Heliconols A-C: antimicrobial hemiketals from the freshwater aquatic fungus Helicodendron giganteum

[Structure: see text] Cultures of the freshwater aquatic fungus Helicodendron giganteum afforded three new compounds, heliconols A-C (1-3), that contain an unusual reduced furanocyclopentane unit. The structures of these metabolites were assigned by analysis of 1D and 2D NMR data. The absolute configuration of heliconol A (1) was assigned by single-crystal X-ray crystallographic analysis of its dibromobenzoate derivative. Heliconol A showed antifungal and antibacterial activities in disk diffusion assays.     

Resident neuroelectrochemical interfacing using carbon nanofiber arrays

Carbon nanofiber electrode architectures are used to provide for long-term, neuroelectroanalytical measurements of the dynamic processes of intercellular communication between excitable cells. Individually addressed, vertically aligned carbon nanofibers are incorporated into multielement electrode arrays upon which excitable cell matrixes of both neuronal-like derived cell lines (rat pheochromocytoma, PC-12) and primary cells (dissociated cells from embryonic rat hippocampus) are cultured over extended periods (days to weeks). Electrode arrays are characterized with respect to their response to easily oxidized neurotransmitters, including dopamine, norepinephrine, and 5-hydroxytyramide. Electroanalysis at discrete electrodes following long-term cell culture demonstrates that this platform remains responsive for the detection of easily oxidized species generated by the cultured cells. Preliminary data also suggests that quantal release of easily oxidized transmitters can be observed at nanofiber electrodes following direct culture and differentiation on the arrays for periods of at least 16 days.     

3.0-T MRI evaluation of patients with chronic liver diseases: initial observations

PURPOSE: To describe the use of 3.0-T magnetic resonance imaging (MRI) for the evaluation of chronic liver diseases. MATERIALS AND METHODS: Two groups of patients who had chronic liver diseases and underwent 3.0-T MRI for evaluation of the liver were included in the study. The first group of patients included 66 consecutive patients (33 male, 33 female; mean age+/-standard deviation, 56+/-11). The second group of patients included 30 consecutive patients (18 males, 12 females; mean age+/-standard deviation, 53+/-10) in whom Variable-Rate Selective Excitation (VERSE) pulses and improved adjustments procedure were used during the acquisitions. Imaging findings of chronic liver diseases, predetermined artifacts and image quality of all individual sequences in the first group and predetermined artifacts and image quality of T2-weighted sequences in the second group were reviewed retrospectively and independently by two reviewers. chi-Square tests were used to compare the findings between two groups of patients and individual sequences. Kappa statistics were used to determine the extent of agreement between the reviewers. RESULTS: Fifteen dysplastic nodules in 6 of 66 (9%) patients and 12 hepatocellular carcinomas in 11 of 66 (17%) patients were detected. Excluding motion artifacts, three-dimensional (3D) T1-weighted gradient-echo (GE) sequence was the least affected sequence by the artifacts. Image quality of T1-weighted 3D-GE sequences was excellent in 43 of 66 (65%) patients. In-phase and out-of-phase T1-weighted spoiled GE (SGE) images were fair in 62 of 66 (94%) and 61 of 66 (92%) patients, respectively. The image quality of short tau inversion recovery (STIR) and half-Fourier rapid acquisition with relaxation enhancement (RARE) sequences were fair in 31 of 66 (47%) and 53 of 66 (80%) patients. STIR and half-Fourier RARE sequences in the second group demonstrated significantly better image quality (P=.03 and P<.0001). CONCLUSION: 3.0-T MRI allows the acquisition of very high quality postgadolinium 3D-GE sequence, which permitted the detection and characterization of lesions in the setting of chronic liver diseases. The use of VERSE pulses and improved adjustments procedure improved the image quality of T2-weighted sequences. In-phase/out-of-phase SGE sequences are at present of fair quality.     

Complexation properties of monoaza crown ethers

A series of five monoaza crown ethers with 12-crown-4 and 15-crown-5 rings were studied with respect to their complexation of Li⁺, Na⁺, K⁺, Ca²⁺ and Sr²⁺ ions in 95/5 (v/v) methanol/ water. The complexes were studied by potentiometric titrations, with pH and sodium ion-selective electrodes. The acidity constants of the protonated ligands, and the stability constants of the 1:1 metal complexes were determined. The results show that the stability constants increase with the total number of oxygen atoms in the ligand, and mostly also in the sequence Li⁺ < K⁺ < Na⁺ < Ca²⁺ < Sr²⁺.     

Synthesis and evaluation of chlorinated substrate analogues for farnesyl diphosphate synthase

Substrate analogues for isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), where the C3 methyl groups were replaced by chlorine, were synthesized and evaluated as substrates for avian farnesyl diphosphate synthase (FPPase). The IPP analogue (3-ClIPP) was a cosubstrate when incubated with dimethylallyl diphosphate (DMAPP) or geranyl diphosphate (GPP) to give the corresponding chlorinated analogues of geranyl diphosphate (3-ClGPP) and farnesyl diphosphate (3-ClFPP), respectively. No products were detected in incubations of 3-ClIPP with 3-ClDMAPP. Incubation of IPP with 3-ClDMAPP gave 11-ClFPP as the sole product. Values of K(M)(3-ClIPP) (with DMAPP) and K(M)(3-ClDMAPP) (with IPP) were similar to those for IPP and DMAPP; however, values of k(cat) for both analogues were substantially lower. These results are consistent with a dissociative electrophilic alkylation mechanism where the rate-limiting step changes from heterolytic cleavage of the carbon-oxygen bond in the allylic substrate to alkylation of the double bond of the homoallylic substrate.     

Catalytic enantioselective Diels-Alder reaction by self-assembly of the components on a Lewis acid template

Thermal Diels-Alder reaction of 2,4-hexadienol with methyl acrylate is unselective. By simultaneous coordination of diene and dienophile to a chiral bimetallic Lewis acid catalyst, a LACASA-DA reaction occurs with complete control of regio-, diastereo-, and enantioselectivity to give a single adduct. [reaction: see text]     

New pathways for chlorine dioxide decomposition in basic solution

The product distribution from the decay of chlorine dioxide in basic solution changes as the ClO(2) concentration decreases. While disproportionation reactions that give equal amounts of ClO(2)(-) and ClO(3)(-) dominate the stoichiometry at millimolar or higher levels of ClO(2), the ratio of ClO(2)(-) to ClO(3)(-) formed increases significantly at micromolar ClO(2) levels. Kinetic evidence shows three concurrent pathways that all exhibit a first-order dependence in [OH(-)] but have variable order in [ClO(2)]. Pathway 1 is a disproportionation reaction that is first order in [ClO(2)]. Pathway 2, a previously unknown reaction, is also first order in [ClO(2)] but forms ClO(2)(-) as the only chlorine-containing product. Pathway 3 is second order in [ClO(2)] and generates equal amounts of ClO(2)(-) and ClO(3)(-). A Cl(2)O(4) intermediate is proposed for this path. At high concentrations of ClO(2), pathway 3 causes the overall ClO(3)(-) yield to approach the overall yield of ClO(2)(-). Pathway 2 is attributed to OH(-) attack on an oxygen atom of ClO(2) that leads to peroxide intermediates and yields ClO(2)(-) and O(2) as products. This pathway is important at low levels of ClO(2).