Reaction Endpoints Research Articles

Optimizing Selective Partial Hydrogenations of 4-Nitroacetophenone via Parallel Reaction Screening

The hydrogenation of 4-nitroacetophenone was optimized for selective reduction to the corresponding aniline-ketone (97%), aniline-alcohol (95%), and aniline-methylene (99%) as a case study demonstrating the optimization of the selective reduction of a polyfunctional substrate using a parallel pressure reactor. The catalyst, catalyst loading, pressure, temperature, and methanesulfonic acid stoichiometry were varied, first in an initial coarse screen (catalyst and acid stoichiometry), and then in a full factorial screen for selected catalysts. Facile profiling of hydrogen uptake in each reaction aided setting reaction time and parameter ranges for the full factorial analysis, allowed for quickly spotting under- and overreduction, aided predicting robust reaction endpoints, and provided data for analyzing kinetic behavior.

Dynamic Imaging of Process Plant Reactors and Separators Using Electrical Process Tomography

The use of electrical tomography is beginning to find application in industrial processes as a measurement tool for modelling, model verification and on-line monitoring and diagnosis. The method employs simple sensors arranged on the periphery of process reactors that contact the process fluid. Electrical excitation allows to collect information that can be used to deduce the distribution of electrical properties (such as conductivity, or dielectric constant) within the reactor. These can in turn be related to reactant-product concentration profiles within the reactor, provided that such components exhibit inherent differences in electrical properties. A particular attribute of electrical systems is their ability to make measurements rapidly. The author reported the most recent developments in the application of electrical capacitance and electrical resistance tomography to a selection of process systems [3-5]. The objective was to illustrate the capabilities of the method. The rapid data collection process facilitates observation of kinetic processes. Laboratory and industrial studies of the following systems have been presented:- gas-liquid and liquid-liquid stirred tanks (tank design and scale up, mixing kinetics);- solid-liquid stirred tanks (tank design and scale up, crystallisation and precipitation);- gas-liquid bubble columns (flow monitoring and control of interfacial area);- solid-liquid cyclonic separators (fluid dynamic code development, on-line plant monitoring);- solid-liquid separation (cycle time in product washing);- autoclave polymerisers (reaction pathways and endpoints). Prospects for the integration of advanced visualisation and modelling tools with chemical reactor models have been discussed. Future goals were identified, including the possible use of chemical species mapping.

Molecular modeling of trifluoromethanesulfonic acid for solvation theory

Reported here are theoretical calculations on the trifluoromethanesulfonic (triflic) acid with and without an additional water molecule, establishing molecular scale information necessary to molecular modeling of the structure, thermodynamics, and ionic transport of Nafion® membranes. The optimized geometry determined for the isolated triflic acid molecule, obtained from ab initio molecular orbital calculations, agrees with previous studies. In order to characterize side chain flexibility and accessibility of the acid proton, potential energy and free energy surfaces for rotation about both carbon–sulfur and sulfur–oxygen(hydroxyl) bonds are presented. A continuum dielectric solvation model is used to obtain free energies of electrostatic interaction with the solvent. Electrostatic solvation is predicted to reduce the free energy barrier to rotation about the F 3C–SO 3 bond from 3.5 kcal/mol to about 2.7 kcal/mol. This electrostatic effect is associated with slight additional polarization of the CF bond in the eclipsed conformation. The energetic barrier to rotation of the acid hydroxyl group away from the sulfonic acid oxygen plane, out into the solvent is substantially flattened by electrostatic solvation effects. The maximum free energy for those solvent accessible proton conformations is about 1.0 kcal/mol. We carried out additional ab initio electronic structure calculations with a probe water molecule interacting with the triflic acid. The minimum energy structures found here for the triflic acid molecule with the probe water revise results reported previously. To investigate the reaction path for abstraction of a proton from triflic acid, we found minimum energy structures and energies for isolated molecular fragments, and solvation free energies for: (a) a docked configuration of triflate anion and hydronium cation and (b) a transition state for proton interchange between triflic acid and a water molecule. Those configurations are structurally similar but energetically substantially different. The activation free energy for that proton interchange is predicted to be 4.7 kcal/mol above the reaction end-points.

Interactions between ascorbic acid and the radiation of bone marrow, skin, and tumor

In studies of isotransplants of a murine fibrosarcoma, FSaII, ascorbic acid administered 50 min before whole-body radiation significantly increased the dose of radiation required to cause a fatal radiation syndrome and the dose of radiation required to obtain skin desquamation. A single intraperitoneal dose of 4.5 g/kg body wt was not cytotoxic and did not affect the radiation dose required to control 50% of tumors or to achieve remissions. The mechanism of this differential radiomodification of normal tissue sensitivity and tumor tissue response is unclear. The data suggest that after high-dose ascorbic acid the radiation dose given to cancer patients could be increased without increasing acute complications but with an expected increase in tumor-control probability. However, only acute radiation reaction endpoints have been studied. Application of these findings to humans must therefore await further studies confirming that late reacting tissues are similarly protected by ascorbic acid.

