Solvent-Dependent Enthalpic versus Entropic Anion Binding by Biaryl

Article pubs.acs.org/JPCB

Solvent-Dependent Enthalpic versus Entropic Anion Binding by Biaryl Substituted Quinoline Based Anion Receptors Zhan-Hu Sun,†,§ Markus Albrecht,*,† Gerhard Raabe,† Fang-Fang Pan,‡,∥ and Christoph Raü ber† †

Institut für Organische Chemie, RWTH Aachen, Landoltweg 1, D-52074 Aachen, Germany Institut für Anorganische Chemie, RWTH Aachen, Landoltweg 1, D-52074 Aachen, Germany

‡

S Supporting Information *

ABSTRACT: Anion receptors based on an 8-thiourea substituted quinoline with pentafluorinated (1a) or nonfluorinated (1b) biarylamide groups in the 2position show similar binding of halide anions with somewhat higher association constants for the more acidic fluorinated derivative. Surprisingly, binding affinities for the halides in the case of the nonfluorinated 1b are similar in nonpolar chloroform or polar DMSO as solvent. Thorough thermodynamic investigations based on NMR van’t Hoff analysis show that anion binding in chloroform is mainly enthalpically driven. In DMSO, entropy is the driving force for the binding of the ions with replacement of attached solvent.

D

uring the last decades, anion recognition became an important research field of supramolecular chemistry. This was motivated by the remarkable and longtime underestimated role which anions play in natural as well as artificial systems. Often they were considered to be only innocent spectators, but recently their significance in different chemical and biological processes was recognized.1−4 The pioneering work of anion recognition and binding dates back to the late 1960s, when Park and Simmons reported the encapsulation of halide anions by protonated diazabicycloalkane ammonium ions.5 In the following decades, anion chemistry has progressed slowly. However, approaching the 1990s, anion chemistry became an important field of research.1 Many binding forces, such as electrostatics, hydrogen bonding, metal or Lewis acid coordination, hydrophobic effects, and combinations thereof, have been used for the binding. Among these, hydrogen bonding has been intensively studied due to its significant role in enzymatic catalysis and other biological processes.6 Plenty of neutral hydrogen bonding anion receptors have been designed and prepared on the basis of amide and (thio)urea groups7,8 and aromatic systems, including pyrroles,9 indoles,10 carbazoles,10,11 indolocarbazoles,12 etc. In this context, a newly emerging motif is shape-persistent acidic C− H hydrogen bonding.13 Due to their intra- and intermolecular hydrogen bonds, 2amido-8-aminoquinoline derivatives are exploited to construct aromatic oligoamide foldamers,14,15 chemosensors for anions,16 or fluorescent sensors for cations.17 Since 2005, our group has systematically investigated their applications as anion and ion pair receptors.18−20 Herein, two receptors 1a/b (see Figure 1) are described on the basis of 2-amido-8-aminoquinoline and biphenyl/penta© 2014 American Chemical Society

Figure 1. Anion receptors 1a/b discussed in this study.

fluorobiphenyl to construct an anion binding site formed by NH hydrogen bond donors at the quinoline backbone and by the biphenyls. The comparison of binding affinities between the two receptors and anions has been originally expected to provide an insight into anion−π interactions in solution.21 In this respect, the project did not lead to clear and convincing results! However, the system shows some unexpected thermodynamics of anion recognition especially in comparison of the solvents chloroform and DMSO.22 An interesting change of driving forces in anion binding occurs, shifting from enthalpy-driven in CDCl3 to entropy-driven in DMSO-d6. Maitra,23 Still,24 Abraham,25 Mizutani,26 and other groups have intensively studied solvent effects and hydrophobic effects in molecular recognition.27,28 Mizutani et al. switched the influence of driving forces through changing the hydrophobicity of substituents at porphyrins. In 2006, three groups, the Sessler Received: October 28, 2014 Revised: December 2, 2014 Published: December 17, 2014 301

dx.doi.org/10.1021/jp510796f | J. Phys. Chem. B 2015, 119, 301−306

The Journal of Physical Chemistry B

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group, the Schmidtchen group, and the Gale group, collaborated carrying out a comprehensive research on the solvent and countercation effects.22 Their results showed that the driving forces for anion binding behaviors were considerably affected by the solvents using isothermal titration calorimetry. Here, we reported that the switching between enthalpically and entropically driven binding was accomplished through the choice of solvents using variable-temperature 1H NMR titration and van’t Hoff analysis.

