Pesquisas

Artigos em capa de revistas

CiQUS researchers devise new molecular tweezers for fullerene recognition through computational chemistry.

26/06/2015

An article by a research group belonging to the CIQUS which is led by Professor Jesús Rodríguez Otero has been selected as the cover of the latest issue of the journal Physical Chemistry Chemical Physics of the RSC. Using the tools of computational chemistry this work (Phys. Chem. Chem. Phys., 2015, 17, 13206-13214 (link is external)) suggests how to design concave receptors for the fullerene recognition.


Nearly 30 years after their discovery, fullerenes still attract the attention of many researches worldwide due to their unique properties and their applications in a wide range of fields as material science or medicine. Nowadays, one of the most active fields in fullerene chemistry is the search for molecular receptors capable to form stable associates with them. These receptors not only are useful for isolating fullerenes of the soot, but also for developing new materials for solar energy conversion, optoelectronics, catalysis or switching.

Since dispersion forces are predominant in the stabilization of fullerene complexes, a key strategy to design new molecular receptors is to make use of concave-convex complementarity to maximize these forces. Nevertheless, the examples of concave fullerene receptors are relatively scarce given that curved molecules are not always an easy synthetic target due to their tensioned structures. In this context, bowl-shaped polycyclic aromatic hydrocarbons, commonly known as buckybowls or fullerene fragments, seem very attractive because several buckybowls have been synthetized in the last years, being their concave surface highly suitable for fitting to the convex surface of fullerenes through concave-convex "ball-and-socket" π···π interactions.

In this work a series of molecular tweezers have been tested as potential receptors of fullerene C60. In order to design these tweezers three different strategies have been tested: (1) changing the corannulene pincers to other buckybowls, (2) replacing the tetrabenzocyclooctatetraene tether by a buckybowl (for this purpose, a bowl-shaped hexabenzocoronene was employed), and (3) adding methyl groups on the molecular tweezers to favour the development of C-H···π contacts. According to the results (performed at the B97-D2/TZVP level), all the three approaches are effective, in such a way that a combination of the three strategies results in buckycatchers with complexation energies (with C60) up to 2.6 times larger than that of the original buckycatcher, reaching almost -100 kcal mol-1.

On the other hand we have verified that the B97-D2/TZVP//SCC-DFTB-D approach can be a rapid screening tool for testing new molecular tweezers. However, since this approach does not reproduce correctly the deformation energy and this energy represents an important contribution to the total complexation energy of complexes, subsequent higher-level re-optimization is compulsory to achieve reliable results. This re-optimization could be superfluous when quite rigid buckycatchers are studied.

In summary, our calculations lead to the fact that tweezers synthesised so far have much room for improvement. Some possible strategies for achieving this improvement are the three strategies analysed here, which represent promising possibilities.

Fonte: http://www.usc.es/ciqus/en/news/ciqus-researchers-devise-new-molecular-tweezers-fullerene-recognition-through-computational

CiQUS researchers design concave receptors for the fullerene recognition through computational chemistry

10/03/2015

An article by a research group belonging to the CiQUS which is led by Professor Jesús Rodríguez Otero has been selected as the cover of the latest issue of the journal Physical Chemistry Chemical Physics of the Royal Society of Chemistry (RSC). Using the tools of computational chemistry this work (Phys. Chem. Chem. Phys., 2015, 17, 6233-6241 (link is external)) suggests how to design concave receptors for the fullerene recognition.

Nearly 30 years after their discovery, fullerenes still attract the attention of many researches worldwide due to their unique properties and their applications in a wide range of fields as material science or medicine. Nowadays, one of the most active fields in fullerene chemistry is the search for molecular receptors capable to form stable associates with them. These receptors not only are useful for isolating fullerenes of the soot, but also for developing new materials for solar energy conversion, optoelectronics, catalysis or switching.

Since dispersion forces are predominant in the stabilization of fullerene complexes, a key strategy to design new molecular receptors is to make use of concave-convex complementarity to maximize these forces. Nevertheless, the examples of concave fullerene receptors are relatively scarce given that curved molecules are not always an easy synthetic target due to their tensioned structures. In this context, bowl-shaped polycyclic aromatic hydrocarbons, commonly known as buckybowls or fullerene fragments, seem very attractive because several buckybowls have been synthetized in the last years, being their concave surface highly suitable for fitting to the convex surface of fullerenes through concave-convex "ball-and-socket" π···π interactions.

In last years, our group has been devoted to the study of a series of concave-convex interactions between buckybowls and fullerenes in order to find the factors that maximize their interactions.

