A multidisciplinary study is presented to shed light on how pyrylium frameworks, as π-hole donors, establish π-π interactions. The combination of CSD analysis, computational modelling (ab intitio, DFT and MD simulations) and experimental NMR spectroscopy data provides essential information on the key parameters that characterize these intereactions, opening new avenues for further applications of this versatile heterocycle.

In this work, we use electrophysiological and metabolomic tools to determine the role of chitosan as plant defense elicitor in soil for preventing or manage root pests and diseases sustainably. Root exudates include a wide variety of molecules that plants and root microbiota use to communicate in the rhizosphere. Tomato plants were treated with chitosan. Root exudates from tomato plants were analyzed at 3, 10, 20, and 30 days after planting (dap). We found, using high performance liquid chromatography (HPLC) and excitation emission matrix (EEM) fluorescence, that chitosan induces plant hormones, lipid signaling and defense compounds in tomato root exudates, including phenolics. High doses of chitosan induce membrane depolarization and affect membrane integrity. 1H-NMR showed the dynamic of exudation, detecting the largest number of signals in 20 dap root exudates. Root exudates from plants irrigated with chitosan inhibit ca. twofold growth kinetics of the tomato root parasitic fungus Fusarium oxysporum f. sp. radicis-lycopersici. and reduced ca. 1.5-fold egg hatching of the root-knot nematode Meloidogyne javanica.

Among the great challenges facing the Society is the search for solutions to cancer. This disease presents high cellular oxidative stress, as a result of the imbalance between the oxidizing species generated in the cells and antioxidant compounds. One of the strategies used in the treatment of cancer is based on the use of Photodynamic therapy (PDT). PDT is a safe and non-invasive technique for the treatment of different types of cancer in diverse locations, as well as non-cancer diseases. PDT consists of the local or systemic application of a photosensitive compound (the photosensitizer), which accumulates mainly in the pathological tissues. Photosensitive molecules absorb light of the appropriate wavelength, initiating the activation processes that lead to the selective destruction of tumor cells. An adequate photosensitizer must obey a number of features such as maximum absorption length between 600 and 800 nm, minimum absorption length between 400 and 600 nm, high purity and stability at room temperature, and high selectivity with tumor tissues, among others. In this context, selenopyrylium salts emerge as potential candidates to photosensitizers due to fit with most of these features. Therefore, the aims in the present work are the synthesis and characterization of monocationic selenopyrillium salts, using a methodology that does not involve organometallic reagents, and the evaluation of their photophysical properties for their possible application as photosensitizers in PDT.

Chitosan is a natural non-toxic, biodegradable and biocompatible biopolymer, which is derived from chitin, whose structure allows a wide variety of chemical modifications that can confer new physical-chemical properties, functions and applications in different fields. Among the great challenges facing the Society is the search for solutions to Alzheimer's disease. This disease presents high cellular oxidative stress, as a result of the imbalance between the oxidizing species generated in the cells and antioxidant compounds. One of the strategies used in the treatment of Alzheimer's is based on the use of acetylcholinesterase (AChE) inhibitors, an enzyme that catalyzes the hydrolysis of acetylcholine, a neurotransmitter involved in memory. In this context, Tacrine was the first drug approved for this purpose, later withdrawn due to liver damage caused by inducing oxidative stress. Therefore, in the present work, new Tacrine derivatives that could reduce the original hepatotoxicity of the compound while preserving its properties as an AChE inhibitor have been prepared and characterized. Furthermore, by means of the formation of different functional bridges between Tacrine and Chitosan, new hybrid systems Tacrina-Chitosan, have been synthesized and characterized in order to serve as vectors of the drug in the human body. Among them, presence of a selenourea bridge must contribute to reduce oxidative stress, given the property of Se to reduce the number of ROS species in the cell.

A systematic study of the stabilization of glycosyl cations on aromatic rings is reported at the B3LYP, M06-2X and M11 levels of theory. In particular, π-acidic arenes such as fluorobenzenes or naphthalenediimides efficiently stabilize these cations acting cooperatively as sandwich-type ternary cation-π-anion systems. The stabilization and cooperativity in polar (both protic and aprotic) and non-polar solvents has been also evaluated by using the polarizable continuum model. In addition, the role of the protecting group at the C-2 position (methyl, acetyl, benzyl, and pivaloyl) for this noncovalent stabilization has been explored, as well as the behaviour of the corresponding 2-deoxy glycosyl cation.

