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A series of pseudopeptidic compounds have been assayed as organocatalyts for the conversion of CO2 into organic carbonates through a cooperative multifunctional mechanism. Conformationally constrained pseudopeptidic macrocycles 3a and 3b have been revealed to be excellent synzymes for this purpose, being able to provide a suitable preorganization of the different functional elements and reaction components to activate the CO2 molecule and stabilize the different anionic intermediates involved, through a series of cooperative supramolecular interactions. As a result, remarkable catalytic efficiencies are found at low CO2 pressures and moderate temperatures, with TON and TOF values surpassing those reported for other organocatalytic supramolecular systems under similar conditions. The process works well for monosubstituted epoxides. The involvement of the different structural elements has been analyzed in detail and preliminary studies show the potential for recovery and reuse of these catalytic systems. [ABSTRACT FROM AUTHOR]

Six new 6-styryl-2,4-diarylpyrylium salts have been synthesized and fully characterized by means of 1H/13C NMR, HRMS, UV-vis and Steady-State/Time-Resolved Fluorescence spectroscopies. This set of molecules is composed of a core pyrylium fluorophore, an amino acid (valine or phenylalanine), and an alkylic chain of variable length. The emissive properties (fluorescence quantum yields and lifetimes and radiative deactivation rate constants) in dichloromethane, acetonitrile and PBS have been recorded. The interaction of these pyrylium salts with aminoacids in their N-protected forms has been studied by means of fluorescence quenching, using the Stern–Volmer methodology. It has been found that dynamic (collisional) quenching is the most prevalent process for all the fluorescent molecules, irrespective of the amino acid building block or the length of the alkyl chain. The emission of the pyrylium molecules is strongly quenched by Z-Trp-OH and to a lesser extent by Z-Tyr-OH and Z-Met-OH and no quenching was measured with Z-Ala-OH, Z-Val-OH and Z-Phe-OH. A small degree of ground-state complexation was observed for receptor 8a and by Z-Trp-OH (upward curvature in the Stern–Volmer plot). Complementary 1H-NMR titrations demonstrated the existence of such a weak ground state complex. [ABSTRACT FROM AUTHOR]

The ESI-MS, NMR, fluorescence, and molecular modeling techniques were used to study the binding between a pseudopeptidic macrocyclic naphthalenophane and different N-protected amino acid derivatives. The results obtained provide insight into the structure of the supramolecular complexes in which the interactions with the naphthyl ring of the receptor play a fundamental role in the strength and selectivity of the molecular recognition event.

A multidisciplinary approach is used for studying the anion-templated synthesis of different pseudopeptidic macrocycles. The structural diversities observed in the isolated yields are explained in terms of the flexibility and stability of the key supramolecular intermediate complexes.

The studies of NH...[pi] interactions by using conformational behavior of designed macrocyclic naphthalenophanes derived from amino acids and their implication in the folding of peptide-like molecules is demonstrated.

The conformational behavior of 16- to 18-membered ring peptidomimetic p-cyclophanes are studied by NMR. The cycles bearing 16 and 17 atoms showed a dynamic process within the NMR time scale, produced by the rotation of the aromatic p-diphenylene moiety with respect to the macrocyclic main plane.

Three crystal structures of a ditopic cyclophane ligand (L) in which two 1,5,8,12-tetraamine molecules have been attached through methylene spacers to the ortho positions of a benzene ring are described. The analysis of these butterfly like ditopic aza-cyclophane macrocycle shows evidence of the concerted roles that counteranions, metal ions, hydrogen bonding and pi-stacking play in the overall architecture of crystal.

The introduction of the substituents in position 4 of the pyridine ring is a flexible and versatile strategy for the immobilization of chiral pybox ligands. This strategy allows complete modulation of the final chiral catalyst in different ways, including the structure of the support, the length of the spacer, and the electronic properties of the ligand.

Polyazamacrocycles containing an electron-rich aromatic subunit derived from resorcinol is synthesized. Its procedure is based on the use of diethoxyphosphoryl as an amine protecting group.

The self-assembly patterns of a family of C2-symmetric pseudopeptidic compounds have been studied in the crystalline state, analysing the influence of both the nature of the central spacer and that of the side chain of the amino acid on the observed features. The nature of the side chain of the component amino acid is the most important structural element defining the conformational and self-assembly patterns. The presence of an aromatic side chain, in the case of Phe derivatives, seems to play a key role in defining folded conformations with the aromatic side chain located over the central spacer. The formation of β-sheet-like stacks in crystals is predominant in Val derivatives but not in Phe-derived compounds. Side chains are strongly involved in intermolecular contacts, with isopropyl groups defining preferentially knob-into-hole interactions and aromatic groups of Phe pseudopeptides defining preferentially edge-to-face arrangements. NMR and CD data suggest that the conformational differences observed in the crystalline structures are also present in solution, in particular in polar solvents. [ABSTRACT FROM AUTHOR]