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RESULTS AND DISCUSSION The two receptors 1a/b were prepared in four steps: coupling of 8-nitro-2-quinoline carboxylic acid (2) with the corresponding biaryl amines to obtain 3a/b, reduction of the nitro groups and transformation of the amines into isothiocyanates 4a/b, and final addition of butyl amine to form 1a/b (Scheme 1).29 Scheme 1. Synthesis of Receptors 1a and 1ba

a (a) Biaryl amine, EDC·HCl, HOBt, DIPEA, CH2Cl2; (b) Pd/C, H2, CH2Cl2; (c) 1,1′-thiocarbonyldi-2,2′-pyridone, CH2Cl2; (d) n-butyl amine, CH2Cl2.

Crystals of key compounds 3a, 1a, and 1b are obtained by slow evaporation of their solution in CH2Cl2/CH3OH at room temperature. The structures were obtained by X-ray diffraction (Figure 2). 3a shows the basic aromatic unit of the envisaged receptors with the biaryl amide side chain already installed. The pentafluorophenyl unit is oriented toward the “front” of the quinoline unit. In 1a as well as in 1b, the amide proton and one of the thioureido protons are located at the “front” of the quinoline, forming an intramolecular hydrogen bonding array. In the crystal of receptor 1a, the pentafluorophenyl group turns away from the quinoline due to the presence of a methanol molecule with HOH binding to the Sthiourea atom. In receptor 1b, the corresponding phenyl group of the biphenyl is located at the front of the quinoline as observed for the precursor 3a. The anion-binding properties of the novel receptors in solution are examined by 1H NMR titration in CDCl3 as well as in DMSO-d6 at room temperature. In analogy to the earlier examples, it is expected that the anion binds to the three protons within the cleft formed by the molecule.18,19,29 The binding stoichiometry between the receptors and the halide anions is determined to be 1:1. The data in CDCl3 and DMSOd6 are fitted using standard methods of nonlinear regression to reveal the binding constants,30 as shown in Figure 3 and Table 1. In addition, the binding behavior of DMSO to the receptors is studied in CDCl3 as solvent. The examination of the binding data in Table 1 reveals some trends:

Figure 2. X-ray structures of 3a and of the receptors 1a·CH3OH and 1b.

(1) Receptor 1a shows higher binding affinities toward given anions than 1b does. This, in part, might be due to the stronger electron-withdrawing effects of the pentafluorobiphenyl group of receptor 1a leading to a more acidic amide than in receptor 1b. Attractive contributions from CH−anion or anion−π interactions between receptor 1a and the anions might also contribute (vide infra). (2) A preference of both receptors 1a/1b for halide anions is observed in the order Cl− > Br− > I−. This preference is ascribable to the inherent basicity of the halide anions and the size-matching of receptor and anion. No binding constants could be determined for the receptors with iodide anions in DMSO-d6. (3) In order to test the binding ability of DMSO to 1a/b, binding studies were performed in CDCl3. Receptors 1a and 1b show medium binding affinities for DMSO (36 and 16 M−1) fitted for a 1:1 binding ratio, respectively. Thus, DMSO seems to be a strong competitor for the weakly interacting iodide anions. Therefore, it is very surprising that the binding affinities of receptor 1b with a given halide in the more or less “innocent” CDCl3 and in the strongly competing DMSO-d6 are only marginally different (e.g., chloride binding, 70 M−1 in 302



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= 61 M−1; 323 K, K = 60 M−1; 343 K, K = 61 M−1). Van’t Hoff plots representing the data are shown in Figure 4, top.

