NMR relaxation of the orientation of single segments in semiflexible dendrimers

Abstract

We study the orientational properties of labeled segments in semiflexible dendrimers making use of the viscoelastic approach of Dolgushev and Blumen [J. Chem. Phys. 131, 044905 (2009)]. We focus on the segmental orientational autocorrelation functions (ACFs), which are fundamental for the frequency-dependent spin-lattice relaxation times T1(ω). We show that semiflexibility leads to an increase of the contribution of large-scale motions to the ACF. This fact influences the position of the maxima of the [1/T1]-functions. Thus, going from outer to inner segments, the maxima shift to lower frequencies. Remarkably, this feature is not obtained in the classical bead-spring model of flexible dendrimers, although many experiments on dendrimers manifest such a behavior.

Local NMR Relaxation of Dendrimers in the Presence of Hydrodynamic Interactions

“…We note that the behavior of M 1 (t) discussed above is in a qualitative agreement with previous theoretical works [17,15,13]. Hence we have shown that the inclusion of HI into the theoretical approach of Ref.…”

“…5. For semiflexible dendrimers, inclusion of HI leads to a shift of the maxima towards higher frequencies in comparison with the corresponding functions obtained in the model [13] that does not include HI. The reason for this tendency corresponds to decrease of τ br m for the system with HI especially for higher m (vide supra).…”

“…For a more detailed investigation of the influence of HI on the spectral density we compare it with that coming from the model without hydrodynamics [13], see Fig. 5.…”

“…Recently, much of attention has been attracted to the local dynamics in dendrimers, both in theory (analytic theory [12,13,14] and computer simulations [15,16,17]) and experiments [18,19,20,21], see also recent review [22]. Especially the NMR relaxation experiments have remarkably advanced this field.…”

Relaxation Dynamics of Semiflexible Fractal Macromolecules

“…However, the GGS model does not include the excluded volume and the restrictions of the bond angles of macromolecules. An improved description of the polymer's dynamics is achieved by introducing local semiflexibility in the GGS model, which turns out to be very important for dendritic structures [29,30]. Semiflexibility was first introduced to the dynamics of discrete chains by Bixon and Zwanzig [31]; later, it was included to the description of other macromolecular architectures [32][33][34][35][36][37][38][39][40][41][42].…”