Supporting Information

Transcription

1 Solvent Effects and Driving Forces in Pillararene Inclusion Complexes Christian Schönbeck, 1,2,3 Hui Li, 2 Bao-Hang Han* 2 and Bo W. Laursen* 1 1 Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark 2 National Center for Nanoscience and Technology, Beijing , China 3 Sino-Danish Center for Education and Research *Corresponding authors: bwl@nano.ku.dk, hanbh@nanoctr.cn Supporting Information S1

2 Contents H-NMR of DMP5A and estimation of residual solvent content... 3 Why impurities in the pillar-arene samples are not expected to influence K and ΔH... 5 Subsequent removal of residual solvents and a confirmative binding experiment... 7 Calculated enthalpies from the quantum chemical calculations ITC titrations in p-xylene Plots of calculated solvation enthalpies Plots of complexation enthalpies calculated in gas-phase, in implicit solvent, and with a hybrid implicit/explicit solvation model Energy-minimized structures of DMP5A complexes with dichloromethane and chloroform S2

3 H-NMR of DMP5A and estimation of residual solvent content Figure S-1: H-NMR spectrum of one of the DMP5A batches. Approximately 10 mm DMP5A in CDCl 3. The H-NMR spectrum in Figure S-1 is from the DMP5A batch that gave stoichiometries close to 0.75 in the ITC experiments. In addition to the three proton peaks from the DMP5A and the solvent (chloroform), peaks from dichloromethane (DCM) and various alkanes are observed. DCM was used as solvent in the synthesis and the alkanes are from the petroleum ether that was used as eluent in the purification. The integrals in Figure S-1 are normalized by setting the integral of Hc to 10 (there are 10 Hc protons in one DMP5A molecule). For each DMP5A molecule the amount of DCM and CH 2 (representing the alkanes) is: DCM: 1.72/2 = 0.86 molecules. CH 2 : 5.71/2 = units. S3

4 For the batch of DMP5A that gave stoichiometries around 0.82 the numbers are and 2.28 for DCM and CH 2, respectively. Assuming that the sample consists solely of DMP5A (M w = g/mol), DCM (M w = g/mol) and alkanes (represented by (CH 2 ) n, M w = g/mol)), the effective molecular weight for each molecule of DMP5A is: M w,eff (DMP5A): 1* g/mol *84.93 g/mol *14.01 g/mol =863.9 g/mol. For the batch with N=0.82 the number is g/mol. The effective molecular weight of each DMP5A molecule is thus 15.1% and 11.4% higher than the formal molecular weight that was used in the calculation of the concentrations. The actual concentrations of DMP5A are accordingly lower than expected. Fitting the enthalpograms with the corrected concentrations results in stoichiometries, N, that are 15.1% and 11.4% higher than the initial values. Thus, the stoichiometry around 0.75 that was obtained with one of the DMP5A batches increases to 0.86 and the stoichiometry around 0.82 that was obtained with the other batch increases to S4

5 Why impurities in the pillar-arene samples are not expected to influence K and ΔH In principle, impurities in the pillararene samples may influence K and ΔH for two overall reasons: 1) Impurities may interact with the pillararene, the guest molecule, or change the solvent properties. However, the concentrations of impurities are extremely low compared to the concentration of solvent molecules, so it is extremely unlikely that they will change the solvent properties. Specific interactions with the guests also seem unlikely to have a significant impact due to the low concentrations of guest and impurities. The cavity of the pillararene could in principle bind to some of the impurities but it is unlikely that the structure and charge distribution of the impurities matches the rather strict requirements for a strong interaction with pillararenes. In fact, the investigated guest molecules are among the strongest binders to DMP5A. The impurities mainly consist of dichloromethane (residual solvent from the synthesis) and petroleum ether (used as eluent in the column chromatography). Even in chloroform dichloromethane binds weakly to DMP5A with a binding constant of 6-8 M -1, 1 and also alkanes are known to have very weak interactions with pillararenes. 2,3 The low concentrations of these impurities and their weak affinities towards pillararenes results in a negligible impact on the measured values of K and ΔH. Further, if some of the impurities had a significant interaction with the host or guest it is unlikely that the One Set of Sites binding model would be capable of fitting the enthalpograms. Also, the consistency of the obtained binding parameters when the titrations are conducted with different concentrations of host and guest seems to rule out other interactions than the one between host and guest. Additionally, some of the impurities seemed to be insoluble in certain of the used solvents (cloudy solutions were observed and the solutions did not become transparent when additional solvent was added) so they were filtered out when preparing the samples for the ITC. 2) The presence of impurities in the pillararene samples results in the actual concentration of DMP5A to be lower than what is calculated from the weighed out amounts. One may think that concentration errors will lead to wrong estimates of K and ΔH but this is not the case, as will be shown here. The One Set of Sites binding model, which was used to fit the enthalpograms, assumes that one guest molecules, G, binds to one binding site, S, on the host, H. Note the distinction between a binding site, S, and the host, H. S5

