The crystal structure of a Li(+) salt of a glucosyl derivative of lithocholic acid (lithium 3α-(α... more The crystal structure of a Li(+) salt of a glucosyl derivative of lithocholic acid (lithium 3α-(α-d-glucopyranosyl)-5β-cholan-24-oate) has been solved. The crystal belongs to the orthorhombic system, P212121 spatial group, and includes acetone and water in the structure with a 1:1:2 stoichiometry. Monolayers, having a hydrophobic interior and hydrophilic edges, are recognized in the crystal structure. Li(+) is coordinated to three hydroxyl groups of three different glucose residues, with two of them belonging to the same monolayer. A fourth molecule, located in this monolayer, is involved in the coordination of the cation through the carboxylate ion by an electrostatic interaction, thus completing a distorted tetrahedron. All Li(+)-oxygen distances values are very close to the sum of the ionic radius of Li(+) and van der Waals radius of oxygen. Each steroid molecule is linked to other five steroid molecules through hydrogen bonds. Water and acetone are also involved in the hydrogen bond network. A hierarchical organization can be recognized in the crystal, the helical assembly along 21 screw axes being left-handed.
A detailed characterization of a host-guest supramolecular copolymer, formed by adamantane and -c... more A detailed characterization of a host-guest supramolecular copolymer, formed by adamantane and -cyclodextrin dimers (Ad 2 and CD 2 , respectively) in aqueous solution, has been carried out by combining small-angle X-ray scattering and light scattering experiments with molecular dynamics (MD) and Monte Carlo (MC) simulations. First, the solutions of the monomers were studied by a straightforward analysis of the scattering data. Afterward, the complex given by Ad 2 and two -cyclodextrin molecules was investigated by correlating scattering results and MD simulations, to characterize the host-guest linkage. Finally, a detailed interpretation of the polymer scattering data was achieved by MC simulations. These simulations were performed on a single supramolecular aggregate and, in view of its peculiar shape, the complete polymer structure was considered without resorting to more general but simplified chain models. The comparison between simulations with and without excluded volume interaction points out that, at our ionic strength (sodium azide 150 mM), the polymer is close to the theta condition. Fits by reverse MC methods show that the polymer presents a shrunk conformation in solution, but it does not close in stable cyclic structures, as generally hypothesized for this kind of small oligomer. However, a polymerization degree of about 8 (4 Ad 2 and 4 CD 2 ) was estimated which does not show any concentration dependence.
Physical Review B Condensed Matter and Materials Physics, 2008
We report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of mul... more We report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of multielectron excitations at the I-K edge. The photoabsorption cross section of crystalline tetramethylammonium iodide was measured at 28, 50, and 150 K, and room temperature. The latter spectrum has been found to be largely dominated by the opening of multielectron excitation channels, thus providing a very good model of the I- atomic background which can be used in the analysis of ionic iodine compounds. Features due to the simultaneous excitations 1s5p , 1s5s , 1s4d , 1s4p , 1s4s , 1s3d , and 1s3p have been recognized, and their identification is supported by previous experimental and theoretical determinations on Xe and HI.
Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) measurements were accompli... more Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) measurements were accomplished on sodium glycodeoxycholate (NaGDC) aqueous electrolyte solutions as a function of NaGDC and NaCl concentrations with the aim to determine with satisfactory approximation the NaGDC micellar aggregate structure at a gross molecular level, assuming monodispersity. Different conditions of interparticle interactions by varying ionic strength (NaCl concentration from 0 to 0.70 M) and NaGDC concentration (from 0.02 to 0.10 M) were studied. Smeared scattering intensities and electron pair distance distribution functions, radii of gyration, and aggregate heights are in satisfactory agreement with the corresponding functions calculated using a 2(1) helix as model. It is formed by trimers, each one composed by three NaGDC and nine H2O molecules related by a 3-fold rotation axis, and can be described by a hollow cylinder, probably filled by water molecules, characterized by a conventional radius of 23.7 A and a trimer repeat along the helical axis of 3.6 A. The helix is considerably inhomogeneous since the volume of the cylinder occupied by NaGDC molecules is less than one-third of the total. On the other hand, calculations performed with the average radial electronic density of the helix without water molecules or totally filled by water molecules (a NaGDC/H2O molecular ratio of about 1/50) or by using a three-shell average radial electronic density, independently evaluated on absolute scale, do not show significant differences, thus supporting the helical model. The aggregate size increases for all the samples by increasing either the NaCl or NaGDC concentration. The NaGDC low concentration (0.02 M) samples with NaCl within the range 0.30-0.70 M are characterized by short cylindrical aggregates that do not give rise to sensible interference effects. This assertion is supported by the satisfactory fit between the observed apparent mean hydrodynamic radii and the calculated ones by means of the method of Ortega and Garcia de la Torre (J. Chem. Phys. 2003, 119, 9914), valid for rods with a length-to-diameter ratio > or = 0.1 in dilute solution (noninteracting rods). The NaGDC moderate concentration (0.10 M) samples with NaCl within the range 0.20-0.60 M are characterized by cylindrical aggregates that, in the presence of repulsive Coulombic interactions progressively more and more screened, produce interference effects, due to the hard-body repulsion and attractive forces, but the agreement between observed and calculated SAXS data is satisfactory. The results of the low and moderate NaGDC concentration samples seem to indicate that the aggregation number increase, produced by adding 0.10 M NaCl, is constant within an ionic strength range and occurs by the addition of oligomers formed by trimers. The samples with a variable NaGDC concentration (0.02-0.10 M) at a fixed and high NaCl concentration (0.6 M) contain cylindrical aggregates that give rise to an attractive term effect prevailing on the hard-body repulsive one. The same situation seems to occur in the NaGDC moderate concentration samples.
