Francisco Meijide | University of Santiago de Compostela (original) (raw)

Papers by Francisco Meijide

Research paper thumbnail of Análisis de errores aleatorios y sistemáticos introducidos por las pipetas utilizadas en el método de las diluciones para el recuento de microorganismos

Alimentaria Revista De Tecnologia E Higiene De Los Alimentos, 1993

Research paper thumbnail of “Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

Http Dx Doi Org 10 1080 1061027031000078211, May 13, 2010

The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclode... more The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclodextrin (bCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of bCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino bCD derivatives is also presented.

Research paper thumbnail of Bile salts and derivatives: Rigid unconventional amphiphiles as dispersants, carriers and superstructure building blocks

Current Opinion in Colloid & Interface Science, 2015

Research paper thumbnail of Multi stimuli response of a single surfactant presenting a rich self-assembly behavior

RSC Adv., 2015

ABSTRACT This work reports on the multi stimuli sensitivity of a cholic acid derivative in buffer... more ABSTRACT This work reports on the multi stimuli sensitivity of a cholic acid derivative in buffer. The molecules self-organize in single walled tubules at room temperature and pH 8.0-9.5. By increasing the pH to 10.0-12.0, these tubules open up and form scrolls, which transform by aging into different tubular structures. A further evolution from scrolls or tubules into ribbons is induced by increasing the temperature. Moreover, a transition into rolled lamellae can be triggered by adding NaCl. All transitions are reversible and accompanied by drastic molecular rearrangements, manifested by spectroscopic and imaging techniques. Such rich multi stimuli responsiveness is usually accomplished by block copolymers or peptides and seldom by pure surfactants. The reported surfactant provides in addition an uncommon variety of structures. The sharpness of the spectroscopic response suggests that the system could be employed in physico-chemical sensors with a rather narrow dynamic range.

Research paper thumbnail of Diarmed (adamantyl/alkyl) surfactants from nitrilotriacetic acid

Colloids and Surfaces B: Biointerfaces, 2014

The compounds presented here constitute a clear example of molecular biomimetics as their design ... more The compounds presented here constitute a clear example of molecular biomimetics as their design is inspired on the structure and properties of natural phospholipids. Thus novel double-armed surfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospholipids. The hydrophobic arms are linked to the head group through amide bonds (which is also the case of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2)NCH2CO2H (R1 being CH3(CH2)11, CH3(CH2)17, CH3(CH2)7CHCH(CH2)8, and adamantyl, and R2=adamantyl). The dependence of the surface tension with concentration shows the typical profile of surfactants since a breaking point, which corresponds to the critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivatives are about 1-3 orders of magnitude lower than those of classical monoalkyl derivatives used as reference compounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areas at the solution-air interface have been observed. This anomalous behavior is tied to the structure of the surfactants and suggests that long and flexible alkyl chains should self-coil previous to the aggregation or adsorption phenomena. Above cac all compounds form large aggregates, globular in shape, which tend to associate forming giant aggregates.

Research paper thumbnail of Crystal structure of a G-1 dendrimer of aminoisophtalic acid

Proceedings of The 17th International Electronic Conference on Synthetic Organic Chemistry, 2013

Research paper thumbnail of Design of dialkyl surfactants from nitrilotriacetic acid as head group

RSC Advances, 2014

ABSTRACT New double-chain surfactants can be designed in which nitrilotriacetic acid plays the ro... more ABSTRACT New double-chain surfactants can be designed in which nitrilotriacetic acid plays the role of glycerol in phospholipids. The synthetic methodology is applied to the synthesis of (2-(bis(2-dodecylamino)-2-oxoethyl) amino) acetic acid. This is a symmetric dimeric surfactant but the methodology allows the synthesis of asymmetric double-chain surfactants as well. The Krafft temperature is 16-18 degrees C. The critical aggregation concentration of the new surfactant (4.76 x 10(-5) mol dm(-3) in NaOH 0.01 M and 25 degrees C; surface tension measurements) is two hundred times lower than that for sodium 2-dodecanamidoacetate, which can be considered its monoalkyl surfactant analog, indicating the enhanced surfactant properties resulting from the presence of two hydrophobic alkyl chains. The shape of the aggregates was investigated by transmission electron microscopy. At 40 degrees C, the main structure present in solution corresponds to vesicles and, from the size distribution of their radii, values of (0.34 +/- 0.06)kT and 56.7 +/- 2.6 nm were obtained for the effective bending elasticity constant and the spontaneous radius of curvature of vesicles, respectively.

