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Nieto-Ortega B, Nebot VJ, Miravet JF, Escuder B, Navarrete JTL, Casado J, Ramírez FJ. Vibrational Circular Dichroism Shows Reversible Helical Handedness Switching in Peptidomimetic l-Valine Fibrils. J Phys Chem Lett 2012; 3:2120-2124. [PMID: 26295757 DOI: 10.1021/jz300725d] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We elucidate the supramolecular organization in the form of microsize fibrils of gels formed by a l-Valine peptidomimetic compound. Analysis was based on circular dichroism spectroscopies, vibrational (VCD) and electronic (CD), supported by microscopy (atomic force and scanning electron). We show how the VCD spectra give account of the micrometric structure of the fibrils formed by the helicoidal arrangement of simpler proto-fibrils, which are organized in a lower hierarchical level. This ability is used to monitorize a fully reversible change in the handedness of the helix by modulating different external stimuli as pH or ionic strength, thus providing the first observation by VCD of such a phenomenon in a short peptide.
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Affiliation(s)
- Belén Nieto-Ortega
- †Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain
| | - Vicent J Nebot
- ‡Department de Química Inorgànica I Orgànica, Universitat Jaume I, Castellón 12071, Spain
| | - Juan F Miravet
- ‡Department de Química Inorgànica I Orgànica, Universitat Jaume I, Castellón 12071, Spain
| | - Beatriu Escuder
- ‡Department de Química Inorgànica I Orgànica, Universitat Jaume I, Castellón 12071, Spain
| | - Juan T López Navarrete
- †Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain
| | - Juan Casado
- †Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain
| | - Francisco J Ramírez
- †Departamento de Química Física, Facultad de Ciencias, Universidad de Málaga, Málaga 29071, Spain
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Nebot VJ, Armengol J, Smets J, Prieto SF, Escuder B, Miravet JF. Molecular hydrogels from bolaform amino acid derivatives: a structure-properties study based on the thermodynamics of gel solubilization. Chemistry 2012; 18:4063-72. [PMID: 22354848 DOI: 10.1002/chem.201103193] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Indexed: 11/07/2022]
Abstract
Insight is provided into the aggregation thermodynamics associated to hydrogel formation by molecular gelators derived from L-valine and L-isoleucine. Solubility data from NMR measurements are used to extract thermodynamic parameters for the aggregation in water. It is concluded that at room temperature and up to 55 °C, these systems form self-assembled fibrillar networks in water with quite low or zero enthalpic component, whereas the entropy of the aggregation is favorable. These results are explained by considering that the hydrophobic effect is dominant in the self-assembly. However, studies by NMR and IR spectroscopy reveal that intermolecular hydrogen bonding is also a key issue in the aggregation process of these molecules in water. The low enthalpy values measured for the self-assembly process are ascribed to the result of a compensation of the favorable intermolecular hydrogen-bond formation and the unfavorable enthalpy component of the hydrophobic effect. Additionally, it is shown that by using the hydrophobic character as a design parameter, enthalpy-controlled hydrogel formation, as opposed to entropy-controlled hydrogel formation, can be achieved in water if the gelator is polar enough. It is noteworthy that these two types of hydrogels, enthalpy-versus entropy-driven hydrogels, present quite different response to temperature changes in properties such as the minimum gelator concentration (mgc) or the rheological moduli. Finally, the presence of a polymorphic transition in a hydrogel upon heating above 70 °C is reported and ascribed to the weakening of the hydrophobic effect upon heating. The new soft polymorphic materials present dramatically different solubility and rheological properties. Altogether these results are aimed to contribute to the rational design of molecular hydrogelators, which could be used for the tailored preparation of this type of soft materials. The reported results could also provide ground for the rationale of different self-assembly processes in aqueous media.
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Affiliation(s)
- Vicent J Nebot
- Department de Química Inorgánica i Orgánica, Universitat Jaume I, 12071 Castelló, Spain
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Griffiths PC, Knight DW, Morgan IR, Ford A, Brown J, Davies B, Heenan RK, King SM, Dalgliesh RM, Tomkinson J, Prescott S, Schweins R, Paul A. Gelation or molecular recognition; is the bis-(α,β-dihydroxy ester)s motif an omnigelator? Beilstein J Org Chem 2010; 6:1079-88. [PMID: 21160568 PMCID: PMC3002023 DOI: 10.3762/bjoc.6.123] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2010] [Accepted: 11/02/2010] [Indexed: 11/23/2022] Open
Abstract
Understanding the gelation of liquids by low molecular weight solutes at low concentrations gives an insight into many molecular recognition phenomena and also offers a simple route to modifying the physical properties of the liquid. Bis-(α,β-dihydroxy ester)s are shown here to gel thermoreversibly a wide range of solvents, raising interesting questions as to the mechanism of gelation. At gelator concentrations of 5-50 mg ml⁻¹, gels were successfully formed in acetone, ethanol/water mixtures, toluene, cyclohexane and chloroform (the latter, albeit at a higher gelator concentration). A range of neutron techniques - in particular small-angle neutron scattering (SANS) - have been employed to probe the structure of a selection of these gels. The universality of gelation in a range of solvent types suggests the gelation mechanism is a feature of the bis-(α,β-dihydroxy ester) motif, with SANS demonstrating the presence of regular structures in the 30-40 Å range. A correlation between the apparent rodlike character of the structures formed and the polarity of the solvent is evident. Preliminary spin-echo neutron scattering studies (SESANS) indicated the absence of any larger scale structures. Inelastic neutron spectroscopy (INS) studies demonstrated that the solvent is largely unaffected by gelation, but does reveal insights into the thermal history of the samples. Further neutron studies of this kind (particularly SESANS and INS) are warranted, and it is hoped that this work will stimulate others to pursue this line of research.
