Stability of n-covered Circles for Elastic Rods with Constant Planar Intrinsic Curvature

A stability index is computed for the n-covered circular equilibria of inextensible-unshearable elastic rods with constant planar intrinsic curvature û and constant values for the twisting stiffness and two bending stiffnesses. A simple expression is derived for the index as a function of û, (the ratio of bending stiffness out of the plane of curvature to bending stiffness in the plane of curvature), and (the ratio of twisting stiffness to bending stiffness in the plane of curvature). In particular, for intrinsically straight rods (û = 0) we prove that the 1-covered circle is stable if and only if 1, and the n-covered circle (n>1) is stable if and only if >1, >1, and

Reversible structural isomerisation in rare thioether complexes of cobalt(II)--effects of ligand architecture

Rare examples of (high spin) Co(II) complexes with geometrically constrained tetrathioether ligands exhibit a very unusual structural isomerism, switching reversibly between tetrahedral monomers in solution and octahedral chain polymers in the solid; the crystal structures of one polymeric species and a tetrahedral monomer model compound are described.     

PET Oncological Radiopharmaceuticals: Current Status and Perspectives

Molecular imaging is the visual representation of biological processes that take place at the cellular or molecular level in living organisms. To date, molecular imaging plays an important role in the transition from conventional medical practice to precision medicine. Among all imaging modalities, positron emission tomography (PET) has great advantages in sensitivity and the ability to obtain absolute imaging quantification after corrections for photon attenuation and scattering. Due to the ability to label a host of unique molecules of biological interest, including endogenous, naturally occurring substrates and drug-like compounds, the role of PET has been well established in the field of molecular imaging. In this article, we provide an overview of the recent advances in the development of PET radiopharmaceuticals and their clinical applications in oncology.     

Chrysanthemyl 2-acetoxy-3-methylbutanoate: the sex pheromone of the citrophilous mealybug, Pseudococcus calceolariae

Headspace volatiles collected from virgin females of the citrophilous mealybug, Pseudococcus calceolariae, contain three compounds not present in the headspace of control samples. The main female-specific compound is identified as [2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl]methyl 2-acetoxy-3-methylbutanoate (chrysanthemyl 2-acetoxy-3-methylbutanoate). The other two compounds are identified as [2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl]methanol (chrysanthemol) and [2,2-dimethyl-3-(2-methylprop-1-enyl)cyclopropyl]methyl 2-hydroxy-3-methylbutanoate (chrysanthemyl 2-hydroxy-3-methylbutanoate). Traps baited with 100 μg and 1000 μg of chrysanthemyl 2-acetoxy-3-methylbutanoate captured 4- and 20-fold more males than traps baited with virgin females.     

ET743: Chemical analysis of the sea squirt Ecteinascidia turbinata ecosystem

The sea squirt Ecteinascidia turbinata produces the powerful drug ET743. In this study Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) and Matrix Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS) are systematically used to measure elemental and molecular species in a Florida Keys mangrove ecosystem that contains the sea squirt. ICP-AES is used to measure the concentration of 27 elements down to the parts per billion level in 16 organisms and 3 sediment samples that reside in the mangrove ecosystem including turtle grass, blue crabs, fire sponge, and lettuce slugs. MALDI-MS is used to search for ET743 in these same organisms and sediment samples. A mass spectral feature corresponding to ET743 is identified in the extract of the sea squirt, red mangrove root (Rhizophera mangle), the schoolmaster snapper (Lutjanus griseus), and a sediment sample taken from the ecosystem. We use MALDI-MS to study the impact that various environmental conditions, such as UV light, I(2), cation binding (Fe(+3), Zn(+2), Pb(+2), Cu(+2)), metal oxide nanoparticles (FeO, CuO, TiO(2), ZnO, Al(2)O(3)), a common mineral (CaCO(3)), and extremes in acidity (0.1 M HCl, 0.1 M NaOH) have on the ET743 structure. The data provide potential structures (degradation products, metal-ligand complexes, etc.) that might be present in organism or sedimentary extracts that are similar to ET743. We are studying the marine geochemistry of this ecosystem so a broth can be developed and tested for producing this marine natural product.     

