O(N) vector model with twisted boundary conditions

Prompted by a recent article of Chakravarty, we reexamine the<i>O(N)</i> vector model with twisted boundary conditions in<i>d</i> dimensions in the various frameworks of the <img src="/content/l3802355517w6795/xxlarge603.gif" alt="epsiv" align="BASELINE" BORDER="0">=<i>d</i>–2 expansion, the <img src="/content/l3802355517w6795/xxlarge949.gif" alt="epsi" align="BASELINE" BORDER="0">=4–<i>d</i> expansion, and the large-<i>N</i> expansion. These continuum models describe the physics below the critical temperature<i>T</i> <sub>c</sub> and near<i>T</i> <sub>c</sub> of a lattice<i>O(N)</i> spin model. We determine the effect of the twisting on finite-size scaling functions, for various geometries.On leave from G. Nadjakov Institute of Solid State Physics, 1784 Sofia, Bulgaria.     

Effect of Pluronic F127 on the pore structure of macrocellular biodegradable polylactide foams

Thermally induced phase separation technique was utilized to fabricate biodegradable poly(l ‐lactic acid) (PLLA) macrocellular foams which were capable of being applied in tissue engineering. The block copolymer Pluronic F127 composed of (polyethyleneoxide)‐(polypropyleneoxide)‐(polyethyleneoxide) [(PEO)‐(PPO)‐(PEO)] was used as a porogen. Water/dioxane mixtures with different volume ratios were used as solvents. The addition of Pluronic F127 could induce an appearance of large pores (50–200 μm) besides small pores (10–20 μm) or a change from a solid–liquid phase separation to a liquid–liquid phase separation. The role of Pluronic F127 depends on the water/dioxane ratios in the PLLA/dioxane/water system. The X‐ray diffraction patterns and porosity measurement results showed that Pluronic F127 was crystallized and existed on the pore wall. The effect of Pluronic F127 on changing pore structure is attributed to the occurrence of the interaction of the lipophilic PPO blocks in Pluronic F127 with PLLA clews, consequently, this results in PLLA aggregation and early phase separation on cooling. Copyright © 2004 John Wiley & Sons, Ltd.     

Polysulfonylamine. XLI. Ein Silber(I)-Hydrat ungewöhnlicher Zusammensetzung: Röntgenstrukturanalytische und thermochemische Charakterisierung von Tetrakis(dimesylamido)aquatetrasilber(I) [Ag4(N(SO2CH3)2}4(H2O)]

Polysulfonyl Amines. XLI. A Silver(I) Hydrate with an Unusual Composition: Characterization of Tetrakis(dimesylamido)aquatetrasilver(I) [Ag<sub>4</sub>(N)SO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub>}<sub>4</sub>(H<sub>2</sub>O)] by X-Ray Diffraction and Thermal Analysis The title compound is obtained by crystallizing AgN(SO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub> from water at room temperature. Crystallographic data (at ?95°C): Triclinic space group P1 , a = 864.6(4), b = 1 211.2(5), c = 1 399.1(5) pm, α = 90.97(3), β = 90.90(3), γ = 98.25(4)°, V = 1.4496 nm<sup>3</sup>, Z = 2, D<sub>x</sub> = 2.608 Mg m<sup>?3</sup>. The four independent silver atoms and the water molecule form zigzag chains Ag(1)-Ag(2)-(μ-H<sub>2</sub>O)-Ag(3) …? Ag(4) …? Ag(1′) with distances Ag(1)-Ag(2) 309.7, Ag(2)-O(w) 241.8, O(w)-Ag(3) 241.4, Ag(3) …? Ag(4) 342.9, Ag(4) …? Ag(1′) 361.4 pm. The catenated silver atoms are further connected by the dimesylamide anions acting as tridentate bridging (α-O, N, ω-O)-ligands. The resulting strands are interconnected into layers through one O(S)-Ag′ contact (247 pm) and one hydrogen bond O(w)-H(l) …? O′(S) per repeating unit. Between the layers, a weak O(S) …? Ag″ interaction (271 ptn) and a hydrogen bond O(w)-H(2) …? O(S) per repeating unit are observed. The silver atoms Ag(l) to Ag(4) display the coordination numbers 5 [NO,Ag(2), distorted trigonal bipyramid], 5[NO<sub>2</sub>,O(w)Ag(I), distorted trigonal bipyramid], 5[O<sub>4</sub>,O(w), trigonal bipyramid], and 2 + 1 (N<sub>2</sub>, li-near; plus a secondary Ag …? 0 contact). The dehydration of the title compound and a solid-solid phase transformation in anhydrous AgN(SO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub>, were quantitatively investigated by thermoconductometry and time- and temperature-resolved X-ray diffractometry (TXRD).     

