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Scientific Report 2007-2009
Condensed matter physics and biophysics
sized particles to generate materials (and bio-materials) with controlled physical properties.
One of the model system investigated in Rome is made of interacting colloidal particles and
oppositely charged polymers. These systems have recently attracted great interest, due to their
relevance in a number of biological and technological processes, but even more to the fact that their
dynamics and out-of-equilibrium properties offer unceasing challenges. These complexes show a
rich and fascinating phenomenology yet poorly understood. Various novel core-particle aggregates
have been prepared in Rome, by electrostatic self-assembly of polyelectrolytes (and nano particles)
with oppositely charged lipid liposomes. The use of non-covalent forces provides an efficient
method to position the polyelectrolyte chainin a well-defined supra-molecular architecture. In
addition, it is possible to control the macroscopic properties of the assembly through an external
environmental stimulus (C23,C24). We also investigate the interactions between biopolymers
(proteins or nucleic acids) and self-assembled surfactants, a system which has raised increasing
interest within the scientific community. Studies along these lines constitute an interdisciplinary
approach of chemical/physical nature at the bio-molecular level. In addition these investigations
contribute to important applications in biomedicine, as gene therapy. Our research focuses on
a new class of self-assembled amphiphilic aggregates, called cat-anionic vesicles. The acronym
cat-anionic defines surfactant aggregates formed by non-stoichiometric amounts of anionic and
cationic surfactants coexisting with tiny amounts of simple electrolytes (C25).
We also investigate solid-supported lipid-films, considered as an attractive and useful model
system for biological membranes. In particular, amphipathic lipid films on solid support allow the
study of structural investigation of important biological model systems such as the vector like lipid
membranes, in order to improve DNA transfection in non viral gene therapy and as a template
for nanostructure construction (C26).
Structural properties of proteins are also carefully investigated with spectroscopic methods with
the aim of connecting structural changes with the ability to catalyze specific chemical reactions
or the relationship between structural properties of proteins of nutritional relevance, as examined
by FT-IR spectroscopy, and nutrient utilization (C27). Using femtosecond stimulated Raman
scattering spectroscopy (FSRS) we study the reaction of heme proteins with different biological
functions (electron transfer , signaling, etc.). FSRS provides vibrational structural information
with an unprecedented combination of temporal and spectral resolution, unconstrained by the
Fourier uncertainty principle, i.e. in the < 100 fs time domain, unaccessible to conventional
vibrational spectroscopy (C28). We also investigate via small angle X-ray scattering (SAXS), mass
spectroscopy and light scattering techniques different proteins. In particular, we have recently
investigated the protein ferritin , the main iron storage protein in living systems and τ-protein,
one of the few proteins without a secondary structure. Ferritin is a stable complex forming an
hollow sphere (apoferritin) filled with a Fe(II) oxide core and it is important to study since the
ferritin core composition differs between pathological and physiological conditions. τ-protein is
an interesting protein in which fluctuations are expected to be fast and to control the biological
function (C29).
Soft and bio matter is also investigated to address fundamental problems in condensed matter.
Indeed, colloidal suspensions have unambiguous advantages with respect to their atomic counterparts.
Characteristic space and time scales are much larger, allowing for experimental studies in
the light scattering regime and for a better time resolution. The size of the particles allows for
direct observation with confocal microscopy techniques, down to the level of single-particle resolution.
In addition, particle-particle interactions can be tuned by changing the solution conditions
or by additives, as well as by synthesis of functionalized colloids. Colloidal suspensions, despite
being very complex in nature and number of components, can often be well described theoretically
via simple effective potentials. A significant effort is devoted to the investigation of the phase diagram
and self-assembly abilities of patchy colloidal particles, in a combined theoretical, numerical
and experimental study (C9,C20).
One powerful technique to investigate the motion and the interactions between colloidal particles
Sapienza Università di Roma 50 Dipartimento di Fisica