The promoting effect of Pt and Pd in bimetallic Ni–Pt and Ni–Pd catalysts supported on alumina nano-fibre (Alnf) were tested for the liquid phase reforming of sorbitol to produce hydrogen. The mono- and bimetallic catalysts were studied by different characterisation techniques such as: temperature programmed reduction, oxidation, CO desorption, microcalorimetry, TEM and STEM/EDX. Although bimetallic catalysts have long been the subject of great interest because of their exceptional properties compared to the monometallic catalysts, the reason behind their improved activity is still a question of debate. Experimental evidence showed that the addition of both Pt and Pd—even in a very small fraction—to the Ni catalyst increases its reducibility significantly. The TEM and STEM/EDX analysis confirmed that Pt and Ni are present as alloys in nano-sized rod shaped particles. At the same time it was found that the CO differential heat of adsorption is appreciably lowered in the bimetallic catalysts. This is substantial because reducing the CO binding strength can avoid the poisoning of the active metal sites. As a result, we demonstrate that the rate of H formation from sorbitol reforming was 3 to 5 times higher for bimetallic catalysts when compared to the monometallic catalysts.
A “second‐generation” scorpionate ligand was utilized to prepare the nickel(II) borohydride complex [(Tp Ph,Me )Ni(η 3 ‐BH 4 )], wherein the borohydride was coordinated through two bridging B–H bonds, leaving two terminal B–H bonds uncoordinated as determined by X‐ray crystallography. The distorted square‐pyramidal complex is paramagnetic ( S = 1), with 18 valence electrons, and contrasts with a previously reported 20‐electron pseudo‐octahedral “first‐generation” analogue, [(Tp Me,Me )Ni(η 4 ‐BH 4 )] (P. J. Desrochers, et al. Inorg. Chem . 2003 , 42 , 7945–7950). These distinct borohydride coordination modes were distinguished by FTIR spectroscopy, and rationalized by DFT calculations on simplified models, [(Tp)Ni(η n ‐BH 4 )] ( n = 3, 4). The difference in borohydride hapticities is attributed to the steric effect of the scorpionate 3‐pyrazole phenyl substituents disposed proximally to the metal, thus demonstrating the subtle versatility of Trofimenko's scorpionate ligands in controlling ligand field geometries. The precursor complex [(Tp Ph,Me )Ni(κ 2 ‐NO 3 )] was also prepared and characterized. [(Tp Ph,Me )Ni(BH 4 )] exhibits η 3 ‐BH 4 coordination with two bridging and two terminal hydrides on boron. This contrasts with [(Tp Me,Me )Ni(BH 4 )], previously shown to have an η 4 ‐BH 4 ligand. The borohydride hapticities diverge as a result of the different 3‐pyrazole substituents on the scorpionate co‐ligands, and can be distinguished by FTIR spectroscopy.
Mutations of the aryl hydrocarbon receptor interacting protein (AIP) have been associated with familial isolated pituitary adenomas predisposing to young-onset acromegaly and gigantism. The precise tumorigenic mechanism is not well understood as AIP interacts with a large number of independent proteins as well as three chaperone systems, HSP90, HSP70 and TOMM20. We have determined the structure of the TPR domain of AIP at high resolution, which has allowed a detailed analysis of how disease-associated mutations impact on the structural integrity of the TPR domain. A subset of C-terminal alpha-7 helix (C alpha-7h) mutations, R304* (nonsense mutation), R304Q, Q307* and R325Q, a known site for AhR and PDE4A5 client-protein interaction, occur beyond those that interact with the conserved MEEVD and EDDVE sequences of HSP90 and TOMM20. These C-terminal AIP mutations appear to only disrupt client-protein binding to the C alpha-7h, while chaperone binding remains unaffected, suggesting that failure of client-protein interaction with the C alpha-7h is sufficient to predispose to pituitary adenoma. We have also identified a molecular switch in the AIP TPR-domain that allows recognition of both the conserved HSP90 motif, MEEVD, and the equivalent sequence (EDDVE) of TOMM20.