Figure 3. Representative 1H NMR Job plots (top) and titration curves (bottom) of receptor 1a and chloride anions in CDCl3 at room temperature (the total concentrations for Job plots were kept at 0.01 M).

Figure 4. Van’t Hoff plots for the temperature dependent binding constants of 1b (top) and 1a (bottom) with tetrabutylammonium chloride in CDCl3 and DMSO-d6.

Table 1. Binding Constants (K, M−1) of Receptors 1a and 1b with Halide Anions in CDCl3 and in DMSO-d6 and with DMSO in CDCl3 at Room Temperaturea

In addition, a similar behavior is observed for 1a and chloride anions in CDCl3 and DMSO-d6 (CDCl3: 296 K, K = 828 M−1; 303 K, K = 668 M−1; 308 K, K = 555 M−1; 313 K, K = 492 M−1; 318 K, K = 427 M−1; 323 K, K = 378 M−1. DMSO-d6: 298 K, K = 111 M−1; 303 K, K = 112 M−1; 308 K, K = 113 M−1; 313 K, K = 110 M−1; 318 K, K = 111 M−1; 323 K, K = 112 M−1; 328 K, K = 109 M−1; 333 K, K = 108 M−1) (Figure 4, bottom). Thermodynamic data obtained from the van’t Hoff plots for the 1a or 1b and chloride interactions are summarized in Table 2. The obtained thermodynamic parameters clearly show that binding between receptors 1a/1b and chloride anions in CDCl3 is majorly enthalpically driven while the binding in DMSO-d6 is purely entropically driven. Dimethyl sulfoxide is a polar molecule and a good hydrogen bond acceptor. It is bound to the receptor site of 1a/b. Binding of the anions releases this solvent molecule as well as the molecules which solvate the anion. This results in a favorable change of entropy of the system.34,35 In addition, there is a dramatic enthalpy difference for 1a and 1b in chloroform. This is addressed to an interaction of the biaryl unit either by proton Hx or by the electron deficient aryl unit interacting with the anion (see Scheme 2). In the fluorinated receptor 1a, Hx is positively polarized and strong interaction may occur to the halide, resulting in a reduction of the entropy of the system. A similar effect would be observed by anion−π interaction of the C6F5 unit or by a combination of both interactions. The strong enthalpic driving force ΔH for halide binding is reduced by the unfavorable entropic effect. In the case of the less polarized nonfluorinated 1b, the CH···Cl bonding is very weak and anion−π interaction

Cl− b 1a 1b

828 70

1a 1b

111 61

Br− b In CDCl3 129 32 In DMSO-d6 48 42

I− b

DMSO

67 20

36 16

c c

a The binding constants are determined by 1H NMR titration experiments and are fitted according to a 1:1 binding ratio based on Job plots. Errors are estimated to be less than 20%. bAdded as tetrabutylammonium salts. cNo binding observed.

CDCl3 versus 61 M−1 in DMSO-d6; bromide binding, 32 M−1 in CDCl3 versus 42 M−1 in DMSO-d6). This is unexpected. To elucidate this phenomenon, variable-temperature 1H NMR titrations31−33 with receptor 1b and chloride have been carried out in CDCl3 and DMSO-d6. 1 H NMR titration experiments of receptor 1b with chloride anions are performed in CDCl3, and binding constants are obtained at different temperatures (283 K, K = 89 M−1; 293 K, K = 74 M−1; 298 K, K = 70 M−1; 303 K, K = 64 M−1; 313 K, K = 58 M−1; 323 K, K = 53 M−1). As expected, the association constants decrease with increasing temperature. In contrast to this, the corresponding binding constants in DMSO-d6 are not affected by the temperature and surprisingly keep constant in the investigated temperature range (298 K, K = 61 M−1; 303 K, K = 61 M−1; 308 K, K = 61 M−1; 313 K, K = 60 M−1; 318 K, K 303



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Table 2. Thermodynamic Data for Chloride (as Tetrabutylammonium Salt) Binding to 1a or 1b in CDCl3 or DMSO-d6 K (M−1) ΔG (kJ mol−1) ΔH (kJ mol−1) ΔS (J mol−1 K−1) −TΔS (kJ mol−1)

