Reversible photo-control over transmembrane anion transport using visible-light responsive supramolecular carriers

Article abstract of DOI:10.1039/d0sc02745f

Ion transport across lipid bilayer membranes in biology is controlled by membrane proteins, which in turn are regulated in response to chemical-, physical- and photo-stimuli. The design of synthetic supramolecular ion transporters able to be precisely con

Full text of DOI:10.1039/d0sc02745f

View Article Online
View Journal
Chemical
Science
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. Kerckhoffs and
M. J. Langton, Chem. Sci., 2020, DOI: 10.1039/D0SC02745F.
Volume
Number
9
1
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
7
January 2018
Pages 1-268
Chemical
Science
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
rsc.li/chemical-science
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2041-6539
EDGE ARTICLE
Xinjing Tang et al.
Caged circular siRNAs for photomodulation of gene
expression in cells and mice
rsc.li/chemical-science

Page 1 of 9
PleaseCdhoemnoictaal dScjuiesntcme argins
View Article Online
DOI: 10.1039/D0SC02745F
ARTICLE
Reversible photo-control over transmembrane anion transport
using visible-light responsive supramolecular carriers
Aidan Kerckhoffs, Matthew J. Langton*
Received 00th January 20xx,
Accepted 00th January 20xx
Ion transport across lipid bilayer membranes in biology is controlled by membrane proteins, which in turn are regulated in
response to chemical-, physical- and photo-stimuli. The design of synthetic supramolecular ion transporters able to be
precisely controlled by external signals, in particular bio-compatible wavelengths of visible light, is key for achieving spatio-
temporal control over function. Here we report two-colour responsive molecular photo-switches that act as supramolecular
transmembrane anion carriers. Reversible switching of the photo-switch within the lipid bilayer membrane is achieved using
biocompatible visible wavelengths of light, such that temporal control over transmembrane anion transport is achieved
through alternating irradiation with red and blue light.
DOI: 10.1039/x0xx00000x
mobile ion carriers that function in lipid bilayers are extremely
rare, and precise, reversible control over activity is particularly
challenging to achieve. Furthermore, the photo-responsive ion
Introduction
Ion transport across lipid bilayer membranes in biology is
regulated by membrane proteins, which are themselves
regulated by external stimuli such as small molecules,
membrane potential and light. Protein ion channels and their
modified analogues find applications in diverse fields ranging
from optogentics,1 photopharmacology,2 and synthetic
biology.3 Supramolecular anionophores that act as mobile ion
carriers have also attracted significant interest; driven by
potential uses as therapeutics for cancer treatment and
diseases arising from mis-regulated ion channels including
cystic fibrosis, or as tools for studying ion transport processes.4
Significant effort has been devoted to designing mobile carrier
systems with high anion transport activity in vesicles and, more
recently, in cells.5
carriers reported to date employ almost exclusively UV light-
triggered transport mechanisms.7e-g UV-light is generally
unsuitable for biological applications due to poor tissue
penetration and collateral cell damage.2a Because of this
limitation, long wavelength visible light photo-switches are
attracting significant interest as tools for chemical biology
applications.10 Here we report
a supramolecular photo-
switchable carrier able to regulate transmembrane anion
transport using visible light. The system is reversibly controlled
by alternate irradiation with red and blue light, with a high level
of discrimination between the OFF and ON states.
Results and discussion
Whilst the activity of natural ion channels and transporters
can be precisely controlled by external stimuli, stimuli-
responsive supramolecular ion channels6 and mobile ion
carriers7 are rare, and achieving high levels of control (to switch
between inactive “OFF” states and ion transporting “ON”
states) is particularly challenging. Photo-regulated transporters
are particularly attractive targets, because of the possibility of
achieving both spatial and temporal control over ion transport
in a readily adaptable synthetic system. Since the pioneering
work of Shinkai and co-workers on photo-controlled cation
transport in liquid membranes,8 the large amplitude
conformational change afforded by E-Z photo-isomerisation has
been a key component of many light-activated molecular
machines, receptors and catalysts.9 However, light-activated
Approach
Synthetic mobile ion carriers facilitate ion transport down a
concentration gradient by lowering the kinetic barrier to
transmembrane transport. This is achieved through binding of
the ion within a hydrophobic receptor, which diffuses across the
bilayer to release the ion on the opposite side. For the
development of reversible photo-controlled anion carriers, we
identified two key requirements: (i) excellent discrimination
between the inactive “OFF” state (with negligible background
transport) and photo-activated “ON” state and (ii) photo-
switching with visible light for improved biocompatibility.
