Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force.

The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles1,2. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins3. Here, we report a molecular design based on oligo calix[4]arene catenanes—calixarene dimers held together by 16 hydrogen bridges—in which loops within the molecules limit how far the calixarene nanocapsules can be separated. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual n…

Unravelling the fine structure of stacked bipyridine diamine-derived C-3-discotics as determined by X-ray diffraction, quantum-chemical calculations, Fast-MAS NMR and CD spectroscopy

An in depth investigation of the fine structure adopted by the helical stacks of C3-discotics 1 incorporating three 3,3'-diamino-2,2'-bipyridine units is described. In the bulk the molecules display liquid crystalline behaviour in a temperature window of >300 K and an ordered rectangular columnar mesophase (Colro) with an inter-disc distance of 3.4 Å is assigned. X-Ray diffraction on aligned samples has also revealed a helical superstructure in the liquid crystalline state, and a rotation angle of 13–16° between consecutive discs. The proposed superstructure in the bulk phase has been further substantiated by a combination of quantum-chemical calculations and solid-state NMR spectroscopy…

Reversible hydrogen bond network dynamics: molecular dynamics simulations of calix[4]arene-catenanes.

We present detailed molecular dynamics (MD) simulations of mechanically interlocked calix[4]arene-catenanes under external force. Single-molecule force spectroscopy experiments revealed that the separation of dimers with two aliphatic loops results in reversible hydrogen bond breakage through an intermediate in a triple-well potential, while the tetra-loop species separates in a one-step manner (Janke, M.; et al. Nat. Nanotechnol. 2009, 4, 225). MD simulations show that calix[4]arenes interlocked by four loops (1) display a complete restructuring of the hydrogen bond network under mechanical force. All hydrogen bonds of the closed structure open, and new ones are formed in the extended stru…

Practical Synthesis of Vinyl-Substitutedp-Phenylenevinylene Oligomers and Their Triethoxysilyl Derivatives

Luminescent semiconducting organic compounds are widely used as active layers in electro-optical devices. Apart from conjugated polymers, monodisperse oligomers also represent attractive materials. The synthesis of stilbenoid oligomers with polymerizable end groups is presented. Oligo(phenylenevinylene)s with terminal vinyl groups 17–19 are prepared in good yields by Horner–Emmons olefinations or by the Heck reaction of the iodo-substituted oligomers 15, 16 with compressed ethene. Triethoxysilyl groups can be linked via rigid 1,2-vinylene units to the chromophores 26–30, either in the direct reaction of 14, 24 with silanes 21, 22 or by cross-metathesis of 17–19 with the vinylsilanes 21, 22 …

Determining the Geometry of Hydrogen Bonds in Solids with Picometer Accuracy by Quantum-Chemical Calculations and NMR Spectroscopy

The structure of multiply hydrogen-bonded systems is determined with picometer accuracy by a combined solid-state NMR and quantum-chemical approach. On the experimental side, advanced 1H-15N dipolar recoupling NMR techniques are capable of providing proton-nitrogen distances of up to about 250 pm with an accuracy level of +/-1 pm for short distances (i.e., around 100 pm) and +/-5 pm for longer ones (i.e., 180 to 250 pm). The experiments were performed under fast magic-angle spinning, which ensures sufficient dipolar decoupling and spectral resolution of the 1H resonance lines. On the quantum-chemical side, the structures of the hydrogen-bonded systems were computationally optimised, yieldin…

Mechanical Properties of Single Molecules and Polymer Aggregates

This chapter deals with the mechanical properties of single polymer chains, aggregates, and supramolecular complexes. The topics discussed cover a broad range from fundamental statistical mechanics of the equilibrium elastic properties of single polymer chains to details of the behavior of binding pockets in biomolecular assemblies as observed by force spectroscopy. The first section treats the equilibrium mechanical properties of single polymer chains in various environments, investigated via extensive simulations employing coarse-grained models that have proven extremely successful in many branches of polymer physics, namely the bond-fluctuation model and the self-avoiding walk model. Apa…

Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH.

Sulfenic acid (HSOH, 1) has been synthesized in the gas-phase by low-pressure high-temperature (1150 degrees C) pyrolysis of di-tert-butyl sulfoxide (tBu(2)SO, 2) and characterized by means of matrix isolation and gas-phase IR spectroscopy. High-level coupled-cluster (CC) calculations (CCSD(T)/cc-pVTZ and CCSD(T)/cc-pVQZ) support the first identification of the gas-phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix-isolated 1 have been assigned, and its rotational-resolved gas-phase IR spectrum provides additional information on the O-H and S-H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrome…

Parallel Calculation of CCSD and CCSD(T) Analytic First and Second Derivatives.

In this paper we present a parallel adaptation of a highly efficient coupled-cluster algorithm for calculating coupled-cluster singles and doubles (CCSD) and coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations (CCSD(T)) energies, gradients, and, for the first time, analytic second derivatives. A minimal-effort strategy is outlined that leads to an amplitude-replicated, communication-minimized implementation by parallelizing the time-determining steps for CCSD and CCSD(T). The resulting algorithm is aimed at affordable cluster architectures consisting of compute nodes with sufficient memory and local disk space and that are connected by standard co…

Papers accepted for publication in The Analyst