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 Resonance 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 of water and molecular liquids

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. Vibrational spectroscopy is widely used as a probe of the structure and dynamics of water and aqueous solutions in various environments. UVRR exhibits several advantages with respect to the conventional spontaneous Raman technique: i) a significant increment of the detection limit that allows one to investigate the vibrational modes of solutes also in very high diluted conditions and ii) a selective strong enhancement in the UVRR spectra of solutions of the Raman cross-section of vibrations assigned to specific chromopores. In our laboratory we use synchrotron-based UVRR technique for the investigation of the structural rearrangment and of the molecular interactions in water, water solutions, Ionic liquids (ILs) and Deep Eutectic Solvents (DESs). 

Retrieve articlesACS Sustainable Chem. Eng. (2021)
                               JML, Vol. 283, pp. 537-547 (2019); 
                              CMP, Vol. 22, pp. 1-10992 (2019);
                              JRS Vol. 49, pp. 1076-1085 (2018)
                              JPCB, 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.

Retrieve articles: Nanosponges., Vol. 8, pp. 227-258 (2019); 
                              PCCP., Vol. 19 - 33, pp. 22555-22563 (2017)       
                             SM, Vol. 12 - 43, pp. 8861-8868 (2016); 
                             PCCP, Vol. 17 - 2, pp. 963-971 (2015); 
                             SM, 11, 5862 – 5871 (2015).


Investigation of DNA and their assembly

UV resonance Raman (UVRR) spectroscopy has been demonstrated to be a useful non-destructive methodologyfor providing molecular insights on many different materials, including liquids, gels, polymers and bio-macromolecules. As example of the potential of SR-based UVRR spectroscopy we will focus in particular on the research field of Deoxyribonucleic acid (DNA), a macromolecule that contains our unique genetic code, essential for the growth and the functionality of living organisms. UVRR is an effective and versatile probe of DNA trough the identification of several vibrational bands that can be assigned confidently to a base, sugar or phosphate constituent of DNA and many of which can be employed as sensitive markers of either local structure, global conformation and intermolecular interactions. By using a continuously tunable wavelength source it is possible to enhance specific vibrational signals of nitrogenous bases that are extensively used for in detail identifying base stacking interactions and hydrogen-bond rearrangments promoted by different experimental conditions.  
SR-based UVRR technique is widely used in our laboratory for investigating the ligand-binding interactions of DNA and their assembly (such as g-quadruplex structures) , the oxidative damages of DNA under different experimental conditions and the thermal stability of DNA in the presence of ionic liquids. 


Retrieve articles: Molecular and laser spectroscopy Vol 2: pages 447-482 (2020)
                              J. Mol. Liq. 330: page 115433 (2021)
                              PCCP Vol 23 , page(s): 15980-15988 (2021) 
                              Proc. SPIE , 11086: page(s) 1-8 (2019) 
                              NAR Vol 46 , page(s): 11927-11938 (2018)
                              Appl. Spectr. Vol 71 issue: 1, page(s): 152-155
                             Analyst, Vol. 140 - 5, pp. 1477-1485 (2015)


Structural characterization of bio-molecules, i.e. peptides and proteins

UThanks to the resonance effect, UV Resonance Raman (UVRR) spectroscopy offers several advantages with respect to conventional visible Raman technique, such as the significant increment of the detection limit and the selectivity needed to incisively monitor specific chromospheres within the sample. These conditions determine the usefulness of UVRR spectroscopyas highly sensitive and selective spectral probe for exploring the structure and dynamics of many complex systems, including liquids and solutions of bio-macromolecules,  such as peptides and proteins. An appropriate tuning of the excitation wavelength allows to simplify the Raman spectra, disentangling the signals arising from selected molecular portions of the molecule. Additionally, the high sensitivity of UVRR technique is crucial for ensuring to investigate peptides and proteins also in very diluted conditions while maintaining a satisfactory quality of the spectra.  
SR-based UVRR technique is used in our laboratory for the investigation of structure and dynamics of peptides and proteins under different experimental conditions.

Retrieve articlesLife 11(8), 824 (2021)
                              Molecular and laser spectroscopy Vol 2: pages 447-482 (2020)
                              JML Vol 283 , page(s): 537-547 (2019) 
                              Proc. SPIE , 11086: page(s) 1-10 (2019)


Characterization of materials for Cultural Heritage

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.  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. 

Retrieve articles: EPJP, Vol. 133, pp. 9369 (2018); 
                              CBM, Vol. 166, pp. 464-471 (2018).
                              Vibrational Spectroscopy, Vol. 83, pp. 78-84 (2016).
                             Applied Surface Science, Vol. 349, pp. 924-930 (2015);

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).
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                              Phys. Rev. Lett 92, 255507 (2004);

Ultima modifica il Giovedì, 02 Settembre 2021 15:49