Felipe Serna

Fluorogenic and Chromogenic Polymer Chemosensors

The introduction of host units, also called binding sites or receptor subunits, and fluorescence or chromogenic signaling motifs into the lateral or into the main polymer chain opens the way for cutting-edge applications related to the selective interaction of these chemical sites with guest or target molecules (i.e., cations, anions or neutral molecules). Thus, the good mechanical properties of these polymers permit the design and preparation of “á la carte” fluorogenic or colorimetric probes for sensing diverse analytes. These polymeric probes may work in organic or aqueous solutions and, most importantly, in the solid state, as finished materials, can operate in aqueous media, permitting the preparation of “naked-eye” solid probes to be used by non-specialist personnel, for example, to control the concentration of analytes in chemical industries or to test whether environmental polluting chemicals exceed the legal limits.

Recent Patents on Aromatic Polyamides

Aromatic polyamides are high performance materials with superior thermal and mechanical properties which make them extremely useful for advanced technologies. These polymers can be transformed into high-tensile strength synthetic fibers and into flame and cut-resistant materials that have technological applications in the field of coatings and fillers in the aerospace and armaments industry, in asbestos substitutes, electrical insulation, bullet-proof body armor, industrial filters, and sports fabrics, among others. This article sets out to review the existing literature and recent patent claims that describe the design, the preparation and the applications of wholly aromatic polyamides, semiaromatic polyamides and poly(amide imide)s.

Sub-ppm quantification of Hg(II) in aqueous media using both the naked eye and digital information from pictures of a colorimetric sensory polymer membrane taken with the digital camera of a conventional mobile phone

We present colorimetric sensory membranes for detecting Hg(II) in aqueous media. The colour response of the sensory materials can be tuned for detection with the naked eye, such as the maximum contaminant level of Hg(II) that is set by the United States Environmental Protection Agency (EPA) for drinking water. Furthermore, the concentration of Hg(II) can be monitored using digital pictures of the membranes taken with conventional cameras. Thus, nanomolar concentration of Hg(II) could be detected by the naked eye due to colour changes of membranes, and the concentration of Hg(II) could be quantified, within the millimolar to nanomolar range, by means of analysing the digital information of pictures taken of the membranes after dipping them in water containing this environmentally poisonous cation.

Working with water insoluble organic molecules in aqueous media: fluorene derivative-containing polymers as sensory materials for the colorimetric sensing of cyanide in water

This paper describes a strategy followed to achieve a sensing phenomenon in aqueous media using water-insoluble organic molecules. We have prepared a methacrylamide and a methacrylate with pendant cyanide chemosensors based on a fluorene-derivative motif, and we have fabricated highly hydrophilic membranes by means of copolymerising these hydrophobic monomers with others. Therefore, upon absorption of water in the membranes, solvated ions enter the membrane by a simple diffusion mechanism, reaching the hydrophobic chemosensor motifs and giving rise to a macroscopic sensing phenomenon. In this way, we have prepared solid materials (dense membranes or films) capable of selectively detecting cyanide, with an extremely low detection threshold, in aqueous solution by means of colour changes (naked-eye sensing) (13 ppb). Nevertheless, the key point of this research is the description of the possibilities of anchoring organic insoluble molecules (i.e., drugs, fungicides, bactericides, sensing probes, etc.) to solubilise them in water, or to prepare hydrogels, permitting the use of these molecules in aqueous media or in biological media for medical, biological or biochemical purposes.

Novel aromatic polyamides with main chain and pendant 1,2,4-triazole moieties and their application to the extraction/elimination of mercury cations from aqueous media

This work describes five novel aromatic polyamides and copolyamides containing the triazole heterocycle attached by an amine linkage to the main and lateral chains. The polyamides were found to be amorphous and soluble in polar aprotic solvents. They demonstrated a film-forming capability, exhibited good thermal resistance and had high thermal transition temperatures (up to 375 °C). The triazole and amine groups imparted hydrophilicity to the polymers, giving rise to materials that improve their mechanical properties upon water uptake, and were efficient chelating/host units for heavy metal cations. These properties facilitated the preparation of solid polymer phases to be used for the extraction and elimination of environmentally deleterious cations from water environments. In regards to cation extraction from aqueous media with polyamide solid phases, the correct polymer structure designs led to the extraction of high percentages of HgII (neat 100%).

