An Ortho-Tetraphenylene-Based "Geländer" Architecture Consisting Exclusively of 52 sp2 -Hybridized C Atoms

A new type of "Geländer" molecule based on a ortho-tetraphenylene core is presented. The central para-quaterphenyl backbone is wrapped by a 4,4'-di((Z)-styryl)-1,1'-biphenyl banister, with its aryl rings covalently attached to all four phenyl rings of the backbone. The resulting helical chiral bicyclic architecture consists exclusively of sp2 -hybridized carbon atoms. The target structure was assembled by expanding the central ortho-tetraphenylene subunit with the required additional phenyl rings followed by a twofold macrocyclization. The first macrocyclization attempts based on a twofold McMurry coupling were successful but low yielding; the second strategy, profiting from olefin metathesis, provided satisfying yields. Hydrogenation of the olefins resulted in a saturated derivative of similar topology, thereby allowing the interdependence between saturation and physico-chemical properties to be studied. The target structures, including their solid-state structures, were fully characterized. The helical chiral bicycle was synthesized as a racemate and separated into pure enantiomers by HPLC on a chiral stationary phase. Comparison of recorded and simulated chiroptical properties allowed the enantiomers to be assigned.

Substitution Pattern Controlled Quantum Interference in [2.2]Paracyclophane-Based Single-Molecule Junctions

Quantum interference (QI) of electron waves passing through a single-molecule junction provides a powerful means to influence its electrical properties. Here, we investigate the correlation between substitution pattern, conductance, and mechanosensitivity in [2.2]paracyclophane (PCP)-based molecular wires in a mechanically controlled break junction experiment. The effect of the meta versus para connectivity in both the central PCP core and the phenyl ring connecting the terminal anchoring group is studied. We find that the meta-phenyl-anchored PCP yields such low conductance levels that molecular features cannot be resolved; in the case of para-phenyl-coupled anchoring, however, large variations in conductance values for modulations of the electrode separation occur for the pseudo-para-coupled PCP core, while this mechanosensitivity is absent for the pseudo-meta-PCP core. The experimental findings are interpreted in terms of QI effects between molecular frontier orbitals by theoretical calculations based on density functional theory and the Landauer formalism.

Synthesis and Surface Behaviour of NDI Chromophores Mounted on a Tripodal Scaffold: Towards Self-Decoupled Chromophores for Single-Molecule Electroluminescence

This paper reports the efficient synthesis, absorption and emission spectra, and the electrochemical properties of a series of 2,6-disubstituted naphthalene-1,4,5,8-tetracarboxdiimide (NDI) tripodal molecules with thioacetate anchors for their surface investigations. Our studies showed that, in particular, the pyrrolidinyl group with its strong electron-donating properties enhanced the fluorescence of such core-substituted NDI chromophores and caused a significant bathochromic shift in the absorption spectrum with a correspondingly narrowed bandgap of 1.94 eV. Cyclic voltammetry showed the redox properties of NDIs to be influenced by core substituents. The strong electron-donating character of pyrrolidine substituents results in rather high HOMO and LUMO levels of -5.31 and -3.37 eV when compared with the parental unsubstituted NDI. UHV-STM measurements of a sub-monolayer of the rigid tripodal NDI chromophores spray deposited on Au(111) show that these molecules mainly tend to adsorb flat in a pairwise fashion on the surface and form unordered films. However, the STML experiments also revealed a few molecular clusters, which might consist of upright oriented molecules protruding from the molecular island and show electroluminescence photon spectra with high electroluminescence yields of up to 6×10-3 . These results demonstrate the promising potential of the NDI tripodal chromophores for the fabrication of molecular devices profiting from optical features of the molecular layer.

Monitoring Solid-Phase Reactions in Self-Assembled Monolayers by Surface-Enhanced Raman Spectroscopy

Nanopatterned surfaces enhance incident electromagnetic radiation and thereby enable the detection and characterization of self-assembled monolayers (SAMs), for instance in surface-enhanced Raman spectroscopy (SERS). Herein, Au nanohole arrays, developed and characterized as SERS substrates, are exemplarily used for monitoring a solid-phase deprotection and a subsequent copper(I)-catalyzed azide-alkyne cycloaddition "click" reaction, performed directly on the corresponding SAMs. The SERS substrate was found to be highly reliable in terms of signal reproducibility and chemical stability. Furthermore, the intermediates and the product of the solid-phase synthesis were identified by SERS. The spectra of the immobilized compounds showed minor differences compared to spectra of the microcrystalline solids. With its uniform SERS signals and the high chemical stability, the platform paves the way for monitoring molecular manipulations in surface functionalization applications.

