Chemically-synthesised, atomically-precise gold clusters deposited and activated on titania

Synchrotron XPS was used to investigate a series of chemically-synthesised, atomically-precise gold clusters Au(n)(PPh₃)(y) (n = 8, 9, 11 and 101, with y depending on cluster size) immobilized on titania nanoparticles. The gold clusters were washed with toluene at 100 °C or calcined at 200 °C to remove the organic ligand. From the position of the Au 4f₇/₂ peak it is concluded that cluster size is not altered through the deposition. From the analysis of the phosphorous spectra, it can be concluded that the applied heat treatment removes the organic ligands. Washing and calcination leads to partial oxidation and partial agglomeration of the clusters. Oxidation of the clusters is most likely due to the interaction of the cluster core with the oxygen of the titania surface after removal of ligands. The position of the Au 4f₇/₂ peak indicates that the size of the agglomerated clusters is still smaller than that of Au₁₀₁.David P. Anderson, Jason F. Alvino, Alexander Gentleman, Hassan Al Qahtani, Lars Thomsen, Matthew I. J. Polson, Gregory F. Metha, Vladimir B. Golovko and Gunther G. Andersso

Pt Nanocluster Co-Catalysts for Photocatalytic Water Splitting

Degussa P25 is a benchmark form of TiO2 used worldwide in photocatalysis studies. Currently, no such benchmark exists for co-catalysts, which are essential for many photocatalytic reactions. Here, we present the preparation of Pt nanocluster co-catalysts on TiO2 using an unmodified commercial source and equipment that is commonly available. Transmission electron microscopy reveals that the procedure produces TiO2 decorated with Pt atoms and nanoclusters (1⁻5 atoms). Optical reflectance and X-ray diffraction measurements show that the procedure does not affect the TiO2 polymorph or ultraviolet-visible (UV-Vis) absorbance. Gas phase photocatalytic splitting of heavy water (D2O) shows that the Pt nanocluster-decorated TiO2 outperforms Pt nanoparticle (produced by photodeposition) decorated TiO2 in D2 production. Pt nanoclusters, produced directly from a commercial source, with high co-catalyst activity, are prime candidates to be used in benchmark photocatalytic reactions

Identification of the Vibrational Modes in the Far-Infrared Spectra of Ruthenium Carbonyl Clusters and the Effect of Gold Substitution

High-quality far-IR absorption spectra for a series of ligated atomically precise clusters containing Ru₃, Ru₄, and AuRu₃ metal cores have been observed using synchrotron radiation, the latter two for the first time. The experimental spectra are compared with predicted IR spectra obtained following complete geometric optimization of the full cluster, including all ligands, using DFT. We find strong correlations between the experimental and predicted transitions for the low-frequency, low-intensity metal core vibrations as well as the higher frequency and intensity metal–ligand vibrations. The metal core vibrational bands appear at 150 cm^–1 for Ru₃(CO)₁₂, and 153 and 170 cm^–1 for H₄Ru₄(CO)₁₂, while for the bimetallic Ru₃(μ-AuPPh₃)­(μ-Cl)­(CO)₁₀ cluster these are shifted to 177 and 299 cm^–1 as a result of significant restructuring of the metal core and changes in chemical composition. The computationally predicted IR spectra also reveal the expected atomic motions giving rise to the intense peaks of metal–ligand vibrations at <i>ca</i>. 590 cm^–1 for Ru₃, 580 cm^–1 for Ru₄, and 560 cm^–1 for AuRu₃. The obtained correlations allow an unambiguous identification of the key vibrational modes in the experimental far-IR spectra of these clusters for the first time

Chemically synthesised atomically precise gold clusters deposited and activated on titania. Part II

Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au(n)(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f(7/2) peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters.David P. Anderson, Rohul H. Adnan, Jason F. Alvino, Oliver Shipper, Baira Donoeva, Jan-Yves Ruzicka, Hassan Al Qahtani, Hugh H. Harris, Bruce Cowie, Jade B. Aitken, Vladimir B. Golovko, Gregory F. Metha and Gunther G. Andersso

Molecular structure of 3-aminopropyltriethoxysilane layers formed on silanol-terminated silicon surfaces

The use of the coupling agent, 3-aminopropyltriethoxysilane (APTES), in the silanization reaction with silanol-terminated silicon is an important surface modification reaction. Of particular importance is that the terminal amine functionalities of APTES are sufficiently exposed to the gas or liquid phase for further modifications, such as amide coupling reactions. Here, metastable induced electron spectroscopy (MIES) and UV photoelectron spectroscopy (UPS) were used to study the composition of the outermost layer of a silanol-terminated Si surface after silanization with APTES. High-resolution X-ray photoelectron spectroscopy (XPS) was used to validate the attachment of APTES to the surface. Density of States (DOS) calculations were employed for interpreting the MIE spectra. Findings showed that amine functionalities covered only a small fraction of the APTES-modified Si surface. © 2012 American Chemical Society.Robert G. Acres, Amanda V. Ellis, Jason Alvino, Claire E. Lenahan, Dmitriy A. Khodakov, Gregory F. Metha, and Gunther G. Andersso

The major genetic determinants of HIV-1 control affect HLA class I peptide presentation.

Infectious and inflammatory diseases have repeatedly shown strong genetic associations within the major histocompatibility complex (MHC); however, the basis for these associations remains elusive. To define host genetic effects on the outcome of a chronic viral infection, we performed genome-wide association analysis in a multiethnic cohort of HIV-1 controllers and progressors, and we analyzed the effects of individual amino acids within the classical human leukocyte antigen (HLA) proteins. We identified &gt;300 genome-wide significant single-nucleotide polymorphisms (SNPs) within the MHC and none elsewhere. Specific amino acids in the HLA-B peptide binding groove, as well as an independent HLA-C effect, explain the SNP associations and reconcile both protective and risk HLA alleles. These results implicate the nature of the HLA-viral peptide interaction as the major factor modulating durable control of HIV infection