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Photochemical & Photobiological Sciences
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Journal Name
ARTICLE
This material is based on work supported by the National
DOI: 10.1039/C6PP00469E
Science Foundation under Grant No CHE-1112018.
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b
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Notes and references
1
(a)Berridge, M. J., The AM and RM of calcium signalling.
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3
Ellis-Davies, G. C. R., Neurobiology with caged calcium.
Chem. Rev., 2008, 108, 1603.
Fig. 7 Photoinduced gelation of alginate.
photoreactor for 2 hours. : Photolysis at 447 nm using 1 W CW diode laser for
two hours. : Dark control. : Omitted Ca-EDTA. Photolysis at 350 nm in a
a: Photolysis at 350 nm in a Rayonet
(a) Jakkampudi, S.; Abe, M.; Komori, N.; Takagi, R.; Furukawa,
K.; Katan, C.; Sawada, W.; Takahashi, N.; Kasai, H., Design
and synthesis of a 4-nitrobromobenzene derivative bearing
an ethylene glycol tetraacetic acid unit for a new generation
of caged calcium compounds with two-photon absorption
properties in the near-IR region and their application in vivo.
ACS Omega, 2016, 1, 193. (b) Cui, J.; Gropeanu, R. A.;
Stevens, D. R.; Rettig, J.; Del Campo, A., New photolabile
BAPTA-based Ca2+ cages with improved photorelease. J. Am.
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(a) Chueh, B. H.; Zheng, Y.; Torisawa, Y. S.; Hsiao, A. Y.; Ge,
C.; Hsiong, S.; Huebsch, N.; Franceschi, R.; Mooney, D. J.;
Takayama, S., Patterning alginate hydrogels using light-
directed release of caged calcium in a microfluidic device.
Biomed. Microdevices, 2010, 12, 145-51. (b) Asthana, A.; Ho
Lee, K.; Kim, K. O.; Kim, D. M.; Kim, D. P., Rapid and cost-
effective fabrication of selectively permable calcium-alginate
microfluidic device using “modified” embedded template
method. Biomicrofluidics, 2012, 6, 012821. (c) Oh, H.; Lu, A.
X.; Javvaji, V.; DeVoe, D. L.; Raghavan, S. R., Smart Hydrogel-
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b
c
d
Rayonet photoreactor for two hours. e: Omitted riboflavin. Photolysis at 350 nm
in a Rayonet photoreactor for 2 hours. For full experimental see SI.
Photogelation can be effected with both 350 nm
broadband light, or 447 nm light from a laser diode. Control
experiments wherein either light, Ca-EDTA, or riboflavin were
omitted showed no gelation. Future efforts we be aimed at
detailed characterization of the resulting hydrogels, and
specific approaches in photopatterning and microfluidics.
4
Conclusions
Experiments described herein demonstrate that visible
light triggered photorelease of calcium ions in up to millimolar
concentrations can be accomplished using inexpensive and
biocompatible reagents. Results with anthraquinone
derivatives show that the release of calcium ions through
photodecomposition of a chelating agent can be accomplished
with exited state oxidants. Using riboflavin, it is possible to
carry out release of calcium in a photocatalytic manner using
substoichiometric amounts of the light absorbing component.
Under steady-state illumination conditions, the overall rate of
Ca2+ production depends on the intensity of the light source,
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7
8
9
Ellis-Davies, G. C., Caged compounds: photorelease
technology for control of cellular chemistry and physiology.
Nat. Methods, 2007, 4, 619-28.
Adams, S. R.; Kao, J. P. Y.; Grynkiewicz, G.; Minta, A.; Tsien, R.
Y., Biologically useful chelators that release Ca2+ upon
illumination. J. Am. Chem. Soc., 1988, 110, 3212.
Adams, S. R.; LevRam, V.; Tsien, R. Y., A new caged Ca2+, azid-
1, is far more photosensitive than nitrobenzyl-based
chelators. Chem. Biol., 1997, 4, 867.
the molar absorptivity of the sensitizer (
e) and the quantum
Kaplan, J. H.; Ellisdavies, G. C. R., Photoliable chelators for
the rapid release of divalent-cations. PNAS, 1988, 85 (17),
6571-6575.
Agarwal, H. K.; Janicek, R.; Chi, S.; Perry, J. W.; Niggli, E.; Ellis-
Davies, G. C. R., Calcium uncaging with visible light. J. Am.
Chem. Soc., 2016, 138, 3687.
yield for release ( ). The product of the latter two terms, the
f
photochemical efficiency (e´f), can be used to characterize
the effective release rate at a given light intensity. The value
for the current system of e´f= 2700 M-1cm-1 demonstrates
that RBTA/Ca-EDTA can produce calcium ions at a rates
comparable to previously characterized systems.2 Under
pulsed illumination conditions, the relevant consideration
would be the rate-limiting step in the formation of free Ca2+
following light absorption. Additional mechanistic studies will
be aimed at determining that rate constant. Finally, it has
been shown that this photochemically generated free calcium
can be used to trigger gelation in alginate solutions. Future
studies will (a) explore extension of this method to other
chelating agents and metals (b) examine additional
applications of the current system, and (c) develop linked
sensitizer-chelator systems that can be used in biological
systems.
10 (a) Javvaji, V.; Baradwaj, A. G.; Payne, G. F.; Raghavan, S. R.,
Light-activated ionic gelation of common biopolymers.
Langmuir, 2011, 27, 12591. (b) Lee, K. Y.; Mooney, D. J.,
Alginate, Properties and biomedical applications. Prog.
Polym. Sci., 2012, 37, 106. (c) Higham, A. K.; Bonino, C. A.;
Raghavan, S. R., Khan, S. A., Photo-activated ionic gelation of
alginate hydrogel: real-time rheological monitroing of the
two-step crosslinking mechanism. Soft Matter, 2014, 10,
4990.
11 Bort, G.; Gallavardin, T.; Ogden, D.; Dalko, P. I., From one-
photon to two-photon probes: “Caged” compounds,
actuators, and photoswitches. Angew. Chem Int. Ed., 2013
52, 4526.
,
12 Borak, J. B.; Falvey, D. E., Ketocoumarin dyes as electron
mediators in visible light induced carboxylate photorelease.
Photochem. Photobiol. Sci., 2010, 9, 854.
13 Bechtold, T. J., Anthraquinones as mediators for the indirect
cathodic reduction of dispersed organic dyestuffs. J.
Electroanal. Chem., 1999, 465, 80.
Acknowledgements
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