Research paper thumbnail of Crystal Structure of a Head-to-Head Bis(cholic)-Urea Dimer

Proceedings of The 18th International Electronic Conference on Synthetic Organic Chemistry, 2014

Research paper thumbnail of Self-aggregation mechanism of a naphthylamide cationic derivative of cholic acid. From fibers to tubules

RSC Advances, 2014

ABSTRACT The aggregation behavior of a cationic derivative of cholic acid {[3 beta, 5 beta, 7 alp... more ABSTRACT The aggregation behavior of a cationic derivative of cholic acid {[3 beta, 5 beta, 7 alpha, 12 alpha]-3-(2-naphthoylamino)-7,12-dihydroxycholan- 24-triethylamonium iodide} has been studied by surface tension measurements, fluorescence spectroscopy, transmission electronic microscopy (TEM), and circular dichroism. The critical aggregation concentration, the fraction of bound counterions and thermodynamic parameters for the formation of aggregates have been determined, as well as the morphology of the aggregates. TEM images support a consecutive transformation mechanism from fibers to tubules, these having a well-defined geometry and being the only structure observed at the end of the process. Intermediate observed structures are helical ribbons.

Research paper thumbnail of Supramolecular polymer formed by ditopic cyclodextrin and ditopic adamantane derivatives

Novel host-guest supramolecular copolymers have been prepared from a β-cyclodextrin (binded to et... more Novel host-guest supramolecular copolymers have been prepared from a β-cyclodextrin (binded to ethylenediamintetraacetic acid, EDTA) dimer and a ditopic guest with two adamantyl groups bound to pyromellitic acid. Molecular weight and molecular size were determined from static and dynamic light scattering measurements (SLS and DLS, respectively). The analysis of results suggests that the supramolecular polymer adopts a shruck structure with an average molecular weight value of M n = (1.51±0.02)×10 4 g·mol -1 (degree of polymerization equal to 5).

Research paper thumbnail of Characterization of Carbon Nanotube Dispersions in Solutions of Bile Salts and Derivatives Containing Aromatic Substituents

The Journal of Physical Chemistry B, 2014

Bile salts (BS) are known to solubilize high weight fractions of carbon nanotubes (CNTs) in aqueo... more Bile salts (BS) are known to solubilize high weight fractions of carbon nanotubes (CNTs) in aqueous solutions. Here, the efficiency of derivatives of bile salts (BSDs) containing aromatic substituents in dispersing single-wall CNTs (SWCNTs) has been investigated in order to check whether the presence of aromatic residues, because of their affinity toward carbon nanotube surfaces, determines improvements of the BS dispersion efficiency (DE). Electric arc and CoMoCAT SWCNTs were analyzed. The results, reported for the two surfactant concentrations of 0.06 and 1.0 wt %, show that the DE of BSDs depends on the position, orientation, and structure of the introduced aromatic residues. In the case of the CoMoCAT SWCNTs, at low surfactant concentration a DE improvement is observed in BSDs where the aromatic residue is linked either to carbon 3, located on the rigid four-ring system, or to the side chain. For the latter, this improvement is also enhanced in double-charge derivatives and kept at high surfactant concentration. It was also observed that at low concentrations of surfactant, the DE values of BSs and BSDs are usually larger than those of the more conventional detergent sodium dodecylsulfate.

