DFT Studies on the Mechanism of the Iridium-Catalyzed Formal [4 + 1] Cycloaddition of Biphenylene with Alkenes

Recently, we reported an Ir-catalyzed formal [4 + 1] cycloaddition of biphenylenes with alkenes, which gave 9,9-disubstituted fluorenes in moderate to excellent yields. We proposed a reaction mechanism that involved the intermolecular insertion of alkenes, β-elimination, and intramolecular insertion based on the results of experimental mechanistic studies. Herein, we further support the proposed mechanism by density functional theory calculations and explain why [4 + 1] cycloaddition proceeds rather than conventional [4 + 2] cycloaddition

Aggregation Number in Water/<i>n</i>‑Hexanol Molecular Clusters Formed in Cyclohexane at Different Water/<i>n</i>‑Hexanol/Cyclohexane Compositions Calculated by Titration ¹H NMR

Upon titration of <i>n</i>-hexanol/cyclohexane mixtures of different molar compositions with water, water/<i>n</i>-hexanol clusters are formed in cyclohexane. Here, we develop a new method to estimate the water and <i>n</i>-hexanol aggregation numbers in the clusters that combines integration analysis in one-dimensional ¹H NMR spectra, diffusion coefficients calculated by diffusion-ordered NMR spectroscopy, and further application of the Stokes–Einstein equation to calculate the hydrodynamic volume of the clusters. Aggregation numbers of 5–15 molecules of <i>n</i>-hexanol per cluster in the absence of water were observed in the whole range of <i>n</i>-hexanol/cyclohexane molar fractions studied. After saturation with water, aggregation numbers of 6–13 <i>n</i>-hexanol and 0.5–5 water molecules per cluster were found. O–H and O–O atom distances related to hydrogen bonds between donor/acceptor molecules were theoretically calculated using density functional theory. The results show that at low <i>n</i>-hexanol molar fractions, where a robust hydrogen-bond network is held between <i>n</i>-hexanol molecules, addition of water makes the intermolecular O–O atom distance shorter, reinforcing molecular association in the clusters, whereas at high <i>n</i>-hexanol molar fractions, where dipole–dipole interactions dominate, addition of water makes the intermolecular O–O atom distance longer, weakening the cluster structure. This correlates with experimental NMR results, which show an increase in the size and aggregation number in the clusters upon addition of water at low <i>n</i>-hexanol molar fractions, and a decrease of these magnitudes at high <i>n</i>-hexanol molar fractions. In addition, water produces an increase in the proton exchange rate between donor/acceptor molecules at all <i>n</i>-hexanol molar fractions

Stability of Water/Poly(ethylene oxide)₄₃<i>-b-</i>poly(ε-caprolactone)₁₄/Cyclohexanone Emulsions Involves Water Exchange between the Core and the Bulk

The formation of emulsions upon reverse self-association of the monodisperse amphiphilic block copolymer poly­(ethylene oxide)₄₃<i>-<i>b</i>-</i>poly­(ε-caprolactone)₁₄ in cyclohexanone is reported. Such emulsions are not formed in toluene, chloroform, or dichloromethane. We demonstrate by magnetic resonance spectroscopy the active role of the solvent on the stabilization of the emulsions. Cyclohexanone shows high affinity for both blocks, as predicted by the Hansen solubility parameters, so that the copolymer chains are fully dissolved as monomeric chains. In addition, the solvent is able to produce hydrogen bonding with water molecules. Water undergoes molecular exchange between water molecules associated with the polymer and water molecules associated with the solvent, dynamics of major importance for the stabilization of the emulsions. Association of polymeric chains forming reverse aggregates is induced by water over a concentration threshold of 5 wt %. Reverse copolymer aggregates show submicron average hydrodynamic diameters, as seen by dynamic light scattering, depending on the polymer and water concentration

Structural Insights into a Hemoglobin–Albumin Cluster in Aqueous Medium

A hemoglobin (Hb) wrapped covalently by three human serum albumins (HSAs) is a triangular protein cluster designed as an artificial O₂-carrier and red blood cell substitute. We report the structural insights into this Hb-HSA₃ cluster in aqueous medium revealed by 3D reconstruction based on cryogenic transmission electron microscopy (cryo-TEM) data and small-angle X-ray scattering (SAXS) measurements. Cryo-TEM observations showed individual particles with approximately 15 nm diameter in the vitrified ice layer. Subsequent image processing and 3D reconstruction proved the expected spatial arrangements of an Hb in the center and three HSAs at the periphery. SAXS measurements demonstrated the monodispersity of the Hb-HSA₃ cluster having a molecular mass of 270 kDa. The pair-distance distribution function suggested the existence of oblate-like particles with a maximum dimeter of ∼17 nm. The supramolecular 3D structure reconstructed from the SAXS intensity using an <i>ab initio</i> procedure was similar to that obtained from cryo-TEM data