Supporting Information. Effective detection of mycotoxins by a highly luminescent metal-organic framework

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1 Supporting Information Effective detection of mycotoxins by a highly luminescent metal-organic framework Zhichao Hu,, William P. Lustig,, Jingming Zhang, Chong Zheng, # Hao Wang, Simon J. Teat, Qihan Gong, Nathan D. Rudd and Jing Li *, Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Rd, Piscataway, USA # Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, USA S1

2 Table of Contents S1. Materials...S3 S2. Solvent exchange and outgassing of LMOF S3 S3. Powder X-ray diffraction (PXRD) analysis of LMOF S4 S4. Thermogravimetric analysis of LMOF S4 S5. Optical characterization of LMOF S5 S6. Pore characterization of LMOF S6 S7. Stern Volmer curves for Aflatoxins B1 and B2...S7 S8. Limit of detection (LOD) for Aflatoxin B1...S8 S9. Simulation of analyte loaded structures...s9 S10. Extended Hückel calculations... S10 S11. References... S12 S2

3 S1. Materials Reagents and solvents were used as received from: Alfa Aesar [[1,1,2,2-tetraphenylethene (98%), bromide liquid (99.8%), dimethylformamide (99%), tricyclohexylphosphine (98%), sodium sulfate (99%), dichloromethane (99.5+%), chloroform (99.8%), methanol (99.90%), palladium(ii) acetate (99.98%), zinc nitrate hexahydrate (99%), dimethylacetamide (99%), dimethyl sulfoxide (99%), 2- propanol (99.5%), ], Sigma Aldrich - [potassium phosphate tribasic (98%), pyridine-4-boronic acid (90%), and biphenyl-4,4 -dicarboxylic acid (97%)]. All mycotoxin samples (structures shown below) were used as received from Sigma Aldrich: Aflatoxin B 1 (98%, from Aspergillus flavus), Aflatoxin B 2 (98%), Aflatoxin G 1 (98%, from Aspergillus flavus), and Ochratoxin A (98%, from Petromyces albertensis). Figure S1. Chemical structures of selected mycotoxins. S2. Solvent exchange and outgassing of LMOF-241 Residual solvent molecules present in the pores of LMOF-241 were replaced with dichloromethane (DCM) through a solvent exchange process. In this process, a 200 mg sample of as-made LMOF-241 was placed in 15 ml of DCM in a sealed vial. The sample was left for two hours at room temperature, after which the supernatant was decanted and replaced with 15 ml of fresh DCM. This process was repeated six times, and the sample was recovered via filtration. The sample was then heated under vacuum at 60 C overnight to remove the DCM. Powder X-ray diffraction analysis was used to confirm that the sample s structure was retained, and thermogravimetric analysis was used to confirm complete removal of all solvent molecules. S3

4 S3. Powder X-ray diffraction (PXRD) analysis of LMOF-241 Powder X-ray diffraction (PXRD) analyses were performed using a Rigaku Ultima-IV diffractometer at room temperature under Cu Kα radiation (λ= Å). Data was collected from θ, with the operating power set to 40 kv/44 ma. The scan rate was 3 2θ/min, with a step size of 0.2 2θ. Figure S2. The PXRD patterns of simulated (black), as-made (red), and outgassed (blue) LMOF-241. S4. Thermogravimetric analysis of LMOF-241 Thermogravimetric analysis (TGA) was performed using a TA Instruments Q5000 under constant N 2 flow (20 ml/min). Approximately 5 mg of sample was loaded into a platinum pan, which was then heated from C at a rate of 10 C/minute. Figure S3. Thermogravimetric (TG) analysis of as-made (blue) and outgassed LMOF-241 (red). S4

5 S5. Optical characterization of LMOF-241 UV-vis diffuse reflectance spectra were collected for 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane (tppe) and LMOF-241 at room temperature using a Shimadzu UV-3600 spectrophotometer. The diffuse reflectance data was then converted to the Kubelka-Munk Function as follows: F(R) = (1 R)2 2R Equation S1. Kubelka-Munk function F(R), where R is the diffuse reflectance Kubelka-Munk Energy (ev) Figure S4. The optical absorption spectrum (converted to KM function) of the tppe ligand (red) and LMOF-241 (blue). Sold-state excitation and emission spectra were collected for tppe and LMOF-241 at room temperature using a Varian Cary Eclipse spectrophotometer. S5

