Synthetic studies toward pectenotoxin 2. Part I. Stereocontrolled access to the C10-C22 fragment

A highly stereocontrolled and efficient synthesis for a fully functionalized C 10-C 22 fragment of pectenotoxin 2 is described using a convergent sequence involving a stereoselective methylation of beta-hydroxyketone as a key step.     

The complex formation of tetracyclohexylammonium C1-resorcinarene with various guests - an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry study

The complex formation of a tetraammonium C1-resorcinarene (R+4HCl) was studied using electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry. Although R+4HCl easily loses its counter ions in the ESI process, a neutral self-assembled structure with an intramolecular circular hydrogen-bonded 16-membered -N(+)-H ... X(-) ... H-N(+)- array with ammonium ion as the charge-giving species was observed in the gas phase. In addition to chloride, several other counter ions were also studied. The size and basicity of the counter ion as well as the size of the charge-giving cation strongly affected the gas-phase stability of the self-assembled system. H/D exchange experiments showed that the ammonium substituents in the apical position of R affect the hydrogen-bonding system in the resorcinarene. The complexation of the saturated dicarboxylic acids was found to depend on the length of the carbon chain. The rigidity of the molecular skeleton of the acid improved the complexation considerably. The orientation and position of the carboxylic groups also had an effect on the complexation and consequently enabled stereochemical differentiation of the acids. Mass spectrometric observations were supported by theoretical calculations.     

Charge-Assisted Halogen Bonding in an Ionic Cavity of a Coordination Cage Based on a Copper(I) Iodide Cluster

The design of molecular containers capable of selectively binding specific guest molecules presents an interesting synthetic challenge in supramolecular chemistry. Here, we report the synthesis and structure of a coordination cage assembled from Cu₃I₄⁻ clusters and tripodal cationic N-donor ligands. Owing to the localized permanent charges in the ligand core the cage binds iodide anions in specific regions within the cage through ionic interactions. This allows the selective binding of bromomethanes as secondary guest species within the cage promoted by halogen bonding, which was confirmed by single-crystal X-ray diffraction.     

2(S)‐Amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl cyclo­hexylmethyl ether di­hydro­chloride and 2(S)‐amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl 4‐bromo­benzyl ether di­hydro­chloride

(Cyclo­hexyl­methyl­oxy­methyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₂₅N₃O⁺·2Cl^?, and (4‐bromo­benzyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₁₈BrN₃O⁺·2Cl^?, are model compounds with different biological activities for evaluation of the hist­amine H3‐receptor activation mechanism. Both title compounds occur in almost similar extended conformations.     

Determination of the REE content,geological age,and absorbed alpha dose of allanite mineral from Palawan,Philippines

Allanite is a common accessory mineral in igneous rocks that contains significant amounts of rare-earth elements (REEs), thorium (Th), and uranium (U). The presence of Th and U in the allanite exposes it to radiation resulting in radiation damage in its crystal structure and further leads to metamictization. Hence, allanite can be used as a natural analogue to assess the long-term radiation effects in materials for high-level nuclear waste disposal. It provides information on the effect of α-decay on the crystal structure including the stability and integrity of the material. In this study, the absorbed α-dose of allanite from Ombo, Palawan, Philippines, was estimated from the Th and U content and geological age of the mineral using X-ray fluorescence and gamma-ray spectrometry. The amount of Th and REE was measured to be around 1.37 and ~30.4 wt.%, respectively. Radiometric dating using gamma-ray spectrometry estimated the age of the allanite mineral to be around 24–35 million years. Having obtained the amount of radioactivity and the time of exposure, the corresponding absorbed α-dose was estimated to be at 2.84 × 10¹⁴ α-decays/mg. Results suggest that the allanite mineral studied has not accumulated significant radiation damage to cause amorphization and still exhibit a crystalline structure. This study may provide data on the properties of allanite or silicate matrices as part of the ongoing studies on silicate minerals as natural analogues.     

Double-networks based on interconnected amphiphilic “in–out” star first polymer conetworks prepared by RAFT polymerization

Double-network hydrogels were prepared using well-defined first networks comprising interconnected amphiphilic “in-out” star copolymers synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, and second networks based on a photopolymerized mixture of acrylamide and N,N′-methlyenebisacrylamide. All first and double-network hydrogels were characterized in terms of their aqueous degrees of swelling and mechanical properties in compression. The most hydrophobic first and double-network hydrogels exhibited the best mechanical properties, which may be attributed to their low aqueous swelling degrees and good mesoscale organization in water as revealed using small-angle neutron scattering (SANS) which showed that the size of the formed hydrophobic domains could be controlled by the polymer conetwork structure. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2161–2174     

Self-Assembly of Chiral Cyclohexanohemicucurbit[n]urils with Bis(Zn Porphyrin): Size,Shape, and Time-Dependent Binding

In order to investigate the ability of bis(zinc octaethylporphyrin) (bis–ZnOEP) to discriminate cyclohexanohemicucurbit[n]urils (cycHC[n]) of different shapes and sizes, the self-assembly of barrel-shaped chiral cycHC[n] with bis–ZnOEP was studied by various spectroscopic methods (absorption, fluorescence, circular dichroism (CD), and NMR). While the binding of 6-membered cycHC[6] induced a tweezer-like conformation followed by the formation of anti-form of bis–ZnOEP upon further addition of cycHC[6], the interaction of 8-membered cycHC[8] is more complex and proceeds through the featured syn-to-anti conformational change of bis–ZnOEP and further intermolecular self-assembly via multiple noncovalent associations between cycHC[8] and bis–ZnOEP. Whilst bis–porphyrins are known to be effective chemical sensors able to differentiate various guests based on their chirality via induced CD, their ability to sense small differences in the shape and size of relatively large macrocycles, such as chiral cycHC[6] and cycHC[8], is scarcely examined. Both studied complexes exhibited characteristic induced CD signals in the region of porphyrin absorption upon complexation.     

Ion‐Pair Complexation with Dibenzo[21]Crown‐7 and Dibenzo[24]Crown‐8 bis‐Urea Receptors

Synthesis and ion‐pair complexation properties of novel ditopic bis‐urea receptors based on dibenzo[21]crown‐7 ( R¹ ) and dibenzo[24]crown‐8 ( R² ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl₃/[D₆]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb⁺ or Cs⁺, with the halide affinity increasing in order I^?<Br^?<Cl^?. In solution, the rubidium complexes of both receptors have higher halide affinities compared to the caesium complexes. However, Rb⁺ and Cs⁺ complexes of R² show stronger affinities toward all the studied anions compared to the corresponding cationic complexes of R¹ . Similar selectivity of the receptors toward the studied ion pairs was also observed also in the gas phase by competition experiments with mass spectrometry. A total of eight crystal structures with different rubidium and caesium halides and oxyanions were obtained in addition to the crystal structure of R²?BaCl₂ . The selectivity observed in solution and in the gas phase is explainable by the conformational differences observed in the crystal structures of ion‐pair complexes with R¹ and R² . In the solid state, R¹ has an open conformation due to the asymmetric crown‐ether scaffold, whereas R² has a compact, folded conformation. Computational studies of the ion‐pair complexes of R² show that the interaction energies of the complexes increase in the order CsI<CsBr<CsCl<RbCl, supporting the selectivity observed in solution and the gas‐phase.