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Publications 2016


Modulation of the Exfoliated Graphene Work Function through Nitrile Imines Cycloaddition

M. Barrejón, M. J. Gómez-Escalonilla, J. L. G. Fierro, P. Prieto, J. R. Carrillo, A. M. Rodríguez, G. Abellán, M. C. López-Escalante, M. Gabás, T. López-Navarrete, F. Langa.

Physical Chemistry Chemical Physics, 2016, 18, 29582-29590. 

DOI: 10.1039/C6CP05285A

After the feasibility of the 1,3-dipolar cycloaddition reaction between nitrile imines and exfoliated graphene by density functional theory calculations was proved, very few-layer graphene was effectively functionalized using this procedure. Hydrazones with different electronic properties were used as precursors for the 1,3-dipoles, and microwave irradiation as an energy source enabled the reaction to be performed in a few minutes. The anchoring of organic addends on the graphene surface was confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function and band gap of these new hybrids. Our results demonstrate that it is possible to modulate these important electronic valence band parameters by tailoring the electron richness of the organic addends and/or the degree of functionalization. 


Design of Assembled Systems Based on Conjugated Polyphenylene Derivatives and Carbon Nanohorns.

D. Iglesias, J. Guerra, M. V. Gómez, A. M. Rodríguez, P. Prieto, M. Prato, E. Vázquez, M. A. Herrero.

Chem. Eur. J., 2016, 22, 11643-11651.

DOI: 10.1002/chem.201601282

Promising materials have been designed and fully characterised by an effective interaction between versatile platforms such as carbon nanohorns (CNHs) and conjugated molecules based on thiophene derivatives. Easy and non‐aggressive methods have been described for the synthesis and purification of the final systems. Oligothiophenephenylvinylene (OTP) systems with different geometries and electron density are coupled to the CNHs. A wide range of characterization techniques have been used to confirm the effective interaction between the donor (OTP) and the acceptor (CNH) systems. These hybrid materials show potential for integration into solar cell devices. Importantly, surface‐enhanced Raman spectroscopy (SERS) effects are observed without the presence of any metal surface in the system. Theoretical calculations have been performed to study the optimised geometries of the noncovalent interaction between the surface and the organic molecule. The calculations allow information on the monoelectronic energies of HOMO–LUMO orbitals and band gap of different donor systems to be extracted.


Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

Á. Cantín, M. V. Gomez, A. de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188


Diels–Alder cycloaddition between cyclopentadiene and p-benzoquinone has been studied in the confined space of a pure silica zeolite Beta and the impact on reaction rate due to the concentration effect within the pore and diffusion limitations are discussed. Introduction of Lewis or Brønsted acid sites on the walls of the zeolite strongly increases the reaction rate. However, contrary to what occurs with mesoporous molecular sieves (MCM-41), Beta zeolite does not catalyse the retro-Diels–Alder reaction, resulting in a highly selective catalyst for the cycloaddition reaction.

Thematic issue on Green Chemistry. Editor. L. Vaccaro


New insights in the mechanism of the microwave-assisted Pauson-Khand reaction

A. M. Rodriguez, P. Prieto

New insights in the mechanism of the microwave-assisted PausoneKhand reaction

Tetrahedron 72 (2016) 7443-7448

DOI: 10.1016/j.tet.2016.09.048

A complete analysis of the stereoselectivity observed in the PausoneKhand reaction has been performed using computational calculations. The differences observed in the stereoselectivity when this reaction is performed either by conventional means or under microwave conditions have also been studied. The mechanisms suggested by MagnuseSchore and by Gimbert were used as a model in this investigation. The outcomes show that the observed diastereoselectivity is consistent with the mechanism proposed by Gimbert et al. Moreover, the high activation energy of the process could be responsible for the observed improvement under microwave irradiation.


Microwave Assisted Green Chemistry

A. de la Hoz, A. Díaz-Ortiz, P. Prieto

Alternative Energy Sources for Green Chemistry. Chapter 1. pp. 1-33

RSC Green Chemistry No. 47.

