Molecular mobility of lyophilized poly(vinylpyrrolidone) and methyl cellulose as determined by the laboratory and rotating frame spin-lattice relaxation time of 1H and 13C
Laboratory-
and rotating- frame spin-lattice relaxation times (T1 and T1r)
of 1H and 13C in lyophilized poly(vinylpyrrolidone) (PVP)
and methylcellulose (MC) are determined to examine feasibility of using T1
and T1r
as a measure of molecular motions on large timescales related to the storage
stability of lyophilized formulations.
The T1r
of proton and carbon was found to reflect the mobility of PVP and MC backbones,
indicating that it is useful as a measure of large-time-scale molecular motions.
In contrast to the T1r,
the T1 of proton measured in the same temperature range reflected the
mobility of PVP and MC side chains.
The T1 of proton may be useful as a measure of local molecular
motions on a smaller-time-scale, although the measurement is interfered by
moisture under some conditions.
The temperature dependence of T1 and T1r
indicated that methylene in the MC molecule had much higher mobility than that
in the dextran molecule, also indicated that methylene in the PVP side chain had
a higher mobility than that in the MC side chain.