Wavelength-Controlled Dynamic Metathesis: A Light-Driven Exchange Reaction between Disulfide and Diselenide Bonds

Article abstract of DOI:10.1002/anie.201810297

Wavelength-controlled dynamic processes are mostly based on light-triggered isomerization or the cleavage/formation of molecular connections. Control over dynamic metathesis reactions by different light wavelengths, which would be useful in controllable dynamic chemistry, has rarely been studied. Taking advantage of the different bond energies of disulfide and diselenide bonds, we have developed a wavelength-driven exchange reaction between disulfides and diselenides, which underwent metathesis under UV light to produce Se?S bonds. When irradiated with visible light, the Se?S bonds were reversed back to those of the original reactants. The conversion of the exchange depends on the wavelength of the incident light. This light-driven metathesis chemistry was also applied to tune the mechanical properties of polymer materials. The visible-light-induced reverse reaction was compatible with reductant-catalyzed disulfide/diselenide metathesis, and could be utilized to develop a dissipative system with light as the energy input.

Full text of DOI:10.1002/anie.201810297

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Wavelength-Controlled Dynamic Metathesis: A Light-Driven
Exchange Reaction Between Disulfide and Diselenide Bonds
Authors: Fuqiang Fan, Shaobo Ji, Chenxing Sun, Cheng Liu, Ying Yu,
Yu Fu, and Huaping Xu
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201810297
Angew. Chem. 10.1002/ange.201810297
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10.1002/anie.201810297
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Wavelength-Controlled Dynamic Metathesis: A Light-Driven
Exchange Reaction Between Disulfide and Diselenide Bonds
Fuqiang Fan‡, Shaobo Ji‡, Chenxing Sun, Cheng Liu, Ying Yu, Yu Fu, and Huaping Xu*
Abstract: Though wavelength-controlled dynamic processes have
been well developed, they mostly consist of light-triggered
isomerization or the cleavage/formation of molecular connections.
Control over dynamic metathesis reactions by different light
spiropyran29
diarylethenes30-33
metathesis, have had a tremendous impact on scientific research
as well as on industrial production34-36. In contrast to isomerization
and
.
photoinduced
Metathesis reactions, especially olefin
π-electrocyclization
of
wavelengths, which would be useful in controllable dynamic chemistry, (from 1 molecule to 1 molecule), metathesis reactions (from 2 to
has rarely been studied. Herein, taking advantage of the different
bond energies of disulfide bonds and diselenide bonds, we realized a
wavelength-driven exchange reaction between disulfides and
diselenides. These molecules underwent metathesis under UV light
to produce Se-S bonds. When irradiated by specific visible light, the
Se-S bonds were reversed to the original reactants. The conversions
of the exchange reaction were found to depend on the wavelength of
light, and the exchange mechanism was studied. This light-driven
metathesis chemistry was also applied to tune mechanical properties
of polymer materials. Furthermore, the visible light-induced reverse
reaction was compatible with reductant catalyzed disulfide/diselenide
metathesis and provides the potential for a dissipative system using
light as the input energy.
2) involve information transformation between different molecules.
Manipulation of the dynamic reaction with different wavelengths
will provide new opportunities for reversible dynamic chemistry
and control over molecular information flow. However, only a few
investigators have studied this process with complex design24, 37
Disulfide bonds and diselenide bonds are both DCBs38-50
.
.
Disulfide (~240 kJ/mol)-containing molecules can exchange with
each other under UV irradiation, which is realized by
photodissociation. The generation of S radicals under different
wavelengths of light, is very important in the photostability of
materials and atmospheric chemistries51,52
.
Diselenide
compounds undergo similar dynamic metathesis reaction. Due to
the lower bond energies (~172 kJ/mol)53, visible light is sufficient
for the exchange of diselenide-containing molecules. Considering
the different wavelengths requirements for these two DCBs, upon
simply mixing, different states can be attained with light of
different wavelengths. The transformations between disulfide,
diselenide and Se-S bonds are key steps in the catalytic cycles of
some enzymes in the human body54, so control over these
transformations is also of significance to understand these
enzymatic processes. Therefore, we studied the wavelength-
controlled metathesis between disulfides and diselenides. As
expected, the reaction showed wavelength dependence (Scheme
1). The exchange between disulfides and diselenides to produce
Se-S bonds proceeded under UV light and reversed under visible
light without any complicated design.
Dynamic covalent bonds (DCBs) are capable of being cleaved or
formed under certain conditions and have been extensively used
in stimuli-responsive systems, dynamic combinatorial chemistry,
and dynamic materials1-6
.
