Study of the fragmentation of small sulphur clusters

The fragmentation of sulphur clusters caused by electron impact ionization was studied. For this purpose, a beam ofS _n -clusters withn≦8 was generated in a gas aggregation source and ionized by electrons of variable energy. Special care was taken to maintain constant nucleation conditions so that the neutral cluster composition remained unchanged. It was found that the cluster ion mass spectra drastically depend on the electron energy. Even near threshold fragmentation processes contribute significantly to the dependence of the ion intensities on the electron energy.     

Theoretical Definition of a Functional Group and the Molecular Orbital Paradigm

It is the purpose of this review to demonstrate that the empirical classification of the observations of chemistry in terms of the properties assigned to functional groups is a consequence of and is predicted by physics. This is accomplished by showing that the atoms and functional groups of chemistry can be identified with bounded space-filling objects whose properties are defined by quantum mechanics. The quantum mechanical definition of a group is combined with a new pictorial representation of its form to obtain a unified picture which should make it eminently recognizable to chemists. This picture, when combined with the demonstrated ability of these groups to recover the measured properties of atoms in molecules, is offered as one which meets the expectations a chemist associates with the concept of a functional group. The manner in which this physical definition of a group differs fundamentally from models of functional groups based upon molecular orbital theory is discussed.     

Palladium-catalyzed, stereoselective rearrangement of a tetracyclic allyl cyclopropane under arylation

The first example of a pi,sigma domino-Heck reaction under concomitant rearrangement of the tetracyclic allylcyclopropane endo,exo-bishomobarrelene (5) is reported; the stereoselective reaction proceeds via an intramolecular insertion of a primarily-formed carbopalladation intermediate into a strained cyclopropane C-C sigma-bond, giving 9.     

Simultaneous measurement of glucose and glutamine in aqueous solutions by near infrared spectroscopy

A method is described for measuring the concentrations of both glucose and glutamine in binary mixtures from near infrared (NIR) absorption spectra. Spectra are collected over the range from 5000–4000/cm (2.0–2.5μm) with a 1-mm optical path length. Glucose absorbance features at 4710, 4400, and 4300/cm and glutamine features at 4700, 4580, and 4390/cm provide the analytical information required for the measurement. Multivariate calibration models are generated by using partial least squares (PLS) regression alone and PLS regression combined with a preprocessing digital Fourier filtering step. The ideal number of PLS factors and spectral range are identified separately for each analyte. In addition, the optimum Fourier filter parameters are established for both compounds. The best overall analytical performance is obtained by combining Fourier filtering and PLS regression. Glucose measurements are established over the concentration range from 1.66–59.91 mM, with a standard error of prediction (SEP) of 0.32 mM and a mean percent error of 1.84%. Glutamine can be measured over the concentration range from 1.10–30.65 mM with a SEP of 0.75 mM and a mean percent error of 6.67%. These results demonstrate the analytical utility of NIR spectroscopy for monitoring glucose and glutamine levels in mammalian and insect cell cultures.     

Studies on the distribution and concentration of thiamine in blood and urine

Studies are reported resulting in a reliable procedure for estimating the thiamine content in human blood and urine. For the determination in blood, heparinized blood is hemolyzed with 0.3 N hydrochloric acid at 100 °C. Cocarboxylase is then converted to free thiamine by means of wheat germ acid phosphatase at pH 5.0 in an acetate buffer. The liberated thiamine is adsorbed to a CG-50 (Rohm & Haas) carboxylic acid ion exchange acrylic resin column and then eluted with 1 N H₂SO₄. The thiamine is then oxidized to thiochrome and extracted with n-butyl alcohol, at pH 9.8–10.0, in the presence of disodium phosphate. Readout is by fluorometry at an excitation wavelength of 371 nm and an emission wavelength of 425 nm. The range found for thiamine in whole blood by this procedure on 18 normal adults was 1.9–3.9 μg/100 ml, with a mean value of 2.77 μg/100 ml of whole blood. The mean recovery of 12 recovery experiments was 94.1%. The same procedure is applicable to the determination of thiamine in urine. Conversion of cocarboxylase to free thiamine is not necessary since it was determined that practically all of the thiamine found in urine is not phosphorylated. Urine values were variable, the range for 11 healthy adults being 5.6–77.9 μg/100 ml with a mean value of 19.2 μg/100 ml. This corresponds to a value of 346 μg of thiamine/24 hours.     

