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Ciferri A.,Duke University | Ciferri A.,CNR Institute for Macromolecular Studies
Chemistry - A European Journal | Year: 2010

Purely ionic interactions in natural and synthetic macromolecules involve the mutual interaction of fixed charges and their interaction with mobile ions. Such charge-dependent interactions lead to well-documented effects, including chain expansion of polyelectrolytes, globularization of polyampholytes, distributions of mobile ions according to charge screening, or ion condensation models. A variety of structural features, functions, and applications of these systems is amplified by the superimposition of charge-independent effects associated with the occurrence of less polar or hydrophobic groups, special salts, surfactants, or complementary protein assemblies. For instance, ionic and hydrophobic attractive interactions stabilize pearls (or rings)-on-a-string conformations, possibly a model for the formation of the chromatin assembly. The attractive interactions due to hydrophobic fatty acid groups attached to polysaccharides promote the formation of vesicles that entrap and slowly release water-soluble drugs. Intra- and intermolecular associations based on ion-pairing mixed interactions also control the formation of host-guest compounds, protein conformation, and the assembly of layered polyelectrolytes. Metallo-supramolecular polymers and networks are formed due to the coordination of multivalent cations with bi- and trifunctional organic ligands. The association of lithium salts to polymers in the absence of water allows the formation of highly efficient energy sources. It also allows the identification of the ionic species that control charge-independent contributions to Hofmeister effects. This critical review presents a synthetic classification of systems displaying ionic mixed interactions, and a discussion of underlying molecular mechanisms. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Periolatto M.,Polytechnic University of Turin | Ferrero F.,Polytechnic University of Turin | Vineis C.,CNR Institute for Macromolecular Studies
Carbohydrate Polymers | Year: 2012

The purpose of this work was to develop a textile finish based on radical UV-curing of chitosan on cotton and silk to confer antimicrobial properties. Fabrics were impregnated with a solution of 2% w chitosan in aqueous acetic acid (2% v/v) added of 2-hydroxy-2-methylphenylpropane-1-one (2% w/w with respect to chitosan) as photoinitiator and cured at room temperature by exposure to UV lamp for 60 s on both the sides. The antimicrobial activity of finished fabrics was tested according to ASTM standard test performed with Escherichia coli. Obtained results showed a strong antimicrobial activity conferred by the treatment, homogeneous on fabric surface, without affecting the hand properties of fabrics due to the low chitosan weight on (about 2%). The treatment durability to domestic laundering was tested after 5 cycles using either anionic or nonionic detergents. The antimicrobial activity resulted completely maintained after washing with a nonionic surfactant, while with anionic detergents the treatment durability was better for samples prepared with a deeper penetration of chitosan inside the fibers. The fabrics were characterized by dyeing tests, SEM and FTIR-ATR analyzes. © 2011 Elsevier Ltd All rights reserved.

La Penna G.,CNR Institute of Chemistry of organometallic Compounds | Perico A.,CNR Institute for Macromolecular Studies
Biophysical Journal | Year: 2010

The protein-DNA complex, involved in the lac operon of enteric bacteria, is paradigmatic in understanding the extent of DNA bending and plasticity due to interactions with protein assemblies acting as DNA regulators. For the lac operan, two classes of structures have been proposed: 1 ), with the protein tetramer lying away from the DNA loop (wrapped-away model); and 2), with the protein tetramer lying inside the DNA loop (wrapped-around model). A recently developed electrostatic analytical model shows that the size and net charge of the Lac protein tetramer allow the bending of DNA, which is consistent with another wrapped-around model from the literature. Coarse-grained models, designed based on this observation, are extensively investigated and show three kinds of wrapped-around arrangements of DNA and a lower propensity for wrapped-away configurations. Molecular dynamics simulations of an all-atom model, built on the basis of the most tightly collapsed coarse-grained model, show that most of the DNA double-helical architecture is maintained in the region between O3 and O1 DNA operators, that the DNA distortion is concentrated in the chain beyond the O1 operator, and that the protein tetramer can adapt the N-terminal domains to the DNA tension. © 2010 by the Biophysical Society.

Ruzicka B.,University of Rome La Sapienza | Zaccarelli E.,University of Rome La Sapienza | Zulian L.,CNR Institute for Macromolecular Studies | Angelini R.,University of Rome La Sapienza | And 4 more authors.
Nature Materials | Year: 2011

The relevance of anisotropic interactions in colloidal systems has recently emerged in the context of the rational design of new soft materials. Patchy colloids of different shapes, patterns and functionalities are considered the new building blocks of a bottom-up approach toward the realization of self-assembled bulk materials with predefined properties. The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and micro-scales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies suggest that the phase diagram of patchy colloids can be significantly altered by limiting the particle coordination number (that is, valence). New concepts such as empty liquids-liquid states with vanishing density-and equilibrium gels-arrested networks of bonded particles, which do not require an underlying phase separation to form-have been formulated. Yet no experimental evidence of these predictions has been provided. Here we report the first observation of empty liquids and equilibrium gels in a complex colloidal clay, and support the experimental findings with numerical simulations. © 2011 Macmillan Publishers Limited. All rights reserved.

Boggioni L.,CNR Institute for Macromolecular Studies | Tritto I.,CNR Institute for Macromolecular Studies
MRS Bulletin | Year: 2013

Highly active metallocenes and other single site catalysts as well as Grubbs and Schrock metathesis catalytic systems have opened up the possibility to polymerize cycloolefins or to copolymerize them with ethene or propene. The polymers obtained show exciting structures and properties. Cycloolefins such as cyclopentene, cyclooctene, norbornene, and their substituted derivatives are incorporated into the polymer chain either by double bonds or by ring-opening metathesis polymerization. Materials with elastomeric properties or tactic polymers with high glass transition temperatures and melting points are obtained with a wide range of microstructures. For example, cycloolefin copolymers and other homo-and copolymers of norbornene are of great academic and industrial interest because of their properties and applications in optoelectronics, lenses, and coatings. © 2013 Materials Research Society.

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