6 S G S : G [1] with the binding constant K S : G S G [2] The conservation of mass requires that S S G NH t St : [3] G S G G t : [4] where H t is the total concentration of host molecules (DMP5A) and G t is the total concentration of guest molecules. N is the number of binding sites on each host molecule. For this reason, N, is usually referred to as the stoichiometry. However, N may also serve as a concentration correction factor by assuming that the species form 1:1 complexes (only one binding site per host molecule). In such case, the assumed total concentration of macromolecule is H t while the real concentration of macromolecule is S t. An experimentally obtained value of N = 0.75, may therefore indicate the formation of a 4:3 host:guest complex (0.75 binding sites per host molecule) or that the concentration of macromolecule is 25% lower than expected. In the present case the latter option certainly seems the most likely. Thus, when the enthalpograms are analyzed with the One Sites model and N denotes the number of binding sites on the macromolecule, possible concentration errors will be absorbed into the value of N, and the binding constant, K, will not be affected by errors in the concentration of the macromolecule. Similarly, the concentration correction factor, N, also appears in the equation that links the observable in the ITC experiments, the evolved heat, Q, to the binding enthalpy, ΔH: Q fnh HV [5] t Where V is the volume of the titration cell and f denotes the fraction of host molecules (or sites) that are bound to a guest: S6

7 f S : G S t Therefore, errors in the concentration of the host will not influence the obtained value of ΔH. Maybe the easiest way to convince oneself that this is indeed the case is to fit an enthalpogram, then change the nominal value of the host concentration and observe that only N changes, but ΔH and K are unchanged. Subsequent removal of residual solvents and a confirmative binding experiment After completing the bulk of the calorimetric titrations we managed to remove most of the dichloromethane from a sample. The original sample of DMP5A had been dried in vacuum overnight at 40 C but still contained dichloromethane and some alkanes (See H-NMR in Figure S-1). The bulk of these residual solvents are presumably lost upon heating to 180 C as shown by TGA (Figure S-2, Top). The mass loss corresponds reasonably well to the content of dichloromethane and alkanes estimated from the 1 H- NMR spectrum. After additional drying in vacuum, first at 160 C for 2 hours, then at 190 C for 2 hours, the mass loss drops to 7.5% and less than 3%, respectively. 1 H-NMR revealed that the drying steps reduced the content of dichloromethane from around 9% in the original sample to around 2% (Figure S-3). To test whether or not the removed dichloromethane had an impact on the binding thermodynamics a new binding experiment was conducted with the dried sample of DMP5A, which was titrated with the guest CN- C2-CN in toluene (Figure S-4). The obtained binding parameters are basically identical to those obtained with the original sample, except for the stoichiometry (N) which has increased from 0.73 to This shows that original low values for the stoichiometry indeed was due to the content of residual solvents. Further, it also confirms that the presence of these residual solvents do not affect the obtained binding thermodynamics. S7

8 Weight (%) [ ] Deriv. Weight (%/ C) Weight (%) [ ] Deriv. Weight (%/ C) Sample: DMP5a Size: mg Method: screenstd Comment: TGA-02 Analysenummer: TGA File: C:\TA\Data\TGA\2015\CBEC\DMP5a.001 Operator: CBEC/CNO Run Date: 17-Apr :59 Instrument: TGA Q500 V6.7 Build C % C Temperature ( C) Universal V4.7A TA Instruments Sample: DMP5A Size: mg Method: screenstd Comment: TGA-02 Analysenummer: 2015-V C TGA File: C:\TA\Data\TGA\2015\CBEC\DMP5A.001 Operator: LEOL Run Date: 27-Apr :40 Instrument: TGA Q500 V6.7 Build % C Temperature ( C) Universal V4.7A TA Instruments S8

9 Weight (%) [ ] Deriv. Weight (%/ C) Sample: DMP5A tør 2 Size: mg Method: screenstd Comment: TGA-02 Analysenummer: 2015-V TGA C File: C:\TA\Data\TGA\2015\CBEC\DMP5A tør Operator: TEBI Run Date: 28-Apr :45 Instrument: TGA Q500 V6.7 Build % C Temperature ( C) Universal V4.7A TA Instruments Figure S-2: Thermogravimetric analysis (TGA) of DMP5A. Top: Original sample used in most of the experiments, yielding stoichiometries around N = Middle: After drying in vacuum at 160 C for 2 hours. Bottom: After drying in vacuum at 190 C for 2 hours. Figure S-3: 1 H-NMR of DMP5A sample after drying at 190 C for 2 hours. The content of dichloromethane corresponds to around 2% of the mass. S9