1a, CDCl3

1b, CDCl3

1a, DMSO-d6

1b, DMSO-d6

828 −16.5 −23.3 ± 0.5 −22.8 ± 1.6 6.8 ± 0.5

70 −10.5 −9.78 ± 0.60 2.54 ± 1.97 −0.757 ± 0.587

111 −11.7 −0.73 ± 0.35 36.80 ± 1.1 −11.0 ± 0.3

61 −11.0 −0.087 ± 0.24 33.85 ± 0.78 −10.09 ± 0.23

purification, unless otherwise indicated. After stirring with CaH2 overnight, dichloromethane and CH3CN were distilled for use. All NMR spectra were recorded in deuterated chloroform (CDCl3), deuterated acetonitrile (CD3CN), or deuterated dimethyl sulfoxide (DMSO-d6) by using a Varian Mercury 300, Varian 400, or Varian 600 spectrometer. Mass spectra were measured by using EI (70 eV) or ESI techniques on a Finnigan SSQ 7000 or Thermo Deca XP spectrometer. Infrared spectra were obtained on a PerkinElmer FTIR spectrometer spectrum 100. The samples were measured in KBr (400−650 cm−1). Elemental analyses were performed on a CHN-O-Rapid Vario EL instrument from Heraeus. Melting points were obtained on a Büchi B-540 melting point apparatus. X-ray diffraction data has been collected at 100 K on a Bruker D8 goniometer equipped with an APEX CCD detector using Mo Kα radiation (λ = 0.71073 Å). The radiation source was an INCOATEC I-μS microsource. A cooling device Oxford Cryosystems 700 controller was used to ensure temperature stability during data collection. The SAINT software36 was used for integration and SADABS37 for multiscan absorption correction. The structures were solved with direct methods (SHELXS97) and refined by full-matrix least-squares on F^2 (SHELXL97).38 Anisotropic displacement parameters were assigned to non-H atoms. H atoms bonded to N were localized in difference Fourier maps; their positions were refined freely. CCDC 993795 (3a), 993407 (1a), and 992710 (1b) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif. 3a: DIPEA (0.5 mL), HOBt (236 mg, 1.75 mmol, 2.0 equiv), and EDC·HCl (336 mg, 1.75 mmol, 2.0 equiv) were successively added to an anhydrous CH2Cl2 (20 mL) solution of a mixture of 4-isobutoxy-8-nitroquinoline-2-carboxylic acid 2 (254 mg, 0.875 mmol, 1.0 equiv) and freshly prepared 2,3,4,5,6pentafluoro-2′-aminobiphenyl39 (ca. 0.875 mmol, 1.0 equiv). After 6 h under nitrogen at room temperature, the reaction mixture was washed with saturated aqueous NH4Cl. The organic extract was dried over Na2SO4 and filtered off. Solvent was evaporated to dryness, and the residue was purified on silica gel with dichloromethane or by recrystallization from dichloromethane/MeOH. Yield: 409 mg (M = 531.43 g mol−1, n = 0.77 mmol, 88%). M.p.: 204−206 °C. 1H NMR (600 MHz, CDCl3): δ = 9.98 (s, 1 H), 8.69 (d, J = 8.4 Hz, 1 H), 8.44 (d, J = 8.4 Hz, 1 H), 8.01 (d, J = 7.2 Hz, 1 H), 7.82 (s, 1 H), 7.60 (m, 2 H), 7.28 (m, 2 H), 4.12 (d, J = 6.6, 2 H), 2.29 (m, 1 H), 1.13 (d, J = 6.6 Hz, 6 H). 19F NMR (564 MHz, CDCl3): δ = −140.20 (dd, J = 4.8, 5.1 Hz, 2F), −151.95 (t, J = 21.0, 21.0 Hz, 1F), −160.73 (td, J = 1.1, 6.2, 6.8 Hz, 2F). 13C NMR (151 MHz, CDCl3): δ = 180.47, 163.77, 162.37, 150.08, 145.07, 143.40, 139.55, 137.27, 135.58, 134.19, 131.82, 130.55, 127.02, 125.97, 125.09, 123.27, 120.05, 118.07, 99.78, 75.58, 45.37, 30.88, 28.17, 20.18, 19.21, 13.74. IR (KBr): 3748, 3289, 2974, 2327, 2111, 1691, 1583, 1523, 1497, 1352, 1102, 1058, 1017,

