title: Spectral density mapping at multiple magnetic fields suitable for (13)C NMR relaxation studies.
abstract: Standard spectral density mapping protocols, well suited for the analysis of (15)N relaxation rates, introduce significant systematic errors when applied to (13)C relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and (13)C frequencies can be obtained from data acquired at three magnetic fields for uniformly (13)C-labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions.
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Institute of Biophysics of Academy of Sciences of the Czech Republic, Královopolská 135, CZ-612 65 Brno, Czech Republic. Electronic address: kada@chemi.muni.cz.
authors.forename: Pavel
authors.initials: P
authors.lastname: Kadeřávek
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: vojtis@mail.muni.cz.
authors.forename: Vojtěch
authors.initials: V
authors.lastname: Zapletal
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: fiala@chemi.muni.cz.
authors.forename: Radovan
authors.initials: R
authors.lastname: Fiala
authors.affiliation: Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: pavel.srb@gmail.com.
authors.forename: Pavel
authors.initials: P
authors.lastname: Srb
authors.affiliation: Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: padrta@chemi.muni.cz.
authors.forename: Petr
authors.initials: P
authors.lastname: Padrta
authors.affiliation: Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: j.precechtelova@gmail.com.
authors.forename: Jana Pavlíková
authors.initials: JP
authors.lastname: Přecechtělová
authors.affiliation: Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, CZ-180 00 Prague, Czech Republic. Electronic address: maria.soltesova@gmail.com.
authors.forename: Mária
authors.initials: M
authors.lastname: Šoltésová
authors.affiliation: Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden. Electronic address: jozef.kowalewski@mmk.su.se.
authors.forename: Jozef
authors.initials: J
authors.lastname: Kowalewski
authors.affiliation: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden. Electronic address: gw@organ.su.se.
authors.forename: Göran
authors.initials: G
authors.lastname: Widmalm
authors.affiliation: Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, CZ-142 00 Prague 4 - Krč, Czech Republic. Electronic address: chmelik@biomed.cas.cz.
authors.forename: Josef
authors.initials: J
authors.lastname: Chmelík
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: sklenar@chemi.muni.cz.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Sklenář
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic; Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic. Electronic address: lzidek@chemi.muni.cz.
authors.forename: Lukáš
authors.initials: L
authors.lastname: Žídek
mesh_terms: D000465:Algorithms; D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000379:methods*; D003627:Data Interpretation, Statistical; D060526:Magnetic Fields; D034741:RNA, Small Interfering / Q000032:analysis* / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
chemical_list: D034741:RNA, Small Interfering
keywords: Carbohydrates; Magnetic field; Nuclear magnetic resonance; Nucleic acids; Relaxation; Spectral density function