Journal of Polymer Science Part A: Polymer Chemistry, 2008
Side-chain supramolecular polymers that show columnar mesomorphism have been prepared through H-b... more Side-chain supramolecular polymers that show columnar mesomorphism have been prepared through H-bonding interactions between a polyvinylpyridine polymer as H-acceptor and different H-donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk-like or banana-like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H-bonds and demonstrated that the H-bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Associations containing poly-3-methyl-4-vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528-5541, 2008 Figure 6. (a) CD and (b) UV-vis spectra of P3-A3*[1:0.75] at room temperature. 5536 VERA ET AL. a Lattice parameters of mesogenic V-shaped H-donor acids, as reference, are the following: A5: a ¼ 47.2; A6: a ¼ 77.0, b ¼ 36.0. 5538 VERA ET AL.
... DGA. References. 1, L. Brunsveld, BJB Folmer, EW Meijer and RP Sijbesma, Chem. Rev ... Am. Ch... more ... DGA. References. 1, L. Brunsveld, BJB Folmer, EW Meijer and RP Sijbesma, Chem. Rev ... Am. Chem. Soc., 2001, 123, 409416 Article ChemPort ; AW Bosman, L. Brunsveld, BJB Folmer, RP Sijbesma and EW Meijer, Macromol. Symp ...
This tutorial review provides insight into helical columnar assemblies based on thermotropic as w... more This tutorial review provides insight into helical columnar assemblies based on thermotropic as well as lyotropic liquid crystals on the basis of the structural characteristics that promote hierarchical self-organization. The structural features of molecular materials that can present helical organizations imply the action of different driving forces that include pi-interactions, hydrogen bonding or metal-coordination. In addition, columnar liquid crystals offer the possibility of combining these interactions towards the control of the geometry and orientation of the supramolecular organization leading to well-defined helical columnar assemblies.
The synthesis and characterization of tetrasubstituted tetrathiafulvalenes 7 a-b and 18 a-b, whic... more The synthesis and characterization of tetrasubstituted tetrathiafulvalenes 7 a-b and 18 a-b, which bear promesogenic units such as 44ecyloxybemoyl and 3,4,5-tris(decyloxy)benzoyl groups, are described. Such units are linked to the 'ITF core through spacers of different lengths. Compound Mb exhibits a metastable discotic mesophase and constitutes the first example of a discotic liquid crystal with a tetratbiafulvalene central core. 0
The synthesis and study of optically active polymers whose chirality is based on a helical main-c... more The synthesis and study of optically active polymers whose chirality is based on a helical main-chain conformation have generated wide interest across a broad range of scientific disciplines. 1 As a consequence, the preparation of synthetic chiral macromolecules with helical structures and the understanding and control of the different mechanisms governing the induction of an excess of one helical sense might have far-reaching implications in biology and biomolecular materials. 2 Polymers with exclusively helical conformational chirality can only be obtained when isotacticity and atropisomerism are simultaneously present in their structures, that is, when their repeating units have the same stereochemistry, and the rigidity of the polymer backbone and/or sterical repulsion of the side groups prevent random coil-like conformations. 1b Synthetic polymers with such chiral conformations may show a high optical activity if an excess of a one-handed helical conformation exists. This has been attained for only very few cases; for example, with chloral, 3 bulky substituted methacrylates, 1,4 isocyanates, 5 and isocyanides, 6 along with some substituted π-conjugated polymers. 7 Noteworthy are the results achieved with isocyanides since the stereochemistry of their polymerizations has been studied in great detail. 8 Optically active polyisocyanides, with an excess of a one-handed helical conformation, can be obtained by direct polymerization of chiral isocyanides with the general formula depicted in . 8 In all these polymerizations, the chiral moiety responsible for the stereoselectivity is joined directly (or very close) to polymerizable isocyanide groups. This proximity encourages the inserting monomers with a stereogenic center configuration (R or S) to approach to one side of the reactive adduct, thereby generating a unique helical sense (plus, P, or minus, M) in the growing polymer.
