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A new hemicryptophane host with a ditopic molecular cavity combining a cyclotriveratrylene (CTV) unit with a tris‐urea moiety was synthesized. The complexation of halides, tetramethylammonium (TMA+) cation, and ion pairs was investigated. A positive cooperativity was observed, since halides display a higher binding constant when a TMA+ cation is already present inside the cage. When TMA+ was complexed alone, a decrease of temperature from 298 K to 230 K was required to switch from a fast to a slow exchange regime on the NMR time scale. Nevertheless, the prior complexation of a halide guest in the lower part of the host resulted in significant decrease of the exchange rate of the subsequent complexation of the TMA+ cation. Under these conditions, the 1H NMR signals characteristic of a slow exchange regime were observed at 298 K. Addition of an excess of salts, increases the ionic strength of the solution, restoring the fast exchange dynamics. This result provides insight on how the exchange rate of a cation guest can be modulated by the complexation of a co‐guest anion. [ABSTRACT FROM AUTHOR]

Hyperpolarized 129Xe NMR can detect the presence of specific low-concentration biomolecular analytes by means of the xenon biosensor, which consists of a water-soluble, targeted cryptophane-A cage that encapsulates xenon. In this work we use the prototypical biotinylated xenon biosensor to determine the relationship between the molecular composition of the xenon biosensor and the characteristics of protein-bound resonances. The effects of diastereomer overlap, dipole-dipole coupling, chemical shift anisotropy, xenon exchange, and biosensor conformational exchange on protein-bound biosensor signal were assessed. It was found that optimal protein-bound biosensor signal can be obtained by minimizing the number of biosensor diastereomers and using a flexible linker of appropriate length. Both the linewidth and sensitivity of chemical shift to protein binding of the xenon biosensor were found to be inversely proportional to linker length.

The design of molecular cages with low symmetry could allow for more specific tuning of their properties and better mimic the unsymmetrical and complex environment of protein pockets. However, the added value of lowering symmetry of molecular receptors has been rarely demonstrated. Herein, C3‐ and C1‐symmetrical cages, presenting the same recognition sites, have been synthesized and investigated as hosts for carbohydrate recognition. Structurally related derivatives of glucose, galactose and mannose were found to have greater affinity to the receptor with the lowest symmetry than to their C3‐symmetrical analogue. According to the host cavity modelling, the C1 symmetry receptor exhibits a wider opening than its C3‐symmetrical counterpart, providing easier access and thus promoting guest proximity to binding sites. Moreover, our results show the high stereo‐ and substrate selectivity of the C1 symmetry cage with respect to its C3 counterpart in the recognition of sugars. [ABSTRACT FROM AUTHOR]

Haloazaphosphatranes are the halogenated parents of proazaphosphatranes, also known as Verkade's superbase. While the synthesis of iodo‐, bromo‐ and chloroazaphosphatranes was reported more than thirty years ago by J. G. Verkade, the first synthesis of fluoroazaphosphatranes was only described in 2018 by Stephan et al. Currently, no common and versatile procedure exists to access fluoroazaphosphatranes platform with different structural characteristics. In this report, a new and simple synthesis of this class of compounds was developed based on the nucleophilic attack of the fluoride anion on chloroazaphosphatrane derivatives with good to high isolated yields for the corresponding fluoroazaphosphatranes (70–92%). The scope of the reaction was widened to fluoroazaphosphatranes bearing various substituents and X‐ray molecular structures of two of them are reported. The stability of fluoroazaphosphatranes toward nucleophilic solvents like water has been investigated. As they revealed much more robust cations than their chloroazaphosphatrane parents, their chloride salts were tested as organocatalysts for the formation of cyclic carbonates from epoxides and CO2. Fluoroazaphosphatranes proved to be both efficient and stable catalytic systems for CO2 conversion with catalytic activities similar to those of azaphosphatranes, and no decomposition of the cation was observed at the end of reaction. [ABSTRACT FROM AUTHOR]

The structural and dynamical behaviors of the cryptophanes bearing molecules as well as their interaction with xenon are studied by using [.sup.1.H] and [.sup.128.Xe] NMR. The host molecules are shown to exist in aqueous solution under different conformations in very slow exchange whereas the cryptophanes in such conformation are unable to complex xenon.

