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1. The role of polymer structure on water confinement in poly(N-isopropylacrylamide) dispersions

Author

Buratti, E., Tavagnacco, L., Zanatta, M., Chiessi, E., Buoso, S., Franco, S., Ruzicka, B., Angelini, R., Orecchini, A., Bertoldo, M., and Zaccarelli, E.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

Poly(N-isopropylacrylamide) (PNIPAM) is a synthetic polymer that is widely studied for its thermoresponsive character. However, recent works also reported evidence of a low temperature (protein-like) dynamical transition around 225 K in concentrated PNIPAM suspensions, independently of the polymer architecture, i.e., both for linear chains and for microgels. In this work, we investigate water-polymer interactions by extensive differential scanning calorimetry (DSC) measurements of both systems, in order to understand the effect of the different topological structures on the solution behaviour, in particular regarding crystallization and melting processes. In addition, we compare protiated and deuterated microgels, in both water and deuterated water. The DSC results are complemented by dynamic light scattering experiments, which confirm that the selective isotopic substitution differently affects the solution behaviour. Our findings highlight the important role played by the polymer architecture on the solution behaviour: indeed, microgels turn out to be more efficient confining agents, able to avoid water crystallization in a wider concentration range with respect to linear chains. Altogether, the present data will be valuable to interpret future low-temperature investigations of PNIPAM dispersions, particularly by neutron scattering experiments., Comment: 33 pages, 10 figures

Published
2022

2. Atomic scale investigation of the volume phase transition in concentrated PNIPAM microgels

Author

Zanatta, M., Tavagnacco, L., Buratti, E., Chiessi, E., Natali, F., Bertoldo, M., Orecchini, A., and Zaccarelli, E.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

Combining elastic incoherent neutron scattering and differential scanning calorimetry, we investigate the occurrence of the volume phase transition (VPT) in very concentrated PNIPAM microgel suspensions, from a polymer weight fraction of 30~wt\% up to dry conditions. Although samples are arrested at the macroscopic scale, atomic degrees of freedom are equilibrated and can be probed in a reproducible way. A clear signature of the VPT is present as a sharp drop of the mean square displacement of PNIPAM hydrogen atoms obtained by neutron scattering. As a function of concentration, the VPT gets smoother as dry conditions are approached whereas the VPT temperature shows a minimum at about 43~wt\%. This behavior is qualitatively confirmed by calorimetry measurements. Molecular dynamics simulations are employed to complement experimental results and gain further insights into the nature of the VPT, confirming that it involves the formation of an attractive gel state between the microgels. Overall, these results provide evidence that the VPT in PNIPAM-based systems can be detected at different time- and length-scales as well as in overcrowded conditions.

Published
2020
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3. Protein-like dynamical transition of hydrated polymer chains

Author

Tavagnacco, L., Zanatta, M., Buratti, E., Rosi, B., Frick, B., Natali, F., Ollivier, J., Chiessi, E., Bertoldo, M., Zaccarelli, E., and Orecchini, A.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

Combining elastic incoherent neutron scattering experiments at different resolutions with molecular dynamics simulations, we report the observation of a protein-like dynamical transition in linear chains of Poly(N-isopropylacrylamide). We identify the onset of the transition at a temperature $T_d$ of about 225~K. Thanks to a novel global fit procedure, we find quantitative agreement between measured and calculated polymer mean-squared displacements at all temperatures and time resolutions. Our results confirm the generality of the dynamical transition in macromolecular systems in aqueous environments, independently of the internal polymer topology.

Published
2020
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4. On the Molecular Origin of the Cooperative Coil-to-globule Transition of Poly(N-isopropylacrylamide) in Water

Author

Tavagnacco, L., Zaccarelli, E., and Chiessi, E.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

