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The research in disordered systems is fascinating scientists since many years and it allowed to develop innovative experimental methods for the study of the structural organization and dynamics in condensed matter.  These techniques can be directly exploited to investigate the physical-chemical properties of many different materials, including liquids, gels, polymers, bio-macromolecules and glasses. Inelastic light scattering techniques, including Raman and Brillouin spectroscopy, are useful methods for studying a large class of materials through the measurements of collective and molecular excitations propagating in the system. They can complement the information gained from other experimental methods such as inelastic X-ray scattering (IXS) and inelastic neutron scattering (INS) that cover the largest momentum Q and energy E transfer region of the kinematic window where the condensed matter dynamics takes place. However, ILS have the limitation that only very low-momentum transfers, no higher than 0.03 nm-1, can be studied because of the small momentum carried by the photons at visible light wavelengths.

The UV synchrotron source exploited by IUVS beamline enables to push the inelastic light scattering technique up to 0.1 nm-1 of momentum transfer, thus allowing to cover a range of fundamental importance to gain insight into the structure and dynamics of disordered systems.

The characteristics of the experimental setup for UV Brillouin experiments available on IUVS allows to measure the dynamic structure factor S(Q,E) over the intermediate, mesoscopic, region in the E-Q diagram, giving access to a frequency range close to the inverse of the Hydrogen-bond lifetime in water at room temperature. For this reason, IUVS can probe the 0.1 THz acoustic dynamics which is required to match the sensitivity condition for studying the structural relaxation processes in H-bonding systems, as molecular liquids and water solutions.

The UV Resonant Raman scattering setup available on IUVS enables to gain additional information on samples whenever the complexity of the system analysed does not allow to get an easy and unique interpretation of the spontaneous Raman spectra. The tunable radiation source in the deep-UV range (4-6 eV, 200-300 nm) offered by IUVS beamline makes possible a fine mapping of the whole resonance landscape range providing the advantage to a better selection of the resonant conditions for very different systems, ranging from graphene and carbon-related materials, DNA and proteins and aromatic compounds.

The research projects at the IUVS beamline include the characterization of dynamics of systems relevant in many scientific fields: water and liquids, polymers and gels, drug-carriers, biological molecules such as proteins and DNA, nanostructures and materials interesting for cultural heritage. 

Hydrogen-bond dynamics in hydration shell of biomolecules

The presence in water of an extensive H-bonding (HB) network and its rapid continuous rearrangement is considered to be the responsible of the unique and peculiar properties exhibited by this ubiquitous liquid. Since the most of biological processes occur in an aqueous environment, the hydrogen-bond rearrangement and the intermolecular organization of water molecules in the hydration shell can strongly influence the structure and function of biomolecules within it. The role of water in determining the behaviour of small and larger biomolecules, i.e. sugars, peptides, proteins, DNA,…, in different experimental conditions is still a matter of interest, and despite many decades of intense studies several contrasting results clearly underline how a comprehensive understanding of the interaction mechanisms between water and biomolecules is still lacking. Among various experimental techniques able to provide information on the hydrogen-bond dynamics of water in the hydration shell of biological molecules, UV Resonant Raman spectroscopy (UVRR) allows to extract insights both on the behaviour of the single parts of a molecule with respect to the whole system and on the local (intermolecular) environment.
For instance, UVRR has been recently used for shed light on the solvation processes in acetamide aqueous solutions, by investigating the dynamics of different HB interactions established between water and specific chemical groups of the solute. Furthermore, the spectral analysis of the OH stretching band of water in the high frequency range of Raman spectra allows to obtain quantitative information on the supramolecular organization of interfacial water.

Retrieve articles: Journal of Physical Chemistry B, Vol. 120 - 15, pp. 3746-3753 (2016)
                              Phys. Chem. Chem. Phys., Vol. 18 - 19, pp. 13478-13486 (2016); 
                              Physical Chemistry Chemical Physics, Vol. 17 - 16, pp. 10987-10992 (2015);
                              The Journal of Physical Chemistry B, Vol. 116 - 44, pp. 13219-13227 (2012).

