Rel Values Research Articles

Heavy ion ranges in plastic track detectors

Plastic track detectors, viz. CR-39 and Lexan polycarbonate were irradiated at GSI, UNILAC using 208Pb(13.6 MeV/u), 238U(15 MeV/u), 132Xe(5.6 and 14.5 MeV/u) and 139La(14.6 MeV/u) beams. The experimental ranges of heavy ions are in good agreement with the theoretical ranges computed by using the computer programme based on equations of Mukherji and Nayak. Critical angle etching efficiency and REL values for plastic detectors are determined from their bulk and track etch rates. REL for Lexan polycarbonate is found to be 4.25 MeV mg-1 cm-2 . The efficacy of ‘Single Sheet Identification’ technique for low energy cosmic ray particles is established.

Measurements of transversal etching rates of uranium tracks in CR-39

The transversal etch rate of tracks of 238 U-ions (410 MeV/nuc) has been measured by electrochemical etching. The irradiations of CR-39 sheets were carried out by the Bevelac Laboratory, Berkeley (USA). In a special two chamber etching equipment the sheets of CR-39 were etched from both sides using 6n-NaOH at a temperature of 50°C having electrodes in both chambers. During the etching process a current through a track is measured, from which the pore radius can be determined as a function of the etching time. Thus the transversal track development could be studied. This was done at different values of REL. The dimensions of the regions of preferred etching around the tracks were registered.

38] Analysis of vitamin D2 isomers

Publisher Summary This chapter discusses the study analyzing vitamin D 2 isomers. There exist two important facets of vitamin D analysis. One is an establishment of microanalysis of vitamin D in complex media containing a large excess of other fat-soluble vitamins, such as vitamins A and E. The second is the accomplishment of a clear separation, as well as a rapid and accurate quantitation of vitamin D and its isomers. Relative paramagnetic shift value ( v rel ) method depends upon the fact that the acetoxyl NMR signals of acetylated vitamin D 2 isomers induce paramagnetic shifts with their own v rel values when a shift reagent is sequentially added into the sample solution. A ratio of the relative contents of the isomers can be determined simultaneously from integrated signal areas of the respective acetoxyl protons. Quantitation of each isomer in a mixture, if necessary, can be performed by employing an appropriate internal standard for determination or by comparison with an increased signal area resulting from the addition of a definite amount of vitamin D 2 acetate. This method permits immediate identification of the isomers and provides valuable information on their stereochemistry. This technique also facilitates simultaneous determination of these isomers in a mixture by estimating each signal area.

Stable carbocations : XX. A kinetic study of the SN hydrolysis of aryl(ferrocenyl)methyl acetates

Rate constants ( k) for solvolysis of a series of acetates, p-RC 6H 4CH(OAc)Fc, in aqueous acetone have been determined. The log K rel values correlate linearly with Hammett σ + substituent constants ( p  1.39) and with p K R+ values for the intermediate ferrocenyl-stabilised carbocations, whose 1H NMR spectra have been recorded. The mechanistic significance of the rate data is discussed.

Chemical structure and biodegradability of halogenated aromatic compounds substituent effects on 1,2-dioxygenation of benzoic acid

Dioxygenation of substituted benzoic acid by whole cells of 3-chlorobenzoate-utilizing Pseudomonas sp. B13, benzoate-induced cells of Alcaligenes eutrophus B 9 and toluate-grown cells of Pseudomonas putida mt-2 was examined. Electron-attracting substituents like halogen decreased the reaction rates of benzoate 1,2-dioxygenation. Dioxygenation of substituted benzoic acids by P. putida mt-2 was mostly undisturbed by steric effects of the substituents. Good correlation resulted between the log V rel values and the Hammett substituent constant σ. In contrast the reaction rates of dioxygenation by Pseudomonas sp. B 13 and A. eutrophus were decreased predominantly by steric effects of substituents. A non-polar reaction mechanism of benzoate 1,2-dioxygenation is discussed. Results from inhibition studies demonstrate high stereospecificities for the 1,2-dioxygenation by Pseudomonas sp. B 13 of benzoic acids with substituents in ortho- or para-position. In the case of P. putida mt-2 steric handrance by substituents was observed only with ortho-substituted benzoic acids. Stereospecificities of the benzoate 1,2-dioxygenation by Pseudomonas sp. B 13 and P. putida mt-2 are illustrated schematically.

Chemical structure and biodegradability of halogenated aromatic compounds substituent effects on dehydrogenation of 3,5-cyclohexadiene-1,2,-diol-1-carboxylic acid

The dehydrogenation of substituted 3,5-cyclohexadiene-1,2-diol-1-carboxylic acids by dihydrodihydroxybenzoic acid dehydrogenases from benzoate grown cells of Alcaligenes eutrophus and Pseudomonas sp. B 13 and 3 -chlorobenzoate grown cells of the latter organism was examined. No significant differences ( K m and V rel values) were detected for the enzymes from both organisms. The same dihydrodihydroxybenzoic acid dehydrogenase is formed in Pseudomonas sp. B13 during growth on benzoate as well as on 3-chlorobenzoate. The lower turnover rates of 3- and 5-chlorodihydrodihydroxybenzoic acid compared to dihydrodihydroxybenzoic acid are counterbalanced by an increase in specific activity. With the exception of 4-substituted dihydrodihydroxybenzoic acids exhibiting relative high K m values, only slight sterical and electronic substituent effects are evident. Reaction rates were never reduced to a critical level.

