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Metal–Organic Frameworks and Self-Assembled Supramolecular Coordination Complexes: Comparing and Contrasting the Design, Synthesis, and Functionality of Metal–Organic Materials

There has been a renaissance of interest in exploring highly efficient thermoelectric materials as a possible route to address the worldwide energy generation, utilization, and management. This review describes the recent advances in designing high-performance bulk thermoelectric materials. We begin with the fundamental stratagem of achieving the greatest thermoelectric figure of merit ZT of a given material by carrier concentration engineering, including Fermi level regulation and optimum carrier density stabilization. We proceed to discuss ways of maximizing ZT at a constant doping level, such as increase of band degeneracy (crystal structure symmetry, band convergence), enhancement of band effective mass (resonant levels, band flattening), improvement of carrier mobility (modulation doping, texturing), and decrease of lattice thermal conductivity (synergistic alloying, second-phase nanostructuring, mesostructuring, and all-length-scale hierarchical architectures). We then highlight the decoupling of th...

Rationally Designing High-Performance Bulk Thermoelectric Materials

The nucleolus is a distinct subnuclear compartment that was first observed more than 200 years ago. Nucleoli assemble around the tandemly repeated ribosomal DNA gene clusters and 28S, 18S and 5.8S ribosomal RNAs (rRNAs) are transcribed as a single precursor, which is processed and assembled with the 5S rRNA into ribosome subunits. Although the nucleolus is primarily associated with ribosome biogenesis, several lines of evidence now show that it has additional functions. Some of these functions, such as regulation of mitosis, cell-cycle progression and proliferation, many forms of stress response and biogenesis of multiple ribonucleoprotein particles, will be discussed, as will the relation of the nucleolus to human diseases.

The multifunctional nucleolus

The Golden Age of Transfer Hydrogenation

Nucleoli are the prominent contrasted structures of the cell nucleus. In the nucleolus, ribosomal RNAs are synthesized, processed and assembled with ribosomal proteins. RNA polymerase I synthesizes the ribosomal RNAs and this activity is cell cycle regulated. The nucleolus reveals the functional organization of the nucleus in which the compartmentation of the different steps of ribosome biogenesis is observed whereas the nucleolar machineries are in permanent exchange with the nucleoplasm and other nuclear bodies. After mitosis, nucleolar assembly is a time and space regulated process controlled by the cell cycle. In addition, by generating a large volume in the nucleus with apparently no RNA polymerase II activity, the nucleolus creates a domain of retention/sequestration of molecules normally active outside the nucleolus. Viruses interact with the nucleolus and recruit nucleolar proteins to facilitate virus replication. The nucleolus is also a sensor of stress due to the redistribution of the ribosomal proteins in the nucleoplasm by nucleolus disruption. The nucleolus plays several crucial functions in the nucleus: in addition to its function as ribosome factory of the cells it is a multifunctional nuclear domain, and nucleolar activity is linked with several pathologies. Perspectives on the evolution of this research area are proposed.

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Nucleolus: the fascinating nuclear body

In cycling cells, the rDNAs are expressed from telophase to the end of G2 phase. The early resumption of rDNA transcription at telophase raises the question of the fate of the rDNA transcription machinery during mitosis. At the beginning of mitosis, rDNA transcription is arrested, and the rDNAs are clustered in specific chromosomal sites, the nucleolar organizer regions (NOR). In human cells, we demonstrate that the rDNA transcription machinery, as defined in vitro, is colocalized in some NORs and absent from others whatever the mitotic phase: RNA polymerase I and the RNA polymerase I transcription factors, upstream binding factor and promoter selectivity factor (as verified for TATA-binding protein and TATA-binding protein-associated factor for RNA polymerase I [110]), were colocalized in the same NORs. The RNA polymerase I complex was localized using two different antibodies recognizing the two largest subunits or only the third largest subunit, respectively. These two antibodies immunoprecipitated the RNA polymerase I complex in interphase cells as well as in mitotic cells. These results clearly indicated that the RNA polymerase I complex remained assembled during mitosis. In addition, RNA polymerase I and the transcription factors varied in the same proportions in the positive NORs, suggesting stoichiometric association of these components. The fact that the rDNA transcription machinery is not equally distributed among NORs most likely reflects the implication of the different NORs during the subsequent interphase. Indeed, we demonstrate that only positive NORs exhibit transcription activity at telophase and that the level of transcription activity is related to the amount of rDNA transcription machinery present in the NOR. We propose that assembly of rDNA transcription machinery preceding mitosis determines expression of the rDNAs at the beginning of the next cell cycle. Consequently, the association of rDNAs with the rDNA transcription machinery defines the "active" NORs and the level of activity at the transition telophase/interphase.

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Pascal Roussel

Papers

Nucleolus: the fascinating nuclear body

The rDNA transcription machinery is assembled during mitosis in active NORs and absent in inactive NORs.

Structures and oxide mobility in Bi-Ln-O materials: heritage of Bi2O3.

Structure and catalytic performance of Pt-promoted alumina-supported cobalt catalysts under realistic conditions of Fischer–Tropsch synthesis

A new investigation of the system Ni–Sn