Structure and dynamics of polymeric hydrogels

Hydrogels have existed for more than half a century and today they find many applications in many materials of common use and in various processes ranging from industrial to biological. They are a unique class of cross-linked polymers that are able to adsorb a large amount of water while preserving their three-dimensional structure.  Among the wide range of polymeric formulation that gives rise to biocompatible hydrogels, an attractive class of ‘intelligent gels’ is represented by stimuli-responsive hydrogels, whose swelling behaviour, network structure, permeability or mechanical strength can be triggered in response to different stimuli, such as temperature, pH and ionic strength. The recently growing use of hydrogels especially in technological fields of high social impact has led to the need of the systematic exploration of the strict relationship between the molecular properties and the macroscopic behaviours observed in responsive hydrogels.
The nature and the extent of the water-water and water-polymer interactions that are established inside the hydrogel phases can be efficiently explored by using UV Resonant Raman (UVRR) scattering experiments taking advantage of the selective enhancement of specific Raman modes that occurs at resonance conditions. Changes in the gel structure can be probed by following the intensity, frequency position and spectral shape of Raman peaks that represent the vibrational signatures of the reorganization of hydrogen-bond network of water molecules and of the solvation-effects in the proximity of hydrophobic/hydrophilic groups of the polymer backbone in the hydrogel state at variable experimental conditions, such as temperature, hydration level or pH.
As prototype case study, the thermal activation of pH-responsive cyclodextrin-based hydrogels, namely cyclodextrin nanosponges (NS), has been explored by UVRR.
The rearrangement of HB network of water molecules in the gel phase and the nature of the interactions established among hydrophobic/hydrophilic moieties of the polymer matrix with the solvent have been probed by the analysis of the spectral changes observed in UVRR spectra. The main effects in the solvation of hydrogels appear due to the changes occurring, with T, in the hydrophobicity of specific moieties of the polymer, as triggered by pH variations. These results assume a particular practical importance in view of future engineering of hydrogels for targeted delivery and release of bioactive agent and corroborate the potentiality of UV Raman scattering technique to provide a “molecular view” of complex macroscopic phenomena in gel systems.

Retrieve articles: Phys. Chem. Chem. Phys., Vol. 19 - 33, pp. 22555-22563 (2017); 
                              Expert Opinion on Drug Delivery, Vol. 14 - 3, pp. 331-340 (2017); 
                              Soft Matter, Vol. 12 - 43, pp. 8861-8868 (2016); 
                              Physical Chemistry Chemical Physics, Vol. 17 - 2, pp. 963-971 (2015); 
                              Soft Matter, 11, 5862 – 5871 (2015).

Biological applications of UV Raman spectroscopy: investigation of DNA and nucleic acids

Raman spectroscopy is widely employed in the scientific community to characterize the chemical structure of DNA. By using UV excitation instead of visible one it is possible to get a higher scattering efficiency together with a significant reduction of the interfering fluorescence background. Furthermore, thanks to the resonance conditions, by exciting the UV Raman spectra of DNA with specific wavelengths it is possible to selectively enhance the vibrational modes associated to specific nitrogenous basis, thus obtaining complementary information with respect to those provided by other vibrational spectroscopy technniques such as FTIR adsorption. This allows to use UVRR for detailed investigations of the chemical modifications induced in the nitrogenous bases by oxidation processes involving DNA, also on samples directely extracted from cells. 