Research paper thumbnail of New Lamellar Structure Formed by an Adamantyl Derivative of Cholic Acid

The Journal of Physical Chemistry B, 2006

Figure 5. Schematic representations of (a) the structure of the H-AdC molecule and (b) the struct... more Figure 5. Schematic representations of (a) the structure of the H-AdC molecule and (b) the structure of the crystal (compare with Figure 4b). It illustrates how the adamantane residues are mutually interlocked. Letters

Research paper thumbnail of Determination of Microscopic Equilibrium Constants for the Complexation of Ditopic Guests by Cyclodextrins from NMR Experiments

The Journal of Physical Chemistry B, 2004

Research paper thumbnail of pH Dependent In−Out Isomerism of an Amino-β-cyclodextrin Derivative

The Journal of Physical Chemistry B, 2006

An amino derivative of beta-cyclodextrin [6-(6-aminehexanamide)-6-deoxy)-beta-cyclodextrin (6-bet... more An amino derivative of beta-cyclodextrin [6-(6-aminehexanamide)-6-deoxy)-beta-cyclodextrin (6-betaCD)] was synthesized, and the formation of an intramolecular inclusion complex was studied by NMR techniques. The deprotonation/protonation of the amino group stimulates an in/out movement of the pendant group toward/from the cyclodextrin cavity, the protonated species lying outside the hydrophobic cyclodextrin cavity but the unprotonated one residing inside and outside the cavity. The protonation of the amino group is a fast exchange rate NMR time-scale process, but the chain movement is a slow one. The equilibrium constants of both processes were determined from 1H NMR experiments and the kinetic constants for the slow process were determined from exchange spectroscopy (EXSY) experiments.

Research paper thumbnail of Early Stages of Formation of Branched Host−Guest Supramolecular Polymers

The Journal of Physical Chemistry B, 2008

A structural characterization of host-guest supramolecular copolymers, formed by an adamantane di... more A structural characterization of host-guest supramolecular copolymers, formed by an adamantane dimer and two beta-cyclodextrin trimers in aqueous solution, has been carried out by combining small angle X-ray scattering and light scattering experiments. A shape-reconstruction method was applied to the SAXS data to obtain relatively high-resolution conformation information, and a correlation with the experimental dynamic light scattering results was performed, by estimating the hydrodynamic radii of the reconstructed shape through a shell model method. When applied on the solutions of the trimers, the analysis provides a globular reconstructed shape with a hydrodynamic radius in agreement with the experimental one. For the polymers, elongated structures were inferred which grow both in length and in cross section by increasing the concentration. Depending on the beta-cyclodextrin trimer employed in the polymer preparation, polymerization degrees ranging between roughly 7 and 14 or 9 and 22 were obtained in the concentration range 4.00-10.0 or 3.10-6.60 mM of the trimer (6.00-15.0 or 4.65-9.90 mM of the dimer). Aggregation schemes were proposed accounting for the formation of hyperbranched, linear, and network like polymers. The experimental results are not far from those expected on the basis of the aggregation in hyperbranched structure, for which the growth of elongated aggregates can be predicted in the early stages of the polymerization. However, the coexistence of the other structures, in particular of the linear one, cannot be ruled out.

Research paper thumbnail of Complexation of Adamantyl Compounds by β-Cyclodextrin and Monoaminoderivatives

The Journal of Physical Chemistry B, 2005

Since the beta-cyclodextrin cavity is not a smooth cone but has constrictions in the neighborhood... more Since the beta-cyclodextrin cavity is not a smooth cone but has constrictions in the neighborhoods of the H3 and H5 atoms, the hypothesis that bulky hydrophobic guests can form two isomeric inclusion complexes (one of them, c(p), is formed by the entrance of the guest by the primary side of the cavity, and the other one, c(s), results from the entrance by the secondary side) is checked. Thus, the inclusion processes of two 1-substituted adamantyl derivatives (rimantidine and adamantylmethanol) with beta-cyclodextrin and its two monoamino derivatives at positions 6 (6-NH2beta-CD) and 3 (3-NH2beta-CD) were studied. From rotating-frame Overhauser enhancement spectroscopy experiments, it was deduced that both guests form c(s) complexes with beta-CD and 6-NH2beta-CD but c(p) complexes with 3-NH2beta-CD. In all cases, the hydrophilic group attached to the adamantyl residue protrudes toward the bulk solvent outside the cyclodextrin cavity. The thermodynamic parameters (free energy, equilibrium constant, enthalpy, and entropy) associated with the inclusion phenomena were measured by isothermal titration calorimetry experiments. From these results, the difference in the free energy for the formation of the two complexes, c(s) and c(p), for the same host/guest system has been estimated as being 11.5 +/- 0.8 kJ mol(-1). This large difference explains why under normal experimental conditions only one of the two complexes (c(s)) is detected. It is also concluded that a hyperboloid of revolution can be a better schematic picture to represent the actual geometry of the cyclodextrin cavities than the usual smooth cone or trapezium.

