ChemComm
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(
(
Fig. S6b, ESI†). L2-NO reduced OH generation by ca. 50%
L2-b, ca. 70%) in comparison to compound-free samples. Both
studies demonstrate that L2-NO can scavenge ROS and regulate
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its formation. Lastly, L2-NO, as for L2-b, was predicted to be
BBB permeable by calculated values (i.e., logBB = 0.007) and
experimental data (Àlog P = 4.50 (Æ0.06), obtained by a parallel
e
artificial membrane permeability assay) (Table S1, ESI†).
A small molecule with structural moieties for metal chelation
and Ab interaction was designed using coordination chemistry
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principles to target and react with Cu(II)–Ab over Zn(II)–Ab. The
design concept was validated by various biochemical and physical
studies, which demonstrated that L2-NO modulated Ab aggre-
gation triggered by Cu(II) over Zn(II). Ab interaction with L2-NO
was confirmed by 2D SOFAST-HMQC NMR and ITC. In addition,
L2-NO could control oxidative stress as a potent antioxidant and
regulator of ROS production. Taken together, our present studies
demonstrate the feasibility of constructing a small molecule capable
of specific reactivity against redox active metal–Ab. This work will be
a stepping-stone in the preparation of a toolkit of bifunctional small
molecules for elucidating the role of metal–Ab species in AD.
The authors declare no competing financial interest.
This study was supported by the Ruth K. Broad Biomedical
Foundation, American Heart Association, Alfred P. Sloan Founda-
tion, NSF (CHE-1253155), and the 2013 Research Fund (Project
Number 1.130068.01) of Ulsan National Institute of Science and
Technology (to M.H.L.), and NIH (GM095640 to A.R.). We thank
Akiko Kochi, Younwoo Nam, & Dr. Janarthanan Krishnamoorthy
for experimental assistance.
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Fig. 3 SOFAST-HMQC NMR (900 MHz) spectra of uniformly- N-labeled
Ab40 with L2-NO ((a) blue and red, 0 and 10 equiv., respectively). Reso-
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nances of Ab40 were assigned as reported previously. (b) Expanded
spectra of the boxed green area of (a). (c) Normalized chemical shifts of
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H and amide N atoms for all Ab40 residues (see ESI† for details). Two
horizontal lines represent the average chemical shift (dashed line) plus one
standard deviation (dotted line). * Residues could not be resolved for
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analysis ( no chemical shift was observed).
Notes and references
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Fig. 4 Metal selectivity of L2-NO for Cu(II) over (a) 1 equiv. and (b) 25 equiv.
of divalent metal ions, expressed as a ratio of A
purple) and following (grey) Cu(II) addition. Lanes: 1, Mg(II); 2, Ca(II); 3, Mn(II);
, Fe(II); 5, Co(II); 6, Ni(II); 7, Zn(II); 8, Cu(II). A /ACu E 1 after Cu(II) addition
M
/ACu at 435 nm, prior to
(
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observed (Fig. S5a and c, ESI†). Subsequent addition of 1 equiv.
Cu(II) produced a spectrum indiscernible to L2-NO only treated
with Cu(II), implying relative selectivity of L2-NO for Cu(II)
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A. S. DeToma, B. T. Ruotolo and M. H. Lim, Inorg. Chem., 2012, 51,
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2959–12967; (b) Y. Liu, A. Kochi, A. S. Pithadia, S. Lee, Y. Nam,
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Fe(II)-treated L2-NO did not revert the spectrum fully to Cu(II)– 11 H. Irving and R. J. P. Williams, J. Chem. Soc., 1953, 3192–3210.
(Fig. 4, Fig. S4b and d, ESI†). The spectrum of L2-NO with
Fe(II) was unaltered; however, subsequent Cu(II) addition to
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1
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4 L2-NO is susceptible to oxidation by redox-active metals in protic
solvents (Fig. S4a and b, ESI†); thus, metal binding was studied in
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CH CN.
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L2-NO suggesting that Fe(II) interacts with L2-NO (Fig. 4, Fig. S4e
and f, ESI†). Overall, L2-NO is relatively selective for Cu(II) over
most divalent metal ions, with the exception of Fe(II).
The trolox equivalent antioxidant capacity (TEAC) of L2-NO is
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.2 (Æ0.2) (for L2-b, 2.4 (Æ0.2)), compared to 1.0 (Æ0.1) for trolox
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(a known antioxidant vitamin E analogue) (Fig. S6a, ESI†). The
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antioxidant ability of L2-NO was pH dependent (Fig. S6a, ESI†).
In addition, L2-NO could control Cu(I/II)-triggered hydroxyl radical
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(
OH) production, as confirmed by a 2-deoxyribose assay
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