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José Luis Serrano

Publications and source records attributed to José Luis Serrano.

14 recordsLinked to original sources
PubMed2006

Supramolecular structures and columnar mesophase induction in nondiscoid pyrazoles by complexation to rhodium(I).

Several new cis-[RhCl(CO)2(Ln)] complexes have been prepared using different polycatenar pyrazole ligands (Ln) in order to obtain columnar liquid crystalline arrangements. The topology of the ligand plays an essential role, and a mesophase is induced at room temperature from a nonmesogenic pyrazole only when it is symmetrically substituted with six decyloxy chains. The single-crystal structure of a methoxy-substituted analogue, 3,5-bis(3,4,5-trimethoxyphenyl)pyrazole, is formed by globular tetrameric structures held together by H-bonding. However, parallel dimers are present in the corresponding cis-chlorodicarbonylrhodium(I) complex, a situation that explains the induction of a columnar mesophase in the decyloxy-substituted complex. The XRD pattern of the mesophase is consistent with a hexagonal symmetry in which the columns are formed by molecules assembled in an antiparallel mode. The crystal-to-mesophase transition was also detected by spectroscopic techniques as a shift in the IR carbonyl stretching bands and the appearance of a charge-transfer band in the absorption spectrum with thermochromic behavior.

Journal Article↗
PubMed2006

Propeller-like hydrogen-bonded banana-melamine complexes inducing helical supramolecular organizations.

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 pi-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.

Hydrogen Bonding↗
PubMed2005

Changes in erythrocyte enzymes in humans long-term exposed to pesticides: influence of several markers of individual susceptibility.

Changes in erythrocyte delta-aminolevulinic acid dehydratase (ALA-D) have been reported after exposure to different pesticides, including organophosphates and paraquat. In this study, we have determined ALA-D in 135 pesticide applicators (sprayers) from an intensive agriculture setting at two periods with different pesticide exposure. Acetylcholinesterase (AChE) was used as a reference biomarker. The effects of the combined polymorphism of enzymes involved in the detoxification of pesticides (paraoxonase (PON1), benzoylcholinesterase (BChE), and glutathione S-transferase (GSTM1 and GSTT1)) on the level of the target erythrocyte enzymes were also studied as biomarkers of individual susceptibility. Sprayers presented significant lower levels of ALA-D and AChE than controls (41.3% and 14.5%, respectively) at the high exposure period. When all biomarkers of individual susceptibility to pesticides were considered at the same time, the GSTT1 null allele determined higher ALA-D and AChE activities at the period of high exposure to pesticides. PON1 R allele in turn determined lower AChE activity at the low exposure period. Null genotype for both GST subclasses (GSTM1 and GSTT1) was found to be the unique independent predictor of pesticide-related symptomatology. Interestingly, sprayers were consistently underrepresented among carriers of "unfavourable" BChE variants. In conclusion, ALA-D appears to be an important biological indicator of pesticide exposure and PON1 and GSTT1 are relevant determinants of susceptibility to chronic pesticide poisoning.

Acetylcholine↗
PubMed2005

Columnar mesomorphic organizations in cyclotriphosphazenes.

A synthetic strategy has been developed to prepare cyclotriphosphazenes that bear polycatenar aromatic esters as promesogenic units linked to phosphorus atoms. The microsegregation of the rigid and flexible parts of the system and the space-filling properties are the driving forces that determine the kind of mesomorphism exhibited by the organocyclotriphosphazenes. Mesogenic units that contain only one terminal alkyl chain give rise to calamitic mesomorphism, since the molecules are arranged to give a cylindrical superstructure with the aromatic promesogenic cores elongated in a manner approximately perpendicular to the cyclotriphosphazene ring. On the other hand, mesogenic units that contain three long terminal chains exhibit columnar mesophases. In this case, a discotic structure consisting of promesogenic cores arranged approximately parallel to the cyclotriphosphazene ring can explain the columnar organization. The X-ray diffraction patterns corresponding to the Col(h) mesophase of the cyclotriphosphazene with dodecyloxy chains (8) indicate the presence of helical ordering, which was confirmed for a homologous compound bearing stereogenic centers on two of the terminal chains (11). All of the synthesized phosphazenes show a high thermal stability.