Herein, the synthesis of five novel ionic dendrimers and their evaluation as biological carriers ... more Herein, the synthesis of five novel ionic dendrimers and their evaluation as biological carriers is reported. The compounds include an ionic bis-MPA dendrimer and four PAMAM dendrimers of different generations decorated with negatively charged hydrophilic chains of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid as counter ions in order to increase their biocompatibility. The ionic dendrimers derived from bis-MPA have a low cytotoxicity at 0.5 mg Á mL À 1 against U251MG and are even less toxic against mesenchymal stem cells; however, the PAMAM derivatives show high cytotoxicity at the same concentration. The five compounds are able to form complexes with plasmid DNA at different N/P ratios. The cytotoxicity and complexation ability of the new dendrimers were also compared with jetPEI, a linear polyethylenimine derivative commercially available as transfection reagent. The results indicate that the cytotoxicity of the ionic PAMAM dendrimers remains as an important drawback, whereas the ionic I-bis-MPA compound exhibits a high ability to complex pDNA and very low toxicity compared with jetPEI.
The present paper is aimed at providing a survey of investigations undertaken regarding the prepa... more The present paper is aimed at providing a survey of investigations undertaken regarding the preparation and characterization of helical supramolecular architectures using a strategy based on two concepts: coordination chemistry and mesomorphic behavior. Metal-coordination procedures have been used to design and synthesize molecular units capable of organizing into helical superstructures. In order to ensure this capability, the molecular building blocks have been complemented with a pro-mesogenic character, most commonly columnar, so that this type of mesophase is used as a template to build up helical supramolecular architectures with long-range orientational order and long-range positional order. For example, metal-containing liquid crystals have been described that organize into helical columnar mesophases whose structure has been fully investigated. To date, molecular units that display this organizational behavior have been found to be very different in shape, and hence the formation of helical structures has a different origin in each case. In this paper, three molecular structures are discussed (i.e. 'disk-like' molecules, 'propeller-like' molecules and polycatenar elongated molecules) that have been shown to give rise to helical organizations. Models have been proposed for the three systems described and in the present overview these have been classified as azimuthal rotation of planar disk-like complexes, interdigitated stacking of octahedral complexes and staggered stacking of polycatenar elongated planar complexes, respectively. Throughout this paper, emphasis is placed on studies carried out in the mesophase that have allowed authors to propose the corresponding models. #
It can be foreseen that in a future scenario of malaria eradication, a varied armamentarium will ... more It can be foreseen that in a future scenario of malaria eradication, a varied armamentarium will be required, including strategies for the targeted administration of antimalarial compounds. The development of nanovectors capable of encapsulating drugs and of delivering them to Plasmodium-infected cells with high specificity and efficacy and at an affordable cost is of particular interest. With this objective, dendritic derivatives based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and Pluronic ® polymers have been herein explored. Four different dendritic derivatives have been tested for their capacity to encapsulate the antimalarial drugs chloroquine (CQ) and primaquine (PQ), their specific targeting to Plasmodium-infected red blood cells (pRBCs), and their antimalarial activity in vitro against the human pathogen Plasmodium falciparum and in vivo against the rodent malaria species Plasmodium yoelii. The results obtained have allowed the identification of two dendritic derivatives exhibiting specific targeting to pRBCs vs. non-infected RBCs, which reduce the in vitro IC 50 of CQ and PQ by ca. 3-and 4-fold down to 4.0 nM and 1.1 mM, respectively. This work on the application of dendritic derivatives to antimalarial targeted drug delivery opens the way for the use of this new type of chemicals in future malaria eradication programs.
