Fluorous gels of a fluorous alcohol using a low molecular weight anthracene organogelator
Graphical abstract
Introduction
Fluorous solvents such as fluorous alcohol are stable and inert [1]. They have unique properties due to the stability of C-F bond. Their fluorophilicity has made the separation of chemical compounds easy [2], and has found application for waterproof materials [3]. In addition, these solvents have 20–25 times higher gas solubility than the aqueous medium has [4]. Based on their ability to dissolve and carry oxygen, fluorous solvents had been investigated as blood substitutes [5] or for liquid breathing [6]. Previously, we reported that the fluorous (perfluoroalkyl) alcohol 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-heptanol (Fig. 1B) can be used as oxygen reservoir during cell culture [7], considering the dissolved oxygen in fluorous solvents. In order to facilitate the use of this fluorous alcohol, we considered gelling the solvent with an organogelator yielding a thermoreversible gel.
Gels are functional soft materials that help include or release a substance in drug delivery system [8], and serve as scaffolds for bioengineering [9]. Physical gels that are triggered by low-molecular mass gelator (LMMG) [10] via noncovalent interactions, such as hydrogen bonding, van der Waals force or π-π stacking interactions, have received much attention as compared with chemical gels formed by cross-linking polymers. Self-assembly of LMMGs causes gelation and the formed gel easily turns into sol due to their sensitiveness to the conditions. Gels formed by intermolecular interactions respond to the stimuli such as heat, pH, light and sound [11], [12], [13]. Various kinds of gels have been reported depending on the target application. However, gels of fluorous solvents are rare [14].
2,3-di-n-decyloxyanthracene (DDOA) shown in Fig. 1A is a LMMG, which forms organogels thanks to π-π interactions of the anthracene moiety, dipolar interactions, and the tight packing of alkyl chains with a hexagonal symmetry [15]. Organic solvents such as methanol, ethanol, DMSO and acetonitrile can be thermo-reversibly gelated by DDOA [16]. This LMMG belongs to the class of super-gelators of alcohols, and for the gelation of methanol only 0.5-1.0 × 10−3 mol dm−3 of DDOA are necessary [16]. Focusing on the ability of DDOA to turn alcohols into gel, we applied DDOA to the aforementioned fluorous alcohol. The tuning of the reversible gelation around physiological temperature of 37 °C was explored.
Section snippets
Gelation using DDOA
DDOA was synthesized in five steps according to literature [15], [17]. The obtained DDOA was used for gelation of the fluorous alcohol, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-heptanol. Initially, DDOA was dissolved in chloroform to prepare a stock solution, and the aliquot was poured in a tube. Chloroform was evaporated under a stream of N2 gas and the residual DDOA (1 mg) was completely dissolved in dodecafluoro-1-heptanol (500 μl) by heating (75 °C). After cooling to ambient temperature, the
Conclusions
This research demonstrated that a thermoreversible fluorous gel could be prepared using a fluorous alcohol, 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1-heptanol and a low-molecular mass gelator, 2,3-di-n-decyloxyanthracene (DDOA). Using a mixture of DDOA and 2,3-di-methoxyanthracene (DMOA), the melting temperature of the fluorous gel could be fine-tuned and embraced 37 °C, as required for its application in cell growth. Cell culture using this gel is in progress.
Chemical synthesis of (a) 2,3-di-n-decyloxyanthracene (DDOA), and (b) 2,3-dimethoxyanthracene (DMOA)
DDOA and DMOA were prepared according to literature [15], [17]. 1H NMR spectra were measured with a 600 MHz spectrometer (JEOL ECP-600), and the mass spectrum was recorded on JEOL-JMS600H mass spectrometer.
(a) DDOA
1H NMR (600 MHz, CDCl3): δ (in ppm) = 0.88 (t, J = 7.2 Hz, 6H), 1.29 (m, 20H), 1.39 (m, 4H), 1.52 (m, 4H), 1.91 (m, 4H), 4.12 (t, J = 7.2 Hz, 4H), 7.15 (s, 2H), 7.36 (m, 2H),7.89 (m, 2H), 8.16 (s, 2H). 13C NMR (600 MHz, CDCl3): δ (in ppm) = 14.3 (CH3), 22.9(CH2CH3), 26.3 (OCH2CH2CH2), 29.2 (OCH2CH2
Acknowledgment
We are grateful to Prof. Yoshitaka Mitsuda and Dr. Kenji Nose, Prof. Hirohiko Houjou and Mr. Isao Yoshikawa, and Dr. Yoshiho Ikeuchi of the Institute of Industrial Science (IIS), The University of Tokyo, for the SEM, HRMS, and UV–vis absorption spectra measurements, respectively.
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