Research paper thumbnail of Complexation of Bile Salts by Natural Cyclodextrins

Supramolecular Chemistry, 2003

The complexation of three trihydroxy sodium bile salts--cholate, glycocholate, and taurocholate--... more The complexation of three trihydroxy sodium bile salts--cholate, glycocholate, and taurocholate--and their three related sodium dihydroxy bile salts--deoxycholate, glycodeoxycholate, and taurodeoxycholate--by f-, g-and n-cyclodextrins (f-CD, g-CD and n ...

Research paper thumbnail of “Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

Supramolecular Chemistry, 2003

The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclode... more The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclodextrin (bCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of bCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino bCD derivatives is also presented.

Research paper thumbnail of Supramolecular Linear Conglomerates Formed by β-Cyclodextrin Dimers and Sodium Deoxycholate

Supramolecular Chemistry, 2002

The formation of supramolecular structures by the complexation of two bile salts-sodium cholate (... more The formation of supramolecular structures by the complexation of two bile salts-sodium cholate (NaC) and sodium deoxycholate (NaDC)-with four new headto-head b-cyclodextrin dimers was studied by NMR techniques. All dimers form 1:2 (dimer:bile salt) stoichiometry complexes with NaC. With NaDC, linear supramolecular conglomerates of an n:n stoichiometry were obtained for all dimers. ROESY spectra confirmed the presence of electrostatic interactions when a protonated amino group is present in the linking group. The dependence of the pseudo-equilibrium constants with the electrostatic interactions and steric hindrance is discussed.

Research paper thumbnail of Formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxycholic acids in aqueous solution

Steroids, 2012

The formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxy... more The formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxycholic acids in aqueous solution is investigated. The critical aggregation concentrations of the new surfactants are much lower than those of ursodeoxycholate and chenodeoxycholate, indicating the enhanced surfactant properties resulting by the presence of the hydrophobic p-tert-butylphenyl group. The molecular areas at the air-water interface suggest the formation of monolayer films with molecules upright oriented. The shape of the aggregates was investigated by TEM. The main structure present in solution corresponds to tubules. The estimated value for the wall thickness of tubules suggests that a bilayer structure is formed. Host of positively charged latex beads by tubules suggests that their inner and outer surfaces are negatively charged. The acid form of the chenodeoxycholate derivative was recrystallized from toluene and its crystal structure analyzed. (J. Vázquez Tato). 1 Na-AdC: sodium [3b,5b,7a,12a]-3-(adamantoylamino)-7,12-dihydroxycholan-24-oate;Na-tbutPhC, sodium [3b,5b,7a,12a]-3-(4-t-butylbenzoylamino)-7, 1 2 -d i h y d r o x y c h o l a n -2 4 -o a t e ; N a -t b u t P h D C , s o d i u m [ 3 b , 5 b , 1 2 a ] -3 -

Research paper thumbnail of Análisis de errores aleatorios y sistemáticos introducidos por las pipetas utilizadas en el método de las diluciones para el recuento de microorganismos

Alimentaria Revista De Tecnologia E Higiene De Los Alimentos, 1993

Research paper thumbnail of “Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

Http Dx Doi Org 10 1080 1061027031000078211, May 13, 2010

The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclode... more The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclodextrin (bCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of bCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino bCD derivatives is also presented.