IR and VCD spectroscopies are employed to clarify the molecular origins of supramolecular chirali... more IR and VCD spectroscopies are employed to clarify the molecular origins of supramolecular chirality in azobenzene-containing columnar liquid crystals. The different columnar mesomorphic assemblies, Colr and Colh, of an achiral and a chiral propeller-like hydrogen-bonded complex, respectively, are used for this study. The mesomorphic behavior of the achiral complex is studied here for the first time, and the structural parameters of its Colr mesophase are determined by X-ray diffraction. Both complexes bear azobenzene units and this makes it possible to implement photoresponsive columnar architectures, the chirality of which can be induced and modulated by irradiation with 488 nm circularly polarized light (CPL). Thin films of the respective rectangular and hexagonal columnar phases of these complexes have been processed in order to study the IR absorption spectra and the vibrational circular dichroism responses upon irradiation with CPL. These studies allow confirming that the outer part of the columns, consisting on azobenzene groups, is mainly involved in the photoinduced supramolecular chirality, rather than the inner part of the columns where a melamine core is located. This supports a structural model based on the helical disposition of the azobenzene groups along the stacked propeller-like complexes.
A nine-channel multiplexed electrospray (MUX) liquid chromatography ultraviolet time-of-flight ma... more A nine-channel multiplexed electrospray (MUX) liquid chromatography ultraviolet time-of-flight mass spectrometry (LC/UV/TOFMS) system has been used to simultaneously measure accurate masses of eluting components from eight parallel gradient LC columns. Accuracies better than 5 and 10 ppm were achieved for 50 and 80% of samples, respectively, from a single batch analysis of ten plates (960 samples) of a Fmoc-Asp(OtBu)-OH and reserpine mixture. Combinatorial library compounds were analyzed using this parallel high-throughput system in both positive and negative modes to rigorously verify expected products and identify side products. A mass accuracy of 10 ppm root mean square (RMS) is routinely obtained for combinatorial library samples from this high-throughput accurate mass LC/MS system followed by automated data processing. This mass accuracy is critical in revealing combinatorial synthesis problems that would be missed by unit mass measurement.
Liquid crystals (LC) containing azobenzene moieties are materials of interest in different optica... more Liquid crystals (LC) containing azobenzene moieties are materials of interest in different optical technologies. Applications of azomaterials derived from the capability of reversible isomerization between the E- and Z-configurations. Among the different applications reported so far, photoinduction or chirality deserves to be studied in details as can provide, e.g., new chiroptical switches and molecular rotors based on achiral compounds. Here,
ABSTRACT The dielectric response in 2-hydroxy-4-decyloxybenzilidene-4′-(2S-2-chloro-3-methylbutyl... more ABSTRACT The dielectric response in 2-hydroxy-4-decyloxybenzilidene-4′-(2S-2-chloro-3-methylbutyloxy) aniline, a ferroelectric liquid crystal which shows a C-Sc*-SA-I phase transition sequence has been determined. The influence of a bias electric field, applied parallel to the smectic layers, on the parameters that characterize the contributions of the different modes to this response has been analysed. In addition to the soft mode and Goldstone mode contributions we have observed a low frequency relaxation mechanism which could be related to the defect structure present in samples with planar alignment. Moreover, the deconvolution process has allowed us to characterize the soft mode in the ferroelectric phase without unwinding the helical structure.
Chiral oxovanadium (IV), copper (II), and palladium (II) β-diketonates show a room-temperature co... more Chiral oxovanadium (IV), copper (II), and palladium (II) β-diketonates show a room-temperature columnar mesophase which undergoes ferroelectric switching. All the compounds were obtained as liquid crystals at room temperature, and crystallization or ...
The work described here concerns a challenge of general interest in supramolecular chemistry: the... more The work described here concerns a challenge of general interest in supramolecular chemistry: the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform.
... David B. Amabilino, † Elena Ramos, † José-Luis Serrano,* ‡ Teresa Sierra, ‡ and Jaume Veciana... more ... David B. Amabilino, † Elena Ramos, † José-Luis Serrano,* ‡ Teresa Sierra, ‡ and Jaume Veciana* †. Contribution from the Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Científicas (CSIC ...
