Electronic states of cyclophanes with small bridges

Electronic absorption and magnetic circular dichroism were recorded for five cyclophanes with ethano bridges: [2.2]paracyclophane, (1,2,4)[2.2.2]cyclophane, (1,2,4;1,2,5)[2.2.2]cyclophane, (1,2,3,4,5,6)(1,2,3,4,5,6)cyclophane, and trans-[2.2]metacyclophane. Spectral and structural analyses were based on geometry optimization and calculations of transition energies, carried out using density functional theory methods. The assignments have been proposed for several electronic transitions observed in the region below 52,000 cm(-1). The observation of transitions which should be forbidden in the high D(2h) symmetry [2.2]paracyclophane suggests a twisted ground state structure of D(2) symmetry, although the former structure with large amplitude vibrations at room temperature cannot be excluded. The PBE0 functional turned out to appropriately reproduce the inter-ring distances and electronic transition energies.     

Oxidation and nitridation of niobium films by rapid thermal processing

The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200 and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination of the Nb films from the substrates was observed.     

A Long‐Living Bioengineered Neural Tissue Platform to Study Neurodegeneration

The prevalence of dementia and other neurodegenerative diseases continues to rise as age demographics in the population shift, inspiring the development of long‐term tissue culture systems with which to study chronic brain disease. Here, it is investigated whether a 3D bioengineered neural tissue model derived from human induced pluripotent stem cells (hiPSCs) can remain stable and functional for multiple years in culture. Silk‐based scaffolds are seeded with neurons and glial cells derived from hiPSCs supplied by human donors who are either healthy or have been diagnosed with Alzheimer's disease. Cell retention and markers of stress remain stable for over 2 years. Diseased samples display decreased spontaneous electrical activity and a subset displays sporadic‐like indicators of increased pathological β‐amyloid and tau markers characteristic of Alzheimer's disease with concomitant increases in oxidative stress. It can be concluded that the long‐term stability of the platform is suited to study chronic brain disease including neurodegeneration.     

Interfacial interactions and colloid retention under steady flows in a capillary channel

Colloidal interfacial interactions in a capillary channel under different chemical and flow conditions were studied using confocal microscopy. Fluorescent latex microspheres (1.1 microm) were employed as model colloids and the effects of ionic strength and flow conditions on colloidal retention at air-water interface (AWI) and contact line were examined in static and dynamic (flow) experiments. Colloids were preferentially attached to and accumulated at AWI, but their transport with bulk solution was non-negligible. Changing solution ionic strength in the range 1-100 mM had a marginal effect on colloidal accumulation, indicating forces other than electrostatic are involved. Flow through the open channel resembled Poiseuille flow with AWI acting as a non-stress-free boundary, which resulted in near stagnation of AWI and consequently promoted colloid accumulation. Retention on contact line was likely dominated by film-straining and was more significant in flow relative to static experiments due to hydrodynamic driving force. Modeling and dimensionless analysis of the flow behavior in the capillary channel clearly indicate the important role of apparent surface viscosity and surface tension in colloidal interfacial retention at the pore scale, providing insight that could improve understanding of colloid fate and transport in natural unsaturated porous media.     

Nitridation of Niobium Pentoxide Films in Ammonia by Rapid Thermal Processing

The feasibility of niobium oxynitride formation through nitridation of niobium pentoxide films in ammonia by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited by sputtering on Si(100) wafers covered by a 100 nm thick thermally grown SiO₂ layer. These as‐deposited films exhibited distinct texture effects. They were processed in three steps using an RTP system. The as‐deposited niobium films were first nitridated in an ammonia atmosphere at 1000 °C for 1 min and then oxidised in molecular oxygen at temperatures ranging from 400 to 600 °C. Those samples in which a single Nb₂O₅ phase was determined after oxidation were additionally nitridated in ammonia at 1000 °C for 1 min. Investigations show that surface roughness of the samples after oxidation of niobium films first nitridated in ammonia is lower than after direct oxidation of as‐deposited films in oxygen, although the niobium pentoxide phase formed after annealing was the same in both cases. We explain this result as being due to the large expansion of the niobium lattice during the direct oxidation of the niobium film in molecular oxygen and also to the high oxidation rate of the as‐deposited niobium film in oxygen. By incorporation of oxygen in the crystal lattice of niobium and rapid formation of niobium pentoxide, substantial intrinsic stress was built up in the film, frequently resulting in delamination of the film from the substrate. Nitrogen hinders the diffusion of oxygen in nitridated films, which leads to a decrease of the oxidation rate and thus slower formation of Nb₂O₅. Nitridation of the completely oxidised niobium films in ammonia leads to the formation of niobium oxynitride and niobium nitride phases.     

Biological Production of Gold Nanoparticles at Different Temperatures: Efficiency Assessment

The study aims to compare different approaches and efficacies during the biological production of nanoparticles (NPs). Gold nanoparticles (AuNPs) are produced by Fusarium oxysporum at two different temperatures. One flask is incubated at 37 °C (“Common”) and the other is directly heated for 5 min at 80 °C (“Heat-treated”). Obtained AuNPs are analyzed and compared by spectrophotometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Graphite furnace atomic absorption spectroscopy (GF-AAS) is used to determine the particle concentration after the AuNPs production. The AuNPs prepared by both (the Common and the Heat-treated) methods exhibit maximum absorption peaks at 541 and 528 nm, respectively, and have round shapes and sizes of less than 50 nm. Their zeta potential is about −28 mV. GF-AAS shows that the efficiency of AuNP production in Common- and Heat-treated samples is equal, between 65% and 68%. Since the Heat-treated sample shows a better size distribution, the use of higher temperature and shorter time period is preferable for the bioproduction of AuNPs. It seems that shortening the time for the production of AuNPs prevents the formation of larger NPs.     

Three Modes of Proton Transfer in One Chromophore: Photoinduced Tautomerization in 2‐(1H‐Pyrazol‐5‐yl)Pyridines,Their Dimers and Alcohol Complexes

Studies of 2‐(1H‐pyrazol‐5‐yl)pyridine (PPP) and its derivatives 2‐(4‐methyl‐1H‐pyrazol‐5‐yl)pyridine (MPP) and 2‐(3‐bromo‐1H‐pyrazol‐5‐yl)pyridine (BPP) by stationary and time‐resolved UV/Vis spectroscopic methods, and quantum chemical computations show that this class of compounds provides a rare example of molecules that exhibit three types of photoreactions: 1) excited‐state intramolecular proton transfer (ESIPT) in the syn form of MPP, 2) excited‐state intermolecular double‐proton transfer (ESDPT) in the dimers of PPP in nonpolar media, as well as 3) solvent‐assisted double‐proton transfer in hydrogen‐bonded 1:1 complexes of PPP and MPP with alcoholic partners. The excited‐state processes are manifested by the appearance of a dual luminescence and a bimodal irreversible kinetic coupling of the two fluorescence bands. Ground‐state syn–anti equilibria are detected and discussed. The fraction of the higher‐energy anti form varies for different derivatives and is strongly dependent on the solvent polarity and hydrogen‐bond donor or acceptor abilities.