Dissolved organic carbon--contaminant interaction descriptors found by 3D force field calculations

Enthalpies of transfer at 300 K of various partitioning processes were calculated in order to study the suitability of 3D force fields for the calculation of partitioning constants. A 3D fulvic acid (FA) model of dissolved organic carbon (DOC) was built in a MM+ force field using AMI atomic charges and geometrical optimization (GO). 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (Atrazine) were inserted into different sites and their interaction energies with FA were calculated. Energies of hydration were calculated and subtracted from FA-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to DOC were 2.8, -1.4, -6.4 and 0.0 kcal/mol for PCB 14, PCB15, PPDDT and Atrazine, respectively. The value of PPDDT compared favorably with the experimental value of -5.0 kcal/mol. Prior to this, the method was studied by the calculation of the enthalpies of vaporization and aqueous solution using various force fields. In the MM + force field GO predicted enthalpies of vaporization deviated by +0.7 (PCB14), +3.6 (PCB15) and -0.7 (PPDDT)kcal/mol from experimental data, whereas enthalpies of aqueous solution deviated by -3.6 (PCB14), +5.8 (PCB15) and +3.7 (PPDDT) kcal/mol. Only for PCB14 the wrong sign of this enthalpy value was predicted. Potential advantages and limitations of the approach were discussed.     

Preparation and properties of La0.67Pb0.33(Mn1-xFex)O3 compounds

La_0.67Pb_0.33(Mn_1-xFe_x)O₃ materials with x=0, 0.01, 0.03, 0.06, 0.1, 0.15 have been prepared by a wet chemical malic acid gel method followed by heat treatment at 1000 °C in air or oxygen. X-ray diffraction showed that the compounds were phase pure. The crystal structure of the compounds were interpreted in the rhombohedral space group (R3̄c). The temperature dependence of the resistance depended strongly on the Fe-content and showed metal–insulator transitions for all compounds. The Curie temperatures were determined from the dependence of the magnetization on the temperature and on the magnetic field. Both the Curie temperatures and saturation magnetic moments decreased linearly with increasing iron content. The metal–insulator transitions did not coincide with the relevant Curie temperatures. Reasons for this behavior are discussed. PACS 72.80.Ga; 75.47.Lx; 75.60.Ej     

A semi-automated method for fluorimetric determination of epinephrine and norepinephrine, without mutual interference, in single brain samples

A method is described for the separation and automated fluorimetric determination of epinephrine and norepinephrine in brain tissue extracts without mutual interference. The catecholamines are isolated and purified by extraction from activated alumina. Oxidation and rearrangement to their fluorescent lutines is carried out on two separate AutoAnalyzer manifolds and fluorescence is read in an Aminco-Bowman spectrophotofluorimeter. The interference by one amine with the determination of the other is less than 1% for determination of epinephrine in the presence of an equimolar concentration of norepinephrine, and, conversely, less than 4% for determination of norepinephrine. This eliminates the need for solution of simultaneous equations, the results of which are often misleading when the ratio of one amine to the other in brain exceeds 10:1. This method can be useful for rapid screening of psychoactive compounds affecting central and peripheral adrenergic stores.     

The Second Indicator and the Trace of the Antipode for Representations of a Class of Hopf Algebras of Andruskiewitch-Schneider Type

We give definition of the second indicator for any finite-dimensional Hopf algebra over an algebraically closed field of characteristic 0 with the square of antipode an inner automorphism. We derive a closed formula for the trace of the antipode on endomorphism algebras of simple self-dual modules of nilpotent type liftings of quantum linear spaces and compute the value of their second indicators. Uniqueness of indicators is examined.     

On the number of unlabeled vertices in edge-friendly labelings of graphs

Let $G$ be a graph with vertex set $V\left(G\right)$ and edge set $E\left(G\right)$, and $f$ be a $0?1$ labeling of $E\left(G\right)$ so that the absolute difference in the number of edges labeled $1$ and $0$ is no more than one. Call such a labeling $f$ edge-friendly. We say an edge-friendly labeling induces a partial vertex labeling if vertices which are incident to more edges labeled $1$ than $0$, are labeled $1$, and vertices which are incident to more edges labeled $0$ than $1$, are labeled $0$. Vertices that are incident to an equal number of edges of both labels we call unlabeled. Call a procedure on a labeled graph a label switching algorithm if it consists of pairwise switches of labels. Given an edge-friendly labeling of $K_n$, we show a label switching algorithm producing an edge-friendly relabeling of $K_n$ such that all the vertices are labeled. We call such a labeling opinionated.