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Juan F Miravet

Publications and source records attributed to Juan F Miravet.

11 recordsLinked to original sources
PubMed2006

Insight on the NMR study of supramolecular gels and its application to monitor molecular recognition on self-assembled fibers.

The 1H NMR study of supramolecular gels formed by two organogelators derived from valine is described. The analysis of the variation of chemical shift values and relaxation times in the gel samples reveals that in these systems only discrete species are observed by 1H NMR. The reduced T2 values and negative NOEs that are measured upon gel formation can be ascribed to an exchange between discrete organogelator species and the gel network. This process is found to be fast in the time scale of 1H NMR relaxation and slow in the NMR observation frequency time scale. It is shown here that other molecules, aside from the gelator itself, can interact with the gel network and this process can be monitored easily by measurement of relaxation times. As a proof of principle, the selective interaction of 2,2'-bis(hydroxymethyl)biphenyl over diphenylmethane with the self-assembled fibers formed by one of the gelators in benzene is described.

Journal Article↗
PubMed2006

Silk-inspired low-molecular-weight organogelator.

A minimal sequence from natural silks, the tetrapeptide GAGA, has been used as inspiration for the design of a new organogelator. Gels were obtained in several organic solvents, and their microscopic aspects were studied by transmission and cryo-scanning electron microscopies (TEM and cryo-SEM). FT-IR spectroscopy, circular dichroism, and wide-angle X-ray diffraction were used to study the self-assembly features of this molecule, and evidence of an antiparallel beta-sheet organization was obtained. Remarkably, the precise secondary structure uniqueness found in Nature was successfully transferred into a small synthetic analogue that self-assembles driven only by noncovalent interactions.

Journal Article↗
PubMed2006

Silver complexes of peptidomimetic polyazapyridinophanes. The influence of the bonding cavity size and the nature of side chains.

Several peptidomimetic macrocycles containing a pyridine spacer and ring sizes ranging from 15 to 17 have been efficiently synthesized starting from valine and phenylalanine. The complexes formed have been investigated by potentiometry and NMR. Log K values show that phenylalanine derivatives are consistently more stable than valine derivatives , whilst macrocycles with ring sizes of 16 members are the most appropriate for the complexation. The NMR data, in combination with molecular modeling, allow rationalization of the structure of the complexes formed and the participation of the aromatic rings from the side chain of phenylalanine in pi-Ag+ interactions to be discarded.

Journal Article↗
PubMed2005

Reactive organogels: self-assembled support for functional materials.

[reaction: see text] An organogel bearing reactive groups has been used as a platform for the gel-phase synthesis of more sophisticated materials. The results show that reactions take place on the gel fibers and that supramolecular aggregation modifies the product distribution in cases where several compounds can be obtained.

Acetonitriles↗
PubMed2005

Organogel formation by coaggregation of adaptable amidocarbamates and their tetraamide analogues.

Mixtures of derivatives of Hanabusa's bolaamphiphilic amidocarbamates containing two Z-valinyl subunits and aliphatic spacers that range from ethylenic to octamethylenic are able to form organogels. A coassembly of them is observed in their acetonitrile and toluene gels; namely, the concentration of a given compound at which a gel is formed is lowered by the presence of equimolar quantities of any other compound in the series. The aggregates were studied by wide-angle X-ray diffraction (WAXD) and the results can be rationalized if the gel fibers are formed by supramolecular copolymers. NMR studies reveal that in solution these molecules adopt folded conformations containing intramolecular H-bonds, but IR studies indicate that these are not present in their aggregates. Additionally, analogues of the amidocarbamates obtained by replacement of the carbamate functionality by amide have been shown to behave in a similar way. For these molecules it can be shown that the central aliphatic subunit is not completely extended in the conformations present in the aggregates according to IR and WAXD studies. The tetraamide-type compounds described are robust organogelators that form gels in a variety of organic solvents with good thermostability and present improved feasibility for the synthesis of envisaged functional organogelators.

Journal Article↗
PubMed2005

Shape-complementarity in the recognition of tricarboxylic acids by a [3+3] polyazacyclophane receptor.

[structure: see text] The interaction of a macrocycle containing three trans-(1R,2R)-diaminocyclohexane units connected by p-xylene spacers with the isomers 1,3,5-benzenetricarboxylic (1,3,5-BTC), 1,2,4-benzenetricarboxylic (1,2,4-BTC), and 1,2,3-benzenetricarboxylic (1,2,3-BTC) acids and their relevant anions is studied by means of potentiometric and NMR analysis. The interaction is highest for the isomer 1,3,5-BTC, which perfectly fits within the macrocyclic cavity of the host species. The studies have been extended to the triacid 1,3,5-benzenetriacetic observing in this case the effect of a size mismatch between host and guest species.

Binding, Competitive↗
PubMed2004

Self-assembly of small peptidomimetic cyclophanes.

The self-assembly of a series of small peptidomimetic cyclophanes in organic solvents was studied. X-ray diffraction, NMR spectroscopy, and molecular modelling were used to understand the structural features of these self-assembling compounds both at the molecular and supramolecular level. The factors that could influence the formation of gels rather than crystals were studied and a model for the arrangement of molecules in the gel was proposed. Furthermore, scanning electron microscopy revealed that in some cases these compounds undergo a transcription of chirality when going from organogelator to helicoidal gel fibres.

Circular Dichroism↗
PubMed2003

New efficient procedure for the use of diethoxyphosphoryl as a protecting group in the synthesis of polyazamacrocycles. Preparation of polyazacyclophanes derived from resorcinol.

The synthesis of polyazamacrocycles containing an electron-rich aromatic subunit derived from resorcinol is described. The reported synthetic procedure is based on the use of diethoxyphosphoryl (Dep) as an amine protecting group. The new conditions employed for the cyclization reaction allow for a generalized use of Dep in the synthesis of polyazamacrocycles.

Amines↗
PubMed2003

Efficient macrocyclization of U-turn preorganized peptidomimetics: the role of intramolecular H-bond and solvophobic effects.

Simple peptidomimetic molecules derived from amino acids were reacted with meta- and para-bis(bromomethyl)benzene in acetonitrile to very efficiently yield macrocyclic structures. The cyclization reaction does not require high dilution techniques and seems to be insensitive to the size of the formed macrocycle. The analysis of data obtained by (1)H NMR, single-crystal X-ray diffraction, fluorescence measurements, and molecular mechanics indicate that folded conformations can preorganize the system for an efficient cyclization. The role played by intramolecular hydrogen-bonding and solvophobic effects in the presence of folded conformations is analyzed.

Amides↗