Mapping prehistoric ghosts in the synchrotron

The detailed chemical analysis of fossils has the potential to reveal great insight to the composition, preservation and biochemistry of ancient life. Such analyses would ideally identify, quantify, and spatially resolve the chemical composition of preserved bone and soft tissue structures, but also the embedding matrix. Mapping the chemistry of a fossil in situ can place constraints on mass transfer between the enclosing matrix and the preserved organism(s), and therefore aid in distinguishing taphonomic processes from original chemical zonation remnant within the fossils themselves. Conventional analytical methods, such as scanning electron microscopy (SEM) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) have serious limitations in this case, primarily, an inability to provide large (i.e., decimeter) scale chemical maps. Additionally, vacuum chamber size and the need for destructive sampling preclude analysis of large and precious fossil specimens. However, the recent development of Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) at the Stanford Synchrotron Radiation Lightsource (SSRL) allows the non-destructive chemical analysis and imaging of major, minor, and trace element concentrations of large paleontological and archeological specimens in rapid scanning times. Here we present elemental maps of a fossil reptile produced using the new SRS-XRF method. Our results unequivocally show that preserved biological structures are not simply impressions or carbonized remains, but possess a remnant of the original organismal biochemistry. We show that SRS-XRF is a powerful new tool for the study of paleontological and archaeological samples.     

Protonation Sequence Study of the Solution Structure of DTPA by 1H NMR

The protonation sequence of DTPA is evaluated using a 300 MHz H NMR instrument. A terminal nitrogen is protonated first (pK_a1,2=10.02, 8.45). Upon the first protonation a dynamic hydrogen bonded five membered ring is formed between the terminal nitrogen and the central nitrogen. The second equivalent of protons protonates the opposite terminal amine and causes the ring to open. The third protonation (pK_a3=4.65) takes place on the central acetate and forms a ring with the central amine. The fourth protonation is assigned to a terminal acetate. The formation of five membered rings involving hydrogen bonding gives a better quantitative and qualitative account for the unusual shifts observed in the H NMR spectra than previous explanations.     

Graft Copolymerizations of Polysaccharides. II. Acrylamide Grafting to Yellow Dextrin

Graft copolymers of acrylamide and yellow dextrin were prepared using cerium(IV) as initiator. The yellow dextrin had a very broad molecular weight distribution but was fractionated utilizing dialysis and ultrafiltration membranes. Initiator efficiencies were determined using size exclusion chromatography and were found to be between 2.4 and 34%. Initiator efficiency increased with acrylamide concentration at constant cerium (IV) and yellow dextrin concentrations, and decreased with increasing cerium(IV) concentration at constant acrylamide and yellow dextrin concentrations. Plots of acrylamide conversion and intrinsic viscosity vs initial acrylamide concentration at constant yellow dextrin and ceric ion concentrations showed a maximum at about 2.0 M.     

Organometallic Polymers. XXVII. Radical-Initiated Polymerization and Copolymerization of π-(2, 4-Hexadien-1-yl Acrylate) tricarbonyliron

The novel monomer, π-(2, 4-hexadiene- l-yl acrylate) tricarbonyliron (HATI), has been prepared by two routes. It was homopolymerized and copolymerized with acrylonitrile, vinyl acetate, styrene, and methyl acrylate in benzene solutions. In all cases azobisisobutyronitrile was the initiator. The relative reactivity ratios, where HATI is defined as M₁, were determined: r₁ = 0.34, r₂ = 0.74, M₂ = acrylonitrile; r₁ = 2.0, r₂ = 0.05, M₂ = 0.74, M₂ = acrylonitrile; r₁ = 2.0, r₂ = 0.05, M₂ = vinyl acetate; r₁ = 0.26, r₂ = 1.81, M₂ = styrene; and r₁ = 0.30, r₂ = 0.74, M₂ = methyl acrylate. The homo-and copolymers had high values of T_g. When polymerizations are carried out at high concentrations, a very high molecular weight tail is observed in HATI hompolymerizations and in HATI-methyl acrylate copolymerizations. The polymers were characterized by IR, gel permeation chromatography, viscosity, and differential scanning calorimetry studies. Finally, thermal decompositions carried out in air resulted in decomposition of the Fe(CO)₃ group, producing Fe₂O₃ as a fine powder. Thermal decomposition under nitrogen (in solution and on solids ground into KBr pellets) resulted in slow destruction of the Fe(CO)₃ groups but the resulting polymer mass was insoluble, and the question of what form the iron exists in (Fe metal, oxides, carbides, etc.) has not been answered.     

Polymerization of Methane and Olefin Mixtures over Fluosulfonic Acid and Antimony Pentafluoride

Mixtures of methane and olefins (ethylene, propylene, butenes, butadiene, and styrene) have been polymerized over HSO₃ F-SbF₃ to yield an oily oligomer with a molecular weight ranging from 100 to 700. The NMR spectra of each polymer showed a sharp peak at or near 1.25 &, suggesting the presence of block methylene in the polymer. The formation of block methylene is surprising considering the fact that the polymerization reaction is carbonium ion in nature. A primary cation has been invoked to explain the results. The formation of this primary cation must involve some extraordinary stabilization by some component in the acid.