By means of atomistic molecular dynamics simulations we investigate the behaviour of poly(N-isopropylacrylamide), PNIPAM, in water at temperatures below and above the lower critical solution temperature (LCST), including the undercooled regime. The transition between water soluble and insoluble states at the LCST is described as a cooperative process involving an intramolecular coil-to-globule transition preceding the aggregation of chains and the polymer precipitation. In this work we investigate the molecular origin of such cooperativity and the evolution of the hydration pattern in the undercooled polymer solution. The solution behaviour of an atactic 30-mer at high dilution is studied in the temperature interval from 243 to 323 K with a favourable comparison to available experimental data. In the PNIPAM water soluble states we detect a correlation between polymer segmental dynamics and diffusion motion of bound water, occurring with the same activation energy. Simulation results show that below the coil-to-globule transition temperature PNIPAM is surrounded by a network of hydrogen bonded water molecules and that the cooperativity arises from the structuring of water clusters in proximity to hydrophobic groups. Differently, the perturbation of the hydrogen bond pattern involving water and amide groups occurs above the transition temperature. Altogether these findings reveal that even above the LCST PNIPAM remains largely hydrated and that the coil-to-globule transition is related with a significant rearrangement of the solvent in proximity of the surface of the polymer. The comparison between the hydrogen bonding of water in the surrounding of PNIPAM isopropyl groups and in bulk displays a decreased structuring of solvent at the hydrophobic polymer-water interface across the transition temperature, as expected because of the topological extension along the chain of such interface.

Published
2019
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5. Molecular insights on poly(N-isopropylacrylamide) coil-to-globule transition induced by pressure†

Author

Tavagnacco L., Chiessi E., and Zaccarelli E.

Subjects
Condensed Matter::Soft Condensed Matter, Quantitative Biology::Biomolecules, Chemistry, PNIPAM, molecular dynamics simulation, Settore CHIM/02, phase behaviour, Atmospheric pressure, Molecular dynamics, Amides, Acrylic monomers
Abstract

By using extensive all-atom molecular dynamics simulations of an atactic linear polymer chain, we provide microscopic insights into poly(N-isopropylacrylamide) (PNIPAM) coil-to-globule transition addressing the roles played by both temperature and pressure. We detect a coil-to-globule transition up to large pressures, showing a reentrant behavior of the critical temperature with increasing pressure in agreement with experimental observations. Furthermore, again confirming the experimental findings, we report the existence at high pressures of a new kind of globular state. It is characterized by a more structured hydration shell that is closer to PNIPAM hydrophobic domains, as compared to the globular state observed at atmospheric pressure. Our results highlight that temperature and pressure induce a PNIPAM coil-to-globule transition through different molecular mechanisms, opening the way for a systematic use of both thermodynamic variables to tune the location of the transition and the properties of the associated swollen/collapsed states., By using extensive all-atom molecular dynamics simulations of an atactic linear polymer chain, we unveil the role of pressure in the coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM).

Published
2021

6. Modeling Solution Behavior of Poly(N-isopropylacrylamide): A Comparison between Water Models

Author

Tavagnacco, L, Zaccarelli, E, and Chiessi, E

Subjects
Settore CHIM/02, Polymers, Molecular Conformation, Acrylic Resins, Water, Acrylic monomers, Amides, Atmospheric pressure, Molecular dynamics
Abstract

Water is known to play a fundamental role in determining the structure and functionality of macromolecules. The same crucial contribution is also found in the in silico description of polymer aqueous solutions. In this work, we exploit the widely investigated synthetic polymer poly(N-isopropylacrylamide) (PNIPAM) to understand the effect of the adopted water model on its solution behavior and to refine the computational setup. By means of atomistic molecular dynamics simulations, we perform a comparative study of PNIPAM aqueous solution using two advanced water models: TIP4P/2005 and TIP4P/Ice. The conformation and hydration features of an atactic 30-mer at infinite dilution are probed at a range of temperature and pressure suitable to detect the coil-to-globule transition and to map the P-T phase diagram. Although both water models can reproduce the temperature-induced coil-to-globule transition at atmospheric pressure and the polymer hydration enhancement that occurs with increasing pressure, the PNIPAM-TIP4P/Ice solution shows better agreement with experimental findings. This result can be attributed to a stronger interaction of TIP4P/Ice water with both hydrophilic and hydrophobic groups of PNIPAM, as well as to a less favorable contribution of the solvent entropy to the coil-to-globule transition.

Published
2022

7. On the molecular origin of the cooperative coil-to-globule transition of poly(N-isopropylacrylamide) in water† †Electronic supplementary information (ESI) available: Stereochemistry and initial conformation of PNIPAM 30-mer; pair distribution functions of PNIPAM methyl groups; average time of transitions of dihedral angles; distribution of methyl dihedral angles; temperature dependence of average number of hydration water molecules; correlation between hydrogen bonding of water molecules per repeating unit in the FHS and end to end distance and correlation between PNIPAM–water hydrogen bonding and end to end distance. Time evolution of PNIPAM with the first hydration shell: movie FHSpnipam.avi. See DOI: 10.1039/c8cp00537k

Author

Tavagnacco, L., Zaccarelli, E., and Chiessi, E.

