₀(n₀ ? 1)〉², are also presented.     

Effective handling of a large configuration state function expansion for an MCSCF state and improved efficiency for two-electron integral transformations in MCSCF

Effective solutions for two difficulties which may be present in MCSCF calculation are discussed: (i) We show how the large configuration state function state expansion case may be handled simply and effectively without the introduction of extraneous projection operators or Lagrange multipliers; (ii) we present a simplified two-electron integral transformation procedure which significantly reduces the operation count (and hence computational efficiency is increased) for second order and particularly for third order MCSCF procedures. The procedures we introduce use some freedom available in the orthogonal complement Cl space and the virtual orbital space to simplify MCSCF calculations.     

Probing the mechanism of a fungal glycosyltransferase essential for cell wall biosynthesis. UDP-chitobiose is not a substrate for chitin synthase

Chitin synthase is responsible for the biosynthesis of chitin, an essential component of the fungal cell wall. There is a long-standing question as to whether "processive" transferases such as chitin synthase operate in the same manner as non-processive transferases. The question arises from analysis of the polysaccharide structure--in chitin, for instance, each sugar residue is rotated approximately 180 degrees relative to the preceding sugar in the chain. This requires that the enzyme account for the alternating "up/down" configuration during biosynthesis. An enzyme with a single active site, analogous to the non-processive transferases--would have to accommodate a distorted glycosidic linkage at every other synthetic step. An alternative proposal is that the enzyme might assemble the disaccharide donor, addressing the "up/down" conformational problem prior to polymer synthesis. We present compelling evidence that this latter hypothesis is incorrect.     

Second- and higher-order convergence in linear and nonlinear multiconfigurational Hartree–Fock theory

We discuss how the local convergence of Newton–Raphson and fixed Hessian MCSCF iterative models may be rationalized in terms of a total order of convergence in an error vector and a corresponding error term. We demonstrate that a sequence of N Newton–Raphson iterations has a total order of convergence of 2^N and that a sequence of N fixed Hessian iterations has a total order of convergence of N + 1. We derive the error terms of a Newton–Raphson and a fixed Hessian sequence of iterations. We discuss the implementation of the fixed Hessian and the Newton–Raphson approaches both when linear and nonlinear transformations of the variables are carried out. Sample calculations show that insight into the structure of the local convergence of Newton–Raphson and fixed Hessian models can be based on an order of convergence and an error term analysis.     

Comparison of perturbative and multiconfigurational electron propagator methods

Ionization energies below 20 eV of 10 molecules calculated with electron propagator techniques employing Hartree-Fock orbitals and multiconfigurational self-consistent field orbitals are compared. Diagonal and nondiagonal self-energy approximations are used in the perturbative formalism. Three diagonal methods based on second- and third-order self-energy terms, all known as the outer valence Green's function, are discussed. A procedure for selecting the most reliable of these three versions for a given calculation is tested. Results with a polarized, triple ζ basis produce root mean square errors with respect to experiment of approximately 0.3 eV. Use of the selection procedure has a slight influence on the quality of the results. A related, nondiagonal method, known as ADC (3), performs infinite-order summations on several types of self-energy contributions, is complete through third-order, and produces similar accuracy. These results are compared to ionization energies calculated with the multiconfigurational spin-tensor electron propagator method. Complete active space wave functions or close approximations constitute the reference states. Simple field operators and transfer operators pertaining to the active space define the operator manifold. With the same basis sets, these methods produce ionization energies with accuracy that is comparable to that of the perturbative techniques. © 1996 John Wiley & Sons, Inc.