Comparison of MOVPE grown GaAs solar cells using different substrates and group-V precursors

We have investigated the influence of substrate type (GaAs vs. germanium) and of group-V precursor (AsH₃ vs. TBAs) on the epitaxial quality of (In)(Al)GaAs layers. We evaluated these layers in terms of morphology, background contamination and doping characteristics. For final benchmarking of the individually optimised processes, we produced p-on-n single junction GaAs solar cells and compared their relative performance. This type of device is an excellent performance monitor for epitaxial layers as the fundamental operating mechanism is drift of minority carriers. The solar cell grown with TBAs on a germanium-substrate has a conversion efficiency under the AM1.5 solar spectrum, which compares favourably with the highest reported value for a p-on-n GaAs solar cell on Ge (Prog. Photovolt. Res. Appl. 8 (2000) 377).     

Growth technology and X-ray investigation results of CuFeSe2 crystal modifications

The growth technologies of CuFeSe₂ monocrystals from melt and GTR methods were developed. The existence of two polytypes of tetragonal (primitive and inverse-type) lattices with slightly different parameters and one modification of spinel-type pseuodocubic lattice was established from X-ray investigations.     

Transport in a flashing ratchet in the presence of anomalous diffusion

Transport of a particle in a flashing ratchet coupled to a non-Ohmic environment with spectrum ∝ω^μ−1 (0<μ<2) is considered. If the temperature is much less than the barrier height of the ratchet potential and the waiting time of the particle in the potential on is long enough, the current J is evaluated approximately by the step periodic number per cycle. The results show that the maximum of peak for J is a non-monotonous function of μ, the optimal μ appears in the region of superdiffusion. The current in the anomalous ratchet is much larger than in the normal one.     

Coagulation by hydrolysing metal salts

Aluminium and iron salts are widely used as coagulants in water and wastewater treatment and in some other applications. They are effective in removing a broad range of impurities from water, including colloidal particles and dissolved organic substances. Their mode of action is generally explained in terms of two distinct mechanisms: charge neutralisation of negatively charged colloids by cationic hydrolysis products and incorporation of impurities in an amorphous hydroxide precipitate (‘sweep flocculation’). The relative importance of these mechanisms depends on factors such as pH and coagulant dosage. Alternative coagulants, based on prehydrolysed forms of aluminium and iron, are more effective than the traditional additives in many cases, but their mode of action is not completely understood, especially with regard to the role of charge neutralisation and hydroxide precipitation. Some basic features of metal hydrolysis and precipitate formation are briefly reviewed and the action of hydrolysing coagulants is then discussed, with examples from the older literature and from some recent studies on model systems. Dynamic monitoring of floc formation and breakage can give useful insights into the underlying mechanisms. Although the results can be reasonably well explained in terms of established ideas, a detailed understanding of the ‘sweep flocculation’ mechanism is not yet available. There are also still some uncertainties regarding the action of pre-hydrolysed coagulants.     

Avoiding numerical instabilities in R12 calculations through universal R12 consistent basis sets

We show that the incidental numerical instabilities in explicitly correlated coupled cluster R12 (CC-R12) calculations can be a priori removed by using systematically developed R12 suited basis sets. Those are quite different from basis sets developed for conventional calculations mainly in polarization functions. Using even tempered polarization sets for carbon and oxygen we were able to define compromise R12 suited bases which describe equally well atomic ground states, positive and negative ions and electric field polarized atoms. Corresponding energies obtained with such ‘R12 universal’ sets remain accurate to within a few μE_h with respect to the ‘R12 optimal’ bases of individual systems.     

In‐Depth Understanding of the Chemical Properties of Rarely Explored Carbide Cluster Metallofullerenes: A Case Study of Sc2C2@C3v(8)‐C82 that Reveals a General Rule