Retrieve articles: Appl. Spectr. Vol 71 issue: 1, page(s): 152-155
                             Analyst, Vol. 140 - 5, pp. 1477-1485 (2015)

Vibrational spectroscopy for Cultural Heritage Materials

It is well known that Raman spectroscopy has become in recent decades a fundamental tool for the analysis of a wide variety of materials related to the field of cultural heritage and archeology. The Raman spectra can be used as fingerprints for the chemical identification of the components of the material under investigation in a non-destructive and non-invasive manner due to the fact that Raman spectroscopy is a scattering technique that does not require any preparation or preparatory handling of the artefacts. This is particularly useful in the analysis of artistic materials where the molecular specificity combined with the characteristics of spatial resolution (up to 1 mm) and confocality of the instruments make Raman spectroscopy a versatile tool for the cultural heritage scientists. The synchrotron-based UV resonant Raman scattering facility implemented at IUVS has been demonstrated to be a valid tool for addressing a large array of open problems in the field of cultural heritage, allowing to overcome the most critical limitations in the application of conventional Raman spectroscopy to the analytical characterization of art materials. The advantages offered by UV Resonant Raman technique concern i) the improvement of signal-to-noise ratio of Raman bands excited by using wavelengths in the UV range, ii) the strong quenching in the Raman spectra of the fluorescence emission backgrounds (arising also from specimen degradation and presence of impurities) that in many cases constitute a serious limitation in the acquisition and analysis of Raman spectra of historical-artistic materials and iii) the selective enhancement of the Raman bands associated to specific functional groups by exploiting the resonance conditions occurring at different excitation wavelengths in the UV-range. The unique tunability provided by the synchrotron radiation source gives the possibility to a selective choice of the excitation energy that it is possible to match with the experimental conditions, allowing to overcome the limitation of conventional UV laser sources at fixed energy of emission. Additionally, the experimental layout available on IUVS offers the opportunity to choice two different sampling modalities, by carrying out macro- or micro- UVRR measurements, in order to select the best experimental conditions depending on the type of sample under investigation. 

Retrieve articles: Applied Surface Science, Vol. 349, pp. 924-930 (2015); 
                             Vibrational Spectroscopy, Vol. 83, pp. 78-84 (2016).

Structural relaxation processes in hydrogen-bonding liquids

Structural relaxation are cooperative processes by which the local structure, after being perturbed by an external disturbance or by a spontaneous fluctuation, rearranges towards a new equilibrium position. In hydrogen-bonding liquids, such as water, aqueous solutions or molecular liquids, the structural relaxation reflect diffusive molecular reorientations involving the formation and breaking of hydrogen bond network. The study of relaxation can therefore yield insight into the timescale and degree of these H-bonding that are strictly related to the peculiar behaviour of water and HB systems. The structural relaxation time tin water, liquids and aqueous solutions of biological molecules have been studied in different conditions by inelastic ultraviolet scattering spectroscopy at IUVS.
For instance, the dynamic structure factor of normal and supercooled liquid water has been measured at a momentum transfer Q≈0.02-0.1  nm-1, in the temperature range 253–340 K.
The structural (α) relaxation has been observed in the supercooled temperature region (T≤273  K), where the inverse relaxation time matches the frequency of the probed sound modes. The T dependence of the relaxation time shows a diverging behavior with a critical temperature T≈220  K. These results provide a unique experimental opportunity to frame the dynamics of water in the mode-coupling theory. Furthermore we observe the neat departure of the apparent speed of sound from the adiabatic regime as a function of decreasing temperature. Our evaluation of the infinite frequency limit of sound velocity, cinf, matches with the results obtained in the high momentum transfer limit by inelastic neutron and x-ray scattering. These results strongly support the viscoelastic interpretation of the dynamics of water.

Retrieve articles: Journal of Chemical Physics, Vol. 134 - 5 (2011).
                              J. Phys. Chem. B 114, 10628 (2010)
                              J. Chem. Phys. 131, 154507 (2009);  
                              J. Chem. Phys. 131, 144502 (2009);
                              J. Phys. Chem A 111. 12577 (2007)
                              Phys. Rev. Lett  97, 225701 (2006)
                              Phys. Rev. Lett 92, 255507 (2004);

Last Updated on Thursday, 25 January 2018 15:34