Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt

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1 Electronic Supplementary Material (ESI) for RSC Advances. This journal is The Royal Society of Chemistry 2018 Electronic Supplementary Information Electron paramagnetic resonance spectroscopic studies of the electron transfer reaction of Hantzsch ester and a pyrylium salt K. Sebők-Nagy, a D. Rózsár, b L. G. Puskás, b Á. Balázs, b and T. Páli a a Institute of Biophysics, Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, H-6726 Szeged, Hungary. pali.tibor@brc.mta.hu b AVICOR Ltd., Alsó kikötő sor 11/D, H-6726 Szeged, Hungary. a.balazs@avicorbiotech.com Materials 2,2,6,6-Tetramethylpiperidine-N-oxyl (TEMPO) and Diethyl 2,6-dimethyl-1,4-dihydropyridine- 3,5-dicarboxylate (Hantzsch ester, HEH) from AK Scientific, Acrylamide from Fluka, 5,5- Dimethyl-1-pyrroline-N-oxide (DMPO), Benzaldehyde and Dimethyl sulfoxide from Sigma- Aldrich were purchased. All compounds were of analytical grade purity and used as received. Synthesis 2,4,6-Tris(4-methoxyphenyl)pyrilium tetrafluoroborate (1) [1,2] ; N-(Ethoxy(phenyl)methyl)- acrylamide (3): This material was synthesized in 40 % isolated yield on the basis of the reported literature [3] procedure starting from benzaldehyde and acrylamide. Preparation of samples Measurements of TEMPO consumption: I. HEH (0.22 M), 3 (0.2 M); II. TMPP (0.02 M); III. TEMPO (0.2 M) in DMSO. Stock solutions for the measurements of DMPO adducts: I. TMPP (0.04 M), 3 (0.2 M) and DMPO (0.045 M) in DMSO; II. HEH, solid. All stock solutions were kept under argon atmosphere at room temperature (22 C) before use. The initial concentrations were 0.04, 0.1 and 0.2 M for HEH, 0.02 M for TMPP, 0, 0.04 and 0.2 M for 3 and 0.2 M for TEMPO in case of the measurement of TEMPO consumption, while in DMPO adduct measurements the concentrations were 0.04 M for HEH, 0.04 M for TMPP, 0 and 0.2 M for 3 and M for DMPO in the reaction mixture. The reactions were carried out under either air or argon atmosphere. The solubility of HEH and the reaction partners was acceptable only in DMSO. Therefore we could not perform the measurements in other widely used solvents such as, e.g., acetonitrile. Since, however, DMSO is known to have radical scavenging properties with respect to OH, and OOH radicals in water [4] we had to exclude any solvent related effects in the reactions: Firstly, these radicals can not be formed in our experiments as there was no water in the reaction mixture, and the experiments were done under argon, except for a test with O2 (see note 12 in the main text). Secondly, we did not find any un-identified spectral component (there was no EPR intensity left for OH, OOH or other radicals trapped by DMPO). Thirdly, as a test, we generated OH, OOH radicals in water according to literature data [5] and trapped related radicals with DMPO, but the respective spectral shapes did not show up with HEH in our water-free system.

2 EPR spectroscopy All measurements were carried out at room temperature. For the experiments carried out in oxygen-free atmosphere, EPR glass capillaries were purged with argon prior to loading the samples into them, then they were sealed with parafilm. EPR spectra were recorded on a Bruker (Rheinstetten, Germany) ECS106 X-band CW EPR spectrometer with the following settings: scan range G, microwave frequency ~ 9.41 GHz (with a typical sample in the resonator), microwave power 5.07 mw, modulation frequency 100 khz, modulation amplitude 1.06 G, receiver gain , resolution of field axes 1024, number of scans 4. The spectra were recorded during the reaction, which lasted 3-4 days in the case of the measurements with TEMPO. EPR spectra of DMPO adducts were detected approximately for 1 hour and the signal/noise ratio was greater than 1:1 even in the end of the measurement period. Evaluation of data The analysis was carried out using custom code written in Igor (WaveMetrics, Inc., Lake Oswego, OR. USA). The simulation-fitting method applied for the deconvolution of EPR spectra was based on the Levenberg-Marquardt algorithm. TEMPO decay Figure 1.S Decay of the concentration of TEMPO, measured as the integrated intensity of EPR absorption spectra. Conditions: [TMPP + ] 0 = 0.02 M, [TEMPO] 0 = 0.2 M, DMSO, under argon, room temperature, ( ): [HEH] 0 = 0.04 M, [3] 0 = 0.04 M; ( ): [HEH] 0 = 0.1 M, [3] 0 = 0 M; ( ): [HEH] 0 = 0.2 M, [3] 0 = 0.2 M. Lines are the best fit according to Eq. (1). The function used to fit the TEMPO decay curves: I (t )=y (0)+A 1 e k 1 t +A 2 e k 2 t (1)