The results of the study presented here show a new example of the use of liquid crystals and the ... more The results of the study presented here show a new example of the use of liquid crystals and the interactions involved in the mesomorphic state to build up complex molecular organizations. We have pursued a design strategy in which hydrogen bonding allows the combination of the π-stacking tendency of melamine and the lateral interaction capability of V-shaped molecules, which has been extensively demonstrated through nematic, smectic, or columnar mesophases. This combination addresses the formation of columnar arrangements with inherent helical organization. In this work, nonmesomorphic as well as mesomorphic V-shaped acids, with a structure similar to banana liquid crystals, have been complexed to a 2,4,6-triamino-1,3,5-triazine derivative in a proportion 3 to 1, respectively. Hydrogen-bonded supramolecules whose formation and stability in solution have been proven by infrared and NMR techniques have been thus obtained. DOSY experiments have allowed us to assess in solution the presence of the complexes and their tetrameric composition. All the complexes display mesogenic ability, and their mesomorphic organization has been studied by X-ray diffraction and CD spectroscopy. Results allow us to propose a helical columnar model for the mesophase originated from a propeller-like conformation of the supramolecular complexes.
Page 1. JOURNAL OF CHEMISTRY Materials Synthesis and liquid crystal behaviour of tetrathiafulvale... more Page 1. JOURNAL OF CHEMISTRY Materials Synthesis and liquid crystal behaviour of tetrathiafulvalenes containing cyanobiphenylyloxy groups Raquel Andreu,a Joaquın Barberá,a Javier Garın,a* Jesús Orduna,a José Luis ...
Journal of Polymer Science Part A: Polymer Chemistry, 2008
Side-chain supramolecular polymers that show columnar mesomorphism have been prepared through H-b... more Side-chain supramolecular polymers that show columnar mesomorphism have been prepared through H-bonding interactions between a polyvinylpyridine polymer as H-acceptor and different H-donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk-like or banana-like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H-bonds and demonstrated that the H-bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Associations containing poly-3-methyl-4-vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528-5541, 2008 Figure 6. (a) CD and (b) UV-vis spectra of P3-A3*[1:0.75] at room temperature. 5536 VERA ET AL. a Lattice parameters of mesogenic V-shaped H-donor acids, as reference, are the following: A5: a ¼ 47.2; A6: a ¼ 77.0, b ¼ 36.0. 5538 VERA ET AL.
... DGA. References. 1, L. Brunsveld, BJB Folmer, EW Meijer and RP Sijbesma, Chem. Rev ... Am. Ch... more ... DGA. References. 1, L. Brunsveld, BJB Folmer, EW Meijer and RP Sijbesma, Chem. Rev ... Am. Chem. Soc., 2001, 123, 409416 Article ChemPort ; AW Bosman, L. Brunsveld, BJB Folmer, RP Sijbesma and EW Meijer, Macromol. Symp ...
This tutorial review provides insight into helical columnar assemblies based on thermotropic as w... more This tutorial review provides insight into helical columnar assemblies based on thermotropic as well as lyotropic liquid crystals on the basis of the structural characteristics that promote hierarchical self-organization. The structural features of molecular materials that can present helical organizations imply the action of different driving forces that include pi-interactions, hydrogen bonding or metal-coordination. In addition, columnar liquid crystals offer the possibility of combining these interactions towards the control of the geometry and orientation of the supramolecular organization leading to well-defined helical columnar assemblies.
