Solid-State Supramolecular Assemblies of Tryptophan and

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Solid-State Supramolecular Assemblies of Tryptophan and Tryptamine with Cucurbit[6]Uril Oksana Danylyuk*,† and Vladimir P. Fedin‡ †

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 3 Acad. Lavrentiev. Ave., 600090 Novosibirsk, Russian Federation

‡

S Supporting Information *

ABSTRACT: The crystal structure of the supramolecular exclusion complexes of cucurbit[6]uril with amino acid D-tryptophan and its decarboxylation product tryptamine have been determined. The supramolecular self-assembly of the cucurbit[6]uril with aromatic guests is guided by the combination of ion-dipole, hydrogen bonding, and stacking interactions between indole rings and glycouril groups of cucurbit[6]uril and leads to the formation of helical nanotubules in the case of tryptophan and stacked columns in the case of tryptamine. The formation of the solid-state complexes is dependent on the type of salt used for solubilization of cucurbit[6]uril which is explained in terms of the specific coordination mode of cucurbit[6]uril with magnesium ion.

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than to the other CB6 unit due to shape-matching host−guest interactions.5 Therefore, continuing our research on the solidstate assembly of synthetic receptors with biologically and pharmaceutically relevant molecules,6 we would like to present our recent results on the complexation of the aromatic amino acid tryptophan and its decarboxylation product tryptamine by the CB6 in the solid state driven by hydrogen bonding and stacking interactions. It should be mentioned that binding of amino acids L-glutamate, L-tyrosine, and L-histidine with tetramethylcucurbit[6]uril in the solid state were studied by Tao et al.7 Recently, Thuery reported the use of L-cysteine as a chiral linker in the building of lanthanide-CB6 supramolecular assemblies.8 Tryptophan (Trp) with its amphiphilic nature is unique among 20 amino acid residues found in proteins because its large indole side chain can participate in nonpolar interactions, hydrogen bonding, NH···π, CH···π, and electrostatic interactions via the inherent quadruples of aromatic ring and plays a prominent role in the folded structure and binding sites of many proteins,9 such as acetylcholinesterase,10 streptavidin,11 myosin,12 and others. The indole ring of Trp is often found near catalytic or substrate-recognition sites, forming a hydrophobic environment. For example, in the active site of the nucleoside hydrolase of the parasite Trypanosoma vivax the nucleic base of the substrate was found to be sandwiched between the aromatic side chains of two Trp. The face-to-face stacking with indole rings promotes the protonation of

ucurbit[n]urils are pumpkin-shaped macrocyclic host molecules that have attracted much attention owing to their excellent ability to bind various inorganic, organic, and biological molecules and ions in both aqueous solution and solid state.1 Cucurbit[n]urils (n = 5−8, 10) are characterized by a varying hydrophobic cavity accessible through two oxygencrowned portals which allow the formation of inclusion or exclusion complexes via a combination of ion-dipole, hydrogen bonding, and hydrophobic interactions. The easy synthesis from cheap starting materials glycouril and formaldehyde, high chemical and thermal stability, together with first reports concerning their low toxicity2 make them attractive as receptors for molecular recognition and building blocks for the construction of supramolecular materials. The investigation of the interactions between cucurbiturils and various biomolecules is crucial for the development of new functional materials, selective sensors, new therapeutics, and smart drug delivery systems based on these supramolecular host molecules.3 The cation binding and inclusion properties of cucurbit[6]uril (CB6) are well-studied both in solution and solid state. Ripmeester et al. shed some light on the delicate balance of the weak interactions in the cucurbituril crystals and proposed that the multiplicity of cucurbituril CH···O interactions is an important structure directing factor that explains their physical properties such as solubility, crystallinity, and thermal stability.4 However, the chemical behavior of glycouril outer walls of CB6 and their role in the formation of supramolecular complexes with aromatic guests via stacking interactions remain little explored. Chen and her co-workers demonstrated that convexshaped glycoluril backbones of CB6 exhibit a much higher affinity to the iodoaromatic moieties of copper(II) complex © 2011 American Chemical Society