Preparation of filamentous hemagglutinin from Bordetella pertussis and assay for serum antibodies to filamentous hemagglutinin and pertussis toxin for clinical and public health laboratories

A procedure that is sufficiently simple and economical for use in clinical and public health laboratories for producing and purifying filamentous hemagglutinin (FHA) and determining antibodies to this major antigen of Bordetella pertussis in serum is described. High yields of FHA (40 to 80 mg/liter) were obtained in the supernatant by cultivating B. pertussis in modified CL medium. The FHA antigen was separated from pertussis toxin (PT) and other antigens by chromatography on hydroxylapatite. Removal of residual PT activity in the FHA fraction was effected by affinity absorption of PT with Fetuin immobilized to Sepharose 4B. The FHA was used as the antigen for determining titers of immunoglobulin G (IgG), IgA, and IgM to FHA in sera of patients with pertussis by an improved enzyme-linked immunosorbent assay. Development of the interfering background color commonly observed in conventional FHA enzyme-linked immunosorbent assay procedures was eliminated by washing the reaction wells with a buffer of high ionic strength before adding the peroxidase conjugates. In the absence of nonspecific background color, the reaction endpoints were easy to read. The FHA prepared by the procedure described was identical to a reference preparation of purified FHA in sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles and serological specificity assays. High yields of FHA were obtained from all four strains of B. pertussis tested in this study, indicating that the procedure for enhanced production of FHA may be generally applicable to other strains of B. pertussis. Results from tests of 50 serum specimens with clinical information on pertussis for FHA and PT antibodies by the assay procedures described exemplified the usefulness and caveats of serodiagnosis for pertussis.

Serological Studies on the Relationships of Some Isometric Viruses of Gramineae

SUMMARY Particles of 17 isolates of viruses from Gramineae were purified and the virus relationships assessed by different serological techniques. From the reaction end-points of antisera in agar gel double diffusion tests the serological differentiation indices of reciprocal tests were calculated. These indices were used to construct a scheme of serological interrelationship. Spur formation tests were used to distinguish between closely related, non-identical viruses. The isolates were shown to belong to four groups, one of which (the cocksfoot mild mosaicpanicum mosaic virus group) contains most of the isolates and can be subdivided into two main clusters (typified by cocksfoot mild mosaic and panicum mosaic viruses, respectively). Additional information was obtained by immunoelectrophoresis of the viruses with their homologous antisera and by the determination of the mol. wt. of the coat protein subunits using SDS-polyacrylamide gel electrophoresis. The data obtained by both methods agree with the above mentioned results, although some minor differences were found between the immunoelectrophoretic patterns of panicum mosaic virus and its relatives and also the three isolates of Cynosurus mottle virus. Reversed rocket electrophoresis did not provide any information of use in virus grouping. Brome mosaic virus did not react with the antisera to the 17 viruses, but tobacco mosaic virus reacted weakly with all the antisera and also with one of the antisera to brome mosaic virus. These and other recently published results are discussed.

ANTIGENIC RELATIONSHIPS AMONG TRYPANOSOMA LEWISI--COMPLEX CELLS. I. AGGLUTININS IN ANTISERA.

Cells of six isolates ofTrypanosoma lewisifrom the United States, England, Puerto Rico, Costa Rica, and Singapore were matched against antiserum to the ‘L’ isolate in microagglutinin chambers. Antisera were prepared in Sprague-Dawley rats. Serum protein determinations were made by the biuret reaction; electrophoretic fractionations of serum proteins were done with a semi-closed horizontal system (Evans & Stirewalt, 1947) at 4°C for 24 h, 120 V, and 8 mA with paper strips. Electrolyte was veronal buffer, pH 8·6 and μ 0·058. Agglutinin absorptions were carried out using inactivated anti-‘L’ sera.Total protein (mg/ml) values were higher in all infected animals (60vs.54). Albumin values (%) were higher in controls (47vs.40);α-1 fractions were essentially unchanged (15%) as were α-2 values (6%). β Fractions were elevated in infected groups (21vs.17%), as were the γ globulins (19vs.12%).Three protocols employing agglutinin reactions were completed. In two protocols 3+ agglutinin end-points were obtained with four isolates using 1·45–1·47 μg of immune γ globulin. Two of the isolates (Puerto Rico and Singapore) required 10 times this amount of immune globulin for the same end-point. In two other tests all isolates gave reaction end-points that required greater quantities (by a factor ofca.500) of immune γ globulin than obtained in the first two tests, and there was further evidence that the Costa Rican isolate was quantitatively different from the others. These facts are interpreted to mean that all six geographic isolates show close qualitative relationships to each other, but that the relationships for the Puerto Rican, Singapore and Costa Rican isolates are quantitatively different. Agglutinins could not be absorbed from immune serum by any of the cells.