A theoretical method based on Dissipative Particle Dynamics (DPD) was applied for the study of the interaction between coarse-grained models of chitosan and gold nanoparticles. These models were used to understand the role of chitosan in the stabilization of gold nanoparticles (5 and 7 nm). In addition, this stabilization was also supported by synthesized and characterized chitosan-gold nanoparticles comparing their stabilities with typical citrate-gold nanoparticles. Finally, the role of chitosan as a capping agent through the steric and electrosteric mechanisms in aqueous media with different pH values was also evaluated.

An efficient and mild procedure was developed for the preparation of three chitosan-supported ureas containing electron-withdrawing groups. These catalysts were characterized and employed as organocatalysts in different transformations, including the enantioselective cyanosilylation of α-ketoesters and aldehydes, the asymmetric addition of formaldehyde tert-butyl hydrazone to prochiral α-ketoesters and a Friedel-Crafts reaction. Several parameters that can affect the activity and selectivity of the reactions were analysed. The supported catalysts can be reused for more than 10 cycles with only a small loss in their properties. Finally, theoretical DFT calculations were carried out to interpret the results of the catalysed reactions.

Selenium is an essential trace element. In Nature, its main biological function is associated with the incorporation in the form of selenocysteine into certain proteins having redox motifs, such as Glutathione Peroxidase (GPx), among others. Different selenium containing compounds resulted to be bio-inspired catalysts, good antioxidant agents and good GPx-mimics. On the other hand, chitosan the chiral polysaccharide obtained by alkaline deacetylation of chitin has been applied in many fields, due to its biocompatible and biodegradable properties as well as its relative ease to manage compared to its chemical N-acetylated precursor. The control of their chemical and physical properties allows chitosan derivatives to be used for different biomedical and industrial applications. Degree of deacetylation (DD) and polymer chain length (molecular weight, Mw) can be considered the most important features to determine the physico-chemical properties of these systems and consequently decisive factors to give desired results in formulations and applications. We report here, the synthesis of new selenoureidyl chitosan derivatives with tunable physicochemical properties by reaction of the biopolymer with a series of diversely substituted aryl isoselenocyanates. All new compounds have been characterized by NMR techniques both in solution and in solid state. Finally, in order to study the applicability of the new chitosan-derived selenoureas, antioxidant capacity and GPx-mimics ability have been investigated. The authors thank the Junta de Andalucía (2011/FQM-142, and Project P09-AGR-4597); Spanish Ministerio de Economía, Industria y Competitividad (MINECO), Spain (CTQ2016-78703-P); A. J. Galera-Carrillo also thanks Universidad de Sevilla (PEJUS-2, 2017-2-EJ-070) for funding support. The authors also thank the CITIUS, Universidad de Sevilla, for the facilities.

Antonio J. Galera-Carrillo, Elizabeth Torres-Párraga, Antonio Franconetti, Francisca Cabrera-Ecribano Departamento de Química Orgánica, Facultad de Química, Universidad de Sevilla, C/Profesor García González 1, 41012 Sevilla, España Contact email: agalera@us.es Chitosan is a biodegradable, biocompatible and non-toxic natural polymer derived from chitin. It presents a structure that provides with a wide number of features which could be interesting for its applicability in different fields. On the other hand, polyphenolic compounds, such as hydroxytyrosol, have shown a marked anti-inflammatory and antioxidant properties directly related to cardiovascular diseases, neurodegeneration, metabolic syndrome or cancer. Preparation of a serie of chitosan derivates, particulary polyphenolic systems, will be described in this work. This purpose will be carried out by taking advantage of the reactivity of chitosan´s amino group. These new compounds consist of quaternized salts with structure of pyrylium or quinolinium salts depending on they were synthesized by reaction of chitosan with polyphenolic pyrylium salts or polyhydroxysubstituted 3-desoxyanthocianines salts respectively . Pyrylium and anthocyanin salts used to obtain such systems were previously synthesized by means of a methodology optimized by this group. It consists of using ortho, meta and/or para-substituted acetophenones as well as ortho, meta and / or para-substituted benzaldehyde in the presence of a Lewis acid, which mediates in the dehydration and cyclation process. All the new compounds have been characterized by NMR and MS techniques. Finally, in order to study the applicability of these compounds, photophysical properties, antioxidant capacity and glutathione peroxidase mimetics will be studied. The authors thank the Junta de Andalucía (2011/FQM-142, and Project P09-AGR-4597); Spanish Ministerio de Economía, Industria y Competitividad (MINECO), Spain (CTQ2016-78703-P); A. J. Galera-Carrillo also thanks Universidad de Sevilla (PEJUS-2, 2017-2-EJ-070) for funding support. The authors also thank the CITIUS, Universidad de Sevilla, for the facilities.