The synthesis and characterization of tetrasubstituted tetrathiafulvalenes 7 a-b and 18 a-b, whic... more The synthesis and characterization of tetrasubstituted tetrathiafulvalenes 7 a-b and 18 a-b, which bear promesogenic units such as 44ecyloxybemoyl and 3,4,5-tris(decyloxy)benzoyl groups, are described. Such units are linked to the 'ITF core through spacers of different lengths. Compound Mb exhibits a metastable discotic mesophase and constitutes the first example of a discotic liquid crystal with a tetratbiafulvalene central core. 0
The synthesis and study of optically active polymers whose chirality is based on a helical main-c... more The synthesis and study of optically active polymers whose chirality is based on a helical main-chain conformation have generated wide interest across a broad range of scientific disciplines. 1 As a consequence, the preparation of synthetic chiral macromolecules with helical structures and the understanding and control of the different mechanisms governing the induction of an excess of one helical sense might have far-reaching implications in biology and biomolecular materials. 2 Polymers with exclusively helical conformational chirality can only be obtained when isotacticity and atropisomerism are simultaneously present in their structures, that is, when their repeating units have the same stereochemistry, and the rigidity of the polymer backbone and/or sterical repulsion of the side groups prevent random coil-like conformations. 1b Synthetic polymers with such chiral conformations may show a high optical activity if an excess of a one-handed helical conformation exists. This has been attained for only very few cases; for example, with chloral, 3 bulky substituted methacrylates, 1,4 isocyanates, 5 and isocyanides, 6 along with some substituted π-conjugated polymers. 7 Noteworthy are the results achieved with isocyanides since the stereochemistry of their polymerizations has been studied in great detail. 8 Optically active polyisocyanides, with an excess of a one-handed helical conformation, can be obtained by direct polymerization of chiral isocyanides with the general formula depicted in . 8 In all these polymerizations, the chiral moiety responsible for the stereoselectivity is joined directly (or very close) to polymerizable isocyanide groups. This proximity encourages the inserting monomers with a stereogenic center configuration (R or S) to approach to one side of the reactive adduct, thereby generating a unique helical sense (plus, P, or minus, M) in the growing polymer.
Herein, the synthesis of five novel ionic dendrimers and their evaluation as biological carriers ... more Herein, the synthesis of five novel ionic dendrimers and their evaluation as biological carriers is reported. The compounds include an ionic bis-MPA dendrimer and four PAMAM dendrimers of different generations decorated with negatively charged hydrophilic chains of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid as counter ions in order to increase their biocompatibility. The ionic dendrimers derived from bis-MPA have a low cytotoxicity at 0.5 mg Á mL À 1 against U251MG and are even less toxic against mesenchymal stem cells; however, the PAMAM derivatives show high cytotoxicity at the same concentration. The five compounds are able to form complexes with plasmid DNA at different N/P ratios. The cytotoxicity and complexation ability of the new dendrimers were also compared with jetPEI, a linear polyethylenimine derivative commercially available as transfection reagent. The results indicate that the cytotoxicity of the ionic PAMAM dendrimers remains as an important drawback, whereas the ionic I-bis-MPA compound exhibits a high ability to complex pDNA and very low toxicity compared with jetPEI.
The present paper is aimed at providing a survey of investigations undertaken regarding the prepa... more The present paper is aimed at providing a survey of investigations undertaken regarding the preparation and characterization of helical supramolecular architectures using a strategy based on two concepts: coordination chemistry and mesomorphic behavior. Metal-coordination procedures have been used to design and synthesize molecular units capable of organizing into helical superstructures. In order to ensure this capability, the molecular building blocks have been complemented with a pro-mesogenic character, most commonly columnar, so that this type of mesophase is used as a template to build up helical supramolecular architectures with long-range orientational order and long-range positional order. For example, metal-containing liquid crystals have been described that organize into helical columnar mesophases whose structure has been fully investigated. To date, molecular units that display this organizational behavior have been found to be very different in shape, and hence the formation of helical structures has a different origin in each case. In this paper, three molecular structures are discussed (i.e. 