Quantitative characterization of chaotic instabilities in semiconductors

A method for quantitative characterization of chaotic dynamical systems is discussed. An electronic instrument for determining the number of independent variablesk ^*, involved in the motion, is described. It allows one to obtain these in real time from a single observable. The suggested technique has been applied to quantification of strange attractors underlying chaotic instabilities in semi-insulating GaAsCr, and n-Ge, irradiated with high energy electrons. In n-Ge, for instance, the measured numbersk ^* range from 2 to 4 depending on control parameters. These measurements reveal the highly deterministic nature of the observed chaotic oscillations. The physical mechanisms responsible for the current instabilities and chaotic behaviour are discussed.     

Kinetic studies of some substituted hexarhodium carbonyl clusters

Reactions of the halides X- (X- = chloride, bromide or iodide) with the substituted cluster Rh6(CO)15(PPh3) in oxygen-free chloroform lead to [Rh5(CO)14(PPh3)]-, Rh(CO)2(PPh3)2X and [Rh(CO)2X2]- in the molar ratios 2:1: approximately 13. Oxidation by the solvent is assumed to lead to most of the Rh(I) product, and the stoichiometry for reactions with I- can be defined as 4Rh6(CO)15(PPh3) + 27I- + 12CHCl3 --> 2[Rh5(CO)14(PPh3)]- + Rh(CO)2(PPh3)2I + 13[Rh(CO)2I2]- + 6C2H2Cl4 + 4CO + 12Cl-. This can be rationalized quite simply with the aid of a few generally justifiable assumptions. Rate constants for reactions with bromide increase to a limiting value with increasing [Br-] in a way that shows that breaking of one Rh-Rh bond, with an unusual closo to nido structural change, is rate determining. This opening of the cluster might be spontaneous or solvent induced. To complete the reaction, the bromide has to compete with the reverse nido to closo change. The same closo to nido change is also a major rate determining step for reactions with P(OPh)3 in oxygen-free solutions, and for reactions with bromide in oxygenated solutions in the presence of trifluoroacetic and some other acids. The limiting rates increase slightly with increasing basicity of the ligands P(p-XC6H4)3 along the series X = F3C, Cl, F, H and MeO. Activation parameters for these reactions are reported.     

Sequestration within biomolecular condensates inhibits Aβ-42 amyloid formation

Biomolecular condensates are emerging as an efficient strategy developed by cells to control biochemical reactions in space and time by locally modifying composition and environment. Yet, local increase in protein concentration within these compartments could promote aberrant aggregation events, including the nucleation and growth of amyloid fibrils. Understanding protein stability within the crowded and heterogeneous environment of biological condensates is therefore crucial, not only when the aggregation-prone protein is the scaffold element of the condensates but also when proteins are recruited as client molecules within the compartments. Here, we investigate the partitioning and aggregation kinetics of the amyloidogenic peptide Abeta42 (Aβ-42), the peptide strongly associated with Alzheimer''s disease, recruited into condensates based on low complexity domains (LCDs) derived from the DEAD-box proteins Laf1, Dbp1 and Ddx4, which are associated with biological membraneless organelles. We show that interactions between Aβ-42 and the scaffold proteins promote sequestration and local increase of the peptide concentration within the condensates. Yet, heterotypic interactions within the condensates inhibit the formation of amyloid fibrils. These results demonstrate that biomolecular condensates could sequester aggregation-prone proteins and prevent aberrant aggregation events, despite the local increase in their concentration. Biomolecular condensates could therefore work not only as hot-spots of protein aggregation but also as protective reservoirs, since the heterogenous composition of the condensates could prevent the formation of ordered fibrillar aggregates.

Biomolecular condensates sequester an aggregation-prone peptide and prevent its aggregation, showing that heterotypic interactions within the condensates can prevent the formation of amyloid fibrils, despite the local increase in concentration.     

Theoretical studies on the metathesis processes, (Tp(PH3)MR(eta 2-H[bond]CH3)]-->[Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe,Ru, and Os; R=H and CH3)

Theoretical calculations on the metathesis process, [Tp(PH3)MR(eta 2-H[bond]CH3)] --> [Tp(PH3)M(CH3)(eta 2-H[bond]R)] (M=Fe, Ru, and Os; R=H and CH3), have been systematically carried out to study their detailed reaction mechanisms. Other than the one-step mechanism via a four-center transition state and the two-step mechanism through an oxidative addition/reductive elimination pathway, a new one-step mechanism, with a transition state formed under oxidative addition, has been found. Based on the intrinsic reaction coordinate calculations, we found that the trajectories of the transferring hydrogen atom in the metathesis processes studied are similar to each other regardless of the nature of reaction mechanisms.     

