Some aspects of the model potential method

The theoretical justification of the model potential method is studied in some detail. The correct equations within the framework of Roothaan's open-shell scheme are derived and the approximations necessary to get a workable method are discussed. Analysis of the local part of the model potential suggests a new analytical form for it. The new expression is theoretically more consistent than the original one, and it can be determined in a more straightforward way. A basis set approximation, which is particularly suitable for approximate evaluation of two-electron integrals when only valence orbitals are involved, is discussed and tested with encouraging results. The ideas are tested on the Fe and I atoms.     

The mucosal adjuvanticity of two nontoxic mutants of Escherichia coli heat-labile enterotoxin varies with immunization routes

Escherichia coli heat-labile enterotoxin (LT), which causes a characteristic diarrhea in humans and animals, is a strong mucosal immunogen and has powerful mucosal adjuvant activity towards coadministered unrelated antigens. Here we report the different mucosal adjuvanticity of nontoxic LT derivatives, LTS63Y and LTdelta110/112, generated by immunizing through two different mucosal routes. Intragastric (IG) immunization with Helicobacter pylori urease alone resulted in poor systemic IgG and IgA responses and no detectable local secretory IgA, but IG co-immunization with urease and LTdelta110/112 induced high titers of urease-specific local secretory IgA and systemic IgG and IgA, comparable to those induced by wild-type LT. LTS63Y showed far lower adjuvant activity towards urease than LTdelta110/112 in IG immunization, but was more active than LTdelta110/112 in inducing immune responses to urease by intranasal (IN) immunization. LTdelta110/112 predominantly enhanced the induction of urease-specific IgG1 levels following IG immunization, whereas LTS63Y induced high levels of IgG1, IgG2a and IgG2b following IN immunization. In addition, quantitative H. pylori culture of stomach tissue following challenge with H. pylori demonstrated a 90-95% reduction (p < 0.0002) in bacterial burden in mice immunized intranasally with urease using either mutant LT as an adjuvant. These results indicate that the mechanism(s) underlying the adjuvant activities of mutant LTs towards coadmnistered H. pylori urease may differ between the IN and IG mucosal immunization routes.     

Biomonitoring of environmental pollution based on studies of trace elements in soil and crops

Most elemental concentrations in crops should be related to those in soil and other circumferential environments. In the present study, more than thirty minor and trace elements in soils and crops were determined by the use of ICP, XRF and NAA. Soil and crop samples were collected at eleven abandoned mine regions in Chungnam province located in the middle part of Korea. The elemental concentrations in soils were compared to the crustal mean concentrations in both Chungnam area and worldwide. The concentration ratios of the elements in soils and crop compartments were calculated and the distribution characteristics of each element were investigated between soil and crop compartments.     

Molecular Structure of the Macrocyclic Ligand Complex (5, 7, 12, 14-Tetraethyl-7, 14-Dimethyl-1, 4, 8, 11-Tetraazacyclotetra Decane) Nickel (II) Perchlorate

The structure of macrocyclic ligand complex, (5, 7, 12, 14-tetraethyl-7, 14-dimethyl-1, 4, 8, 11-tetraazacyclotetra decane)·Ni^II·(ClO₄)₂ has been determined by X-ray diffraction with three dimensional counter data. This compound, C₂₀H₄₄N₄Ni^II·(ClO₄)₂, crystallizes in orthorhombic space group Pbca, with cell parameters a=14.369, b=11.752, c=16.207 A, V=2736.8 A³, determined from Syntex Pl autodiffractomter. The formula weight (598.21) and a measured density of 1.45 gm cm^?3 (by flotation) indicate the presence of four molecules per unit cell (D_c=1.452 gm cm^?3). The structure was solved, using Patterson and Fourier methods and refined by full-matrix least-squares techniques to a reliability index, R(F) of 0.09, based on 1480 independent observed data corrected for absorption, L-p factors. In this molecule, in addition to the usual covalent and ionic bonds, there exist two hydrogen bonds between the perchlorate ions and the amine groups. The Ni and the four N atoms are coplanar. The six membered ring subtends a larger angle (93.5(3)°) over the Ni atom than the five membered ring (86.5(3)°) does. The former belongs to the chair form and the latter pertains to the gauche form.     