Solid Polymer Substrates and Coated Fibers Containing 2,4,6- Trinitrobenzene Motifs as Smart Labels for the Visual Detection of Biogenic Amine Vapors

Attempts to polymerize trinitrobenzene derivatives (TNB) have been fruitless so far. Accordingly, polymers containing TNB have not been exploited in spite of their envisaged potential applications. Here, we describe two ways for preparing polymers with TNB moieties thus overcoming the previously reported polymerization impairments. We also report on the exploitation of the materials, both obtained as tractable transparent films and coated fibers, as smart labels for the visual detection of amine vapors. More precisely, amines in the atmosphere surrounding the sensory materials diffuse into them reacting with the TNB motifs forming highly colored Meisenheimer complexes, giving rise to development of color and to the naked eye sensing phenomenon. This is the case of highly volatile amines, such as trimethylamine, produced in food spoilage, specifically in the deterioration of fish or meat, for which the color development of the smart labels can be used as a visual test for food freshness.

Solid polymer substrates and smart fibres for the selective visual detection of TNT both in vapour and in aqueous media

This work describes the design of efficient, inexpensive and easily prepared selective sensory polymers with chemically anchored amine groups as 2,4,6-trinitrotoluene (TNT)-sensing motifs as materials for the selective visual detection of TNT in aqueous media and as vapours. The materials are prepared as handleable sensory films or dense membranes from which sensory discs are cut, as well as smart fibres by coating conventional and commercial cotton fabrics. Both types of material exhibited a highly visible colour development from colourless to red upon contact with TNT both in the gas phase and in solution, and the colour change was used to build titration curves using the colour definition parameters of a digital image acquired with a smartphone, i.e., the RGB system. The materials were selective, remaining silent with other nitroaromatic compounds, such as 4-nitrotoluene and 2,4-dinitrotoluene, and the detection limit in solution was close to the micromolar range.

Polyamide model compound containing the urea group as selective colorimetric sensing probe towards aromatic diamines

A colorimetric diacid monomer for aromatic diamine sensing containing the urea binding site has been synthesised and characterised. A colour development from colourless to blue, brown or yellow was observed upon addition of metha, para or ortho-phenylenediamine, respectively, to polar aprotic organic solvent solutions of the monomers. The solutions remained colourless upon addition of other amines or diamines. The model polyamide compound derived from the diacid monomer maintains the colorimetric sensing selectivity towards the aromatic diamines; so the polyamides derived from the diacid monomer described herein are supposed to retain the ability to interact selectively with the aromatic diamines; hence cheap future sensing devices could be built by means of easy-to-use naked eye polyamide film chemosensor or by incorporating a polyamide coating in the end of an optic fibre connected to a portable diode array visible detector. A novel polyamide model compounds for aromatic diamine colorimetric sensing is described. Colourless solutions of the models in NMP develop a yellow-greenish, red or blue colour upon addition of ortho, meta or para-phenylenediamine, respectively, while remain silent upon addition of other aliphatic and aromatic amines and diamines.

Forced Solid-State Interactions for the Selective “Turn-On” Fluorescence Sensing of Aluminum Ions in Water Using a Sensory Polymer Substrate

Selective and sensitive solid sensory substrates for detecting Al(III) in pure water are reported. The material is a flexible polymer film that can be handled and exhibits gel behavior and membrane performance. The film features a chemically anchored salicylaldehyde benzoylhydrazone derivative as an aluminum ion fluorescence sensor. A novel procedure for measuring Al(III) at the ppb level using a single solution drop in 20 min was developed. In this procedure, a drop was allowed to enter the hydrophilic material for 15 min before a 5 min drying period. The process forced the Al(III) to interact with the sensory motifs within the membrane before measuring the fluorescence of the system. The limit of detection of Al(III) was 22 ppm. Furthermore, a water-soluble sensory polymer containing the same sensory motifs was developed with a limit of detection of Al(III) of 1.5 ppb, which was significantly lower than the Environmental Protection Agency recommendations for drinking water.

An organic/inorganic hybrid membrane as a solid "turn-on" fluorescent chemosensor for coenzyme A (CoA), cysteine (Cys), and glutathione (GSH) in aqueous media.

The preparation of a fluorogenic sensory material for the detection of biomolecules is described. Strategic functionalisation and copolymerisation of a water insoluble organic sensory molecule with hydrophilic comonomers yielded a crosslinked, water-swellable, easy-to-manipulate solid system for water “dip-in” fluorogenic coenzyme A, cysteine, and glutathione detection by means of host-guest interactions. The sensory material was a membrane with gel-like behaviour, which exhibits a change in fluorescence behaviour upon swelling with a water solution of the target molecules. The membrane follows a “turn-on” pattern, which permits the titration of the abovementioned biomolecules. In this way, the water insoluble sensing motif can be exploited in aqueous media. The sensory motif within the membrane is a chemically anchored piperazinedione-derivative with a weakly bound Hg(II). The response is caused by the displacement of the cation from the membrane due to a stronger complexation with the biomolecules, thus releasing the fluorescent sensory moieties within the membrane.