A Calibration Reaction for Rapid Freeze-Quench W-Band EPR

A simple setup for rapid freeze-quench electron paramagnetic resonance (EPR) at W-band is described. It is based on a BioLogic commercial apparatus and a modified sample collection appropriate for W-band capillaries. The standard reaction of myoglobin with azide, which converts high-spin Fe(III) to low-spin Fe(III), used for calibration of rapid freeze-quench X-band EPR is very inconvenient for high-field measurements. Here we propose a different simple calibration reaction for W-band: the reduction of a nitroxide free radical with sodium dithionite using Mn²⁺ as an internal standard. Using this calibration reaction we determined the dead time of our system to be less than 10 ms.     

High field 27Al ENDOR reveals the coordination mode of Cu2+ in low Si/Al zeolites

The siting of Cu2+ in zeolites with low exchange levels has been a subject for debate due to the lack of experimental evidence that provide directly the interaction between the Cu2+ ion and the zeolite framework. High field 27Al ENDOR provided highly resolved orientation selective ENDOR spectra from which both the 27Al hyperfine and quadrupole principal components and orientations relative to the g tensor principal axis system were determined for a dehydrated Cu2+ exchanged zeolite X with Si/Al = 1. The results show that all three Cu-Al distances in the six-member ring are equivalent, in contrast to DFT predictions using cluster models.     

Electronic structure of binuclear mixed valence copper azacryptates derived from integrated advanced EPR and DFT calculations

Binuclear, mixed valence copper complexes with a [Cu(+1)(.5), Cu(+1)(.5)] redox state and S = (1)/(2) can be stabilized with rigid azacryptand ligands. In this system the unpaired electron is delocalized equally over the two copper ions, and it is one of the very few synthetic models for the electron mediating Cu(A) site of nitrous oxide reductase and cytochrome c oxidase. The spatial and electronic structures of the copper complex in frozen solution were obtained from the magnetic interactions, namely the g-tensor and the (63,65)Cu, (14)N, (2)H, and (1)H hyperfine couplings, in combination with density functional theory (DFT) calculations. The magnetic interactions were determined from continuous wave (CW) electron paramagnetic resonance (EPR), pulsed electron nuclear double resonance (ENDOR), two-dimensional TRIPLE, and hyperfine sublevel correlation spectroscopy (HYSCORE) carried out at W-band or/and X-band frequencies. The DFT calculated g and Cu hyperfine values were in good agreement with the experimental values showing that the structure in solution is indeed close to that of the optimized structure. Then, the DFT calculated hyperfine parameters were used as guidelines and starting points in the simulations of the various experimental ENDOR spectra. A satisfactory agreement with the experimental results was obtained for the (14)N hyperfine and quadrupole interactions. For (1)H the DFT calculations gave good predictions for the hyperfine tensor orientations and signs, and they were also successful in reproducing trends in the magnitude of the various proton hyperfine couplings. These, in turn, were very useful for ENDOR signals assignments and served as constraints on the simulation parameters.     

Alternating direction augmented Lagrangian methods for semidefinite programming

We present an alternating direction dual augmented Lagrangian method for solving semidefinite programming (SDP) problems in standard form. At each iteration, our basic algorithm minimizes the augmented Lagrangian function for the dual SDP problem sequentially, first with respect to the dual variables corresponding to the linear constraints, and then with respect to the dual slack variables, while in each minimization keeping the other variables fixed, and then finally it updates the Lagrange multipliers (i.e., primal variables). Convergence is proved by using a fixed-point argument. For SDPs with inequality constraints and positivity constraints, our algorithm is extended to separately minimize the dual augmented Lagrangian function over four sets of variables. Numerical results for frequency assignment, maximum stable set and binary integer quadratic programming problems demonstrate that our algorithms are robust and very efficient due to their ability or exploit special structures, such as sparsity and constraint orthogonality in these problems.     

Development of Efficient Zeolite-Containing Catalysts for Petroleum Refining and Petrochemistry

The role of various technologies in oil refining and petrochemistry changes due to amendments to the requirements for fuel quality. The development of these technologies requires the improvement of catalysts. This paper outlines main procedures for the production of dealuminated zeolites, as well as the advantages and drawbacks of these procedures. Catalysts with a high desulfurizing ability for the hydrocracking of vacuum gas-oil to gasoline and diesel fractions and catalysts for the isomerization of fuel hydrocarbons can be prepared using ultrastable Y-type zeolites. The results of testing of zeolite-containing binary catalytic systems in Fischer-Tropsch synthesis are presented.     

Two-dimensional electrophoretic analysis of immunoglobulin patterns in monoclonal gammopathies.

Two-dimensional (2-D) electrophoresis was performed on 24 serum samples from patients diagnosed with monoclonal gammopathies. These samples had been shown to have a homogeneous immunoglobulin (M component) by zone electrophoresis and immunofixation. Using 2-D electrophoresis, the nature of this aberrant protein was further analyzed. It has been presumed that the sharp, dark stained band identified by immunofixation was the production of a monoclonal immunoglobulin. The increased resolution afforded by 2-D methodology reveals several different patterns. On 2-D electrophoresis, a monoclonal antibody has a unique pattern. It consists of 3 to 6 strong, restricted heavy chain bands and a single distorted light chain spot. The 3-6 bands are microheterogeneity of the isoelectric point, attributed to posttranslational glycosylation and/or amidation/deamidation. Analysis by 2-D electrophoresis indicated only 5 samples with a true monoclonal pattern. All but 2 of the samples clearly had aberrant immunoglobulin, but interpretation of the pattern would suggest the protein is other than a fully synthesized monoclonal antibody. The samples showed the following: a monoclonal heavy chain pattern with multiple distorted light chain spots, only an aberrant light chain area, only an aberrant heavy chain, and only a polyclonal increase. Several IgG gammopathies had, in addition, concentrations of gamma heavy chain at a reduced size (34 kDa).     

New synthesis and insight into the structure of blue ultramarine pigments

A new and easy method for preparing blue sodalite pigments which involves high-temperature calcination of sodalite samples synthesized with aluminum sulfate and an organic template, is presented. Calcination generated the S(3)(-) and S(2)(-) radicals, and the effects of the Al/Si ratio and the calcination temperature on the nature and amounts of the radicals were examined. The radicals were characterized in detail by continuous wave and pulsed EPR at X- and W-band frequencies (approximately 9 and 95 GHz, respectively) complemented by UV-vis measurements. The high-field electron-paramagnetic resonance (EPR) measurements allowed us to clearly resolve the g anisotropy of S(3)(-) and W-band electron nuclear double resonance (ENDOR) measurements detected strong coupling with extra-framework (23)Na cations and weak coupling with framework (27)Al. On the basis of the spectroscopic results and density functional theory (DFT) calculations of the g-tensors of S(3)(-) and S(2)(-) radicals, the EPR signals were attributed to three different radicals, all with the open structure C(2v), that are located within the sodalite beta cages. While two of these radicals are well isolated, the third one is associated with an exchange-narrowed signal originating from S(3)(-) radicals in nearby sodalite cages.     

On solution-containing ellipsoids in linear programming

Ellipsoids that contain all optimal dual slack solutions and those that contain all optimal primal solutions and that are independent of the algorithm used are derived. Based upon these ellipsoids, two criteria each for detecting optimal basic and nonbasic variables prior to optimality in interior-point methods are obtained. Using these results, we then derive a sufficient condition for a linear program to be feasible.This research was supported in part by NSF Grant DMS-85-12277, DMS-91-06195, CDR-84-21402 and ONR Contract N00014-87-K-0214.