Highly conformationally constrained halogenated 6-spiroepoxypenicillins as probes for the bioactive side-chain conformation of benzylpenicillin

Summary The halogenated 6-spiroepoxypenicillins are a series of novel semisynthetic<i><img src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"></i>-lactam compounds with highly conformationally restricted side chains incorporating an epoxide. Their biological activity profiles depend crucially on the configuration at position C-3 of that epoxide. In derivatives with aromatic-containing side chains, e.g., anilide, the 3<i>R</i>-compounds possess notable Gram-positive antibacterial activity and potent<i><img src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"></i>-lactamase inhibitory properties. The comparable 3S-compounds are antibacterially inactive, but retain<i><img src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"></i>-lactamase inhibitory activity.Using the molecular simulation programs COSMIC and ASTRAL, we attempted to map a putative, lipophilic accessory binding site on the PBPs that must interact with the side-chain aromatic residue. Comparative computer-assisted modelling of the 3<i>R</i>, and 3<i>S</i>-anilides, along with benzylpenicillin, indicated that the available conformational space at room temperature for the side chains of the 3<i>R</i> and the 3<i>S</i>-anilides was mutually exclusive. The conformational space for the more flexible benzylpenicillin could accommodate the side chains of<i>both</i> the constrained penicillin derivatives. By a combination of van der Waals surface calculations and a pharmacophoric distance approach, closely coincident conformers of the 3<i>R</i>-anilide and benzylpenicillin were identified. These conformers must be related to the antibacterial, <img src="/content/m85x27l4758x6745/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">bioactive<img src="/content/m85x27l4758x6745/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> conformer for the classical<i><img src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"></i>-lactam antibiotics. From these proposed bioactive conformations, a model for the binding of benzylpenicillin to the PBPs relating the three-dimensional arrangement of a putative lipophilic S<sub>2</sub>-subsite, specific for the side-chain aromatic moiety, and the 3<i><img src="/content/m85x27l4758x6745/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"></i>-carboxylate functionality is presented.This work has been reported in preliminary form at the 4th Royal Society of Chemistry International Symposium on Recent Advances in the Chemistry of<i><img src="/content/m85x27l4758x6745/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"></i>-lactam Antibiotics, Churchill College, Cambridge, U.K., 3–6 July 1988.     

Solubility Enhancement of Low Soluble Biologically Active Compounds by β-Cyclodextrin and Dimethyl-β-cyclodextrin

The solubility enhancement of triflumizole by complexation with <img src="/content/l228q828p4586834/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin and with dimethyl-<img src="/content/l228q828p4586834/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin is compared with respect to the different physico-chemical properties of the host molecules. Although the inclusion reaction constants are rather similar for both complexation reactions, a completely different temperature dependence of the host-guest interaction is observed, which indicates a change of the reaction mechanisms. Moreover, the influence of ethanol as cosolvent is studied.     

All-Solid-State PVC Membrane Ag+-Selective Electrodes Based on Diaza-18-Crown-6 Compounds

Two diaza-crown ether compounds were synthesized and evaluated as Ag<sup>+</sup>-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75±10<img src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">mV per decade) over the concentration range of 1×10<sup>–1</sup> to 7×10<sup>–6</sup><img src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">M of Ag<sup>+</sup> ion and a detection limit of 3×10<sup>–6</sup><img src="/content/m6d5ltjf7br53l8v/xxlarge8201.gif" alt="thinsp" align="MIDDLE" BORDER="0">M, at a wide range of pH (pH 4–7). The response time of the electrode was fast (less than <img src="/content/m6d5ltjf7br53l8v/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag<sup>+</sup> ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag<sup>+</sup>-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag<sup>+</sup> ion in solution.     

Improvement in the Physicochemical Properties of Ketoconazole through Complexation with Cyclodextrin Derivatives

Highly-soluble cyclodextrin derivatives, such as hydroxypropyl-<img src="/content/rg3360t010l9465u/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin(HP-<img src="/content/rg3360t010l9465u/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD) and methyl-<img src="/content/rg3360t010l9465u/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin (MEB), were tested as solubilizingagents for ketoconazole, with the aim of improving the physicochemical andbiopharmaceutical properties of this lipophilic imidazole antifungal agent. Productswere prepared in four molecular ratios by physical mixing, kneading and spray-dryingmethods. The kneaded products in a ratio of 1:2 and the spray-dried products exhibitedthe highest dissolution rates. The phase solubility diagrams of ketoconazole with thesecyclodextrins at 25 °C in water and in simulated intestinal medium wereconstructed. A solubility diagram of A<sub>L</sub> type was obtained with HP-<img src="/content/rg3360t010l9465u/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD, and one of A<sub>P</sub> type with MEB. The complexes were characterized by thermal methods(DSC, TG, DTG and DTA). Multicomponent systems were prepared with tartaric acid.The effects of water-soluble polymers, e.g., polyvinylpyrrolidone, on the aqueous solubility of ketoconazole were investigated. Particle size distribution, surface area, partition coefficient, heat of dissolution and wettability studies were also carried out. The formation of inclusion complexes was observed by means of thermoanalytical studies.     

