Sharper approximation of extreme points by far points

This research was supported in part by the National Science Foundation, U.S.A.     

Temporary attachment of carbohydrates to cyclopeptide templates: a new strategy for single-bead analysis of multivalent neoglycopeptides

Employing a cleavable carbohydrate–peptide linker, a new strategy for single-bead analysis of multivalent cyclic neoglycopeptides based on Edman degradation is described. Edman degradation of glycopeptides is hampered by the acid lability of the glycosidic bond and potential incompatibilities of phenylthiohydantoin (PTH) derivatives of glycosylated amino acids with PTH derivatives of the proteinogenic amino acids. To overcome this problem, carbohydrates are detached from the cyclopeptide templates before single-bead analysis, allowing for micro sequencing under routine conditions. With this strategy, application of multivalent cyclic neoglycopeptides in split-mix libraries with a subsequent screening process becomes possible for the first time.     

Synthesis and characterization of poly(vinyl alcohol)‐graft‐[poly(D,L‐lactide)/poly(D,L‐lactide‐co‐glycolide)] hydrogels

Poly(D ,L ‐lactide) and poly(D ,L ‐lactide‐co‐glycolide) with various composition and with one methacrylate and one carboxylate end group were synthesized and grafted onto poly(vinyl alcohol) (PVA) via the carboxylate group. The graft copolymers were crosslinked via the methacrylate groups using a free radical initiator. The polymer networks were characterized by means of NMR and studied qualitatively by means of IR spectroscopy. The influence of the glycolide content in the polyester grafts and of the number of ester units in the grafts on thermal properties and swellability were studied as well. The high swellability in water is characteristic of all hydrogels. Differential scanning calorimetry (DSC) showed a single glass transition temperature that occurs in the range between 51 and 69 °C. Thermogravimetric analysis (TGA) of the networks showed the main loss in weight in the temperature range between 290 and 370 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4536–4544, 2007     

Untersuchungen über Radium- und Bariumfällungen unter Anwendung von Thorium X als Indikator

Zusammenfassung Zunächst wird im Zusammenhang mit Messungen der Fällungsgeschwindigkeit von Thorium X in sulfathaltigen Lösungen eine Methode beschrieben, die es gestattet, während der Fällung, und zwar ohne Störung des Fällungsvorganges, diejenigen Mengen von Thorium X zu bestimmen, die sich jeweils zu bestimmten Zeitpunkten noch in Lösung befinden; dabei konnte der Gehalt an Th X mit Hilfe einer Emanationsmethode genau ermittelt werden.Die Versuchsergebnisse, die in Kurven wiedergegeben sind, lassen deutlich erkennen, daß die Fällung von Th X nicht momentan erfolgt, sondern eine gewisse Zeit beansprucht, die von der Konzentration der zugesetzten Sulfat- und Bariumchloridlösung sowie vom Zusatz anderer Fremdionen abhängig ist; es wird jedoch schließlich immer der gleiche Endzustand vollständiger Ausfällung erreicht, wenn mit äquivalenten Mengen gearbeitet wird.Die Annahme, daß die Fällung momentan erfolgt, daß aber das Fällungsprodukt sich im Laufe der Zeit von einem feinkristallinischen Zustand mit großer Emanierfähigkeit in einen grobkristallinen mit geringer Emanationsabgabe umwandelt, konnte durch besondere Experimente widerlegt werden.Schließlich wird noch eine Apparatur zur Messung des Thorongehalts angegeben, die auch für Untersuchungen des Thoriumgehalts von Quellwässern Anwendung finden kann.

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Summary A method has been worked out which makes it possible to determine the rate of precipitation of thorium X in solutions containing sulphate ion. The amount of thorium X is determined rapidly and accurately by the thorium emanation—thoron—evolved under fixed conditions. Determinations have been made every 5 minute during the time following precipitation, and the results are given graphically.They bring forward, very clearly, that the precipitation of thorium X requires a certain length of time, depending on the concentration of the sulphate and barium-chloride solutions used and on the presence of other ions. However, if equivalent quantities of barium- and sulphate ions are used, the same final result is always reached.It might have been supposed that the precipitation takes place instantaneously but that in course of time, the precipitate undergoes changes through recrystallisations and that the emanating power changes accordingly. That hypothesis, however, could be disproved by special experiments.At last an apparatus for measuring the thoron content is given which can also be applied for investigations of the thorium content of source waters.

