Stereochemistry and the use of H2/D2 mixtures as probes into the mechanism of hydrogenations catalyzed by cationic rhodium (DIPHOS) complexes

The stereochemistry of the hydrogenation of 4-tert-butylmethylenecyclohexane (1) and the use of D₂ or D₂/H₂ mixtures in place of H₂ furnishes evidence that hydrogenations using the catalyst precursor [Rh(DIPHOS)(COD)]⁺BF ₄ ⁻ proceed via more than one mechanism. This evidence includes the effect of changes in pressure and added triethylamine upon the kinetics and isomerization of 1, as well as the distribution of the added deuterium in the products of the reaction of 1 or norbornene with either D₂ or H₂/D₂ mixtures. That an alkene necessarily causes the equilibration of H₂/D₂ mixtures, although it need not involve any of the alkenes’s hydrogen atoms (e.g., norbornene), provides a clue to the process by which the mononuclear mechanism proposed by Halpern, which is dominant near one atmosphere of H₂, merges into another with increasing pressure. It has been proposed that the cationic complex [Rh(DIPHOS)S₂]⁺ is transformed in the presence of an alkene and hydrogen into a binuclear hydrido complex, such as those described by Sivak and Muetterties (1979) and Fryzuk (1982), which represent a far more active catalyst than its mononuclear precursor. Such an intermediate should readily catalyze the H₂-D₂ equilibration and the isomerization of an alkene in the presence of D₂ without necessarily introducing deuterium into the product. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 88–97. Deceased. The text was submitted by the authors in English. This work was conducted at the University of Arkansas.     

Proteomic analysis of simulated occupational jet fuel exposure in the lung

We analyzed protein expression in the cytosolic fraction prepared from whole lung tissue in male Swiss-Webster mice exposed 1 h/day for seven days to aerosolized JP-8 jet fuel at concentrations of 1000 and 2500 mg/m3, simulating military occupational exposure. Lung cytosol samples were solubilized and separated via large scale, high resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Significant quantitative and qualitative changes in tissue cytosol proteins resulted from jet fuel exposure. Several of the altered proteins were identified by peptide mass fingerprinting, confirmed by sequence tag analysis, and related to impaired protein synthetic machinery, toxic/metabolic stress and detoxification systems, ultrastructural damage, and functional responses to CO2 handling, acid-base homeostasis and fluid secretion. These results demonstrate a significant but comparatively moderate JP-8 effect on protein expression and corroborate previous morphological and biochemical evidence. Further molecular marker development and mechanistic inferences from these observations await proteomic analysis of whole tissue homogenates and other cell compartment, i.e., mitochondria, microsomes, and nuclei of lung and other targets.     

An Isoperimetric Theorem in Plane Geometry

Abstract. Let P be a simple polygon. Let the vertices of P be mapped, according to a counterclockwise traversal of the boundary, into a strictly increasing sequence of real numbers in [0, 2π) . Let a ray be drawn from each vertex so that the angle formed by the ray and a horizontal line pointing to the right equals, in measure, the number mapped to the vertex. Whenever the rays from two consecutive vertices intersect, let them induce the triangular region with extreme points comprising the vertices and the intersection point. It is shown that there is a fixed α such that if all of the assigned angles are increased by α , the triangular regions induced by the redirected rays cover the interior of P . This covering implies the standard isoperimetric inequalities in two dimensions, as well as several new inequalities, and resolves a question posed by Yaglom and Boltanskii.     

Macromolecular Diffusion in Self-Assembling Biodegradable Thermosensitive Hydrogels

Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A blocks (~22 kDA) but differing PEG-midblock lengths (2, 4 and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDA). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery.     

TASS: The Toolkit for Accurate Scientific Software

The Toolkit for Accurate Scientific Software (TASS) is a suite of integrated tools for the formal verification of programs used in computational science, including numerically-intensive message-passing-based parallel programs. While TASS can verify a number of standard safety properties (such as absence of deadlocks and out-of-bound array indexing), its most powerful feature is the ability to establish that two programs are functionally equivalent. These properties are verified by performing an explicit state enumeration of a model of the program(s). In this model, symbolic expressions are used to represent the inputs and the values of variables. TASS uses novel techniques to simplify the symbolic representation of the state and to reduce the number of states explored and saved. The TASS front-end supports a large subset of C, including (multi-dimensional) arrays, structs, dynamically allocated data, pointers and pointer arithmetic, functions and recursion, and other commonly used language constructs. A number of experiments on small but realistic numerical programs show that TASS can scale to reasonably large configurations and process counts. TASS is open source software distributed under the GNU Public License. The Java source code, examples, experimental results, and reference materials are all available at .     

Improving the 1H indirect dimension resolution of 2D CRAMPS NMR spectra: a simulation and experimental investigation

An experimental and simulation investigation regarding the effect of various CRAMPS parameters (delays interleaved with the decoupling shape, z-rotation symmetry and offset frequency) on the DUMBO decoupling performance is presented using two model compounds, glycine and tyrosine·HCl. Although the conclusions of this work may be extended to the other homonuclear-decoupling schemes, this work focuses essentially on the effect of adding interleaved delays to DUMBO decoupling during the indirect dimension using different 2D pulse-scheme architectures. While the simulations revealed an increasing loss of the spectral resolution with longer delays (from 0 to 6 μs), the experimental 2D (1)H DUMBO NMR correlation spectra revealed that the inclusion of delays, during the indirect dimension, improves the (1)H resolution whether the z-rotation symmetry was used or not. The best experimental spectra are obtained when z-rotation symmetry and windows are combined.     

FEVS: A Functional Equivalence Verification Suite for High-Performance Scientific Computing

Scientific computing poses many challenges to formal verification, including the facts that typical programs: (1) are numerically-intensive, (2) are highly-optimized (often by hand), and (3) often employ parallelism in complex ways. Another challenge is specifying correctness. One approach is to provide a very simple, sequential version of an algorithm together with the optimized (possibly parallel) version. The goal is to show the two versions are functionally equivalent, or provide useful feedback when they are not. We present a new verification suite consisting of pairs of programs of this form. The suite can be used to evaluate and compare tools that verify functional equivalence. The programs are all in C and the parallel versions use the Message Passing Interface. They are simpler than codes used in practice, but are representative of real coding patterns (e.g., manager-worker parallelism, loop tiling) and present realistic challenges to current verification tools. The suite includes solvers for the 1-d and 2-d diffusion equations, Jacobi iteration schemes, Gaussian elimination, and N-body simulation.     

Some Dido-type Inequalities

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Some Dido-type Inequalities

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