<strong>Soft</strong> Resonant X-ray Scattering (RIXS) from solids:Results on InstrumentationA X Em d va nc ed -Ra y issio n Sp ec tro sc op ySAXES& Swiss Lig ht So urc ePolitecnico <strong>di</strong> Milanoallowing to scan the scattering cross section at allangles. The second instrument is less versatile interms of angular scan but is much more effective inthe selection of the energy window because it isbased on a multilayer system. In this case it is alsopossible to carry out the polarization analysis of thescattered ra<strong>di</strong>ation.It is in the scientific tra<strong>di</strong>tion of the AXES group todevelop new instrumentation at the forefront of theinternational standard. This implies a continuousupgra<strong>di</strong>ng of the existing instruments and the designand development of new machines. In thisconnection the main achievements are the following.1. Equipment for RIXS measurements at the ESRF(ID08 beamline)This is the instrument used at the ESRF to takespectra with resolution both in the incident and inthe scattered photon beam. The instrument entirelydeveloped at the Politecnico <strong>di</strong> Milano and fullysupported by INFM/CNR consists of amonochromator used to prepare the incident beam(this instrument is called Polifemo) and in aspectrograph used to measure the scattered photonenergy past the sample (this instrument is calledAXES). The first spectra from AXES came out in 1994with white beam excitation and Polifemo wasinstalled in 1997. Due to continuous upgra<strong>di</strong>ng onlythe mechanical setup remains essentially the same.A part of the optics has been changed and thedetector (a CCD ) is completely new. Thanks to theseimprovements the system has top levelperformances at the international level among theinstruments operated routinely in the range from450 eV to about 1300 eV. The typical resolvingpower around 600 eV is 2000 (note that this is thecombined resolving power inclu<strong>di</strong>ng both Polifemoand AXES).3. Equipment for RIXS measurements at the SwissLight Source (ADRESS beamline)This instrument is property of the Paul ScherrerInsitut (PSI, Villigen, Switzerland) and has beendesigned and built at the Politecnico <strong>di</strong> Milano. Itexploits the expertise accumulate by our group in the10 years of the AXES project and is conceived toreach even better performances. For this reason theinstrument is called SAXES (Super-AXES). It isdesigned to have a resolving power around 8000-10000 and it will be mounted on a rotating opticalbench in order to do measurements as a function ofthe transferred momentum. The better energyresolution is obtained at the price of a lowerefficiency in SAXES than in AXES: the twospectrometers are complementary and they will beboth kept operational in the future. SAXES shouldbecome operational at the ADRESS beam line of theSwiss Light Source at the beginning of 2007. Thefirst tests on energy resolution made withconventional x-ray sources in Milano have shownthat the target performances have been reached.SAMPLEAREA INCLUDED INTHE SPECTROMETERACCEPTANCEILLUMINATEDSURFACEINCIDENTBEAM2D POSITIONSENSITIVEDETECTOREMITTEDPHOTONSSPECTROMETERENTRANCE SLIT SPECTROMETERGRATING2. Equipments for Integrated Raman (IRRS)measurements at the ESRF (ID08 beamline)We have developed two instruments to exploit thisnew experimental approach. The first instrumentselects the scattering channel with absorption filtersinstalled on a goniometer in ultra high vacuumPartecipantsL.Braicovich, C.Dallera, G.Ghringhelli, A.Tagliaferri,A. Piazzalunga, F. Fracassi, INFM-CNR and Dip. <strong>di</strong><strong>Fisica</strong>, Politecnico <strong>di</strong> Milano, Italy.101SOFT Scientific <strong>Report</strong> 2004-06