Subjects
Chemistry, genetic structures, digestive, oral, and skin physiology
Abstract

The cooperativity of PNIPAM coil-to-globule transition in water arises from the structuring of solvent in proximity to hydrophobic groups., By means of atomistic molecular dynamics simulations we investigate the behaviour of poly(N-isopropylacrylamide), PNIPAM, in water at temperatures below and above the lower critical solution temperature (LCST), including the undercooled regime. The transition between water soluble and insoluble states at the LCST is described as a cooperative process involving an intramolecular coil-to-globule transition preceding the aggregation of chains and the polymer precipitation. In this work we investigate the molecular origin of such cooperativity and the evolution of the hydration pattern in the undercooled polymer solution. The solution behaviour of an atactic 30-mer at high dilution is studied in the temperature interval from 243 to 323 K with a favourable comparison to available experimental data. In the water soluble states of PNIPAM we detect a correlation between polymer segmental dynamics and diffusion motion of bound water, occurring with the same activation energy. Simulation results show that below the coil-to-globule transition temperature PNIPAM is surrounded by a network of hydrogen bonded water molecules and that the cooperativity arises from the structuring of water clusters in proximity to hydrophobic groups. Differently, the perturbation of the hydrogen bond pattern involving water and amide groups occurs above the transition temperature. Altogether these findings reveal that even above the LCST PNIPAM remains largely hydrated and that the coil-to-globule transition is related with a significant rearrangement of the solvent in the proximity of the surface of the polymer. The comparison between the hydrogen bonding of water in the surrounding of PNIPAM isopropyl groups and in the bulk displays a decreased structuring of solvent at the hydrophobic polymer–water interface across the transition temperature, as expected because of the topological extension along the chain of such interface. No evidence of an upper critical solution temperature behaviour, postulated in theoretical and thermodynamics studies of PNIPAM aqueous solution, is observed in the low temperature domain.

Published
2018

8. Proteinlike dynamical transition of hydrated polymer chains

Author

Tavagnacco, L., primary, Zanatta, M., additional, Buratti, E., additional, Rosi, B., additional, Frick, B., additional, Natali, F., additional, Ollivier, J., additional, Chiessi, E., additional, Bertoldo, M., additional, Zaccarelli, E., additional, and Orecchini, A., additional

Published
2021
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10. Probing structure and mobility of proteins in the amorphous state at low hydration

Author

Chiessi, E, Paradossi, G, Sara, G, and Mark, T

Subjects
quens, insulin, Protein, lyophilization, molecular dynamics simulations, quens, neutron scattering, Protein, neutron scattering, lyophilization, secondary structure, molecular dynamics simulations, biomolecules, molecular dynamic simulations, molecular dynamics simulation, Settore CHIM/02, dry proteins, apoferritin, lyophilized proteins, molecular dynamic simulations, neutron scattering, hydration, biomolecules, methyl groups, secondary structure, hydration, methyl groups, lyophilized proteins, Settore CHIM/02 - Chimica Fisica
Published
2019

11. Phase Change Ultrasound Contrast Agents with a Photopolymerized Diacetylene Shell

Author

Toumia, Y, Cerroni, B, Domenici, F, Lange, H, Bianchi, L, Cocior, M, Brasili, F, Chiessi, E, D'Agostino, E, Van Den Abeele, K, Heymans, S, D'Hooge, J, Paradossi, G, Heymans, SV, Toumia, Y, Cerroni, B, Domenici, F, Lange, H, Bianchi, L, Cocior, M, Brasili, F, Chiessi, E, D'Agostino, E, Van Den Abeele, K, Heymans, S, D'Hooge, J, Paradossi, G, and Heymans, SV