ICP-MS determination of heavy metals in submerged cultures of wood-rotting fungi

Accumulation of five heavy metal ions by five species of wood-rotting basidiomycetes during a 9-day cultivation was studied. Contents of Cd, Cu, Pb, and Zn were measured using ICP-MS; the amount of mercury was determined directly in solid samples using the Advanced Mercury Analyser. A standard operation procedure for the sample preparation and determination of metal content was developed and validated. Presence of Cd, Cu, Hg, and Pb decreased the accumulation of zinc by the fungi. The basidiomycete Pycnoporus cinnabarinus exhibited the highest metal binding capacity of all fungi tested.     

Quantitative analysis of nicotinic acid, nicotinamide and 3-cyanopyridine in industrial effluent by high performance liquid chromatography

A rapid and reliable high performance liquid chromatographic (HPLC) method for the simultaneous determination of heterocyclic compounds, namely nicotinic acid, nicotinamide, and 3-cyanopyridine, in industrial effluent is described. A Φ4.6 mm × 150 mm, 5 μm C-18 reversed phase stationery phase, and a methanol-acetonitrile-water tertiary mobile phase (20:20:60 v/v) were used for separation. The detection wavelength of a diode array (DAD) was set at 216 nm with a bandwidth of 16 nm. Phenol was used as an internal standard. The regression equations revealed a linear relationship between the concentration of the analytes injected and the peak area detected by DAD. The limits of detection (S/N = 3) ranged from 0.70 to 1.18 mg L⁻¹, the recoveries ranged from 87% to 102% and the precision expressed as % RSD intra-day and inter-day varied from 0.9 to 3.9 and 1.2 to 5.6, respectively. This method is rapid, sensitive and suitable for the monitoring of nicotinic acid, nicotinamide, and 3-cyanopyridine in effluent of related pharmaceutical manufacturing plants.     

A mesoporous Pt/TiO2 nanoarchitecture with catalytic and photocatalytic functions

A novel metal/semiconductor nanocomposite with catalytic and photocatalytic functions has been prepared. The new material consists of highly dispersed platinum (Pt) nanoparticles embedded in a cubic mesoporous nanocrystalline anatase (meso-nc-TiO2) thin film. The porous thin film possesses a narrow pore-size distribution and a large surface area. The diameter of the Pt cluster can be controlled to below 5 nm, and the high dispersion of these clusters gives rise to catalytic activity for the oxidation of carbon monoxide, an important reaction for automobile exhaust treatment. This novel ordered mesoporous Pt/TiO2 nanoarchitecture is also a promising photochemical material, as demonstrated by the photo-driven killing of Micrococcus lylae cells on the film.     

Modification of polysulfone membranes 4. Ammonia plasma treatment

The effect of NH₃ and NH₃/Ar plasma on ultrafiltration polysulfone membranes have been studied. Results of contact angle, FTIR-ATR and X-ray photoelectron spectroscopy experiments clearly showed that both plasmas introduced hydrophilic, nitrogen- and oxygen-containing moieties on the polymer surface and that NH₃/Ar plasma was more efficient. That plasma was also more aggressive--signs of strong etching could be seen on the SEM pictures. Redeposition of etched material seemed to take place inside the pores. On the contrary, ammonia plasma was soft and caused cleaning the surface and pores enlargement. Performance of ammonia plasma modified membranes was greatly improved and independent on solution pH. The last observation proved amphoteric character of the surface. NH₃/Ar plasma treatment gave membranes of acidic surface and filtration indices not so good as for ammonia plasma.     

Cadmium speciation in Arabidopsis thaliana as a strategy to study metal accumulation system in plants

The strategy to identify cadmium deactivation mechanism in Arabidopsis thaliana has been developed using selective and sensitive hyphenated techniques. Cadmium concentrations, in main parts of the plant, were determined by ICP-MS and total amount was found as 0.43-0.44 μg g⁻¹ in leaves and 3.3-3.4 μg g⁻¹ in roots. Speciation of the metal complexes in cells was investigated by SEC-ICP-MS in order to estimate the accumulation process. Phytochelatins, desglycyl-phytochelatins and phytochelatins homologues lacking the N-terminal γ-linked glutamic acid were extracted from plant and were identified by RPLC-ESI-MS. Two-dimensional chromatography allowed to link the metal complexes separated by SEC with isoforms of phytochelatins analyzed by high resolution RPLC and confirm their significant responsibility for metal accumulation. The potential of the cadmium complexes speciation indicates that obtained results could be reliable source of knowledge to confirm the information coming from the well-known genomic sequence of Arabidopsis and to estimate the role of γ-glutamyl transpeptidase in metabolism of glutathione.     

Glass capillary columns for separation of free organic acids

Glass capillary columns have been prepared without acidic additive in the stationary phase, from which free organic acids elute as sharp and symmetrical peaks. The required surface in the borosilicate glass capillary was generated by a combination of leaching with aqueous HCl and deposition of colloidal silica particles; it can be coated with stationary phases have a broad range of polarity. Aqueous samples containing free organic acids can also be analyzed in such columns in an isothermal mode.