11 research outputs found
Chiral recognition with broad selective sensor arrays
The detection and discrimination of chiral analytes has always been a topical theme in food and pharmaceutical industries and environmental monitoring, especially when dealing with chiral drugs and pesticides, whose enantiomeric nature assessment is of crucial importance. The typical approach matches novel chiral receptors designed ad hoc for the discrimination of a target enantiomer with emerging nanotechnologies. The massive synthetic efforts requested and the difficulty of analyzing complex matrices warrant the ever-growing exploitation of sensor array as an alternative route, using a limited number of chiral or both chiral and achiral sensors for the stereoselective identification and dosing of chiral compounds. This review aims to illustrate a little-explored winning strategy in chiral sensing based on sensor arrays. This strategy mimics the functioning of natural olfactory systems that perceive some couples of enantiomeric compounds as distinctive odors (i.e., using an array of a considerable number of broad selective receptors). Thus, fundamental concepts related to the working principle of sensor arrays and the role of data analysis techniques and models have been briefly presented. After the discussion of existing examples in the literature using arrays for discriminating enantiomers and, in some cases, determining the enantiomeric excess, the remaining challenges and future directions are outlined for researchers interested in chiral sensing applications
The kinetic studies of the solvent-promoted aggregation of a steroid-porphyrin derivative
The study of the aggregation of a steroid-functionalised porphyrin derivative shows the
formation of chiral suprastuctures. Kinetic studies indicate that the mechanism of the aggregation strongly
depends on both the nature of the media and on the concentration of the tetrapyrrolic macrocycle
Proline enantiomers discrimination by (L)-prolinated porphyrin derivative Langmuir-Schaefer films: proof of concept for chiral sensing applications
A porphyrin derivative functionalized with the L-enantiomer of proline amino acid was characterized at the air-pure water interface of the Langmuir trough. The porphyrin derivative was dissolved in dichloromethane solution, spread at the air-subphase interface and investigated by acquiring the surface pressure vs. area per molecule Langmuir curves. It is worth observing that the behavior of the molecules of the porphyrin derivative floating film was substantially influenced by the presence of L-proline amino acid dissolved in the subphase (10(-5) M); on the contrary, the physical chemical features of the floating molecules were only slightly influenced by the D-proline dissolved in the subphase. Such an interesting chirality-driven selection was preserved when the floating film was transferred onto solid supports by means of the Langmuir-Schaefer method, but it did not emerge when a spin-coating technique was used for the layering of the tetrapyrrolic derivatives. The obtained results represent proof of concept for the realization of active molecular layers for chiral discrimination: porphyrin derivatives, due to their intriguing spectroscopic and supramolecular properties, can be functionalized with the chiral molecule that should be detected. Moreover, the results emphasize the crucial role of the deposition technique on the features of the sensing layers
Spectroscopic, Morphological and Mechanistic Investigation of the Solvent.Promoted Aggregation of Porphyrins Modified in meso-positions by Glucosylated steroids
Solvent-driven aggregation
of a series of porphyrin derivatives was
studied by UV/Vis and circular dichroism
spectroscopy. The porphyrins are
characterised by the presence in the
meso positions of steroidal moieties
further conjugated with glucosyl
groups. The presence of these groups
makes the investigated macrocycles
amphiphilic and soluble in aqueous solvent,
namely, dimethyl acetamide/
water. Aggregation of the macrocycles
is triggered by a change in bulk solvent
composition leading to formation of
large architectures that express supramolecular
chirality, steered by the presence
of the stereogenic centres on the
periphery of the macrocycles. The aggregation
behaviour and chiroptical
features of the aggregates are strongly
dependent on the number of moieties
decorating the periphery of the porphyrin
framework. In particular, experimental
evidence indicates that the
structure of the steroid linker dictates
the overall chirality of the supramolecular
architectures. Moreover, the porphyrin
concentration strongly affects
the aggregation mechanism and the
CD intensities of the spectra. Notably,
AFM investigations reveal strong differences
in aggregate morphology that
are dependent on the nature of the appended
functional groups, and closely
in line with the changes in aggregation
mechanism. The suprastructures
formed at lower concentration show a
network of long fibrous structures
spanning over tens of micrometres,
whereas the aggregates formed at
higher concentration have smaller rodshaped
structures that can be recognised
