Claudia Mazzuca

New cationic liposomes as vehicles of m-tetrahydroxyphenylchlorin in photodynamic therapy of infectious diseases.

Antimicrobial photodynamic therapy is emerging as a promising therapeutic modality for bacterial infections. For optimizing the antibacterial activity of the photosensitizer m-tetrahydroxyphenylchlorin, it has been encapsulated in mixed cationic liposomes composed of different ratios of dimyristoyl- sn-glycero-phosphatidylcholine and any of four cationic surfactants derived from l-prolinol. The delivery efficiency of the different liposomes formulations has been evaluated on a methicillin-resistant Staphylococcus aureus bacterial strain (MRSA), and one of the tested formulations shows a biological activity comparable to that of the free chlorin. In order to rationalize the physicochemical parameters of the carriers that control the biological activity, the new liposome formulations have been characterized by measuring (a) the zeta potential, (b) their capability of chlorin entrapping efficiency, i.e. entrapment efficacy, (c) the effect of storage on chlorin entrapment and (d) the localization of chlorin in the bilayer. The correlation of the physicochemical and biological features of formulations has allowed us to rationalize, to some extent, some of the parameters that may control the interactions with the biological environment.

Aggregation and water-membrane partition as major determinants of the activity of the antibiotic peptide trichogin GA IV.

Water-membrane partition and aggregation behavior are fundamental aspects of the biological activity of antibiotic peptides, natural compounds causing the death of pathogenic organisms by perturbing the permeability of their membranes. A synthetic fluorescent analog of the natural lipopeptaibol trichogin GA IV was used to study its interaction with model membranes. Time-resolved fluorescence data show that in water, an equilibrium between monomers and small aggregates is present, the two species having different affinity for membranes. Therefore, association curves are strongly dependent on peptide concentration. A similar heterogeneity is present in the membrane phase, which strongly suggests the occurrence of a monomer-aggregate equilibrium in this case, too. The relative population of each species was determined and a strong correlation between the concentration of membrane-bound aggregates and membrane leakage was found, thereby suggesting that liposome perturbation is due to peptide aggregates only. Light-scattering measurements demonstrate that leakage is not due to liposome micellization. Moreover, experiments with markers of different sizes show that molecules with a diameter of approximately 4 nm are released only to a minor extent. Overall, these results suggest that, within the concentration range explored, pore formation by peptide aggregates is the most likely mechanism of action for trichogin in membranes.

Fluctuations and the Rate-Limiting Step of Peptide-Induced Membrane Leakage

Peptide-induced vesicle leakage is a common experimental test for the membrane-perturbing activity of antimicrobial peptides. The leakage kinetics is usually very slow, requiring minutes to hours for complete release of vesicle contents, and exhibits a biphasic behavior. We report here that, in the case of the peptaibol trichogin GA IV, all processes involved in peptide-membrane interaction, such as peptide-membrane association, peptide aggregation, and peptide translocation, take place on a timescale much shorter than the leakage kinetics. On the basis of these findings, we propose a stochastic model in which the leakage kinetics is determined by the discrete nature of a vesicle suspension: peptides are continuously exchanging among vesicles, producing significant fluctuations over time in the number of peptide molecules bound to each vesicle, and in the formation of pores. According to this model, the fast initial leakage is caused by vesicles that contain at least one pore after the peptides are randomly distributed among the liposomes, whereas the slower release is associated with the time needed to occasionally reach in an intact vesicle the critical number of bound peptides necessary for pore formation. Fluctuations due to peptide exchange among vesicles therefore represent the rate-limiting step of such a slow mechanism.

Guar Gum and Scleroglucan Interactions with Borax: Experimental and Theoretical Studies of an Unexpected Similarity

Guar gum is a galactomannan that assumes a very flexible conformation in solution, while Scleroglucan is a very rigid polysaccharide that dissolves in water as triple helices. Both polymers can form gels in the presence of borax. Despite their structural differences, the freeze-dried gel systems of both polymers, when compressed to form tablets, show a peculiar anisotropic swelling in water that reflects an amazing similarity in terms of their molecular properies. In this paper the behavior of the Guar/borax gel is compared with that of Scleroglucan/borax. The macroscopic properties of the two systems were characterized in terms of rheological measurements. Atomic force microscopy images and molecular dynamics simulation allowed to evaluate, at molecular level, the effect of borax addition to the Guar polymer. Both experiments show that an increasing of the polymer rigidity is produced by borax. The role played by galactose in the side chain was also discussed.

Gellan hydrogel as a powerful tool in paper cleaning process: a detailed study.

HYPOTHESIS Wet cleaning of ancient papers is one of the most critical steps during a conservation treatment. It is used to improve the optical qualities of a graphic work and remove dust and by-products resulting from cellulose degradation. Nevertheless, washing treatment usually involves a substantial impact on the original morphological structure of paper and can sometimes be dangerous for water sensitive inks and pigments. EXPERIMENTS The use of rigid hydrogel of Gellan gum as an alternative paper cleaning treatment is developed. The application of a rigid hydrogel minimizes damages caused by the use of water, and therefore is much more respectful for the original integrity of ancient paper. FINDINGS Gellan hydrogel has been used to clean paper samples belonging to different centuries (from XVI to XIX) and therefore, characterized by a different story in terms of degradation condition and paper composition. Several techniques, such as high-performance liquid chromatography, Fourier transform infrared spectroscopy, scanning electron microscopy and pH measurements, has been employed to assess the effectiveness and safety of the proposed cleaning method.

