Heat capacity and thermodynamic functions of crystalline poly(p‐phenylenebenzobisoxazole), the synthetic polymer with the highest Young's modulus

The heat capacity of crystalline poly(p‐phenylenebenzobisoxazole) was measured below room temperature by adiabatic calorimetry. The standard thermodynamic functions (enthalpy, entropy, and Gibbs energy) were established and tabulated. The temperature dependence of the heat capacity was compared with those of polyethylene and poly(p‐phenylene), with attention paid to the low dimensionality of the systems. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1584–1588, 2000     

Fine pore mouth structure of molecular sieve carbon with GCMC-assisted supercritical gas adsorption analysis

N₂ adsorption isotherms of molecular sieve carbon were measured at 77 K and 303 K. The Ar adsorption isotherms of molecular sieve carbon samples were also measured at 303 K. The grand canonical Monte Carlo (GCMC) simulation technique was applied to calculate the N₂ and Ar adsorption isotherms at 303 K using the ultramicropore volume determined by H₂O adsorption. The comparative method of experimental and simulated isotherms of supercritical N₂ and Ar at 303 K gave the width of the micropore mouth of the molecular sieve carbon, which can be applied to the ultramicropore width determination for other noncrystalline porous solids.     

Hydnellins A and B, nitrogen-containing Terphenyls from the mushrooms Hydnellum suaveolens and Hydnellum geogerirum

Fractionation of methanol extracts of the fruit bodies of two inedible mushrooms Hydnellum suaveolens and Hydnellum geogerirum (Thelephoraceae) resulted in isolation of two new p-terphenyl derivatives named hydnellins A and B and sarcodonin delta possessing N-oxide. Their structures were determined by 2D NMR, IR, UV spectroscopy, and chemical reaction. These terphenyls showed moderate antioxidant activity.     

Analysis of lanthanide-induced NMR shifts of the Ce@C82 anion

The mapping of bond connectivity in the carbon cage of [Ce@C82]- and full assignment of the NMR lines were successfully achieved by means of 2D INADEQUATE NMR measurement. Paramagnetic NMR analysis shows that the Ce atom in [Ce@C82]- is located at an off-centered position adjacent to a hexagonal ring along the C2 axis of the C2v-C82 cage.     

Melophlins P, Q, R, and S: four new tetramic acid derivatives, from two Palauan marine sponges of the genus Melophlus

Four new tetramic acid derivatives, named melophlins P, Q, R, and S (1-4), were isolated from two marine sponges of the genus Melophlus collected at Palau, together with seven known melophlins A, D, E, G, H, I, and O. The structures of the new compounds were elucidated on the basis of their spectral data. The absolute stereochemistries at the tetramic acid moieties of the new compounds were determined as 1 : 1 mixtures (racemic) by ESI-LC/MS analysis of derivatives obtained by oxidation and hydrolysis of the respective parent compounds. Melophlins P-S (1-4) showed cytotoxicity against the murine leukemia cell line L1210 with IC(50) values of 20.0, 10.5, 0.85, and 5.13 muM, respectively.     

Electrospray ionization mass spectrometric analysis of microcystins, cyclic heptapeptide hepatotoxins: modulation of charge states and [M+H]+ to [M+Na]+ ratio

Electrospray ionization mass spectrometry was used to develop a rapid, sensitive, and accurate method for determination and identification of hepatotoxic microcystins, cyanobacterial cyclic heptapeptides. To optimize the electrospray ionization conditions, factors affecting charge state distribution, such as amino acid components of sample, proton affinity of the additives, and additive concentration, were investigated in detail and a method for controlling charge states was developed to provide molecular-related ions for assignment of molecular weight and reasonably abundant precursor ions for MS/MS analysis. A procedure for identification of microcystins consisting of known amino acids was proposed: for microcystins giving abundant [M + 2H]2+ ions, the addition of nitrogen-containing bases to the aqueous sample solution is effective to obtain an increased intensity of [M + H]+ ions, whereas the addition of Lewis acids containing nitrogen can produce increased abundances of [M + 2H]2+ ions for microcystins giving weak [M + 2H]2+ ions. Microcystins possessing no arginine residue always give sodium adduct ions [M + Na]+ as the base peak, and these are difficult to fragment via low energy collision-induced dissociation to yield structurally informative products; the addition of oxalic acid increases [M + H]+ ion abundances, and these fragment readily.     

The charge‐transfer complex trans‐STB–TCNQF4

In the crystal structure of the title charge‐transfer complex, namely trans‐stilbene–2,2′‐(2,3,5,6‐tetra­fluoro­benzene‐1,4‐diyl­idene)­propane­di­nitrile (1/1) (trans‐STB–TCNQF₄), C₁₄H₁₂·C₁₂F₄N₄, the planar STB and TCNQF₄ mol­ecules are stacked alternately. The structure is not isostructural with that of STB–TCNQ. No anomaly was found in the displacement parameters of any atoms, while the bond length of the central C=C moiety was shorter than the corresponding bond in ethyl­ene. This suggests that the central C=C moiety of the STB mol­ecule vibrates with a large amplitude, similar to the case in free STB and STB–TCNQ.     

Fusion of the eight vertex SOS model

A higher spin analogue is presented of the eight vertex-SOS correspondence in the sense of Andrews-Baxter-Forrester. The resulting hierarchy of solvable models contain the hard hexagon model and its recent multi-state generalizations.