Previously, structural units inferred from X-ray diffraction analysis of fibers, crystals, and co... more Previously, structural units inferred from X-ray diffraction analysis of fibers, crystals, and concentrated aqueous solutions were identified as models of dihydroxy and trihydroxy bile salt micellar aggregates. Dimers and their multiples (mainly octamers and hexadecamers) or structures derived from 7/1 helices (formed by trimers) were proposed for trihydroxy salts sodium glycocholate (NaGC) and taurocholate (NaTC) or for dihydroxy salts sodium glycodeoxycholate (NaGDC) and taurodeoxycholate (NaTDC), respectively, on the basis of strong experimental evidences. However, the radii of the cylindrical structures derived from 7/1 helices were unknown. This paper deals with small-angle X-ray scattering (SAXS) measurements that have permitted to estimate the cylindrical aggregate radius of NaGDC (about 22 Å), whereas that of NaTDC is very probably about 3 Å longer. SAXS and quasi-elastic light-scattering (QELS) data have shown a linear increase of the apparent mean hydrodynamic radius (within the approximate range 40-70 Å) with the height of NaGDC and NaTDC cylindrical aggregates, suggesting that the main interparticle correlation effects, ascribed to charge, van der Waals, and volume excluded interactions, are small or compensate each other. Moreover, aqueous solutions containing one dihydroxy and one trihydroxy bile salt (NaGDC and NaGC, NaTDC and NaTC, NaGDC and NaTC, NaTDC and NaGC) and 0.8 M NaCl have been studied. QELS measurements give information on the growing processes of NaGDC and NaTDC aggregates as a function of NaGC and NaTC concentration. Experimental data and calculations performed using the above-mentioned models support that a small amount of the bile salt forming smaller size aggregates (trihydroxy salt) inhibits the growth of the bile salt forming bigger size aggregates (dihydroxy salt), giving rise to smaller size aggregates. Reasonably, this phenomenon is due to the very different and not interchangeable structures of dihydroxy and trihydroxy bile salt aggregates. It seems also that the aggregate growth is a little more inhibited when the trihydroxy molecule polar head is different from that of the aggregate molecules. Trihydroxy salt monomers and oligomers compete with dihydroxy salt trimers in the growth process and interact with their cylindrical aggregates especially by means of polar forces.
An approach for tailoring self-assembled tubular structures is described. By controlling the rela... more An approach for tailoring self-assembled tubular structures is described. By controlling the relative composition of atwo-component surfactant mixture comprising the natural bile salt lithocholate and its bolamphiphilic derivative,i tw as possible to finely tune the nanotube cross-section of the mixed tubular aggregates that self-associated spontaneously in aqueous solution at pH 12. The diameter was found to vary up to 50 %w hen the stoichiometric ratio of the two bile salts was changed. The tuning of supramolecular nanochannels with such remarkable precision is of significant interest for technological applications of these materials.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
Please cite this article in press as: L. Travaglini, et al., A tryptophan-substituted cholic acid... more Please cite this article in press as: L. Travaglini, et al., A tryptophan-substituted cholic acid: Expanding the family of labelled biomolecules, Colloids Surf. A: Physicochem. Eng. Aspects (2015), http://dx.