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Résumé Les auteurs décrivent une méthode qui leur a permis de déterminer la vitesse de précipitation du thorium X en solutions contenant de l'ion sulfurique. Le thorium X est dosé par son émanation — le thoron — sous des conditions fixées, et les dosages peuvent se faire à intervalles régulières pendant le temps que demande la précipitation.Les résultats montrent que la précipitation du thorium X ne se fait point à l'instant, mais demande un certain temps, dépendant de la concentration des solutions de sulfate et de chlorure de baryum ajoutées et aussi de la présence d'ions étrangers.Les auteurs réfutent par leurs expériences la théorie que la précipitation se fait momentanément et que le précipité change peu à peu son état cristallin et par cela même, sa faculté de dégager l'émanation.Enfin les auteurs décrivent un appareil pour les dosages de thoron, qui pourra servir de même pour déterminer la teneur en thorium dans les eaux vives.

     

Manipulation of microalgal lipid production using genetic engineering

Applied Biochemistry and Biotechnology - Genetic transformation of two species of diatoms has been accomplished by introducing chimeric plasmid vectors containing a bacterial antibiotic resistance...     

Review: mass spectrometry of step-growth polymers

For at least two decades different mass spectrometric techniques have been applied for polymer analysis, including the qualitative determination of chemical compositions, end group identification, functionality type distribution and the determination of the cyclisation extend at each degree of polymerisation. Molecular weights exceeding 100 KDa are provable by MALDI-ToF mass spectrometry. Further, molecular weight distributions are determined by MADLI-ToF. However, there are some hints that, there is a discrimination against higher molecular weight species in samples with polydispersity of more than 1.2. Furthermore, pathways for dendritic and hyper-branched polymers, supramolecular polymers and nano condensates are analysed by help of mass spectrometry.     

Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1)

The high resolution Fourier transform far-infrared (FIR) spectrum of the torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.     

Simulation of 59Co NMR chemical shifts in aqueous solution

59Co chemical shifts were computed at the GIAO-B3LYP level for [Co(CN)6]3-, [Co(H2O)6]3+, [Co(NH3)6]3+, and [Co(CO)4]- in water. The aqueous solutions were modeled by Car-Parrinello molecular dynamics (CPMD) simulations, or by propagation on a hybrid quantum-mechanical/molecular-mechanical Born-Oppenheimer surface (QM/MM-BOMD). Mean absolute deviations from experiment obtained with these methods are on the order of 400 and 600 ppm, respectively, over a total delta(59Co) range of about 18,000 ppm. The effect of the solvent on delta(59Co) is mostly indirect, resulting primarily from substantial metal-ligand bond contractions on going from the gas phase to the bulk. The simulated solvent effects on geometries and delta(59Co) values are well reproduced by using a polarizable continuum model (PCM), based on optimization and perturbational evaluation of quantum-mechanical zero-point corrections.     

Synthesis and reactivity of rhodium fluoro complexes

[RhH(CO)(PPh₃)₂] (1) reacts with Et₃N·3HF to give the fluoro compound [RhF(CO)(PPh₃)₂] (2). In a comparable reaction [RhF(PEt₃)₃] (5) has been obtained from [RhH(PEt₃)₃] (3) or [RhH(PEt₃)₄] (4) with substoichiometric amounts of Et₃N·3HF in THF. If the latter reaction is carried out in benzene, the complexes 5, cis-mer-[Rh(H)₂F(PEt₃)₃] (6) and cis-fac-[Rh(H)₂F(PEt₃)₃] (7) are obtained. Treatment of 5 with HCl in ether effects the generation of [RhCl(PEt₃)₃] (8) and the bifluoride compound [Rh(FHF)(PEt₃)₃] (9), which can be converted into 5 in the presence of Et₃N and Cs₂CO₃. Treatment of 5 with HSiR₂Ph (R=Ph, Me) leads to the formation of 3 and the rhodium(III) silyl complexes fac-[Rh(H)₂(SiR₂Ph)(PEt₃)₃] (10: R=Ph, 11: R=Me).