Abstract

Phase change contrast agents for ultrasound (US) imaging consist of nanodroplets (NDs) with a perfluorocarbon (PFC) liquid core stabilized with a lipid or a polymer shell. Liquid → gas transition, occurring in the core, can be triggered by US to produce acoustically active microbubbles (MBs) in a process named acoustic droplet vaporization (ADV). MB shells containing polymerized diacetylene moiety were considered as a good trade off between the lipid MBs, showing optimal attenuation, and the polymeric ones, displaying enhanced stability. This work reports on novel perfluoropentane and perfluorobutane NDs stabilized with a monolayer of an amphiphilic fatty acid, i.e. 10,12-pentacosadiynoic acid (PCDA), cured with ultraviolet (UV) irradiation. The photopolymerization of the diacetylene groups, evidenced by the appearance of a blue color due to the conjugation of ene-yne sequences, exhibits a chromatic transition from the nonfluorescent blue color to a fluorescent red color when the NDs are heated or the pH of the suspension is basic. An estimate of the molecular weights reached by the polymerized PCDA in the shell, poly(PCDA), has been obtained using gel permeation chromatography and MALDI-TOF mass spectrometry. The poly(PCDA)/PFC NDs show good biocompatibility with fibroblast cells. ADV efficiency and acoustic properties before and after the transition were tested using a 1 MHz probe, revealing a resonance frequency between 1 and 2 MHz similar to other lipidic MBs. The surface of PCDA shelled NDs can be easily modified without influencing the stability and the acoustic performances of droplets. As a proof of concept we report on the conjugation of cyclic RGD and PEG chains of the particles to support targeting ability toward endothelial cells.

Published
2019

12. Thermodynamics, spectroscopy, and molecular modeling

Author

Chiessi, E., Branca, M., Palleschi, A., and Pispisa, B.

Subjects
Chemistry, Inorganic -- Research, Coordination compounds -- Research, Complex compounds -- Research, Copper compounds -- Research, Stereochemistry -- Research, Chemistry
Abstract

Copper(II) complexes immobilized through the use of chitosan derivatives as polymeric ligands were investigated via spectroscopic and thermodynamic methods. The metal complexes, which have a tetragonal symmetry, have their stereochemical characteristics regulated by the charge state of the ionizable groups and the chirality of the carbon atom. Molecular characterization of the Cu(II)-1 and Cu(II)-2 active sites was also carried out under different pH conditions.

Published
1995

26. Soft Matter for Biomedicine: Two Case Studies

Author

Paradossi, G, Finelli, I, Ghugare, Sv, and Chiessi, E

Subjects
microgels, thermoresponsivity, Polymer hydrogels, hyaluronic acid, drug delivery, Settore CHIM/02 - Chimica Fisica
Published
2009

29. Structural flexibility modulates the activity of human glutathione transferase P1-1. Influence of a poor co-substrate on dynamics and kinetics of human glutathione transferase

Author

Caccuri AM, ASCENZI, Paolo, Parker MW, Oakley AJ, Chiessi E, Nuccetelli M, Battistoni A, Bellizia A, Ricci G., ANTONINI, GIOVANNI, Caccuri, Am, Ascenzi, Paolo, Antonini, Giovanni, Parker, Mw, Oakley, Aj, Chiessi, E, Nuccetelli, M, Battistoni, A, Bellizia, A, and Ricci, G.

Subjects
structural, isoenzymes, mathematics, binding sites, Models, Theoretical, recombinant proteins, Protein Structure, Secondary, Models, Structural, models, thermodynamics, dinitrochlorobenzene, kinetics, glutathione transferase, protein structure, glutathione, point mutation, Settore BIO/10, secondary, humans, theoretical, protein structure, secondary, models, structural, 4-chloro-7-nitrobenzofurazan, models, theoretical
Abstract

Presteady-state and steady-state kinetics of human glutathione transferase P1-1 (EC 2.5.1.18) have been studied at pH 5.0 by using 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, a poor co-substrate for this isoenzyme. Steady-state kinetics fits well with the simplest rapid equilibrium random sequential bi-bi mechanism and reveals a strong intrasubunit synergistic modulation between the GSH-binding site (G-site) and the hydrophobic binding site for the co-substrate (H-site); the affinity of the G-site for GSH increases about 30 times at saturating co-substrate and vice versa. Presteady-state experiments and thermodynamic data indicate that the rate-limiting step is a physical event and, probably, a structural transition of the ternary complex. Similar to that observed with 1-chloro-2, 4-dinitrobenzene (Ricci, G., Caccuri, A. M., Lo Bello, M., Rosato, N. , Mei, G., Nicotra, M., Chiessi, E., Mazzetti, A. P., and Federici, G.(1996) J. Biol. Chem. 271, 16187-16192), this event may be related to the frequency of enzyme motions. The observed low, viscosity-independent kcat value suggests that these motions are slow and diffusion-independent for an increased internal viscosity. In fact, molecular modeling suggests that the hydroxyl group of Tyr-108, which resides in helix 4, may be in hydrogen bonding distance of the oxygen atom of this new substrate, thus yielding a less flexible H-site. This effect might be transmitted to the G-site via helix 4. In addition, a new homotropic behavior exhibited by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole is found in Cys-47 mutants revealing a structural intersubunit communication between the two H-sites.