Journal of Polymer Science Part a-Polymer Chemistry, 1978
Ethylene-butadiene (PEBU) copolymer with low percentage of butadiene was previously investigated ... more Ethylene-butadiene (PEBU) copolymer with low percentage of butadiene was previously investigated by van der Waals potential energy calculations. The trans -HC=CH-group (TDB) was found to show fold-supporting behavior, so that it was supposed that many TDB's were located on the surface of PEBU single crystals under favorable conditions of TDB concentration and of thickness of crystal platelets. In order to verify this hypothesis, three PEBU samples with a butadiene/ (ethylene + butadiene) molar ratio of 2.3% (B), 3.6% (C), and 4.6% (D), by assuming that the -HC==CH-groups are all trans, were studied and compared with a polyethylene (PE) sample (A). Samples A, B, C, and D were grown isothermally at temperatures of 50,55,60,61,70,71,75, and 80°C from dilute xylene solutions. Infrared, differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), bromination kinetics, and density measurements were performed. B, C, and D lamellar crystals show a long spacing L nearly equal to that of A at crystallization temperatures T, of 50 and 60°C. For T, 1 70°C, the fold period of samples B, C, and D increases more rapidly than that of A in the order D > C > B. The melting temperature T,,, and the enthalpy of fusion AHf decrease with increasing content of butadiene, except for B and C, which show nearly equal T,,, and AHf values. Two peaks appear in the fusion curves at temperatures TI and Tz, T I > Tz. The area of the peak a t T2 increases with the butadiene content, and, in the same sample, with T,. Results of bromination in suspension of B, C, and D single crystals, crystallid in the range 50-7loC, indicate that a high percentage of TDBs react on the fold surfaces. The chemical attack is more successful with crystals grown in the range 60-66"C, and, in the case of sample C, as much as 81% of the TDB's are consumed. The density of the samples increases with both T, and TDB percentage. On the basis of these observed results a simple model for PEBU is proposed.
The unfolding pathway of the defatted human serum albumin (HSA) binding ibuprofen and propofol ha... more The unfolding pathway of the defatted human serum albumin (HSA) binding ibuprofen and propofol has been studied by using small-angle X-ray scattering (SAXS) and the support of circular dichroism data. A set of HSA solutions with urea concentrations between 0.00 and 9.00 M was analyzed, and the singular value decomposition method applied to the complete SAXS data set allowed us to distinguish four different states in solution. Besides the native and unfolded forms, two intermediates I1 and I2 have been identified, and the low-resolution structures of these states were obtained by exploiting both ab initio and rigid body fitting methods. The I1 structure was characterized by only one open domain (domain I, which does not host a binding site for either of the ligands), whereas I2 presents only one closed domain (domain III). A direct comparison with the unfolding pathway of the HSA:Ibu complex (Galantini et al. Biophys. Chem. 2010, 147, 111-122) pointed out that the presence of propofol as a second ligand, located in subdomain IIIB, leads to the appearance of an intermediate with two closed domains (domains II and III), which are those that accommodate the ligands. Moreover, the equilibrium between I2 and the unfolded form is slightly shifted toward higher urea concentrations. These results suggest that the cobinding significantly hinders the unfolding process.
Self-assembly of peptides and bile acids has been widely investigated because of their biological... more Self-assembly of peptides and bile acids has been widely investigated because of their biological role and their potential as a tool for the preparation of nanostructured biomaterials. We herein report both the synthesis and the self-association behavior of a compound that combines the aggregation properties of bile acid- and amino acid-based molecules. The derivative has been prepared by introducing a L-tryptophan residue into the C-3 position of the deoxycholic acid skeleton and resulted in an amphoteric fluorescent labeled bile acid that shows a pH-dependent self-assembly. Under alkaline conditions it assembles into 28 nm diameter tubules, thus showing a completely different behavior compared to the precursor bile acid, which forms micelles under similar conditions. Upon heating the tubules break and turn into micelles, leading to an increase in the exposure to water of the tryptophan residue. On the other hand, in acidic solutions it aggregates into elongated micelles that further self-assemble forming a gel network, when an electrolyte is added.
studies on pure (E)-p-dimethylaminoazobenzene (hereafter indicated as DAB) and the DAB-choleic ac... more studies on pure (E)-p-dimethylaminoazobenzene (hereafter indicated as DAB) and the DAB-choleic acid (DCADAB) were accomplished by means of the torsion effusion method. The pressure of the vapour in equilibrium with the solid phase was determined for DAB as log P(kPa) = (15.05+0.18)-(6887*500)/T and by the second-law treatment of the vapour pressure data a AH& = 132 * 8 kJ mol-' was obtained for DAB vaporization from the pure compound. Since the tensimetric data of DCADAB lie at the limit of the instrument's working range only a rough value of AH&, =138 kJ mol-' was obtained for DAB vaporization from DCADAB.
