Euphorbiane: A Novel Triterpenoid with an Unprecedented Skeleton from Euphorbia tirucalli

Euphorbiane ( 1 ), a novel triterpenoid exhibiting a unique skeleton, together with seven known compounds were isolated from the 95% EtOH extract of the fresh stems of Euphorbia tirucalli. The structure of 1 and relative stereochemistry were elucidated by extensive NMR and a single‐crystal X‐ray crystallographic analysis.     

Rb3In(H2O)Si5O13: a novel indium silicate with a CdSO4-topological-type structure

A novel indium silicate, Rb3In(H2O)Si5O13, has been synthesized using a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction. The structure consists of five-membered rings of corner-sharing SiO4 tetrahedra connected via corner sharing to four adjacent five-membered rings to form a 3D silicate framework that belongs to the CdSO4 topological type. The InO6 octahedron shares five of its corners with five different SiO4 tetrahedra to form a 3D frame-work that delimits two types of channels to accommodate the rubidium cations. The sixth corner of InO6 is coordinated H2O. The structure is related to that of the titanium silicate ETS-10, and these are the only two metal silicates that have the CdSO4-topological-type structure. In addition, the crystal of Rb3In(H2O)Si5O13 shows an intense second harmonic generation signal. Crystal data: H2Rb3InSi5O14, monoclinic, space group Cc (No. 9), a = 9.0697(5) A, b = 11.5456(6) A, c = 13.9266(8) A, beta = 102.300(1) degrees, V = 1424.8(1) A3, and Z = 4.     

Catalytic and direct oxidation of cysteine by octacyanomolybdate(V)

The oxidation of cysteine by [Mo(CN)(8)](3-) in deoxygenated aqueous solution at a moderate pH is strongly catalyzed by Cu(2+), to the degree that impurity levels of Cu(2+) are sufficient to dominate the reaction. Dipicolinic acid (dipic) is a very effective inhibitor of this catalysis, such that with 1 mM dipic, the direct oxidation can be studied. UV-vis spectra and electrochemistry show that [Mo(CN)(8)](4-) is the Mo-containing product. Cystine and cysteinesulfinate are the predominant cysteine oxidation products. The stoichiometric ratio (Deltan(Mo(V))/Deltan(cysteine)) of 1.4 at pH 10.8 is consistent with this product distribution. At pH 1.5, the reaction is quite slow and yields intractable kinetics. At pH 4.5, the rates are much faster and deviate only slightly from pseudo-first-order behavior. With 2 mM PBN (N-phenyl-tert-butyl nitrone) present at pH 4.5, the reaction rate is about 20% less and shows excellent pseudo-first-order behavior, but the stoichiometric ratio is not significantly changed. The rates also display a significant specific cation effect. In the presence of spin-trap PBN, the kinetics were studied over the pH range 3.48-12.28, with [Na(+)] maintained at 0.09-0.10 M. The rate law is -d[Mo(V)]/dt = k[cysteine](tot)[Mo(V)], with k = {2(k(b)K(a1)K(a2)[H(+)] + k(c)K(a1)K(a2)K(a3))}/([H(+)](3) + K(a1)[H(+)](2) + K(a1)K(a2)[H(+)] + K(a1)K(a2)K(a3)), where K(a1), K(a2), and K(a3) are the successive acid dissociation constants of HSCH(2)CH(NH(3)(+))CO(2)H. Least-squares fitting yields k(b) = (7.1 +/- 0.4) x 10(4) M(-1) s(-1) and k(c) = (2.3 +/-0.2) x 10(4) M(-1) s(-1) at mu = 0.1 M (NaCF(3)SO(3)) and 25 degrees C. A mechanism is inferred in which k(b) and k(c) correspond to electron transfer to Mo(V) from the thiolate forms of anionic and dianionic cysteine.     

An investigation of the microstructure,optical and electrical properties of ZITO thin film using the sol–gel method

The multi-compound ZITO transparent conductive oxide (TCO) thin films were synthesized using the sol–gel method. The ZITO thin films with various volume ratios of ZnO to ITO (1:1, 2:1 and 9:1) were crystallized at different temperatures (600–700 °C). The results showed that the crystalline characteristics and optical transmittance were mainly dependent on ITO content and crystallization. Notably, the 650 °C Z₉ITO film not only had better conductivity but also possessed excellent optical transmittance. In addition, the surface roughness of the ZITO films and optoelectric properties of IZO (indium doped ZnO) films were analyzed to confirm the contribution of indium dopants on the optical transmittance. Also, the ZITO films were subjected to the effects of indium and tin dopants and this improved the related characteristics of ZnO films.     

