Hydration structure analysis of lysozyme amyloid fibrils by thermally stimulated depolarization currents (TSDC) technique

Thermally stimulated depolarization currents technique has been employed to investigate the conformation of hen egg white lysozyme in native and amyloid form, in the state of powder at very low hydration level. The technique, able to detect the current generated by thermally activated reorientation of water dipoles previously oriented by an electric field, exploits H2O dipoles, belonging to the solvation shell, as a probe to gain information on the protein conformation.Large differences are detected between the TSDC spectra related to the two different protein conformations, for what concerns the number and position of the main peaks, the native form displaying two peaks, atTM=175 K and atTM=297 K, and the amyloid one, only one at intermediate temperature (TM=235 K). The spectra have been compared with those monitored for poly-L-lysine (MW 80400), as received and prepared in different ways, i.e.α-helix,β-sheet, and coil conformation, respectively. The poly-L-lysine spectra show specific features that can be attributed to water texture around the secondary structure adopted by the macromolecule: the results stress how TSDC technique is a tool of great potential value in the conformational analysis of proteins

Hydration structure analysis of lysozyme amyloid fibrils by thermally stimulated depolarization currents (TSDC) technique

Abstract. Thermally stimulated depolarization currents technique has been employed to investigate the conformation of hen egg white lysozyme in native and amyloid form, in the state of powder at very low hydration level. The technique, able to detect the current generated by thermally activated reorientation of water dipoles previously oriented by an electric field, exploits H 2 O dipoles, belonging to the solvation shell, as a probe to gain information on the protein conformation. Large differences are detected between the TSDC spectra related to the two different protein conformations, for what concerns the number and position of the main peaks, the native form displaying two peaks, at T M = 175 K and at T M = 297 K, and the amyloid one, only one at intermediate temperature (T M = 235 K). The spectra have been compared with those monitored for poly-L-lysine (MW 80400), as received and prepared in different ways, i.e. α-helix, β-sheet, and coil conformation, respectively. The poly-L-lysine spectra show specific features that can be attributed to water texture around the secondary structure adopted by the macromolecule: the results stress how TSDC technique is a tool of great potential value in the conformational analysis of proteins

High resolution spectroscopy to investigate impurities in YAB single crystals

The work explores the feasibility of high resolution (as fine as 0.02 cm-1) Fourier transform spectroscopy applied at 9 K in the 500-25000 cm-1 range to detect traces of unwanted impurities, mainly rare earths (RE3+) in crystals: the system chosen is YAl3(BO3)4 (YAB). Weak traces of RE3+ (Nd, Dy, Er, Tm, Yb), but also of Cr3+ and OH-, were successfully monitored by comparing the spectra of YAB samples under examination with those intentionally doped with a given ion. The analysis performed on a variety of samples shows how Cr3+, Nd3+, and Yb3+ are the most frequent unwanted dopants and can provide suggestions to the crystal growers about the performances of different crystal growth lines. According to a preliminary evaluation, the Er3+ traces detection limit is as low as 1-2x10-4 mol% in 1 cm thick samples. The advantages of the method, which is sample non-destructive, are discussed in comparison with those currently applied

Hyperfine interactions in YAB:Ho3+: A high-resolution spectroscopy investigation

High-resolution spectroscopy (as fine as 0.01 cm−1) was applied to a 1 mol % holmium-doped single crystal of yttrium aluminum tetraborate with the purpose of studying the hyperfine splitting of Ho3+ energy levels of interest for possible quantum manipulation media. The hyperfine structure was clearly revealed for a high number of lines in a wide wave number range (up to 21300 cm−1) and for a large number of multiplets. Several different hyperfine patterns were monitored, differing in the number of lines, in their separation, and in their relative statistical weight. These features were all understood by a crystal-field model, whose results are in very good agreement with experiments and account for the involved level symmetry, the type of transitions (electric and magnetic dipole allowed), the possibility of a second-order (pseudoquadrupolar) hyperfine coupling between close levels, and a slight distortion of the local D3 symmetry in Ho-occupied sites