Biomedical subjects

Valentina Villari

Publications and source records attributed to Valentina Villari.

10 recordsLinked to original sources

PubMed2006

Vesicle-to-micelle transition in aqueous solutions of amphiphilic calixarene derivatives.

Structure and conformation of spontaneous self-assembled calix[8]arenes derivatives are studied by means of static and dynamic light scattering and electrophoretic mobility. These amphiphilic molecules are in the aggregated form in aqueous solution, in a wide range of pH; they take a vesicle structure in neutral and basic pH environment, but, in relatively strong acidic conditions (below pH=4.5), a transition from vesicle to micelle occurs. The structural change is driven by the surface charge density. At neutral pH calix[8]arenes take a negative surface charge, which prevents coagulation and ensures stability; at acidic pH the surface charge tend to become positive because of the protonation of the hydrophilic head. These pH-responsive aggregates, able to release an encapsulated hydrophilic guest, are promising systems for application as nanocarriers.

Journal Article↗

PubMed2006

From fractal to nanorod porphyrin J-aggregates. Concentration-induced tuning of the aggregate size.

A structural change from fractal to nanorod J-aggregates of tetrakis(4-sulfonatophenyl)porphyrin has been obtained by acting on the intermolecular interaction potential. The size and shape of these self-assembled porphyrin clusters have been monitored under different experimental conditions, by means of polarized and depolarized dynamic light scattering and small and wide angle elastic light scattering. At sufficiently low porphyrin concentration and high ionic strength, the shielded repulsive potential seems to be responsible for the fractal structure of the aggregates. On the contrary, at low ionic strength (nonshielded potential) and high porphyrin concentration, these species self-assemble in a rodlike arrangement. The length of the so-formed rod-shaped aggregates decreases on increasing porphyrin concentration. Moreover, both fractals and rods display a structure-dependent optical activity induced by a chiral template.

Journal Article↗

PubMed2005

Light scattering enhancement in an aqueous solution of spermine-induced fractal -aggregate composite.

We performed an experimental investigation on the scattering and extinction properties of an aqueous solution of spermine-induced fractal J aggregates, constituted by porphyrin molecules. In analogy with nanostructured particle composites, the dipolar moments of different porphyrins, not belonging to the aggregates J, are coupled and generate a strong light scattering enhancement. Both the enhanced scattered intensity and the imaginary part of the polarizability of the system obey scaling laws with the optical spectral dimension d0=0.3.

Computer Simulation↗

PubMed2005

Uncharged water-soluble Co(II)-porphyrin: a receptor for aromatic alpha-amino acids.

Changes in the UV-vis spectra and induced circular dichroism (ICD) signals observed, in correspondence with the porphyrin Soret region, for aqueous solutions of achiral 5,10,15,20-tetrakis{p-[omega-methoxy poly(oxy-ethylene)]phenyl}porphyrin cobalt (II) (Co-P) and aromatic alpha-L-amino acids (Trp and Phe) give direct evidence for the coordination between the Co-P and amino acids. Considering that Co-P, besides the Co atom (one-fixation-point system), does not contain in the molecule active ligand groups and that no ICD signals have been observed in the case of Co-P/Ala, it has been concluded that hydrophobic interactions or stacking interactions between the aromatic rings of the porphyrin and those of Trp or Phe, acting as further amino acid (AA) fixation points, can strongly reduce the mobility of the chiral guest, thus permitting the generation of ICD signals. The effects of changes of both pH (in the range 2-9) and amino acid structure on the ICD phenomenon have also been investigated. In particular, the following have been observed: (i) strong ICD signals for all of the Co-P/N-acetyl amino acid aqueous solutions at pH 7, (ii) an unexpected ICD band with a bisignate form for the Co-P/Ala solution at pH 9 after long aging, and (iii) an opposite ICD signal when alpha-D-Phe and alpha-D-Trp enantiomers have been used. The data reported in this paper show how the binding mechanism between receptor and AAs changes by modulating properly the pH or the molecular structures and indicate that in these aqueous solutions the coordination Co-N is not the fundamental mechanism giving rise to the formation of the complexes and that the binding can be driven by hydrophobic interactions. These occurrences, through the analysis of the spectroscopic response (and, in particular, the form of the ICD band), can allow the recognition of AAs.

