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Mechanochemical Generation of Singlet Oxygen† RSC Advances View Article Online PAPER View Journal | View Issue Mechanochemical generation of singlet oxygen† a a a a Cite this: RSC Adv., 2020, 10,9182 Abdurrahman Turksoy,‡ Deniz Yildiz, ‡ Simay Aydonat, ‡ Tutku Beduk, Merve Canyurt,a Bilge Baytekin*a and Engin U. Akkaya *b Controlled generation of singlet oxygen is very important due to its involvement in scheduled cellular maintenance processes and therapeutic potential. As a consequence, precise manipulation of singlet oxygen release rates under mild conditions, is crucial. In this work, a cross-linked polyacrylate, and a polydimethylsiloxane elastomer incorporating anthracene-endoperoxide modules with chain extensions at the 9,10-positions were synthesized. We now report that on mechanical agitation in Received 28th January 2020 cryogenic ball mill, fluorescence emission due to anthracene units in the PMA (polymethacrylate) Accepted 21st February 2020 polymer is enhanced, with a concomitant generation of singlet oxygen as proved by detection with DOI: 10.1039/d0ra00831a a selective probe. The PDMS (polydimethylsiloxane) elastomer with the anthracene endoperoxide rsc.li/rsc-advances mechanophore, is also similarly sensitive to mechanical force. Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Introduction The stability of the endoperoxides differ widely, and in a large number of 2-pyridone, naphthalene and anthracene Singlet oxygen refers to the lowest energy excited state of the endoperoxides, high yield release of singlet oxygen without side 8 molecular oxygen. Since the direct excitation of the ground state reactions was documented. As a matter of fact, the diversity in oxygen is forbidden by spin, symmetry and parity rules, it is the rates of cycloreversion reactions may eventually prove to be most commonly generated by photosensitization, making use very useful for ne tuning a biologically relevant singlet oxygen of the intermediacy of photosensitizer organic compounds with release. Release of singlet oxygen in cancer cell cultures were 9 high triplet efficiencies.1 Such photosensitized generation of shown to induce apoptotic response. This article is licensed under a singlet oxygen is of particular importance due to its involvement Mechanochemistry provides various avenues for trans- in photodynamic therapy (PDT) of cancer.2 Thus, a singlet duction of mechanical stress towards selective chemical trans- 10,11 oxygen releasing mechanophoric group would be a valuable formations. Bonds or molecular modules sensitive to “ ” Open Access Article. Published on 02 marts 2020. Downloaded 26-09-2021 20:18:53. addition to the growing list of mechanically activatable mechanical stress are known as mechanophores . In poly- functionalities. meric systems, the shear forces to induce, or facilitate selective Reversible storage and delivery of singlet oxygen may provide bond cleavage at a weak bond. An anthracene–dienophile 12 a viable alternative to photosensitized generation of singlet adduct cycloreversion reported by Craig and coworkers and oxygen.3 Photodynamic therapy has a number of advantages generation of chemiluminescence as a result of dioxetane 13 and superiorities compared to the classical therapeutic regi- cleavage. are two recent relevant examples. mens, yet it is not considered to be a rst line therapy. Two In this work, we wanted to demonstrate that a reactive easily identiable reasons for this reluctance are; rst, the fact oxygen species with a microsecond lifetime could be generated that light is required for the sensitization, but tissue penetra- on a polymer support when mechanical shear forces are tion is limited,4 and second, tumor oxygen concentrations are applied. typically low,5 and especially in the most aggressive tumors where a hypoxic region with a very low oxygen concentration Experimental develops.6 These lingering problems, unfortunately limit the Materials and instrumentation practice of PDT to mostly supercial tumors. In our previous work, we presented a different strategy to circumvent these All chemicals and reaction solvents purchased from Sigma issues.7 Aldrich, Acros Organics and ABCR were used without purica- tion. Column chromatography purications were performed with glass columns using Merck Silica gel 60 (particle size: aDepartment of Chemistry, Bilkent University, 06800 Ankara, Turkey 0.040–0.063 mm, 230–400 mesh ASTM) and reactions were bState Key Laboratory of Fine Chemicals, Department of Pharmacy, Dalian University monitored by thin layer chromatography (TLC) using precoated of Technology, 2 Linggong Road, 116024, Dalian, China † Electronic supplementary information (ESI) available. See DOI: silica gel plates (Merck Silica Gel PF-254). Chromatography 