G. Stefanidis, A. Stankiewicz Eds.

Royal Society of Chemistry. ISBN: 9781782621409

Since the first publications on the use of microwave irradiation in synthetic chemistry, it was clear that this methodology would have a marked influence in all areas of this discipline. Reduction of reaction times, improved yields, modifications of selectivities, increased product purities and simplification of work-up procedures were described and, in most cases, these conditions and results could not be achieved by classical heating. This methodology can be included within the concept of Green Chemistry because the strong absorption of microwave irradiation by one component of the reaction would lead to shorter reaction times and improved energy efficiency. Moreover, the synergy with solvent-free conditions, solid catalysts and green solvents has expanded the green applications of this non-conventional energy source. Finally, the use of flow systems, another green methodology, has permitted the scale-up of microwave-assisted reactions under green conditions.


Triazine-Carbon Nanotubes: New Platforms for the Design of Flavin Receptors

M. I. Lucío, F. Pichler, J. R. Ramírez, A. de la Hoz, A. Sánchez-Migallón, C. Hadad, M. Quintana, A. Giulani, M. V. Bracamonte, J. L. G. Fierro, C. Tavagnacco, M. A. Herrero, M. Prato, E. Vázquez

Chem. Eur. J2016, 22, 8879 –8888

DOI: 10.1002/chem.201600630

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single-walled and multi-walled, have been functionalised with 1,3,5-triazines and p-tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the π-π stacking interactions between riboflavin and the nanotube walls. Comparison of p-tolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern–Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin.


Bistriazine-based streptocyanines. Preparation, structural determination and optoelectronic properties

F. León, P. Elizalde, P. Prieto, A. Sánchez-Migallón, A. M. Rodríguez, A. de la Hoz.

Dyes Pigments 2016, 131, 307–319

DOI: 10.1016/j.dyepig.2016.04.016

A series of bistriazine-based streptocyanines has been selectively prepared. A variety of substituents has been introduced into the triazine ring with p-phenylenediamine as a conjugated spacer between the triazine and the streptocyanine moieties. Fukui indices have been used to explain the different sequential reactivity of the chlorine atoms in the triazine ring. 1D- and 2D-DNMR spectroscopy and computational calculations have been carried out to explain the dynamic behavior of these complex systems, which can be explained by the presence of a Cl … H bond. This method was used to build conjugated systems and to show the interaction between the triazine part, the spacer, and the streptocyanine moiety. A study of the optoelectronic properties has been performed by UV–vis and fluorescence spectroscopy. Streptocyanine-based bistriazines are violet-blue emitters and large Stokes shifts of more than 6000 cm−1 were observed. The title compounds showed interesting properties which have potential for use in optoelectronic devices.

Synthesis of Imine-Derived Triazines with Donor-Acceptor Properties

D. R. Corrochano, A. de la Hoz, A. M. Sánchez-Migallón,, R. Caballero, J. R. Ramírez

J. Clean. Prod.  2016, 118, 223-226.

The design of new systems with Donor–Acceptor properties is of great interest for the construction of optoelectronic new devices. Considering the strong supramolecular interaction of triazines with graphene a series of imine-derived triazines with Donor–Acceptor properties have been designed. These compounds have been prepared in good to excellent yields (47–92%) using Green conditions, i.e. microwave irradiation in the absence of an acid catalyst. Their properties as Donor–Acceptor systems have been studied by Ultraviolet–visible and fluorescence spectroscopy and by electrochemical studies. These imine derived triazines are blue-violet emitters (ca. 396 nm) and show large Stokes shifts (c.a. 6700 cm−1) and the electrochemical studies shows a high degree of communication between the acceptor triazines and the donor moieties (oxidation potentials up to 1.10 V). These characteristics makes them excellent candidates for the interaction with graphene and the construction of optoelectronic devices, as blue Light Emitting-Diodes (LEDs).


Stereoselective Synthesis of 1,3-Diaminotruxillic acid derivatives: An Advantageous Combination of CH-ortho-Palladation and on-flow [2+2]-photocycloaddition in microreactors.