The interplay between noncovalent interactions that involve oxygenated heteroaromatic rings have been studied for the first time in this work. In particular, we report an advance in knowledge-based anion-π interactions together with (C-H)+ ⋅⋅⋅anion contacts. To understand how the anion modulates these interactions, the synthesis of pyrylium salts with a variety of anions was performed by using an anionic metathesis methodology. The synthesized pyrylium complexes were classified in series, for example, anions derived from halogens, from oxoacids, from p-block elements, and from transition metals. Crystallographic data, DFT calculations, and NMR spectroscopy methods provided access to an overall insight into the noncovalent behavior of the anion in this kind of system. Based on the DFT calculations and 1 H NMR spectroscopy, pyrylium protons can be used as chemical tags to detect noncovalent interactions in this type of compound.

A straightforward route to diversely functionalized glycopyranosides is reported. 2,3-Enopyranosides, 2- and/or 3-azido-, 2-halopyranosides, and a hex-3-ulose, among other - and -glycopyranosides are easily obtained in good to excellent yields from 2-hydroxyglycopyranosides by means of a two-step process involving trifluoromethanesulfonation and subsequent treatment with the appropriate nucleophilic agent.

Adenoviruses is a common pathogen associated to multiple diseases. Carbohydrates containing a diversely substituted urea moiety were synthesized from the corresponding isocyanate and used on Human adenovirus as target. The structure with phenyl ring as substituent provides a potential anti- Ads with an inhibition about 50%.

A variety of methylenemalononitriles and ethyl cyanoacrylates derived from both aromatic and heteroaromatic aldehydes were synthesized by Knoevenagel condensation catalysed with native and modified chitosan-based heterogeneous catalysts. The efficiency of our hydrogel organocatalysts, chitosan hydrogel beads and ureidyl-chitosan derivative hydrogel disks, was evaluated as function of pH, temperature and catalyst concentration by considering reaction rates, conversions, E/Z stereoselectivities, and kinetic studies of a model reaction between 4-nitrobenzaldehyde and ethyl cyanoacetate. An unprecedented study by solid state C-13 CP MAS NMR of the employed catalyst when reaction was quenched after a 50% of conversion, has demonstrated that an imine-chitosan intermediate is formed during this process. Analysis of E/Z ethyl cyanoacrylate isomer mixtures for determining the corresponding stereoselectivity was carried out by NMR measuring carbon-proton coupling constants ((3)J(C,H)) using a novel CLIP-HSQMCB experiment. Additionally, DFT calculations let us rationalise the observed E/Z stereoselectivities as well as to evaluate the role of ureidyl moiety on interaction with aldehydes and imine intermediate formation with chitosan derivative. (C) 2016 Elsevier B.V. All rights reserved.

A variety of fluorescent imino and secondary amino chitosans were synthesized under very mild conditions by reaction of the biopolymer amino functions with aromatic aldehydes in an acidified methanolic suspension. Simultaneous reactions of several aldehydes with chitosan were successfully carried out, and kinetic studies showed that 1-pyrenecarboxaldehyde reacts the fastest among them. An unprecedented study on the evaluation of the degree of N-substitution (DS, ranging from 31.7% to 12.0%) for the chitosan Schiff bases by using solid state CPMAS (13)C NMR is performed. A linear correlation between the DS obtained for the secondary amino chitosans by (1)H NMR (55.3-10.2%) and those obtained by CPMAS (13)C NMR (34.4-13.8%) has allowed us to calculate an empirical correlation factor that could be applied on chitosan-based aromatic systems. The new chiral-labelled chitosan derivatives exhibit a stable fluorescent behaviour, which was used to explore solvent sensoring applications.