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.
This paper deals with electrospray ionization mass spectrometry (ESIMS), small-angle X-ray scatte... more This paper deals with electrospray ionization mass spectrometry (ESIMS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) measurements in order to provide information on the existence, aggregation, composition, and structure of the two-component aggregates of sodium glycocholate (NaGC) and sodium glycodeoxycholate (NaGDC) in the gas and solution phases. Five samples, containing 100% NaGC and 100% NaGDC, and NaGDC/NaGC molar ratios of 3 (75D), 1 (50D), and 1/3 (25D), have been analyzed by ESIMS in positive-ion detection mode starting from 10 -3 and 10 -2 M total bile salt concentration in aqueous solutions. Generally, dimers or trimers prevail in the 100% NaGC or NaGDC samples, respectively, as observed in the preceding one-component ESIMS measurements and in agreement with the proposed micellar aggregate structures in aqueous solution. Moreover, it is observed that the composition of multimers in the samples 75D, 50D, and 25D deviates from the one expected on the basis of a random association of the monomers, the NaGDC contribution generally prevailing on the NaGC one. It happens also under the same percentage condition (50D sample), in agreement with a greater aggregation ability of NaGDC with respect to NaGC. SAXS and DLS data were recorded on six samples containing a NaGC + NaGDC 40 mM total concentration, one bile salt having 40, 32, 24, 16, 8, and 0 mM concentration and the other the complementary one, keeping constant the NaCl concentration (0.6 M). The NaGDC 40 mM sample presents SAXS curves in agreement with a cylindrical shape of the aggregates as shown in a previous paper. For the bile salt mixtures, the progressive decrease of the sizes and change of the aggregate morphology, toward a globular-like geometry, are observed by increasing the NaGC fraction, thus confirming the hypothesis about the ability of trihydroxy salts to inhibit the growth of dihydroxy salt aggregates. Fits on the basis of cylindrical model can be accomplished for all the SAXS spectra, however, when the extracted cylinder parameters are used to estimate theoretical hydrodynamic radii a reasonable agreement is obtained only for the samples at high fraction of NaGDC (NaGDC g 24 mM).
We report a study on the unfolding behavior of the most abundant protein contained in plasma, the... more We report a study on the unfolding behavior of the most abundant protein contained in plasma, the fatted and defatted human serum albumin, in denaturing conditions induced by guanidine hydrochloride. Low-resolution three-dimensional structures are reconstructed from the one-dimensional (1D) small-angle X-ray scattering patterns, and they are correlated with the parameters obtained from static and dynamic light scattering experiments. The unfolding process is pointed out by both ab initio and rigid body fitting methods which highlight a stepwise evolution of the protein structure toward open conformations. The superpositions of the 3D structures provided independently by the two methods show very good agreements. The hydrodynamic radii estimated for the protein best fitting conformations are in satisfactory agreement with the experimental ones. The results show that the unfolding process is consistent with previous spectroscopic studies which suggest a multistep unfolding pathway. In particular, a scheme in which domains III and II are opened in sequence and the presence of two intermediates are evidenced is presented.
The crystal structure of a Li(+) salt of a glucosyl derivative of lithocholic acid (lithium 3α-(α... more The crystal structure of a Li(+) salt of a glucosyl derivative of lithocholic acid (lithium 3α-(α-d-glucopyranosyl)-5β-cholan-24-oate) has been solved. The crystal belongs to the orthorhombic system, P212121 spatial group, and includes acetone and water in the structure with a 1:1:2 stoichiometry. Monolayers, having a hydrophobic interior and hydrophilic edges, are recognized in the crystal structure. Li(+) is coordinated to three hydroxyl groups of three different glucose residues, with two of them belonging to the same monolayer. A fourth molecule, located in this monolayer, is involved in the coordination of the cation through the carboxylate ion by an electrostatic interaction, thus completing a distorted tetrahedron. All Li(+)-oxygen distances values are very close to the sum of the ionic radius of Li(+) and van der Waals radius of oxygen. Each steroid molecule is linked to other five steroid molecules through hydrogen bonds. Water and acetone are also involved in the hydrogen bond network. A hierarchical organization can be recognized in the crystal, the helical assembly along 21 screw axes being left-handed.
