Combining Proton and Electron Transfer to Modulate the Stability of Cucurbit[7]uril Complexes

Transcription

1 LANGMUIR Combining Proton and Electron Transfer to Modulate the Stability of Cucurbit[7]uril Complexes Wei Li and Angel E. Kaifer* Center for Supramolecular Science and Department of Chemistry, University of Miami, Coral Gables, FL SUPPORTING INFORMATION TABLE OF CONTENTS Page Experimental S2 1 H NMR spectroscopic data for CB7 inclusion of 1 and 1H + S3 High resolution ESI- TOF mass spectrum of Na + CB7 1H + S4 1 H NMR spectra of 1 as a function of ph S5 1 H NMR spectra of CB7 1 as a function of ph S6 Determination of binding constants by competition experiments Half- wave potentials measured in CV experiments Cubic scheme showing all equilibria involving the redox and acid/base forms of 1 and their CB7 complexes Table summarizing all relevant equilibrium constants References S7- S9 S10 S11 S11 S12 Page S1

2 Experimental Cobaltocinium hexafluorophosphate, 1- (1- adamantyl)- pyridinium bromide, deuterium chloride, d3- sodium acetate, ferrocenecarboxaldehyde, N- mehtylamine and NaBH4 were all commercially available. Compound 1 was prepared by the reductive amination of ferrocenecarboxaldehyde with methylamine, as reported before. 1 Cyclic voltammetric experiments were performed on a BAS- 100 electrochemical station at room temperature. Glassy carbon working electrodes, Pt counter electrode and Ag/AgCl reference electrodes were used. The glassy carbon working electrodes were polished with μm alumina powder (0.05- µm, BUEHLER MICROPOLISH II) on a felt surface before every measurement. 1 H NMR spectra were recorded using a 500 MHz Bruker Avance NMR spectrometer. The ph measurements in H2O and D2O were done using a PHR- 146 Micro Combination ph Electrode on Accumet model 50 ph/ion/conductivity meter from Fisher Scientific, calibrated using standard buffers, ph 4, 7 and 10. Page S2

3 Figure S1. 1 H NMR spectra of 1 mm 1H + in the (A) absence and (B) presence of 1.0 equiv of CB7 in 0.1 M NaCl/D2O solution pd~4 at 25 o C Figure S2. 1 H NMR spectra of 1 mm 1 in the (A) absence and (B) presence of 1.0 equiv of CB7 in 0.1 M NaCl/D2O solution pd~12 at 25 o C Page S3

4 Figure S3. High- resolution ESI- TOF mass spectra of the complex Na + CB7 1H +. (A) Full m/z range, (B) experimental isotopic distribution pattern for the most intense peak (expanded scale) and (C) theoretical simulation of the isotopic distribution pattern corresponding to the chemical formula C54H58FeN29O14Na 2+. Page S4

5 Figure S4. (Top) 1 H NMR spectra of a 1 mm solution of guest 1 in 0.1 M NaCl/D2O at increasing pd values. (Bottom) Measured chemical shift values of the indicated protons as a function of the solution pd, which was adjusted by addition of DCl or NaOD. Page S5

6 Figure S5. (Top) 1 H NMR spectra of a 1 mm solution of guest 1 in 0.1 M NaCl/D2O in the presence of 1.0 equiv of CB7 at increasing pd values. (Bottom) Measured chemical shift values of the indicated guest protons as a function of the solution pd, which was adjusted by addition of DCl or NaOD. Page S6

7 Determination of the association equilibrium constants by competition experiments Let us consider a single host, H, that can form complexes with two different guests, G1 and G2. The following equations (Eqs. 1-4) define the equilibrium situation in experiments in which the concentration of host is not enough to fully bind both guests K G1 = [H G1] eq. [G1] eq. [H] eq. (1) K G2 = [H G2] eq. [G2] eq. [H] eq. (2) [H] total = [H G1] eq. +[H G2] eq. +[H] eq (3) K G1 = K G 2 [H G1] eq. [G2] eq. [G1] eq. [H G2] eq. (4) Here, G1 is the guest, for which the association equilibrium constant K G1 is to be determined, G2 is the reference guest with known association equilibrium constant K G2 and H refers to the host. In eq. 3, we can assume that [H]eq is negligible if both K values are high and [G1]total + [G2]total > [H]total. 1- (1- Adamantyl)- pyridinium (Ad- Py) and cobaltocenium (Cob + ) were selected as the reference guests for 1H + and 1, respectively. The association equilibrium constant values of M - 1 (for the CB7 Ad- Py complex) 2 and M - 1 (for the CB7 Cob + complex) 3 in 50 mm sodium acetate aqueous solution were measured by Isaacs and co- workers and our own group, respectively. 1 H NMR Page S7

