Self-organization of supramolecular helical dendrimers into complex electronic materials.

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use.

High charge carrier mobility in conjugated organometallic polymer networks.

The improvement of charge transport in conjugated polymers is a focal point of current research. It is shown here that the carrier mobility can be substantially increased through the introduction of conjugated cross-links between the conjugated chains. Novel organometallic polymer networks based on a poly(p-phenylene ethynylene) (PPE) derivative and Pt0 were synthesized by ligand-exchange reactions between the linear PPE and a low-molecular Pt complex.

Electronic transport in smectic liquid crystals.

Time-of-flight measurements of transient photoconductivity have revealed bipolar electronic transport in phenylnaphthalene and biphenyl liquid crystals (LC), which exhibit several smectic mesophases. In the phenylnaphthalene LC, the hole mobility is significantly higher than the electron mobility and exhibits different temperature and phase behavior. Electron mobility in the range approximately 10(-5) cm(2)/V s is temperature activated and remains continuous at the phase transitions.

Solid-state NMR studies of magnetically aligned phospholipid membranes: taming lanthanides for membrane protein studies.

The addition of lanthanides (Tm3+, Yb3+, Er3+, or Eu3+) to a solution of long-chain phospholipids such as dimyristoylphosphatidylcholine (DMPC) and short-chain phospholipids such as dihexanoylphosphatidylcholine (DHPC) is known to result in a bilayer phase in which the average bilayer normal aligns parallel to an applied magnetic field. Lanthanide-doped bilayers have enormous potential for the study of membrane proteins by solid-state NMR, low-angle diffraction, and a variety of optical spectroscopic techniques. However, the addition of lanthanides poses certain challenges to the NMR spectroscopist: coexistence of an isotropic phase and hysteresis effects, direct binding of the paramagnetic ion to the peptide or protein of interest, and severe paramagnetic shifts and line broadening.

Novel chelate-induced magnetic alignment of biological membranes.

A phospholipid chelate complexed with ytterbium (DMPE-DTPA:Yb3+) is shown to be readily incorporated into a model membrane system, which may then be aligned in a magnetic field such that the average bilayer normal lies along the field. This so-called positively ordered smectic phase, whose lipids consist of less than 1% DMPE-DTPA:Yb3+, is ideally suited to structural studies of membrane proteins by solid-state NMR, low-angle diffraction, and spectroscopic techniques that require oriented samples. The chelate, 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine diethylenetriaminepentaacetic acid, which strongly binds the lanthanide ions and serves to orient the membrane in a magnetic field, prevents direct lanthanide-protein interactions and significantly reduces paramagnetic shifts and line broadening.