Ultra-low-temperature non-aqueous capillary electrophoretic separation--77 K fluorescence spectroscopic detection for the on-line identification of photo-converted analytes of trans-resveratrol

We demonstrate here, for the first time, that non-aqueous capillary electrophoresis (NACE) can be interfaced with any ultra-low-temperature (ULT) separation method and 77 K fluorescence spectroscopy (FS). This novel ULT-NACE-FS system consists of a modular CE system, a dry ice bath, and instrumentation for 77 K fluorescence detection. The ULT-NACE method serves to separate structurally similar molecules by a combination of a low electrophoresis current and a high voltage at approximately -70 degrees C. When the ULT-NACE-separated analytes move into the quartz Dewar flask and traverse into the capillary detection window, liquid nitrogen was added, thus freezing the separating analyte zones, allowing the collection of 77 K fluorescence spectra for on-line spectral fingerprint identification. The first application of the ULT-NACE-FS system is described for the analysis of photo-converted analytes of trans-resveratrol; prospects and future applications of ULT-NACE-FS are also briefly addressed.     

A New Calibration Method for the Gel Permeation Chromatographic Fractionation of Polymers

A model for the mechanism of the Gel permeation chromatographic separation of a polymer and a new calibration method have been developed, based on the exclusion of the polymer from the pores of the packing material. We propose that the calibration curve a plot of log (1—√K) versus log (molecular weight), where K is the elution volume coefficient, is close to linear over a K range of 0.15–0.85. We compare our procedure with that of Haller for various sets of data. Our procedure is generally better with lower standard deviations. When extrapolated, it gives a critical permeation size characteristic of the glass column packings.     

Lewis acid promoted aldol reaction of fluorinated silyl enol ethers from new fluoroacetylsilane derivatives

New fluorinated silyl enol ethers with various trialkylsilyl groups were synthesized. Various fluorinated β-hydroxy ketones were synthesized by Lewis acid promoted aldol reaction of silyl enol ethers with diverse aldehydes. Reactivity of various trialkylsilyloxy groups toward Lewis acid was also studied.     

Cytotoxic Acridone Alkaloids from the Stem Bark of Citrus Maxima

A new acridone alkaloid, 5‐hydroxynoracronycine alcohol (4), along with six known acridone alkaloids, glycocitrine‐I (1), 5‐hydroxynoracronycine (2), citrusinine‐I (3), grandisine‐I (5), natsucitrine‐II (6), and citracridone‐III (7), were isolated from the stem bark of Citrus maxima f. buntan. Their structures were established on the basis of spectroscopic methods. Compounds 1‐4 and 7 were found to be cytotoxic on two tumor cell lines.     

The maximum number of edges in a 3-graph not containing a given star

Suppose that is a collection of 3-subsets of{1, 2,..., n} which does not contain ak-star (i.e.,k 3-sets any two of which intersect in the same singleton). Fork 3 andn n ₀ (k), the collections having largest possible sizes are determined.     

Tautomerism and isomerism of guanine–cytosine DNA base pair: Ab initio and density functional theory approaches

The relative stabilities of guanine–cytosine (G–C) DNA base pairs are theoretically investigated with a focus on the keto–enol tautomerism as well as on the cis–trans enol isomerism by using both ab initio method and the density functional theory. The G–C pairs of the keto tautomers turn out to be in general more stable than those of the enol tautomers, 9H-guanine pair, 9KK (see the notation below), being the most stable one. The stability of the G–C pairs appears to be affected by various factors including the keto–enol tautomerization, cis–trans enol isomerization, and the steric hindrance between two tautomeric pairs. Although the B3LYP calculations tend to underestimate the binding energies, in addition, it is shown that the binding energy of G–C pairs interacting through hydrogen bonds can be reasonably calculated with the DFT method, contrary to the base pairs with stacked configurations.