8 spectroscopic methods were applied to determine the values of K + for the CB7 1H + complex and K for CB7 1. 1H + competes with Ad- Py for insufficient CB7 in 50 mm CD3COONa/D2O solution at pd 4. Free and CB7- bound Ad- Py are in slow exchange in the NMR time scale, that is, separated sets of peaks for the free and CB7- bound species are observed simultaneously in the 1 H NMR spectra. Integration of the signals for a given proton on the free and bound species allows the calculation of the molar fractions of free ( χ free ) and CB7- bound ( χ bound ) Ad- Py. From these molar fractions, the value of K+ can be readily derived. For instance, using the data for peak 1 in the spectrum of Figure S6, the concentrations of free Ad- Py ([Ad] free ) and CB7- bound Ad- Py ([Ad] bound ) and K + are determined by the following equations (Eq. 5-7), 1.00 [Ad] free = 0.5mM χ free = 0.5mM = 0.23mM (5) [Ad] bound = 0.5mM 0.23mM = 0.27mM (6) K + = M mM 0.23mM 0.27mM 0.27mM = M 1 The average value of the equilibrium association constant K + for 1H + was found to be M - 1 in 50 mm sodium acetate solution at room temperature. (7) Page S8

9 Figure S6. 1 H NMR spectrum of a sample containing 0.5 mm 1H +, 0.5 mm Ad- Py and 0.5 CB7 in 50 mm CD3COONa/D2O solution pd 4.5 at 25 o C. Guest 1 competes with Cob + for a limited amount of CB7 in 50 mm CD3COONa/D2O solution at pd 12. The free and CB7- bound Cob + are in fast exchange in the NMR time scale, when both free and bound species co- exist. Therefore, only one average peak with the chemical shift δ observed is recorded. The molar fractions of the free Cob + ( χ free ) and CB7- bound Cob + ( χ bound ) can be determined from the values of δ observed as well as δ free and δ bound (see Eq. 8-10, and the chemical shift values in Figure S7). Following calculations similar to those shown to extract the value of K +, the average association equilibrium constant K for guest 1 is determined to be 3.4 x 10 9 M - 1. δ observed = δ free χ free +δ bound χ bound (8) χ free + χ bound =1 (9) δ observed = 5.74 χ free χ bound (10) Page S9

10 Figure S7. 1 H NMR spectra of (A) free Cob + and (B) CB7- bound Cob + in 50 mm CD3COONa/D2O solution pd 12 at 25 o C Half-wave potentials (Volts vs Ag/AgCl) measured directly in CV experiments 1H 2+ + e 1H + E1/2,H+ = V e 1 E1/2 = V CB7 1H 2+ + e CB7 1H + CB e CB7 1 E1/2,c/H+ = V E1/2,c= V Page S10

11 Scheme S1. Complete schematic representation of the relevant equilibria between all acid/base and redox species associated with guest 1 and their corresponding CB7 complexes. E 1/2,H+ -e 1H 2+ -H +, K a/ox E 1/2 -e 1 + 1H + -H +, K a,f 1 +CB7 K +/ox +CB7 K + +CB7 K +CB7 K ox CB7-1H 2+ -H +, K a,c/ox CB7-1 + E 1/2,c/H+ -e E 1/2,c -e CB7-1H + -H +, K a,c CB7-1 Table 1. Equilibrium constants values as labeled in Scheme 1. Values in red are determined directly from 1 H NMR spectroscopic and electrochemical experiments and values in black are extracted using calculations based on the thermodynamic cycles in the cube of Scheme 1. Acid Dissociation Constant Equilibrium Association Constant Ka,f K M - 1 Ka,c K M - 1 Ka/ox K+/ox M - 1 Ka,c/ox Kox M - 1 Page S11

12 References 1. Norrild, J. C.; Sotofte, I. J. Chem. Soc., Perkin Trans , Liu, S.; Ruspic, C.; Mukhopadhyay, P.; Chakrabarti, S.; Zavalij, P. Y.; Isaacs, L. J. Am. Chem. Soc. 2005, 127, Sobransingh, D.; Kaifer, A. E. Langmuir 2006, 22, Page S12