Molecular dynamics simulation of spin–lattice NMR relaxation in poly-l-lysine dendrimers: manifestation of the semiflexibility effect

Abstract

NMR relaxation experiments are widely used to investigate the local orientation mobility in dendrimers. In particular, the NMR method allows one to measure the spin-lattice relaxation rate, 1/T1, which is connected with the orientational autocorrelation function (ACF) of NMR active groups. We calculate the temperature (Θ) and frequency (ω) dependences of the spin-lattice NMR relaxation rates for segments and NMR active CH2 groups in poly-L-lysine (PLL) dendrimers in water, on the basis of full-atomic molecular dynamics simulations. It is shown that the position of the maximum of 1/T1(ω) depends on the location of the segments inside the dendrimer. This dependence of the maximum is explained by the restricted flexibility of the dendrimer. Such behavior has been predicted recently by the analytical theory based on the semiflexible viscoelastic model. The simulated temperature dependences of 1/T1 for terminal and inner groups in PLL dendrimers of n = 2 and n = 4 generations dissolved in water are in good agreement with the NMR experimental data, which have been obtained for these systems previously by us. It is shown that in the case of PLL dendrimers, the traditional procedure of the interpretation of NMR experimental data - when smaller values of 1/T1 correspond to higher orientation mobility - is applicable to the whole accessible frequency interval only for the terminal groups. For the inner groups, this procedure is valid only at low frequencies.

Local NMR Relaxation of Dendrimers in the Presence of Hydrodynamic Interactions

“…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.…”

Molecular dynamics simulation of lysine dendrimer and semax peptides interaction

“…Потенциальная энергия в этом силовом поле состоит из энергий деформации валентных связей и углов, углов внутреннего враще-ния, ван-дер-ваальсовых и электростатических взаимодействий. Процедура моделирования подробно описана в работах [11][12][13][14][15][16]. Во всех расчетах были выбраны следующие условия: температура 300 К, дав-ление 1 атм, растворитель: вода, содержащая противоионы Cl -для компенсации избыточного заряда сис-темы дендример-пептиды.…”

Relaxation Dynamics of Semiflexible Fractal Macromolecules

“…However, the GGS model does not include the excluded volume and dynamics is achieved by introducing local semiflexibility in the GGS model, which turned out to be 36 very important for dendritic structures [28,29]. Semiflexibility was first introduced to the dynamics 37 of discrete chains by Bixon and Zwanzig [30], later it was included to the description of other 38 macromolecular architectures [31][32][33][34][35][36][37][38][39][40][41]. This work employs the framework of semiflexible treelike 39 polymers (STP) [34] which allows to study arbitrary treelike architectures and to obtain many results 40 in closed form.…”

“…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].…”

“…The number of independent variables F(n), Equation (30), in combination with the degeneracy D n (G) for the corresponding group, Equation (34), gives the total number of eigenmodes N :…”