Stereoselective synthesis of trans-threo-trans-oligopyrrolidines: potential agents for RNA cleavage

The 2,5-trans-substituted oligopyrrolidines constitute a promising class of novel RNA-binding agents as well as potential building blocks for artificial anion channels. A convergent synthesis of terpyrrolidine 1 and pyrrolidino-THF-pyrrolidine 2 is reported, relying upon convergent coupling of 2,5-trans-pyrrolidinecarboxaldehydes through bridging alkyne units under Felkin-Anh control and subsequent closure of the central ring. After complete deprotection, the free polyamine products were isolated in excellent yield and purity. Crystal structure analyses of a terpyrrolidine and a pyrrolidino-THF-pyrrolidine documented their helical privileged conformations. The compounds were then screened for RNA cleavage activity. Unlike the only weakly active simple polyamines, p-nitrosulfonamide 33 was found to induce cleavage at mM concentrations under physiologically relevant conditions.     

Multidimensional density operator propagations in open systems: model studies on vibrational relaxations and surface sticking processes

An efficient method for the numerical treatment of multidimensional dynamics of open systems is presented: the multiconfiguration time-dependent Hartree (MCTDH) method extended to the propagation of density operators. With this method we investigate the relaxation process of a CO molecule adsorbed on a copper surface, i.e., CO/Cu(100), after the excitation with an infrared (IR) pulse. The interaction potential was taken from the literature. Lifetime estimations and thermalization studies were performed on the IR excited CO molecule. We were able to treat this system with all six degrees of freedom (DOF) and thus 12 dynamical variables, but most of our studies used a two or four DOF model. Finally, we demonstrate the applicability of MCTDH to the analysis of scattering processes in an open environment. We calculate sticking coefficients of a scattered particle to a model surface, the latter acting as heat bath. The surface corrugation and the initial particle energy have been varied, and six different relaxation strengths have been studied. These calculations were done under the inclusion of three DOFs: the two surface coordinates and the distance between the particle and the surface.     

Kinetics of Mass Transfer in the Melt Polycondensation of Poly(Ethylene Terephthalate)

For a four-parameter reaction-mass transport model of melt polycondensation, the constants of polycondensation, thermolysis, and diffusion were determined by means of experiments in thin-layer polycondensation. Based on these constants, the convectional mass transport and efficient melt thickness in polycondensation systems under conditions of compelled mixing can be estimated. However, for stirred polycondensation systems a reaction-mass transfer model proves more suitable. The constants of polycondensation and thermolysis obtained by the diffusion model can be transferred to the reaction-mass transfer model. Thus, only the mass transfer coefficient has to be determined.     

Li ion diffusion in the anode material Li12Si7: ultrafast quasi-1D diffusion and two distinct fast 3D jump processes separately revealed by 7Li NMR relaxometry

The intermetallic compounds Li(x)Si(y) have attracted considerable interest because of their potential use as anode materials in Li ion batteries. In addition, the crystalline phases in the Li-Si phase diagram turn out to be outstanding model systems for the measurement of fast Li ion diffusion in solids with complex structures. In the present work, the Li self-diffusivity in crystalline Li(12)Si(7) was thoroughly probed by (7)Li NMR spin-lattice relaxation (SLR) measurements. Variable-temperature and -frequency NMR measurements performed in both the laboratory and rotating frames of reference revealed three distinct diffusion processes in Li(12)Si(7). The diffusion process characterized by the highest Li diffusivity seems to be confined to one dimension. It is one of the fastest motions of Li ions in a solid at low temperatures reported to date. The Li jump rates of this hopping process followed Arrhenius behavior; the jump rate was ~10(5) s(-1) at 150 K and reached 10(9) s(-1) at 425 K, indicating an activation energy as low as 0.18 eV.