Chemistry Reference
In-Depth Information
of polyethylenimine with Cu(
I
)(
2
)
2
, two molecules of
2
preassembled by Cu(
I
) ion were
cross-linked with polyethylenimine to obtain [Cu
I
Phen
2
]
PA
PEI (Eq. 4). By the reaction
of
2
with polyethylenimine in the absence of Cu(
I
) ion, phenanthroline moieties were
attached randomly to polyethylenimine to obtain [Phen]
Ran
PEI, and then the primary
and secondary amino groups of polyethylenimine were acetylated to obtain [Phen]
Ra-
n
AcPEI.
ð
4
Þ
The two preassembled phenanthrolines cross-linked by PEI would remain in close
proximity when the conformational freedom of the resulting two macrocycles is suffi-
ciently suppressed. If the two phenanthroline moieties are very close, they will affect
the protonation of each other considerably. For [Phen]
Ran
PEI and [Phen]
Ran
AcPEI, the
phenanthroline moieties attached randomly to the polymer behaved as monobasic spe-
cies (Eq. 5) with a pK
a
of 1.2. For [Phen
2
]
PA
PEI or [Phen
2
]
PA
AcPEI, the pair of phenan-
throlines originally preassembled by Cu(
I
) behaved as one ionizing unit (Eq. 6) with
two pK
a
s of ca. 1.3 and ca. 10.8. The pK
a2
of [Phen
2
]
PA
PEI or [Phen
2
]
PA
AcPEI is greater
by ca. 9.5 pK
a
units than the corresponding pK
a1
. This pK
a
difference is attributable to
destabilization of the diprotonated form of Eq. (6) by electrostatic interaction between
the two cationic sites and stabilization of the corresponding monoprotonated form by
hydrogen bonding between two phenanthroline moieties. Both these interactions ori-
ginate from the close proximity of the two preassembled phenanthrolines.
ð
5
Þ
