Experimental transition state for the B-chlorodiisopinocampheylborane (DIP-Cl) reduction

Asymmetric reductions of prochiral ketones are important transformations in the syntheses of natural products, pharmaceuticals, and fine chemicals. B-Chlorodiisopinocampheylborane (DIP-Cl), a stoichiometric reagent that is capable of reducing prochiral aralkyl ketones with high selectivity. Here, we utilize a recently developed ¹³C kinetic isotope effect (KIE) methodology to probe the symmetry breaking process inherent to this asymmetric reduction. Experimental KIEs and computed transition structures indicate significant roles for non-bonding interaction, specific directed orbital interactions, and hydrogen tunneling in this reaction.     

Radiative properties of mixed nested cylindrical wire arrays on Zebra at UNR

The dynamics of mixed nested cylindrical wire arrays were studied at the UNR Zebra generator with our existing theoretical and experimental tools to better understand the contributions of each array to the emitted radiation. In particular, experimental results of mixed brass (70% Cu, 30% Zn) and Al (5056, 5% Mg) nested cylindrical wire arrays are analyzed and compared. The loads used brass in the inner array and Al in the outer array, or alternately, Al in the inner array and brass in the outer array, with a mass ratio of 1:1 (outer to inner). Consequently, radiative properties of K-shell Al and Mg ions and L-shell Cu and Zn ions are compared as functions of the placements of the brass and Al wires on the inner and outer arrays. Results show that the placement of brass and Al, whether on the inner or outer array, dramatically affects the intensity of the X-ray emission. Specifically, the ratio of Cu L-shell to Al K-shell emissions changed from 4 when Al is in the outer array to 40 when brass is in the outer array, and the total radiated yield was highest when the brass was on the outer array (18 kJ, versus 15 kJ when brass is on the inner array). Each load was fielded twice to vary the timing of the time-gated imaging and spectral diagnostics. This provides a more complete understanding of the evolution of the plasma parameters over the X-ray pulse and highlights the importance of the time-gated diagnostics.     

A Parallel Micro Turbulent Flow Chromatography-Tandem Mass Spectrometry Method for the Analysis of a Pharmaceutical Compound in Plasma

Turbulent flow chromatography coupled to tandem mass spectrometry (TFC-MS-MS) has been widely used within bioanalysis, because of the ability to inject directly neat biological samples with no prior pretreatment. TFC-MS-MS removes the need for time consuming sample preparation procedures such as protein precipitation, liquid-liquid extraction or solid-phase extraction. There are two standard configurations that are commonly adopted for the use of TFC, namely fast elute and focus mode. In this paper, a new micro TFC column which has the advantages of reducing solvent consumption and improving mass sensitivity, was used to develop a fast elute method. A wide range of pharmaceutical compounds with various physicochemical properties was used to assess the system performance. Carry-over has often been identified as a potential source of inaccuracy in a fast elute mode. This paper shows how by using a systematic approach, carryover was eliminated. The parameters influencing the robustness of the micro TFC column are also discussed. This method was fully validated for a Pfizer development compound in human plasma using a new TFC parallel platform allowing two systems to be operated in parallel. Multiplexing the sample analysis allowed a 2-fold increase in throughput and provided an efficient use of the mass spectrometer.     

Dealing with large diagonals in kernel matrices

In kernel methods, all the information about the training data is contained in the Gram matrix. If this matrix has large diagonal values, which arises for many types of kernels, then kernel methods do not perform well: We propose and test several methods for dealing with this problem by reducing the dynamic range of the matrix while preserving the positive definiteness of the Hessian of the quadratic programming problem that one has to solve when training a Support Vector Machine, which is a common kernel approach for pattern recognition.     

Algebras without noetherian filtrations

We provide examples of finitely generated noetherian PI algebras for which there is no finite dimensional filtration with a noetherian associated graded ring; thus we answer negatively a question of Lorenz (1988).

     

Evaluation of penetrometers for measuring soil strength

Cone index, as determined by a cone penetrometer, is frequently used as a measure of soil strength. The index is a compound parameter involving components of shear, compressive and tensile strength and soil metal friction. In order to assess the effect of soil type and condition on the relative contributions of these components to penetration resistance, the forces required to push blunt and sharp probes into two soils under a range of moisture contents and bulk densities were investigated. The maximum penetration force in homogeneous soil was not uniquely related to dry bulk density or cohesion, but varied with soil moisture content.At high and low moisture contents, the soil tended to interact with the shaft of the penetrometer thus increasing the resistance to penetration. At low moisture content, bodies of compressed soil formed in front of the probe, effectively changing the probe geometry.It was concluded that interpretation of cone index in typical layered field soils is difficult. Even in homogeneous soils, the proportion of shear, compressive and tensile components that the cone index reflects varies with soil condition.     

Swelling of ultrathin crosslinked polyamide water desalination membranes

We study the water swelling behavior of semiaromatic crosslinked polyamide (PA) ultrathin films to characterize the network properties of the polymer. Specifically, we use X-ray reflectivity to measure film thickness increase and polymer density decrease of the PA films due to swelling. With the aid of a modified Flory–Rehner theory used to describe the constrained swelling behavior of polymer networks, we are able to extract the Flory interaction parameter and the monomer units between crosslinks by performing the swelling experiments at different levels of hydration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

The Effect of the Removal of One Product on the Optimum Yield in an Equilibrium Process

Abstract

Except for a first-order dissociation, complete conversion is not possible in an equilibrium process no matter how efficient the removal of a byproduct may be. In a first-order dissociation process, complete reaction is only possible when the ratio of the rate constants of the forward to the backward reaction is greater than unity.