Crystallography, X-Ray↗
PubMed2005

Discotic liquid crystalline poly(propylene imine) dendrimers based on triphenylene.

The design, synthesis, and mesomorphic properties of a new series of homodendrimers consisting of the commercially available poly(propylene imine) (PPI) dendrimers (G = 1-5), PPI-(NH(2))(n)() (n = 4, 8, 16, 32, 64), functionalized with a discotic triphenylene moiety are reported. The liquid crystalline behavior was investigated by means of differential scanning calorimetry (DSC), polarizing-light optical microscopy (POM), and X-ray diffractometry (XRD). All of the homodendrimers showed mesomorphic properties, with the second to fifth generations giving a hexagonal columnar mesophase (Col(h)) and the first generation a rectangular columnar mesophase (Col(r)). The X-ray study reveals that these mesophases show a highly ordered structure with segregation of triphenylenes and dendrimers into separate columns and a regular stacking distance inside the triphenylene columns. GPC analysis showed that the dendrimers had good monodispersity and MALDI-TOF studies of the first three generations gave good evidence that all of the terminal amino groups of the dendrimers were functionalized with a discotic unit.

Journal Article↗
PubMed2005

Supramolecular helical mesomorphic polymers. Chiral induction through H-bonding.

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.

Adipates↗
PubMed2004

Mono- and binuclear cyclometallated palladium(II) complexes containing bridging (N,O-) and terminal (N-) imidate ligands: air stable, thermally robust and recyclable catalysts for cross-coupling processes.

Novel dinuclear cyclometallated palladium complexes [{Pd(mu-NCO)(C circumflex accent N)}(2)], containing asymmetric imidato -NCO- bridging units have been synthesised [C circumflex accent N = 7,8-benzoquinolyl; -NCO- = succinimidate (1c), phthalimidate (1a-3a) or maleimidate (3c)]. The reaction of these complexes, and the previously reported analogous imidate precursors containing a phenylazophenyl (1a-3a) or 2-pyridylphenyl (1b-3b) backbone, with tertiary phosphines provides novel mononuclear N-bonded imidate derivatives of the general formula [Pd(C circumflex accent N)(imidate)(L)][L = PPh(3), P(4-F-C(6)H(4))(3) or P(4-MeO-C(6)H(4))(3)]. The single crystal structures of [Pd(azb)(phthalimidate)(P(4-MeO-C(6)H(4))(3))](9a) and [Pd(bzq)(phthalimidate)(PPh(3))](7c) have been established. Dinuclear complexes (1a-3a, 1b-3b, 1c-3c) demonstrate outstanding thermal stability in the solid-state, as shown by thermoanalytical techniques. A marked influence of bridging imidate groups on the initial decomposition temperature is observed. The dinuclear and mononuclear derivatives are shown to be active catalysts/precatalysts for the Suzuki-Miyaura cross-coupling reactions of aryl bromides with aryl boronic acids, and the Sonogashira reactions of aryl halides with phenyl acetylene (in the presence and absence of Cu(I) salts). The conversions appear to be dependent, to some extent, on the type of imidate ligand, suggesting a role for these pseudohalides in the catalytic cycle in both cross-coupling processes. Lower catalyst loadings in 'copper-free' Sonogashira cross-couplings favour higher turnover frequencies. We have further determined that these catalysts may be recycled using a poly(ethylene oxide)(PEO)/methanol solvent medium in Suzuki-Miyaura cross-coupling. Once the reaction is complete, product extraction into a hexane/diethyl ether mixture (1 : 1, v/v) gives cross-coupled products in good yields (with purity > 95%). The polar phase can then be re-used several times without appreciable loss of catalytic activity.

Boronic Acids↗
PubMed2004

Mesomorphism of a tetrahedral zinc complex.

Thermotropic smectic phases have been observed for the first time in a zinc coordination complex with tetrahedral geometry; this complex, which contains the pyrazole dimer bis[3,5-bis(p-decyloxyphenyl)pyrazolyl]ethane as the ligand, exhibits fluorescence.

Journal Article↗
PubMed2004

SmCP-networked films obtained by in situ photopolymerization of neat reactive banana-shaped liquid crystals.

The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field.

Journal Article↗