Amino Acids↗

PubMed2005

Aggregation behavior of tetrakis(4-sulfonatophenyl)porphyrin in AOT/water/decane microemulsions.

AOT/water/decane microemulsions have been used to entrap the water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4). Quasi-elastic light scattering technique has confirmed the confinement of the porphyrin and its various aggregates into the inner water pool. Various species have been detected as function of the size of the microemulsions, concentration of the porphyrin, pH, and aging of the solutions by using a combination of UV-vis absorption, steady fluorescence emission, fluorescence lifetime measurements, and time-resolved fluorescence anisotropy. Under neutral pH conditions, the porphyrin is present as the free base monomer (S414) in the inner water compartment, and it is free to rotate when the size of the droplet is large enough and the porphyrin concentration is low. On increasing the concentration and/or decreasing the microemulsion size, a H-dimer of the free base (S406) is prevalently formed. Aging both the S414 and S406 species leads to the formation of a new species (S424), which has been postulated as a H-type dimer of the diacid porphyrin. On decreasing the pH, the species S414 and S406 almost instantaneously convert into the diacid porphyrin, which is monomeric (S434). This latter is an intermediate in the eventual formation of J-aggregated TPPS4 (S490). A marked stability has been observed for the S424 species, which do not interconvert on changing the pH of the bulk aqueous phase.

Journal Article↗

PubMed2005

Amphiphilic cyclodextrin carriers embedding porphyrins: charge and size modulation of colloidal stability in heterotopic aggregates.

The interaction between the anionic 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphyrin (TPPS) and cationic vesicles formed by heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-cyclodextrin (SC6CDNH2) has been investigated in detail through a combination of elastic light scattering (ELS), quasi-elastic light scattering (QELS), zeta potential measurements, and time-resolved fluorescence anisotropy. ELS experiments provided the first structural characterization of these cationic vesicles both in the absence and in the presence of TPPS porphyrin, modeling the system as a spherical particle described by a single thin shell form factor. The structure of mixed hetero-aggregates is modulated by charge and size of the two components as function of different porphyrin/cyclodextrin (CD) molar ratios. At the limiting molar ratio studied, the absolute value of zeta potential (/zeta/ = 12.5 mV) seems to be a reference value for the formation of stable colloidal CD vesicular aggregates at thermodynamic equilibrium. New insights on the structure of these heterotopic colloids have been obtained by analysis of rotational correlation times at different molar ratios exploiting time-resolved fluorescence anisotropy experiments. At high porphyrin loads, the anisotropy decays behave as monoexponentials and the rotational correlation times (1-2 ns) together with the r(0) values close to zero suggest the presence of small amounts of TPPS embedded in a hydrophobic environment either in monomeric or in aggregated form. At the lower porphyrin/CD molar ratios, the anisotropy decays exhibit a double-exponential behavior showing a predominant component with a slow rotational correlation time (20-25 ns) and limiting anisotropy values of approximately 0.15. This component has been assigned to molecules that are more stabilized onto the CD vesicles, that is, porphyrins embedded into the oligo-ethylene "wall" of the CD vesicles. Scanning near-field optical microscopy of the samples evaporated on glass surfaces gave further insights on the morphology and optical properties of these systems, confirming the embedding of TPPS on the vesicles and evidencing the role of the solvent.

Anions↗

PubMed2005

Interactions between water soluble porphyrin-based star polymer and amino acids: spectroscopic evidence of molecular binding.