Efficient anion transporters require sufficient lipophilicity to
ensure optimum partitioning into the membrane, excellent
anion binding affinity,11 and also benefit from encapsulation of
the hydrophilic anion within
a
hydrophobic receptor.12
Conversely, carriers with weak anion binding affinity, poor
encapsulation and extended conformations typically exhibit low
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford,
OX1 3TA. Email: matthew.langton@chem.ox.ac.uk.
Electronic Supplementary Information (ESI) available. See DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 2 of 9
ARTICLE
Journal Name
activity; the latter attributed to reduced mobility and high
reorganization penalties within the membrane.13
View Article Online
DOI: 10.1039/D0SC02745F
We identified red-shifted azobenzenes bearing anion
binding groups of the general structure 1 (Figure 1) as a possible
scaffold that fulfils these requirements, where E-Z photo-
isomerization of azobenzenes is exploited to enhance anion
recognition by cooperative binding between two appended
receptors. A greater degree of anion encapsulation and
increased mobility of the less extended Z isomer relative to the
E isomer enhances the anion transport capability further.
Design and Synthesis
The E-Z photo-isomerisation of azobenzenes is achieved using
UV light and reversed with visible light or by thermal relaxation;
the rate of which depends on the substituents but can often be
fast (t1/2 milliseconds to minutes).14 To address the key
challenge of achieving reversible, visible light mediated control
over ion transport, we designed molecular photo-switches
incorporating ortho-chloro-substituted azobenzene derivatives.
Recent work by a number of groups including those of Hecht
and Woolley have demonstrated that heteroatom ortho-
substitution of azobenzenes leads to significant red shifting of
the n−π* band of the E isomer, separating it from the Z n−π*
transition.15 This allows for bi-directional photo-switching with
orthogonal wavelengths of visible light, and significantly
Fig. 2 Calculated structure of the chloride complex 1aZ∙Cl (MM+ force field,
HyperChem)
enhanced
Z isomer lifetimes. Remarkably, ortho-chloro-
derivatives have been shown to allow photo-switching with red
light, which is highly beneficial for biological applications.15d
Scheme 1. Synthesis of squaramide-functionalized azobenzene anion carriers.
Conditions: (i) LiAlH4, THF, 3h, rt; (ii) Boc2O, THF, 3h, rt, 59% over two steps; (iii) NCS,
DBU, CH2Cl2, 10 min, -78°C, 43%; (iv) TFA, CH2Cl2, 4h, quant.; (v) 6a-i; DIPEA, MeOH, 16
hr, 55°C, 49 – 83%
-
Direct conjugation of anion binding motifs to the azobenzene
core is known to significantly decrease the lifetime of the Z
isomer (such as in azobenzene-urea derivatives).16 Molecular
mechanics calculations indicated that incorporation of
methylene spacers between the photo-switch and the anion
binding squaramides allows for cooperative chloride anion
binding between both squaramide motifs in the Z isomer (Figure
2). Squaramides are potent halide ion binders, and highly
effective anion transporters.17
ON
OFF
-
(E)
(Z)
Red-shifted azobenzene derivatives 1a-i were prepared as
shown in Scheme 1. Reduction and immediate protection of 4-
-
-
cyano-2,6-dichloroaniline
2 afforded 3, which was subjected to
oxidative coupling conditions18 to afford red-shifted
azobenzene
gave rise to
4 in good yields. Quantitative Boc-deprotection
Fig.
1
Schematic representation of two-colour photo-switching of
a
supramolecular ion carrier
1.
