Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

Synthesis of simplified analogues of eleutherobin via a Claisen rearrangement/RCM strategy

The enantioselective synthesis of a number of simplified analogues of the cytotoxic natural product eleutherobin is reported.     

Dual Esterase‐ and Steroid‐Responsive Energy Transfer Modulation of Ruthenium(II) and Rhenium(I) Complex Functionalized Gold Nanoparticles

A number of adamantane‐containing ruthenium(II) and rhenium(I) complexes have been synthesized, characterized, and noncovalently functionalized with β‐cyclodextrin‐capped gold nanoparticles (β‐CD–GNPs) through the host–guest interaction between cyclodextrin and adamantane. The resultant nanoconjugates have been characterized by transmission electron microscopy (TEM), energy‐dispersive X‐ray analysis (EDX), and 2D ROESY ¹H NMR experiments. The Förster resonance energy transfer (FRET) properties of the nanoconjugates can be modulated by both esterase‐accelerated hydrolysis and competitive displacement of steroid, by monitoring the emission intensity and luminescence lifetime. The FRET efficiencies are found to vary with the nature of the chromophores and the length of the spacer between the transition metal complexes and the GNPs. This work constitutes a “proof‐of‐principle” assay method for the dual‐functional detection of important classes of biomolecules, such as enzymes and steroids.     

Non-hemolytic α-AApeptides as antimicrobial peptidomimetics

We report a new class of peptide mimetics, α-AApeptides, that display broad-spectrum activity against both Gram-negative and Gram-positive bacteria and fungi. With non-hemolytic activity, resistance to protease hydrolysis, and easy sequence programmability, α-AApeptides may emerge as a novel class of antibiotics.     

Crosslinked Copolyimide Membranes for Phenol Recovery from Process Water by Pervaporation

The effectiveness of different copolyimide membranes in the process of recovering phenol from water by pervaporation has been investigated. The polyimides were obtained by the polycondensation of 6FDA (4,4′-hexafluoro-isopropylidene diphthalic anhydride) with different diamines. The diamines 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine), 6FpDA (4,4′-hexafluoro-isopropylidene dianiline), 6FpODA (4,4′-bis-(4′-aminophenoxyphenyl)hexafluoropropane), and DABA (3,5-diaminobenzoic acid) as a monomer providing a crosslinkable group, were used. In order to reach chemical stability at high phenol concentrations, the polymer structures were crosslinked with 1,10-decanediol and OFHD (2,2,3,3,4,4,5,5-octafluorohexanediol). Pervaporation experiments were performed at 60 °C, covering a concentration range of phenol between 2 and 11 wt. %. The best separation characteristics were obtained with a 6FDA-6FpDA/DABA 2:1 membrane crosslinked with 1,10-decanediol. Using a 7.8 wt. % phenol feed mixture, a total flux of 14 kg μm m⁻² h⁻¹ was reached with an enrichment of 40 wt. % phenol in the permeate. It was found that conditioning the membrane using high phenol concentrations (between 8 and 11 wt. %) is a necessary pretreatment in order to enhance the flux and improve enrichment, especially if process water with low phenol concentrations is to be treated. In addition to the experimental results, a comparison with rubbery membrane materials is presented in the discussion.     

Synthesis of 5-Alkyl- and 5-Phenylamino-Substituted Azothiazole Dyes with Solvatochromic and DNA-Binding Properties

A series of new 5-mono- and 5,5′-bisamino-substituted azothiazole derivatives was synthesized from the readily available diethyl azothiazole-4,4′-dicarboxylate. This reaction most likely comprises an initial Michael-type addition by the respective primary alkyl and aromatic amines at the carbon atom C5 of the substrate. Subsequently, the resulting intermediates are readily oxidized by molecular oxygen to afford the amino-substituted azothiazole derivatives. The latter exhibit remarkably red-shifted absorption bands (λ_abs=507–661 nm) with high molar extinction coefficients and show a strong positive solvatochromism. As revealed by spectrometric titrations and circular and linear dichroism studies, the water-soluble, bis-(dimethylaminopropylamino)-substituted azo dye associates with duplex DNA by formation of aggregates along the phosphate backbone at high ligand–DNA ratios (LDR) and by intercalation at low LDR, which also leads to a significant increase of the otherwise low emission intensity at 671 nm.     

