Accurate determination of frequency dependent cross-relaxation terms in homonuclear and heteronuclear two spin-1/2 systems

Abstract

One-dimensional N.M.R. methods are proposed for accurately determining homo-and heteronuclear longitudinal cross-relaxation terms. These sequences employ exclusively hard pulses and do not require critical adjustments of the instrument even in the case of selective perturbation (inversion) of one magnetization in a homonuclear two-spin system. Emphasis is put on the initial conditions which prevail at the beginning of the relaxation interval; they are determined by means of adequate experimental or numerical procedures. An algorithm, based on analytical solutions of Solomon equations, is described; it allows to analyse as many sets of data as desired for arbitrary initial conditions. These methods have been applied to the tH-1H spin system of ortho protons in an aromatic ring, which bears in para positions the polar head and the aliphatic chain of benzene-sulphonate surfactants. Proton homonuclear crossrelaxation parameters are complemented by heteronuclear carbon-proton parameters and classical carbon-13 longitudinal relaxation rates. Measurements have been performed at several frequencies and allow to delineate dynamical features of two surfactants which differ by their alkyl chains. Results are discussed in terms of slow and fast local motions, and of order parameters relative to the benzenic ring.

From monomers to micelles: investigation of the parameters influencing proton relaxivity

“…The global correlation times increase continuously with increasing chain length within the series. Their order of magnitude corresponds well to s g values previously published for sulphonate surfactants with similar-size aliphatic side chains [41]. This parameter is directly linked to the overall mass of the micelles; thus, the augmentation of s g observed here would indicate an increase in the micelle size with the chain length.…”

The Impact of Rigidity and Water Exchange on the Relaxivity of a Dendritic MRI Contrast Agent

“…As previously for other macromolecular systems,2, 26 we applied the spectral density functions of the Lipari–Szabó model for the analysis of both 17 O and 1 H longitudinal relaxation data. This model has been already used to analyse nuclear magnetic resonance relaxation data in terms of rotational dynamics for solutions of proteins,27–28 peptides,29 sugars,30–31 micellised surfactants32 and calixarenes 33. In this approach, the modulation of the interaction causing the relaxation is considered as the result of two statistically independent motions; a rapid local motion, which is in the extreme narrowing conditions, with a correlation time τ l , and a slower global motion of the whole molecule with a correlation time τ g .…”

Gd(DTPA-bisamide)alkyl Copolymers: A Hint for the Formation of MRI Contrast Agents with Very High Relaxivity

“…The model-free Lipari ± Szabo treatment has already proved to be efficient for micellized surfactant solutions. [21] The longitudinal 17 O relaxation rates of [Gd(DTPA À BA)À(CH 2 ) 10 ] x and [Gd(DTPAÀBA)À(CH 2 ) 12 ] x measured at four different temperatures and five different magnetic fields between 0.572 and 14.1 T are shown in Figure 5. The data were fitted separately for each temperature to Equations (3) ± (11), by fixing the water exchange rate and the electronic relaxation parameters, as obtained from the simultaneous fit of transverse 17 O relaxation rates, chemical shifts, and EPR data, and adjusting t g , t l , and S 2 .…”

“…The model-free approach developed by Lipari and Szabo [17] has become a widely used method for evaluation of relaxation data for polysaccharides, [18,19] proteins, [20] micellized surfactants, [21] or calixarenes. [22] In this model two kinds of motion are assumed to modulate the interaction causing the relaxation: a rapid local motion, which lies in the extreme narrowing limit, and a slower global motion.…”