Research paper thumbnail of Bile salts and derivatives: Rigid unconventional amphiphiles as dispersants, carriers and superstructure building blocks

Current Opinion in Colloid & Interface Science, 2015

Research paper thumbnail of Multi stimuli response of a single surfactant presenting a rich self-assembly behavior

RSC Adv., 2015

ABSTRACT This work reports on the multi stimuli sensitivity of a cholic acid derivative in buffer... more ABSTRACT This work reports on the multi stimuli sensitivity of a cholic acid derivative in buffer. The molecules self-organize in single walled tubules at room temperature and pH 8.0-9.5. By increasing the pH to 10.0-12.0, these tubules open up and form scrolls, which transform by aging into different tubular structures. A further evolution from scrolls or tubules into ribbons is induced by increasing the temperature. Moreover, a transition into rolled lamellae can be triggered by adding NaCl. All transitions are reversible and accompanied by drastic molecular rearrangements, manifested by spectroscopic and imaging techniques. Such rich multi stimuli responsiveness is usually accomplished by block copolymers or peptides and seldom by pure surfactants. The reported surfactant provides in addition an uncommon variety of structures. The sharpness of the spectroscopic response suggests that the system could be employed in physico-chemical sensors with a rather narrow dynamic range.

Research paper thumbnail of Diarmed (adamantyl/alkyl) surfactants from nitrilotriacetic acid

Colloids and Surfaces B: Biointerfaces, 2014

The compounds presented here constitute a clear example of molecular biomimetics as their design ... more The compounds presented here constitute a clear example of molecular biomimetics as their design is inspired on the structure and properties of natural phospholipids. Thus novel double-armed surfactants have been obtained in which nitrilotriacetic acid plays the role of glycerol in phospholipids. The hydrophobic arms are linked to the head group through amide bonds (which is also the case of sphingomyelin): (R1NHCOCH2)(R2NHCOCH2)NCH2CO2H (R1 being CH3(CH2)11, CH3(CH2)17, CH3(CH2)7CHCH(CH2)8, and adamantyl, and R2=adamantyl). The dependence of the surface tension with concentration shows the typical profile of surfactants since a breaking point, which corresponds to the critical aggregation concentration (cac), is observed in all cases. The cac of these diarmed derivatives are about 1-3 orders of magnitude lower than those of classical monoalkyl derivatives used as reference compounds. In contrast to conventional surfactants, reversed trends in cac values and molecular areas at the solution-air interface have been observed. This anomalous behavior is tied to the structure of the surfactants and suggests that long and flexible alkyl chains should self-coil previous to the aggregation or adsorption phenomena. Above cac all compounds form large aggregates, globular in shape, which tend to associate forming giant aggregates.

Research paper thumbnail of Crystal structure of a G-1 dendrimer of aminoisophtalic acid

Proceedings of The 17th International Electronic Conference on Synthetic Organic Chemistry, 2013

Research paper thumbnail of Design of dialkyl surfactants from nitrilotriacetic acid as head group

RSC Advances, 2014

ABSTRACT New double-chain surfactants can be designed in which nitrilotriacetic acid plays the ro... more ABSTRACT New double-chain surfactants can be designed in which nitrilotriacetic acid plays the role of glycerol in phospholipids. The synthetic methodology is applied to the synthesis of (2-(bis(2-dodecylamino)-2-oxoethyl) amino) acetic acid. This is a symmetric dimeric surfactant but the methodology allows the synthesis of asymmetric double-chain surfactants as well. The Krafft temperature is 16-18 degrees C. The critical aggregation concentration of the new surfactant (4.76 x 10(-5) mol dm(-3) in NaOH 0.01 M and 25 degrees C; surface tension measurements) is two hundred times lower than that for sodium 2-dodecanamidoacetate, which can be considered its monoalkyl surfactant analog, indicating the enhanced surfactant properties resulting from the presence of two hydrophobic alkyl chains. The shape of the aggregates was investigated by transmission electron microscopy. At 40 degrees C, the main structure present in solution corresponds to vesicles and, from the size distribution of their radii, values of (0.34 +/- 0.06)kT and 56.7 +/- 2.6 nm were obtained for the effective bending elasticity constant and the spontaneous radius of curvature of vesicles, respectively.

