nπ-ct-π* Transitions: nπ* Transitions of the second kind

Two important classes of molecules, maleimides and syn-bimanes [syn-bicyclo[3.3.0]octadienediones], are shown to exhibit charge-transfer absorptions and emissions, mainly on the basis of solvent effects on emissions. The electronic excitation originates mainly in a “non-bonding” p-orbital substantially localized on N, and oriented parallel to the π-system, hence n_π. The label, n_π-ct→π*, is proposed for these transitions. For the first time, two n_π-ct→π* transitions for a molecule containing a pair of adjacent nitrogens adjacent to a π-acceptor system are reported.     

Novel Cytostatic Lanostanoid Triterpenes from Ganoderma australe

Two new compounds 1 and 2 , together with the known sterols ergosterol, 5,6‐dehydroergosterol, and ergosterol peroxide, and four polyoxygenated lanostanoid triterpenes named applanoxidic acid A ( 3 ), C ( 4 ), F ( 5 ), and G ( 6 ) were isolated from the fungus Ganoderma australe. The structures of the new compounds were elucidated by means of spectroscopic techniques, while the known triterpenoids 3 – 6 were identified by comparing their spectral data with those reported in the literature. Compounds 1 – 6 inhibited the viability and growth of the HL‐60 cell line.     

Heteroduplex analysis of minisatellite variability

Minisatellites are tandem repeat arrays of middle size (5-100 bp) repeat units widely distributed in eukaryotic genomes. They have been related to several important features of human genome biology, including gene regulation, chromosomal fragile sites, and imprinting. In this report, we have critically assessed and employed heteroduplex analysis (HA) for the identification of different human minisatellite MsH43 alleles. This minisatellite is organized as a repeat array of 5-6 bp units spanning 0.5 kbp. Our results demonstrate that this procedure is an easy, rapid, and reliable method to document allelic diversity for this locus. This work suggests that HA will also be a useful tool for studying the polymorphism of other minisatellites with small repeat units.     

Ligninases fromChrysonilia sitophila (TFB-27441 strain)

Ligninase found in the extracellular medium of cultures ofChrysonilia sitophila was purifieded by ion exchange chromatography. Sodium dodecylsulfate/polyacrylamide gel electrophoresis allowed the determination of 68,000, 48,300, and 48,000 daltons for the molecular weights of ligninase I, II, and III, respectively. The absorption spectrum of the enzymes indicated the presence of a heme prosthetic group. The absorption maximum of the native enzyme II at 400 nm decreased in the presence of one equivalent of hydrogen peroxide. With an additional equivalent of phenol the maximum at 400 nm shifted to 417 nm. This spectrum is similar to horseradish peroxidase compound II. The pyridine hemochromogen absorption spectrum and iron content indicated that ligninases I, II, and III contained a Fe/heme ratio values of 0.8, 1.3, and 1.2 by a molecule of protein, respectively. These enzymes oxidize lignin efficiently, followed by the fluorescence technique and by the photon emission method.     

Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene

Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.     

General change of variable formulas for semimartingales in one and finite dimensions

Summary A general one dimensional change of variables formula is established for continuous semimartingales which extends the famous Meyer-Tanaka formula. The inspiration comes from an application arising in stochastic finance theory. For functions mapping ⁿ to , a general change of variables formula is established for arbitrary semimartingales, where the usualC ² hypothesis is relaxed.Supported in part by NSF grant No. DMS-9103454Supported in part by John D. and Catherine T. MacArthur Foundation award for US-Chile Scientific CooperationSupported in part by FONDECYT, grant 92-0881     

Unambiguous transformation of eremanthin into (−)-estafiatin

A stereoselective synthesis of (?)-estafiatin ($\text{2a}$) from eremanthin ($\text{1}$) has been achieved. The α configuration of the epoxide in the former is confirmed by chemical shift correlation with related oxides.     

Experimental (NMR) and Theoretical (MD Simulations) Studies on the Conformational Preference of Three Cycloalkanols when Included in β-Cyclodextrin

The inclusion complexes between three cycloalkanols (cyclopentanol, cyclohexanol and cycloheptanol) and β-cyclodextrin (β-CD) have been studied by NMR experiments, and by molecular dynamics (MD) simulations. Complexes present medium to small association constants. All experimental data show the equatorial conformer as the most stable after complexation because no changes were detected in the coupling constants of the H1 protons. Intermolecular ROE experiments suggest that while cyclopentanol is deeply included into the β-CD cavity, cyclohexanol and cycloheptanol occupy mainly the wider entrance. The MD simulations agree with the experimental data (equatorial conformers are always the most stable), and average geometries coincide with those deduced from the ROE experiments.     

Magnetic studies on hexaiodorhenate(IV) salts of univalent cations. Spin canting and magnetic ordering in K2[ReI6] with Tc = 24 K

The ionic salts of rhenium(IV) of formula (Cat)(2)[ReI(6)] with Cat = Li(+) (1), Na(+) (2), K(+) (3), Rb(+) (4), Cs(+) (5), NH(4)(+) (6), and AsPh(4)(+) (7) [AsPh(4)(+) = tetraphenylarsonium cation] have been synthesized, and the structures of two of them (namely, 3 and 6) were determined by single-crystal X-ray diffraction. 3 crystallizes in the monoclinic system, space group Pn, with a = 7.815(1) A, b = 7.874(1) A, c = 11.335(1) A, beta = 90.38(1) degrees, and Z = 2 whereas 6 crystallizes in the tetragonal system, space group P4/mnc, with a = 7.881(1) A, b = 7.881(1) A, c = 11.474(2) A, and Z = 2. The structures of 3 and 6 are made up of discrete [ReI(6)](2)(-) anions and K(+) (3) or NH(4)(+) (6) cations held together by electrostatic forces (3 and 6) and N-H.I hydrogen bonds (6). The rhenium(IV) cation in 3 and 6 is surrounded by six iodide ligands in an octahedral environment with the Re-I bond lengths varying in a very narrow range [2.704(3)-2.738(3) and 2.716(1)-2.722(2) A for 3 and 6, respectively]. The [ReI(6)](2)(-) anions in 6 describe a tetragonally distorted body-centered cubic structure. In 3, the arrangement of these units is similar but more distorted. The different arrangement of the anions in 3 and 6 accounts for the centrosymmetric (6) and non-centrosymmetric (3) structures observed. The magnetic properties of 1-7 were investigated in the temperature range 2.0-300 K. The magnetic behavior of 7 is that of a magnetically diluted Re(IV) complex with a large value of the zero-field splitting of the ground level (|2D| = 49.8 cm(-)(1)) whereas those of 1, 2, and 4-6 are typical of antiferromagnetically coupled systems with susceptibility maxima at 28 (1), 27 (2), 21 (4), 16 (5), and 20 K (6). In the case of compound 3, its magnetic behavior in the high-temperature range is parallel to that observed in the parent salts but below 24 K it is a weak ferromagnet with a canting angle of ca. 1.2 degrees.