10 Figure S-4: Titration of the dried sample of DMP5A (0.4 mm) with CN-C2-CN (4 mm) in toluene at 25 C. The obtained binding thermodynamics corresponds to those obtained with the original sample (see Table 1 in manuscript) S10

11 Calculated enthalpies from the quantum chemical calculations Table S-1: Calculated complexation enthalpies in kj/mol for the complexes of DMP5A with various guest molecules, including solvent molecules, in the gas phase and in various implicit solvents. The DFT calculations were performed with the cam-b3lyp functional and the 6-31G(d,p) basis set. Guest Gas phase DMSO Acetonitrile Acetone o-xylene Toluene p-xylene CNC2CN BrC4Br Butane MDBG DMSO Acetontitrile o-xylene Toluene Table S-2: Calculated solvation enthalpies in kj/mol for the free species and the complexes in various implicit solvents. The DFT calculations were performed with the cam-b3lyp functional and the 6-31G(d,p) basis set. Free Species DMSO Acetonitrile Acetone o-xylene Toluene p-xylene CNC2CN BrC4Br Butane DMP5A Complexes DMSO Acetonitrile Acetone o-xylene Toluene p-xylene DMP5A:CNC2CN DMP5A:BrC4Br DMP5A:Butane S11

12 ITC titrations in p-xylene Figure S-5: Titration of mm DMP5A with 10.6 mm CNC2CN in p-xylene. S12

13 Figure S-6: Titration of mm DMP5A with 10.6 mm CNC2CN in p-xylene. S13

14 Figure S-7: Titration of mm DMP5A with 2.12 mm CNC2CN in p-xylene. S14

15 Figure S-8: Titration of mm DMP5A with 1.06 mm CNC2CN in p-xylene. S15

16 Figure S-9: Titration of mm DMP5A with 8.53 mm CNC3CN in p-xylene. S16

17 Figure S-10: Titration of mm DMP5A with 1.71 mm CNC3CN in p-xylene. S17

18 Figure S-11: Titration of mm DMP5A with 11.0 mm CNC2CN in p-xylene. S18

19 Plots of calculated solvation enthalpies Figure S-12: Solvation enthalpies for the species involved in the DMP5A:CNC2CN complex. The difference in complexation enthalpies in the gas phase and in the solvent is called the solvent effect and is calculated as the difference in solvation enthalpies between the free species and the complex. S19

20 Figure S-13: Solvation enthalpies for the species involved in the DMP5A:BrC4Br complex. The difference in complexation enthalpies in the gas phase and in the solvent is called the solvent effect and is calculated as the difference in solvation enthalpies between the free species and the complex. S20

21 Figure S-14: Solvation enthalpies for the species involved in the DMP5A:Butane complex. The difference in complexation enthalpies in the gas phase and in the solvent is called the solvent effect and is calculated as the difference in solvation enthalpies between the free species and the complex. S21

22 Plots of complexation enthalpies calculated in gas-phase, in implicit solvent, and with a hybrid implicit/explicit solvation model. Figure S-15: Calculated and experimental enthalpies for the binding of BrC4Br to DMP5A. S22

23 Figure S-16: Calculated enthalpies for the binding of Butane to DMP5A. S23

24 Energy-minimized structures of DMP5A complexes with dichloromethane and chloroform Figure S-17: Inclusion of dichloromethane (top) and chloroform (bottom) in the cavity of DMP5A obtained by energy-minimizing the structures by the MMFF94 force field in the Avogadro software 4. While dichloromethane exhibits a good fit to the cavity of DMP5A, chloroform is too bulky and induces large distortions to the otherwise pillar-shaped structure of DMP5A. It is therefore expected that chloroform is easily displaced from the DMP5A cavity when a more suitable guest molecule is present. S24

25 Reference List 1. Tan, L. L.; Zhang, Y.; Li, B.; Wang, K.; Zhang, S. X.-A.; Tao, Y.; Yang, Y. W. Selective Recognition of "Solvent" Molecules in Solution and the Solid State by 1,4-Dimethoxypillar[5]arene Driven by Attractive Forces. New J. Chem. 2014, 38, Hu, X. S.; Deng, H. M.; Li, J.; Jia, X. S.; Li, C. J. Selective Binding of Unsaturated Aliphatic Hydrocarbons by a Pillar[5]arene. Chin. Chem. Lett. 2013, 24, Ogoshi, T.; Demachi, K.; Kitajima, K.; Yamagishi, T. a. Selective Complexation of n-alkanes with Pillar[5]arene Dimers in Organic Media. Chem. Commun. 2011, 47, Hanwell, M. D.; Curtis, D. E.; Lonie, D. C.; Vandermeersch, T.; Zurek, E.; Hutchison, G. R. Avogadro: An Advanced Semantic Chemical Editor, Visualization, and Analysis Platform. J. Cheminf. 2012, 4, 17. S25