MAO inhibitors have increased their importance as a result of the high incidence of neurodegenerative diseases such as Parkinson or Alzheimer. Herein, we report the synthesis and characterization of coumarin glycosides by reaction of a glycosyl halide with coumarin derivatives as well as mechanistic considerations based on DFT calculations. Additionally, the determination of the enzymatic parameters has shown that the carbohydrate-coumarin derivative is an efficient drug-releasing system.

Involved in several physiological processes, redox behaviour has recently emerged as a promise research target requiring the design of compounds to be applied as sensor in a wide working window.In this communication, the synthesis of new quaternized pyridinium-chitosan derivatives by reaction of the biopolymer with electronically tuneable 2,4,6-triarylpyrylium tetrafluoroborates in mild conditions, and their characterization are described.

Novel types of fluorescent and quaternized pyridinium–chitosan derivatives have been synthesized and their characteristics as potential NLO-phore biomaterials have been disclosed by DFT calculations.

Nowadays, the synthesis of applicable products in everyday life is an increasing research topic. Knoevenagel condensation presents a broad range of applications in synthesis of multiple substances involving domino reactions to obtain five- and six-membered heterocycles such as polysubstituted pyrrolidines, dihydrothiophenes and 1,4-dihydropyridines. Chitosan has been employed as support of metallic catalysts in hydrogenation of ethyl cinnamate, Suzuki cross coupling or to transform nitriles into amides. Very recently, this polymer has been used in several reactions (e.g. aldol, Henry o Michael reactions) as heterogeneous catalyst using simple aldehydes. We report here, the synthesis of new Knoevenagel switchable products obtained from malononitrile and highly modified aldehydes owning different steric hindrance and electronic effects. The heterogeneous chitosan catalyst role has been studied to improve on conversion, time and yields compared with non-catalyzed reactions.We thank the AECID (Projects A/023577/09 and A/030422/10) and the 'Junta de Andalucía' (FQM 142 and Project P09-AGR-4597) for financial support.

Pyridinium salts are very useful synthetic building blocks to obtain substituted pyridines, dihydropyridines or piperidines. Furthermore, pyridinium dyes present a multiple application fields including biological and optical responses due to their photophysical features, in particular, high fluorescence, charge transfer character and solvatochromic properties. Different methods are available for the synthesis of pyridinium salts depending on the symmetry around of the cation. One of them involves the use of pyrylium salts as precursor. Linear and non-linear optical behaviour are controlled by different parameters both macro- and microscopically level. At molecular level is necessary to know parameters such as dipole moment, polarizatility, first-order hyperpolarizability, among others. Herein we report, a novel easy synthesis and characterization of new anchored pyridinium moiety into a polymeric backbone. Moreover, DFT calculations have been performed on suitable model to explore molecular parameters involved in lineal and non-lineal optical properties. We thank the AECID (Projects A/023577/09 and A/030422/10) and the 'Junta de Andalucía' (FQM 142 and Project P09-AGR-4597) for financial support.

Chitosan, the N-deacetylation product of chitin has been applied in many fields, due to its biocompatible and biodegradable properties as well as its relative ease to manage compared to its chemical precursor. The control of their chemical and physical properties allows Chitosan derivatives to be used for different biomedical and industrial applications. Degree of deacetylation (DD) and polymer chain length (molecular weight, Mw) can be considered the most important features to determine the physico-chemical properties of these systems and consequently decisive factors to give desired results in formulations and applications. On the other hand, ureide compounds have been employed in different applications fields such as catalysis involving the selective synthesis of tertiary thiols or medicinal chemistry as glutathione analog. We report here, the synthesis in water of new ureidyl chitosan derivatives and their characterization by NMR techniques both in solution and solid state. Aliphatic and aromatic diisocyanates were used as crosslinking agents to obtain a chitosan network with potential physicochemical properties in gel formation. We thank the AECID (Projects A/023577/09 and A/030422/10) and the 'Junta de Andalucía' (FQM 142 and Project P09-AGR-4597) for financial support.