Received: October 20, 2011 Revised: December 14, 2011 Published: December 19, 2011 550

dx.doi.org/10.1021/cg2013914 | Cryst. Growth Des. 2012, 12, 550−555

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nucleobase and explains the catalytic role of Trp.13 Trp residue is also useful for the study of protein dynamics and structural changes with ligand binding, as the fluorescence properties of the indole are highly environment-sensitive.14 Careful analysis of host−guest binding of the CB6 with tryptophane and tryptamine as well as the supramolecular aggregation of the resulting complexes via face-to-face π−π stacking interactions between guest indole rings and glycouril CB6 outer walls will help to better understand the key factors for the construction of novel structures and functional supramolecular materials based on cucurbiturils. In order to establish the interaction mode of CB6 with amino acid tryptophan and its decarboxylation product tryptamine in the solid state, we obtained the crystal structure of the corresponding complexes. Crystals of the complexes were grown from aqueous solution containing CB6, magnesium chloride, and D-tryptophan15 or tryptamine. Alkali and alkaliearth metal cation complexation has been recognized as a way of increasing solubility of CB6, which otherwise is only soluble in strongly acidic aqueous solutions.16 It should be noted that formation of the solid-state complexes is dependent on the type of salt used for solubilization of CB6, and the crystals were obtained only from the MgCl2 solution. The crystallization attempts from NaCl, KCl, and CaCl2 solutions of CB6 afforded typical coordination polymers of CB6 with metal cations coordinated to two portals thus preventing guest complexation. It is well-known that the solubility of CB6 in alkali and alkaline earth salt solutions arises from the complexation of the carbonyl rims by the metal cations. The addition of tryptophan or tryptamine to the MgCl2 solution of CB6 must somehow displace coordinated magnesium cations and significantly reduce the CB6 solubility resulting in crystalline complex formation. Then the important question arises: why tryptophan and tryptamine are able to compete with magnesium cations for the complexation to carbonyl rims? Obviously, the answer lies in the specific interaction mode of CB6 with magnesium cations. Having not found the crystal structure of CB6 complex with magnesium in the Cambridge Structural Database, we performed crystallization experiments and obtained the desired crystalline complex [Mg(CB6)(H2O)4]·2Cl·16H2O (1).17 As expected, crystallographic analysis18 revealed the specific coordination mode of magnesium cation to CB6 that differs significantly from 1-D coordination polymers reported for sodium,5 potassium,19 and calcium;20 namely, only one portal of CB6 is coordinated by two carbonyl oxygen atoms to one magnesium aqua complex cation, while another portal remains noncoordinated, Figure 1. It should be pointed out that this is the first supramolecular assembly of cucurbituril with magnesium ion that has the smallest ionic radius (0.72 Å for hexa-coordinated Mg2+) of the metals that have been studied on their coordination to unsubstituted cucurbituril ligands. Mg2+ ions, possessing a high charge-to-radius ratio, are strongly hydrated in aqueous solutions; moreover, the magnesium interactions with water molecules in the first solvation shell are far stronger than most other cations. The high energetic barrier to removing a water molecule from a magnesium dication may be the main reason for the slow replacement of water molecules in the coordination sphere by cucurbituril ligands and may explain why only one portal of CB6 is coordinated. To the best of our knowledge, no solution studies on the magnesium complexation by CBs have been reported so far. We think that both solution and solid state studies on CB-Mg2+ interaction are necessary in the context of the emerging field of cucurbituril

Figure 1. The asymmetric unit of complex 1 (noncoordinated water molecules and chloride anions omitted for clarity) showing the coordination mode of CB6 with magnesium ion.