Research paper thumbnail of Crystal Structure of a Head-to-Head Bis(cholic)-Urea Dimer

Proceedings of The 18th International Electronic Conference on Synthetic Organic Chemistry, 2014

Research paper thumbnail of Self-aggregation mechanism of a naphthylamide cationic derivative of cholic acid. From fibers to tubules

RSC Advances, 2014

ABSTRACT The aggregation behavior of a cationic derivative of cholic acid {[3 beta, 5 beta, 7 alp... more ABSTRACT The aggregation behavior of a cationic derivative of cholic acid {[3 beta, 5 beta, 7 alpha, 12 alpha]-3-(2-naphthoylamino)-7,12-dihydroxycholan- 24-triethylamonium iodide} has been studied by surface tension measurements, fluorescence spectroscopy, transmission electronic microscopy (TEM), and circular dichroism. The critical aggregation concentration, the fraction of bound counterions and thermodynamic parameters for the formation of aggregates have been determined, as well as the morphology of the aggregates. TEM images support a consecutive transformation mechanism from fibers to tubules, these having a well-defined geometry and being the only structure observed at the end of the process. Intermediate observed structures are helical ribbons.

Research paper thumbnail of Supramolecular polymer formed by ditopic cyclodextrin and ditopic adamantane derivatives

Novel host-guest supramolecular copolymers have been prepared from a β-cyclodextrin (binded to et... more Novel host-guest supramolecular copolymers have been prepared from a β-cyclodextrin (binded to ethylenediamintetraacetic acid, EDTA) dimer and a ditopic guest with two adamantyl groups bound to pyromellitic acid. Molecular weight and molecular size were determined from static and dynamic light scattering measurements (SLS and DLS, respectively). The analysis of results suggests that the supramolecular polymer adopts a shruck structure with an average molecular weight value of M n = (1.51±0.02)×10 4 g·mol -1 (degree of polymerization equal to 5).

Research paper thumbnail of Characterization of Carbon Nanotube Dispersions in Solutions of Bile Salts and Derivatives Containing Aromatic Substituents

The Journal of Physical Chemistry B, 2014

Bile salts (BS) are known to solubilize high weight fractions of carbon nanotubes (CNTs) in aqueo... more Bile salts (BS) are known to solubilize high weight fractions of carbon nanotubes (CNTs) in aqueous solutions. Here, the efficiency of derivatives of bile salts (BSDs) containing aromatic substituents in dispersing single-wall CNTs (SWCNTs) has been investigated in order to check whether the presence of aromatic residues, because of their affinity toward carbon nanotube surfaces, determines improvements of the BS dispersion efficiency (DE). Electric arc and CoMoCAT SWCNTs were analyzed. The results, reported for the two surfactant concentrations of 0.06 and 1.0 wt %, show that the DE of BSDs depends on the position, orientation, and structure of the introduced aromatic residues. In the case of the CoMoCAT SWCNTs, at low surfactant concentration a DE improvement is observed in BSDs where the aromatic residue is linked either to carbon 3, located on the rigid four-ring system, or to the side chain. For the latter, this improvement is also enhanced in double-charge derivatives and kept at high surfactant concentration. It was also observed that at low concentrations of surfactant, the DE values of BSs and BSDs are usually larger than those of the more conventional detergent sodium dodecylsulfate.