Vibrational circular dichroism (VCD) measurements and density functional theory (DFT) calculations were used to obtain the absolute configuration of optically pure cryptophane-A molecule. The ab initio calculations performed at the DFT level (B3PW91 functional) showed that both the simulated IR and VCD spectra strongly depend on the chosen basis set used.

The study of the interaction between xenon and two cryptophane derivatives in organic solution is carried out. The results clearly indicate that in the design of new cage molecules for biosensing, the separation of cryptophane diastereomers is important because their affinity and their properties vis-a-vis could be strongly different.

We have investigated in the present study the interaction between G-actin and various types of liposomes, zwitterionic, positively charged, and negatively charged. To investigate at the molecular level the conformation of actin in the presence of lipids, we have selectively attached a fluorinated probe, 3-bromo-1,1,1-trifluoropropanone, to the actin cysteine residues 10, 285, and 374 and used high-resolution 19F nuclear magnetic resonance spectroscopy to investigate the probe resonances. The results indicate a change in the mobility of the 19F labels when G-actin is in the presence of positively charged liposomes made of DMPC and stearylamine and in the presence of DMPG, a negatively charged lipid. No conformational change was observed in the actin molecule in the presence of neutral liposomes. Electron micrographs of these systems reveal the formation of paracrystalline arrays of actin filaments at the surface of the positively charged liposomes, while no evidence of actin polymerization or paracrystallization was observed in the presence of DMPG. The interaction between actin and the lipid polar headgroup has also been investigated using solid-state phosphorus and deuterium NMR. The results indicate no evidence of interaction between actin and zwitterionic liposomes but show an interaction between the positively charged liposomes and a negative charge on the actin molecules. Interestingly, the negatively charged liposomes interact with a positive charge, which is most likely associated with the three residues (His-Arg-Lys) preceding the cysteine 374 residue in the protein.

A study was conducted on the interaction of xenon with cryptophane-A in 1,1,2,2-tetrachloroethane-d2 using 129Xe and 1H NMR spectroscopy. The stability of the xenon complex seems to be much greater than that of the previously described xenon complex of alpha-cyclodextrin in water. The findings indicate that the incoming xenon atom must displace the departing one to enter the cryptophane cavity. Moreover, the results suggest that the complexation equilibrium does not involve the empty cryptophane.

The series of semirigid phosphonamide macrocyclic ligands with bis(N-phenylamino)phosphine oxide units were synthesized from macrocyclic phosphorus(III) precursors. The synthetic process involves the alkylation of the NH functions of macrocyclic phosphonamides with ethylene or propylene bridges which led to the formation of semirigid phosphorylated macrorings. Furthermore, exo-endo equilibrium of the reaction is dependent on the temperature and polarity of the solvent during conformational change.

The presence of molecular structure fluctuations in a crytophane host-guest complex was analyzed via molecular dynamics simulations. Conformational analysis of the structural fluctuations in the uncomplexed hosts indicated the presence of the TMA+ molecule within the cavity. The TMA+ molecule also induced the stretching of the cryptophane conformation and enhanced the rigidity of the cage region. Furthermore, the presence of the guest compound hindered the release of the host from the cavity.

Macrocyclic precursors 6-9 reacted with 1,3-propanediol ditosylate or 1,2-dichloroethaene to derive semirigid phosphonamide ligands 1-5. Reactions for thiophosphoryl compounds 1 and 2 and phosphoryl derivative 5 were conducted in biphasic aqueous NaOH solutions. The 18- and 21-membered macrocycle products were characterized by a flexible crown ether part and a rigidified phosphoryl binding unit was integrated into the structure.