Magnetic and thermal properties of 4f-3d ladder-type molecular compounds

We report on the low-temperature magnetic susceptibilities and specific heats of the isostructural spin-ladder molecular complexes L$_{2}$[M(opba)]_{3\cdot xDMSO$\cdot y$H$_{2}$O, hereafter abbreviated with L$_{2}$M$_{3}$ (where L = La, Gd, Tb, Dy, Ho and M = Cu, Zn). The results show that the Cu containing complexes (with the exception of La$_{2}$Cu$_{3}$) undergo long range magnetic order at temperatures below 2 K, and that for Gd$_{2}$Cu$_{3}$ this ordering is ferromagnetic, whereas for Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ it is probably antiferromagnetic. The susceptibilities and specific heats of Tb$_{2}$Cu$_{3}$ and Dy$_{2}$Cu$_{3}$ above $T_{C}$ have been explained by means of a model taking into account nearest as well as next-nearest neighbor magnetic interactions. We show that the intraladder L--Cu interaction is the predominant one and that it is ferromagnetic for L = Gd, Tb and Dy. For the cases of Tb, Dy and Ho containing complexes, strong crystal field effects on the magnetic and thermal properties have to be taken into account. The magnetic coupling between the (ferromagnetic) ladders is found to be very weak and is probably of dipolar origin.Comment: 13 pages, 15 figures, submitted to Phys. Rev.

The Arabidopsis Nuclear Pore and Nuclear Envelope

The nuclear envelope is a double membrane structure that separates the eukaryotic cytoplasm from the nucleoplasm. The nuclear pores embedded in the nuclear envelope are the sole gateways for macromolecular trafficking in and out of the nucleus. The nuclear pore complexes assembled at the nuclear pores are large protein conglomerates composed of multiple units of about 30 different nucleoporins. Proteins and RNAs traffic through the nuclear pore complexes, enabled by the interacting activities of nuclear transport receptors, nucleoporins, and elements of the Ran GTPase cycle. In addition to directional and possibly selective protein and RNA nuclear import and export, the nuclear pore gains increasing prominence as a spatial organizer of cellular processes, such as sumoylation and desumoylation. Individual nucleoporins and whole nuclear pore subcomplexes traffic to specific mitotic locations and have mitotic functions, for example at the kinetochores, in spindle assembly, and in conjunction with the checkpoints. Mutants of nucleoporin genes and genes of nuclear transport components lead to a wide array of defects from human diseases to compromised plant defense responses. The nuclear envelope acts as a repository of calcium, and its inner membrane is populated by functionally unique proteins connected to both chromatin and—through the nuclear envelope lumen—the cytoplasmic cytoskeleton. Plant nuclear pore and nuclear envelope research—predominantly focusing on Arabidopsis as a model—is discovering both similarities and surprisingly unique aspects compared to the more mature model systems. This chapter gives an overview of our current knowledge in the field and of exciting areas awaiting further exploration