Vertebrate Tpr and its yeast homologs Mlp1/Mlp2, long coiled-coil proteins of nuclear pore inner basket filaments, are involved in mRNA export, telomere organization, spindle pole assembly, and unspliced RNA retention. We identified Arabidopsis thaliana NUCLEAR PORE ANCHOR (NUA) encoding a 237-kD protein with similarity to Tpr. NUA is located at the inner surface of the nuclear envelope in interphase and in the vicinity of the spindle in prometaphase. Four T-DNA insertion lines were characterized, which comprise an allelic series of increasing severity for several correlating phenotypes, such as early flowering under short days and long days, increased abundance of SUMO conjugates, altered expression of several flowering regulators, and nuclear accumulation of poly(A)⁺ RNA. nua mutants phenocopy mutants of EARLY IN SHORT DAYS4 (ESD4), an Arabidopsis SUMO protease concentrated at the nuclear periphery. nua esd4 double mutants resemble nua and esd4 single mutants, suggesting that the two proteins act in the same pathway or complex, supported by yeast two-hybrid interaction. Our data indicate that NUA is a component of nuclear pore-associated steps of sumoylation and mRNA export in plants and that defects in these processes affect the signaling events of flowering time regulation and additional developmental processes.
The work reported here was aimed at determining differences in redox properties of simple and double oxides. Comparison between the reduction of double oxides (Mn,Co)(3)O-4 and simple oxides Co3O4 and Mn3O4 was performed using in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The double oxides with a ratio of cations Mn:Co = 1:1 were prepared by the coprecipitation method and contained a mixture of 50% MnCo2O4 and 50% CoMn2O4. It was shown that the mechanism of reduction of double oxides with hydrogen differs significantly from the processes occurring on simple oxides. For simple cobalt and manganese oxides, transformations Co3O4 CoO Co and Mn3O4 MnO are observed under a hydrogen atmosphere. The reduction of mixed-metal oxides occurs in two steps. In the first step, at 300-450 degrees C, (Mn,Co)(3)O-4 transforms to (Mn,Co)O solid solutions. In situ XRD under isothermal conditions illustrates that Co-rich Co2MnO4 oxide starts to be reduced to Co0.6Mn0.4O first, and then Mn-rich Mn2CoO4 passes into Mn0.6Co0.4O. In the second step, at 450-700 degrees C, the reduction of solid solutions (Mn,Co)O to metallic cobalt Co and MnO proceeds. Again, the reduction begins with transformation of Co-rich oxide with the Co0.6Mn0.4O structure. The temperature of appearance of the intermediate phase (Mn,Co)O shifts to the higher values as compared to those observed for CoO, and to lower temperatures as compared to MnO during simple oxide reduction.
The mitotic arrest-deficient protein Mad1 forms a complex with Mad2, which is required for imposing mitotic arrest on cells in which the spindle assembly is perturbed. By mass spectrometry of affinity-purified Mad2-associated factors, we identified the translocated promoter region (Tpr), a component of the nuclear pore complex (NPC), as a novel Mad2-interacting protein. Tpr directly binds to Mad1 and Mad2. Depletion of Tpr in HeLa cells disrupts the NPC localization of Mad1 and Mad2 during interphase and decreases the levels of Mad1-bound Mad2. Furthermore, depletion of Tpr decreases the levels of Mad1 at kinetochores during prometaphase, correlating with the inability of Mad1 to activate Mad2, which is required for inhibiting APC(Cdc20). These findings reveal an important role for Tpr in which Mad1-Mad2 proteins are regulated during the cell cycle and mitotic spindle checkpoint signaling.
