Catalytic efficiency of iron(III) oxides in decomposition of hydrogen peroxide: competition between the surface area and crystallinity of nanoparticles

Various iron(III) oxide catalysts were prepared by controlled decomposition of a narrow layer (ca. 1 mm) of iron(II) oxalate dihydrate, FeC(2)O(4).2H(2)O, in air at the minimum conversion temperature of 175 degrees C. This thermally induced solid-state process allows for simple synthesis of amorphous Fe(2)O(3) nanoparticles and their controlled one-step crystallization to hematite (alpha-Fe(2)O(3)). Thus, nanopowders differing in surface area and particle crystallinity can be produced depending on the reaction time. The phase composition of iron(III) oxides was monitored by XRD and (57)Fe M?ssbauer spectroscopy including in-field measurements, providing information on the relative contents of amorphous and crystalline phases. The gradual changes in particle size and surface area accompanying crystallization were evaluated by HRTEM and BET analysis, respectively. The catalytic efficiency of the synthesized nanoparticles was tested by tracking the decomposition of hydrogen peroxide. The obtained kinetic data gave an unconventional nonmonotone dependence of the rate constant on the surface area of the samples. The amorphous nanopowder with the largest surface area of 401 m(2) g(-1) revealed the lowest catalytic efficiency, while the highest efficiency was achieved with the sample having a significantly lower surface area, 337 m(2) g(-1), exhibiting a prevailing content of crystalline alpha-Fe(2)O(3) phase. The obtained rate constant, 26.4 x 10(-3) min(-1) (g/L)(-1), is currently the highest value published. The observed rare catalytic phenomenon, where the particle crystallinity prevails over the surface area effects, is discussed with respect to other processes of heterogeneous catalysis.     

ClnH6-nSiGe compounds for CMOS compatible semiconductor applications: synthesis and fundamental studies

We describe the synthesis of a new family of chlorinated Si-Ge hydrides based on the formula ClnH6-nSiGe. Selectively controlled chlorination of H3SiGeH3 is provided by reactions with BCl3 to produce ClH2SiGeH3 (1) and Cl2HSiGeH3 (2). This represents a viable single-step route to the target compounds in commercial yields for semiconductor applications. The built-in Cl functionalities are specifically designed to facilitate selective growth compatible with CMOS processing. Higher order polychlorinated derivatives such as Cl2SiHGeH2Cl (3), Cl2SiHGeHCl2 (4), ClSiH2GeH2Cl (5), and ClSiH2GeHCl2 (6) have also been produced for the first time leading to a new class of highly reactive Si-Ge compounds that are of fundamental and practical interest. Compounds 1-6 are characterized by physical and spectroscopic methods including NMR, FTIR, and mass spectroscopy. The results combined with first principles density functional theory are used to elucidate the structural, thermochemical, and vibrational trends throughout the general sequence of ClnH6-nSiGe and provide insight into the dependence of the reaction kinetics on Cl content in the products. The formation of 1 was also demonstrated by an alternative route based on the reaction of (SO3CF3)SiH2GeH3 and CsCl. Depositions of 1 and 2 at very low temperatures (380-450 degrees C) produce near stoichiometric SiGe films on Si exhibiting monocrystalline microstructures, smooth and continuous surface morphologies, reduced defect densities, and unusual strain properties.     

Mössbauer investigation of the reaction of ferrate(VI) with sulfamethoxazole and aniline in alkaline medium

Mechanisms on the oxidation of sulfamethoxazole (SMX) and aniline by ferrate(VI) (Fe^VIO $_{4}{^{2-}}$ , Fe(VI)) in alkaline medium suggested the formation of Fe(VI)-SMX or Fe(VI)-aniline intermediates, respectively. Fe(V) and Fe(IV) as other intermediate iron species have also been proposed in the mechanism. In this paper, rapid freeze Mössbauer spectroscopy was applied in rapidly frozen samples to explore intermediate iron species in the reactions of SMX and aniline with Fe(VI). In both reactions, Fe(VI)-SMX and Fe(VI)-aniline intermediates were not seen in second-minute time scale. Fe(V) and Fe(IV) were also not observed. Fe(III) was the only final species of the reactions.     

Formation of arenicin-1 microdomains in bilayers and their specific lipid interaction revealed by Z-scan FCS

Z-scan fluorescence correlation spectroscopy (FCS) is employed to characterize the interaction between arenicin-1 and supported lipid bilayers (SLBs) of different compositions. Lipid analogue C8-BODIPY 500/510C5-HPC and ATTO 465 labelled arenicin-1 are used to detect changes in lipid and peptide diffusion upon addition of unlabelled arenicin-1 to SLBs. Arenicin-1 decreases lipid mobility in negatively charged SLBs. According to diffusion law analysis, microdomains of significantly lower lipid mobility are formed. The analysis of peptide FCS data confirms the presence of microdomains for anionic SLBs. No indications of microdomain formation are detected in SLBs composed purely of zwitterionic lipids. Additionally, our FCS results imply that arenicin-1 exists in the form of oligomers and/or aggregates when interacting with membranes of both compositions.     