Research paper thumbnail of New Lamellar Structure Formed by an Adamantyl Derivative of Cholic Acid

The Journal of Physical Chemistry B, 2006

Figure 5. Schematic representations of (a) the structure of the H-AdC molecule and (b) the struct... more Figure 5. Schematic representations of (a) the structure of the H-AdC molecule and (b) the structure of the crystal (compare with Figure 4b). It illustrates how the adamantane residues are mutually interlocked. Letters

Research paper thumbnail of Determination of Microscopic Equilibrium Constants for the Complexation of Ditopic Guests by Cyclodextrins from NMR Experiments

The Journal of Physical Chemistry B, 2004

Research paper thumbnail of pH Dependent In−Out Isomerism of an Amino-β-cyclodextrin Derivative

The Journal of Physical Chemistry B, 2006

An amino derivative of beta-cyclodextrin [6-(6-aminehexanamide)-6-deoxy)-beta-cyclodextrin (6-bet... more An amino derivative of beta-cyclodextrin [6-(6-aminehexanamide)-6-deoxy)-beta-cyclodextrin (6-betaCD)] was synthesized, and the formation of an intramolecular inclusion complex was studied by NMR techniques. The deprotonation/protonation of the amino group stimulates an in/out movement of the pendant group toward/from the cyclodextrin cavity, the protonated species lying outside the hydrophobic cyclodextrin cavity but the unprotonated one residing inside and outside the cavity. The protonation of the amino group is a fast exchange rate NMR time-scale process, but the chain movement is a slow one. The equilibrium constants of both processes were determined from 1H NMR experiments and the kinetic constants for the slow process were determined from exchange spectroscopy (EXSY) experiments.

Research paper thumbnail of Early Stages of Formation of Branched Host−Guest Supramolecular Polymers

The Journal of Physical Chemistry B, 2008

A structural characterization of host-guest supramolecular copolymers, formed by an adamantane di... more A structural characterization of host-guest supramolecular copolymers, formed by an adamantane dimer and two beta-cyclodextrin trimers in aqueous solution, has been carried out by combining small angle X-ray scattering and light scattering experiments. A shape-reconstruction method was applied to the SAXS data to obtain relatively high-resolution conformation information, and a correlation with the experimental dynamic light scattering results was performed, by estimating the hydrodynamic radii of the reconstructed shape through a shell model method. When applied on the solutions of the trimers, the analysis provides a globular reconstructed shape with a hydrodynamic radius in agreement with the experimental one. For the polymers, elongated structures were inferred which grow both in length and in cross section by increasing the concentration. Depending on the beta-cyclodextrin trimer employed in the polymer preparation, polymerization degrees ranging between roughly 7 and 14 or 9 and 22 were obtained in the concentration range 4.00-10.0 or 3.10-6.60 mM of the trimer (6.00-15.0 or 4.65-9.90 mM of the dimer). Aggregation schemes were proposed accounting for the formation of hyperbranched, linear, and network like polymers. The experimental results are not far from those expected on the basis of the aggregation in hyperbranched structure, for which the growth of elongated aggregates can be predicted in the early stages of the polymerization. However, the coexistence of the other structures, in particular of the linear one, cannot be ruled out.

Research paper thumbnail of Complexation of Adamantyl Compounds by β-Cyclodextrin and Monoaminoderivatives

The Journal of Physical Chemistry B, 2005

Since the beta-cyclodextrin cavity is not a smooth cone but has constrictions in the neighborhood... more Since the beta-cyclodextrin cavity is not a smooth cone but has constrictions in the neighborhoods of the H3 and H5 atoms, the hypothesis that bulky hydrophobic guests can form two isomeric inclusion complexes (one of them, c(p), is formed by the entrance of the guest by the primary side of the cavity, and the other one, c(s), results from the entrance by the secondary side) is checked. Thus, the inclusion processes of two 1-substituted adamantyl derivatives (rimantidine and adamantylmethanol) with beta-cyclodextrin and its two monoamino derivatives at positions 6 (6-NH2beta-CD) and 3 (3-NH2beta-CD) were studied. From rotating-frame Overhauser enhancement spectroscopy experiments, it was deduced that both guests form c(s) complexes with beta-CD and 6-NH2beta-CD but c(p) complexes with 3-NH2beta-CD. In all cases, the hydrophilic group attached to the adamantyl residue protrudes toward the bulk solvent outside the cyclodextrin cavity. The thermodynamic parameters (free energy, equilibrium constant, enthalpy, and entropy) associated with the inclusion phenomena were measured by isothermal titration calorimetry experiments. From these results, the difference in the free energy for the formation of the two complexes, c(s) and c(p), for the same host/guest system has been estimated as being 11.5 +/- 0.8 kJ mol(-1). This large difference explains why under normal experimental conditions only one of the two complexes (c(s)) is detected. It is also concluded that a hyperboloid of revolution can be a better schematic picture to represent the actual geometry of the cyclodextrin cavities than the usual smooth cone or trapezium.