Monofunctionalized Gold Nanoparticles: Fabrication and Applications

An overview of various approaches to synthesize gold nanoparticles (AuNPs) bearing one single chemically addressable unit and their diverse fields of application is presented. This comprehensive review not only describes the strategies pursued to obtain monofunctionalized AuNPs, but also reports their behavior as 'massive' molecules in wet chemical protocols and the scope of their applications. The latter reaches from site-specific labels in biomolecules over mechanical barriers in superstructures to building blocks in hybrid nano-architectures. The complementing physical properties of AuNPs combined with precise chemical control of their attachment makes these objects promising building blocks for numerous proof-of-concept experiments and applications.

Bicyclic Phenyl-Ethynyl Architectures: Synthesis of a 1,4-Bis(phenylbuta-1,3-diyn-1-yl) Benzene Banister

The novel diacetylene bridged terphenylic macrocycle 1 is presented and discussed in the context of rotationally restricted “Geländer” oligomers. The 1,4‐bis(phenylbuta‐1,3‐diyn‐1‐yl) benzene bridge of diacetylene 1 is significantly longer than its terphenyl backbone, forcing the bridge to bend around the central pylon. The synthesis of molecule 1 is based to a large extent on acetylene scaffolding strategies, profiting from orthogonal alkyne protection groups to close both macrocyclic subunits by oxidative acetylene coupling sequentially. The spatial arrangement and the dynamic enantiomerization process of the bicyclic target structure 1 are analyzed. In‐depth NMR investigations not only reveal an unexpected spatial arrangement with both oligomer strands bent alongside the backbone, but also display the limited stability of the model compound in the presence of molecular oxygen.

Enantiomeric Separation of Semiconducting Single-Walled Carbon Nanotubes by Acid Cleavable Chiral Polyfluorene

Helical wrapping by conjugated polymer has been demonstrated as a powerful tool for the sorting of single-walled carbon nanotubes (SWCNTs) according to their electronic type, chiral index, and even handedness. However, a method of one-step extraction of left-handed (M) and right-handed (P) semiconducting SWCNTs (s-SWCNTs) with subsequent cleavage of the polymer has not yet been published. In this work, we designed and synthesized one pair of acid cleavable polyfluorenes with defined chirality for handedness separation of s-SWCNTs from as-produced nanotubes. Each monomer contains a chiral center on the fluorene backbone in the 9-position, and the amino and carbonyl groups in the 2- and 7-positions maintain the head-to-tail regioselective polymerization resulting in polyimines with strictly all-(R) or all-(S) configuration. The obtained chiral polymers exhibit a strong recognition ability toward left- or right-handed s-SWCNTs from commercially available CoMoCAT SWCNTs with a sorting process requiring only bath sonication and centrifugation. Interestingly, the remaining polymer on each single nanotube, which helps to prevent aggregation, does not interfere with the circular dichroism signals from the nanotube at all. Therefore, we observed all four interband transition peaks (E₁₁, E₂₂, E₃₃, E₄₄) in the circular dichroism (CD) spectra of the still wrapped optically enriched left-handed and right-handed (6,5) SWCNTs in toluene. Binding energies obtained from molecular dynamics simulations were consistent with our experimental results and showed a significant preference for one specific handedness from each chiral polymer. Moreover, the imine bonds along the polymer chains enable the release of the nanotubes upon acid treatment. After s-SWNT separation, the polymer can be decomposed into monomers and be cleanly removed under mild acidic conditions, yielding dispersant-free handedness sorted s-SWNTs. The monomers can be almost quantitatively recovered to resynthesize the chiral polymer. This approach enables high selective isolation of polymer-free s-SWNT enantiomers for their further applications in carbon nanotube (CNT) devices.

