Die Schätzung der Parameterwerte einer abgeschnittenen Gammaverteilung

Summary In biological, meteorological and other applications, the statistical data often belong to a truncated -distribution. In other cases, having also a -distributed population, one has to deal with censored data. To estimate the 3 parameters of the -distribution simultaneously, the authors suggest for these cases an iterative procedure for the solution of the Maximum-Likelihood-equation.     

Catalysis of ionic reactions by polyelectrolytes. IV. Quenching of the quinine cation fluorescence by Fe++, Ag+, and Br− in solutions of poly(vinylsulfonic acid)

The fluorescence quenching of the doubly charged quinine cation by Fe⁺⁺, Ag⁺, and Br^? was studied in the presence and absence of polyvinylsulfonate (PVS). The quenching by cationic species was greatly enhanced by PVS at low polyion concentrations; at higher concentrations of PVS, the fluorescence intensity increased owing to displacement of the quinine cations from the polyion domain. Quenching of quinine fluorescence by Br^? was repressed by PVS. Interpretation of the data with the use of Fe⁺⁺ as the quenching agent led to “effective concentrations” of counterions in the polyion domain similar to those calculated from the catalysis of the redox reaction of Co(NH₃)₅Cl⁺⁺ with Fe⁺⁺. This may indicate that the reagent ions are not rigidly bound to the polyion chain, since such binding would affect differently processes with high and low activation energies. The Stern-Volmer constant for self-quenching of the quinine fluorescence can also be obtained from fluorescence intensity data in PVS solution.     

Preparation and conformation of octaethylbiphenylene

Dimerization of tetraethylbenzyne (generated by reaction of 1, 2-dibromo-3,4,5,6-tetraethylbenzene (8) with 1 equiv of BuLi) afforded in low yield octaethylbiphenylene (3), together with a major product which was characterized as 2,3,4,5,3',4', 5'-heptaethyl-2'-vinylbiphenyl (9). X-ray diffraction indicates that biphenylene 3 adopts in the crystal a conformation of approximate C(2)(h )()symmetry with the ethyl groups within each phenylene ring arranged in an alternated up-down fashion. Notably, pairs of vicinal ethyl groups located at peri positions are oriented in a syn arrangement in the crystal. Low temperature NMR spectroscopy is consistent with the presence in solution of either the crystal conformation or a fully alternated conformation lacking any syn interaction. Molecular mechanics (MM3), semiempirical (AM1, PM3), and ab initio calculations indicate that the crystal conformation is a high energy form, and that the lowest energy conformation is the fully alternated form. The topomerization barrier of the methylene protons of the ethyl groups of 3 is 9.4 +/- 0.1 kcal mol(-)(1), which is between the rotational barriers of 8 and 1,2,3, 4-tetraethylbenzene 7 (9.9 +/- 0.1 and 8.2 +/- 0.1 kcal mol(-)(1), respectively). The similarity in rotational barriers suggests that a given tetraethylphenylene subunit does not markedly affect the rotational barrier of the ethyl groups of the other subunit.     

A Stable Integrated Photoelectrochemical Reactor for H2 Production from Water Attains a Solar‐to‐Hydrogen Efficiency of 18 % at 15 Suns and 13 % at 207 Suns

The major challenge in solar water splitting to H₂ and O₂ is in making a stable and affordable system for large‐scale applications. We have designed, fabricated, and tested a photoelectrochemical reactor characterized as follows: 1) it comprises an integrated device to reduce the balance of the system cost, 2) it utilizes concentrated sunlight to reduce the photoabsorber cost, and 3) it employs and alkaline electrolyte to reduce catalyst cost and eliminate external thermal management needs. The system consists of an III‐V‐based photovoltaic cell integrated with Ni foil as an O₂ evolution catalyst that also protects the cell from corrosion. At low light concentration, without the use of optical lenses, the solar‐to‐hydrogen (STH) efficiency was 18.3 %, while at high light concentration (up to 207 suns) with the use of optical lenses, the STH efficiency was 13 %. Catalytic tests conducted for over 100 hours at 100–200 suns showed no sign of degradation nor deviation from product stoichiometry (H₂/O₂=2). Further tests projected a system stability of years.     