5
, which was subsequently reacted with
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
PleaseCdhoemnoictaal dScjuiesntcme argins
View Article Online
DOI: 10.1039/D0SC02745F
Table 1. Characteristics of photo-switchable anion carriers 1
Carriers
Entry
Characteristic
K1E (M-1)a
1a
1b
72 ± 3
1c
77 ± 3
1d
126 ±1
346 ± 2
146 ± 40
42 ± 12
1.0 ± 0.2
0.76 ± 0.1
2.7
1e
1f
1g
47 ± 1
1h
1I
e
1
2
3
4
5
6
7
8
90 ± 2
267 ± 2.5
181 ± 16
22 ± 2
2.6 ± 0.5
1.1 ± 0.1
3.1
137 ± 10
358 ± 12
232 ± 143
64 ± 13
0.62±0.1
0.74±0.1
2.6
139 ± 10
402 ± 6
246 ± 121
90 ± 55
0.58 ± 0.1
0.67 ± 0.1
2.9
65 ± 5
204 ± 21
204 ± 42
28 ± 2
0.8 ± 0.1
1.2 ± 0.1
3.1
−
−
e
K1Z (M-1)a
201 ± 2.5
591 ± 341
101 ± 18
0.63 ± 0.1
1.0 ± 0.2
2.8
231 ± 12
1020±477
218 ± 54
0.62 ±0.1
0.64 ±0.1
3.0
142 ± 7
>5000f
432 ± 41
EC50E (nM)b
EC50Z,PSS (nM)b,c
>20,000f
>20,000f
d
e
e
nE
nZ
−
−
d
e
1.41 ± 0.1
3.0
>10f
−
E
e
K1Z / K1
−
E
e
EC50Z,PSS/ EC50
8.2
5.9
4.7
3.5
3.6
2.7
7.3
−
a 1:1 association constant for chloride binding in d6-DMSO. K1E is statistically corrected to account for affinity to one squaramide, where K1E = Kobs / 2. Errors at the 95%
confidence limit. bEffective concentration to reach 50% of maximal activity in the HPTS assay, in LUVs of POPC (mean diameter 200 nm, lipid concentration 31 μM) loaded
with 1 mM HPTS, NaCl (100 mM) and buffered at pH 7.0 with 10 mM HEPES. For compounds of low activity, estimated lower bounds for the EC50 value are given. cFor
the Z isomer, EC50Z,PSS indicates apparent value achieved by addition of the 77:23 Z/E PSS mixture. dHill coefficient. eNot determined. fPoor solubility in DMSO prevented
full Hill analysis.
mono-squaramide derivatives (6a-i, prepared from dimethyl NMR anion binding titrations
squarate and the corresponding amine derivative), to afford the
anion carriers 1a-i. For full experimental procedures and
characterization see the ESI.
We first examined the photo-switching properties of the
parent azobenzene 4
. Irradiation of 4E with red light from an LED
With the library of squaramide-functionalized bistable switches
in hand, we examined their chloride binding capability by
conducting 1H NMR titration experiments in d6-DMSO by
addition of aliquots of tetrabutylammonium chloride, and
monitoring the binding induced chemical shift perturbations.
Data were fitted to the appropriate binding isotherms using the
Dynafit software package,19 and the association constants are
shown in Table 1. K1E is the 1:1 binding constant for chloride
recognition by one squaramide motif of the bi-functional E-
isomer, weighted by the appropriate statistical factor, and K1Z is
the corresponding 1:1 binding constant for chloride recognition
by the Z isomer. The latter were determined by repeating the
titration with the PSS mixture formed by irradiating the sample
in the NMR tube with 625 nm light (77% Z for 1a-i), and
accounting for the binding competition to the minor population
of E isomer in the analysis (see ESI for data and binding models).
The affinity of 1E for chloride was relatively weak in this
competitive polar solvent, and binding of a second equivalent
of anion was too weak to be determined, presumably due to
(625 nm, ~0.9 W) allowed for high conversion to the Z isomer in
the photo-stationary state (PSS) (80% 4Z as determined by NMR
integration). The UV-vis spectra of 4E and 4Z are shown in Figure
3. As with similar ortho-chloro-substituted azobenzenes,15d
significant red-shifting of the n−π* transition is observed, and
separation of the E n−π* from the Z n−π* transitions allows for
efficient switching (Figure 2). Irradiation with blue light (LED,
455 nm, ~1.1 W) was effective at triggering the reverse Z → E
photo-isomerisation (86% Z → E). The Z isomer exhibited
excellent thermal stability, with a half-life for the thermally
promoted Z → E isomerization of ~7 days at 298 K (Figure S78).
