Saul Vallejos - Academia.edu (original) (raw)

Papers by Saul Vallejos

Plant Physiology

Plant–pest interactions involve multifaceted processes encompassing a complex crosstalk of pathwa... more Plant–pest interactions involve multifaceted processes encompassing a complex crosstalk of pathways, molecules, and regulators aimed at overcoming defenses developed by each interacting organism. Among plant defensive compounds against phytophagous arthropods, cyanide-derived products are toxic molecules that directly target pest physiology. Here, we identified the Arabidopsis (Arabidopsis thaliana) gene encoding hydroxynitrile lyase (AtHNL, At5g10300) as one gene induced in response to spider mite (Tetranychus urticae) infestation. AtHNL catalyzes the reversible interconversion between cyanohydrins and derived carbonyl compounds with free cyanide. AtHNL loss- and gain-of-function Arabidopsis plants showed that specific activity of AtHNL using mandelonitrile as substrate was higher in the overexpressing lines than in wild-type (WT) and mutant lines. Concomitantly, mandelonitrile accumulated at higher levels in mutant lines than in WT plants and was significantly reduced in the AtHNL...

The 1st International Electronic Conference on Chemical Sensors and Analytical Chemistry, 2021

Aromatic polyamides or aramids are materials with exceptional thermal and mechanical properties. ... more Aromatic polyamides or aramids are materials with exceptional thermal and mechanical properties. For this reason, they are considered high-performance materials with many applications in fields such as civil security (bullet-proof body armour or fire, chemical, and saw protection suits), transport (automotive and aerospace), and civil engineering, among many others. The remarkable properties arise from the high cohesive energy due to their chemical structure, including the rigidity of the main chain due to the wholly aromatic structure conjugated with the amide groups, the high average bond energy, and a strong and highly directional interchain hydrogen bonds between the amide moieties. Although the natural yellowish colour of the fibres is used, generally, most of the applications require coloured fibres. However, aramid fibres have poor dyeing properties for the same reasons that make them thermally and mechanically resistant, and traditional dyeing methods, such as dope dyeing, are inefficient and aggressive, which impairs the fibres' properties. The ideal colour fastness of fibres is achieved by intrinsically, inherently, or self-coloured polymers by introducing a dye motif or chromophore monomer in the chemical structure of the polymer. In addition, the colour hue can be controlled by tuning the chromophore monomer molar content in the final composition. In previous research, we successfully obtained inherently blue-coloured aramids, with blue chromophore motifs unable to migrate and evenly distribute along the polymer chain and maintain their high-performance properties, and our aim now is to obtain red-coloured aramids prepared in the same fashion.

Polymers, 2020

We anchored a colourimetric probe, comprising a complex containing copper (Cu(II)) and a dye, to ... more We anchored a colourimetric probe, comprising a complex containing copper (Cu(II)) and a dye, to a polymer matrix obtaining film-shaped chemosensors with induced selectivity toward glycine. This sensory material is exploited in the selectivity detection of glycine in complex mixtures of amino acids mimicking elastin, collagen and epidermis, and also in following the protease activity in a beefsteak and chronic human wounds. We use the term inducing because the probe in solution is not selective toward any amino acid and we get selectivity toward glycine using the solid-state. Overall, we found that the chemical behaviour of a chemical probe can be entirely changed by changing its chemical environment. Regarding its behaviour in solution, this change has been achieved by isolating the probe by anchoring the motifs in a polymer matrix, in an amorphous state, avoiding the interaction of one sensory motif with another. Moreover, this selectivity change can be further tuned because of th...

Sensors and Actuators B: Chemical, 2021

Polymers, 2018

A report on the syntheses, thermal, mechanical and dielectric characterizations of two novel poly... more A report on the syntheses, thermal, mechanical and dielectric characterizations of two novel polymeric acrylic materials with azide groups in their pendant structures is presented. Having the same general structure, these polymers differ in length of oxyethylene units in the pendant chain [-CONH-CH2CH2-(O-CH2CH2)nN3], where n is 1 (poly(N-(2-(2-azidoethoxy)ethyl)methacrylamide), PAzMa1) or 2 (poly(N-2-(2-(2-azidoethoxy)ethoxy)ethyl)methacrylamide), PAzMa2), leading with changes in their dynamics. As the thermal decomposition of the azide group is observed above 100 °C, dielectric analysis was carried out in the temperature range of −120 °C to 100 °C. Dielectric spectra of both polymers exhibit in the glassy state two relaxations labelled in increasing order of temperature as γ- and β-processes, respectively. At high temperatures and low frequencies, the spectra are dominated by ohmic conductivity and interfacial polarization effects. Both, dipolar and conductive processes were chara...