'disk-like' molecules, 'propeller-like' molecules and polycatenar elongated molecules) that have been shown to give rise to helical organizations. Models have been proposed for the three systems described and in the present overview these have been classified as azimuthal rotation of planar disk-like complexes, interdigitated stacking of octahedral complexes and staggered stacking of polycatenar elongated planar complexes, respectively. Throughout this paper, emphasis is placed on studies carried out in the mesophase that have allowed authors to propose the corresponding models. #
It can be foreseen that in a future scenario of malaria eradication, a varied armamentarium will ... more It can be foreseen that in a future scenario of malaria eradication, a varied armamentarium will be required, including strategies for the targeted administration of antimalarial compounds. The development of nanovectors capable of encapsulating drugs and of delivering them to Plasmodium-infected cells with high specificity and efficacy and at an affordable cost is of particular interest. With this objective, dendritic derivatives based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and Pluronic ® polymers have been herein explored. Four different dendritic derivatives have been tested for their capacity to encapsulate the antimalarial drugs chloroquine (CQ) and primaquine (PQ), their specific targeting to Plasmodium-infected red blood cells (pRBCs), and their antimalarial activity in vitro against the human pathogen Plasmodium falciparum and in vivo against the rodent malaria species Plasmodium yoelii. The results obtained have allowed the identification of two dendritic derivatives exhibiting specific targeting to pRBCs vs. non-infected RBCs, which reduce the in vitro IC 50 of CQ and PQ by ca. 3-and 4-fold down to 4.0 nM and 1.1 mM, respectively. This work on the application of dendritic derivatives to antimalarial targeted drug delivery opens the way for the use of this new type of chemicals in future malaria eradication programs.
IR and VCD spectroscopies are employed to clarify the molecular origins of supramolecular chirali... more IR and VCD spectroscopies are employed to clarify the molecular origins of supramolecular chirality in azobenzene-containing columnar liquid crystals. The different columnar mesomorphic assemblies, Colr and Colh, of an achiral and a chiral propeller-like hydrogen-bonded complex, respectively, are used for this study. The mesomorphic behavior of the achiral complex is studied here for the first time, and the structural parameters of its Colr mesophase are determined by X-ray diffraction. Both complexes bear azobenzene units and this makes it possible to implement photoresponsive columnar architectures, the chirality of which can be induced and modulated by irradiation with 488 nm circularly polarized light (CPL). Thin films of the respective rectangular and hexagonal columnar phases of these complexes have been processed in order to study the IR absorption spectra and the vibrational circular dichroism responses upon irradiation with CPL. These studies allow confirming that the outer part of the columns, consisting on azobenzene groups, is mainly involved in the photoinduced supramolecular chirality, rather than the inner part of the columns where a melamine core is located. This supports a structural model based on the helical disposition of the azobenzene groups along the stacked propeller-like complexes.
A nine-channel multiplexed electrospray (MUX) liquid chromatography ultraviolet time-of-flight ma... more A nine-channel multiplexed electrospray (MUX) liquid chromatography ultraviolet time-of-flight mass spectrometry (LC/UV/TOFMS) system has been used to simultaneously measure accurate masses of eluting components from eight parallel gradient LC columns. Accuracies better than 5 and 10 ppm were achieved for 50 and 80% of samples, respectively, from a single batch analysis of ten plates (960 samples) of a Fmoc-Asp(OtBu)-OH and reserpine mixture. Combinatorial library compounds were analyzed using this parallel high-throughput system in both positive and negative modes to rigorously verify expected products and identify side products. A mass accuracy of 10 ppm root mean square (RMS) is routinely obtained for combinatorial library samples from this high-throughput accurate mass LC/MS system followed by automated data processing. This mass accuracy is critical in revealing combinatorial synthesis problems that would be missed by unit mass measurement.