6 1.0 Relative Intensity (A.U.) Wavelength (nm) Figure S5. The excitation (dotted line) and emission (solid line) spectra of tppe (red) and LMOF-241 (blue), with intensities scaled to the material s internal quantum yield. Section S6. Pore characterization of LMOF-241 Gas sorption isotherms of out outgassed LMOF-241 were collected on a Quantachrome Instruments Autosorb-1 MP volumetric gas sorption analyzer using ultra high purity N2 (99.999%). Liquid nitrogen was used as coolant to achieve cryogenic temperature (77 K). The N 2 isotherm was collected in a pressure range from 10-7 to 1 atm. The BET surface area was obtained using Autosorb v1.50 software. Figure S6. N 2 77K adsorption (black) and desorption (red) isotherms of degassed LMOF S6

7 I o /I I o /I S7. Stern Volmer curves for Aflatoxins B 1 and B 2 The Stern-Volmer equation was used to quantify the quenching efficiency of Aflatoxin B 1 and Aflatoxin B 2 with respect to LMOF-241. At low concentrations, the Stern-Volmer plots are linear, allowing the quenching efficiency (K SV) to be calculated from the slope of the line. I 0 I Q = 1 + K SV [Q] Equation S2. Stern-Volmer equation, where I 0 is the initial fluorescence intensity, I Q is the fluorescence intensity at a given concentration of quenching agent, K SV is the quenching efficiency, and Q is the concentration of quenching agent. 1.5 y = 54227x + 1 R² = E E E E E E-06 Concentration (M) 2 y = 32436x + 1 R² = E E E E-05 Concentration (M) Figure S7. SV curves for Aflatoxin B 1 (top) and Aflatoxin B 2 (bottom). S7

8 Intensity (A.U.) Intensity (A.U.) I o /I S8. Limit of detection (LOD) for Aflatoxin B 1 The limit of detection of Aflatoxin B 1 was defined as the concentration of toxin at which the change in intensity was greater than the average standard deviation in repeated measurements of the same sample. The average standard deviation in intensity for the Aflatoxin B 1 fluorescence titration was A.U. Using the SV curve for the Aflatoxin B 1 fluorescence titration in Figure S7, we determined that the limit of detection for Aflatoxin B 1 was 43 ppm. To confirm, a low-concentration titration of LMOF-241 with Aflatoxin B 1 was performed, and the addition of 46 ppb was detected Concentration (ppb) Wavelength (nm) Wavelength (nm) Figure S8 Top: SV curve for low-concentration fluorescence titration of LMOF-241 with Aflatoxin B 1. Bottom: LMOF-241 emission spectra from the low concentration fluorescent titration of LMOF-241 with Aflatoxin B 1, with peak detail inset. Key: 0 ppb AFB 1 (black), 46 ppb AFB 1 (red), 91 ppb AFB 1 (green), 134 ppb AFB 1 (orange), 177 ppb AFB 1 (blue). S8

9 S9. Simulation of analyte loaded structures The Materials Studio Sorption package was used to simulate adsorption of Aflatoxin B 1 and B 2 into the pores of LMOF-241, generating an optimized toxin-loaded MOF structure. The simulation utilized the GCMC method and Burchard Universal Force Field, and was performed at room temperature for 10 7 equilibirum steps. The LMOF-241 supercell used in the simulation was composed of unit cells (approximately Å). Six and five configurations, chosen on the basis of close contact of toxin with the MOF, were selected for Aflatoxin B 1 and B 2 respectively. A fragment of the overall structure (toxin@lmof-241) was taken for Extended Hückel calculations. The LMOF-241 fragments were chosen such that the closest PBU to the toxin molecule was included, with all Zn clusters full coordinated. H atoms were manually added to any non-coordinated carboxylate groups for charge balancing purposes. Figure S9. Selected AFB 1@LMOF-241 fragments used in Extended Hückel calculations. The LMOF- 241 framework is shown using the thin wire/ball model, while the Aflatoxin B 1 molecule is shown using the thick bar/ball model. Close atom-atom interactions (< 3 Å) are shown as dotted purple lines, and the minimum toxin-framework distance (d min) is given below, along with the composition of each framework fragment. (a) Fragment AFB1_A, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (b) Fragment AFB1_B, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (c) Fragment AFB1_C, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (d) Fragment AFB1_D, d min = Å, Zn 2H 4(bpdc) 4(tppe) 2. (e) Fragment AFB1_E, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (f) Fragment AFB1_F, d min = Å, ZnH 2(bpdc) 2(tppe) 2. Key: Zn (teal), C (grey), O (red), N (blue), H (white). S9

