Gold catalysis and photoactivation: a fast and selective procedure for the oxidation of free sugars

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1 Supporting Information Gold catalysis and photoactivation: a fast and selective procedure for the oxidation of free sugars Mehdi Omri, 1 Frédéric Sauvage, 2 Yan Busby, 3 Matthieu Becuwe, 2 Gwladys Pourceau,*,1 and Anne Wadouachi 1 1 Laboratoire de Glycochimie, des Antimicrobiens et des Agroressources (LG2A) UMR CNRS Institut de Chimie de Picardie FR 3085,Université de Picardie Jules Verne, 33 rue Saint Leu, FR Amiens Cedex, France. 2 Laboratoire de Réactivité et Chimie des Solides (LRCS), UMR CNRS Institut de Chimie de Picardie FR 3085, Université de Picardie Jules Verne, 33 rue Saint Leu, FR Amiens Cedex, France. 3 Laboratoire Interdisciplinaire de Spectroscopie Electronique (LISE), Namur Institute of Structured Matter (NISM), University of Namur, 61 Rue de Bruxelles, 5000 Namur, Belgium gwladys.pourceau@u-picardie.fr Contents Materials... 1 Instruments... 2 Photo-oxidation procedure... 2 Catalysts characterization... 3 Conversion rate determination... 5 Photo-assisted oxidation of glucose depending on the catalyst H NMR spectra of the crude products References Experimental Section Materials Chemical reagents such as glucose, maltose, lactose, cellobiose and maltotriose, and H 2 O 2 (ACS reagent, 30 wt% solution in water, non stabilized) were purchased from Sigma- Aldrich, Acros or Alfa Aesar (France) and used as received. Maltohexose was obtained by protection followed by acetolysis and deprotection of α-cyclodextrine, as previously described. 1 Milli-Q water was used for synthesis and analysis. Photocatalysts (Au/Al 2 O 3, Au/TiO 2 and Au/CeO 2 ) were those previously described. 2 S1

2 Instruments Incident sunlight irradiation was performed under standard AMG.1.5.G conditions (100 mw/cm 2 ) using Newport LCS100 sun simulator with class A spectral match.. Transmission electron microscopy (TEM) observation was performed using a Philips TECNAI 200F20 microscope. Images were recorded in bright-field. The samples for TEM were prepared as follow: the catalyst was suspended in EtOH, a drop was deposit on a Cu grid with a carbon support membrane and the grid was let dried 15 h. Gold particle size distribution was determined by counting 100 particles from multiple separate catalyst particles. After dissolving the catalyst into aqua regia (HCl/HNO 3 3:1), the metal content of the catalysts was determined by Atomic Absorption Spectroscopy (AAS) using a Perkin Elmer AAnalyst 300 equipped with a gold lamp (λ=242.8 nm, slit = 0.7 nm). The powder X-ray diffraction (XRD) experiments were performed at room temperature on a diffractometer (Bruker D8 Advance XRD) equipped with a Cu X-ray tube (40 kv, 40 ma). The step size was 0.02 degree. The chemical analysis of the photocatalysts was performed by X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Xi by Thermo Scientific) using a 500 µm monochromatized Al K-alpha X-ray source, equipped with a dual ion-electron flood gun. High-resolution Au 4f core levels spectra have been acquired with 20 ev pass energy, while the scan number has been adjusted to get a similar signal-to-noise ratio for each spectrum. Data analysis was performed with Avantage software using a Shirley background and asymmetric peak line shape for metallic components. Conversion rate of sugars into corresponding aldonates was determined using 1 H NMR and High-Performance Liquid Chromatography. 1 H and 13 C NMR spectra were recorded on a BRUKER DMX300 spectrometer (at 300 and 75 MHz respectively) or on a BRUKER 400 MHz Advance III HD spectrometer (at 400 and 100 MHz respectively). Assignments of 1 H and 13 C signals were performed using correlated spectroscopy (COSY) and heteronuclear single quantum correlation (HSQC). Oxidized sugars were identified by comparing the 1 H NMR spectrum with that of initial sugars. Conversion rate was determined comparing the H 2 signal of aldonate to the H 1 signals (α and β) of initial sugar. The as-obtained conversion rate was compared with that determined by HPLC. HPLC analyses were performed on a Waters system equipped with an Evaporating Light Scattering Detector (ELSD) (Polymer Laboratoire), a Waters 2996 Photodiode Array Detector, a Waters 2767 Sample Manager and DEAE column (Tosoh Bioscience, TSKgel, 5PW). The elution was carried out using a gradient of ammonium formiate with a flow of 1 ml/min: 1mM for 10 min; then reached to 1 M in 10 min and continued for 10 min. Finally, the elution gradient was brought to 1 mm in 15min. Photo-oxidation procedure In a typical experiment, a 5% aqueous solution of the desired saccharide (250 mg in 5 ml of H 2 O) was placed in a sealed 10 ml glass tube, and the base (NaOH, 1 equiv) was added under stirring. The catalyst (2.5 mg) and a 30% aqueous H 2 O 2 solution (1.1 equiv) were added, and then the mixture was illuminated at RT (standard A.M.1.5G conditions, 100 mw/cm²). The photocatalyst was then removed by filtration and the filtrate was freeze-dried. The crude product was analyzed by NMR spectroscopy in order to determine the conversion rate. S2