Analysis of pseudopartial and partial wetting of various substrates by lead

Lead drops exhibit partial wetting on some substrates and pseudopartial wetting on others. In pseudopartial wetting, a film is in equilibrium with a capillary body with a nonzero contact angle. Using a free energy formulation appropriate for the experiments, we show the conditions under which minimization of the system energy is accurately achieved by minimizing the energy of the film alone. Using a set of simple surface energy isotherms, we explain the various wetting behaviors of lead. We contrast isotherms for autophobing systems and the metallic systems considered here.     

First principles resonance widths for Li near an Al(001) surface: predictions of scattered ion neutralization probabilities

By combining a first-principles periodic density functional theory calculation of adsorbate resonance widths with a many-body dynamical theory of charge transfer, we assess charge-transfer rates for ions scattering off metal surfaces. This goes beyond previous approaches, which have been limited to modeling the surfaces with either static potentials or finite clusters. Here we consider Li(+) scattering from an Al(001) surface. We show how the Li 2s orbital hybridizes with metal valence bands, near the surface, increasing the width of the 2s energy level. This in turn affects the charge-transfer rates between the ion and the metal surface. Our predictions for Li(+)-Al(001) scattering yield the correct angular dependence of the fraction of neutral Li atoms formed when compared to experiment.     

Isolierung und Aminosäuresequenz von Substanz P aus Pferdedarm

The isolation and amino acid sequence of substance P from horse intestine is reported. The sequence, H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂ is identical with the sequence reported for substance P isolated from bovine hypothalami.     

Picosecond acoustic transmission measurements. II. Probing high frequency structural relaxation in supercooled glycerol

The high frequency acoustic response of liquids is measured in a manner directly analogous to conventional ultrasonic measurements. Two thin metal films act as acoustic transducer and receiver for a liquid layer between them. Pulsed optical excitation generates high bandwidth wave packets in the transducer, and these are detected in the receiver after damping and dispersion by the liquid. This initial measurement probes structural relaxation dynamics of glycerol in the frequency range 2-20 GHz, for temperatures between 235 and 291 K. The analysis presented here demonstrates the presence of excess relaxation, not accounted for by either the alpha or beta relaxation of the mode-coupling theory, and suggests the presence of constant loss in the susceptibility spectrum of supercooled glycerol.     

Cartilage degradation by stimulated human neutrophils: reactive oxygen species decrease markedly the activity of proteolytic enzymes

BACKGROUND: Although neutrophilic granulocytes clearly contribute to cartilage degradation in rheumatic diseases, it is unclear if reactive oxygen species (ROS) or proteolytic enzymes are the most important components in cartilage degradation and how they interact. RESULTS: Neutrophils were stimulated by chemicals conferring a different degree of ROS formation and enzyme release. Supernatants of neutrophils were incubated with thin slices of pig articular cartilage. Supernatants of cartilage were assayed by NMR spectroscopy, MALDI-TOF mass spectrometry and relevant biochemical methods. Stimulation conditions of neutrophils correlated well with the extent of cartilage degradation. Due to the release of different enzymes, cartilage degradation could be best monitored by NMR since mainly low-mass degradation products were formed. Astonishingly, the suppression of the formation of ROS resulted in decreased cartilage degradation. CONCLUSION: ROS formed by neutrophils are not directly involved in cartilage degradation but influence the activity of proteolytic enzymes, which are the main effectors of cartilage degradation.