Interpretation of substituent effects on 13C and 15N NMR chemical shifts in 6-substituted purines

A range of purine derivatives modified at position 6 of the basic purine skeleton exhibit a variety of biological activities. Several derivatives are used or tested nowadays for pharmacological treatments. The present work aims to analyze the effects of substituents on the electron distribution in the purine core as reflected by NMR chemical shifts. We collected a comprehensive set of experimental NMR data for a variety of 6-substituted purines (-NH(2), -NHMe, -NMe(2), -OMe, -Me, -CCH, and -CN) and determined the molecular and crystal structures of three derivatives (-NHMe, -CCH, and -CN) by X-ray diffraction. The density-functional methods calibrated in our recent study (Phys. Chem. Chem. Phys., 2010, 12, 5126) have been employed to enable understanding of the substituent-induced changes in the NMR chemical shifts of the atoms in the purine skeleton. Analyses of the nuclear shielding using localized molecular orbitals (LMOs), specifically the natural LMOs (NLMOs) and Pipek-Mezey LMOs, were used to break down the values of the isotropic (13)C and (15)N NMR chemical shifts and the chemical shift tensors into the contributions of the individual LMOs. The experimental and calculated trends in the chemical shift of the N-3 atom correlate nicely with the Hammett constants (σ(para)) and the calculated natural charges on N-3, whereas the contributions of the LMOs to the N-1 and C-6 chemical shifts are found to be more complex.     

Distribution of BODIPY-labelled phosphatidylethanolamines in lipid bilayers exhibiting different curvatures

In this paper we have investigated the behaviour of newly synthesised mono-palmitoyl- and dipalmitoyl-phosphatidylethanolamine probes (abbreviated as mPE and dPE, respectively) labelled in the polar headgroup region by either the FL-BODIPY or the 564/570-BODIPY fluorophore and solubilised in lipid systems that exhibit different curvatures. Because of the bulky BODIPY-groups, the monoacyl-form derivatives have a conic-like shape, whereas that for the diacyl derivatives is rather cylindrical. A careful analysis of time-resolved resonance energy transfer experiments by means of analytical models as well as Monte Carlo simulations shows that the mPE derivatives have a comparable affinity to highly curved bilayer regions (torroidal pores formed by magainin-2 in lipid bilayers, or the rims of discoid bicelles) and to planar bilayer regions (i.e. the flat region of lipid bilayers and bicelles). Furthermore, the monoacyl-probes are as compared to the diacyl-probes effectively closer to each other in a lipid bilayer, while none of these probes seems to be randomly distributed. Self-aggregation is most efficiently induced by the larger aromatic 564/570-BODIPY chromophore, but it is suppressed when using the diacyl instead of the monoacyl-form, and/or by attaching BODIPY-groups to the acyl-chain.     

Power law Stokes equations with threshold slip boundary conditions: Numerical methods and implementation

For the power law Stokes equations driven by nonlinear slip boundary conditions of friction type, we propose three iterative schemes based on augmented Lagrangian approach and interior point method to solve the finite element approximation associated to the continuous problem. We formulate the variational problem which in this case is a variational inequality and construct the weak solution of the continuous problem. Next, we formulate two alternating direction methods based on augmented Lagrangian formalism in order to separate the velocity from the symmetric part the velocity gradient and tangential part of the velocity. Thirdly, we present some salient points of a path‐following variant of the interior point method associated to the finite element approximation of the problem. Some numerical experiments are performed to confirm the validity of the schemes and allow us to compare them.     

Novel adamantane-bearing anilines and properties of their supramolecular complexes with β-cyclodextrin

Several novel anilines bearing 1-adamantyl substituents that are useful for drug modification were synthesised from the corresponding 1-adamantyl (nitrophenyl) ketones. The host–guest systems of these prepared ligands with β-cyclodextrin (β-CD) were studied using electrospray ionisation mass spectrometry, NMR spectroscopy, titration calorimetry and semi-empirical calculations. The complexes with 1:1 stoichiometry were found to predominantly exist as pseudorotaxane-like threaded structures with the adamantane cage sitting deep in the cavity of β-CD close to the wider rim. Such geometry was observed for all examined amines and is independent of their structure and/or presence of protic substituents.     

The observed and calculated 1H and 13C chemical shifts of tertiary amines and their N-oxides

A series of model tertiary amines were oxidized in situ in an NMR tube to amine N-oxides and their (1)H and (13)C NMR spectra were recorded. Next, the chemical shifts induced by oxidation (Δδ) were calculated using different GIAO methods investigating the influence of the method [Hartree-Fock (HF), Moeller-Plesset perturbation, density functional theory (DFT)], the functional applied in the DFT (B3LYP, BPW, OPBE, OPW91) and the basis set used [6-31G*, 6-311G**, 6-311 + + G** and 6-311 + + G(3df,3pd)]. The best results were obtained with the HF/6-311 + + G** and OPBE/6-311 + + G** methods. The computation/experiment comparison approach was used for the configuration prediction of chiral amine N-oxides-(R) and (S)-agroclavine-6-N-oxide.     

Antibacterial Nanomaterials: Mechanisms,Impacts on Antimicrobial Resistance and Design Principles

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.