Component B binding to the soluble methane monooxygenase hydroxylase by saturation-recovery EPR spectroscopy of spin-labeled MMOB

Spin-labeled Cys89 of the soluble methane monooxygenase regulatory protein (MMOB) from Methylococcus capsulatus (Bath) binds within 15 +/- 4 A of the hydroxylase (MMOH) diiron center, placing the MMOB docking site in the MMOH "canyon" region on iron-coordinating helices E and F of the alpha-subunit.     

Element determination in medieval soil samples by total reflection X-ray fluorescence analysis

An aqua regia extraction procedure for heavy metals in soils optimised for total reflection X-ray fluorescence analysis is presented. The procedure is applied to 92 soil samples of medieval layers from the city area of Dortmund. Sixteen elements (P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ag, Sn, and Pb) were used to characterise 17 sample sites. The results are projected onto the medieval urban structure of Dortmund. Two sites loaded with non-ferrous heavy metal could be detected and correlated with archaeological data. The efficiency and repeatability of the proposed extraction procedure is discussed.     

Stereoselective Oxidative Bioconjugation of Amino Acids and Oligopeptides to Aldehydes

The first stereoselective, near-equimolar, and metal-free oxidative bioconjugation of amino acids and oligopeptides to aldehydes is presented. Based on a newly developed organocatalytic oxidative concept, the C-terminal and side-chain carboxylic acid functionalities of amino acids and oligopeptides are shown to couple in a stereoselective manner to α-branched aldehydes catalyzed by a chiral primary amine and a quinone as oxidizing agent. The oxidative coupling generally proceeds in high yield. For aspartic acid, selective coupling of the side-chain, or the C-terminal carboxylic acid, is demonstrated depending on the protection strategy. The stereoselective, oxidative bioconjugation concept is extended to a series of oligopeptides where coupling to carboxylic acid functionalities is presented. Bioorthogonal linker molecules for further functionalization are obtained by merging the oxidative coupling strategy with the click concept. It is demonstrated that the configuration of the new stereocenter is determined exclusively by the organocatalyst.     

Perhydro dioxazepines-1,5,3 : Methode generale de synthese

Perhydrodioxazepines-1,5,3 are obtained by reacting a primary amine with a 1,2-diol and paraformaldehyde.     

Site‐Specific Investigation of the Steady‐State Kinetics and Dynamics of the Multistep Binding of Bile Acid Molecules to a Lipid Carrier Protein

The investigation of multi‐site ligand–protein binding and multi‐step mechanisms is highly demanding. In this work, advanced NMR methodologies such as 2D ¹H–¹⁵N line‐shape analysis, which allows a reliable investigation of ligand binding occurring on micro‐ to millisecond timescales, have been extended to model a two‐step binding mechanism. The molecular recognition and complex uptake mechanism of two bile salt molecules by lipid carriers is an interesting example that shows that protein dynamics has the potential to modulate the macromolecule–ligand encounter. Kinetic analysis supports a conformational selection model as the initial recognition process in which the dynamics observed in the apo form is essential for ligand uptake, leading to conformations with improved access to the binding cavity. Subsequent multi‐step events could be modelled, for several residues, with a two‐step binding mechanism. The protein in the ligand‐bound state still exhibits a conformational rearrangement that occurs on a very slow timescale, as observed for other proteins of the family. A global mechanism suggesting how bile acids access the macromolecular cavity is thus proposed.     

Desamination directe d'amines tertiaires N,N-dimethylees

We report three cases, in the steroid field, in which a tertiary N,N-dimethylamine on treatment with 2,2,2-trichloroethylchloroformate, leads predominantly and in one case exclusively to a deamination product rather than the expected N-demethylation product.