Investigations of cyclophilin interactions with oligopeptides containing proline by affinity capillary electrophoresis

Affinity capillary electrophoresis using mobility-shift analysis was utilized to characterize the binding of peptide ligands to cyclophilins, which are members of the enzyme family of peptidyl-prolyl cis/trans isomerases. Peptides derived from the human immunodeficiency virus capsid protein p24 exhibited different affinities to the isoenzymes cyclophilin18 and cyclophilin20. For the interaction of the peptide hormone bradykinin with cyclophilin18, a dissociation constant of 1.4 +/- 0.1 mM was determined. Finally, the affinity of cyclophilin20 to peptides from a cellulose-bound peptide library scanning the sequence of Drosophila melanogaster protein cappuccino was investigated. The affinities of selected peptides to cyclophilin20 and a green fluorescent fusion protein with cyclophilin20 were compared.     

EPR investigation of persistent radicals produced from the photolysis of dibenzyl ketones adsorbed on ZSM-5 zeolites

Photolysis of ketones (1, 1-oMe, 2, 2-oMe, 3, and 4) adsorbed on ZSM-5 zeolites produces persistent carbon-centered radicals that can be readily observed by conventional steady-state EPR spectroscopy. The radicals are persistent for time periods of seconds to many hours depending on the supramolecular structure of the initial radical@zeolite complex and the diffusion and reaction dynamics of radicals produced by photolysis. The structures of the persistent radicals responsible for the observed EPR spectra are determined by a combination of alternate methods of generation of the same radical, by deuterium substitution, and by spectral simulation. A clear requirement for persistence is that the radicals produced by photolysis must either separate and diffuse from the external to the internal surface or be generated within the internal surface and separate and diffuse apart. The persistence of radicals located on the internal surface is the result of inhibition of radical-radical reactions. Radicals that are produced on the external surface and whose molecular structure prevents diffusion into the internal surface are transient because radical-radical reactions occur rapidly on the external surface. The reactions of the persistent radicals with oxygen and nitric oxide were directly studied in situ by EPR analysis. In the case of reaction with oxygen, persistent peroxy radicals are formed in high yield. The addition of nitric oxide scavenges persistent radicals and leads initially to a diamagnetic nitroso compound, which is transformed into a persistent nitroxide radical by further photolysis. The influence of variation of radical structure on transience/persistence is discussed and correlated with supramolecular structure and reactivity of the radicals and their parent ketones.     

Direct conversion of EPR dipolar time evolution data to distance distributions

Shallow electron spin echo envelope modulations due to dipole-dipole couplings between electron spins provide information on the radial distribution function of the spins in disordered systems while angular correlations between spin pairs are negligible. Under these conditions and in the absence of orientational selection, the dipolar time evolution data can be quantitatively simulated for arbitrary radial distribution functions by shell factorization, i.e., by performing the orientational average separately for thin spherical shells and multiplying the signals of all the shells. For distances below 5 nm, a linear superposition of the signals of the shells is sufficient. The dipolar time evolution data can be separated into this linear contribution and a nonlinear background. The linear contribution can then be converted directly to a radial distribution function. For a series of shape-persistent and flexible biradicals with end-to-end distances between 2 and 5 nm, shell factorization and direct conversion of the data are in good agreement with each other and with force-field computations of the end-to-end distances. The neglect of orientation selection does not cause significant distortions of the determined distance distributions.     

Conjugated organometallic polymers containing Vollhardt's cyclobutadiene complex: aggregation and morphologies

Organometallic polymers were prepared by acyclic diyne metathesis (ADIMET) or by Pd-catalyzed coupling of 1,3-diethynylcyclobutadiene(cyclopentadienyl)cobalt with a suitably substituted diiodobenzene. The polymers obtained by Heck coupling show a degree of polymerization (Pn) of 20-60. The monomers for ADIMET were made by the Pd-catalyzed coupling of [1,3-bis(trimethylsilylethynyl)-2,4-bis(trimethylsilyl)cyclobutadiene](cyclopentadienyl)cobalt to 1-bromo-2,5-dialkyl-4-propynylbenzenes in the presence of KOH in yields of 40-48%. The monomers carry hexyl, ethylhexyl, and (S)-3,7-dimethyloctyl side chains. Polymerization of the propynylated monomers furnishes organometallic polymers with a Pn of up to 230 arylene-ethynylene units. The polymers were fully characterized by polarizing microscopy, transmission electron microscopy, circular dichroism, differential scanning calorimetry, and X-ray diffraction (XRD). They show nematic, lyotropic liquid crystalline phases as well as chiroptical properties from which aggregation in poor solvents and in the solid state can be concluded. Lamellar or irregular honeycomb-shaped morphologies in these organometallic polymers can be detected by electron microscopy.     

Pure absorption electron spin echo envelope modulation spectra by using the filter-diagonalization method for harmonic inversion

Harmonic inversion of electron spin echo envelope (ESEEM) time-domain signals by filter diagonalization is investigated as an alternative to Fourier transformation. It is demonstrated that this method features enhanced resolution compared to Fourier-transform magnitude spectra, since it can eliminate dispersive contributions to the line shape, even if no linear phase correction is possible. Furthermore, instrumental artifacts can be easily removed from the spectra if they are narrow either in time or frequency domain. This applies to echo crossings that are only incompletely eliminated by phase cycling and to spurious spectrometer frequencies, respectively. The method is computationally efficient and numerically stable and does not require extensive parameter adjustments or advance knowledge of the number of spectral lines. Experiments on gamma-irradiated methyl-alpha-d-glucopyranoside show that more information can be obtained from typical ESEEM time-domain signals by filter-diagonalization than by Fourier transformation.     

The phase φ+− of CP violation in the K0 → π+π− decay

The phase φ_+? is evaluated on the basis of measurements of the K_S-K_L interference in the π⁺π^? decay mode and the mass difference Δm, both reported previously by this group. The result is: φ_{+? = 45.9° ± 1.6°}. This, together with previous results on $\text{|η}{}_{\mathrm{+?}}\text{|, |}\text{η}{}_{00}\text{η}{}_{\mathrm{+?}}\text{|}$ and the charge asymmetry δ in leptonic decay, is compared with the prediction of the superweak model, with good agreement.Finally the result is used to find, on the basis of unitarity, a new upper limit on CP violation in the decay K⁰ → 3π⁰. This limit is |η₀₀₀|^2? 0.21.