Two new xeniolides from a Taiwanese Xenia soft coral

Chromatographic investigation of an extract of the octocoral Xenia umbellata afforded two new diterpenes, xenibelatols A (1) and B (2), in addition to three known xenicane diterpenes, 7,8-oxidoisoxeniolide (3), 9-hydroxyxeniolide F (4), and florlide C, and a cadinene sesquiterpene, xenitorin A (5). The structures were elucidated through spectroscopic analysis, especially 2D NMR.     

Asymmetric hydroformylation of vinyl acetate: application in the synthesis of optically active isoxazolines and imidazoles

(R)- and (S)-2-(Acetyloxy)-propanal were prepared [93.8% ee, 102 b/l for (R), 96.9% ee, 149 b/l for (S)] via asymmetric hydroformylation of vinyl acetate on a 150-180 g scale and were used as the starting materials in the synthesis of chiral isoxazoline and imidazole derivatives which proceeded without racemization of the chiral center.     

Quantum state-resolved probing of strong-field-ionized xenon atoms using femtosecond high-order harmonic transient absorption spectroscopy

Femtosecond high-order harmonic transient absorption spectroscopy is used to resolve the complete |j,m quantum state distribution of Xe+ produced by optical strong-field ionization of Xe atoms at 800 nm. Probing at the Xe N4/5 edge yields a population distribution rhoj,|m| of rho3/2,1/2ratiorho1/2,1/2ratiorho3/2,3/2=75+/-6 :12+/-3 :13+/-6%. The result is compared to a tunnel ionization calculation with the inclusion of spin-orbit coupling, revealing nonadiabatic ionization behavior. The sub-50-fs time resolution paves the way for tabletop extreme ultraviolet absorption probing of ultrafast dynamics.     

Neural field dynamics with heterogeneous connection topology

Neural fields receive inputs from local and nonlocal sources. Notably in a biologically realistic architecture the latter vary under spatial translations (heterogeneous), the former do not (homogeneous). To understand the mutual effects of homogeneous and heterogeneous connectivity, we study the stability of the steady state activity of a neural field as a function of its connectivity and transmission speed. We show that myelination, a developmentally relevant change of the heterogeneous connectivity, always results in the stabilization of the steady state via oscillatory instabilities, independent of the local connectivity. Nonoscillatory instabilities are shown to be independent of any influences of time delay.     

Electrochemical Properties of Th(IV)‐Hexacyanoferrate Sol‐Gel Carbon Composite Electrode: Electrocatalytic Oxidation of Dopamine and Ascorbic Acid

A new sol‐gel carbon composite electrode using hexacyanoferrate (HCF)‐Th(IV) ion pair as a suitable modifier is fabricated in the present study. The Th(IV)‐HCF‐sol‐gel carbon composite electrode (THCF‐CCE) has been prepared by mixing methyl trimethoxysilan (MTMOS) sol‐gel precursor and carbon powder with ion pair and then to fix in a plastic tube. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical and electrocatalytic properties of proposed electrode. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between ion‐pair and sol‐gel CPE were calculated as 3.10 ± 0.10 s^?1 and 0.52, respectively. The THCF‐CCE showed a significant electrocatalytic activity towards oxidation of ascorbic acid (AA) and dopamine (DA) in 0.1 M acidic phosphate buffer solutions (pH 3) containing KCl as a supporting electrolyte. The mean value of the diffusion coefficients for ascorbic acid and dopamine were found 4.12 × 10^?5 and 4.43 × 10^?5 (cm²s^?1), respectively. High stability, good reproducibility, rapid response, easy surface regeneration and fabrication are the important characteristics of the proposed sensor. The resulting peaks from the electrocatalytic oxidation of AA and DA were well resolved with good sensitivity. A linear response was observed for AA and DA in the concentration range of 1 × 10^?5 to 3 × 10^?3 M and 4 × 10^?6 to 2.2 × 10^?4 M, respectively.     

Cold Deposition as a Novel Procedure for the Preparation of Titania Sol‐Gel: A Development of a High Sensitive Electrochemical Method for Determination of Cu(II) in the Presence of Arsenic(III)

Titania sol‐gel modified gold electrode (TSGMGE) was prepared with the usage of a new proposed cold deposition method at ?10 °C. Scanning electron microscope (SEM) operating at 30 kV was used to obtain micrographs of unmodified and modified electrodes. The obtained results showed that this procedure yields a sol‐gel with high porosity in comparison to conventional methods. The modified Au electrode was fabricated by trapping the L‐glutamine in titania sol‐gel at low temperatures to preparation of a new titania sol‐gel glutamine modified gold electrode (TSGGMGE). The possibility determination of traces of Cu(II) in the presence of As(III) was investigated using proposed electrode. Under the optimized conditions, copper was accumulated at ?0.35 V (vs. Ag/AgCl) for 40 s in 0.1 M acetate buffer (pH 4.0) in the presence of different amounts of arsenic. Two dynamic linear responses with good reproducibility were observed for copper ions in the concentration range of 1 × 10^?6 ?4 × 10^?4 M and 4 × 10^?8 ?6 × 10^?7 M.     