Polyimidines,a new class of polymers. II. Polyhexamethylenetetraphenyldithiopyromellitimidine

Polyimidines have been shown to be soluble, thermally stable polymers. In searching for an alternate synthetic method the thio analog of this system has been discovered. The brightly colored (red-orange) perthio derivatives of 3,3-diphenylphthalide and 3,3,5,5-tetraphenyipyromellitide were synthesized from their oxo analogs with P₂S₅. The model compound thioimidines were synthesized by reacting 3,3-diphenyldithiophthalide with aniline and with 1,6-hexane diamine and by reacting 3,3,5,5-tetraphenyltetrathiopyromellitide with aniline and n-hexylamine. The polymerization of tetraphenyltetrathiopyromellitide occurred readily with 1,6-hexanediamine in boiling carbon tetrachloride with complete cyclization. This reaction gave an 80% yield with inherent viscosities up to 0.89 and molecular weights up to approximately 11,000. Thermogravimetric analysis showed a 2% weight loss at 200°C and 10% weight loss at 300°C with rapid decomposition above 300°C. Although the polythioimidine was less thermally stable than its oxo analog, it was much more soluble in common solvents (aromatic and chlorinated aliphatic hydrocarbons) and more readily synthesized in higher yield.     

Excess Chemical Potentials and Partial Molar Enthalpies in Aqueous 1,2- and 1,3-Propanediols at 25°C

Excess chemical potentials and excess partial molar enthalpies of 1,2- and 1,3-propanediols (abbreviated as 12P and 13P), ^E _i, and H ^E _i (i = 12P or 13P) were determined in the respective binary aqueous solutions at 25^°C. For both systems, the values of ^E _i are almost zero, within ±0.4 kJ-mol^–1. However, the excess partial molar enthalpies, H ^E _i show a sharp mole fraction dependence in the water-rich region. Thus, the systems are highly nonideal, in spite of almost zero ^E _i. Namely, the enthalpy-entropy compensation is almost complete. From the slopes of the H ^E _i against the respective mole fraction x _i we obtain the enthalpic interaction functions between solutes, H _i–i ^E, (i = 12P or 13P). Using these quantities and comparing them with the equivalent quantities for binary aqueous solutions of 1-propanol (1P), 2-propanol (2P), glycerol (Gly), and dimethyl sulfoxide (DMSO), we conclude that there are three composition regions in each of which mixing schemes are qualitatively different. Mixing Schemes II and III, operative in the intermediate and the solute-rich regions, seem similar in all the binary aqueous solutions mentioned above. Mixing Scheme I in the water-rich region is different from solute to solute. 12P shows a behavior similar to that of DMSO, which is somewhat different from typical hydrophobic solute, 1P or 2P. 13P, on the other hand, is less hydrophobic than 12P, and shows a behavior closer to glycerol, which shows hydrophilic behavior.     

Advancing understanding of actinide(iii) (Ac,Am, Cm) aqueous complexation chemistry

The positive impact of having access to well-defined starting materials for applied actinide technologies – and for technologies based on other elements – cannot be overstated. Of numerous relevant 5f-element starting materials, those in complexing aqueous media find widespread use. Consider acetic acid/acetate buffered solutions as an example. These solutions provide entry into diverse technologies, from small-scale production of actinide metal to preparing radiolabeled chelates for medical applications. However, like so many aqueous solutions that contain actinides and complexing agents, 5f-element speciation in acetic acid/acetate cocktails is poorly defined. Herein, we address this problem and characterize Ac³⁺ and Cm³⁺ speciation as a function of increasing acetic acid/acetate concentrations (0.1 to 15 M, pH = 5.5). Results obtained via X-ray absorption and optical spectroscopy show the aquo ion dominated in dilute acetic acid/acetate solutions (0.1 M). Increasing acetic acid/acetate concentrations to 15 M increased complexation and revealed divergent reactivity between early and late actinides. A neutral Ac(H₂O)₆₍₁₎(O₂CMe)₃₍₁₎ compound was the major species in solution for the large Ac³⁺. In contrast, smaller Cm³⁺ preferred forming an anion. There were approximately four bound O₂CMe¹⁻ ligands and one to two inner sphere H₂O ligands. The conclusion that increasing acetic acid/acetate concentrations increased acetate complexation was corroborated by characterizing (NH₄)₂M(O₂CMe)₅ (M = Eu³⁺, Am³⁺ and Cm³⁺) using single crystal X-ray diffraction and optical spectroscopy (absorption, emission, excitation, and excited state lifetime measurements).

Actinide complexation from aqueous acetic acid/acetate buffered solutions is described. The number of water ligands was directly correlated with the acetate concentration and characterized by X-ray absorption and optical spectroscopy.     

Ethyl and isopropyl 4‐ferrocenylbenzoate

The title compounds, [Fe(C₅H₅)(C₁₄H₁₃O₂)] and [Fe(C₅H₅)(C₁₅H₁₅O₂)], respectively, contain the ferrocenyl η⁵(C₅H₄) and phenyl­ene –C₆H₄– rings in a nearly coplanar arrangement, with interplanar angles of 6.88 (12) and 10.5 (2)°, respectively. Molecules of the ethyl ester form dimers through η⁵(C₅H₅)C—H⋯O=C hydrogen bonds, with graph set R(20), and, together with Csp³—H⋯π(C₅H₅) interactions, generate a one‐dimensional column (irregular ladder). Molecules of the iso­propyl ester aggregate through η⁵(C₅H₅)C—H⋯π(C₆H₄) interactions.