Self-assembly of a peptide amphiphile: transition from nanotape fibrils to micelles

A thermal transition is observed in the peptide amphiphile C16-KTTKS (TFA salt) from nanotapes at 20 degrees C to micelles at higher temperature (the transition temperature depending on concentration). The formation of extended nanotapes by the acetate salt of this peptide amphiphile, which incorporates a pentapeptide from type I procollagen, has been studied previously [V. Castelletto et al., Chem. Commun., 2010, 46, 9185]. Here, proton NMR and SAXS provide evidence for the TFA salt spherical micelles at high temperature. The phase behavior, with a Krafft temperature separating insoluble aggregates (extended nanotapes) at low temperature from the high temperature micellar phase resembles that for conventional surfactants, however this has not previously been reported for peptide amphiphiles

Switchable and tunable ligands for homogeneous catalysis

La presente tesis doctoral trata sobre el desarrollo de ligandos con propiedades inusuales para catálisis homogénea. Para conseguir estas propiedades, se han utilizado diferentes estrategias, por lo que la tesis está dividida en tres partes diferenciadas.En la primera parte se describe el desarrollo de ligandos fosfina que incorporan en su estructura la unidad azobenceno, la cual puede presentar dos isómeros estructuralmente diferentes. Se estudia el efecto de la isomerización sobre diferentes reacciones catalíticas.En la segunda parte se utilizan interacciones supramoleculares para inducir quiralidad sobre una difosfina biarílica proquiral. Se estudian los complejos supramoleculares formados, así como su efecto en catálisis asimétrica.En la última parte se describe la obtención de ligandos trans-bidentados. Se sintetizan fosfininas y piridinas monodentadas que forman ligandos bidentados al asociarse mediante enlaces de hidrógeno. Adicionalmente, se incorpora la unidad azobenceno en la estructura de fosfininas y piridinas bidentadas para conseguir la coordinación trans mediante la isomerización del doble enlace.This thesis describes the development of new ligands with unusual properties to be applied in homogeneous catalysis. Three strategies were envisaged to obtain the the new ligand systems. Accordingly, the thesis is divided in three parts.The first part describes the design of phosphine ligands that include in their structure the azobenzene moiety, which occurs in two structurally different isomers. The effect of the isomerization on several catalytic reactions was studied.The second part presents the use of supramolecular interactions to induce chirality in a prochiral biaryl diphosphine. The formation of the supramolecular complexes and the effect on asymmetric catalysis were also investigated

Cooperativity in multiply H-bonded complexes

The free energy of complexation of supramolecular complexes containing phenol–carbamateH-bonds is an additive function of the number of H-bonds, with a constant increment of 6 kJ mol−1 per interaction in carbon tetrachloride

Selfassembly of a peptide amphiphile: transition from nanotape fibrils to micelles Self-assembly of a peptide amphiphile: transition from nanotape fibrils to micelles †

A thermal transition is observed in the peptide amphiphile C 16 -KTTKS (TFA salt) from nanotapes at 20 C to micelles at higher temperature (the transition temperature depending on concentration). The formation of extended nanotapes by the acetate salt of this peptide amphiphile, which incorporates a pentapeptide from type I procollagen, has been studied previously [V. Castelletto et al., Chem. Commun., 2010, 46, 9185]. Here, proton NMR and SAXS provide evidence for the TFA salt spherical micelles at high temperature. The phase behavior, with a Krafft temperature separating insoluble aggregates (extended nanotapes) at low temperature from the high temperature micellar phase resembles that for conventional surfactants, however this has not previously been reported for peptide amphiphiles