3 Catalysts characterization A) Au/Al 2 O 3 mean size: 2.4 ± 0.5 nm B) Au/TiO 2 mean size: 2.4 ± 0.6 nm Size (nm) Size (nm) C) Au/CeO 2 mean size: 2.9 ± 0.7 nm D) Au/CeO 2 after 5 runs: 3.1 ± 0.6 nm Size (nm) 0 2Size 4 6(nm) Figure S1: TEM micrographs and gold particle size distribution (inset, measured on 100 particles) of the catalysts. Catalyst Dispersion Gold content (wt%) Au/Al 2 O ± 0.01 Au/TiO ± 0.02 Au/CeO ± 0.02 Au/CeO 2 after 5 runs ± 0.01 Table S1: Dispersion (determined using TEM 3 ) and gold content (measured by AAS) of the catalysts S3

4 Al2O3 Au/Al2O3 TiO2 Au/TiO2 CeO 2 Au/CeO Scattering angle ( 2θ, Cu Kα) Scattering angle ( 2θ, Cu Kα) Scattering angle ( 2θ, Cu Kα) Figure S2: X-ray diffractograms before (red line) and after gold deposition (blue line) on Al 2 O 3 (left), TiO 2 (center) and CeO 2 (right) Figure S3: Illumination spectrum of A class Newport LCS100 sun simulator with A.M.1.5G filter ( and UV-Visible absorption spectra gold nanoparticles supported upon Al 2 O 3, TiO 2 and CeO 2 semi-conductor measured in reflectance mode with an integration sphere. S4

5 Figure S4: High-resolution XPS showing Au 4f spectra from the pristine Au/CeO 2 photocatalyst (a) and after 5 photocatalytic cycles (b). The relative peak area associated with Au 0 (light-blue) and Au +1 (dark blue) doublets are indicated in the panels. The at% of gold evaluated on survey spectra was 0.4% in both samples. Conversion rate determination The same characterization procedure as previously described 2 was applied for each experiment to determine the conversion rate. By NMR (Fig. S5), the calculation performed for glucose oxidation is shown here: the area of H 2 peak of synthesized gluconate (δ=4.14 ppm, d, J=3.7 Hz) was compared to the area of H 1 peaks of residual glucose (H 1 α: δ=5.24 ppm, d, J=3.7 Hz and H 1 β: δ=4.65 ppm, d, J=7.9 Hz,) to calculate a conversion rate according to the formula : The conversion rate calculated by NMR can be confirmed by integration of HPLC peaks of gluconate (RT 14.5 min) and residual glucose (RT 2.6 min) (Fig. S6). S5

6 (A) (B) (C) (D) Figure S5: 1 H NMR spectra (in D 2 O) obtained for glucose (A), commercial gluconic acid (B), photo-assisted oxidation of glucose using Au/CeO 2 after 5 min (C) and 10 min (D). Reaction conditions: 5 % sugar solution, 1.1 eq. H 2 O 2, 1 eq. NaOH, illumination (A.M.1.5G conditions mw/cm 2 ) S6

7 (A) % Time (min) (B) % Time (min) (C) % * Time (min) (D) % 2.33 * Time (min) Figure S6: HPLC profiles obtained for glucose (A), commercial gluconic acid (B), photoassisted oxidation of glucose using Au/CeO 2 after 5 min (C) and 10 min (D). The peak at 2.3 min (*) is due to the Na + salts. Reaction conditions identical to S5. S7

8 Au/Al 2 O 3 Au/CeO 2 Au/TiO 2 Figure S7: EDX spectra acquired on lyophilized photocatalytic bath using Au/Al 2 O 3, Au/CeO 2 and Au/TiO 2 photocatalysts (analysis performed on ca. 5 x 5 mm 2 magnified sample; reaction conditions: 5 % sugar solution, 1.1 eq. H 2 O 2, 1 eq. NaOH, illumination (A.M.1.5G conditions mw/cm 2, 10 min)) S8

9 Photo-assisted oxidation of glucose depending on the catalyst (A) (B) (C) (D) Figure S8: 1 H NMR spectra (in D 2 O) obtained for photo-assisted oxidation of glucose using Au/Al 2 O 3 (A), Au/TiO 2 (B), Au/ CeO 2 (C) and reused Au/ CeO 2 (D, 6th run). Reaction conditions identical to S5 but 5 min). The 6 th run using Au/CeO 2 led to 63% conversion after 5 min leading to a TOF value of h -1 (calculated as described earlier 3 using the dispersion of the reused catalyst (Table S1). S9

10 1H NMR spectra of the crude products A) B) C) Figure S9: 1 H NMR spectra (in D 2 O) obtained for photo-assisted oxidation of glucose (A), maltose (B) and lactose (C) using Au/CeO 2. Reaction conditions: 5 % sugar solution, 1.1 eq. H 2 O 2, 1 eq. NaOH, illumination (A.M.1.5G conditions mw/cm 2, 10 min). S10

11 Figure S10: 1 H NMR spectra (in D 2 O) obtained for photo-assisted oxidation of cellobiose (A), maltotriose (B) and maltohexose (C) using Au/CeO 2. Reaction conditions: 5 % sugar solution, 1.1 eq. H 2 O 2, 1 eq. NaOH, illumination (A.M.1.5G conditions mw/cm 2, 10 min). References 1 Hoffmann B., Zanini D., Ripoche I., Burli R., Vasella A. Helv Chim Acta 2001, 84, Omri M., Pourceau G., Becuwe M., Wadouachi A. ACS Sustain. Chem. Eng. 2016, 4, Delidovich I.V., Moroz B.L., Taran O.P., Gromov N.V., Pyrjaev P.A., Prosvirin I.P., Bukhtiyarov V.I., Parmon V.N. Chem. Eng. J. 2013, S11