2000
12000
1Z
400
8000
1E
300
0
400
500
600
4000
0
4E
200
PSS 4Z (80%)
4Z
-0.4
0.0
0.4
0.8
300
400
500
600
700
s
l / nm
Fig. 3 Absorption spectra of
DMSO at 25 °C. Inset: n→π* bands and composition of the PSS mixtures upon
irradiation with red light (625 nm, determined by NMR integration). Pure Z-isomer
spectrum was calculated from the spectra of pure
4 as the E and Z isomer, as well as the PSS mixture in
Fig. 4 Plot of K vs Hammett parameter σ for aryl derivatives of 1E and 1Z. Values taken
from reference 20.
4
E and the PSS mixture of known
composition.
Please do not adjust margins

PleaseCdhoemnoictaal dScjuiesntcme argins
Page 4 of 9
View Article Online
A
B
C
DOI: 10.1039/D0SC02745F
100
1.5
1.0
1aZ PSS
1aZ PSS
Li+
80
60
40
20
0
Rb+
Na+
K+
Cl-
1aE
Cs+
1.0
0.5
0.0
Br-
0.5
0.0
I-
OH−
1aE
1a
-
NO3
Lysis
300
0
100
200
10
100
[1a] / nM
1000
-525 -520
-400
-350
-300
-250
DGhyd (kJ mol-1)
t / s
Fig. 5 (A) Change in ratiometric emission (lem = 510 nm; lex1 = 405 nm, lex2 = 460 nm) upon addition of 62.5 nM 1aE (black) and 1aZ (red) in DMSO to POPC LUVs (31
μM) containing 1 mM HPTS, 100 mM internal and external NaCl, buffered with 10 mM HEPES at pH 7.0. A pH gradient is generated by addition of a NaO H base pulse
(5 mM), followed by 1a in DMSO. Lysis by Triton X-100 calibrates the assay. (B) Dependence on Irel immediately prior to lysis on concentration of 1aE ) and 1aZ
(▲ (■),
and fit to the Hill equation (solid line). (C) Dependence of the activity of 1aZ (62.5 nM) on extra-vesicular ions (100 mM MCl or NaX; inside 100 mM NaCl). Error bars
represent standard deviations. Original data for all other compounds is available in the ESI.
unfavourable anion-anion repulsion. The affinity of 1Z Quantifying anion transport activity
derivatives for chloride were higher than the analogous 1E The EC50 and n values for the analogues of 1E, and for the 1Z
Z
isomers, with a ratio of K1 /K1E ~ 3, indicating cooperative anion enriched PSS (Z:E 77:23) are given in Table 1, entries 3-6; and
binding by both squaramide motifs in the Z isomer, consistent the corresponding EC50Z,PSS / EC50E ratios (entry 8). A significant
with the calculated structure. Varying the electron donating or enhancement of activity, up to a maximum of 8-fold for
withdrawing nature of the squaramide translated into changes compound 1a, was observed for the Z isomers.21 In general,
in the binding affinity for chloride in both E and Z isomers, and squaramides with electron withdrawing aryl substituents
for the aryl substituents this showed good correlation with resulted in efficient transport. The optimal chain length of alkyl
Hammett constant20 (Figure 4).
derivatives was six carbons, with both ethyl and octyl chains
proving detrimental to transport efficiency. The difference in
activity between both photo-isomers could be estimated by the
1
were ratio EC50Z,PSS / EC50E, which was found to be generally higher for
Anion transport studies
The anion transport activities of the derivatives of
determined
in
1-palmitoyl-2-oleoyl-sn-glycero-3- the less active compounds, presumably arising from a
phosphocholine large unilamellar vesicles (POPC LUVs, lipid decreased ability of the E isomer to bind and transport anions.
