Nagelamides K and L, dimeric bromopyrrole alkaloids from sponge Agelas species

Two new dimeric bromopyrrole alkaloids, nagelamides K (1) and L (2), have been isolated from Okinawan marine sponges Agelas species, and the structures and stereochemistry were elucidated from spectroscopic data. Nagelamide K (1) is a bromopyrrole alkaloid possessing a rare piperidinoiminoimidazolone ring with an aminoimidazole ring and a taurine unit, while nagelamide L (2) is a unique dimeric bromopyrrole alkaloid containing an ester linkage. Nagelamides K (1) and L (2) exhibited antimicrobial activity.     

Rhenium-catalyzed synthesis of multisubstituted aromatic compounds via C-C single-bond cleavage

A reaction between a beta-keto ester and an acetylene in the presence of a rhenium complex, [ReBr(CO)3(thf)]2, as a catalyst, provided a 2-pyranone derivative in excellent yield via retro-aldol reaction (C-C single bond cleavage). By adding an acetylene-bearing ester group(s) after the formation of 2-pyranones, an aromatization reaction proceeded and multisubstituted aromatic compounds were obtained in good to excellent yields.     

Electronic modulation of fused oligothiophenes by chemical oxidation

The reaction of pentathienoacene (f-5T) with mCPBA produced a series of oxidized derivatives containing one or two thiophene- S, S-dioxide rings. The regioselectivity of the oxidation reflects the aromaticity of each thiophene ring in the f-5T skeleton, and the extent of the oxidation significantly affects the fluorescence and redox properties.     

Blending to Make Nonhealable Polymers Healable: Nanophase Separation Observed by CP/MAS 13C NMR Analysis

Can commodity polymers are made to be healable just by blending with self-healable polymers? Here we report the first study on the fundamental aspect of this practically challenging issue. Poly(ether thiourea) (PTUEG₃; T_g=27 °C) reported in 2018 is extraordinary in that it is mechanically robust but can self-heal even at 12 °C. In contrast, poly(octamethylene thiourea) (PTUC₈; T_g=50 °C), an analogue of PTUEG₃, cannot heal below 92 °C. We found that their polymer blend self-healed in a temperature range above 32 °C even when its PTUEG₃ content was only 20 mol %. Unlike PTUEG₃ alone, this polymer blend, upon exposure to high humidity, barely plasticized, keeping its excellent mechanical properties due to the non-hygroscopic nature of the PTUC₈ component. CP/MAS ¹³C NMR analysis revealed that the polymer blend was nanophase-separated, which possibly accounts for why such a small amount of PTUEG₃ provided the polymer blend with humidity-tolerant self-healable properties.     

An Electron-Deficient CpE Iridium(III) Catalyst: Synthesis,Characterization, and Application to Ether-Directed C−H Amidation

The synthesis, characterization, and catalytic performance of an iridium(III) catalyst with an electron-deficient cyclopentadienyl ligand ([Cp^EIrI₂]₂) are reported. The [Cp^EIrI₂]₂ catalyst was synthesized by complexation of a precursor of the Cp^E ligand with [Ir(cod)OAc]₂, followed by oxidation, desilylation, and removal of the COD ligand. The electron-deficient [Cp^EIrI₂]₂ catalyst enabled C−H amidation reactions assisted by a weakly coordinating ether directing group. Experimental mechanistic studies and DFT calculations suggested that the high catalytic performance of [Cp^EIrI₂]₂ is due to its electron-deficient nature, which accelerates both C−H activation and Ir^V-nitrenoid formation.     

Improved stability of Opalmon tablets under humid conditions IV: effect of polysaccharides and disintegrants on the stability and dissolution property of Opalmon tablets

We studied the effects of dextran, dextrin, and disintegrants on the chemical stability of Opalmon tablets containing Limaprost-alfadex (Limaprost/alpha-cyclodextrin complex) and found that the addition of dextran or dextrin significantly improved the chemical stability of Opalmon tablets under high humidity, compared to lactose. We also examined how dextran stabilizes Limaprost in Opalmon tablets and studied the formulation of Opalmon tablets in order to achieve higher chemical stability, rapid dissolution and reduced stickiness. The results suggested that dextran increases stabilization after moisture adsorption by decreasing the dissociation of Limaprost-alfadex to the free drug and alpha-cyclodextrin in the dextran matrix, when compared with the lactose matrix. The stickiness of Opalmon tablets containing dextran and dextrin was negligible when dextran and dextrin amounted to less than 20% of the formulation. By selecting a proper disintegrant, we obtained Opalmon tablets with higher chemical stability and rapid dissolution properties.     