biopharmaceutical applications and due to the essential role of magnesium in biological systems. It should be mentioned that in the complex of TMeCB6 with lithium (ionic radius 0.60 Å for tetra-coordinated Li+) a 1-D polymer of alternating TMeCB6s and lithium ions through direct coordination also has not been observed, although both portals of cucurbituril are metal coordinated.21 Evidently, the ionic radii of these metal ions are too small to effectively coordinate adjacent cucurbituril molecules. However, additional structural studies on the coordination mode with these metals are necessary to give more insight into the problem. If we suppose the similar coordination mode of CB6 with magnesium in the solution and/or in the transition state between solution and solid, it is clear that noncoordinated oxygen atoms can easily interact with organic cations present in solution and in this way further remove coordinated magnesium cations. The detailed description of the crystalline CB6 complex with magnesium highlighting the channel type character of the extended structure will be provided elsewhere. The asymmetric unit of H[Cl@(CB6)·2HTrp]Cl·9H2O (2) complex contains two molecules of Trp associated with each portal of CB6 molecule, forming an exclusion complex of 1:2 stoichiometry, chloride anions, and water molecules (some of which are disordered and have fractional occupancies), Figure 2. The amine group of each Trp is protonated, and charge neutrality for the system implies the presence of oxonium ions in the structure. The CB6 cavity is considerably distorted from ideal D6h symmetry to an elliptical shape with a max and min distances between opposite carbon atoms of the CB6 methine groups of 10.70 and 9.66 Å; in other words, the major axis of ellipsoid is ∼11% longer than the minor axis. Similar deformation of the CB6 host (∼13%) was observed by Fedin et al.22 by the inclusion of 4-methylpyridinium cation in the internal cavity of the CB6 molecule. The authors postulated that distortion is not a simple result of the bulky guest inclusion but also depends on the interaction of external CB6 surface with the environment, which is our case. Interestingly, the internal CB6 cavity is occupied by the disordered chloride anion. The cavity of cucurbituril is routinely supposed to be hydrophobic; however, ureido π systems are strongly polarized toward oxygens which leads to the electropositive microenvironment in the inner cavity. The 551



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bonding between ammonium groups and portal oxygen atoms is the important driving force for the exclusion complex formation. However, the N-terminal ammonium group is common to all amino acids and cannot solely explain the high affinity of CB6 to Trp. Obviously, the complexation is guided by the combination of charge, size, shape, and hydrophobicity, and the relatively large and flat indole group of Trp is too large to be included into the inner CB6 cavity, but instead of this provides unique complementarity to the glycouril outer walls of CB6 molecule. The indole groups of Trp are inserted between adjacent CB6 that provide suitable hydrophobic pockets and are favorably stacked with the glycouril walls of CB6 molecules; in other words, the outer surface of each CB6 molecule is stacked through four glycouril units with four Trp guests. A close look at the structure reveals that 1:2 ternary supermolecules pack together in the crystal lattice to form a chiral infinite helical tubular assembly ∼25 Å in diameter, which runs along a 4-fold screw helical axis of symmetry. Each multicomponent helix completes a full turn every 14.7 Å, which corresponds to the c dimension of the unit cell. As can be seen in Figure 3, the supermolecules point to the interior of the helix

Figure 3. Partial space-fill view of the helical nanotubule selfassembled from CB6·Trp supermolecules in complex 2. Trp X pointing to the interior of the tube are shown in space-fill mode, Trp Y at the exterior of the tube in stick mode. The helical channel is occupied by disordered water molecules and chloride anions.