Development and validation of an ELISA kit for the detection of ricin toxins from biological specimens and environmental samples

Ricin is a toxin that can be easily extracted from seeds of Ricinus communis plants. Ricin is considered to be a major bio-threat as it can be freely and easily acquired in large quantities. A deliberate release of such toxin in civilian populations would very likely overwhelm existing public health systems, resulting in public fear and social unrest. There is currently no commercially available or FDA-approved prophylaxis such as vaccines, or therapeutic antitoxins or antidotes, available for ricin intoxication. Patient treatment is typically supportive care based on symptoms, often designed to reinforce the body’s natural response. This paper describes the development and validation of a robust ELISA test kit, which can be used to screen for ricin in biological specimens such as whole blood and faeces. Faecal specimens are shown in this study to have better diagnostic sensitivity and a wider diagnostic window compared to whole blood. From these results, it is concluded that faeces is the most suitable clinical specimen for diagnosis of ricin poisoning via the oral route. The ELISA test kit can also detect ricin in environmental samples. An advantage of this ELISA kit over other commercial off-the-shelf (COTS) detection kits currently on the market that are developed to screen environmental samples only is its ability to diagnose ricin poisoning from clinical specimens as well as detect ricin from environmental samples.     

Modulation versus Templating: Fine‐Tuning of Hierarchally Porous PCN‐250 Using Fatty Acids To Engineer Guest Adsorption

Modulation and templating are two synthetic techniques that have garnered significant attention over the last several years for the preparation of hierarchically porous metal–organic frameworks (HP‐MOFs). In this study, by using fatty acids with different lengths and concentrations as dual‐functional modulators/templates, we were able to obtain HP‐MOFs with tunable mesopores that exhibit different pore diameters and locations. We found that the length and concentration of the fatty acids can determine if micelle formation occurs, which in turn dictates the porosity of the resulting HP‐MOFs. The HP‐MOFs with different mesopores differed in their performance in gas uptake and dye adsorption, and the structure–performance relationships were ascribed to the pore diameters and locations. This approach could provide a potentially universal method to efficiently introduce hierarchal mesopores into existing microporous MOF adsorbents with tunable properties.     

Dynamic information for cardiotoxin protein desorption from a methyl-terminated self-assembled monolayer using steered molecular dynamics simulation

Dynamic information, such as force, structural change, interaction energy, and potential of mean force (PMF), about the desorption of a single cardiotoxin (CTX) protein from a methyl-terminated self-assembled monolayer (SAM) surface was investigated by means of steered molecular dynamics (SMD) simulations. The simulation results indicated that Loop I is the first loop to depart from the SAM surface, which is in good agreement with the results of the nuclear magnetic resonance spectroscopy experiment. The free energy landscape and the thermodynamic force of the CTX desorption process was represented by the PMF and by the derivative of PMF with respect to distance, respectively. By applying Jarzynski's equality, the PMF can be reconstructed from the SMD simulation. The PMFs, calculated by different estimators based upon Jarzynski's equality, were compared with the conventional umbrella sampling method. The best estimation was obtained by using the fluctuation-dissipation estimator with a pulling velocity of v = 0.25 nm/ns for the present study.     

Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms

Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an Fe^II‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)₂‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)₂‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment.     

Ag8Cl2[Se2P(OEt)2]6: A rare example containing a combination of discrete clusters and chains

The novel halide-centered Ag(I)8 cubic clusters containing diethyl diselenophosphato ligands are prepared and their solid state structures, a discrete unit or a one-dimensional chain, are dictated by the counter anions.     

Cu(OTf)2-catalyzed Et3SiH-reductive etherification of various carbonyl compounds with trimethylsilyl ethers

A triethylsilane-reductive etherification of the trimethylsilyl ethers with a variety of carbonyl compounds in good yields at room temperature employing 0.5 mol% Cu(OTf)₂ as an extremely efficient catalyst is described here.