Formulation design of an oral, fast-disintegrating dosage form containing taste-masked particles of famotidine

A fast-disintegrating dosage form has been developed as a user-friendly formulation that disintegrates in the mouth immediately. Patients can take it without water like a liquid formulation. In this study famotidine taste-masking technology was applied to the new fast-disintegrating tablet in an attempt to produce a novel, taste-masked, fast-disintegrating tablet. Partial granulation was found to be an effective and practical way to address content uniformity, however, oral disintegration time tended to become longer as content uniformity improved. The disintegration time was improved considerably by controlling ambient humidity during the compression process (>50% RH). Furthermore, since the new fast-disintegrating technology made it possible to use low compression force, there was no change in the structure or dissolution rate of the taste-masked particles after compression. Therefore, this system can produce a taste-masked fast-disintegrating tablet with satisfactory attributes.     

Ferromagnetic Dy-Ni and antiferromagnetic Dy-Cu couplings in single-molecule magnets [Dy2Ni] and [Dy2Cu

The exchange couplings in [{Dy(hfac)3}2Cu(dpk)2] and [{Dy(hfac)3}2Ni(dpk)2(py)2] (Hdpk = di-2-pyridyl ketoxime) were precisely evaluated by high-frequency electron paramagnetic resonance and pulsed-field magnetization studies, giving J(Dy-Cu)/kB = -0.126 K and J(Dy-Ni)/kB = +0.031 K.     

Electrochemical and complexation behavior of neptunium in aqueous perchlorate and nitrate solutions

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption, and Np L(III)-edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo structural rearrangement from spherical coordinating ions (Np(3+) and Np(4+)) to transdioxoneptunyl ions (NpO2(n+), n = 1 for Np(V) and 2 for Np(VI)). The redox reaction of the Np(V)/Np(VI) couple involves no structural rearrangement on their equatorial planes in acidic perchlorate and nitrate solutions. A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H2O)10](4+) in 1.0 M HClO4, while Np(V) and Np(VI) exist dominantly as pentaaquoneptunyl complexes, [NpO2(H2O)5](n+) (n = 1 for Np(V) and 2 for Np(VI)). A systematic change is observed on the Fourier transforms of the EXAFS spectra for all of the Np oxidation states as the nitrate concentration is increased in the sample, revealing that the hydrate water molecules are replaced by bidentate-coordinating nitrate ions on the primary coordination sphere of Np.     

Experimental and theoretical characterization of MSi16(-), MGe16(-), MSn16(-), and MPb16(-) (M = Ti, Zr, and Hf): the role of cage aromaticity

Silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) clusters mixed with a group-4 transition metal atom [M = titanium (Ti), zirconium (Zr), and hafnium (Hf)] were generated by a dual-laser vaporization method, and their properties were analyzed by means of time-of-flight mass spectroscopy and anion photoelectron spectroscopy together with theoretical calculations. In the mass spectra, mixed neutral clusters of MSi(16), MGe(16), and MSn(16) were produced specifically, but the yield of MPb(16) was low. The anion photoelectron spectra revealed that MSi(16), MGe(16), and MSn(16) neutrals have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of 1.5-1.9 eV compared to those of MPb(16) (0.8-0.9 eV), implying that MSi(16), MGe(16), and MSn(16) are evidently electronically stable clusters. Cage aromaticity appears to be an important determinant of the electronic stability of these clusters: Calculations of nucleus-independent chemical shifts (NICSs) show that Si(16)(4-), Ge(16)(4-), and Sn(16)(4-) have aromatic characters with negative NICS values, while Pb(16)(4-) has an antiaromatic character with a positive NICS value.