Z
E
concentration 31 μM), loaded with 8-hydroxypyrene-1,3,6- In contrast, the ratio of 1:1 binding constants, K1 /K1 , remains
trisulfonate (HPTS) buffered to pH 7.0 in NaCl solution. A pH consistent at ~3 across the whole family of compounds. We
gradient was applied across the membrane by addition of a base hypothesise that the larger increase in transporter efficiency for
pulse, followed by addition of the carrier as a DMSO solution the 1Z derivatives, compared to that predicted by the ratio of
(<0.5% v/v). The ability of the anionophore to dissipate the pH binding constants alone, arises in part from reduced mobility of
gradient by transmembrane ion transport was determined by the linear E isomer-anion complex in the membrane, and
recording the change in the HPTS emission, Irel (λem = 510 nm), diminished ability to fully encapsulate the anion compared to
with time following excitation at λex=405/465 nm (Figure 5A). the Z isomer. It has been previously shown that the relationship
Detergent (Triton X-100) was added at the end of each between anion binding affinity and EC50 is complex, often
experiment to lyse the vesicles for calibration. For the Z isomers, without direct correlation, because transport efficiency is also
the experiment was run using the 77:23 Z/E PSS mixture formed strongly dependent on other factors including molecular size
by irradiating the sample with 625 nm light.
and hydrophobicity.11b The important role of encapsulation in
The concentration dependence of the activity of the E and Z increasing transport affinity has also previously been
isomers of each anion carrier was determined by adding demonstrated.12
increasing concentrations of the transporter in DMSO. The
Hill coefficients of ~1 for 1Z analogues suggests ion
fractional activities (relative intensity just prior to lysis) were complexation with a likely 1:1 stoichiometry (1Z∙Cl−) in the
plotted as a function of concentration (Figure 5B) and the dose- transport complex, consistent with results from titration
response curves fitted to the Hill equation. This is used to experiments and calculation. Enhanced binding interactions in
describe the dependence of the anion transport activity membranes, arising from two-dimensional confinement and
(reported by Irel) on the n-th power of the carrier concentration, the hydrophobic, low polarity environment,22 may also allow for
and facilitates comparison of the relative activities of carriers competing formation of the E isomer 2:1 transporter-anion
through an effective concentration value (EC50) required to complex (1E ∙Cl−), as well as hydrogen bonding aggregates of 1E
2
reach 50% activity.
in the membrane. Hill coefficients ranging between ~0.6–2.6
are indicative of a range of competing equilibria in the
Please do not adjust margins

Page 5 of 9
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Anion transport by 1aE and 1aZ in the lipid gel phase of
View Article Online
DOI: 10.1039/D0SCC027w4a5Fs
dipalmitoylphosphatidylcholine (DPPC) lipids at 25
inhibited and restored at 45 C, above the gel-liquid phase
transition temperature (Tc = 41 C) (Figure 6A). This behaviour


is consistent with the proposed mobile carrier mechanism, in
which mobility is significantly reduced in the gel phase, and
rules out alternative formation of a membrane spanning
channel structure whose activity would be independent of the
lipid phase. Inactivity in the calcein release assays further rules
out carrier-induced non-specific leakage (Figure 6B).
Reversible photo-switching of anion transport.
To investigate in-situ, reversible photo-switching of ion
transport in vesicles, we measured the transporter-induced
chloride efflux from POPC vesicles containing buffered NaCl,
suspended in NaNO3 in real time using a chloride ion selective
electrode (ISE). Sample illumination was achieved using high
powered LEDs (see ESI for details). Initial studies confirmed that
–
the system could facilitate Cl– / NO3 antiport in this assay,
following external addition of the 1aZ-rich PSS, with minimal
background transport by 1aE in this assay (Figure S145).
Reversible control over ion transport by in-situ photo-
switching of 1a in the vesicle membrane was achieved by adding
1aE as a DMSO solution (0.5 mol% relative to lipid) to the gently
stirred vesicle suspension. Irradiation with red light (625 nm)
was used to photo-isomerise the transporter within the lipid
–
bilayer membrane, and turn-on the Cl–/NO3 transmembrane
transport process, which could be turned off by subsequent
irradiation with blue light (455 nm) (Figure 7). The rate of ion
Fig. 6 (A) HPTS assay with DPPC LUVs: 200 nM 1aE (dashed lines) and 62.5 nM 1aZ
(solid lines) at 25 C (black data) and 45 C (red data). (B) Calcein release assay with
1aE (dashed line) and 1aZ (solid line) in POPC LUVs.