This work focuses on characterizing the structural and surface properties of TixCe1-xO2 (TiO2-CeO2) mixed oxides using XRD, XPS, BET, H-2-TPR, and NH3-TPD techniques. The TixCe1-xO2 mixed oxides synthesized by the urea coprecipitation method showed unimodal nanoporous structure with pore sizes increasing from 3.7 nm for X = 0.9 to 5.3 nm for X = 0.1. Concomitant with their higher surface area and pore volume, the mixed oxides were nanocrystalline, about 4.0 nm in crystallite size when X = 0.9, and 4.8-5.4 rim when X = 0.1-0.3, which are significantly smaller than TiO2 and CeO2 single oxides prepared by the same method (8.1 to 8.4 nm). A dominant anatase phase was detected by XRD when X was 0.9 or higher while a cubic fluorite phase was dominant when X was 0.3 or lower. Lattice parameters were changed by incorporating Cc into TiO2, and Ti into CeO2, respectively. This change indicates distortion of structure and was attributed to reduction of Ti4+ to Ti3+, and Ce4+ to Ce3+. XPS (Ce 3d, Ti 2p, O 1s) and H-2-TPR revealed that the oxidation state of surface cations decreased, and oxygen deficiency of the surface was significantly enhanced by introducing Cc into TiO2, and Ti into CeO2. The structural and surface modification by introducing Cc into TiO2 increased the reducibility of mixed oxides in H-2-TPR. NH3-TPD showed that increasing Ti content in TixCe1-xO2 enhanced surface acidity. Furthermore, H2O and N-2 formation from NH3 was detected by mass spectrometry, which was attributed to the oxidation activity of the TixCe1-xO2 mixed oxides. The highest NH3 oxidation activity was observed when X = 0.9. The present study clearly established that the structural (crystal phase, crystal size, nanoporosity, pore size) and surface properties (reducibility, oxygen deficiency, acidity, oxidation activity of the TixCe1-xO2 mixed oxides can be tailored by controlling their composition by the urea coprecipitation procedure.
Amassments of heterochromatin in somatic cells occur in close contact with the nuclear envelope (NE) but are gapped by channel‐ and cone‐like zones that appear largely free of heterochromatin and associated with the nuclear pore complexes (NPCs). To identify proteins involved in forming such heterochromatin exclusion zones (HEZs), we used a cell culture model in which chromatin condensation induced by poliovirus (PV) infection revealed HEZs resembling those in normal tissue cells. HEZ occurrence depended on the NPC‐associated protein Tpr and its large coiled coil‐forming domain. RNAi‐mediated loss of Tpr allowed condensing chromatin to occur all along the NE's nuclear surface, resulting in HEZs no longer being established and NPCs covered by heterochromatin. These results assign a central function to Tpr as a determinant of perinuclear organization, with a direct role in forming a morphologically distinct nuclear sub‐compartment and delimiting heterochromatin distribution.
The ATP-hydrolyzing molecular chaperones Hsc70/Hsp70 and Hsp90 bind a diverse set of tetratricopeptide repeat (TPR)-containing cofactors via their C-terminal peptide motifs IEEVD and MEEVD. These cochaperones contribute to substrate turnover and confer specific activities to the chaperones. Higher eukaryotic genomes encode a large number of TPR-domain-containing proteins. The human proteome contains more than 200 TPR proteins, and that of , about 80. It is unknown how many of them interact with Hsc70 or Hsp90. We systematically screened the proteome for TPR-domain-containing proteins that likely interact with Hsc70 and Hsp90 and ranked them due to their similarity with known chaperone-interacting TPRs. We find to encode many TPR proteins, which are not present in yeast. All of these have homologs in fruit fly or humans. Highly ranking uncharacterized open reading frames C33H5.8, C34B2.5 and ZK370.8 may encode weakly conserved homologs of the human proteins RPAP3, TTC1 and TOM70. C34B2.5 and ZK370.8 bind both Hsc70 and Hsp90 with low micromolar affinities. Mutation of amino acids involved in EEVD binding disrupts the interaction. , ZK370.8 is localized to mitochondria in tissues with known chaperone requirements, while C34B2.5 colocalizes with Hsc70 in intestinal cells. The highest-ranking open reading frame with non-conserved EEVD-interacting residues, F52H3.5, did not show any binding to Hsc70 or Hsp90, suggesting that only about 15 of the TPR-domain-containing proteins in interact with chaperones, while the many others may have evolved to bind other ligands.