Figure 2. The asymmetric unit of complex 2 showing 1:2 supermolecule (some water molecules and chloride anions omitted for clarity). Two CB6 portals are closed with the chelated ammonium groups of two crystallographically independent Trp molecules (Trp X in violet and Trp Y in yellow) and two hydrogen bonded water molecules. The CB6 cavity is occupied by the disordered chloride anion (in green).

with Trp X (in violet), while Trp Y (in yellow) is situated on the tube periphery. The CB6·Trp helical nanotube reminded us of Atwood’s tubular assembly of p-sulfonatocalix[4]arene with pyridine N-oxide formed in the presence of sodium and lanthanide ions.23 The significant point of supramolecular organization is the entrapment of water molecules and chloride anions in the helical channels inside the nanotube. These water molecules form a hydrogen bonded helical chain and are also hydrogen bonded to Trp X carboxylate groups (2.564 Å) and one of the CB6 carbonyl oxygen atoms (2.869 Å) which are oriented toward the interior of the tube. The main driving force for the helical array formation is the π−π stacking interaction between the indole ring of Trp X (in violet) of one supermolecule and glycouril groups of two adjacent CB6 molecules (average distances between the indole plane and two glycouril planes are 3.37 and 3.24 Å, dihedral angles are 4.3 and 9.0°). The helix is additionally stabilized by quite strong CH···O interactions between methine (3.187 Å) and methylene (2.965 Å) carbon atoms of one cucurbituril and carbonyl oxygen atoms from adjacent CB6 molecule in the helix. The Trp Y also contributes to the helix stability by stacking with the glycouril group (distance 3.30 Å and angle 10.0°) and stitch neighboring helices together through the stacking of another side of its indole ring with the glycouril group of CB6 from the

inclusion of chloride anion is more often observed for CB5 due to a more compact cavity, and the anion is always closer to ureido carbons than to the nitrogens.4 In complex 2, the included chloride anion is disordered over three positions; the close look reveals that all of them are in close proximity to electropositive ureido carbons (the shortest Cl−C distances are 3.74, 3.75, and 3.13 Å, while the shortest Cl−N distances are 4.03, 4.02, and 3.42 Å, respectively). Additionally, stacking of ureido π systems with indole rings may promote the inclusion of anion into the CB6 cavity. The N-terminal ammonium groups of Trp are chelated by the carbonyl groups at each portal of the CB6 (N−O distances are 2.788 and 3.120 Å for Trp X; 2.652 and 2.779 Å for Trp Y). The pyrrolic nitrogen atoms of Trp are hydrogen bonded to chloride anions. Two opposite portals of CB6 are closed with the chelated ammonium groups of Trp and water molecules hydrogen bonded to carbonyl oxygen atoms of CB6. Evidently, the ion−dipole interaction between N-terminal nitrogen of Trp and carbonyl oxygen atoms of CB6 accompanied by hydrogen 552



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adjacent helix (distance 3.08 Å and angle 18.5°). If we consider the CB6 and Trp as separate building units, the resulting helical array can be described as a double helix consisting of cucurbituril (in blue) and Trp X (in violet) helical chains with additional Trp Y stacking on the periphery. The tetragonal assembly of helical nanotubes creates another small water-filled pore for which the surface is defined by four adjacent helices, Figure 4.

Figure 5. The asymmetric unit of complex 3 showing 1:2 supermolecule (some water molecules and chloride anions omitted for clarity). Two crystallographically independent tryptamine molecules (X in violet and Y in yellow) interact with one portal via hydrogen bonding of ammonium and pyrollic groups.

the same CB6 portal through its pyrrolic nitrogen (N−O distance is 2.822 Å), while its amino group is hydrogen bonded with the portal of adjacent CB6 (N−O distances are 2.849 and 2.905 Å) leading to the formation of supramolecular column composed of CB6 molecules that are linked via direct hydrogen bonding with tryptamine Y and indirect hydrogen bonding of tryptamine X through bridging water molecule, Figure 6.

Figure 4. The packing of four adjacent helices (orange, green, blue, and dark blue) viewed from he c axis in complex 2; Trp X contributing to helix formation in violet, Trp Y stitching neighboring helices together in yellow.

