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Cedro Beamline

CEDRO (Circular DichROism Beamline) will be a beamline dedicated to Circular Dichroism (CD) spectroscopy in the ultraviolet region. This spectroscopy is applied to the structural analysis of chiral molecules, including biomolecules such as proteins, nucleic acids, and carbohydrates. Proteins are extensively studied by CD to quantify their secondary structure content and to analyze folding, stability and interactions in solution.

If the light source is synchrotron radiation (SR), the technique is called SRCD (Synchrotron Radiation Circular Dichroism). SR offers enhanced photon flux compared to conventional lamps used in laboratory-based instruments and it enables data collection at lower wavelengths in the vacuum ultraviolet region (VUV, below 200 nm), which is commonly inaccessible in a conventional instrument [1].

The extension of wavelength range to the VUV region allows the detection of high-energy transitions. For instance, the n–σ* transitions of acetal and hydroxyl groups of saccharides produce bands at 140–180 nm [2]. Besides, the proteins secondary structure content can be quantified from the CD spectra, which can be considered as the weighted sum of the secondary structure components. The amount of information that can be extracted depends on the number of transitions included in the spectrum. It is known that spectra achieving wavelengths not lower than 200 nm can be described by two eigenvectors allowing the estimation of helices only. This value increases to three or four when the spectrum is extended to 190 nm and six to eight to 170 nm, and then, the distinction among a greater number of secondary structures is possible [3,4]. Therefore, the use of synchrotron radiation as the light source enhances the circular dichroism spectroscopy utility.

[1] B. A. Wallace, “The role of circular dichroism spectroscopy in the era of integrative structural biology”, Current Opinion in Structural Biology, vol. 58, pp. 191–196, 2019. DOI: 10.1016/j.sbi.2019.04.001.

[2] K. Gekko, “Synchrotron-radiation vacuum-ultraviolet circular dichroism spectroscopy in structural biology: an overview”, Biophysics and Physicobiology, vol. 16, pp. 41-58. 2019. DOI:10.2142/biophysico.16.0_41

[3] J. G. Lees, A. J. Miles, F. Wien, B. A. Wallace, “A reference database for circular dichroism spectroscopy covering fold and secondary structure space”, Bioinformatics, vol. 22, pp. 1955–1962, 2006. DOI: 10.1093/bioinformatics/btl327

[4] A. Toumadje, S. W. Alcorn, W. C. Johnson, “Extending CD spectra of proteins to 168 nm improves the analysis for secondary structures”, Analytical Biochemistry, vol 200, pp. 321–331, 1992. DOI: 10.1016/0003-2697(92)90473-K.

CONTACT & STAFF

Coordination: Juliana S. Yoneda
Tel.: +55 19 3512 1045
E-mail: juliana.yoneda@lnls.br

Click here  for more information on this Facility team.

EXPERIMENTAL TECHNIQUES

The CEDRO beamline will be initially comprised by a station to perform the “conventional” SRCD experiments. Sample holders for liquid samples with temperature control will be available. The construction of a sample holder with humidity control and rotation stage is also planned for measurements in solid phase (dehydrated films) for oriented CD experiments, for example. In addition, microfluidic devices will be developed in the future envisaging kinetic studies.

LAYOUT & OPTICAL ELEMENTS

Element Type Position [m] Description
Source Dipole (BM) B2
M1 Plane mirror 90º 1.2 Radiation extraction
SW Sapphire window (Al2O3) 1.62 Ultra-vacuum environment isolation
M2 Cylindrical mirror 4.5 Mirror Si
M3 Cylindrical mirror 4.9 Mirror Si
FW Calcium fluoride window (CaF2) 6.0 Separation of the vacuum and the N2 purged region

PARAMETERS

Parameter Value Condition
Energy range 3 – 9 eV UV-VUV
Resolution 0.5 nm Estimated
Beam size ~ 4 x 2 mm2 Variable to control the flux density, avoiding sample degradation
Photon flux ~ 1010 – 1011 photons . s-1 Estimated
Flux density Variable with the beam size on the sample