Research paper thumbnail of Complexation of Bile Salts by Natural Cyclodextrins

Supramolecular Chemistry, 2003

The complexation of three trihydroxy sodium bile salts--cholate, glycocholate, and taurocholate--... more The complexation of three trihydroxy sodium bile salts--cholate, glycocholate, and taurocholate--and their three related sodium dihydroxy bile salts--deoxycholate, glycodeoxycholate, and taurodeoxycholate--by f-, g-and n-cyclodextrins (f-CD, g-CD and n ...

Research paper thumbnail of “Three-in-one” Complexes Formed by Anionic Guests and Monosubstituted Cationic Alkyldiamino β-Cyclodextrin Derivatives

Supramolecular Chemistry, 2003

The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclode... more The effect of electrostatic interactions on the complexation of ionic guests by charged b-cyclodextrin (bCD) derivatives is reviewed. Special attention is paid to the numerous studies concerning the effect of electrostatic interactions on (i) the complexation of fluorescent and UV probes; (ii) the catalytic and chiral recognition properties of bCD derivatives; and (iii) the complexation of two bile salts (sodium cholate, NaC, and sodium deoxycholate, NaDC). The formation of three-in-one complexes between NaC and alkyldiamino bCD derivatives is also presented.

Research paper thumbnail of Supramolecular Linear Conglomerates Formed by β-Cyclodextrin Dimers and Sodium Deoxycholate

Supramolecular Chemistry, 2002

The formation of supramolecular structures by the complexation of two bile salts-sodium cholate (... more The formation of supramolecular structures by the complexation of two bile salts-sodium cholate (NaC) and sodium deoxycholate (NaDC)-with four new headto-head b-cyclodextrin dimers was studied by NMR techniques. All dimers form 1:2 (dimer:bile salt) stoichiometry complexes with NaC. With NaDC, linear supramolecular conglomerates of an n:n stoichiometry were obtained for all dimers. ROESY spectra confirmed the presence of electrostatic interactions when a protonated amino group is present in the linking group. The dependence of the pseudo-equilibrium constants with the electrostatic interactions and steric hindrance is discussed.

Research paper thumbnail of Formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxycholic acids in aqueous solution

Steroids, 2012

The formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxy... more The formation of tubules by p-tert-butylphenylamide derivatives of chenodeoxycholic and ursodeoxycholic acids in aqueous solution is investigated. The critical aggregation concentrations of the new surfactants are much lower than those of ursodeoxycholate and chenodeoxycholate, indicating the enhanced surfactant properties resulting by the presence of the hydrophobic p-tert-butylphenyl group. The molecular areas at the air-water interface suggest the formation of monolayer films with molecules upright oriented. The shape of the aggregates was investigated by TEM. The main structure present in solution corresponds to tubules. The estimated value for the wall thickness of tubules suggests that a bilayer structure is formed. Host of positively charged latex beads by tubules suggests that their inner and outer surfaces are negatively charged. The acid form of the chenodeoxycholate derivative was recrystallized from toluene and its crystal structure analyzed. (J. Vázquez Tato). 1 Na-AdC: sodium [3b,5b,7a,12a]-3-(adamantoylamino)-7,12-dihydroxycholan-24-oate;Na-tbutPhC, sodium [3b,5b,7a,12a]-3-(4-t-butylbenzoylamino)-7, 1 2 -d i h y d r o x y c h o l a n -2 4 -o a t e ; N a -t b u t P h D C , s o d i u m [ 3 b , 5 b , 1 2 a ] -3 -