Molecular interactions giving rise to stable complexes between an uncharged water soluble cobalt-porphyrin and amino acids are investigated by time-resolved fluorescence, uv-vis, and circular dichroism measurements. This metalloporphyrin seems to act, by means of the coordination site of the cobalt of the core, as a recognition host, preferentially, with amino acids possessing aromatic groups. The binding with aliphatic amino acids requires longer time scales to be efficient and likely involves a slow kinetic process. The experimental findings suggest that, besides the metal(host)-N(guest) coordination bond, which is the common requisite for all amino acids, a preferential interaction with aromatic groups exists there. The solubility in water of the molecule, guaranteed by the polyethylene glycol arms as peripheral substituents, in the absence of electric charges, allows for a more selective discrimination of the binding process with respect to other water-soluble charged porphyrins. The interest devoted to the porphyrin-based star polymer and its recognition properties is, therefore, founded on the potential use either in polymeric matrices for material science or in aqueous solution for bioscience.

Amino Acids↗

PubMed2004

Large structures in diblock copolymer micellar solution.

The association properties in water solution of poly(dimethylsiloxane)-b-poly(ethyleneoxide) diblock copolymer was investigated by static and dynamic light scattering in a wide range of concentrations and temperatures. The presence of a long hydrophilic poly(ethyleneoxide) (PEO) chain causes a weak tendency to microphase separation of the system which is responsible for some relevant effects. First of all we observe a late micellization process which is characterized by an unusually high value of the critical micellar concentration (c(cmc) =0.007 g/cm3) and by an unusually small aggregation number (approximately 6) of the generated micelles. Moreover, the composition of the highly hydrated micelles has been found to change sensitively with temperature. On increasing temperature dehydration of micelles has been observed together with a contemporaneous increase in the aggregation number, whereas the hydrodynamic radius remains constant in the whole range investigated. The long hydrophilic chains also stimulate an efficient entanglement process between micelles. The interpenetrating PEO chains belonging to different micelles causes the depletion of the solvent in the outer layer of micelles. The result is the formation, just after the micellization process takes place, of thermodynamically stable clusters of entangled micelles. These large structures, which are present in the system in small concentrations, maintain their structural properties unchanged in a wide range of concentrations and temperatures, and provide indirect evidence of a weak attractive component to the intermicellar interaction potential.

Journal Article↗

PubMed2003

Novel heterotopic colloids of anionic porphyrins entangled in cationic amphiphilic cyclodextrins: spectroscopic investigation and intracellular delivery.

The entanglement process between water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine and the amphiphilic cyclodextrin (CD) heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-CD and the occurrence of various species at different porphyrin:CD ratios were studied by a combination of UV/Vis absorption, fluorescence anisotropy, time-resolved fluorescence, resonance light scattering, and circular dichroism. The effect of the entanglement process on the mean vesicle diameter was investigated over a wide concentration range by quasielastic light-scattering techniques. The experimental results indicate that the presence of porphyrins in this colloidal system promotes some structural rearrangements, essentially driven by charge interaction, which are responsible for a sensitive change of vesicle dimensions. In the range of porphyrin:CD molar ratios between 1:10 and 1:50, the porphyrin is solubilized in monomeric form (tau(1)=11.5 ns) and photosensitizes the production of singlet oxygen ((1)O(2)). At the same molar ratio the ability of this amphiphilic cyclodextrin to transport porphyrins into tumor cells indicates specificity at the nuclear-compartment level. These findings may be of potential interest for the of development agents for photodynamic therapy of tumors.

Animals↗

PubMed2003

Graft polymer solutions as sticky hard-sphere colloids.

We show that a solution of a graft (comb) polymer can exhibit an adhesive hard-sphere pair potential. In the present paper, static and dynamic light scattering measurements on a comb polymer at low molecular weight are performed and the results discussed in the framework of the colloidal theory for adhesive spheres. Renormalization group calculations are directly compared with experimental data on the cooperative diffusion coefficient using the scaled concentration parameter.

Biocompatible Materials↗