Partitioning Solvophobic and Dispersion Forces in Alkyl and Perfluoroalkyl Cohesion

Fluorocarbons often have distinct miscibility properties compared to their nonfluorinated analogues. These differences may be attributed to van der Waals dispersion forces or solvophobic effects, but their contributions are notoriously difficult to separate in molecular recognition processes. Here, molecular torsion balances were used to compare cohesive alkyl and perfluoroalkyl interactions in a range of solvents. A simple linear regression enabled the energetic partitioning of solvophobic and van der Waals forces in the self‐association of apolar chains. The contributions of dispersion interactions in apolar cohesion were found to be strongly attenuated in solution compared to the gas phase, but still play a major role in fluorous and organic solvents. In contrast, solvophobic effects were found to be dominant in driving the association of apolar chains in aqueous solution. The results are expected to assist the computational modelling of van der Waals forces in solution.     

Reconciling Electrostatic and n→π* Orbital Contributions in Carbonyl Interactions

Interactions between carbonyl groups are prevalent in protein structures. Earlier investigations identified dominant electrostatic dipolar interactions, while others implicated lone pair n→π* orbital delocalisation. Here these observations are reconciled. A combined experimental and computational approach confirmed the dominance of electrostatic interactions in a new series of synthetic molecular balances, while also highlighting the distance-dependent observation of inductive polarisation manifested by n→π* orbital delocalisation. Computational fiSAPT energy decomposition and natural bonding orbital analyses correlated with experimental data to reveal the contexts in which short-range inductive polarisation augment electrostatic dipolar interactions. Thus, we provide a framework for reconciling the context dependency of the dominance of electrostatic interactions and the occurrence of n→π* orbital delocalisation in C=O⋅⋅⋅C=O interactions.     

An Autonomously Reciprocating Transmembrane Nanoactuator

Biological molecular machines operate far from equilibrium by coupling chemical potential to repeated cycles of dissipative nanomechanical motion. This principle has been exploited in supramolecular systems that exhibit true machine behavior in solution and on surfaces. However, designed membrane‐spanning assemblies developed to date have been limited to simple switches or stochastic shuttles, and true machine behavior has remained elusive. Herein, we present a transmembrane nanoactuator that turns over chemical fuel to drive autonomous reciprocating (back‐and‐forth) nanomechanical motion. Ratcheted reciprocating motion of a DNA/PEG copolymer threaded through a single α‐hemolysin pore was induced by a combination of DNA strand displacement processes and enzyme‐catalyzed reactions. Ion‐current recordings revealed saw‐tooth patterns, indicating that the assemblies operated in autonomous, asymmetric cycles of conformational change at rates of up to one cycle per minute.     

Uniform upconversion in high-concentration Er(3+)-doped soda lime silicate and aluminosilicate glasses

Uniform upconversion in erbium-doped silicate glasses is investigated as a function of glass composition, concentration, and fabrication method. Comparisons of upconversion coefficients are made among soda lime silicate and aluminosilicate bulk glasses and soda lime silicate waveguides. Comparisons are also made with studies performed by other researchers. The results indicate that both the composition and the preparation method of the glass affect the value of the upconversion coefficient, with as much as a factor-of-4 variation observed at fixed Er(3+) concentration. Values of the upconversion coefficient are found to be consistent with the F?rster-Dexter microscopic model.     

LnHal2Hn ? Neue Phasen in den ternären Systemen Ln/Hal/H. I. Strukturen

LnHal₂H_n — New Phases in the Ternary System Ln/Hal/H. I. Structures Rare earth hydride halides of the compositions LaBr₂(H,D)_0.90, CeBr₂H_0.87, Cel₂H_0.90, Cel₂D_0.96, and GdI₂H_0.97 have been synthesised by heating either the dihalides, LnHal₂, or mixtures of LnHal₃ and LnH_x at 700°C ?800°C in hydrogen atmosphere. The heavy atom partial structures, as determined by X-ray scattering, correspond to the various sequences found in MoS₂ and NbS₂. From neutron scattering experiments the hydrogen atoms were located in the positions centering the anionic prisms and the cationic triangles.     

Desolvation tips the balance: solvent effects on aromatic interactions

The folding behaviour of the molecular torsion balance framework is rationalised by considering the effects of solvation using the alpha/beta H-bond parameter scheme for estimating the free energies of pairwise functional group interactions in solution.