In this work a series of buckybowls with different sizes and structures have been tested as potential receptors of fullerenes C60, C70 and C40. Among these bowls are corannulene (C20H10), sumanene (C21H12), pinakene (C28H14), hemifullerene (C30H12), circumtrindene (C36H12), pentaindenocorannulene (C50H20) and bowl-shaped hexabenzocoronene derivatives. An exhaustive study, taking into account different orientations of fullerenes, was performed in order to obtain the most favourable arrangement for interacting with the bowls.

According to our calculations (performed at the B97-D2/TZVP level) dispersion plays a crucial role in the interaction energy in these complexes: it is responsible for the binding in them, showing an excellent correlation with the interaction energy (the minimal deviations can be explained by qualitative analysis based on the contribution of electrostatics to the interaction energy). As expected, an increase in dispersion energy shows a fairly good correlation with an increase in bowl size. However, there are some substantial deviations, which can be attributed to the shape of the bowl. In this way, compounds whose structure possesses flaps at the rim of the bowl show an enhanced ability to interact with fullerenes. Therefore, it seems that the addition of these flaps at the bowl rim by benzannelation is an effective strategy for increasing the interaction with fullerenes, providing enough flexibility to extend the contact surface with the fullerene moiety. Accordingly, a bowl-shaped hexabenzocoronene derivative (C72H24) showed the best ability among the buckybowls evaluated for catching the three fullerenes; it is noteworthy that, when interacting with C60, the interaction energy is three times that corresponding to the prototypical buckybowl, corannulene. On the contrary, the more rigid and compact is the structure of a buckybowl, the smaller its ability to interact with fullerenes.

It is also worth mentioning that the interaction energies for the complexes with C70 only show small increases with respect to those obtained with C60. Contrarily, complexes with C40 show a significant decrease in their interaction energies, with differences large enough to allow their selective separation of fullerene mixtures with C60 and C70.

Fonte: http://www.usc.es/ciqus/en/news/ciqus-researchers-design-concave-receptors-fullerene-recognition-through-computational

Tese de Doutorado

CiQUS Thesis: Daniela Josa

16/07/2015
 

Today, July 16th, CiQUS PhD student Daniela Josa has defended his Doctoral Thesis, entitled  "Tailoring buckybowls for fullerene recognition". His work has been supervised by CiQUS Professor Jesús Rodríguez Otero and Enrique M. Cabaleiro Lago.

Nowadays, the design and synthesis of fullerene receptors is a very attractive field of research. Besides their great importance in the development of new materials in nanotechnology and nanoscience, fullerene receptors also could be crucial for separation of fullerenes. A promising strategy to design new molecular receptors for fullerenes is using the concave-convex complementarity.  Nevertheless, the examples of concave fullerene receptors are relatively scarce since curved molecules are not always an easy synthetic target due their tensioned structures.

In this context, bowl-shaped polycyclic aromatic hydrocarbons, commonly known as buckybowls or fullerene fragments seem very attractive because several buckybowls have been synthetized in recent years and their concave surface can fit adequately to the convex surface of fullerenes through concave-convex "ball-and-socket" π···π interactions. In 2007, Sygula and co-workers introduced a novel type of molecular tweezers (a buckycatcher, C60H28) with buckybowl pincers that have attracted a substantial interest of researchers due their ideal architecture for recognizing fullerenes and their potential future applications, in particular as stationary phases in liquid chromatography for the separation of fullerenes or as buckycatcher-fullerene complexes in photovoltaic devices (A. Sygula et al. J. Am. Chem. Soc. 2007, 129, 3842).

Despite their great interest, the number of theoretical studies of concave-convex π···π interactions between buckybowls and fullerenes are limited due to the recent discovery of these structures, to their large size and, especially, to the fact that until a few years ago there were no satisfactory options for the precise calculation of the non-covalent interactions between large molecules. 

For that reason, the goal of this doctoral thesis has been carry out an exhaustive theoretical study of the concave-convex π···π interactions between buckybowls and fullerenes in order to get a better understanding of the supramolecular systems existing and guiding the design of new systems more effective and/or selective. In this doctoral thesis, we devised buckycatchers with complexation energies (with C60) up to 2.6 times larger than that for the original buckycatcher, reaching almost -100 kcal/mol.