Addressing a lattice of rotatable molecular dipoles with the electric field of an STM tip

Functional molecular groups mounted on specific foot structures are ideal model systems to study intermolecular interactions, due to the possibility to separate the functionality and the adsorption mechanism. Here, we report on the rotational switching of a thioacetate group mounted on a tripodal tetraphenylmethane (TPM) derivative adsorbed in ordered islands on a Au(111) surface. Using low temperature scanning tunnelling microscopy, individual freestanding molecular groups of the lattice can be switched between two bistable orientations. The functional dependence of this rotational switching on the sample bias and tip-sample distance allows us to model the energy landscape of this molecular group as an electric dipole in the electric field of the tunnelling junction. As expected for the interaction of two dipoles, we found states of neighbouring molecules to be correlated.

Aqueous assembly of a (pseudo)rotaxane with a donor–π–acceptor axis formed by a Knoevenagel condensation

The incorporation of a linear D–π–A “push–pull” chromophore synthesized by a Knoevenagel condensation as axle of a rotaxane is reported.

Synthesis and Transport Studies of a Cofacial Porphyrin Cyclophane

Porphyrin cyclophane 1, consisting of two rigidly fixed but still movable cofacial porphyrins and exposing acetate-masked thiols in opposed directions of the macrocycle, is designed, synthesized, and characterized. The functional cyclophane 1, as pioneer of mechanosensitive 3D materials, forms stable single-molecule junctions in a mechanically controlled break-junction setup. Its reliable integration in a single-molecule junction is a fundamental prerequisite to explore the potential of these structures as mechanically triggered functional units and devices.

Iron in a Cage: Fixation of a Fe(II)tpy2 Complex by Fourfold Interlinking

The coordination sphere of the Fe(II) terpyridine complex 1 is rigidified by fourfold interlinking of both terpyridine ligands. Profiting from an octa-aldehyde precursor complex, the ideal dimensions of the interlinking structures are determined by reversible Schiff-base formation, before irreversible Wittig olefination provided the rigidified complex. Reversed-phase HPLC enables the isolation of the all-trans isomer of the Fe(II) terpyridine complex 1, which is fully characterized. While temperature independent low-spin states were recorded with superconducting quantum interference device (SQUID) measurements for both, the open precursor 8 and the interlinked complex 1, evidence of the increased rigidity of the ligand sphere in 1 was provided by proton T2 relaxation NMR experiments. The ligand sphere fixation in the macrocyclized complex 1 even reaches a level resisting substantial deformation upon deposition on an Au(111) surface, as demonstrated by its pristine form in a low temperature ultra-high vacuum scanning tunneling microscope experiment.

Matter-wave interference and deflection of tripeptides decorated with fluorinated alkyl chains

Studies of neutral biomolecules in the gas phase allow for the study of molecular properties in the absence of solvent and charge effects, thus complementing spectroscopic and analytical methods in solution or in ion traps. Some properties, such as the static electronic susceptibility, are best accessed in experiments that act on the motion of the neutral molecules in an electric field. Here, we screen seven peptides for their thermal stability and electron impact ionizability. We identify two tripeptides as sufficiently volatile and thermostable to be evaporated and interfered in the long-baseline universal matter-wave interferometer. Monitoring the deflection of the interferometric molecular nanopattern in a tailored external electric field allows us to measure the static molecular susceptibility of Ala-Trp-Ala and Ala-Ala-Trp bearing fluorinated alkyl chains at C- and N-termini. The respective values are 4 π ε 0 × 330 ± 150 Å 3 and 4 π ε 0 × 270 ± 80 Å 3 .

AB1290-HPR UTILITY OF FRAX IN THE RISK DETECTION OF FRACTURE IN SPONDYLOARTHRITIS

Background:

Axial spondyloarthritis (SpAax) presents an increased risk of vertebral fracture not fully detected by Dual energy X-ray absorptiometry (DXA). The FRAX algorithms give the 10-year probability of hip fracture and of mayor osteoporotic fracture (clinical spine, forearm, hip or shoulder fracture), taking into account 11 clinical risk factors.

Objectives:

To analyze the suitability of FRAX to detect the risk of fracture in patients with SpAax. To assess whether the incorporation of SpAax as a clinical risk factor to conventional FRAX provides additional information.