Elena Serrano, Alberto Juan, Angel Garcia-Montero, Tatiana Soler, Francisco Jimenez-Marquez, Carlos Cativiela, M. Victoria Gomez, Esteban Urriolabeitia

Chem. Eur. J2016, 22, 144 –152

DOI: 10.1002/chem.201503742

The stereoselective synthesis of ε-isomers of dimethyl esters of 1,3-diaminotruxillic acid in three steps is reported. The first step is the ortho-palladation of (Z)-2-aryl-4-aryliden-5(4H)-oxazolones 1 to give dinuclear complexes 2 with bridging carboxylates. The reaction occurs through regioselective activation of the ortho-CH bond of the 4-arylidene ring in carboxylic acids. The second step is the [2+2]-photocycloaddition of the CC exocyclic bonds of the oxazolone skeleton in 2 to afford the corresponding dinuclear ortho-palladated cyclobutanes 3. This key step was performed very efficiently by using LED light sources with different wavelengths (465, 525 or 625 nm) in flow microreactors. The final step involved the depalladation of 3 by hydrogenation in methanol to afford the ε-1,3-diaminotruxillic acid derivatives as single isomers.

Inside Cover


Green Synthesis of luminescent blue emitters based on bis-triazines with naphthalene as p-conjugated spacer

J. R. Ramírez, A. Ruiz-Carretero, M. Herrero. A. Sánchez-Migallón, A. de la Hoz

Dyes Pigments, 2016, 124, 203-209.

DOI: 10.1016/j.dyepig.2015.09.009

A new series of luminescent blue emissive bistriazines is described. Bistriazines with a naphthalene spacer were prepared using a green methodology that involved microwave irradiation, solvent free conditions and a reaction time of only 10 min. The synthesis was followed by a simple purification procedure. D-σ-A-σ-π-σ-A-σ-D systems were constructed using 1,5-naphthylidene as a planar π-bridge and different donor substituents were attached to the triazine ring. UV–vis and fluorescence spectroscopy showed that the increased conjugation in bistriazines with respect to monotriazines resulted in a 40-fold increase in the photoluminescence quantum yield (ΦF). The bistriazines were efficient blue emitters with ΦF values up to 0.87. The aggregation behavior and the optical and thermal properties of these systems have been studied. The bistriazines showed good thermal stability in conjunction with high ΦF values and they are therefore very promising materials for use in optoelectronic devices.


Self-assembly of T-shape 2H-benzo[d][1,2,3]-triazoles. Optical waveguide and photophysical properties

I. Torres, J. R. Carrillo, A. Díaz-Ortiz, R. Martín, M. V. Gómez, L. Stegemann, C. A. Strassert, J. Orduna, J. Buendía, E. E. Greciano, J. S. Valera, E. Matesanz, L. Sánchez, P. Prieto

RSC Adv., 2016, 6, 36544–36553

DOI: 10.1039/C6RA02473D

T-Shaped 2H-benzo[d][1,2,3]triazole derivatives have been synthesized by Sonogashira coupling reactions under microwave irradiation. DFT calculations were performed in order to understand the structure–property relationships – an aspect that is of vital importance for the rational design of organic selfassemblies for optoelectronic applications. Concentration-dependent 1H Pulse Field-Gradient Spin-Echo (PFGSE) NMR spectroscopy and UV/Vis spectrophotometry indicated the absence of a tendency for the aggregation of single molecules in solution. In contrast, in the solid state these compounds form organized aggregates and these were studied by scanning electron microscopy (SEM), which showed the influence that the peripheral substitution has on the morphology of the aggregates. For example, methoxy-substituted benzotriazoles self-assemble into thick and crystalline needle-like structures. However, the unsubstituted triazoles give rise to flower-like aggregates. Interestingly, the aggregates formed by benzotriazole 1c exhibit waveguide properties.


A clear coat from a water soluble precursor: a bioinspired paint concept

J. Yang, I. Bos, W. Pranger, A. Stuiver, A. H. Velders, M. A. Cohen Stuart, M. Kamperman.

 J. Mater. Chem. A 2016, 4, 6868–6877.

DOI: 10.1039/c5ta09437b.