A detailed characterization of a host-guest supramolecular copolymer, formed by adamantane and -c... more A detailed characterization of a host-guest supramolecular copolymer, formed by adamantane and -cyclodextrin dimers (Ad 2 and CD 2 , respectively) in aqueous solution, has been carried out by combining small-angle X-ray scattering and light scattering experiments with molecular dynamics (MD) and Monte Carlo (MC) simulations. First, the solutions of the monomers were studied by a straightforward analysis of the scattering data. Afterward, the complex given by Ad 2 and two -cyclodextrin molecules was investigated by correlating scattering results and MD simulations, to characterize the host-guest linkage. Finally, a detailed interpretation of the polymer scattering data was achieved by MC simulations. These simulations were performed on a single supramolecular aggregate and, in view of its peculiar shape, the complete polymer structure was considered without resorting to more general but simplified chain models. The comparison between simulations with and without excluded volume interaction points out that, at our ionic strength (sodium azide 150 mM), the polymer is close to the theta condition. Fits by reverse MC methods show that the polymer presents a shrunk conformation in solution, but it does not close in stable cyclic structures, as generally hypothesized for this kind of small oligomer. However, a polymerization degree of about 8 (4 Ad 2 and 4 CD 2 ) was estimated which does not show any concentration dependence.
Physical Review B Condensed Matter and Materials Physics, 2008
We report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of mul... more We report the direct measurement by x-ray-absorption spectroscopy of the complete spectrum of multielectron excitations at the I-K edge. The photoabsorption cross section of crystalline tetramethylammonium iodide was measured at 28, 50, and 150 K, and room temperature. The latter spectrum has been found to be largely dominated by the opening of multielectron excitation channels, thus providing a very good model of the I- atomic background which can be used in the analysis of ionic iodine compounds. Features due to the simultaneous excitations 1s5p , 1s5s , 1s4d , 1s4p , 1s4s , 1s3d , and 1s3p have been recognized, and their identification is supported by previous experimental and theoretical determinations on Xe and HI.
Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) measurements were accompli... more Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) measurements were accomplished on sodium glycodeoxycholate (NaGDC) aqueous electrolyte solutions as a function of NaGDC and NaCl concentrations with the aim to determine with satisfactory approximation the NaGDC micellar aggregate structure at a gross molecular level, assuming monodispersity. Different conditions of interparticle interactions by varying ionic strength (NaCl concentration from 0 to 0.70 M) and NaGDC concentration (from 0.02 to 0.10 M) were studied. Smeared scattering intensities and electron pair distance distribution functions, radii of gyration, and aggregate heights are in satisfactory agreement with the corresponding functions calculated using a 2(1) helix as model. It is formed by trimers, each one composed by three NaGDC and nine H2O molecules related by a 3-fold rotation axis, and can be described by a hollow cylinder, probably filled by water molecules, characterized by a conventional radius of 23.7 A and a trimer repeat along the helical axis of 3.6 A. The helix is considerably inhomogeneous since the volume of the cylinder occupied by NaGDC molecules is less than one-third of the total. On the other hand, calculations performed with the average radial electronic density of the helix without water molecules or totally filled by water molecules (a NaGDC/H2O molecular ratio of about 1/50) or by using a three-shell average radial electronic density, independently evaluated on absolute scale, do not show significant differences, thus supporting the helical model. The aggregate size increases for all the samples by increasing either the NaCl or NaGDC concentration. The NaGDC low concentration (0.02 M) samples with NaCl within the range 0.30-0.70 M are characterized by short cylindrical aggregates that do not give rise to sensible interference effects. This assertion is supported by the satisfactory fit between the observed apparent mean hydrodynamic radii and the calculated ones by means of the method of Ortega and Garcia de la Torre (J. Chem. Phys. 2003, 119, 9914), valid for rods with a length-to-diameter ratio > or = 0.1 in dilute solution (noninteracting rods). The NaGDC moderate concentration (0.10 M) samples with NaCl within the range 0.20-0.60 M are characterized by cylindrical aggregates that, in the presence of repulsive Coulombic interactions progressively more and more screened, produce interference effects, due to the hard-body repulsion and attractive forces, but the agreement between observed and calculated SAXS data is satisfactory. The results of the low and moderate NaGDC concentration samples seem to indicate that the aggregation number increase, produced by adding 0.10 M NaCl, is constant within an ionic strength range and occurs by the addition of oligomers formed by trimers. The samples with a variable NaGDC concentration (0.02-0.10 M) at a fixed and high NaCl concentration (0.6 M) contain cylindrical aggregates that give rise to an attractive term effect prevailing on the hard-body repulsive one. The same situation seems to occur in the NaGDC moderate concentration samples.
