The structure of the side chain of the frog alkaloid pumiliotoxin B

The E configuration at the double bond and $\text{threo}$ relation for diol moiety of the pumiliotoxin B side chain were defined, respectively, through nuclear- Overhauser effects and comparison with model $\text{threo}$- and $\text{erythro}$- diol compounds.     

High-yield catalytic metathesis of alkenyl tosylates with applications in organic synthesis

Alkenyl tosylates of the type RCHCH(CH₂)_nOTs [RH, n=9; RH, n=7; and RCH₃(CH₂)₇, n=8] undergo metathesis using a WCl₆-Me₃SnCl catalyst system, producing difunctionalised alkenes of the type TsO(CH₂)_nCHCH(CH₂)_nOTs (n=7,8, and 9); examples of the use of these products in synthesis are presented.     

Effects of the detection window on the determination of organic copper speciation in estuarine waters

The complexation of copper by natural organic ligands in sea water was measured by cathodic stripping voltammetry with ligand (catechol and quinolin-8-ol) competition. Two methods to determine copper complexation in estuarine waters were compared, one based on a complete titration of the complexing capacity of the sample and the other on measurement of the labile and total dissolved metal concentrations only. Values for log α_CuL (ihe α-coefficient for complexation of Cu²⁺ by natural organic ligands) ranging from 3.2 to 7.7 and from 3.3 to 7.8 could be detected by varying long α_CuAL (the α-coefficient for complexation of Cu²⁺ by the added competing ligand) from 3.4 to 8.9 in samples from the Tamar estuary and from the Channel. The two methods gave comparable results and showed that the type of sites detected depends on the detection window of the technique. This effect is due to the sea and estuarine water samples containing a series of complexing ligands forming complexes of greatly varying strength, thus causing a rnage of complex stabilities to be measured as a function of the detection window of each technique. A comparison showed that lower values for α_CuL are obtained by anodic stripping voltammetry as a result of that technique having a lower detection window. A detailed study of the Tamar estuary revealed a decrease in log α_CuL from 10.8 to 8.3 with increasing salinity, demonstrating that major cations compete with copper for the complexing sites. The free Cu²⁺ concentrations were very low throughout the estuary (16.2 < pCu²⁺ < 18.2) even though the total measurements to establish potential toxic effects of copper in natural waters.     

Isomers in the N = 83 nucleus 149Dy

Energy levels in the N = 83 nucleus ¹⁴⁹Dy were studied by the reaction ¹⁵²Gd(α, 7n) at 106 MeV bombarding energy using in-beam γ-ray spectroscopy methods. The measurements identified three isomers in this nucleus, at 1073 keV (13 ± 3 ns), at 2700±150keV (5 μs < T_{$\text{1}\text{2}$} < 0.5 s), and above 3.5 MeV (50 ± 15 ns). The low-lying isomer is interpreted as i_{$\text{13}\text{2}$}. The configuration $\text{27}\text{2}$^?(πh_{$\text{11}\text{2}$}²)₁₀₊ ×vf_{$\text{7}\text{2}$} is suggested for the state at 2.7 MeV.     

Evidence for triaxial shapes in Pt nuclei

Positive parity levels in ¹⁹¹Pt obtained from (α, xnγ) reactions and β-decay are presented as a first example of a rather complete $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ level family. The spectrum confirms triaxial shapes found before from $\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ and $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton structures in this mass region. In addition to the usual decoupled yrast band, a second ΔI = 2 band within the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ family, built on a low-lying $\text{j?1 =}\text{11}\text{2}$ state, is observed in agreement with theory.     

Time-resolved luminescence spectra in highly photo-excited CdSe at 1.8K

We report the first observation of very precise time-resolved luminescence from highly photoexcited platelets of CdSe at 1.8 K. The time dependence of both spontaneous and stimulated emission are presented. The results are taken as a further indication for the existence of an electron-hole liquid in CdSe at these excitation densities.     

Discovery, structure and biological activities of the cyclotides

The cyclotides are a family of small disulfide rich proteins that have a cyclic peptide backbone and a cystine knot formed by three conserved disulfide bonds. The combination of these two structural motifs contributes to the exceptional chemical, thermal and enzymatic stability of the cyclotides, which retain bioactivity after boiling. They were initially discovered based on native medicine or screening studies associated with some of their various activities, which include uterotonic action, anti-HIV activity, neurotensin antagonism, and cytotoxicity. They are present in plants from the Rubiaceae, Violaceae and Cucurbitaceae families and their natural function in plants appears to be in host defense: they have potent activity against certain insect pests and they also have antimicrobial activity. There are currently around 50 published sequences of cyclotides and their rate of discovery has been increasing over recent years. Ultimately the family may comprise thousands of members. This article describes the background to the discovery of the cyclotides, their structural characterization, chemical synthesis, genetic origin, biological activities and potential applications in the pharmaceutical and agricultural industries. Their unique topological features make them interesting from a protein folding perspective. Because of their highly stable peptide framework they might make useful templates in drug design programs, and their insecticidal activity opens the possibility of applications in crop protection.