as the result of coalescence of
smaller globular structures. The fully
steroid substituted derivative forms
globular structures over the whole concentration
range explored. Finally, a rationale
for the aggregation phenomena
was given by semiempirical calculations
at the PM6 level
Widening the scope of the corrole sulfonation
The sulfonation reaction has been particularly useful to prepare amphiphilic derivatives of 5,10,15-tris(pentafluorophenyl)corrole, but it has been limited to this corrole. We have studied the scope of this reaction, using 5,10,15-triphenylcorrole as the prototypical example of corrole structure. The reaction protocol has been modified to avoid the corrole aggregation, which limited its reactivity in the neat chlorosulfonic acid. Surprisingly, the reaction shows an unprecedented regioselectivity for corrole derivatives, affording 3 as the main product, but also corrole 5, which is the first example of monosubstituted corrole on pyrrole B. By modulating the corrole: chlorosulfonic acid reagent ratio, it has been possible to obtain the antipodal disubstituted product 6, demonstrating again a not usual regioselectivity for corrole substitution. These results allow the preparation of novel amphiphilic corrole derivatives, which open up their potential applications in different fields
Preparation and spectroscopic studies of silica nanoparticle-porphyrin hybrids held by noncovalent interactions
Amphiphilic porphyrin derivatives adsorbed onto silica nanoparticles via noncovalent interactions have been prepared and characterized. The organic-inorganic hybrids have been obtained by simply stirring a nanoparticle suspension into an aqueous solvent mixture of porphyrin aggregates. The systems obtained show good stability in aqueous solvents, at different pH, and also in toluene. Analogous protocol has been applied to the macrocycles in monomeric form, obtaining the corresponding nanoparticle-porphyrin adducts. These systems are of interest for the development of sensors and medicinal application
The kinetic studies of the solvent-promoted aggregation of a steroid-porphyrin derivative
The study of the aggregation of a steroid-functionalised porphyrin derivative shows the formation of chiral suprastuctures. Kinetic studies indicate that the mechanism of the aggregation strongly depends on both the nature of the media and on the concentration of the tetrapyrrolic macrocycle
Preparation and spectroscopic studies of silica nanoparticle-porphyrin hybrids held by noncovalent interactions
Amphiphilic porphyrin derivatives adsorbed onto silica nanoparticles via noncovalent interactions have been prepared and characterized. The organic-inorganic hybrids have been obtained by simply stirring a nanoparticle suspension into an aqueous solvent mixture of porphyrin aggregates. The systems obtained show good stability in aqueous solvents, at different pH, and also in toluene. Analogous protocol has been applied to the macrocycles in monomeric form, obtaining the corresponding nanoparticle-porphyrin adducts. These systems are of interest for the development of sensors and medicinal application. © 2011 World Scientific Publishing Company
Spectroscopic, Morphological and Mechanistic Investigation of the Solvent.Promoted Aggregation of Porphyrins Modified in meso-positions by Glucosylated steroids
Solvent-driven aggregation
of a series of porphyrin derivatives was
studied by UV/Vis and circular dichroism
spectroscopy. The porphyrins are
characterised by the presence in the
meso positions of steroidal moieties
further conjugated with glucosyl
groups. The presence of these groups
makes the investigated macrocycles
amphiphilic and soluble in aqueous solvent,
namely, dimethyl acetamide/
water. Aggregation of the macrocycles
is triggered by a change in bulk solvent
composition leading to formation of
large architectures that express supramolecular
chirality, steered by the presence
of the stereogenic centres on the
periphery of the macrocycles. The aggregation
behaviour and chiroptical
features of the aggregates are strongly
dependent on the number of moieties
decorating the periphery of the porphyrin
framework. In particular, experimental
evidence indicates that the
structure of the steroid linker dictates
the overall chirality of the supramolecular
architectures. Moreover, the porphyrin
concentration strongly affects
the aggregation mechanism and the
CD intensities of the spectra. Notably,
AFM investigations reveal strong differences
in aggregate morphology that
are dependent on the nature of the appended
functional groups, and closely
in line with the changes in aggregation
mechanism. The suprastructures
formed at lower concentration show a
network of long fibrous structures
spanning over tens of micrometres,
whereas the aggregates formed at
higher concentration have smaller rodshaped
structures that can be recognised
as the result of coalescence of
smaller globular structures. The fully
steroid substituted derivative forms
globular structures over the whole concentration
range explored. Finally, a rationale
for the aggregation phenomena
was given by semiempirical calculations
at the PM6 level