Scheme 2. Binding of Chloride to Receptor 1a or 1b in CDCl3 (Top) Showing Different Possible Secondary Interactions in the Case of 1a; Competitive Chloride Binding of 1a/1b in DMSO (Bottom)

cannot occur. In DMSO, those interactions are not relevant due to competing interactions with solvent molecules.

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CONCLUSION Here, we reported the preparation of biaryl substituted quinoline based anion receptors 1a and 1b. The crystal structures of the two derivatives are reported, and the binding behavior of halide anions in chloroform and DMSO is described. The thermodynamic origin of the binding process has been probed by van’t Hoff analysis, which clearly shows different thermodynamic driving forces (enthalpy versus entropy) in different solvents (chloroform versus DMSO). This is based on a strong competitive binding of DMSO to the anion binding site of the receptor which is energetically similar to the binding of halides. Deliberation of the bound solvent molecule upon anion coordination results in a strong entropic driving force for the exchange of guests at the receptor. Additionally, in chloroform, either some nonclassical CH···Cl hydrogen bonding or anion−π interactions, presumably, contribute to the anion binding.

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EXPERIMENTAL SECTION General. Commercially available reagents were used as received. All solvents were used after distillation without further 304



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984, 858, 758, 710 cm−1. MS (CI): m/z (%) = 532.4 (100.00), [M + H]+ , 560.5 (12.62), [M + C 2 H 5 ]+ . Calcd for C26H18F5N3O4: C, 58.76; H, 3.41; N, 7.91. Found: C, 58.35; H, 3.41; N, 7.80. X-ray quality crystals were obtained from MeOH/dichloromethane (CCDC 993795): C26H18F5N3O4; Mr = 531.43; crystal size 0.3 × 0.3 × 0.3 mm3; triclinic; space group P-1, a = 9.7294(19) Å, b = 10.317(2) Å, c = 12.072(2) Å; β = 86.237(8)°; V = 1166.0(4) Å3; Z = 2; ρcal = 1.514 g cm−3; μ = 1.547 mm−1; F(000) = 544; 40159 collected reflections (θmax = 66.9°) of which 23523 were independent (Rint = 0.061); Tmax = 0.7530; Tmin = 0.6235; T = 100(2) K; full-matrix least-squares on F2 with 0 restraints and 416 parameters; GOF = 2.85; R1 = 0.061 (I > 2σ(I)); ωR2 (all data) = 0.036; peak/hole =1.41/− 1.21 e Å−3. 