Controlling Capture and Release of Guests from Cross-Linked Supramolecular Polymers

Formation of a cross-linked, porous supramolecular polymer leads to instant entrapment of organic guest species. These can be stored and then released upon changing solvent polarity, temperature, pH, and concentration

Separations Using Carbon Dioxide

CO2 causes structural switching in receptors and their host−guest complexes, producing insoluble supramolecular polymers. Upon precipitation these polymers trap, separate, and keep their guests for extended time, with no solvent needed. However, they can dissociate back to their monomers by releasing CO2 upon heating or addition of acid. Greenhouse gas CO2 can thus be used as a building block for separating materials

Revisiting Noncovalent SO₂−Amine Chemistry: An Indicator−Displacement Assay for Colorimetric Detection of SO₂

A supramolecular approach for potential detection of SO2 is presented, which is based on the “old” donor−acceptor chemistry between SO2 and amines and includes an indicator−displacement assay. When amines were added to Zn−tetraphenylporphyrin 1 in CHCl3, the solution changed from red to dark green. A bathochromic shift of Δλ ∼ 10 nm was observed for the Soret band, indicating the formation of 1•amine complexes. After this, SO2 gas was introduced, and the original red color of the solution was restored. The Soret band returned to its position for free porphyrin 1. The 1•amine complexes dissociated, and new SO2•amine adducts formed. Porphyrin 1 thus served as an indirect colorimetric indicator for SO2. The system discriminates between SO2 and such typical exhaust gases as COX, NOX, and H2O. From the indicator−displacement assay, the Kassoc values between 1000 and 30 000 M-1 for SO2•amine complexes were determined, which are comparable to those obtained by direct titration experiments between SO2 and the amines. Spectroscopic features of SO2•amine complexes are also presented

Encapsulated Reagents for Nitrosation

A novel class of stable, mild, and size−shape-selective nitrosating agents for secondary amides is introduced. These are based on reversible entrapment and release of reactive nitrosonium species by calix[4]arenes. The NO+ encapsulation controls the reaction selectivity

Kinetically Stable Caviplexes in Water

Kinetically Stable Caviplexes in Wate

Lower Rim Functionalized Resorcinarenes: Useful Modules for Supramolecular Chemistry

A synthetic scheme for the selective functionalization of all-cis (rccc) resorcinarene platform at the “lower rim” was developed. Self-folding and self-complementary cavitands were prepared for molecular recognition and self-assembly, bearing functionality at remote sites. These molecules promise applications on solid support and as polymeric capsules

A Cavitand−Porphyrin Hybrid

Host−guest complexes of a new open-ended cavitand show unprecedented stabilities. Simultaneous binding in the cavity and at the metalloporphyrin affects both the kinetics and the thermodynamics of caviplex formation

Supramolecular Structures from Lysine Peptides and Carbon Dioxide

The design, synthesis, and characterization of novel linear and cross-linked supramolecular polymers that are easily available from biologically friendly lysine peptides and carbon dioxide (CO2) are reported here. Polymeric structures 5, 6, and 19 readily form from peptides 2, 3, and 15, respectively, at ambient temperatures by simply bubbling CO2 through their solutions in apolar organic solvents (CHCl3, benzene) and even in the presence of 10% MeOH. The resulting gels can be easily isolated from solution, dried, and stored refrigerated for several months. At the same time, they may thermally release CO2 and convert back to the corresponding monomers. As a consequence, their structures and physical properties are switchable. They may also trap, store, and release foreign molecules. The typical entrapment procedure was demonstrated for tripeptide 3, CO2, and the commercially available dye coumarin 2

Self-Folding Cavitands

A novel class of resorcinarene-based cavitands 2a−e that fold into a deep (8 × 10 Å dimensions) open-ended cavity by means of intramolecular hydrogen bonds has been synthesized. As follows from the FTIR and 1H NMR spectral data in apolar solvent, a seam of eight intramolecular hydrogen bonds is stitched along the upper rim of the structure 2a−e; the amide CO...H−N interactions bridge adjacent ringsinterannular bindingand are held in place by the seven-membered intraannular hydrogen bonds. The self-folding in 2a−e is reversibly controlled by solvent and temperature. Complexation of self-folding cavitands 2a−e with organic molecules such as (1-substituted) adamantanes, lactams, and cyclohexane derivatives was demonstrated by 1H NMR spectroscopy in CDCl3, benzene-d6 and p-xylene-d10; the binding energy -ΔG° values of 2−4 kcal mol-1 in p-xylene-d10 at 295 K were calculated. The exchange between complexed and free guest species is slow on the NMR time-scale, and it is proposed that hydrogen bonds are responsible for these unique features. Employing the pronounced upfield 1H NMR shifts of the complexed guest molecules, attempts were made to study the structure of the caviplexes “from inside”, and the orientation of the encapsulated adamantanes 12,13, as well as noncovalent interactions of complexed ε-caprolactam 9b with the host walls were deduced. Even though the guest-exchange process in 2a−e is slow on the NMR time scale (k = 2 ± 1 s-1), it is still faster than that observed for the completely closed hydrogen-bonded calixarene-based capsules or for covalently sealed hemicarceplexes. This places them in an unusual position in the scale of cavity-containing receptors and opens new perspectives to use 2a−e in catalysis and as 1H NMR supramolecular shift reagents

A pH Switch in Supramolecular Polymeric Capsules

A switchable, supramolecular polymer is introduced which is held together through hydrogen bonding and reversibly precipitates−redissolves upon subtle pH control. Precipitating, it entraps and stores guest molecules within the self-assembling capsules incorporated within the polymeric chain