Traditional paints consist of hydrophobic polymers dissolved in hydrocarbons; they are appreciated for their rheological properties and the smooth and glossy films they form upon drying and crosslinking, but are now largely banned because of the hazards associated with the solvents. In terms of health, water borne paints based on colloidal resin dispersions are an improvement but these systems lack the rheological and film forming properties of traditional paints. We present here a bio-inspired alternative that combines the best of both worlds: a water soluble polymer that can crosslink by mild oxidation to a fully water resistant and adhesive coating. Using free radical polymerization, we copolymerized two water soluble monomers, namely borax-protected dopamine acrylamide (DAA-p) and 2-aminoethylmethacrylamide (AEMA) in various proportions. We determined the reactivity ratio of these monomers using an in situ1H NMR monitoring method and found values of 0.0 and 0.46 for DAA-p and AEMA, respectively. From this we conclude that in the polymers DAA-p pairs do not occur, while DAA–AEMA diads are relatively frequent. After removing the protective borax by hydrolysis, we obtain polymers which are soluble in water at low pH (pH 2) but which undergo rapid oxidative crosslinking when the catechol groups of DAA react with amines from AEMA. This leads to a water resistant, mildly hydrophobic film with a water/air contact angle of about 40 degrees which adheres well to glass substrates


Ternary supramolecular quantum-dot network flocculation for selective lectin detection

M. Oikonomou, J. Wang, R. R. Carvalho, A. H. Velders.

Nano Res. 2016, 9, 1904-1912.

DOI: 10.1007/s12274-016-1082-1.

We present a versatile, tuneable, and selective nanoparticle-based lectin biosensor, based on flocculation of ternary supramolecular nanoparticle networks (NPN), formed through the sequential binding of three building blocks. The three building blocks are β-cyclodextrin-capped CdTe quantum dots, tetraethylene glycol-tethered mannose-adamantane cross-linkers (ADTEGMan), and the tetravalent lectin Concanavalin A (ConA). The working principle of this selective sensor lies in the dual orthogonal molecular interactions of the linker, uniting adamantane-β-cyclodextrin and mannose-lectin interaction motifs, respectively. Only when the lectin is present, sequential binding takes place, leading to in situ self-organization of the sensor through the formation of ternary supramolecular networks. Monitoring the loss of fluorescence signal of the quantum dots in solution, caused by controlled network formation and consecutive flocculation and sedimentation, leads to selective, qualitative, and quantitative lectin detection. Fluorescent sedimented networks can be observed by the naked eye or under UV illumination for a lectin concentration of up to 10−8 M. Quantitative detection is possible at 100 min with a lower detection limit of approximately 5 × 10−8 M.


Assembling quantum dots via critical Casimir forces

E. Marino, T. E. Kodger, J. B. ten Hove, A. H. Velders, P. Schall.

Sol. Energy Mat. Sol. C. 2016, 158, 154–159.

DOI: 10.1016/j.solmat.2016.01.016.

Programmed assembly of colloidal inorganic nanocrystal superstructures is crucial for the realization of future artificial solids as well as present optoelectronic applications. Here, we present a new way to assemble quantum dots reversibly using binary solvents. By tuning the temperature and composition of the binary solvent mixture, we achieve reversible aggregation of nanocrystals in solution induced by critical Casimir forces. We study the temperature-sensitive quantum-dot assembly with dynamic light scattering. We show that careful screening of the electrostatic repulsion by adding salt provides a further parameter to tune the reversible assembly.


The Application of NMR Spectroscopy to the Study of Pyranoanthocyanins: Structural Elucidation, Solution Equilibria and Exhibited Color. In Foods and Beverages

M. V. Gómez, S. Gómez-Alonso, I. Hermosin.

Applications of NMR Spectroscopy. 2016, Vol. 4, 96-187.

DOI: 10.2174/9781681081434116040005

Bentham Science.

 ISBN: 978-1-68108-144-1.

Anthocyanins are an important class of natural pigments widely distributed throughout the Plant Kingdom and foodstuffs. They are rather reactive compounds that are involved in several equilibria in aqueous solution and give rise to new classes of anthocyanin-derived pigments. This reactivity creates changes in the exhibited color that is especially interesting with regards to foods and beverages. Among the anthocyanin-derived pigments, pyranoanthocyanins have gained attention in the last two decades because of their higher stability, mainly the resistance to discoloration by changing pH or after the addition of bisulfite, in comparison to their precursor anthocyanins. One of the first challenges regarding pyranoanthocyanins was their structural elucidation, leading to an increasing difficulty due to the finding of several new subclasses of chemical structures, beginning with one the first discovered, relatively simple, vitisin-type pyrano-anthocyanins and continuing with other more complex structures like those of flavanyl-vinyl-pyranoanthocyanins or pyranoanthocyanin dimers. Multidimensional Mass Spectrometry (MSn) and Nuclear Magnetic Resonance (NMR) spectroscopy have been crucial tools for the structure elucidation of pyranoanthocyanins. In addition, NMR spectroscopy has contributed to the gaining of knowledge about the aqueous solution equilibria in which pyranoanthocyanins are involved, thus helping the interpretation of the molecular basis behind the higher stability of such anthocyanin-derived pigments. This review introduces the pyranoanthocyanins by means of a description of the anthocyanin reactivity and the formation of anthocyanin-derived pigments in foods and beverages. The review continues with an overview of the current knowledge about different structures of pyranoanthocyanins, their main properties related to exhibited color, especially their behavior against changing pH and bisulfite bleaching, their reactivity, and the occurrence of pyranoanthocyanins in foods and beverages. Finally, this review deals with the application of NMR spectroscopy to several interesting issues related to pyranoanthocyanin chemistry, namely the structure elucidation of the different classes of pyrano-anthocyanins, the behavior of these compounds in aqueous equilibria of hydration and proton transfer, and the formation of new pyranoanthocyanin-related compounds.