The applications in dynamic
combinatorial chemistry have provided new methods for drug
discovery and simplified the screening of target molecules in
various fields7-10
. Dynamic materials, such as self-healing
polymers and vitrimers, can extend the lifetime of polymer
materials and enhance their recyclability11-13. Thus, DCBs are of
significance at both the molecular level and materials level. The
dynamic properties of DCBs are triggered by various conditions,
such as heating14,15, pH16-18, redox conditions and light19,20
.
Among them, light is an outstanding stimulus to trigger or
control chemical reactions. This stimulus can be introduced at a
distance with high spatial and temporal resolution, which leads to
accurate controllability. The parameters of light are highly
variable—light can be introduced by different sources in various
forms, such as lasers or patterns. In addition, the wavelength,
intensity, and polarization are all tunable. On account of these
advantages, light-controlled reversible/dynamic processes have
also been studied and well established21-24. The commonly used
processes include trans-cis isomerization of azobenzene25-28
,
[*]
F. Fan[‡], Dr. S. Ji[‡], C. Sun, C. Liu, Dr. Y. Yu, Prof. H. Xu
Key Lab of Organic Optoelectronics & Molecular Engineering,
Department of Chemistry, Tsinghua University, Beijing 100084,
China
Scheme 1. Exchange reaction between disulfides and diselenides under light
of different wavelengths.
E-mail: xuhuaping@mail.tsinghua.edu.cn
F. Fan[‡], Prof. Y. Fu
College of Sciences, Northeastern University, Shenyang 110819,
China.
The exchange reaction between di-(1-hydroxylundecyl)
diselenide (DSe1) and diphenyl disulfide (DS1) was tested first
(Figure 1). These compounds were mixed and irradiated by 254
nm UV light, which can trigger the metathesis of both diselenide
bonds and disulfide bonds. Under this condition, the reactants
underwent an exchange reaction, and a product containing a Se-
[‡]
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
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S bond was formed. After exchange, the α-proton of selenium
shifted from 2.91 ppm to 2.94 ppm in 1H NMR (Figure 1d). Similar
to disulfide/diselenide metathesis, the exchange reached a
photostationary state with 50% Se-S, 25% Se-Se and 25% S-S.
77Se NMR spectra also confirmed the exchange reaction. Before
UV irradiation, there was only one peak in the spectrum of the
mixture (Figure 1c). After the exchange reaction, a new peak
belonging to the Se-S bond-containing molecule appeared
(Figure 1e). These results revealed metathesis between
disulfides and diselenides under UV irradiation.
To trigger the reverse reaction, visible light with wavelength
above 410 nm was used to irradiate the exchanged mixture. As
expected, the metathesis was reversed, and the content of Se-S
product dropped to only ~10% after 2 h (Figure 1f, 1g). Under this
condition, disulfide bonds were not fully activated; thus, the
exchange between disulfides and diselenides nearly ceased. On
the other hand, the Se-S and diselenide bonds were still activated
by light above 410 nm, and their dissociation and exchange
reaction continued. Once disulfide was formed, it was kinetically
trapped, resulting in the observed reverse reaction. Another
disulfide with modifiable carboxyl groups, 5,5'-dithiobis-(2-
nitrobenzoic acid) (DS2) was used in the experiment in place of
DS1 (Figure S1). Because of its electron-withdrawing groups, this
disulfide bond can be activated by UV light of higher wavelength.
For the metathesis between DSe1 and DS2, 280-390 nm light was
sufficient. Similar to the former results, Se-S was produced when
the mixture was irradiated by UV light with 50% conversion. Under
visible light above 410 nm, the conversion dropped to ~10%.
These results provided the evidence and foundation for
wavelength-controlled metathesis.
metathesis and visible-light-triggered diselenide metathesis
undergo a similar radical mechanism20. To directly confirm the
radical generation from the diselenide and disulfide compounds,
electron spin resonance (ESR) was used in the presence of a
radical scavenger 5,5-dimethyl-1-pyrroline N-oxide (DMPO)55
(Figure S2). As expected, no signal was detected in the darkness,
(Figure 2a). When irradiated by visible light (above 410 nm), the
signal of the DMPO selenol-radical could be obtained (Figure 2b),
which could be simulated by the values for the nitrogen and
hydrogen hyperfine coupling constants (AN=12.94 G, AHβ=10.25
G, AHγ=1.54 G). However, for the DMPO thiyl-radical, signals
could not be detected unless UV light (below 400 nm) was used
(Figure 2c). The signal could also be simulated by the values for
the similar nitrogen and hydrogen hyperfine coupling constants
(AN= AHβ=13.57 G). Further, when radical scavenger 2,2,6,6-
tetramethylpiperidinyloxy (TEMPO) was added in the system, the
exchange reaction was greatly hindered (Figure S3), which
suggested that radicals are involved in the reaction.
