Inversion symmetry and local vs. dispersive interactions in the nucleation of hydrogen bonded cyclic n-mer and tape of imidazolecarboxamidines.

Substitutional changes to imidazolecarboxamidine that preserved intermolecular hydrogen bonding in the solid state were used to study the relationship between packing and the hydrogen bond motif. Various motifs competed, but the most common imidazolecarboxamidine crystalline phase was a C(i) symmetric dimer that established inversion centers by associating enantiomeric tautomers. Counter to intuition, the calculated gas-phase energies per molecule of the solid state atomic coordinates of the C(i) dimer motifs were higher than those of the C(1) dimer, trimer, tetramer and tape motifs, while the packing densities of C(i) dimers were found to be higher.

De novo design and spectroscopic characterization of a dinucleating copper-binding pentadecapeptide.

A spectroscopic study of aqueous solutions of Ac-WGHGHGHGPGHGHGH-NH(2) (HGP) indicates that copper(II) binds to the peptide to form a 2:1 Cu(2+)/HGP complex with four nitrogen atoms in the copper coordination environment. Electron paramagnetic resonance (EPR) and UV-visible data suggest copper binding through the peptide backbone and imidazole nitrogen donors. Circular dichroism data show that HGP is unbound below pH 5.

Monitoring the growth of polyoxomolybdate nanoparticles in suspension by flow field-flow fractionation.

We follow the evolution of polyoxomolybdate nanoparticles in suspensions derived from the keplerate (NH4)42[MoVI72MoV60O372(CH3CO2)30(H2O)72].ca..

A helical structure with Z' = 10.

The structure of N''-cyano-N,N-diisopropylguanidine, a push-pull nitrile that includes the H(2)N-C=N-CN fragment, has been determined. Although the number of molecules in the asymmetric unit is exceptionally high (Z' = 10), there were no special crystallographic difficulties associated with data collection, structure solution or structure refinement because the individual molecules are small (12 non-H atoms) and because there is no important crystallographic pseudosymmetry. A complete set of N-H.