A practical approach to the preparative purification of peptides using analytical instrumentation with analytical and semipreparative columns

Summary We have examined the effect of particle size of silica-based reversed-phase packings and column packing techniques on the reversed-phase analytical separation of a peptide mixture. A C₁₈ packing of 15–20 μm average particle size produced satisfactory peptide resolution, allowing a relatively inexpensive scale up to the preparative purification of peptides. A shallow gradient (0.1% acetonitrile/min) elution procedure was developed for the preparative purification of closely related decapeptides (differing by one methyl group) on analytical (250×4.1 mm I.D.) and semipreparative (250×10 mm I.D.) columns. Up to 30 mg and 225 mg of the two-peptide mixture was efficiently resolved, with high yields of homogeneous peptides, on analytical and semipreparative columns, respectively, containing the 15–20 μm packing. We have also demonstrated the potential of our purification procedure for resolving more complex multicomponent mixtures by efficiently separating a total of 22 mg of three closely-related peptides on analytical columns containing 7 μm or 15–20 μm particle size reversed-phase packings. The use of the inexpensive 15–20 μm packing, coupled with the ability to pack efficient columns with analytical HPLC instrumentation, offers great cost saving potential.     

Zur Untersuchung von Zuckersirup

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The effect of proton irradiation on the melting and isothermal crystallization of poly(ether‐ether‐ketone)

Amorphous poly(ether‐ether‐ketone) (PEEK) progressively crosslinks on irradiation with 11.0 MeV protons, and this has a marked effect on the extent of crystallinity that subsequently develops and on the kinetics of the high temperature isothermal crystallization. The extent of crystallinity with time was analyzed using the Avrami equation, and the temperature dependence of the rate constants was analyzed in terms of nucleation theory. While irradiation inhibits the overall rates of crystallization by the reduction in the mobility of the chain segments as observed by the progressive increase in the glass transition temperature, it also alters the fold surface free energy. The observed melting points were consistent with depression of the equilibrium melting point by the crosslinks produced by irradiation. These two effects alone are sufficient to account for the inhibition of crystallization on irradiation of PEEK by protons. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1094–1103, 2008     

Por?se Tonfilter

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Elektrochemie

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Analysis and computation for nonlinear elastic surface waves of permanent form

Linear elastic surface waves are nondispersive. All wavelengths travel at the Rayleigh wave speed c _R. This absence of frequency dispersion means that nonlinear waves of permanent form cannot be determined as a small perturbation from a sinusoidal wavetrain. By representing the general Rayleigh wave of the linear theory in terms of a pair of conjugate harmonic functions, waves which propagate without distortion are characterized as those having surface elevation profiles which satisfy a certain nonlinear functional equation. In the small-strain limit, this reduces to a quadratic functional equation. Methods for the analysis of this equation are presented for both periodic and nonperiodic waveforms. For periodic waveforms, the infinite system of quadratic equations for the Fourier coefficients of the profile is solved numerically in the case of a certain harmonic elastic material. Two distinct families of profiles having phase speed differing from the linearized Rayleigh wave speed are found. Additionally, two families of exceptional waveforms are found, describing profiles which travel at the Rayleigh wave speed.     

Experimental measurement of the van der Waals binding energy of X-O2 clusters (X=Xe, CH3I, C3H6, C6H12)

Van der Waals binding energies for the X-O(2) complexes (X=Xe, CH(3)I, C(3)H(6), C(6)H(12)) are determined by analysis of experimental velocity map imaging data for O((3)P(2)) atoms arising from UV-photodissociation of the complex [A. V. Baklanov et al., J. Chem. Phys. 126, 124316 (2007)]. Several dissociation pathways have been observed, we focus on the channel corresponding to prompt dissociation of X-O(2) into X+2O((3)P) fragments, which is present for complexes of O(2) with all partners X. Our method is based on analysis of the kinetic energy of all three photofragments, where the O atom kinetic energy was directly measured in the experiment and the kinetic energy of the X partner was calculated using momentum conservation, along with the measured angular anisotropy for O atom recoil. We exploit the fact that the clusters are all T-shaped or nearly T-shaped, which we also confirm by ab initio calculations, along with knowledge of the transition dipole governing radiative absorption by the complex. The effect of partitioning the kinetic energy between translation along the X-O(2) and O-O coordinates on the angular anisotropy of the O atom recoil direction is discussed. Van der Waals binding energies of 110±20 cm(-1), 280±20 cm(-1), 135±30 cm(-1), and 585±20 cm(-1) are determined for Xe-O(2), CH(3)I-O(2), C(3)H(6)-O(2), and C(6)H(12)-O(2) clusters, respectively.     

Vibrational spectra of benzene chromium tricarbonyl and its mesityl analogue: a study by neutron spectroscopy

We have used high resolution neutron vibrational spectroscopy to study the vibrations of the model compound for arene-to-metal bonding, benzene chromium tricarbonyl, and its mesityl analogue. It is shown that all previously published assignment schemes, based on optical spectroscopy alone, are wrong, and new assignments are given in agreement with ab initio calculations.