Neutralization of HZSM-5 Br?nsted acid sites by shaping with boehmite

The reduction of the concentration of strongly acidic Brönsted sites of HZSM-5 by neutralization due to added boehmite is reported. Strongly acidic Brönsted sites are neutralized by [AlO·(Al₂O₃)_x]⁺ isopolyoxocations proceeding during the calcination treatment.     

A complementary cesium coolant concentration ratio for localizing defective PWR fuel rods during reactor operation

Rough techniques for pinpointing defective fuel pins during actual reactor operation were developed for nuclear power plants. These techniques are based on various fission product concentration ratios. Here, a new cesium concentration ratio,¹³⁴Cs/¹³⁶Cs, was tested in combination with the more usual cesium ratio¹³⁴Cs/¹³⁷Cs. This new cesium ratio confirmed the conclusions drawn from the ratio¹³⁴Cs/¹³⁷Cs and provided some additional information on the location of the defective fuel rods. Application of this second cesium ratio improves the reliability of the rough localization method.     

Structural analysis of underivatized neutral human milk oligosaccharides in the negative ion mode by nano-electrospray MS(n) (part 1: methodology)

Underivatized neutral oligosaccharides from human milk were analyzed by nano-electrospray ionization (ESI) using a quadrupole ion trap mass spectrometer (QIT-MS) in the negative-ion mode. Under these conditions neutral oligosaccharides are observed as deprotonated molecules [M-H]- with high intensity. CID-experiments of these species with the charge localized at the reducing end lead to C-type fragment ions forming a "new" reducing end. Fragmentations are accompanied by cross-ring cleavages that yield information about linkages of internal monosaccharides. Several isomeric compounds with distinct structural features, such as different glycosidic linkages, fucosylation and branching sites were investigated. The rules governing the fragmentation behavior of this class of oligosaccharides were elucidated and tested for a representative number of certain isomeric glycoforms using the MS/MS and MS(n) capabilities of the QIT. On the basis of the specific fragmentation behavior of deprotonated molecules, the position of fucoses and the linkage type (Gal beta-->3 GlcNAc or Gal beta1-->4 GlcNAc) could be determined and linear and branched could be differentiated. Rules could be established which can be applied in further investigations of these types of oligosaccharides even from heterogenous mixtures.     

A new class of Bessel function integrals

A procedure is outlined for evaluating integrals of the form $$PV\int_{ - \infty }^\infty {\frac{{G(x)}}{{H(x)}}f(x)dx} $$ whereG andH are entire functions of exponential type andf is a rational function. This is worked out in detail for the case of Bessel functions and several examples are given.     

Repair processes on deoxyribonucleic acid

Many cells have the ability to recognize and eliminate damage to their DNA, particularly thymine dimers formed by UV light. The elimination of this damage may be achieved by enzymatic, light-dependent cleavage of the dimers into the monomers (photoreactivation) or more frequently by dark repair, in which the damaged part is completely removed from the, DNA. In this repair process, the DNA is incised by an endonuclease in the immediate vicinity of the thymine dimers. Oligonucleotides containing the thymine dimer are removed hydrolytically from the DNA by the 5→3′ exonuclease activity of DNA polymerase I (Kornberg enzyme). The resulting gaps are immediately closed by a de novo synthesis with the aid of the same DNA polymerase I, the complementary strand serving as a template (excision repair). The final step is the formation of the phosphodiester bond between the newly synthesized DNA fragment and the old DNA strand by a DNA ligase. Xeroderma pigmentosum patients lack the endonuclease as a result of a genetic defect; they therefore cannot eliminate thymine dimers from their DNA, and are extremely sensitive to sunlight. All information so far suggests that genetic recombination and DNA repair are performed by the same enzyme system.     

Two-electron homoaromatics with heteroatom bridges

Zwitterionic mono- and bis-homoaromatics 2a–f and 5a comprised of positively charged NMe₂, P(C₆H₅)₂ or As(C₆H₅)₂ bridges and anionic three-center two-electron (3c2e) delocalized boron heterocyclic units, were prepared and characterized by NMR as well as by X-ray structure analyses. The boron chemical shifts of the trishomoaromatic dianion 12a with an oxygen bridge compare well with those computed ab initio for model 12b. Analysis of the electronic structure of the bishomoaromatic 5u and its anionic analog 11u gives insight into the origin of the trend of increasing effectiveness of BC₂, B₂C and B₃ 3c2e bonds: higher electronegativity of carbon vs boron prevents symmetric delocalization in rings with B₂C and especially BC₂ centers.     

Synthesis and X-Ray Analysis of New Spirophosphoranes

Abstract

2- and 3-hydroxyalkyliminophosphoranes and their valencetautomeric pentacoordinated phosphoranes are deprotonated by KH to give anionic pentacoordinated phosphoranes. Upon methylation the latter are converted into N-methyl derivatives. The geometries of these compounds are determined by X-ray analysis and n.m.r. spectroscopy.