3 Table 1.S Kinetic parameters of the decay of the concentration of TEMPO. Conditions: see Figure 1S. Sample Conversion / % k / s -1 k / s ± ± ± ± ± ± 0.18 Fitting EPR spectra and calculation of EPR parameters EPR spectra were fitted with a sum of either pure Lorentzian or Voigt line shape functions. The lines were grouped as individual spectra characterised by a centre and hyperfine splitting paramater, and the number of (hyper fine) lines. The composite spectrum was the sum of the individual spectra. A global linear baseline was used for baseline correction. First derivatives of Lorentzian line shape (L'(B)) (2) and Voigt line shape (V'(B)) (3) [6] : L' (B)= d n m db i= 1 j=1 A i HH i (B B ij ) 2 +HH i 2 (2) V' (B)= d db i= 1 n m j= 1 G (B' )=Ae ( ln2 B' HH ) 2 G (B' B G )L(B B ij )db' (3) (4) where B is the magnetic feld, B ij is the position of a single peak, HH is the half width at half height, A is the constant corresponding to the area, G is the Gaussian function, B G is the magnetic field at the centre of Gaussian, i is the number of component spectra, j is the number of peaks. Half width at half height values for Gaussian-, Lorentzian- and Voigt functions, w G, w L and w V respectively, were calculated from the fitted line widths and the line shape of the derivatives of Voigt functions [6]. Table 2.S Electron Paramagnetic Resonance parameters of DMPO adducts. Adduct a N / G a H / G Centre* / G w V ** / G w L ** / G w G ** / G DMPO-HE ± ± ± ± ± 0.083*** ± DMPO-TMPP(4) ± ± ± ± ± 0.071*** 0.66 ± 0.11 DMPO-TMPP(2,6) ± ± ± ± ± 0.073*** 1.12 ± 0.24 DMPO-TMPP(4H) ± ± ± ± ± 0.074*** 0.62 ± 0.13 DMPO-TMPP(2H) ± ± ± ± ± 0.024*** ± 0.061

4 * The g factor corresponding to Gauss is , from a comparison of the spectra of the DMPO-trapped radicals with those of TEMPO in DMSO (not shown) and its reported g factor [7]. ** Half width at half height, calculated from fitted Voigt parameters *** Contribution is very small Time dependence of the concentrations of DMPO-adducts Fitting function: I (t )=A k f (e k f ( t t 0 ) k c( t t e 0) ) k c k f (5) where k f and k c are the rate constants of the formation and consumption, respectively. Table 3.S Kinetic parameters of DMPO adducts. Conditions: [HEH] 0 = 0.04 M, [TMPP + ] 0 = 0.04 M, [DMPO] 0 = M, DMSO, under argon, room temperature. Symbo l [3] 0 = 0 M Adduct k f 10 3 / s -1 k c 10 3 / s -1 A 10-5 t 0 / s DMPO-HE ± ± ± ± 27.5 DMPO-TMPP(4) (2.722 ± 0.078) 8.77 ± ± 0 0 ± 0 DMPO-TMPP(2,6) (1.595 ± 0.042) 8.41 ± ± 0 0 ± 0 DMPO-TMPP(4H) ± ± ± ± DMPO-TMPP(2H) ± ± ± ± [3] 0 = 0.2 M Symbol Adduct k f 10 3 / s -1 k c 10 3 / s -1 A 10-5 t 0 / s DMPO-HE ± ± ± ± DMPO-TMPP(4) (0.831 ± 0.046) ± ± 0 0 ± 0 DMPO-TMPP(2,6) (0.898 ± 0.045) 6.52 ± ± 0 0 ± 0 DMPO-TMPP(4H) + too noisy to fit too noisy to fit too noisy to fit too noisy to fit DMPO-TMPP(2H) + too noisy to fit too noisy to fit too noisy to fit too noisy to fit In most cases the limited number of points did not allow completely released fits. Instead, the parameters were optimised in an iterative stepwise process. If the fit did not yield the onset time of the formation (because the corresponding reaction was faster than setting up the scan), it was set to zero. These curves are indicated with dashed lines in Fig. 4 and their k f values are in parenthesis in Table 3.S. References 1 R. Lombard and J. P. Stephan, B. Soc. Chim. Fr., 1958, K. Dimroth, C. Reichardt and K. Vogel, Org. Synth., 1969, 49, M. Li, B. Luo, Q. Liu, Y. Hu, A. Ganesan, P. Huang and S. Wen, Org. Lett., 2014, 16, (a) M. K. Eberhardt and R. Colina, J. Org. Chem., 1988, 53, ; (b) C. L. Øpstad, T.-B. Melø, H.-R. Sliwka and V. Partali, Tetrahedron, 2009, 65,

5 5 (a) K. Makino, M. M. Mossoba and P. Reisz, J. Am. Chem. Soc., 1982, 104, ; (b) P. Riesz, D. Berdahl and C. L. Christman, Environ. Health Persp., 1985, 64, U. Platt and J. Stutz in Differential Optical Absorption Spectroscopy Principles and Applications. Springer-Verlag Berlin Heidelberg, Chapter 3. 7 K. Herb, R. Tschaggelar, G. Denninger and G. Jeschke, J. Magn. Reson., 2018, 289, Pages