| 1. |
- Cautela, Jacopo, et al.
(author)
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C-12 vs C-3 substituted bile salts : An example of the effects of substituent position and orientation on the self-assembly of steroid surfactant isomers
- 2020
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In: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 185
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Journal article (peer-reviewed)abstract
- Biomolecule derivatives are transversally used in nanotechnology. Deciphering their aggregation behavior is a crucial issue for the rational design of functional materials. To this end, it is necessary to build libraries of selectively functionalized analogues and infer general rules. In this work we enrich the highly applicative oriented collection of steroid derivatives, by reporting a rare example of C-12 selectively modified bile salt. While nature often exploits such position to encode functions, it is unusual and not trivial to prepare similar analogues in the laboratory. The introduction of a tert-butyl phenyl residue at C-12 provided a molecule with a self-assembly that remarkably switched from rigid pole-like structures to twisted ribbons at a biologically relevant critical temperature (∼25 °C). The system was characterized by microscopy and spectroscopy techniques and compared with the C-3 functionalized analogue. The twisted ribbons generate samples with a gel texture and a viscoelastic response. The parallel analysis of the two systems suggested that the observed thermoresponsive self-assemblies occur at similar critical temperatures and are probably dictated by the nature of the substituent, but involve aggregates with different structures depending on position and orientation of the substituent. This study highlights the self-assembly properties of two appealing thermoresponsive systems. Moreover, it adds fundamental insights hereto missing in the investigations of the relation between self-assembly and structure of synthetic steroids, which are valuable for the rational design of steroidal amphiphiles.
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| 2. |
- D'Annibale, Valeria, et al.
(author)
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A spectroscopic and structural study on the solvent-promoted stereospecific self-assembly of new Porphyrin-Bile Salt conjugates
- 2024
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In: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 700
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Journal article (peer-reviewed)abstract
- The chiral bile salt sodium cholate has been covalently linked to tetra-aryl-porphyrins, conferring them an extrinsic chirality and obtaining new molecules with high tendency to aggregate in solution. The chirality transfer from the molecular to the nano- and meso-scale has been investigated by promoting the self-assembly of the conjugates balancing the ratio of aqueous/organic solvent mixtures and allowing a fine control of the dimensions and morphology of the final supramolecular architectures. The shift from elongated structures with helical ribbon features to monodisperse tubules or from tightly packed rolled sheets to wrapped scrolls was enabled by changing the solvent composition, with the possibility of forming tubular structures with a hollow cavity. From UV–Vis and Circular Dichroism (CD) spectroscopy the ability to self-assemble into J-type aggregates with a strong induction of supramolecular chirality was revealed, shedding light on a two-step process, with a fast monomer nucleation followed by a slow second step of further stereospecific chiral evolution. The results as a whole promote the new porphyrin-cholate conjugates as promising smart and easily tunable chiral materials for the design of stereoselective sensing devices.
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| 3. |
- Santilli, Andrea, et al.
(author)
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Bioderived, chiral and stable 1-dimensional light-responsive nanostructures : Interconversion between tubules and twisted ribbons
- 2022
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 623, s. 723-734
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Journal article (peer-reviewed)abstract
- HYPOTHESIS: Self-assembling molecular structures responding to light stimulus are appealing for applications as sensing and drug delivery. Supramolecular nanotubes have a relevant potential in nanotechnology as they can be used to encapsulate different loads like drugs, biological macromolecules, and nanomaterials. In addition, they are suitable elements for novel supracolloidal materials. Structural responses of supramolecular nanotubes to non-invasive stimuli are very much desired to enable controlled release of the encapsulated guests and to provide these recently developed new materials with an external trigger. Here, we describe the formation of well-defined, single wall tubules that interconvert into twisted ribbons upon UV-light exposure in aqueous environment. The structures are provided by self-assembly of an azobenzene substituted cholic acid, a biological surfactant belonging to the family of bile acids. The azobenzene group allows for the light responsiveness of the molecular packing. Concurrently the steroidal moieties assure both chiral features and extensive hydrophobic interactions for time and temperature resistant aggregates.EXPERIMENTS: The molecular packing interconversion was followed by circular dichroism. Microscopy, small angle X-ray scattering and light scattering measurements demonstrated the drastic morphological variation upon irradiation. A model of the molecular arrangement within the tubular walls was suggested based on the circular dichroism spectra simulation.FINDINGS: Innovatively, the molecular design reported in our work allows for encoding in the same light responsive system multiple desirable features (e.g. bio-origin, temperature resistance and chirality of the aggregates). Such combination of properties, never reported before for a single molecule, might be relevant for the realization of robust, stimuli-responsive bio-vectors.
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