10.1039/d0ra00831a solvents (DCM, n-hexane, EtOAc) were purchased as technical ‡ Equal contribution. grade and were puried employing fractional distillation before 9182 | RSC Adv.,2020,10,9182–9186 This journal is © The Royal Society of Chemistry 2020 View Article Online Paper RSC Advances use. Anhydrous THF was used freshly aer reuxing over Na in (500 W) while O2 (g) was passing through the system for 2 h. The the presence of benzophenone under Ar. progress of reaction was monitored with TLC (eluent : EtOAc). NMR spectra were recorded on Bruker Spectrospin Avance Aer removal of the solvent under reduced pressure, the residue DPX 400 spectrometer (operating at 400 MHz for 1H NMR and was puried with column chromatography over silica gel with 13 100 MHz for C NMR) using deuterated solvents (CDCl3, EtOAc as eluent. Compound 4 was obtained as white solid 1 DMSO-d6) with tetramethylsilane (TMS) as internal standard (0.13 g, 60%). H NMR (400 MHz, DMSO-d6): d 7.65 (d, J ¼ purchased from Merck. Spin multiplicities are reported as 8.1 Hz, 4H), 7.59 (d, J ¼ 8.1 Hz, 4H), 7.33–7.27 (m, 4H), 7.12–7.05 following: s (singlet), d (doublet), t (triplet), q (quartet), quint (m, 4H), 5.38 (t, J ¼ 5.7 Hz, 2H), 4.68 (d, J ¼ 5.7 Hz, 4H). 13C NMR (quintet), sext (sextet), dd (doublet of doublets), dt (doublet of (100 MHz, DMSO-d6): d 143.3, 140.4, 131.0, 128.3, 127.3, 127.0, triplets), td (triplet of doublets), m (multiplet), bs (broad signal). 123.5, 83.8, 63.1. High Resolution Mass Spectroscopy (HRMS) experiments were Synthesis of compound 5. Compound 4 (0.30 g, 0.72 mmol), done on an Agilent Technologies-6530 Accurate-Mass Q-TOF- DCC (0.59 g, 2.85 mmol), DMAP (0.03 g, 0.21 mmol), and acrylic LC/MS. The thermogravimetric analysis (TGA) was performed acid (0.20 mL, 2.85 mmol) were dissolved in mixture of dry THF/ with TA – Q500 TGA. For rheological analysis, hexagonal- DCM (8 : 60 mL) and the slurry mixture was stirred at room squared shaped PDMS-EPO pieces were cut to help the temperature for 24 h under Ar. The DCU was removed by measurements by rheometer. The mechanical characterization vacuum ltration and the ltrate was collected. The solvent was was rstly performed by using Anton Paar MCR-301 Rheometer. removed under reduced pressure and the residue was puried PP08-SN18311 measuring device with 8 mm diameter was used. with column chromatography over silica gel with DCM as Further data were acquired with dynamic mechanical analyzer eluent. Compound 5 was obtained as yellow solid (0.14 g, 38%). 1 d ¼ ¼ (DMA, Q800 TA Instruments) equipped with oscillation mode. H NMR (400 MHz, CDCl3): 7.74 (d, J 8.4 Hz, 4H), 7.67 (d, J 8.4 Hz, 4H), 7.26–7.22 (m, 4H), 7.22–7.17 (m, 4H), 6.57 (dd, J12 ¼ 17.3 Hz J23 ¼ 1.4 Hz, 2H), 6.29 (dd, J12 ¼ 17.3 Hz J34 ¼ 10.4 Hz, Synthesis ¼ ¼ 13 Creative Commons Attribution-NonCommercial 3.0 Unported Licence. 2H), 5.95 (dd, J23 1.4 Hz J34 10.4 Hz, 2H). C NMR (100 Synthesis of compound 2. 9,10-Dibromoanthracene (0.50 g, MHz, CDCl3): d 166.1, 140.1, 136.1, 133.0, 131.4, 128.3, 128.0, 1.50 mmol) and 4-formylphenylboronic acid (0.54 g, 3.57 mmol) 127.8, 127.7, 123.5, 84.1, 65.9. were dissolved in the toluene (10 mL). Tetrabutylammonium Synthesis of PMA-EPO (free radical polymerization). 4 bromide (TBAB, 2.0 mg, cat.) and 2.0 M K2CO3 (aq.) solution (3.2 Compound (22 mg 0.04 mmol) was dissolved in methyl acry- mL) was added to the reaction mixture and the mixture was late (1 mL) under an Ar atmosphere and then, AIBN (4 mg) was stirred at room temperature for 30 min under Ar. Then, added to the solution and well mixed again under Ar atmo- Pd(PPh3)4 (2.0 mg, cat.) was added to the mixture and re uxed sphere. The resulting mixture was added to the mold covered at 90 C for 24 h. The mixture was poured into water and with a glass plate. The mold was irradiated with UV light while This article is licensed under a extracted with DCM. The organic layer was dried over anhy- cooling in an ice bath for 30 min. The resulting polymer was drous sodium sulfate and the solvent was removed under extracted with THF (3 Â 200 mL) over 24 h. Then, the polymer reduced pressure. The residue was puried by column chro- was dried under vacuum for 3 hours. PMA-EPO was obtained as Open Access Article. Published on 02 marts 2020. Downloaded 26-09-2021 20:18:53. matography over silica gel with hexane, and then followed by transparent solid. DCM as eluent. Compound 2 was obtained as yellow solid Synthesis of PDMS-EPO poly(dimethylsiloxaneendoper- 1 oxide). (0.35 g, 61%). H NMR (400 MHz, CDCl3): d 10.24 (s, 2H), 8.18 (d, Sylgard® 184 which is a patented two-part (base (10.0 g) J ¼ 8.1 Hz, 4H), 7.71 (d, J ¼ 8.1 Hz, 4H), 7.68–7.60 (m, 4H), 7.43– and curing agent (1.0 g)) agent was mixed in 10 : 1 ratio in 13 d 7.37 (m, 4H).
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