Griesinger's Group @ The MPIBPC
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NMR structure of calix[4]resorcinarenes Resorcenarenes are macrocyclic compounds that are easily obtained by condensation reactions of resorcinol or resorcinol ethers with a variety of aliphatic as well as aromatic aldehydes under catalysis with mineral acids, carried out in a one-pot reaction. Resorcenarenes exhibit an extensive host-guest chemistry, a property which makes them of potential interest for development of molecular vehicles. In this work, we take advantage of sugar aldehydes to establish the first example of a new type of carbohydrate containing calix[4]resorcinarenes, substituted at their methine bridges with 1,2,3,4,5-acetylated arabityl residues. The condensation procedure is remarkably mild allowing for a large diversity of labile groups to be used The solution structure of one of these structures has been determined by NMR spectroscopy using NOE and coupling constants for molecular dynamics (MD). Chemical shifts were used to validate the conformation with the least NOE and J violations.
Aligning Proteins with the help of lanthanides Solution NMR structures of macromolecules such as proteins and nucleic acids have been determined mainly on the basis of distance (nuclear Overhauser effect, NOE) and dihedral angle (scalar J coupling constants) constraints. Recently, another kind of constraint, dipolar coupling, has been found to be effective in determining macromolecular structures. A dipolar coupling constant can be interpreted as the orientation of the corresponding bond vector with respect to an alignment tensor fixed at a molecular coordinate, thus reflecting long range geometry. Orientational constraints derived from dipolar coupling constants can further refine structures that are constructed only with short range NOE and J coupling constraints. A molecule with an anisotropic magnetic susceptibility is aligned in the static magnetic field. Such an alignment of a molecule provides useful structural and dynamic information including dipolar coupling constants, quadrupolar coupling constants, and chemical shift anisotropy, which would disappear in an isotropic non-alignment condition owing to a motional averaging. Lanthanide ions have recently been used to provide a target molecule with an anisotropic magnetic susceptibility partly because they do not exhibit paramagnetic relaxation effects as severe as other transition metal ions. Here we present another method for attaching metal ions, especially lanthanide ions, to proteins to align the molecules in a static magnetic field. We chemically synthesized a modified EDTA compound that can coordinate a lanthanide ion and bind to a cysteine residue through the disulfide bond. A Dye-bound form of a modified protein exhibited small dipolar couplings and pseudo-contact shifts in 1H-15N amide spin-systems.
Last modification Fri Jan 9 14:53:40 2004 |
