3.2. Structural Dynamics of Hydrogen Bonding
Table 1 compares averaged calculated geometrical parameters of the
radicals in aqueous solution and in gas phase. The listing in the table
demonstrates substantial changes in bond lengths and angles upon
transferring from the gas to the solution phase. In Table 2, the
magnetic moments (MM) of the, and radicals in gas phase and solution
phase are compared. Because of combination of hydrogen bonds associated
with the polar -NH2, -NH3 and -COO(H)
groups, solvent configuration around the radical and leads to the
changes of the geometry.
<Table 1 >
<Table 2 >
A good descriptor of the hydrogen bonded structure with water molecules
around a solute is the radial distribution function (RDF) of the
hydrogen bonds around the O1 and O2oxygens displayed graphically in Fig. 3 while the average numbers of the
hydrogen bonds with water molecules are listed in Table 3. The listings
in the table suggest that , and radicals have approximately similar
number of hydrogen bonds around the carboxyl group and that the number
of hydrogen bonds around the amino group forradical is more than that
around the and radicals.
The average observed number of water molecules in the first hydration
shell for , and radicals are 6.21, 6.96 and 5.92, respectively. The
solvation structure for and radicals shows that O1 and
O2 oxygens have hydrogen bonds of approximately the same
strength centered at 1.74 Å and 1.62 Å for the radical and at 1.65 Å and
1.74 Å for radical, respectively. However, the solvation structure for
the radical shows that O1 oxygen has a stronger hydrogen
bond than O2 oxygen, centered, respectively, at 1.86 Å
and 4.38 Å.
<Table 3 >
<Fig. 3 >