Ligand specificity of CS-35, a monoclonal antibody that recognizes mycobacterial lipoarabinomannan: a model system for oligofuranoside-protein recognition

The CS-35 antibody is widely used in the characterization of glycans containing D-arabinofuranose residues, in particular polysaccharides present in the mycobacterial cell wall. A detailed understanding of the combining site of this antibody and the measurement of its binding to different ligands is of interest as this knowledge will have implications in the characterization of arabinofuranose-containing glycoconjugates that are increasingly recognized as important biological molecules. Of even greater significance is that an in-depth study of this carbohydrate-protein interaction will provide insights into the mechanisms by which oligosaccharides containing furanose rings are bound by proteins, an area that has, to date, received little attention. This system has been refractory to X-ray crystallography, and thus we report here a study of the interaction of CS-35 with its ligands using a combination of chemical synthesis, mass spectrometry, titration microcalorimetry, and NMR spectroscopy. Through these investigations we have established that the binding pocket recognizes, as a minimum epitope, a linear tetrasaccharide motif and that the residues at the reducing and non-reducing end of the oligosaccharide are essential for tight binding. The residue at the non-reducing end appears to be bound in an aliphatic pocket, whereas the rest of the tetrasaccharide interacts more strongly with aromatic amino acids.     

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

Antioxidant activities, total phenolics and HPLC analyses of the phenolic compounds of extracts from common Mediterranean plants

In this study, the total phenolic amounts and antioxidant activities of plant extracts obtained from some common Mediterranean plant species collected from different places in Jordan were determined. The phenolic constituents of these extracts were also determined using HPLC. The total phenolic amounts ranged from 52.8 to 876.9 mg GAE per 100 g dry material. The antioxidant activities were evaluated according to the 2,2-diphenyl-1-picrylhydrazyl radical scavenger method. Sage (Salvia officinalis) showed the highest antioxidant activity (91%), while the lowest (11.3%) was seen in parsley (Petroselinum crispum). A strong correlation (r = 0.85) between antioxidant activity and total phenolic content was found. The phenolic compounds identified by HPLC were gallic acid, protocatechuic acid, catechin, gentisic acid, chlorogenic acid, vanillic acid, syringic acid, caffeic acid, epicatechin and benzoic acid. All the investigated plants contain gallic acid, whose phenolic content ranged from 0.4 to 37.8 mg per 100 g, catechin (0.3-339.9 mg per 100 g), protocatechuic acid (0.3-41.9 mg per 100 g) and gentisic acid (0.3-35.8 mg per 100 g), while caffeic acid (0.3-2.6 mg per 100 g) was detected in six species only. These natural plant phenolics could thus be a good source of antioxidants for applications in food.     

Thujone corrects cholesterol and triglyceride profiles in diabetic rat model

Thujone, which is the major constituent in Salvia sp. (Lamiaceae), was found to correct the lipid profile (cholesterol and triglycerides) in diabetic rats. Oral treatment with thujone (5 mg kg?1 body weight dose) significantly adjusted cholesterol and triglyceride levels in diabetic rats (p ≤ 0.05) to normal levels compared to diabetic untreated rats. This provides a premise in the field of finding new agents to treat diabetic complications.     

The complexation of a novel squaric bis(thiosemicarbazone); 3,4-bis{[(aminothioxomethyl)amino]azamethylene}cyclobut-ene-1,2-diol

A novel chelating agent (Sqtsc; H(4)L) bearing both hard and soft donor atoms was synthesized by the condensation of squaric acid with thiosemicarbazide. The ligand has two symmetrical sets of donor atoms (SNO), therefore, it was allowed to react with the metal ions at the mole ratio 2:1 (M:L). Mono- and bi-nuclear chelates were obtained in which the ligand showed a variety of modes of bonding viz. (OO)(2-), (SNNS)(2-) and (SNO)(2-) per each metal ion supporting the ambidentate and flexidentate characters of the ligand. The mode of bonding and basicity of the ligand depend mainly on the type of the metal cation and its counter anion. All the obtained complexes have the preferable O(h)-geometry except the VO(II)-complex (7) which has also the preferable square pyramid geometry. Structural elucidation was achieved via elemental and spectral data.