jp9b11948_si_001.pdf (2.1 MB)
Dynamics in Amine-Functionalized Mesoporous Hybrid Materials Probed through Deuterium Magic Angle Spinning NMR and Molecular Dynamic Simulations
journal contribution
posted on 2020-03-06, 20:13 authored by V. S. Veena, I. Kavya, A. Lazar, C. P. Vinod, T. G. Ajithkumar, S. JayanthiWe
present a deuterium magic angle spinning (MAS) NMR study on
two widely used hybrid materials (3-glycidyloxy propyl)trimethoxysilane
(3-GPTMS) and 3-(trimethoxysilyl)propyl methacrylate (3-MATMS) grafted
on SBA-15. Methylene-deuterated diamine as a pendent group is anchored
to GPTMS (O3Si-CH2–CH2–CH2–O–CH2–CH(OH)- CH2–NH-CD2-CD2-NH2) and MATMS (O3Si-CH2–CH2–CH2–O-C(N-CD2-CD2-NH2)-C(CH3)CH2) postgrafting.
Proton and deuterium solid state NMR experiments under MAS were performed
at two hydration levels and temperatures ranging from 253 to 315 K.
Deuterium spectra were deconvoluted into three components with different
average quadrupolar parameters: a relatively rigid component arising
from local or librational motion of C–2H2 corresponding to “small angle” jumps, an intermediate
dynamic component, and a large amplitude dynamic component. Population
ratios of rigid versus dynamic components show that diamine-MATMS
is more rigid when compared with diamine-GPTMS at high hydration.
The role of the length of the linkers, steric hindrance, grafting
concentration, etc. in defining mobility is investigated. Finally,
by correlating proton and deuterium MAS NMR spectral analysis, the
role of a few water molecules in inducing dynamics of the linkers
was investigated. Molecular dynamic (MD) simulations support the experimental
analysis. MD simulations indicate different types of mobility arising
from the same molecular binding configuration of diamine-MATMS. Dynamics
induced by a few hydroxyls on the pore surface accessible to the linker,
various molecular conformations, and stabilization of the linker through
hydrogen bonding with the surface, derived from MD simulations, are
discussed.