Published
1996

31. Super-cooled Water in PVA Matrixes: I. An Incoherent Quasi Elastic Neutron Scattering (QENS) Study

Author

Paradossi, G, Cavalieri, F, Chiessi, E, Telling, E, and Mtf

Subjects
chemistry.chemical_classification, Quantitative Biology::Biomolecules, Vinyl alcohol, Materials science, Hydrogen bond, Dynamic structure factor, Relaxation (NMR), Polymer, Neutron scattering, Surfaces, Coatings and Films, Condensed Matter::Soft Condensed Matter, Crystallography, chemistry.chemical_compound, chemistry, Chemical physics, Self-healing hydrogels, Materials Chemistry, Physical and Theoretical Chemistry, Supercooling, Settore CHIM/02 - Chimica Fisica
Abstract

The incoherent quasi-elastic neutron scattering study of poly(vinyl alcohol) based hydrogels was carried out to elucidate the dynamic state of water caged in polymeric matrixes with different degree of cross-linking and nature of the cross-linking agent. This investigation focuses on the determination of the relationship occurring between the diffusional parameters of water and the polymer network architecture. Analyzing the broadening factor of the dynamic structure factor, a marked supercooling of water was detected in all the matrixes under consideration. In all cases, the activation energies were about 4 kcal/mol indicating a hydrogen bond regime governing the matrix-solvent interaction. In some favorable cases, an insight on the polymer dynamics was also possible. The q-dependence of the broadening factor of polymer relaxation component revealed a behavior compatible with a bound random jump dynamics and concerning segmental motions of the chain coupled with the interaction with water.

Published
2003

33. A general strategy for the obtainment of biodegradable polymer shelled microbubbles as theranostic device

Author

Capese, Sabrina, Chiessi, E., Cavalli, R., Giustetto, P., Grishenkov, Dmitry, Paradossi, Gaio, Capese, Sabrina, Chiessi, E., Cavalli, R., Giustetto, P., Grishenkov, Dmitry, and Paradossi, Gaio

Abstract

Introduction Fabrication of multifunctional ultrasound contrast agents (UCAs) has been addressed by many research groups.1,2 Recently a poly(vinyl alcohol) shelled microbubble 3 has shown a remarkable chemical and physical stability and versatility for the surface functionalization, leading to a platform for multimodality imaging (ultrasounds, magnetic resonance, single photon emission computer tomography) and targeting inflammation and tumours4. In this contribution we present a new strategy for the synthesis of UCAs precursors in the form of vesicles with a biodegradable crosslinked polymer shell. Methods Deposition of methacryloyl-derivative of hydrophilic and biodegradable polymers as dextran (DexMA50) or hyaluronic acid (HAMA30) on a lipid vesicle with a liquid perfluoropentane core, 5,6 followed by a photopolymerization of the methacrylate moiety allows the obtainment of polymer shelled vesicles. Results Lipid shelled vesicles with a perfluorocarbon (PFC) core (Figure 1a) undergo an acoustic droplet vaporization (ADV),7 upon ultrasounds (US) irradiation, transforming such particles into ultrasound effective microbubbles (Fig 1b). The process is reversible as the US are switched off (Fig 1c). In the “microbubble” state, i.e. during US irradiation, the system is echogenic at low mechanical index, allowing their use as UCAs. In this contribution we show that additional functions can be implemented into the microbubbles. For example, we demonstrated the possibility to obtain shells with a thermoreversible behaviour. Conclusions This new class of polymer shelled vesicles/microbubbles entails features desired in a potential theranostic microdevice., QC 20140320

Published
2013

35. Mutations of Gly to Ala in human glutathione transferase P1-1 affect helix 2 (G-site) and induce positive cooperativity in the binding of glutathione

