Molecular assembly of multi-wall carbon nanotubes with amino crown ether: synthesis and characterization.

Synthetic methodology and physicochemical characterization of multi-wall carbon nanotubes (MWCNTs) functionalized with a crown ether molecule is reported. The MWCNTs were synthesized by spray pyrolysis technique using toluene as carbon source and ferrocene as catalyst. The nanotubes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Oxidation of MWCNTs was carried out by 8 h of sonication in a mixture of sulfuric and nitric acid (3:1). The MWCNT-COOH was amidated with 4-aminobenzo-15-crown-5 under mild reaction conditions using N,N'-dicyclohexylcarbodiimide and dimethylaminopyridine as catalyst and dimethylformamide as solvent, at room temperature for 24 h. The amidation product was characterized by scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and a mass spectrometry study to determine the fragmentation pattern being m/z 309, 177 and 149 the most important ions.

Enhancement and inhibition of photolumincescence in hydrogenated amorphous silicon nitride microcavities.

A Fabry-Perot microcavity is used for the enhancement and inhibition of photoluminescence in hydrogenated amorphous silicon nitride. The amplitude of the photoluminescence is enhanced 4 times, while its linewidth is reduced 8 times with respect to the bulk hydrogenated amorphous silicon nitride. The transmittance, reflectance, and absorptance spectra of the microcavity were also measured and calculated. The calculated spectra agree well with the experimental ones.

Association of AUUUA-binding protein with A+U-rich mRNA during nucleo-cytoplasmic transport.

Resealed nuclear envelope (NE) vesicles from rat liver containing entrapped exogenous RNA were used to study the effect of adenosine+uridine binding factor (AUBF), present in cytosolic cell extracts, on ATP-dependent transport of A+U-rich RNA (AU+RNA) and A+U-free RNA (AU-RNA) across the NE. This factor specifically binds to A+U-rich sequences present in the 3' untranslated regions of lymphokine and cytokine mRNAs, containing overlapping AUUUA boxes (granulocyte-macrophage colony stimulating factor, interleukin-3). Addition of AUBF to the extravesicular compartment markedly increased the efflux of the in vitro transcribed, capped and polyadenylated AU+ RNAs. Export of entrapped AU- control RNA, such as beta-globin RNA, was not affected by AUBF, in contrast to chimeric AU+ beta-globin RNA containing the A+U-rich sequence of human interferon-alpha mRNA (6 reiterated AUUUA motifs). Competition experiments revealed that AUBF enhances the affinity of poly(A)-containing AU+ RNAs to the NE poly(A)-binding component (poly(A)-recognizing mRNA carrier p106), and thereby accelerates nuclear export of these RNAs. We could demonstrate that AUBF added to the extravesicular space forms stable complexes with polyadenylated AU+ RNA with relative molecular masses of about 45,000, 62,000 and 70,000 inside the vesicles or during ATP-dependent export. In addition we determined that AUBF may affect mRNA stability by protecting A+U-rich RNA against degradation by trans-acting, nuclear matrix-associated and A+U-specific endoribonuclease V.

Purification of a glucose-binding protein from rat liver nuclei. Evidence for a role in targeting of nuclear mRNP to nuclear pore complex.

A nuclear carbohydrate-binding protein with a molecular mass of 67 kDa (CBP67), which is specific for glucose residues, was purified to essential homogeneity from rat liver nuclear extracts. This protein could also be isolated from nuclear ribonucleoprotein (RNP) complexes by extraction in the presence of 0.6 M or 2 M NaCl, but it was absent in polysomal RNP complex. The binding of the purified protein, which has an isoelectric point of 7.3, to glucose-containing glycoconjugates depends on the presence of Ca2+ and Mg2+. Using closed nuclear envelope vesicles as a system to study nuclear transport of RNA, it was shown that both entrapped polysomal mRNA and nuclear RNA precursors are readily exported from the vesicles in an ATP-dependent manner. The transport was unidirectional and strongly promoted by the poly(A) segment attached to these RNAs. In contrast, nuclear RNP complexes entrapped into the vesicles together with glucose-conjugated bovine serum albumin or nucleoplasmin, or bird nest glycoprotein, were not exported into the extravesicular space. However, transport of nuclear RNP complexes could be achieved in the presence of glucose or after co-addition of a glucose-recognizing lectin from Pellina semitubulosa. In Western blots, radioiodinated CBP67 binds to an 80-kDa polypeptide both in isolated rat liver nuclear envelopes and pore-complex laminae. From these results we postulate that CBP67 may direct nuclear RNP complexes to the nuclear pore.