Polymer‐Assisted Solution‐Phase Synthesis and Neurite‐Outgrowth‐Promoting Activity of 15‐Deoxy‐Δ12,14‐PGJ2 Derivatives

An efficient solution‐phase synthesis of rac‐15‐deoxy‐Δ^12,14‐PGJ₂ (15dPGJ₂) derivatives that contain variable α and ω chains based on a polymer‐assisted strategy and their neurite‐outgrowth‐promoting activity are described. The strategy for the synthesis of PGJ₂ derivatives involves the use of a vinyl iodide bearing cyclopentenone as a key intermediate, which undergoes Suzuki–Miyaura coupling and subsequent Lewis acid catalyzed aldol condensation for incorporation of the ω and α chains, respectively. For easy access to the PGJ₂ derivatives, a polymer‐supported catalyst and scavengers were adapted for use in these four diverse steps, in which workup and purification can be performed by simple filtration of the solid‐supported reagents. By using this methodology, we succeeded in the synthesis of 16 PGJ₂ derivatives with four alkyl boranes and four aldehydes. The neurite‐outgrowth‐promoting activity of the 16 synthetic compounds in PC12 cells revealed that the side‐chains play a major role in modulating their biological activity. The carboxylic acid on the α chain improved the biological activity, although it was not absolutely required. Furthermore, a PGJ₂ derivative with a phenyl moiety on the ω chain was found to exhibit an activity comparable to that of natural 15dPGJ₂.     

Collective Effects in Ionic Liquid [emim][Tf2N] and Ionic Paramagnetic Nitrate Solutions without Long-Range Structuring

Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero low-frequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress. A neutron scattering study completes the dynamic mechanical analysis of the paramagnetic nitrate solution, evidencing that the magnetic properties do not induce the formation of a structure in the solution. We conclude that the elastic correlations contained in liquids usually considered as viscous away from any phase transition contribute in an effective way to collective effects under external stress whether mechanical or magnetic fields.     

Anthranilamide-protected vinylboronic acid: rational monomer design for improved polymerization/transformation ability providing access to conventionally inaccessible copolymers

We have studied several protecting groups for vinylboronic-acid derivatives as monomers in radical polymerizations with the objective to improve the polymerization ability and C–B bond-cleaving post-transformation performance. Anthranilamide (aam)-protected vinylboronic acid (VBaam) exhibited experimentally a relatively high polymerization activity, which was theoretically corroborated by density functional theory (DFT) calculations that revealed a peculiar effect of the interaction between the aam groups on the polymerization behavior. The VBaam units in the copolymers can subsequently be transformed into vinyl alcohols or into ethylene units through C–B-bond-cleaving side-chain replacement, which affords valuable copolymers such as poly(vinyl alcohol-co-styrene), poly(ethylene-co-styrene), and poly(ethylene-co-acrylate).

We designed a vinyl-boronic-acid protected by anthranilamide as a “transformable” monomer in radical polymerization to synthesize conventionally inaccessible copolymers, such as poly(vinyl alcohol-co-styrene) and poly(ethylene-co-acrylate).     

A New Supramolecular Tetraruthenated Cobalt (II) Porphyrazine Displaying Outstanding Electrocatalytical Performance in Oxygen Evolution Reaction

A new supramolecular electrocatalyst for Oxygen Evolution Reaction (OER) was synthesized from a central multibridging cobalt tetrapyridylporphyrazine (CoTPyPz) species by attaching four [Ru(bpy)₂Cl]⁺ groups. Both CoTPyPz and the tetraruthenated cobalt porphyrazine species, TRuCoTPyPz, form very homogenous molecular films just by dropcasting their methanol solutions onto GCE electrodes. Such films exhibited low overpotentials for O₂ evolution, e.g., 560 e 340 mV, respectively, displaying high stability, typically exceeding 15 h. The kinetic parameters obtained from the Tafel plots showed that the peripheral complexes are very important for the electrocatalytic activity. Hyperspectral Raman images taken along the electrochemical process demonstrated that the cobalt center is the primary active catalyst site, but its performance is enhanced by the ruthenium complexes, which act as electron-donating groups, in the supramolecular system.     

Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.     

UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes

The photoisomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties, namely, [Co(II)(dmAB)3](BF4)2 [dmAB = 4,4'-bis[3'-(4'-tolylazo)phenyl]-2,2'-bipyridine], [Co(III)(dmAB)3](BF4)3, [Co(II)(mAB)3](BF4)2 [mAB = 4-[3' '-(4' '-tolylazo)phenyl]-2,2'-bipyridine], and [Co(III)(dmAB)3](BF4)3, derived from the effect of gathering azobenzenes in one molecule and the effect of the cobalt(II) or cobalt(III) ion were investigated using UV-vis absorption spectroscopy, femtosecond transient spectroscopy, and 1H NMR spectroscopy. In the photostationary state of these four complexes, nearly 50% of the trans-azobenzene moieties of the Co(II) complexes were converted to the cis isomer, and nearly 10% of the trans-azobenzene moieties of the Co(III) complexes isomerized to the cis isomer, implying that the cis isomer ratio in the photostationary state upon irradiation at 365 nm is controlled not by the number of azobenzene moieties in one molecule but rather by the oxidation state of the cobalt ions. The femtosecond transient absorption spectra of the ligands and the complexes suggested that the photoexcited states of the azobenzene moieties in the Co(III) complexes were strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and a Co(II) center. The cooperation among the photochemical structural changes of six azobenzene moieties in [Co(II)(dmAB)3](BF4)2 was investigated with 1H NMR spectroscopy. The time-course change in the 1H NMR signals of the methyl protons indicated that each azobenzene moiety in [Co(II)(dmAB)3](BF4)2 isomerized to a cis isomer with a random probability of 50% and without interactions among the azobenzene moieties.     

Energy funneling of IR photons captured by dendritic antennae and acceptor mode specificity: anti-stokes resonance raman studies on iron(III) porphyrin complexes with a poly(aryl ether) dendrimer framework

A series of poly(aryl ether) dendrimer chloroiron(III) porphyrin complexes (LnTPP)Fe(III)Cl (number of aryl layers [n]=3 to 5) were synthesized, and their Boltzmann temperatures under IR irradiation were evaluated from ratios of Stokes to anti-Stokes intensities of resonance Raman bands. While the Boltzmann temperature of neat solvent was unaltered by IR irradiation (LnTPP)Fe(III)Cl (n=3 to 5), all showed a temperature rise that was larger than that of the solvent and greater as the dendrimer framework was larger. Among vibrational modes of the metalloporphyrin core, the temperature rise of an axial Fe-Cl stretching mode at 355 cm-1 was larger than that for a porphyrin in-plane mode at 390 cm-1. Although most of the IR energy is captured by the phenyl nu8 mode at 1597 cm-1 of the dendrimer framework, an anti-Stokes Raman band of the phenyl nu8 mode was not detected, suggesting the extremely fast vibrational relaxation of the phenyl mode. From these observations, it is proposed that the energy of IR photons captured by the aryl dendrimer framework is transferred to the axial Fe-Cl bond of the iron porphyrin core and then relaxed to the porphyrin macrocycle.     

Cobaltporphyrin‐adsorbed carbon black: highly efficient electrocatalysts for oxygen reduction

meso‐Substituted cobalt porphyrins adsorbed on carbon black were prepared as catalysts for the electroreduction of O₂. The catalyst, which was prepared by using a homogenizer in mixing cobalt tetraethylporphyrin and carbon black, gave rise to electroreduction of O₂ at a remarkably positive potential (E_p = 0.45 V versus saturated calomel electrode (SCE)) and showed a high selectively for the four‐electron reduction (n = 3.8). Electrochemical study and extended X‐ray absorption fine structure (EXAFS) analysis revealed that the adsorbed face‐to‐face dimeric aggregates of cobalt porphyrin molecules were highly efficient catalysts for electroreduction of O₂. Copyright © 2005 John Wiley & Sons, Ltd.     

Crystalline‐Sponge‐Based Structural Analysis of Crude Natural Product Extracts

Characterization of complex natural product mixtures to the absolute structural level of their components often requires significant amounts of starting materials and lengthy purification process, followed by arduous structure elucidation efforts. The crystalline sponge (CS) method has demonstrated utility in the absolute structure elucidation of isolated organic compounds at miniscule quantities compared to conventional methods. In this work, we developed a new CS‐based workflow that greatly expedites the in‐depth structural analysis of crude natural product extracts. Using a crude extract of the red alga Laurencia pacifica, we showed that CS affinity screening prior to compound isolation enables prioritization of analytes present in the extract, and we subsequently resolved the molecular structures of six sesquiterpenes with stereochemical clarity from around 10 mg crude extract. This study demonstrates a new chemotyping workflow that can greatly accelerate natural product discovery from complex samples.     

Interaction between dyes and polyelectrolytes. XIII. Effect of dye aggregation on the excitation energy transfer between bound dyes

Effect of polyanions on the aggregation of methylene blue (MB) was investigated spectrophotometrically. The following polyanions were used: potassium poly(vinyl sulfate), potassium poly(styrenesulfonate), sodium poly(methacrylate), and sodium poly(acrylate). The state of aggregation was largely dependent on the kind of polyanion and polyanion-MB ratio. MB-photo-sensitized isomerization of cis-p-(phenylazo)phenyltrimethylammonium iodide(cis-PTA) to the transisomer was used advantageously to investigate the effect of dye aggregation on the triplet excitation energy transfer between cationic dyes bound to polyanions. Although the efficiency of the excitation energy transfer between MB and cis-PTA was enhanced by the addition of polyanions, the formation of highly aggregated MB reduced the efficiency of the excitation energy transfer. Correlation with the dye aggregation induced by polyanions and the efficiency of excitation energy transfer between dyes was discussed.