Figure 2. ESR spectra of DSe1 and DS2. 20 mM DSe1 and DS2 were dissolved
in DMSO in the presence of DMPO (80 mM) a) in darkness, b) DSe1 under
visible light (λ ˃ 410 nm). g = 2.00706. c) DS2 under UV light (λ ˂ 400 nm). g
= 2.00748. The red lines in spectra b, c are computer simulations of the
respective spectra using the parameters given in the text. The blue lines are the
detected signals.
To better explore the reverse reaction under different
wavelengths of light, the Se-S exchange product of DSe1 and
DS1 was purified (Figure S4). The purified exchange product or
the 50% conversion mixture was irradiated by visible light passed
through different light filters (Figure S5). When using
a
wavelength of light above 390 nm, the exchange was reversed,
and ~20% conversion was maintained. Above 410 nm or 450 nm,
~10% conversion was maintained (Figure 3b). Similar results
were obtained using the purified exchange product (Figure S6). In
addition, if light with wavelength above 410 nm was used to
directly irradiate the original mixture of DSe1 and DS2, the
conversion also reached ~10% (Figure 3c). With the wavelength
of the light above 500 nm, the purified exchange product or the
50% conversion mixture did not have any change (Figure 3b, S6).
In this way, a brief wavelength range of the reverse reaction was
confirmed. If the wavelength was between 390 and 500 nm, the
Se-S bond could be activated, and the reverse reaction was
Figure 1. a) Exchange reaction between DSe1 and DS1 under light of different
wavelengths. 1H NMR and 77Se NMR spectra of the mixture b), c) before
reaction, d), e) after UV irradiation and f), g) after reversal under visible light.
The wavelength-controlled exchange reaction is assumed to
proceed via radical mechanism, since UV-triggered disulfide
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achieved. The wavelength dependence of the conversion
provides new tunable parameters for controlling the metathesis
between disulfides and diselenides.
Figure 4. a) Exchange reaction between DSe2 and exchange mixture of DSe1
and DS2 till photostationary state. b) 1H NMR spectra of the mixture after
wavelength exceed 500 nm.
For metathesis between disulfides and diselenides,
a
reductant-catalyzed reaction was also investigated (Figure S10,
S11). The catalytic reductants thermodynamically pushed the
exchange forward, while visible light irradiation kinetically pushed
it backward. By the tuning reaction condition, this process has the
potential to become a dissipative system with light as its energy
input.
To demonstrate a potential application of wavelength-controlled
metathesis, light-triggered cleavage of polymer materials was
conducted (Figure 5). Two polyurethane elastomers containing
disulfide bonds or diselenide bonds were fabricated (Scheme S2).
Samples of each material were attached together and irradiated
by UV light. Under this condition, the diselenides and disulfides
exchanged with each other, connecting the polymer chains from
different samples. After irradiation, the samples were welded
together and could be stretched to 75% strain. Then, visible light
with a wavelength above 410 nm was directed onto the welded
samples, and the Se-S bonds connecting the materials were
converted back to disulfides and diselenides, cleaving the
samples (Figure 5b). A 457 nm blue light laser could also induce
the cleavage of the materials. Without the laser, the samples
could sustain a 200 g weight for more than 120 min. With the laser,
the materials broke in 5 min (Supplementary video). Thus, a
remotely laser-controlled cleavage of polymer materials was
realized.
Figure 3. a) Exchange reaction between DSe1 and DS2 under light of different
wavelengths. b) 1H NMR spectra of the mixture after UV irradiation and reaction
reversal under different wavelengths. c) 1H NMR spectra of the mixture after
reaction reversal, or direct irradiation by visible light.
Under wavelengths exceeding 500 nm, the Se-S product might
still exchange with Se radicals. To confirm this assumption, a
second diselenide (DSe2) was added to DSe1 and DS2 after UV
irradiation. With light above 500 nm, a new Se-S product was
obtained (Figure 4). Light of wavelength above 500 nm was also
used to directly irradiate the original mixture of DSe1, DSe2, and
DS2, and no Se-S exchange product was detected (Figure S9).
These results showed that under light above 500 nm, though the
reverse reaction ceased, the Se radical was still exchanging with
Se-S bond. However, under this circumstance, the Se radical
could not swap out the S radical from Se-S or S-S bonds due to
energy limits. When DSe2 was added, the DSe2 radical swapped
out the DSe1 radical from the Se-S product, thus producing the
new Se-S product.
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F. Fan, S. Ji, C. Sun, C. Liu, Y. Yu, Y.
Fu, H. Xu*
Page No. – Page No.
Title
Wavelength-Controlled Dynamic
Metathesis: A Light-Driven Exchange
Reaction Between Disulfide and
Diselenide Bonds
Text for Table of Contents
Controlled Metathesis: metathesis between disulfide bonds and diselenide bonds was realized under light, and the conversion of
the exchange reaction could be controlled by the wavelength of the light. This chemistry is induced into polymer materials to control
cleavage of the polymers from a distance.
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