 

Fonte: http://www.usc.es/ciqus/en/news/thesis_DanielaJosa

Título:Tailoring buckybowls for fullerene recognition
Autor/a:Josa, Daniela
Director/a:Rodríguez Otero, Jesús (dir.)
Cabaleiro Lago, Enrique M. (dir.)
Otro/a autor/a:Universidade de Santiago de Compostela. Facultade de Química. Departamento de Química Física. Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS)
Palabras clave:Química computacional | Interacciones π···π cóncavo-convexo | Receptores moleculares para fulerenos | Fragmentos de fulerenos | Pinzas moleculares |
Fecha:2015-09-28
Resumen:Nowadays, the design and synthesis of fullerenes receptors is a very attractive field of research. Besides their great importance in the development of new materials in nanotechnology and nanoscience, fullerene receptors also could be crucial for separation of fullerenes. A promising strategy to design new molecular receptors for fullerenes is using the concave-­‐convex complementarity. Nevertheless, the examples of concave fullerene receptors are relatively scarce since curved molecules are not always an easy synthetic target due their tensioned structures. In this context, bowl-­‐shaped polycyclic aromatic hydrocarbons, commonly known as buckybowls or fullerene fragments seem very attractive because several buckybowls have been synthetized in recent years and their concave surface can fit adequately to the convex surface of fullerenes through concave-­‐convex "ball-­‐and-­‐socket" π···π interactions. In 2007, Sygula and co-­‐workers introduced a novel type of molecular tweezers (a buckycatcher, C60H28) with buckybowl pincers that have attracted a substantial interest of researchers due their ideal architecture for recognizing fullerenes and their potential future applications, in particular as stationary phases in liquid chromatography for the separation of fullerenes or as buckycatcher-­‐fullerene complexes in photovoltaic devices (A. Sygula et al. J. Am. Chem. Soc. 2007, 129, 3842). Despite their great interest, the number of theoretical studies of concave-­‐convex π···π interactions between buckybowls and fullerenes are limited due to the recent discovery of these structures, to their large size and, especially, to the fact that until a few years ago there were no satisfactory options for the precise calculation of the non-­‐covalent interactions between large molecules. For that reason, the present doctoral thesis is focused in the detailed theoretical study of the concave-­‐convex π···π interactions between buckybowls and fullerenes with ultimate goal of designing new molecular tweezers based in buckybowls for fullerene recognition. To this end, the objectives of this thesis are: (1) selecting a reliable level of calculation to study concave-­‐convex π···π interactions; (2) evaluating the effects that can enhance the interaction between buckybowls and fullerenes. In particular, the addition of substituents and the curvature effects are evaluated; (3) evaluating the performance of the B97-­‐D2//SCC-­‐DFTB-­‐D calculations regarding B97-­‐D2 ones in order to obtain a rapid tool for selecting suitable strategies for the rational design of molecular tweezers; (4) trying to answer the key question: how to modify the buckycatcher C60H28 to improve its efficiency and/or selectivity? The methodology of quantum chemistry was used for this purpose. This methodology offers valuable interpretative information and it can provide very useful information to guide the design of new molecules that make use of concave-­‐convex π···π interactions. Our results indicate that B97-­‐D2 functional seems appropriate to study concave-­‐convex π···π interactions. This model shows a good performance for corannulene dimer regarding to QCISD(T)/aug-­‐cc-­‐pVTZ calculations and it also enables the use of the RI approximation that takes advantage of the noticeable reduction of computational cost. In addition, the utilization of the SCC-­‐DFTB-­‐D method as starting guess enables considerable savings of the calculation time (almost 50% regarding the full B97-­‐D2/TZVP optimization of the emblematic C60H28···C60 complex). The shape of the buckybowl plays a crucial role on its ability for fullerene recognition. Compounds whose structure possess flaps at the rim of the bowl show an enhanced capability for interacting with fullerenes. On the other hand, CH···π interactions also are very important in fullerene recognition. Finally, three different strategies have been tested in order to improve the efficiency of traditional molecular tweezers synthesized by Sygula et al.: (1) changing the corannulene pincers by other buckybowls, (2) replacing the tetrabenzocyclooctatetraene tether by a buckybowl, (3) adding methyl groups on the molecular tweezers. According to the results, the three approaches are effective, in such a way that combination of the three strategies results in buckycatchers with complexation energies (with C60) up to 2.6 times larger than that for the original buckycatcher, reaching almost -­‐100 kcal/mol.
URI:http://hdl.handle.net/10347/13618
Derechos:info:eu-repo/semantics/openAccess

Fonte: http://hdl.handle.net/10347/13618

CIQUS: Jornadas de portas abertas

 

Desde 2011 o centro Singular de Investigación en Química Biológica y Materiales Moleculares (CIQUS) na Espanha realiza jornadas de portas abertas a alunos das escolas de Santiago de Compostela e arredores. Neste projeto alunos de mestrado, doutorado e pós-doutorados são encarregados de realizar oficinas, exposição de painéis sobre os âmbitos de pesquisas do centro e visitas a algumas instalações instrumentais e laboratórios. Os resultados têm sido bastante motivadores, segundo uma pesquisa realizada pelo CIQUS 98,6% das pessoas indicaram que voltariam a visitar as futuras edições.

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