Sensors, 2018

Microcellular sensory polymers prepared from solid sensory polymeric films were tested in an aque... more Microcellular sensory polymers prepared from solid sensory polymeric films were tested in an aqueous Hg(II) detection process to analyze their sensory behavior. First, solid acrylic-based polymeric films of 100 µm thickness were obtained via radical copolymerization process. Secondly, dithizone sensoring motifs were anchored in a simple five-step route, obtaining handleable colorimetric sensory films. To create the microporous structure, films were foamed in a ScCO2 batch process, carried out at 350 bar and 60 °C, resulting in homogeneous morphologies with cell sizes around 5 µm. The comparative behavior of the solid and foamed sensory films was tested in the detection of mercury in pure water media at 2.2 pH, resulting in a reduction of the response time (RT) around 25% and limits of detection and quantification (LOD and LOQ) four times lower when using foamed films, due to the increase of the specific surface associated to the microcellular structure.

Chemosensors, 2018

The present review presents the most recent developments concerning the application of sensory po... more The present review presents the most recent developments concerning the application of sensory polymers in the detection and quantification of different target species. We will firstly describe the main polymers that are being employed as sensory polymers, including, for example, conducting or acrylate-based polymers. In the second part of the review, we will briefly describe the different mechanisms of detection and the target species, such as metal cations and anions, explosives, and biological and biomedical substances. To conclude, we will describe the advancements in recent years concerning the fabrication of micro and nano sensory devices based on smart polymers, with a bibliographic revision of the research work published between 2005 and today, with special emphasis on research work presented since 2010. A final section exposing the perspectives and challenges of this interesting research line will end the present review article.

Journal of Hazardous Materials, 2019

 Sensory polymeric materials change their colour in presence of oxidant atmospheres.  The senso... more  Sensory polymeric materials change their colour in presence of oxidant atmospheres.  The sensory materials are films shaped with embedded aniline.  The detection and quantification are based both on optical and electrical methods.  The detection is achieved visually and also using conventional and simple devices.  The presence of oxidants Cl2 and H2O2 in air is detected in the ppbv range.

Journal of Materials Chemistry A, 2017

Direct visual detection and quantification of mercury in fish and water using easily prepared pol... more Direct visual detection and quantification of mercury in fish and water using easily prepared polymeric labels. In fish, the labels can be used directly through contact with fish meal.

ACS Applied Materials & Interfaces, 2016

We have developed new functionalized polymers capable of being easily coated by gold nanoparticle... more We have developed new functionalized polymers capable of being easily coated by gold nanoparticles, uniformly distributed on the surface of the polymers, by simply adding a gold(III) solution in water to the polymers. The polymer-supported gold nanoparticle material was used as an efficient portable and reusable catalyst for Suzuki reactions in mixed organic-aqueous solvents.

Chemical Communications, 2016

A new polymeric sensing material acts as a smart label for the fluorescent detection of Hg2+ and ... more A new polymeric sensing material acts as a smart label for the fluorescent detection of Hg2+ and MeHg+ in fish samples.

Dyes and Pigments, 2015

ABSTRACT This work describes the preparation of intrinsically blue-colored, high-performance arom... more ABSTRACT This work describes the preparation of intrinsically blue-colored, high-performance aromatic polyamides (aramids). The color was achieved by preparing a diamine monomer containing a chromogenic azadipyrromethene (ADPM) core, which after polymerizing it with commercially available m-phenyleneisophtahlamide and isophthaloyl chloride gave the blue-colored polyisophthalamide copolymers. These materials were structurally compared to commercialized and high-value-added meta-aramid fibers [poly(m-phenyleneisophthalamide), MPIA, brand names: NOMEX® and Teijinconex®]. Blue is the highest demanded color in the market of protective aramid fibers. The coloration efficiency of this special monomer is very high. Furthermore, the aramids showed even better thermal properties than commercial MPIA.

Chemistry – A European Journal, 2015

Attempts to polymerize trinitrobenzene derivatives (TNB) have been fruitless so far. Accordingly,... more 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 freshn...

ABSTRACT Poly(vinylpyrrolidone-co-butyl acrylate) samples with different proportions of monomers ... more ABSTRACT Poly(vinylpyrrolidone-co-butyl acrylate) samples with different proportions of monomers were prepared as tractable and hydrophilic materials. An analysis of the intermolecular interactions between the polymer groups was carried out by FTIR. The dependence of the C-O bands (lactam and pendant butyl ester) with the composition suggests a strong interaction between the lactam groups. They exert an important influence in the molecular mobility, which was studied by DSC and DRS. A single narrow glass transition temperature (Tg) is observed in each random copolymer, consistent with a single phase of low compositional nanoheterogeneity. The dependence of the Tg with the composition suggests significant interactions between polymer components. The dielectric spectra show γ, β, and α relaxations in increasing order of temperature, followed by conductive contributions. The apparent activation energies for secondary relaxations have similar values for all the samples. The γ-process is related to the local motions of the butyl units and the β-process is a Johari−Golstein secondary relaxation that is related to the local motions of the pyrrolidone group together with the motion of polymer backbone segments.