⁰
⁰
transport following in-situ photo-isomerisation in the vesicles
5 μM
,PSS 25
was ~50% of that achieved by direct addition of 1aZ
.
membrane for the 1E isomer derivatives, with n<1 arising from
competing formation of inactive complexes and/or
precipitation at high concentrations.23 Compound 1a provides a
Alternating between 625 and 455 nm light allowed for
reversible switching between the transporting “ON” and
inactive states “OFF” states, directly coupling photo-
isomerisation with ion transport. Inactivity under alternating
red and blue light irradiation in the absence of 1a; and the lack
of switching behaviour when 1a was replaced with a simple
E
balance between good EC50Z / EC50 discrimination and overall
high activity as the Z isomer (EC50 of 22 nM, 0.07 mol% relative
to the lipids), and was used for analysis in subsequent
experiments.
Ion selectivity and mechanistic studies
The activity of transporter 1aZ was unaffected by iso-osmolar
replacement24 of the external Na+ cation with Li+, K+, Rb+ or Cs+,
but was sensitive to replacement of the external Cl– anion with
‒
Br–, I– or NO3 (Figure 5C). No observable transport was
detected when chloride was replaced with gluconate, a large
hydrophilic anion,12 suggesting that 1aZ is unable to overcome
the large dehydration penalty required for OH– / gluconate–
antiport (Figure S138). Diminished activity with anionic lipids
(egg yolk phosphatidylglycerol) was also consistent with the
requirement for formation of an anionic complex 1Z∙Cl−, due to
charge repulsion with the membrane (Figure S139). Together,
these results demonstrate that the dissipation of the pH
gradient reported in the HPTS assay must arise from
transmembrane anion transport (OH– / Cl– antiport, or H+ / Cl–
symport), and not from H+ / M+ cation antiport, in agreement
with the mode of action of previously reported squaramide
anion carriers.17
Fig. 7 Photo-triggered ion transport by 1a (0.5 mol% relative to lipid) from POPC
vesicles containing 489 mM NaCl, suspended in 489 mM NaNO3, and buffered with
phosphate salts at pH 7.0. Chloride efflux from POPC vesicles monitored by a
chloride-selective ISE. Colours indicate commencement of sample irradiation
using 625 nM (0.9 W, red) or 455 nm (1.1 W, blue) LEDs. Black squares: vesicle
exterior Cl− concentration; lines: linear fit.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 6 of 9
ARTICLE
non-photo-responsive squaramide derivative (ESI), confirmed
the role of photo-switch 1a in the photo-switchable transport
behaviour (Figure S147).
Chem., 2014, 6, 885–892. (c) V. Soto-Cerrato, P. Manuel-
Conclusions
We have demonstrated reversible, visible light control over
transmembrane anion transport using a synthetic photo-
switchable anion carrier. Fluorescence anion transport assays in
combination with ISE experiments demonstrate the ability of
the squaramide-substituted azobenzenes to act as mobile anion
carriers. Switching between the less active E isomer and more
active Z isomer can be achieved with red light, whilst back-
switching takes place using blue light; allowing for in-situ,
temporal control over transmembrane ion transport in lipid
bilayer vesicles. We anticipate that these results will provide the
foundation for developing sophisticated photo-controlled
membrane transport systems, with potential longer term
impact in targeted therapeutics and synthetic biology.
6
7
Busschaert, R. B. P. Elmes, D. D. Czech, X. Wu, I. L. Kirby, E.
M. Peck, K. D. Hendzel, S. K. Shaw, B. Chan, B. D. Smith, et
Conflicts of interest
There are no conflicts to declare
al., Chem. Sci., 2014,
5, 3617. (c) Y. R. Choi, B. Lee, J. Park,
W. Namkung, K.-S. Jeong, J. Am. Chem. Soc., 2016, 138
,
15319–15322. (d) X. Wu, J. R. Small, A. Cataldo, A. M.
