Interpenetrated Cage Structures

This Review covers design strategies, synthetic challenges, host–guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal–organic frameworks, but the main focus is on discrete coordination architectures, that is, metal‐mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana‐shaped bis‐pyridyl ligands together with square‐planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double‐cages obeying the formula [M₄L₈]. The peculiar topology of these double‐cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template‐controlled selectivity. In stimuli‐responsive systems, anionic triggers can toggle the binding of neutral guests or even induce complete structural conversions. The increasing structural and functional complexity in this class of self‐assembled hosts promises the construction of intelligent receptors, novel catalytic systems, and functional materials.     

Accessing Frustrated Lewis Pair Chemistry from a Spectroscopically Stable and Classical Lewis Acid‐Base Adduct

B(C₆F₅)₃ and P(MeNCH₂CH₂)₃N form a classical Lewis adduct, (C₆F₅)₃BP(MeNCH₂CH₂)₃N. Although (C₆F₅)₃BP(MeNCH₂CH₂)₃N does not exhibit spectroscopic evidence of dissociation into its constituent acid and base, products of frustrated Lewis pair (FLP) addition reactions are seen with PhNCO, PhCH₂N₃, PhNSO, and CO₂. Computational studies show that thermal access to the dissociated acid and base permits FLP reactivity to proceed. These results demonstrate that FLP reactivity extends across the entire continuum of equilibria governing Lewis acid‐base adducts.     

Hydrogen‐bond patterns in the congruent complex 4‐nitrophenol–acetamide (1/1)

Fusion of 4‐nitrophenol and acetamide in a 1:1 molar ratio gives the title product, C₆H₅NO₃·C₂H₅NO, (III), which has the character of a pure covalently bonded compound, having a high sharp melting point. Complex (III) (m.p. 371.9–372.9 K) can be recrystallized from various solvents and forms eutectics with either acetamide or 4‐nitrophenol. Similar fusion of mixtures of acetamide and 2‐nitrophenol yields no complex similar to (III) and mixtures of acetamide and 3‐nitrophenol produce only a weak low‐melting complex. The significance of this study lies in its demonstration, via graph set analysis, that some of the patterns found individually in crystalline acetamide or 4‐nitrophenol have been preserved in crystals of complex (III), while several higher order graph sets are produced in (III) due to new hydrogen bonds involving the nitro group. In particular, large hydrogen‐bonded rings are formed together with helical chains.     

Is there potential for use of the Hall effect in analytical science?

This article describes the basic principles of the Hall effect and how it has been applied in solid state applications to measure both the magnetic field and material properties. This is followed by an outline of research undertaken in aqueous ionic solutions as a possible precursor to application in chemical studies. However, previous research has shown that factors such as the Nernst effect have reduced the success of reliably measuring the Hall voltage under these conditions. The possibility of a multi-sensing approach using both electrical and acoustic Hall voltages to overcome these challenges is discussed. The article concludes with a brief look at some early efforts to detect biomolecular interactions.     

Noncontact all-optical measurement of corneal elasticity

We report on a noninvasive and noncontact all-optical method to measure the elasticity of the cornea. We use a pulsed laser to excite surface acoustic waves (SAW) that propagate on the corneal surface, then use a phase-sensitive optical coherence tomography system to remotely record the SAWs from which the corneal elasticity is estimated. In addition, the system is able to provide real-time tomographic images of the cornea being examined, an important consideration for clinical studies. While precisely maintaining a range of intraocular pressures (IOP), a series of measurements is performed on ex vivo intact primate eyes. The measurement results not only demonstrate the feasibility of the proposed system to remotely measure the corneal elasticity, but also suggest a strong correlation between the corneal stiffness and the true IOP.     

A structure determination protocol based on combined analysis of 3D-ED data,powder XRD data,solid-state NMR data and DFT-D calculations reveals the structure of a new polymorph of l-tyrosine

We report the crystal structure of a new polymorph of l-tyrosine (denoted the β polymorph), prepared by crystallization from the gas phase following vacuum sublimation. Structure determination was carried out by combined analysis of three-dimensional electron diffraction (3D-ED) data and powder X-ray diffraction (XRD) data. Specifically, 3D-ED data were required for reliable unit cell determination and space group assignment, with structure solution carried out independently from both 3D-ED data and powder XRD data, using the direct-space strategy for structure solution implemented using a genetic algorithm. Structure refinement was carried out both from powder XRD data, using the Rietveld profile refinement technique, and from 3D-ED data. The final refined structure was validated both by periodic DFT-D calculations, which confirm that the structure corresponds to an energy minimum on the energy landscape, and by the fact that the values of isotropic ¹³C NMR chemical shifts calculated for the crystal structure using DFT-D methodology are in good agreement with the experimental high-resolution solid-state ¹³C NMR spectrum. Based on DFT-D calculations using the PBE0-MBD method, the β polymorph is meta-stable with respect to the previously reported crystal structure of l-tyrosine (now denoted the α polymorph). Crystal structure prediction calculations using the AIRSS approach suggest that there are three other plausible crystalline polymorphs of l-tyrosine, with higher energy than the α and β polymorphs.

A new polymorph of l-tyrosine is reported, with the crystal structure determined by combined analysis of 3D-ED data and powder XRD data, augmented by information from periodic DFT-D calculations and solid-state ¹³C NMR data.     

Solvent effects in the chlorination of tetrahydrothiophens with n-chlorosuccinimide

Depending simply on solvent, the reaction of N-chlorosuccinimide with tetrahydrothiophen can be arranged to give either 2-chloro-tetrahydrothiophen or 2,3-dichlorotetrahydrothiophen. In the latter case, a novel compound, 2-(4-chlorobutylthio)thiophen was isolated also. For 2-methyl- and 2,5-dimethyltetrahydrothiophen the solvent dependency was almost entirely eliminated, the principal reaction products being those resulting from dichlorination.