Simple and efficient separation of atomically precise noble metal clusters.

There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study of their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au25L18, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au25L18 with different ligands, as well as to a binary mixture of different cluster cores, Au25 and Au144, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au25 clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties.

Control of the morphology of lipid layers by substrate surface chemistry.

In this study, surface coatings were used to control the morphology of the deposited lipid layers during vesicle spreading, i.e., to control if liposomes self-assemble on a surface into a supported lipid bilayer or a supported vesicular layer. The influence of the properties of the surface coating on formation of the deposited lipid layer was studied with quartz crystal microbalance and two-wavelength multiparametric surface plasmon resonance techniques. Control of lipid self-assembly on the surface was achieved by two different types of soft substrate materials, i.e., dextran and thiolated polyethylene glycol, functionalized with hydrophobic linkers for capturing the lipid layer. The low-molecular-weight dextran-based surface promoted formation of supported lipid bilayers, while the thiolated polyethylene glycol-based surface promoted supported vesicular layer formation. A silicon dioxide surface was used as a reference surface in both measurement techniques. In addition to promoting supported lipid bilayer formation of known lipid mixtures, the dextran surface also promoted supported lipid bilayer formation of vesicles containing the cell membrane extract of human hepatoblastoma cells. The new dextran-based surface was also capable of protecting the supported lipid bilayer against dehydration when exposed to a constant flow of air. The well-established quartz crystal microbalance technique was effective in determining the morphology of the formed lipid layer, while the two-wavelength surface plasmon resonance analysis enabled further complementary characterization of the adsorbed supported lipid bilayers and supported vesicular layers.

Mixed-Monolayer-Protected Au25 Clusters with Bulky Calix[4]arene Functionalities.

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety.

Inkjet-printed gold electrodes on paper: characterization and functionalization.

Gold nanoparticles were synthesized and inkjet-printed on a paper substrate and IR-sintered to produce conductive electrodes. The electrodes were further functionalised by using self-assembled octadecanethiol monolayers (SAMs). The effect of sintering, print quality, and SAM formation were examined by topographical, chemical and electrical methods. With optimised printing parameters, a volume resistivity of ~1.6 × 10(-7) Ω m was attained by a single print layer.

Poly(ethylene imine) and tetraethylenepentamine as protecting agents for metallic copper nanoparticles.

The aim of this research was to explore the use of amine-containing polymeric and low-molar-mass organic protecting agents in the preparation of copper nanoparticles. Particles were synthesized using poly(ethylene imine) (PEI) or tetraethylenepentamine (TEPA) as protecting agents. The resulting particles were studied with UV-vis spectrometry, thermogravimetry, scanning electron microscopy, and transmission electron microscopy, wide-angle X-ray scattering with heating, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The average crystal sizes for the particles were at room temperature 8.5 and 19.4 nm for PEI and TEPA, respectively, and some surface oxidation was observed. The particles were sintered on paper, and the resistance and resistivity were measured. For Cu/PEI samples, the protecting agent was removed upon sintering at relatively low temperatures (between 150 and 200 degrees C). At this temperature range, particles exhibited a rapid increase in the crystal size. Sintered particles exhibited high conductivity, indicating that these kinds of materials might find use in paper-based printing.

Determination of steady-state kinetic parameters for a xylanase-catalyzed hydrolysis of neutral underivatized xylooligosaccharides by mass spectrometry.

A direct mass spectrometric approach was used for the determination of steady-state kinetic parameters, the turnover number (k(cat)), the Michaelis constant (K(M)), and the specificity constant (k(cat)/K(M)) for an enzyme-catalyzed hydrolysis of xylooligosaccharides. Electrospray ionization mass spectrometry was performed to observe product distributions and to determine k(cat), K(M), and k(cat)/K(M) values for Trichoderma reesei endo-1,4-beta-xylanase II (TRX II) with xylohexaose (Xyl(6)), xylopentaose (Xyl(5)), xylotetraose (Xyl(4)), and xylotriose (Xyl(3)) as substrates. The determined k(cat)/K(M) values (0.93, 0.37, 0.027, and 0.00015 microM(-1) s(-1), respectively) indicated that Xyl(6) was the most preferred substrate of TRX II. In addition, the obtained K(M) value for Xyl(5) (136 microM) was roughly twice as high as that for Xyl(6) (73 microM), suggesting that at least six putative subsites contribute to the substrate binding in the active site of TRX II. Previous mass spectrometric assays for enzyme kinetics have been used mostly in the case of reactions that result in a transfer of acidic groups (e.g., phosphate) into neutral oligosaccharides giving rise to negatively charged products. Here we demonstrate that such analysis is also feasible in the case of neutral underivatized oligosaccharides. Implications of the results for the catalytic mechanism of TRX II in particular are discussed.