Withecombe, P. Turner, P. A. Gale, Angew. Chem. Int. Ed.,
2019, 58, 15142–15147. For a visible light responsive cation
transporter see: (e) T. Jin, Mater. Lett. 2007, 61, 805-808.
For UV-triggered anion transporters see: (f) Y. Rin Choi, G.
Chan Kim, H.-G. Jeon, J. Park, W. Namkung, K.-S. Jeong,
Chem. Commun., 2014, 50, 15305–15308. (g) S. B. Salunke,
J. A. Malla, P. Talukdar, Angew. Chem. Int. Ed., 2019, 58
5354–5358.
S. Shinkai, T. Nakaji, T. Ogawa, K. Shigematsu, O. Manabe, J.
Am. Chem. Soc., 1981, 103, 111–115.
For selected recent reviews on molecular machines
including those exploiting photo-switches see: (a) S. Erbas-
Cakmak, D. A. Leigh, C. T. McTernan, A. L. Nussbaumer,
Chem. Rev., 2015, 115, 10081–10206. (b) V. Blanco, D. A.
Leigh, V. Marcos, Chem. Soc. Rev., 2015, 44, 5341–5370. (c)
L. van Dijk, M. J. Tilby, R. Szpera, O. A. Smith, H. A. P. Bunce,
Acknowledgements
A.K. thanks the EPSRC Centre for Doctoral Training in Synthesis
for Biology and Medicine for a studentship (EP/L015838/1),
generously supported by AstraZeneca, Diamond Light Source,
Defence Science and Technology Laboratory, Evotec,
GlaxoSmithKline, Janssen, Novartis, Pfizer, Syngenta, Takeda,
UCB and Vertex. MJL acknowledges funding from the Royal
Society, the John Fell Oxford University Press Research Fund,
the University of Oxford’s EPSRC Capital Award in Support of
Early Career Researchers (EP/S017658/1), and SCG Chemicals
Co. Ltd. for funding through the SCG-Oxford Centre of
Excellence in Chemistry: SCG Innovation Fund. M.J.L. is a Royal
Society University Research Fellow.
,
8
9
S. P. Fletcher, Nat. Rev. Chem., 2018, 2, 1–18.
10 A. A. Beharry, G. A. Woolley, Chem. Soc. Rev., 2011, 40
4422–4437.
,
11 (a) V. Saggiomo, S. Otto, I. Marques, V. Félix, T. Torroba, R.
Quesada, Chem. Commun., 2012, 48, 5274–5276. (b) N.
Busschaert, S. J. Bradberry, M. Wenzel, C. J. E. Haynes, J. R.
Hiscock, I. L. Kirby, L. E. Karagiannidis, S. J. Moore, N. J. Wells,
Notes and references
1
G. Miesenböck, Annual Review of Cell and Developmental
Biology, 2011, 27, 731–758.
J. Herniman, et al., Chem. Sci., 2013, 4, 3036–3045.
2
(a) W. A. Velema, W. Szymanski, B. L. Feringa, J. Am. Chem.
Soc., 2014, 136, 2178–2191. (b) K. Hüll, J. Morstein, D.
Trauner, Chem. Rev., 2018, 118, 10710–10747.
12 X. Wu, L. W. Judd, E. N. W. Howe, A. M. Withecombe, V.
Soto-Cerrato, H. Li, N. Busschaert, H. Valkenier, R. Pérez-
Tomás, D. N. Sheppard, et al., Chem, 2016,
1, 127–146.
3
4
(a) G. Villar, A. D. Graham, H. Bayley, Science, 2013, 340, 48–
52. (b) Y. Elani, R. V. Law, O. Ces, Therapeutic Delivery, 2015,
13 S. J. Edwards, I. Marques, C. M. Dias, R. A. Tromans, N. R.
Lees, V. Félix, H. Valkenier, A. P. Davis, Chem. Eur., 2016, 22
2004–2011.
,
6
, 541–543. (c) K. P. Adamala, D. A. Martin-Alarcon, K. R.