Author

LO BELLO, M, Nuccetelli, M, Chiessi, E, Lahm, A, Mazzetti, A, Battistoni, A, Caccuri, Am, Oakley, A, Parker, M, Tramontano, A, Federici, G, and Ricci, G

Subjects
Models, Molecular, Protein Conformation, cooperativity, Glycine, chemistry, glycine residues, active site loop, alanine, binding sites, chemistry/genetics/metabolism, circular dichroism, cysteine, escherichia coli, genetics, genetics/isolation /&/ purification/metabolism, glutathione, glutathione s-transferase pi, glutathione transferase, glutathione transferases, glycine, humans, isoenzymes, kinetics, metabolism, models, molecular, mutation, protein conformation, recombinant proteins, site-directed mutagenesis, spectrophotometry, tryptophan, ultraviolet, Escherichia coli, Humans, Cysteine, Settore BIO/10, Glutathione Transferase, Alanine, Binding Sites, Circular Dichroism, Tryptophan, Glutathione, Recombinant Proteins, Isoenzymes, Kinetics, Glutathione S-Transferase pi, Mutation, Spectrophotometry, Ultraviolet, models, molecular, spectrophotometry, ultraviolet
Abstract

Previous kinetic studies on human glutathione transferase P1-1 have indicated that the motions of an irregular alpha-helix (helix 2) lining the glutathione (GSH) binding site are viscosity dependent and may modulate the affinity of GSH binding. The effect of single amino acid residue substitutions (Gly to Ala) in this region is investigated here by site-directed mutagenesis. Three mutants (Gly41Ala, Gly50Ala and Gly41Ala/Gly50Ala) were overexpressed in Escherichia coli, purified, and characterized by kinetic, structural, and spectroscopic studies. All these mutant enzymes show kcat values similar to that of the wild-type enzyme, while the [S]0.5 for GSH increases about eight-fold in the Gly41Ala mutant and more than 100-fold in the Gly41Ala/Gly50Ala double mutant. This change in affinity towards GSH is accompanied by an induced positive cooperativity as reflected by Hill coefficients of 1.4 (Gly41Ala) and 1.7 (Gly41Ala/Gly50Ala) upon substrate binding. Taken together, these data suggest that the region around helix 2 is markedly altered leading to the observed intersubunit communication. Molecular modeling of the Gly41Ala/Gly50Ala mutant and of the inactive oxidized form of the native enzyme provides a structural explanation of our results.

Published
1999

45. Stable Polymeric Microballoons as Multifunctional Device for Biomedical Uses:  Synthesis and Characterization

Author

Cavalieri, F., Hamassi, A. El, Chiessi, E., and Paradossi, G.

Abstract

Gas filled hollow microparticles, i.e., microbubbles and microballoons, are soft matter devices used in a number of diverse applications ranging from protein separation and purification in food science to drilling technology and ultrasound imaging. Aqueous dispersions of these mesoscopic systems are characterized by the stabilization of the air/water interface by a thin shell of phospholipid bilayer or multilayers or by a denatured and cross-linked proteic matrix. We present a study of a type of microballoons based on modified poly(vinyl alcohol), PVA, a synthetic biocompatible polymer, with new structural features. A cross-linking reaction carried out at the air/water interface provides polymeric air-filled microbubbles with average dimensions depending on the reaction temperature. Characterization of diameters and shell thicknesses for microbubbles obtained at different temperatures has been carried out. Conversion to solvent-filled hollow microcapsules is possible by soaking microbubbles in dimethyl sulfoxide. Microcapsules permeability to fluorescent labeled dextran molecular weight standards was correlated to the mesh size of the polymer network of the shell. Microbubbles were covalently grafted under very mild conditions with β-cyclodextrin and poly-l-lysine with a view to assay the capability of the device for delivery of hydrophobic drugs or DNA. PVA based microballoons show a remarkable shelf life of several months, their external surface can be decorated with many biologically relevant molecules. These features, together with a tested biocompatibility, make them attractive candidates for use as multifunctional device for diagnosis and therapeutic purposes, i.e., as ultrasound reflectors in ecographic investigation and as drug platforms for in situ sonoporation.

