Just over a century ago, Lewis published his seminal work on what became known as the covalent bond, which has since occupied a central role in the theory of making organic molecules. With the advent of covalent organic frameworks (COFs), the chemistry of the covalent bond was extended to two- and three-dimensional frameworks. Here, organic molecules are linked by covalent bonds to yield crystalline, porous COFs from light elements (boron, carbon, nitrogen, oxygen, and silicon) that are characterized by high architectural and chemical robustness. This discovery paved the way for carrying out chemistry on frameworks without losing their porosity or crystallinity, and in turn achieving designed properties in materials. The recent union of the covalent and the mechanical bond in the COF provides the opportunity for making woven structures that incorporate flexibility and dynamics into frameworks.

http://science.sciencemag.org/content/sci/355/6328/eaal1585.full.pdf

The atom, the molecule, and the covalent organic framework

Carrier-Based Ion-Selective Electrodes and Bulk Optodes. 1. General Characteristics.

Although there are no fundamental factors hindering the development of nanoscale structures, there is a growing realization that “engineering down” approaches, in other words a reduction in the size of structures generated by lithographic techniques below the present lower limit of roughly 1 μm, may become impractical. It has, therefore, become increasingly clear that only by the development of a fundamental understanding of the self-assembly of large-scale biological structures, which exist and function at and beyond the nanoscale, downwards, and the extension of our knowledge regarding the chemical syntheses of small-scale structures upwards, can the gap between the promise and the reality of nanosystems be closed. This kind of construction of nanoscale structures and nanosystems represents the so-called “bottom up” or “engineering up” approach to device fabrication. Significant progress can be made in the development of nanoscience by transferring concepts found in the biological world into the chemical arena. Central to this mission is the development of simple chemical systems capable of instructing their own organization into large aggregates of molecules through their mutual recognition properties. The precise programming of these recognition events, and hence the correct assembly of the growing superstructure, relies on a fundamental understanding and the practical exploitation of non-covalent bonding interactions between and within molecules. The science of supramolecular chemistry—chemistry beyond the molecule in its very broadest sense—has started to bridge the yawning gap between molecular and macro-molecular structures. By utilizing inter-actions as diverse as aromatic π–π stacking and metal–ligand coordination for the information source for assembly processes, chemists have, in the last decade, begun to use biological concepts such as self-assembly to construct nanoscale structures and superstructures with a variety of forms and functions. Here, we provide a flavor of how self-assembly operates in natural systems and can be harnessed in unnatural ones.

Self-Assembly in Natural and Unnatural Systems

The most common approach for quantifying interactions in supramolecular chemistry is a titration of the guest to solution of the host, noting the changes in some physical property through NMR, UV-Vis, fluorescence or other techniques. Despite the apparent simplicity of this approach, there are several issues that need to be carefully addressed to ensure that the final results are reliable. This includes the use of non-linear rather than linear regression methods, careful choice of stoichiometric binding model, the choice of method (e.g., NMRvs.UV-Vis) and concentration of host, the application of advanced data analysis methods such as global analysis and finally the estimation of uncertainties and confidence intervals for the results obtained. This tutorial review will give a systematic overview of all these issues—highlighting some of the key messages herein with simulated data analysis examples.

Determining association constants from titration experiments in supramolecular chemistry

Dynamic combinatorial chemistry.

Cyclic polyethers and their complexes with metal salts

The discovery of the crown ethers stemmed from efforts to control the catalytic activity of vanadium and copper by complexation with multidentate ligands. The first crown ether, 2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclo-octadeca-2,11-diene, was obtained in 0.4% yield during an attempt to prepare a phenolic ligand from catechol and bis(2-chloroethyl)ether. This compound, which complexed with the sodium cation, was the first compound known to display such activity and became known as dibenzo-18-crown-6, an 18-atom heterocycle containing 6 oxygen atoms. Some 60 related compounds were made involving heterocyclic rings containing 12 to 60 atoms including 4 and 10 oxygen atoms. There are optimum polyether ring sizes for the different alkali metal cations: 15 to 18 for sodium, 18 for potassium, and 18 to 21 for cesium. Complexes having polyether to cation ratios of 1:1, 3:2, and 2:1 were prepared. Solubilization of inorganic salts in aprotic solvents, especially by saturated crown ethers, was demonstrated.

http://science.sciencemag.org/content/sci/241/4865/536.full.pdf

The discovery of crown ethers.

Macrocyclic polyethers: Dibenzo-18-crown-6 polyether and dicyclohexyl-18-crown-6 polyether 



reactant: 222 g. (1.55 moles) of bis(2-chloroethyl) ether




product: Dibenzo-18-crown-6 polyether




product: dicyclohexyl-18-crown-6 polyethers




solvent: petroleum ether (b.p. 30–60°, approximately 200 ml. was required)




solvent: dichloromethane–petroleum ether




intermediate: complex of potassium acetate with isomer B of dicyclohexyl-18-crown-6 polyether





Keywords:

annulation, heterocyclic-[>6];
reduction, CC  HCCH;
replacement reactions, miscellaneous;
dicyclohexyl-18-crown-6, irritant, toxic;
macrocyclic polyethers

Macrocyclic polyethers: dibenzo-18-crown-6 polyether and dicyclohexyl-18-crown-6 polyether

Macrocyclic polyether (''''crown'''') compounds wherein the macrocyclic ring contains at least 14 carbon and oxygen atoms, each oxygen in the ring being separated from adjoining oxygens in the ring by two or three carbons; and the macrocyclic ring being fused to 1-4 other rings. These crown compounds find use as complexing agents, dye components, and gelation agents.

Macrocyclic polyether compounds

I regret that I have nothing new to add to this field in which so many able investigators have obtained interesting results extending the scope of my discovery. So I must resort to old material, perhaps so old that some have forgotten, and some of the younger of you never knew of it. Briefly, I will recount how I discovered the crown ethers and the fun I had doing so [1, 2].

The discovery of crown ethers

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