title: 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.
authors.affiliation: Faculty of Physics, St. Petersburg State University, Ulyanovskaya Str. 1, Petrodvorets, St. Petersburg, 198504 Russia. markeloved@gmail.com.
authors.forename: Denis A
authors.initials: DA
authors.lastname: Markelov
authors.forename: Stanislav G
authors.initials: SG
authors.lastname: Falkovich
authors.forename: Igor M
authors.initials: IM
authors.lastname: Neelov
authors.forename: Maxim Yu
authors.initials: MY
authors.lastname: Ilyash
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Matveev
authors.forename: Erkki
authors.initials: E
authors.lastname: Lähderanta
authors.forename: Petri
authors.initials: P
authors.lastname: Ingman
authors.forename: Anatolii A
authors.initials: AA
authors.lastname: Darinskii
mesh_terms: D050091:Dendrimers / Q000737:chemistry*; D004548:Elasticity; D009682:Magnetic Resonance Spectroscopy; D056004:Molecular Dynamics Simulation; D011107:Polylysine / Q000737:chemistry*; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D050091:Dendrimers; D014867:Water; D011107:Polylysine