On the mechanism of the reaction of organosilicon hydrides with dichlorocarbene generated from sodium trichloroacetate

The reaction of sodium trichloroacetate with various organosilicon hydrides in 1,2-dimethoxyethane was investigated and the products, α-triorganosilyldichloromethanes, were formed in yields of 20–50%. The relative rate constants of these hydrosilanes in such insertion reactions of dichlorocarbene were determined by means of competition reactions. The relative reactivities of a series of alkyl substituted hydrosilanes correlate well with the Taft σ* constants for the substituents on silicon, with a ϱ* value of −1.07, and a series of aryl substituted hydrosilanes also shows good linear correlation of the log k rel values with Taft σ* constants, giving ϱ* value of −1.18. The hydrogen isotope effect in the reaction, k H/ k D 1.26 ± 0.02. Based on the observed results, it was concluded that the insertion of CCl 2 into the SiH bond proceeds by a three-center concerted process in which charge separation in the transition state is not large, as suggested by Seyferth for the related PhHgCCl 2Br/XC 6H 4SiMe 2H reactions.

Chromatographic reproducibility in high-performance liquid chromatographic gradient elution

Normal bonded phase chromatography in a syringe pump gradient system satisfies a basic requirement for high-performance liquid chromatography of retention time reproducibility within half a peak width. Reversed bonded phase chromatography is characterized by a retention time variance in excess of this goal in certain cases. The source of the variance was traced to fluid compressibility effects and ambient thermal fluctuations. Fluid compressibility effects, due to the change in system backpressure with changing mobile phase viscosity, generated a retention time variation of the order of a peak width for solutes eluting in the 20–50% B portion of a 0–100% acetonitrile (B) in water (A) gradient. However, the retention of solutes eluting beyond 50% acetonitrile was not significantly affected by fluid compressibility. Thermal effects, due to ambient temperature variation, generated retention time variations of the order of a peak width for solutes eluting throughout the gradient program. A constant backpressure valve was developed which successfully eliminated fluid compressibility effects during gradient elution. Thermal effects were eliminated by use of a water-jacketed column and circulating constant-temperature bath. The dual syringe pump gradient system operating with these modifications reproduced retention times to better than 6 sec out of 1200 sec (σ rel values below 0.5%).

Fine specificity of rabbit anti- p-azophenylphosphorylcholine antibodies; comparison with HOPC-8 myeloma protein

Rabbit antibodies raised against the p-azophenylphosphorylcholine group (APPC) were compared with a phosphorylcholine-binding mouse myeloma protein, HOPC-8, with regard to their specificity for various choline-related haptenic structures. Comparisons were made on the basis of K rel values, relative to p-nitrophenylphosphorylcholine (NPPC) determined from inhibition of binding data, using a radio-iodine labeled protein-APPC conjugate as the reference antigen. The data indicate that anti-APPC antibody sites in general have a lower degree of cross reactivity for substructures of the APPC group than does the HOPC-8 site. The most important structure for binding to both kinds of sites is the positively charged quarternary ammonium group, indicating a close approach of this group a negatively charged carboxylate which we previously have shown to be present in both sites. The negatively charged phosphoryl group appears to be more important for binding to the HOPC-8 site than to the anti-APPC site, indicating that this structure probably more closely approaches the positively charged guanidinium group which we have shown to be present in the HOPC-8 site than it does to a similar group we have shown to be present in the anti-APPC site. The nitrophenyl group of NPPC contributes a great deal in the interaction with the anti-APPC site, but is not very important in the interaction with the HOPC-8 site.

Immunological cross-reactions within a family of related haptens

A method was developed for determining relative affinities of different haptens for an antibody. It was an antigen-binding test, the homologous (immunogenic) hapten was conjugated to radioiodinated bovine serum albumin. Efficiencies of different haptens in the inhibiton of binding were then compared. By using this test and another independent test (inhibition of haptenated bacteriophage) we determined all the twelve K rel values for the following derivatives of 4-hydroxyphenyl acetic acid: 3-5-dinitro NNP, 3-nitro-5-bromo NBrP, 3-nitro-5-iodo NIP, 3-5-diiodo DIP. The log. mean of the two reciprocal K rel values (e.g. DIP versus anti-NIP and NIP versus anti-DIP) were calculated for each six pairs of haptens. These similarity indices suggested that NNP and DIP are the most distant relatives of the four. Closest to NNP in NBrP and closest to DIP is NIP. NNP, NBrP and NIP form a cluster which DIP is a little farther apart. NIP and NBrP formed the most closely related pair.