New Fe4, Fe6, and Fe8 clusters of iron(III) from the use of 2-pyridyl alcohols: structural, magnetic, and computational characterization

The syntheses, crystal structures, magnetochemical characterization, and theoretical calculations are reported for three new iron clusters [Fe 6O 2(NO3) 4(hmp) 8(H 2O) 2](NO3)2 (1), [Fe4(N3)6(hmp)6] (2), and [Fe8O3(OMe)(pdm)4(pdmH) 4(MeOH)2](ClO4)5 (3) (hmpH=2-(hydroxymethyl)pyridine; pdmH2=2,6-pyridinedimethanol). The reaction of hmpH with iron(III) sources such as Fe(NO3) 3.9H2O in the presence of NEt 3 gave 1, whereas 2 was obtained from a similar reaction by adding an excess of NaN3. Complex 3 was obtained in good yield from the reaction of pdmH 2 with Fe(ClO4)3.6H2O in MeOH in the presence of an organic base. The complexes all possess extremely rare or novel core topologies. The core of 1 comprises two oxide-centered [Fe3(mu3-O)](7+) triangular units linked together at two of their apexes by two sets of alkoxide arms of hmp(-) ligands. Complex 2 contains a zigzag array of four Fe (III) atoms within an [Fe4(mu-OR) 6](6+) core, with the azide groups all bound terminally. Finally, complex 3 contains a central [Fe 4(mu4-O)](10+) tetrahedron linked to two oxide-centered [Fe3(mu3-O)](7+) triangular units. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-3 in the 5.0-300 K range. Fitting of the obtained magnetization versus field (H) and temperature (T) data by matrix diagonalization and including only axial anisotropy (zero-field splitting, ZFS) established that 1 possesses an S=3 ground-state spin, with g=2.08, and D=-0.44 cm(-1). The magnetic susceptibility data for 2 up to 300 K were fit by matrix diagonalization and gave J1=-9.2 cm(-1), J2=-12.5 cm(-1), and g=2.079, where J 1 and J 2 are the outer and middle nearest-neighbor exchange interactions, respectively. Thus, the interactions between the Fe(III) centers are all antiferromagnetic, giving an S=0 ground state for 2. Similarly, complex 3 was found to have an S=0 ground state. Theoretically computed values of the exchange constants in 2 were obtained with DFT calculations and the ZILSH method and were in good agreement with the values obtained from the experimental data. Exchange constants obtained with ZILSH for 3 successfully rationalized the experimental S = 0 ground state. The combined work demonstrates the ligating flexibility of pyridyl-alcohol chelates and their usefulness in the synthesis of new polynuclear Fex clusters without requiring the copresence of carboxylate ligands.     

Unusual structural types in polynuclear iron chemistry from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (edteH4): Fe5, Fe6, and Fe12 clusters

The syntheses, crystal structures, and magnetochemical characterization of five new iron clusters [Fe5O2(O2CPh)7(edte)(H2O)] (1), [Fe6O2(O2CBut)8(edteH)2] (2), [Fe12O4(OH)2(O2CMe)6(edte)4(H2O)2](ClO4)4 (3), [Fe12O4(OH)8(edte)4(H2O)2](ClO4)4 (4), and [Fe12O4(OH)8(edte)4(H2O)2](NO3)4 (5) (edteH4= N,N,N',N'-tetrakis(2-hydroxyethyl) ethylenediamine) are reported. The reaction of edteH4 with [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CBut)6(H2O)3](OH) gave 1 and 2, respectively. Complex 3 was obtained from the reaction of edteH4 and NaO2CMe with Fe(ClO4)3, whereas 4 and 5 were obtained from the reaction of edteH4 with Fe(ClO4)3 and Fe(NO3)3, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by four bridging O atoms. The core of 2 consists of two triangular [Fe3(mu3-O)]7+ units linked together by six bridging O atoms. Finally, the cores of 3-5 consist of an [Fe12(mu4-O)4(mu-OH)2]26+ unit. Variable-temperature (T) and -field (H) solid-state direct and alternating current magnetization (M) studies were carried out on complexes 1-3 in the 1.8-300 K range. Analysis of the obtained data revealed that 1, 2, and 3-5 possess an S = 5/2, 5, and 0 ground-state spin, respectively. The fitting of the obtained M/N(muB) vs H/T data was carried out by matrix diagonalization, and this gave values for the axial zero-field splitting (ZFS) parameter D of -0.50 cm-1 for 1 and -0.28 cm-1 for 2.     

A Novel Electrochemical Method for the Sensitive Determination of Aflatoxin B1 Using a Bivalent Binding Aptamer-cDNA Structure

In this study, a simple electrochemical sensing platform with the employment of a bivalent binding aptamer-cDNA probe (BBA-cDNA) structure is constructed for the detection of aflatoxin B₁ (AFB₁) as a mycotoxin. The BBA-cDNA structure is composed of two strands of aptamer (Apts) and their complementary strand (CS). Using a simple but accurate design, the presented measurement approach showed enhanced sensitivity and selectivity for AFB₁ detection with a LOD of 0.1 ng/mL. The approach presented in this study can be applied to the development of biosensors for the measurement of various toxins by substituting the proper aptamers and complementary strands.