Previously, structural units inferred from X-ray diffraction analysis of fibers, crystals, and co... more Previously, structural units inferred from X-ray diffraction analysis of fibers, crystals, and concentrated aqueous solutions were identified as models of dihydroxy and trihydroxy bile salt micellar aggregates. Dimers and their multiples (mainly octamers and hexadecamers) or structures derived from 7/1 helices (formed by trimers) were proposed for trihydroxy salts sodium glycocholate (NaGC) and taurocholate (NaTC) or for dihydroxy salts sodium glycodeoxycholate (NaGDC) and taurodeoxycholate (NaTDC), respectively, on the basis of strong experimental evidences. However, the radii of the cylindrical structures derived from 7/1 helices were unknown. This paper deals with small-angle X-ray scattering (SAXS) measurements that have permitted to estimate the cylindrical aggregate radius of NaGDC (about 22 Å), whereas that of NaTDC is very probably about 3 Å longer. SAXS and quasi-elastic light-scattering (QELS) data have shown a linear increase of the apparent mean hydrodynamic radius (within the approximate range 40-70 Å) with the height of NaGDC and NaTDC cylindrical aggregates, suggesting that the main interparticle correlation effects, ascribed to charge, van der Waals, and volume excluded interactions, are small or compensate each other. Moreover, aqueous solutions containing one dihydroxy and one trihydroxy bile salt (NaGDC and NaGC, NaTDC and NaTC, NaGDC and NaTC, NaTDC and NaGC) and 0.8 M NaCl have been studied. QELS measurements give information on the growing processes of NaGDC and NaTDC aggregates as a function of NaGC and NaTC concentration. Experimental data and calculations performed using the above-mentioned models support that a small amount of the bile salt forming smaller size aggregates (trihydroxy salt) inhibits the growth of the bile salt forming bigger size aggregates (dihydroxy salt), giving rise to smaller size aggregates. Reasonably, this phenomenon is due to the very different and not interchangeable structures of dihydroxy and trihydroxy bile salt aggregates. It seems also that the aggregate growth is a little more inhibited when the trihydroxy molecule polar head is different from that of the aggregate molecules. Trihydroxy salt monomers and oligomers compete with dihydroxy salt trimers in the growth process and interact with their cylindrical aggregates especially by means of polar forces.
An approach for tailoring self-assembled tubular structures is described. By controlling the rela... more An approach for tailoring self-assembled tubular structures is described. By controlling the relative composition of atwo-component surfactant mixture comprising the natural bile salt lithocholate and its bolamphiphilic derivative,i tw as possible to finely tune the nanotube cross-section of the mixed tubular aggregates that self-associated spontaneously in aqueous solution at pH 12. The diameter was found to vary up to 50 %w hen the stoichiometric ratio of the two bile salts was changed. The tuning of supramolecular nanochannels with such remarkable precision is of significant interest for technological applications of these materials.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
Please cite this article in press as: L. Travaglini, et al., A tryptophan-substituted cholic acid... more Please cite this article in press as: L. Travaglini, et al., A tryptophan-substituted cholic acid: Expanding the family of labelled biomolecules, Colloids Surf. A: Physicochem. Eng. Aspects (2015), http://dx.
Journal of Polymer Science Part a-Polymer Chemistry, 1978
Ethylene-butadiene (PEBU) copolymer with low percentage of butadiene was previously investigated ... more Ethylene-butadiene (PEBU) copolymer with low percentage of butadiene was previously investigated by van der Waals potential energy calculations. The trans -HC=CH-group (TDB) was found to show fold-supporting behavior, so that it was supposed that many TDB's were located on the surface of PEBU single crystals under favorable conditions of TDB concentration and of thickness of crystal platelets. In order to verify this hypothesis, three PEBU samples with a butadiene/ (ethylene + butadiene) molar ratio of 2.3% (B), 3.6% (C), and 4.6% (D), by assuming that the -HC==CH-groups are all trans, were studied and compared with a polyethylene (PE) sample (A). Samples A, B, C, and D were grown isothermally at temperatures of 50,55,60,61,70,71,75, and 80°C from dilute xylene solutions. Infrared, differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), bromination kinetics, and density measurements were performed. B, C, and D lamellar crystals show a long spacing L nearly equal to that of A at crystallization temperatures T, of 50 and 60°C. For T, 1 70°C, the fold period of samples B, C, and D increases more rapidly than that of A in the order D > C > B. The melting temperature T,,, and the enthalpy of fusion AHf decrease with increasing content of butadiene, except for B and C, which show nearly equal T,,, and AHf values. Two peaks appear in the fusion curves at temperatures TI and Tz, T I > Tz. The area of the peak a t T2 increases with the butadiene content, and, in the same sample, with T,. Results of bromination in suspension of B, C, and D single crystals, crystallid in the range 50-7loC, indicate that a high percentage of TDBs react on the fold surfaces. The chemical attack is more successful with crystals grown in the range 60-66"C, and, in the case of sample C, as much as 81% of the TDB's are consumed. The density of the samples increases with both T, and TDB percentage. On the basis of these observed results a simple model for PEBU is proposed.
The unfolding pathway of the defatted human serum albumin (HSA) binding ibuprofen and propofol ha... more The unfolding pathway of the defatted human serum albumin (HSA) binding ibuprofen and propofol has been studied by using small-angle X-ray scattering (SAXS) and the support of circular dichroism data. A set of HSA solutions with urea concentrations between 0.00 and 9.00 M was analyzed, and the singular value decomposition method applied to the complete SAXS data set allowed us to distinguish four different states in solution. Besides the native and unfolded forms, two intermediates I1 and I2 have been identified, and the low-resolution structures of these states were obtained by exploiting both ab initio and rigid body fitting methods. The I1 structure was characterized by only one open domain (domain I, which does not host a binding site for either of the ligands), whereas I2 presents only one closed domain (domain III). A direct comparison with the unfolding pathway of the HSA:Ibu complex (Galantini et al. Biophys. Chem. 2010, 147, 111-122) pointed out that the presence of propofol as a second ligand, located in subdomain IIIB, leads to the appearance of an intermediate with two closed domains (domains II and III), which are those that accommodate the ligands. Moreover, the equilibrium between I2 and the unfolded form is slightly shifted toward higher urea concentrations. These results suggest that the cobinding significantly hinders the unfolding process.
Self-assembly of peptides and bile acids has been widely investigated because of their biological... more Self-assembly of peptides and bile acids has been widely investigated because of their biological role and their potential as a tool for the preparation of nanostructured biomaterials. We herein report both the synthesis and the self-association behavior of a compound that combines the aggregation properties of bile acid- and amino acid-based molecules. The derivative has been prepared by introducing a L-tryptophan residue into the C-3 position of the deoxycholic acid skeleton and resulted in an amphoteric fluorescent labeled bile acid that shows a pH-dependent self-assembly. Under alkaline conditions it assembles into 28 nm diameter tubules, thus showing a completely different behavior compared to the precursor bile acid, which forms micelles under similar conditions. Upon heating the tubules break and turn into micelles, leading to an increase in the exposure to water of the tryptophan residue. On the other hand, in acidic solutions it aggregates into elongated micelles that further self-assemble forming a gel network, when an electrolyte is added.
studies on pure (E)-p-dimethylaminoazobenzene (hereafter indicated as DAB) and the DAB-choleic ac... more studies on pure (E)-p-dimethylaminoazobenzene (hereafter indicated as DAB) and the DAB-choleic acid (DCADAB) were accomplished by means of the torsion effusion method. The pressure of the vapour in equilibrium with the solid phase was determined for DAB as log P(kPa) = (15.05+0.18)-(6887*500)/T and by the second-law treatment of the vapour pressure data a AH& = 132 * 8 kJ mol-' was obtained for DAB vaporization from the pure compound. Since the tensimetric data of DCADAB lie at the limit of the instrument's working range only a rough value of AH&, =138 kJ mol-' was obtained for DAB vaporization from DCADAB.
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.
