Effect of band structure on quantum interference in multiwall carbon nanotubes

We report conductance measurements on multiwall carbon nanotubes in a perpendicular magnetic field. A gate electrode with large capacitance is used to considerably vary the nanotube Fermi level. This enables us to search for signatures of the unique electronic band structure of the nanotubes in the regime of diffusive quantum transport. We find an unusual quenching of the magnetoconductance and the zero bias anomaly in the differential conductance at certain gate voltages, which can be linked to the onset of quasi-one-dimensional subbands.     

The potential of arsenic speciation in molluscs for environmental monitoring

This paper reports the assessment of total arsenic and six arsenic species (As(III), As(V), MMA, DMA, AsBet, AsCol) as contaminants of mussel samples collected around the island of Sardinia and in the Gulf of Venice. The samples were analysed using cation- and anion-exchange HPLC-HG-AFS for speciation and ICP-AES for the total As determination. To ensure the robustness of the routine analytical method, the technique was validated using a candidate reference material, BCR-710, and good agreement was obtained. It was recognised that higher total arsenic concentration in mussels does not necessarily result in higher toxicity of mussel samples.     

Stabilization effect of single-walled carbon nanotubes on the functioning of photosynthetic reaction centers

The interaction between single-walled carbon nanotubes and photosynthetic reaction centers purified from purple bacterium Rhodobacter sphaeroides R-26 has been investigated. Atomic force microscopy studies provide evidence that reaction center protein can be attached effectively to the nanotubes. The typical diameter of the nanotube is 1-4 nm and 15 +/- 2 nm without and with the reaction centers, respectively. Light-induced absorption change measurements indicate the stabilization of the P+(Q(A)Q(B))- charge pair, which is formed after single saturating light excitation after the attachment to nanotubes. The separation of light-induced charges is followed by slow reorganization of the protein structure. The stabilization effect of light-initiated charges by the carbon nanotubes opens a possible direction of several applications, the most promising being in energy conversion and storage devices.     

Novel resolution of chiral lactams

A practical method of resolving chiral lactams, e.g. 1 , has been evolved, based on the hydroxymethylation of the lactam, followed by esterification of the product 2 with an optically active N-protected amino acid derivative, e.g. N-benzyloxycarbonylphenylalanine pentafluorophenyl ester 3 . Chromatographic separation of the unreacted hydroxymethylated lactam 2 and the ester 4 and subsequent dehydroxymethylation of the former and aminolysis of the latter afforded pure enantiomer, (R)- 1 and (S)- 1 .     

Human serum albumin self-assembly on weak polyelectrolyte multilayer films structurally modified by pH changes

Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior.     

Microchip gel electrophoretic analysis of perchloric acid‐soluble serum proteins in systemic inflammatory disorders

Perchloric acid (PCA) precipitation is a well‐known method for the separation of heavily glycosylated proteins and for reducing the masking effect of major serum proteins. The aim of this study is to characterize PCA‐soluble serum proteins in healthy individuals and in patients with systemic inflammatory diseases, such as Crohn's disease and sepsis. A PCA precipitation protocol was prepared and adapted to the analytical methods. After PCA treatment of the serum, the soluble proteins in the supernatant were analyzed by SDS‐PAGE and by microchip gel electrophoresis (MGE). Characteristic changes of the electrophoretic patterns of the PCA‐soluble fractions were observed. Four characteristic bands (at ～11, ～65, ～85, and ～120 kDa) with varying intensity were detected by MGE. The proportion of the ～65, ～85, and ～120 kDa bands were significantly higher in systemic inflammatory conditions than in healthy individuals (p < 0.001), and characteristic patterns were observed in patients with acute inflammation. The marked differences in the acid‐soluble protein patterns, which were observed in patients with ongoing systemic inflammation, might be a good indicator of inflammation. The MGE analysis is a fast screening and quantification method for the detection of characteristic changes among acid‐soluble serum proteins.     

Color-bounded hypergraphs, IV: Stable colorings of hypertrees

We consider vertex colorings of hypergraphs in which lower and upper bounds are prescribed for the largest cardinality of a monochromatic subset and/or of a polychromatic subset in each edge. One of the results states that for any integers s≥2 and a≥2 there exists an integer f(s,a) with the following property. If an interval hypergraph admits some coloring such that in each edge E_i at least a prescribed number s_i≤s of colors occur and also each E_i contains a monochromatic subset with a prescribed number a_i≤a of vertices, then a coloring with these properties exists with at most f(s,a) colors. Further results deal with estimates on the minimum and maximum possible numbers of colors and the time complexity of determining those numbers or testing colorability, for various combinations of the four color bounds prescribed. Many interesting problems remain open.     

Chemistry and Pharmacology of Cyperaceae Stilbenoids: A Review

Cyperaceae is a cosmopolitan plant family with approx. 5000 species distributed worldwide. Several members of this family are used in traditional medicines for the treatment of different diseases. In the last few decades, constituents with great chemical diversity were isolated from sedges, and a wide range of biological activities were detected either for crude extracts or for pure compounds. Among the isolated compounds, phenolic derivatives are the most important, especially stilbenoids, and flavonoids. To date, more than 60 stilbenoids were isolated from 28 Cyperaceae species. Pharmacological investigation of Cyperaceae stilbenoids revealed that several compounds possess promising activities; mainly antiproliferative, antibacterial, antioxidant and anthelmintic effects. Isolation, synthesis and pharmacological investigation of stilbenes are increasing constantly. As Cyperaceae species are very good sources of a wide variety of stilbenes, and several of them occur in large amount worldwide, they are worthy for phytochemical and pharmacological investigations. Moreover, stilbenes are important from chemotaxonomical point of view, and they play a key role in plant defense mechanisms as well. This review summarizes the stilbenoids isolated from sedges, and their biological activities.     

Nanofiltration and electrodialysis: alternatives in heavy metal containing high salinity process water treatment

Desalination is priority in process water treatment and several different technologies can be applied to minimize the total salinity of water. Our aim was to study desalination and simultaneous elimination of heavy metal residues from process waters. Nanofiltration (NF) and electrodialysis (ED) treatment technologies were applied for high salinity model solutions and high salinity, heavy metal containing real process waters originating from electroplating industry. Efficiencies of two technologies were compared in respect to salt and heavy metal removal both for model solutions (NaCl and Na₂SO₄) and three real process water samples. Initial concentrations of model solutions chosen accordingly the most common process water salt composition. Both technologies showed similar efficiency of heavy metal (Ni²⁺ and Cu²⁺) removal; however, they provide different demineralization rates, rejection, and extraction percentage for sodium and chloride ions. ED experiments of model solutions showed complete desalination after 1 h operating time at 6 V applied voltage; on the other hand, the increasing conductivities of NF permeates verified the selectivity of NF membrane, therefore, representing partial desalination. These phenomena were confirmed by demineralisation rate values as well (NF: for NaCl: 41.5–66.6%, for Na₂SO₄: > 96.6%; ED: both for NaCl and Na₂SO₄ > 98%). Significantly. higher demineralisation rates were achieved by ED (37.3–99.2%) than NF (20.2–62.3%) during the treatment of real process waters. We successfully demonstrated that ED is more efficient for simultaneous salt and heavy metal removal for process waters originating of electroplating industry.