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Affiliation(s)
- Peter C Griffiths
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - David W Knight
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - Ian R Morgan
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - Amy Ford
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - James Brown
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - Ben Davies
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
| | - Richard K Heenan
- Rutherford Appleton Laboratory, Science and Technology Research Council, Didcot, Oxfordshire OX11 0QX U.K
| | - Stephen M King
- Rutherford Appleton Laboratory, Science and Technology Research Council, Didcot, Oxfordshire OX11 0QX U.K
| | - Robert M Dalgliesh
- Rutherford Appleton Laboratory, Science and Technology Research Council, Didcot, Oxfordshire OX11 0QX U.K
| | - John Tomkinson
- Rutherford Appleton Laboratory, Science and Technology Research Council, Didcot, Oxfordshire OX11 0QX U.K
| | - Stuart Prescott
- School of Chemistry, Bristol University, Cantock’s Close, Bristol BS8 1TS U.K
| | - Ralf Schweins
- Institut Laue Langevin, 6 rue Jules Horowitz, 38042 Grenoble, Cedex 9, France
| | - Alison Paul
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, U.K
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Rodríguez-Llansola F, Escuder B, Miravet JF. Switchable performance of an L-proline-derived basic catalyst controlled by supramolecular gelation. J Am Chem Soc 2009; 131:11478-84. [PMID: 19459635 DOI: 10.1021/ja902589f] [Citation(s) in RCA: 146] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An L-proline-derived low molecular weight gelator forms gels in nitromethane and nitroethane and acts as a basic catalyst for the Henry nitroaldol reaction of these solvents with 4-nitrobenzaldehyde and 4-chlorobenzaldehyde. The reported catalyst is efficient only upon aggregation into self-assembled fibrillar networks. The formation of the gels is associated to a basicity boost of the L-proline residues. Gel dissociation blocks the catalytic efficiency for the nitroaldol reaction but enhances a reaction pathway leading to alkenes. Because of the reversible nature of supramolecular gels, subtle temperature changes allow for a reversible sol-gel transition associated to an activation of the catalyst. The catalytic gel from nitroethane is significantly more active than the one from nitromethane probably because of its different structure as revealed by X-ray diffraction and thermal stability studies. The results shown indicate that in solution the L-proline moiety catalyzes the reaction of nitroalkanes with aldehydes via iminium intermediates while efficient nitroaldol reactions are promoted in the gel phase through an ionic pair type mechanism. The fact that upon aggregation the amino acid-based molecule used as gelator plays both a structural (gel formation) and catalytic role is interesting for the point of view of life origin studies.
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Côte M, Nicholls T, Knight DW, Morgan IR, Rogueda PGA, King SM, Heenan RK, Griffiths PC. Self-assembling chiral gelators for fluorinated media. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:8678-8684. [PMID: 19402688 DOI: 10.1021/la804277z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Formulations involving partially and fully fluorinated media represent a technological challenge given the lipophobic and hydrophobic nature of such liquids. The identification of self-associating materials with which to control the viscosity and solubilizing characteristics of fluorinated solvents is a particularly interesting area of research. It is shown here that the presence of the stereogenic centers inherent in a family of bis-(alpha,beta-dihydroxy ester)s is an essential requirement for the thermoreversible gelation of mixtures of partially fluorinated liquids 2H,3H-perfluoropentane (HPFP) and 1H,1H-heptafluorobutanol (HFB). Gelation is driven by hydrogen bonding, which induces a nonpreferred conformation around the bis-(alpha,beta-dihydroxy ester) structural motif. An analysis of the melting temperature yields an enthalpy of melting that is consistent with three to four hydrogen bonds, commensurate with the end-group structure of the gelator. Small-angle neutron scattering demonstrated the existence of the common fibrillar structures whose dimensions showed no obvious correlation with the molecular structure of the gelator.
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Affiliation(s)
- Marie Côte
- School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK
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Jokić M, Čaplar V, Portada T, Makarević J, Vujičić NŠ, Žinić M. Stereoisomeric bis(phenylglycinol)malonamide gelators: rare examples of gelling meso-compounds. Tetrahedron Lett 2009. [DOI: 10.1016/j.tetlet.2008.11.037] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Rodríguez-Llansola F, Miravet JF, Escuder B. Supramolecular gel formation and self-correction induced by aggregation-driven conformational changes. Chem Commun (Camb) 2009:209-11. [DOI: 10.1039/b816234d] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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