ISMSC 2007 - Università degli Studi di Pavia

PSB 67
Cooperative Complexation of -Cyclodextrin with Micelle-like Aggregates
Formed from Amphiphilic Polyanions
Daisuke Taura, Akihito Hashidzume, and Akira Harada
Department of Macromolecular Science, Graduate School of Science, Osaka University,
Toyonaka, Osaka 560-0043, Japan
Molecular recognition in biological
systems often exhibits high selectivity to
form precisely controlled supramolecular
structures, which express various
functions necessary for maintaining living
activities. We have been aware of the
importance of macromolecular chains in
the biological molecular recognition for
the past decade, and thus studying the
interaction of cyclodextrins (CDs) with
hydrophobic side chains attached to
water soluble polymers (WSPs). The
previous studies focused on the
interaction of CDs with WSPs modified
with a small amount of hydrophobes, whereas this study focuses on the interaction of CDs with
WSPs bearing a number of hydrophobes to investigate the effect of competition with
self-association of hydrophobes. In this study, we employed alternating copolymers of sodium
maleate and dodecyl vinyl ether with different molecular weights (pC12MAn, Figure 1).
Steady state fluorescence and sedimentation equilibrium measurements confirmed that
pC12MAn formed micelle-like aggregates in aqueous media. The interaction of -, -, and -CDs
with pC12MAn was investigated by several NMR techniques. These spectra indicated that only
-CD interacted significantly with dodecyl (C12) groups in pC12MAn. Then, the complexation
equilibrium between -CD with pC12MAn was explored by 1 H NMR spectra measured in the
presence of varying concentrations of -CD. These spectra exhibit resonance bands due to free
and complexed C12 groups separately at intermediate -CD concentrations, indicating slow
exchange between the free and complexed states comparing with the NMR time scale. Using the
concentrations of free and complexed C12 groups, the concentrations of free and complexed
-CD (CCD,f and CCD,c, respectively) were calculated. Values of CCD,c were plotted against CCD,f to
prepare binding isotherms. The binding isotherms exhibit sigmoidal curves, indicative of
cooperative complexation of -CD with pC12MAn. Figure 1 shows a conceptual illustration for the
cooperative complexation of -CD with pC12MAn. The binding isotherms were analyzed using a
model based on one dimensional lattice model although it may not be a proper model. The
analysis indicated that -CD interacted more cooperatively with pC12MAn of a higher molecular
weight.
Dissociation Kinetics of Tl + , Pb 2+ , Cd 2+ , and Bi 3+ Cryptates
Gary. L. N. Smith, Olajumoke O. Oluwu, Baige Bian, Richard W. Taylor
Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval,
Norman, OK 73019, USA
Cryptands form stable complexes with heavy metal ions such as Tl + , Pb 2+ , Cd 2+ , and Bi 3+ .
Structural factors that affect the complexation selectivity include: i) cavity size, ii) type of donor
atoms (O, N, S), and iii) backbone substituents (benzo, cyclohexano). We have studied the
dissociation kinetics for the compounds shown below to examine the role of these structural
factors. In the presence of excess strong acid the observed rate constant, kobs, shows several
types of [H + ] dependence. For most cryptates studied, a linear dependence on [H + ] is observed
(kobs = kd + kH [H + ]), where kd and kH are the rate constants for the acid-independent and aciddependent
pathways, respectively. However, the dissociation of Tl(2.2.2) + shows saturation
type behavior (kobs = (kd + kH [H + ])/(1 + k’[H + ]). For complexes with polyaza-cryptands such as
Pb(2N.2.2) 2+ and Bi(2N.2N.2N) 3+ pathways indicating higher-order [H + ] dependence are observed
(kobs = (kd + kH1 [H + ] + kH2[H + ] 2 ). The role of various structural factors on the dissociation
kinetics and the detailed mechanisms consistent with [H + ] dependence of kobs are discussed.
O
N O O N
O O
N O O N
a
a = 1; 2.2.1
a = 2; 2.2.2
a = 3; 3.2.2
R
O O
O O
R
R = C 6H 4 ; 2 B.2 B.2
R = C 6H 10 ; 2 C.2 C.2
X X
N O O N
O O
X = O; 2.2.2
X = S; 2 S.2.2
X = N; 2 N.2.2
NH HN
H
N N N
H N
NH HN
2 N.2 N.2 N
O O
N O O N
O O
An2.2.2
N N
N O O N
O O
2.2.2 BIPY
PSB 68