10 Figure S10. Selected AFB fragments used in Extended Hückel calculations. The LMOF-241 framework is shown using the thin wire/ball model, while the Aflatoxin B 2 molecule is shown using the thick bar/ball model. Close atom-atom interactions (< 3 Å) are shown as dotted purple lines, and the minimum toxin-framework distance (d min) is given below, along with the composition of each framework fragment. (a) Fragment AFB2_A, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (b) Fragment AFB2_B, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (c) Fragment AFB2_C, d min = Å, ZnH 2(bpdc) 2(tppe) 2. (d) Fragment AFB2_D, d min = 2.237Å, ZnH 2(bpdc) 2(tppe) 2. (e) Fragment AFB2_D, d min = Å, ZnH 2(bpdc) 2(tppe) 2. Key: Zn (teal), C (grey), O (red), N (blue), H (white). S10. Extended Hückel calculations Because of the large size of the analyte-lmof complex with more than 200 atoms in the asymmetric unit, the semi-empirical extended Hückel (EH) method was employed to calculate the orbital energy levels and to estimate the interaction between the toxin and the LMOF. 1-2 A 64 k-point set in the irreducible wedge of the Brillouin zone was used. The EH parameters used in the computation are (atomic energy in ev and orbital exponent in parenthesis): H 1s: (1.30); C 2s: (1.625), 2p: (1.625); N: 2s: (1.95), 2p: (1.95); O 2s: (2.275), 2p: (2.275) ; Zn 4s: (2.01), 4p: (1.70), 3d: (6.15, 2.60) with double-zeta linear combination coefficients of C and C The fragment molecular orbital overlaps and reduced overlap populations between the toxin and the LMOF were calculated using the EH package CACAO. 3 The six interaction S10

11 configurations for AFB 1 corresponding to Figure S10 (a)-(f), five configurations for AFB 2 corresponding to Figure S11 (a)-(e) were calculated using the EH package CACAO. 1 The EH parameters used are the default values in the package. The calculated HOMO/LUMO energy levels of the selected mycotoxins and LMOF-241 are given in Table S1. Table S2 lists the sum of the absolute fragment molecular orbital overlap (SAFMOOP) and the absolute reduced overlap population (AROP) between the two toxins and the LMOF-241. SAFMOOP was used because some molecular orbital overlap is positive and some negative depending on the orientation and coordinate system chosen. If only the overlaps are summed, many will cancel each other. Thus a better measure of the orbital interaction strength is the sum of the absolute overlap. For the same reason, AROP is used. Table S1. The calculated HOMO/LUMO energy levels of AFB 1, AFB 2 and LMOF-241. Mycotoxin/MOF HOMO (ev) LUMO (ev) Energy Gap (ev) Aflatoxin B Aflatoxin B LMOF Table S2. Sum of the absolute fragment molecular orbital overlap (SAFMOOP) and the absolute reduced overlap population (AROP) between AITC and the MOF of the four configurations calculated. Configuration SAFMOOP AROP AFB1@LMOF241 Site A AFB1@LMOF241 Site B AFB1@LMOF241 Site C AFB1@LMOF241 Site D AFB1@LMOF241 Site E AFB1@LMOF241 Site F Average AFB2@LMOF241 Site A AFB2@LMOF241 Site B AFB2@LMOF241 Site C AFB2@LMOF241 Site D AFB2@LMOF241 Site E Average S11

12 S11. References 1. Hoffmann, R. J. Chem. Phys. 1963, 39, Whangbo, M. H.; Hoffmann, R.; Woodward, R. B. Proc. R. Soc. London 1979, A366, Mealli, C.; Proserpio, D. M. MO Theory Made Vsible J. Chem. Edu. 1990, 67, S12