Theoretical modeling of UV-Vis absorption and emission spectra in liquid state systems including vibrational and conformational effects: the vertical transition approximation.

In this paper we describe in detail a general and efficient methodology, based on the perturbed matrix method and molecular dynamics simulations, to model UV-Vis absorption and emission spectra including vibrational and conformational effects. The basic approximation used is to consider all the chromophore atomic coordinates as semiclassical degrees of freedom, hence allowing the calculation of the complete spectral signal by using the electronic vertical transitions as obtained at each possible chromophore configuration, thus including the contributions of vibrations and conformational transitions into the spectrum. As shown for the model system utilized in this paper, solvated 1-phenyl-naphthalene, such an approximation can be rather accurate to reproduce the absorption and emission spectral line shape and properties when, as it often occurs, the vertical vibronic transition largely overlaps the other non-negligible vibronic transitions.

Combining a hydrogel and an electrochemical biosensor to determine the extent of degradation of paper artworks

AbstractPaper-based artworks are among the most valuable assets for transmission of knowledge. Historical paper is composed of different polysaccharides (e.g. cellulose), binders, and glues. During aging all of these components undergo several degradation processes, as a result of external and intrinsic causes, and these can compromise the state of conservation of the document. In this work, application of a new biotechnological strategy for paper artefact preservation is reported. By making use of innovative and non-invasive materials, for example appropriate hydrogels, in combination with selective electrochemical biosensors, it is possible to simultaneously verify the degradation condition of the paper artwork and then to efficiently clean it, while monitoring the process of removal of both pollution and degradation products. In this paper, we focus on specific examples in which such techniques have been applied to paper artworks and that illustrate the advantages and potential of this biotechnology compared with the traditional paper-cleaning methods currently in use. FigureScheme of cleaning treatment of old paper and determination of the interested analyte using Flow Injection Analysis system (FIA) with integrated electrochemical biosensor

Self-assembly of a Model Peptide incorporating a Hexa-Histidine sequence attached to an Oligo-Alanine sequence, and binding to Gold NTA/Nickel nanoparticles

Amyloid fibrils are formed by a model surfactant-like peptide (Ala)10-(His)6 containing a hexa-histidine tag. This peptide undergoes a remarkable two-step self-assembly process with two distinct critical aggregation concentrations (cacs), probed by fluorescence techniques. A micromolar range cac is ascribed to the formation of prefibrillar structures, whereas a millimolar range cac is associated with the formation of well-defined but more compact fibrils. We examine the labeling of these model tagged amyloid fibrils using Ni-NTA functionalized gold nanoparticles (Nanogold). Successful labeling is demonstrated via electron microscopy imaging. The specificity of tagging does not disrupt the β-sheet structure of the peptide fibrils. Binding of fibrils and Nanogold is found to influence the circular dichroism associated with the gold nanoparticle plasmon absorption band. These results highlight a new approach to the fabrication of functionalized amyloid fibrils and the creation of peptide/nanoparticle hybrid materials.

Cleaning of paper artworks: Development of an efficient gel-based material able to remove starch paste

The removal of old glue from paper artworks is of paramount importance for the preservation of its integrity during the restoration process. Wet cleaning is one of the traditional methods, although it may cause damages on artworks. In this work, an advantageous alternative method, based on the use of a rigid hydrogel, for a simple and localized removal of starch paste from paper supports is presented. The use of an appropriate hydrogel allows to overcome many of the problems faced by restorers minimizing damages, through a controlled release of water to the artwork, and a simple and not invasive application and removal. At the same time, the specific and targeted enzyme activity leads to a significant reduction in the application time of the cleaning procedure. In this context, experiments were carried out applying Gellan hydrogel carrying α-amylase enzyme on several paper samples soiled with starch paste. To assess the cleaning efficacy of the proposed hydrogel, we have used a multidisciplinary approach, by means of spectroscopic techniques, scanning electron microscopy, chromatographic analysis, and pH investigations.

Theoretical and Experimental Study on a Self-Assembling Polysaccharide Forming Nanochannels : Static and Dynamic Effects Induced by a Soft Confinement

It is well-known that the polysaccharide scleroglucan (Sclg) exhibits a triple-helix conformation (triplex) and it is able to form hydrogels in water solution. Furthermore, these hydrogels are influenced by the presence of borax, in terms of rheological and drug release properties. In previous works, we showed that the presence of borax stabilizes the intertriplex interactions and that the property variations, induced by borax, can be fully explained, considering that the Sclg triplexes can form nanochannel-like structures. In this paper, the stability of these aggregates has been experimentally studied by means of atomic force microscopy (AFM) and theoretically investigated by means of molecular dynamics (MD) simulations. The simulations indicate that the borax stabilizes nanochannel-like structures when seven triplexes are considered. The simultaneous presence of different Sclg triplexes in a narrow space strongly influences the properties of confined water molecules in a way similar, in many aspects, to that of water molecules located in the inner part of well-defined nanochannels (e.g., diffusion inside carbon nanotubes). As a consequence, also the conformational properties of flanking regions of Sclg triplexes are influenced. Furthermore, differential scanning calorimetry (DSC) data show that the well-known conformational transition occurring at 280 K for Sclg does not take place in the presence of borax. The MD simulations suggest that such lack of transition is a direct consequence of the presence of borax. The role of Na+ counterions in the hydrogel structure is also investigated.