166 research outputs found
Two-Step Transformation of Aliphatic Polyketones into pi-Conjugated Polyimines
No full textThe chemo- and stereo-selective two-step transformation of aliphatic polyketones composed of 3,3-dimethylpentane-2,4-dione units was achieved to generate pi-conjugated polyimines. Upon treatment with hydrazine, discrete oligoketones with 4-8 carbonyl groups afforded ethylene-bridged oligoisopyrazoles in 80-89% yields. These oligoisopyrazoles underwent stereoselective oxidation at the ethylene bridge to give fully pi-conjugated oligo(isopyrazole-3,5-diyl-trans-vinylene)s in 73-87% yields. Oxidation of the oligoimines drastically changed their absorption and metal-coordination behaviors. Finally, this two-step transformation was applied to polydisperse polymers. Imine formation proceeded almost quantitatively, even for longer polyketones, including docosamer. Subsequent oxidation of the polyimines furnished a virtually insoluble material that showed broad and red-shifted solid-state absorption over the whole visible region resulting from extended pi-conjugation
Supramolecular Conformational Control of Aliphatic Oligoketones by Rotaxane Formation
No full textConformational control of aliphatic oligoketones bearing two 1,3-diketone subunits is achieved by molecular recognition with pillar[5]arene. Pillar[S]arene binds to aliphatic ketones, with association constants K of similar to 10 M-1, to form pseudorotaxanes. The pseudorotaxanes are locked by BF, complexation at the 1,3-diketone sites through quasi-solid-state reactions. X-ray crystallography reveals linear conformations for the axis molecules. The effect of supramolecular conformational restriction is evaluated using an alkyl-linked dyad chromophore system that shows solvatochromism upon intramolecular aggregation
New Trends in Vascular Inflammation Research: From Biology to Therapy
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Insoluble π‐Conjugated Polyimine as an Organic Adsorbent for Group 10 Metal Ions
No full textMetal ion adsorbents are indispensable materials for the recovery of noble metal ions in a sustainable society. Herein, we report that poly(isopyrazole-3,5-diyl-trans-vinylene) (1) effectively adsorbed group 10 metal ions from solution in acetonitrile. Owing to its fully pi-conjugated and rigid structure, polyimine 1 was virtually insoluble in common organic solvents and water, making it advantageous for metal ion adsorption via a solid/liquid interface. Inductively coupled plasma (ICP) analysis showed that >= 90 % of Ni2+, Pd2+, and Pt2+ ions were adsorbed at a concentration of 10 mu M (order of <= 2 ppm) after stirring suspensions at room temperature. Metal ion desorption was achieved by treatment with ethylenediaminetetraacetic acid disodium salt (EDTA . 2Na), and the adsorbent was reused. Theoretical calculations supported that the desolvation energy was an important factor for effective adsorption in acetonitrile
Luminescent Coordination Polymers Constructed from a Flexible, Tetradentate Diisopyrazole Ligand and Copper(I) Halides
No full textOne- and two-dimensional coordination polymers composed of a structurally flexible, tetradentate diisopyrazole ligand and copper(I) halides were synthesized as crystalline solids. Complexation with copper(I) chloride or bromide resulted in the formation of infinite coordination chains through connecting each diisopyrazole ligand with two copper(I) ions in a trigonal planar coordination geometry. Contrarily, the combination of a diisopyrazole ligand and copper(I) iodide gave a two-dimensional coordination network comprising Cu4I4 units with stair-step type geometry and diisopyrazoles that acted as both tetradentate and bidentate bridging ligands. All the coordination polymers exhibited visible photo-emission upon UV irradiation, and the Cu4I4 complex showed thermochromic behavior
Isopyrazole‐Masked Tetraketone: Tautomerism and Functionalization for Fluorescent Metal Ligands
No full textAn isopyrazole (4H-pyrazole)-embedded nonane-2,4,6,8-tetraone derivative was synthesized as a masked-tetraketone for stepwise and multiple functionalization. The masked-tetraketone has six possible tautomers, but exists predominantly as a 12 pi-electron conjugated keto-enamine-imine-enol form, which was also observed in the solid state by single crystal X-ray analysis. Stepwise functionalization to introduce metal-coordination and fluorescence-enhancement sites into the masked tetraketone furnished a fluorescent chromophore that indicates metal coordination on a microgram scale by considerably changing the solid-state emission
Absorption spectra of calix[3]pyrrole analogs as probes for contracted macrocycles
No full textCalix[3]pyrrole and its furan derivatives exhibited bathochromically shifted lowest-energy electronic transition bands in their absorption spectra compared with their calix[4]- and calix[6]-pyrrole analogues, despite the repeating units being the same. We also observed fluorescence emission for calix[3]-type macrocycles. The Stokes shift of the furan/pyrrole hybrid macrocycles, calix[2]furan[1]-pyrrole, and calix[1]furan[2]pyrrole, substantially varied depending on the solvent polarity. Non-covalent interaction (NCI) analyses indicated enhanced interactions between neighboring aromatic rings in the calix[3]pyrrole macrocycle, whereas such interactions were weak in calix[4]pyrrole, in which the interchromophore distance is remarkably longer than in calix[3]pyrrole. Theoretical analyses indicated that the red-shifted, lowest-energy bands of calix[3]pyrrole correspond to HOMO-LUMO transitions, the energy gap of which was narrow compared with calix[4]pyrroles. The characteristic absorption bands for calix[3]pyrrole and its related macrocycles are useful as probes for distinguishing such macrocycles from higher calix[n]pyrrole (n & GE; 4) analogues that exhibit almost identical absorption spectra
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