The chemical properties of carbide‐cluster metallofullerenes (CCMFs) remain largely unexplored, although several new members of CCMFs have been discovered recently. Herein, we report the reaction between Sc₂C₂@C_3v(8)‐C₈₂, which is viewed as a prototypical CCMF because of its high abundance, and 3‐triphenylmethyl‐5‐oxazolidinone ( 1 ) to afford the corresponding pyrrolidino derivative Sc₂C₂@C_3v(8)‐C₈₂(CH₂)₂NTrt ( 2 ; Trt=triphenylmethyl). Single‐crystal X‐ray crystallography studies of 2 revealed that the reaction takes place at a [6,6]‐bond junction, which is directly over the encapsulated C₂ unit and is far from either of the two scandium atoms. On the basis of theoretical calculations and by considering previously reports, we have found that a hexagonal carbon ring on the cage of Sc₂C₂@C_3v(8)‐C₈₂ is highly reactive toward different reagents due to the overlap of high p‐orbital axis vector (POAV) angles and large LUMO coefficients. We propose that this highly concentrated area of reactivity is generated by the encapsulation of the Sc₂C₂ cluster because this region is absent from the empty fullerene C_3v(8)‐C₈₂. Moreover, the absorption and electrochemical results confirm that derivative 2 is more stable than pristine Sc₂C₂@C_3v(8)‐C₈₂, thus illuminating its potential applications.     

Multi-enzyme anode composed of FAD-dependent and NAD-dependent enzymes with a single ruthenium polymer mediator for biofuel cells

A multi-enzyme electrode composed of FAD-dependent and NAD-dependent enzymes was fabricated using a poly-ruthenium complex (PAHA–Ru), which has two 1,10-phenanthroline-5,6-dione molecules as ligands. PAHA–Ru was used to immobilize FAD-dependent glucose dehydrogenase (FAD–GDH) onto an electrode and to examine PAHA–Ru containing the quinone moieties as an electron mediator. In cyclic voltammetry measurements of the FAD–GDH modified electrode in the presence of D-glucose, a catalytic current was obtained, which indicated electron transfer from FAD–GDH to PAHA–Ru. Our previous study has reported that PAHA–Ru with the quinone ligands also works as a mediator for NADH oxidation on an NAD-dependent alcohol dehydrogenase (NAD–ADH) modified electrode. Hence, FAD–GDH and NAD–ADH were co-immobilized with PAHA–Ru to make a multi-enzyme electrode. Using this multi-enzyme electrode as an anode, catalytic currents were observed in D-glucose solution, ethanol solution, and a mixed D-glucose and ethanol solution. The catalytic current in the mixed solution was greater than the currents obtained in the single substrate solutions, indicating bioelectrocatalysis reactions by the two enzymes and the single mediator in the mixed solution. Thus, we demonstrated that PAHA–Ru modified electrode enables selection of enzymes and their substrates from a wider range for enzymatic biofuel cells.     

Simultaneous Induction of Axial and Planar Chirality in Arene–Chromium Complexes by Molybdenum‐Catalyzed Enantioselective Ring‐Closing Metathesis

The molybdenum‐catalyzed asymmetric ring‐closing metathesis of the various C_s‐symmetric (π‐arene)chromium substrates provides the corresponding bridged planar‐chiral (π‐arene)chromium complexes in excellent yields with up to >99 % ee. With a bulky and unsymmetrical substituent, such as N‐indolyl or 1‐naphthyl, at the 2‐positions of the η⁶‐1,3‐diisopropenylbenzene ligands, both biaryl‐based axial chirality and π‐arene‐based planar chirality are simultaneously induced in the products. The axial chirality is retained even after the removal of the dicarbonylchromium fragment, and the chiral biaryl/heterobiaryl compounds are obtained with complete retention of the enantiopurity.     

Chemistry of Lipid A: At the Heart of Innate Immunity

In many Gram‐negative bacteria, lipopolysaccharide (LPS) and its lipid A moiety are pivotal for bacterial survival. Depending on its structure, lipid A carries the toxic properties of the LPS and acts as a potent elicitor of the host innate immune system via the Toll‐like receptor 4/myeloid differentiation factor 2 (TLR4/MD‐2) receptor complex. It often causes a wide variety of biological effects ranging from a remarkable enhancement of the resistance to the infection to an uncontrolled and massive immune response resulting in sepsis and septic shock. Since the bioactivity of lipid A is strongly influenced by its primary structure, a broad range of chemical syntheses of lipid A derivatives have made an enormous contribution to the characterization of lipid A bioactivity, providing novel pharmacological targets for the development of new biomedical therapies. Here, we describe and discuss the chemical aspects regarding lipid A and its role in innate immunity, from the (bio)synthesis, isolation and characterization to the molecular recognition at the atomic level.