It is interesting to compare the supramolecular array in 1:2 CB6·Trp complex with the structure of 1:1 CB8·Trp-Gly-Gly,24 where the indole side chain is bound within the large CB8 cavity. Despite the molecular inclusion, one side of indole ring is favorably aligned with the urea group of proximal CB8 molecule and this interaction is sufficiently strong to generate helical chains. However, in the absence of additional stacking interactions, adjacent helices are assembled more loosely creating large solvent-filled channels. In the CB6·Trp complex, we observe the formation of helical tubes instead of chains due to the presence of additional stacking interactions and more compact packing of adjacent helical arrays due to stacking between neighboring helical nanotubes. The asymmetric unit of [(H2O)@(CB6)·2HTrpm]·2Cl· 16H2O (3) comprises two tryptamine molecules (one of them is disordered over two positions) interacting with one portal of CB6, chloride anions, and water molecules (some of which are disordered and have fractional occupancies), Figure 5. CB6 cavity is occupied with water molecules and is distorted to elliptical shape but to a lesser degree than in complex 1 (the major axis of ellipsoid is only ∼4% longer than the minor axis). Two independent tryptamine molecules interact with the CB6 host in different ways. The protonated amino group of tryptamine X (in violet) is hydrogen bonded to portal oxygen atoms (N−O distances are 2.694 and 2.873 Å), while the pyrrolic nitrogen atom donates hydrogen bond to water molecule. Tryptamine Y (in yellow) is hydrogen bonded to

Figure 6. The supramolecular column in complex 3 composed of CB6 molecules linked via hydrogen bonding with tryptamine guests.

Additionally, ion−dipole interactions between tryptamine protonated amino groups and carbonyl oxygen atoms of CB6 contribute to column stabilization. Like in previous complexes, the indole rings of tryptamine guests are involved in stacking interactions with outer walls of CB6 molecules and in this way are responsible for the supramolecular organization of neighboring columns into a 3-D supramolecular structure, Figure 7. The columns are assembled in typical cucurbiturils “bumps” to “hollows” mode: the “bumps” (cucurbiturils) of one column fit into “hollows” (tryptamines) of the neighboring column and are held together by stacking interactions between indole rings and glycouril groups of CB6. In other words, the outer surface of each CB6 molecule is stacked with four tryptamine guests: two tryptamine X (average distances between the indole plane and two glycouril planes are 3.40 and 3.44 Å, dihedral angles are 4.39 and 3.35°) and two tryptamine Y (average distances between the indole plane and 553



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two glycouril planes are 3.47 and 3.38 Å, dihedral angles are 3.19 and 3.33°). The new exclusion complexes of CB6 with tryptophan and tryptamine show a number of interesting features, namely, 1:2 stoichiometry resulting from chelation of ammonium groups by carbonyl oxygen atoms on CB6 portals and complementarity of large and flat indole groups with the outer surface of CB6 molecules. While hydrogen bonding assisted with ion−dipole interactions rules the guest binding at the cucurbituril portals, the stacking properties of indole rings drive the supramolecular organization of the resulting complexes into helical natotubes for tryptophan or bumps-to-hollows stacked supramolecular columns for tryptamine. The present study has established the complex-stabilizing role of stacking interactions between electron-rich indole rings and glycouril groups of CB6 in the formation of solid-state supramolecular assemblies. Additionally, a novel simple strategy for supramolecular synthesis of CB6 crystalline complexes with organic guest molecules implying usage of magnesium chloride solution of cucurbituril offers new possibilities to explore host−guest chemistry of CB6 for biochemical and pharmaceutical application, and we are currently investigating the complexation ability of CB6 toward short peptides and various active pharmaceutical ingredients in the solid state.

ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic files in CIF format for complexes 1−3. This information is available free of charge via the Internet at http://pubs.acs.org/

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REFERENCES

(1) (a) Lagona, J.; Mukhopadhyay, P.; Chakrabarti, S.; Isaacs, L. Angew. Chem., Int. Ed. 2005, 44, 4844−4870. (b) