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Luigi Paduano

Publications and source records attributed to Luigi Paduano.

12 recordsLinked to original sources
PubMed2006

A study of the microstructural and diffusion properties of poly(vinyl alcohol) cryogels containing surfactant supramolecular aggregates.

Surfactant-containing poly(vinyl alcohol) (PVA) cryogels have been prepared by drying and reswelling hydrogel patches, previously obtained by the freeze/thaw procedure, in decyltrimethylammonium bromide (C10TAB) aqueous solutions. The microstructural and diffusive properties of the resulting material have been characterized by a combined experimental strategy. Gravimetric measurements show that the cryogel maximum swelling is not affected by the surfactant. The surfactant concentration within the cryogel, measured by ion chromatography, is the same as that in the rehydrating surfactant solution. Electron paramagnetic resonance (EPR) spin-probe and small-angle neutron scattering (SANS) measurements show that surfactant self-aggregation in the gel is similar to that in water, occurring at the same critical concentration and resulting in the formation of micellar aggregates whose structure is not affected by the cryogel polymeric scaffold. However, both the micelle intradiffusion coefficients, measured by PGSE-NMR, and the spin-probe correlation times, measured by EPR, indicate that dynamic processes in the hydrogel are much slower than in bulk water. A quantitative analysis of these results suggests that the cryogel polymer-poor domains, in which surfactant molecules are solubilized, have an average dimension of approximately 0.1 microm. Interestingly the experimental data also show that the polymer-poor phase contains more polymer than expected, suggesting that the spinodal decomposition, which occurs during the freezing step of cryogel preparation, is not complete or prevented by ice formation.

Journal Article↗
PubMed2006

High-relaxivity supramolecular aggregates containing peptides and Gd complexes as contrast agents in MRI.

Mixed supramolecular aggregates, obtained by assembling together two amphiphilic monomers (C(18)H(37))(2)NCO(CH(2))(2)CO(AdOO)(5)-G-CCK8 (AdOO is 8-amino-3,6-dioxaoctanoic acid, CCK8 is C-terminal octapeptide of cholecystokinin) and (C(18)H(37))(2)NCO(CH(2))(2)COLys(DTPAGlu)CONH(2) (DTPAGlu is N,N-bis[2-[bis(carboxyethyl)amino]ethyl]-L-glutamic acid), are characterized for their structural parameters by dynamic light scattering and for their relaxometric properties, in the absence and in the presence of 0.9 wt% NaCl. Two different aggregates (micelles and bilayer structures) are present in the absence of NaCl, while only bilayer structures are observed at physiological ionic strength. The presence of NaCl increases the ionic strength, promoting a decrease in the repulsions between the polar heads and among the aggregates in solution, thus supporting the formation of large-curvature aggregates such as bilayer structures like vesicles. In these conditions the closed, vesicular shape and the large size (hydrodynamic radius of about 300 A) of the aggregates allow a high number of paramagnetic gadolinium complexes and bioactive peptides to be accommodated on the inner and external surfaces . The presence of the salt causes a variation in the structural arrangement of the molecules and a partial rigidification of the assembled Gd(III) complexes on the surface vesicles, reducing their internal motions and giving an approximately 15% higher relaxivity value (r (1p) = 21.0 and 18.6 Mm(-1) s(-1) in the presence and in the absence of NaCl, respectively). The vesicles obtained, for the high relaxivity of each gadolidium complex and for the presence of a surface-exposed bioactive peptide, are very promising candidates as target-selective MRI contrast agents.

Chelating Agents↗
PubMed2006

The effect of salt stoichiometry on protein-salt interactions determined by ternary diffusion in aqueous solutions.

We report the four diffusion coefficients for the lysozyme-MgCl2-water ternary system at 25 degrees C and pH 4.5. The comparison with previous results for the lysozyme-NaCl-water ternary system is used to examine the effect of salt stoichiometry on the transport properties of lysozyme-salt aqueous mixtures. We find that the two cross-diffusion coefficients are very sensitive to salt stoichiometry. One of the cross-diffusion coefficients is examined in terms of common-ion, excluded-volume, and protein-preferential hydration effects. We use the four ternary diffusion coefficients to extract chemical-potential cross-derivatives and protein-preferential interaction coefficients. These thermodynamic data characterize the protein-salt thermodynamic interactions. We demonstrate the presence of the common-ion effect (Donnan effect) by analyzing the dependence of the preferential-interaction coefficient not only with respect to salt concentration but also with respect to salt stoichiometry. We conclude that the common-ion effect and the protein-preferential hydration are both important for describing the lysozyme-MgCl2 thermodynamic interaction.

Diffusion↗
PubMed2006

Supramolecular aggregates of amphiphilic gadolinium complexes as blood pool MRI/MRA contrast agents: physicochemical characterization.

In this paper, we present the development of a new potential blood pool contrast agent for magnetic resonance imaging applications (MRA/MRI) based on gadolinium complexes containing amphiphilic supramolecular aggregates. A novel amphiphilic unimer, containing the DTPAGlu chelating agent covalently bound to two C18 alkylic chains, has been synthesized. DTPAGlu is a well-known chelating agent for a wide number of ions such as the paramagnetic metal ion Gd3+ used as contrast agent in MRA/MRI. The wide aggregation behavior of this surfactant, as free base or as gadolinium complex, has been studied and compared by means of dynamic light scattering, small-angle neutron scattering and cryogenic transmission electron microscopy techniques. Near neutral pH in both cases, the dominant aggregates are micelles. The high negative actual charge of the surfactant headgroup causes a strong headgroups repulsion, promoting the formation of large and high curvature aggregates. By decreasing pH and less markedly increasing the ionic strength, we observe a micelle-to-vesicle transition driven by a decreased electrostatic repulsion. A straightforward switch between different aggregation states can be particularly useful in the development of pH-responsive MRA/MRI contrast agents.

Chemical Phenomena↗
PubMed2006

Interaction between cationic, anionic, and non-ionic surfactants with ABA block copolymer Pluronic PE6200 and with BAB reverse block copolymer Pluronic 25R4.

The interaction in aqueous solution between either the normal block copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide): Pluronic PE6200 [(EO)(11)-(PO)(28)-(EO)(11)], or the reverse block copolymer poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide): Pluronic 25R4 [(PO)(19)-(EO)(33)-(PO)(19)] and the surfactants sodium decylsulfate, C(10)OS, decyltrimethyl ammonium bromide, C(10)TAB, and pentaethylene glycol monodecyl ether, C(10)E(5), was investigated and the aggregation behavior of these surfactants with Pluronics was compared. Surface tension measurements show that Pluronics in their non-aggregated state better interact with the anionic surfactant C(10)OS than with cationic and non-ionic ones. The presence of the two Pluronics induces the same lowering of the aggregation number of C(10)OS as shown by fluorescence quenching measurements. The number of polymer chains necessary to bind each C(10)OS aggregate has been estimated to be approximately 6 for PE6200 and approximately 2 for 25R4. Furthermore, this surfactant also induces the same increment in the gyration radius of the polymers as revealed by viscosimetry. Calorimetric results have been reasonably reproduced by applying a simple equilibrium model to the aggregation processes.

Journal Article↗
PubMed2006

The effect of salt on protein chemical potential determined by ternary diffusion in aqueous solutions.

We use accurate thermodynamic derivatives extracted from high-precision measurements of the four volume-fixed diffusion coefficients in ternary solutions of lysozyme chloride in aqueous NaCl, NH4Cl, and KCl at pH 4.5 and 25 degrees C to (a) assess the relative contributions of the common-ion and nonideality effects to the protein chemical potential as a function of salt concentration, (b) compare the behavior of the protein chemical potential for the three salts, which we found to be consistent with the Hofmeister series, and (c) discuss our thermodynamic data in relation to the dependence of the protein solubility on salt concentration. The four diffusion coefficients are reported at 0.6 mM lysozyme chloride and 0.25, 0.5, 0.9, 1.2, and 1.5 M KCl and extend into the protein-supersaturated region. The chemical potential cross-derivatives are extracted from diffusion data using the Onsager reciprocal relation and the equality of molal cross-derivatives of solute chemical potentials. They are compared to those calculated previously from diffusion data for lysozyme in aqueous NaCl and NH4Cl. We estimate the effective charge on the diffusing lysozyme cation at the experimental concentrations. Our diffusion measurements on the three salts allowed us to analyze and interpret the four diffusion coefficients for charged proteins in the presence of 1:1 electrolytes. Our results may provide guidance to the understanding of protein crystallization.

Ammonium Chloride↗
PubMed2005

Effect of the addition of a nonionic surfactant on the complex poly(asparagine)--cationic surfactant.

Poly(asparagine) (pAsn) at 0.1wt % in the presence of dodecyltrimethylammonium bromide (DTAB) and pentaoxyethylene octyl ether (C(8)E(5)) at 1:1 molar ratio leads to the formation of mixed DTAB/C(8)E(5) micelle-like aggregates onto the polypeptide as a total surfactant critical association concentration (cac) is reached, as revealed by surface tension measurements and NMR chemical shifts. Two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) capable of revealing spatial relationships among proximal protons has been performed on the pAsn-DTAB-C(8)E(5)-water system to study structural details of the surfactant-polypeptide aggregates. NOESY cross-peaks at sample temperature of 298.15 K indicate that the polypeptide interacts with the DTAB/C(8)E(5) micelle-like aggregates. The NOE intermolecular effects also show direct interactions between surfactant and polypeptide in the pAsn-DTAB-water system, whereas no interaction has been revealed in the pAsn-C(8)E(5)-water system. Furthermore, the experimental evidence suggest that the DTAB-polypeptide complex is mainly driven by the polar attraction between the two molecules.

Cations↗
PubMed2004

Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)-b-poly(ethylene oxide)- b-poly(propylene oxide) copolymers of different composition in aqueous mixtures, 1.

The phase behavior (temperature vs composition) and microstructure for the two binary systems Pluronic 25R4 [(PO)19(EO)33(PO)19]-water and Pluronic 25R2 [(PO)21(EO)14(PO)21]-water have been studied by a combined experimental approach in the whole concentration range and from 5 to 80 degrees C. The general phase behavior has been identified by inspection under polarized light. Precise phase boundaries have been determined by analyzing 2H NMR line shape. The identification and microstructural characterization of the liquid crystalline phases have been achieved using small-angle X-ray scattering (SAXS). The isotropic liquid solution phases have been investigated by self-diffusion measurements (PGSE-NMR method). 25R2 does not form liquid crystals and is miscible with water in the whole concentration range; with increasing temperature, the mixtures split into water-rich and a copolymer-rich solutions in equilibrium. 25R4 shows rich phase behavior, passing, with increasing copolymer concentration, from a water-rich solution to a lamellar and copolymer-rich solution. A small hexagonal phase, completely encircled in the stability region of the water-rich solution, is also present. In water-rich solutions, at low temperatures and low copolymer concentrations, the copolymers are dissolved as independent macromolecules. With increasing copolymer concentrations an interconnected network of micelles is formed in which micellar cores of hydrophobic poly(propylene oxide) are interconnected by poly(ethylene oxide) strands. In copolymer-rich solutions water is molecularly dissolved in the copolymer. The factors influencing the self-aggregation of Pluronic R copolymers (PPO-PEO-PPO sequence) are discussed, and their behavior in water is compared to that of Pluronic copolymers (PEO-PPO-PEO sequence).

Macromolecular Substances↗
PubMed2004

Physicochemical properties of mixed micellar aggregates containing CCK peptides and Gd complexes designed as tumor specific contrast agents in MRI.