Electrostatic repulsion governs TDP-43 C-terminal domain aggregation

M. Mompeán, A. Chakrabartty, E. Buratti, D. V. Laurents.

PLoS Biology, 2016, 14(4), e1002447.

DOI: 10.1371/journal.pbio.1002447.


Complex system assembly underlies a two-tiered model of highly delocalized electrons

M. Mompeán, A. Nogales, T. A. Ezquerra, D. V. Laurents.

J. Phys. Chem. Lett. 2016, 7, 1859-1864.

DOI: 10.1021/acs.jpclett.6b00699.

Amyloid fibrils are exceptionally stable oligomeric structures with extensive, highly cooperative H-bonding networks whose physical origin remains elusive. While nonpolar systems benefit from both H-bonds and hydrophobic interactions, we found that highly polar sequences containing glutamine and asparagine amino acid residues form hyperpolarized H-bonds. This feature, observed by density functional theory calculations, encodes the origin of these polar oligomers’ high stability. These results are explained in a theoretical model for complex amyloid assembly based on two different types of cooperative effects resulting from highly delocalized electrons, one of which is always present in both polar and hydrophobic systems. Experimental electric conductivity measurements, ThT fluorescence enhancement, and NMR spectroscopy support this proposal and reveal the conditions for disassembly.


An amyloid-like pathological conformation of TDP-43 is stabilized by hypercooperative hydrogen bonds.

M. Mompeán, M. Baralle, E. Buratti, D. V. Laurents.

Front. Mol. Neurosci. 2016, 9, 125.

DOI: 10.3389/fnmol.2016.00125.

ITDP-43 is an essential RNA-binding protein forming aggregates in almost all cases of sporadic amyotrophic lateral sclerosis (ALS) and many cases of frontotemporal lobar dementia (FTLD) and other neurodegenerative diseases. TDP-43 consists of a folded N-terminal domain with a singular structure, two RRM RNA-binding domains, and a long disordered C-terminal region which plays roles in functional RNA regulatory assemblies as well as pernicious aggregation. Evidence from pathological mutations and seeding experiments strongly suggest that TDP-43 aggregates are pathologically relevant through toxic gain-of-harmful-function and/or harmful loss-of-native-function mechanisms. Recent, but not early, microscopy studies and the ability of TDP-43 aggregates to resist harsh treatment and to seed new pathological aggregates in vitro and in cells strongly suggest that TDP-43 aggregates have a self-templating, amyloid-like structure. Based on the importance of the Gln/Asn-rich 341–367 residue segment for efficient aggregation of endogenous TDP-43 when presented as a 12X-repeat and extensive spectroscopic and computational experiments, we recently proposed that this segment adopts a beta-hairpin structure that assembles in a parallel with a beta-turn configuration to form an amyloid-like structure. Here, we propose that this conformer is stabilized by an especially strong class of hypercooperative hydrogen bonding unique to Gln and Asn sidechains. The clinical existence of this conformer is supported by very recent LC-MS/MS characterization of TDP-43 from ex vivo aggregates, which show that residues 341–367 were protected in vivo from Ser phosphorylation, Gln/Asn deamidation and Met oxidation. Its distinct pattern of SDS-PAGE bands allows us to link this conformer to the exceptionally stable seed of the Type A TDP-43 proteinopathy.