3b: Compound 3b was prepared as described for 3a using 2aminobiphenyl and was purified by column chromatography on silica with dichloromethane/hexane (1/1 v/v) or by recrystallization from dichloromethane/MeOH. Yield: 352 mg (M = 441.48 g mol−1, n = 0.80 mmol, 80%). M.p.: 168−170 °C. 1H NMR (600 MHz, CDCl3): δ = 10.20 (s, 1 H), 8.57 (d, J = 8.4 Hz, 1 H), 8.45 (d, J = 8.4 Hz, 1 H), 8.03 (d, J = 1.2 Hz, 1 H), 7.84 (s, 1 H), 7.57 (m, 3 H), 7.49 (t, J = 7.8, 7.2 Hz, 1 H), 7.45 (m, 3H), 7.33 (dd, J = 1.2, 1.2, 1H), 7.24 (m, 1H), 4.12 (d, J = 6.6 Hz, 2H), 2.29 (m, 1H), 1.13 (d, J = 7.2 Hz, 6H). 13C NMR (151 MHz, CDCl3): δ = 163.31, 161.47, 153.45, 147.70, 138.83, 137.70, 134.37, 133.60, 130.55, 129.26, 128.99, 128.23, 128.19, 126.48, 125.29, 125.21, 124.66, 123.28, 121.26, 99.94, 75.76, 28.08, 19.15. IR (KBr): 3328, 3064, 2971, 2881, 2326, 1897, 1677, 1579, 1523, 1355, 1268, 1207, 1103, 1014, 870, 750, 687 cm−1. MS (EI): m/z (%) = 441.3(100) [M]+. Calcd for C26H23N3O4·H2O: C, 69.32; H, 5.37; N, 9.33. Found: C, 69.87; H, 4.82; N, 9.24. 4a/b: A mixture of 3a (118 mg, 0.222 mmol) dissolved in CH2Cl2 (15 mL) and 10% Pd/C (30 mg) was stirred at room temperature under an atmosphere of hydrogen (20 bar) overnight. The solution was filtered through Celite, and the filtrate was evaporated to dryness. To an anhydrous CH2Cl2 (20 mL) solution of the residue (0.222 mmol, 1.0 equiv), 1,1′thiocarbonyldi-2,2′-pyridone (62 mg, 0.266 mmol, 1.2 equiv) was added. After 8 h under nitrogen at room temperature, the solvent was evaporated to dryness, and the residue was chromatographed on silica gel with hexane as an eluent to allow isolation of 4a as a colorless oil, which was used for the next reaction without characterization. 4b was obtained analogously to 4a. 1a: n-Butylamine (110 μL, 1.11 mmol, 5.0 equiv) was added to a solution of 4a (0.222 mmol, 1.0 equiv) in dry dichloromethane (15 mL) in a round flask filled with nitrogen. The mixture was stirred overnight, and the solvent was evaporated. The residue was chromatographed on silica gel with dichloromethane as an eluent to obtain 1a as a light yellow solid. Yield: 87 mg (M = 616.64 g mol−1, n = 0.141 mmol, 64%). M.p.: 138−140 °C. 1H NMR (600 MHz, CDCl3): δ = 9.74 (s, 1 H), 8.63 (s, 1 H), 8.04 (m, 3 H), 7.71 (s, 1 H), 7.55 (m, 2 H), 7.37 (m, 2 H), 6.49 (s, 1 H), 4.06 (d, J = 6.0 Hz, 2 H), 3.65 (m, 2 H), 2.27 (m, 1 H), 1.61 (m, 2 H), 1.35 (m, 2 H), 1.13 (d, J = 7.2 Hz, 6 H), 0.91 (t, J = 7.2, 7.8 Hz, 3 H). 19F NMR (564 MHz, CDCl3): δ = −139.94 (s, 2F), −152.49 (s, 1F), −160.48 (s, 2F). 13C NMR (151 MHz, CDCl3): δ = 180.47, 163.77, 162.37, 150.08, 145.07, 143.41, 142.09, 139.55, 138.92, 137.30, 137.15, 135.58, 134.19, 131.82, 130.55, 127.02, 125.97, 125.09, 123.27, 120.05, 118.07, 99.78, 75.58, 30.88, 28.17, 20.18, 19.21, 13.74. IR (KBr): 3327, 3066, 2970, 2324,