Published
2005

46. Tailoring of Physical and Chemical Properties of Macro- and Microhydrogels Based on Telechelic PVA

Author

Paradossi, G., Cavalieri, F., Chiessi, E., Ponassi, V., and Martorana, V.

Abstract

Poly(vinyl alcohol), PVA, is amenable to several structural modifications because of the presence of the hydroxyl moiety in the backbone. The chemical versatility of this polymer can be used for the obtainment of new wall-to-wall pH-responsive PVA chemical hydrogels and for the preparation of air-filled microspheres, for example, microbubbles. Here, we report on the characterization of the physical and chemical properties of these novel networks that can be potentially used in different biomedical applications as controlled drug delivery and as ultrasonic contrast agent.

Published
2002
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47. A Conformational Study on the Algal Polysaccharide Ulvan

Author

Paradossi, G., Cavalieri, F., and Chiessi, E.

Abstract

The conformational behavior of the algal polysaccharide ulvan in aqueous solution has been studied. This biopolymer, containing limited regular regions of aldobiuronic sequences made of β-d-glcpA(1→4)-α-l-rhap 3-sulfate and of α-l-idopA(1→4)-α-l-rhap 3-sulfate, can be considered as a low-cost source of rare sugars with a potential impact on several industrial applications, from pharmaceutical to fine chemistry industry. The relationship of structure with the chemical composition of the saccharidic residues in the biopolymer is evidenced with respect to the ability of iduronic acid moiety to assume two main ring conformations, namely the 1C4 chair and the 2S0 skew boat conformations. Experimental results are interpreted in the light of models obtained from conformational analysis calculations.

Published
2002
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48. Xanthan and Glucomannan Mixtures:  Synergistic Interactions and Gelation

Author

Paradossi, G., Chiessi, E., Barbiroli, A., and Fessas, D.

Abstract

The synergistic interaction between xanthan and glucomannan in solution and in the gel phase has been studied by circular dichroism spectroscopy and differential scanning calorimetry. The study in solution of the polysaccharidic mixture indicates a preferred stoichiometry of the interaction corresponding to a weight fraction of xanthan around 0.55. This finding is in reasonable agreement with the differential scanning calorimetry measurements carried out on the gel phase. Models from conformational analysis based on these results were formulated in terms of 1:1 and 2:1 Konjac glucomannan/xanthan molecular assemblies. The experimental and calculation results clearly indicate the involvement of the side chains of xanthan and suggest that the ordered portions of the macromolecular complex in solution act in the gel phase as junction zones.

Published
2002
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49. Conformational Dynamics of Hyaluronan in Solution. 2. Mode-Coupling Diffusion Approach to Oligomers

Author

Letardi, S., Penna, G. La, Chiessi, E., Perico, A., and Cesaro, A.

Abstract

A detailed study of structure and dynamics of hyaluronan oligomers (UA)4 and (UA)2 is presented. Recent advances in macromolecule diffusion theory are applied to second order in the mode-coupling expansion to derive second-rank time-correlation functions of the C−H vectors along the chains. The required equilibrium averages are approximated by time averages along an atomistic molecular dynamics simulation. The results are compared with experimental 13C NMR relaxation parameters of different nuclei in the molecule. The pronounced structure in the relaxation pattern found in the experiments for (UA)4 can be qualitatively interpreted in terms of rotational diffusion anisotropy with partially screened hydrodynamic interactions. Interresidue hydrogen bonds concerning the side chains are weak and do not have significant local effects while O5(i)−HO3/4(i + 1) hydrogen bonds can play a significant role in coupling conformational degrees of freedom with solvation. The implications of this study on the knowledge of the hyaluronan polymer structure and dynamics are addressed.

Published
2002

50. Conformational Study of the Diastereomeric Pairs in Poly(lysine)−Pectate Complexes

Author

Paradossi, G., Chiessi, E., and Malovikova, A.

Abstract

The complex formation in aqueous solution between the polyelectrolytes poly(lysine) and pectate was studied focusing on the conformational changes of the polysaccharidic moiety. The findings suggest that the pectate adopts a superhelical conformation around the α helix of the poly(l-lysine). A threshold value of the degree of polymerization of the pectate chain enabling the transition of the peptide was determined by chromatographic and circular dichroism methods. Conformational analysis results are in agreement with the experimental findings and support the superhelical topology of the polyelectrolyte poly(l-lysine)−pectate complex.

Published
2001

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