Guthrie-Honea, E. S. Boyden, Nat. Chem., 2017, , 431–439.
9
14 H. M. Dhammika Bandara, S. C. Burdette, Chem. Soc. Rev.,
2012, 41, 1809–1825.
For recent reviews see: (a) J. T. Davis, O. Okunola, R.
Quesada, Chem. Soc. Rev., 2010, 39, 3843–3862; (b) S.
Matile, A. V. Jentzsch, J. Montenegro, A. Fin, Chem. Soc.
Rev., 2011, 40, 2453–2474. (c) P. A. Gale, J. T. Davis, R.
Quesada, Chem. Soc. Rev., 2017, 46, 2497–2519.
15 (a) A. A. Beharry, O. Sadovski, G. A. Woolley, J. Am. Chem.
Soc., 2011, 133, 19684–19687. (b) M. J. Hansen, M. M.
Lerch, W. Szymanski, B. L. Feringa, Angew. Chem. Int. Ed.,
2016, 55, 13514–13518. (c) D. Bléger, J. Schwarz, A. M.
Brouwer, S. Hecht, J. Am. Chem. Soc., 2012, 134, 20597–
20600. (d) S. Samanta, A. A. Beharry, O. Sadovski, T. M.
McCormick, A. Babalhavaeji, V. Tropepe, G. A. Woolley, J.
5
(a) B. Díaz de Greñu, P. I. Hernández, M. Espona, D.
Quiñonero, M. E. Light, T. Torroba, R. Pérez‐Tomás, R.
Quesada, Chem. Eur., 2011, 17, 14074–14083. (b) S.-K. Ko,
S. K. Kim, A. Share, V. M. Lynch, J. Park, W. Namkung, W. Van
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
Chemical Science
Please do not adjust margins
Journal Name
ARTICLE
Am. Chem. Soc., 2013, 135, 9777–9784. (e) M. Dong, A.
Babalhavaeji, M. J. Hansen, L. Kálmán, G. A. Woolley, Chem.
Commun., 2015, 51, 12981–12984.
View Article Online
DOI: 10.1039/D0SC02745F
16 K. Dąbrowa, P. Niedbała, J. Jurczak, Chem. Commun., 2014,
50, 15748–15751.
17 N. Busschaert, I. L. Kirby, S. Young, S. J. Coles, P. N. Horton,
M. E. Light, P. A. Gale, Angew. Chem. Int. Ed., 2012, 51
4426–4430.
,
18 A. Antoine John, Q. Lin, J. Org. Chem., 2017, 82, 9873–9876.
19 P. Kuzmič, Anal. Biochem., 1996, 237, 260–273.
20 C. Hansch, A. Leo, R. W. Taft, Chem. Rev., 1991, 91, 165–195.
21 Note that the measured EC50Z,PSS is an underestimate of the
intrinsic transport ability of 1Z, with the actual activity
~1.25 higher (EC50 0.8 smaller) due to the incomplete
isomerisation to the Z isomer in the PSS.
22 E. L. Doyle, C. A. Hunter, H. C. Phillips, S. J. Webb, N. H.
Williams, J. Am. Chem. Soc., 2003, 125, 4593–4599.
23 Compatibility of the dose-response curves with the Hill
equation with Hill coefficients n > 1 reveals endergonic self-
assembly (un-stable supramolecules) and provides
information on the stoichiometry; n = 1 or n < 1 reveals
exergonic self-assembly (stable supramolecules). See S.
Bhosale, S. Matile, Chirality, 2006, 18, 849–856.
24 N. Sakai, S. Matile, J. Phys. Org., 2006, 19, 452–460.
25 Similar results were obtained for in-situ photo-isomerisation
of 1aE in the HPTS assay. See ESI for further details.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Chemical Science
Page 8 of 9
View Article Online
Supramolecular anion carriers responsive to visible light enable reversible two-colour phDoOtoI: -1c0.o10n3t9r/oDl0SC02745F
over transmembrane anion transport

Page 9 of 9
Chemical Science
View Article Online
DOI: 10.1039/D0SC02745F
1351x729mm (144 x 144 DPI)