2105, 1899, 1678, 1579, 1514, 1353, 1267, 1206, 1162, 1113, 1014, 870, 816, 748, 687 cm−1. MS (ESI): m/z (%) = 57.5 (100.00), [C4H9]+; 501.3 (35.23), [C26H20F5N3O2]+; 543.4 (14.70), [C27H18F5N3O2S]+, 616.5 (13.56), [M]+. Calcd for C31H29N4F5O2S·0.5H2O: C, 59.51; H, 4.83; N, 8.95. Found: C, 59.44; H, 4.37; N, 8.71. X-ray quality crystals were obtained from MeOH/dichloromethane (CCDC 993407): C31H29N4F5O2S; Mr = 616.64; crystal size 0.272 × 0.335 × 0.806 mm3; triclinic; space group P-1, a = 8.1926(9) Å, b = 13.4425(16) Å, c = 16.253(3) Å; β = 97.983(3)°; V = 1575.4(4) Å3; Z = 2; ρcal = 1.367 g cm−3; μ = 0.178 mm−1; F(000) = 676; 83520 collected reflections (θmax = 26.3°) of which 46227 were independent (Rint = 0.053); Tmax = 0.7453; Tmin = 0.5955; T = 100(2) K; full-matrix least-squares on F2 with 40 restraints and 666 parameters; GOF = 5.17; R1 = 0.085 (I > 2σ(I)); ωR2 (all data) = 0.09; peak/hole = 2.47/−1.14 e Å−3. 1b: 1b was prepared analogously to 1a. Yield: 120 mg (M = 526.69 g mol−1, n = 0.228 mmol, 62%). M.p.: 178−180 °C. 1H NMR (600 MHz, CDCl3): δ = 9.93 (s, 1 H), 8.82 (s, 1 H), 8.67 (s, 1 H), 8.34 (d, J = 7.8 Hz, 1 H), 7.64 (s, 1 H), 7.51 (m, 4 H), 7.41 (m, 3 H), 7.24 (m, 3 H), 6.98 (s, 1 H), 3.84 (d, J = 4.8 Hz, 2 H), 3.69 (s, 2 H), 2.18 (m, 1 H), 1.71 (m, 2 H), 1.46 (m, 2 H), 1.10 (d, J = 6.6 Hz, 6 H), 0.97 (t, J = 0.1 Hz, 3 H). 13C NMR (151 MHz, CDCl3): δ = 179.66, 163.18, 162.85, 149.69, 138.12, 134.85, 133.93, 132.56, 130.20, 129.17, 129.16; 128.36, 128.07, 126.92, 124.91, 121.84, 121.09, 118.14, 115.89, 98.69, 75.02, 44.49, 30.98, 28.09, 20.28, 19.15, 13.88. IR (KBr): 3306, 3060, 2959, 2871, 2116, 1665, 1577, 1529, 1452, 1356, 1316, 1259, 1178, 1126, 1031, 811, 753, 694 cm−1. MS (ESI): m/z (%) = 527.24854 (100.00), [M + H]+. Calcd for C31H34N4O2S: C, 70.69; H, 6.51; N, 10.64. Found: C, 70.17; H, 6.65; N, 10.35. X-ray quality crystals were obtained from MeOH/dichloromethane (CCDC 992710): C31H34N4O2S; Mr = 526.68; crystal size 0.29 × 0.24 × 0.20 mm3; triclinic; space group P-1, a = 13.6960(16) Å, b = 14.7436(17) Å, c = 15.3268(18) Å; β = 77.575(2)°; V = 2756.3(6) Å3; Z = 4; ρcal = 1.269 g cm−3; μ = 0.15 mm−1; F(000) = 1120.0; 25303 collected reflections (θmax = 26.59°) of which 11475 were independent (Rint = 0.058); Tmax = 0.970; Tmin = 0.957; T = 100(2) K; full-matrix leastsquares on F2 with 40 restraints and 666 parameters; GOF = 1.05; R1 = 0.087 (I > 2σ(I)); ωR2 (all data) = 0.254; peak/hole = 0.61/−0.65 e Å−3.

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ASSOCIATED CONTENT

* Supporting Information S

NMR spectra, NMR titration curves, and other data were included in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Addresses §

Z.-H.S.: Adaptive Supramolecular Nanosystems Group, Institut Européen des Membranes, ENSCM-UMII-UMRCNRS5635, Place E. Bataillon CC047, 34095 Montpellier Cedex 5, France. ∥ F.-F.P.: Department of Chemistry, Nanoscience Center, University of Jyväskylä, Survontie 9, 40014 Jyväskylä, Finland. 305



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Author Contributions

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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Z.-H.S. and F.-F.P. are thankful to the China Scholarship Council for scholarship assistance.

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REFERENCES

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