Carbon-13 Nuclear Magnetic Relaxation in Macromolecules with Side Chains Undergoing Multiple Internal Rotations. Effects of the Distribution of Correlation Times and Overall Anisotropic Motion

Tsutsumi, Atsushi; Chachaty, C.

doi:10.1021/ma60069a017

Cited by 22 publications

(5 citation statements)

References 17 publications

(38 reference statements)

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“…For DP = 140, l = 3.77 Á (length of the monomer unit), and K = 1.324 one finds (fiG2)1/2 = 50.8 Á. For a rigid spherical structure at 20 °C in aqueous solution, one should have indeed rR = 1.3 X 10"7 s instead of the observed value of 5 X 10"10 s.…”

Section: Resultsmentioning

confidence: 85%

“…The populations of the sites are given by PI = 1/(2u + 1) P2 = P3 = u / ( 2 u + 1) (20) with u = W,/ W2; W3 has only an influence on the effective correlation times governing the relaxation of side-chain nuclei. The expressions of the spectral densities intervening in eq 9 and 10, which depend also on the distribution of correlation times TR, may be found in ref 20.…”

Section: Resultsmentioning

confidence: 99%

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NMR and ESR study of the conformations and dynamical properties of poly(L-lysine) in aqueous solutions

Perly¹,

Chevalier²,

Chachaty³

1981

Macromolecules

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values of ui '+I and li,+l were kept at 3.8 A, and those for d,j+2, dij+3, and dij+, were adjusted by the triangle inequality. In general, the Values ofuij and lij for small lijl have little effect in constraining the conformation of the whole protein.(40) A cutoff distance of 10 A for both the "contact" and "noncontact" distances means that ui, = 10 A and li. = 5 A if d*, < 10 A, and uij = 40 A and I, = 10 A if dei, > 16 A. The triangle inequalities (6) are then applied to every set of three points to modify all of the uiis and lij's, except ~i , i +~ and li,+l, which are then used to calculate H.(44) Richmond, T.ABSTRACT The conformations and dynamical behavior of poly@-lysine) (PLL) in aqueous solutions have been investigated by 'H and NMR as well as by ESR on the end-chain spin-labeled polymer. The ESR allowed the motion of the macromolecular chain to be studied up to pH 13, showing that the random coil a-helix transition a t pH 11 gives rise to a twofold increase in the correlation time, with evidence of an anisotropic reorientation. In the random coil state a t pH 7, where the segmental motion of the backbone is quasi-isotropic, the correlation time given by ESR is compared to that obtained by the relaxation of the methyl protons of the reduced Tempo radical residue and of the a carbons. The different methods yield an activation energy of 6.5 kcal mol-' for this motion whereas the frequency dependence of the C, relaxation may be interpreted by a Cole-Cole distribution of correlation times with a width parameter y = 0.7. The rotational isomerism and temperature dependences of interconversion rates of the aminobutyl side chains have been analyzed from the proton vicinal couplings and the 13C and 'H relaxation a t different frequencies, assuming that the methylene groups undergo 120' jumps among three sites, two of them being equiprobable.These two kinds of information concur to show that the PLL side chains are less flexible than a hydrocarbon chain of same length, possibly because of the hydration of the NH3+ terminal group.

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Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

NMR and ESR study of the conformations and dynamical properties of poly(L-lysine) in aqueous solutions

Perly¹,

Chevalier²,

Chachaty³

1981

Macromolecules

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“…Empirical rules have been developed to fit the relaxation data to the molecular tumbling time combined with internal segmental motions.6"8 Alternatively, the experimental results have been interpreted in terms of analytically tractable descriptions of the dynamics based on continuous diffusion,9,24 restricted diffusion,25"28 and lattice jump models. 24,26,29,30 While it is usually possible to fit the experimental results in this way, the data in themselves generally are not sufficient to determine by computer-generated trajectories that make use of realistic potentials to simulate the motion of the system of interest. From such trajectories, the time-dependent correlation functions can be determined and Th T2, and can be calculated.…”

Section: Introductionmentioning

confidence: 99%

NMR relaxation parameters in molecules with internal motion: exact Langevin trajectory results compared with simplified relaxation models

Levy¹,

Karplus²,

Wolynes³

1981

J. Am. Chem. Soc.

111

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The interpretation of NMR relaxation experiments on flexible molecules is explored by use of stochastic dynamics trajectories. The effect of internal motion on the relaxation parameters ( ,, T2, and NOE) of simple alkanes and of aliphatic side chains of proteins is determined. The correlation functions and spectral densities required for the evaluation of 13C NMR relaxation times are evaluated from trajectories lasting up to 100 ns and the results are compared with the predictions of simplified analytical models for the motion. It is shown that for small molecules tumbling in the motional narrowing limit it is possible to approximately separate the NMR relaxation into contributions from tumbling and internal motions. For butane and heptane in aqueous solution, the spin-lattice relaxation times ( ]) are predicted and the gradient in relaxation times along the heptane chain is found to be close to that observed in the pure liquid. Detailed trajectory results are presented for 13C relaxation of an alkane side chain on macromolecules. Wigner functions are used to express the side chain relaxation with respect to the coordinate frame embedded in the macromolecule. Uncoupling the motions about the individual side chain internal rotation axes or introduction of the independent lattice jump model for the motion is shown to describe incorrectly the short-time and long-time relaxation behavior. Nevertheless, for short side chains with barriers to rotation on the order of 3 kcal/mol, both models provide a good approximation for the ,3C NMR relaxation. This suggests that the models can be used for the interpretation of NMR experiments on lipids and aliphatic amino acid side chains protruding into solution, although errors are expected when the motion of the chain under consideration is constrained by the rest of the system.

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“…The latter are proportional to the spherical harmonics of order 2. For later convenience we define = m ( $ ) y 2 m ( e , 9) (5) 8, 9 being the orientational angles of the vector joining the two nuclei with respect to the laboratory coordinate frame. These angles are, of course, time dependent.…”

Section: Theorymentioning

confidence: 99%

Simple model for NMR relaxation times of flexible molecules in solution

Baldo

Grassi²

1989

Magnetic Reson in Chemistry

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The motion of a flexible molecule in solution can be described as a Brownian motion between the different conformations that the molecule can assume. Each conformation corresponds to a local minimum of the energy surface.A simple model is given for this type of motion in relation to nuclear magnetic resonance (NMR) relaxation measurements. This is based only on the assumption that the diffusion tensor for the overall tumbling is not appreciably affected by jumping between the different conformations. The limits of the model are discussed and an illustrative application to 2-fluorobutane is given.

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Carbon-13 Nuclear Magnetic Relaxation in Macromolecules with Side Chains Undergoing Multiple Internal Rotations. Effects of the Distribution of Correlation Times and Overall Anisotropic Motion

Cited by 22 publications

References 17 publications

NMR and ESR study of the conformations and dynamical properties of poly(L-lysine) in aqueous solutions

NMR and ESR study of the conformations and dynamical properties of poly(L-lysine) in aqueous solutions

NMR relaxation parameters in molecules with internal motion: exact Langevin trajectory results compared with simplified relaxation models

Simple model for NMR relaxation times of flexible molecules in solution

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