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.     

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.     

Macrolide antibiotics—VIII The absolute configuration of certain centers in neomethymycin, erythromycin and related antibiotics

Neomethymycin (I) has been transformed into “anhydrocycloneomethynolide” (V) which could be degraded via (−)--methyllevulinic acid to (−)--methylsuccinic acid, thus establishing the absolute configuration of positions 4 and 6 in the lactonic acid (XIII). This acid is a common degradation product of methymycin, neomethymycin, pikromycin and narbomycin and there is thus available a standard of absolute configuration for these macrolide antibiotics. By a different sequence of reactions, erythromycin (XXIII) has been converted into (+)--methyllevulinic acid and (+)--methylsuccinic acid. Coupled with earlier results reported in the literature, it is now possible to assign absolute configurations to positions 10 (R) and 8 (R) of erythromycin and this applies most likely also to positions 4 (R) and 2 (S). Attention is called to the biogenetic significance of these observations.     

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.     

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.     

The heats of reaction of phosphines and phosphites with toluene-molybdenum tricarbonyl. Importance of both steric and electronic factors in determining the Mo---PR3 bond strength

The heats of reaction of tolueneMo(CO)₃ with a series of phosphines and phosphites have been measured by solution calorimetry. The order of stability toward formation of fac-(PR₃)₃Mo(CO)₃ in THF solution is: P(OCH₃)₃s> PMe₃ > PⁿBu₃ > PMe₂Ph> PEt₃ > triphos> P(OPh)₃ > PMePh₂ > PPh₃ > PCl₃ and spans a range of 25 kcal/mol reflecting individual bond strength differences up to 8 kcal/mol. The bulky phosphines PCy₃ and P^tBu₃ react with tolueneMo(CO)₃ in THF, but 30–40 kcal/mol less heat is evolved in these reactions than with the other phosphines and phosphites. The coordinately unsaturated five-coordinate complexes (PR₃)₂Mo(CO)₃ are proposed as the reaction products. The importance of both steric and electronic factors in the Mo---P bond is discussed.     

Synthesis and first molecular structure of a bis-2-spiro-1-boraadamantane derivative

[reaction: see text] A new method for synthesizing the 2-spiro-boraadamantane pyridine complex (2) from 1-ethynylcyclohexylmethyl ether has been developed. The chemistry has been applied to the synthesis of bis-2-spiro-1-boraadamantane.pyridine (1) from trans-1,4-diethynyl-1,4-dimethoxycyclohexane (8). This bis-Lewis acid serves as a self-assembling molecular building block with difunctional Lewis bases.     

Extended theoretical considerations for Mass resolution in the resonance ejection mode of quadrupole Ion Trap Mass Spectrometry

Proceeding from the pseudopotential-well approximation for ion motion in a quadrupole ion trap, mathematical expressions are derived to describe the excitation amplitude of an ion packet at a given mass-to-charge ratio. Ion-neutral collisions are incorporated to describe the damping of ion trajectories and to describe the distribution of individual ion trajectories about a mean amplitude for the ion packet. The rate of increase of the amplitude during scanning is related to expressions that describe the amplitude dispersion of the ions at the time of ejection from the trap, which is operating in a resonance ejection scanning mode to describe the temporal line width of the ejected ion packet. The temporal line width is related to mass resolution under a number of different scanning conditions. Included in the discussion are considerations of the effect on resolution of the resonance excitation voltage, temperature, pressure, noise, and buffer-gas composition. An expression for the maximum possible resolution at high ion mass-to-charge ratios is developed, and these results are compared to an existing theoretical construction. The expressions derived under the pseudopotential-well approximation are further extended to high q _z values and compared to experimental data previously published by two other researchers.