Pressure‐Tuneable Visible‐Range Band Gap in the Ionic Spinel Tin Nitride

The application of pressure allows systematic tuning of the charge density of a material cleanly, that is, without changes to the chemical composition via dopants, and exploratory high‐pressure experiments can inform the design of bulk syntheses of materials that benefit from their properties under compression. The electronic and structural response of semiconducting tin nitride Sn₃N₄ under compression is now reported. A continuous opening of the optical band gap was observed from 1.3 eV to 3.0 eV over a range of 100 GPa, a 540 nm blue‐shift spanning the entire visible spectrum. The pressure‐mediated band gap opening is general to this material across numerous high‐density polymorphs, implicating the predominant ionic bonding in the material as the cause. The rate of decompression to ambient conditions permits access to recoverable metastable states with varying band gaps energies, opening the possibility of pressure‐tuneable electronic properties for future applications.     

Three‐Dimensional Branched and Faceted Gold–Ruthenium Nanoparticles: Using Nanostructure to Improve Stability in Oxygen Evolution Electrocatalysis

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low‐index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close‐packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low‐index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.     

Enhancement of antibacterial efficiency at silver electrodeposited on coconut shell activated carbon by modulating pulse frequency

The natural antibacterial activity of silver represents an alternative to deal with the ever increasing pathogenic breakouts related with contaminated water resources. In this study, silver was deposited on the surface of activated carbon (AC) particles via pulsed electrodeposition (PED) employing an electrochemical reactor operating at fixed and fluidized bed regimes. Silver-coated activated carbon (Ag/AC) particles were prepared at different current pulse frequency values. Antimicrobial properties of the produced material were tested against two well-known foodborne pathogens, i.e., Escherichia coli O157:H7 and Salmonella typhimurium. The results demonstrate a strong influence of the applied current pulse frequency on both the bactericidal efficiency and the specific surface of silver deposited on the activated carbon. Antibacterial results demonstrate up to eight orders of magnitude decrease in the CFU cm^?3 (colony-forming units per cm³) against both microorganisms in just 20 min contact time. Additional chronoamperometry transient data were fitted to the Scharifker-Hills nucleation model for the electrodeposition of silver at a rotating disk electrode, revealing an instantaneous nucleation growth processes. The Ag/AC particles were characterized by field emission scanning electron microscopy (FE-SEM), specific surface area (S_BET), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD), demonstrating the existence of crystalline phase formation of a preferential (200) plane growth with silver and silver oxide being present.

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Adsorption behavior of statherin and a statherin peptide onto hydroxyapatite and silica surfaces by in situ ellipsometry

The salivary protein statherin is known to adsorb selectively onto hydroxyapatite (HA), which constitutes the main mineral of the tooth enamel. This adsorption is believed to be crucial for its function as an inhibitor of primary (spontaneous) and secondary (crystal growth) precipitation of calcium phosphate salts present in saliva. A fragment corresponding to the first 21 N-terminus amino acids of statherin (StN21) was previously found to reduce the rate of demineralization of HA. Therefore, the interfacial properties of this peptide and statherin onto silica, hydrophobized silica and HA discs was studied by in situ ellipsometry. Their reversibility induced by dilution and elutability induced by buffer and sodium dodecyl sulfate (SDS) was also determined. The results revealed that statherin adsorbed at a greater extent onto the HA as compared to StN21, suggesting that the hydrogen bonding between the uncharged polar residues at the C-terminal region of statherin and HA contributes to its adsorption. However, on both silica surfaces the peptide adsorption appeared to proceed in a similar way. Onto the hydrophobized silica the adsorption of both peptides was suggested to occur either via multilayer formation or adsorption of aggregates from solution, while onto the hydrophilic silica adsorption of peptide aggregates from solution was the suggested mechanism. Further, both peptides were observed to be strongly adsorbed onto HA, even after SDS treatment, in comparison to the layers adsorbed onto hydrophobized silica. Both peptide layers were found to be weakly adsorbed onto the hydrophilic silica surface as they were totally removed by buffer dilution.     

The Role of Mechanical Properties and Structure of Type I Collagen Hydrogels on Colorectal Cancer Cell Migration

Mechanical interactions between cells and their microenvironment play an important role in determining cell fate, which is particularly relevant in metastasis, a process where cells invade tissue matrices with different mechanical properties. In vitro, type I collagen hydrogels have been commonly used for modeling the microenvironment due to its ubiquity in the human body. In this work, the combined influence of the stiffness of these hydrogels and their ultrastructure on the migration patterns of HCT-116 and HT-29 spheroids are analyzed. For this, six different types of pure type I collagen hydrogels by changing the collagen concentration and the gelation temperature are prepared. The stiffness of each sample is measured and its ultrastructure is characterized. Cell migration studies are then performed by seeding the spheroids in three different spatial conditions. It is shown that changes in the aforementioned parameters lead to differences in the mechanical stiffness of the matrices as well as the ultrastructure. These differences, in turn, lead to distinct cell migration patterns of HCT-116 and HT-29 spheroids in either of the spatial conditions tested. Based on these results, it is concluded that the stiffness and the ultrastructural organization of the matrix can actively modulate cell migration behavior in colorectal cancer spheroids.     

