1,721,068 research outputs found
The solution conformation and dynamics of biomolecules in the presence of internal motions: The use of jump models for the 1H NMR analysis of relaxation data
No full textA jump model has been used to obtain motional information from proton relaxation parameters in complex molecular systems in which multiple internal motions are present. The proposed analysis takes into account changes in orientation and magnitude of interproton vectors, due to overall and internal motions. Intrinsic relaxation contributions can be calculated if the probability for each spatial configuration is independently known. From these contributions jump frequencies may be evaluated, yielding information on local molecular mobility. © 1982 Società Italiana di Fisica
Internal motions of aromatic amino acid side chains. Selective excitation nuclear relaxation and scalar coupling constant analysis on a model system
No full textThe model compound N-acetyl-L-phenylalanine methyl ester was used to investigate the motional behavior of aromatic amino acid residues in peptides and proteins. A combined analysis of proton scalar coupling constants and selective excitation spin-lattice relaxation rates yields a self-consistent insight into (i) relaxation mechanisms, (ii) overall molecular motion, and (iii) local mobilities along the side chain. At the operative frequency of 270 MHz, the amino acid derivative tumbling fulfilled the condition ωo2τc2 ≪1. The proton relaxation pathway was dominated by the intramolecular dipole-dipole relaxation mechanism. Extensive internal motions of the side chain were found. © 1979 American Chemical Society
The Measurement of Direct H-1-c-13 Dipolar Relaxation Terms From Proton Spin-lattice Relaxation Experiments
No full textThe possibility of determining the direct proton-carbon relaxation term, ρ{variant}CH, as the difference between the spin-lattice relaxation rate of proton nuclei and their satellite signals is investigated. Comparison of the ρ{variant}CH values obtained from carbon and proton relaxation measurements in a 0.5 mol dm-3 purine solution confirms the reliability of the proposed method. The existence in bio-organic molecules of proton nuclei with different relaxation pathways depending on the magnetic properties of the vicinal carbon is demonstrated. © 1987
Measuring the dynamic surface accessibility of RNA with the small paramagnetic molecule TEMPOL
No full textThe surface accessibility of macromolecules plays a key role in modulating molecular recognition events. RNA is a complex and dynamic molecule involved in many aspects of gene expression. However, there are few experimental methods available to measure the accessible surface of RNA. Here, we investigate the accessible surface of RNA using NMR and the small paramagnetic molecule TEMPOL. We investigated two RNAs with known structures, one that is extremely stable and one that is dynamic. For helical regions, the TEMPOL probing data correlate well with the predicted RNA surface, and the method is able to distinguish subtle variations in atom depths, such as the relative accessibility of pyrimidine versus purine aromatic carbon atoms. Dynamic motions are also detected by TEMPOL probing, and the method accurately reports a previously characterized pH-dependent conformational transition involving formation of a protonated CA pair and base flipping. Some loop regions are observed to exhibit anomalously high accessibility, reflective of motions that are not evident within the ensemble of NMR structures. We conclude that TEMPOL probing can provide valuable insights into the surface accessibility and dynamics of RNA, and can also be used as an independent means of validating RNA structure and dynamics in solution
NMR and Biomolecular Structure
No full textAnalysis of bimolecular structures and dynamic processes.
conformational analysis of proteins by means of 2 and 3D NMR experiment
13C spin-lattice relaxation study of some amino-acid, their phospho-derivatives and some small peptides
No full textCarbon C-13 spin-lattice relaxation times, T1, of Serine, Threonine, Phospho-serine and Phosphothreonine have been measured in D2O at neutral pD. Changes in over-all motions under phosphorylation has been detected. Segmental motions are not affected by phosphorylation. With the aid of T1(C-13) values of other amino acids an empirical relationship between NT1 and molecular weights (Mw) is tested that seems valid also for small peptides. Such relationship allows to interpret results from T1 measurements with the aid of a simple spherical model. © 1984, Taylor & Francis Group, LLC. All rights reserved
Manganese(II) as magnetic relaxation probe in the study of biomechanisms and of biomacromolecules
No full textMolecular structures of iron-nitrosyl complexes on the basis of EPR and NMR spectra
No full textIsotopic substitution with 15N and computer simulation have been used in elucidating the hyperfine structure of the EPR spectra of iron-dinitrosyl complexes in solution. Additional information for the identification of the binding sites and of the molecular structures of the complexes have been obtained from 1H and 13C Fourier transform NMR spectra. Carbazides, thiocarbazides, amino acids, and other amino derivatives have been taken into consideration as ligands for the Fe(NO)2 group
The sudden character of the sudden polarization effect
No full textThe evolution of the suggested sudden polarization parameter in excited singlet states in one-end pyramidalized ethylene, propylene and butadiene during geometrical relaxation of the double bond was investigated. As the sudden polarization parameter decreases the energy gap grows between the corresponding excited polar states. © 1984
Cross relaxation effects on the longitudinal relaxation rate of water in protein solutions
No full textNon-selective and selective longitudinal relaxation rates were measured for water protons in protein solutions. The perturbations on water spin-lattice relaxation from cross relaxation between water and protein protons were shown to be significant at low temperature and small isotopic dilution. © 1981
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