New amphiphilic molecules containing a bioactive peptide or a claw moiety have been prepared in order to obtain mixed micelles as target-specific contrast agents in magnetic resonance imaging. The first molecule, C(18)H(37)CONH(AdOO)(2)-G-CCK8 (C18CCK8), contains a C18 hydrophobic moiety bound to the C-terminal cholecystokinin octapeptide amide (CCK 26-33 or CCK8). The second amphiphilic compound, C(18)H(37)CONHLys(DTPAGlu)CONH(2) (C18DTPAGlu) or its gadolinium complex, (C18DTPAGlu(Gd)), contains the same C18 hydrophobic moiety bound, through a lysine residue, to the DTPAGlu chelating agent. The mixed aggregates as well as the pure C18DTPAGlu aggregate, in the presence and absence of Gd, have been fully characterized by surface tension measurements, FT-PGSE-NMR, fluorescence quenching, and small-angle neutron scattering measurements. The structural characterization of the mixed aggregates C18DTPAGlu(Gd)-C18CCK8 indicates a spherical arrangement of the micelles with an external shell of approximately 21 A and an inner core of approximately 20 A. Both the DTPAGlu(Gd) complexes and the CCK8 peptides point toward the external surface. The measured values for relaxivity in saline medium at 20 MHz proton Larmor frequency and 25 degrees C are 18.7 mM(-)(1) s(-)(1). These values show a large enhancement in comparison with the isolated DTPAGlu(Gd) complex.

Contrast Media↗
PubMed2004

Interaction between pentaethylene glycol n-octyl ether and low-molecular-weight poly(acrylic acid).

The interaction between pentaethylene glycol n-octyl ether (C8E5) and low-molecular-weight poly(acrylic acid) (PAA, M(w)=2000) in aqueous solution has been investigated by various experimental techniques at constant polymer concentration (0.1% w/w) with varying surfactant molality. Spectrofluorimetry, using pyrene as molecular probe, shows (i) the formation of surfactant-polymer aggregates at a surfactant molality (T(1)) lower than the critical micelle concentration (cmc) of C8E5 in water and (ii) the formation of free micelles at a surfactant molality (T(2)) slightly higher than the cmc. Fluorescence quenching measurements indicate that the presence of PAA induces a lowering of the C8E5 aggregation number. Calorimetry confirms spectrofluorimetric evidence; in addition, it shows the presence of weak interactions below T(1) between monomeric surfactant molecules and the polymer chains. Tensiometry shows that, above T(1), only a low fraction of surfactant molecules interact with the polymer and that free micelle formation occurs before polymer saturation. The peculiarities of the interaction between surfactants and low-molecular-weight polymers have been discussed.

Acrylates↗
PubMed2001

Transport Properties of Aqueous Solutions of Alkyltrimethylammonium Bromide Surfactants at 25 degrees C.

Intradiffusion coefficients, D, of n-alkyltrimethylammonium bromides [CH(3)-(CH(2))(n-1)-N(CH(3))(3)Br, C(n)TAB] (n=6, 8, 10, 12) in mixtures with heavy water were measured by the PGSE-NMR technique at 25 degrees C. The experimental data permitted evaluation of the influence of the alkyl chain length on the surfactant self-aggregation process. For all the surfactants considered, the D trend showed a slope change corresponding to the critical micellar composition (cmc). In the premicellar composition range, D decreased linearly with the square root of the surfactant molality. The D values extrapolated at infinite dilution were related to the limiting mutual diffusion coefficients, determined through the Taylor dispersion technique. In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, D(M), from which the aggregate radii and the aggregation numbers were obtained. The decreasing trend of D(M) with increasing surfactant molality was interpreted in terms of interparticle electrostatic repulsion. D(M) values allowed evaluation of the Gouy-Chapman layer thickness. The solvent intradiffusion coefficient in the heavy water-C(n)TAB mixtures, D(w), was also measured. It decreased with increasing surfactant molality. For n=8, 10, 12 the D(w) trend presented a slope change at the cmc, which could be ascribed to the strong decrease in hydration of surfactant molecules upon micellization. Because of its short hydrophobic tail, C(6)TAB exhibited peculiar aggregation behavior. Its cmc, which is poorly marked, is lower than the value predicted by extrapolating the cmc values obtained for the other terms of the series. The C(6)TAB aggregates do not solubilize TMS molecules; the estimated aggregation number is extremely low ( approximately 3). Finally, no abrupt slope change in the solvent intradiffusion coefficient trend was detected. This evidence suggests that C(6)TAB molecules do not micellize in aqueous solution, but form trimers in which the surfactant hydrophobic tails are not hidden from contact with water molecules. Copyright 2001 Academic Press.

Journal Article↗