Scientific <strong>Report</strong> – Elastic and inelastic scattering of neutrons and X-raysPicosecond-Timescale Fluctuations of Proteins in GlassyMatrices: The Role of viscosityProteins perform most of the functions of livingthings. They are real nano-engines, whosefunctioning deserves to be stu<strong>di</strong>ed in action.Actually, despite its importance, the precise natureof the internal motions of proteins remains amistery. In particular fast relaxations in thepicosecond-timescale play a key role for biologicalactivity. When proteins are embedded in glassymatrices both the onset and the amplitude of thesefluctuations appear to be driven by the environmentjust around the protein surface [1]. Here we report astudy performed via elastic neutron scatteringexperiments at the backscattering spectrometerIN13 [2]. In particular we investigated lysozyme, asimple model enzyme, in the hydrated powder stateand when it is plunged in <strong>di</strong>fferent kind of glassymatrices, in the temperature range 20 ÷ 320 K. Thecalculated protein mean square <strong>di</strong>splacements (MSD) follow a purely vibrational behaviour at lowtemperature.MSD show a temperature critical behaviour that istightly linked with that of η, with crucial changes justin proximity of the glass transition. Indeed, theinternal dynamics of proteins is strongly determinedby the ability of the surface protein side-chains tomove. If we describe the picosecond timescalemotions of a particle in terms of Brownian <strong>di</strong>ffusion,then the Stokes-Einstein law leads to an inverserelationship between the relevant MSD and bulkviscosity ~η -1 . Actually, from our results itfollows that ~(logη) -1 . This weaker dependencecould be due to the fact that it is the microviscositysensed by the particle, possibly <strong>di</strong>fferent from η,which is related to the correspon<strong>di</strong>ng dynamics. Inad<strong>di</strong>tion, the evidence that both solvent and proteinMSD are related to η by the same functionaldependence in<strong>di</strong>cates that the protein local dynamicsis closely coupled with that of the host. Thus ourfin<strong>di</strong>ngs in<strong>di</strong>cate that it is just the molecular networkimme<strong>di</strong>ately around the protein surface to drive thefast fluctuations in proteins.log(η in Poise)1086420lysozyme+glycerol0h-20.42h0.83h-40 2 4 6 8 101/6 2w(Å -2 )Fig. 1. Logarithm of solvent bulk viscosity vs. theinverse of the protein double-well (relaxational)contribution to total mean square <strong>di</strong>splacements (h =grams of water/grams of lysozyme).At around 100 K a gradual departure from thisvibrational behaviour takes place. This marks theonset of jumps from the ground to the excited statein a double-well model with correspon<strong>di</strong>ng MSD of 2w. In Fig. 1 we represent the logarithm of thebulk viscosity η of some glycerol-water mixtures vs.the inverse of 6 2w of lysozyme in thecorrespon<strong>di</strong>ng glycerol-water matrices. Quitesurprisingly we observe that a linear relationshipexists in the whole investigated temperature range.We verified that such a law is obeyed in all thesystems we stu<strong>di</strong>ed, as Fig. 2 shows. It should beremarked that the linear relationship between logηvs. 1/6 2w is satisfied also in some glass formers[3]. Anyway, in these materials it is the bulkviscosity and the fast dynamics of the same systemthat are correlated. What’s the meaning of therelationship we found in a complicated system suchas a protein in glassy environments? The existenceof a linear dependence tells us that protein relaxationlog(η in Poise)1412108642012 108641/6 2w(Å -2 )200.20.00.40.60.81.0 hFig. 2. The law logη ~ 1/6 2w is verified for allthe measured samples. Lysozyme at 0.3h (purple)and 0.4h (violet); lysozyme in glycerol at 0h (blue),0.2h (gray), 0.42h (red) and 0.83h (black);lysozyme in glucose at 0h (pink), 0.15h (orange),0.41h (dark green), 0.59h (cyan) and 0.71h (green).References[1] A. Paciaroni, S. Cinelli, G. Onori, Biophys. J. 83,1157 (2002).[2] E. Cornicchi, G. Onori and A. Paciaroni, Phys.Rev. Lett. 95, 158104 (2005).[3] U. Buchenau, and R. Zorn, Europhys. Lett. 18,523 (1992); J. C. Dyre and N. Boye Olsen, Phys.Rev. E 69, 042501 (2004) and references therein.AuthorsE. Cornicchi, G. Onori and A. Paciaroni<strong>Dipartimento</strong> <strong>di</strong> <strong>Fisica</strong>, Università <strong>di</strong> Perugia, CRS-SOFT Unità <strong>di</strong> Perugia and Centro per i MaterialiInnovativi e Nanostrutturati (CEMIN), Via A. Pascoli,I-06123 Perugia, Italy.SOFT Scientific <strong>Report</strong> 2004-06102
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