Gateaux differentiability in Orlicz–Lorentz spaces and applications

Let Λ_w,? be the Orlicz–Lorentz space. We study Gateaux differentiability of the functional ψ_w,? (f) = ? (f *)w and of the Luxemburg norm. More precisely, we obtain the one‐sided Gateaux derivatives in both cases and we characterize those points where the Gateaux derivative of the norm exists. We give a characterization of best ψ_w,? ‐approximants from convex closed subsets and we establish a relation between best ψ_w,? ‐approximants and best approximants from a convex set. A characterization of best constant ψ_w,? ‐approximants and the algorithm to construct the best constant for maximum and minimum ψ_w,? ‐pproximants are given. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation, characterization, and structural systematics of diphosphane and diarsane complexes of gallium(III) halides

The diphosphane o-C6H4(PMe2)2 reacts with GaX3 (X = Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give trans-[GaX2{o-C6H4(PMe2)2}2][GaX4], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl3 ratio produced [GaCl2{o-C6H4(PMe2)2}][GaCl4], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX2{o-C6H4(PPh2)2}][GaX4] complexes are the only products isolated with the bulkier o-C6H4(PPh2)2. On the other hand, Et2P(CH2)2PEt2, which has a flexible aliphatic backbone, formed [(X3Ga)2{mu-Et2P(CH2)2PEt2}], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane, o-C6H4(AsMe2)2, formed [GaX2{o-C6H4(AsMe2)2}][GaX4], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}] and [GaX3(AsMe3)] are also described. The X-ray structures of trans-[GaX2{o-C6H4(PMe2)2}2][GaX4] (X = Cl, Br or I), [GaCl2{o-C6H4(PPh2)2}][GaCl4], [GaX2{o-C6H4(AsMe2)2}][GaX4] (X = Cl or I), [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}], and [GaX3(AsMe3)] (X = Cl, Br or I) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of 31P{1H} and 71Ga NMR spectroscopy.     

Surface characterization of electrodeposited silver on activated carbon for bactericidal purposes

The use of an electrochemical reactor operated under different flow conditions to deposit silver from aqueous AgNO(3) solutions and tartaric acid as an organic additive on a commercial activated carbon with ultimate bactericidal applications in water purification processes is presented. The characterization of carbon/silver samples was studied by BET, FTIR, X-ray diffraction, XPS, and SEM techniques. The bactericidal activity of the carbon/silver samples was tested on drinking water samples inoculated with E. coli. A reduction of carbon surface area was detected and was caused by increased amounts of silver deposited on carbon samples. Adherent silver deposits were obtained on the carbon/silver samples. X-ray diffraction studies of carbon with electrodeposited silver showed two different preferential deposition planes, [111] and [220]. The FTIR results confirm the presence of carboxyl, phenolic, quinone, and ether surface groups. The XPS results suggest the formation of Ag(2)O and AgO surface species and confirm the reduction of silver to the metallic form. Antimicrobial activity toward E. coli indicated reductions by up to 7 orders of magnitude in the log CFU/mL in just 10 min contact time and for silver contents of 2.47 wt%.     

Self-aggregation of the SDS surfactant at a solid-liquid interface

Molecular dynamics simulations of sodium dodecyl sulfate (SDS) molecules on a graphite surface are presented. The simulations were conducted at low and high surface coverage to study aggregation at the water/graphite interface. Results showed that at low surface coverage, the SDS molecules form hemicylindrical aggregates, in agreement with AFM experiments, whereas at high surface coverage, the surfactants form full cylinders. The latter aggregates have not been reported in systems of SDS on hydrophobic substrates, such as graphite. The unexpected results are explained in terms of a water layer adsorbed at the solid surface which was the responsible for the formation of these aggregates. Moreover, the SDS tails in the full cylindrical configuration became straighter than those of the hemicylindrical aggregate. Hydrogen bond formation between water and surfactant head groups was also studied, and it was found that they did not depend on the surfactant concentration.     

Electrochemical properties and structures of the mixed-valence lithium cuprates Li3Cu2O4 and Li2NaCu2O4

The electrochemical performances of Li₃Cu₂O₄ and Li₂NaCu₂O₄ as cathode materials in lithium coin type batteries have been studied. In Li₃Cu₂O₄, the copper was oxidised to the III level when cycling. The replacement of the lithium by the sodium ions in the octahedral sites in Li₂NaCu₂O₄ might have an effect on the pathway of the lithium ions during the (de)intercalations. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.