Liquid crystals (LC) containing azobenzene moieties are materials of interest in different optica... more Liquid crystals (LC) containing azobenzene moieties are materials of interest in different optical technologies. Applications of azomaterials derived from the capability of reversible isomerization between the E- and Z-configurations. Among the different applications reported so far, photoinduction or chirality deserves to be studied in details as can provide, e.g., new chiroptical switches and molecular rotors based on achiral compounds. Here,
ABSTRACT The dielectric response in 2-hydroxy-4-decyloxybenzilidene-4′-(2S-2-chloro-3-methylbutyl... more ABSTRACT The dielectric response in 2-hydroxy-4-decyloxybenzilidene-4′-(2S-2-chloro-3-methylbutyloxy) aniline, a ferroelectric liquid crystal which shows a C-Sc*-SA-I phase transition sequence has been determined. The influence of a bias electric field, applied parallel to the smectic layers, on the parameters that characterize the contributions of the different modes to this response has been analysed. In addition to the soft mode and Goldstone mode contributions we have observed a low frequency relaxation mechanism which could be related to the defect structure present in samples with planar alignment. Moreover, the deconvolution process has allowed us to characterize the soft mode in the ferroelectric phase without unwinding the helical structure.
Chiral oxovanadium (IV), copper (II), and palladium (II) β-diketonates show a room-temperature co... more Chiral oxovanadium (IV), copper (II), and palladium (II) β-diketonates show a room-temperature columnar mesophase which undergoes ferroelectric switching. All the compounds were obtained as liquid crystals at room temperature, and crystallization or ...
The work described here concerns a challenge of general interest in supramolecular chemistry: the... more The work described here concerns a challenge of general interest in supramolecular chemistry: the achievement of chiral helical organizations with controlled structures. This work provides a strategy to obtain supramolecular polymers in which a chiral helical conformation has been induced by a noncovalent association, that is, through hydrogen bonding. Polycatenar 2,4,6-triarylamino-1,3,5-triazines, which organize into columnar mesophases and are susceptible to H-bonding interactions, were chosen as a starting point to build up the chiral supramolecular structure. The stacking of these mesogens has been forced to wind in a helical way by means of H-bond association with (R)-3-methyladipic acid, within the mesophase. The optically active columnar organization has been studied in depth by optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction, and circular dichroism. Formation of stable complexes between the triazine units and (R)-3-methyladipic acid has also been investigated by means of NMR diffusion-ordered spectroscopy (DOSY) experiments in chloroform.
... David B. Amabilino, † Elena Ramos, † José-Luis Serrano,* ‡ Teresa Sierra, ‡ and Jaume Veciana... more ... David B. Amabilino, † Elena Ramos, † José-Luis Serrano,* ‡ Teresa Sierra, ‡ and Jaume Veciana* †. Contribution from the Institut de Ciència de Materials de Barcelona, Consejo Superior de Investigaciones Científicas (CSIC ...
The results of the study presented here show a new example of the use of liquid crystals and the ... more The results of the study presented here show a new example of the use of liquid crystals and the interactions involved in the mesomorphic state to build up complex molecular organizations. We have pursued a design strategy in which hydrogen bonding allows the combination of the π-stacking tendency of melamine and the lateral interaction capability of V-shaped molecules, which has been extensively demonstrated through nematic, smectic, or columnar mesophases. This combination addresses the formation of columnar arrangements with inherent helical organization. In this work, nonmesomorphic as well as mesomorphic V-shaped acids, with a structure similar to banana liquid crystals, have been complexed to a 2,4,6-triamino-1,3,5-triazine derivative in a proportion 3 to 1, respectively. Hydrogen-bonded supramolecules whose formation and stability in solution have been proven by infrared and NMR techniques have been thus obtained. DOSY experiments have allowed us to assess in solution the presence of the complexes and their tetrameric composition. All the complexes display mesogenic ability, and their mesomorphic organization has been studied by X-ray diffraction and CD spectroscopy. Results allow us to propose a helical columnar model for the mesophase originated from a propeller-like conformation of the supramolecular complexes.
Page 1. JOURNAL OF CHEMISTRY Materials Synthesis and liquid crystal behaviour of tetrathiafulvale... more Page 1. JOURNAL OF CHEMISTRY Materials Synthesis and liquid crystal behaviour of tetrathiafulvalenes containing cyanobiphenylyloxy groups Raquel Andreu,a Joaquın Barberá,a Javier Garın,a* Jesús Orduna,a José Luis ...
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