Methods:

Cross-sectional study in which SpAax patients (ASAS criteria) were included. Clinical-demographic and related to the disease variables were collected. FRIDEX model for Spanish population was used to determine low, intermediate or high risk of mayor fracture by FRAX. These results were compared with those obtained by DXA and trabecular bone score (TBS). In the statistical analysis we used mean and standard deviation (SD) in quantitative variables and frequency in qualitative ones. To compare means among 3 groups, ANOVA test was used.

Results:

The characteristics of the patients are shown in Table 1. According to FRIDEX, no patient had high risk of fracture and 2.4% had intermediate risk. When SpAax was added as a risk factor, no patient had high risk of fracture and 6.1% presented intermediate risk. According to DXA, 7.3% had high risk of fracture and 41.3% intermediate risk. TBS detected high risk of fracture in 18.3% and intermediate risk also in 18.3% of patients.

Table 1.

Sociodemographic, clinical and related characteristics with the disease (BMD: bone mineral density, BMI: index of body mass)

Gender (Male), n (%)61 (74.4)Age, mean ± SD49.48 ± 12.47BMI, mean ± SD27.13 ± 4.42Smoking, n (%)26 (31.7)Diabetes mellitus, n (%)9 (11)Osteoporotic fracture, n (%)1 (1.2)Disease duration (years), mean ± SD11.77 ± 10syndesmophytes, n (%)38 (46.3)ASDAS-PCR, mean ± SD2.55 ± 1.07Lumbar BMD (g / cm2), mean ± SD1.032 ± 0.180BMD femoral neck (g / cm2), mean ± SD0.816 ± 0.140Lumbar TBS, mean ± SD1.383 ± 0.133

Conclusion:

FRAX does not seem an adequate tool to detect the risk of fracture in patients with SpAax since it did not improve the results obtained by DXA meanwhile TBS did. The incorporation of SpAax as a clinical risk factor to conventional FRAX did not provide additional information in most cases

Disclosure of Interests:

None declared

Chirality sensing of terpenes, steroids, amino acids, peptides and drugs with acyclic cucurbit[n]urils and molecular tweezers

Achiral chromophoric hosts, i.e. acyclic cucurbit[n]urils and molecular tweezers, were found to respond with characteristic Circular Dichroism (CD) spectra to the presence of micromolar concentrations of chiral hydrocarbons, terpenes, steroids, amino acids and their derivates, and drugs in water. In favourable cases, this allows for analyte identification or for reaction monitoring.

Improved Photostability of a CuI Complex by Macrocyclization of the Phenanthroline Ligands

The development of molecular materials for conversion of solar energy into electricity and fuels is one of the most active research areas, in which the light absorber plays a key role. While copper(I)‐bis(diimine) complexes [Cu^I(L)₂]⁺ are considered as potent substitutes for [Ru^II(bpy)₃]²⁺, they exhibit limited structural integrity as ligand loss by substitution can occur. In this article, we present a new concept to stabilize copper bis(phenanthroline) complexes by macrocyclization of the ligands which are preorganized around the Cu^I ion. Using oxidative Hay acetylene homocoupling conditions, several Cu^I complexes with varying bridge length were prepared and analyzed. Absorption and emission properties are assessed; rewardingly, the envisioned approach was successful since the flexible 1,4‐butadiyl‐bridged complex does show enhanced MLCT absorption and emission, as well as improved photostability upon irradiation with a blue LED compared to a reference complex.

2-(3-Cyanopropyldimethylsilyl)ethyl as a Polar Sulfur Protecting Group

Organosulfur compounds are ubiquitous in synthetic chemistry, biology and materials chemistry. The reactivity of free sulfhydryls requires their masking in many synthetic strategies. To facilitate the isolation of protected thiols by chromatography, we propose 2-(3-cyanopropyldimethylsilyl)ethyl as a polar protecting group analogue of 2-(trimethylsilyl)ethyl. The masked thiophenol is obtained in two synthetically complementing ways. Either an existing thiophenol is protected, or the protected thiol group is introduced by a cross-coupling reaction. In both cases the required reagents are readily available from inexpensive starting materials. Thiol protection and thiol introduction both tolerate a large variety of functional groups and substitution patterns, and the protected thiophenols are stable toward a broad range of reaction conditions. The stability of the protected derivatives in cross-coupling reactions and the mild reaction conditions for the release of the protecting group further emphasizes the potential of the methodology.