This paper deals with electrospray ionization mass spectrometry (ESIMS), small-angle X-ray scatte... more This paper deals with electrospray ionization mass spectrometry (ESIMS), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) measurements in order to provide information on the existence, aggregation, composition, and structure of the two-component aggregates of sodium glycocholate (NaGC) and sodium glycodeoxycholate (NaGDC) in the gas and solution phases. Five samples, containing 100% NaGC and 100% NaGDC, and NaGDC/NaGC molar ratios of 3 (75D), 1 (50D), and 1/3 (25D), have been analyzed by ESIMS in positive-ion detection mode starting from 10 -3 and 10 -2 M total bile salt concentration in aqueous solutions. Generally, dimers or trimers prevail in the 100% NaGC or NaGDC samples, respectively, as observed in the preceding one-component ESIMS measurements and in agreement with the proposed micellar aggregate structures in aqueous solution. Moreover, it is observed that the composition of multimers in the samples 75D, 50D, and 25D deviates from the one expected on the basis of a random association of the monomers, the NaGDC contribution generally prevailing on the NaGC one. It happens also under the same percentage condition (50D sample), in agreement with a greater aggregation ability of NaGDC with respect to NaGC. SAXS and DLS data were recorded on six samples containing a NaGC + NaGDC 40 mM total concentration, one bile salt having 40, 32, 24, 16, 8, and 0 mM concentration and the other the complementary one, keeping constant the NaCl concentration (0.6 M). The NaGDC 40 mM sample presents SAXS curves in agreement with a cylindrical shape of the aggregates as shown in a previous paper. For the bile salt mixtures, the progressive decrease of the sizes and change of the aggregate morphology, toward a globular-like geometry, are observed by increasing the NaGC fraction, thus confirming the hypothesis about the ability of trihydroxy salts to inhibit the growth of dihydroxy salt aggregates. Fits on the basis of cylindrical model can be accomplished for all the SAXS spectra, however, when the extracted cylinder parameters are used to estimate theoretical hydrodynamic radii a reasonable agreement is obtained only for the samples at high fraction of NaGDC (NaGDC g 24 mM).
We report a study on the unfolding behavior of the most abundant protein contained in plasma, the... more We report a study on the unfolding behavior of the most abundant protein contained in plasma, the fatted and defatted human serum albumin, in denaturing conditions induced by guanidine hydrochloride. Low-resolution three-dimensional structures are reconstructed from the one-dimensional (1D) small-angle X-ray scattering patterns, and they are correlated with the parameters obtained from static and dynamic light scattering experiments. The unfolding process is pointed out by both ab initio and rigid body fitting methods which highlight a stepwise evolution of the protein structure toward open conformations. The superpositions of the 3D structures provided independently by the two methods show very good agreements. The hydrodynamic radii estimated for the protein best fitting conformations are in satisfactory agreement with the experimental ones. The results show that the unfolding process is consistent with previous spectroscopic studies which suggest a multistep unfolding pathway. In particular, a scheme in which domains III and II are opened in sequence and the presence of two intermediates are evidenced is presented.
Small-Angle X-ray Scattering (SAXS) and Dynamic Light Scattering (DLS) measurements were carried ... more Small-Angle X-ray Scattering (SAXS) and Dynamic Light Scattering (DLS) measurements were carried out on aqueous micellar solutions of the ionic biological detergent sodium taurodeoxycholate (NaTDC). Apparent diffusion coefficients (D(app)) and SAXS spectra of NaTDC 0.1 M solutions at different ionic strengths (0.1-0.3 M NaCl) were reported. A comparative analysis of SAXS spectra and D(app) data was performed to infer information on particle structure and interaction potential. Uniform particles with a spherical, an oblate, and a prolate symmetry were used to model the micelles in the data interpretation. A hard-core interaction shell of suitable thickness and a screened Coulomb potential of the electric double layer (EDL potential) were alternatively used to represent the long-range repulsive tail of the interaction potential. The Percus Yevick and the Rescaled Mean Spherical Approximation were applied. To compare the data of the two techniques, for each sample, a D(app) was calculated from the SAXS best-fitting geometrical parameters and interparticle structure factor of the micelles. Hence, a fitting procedure involving both the scattering and D(app) data was performed. The interpretation of SAXS spectra does not allow the discrimination between the oblate and the prolate symmetries of the aggregates. On the other hand, the comparison of calculated and experimental D(app) values indicates that the prolate ellipsoid is better suited to represent the micelle shape. Moreover, the agreement between calculated and experimental D(app) values is sensitively better at the lowest NaCl concentration when the EDL potential is used. A rodlike micellar growth and a progressive screening of the electrostatic interactions is testified by the trends of best-fitting parameters as a function of the added electrolyte.
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Review by Nicolae Pavel
Papers by Nicolae Pavel