Exo-H- andendo-H-η4-pentamethylcyclopentadiene complexes of platinum

A mixture of<i>endo-H</i> and<i>exo-H</i> isomers (<b>1a</b> and<b>1</b>b) of the (<img src="/content/nh349541l11162mv/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"><sup>4</sup>-C<sub>5</sub>Me<sub>5</sub>H)PtCl<sub>2</sub> complex was prepared by the reaction of K<sub>2</sub>PtCl<sub>4</sub> with C<sub>5</sub>Me<sub>5</sub>H in MeOH. The mixture of isomers reacts with CpTl in the presence of TiBF<sub>4</sub> to give a novel complex, [(<img src="/content/nh349541l11162mv/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"><sup>4</sup>-C<sub>5</sub>Me<sub>5</sub>H)Pt(<img src="/content/nh349541l11162mv/xxlarge951.gif" alt="eegr" align="MIDDLE" BORDER="0"><sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)]<sup>+</sup>BF<sub>4</sub> <sup>–</sup>, as a mixture of<i>endo-H</i>- and<i>exo-H</i>-isomers (<b>2a</b> and<b>2b</b>). The data of<sup>1</sup>H and<sup>13</sup>C NMR spectroscopy of the resulting complexes are discussed.Translated from<i>Izvestiya Akademii Nauk. Seriya Khimicheskaya</i>, No. 3, pp. 514–517, March, 1994.     

Determination of the uronic acid composition of seaweed dietary fibre by HPLC

A high-performance liquid chromatographic (HPLC) method is described for determination of the ratio of beta-d-mannuronic acid to alpha-l-guluronic acid (M/G ratio) in dietary fibre of edible seaweeds. Total dietary fibre (TDF) content was determined gravimetrically. The TDF fraction was hydrolysed with 12 m and 1 m H(2)SO(4), then neutralized with AG 4 x 4 resin. The uronic acids were separated in a Tracer Extrasil SAX 5 micro m column (25 cm x 4 mm) at 35 degrees C, with 2 mm KH(2)PO(4) containing 5% methanol as mobile phase at a fl ow rate of 1.5 mL/min. The detection wavelength was UV 210 nm. The chromatographic identifications of beta-d-mannuronic acid and alpha-l-guluronic acid were confirmed by liquid chromatography-mass spectrometry (LC-MS). The method precision was 1.4% for beta-d-mannuronic acid and 3.5% for alpha-l-guluronic acid. The method was used to determine M/G ratio in canned seaweeds (Saccorhiza polyschides and Himanthalia elongata) and in dried seaweeds (H. elongata, Laminaria ochroleuca, Undaria pinnatifida, Palmaria sp. and Porphyra sp.).     

On the mathematical formulation and interpretation of LACO MO theory

The mathematical basis of LCAO MO theory is studied, both within the Hartree-Fock approximation and in more exact formulations. The basic LCAO expansion for molecular orbitals ¦<img src="/content/l224455877q11756/xxlarge966.gif" alt="phgr" align="MIDDLE" BORDER="0">> in terms of atomic orbitals ¦x> is conveniently written ¦<img src="/content/l224455877q11756/xxlarge966.gif" alt="phgr" align="MIDDLE" BORDER="0">> = ¦x> <i>S</i> <sup>–1</sup> <i>B</i> where <b>S</b> is the overlap matrix for atomic orbitals and <b>B</b> is the matrix of atomic orbital-molecular orbital overlaps. It is suggested that matrices <b>P</b> and <b>Q</b>, defined by <b><i>P=B B</i></b><img src="/content/l224455877q11756/xxlarge8224.gif" alt="dagger" align="MIDDLE" BORDER="0"> and <b><i>Q=BnB</i></b><img src="/content/l224455877q11756/xxlarge8224.gif" alt="dagger" align="MIDDLE" BORDER="0"> where <b>n</b> is the matrix of molecular orbital occupation numbers, are appropriate to the interpretation of molecular calculations in terms of atomic orbital components, electronic populations and the degree of bonding. Implications for Hartree-Fock calculations are investigated.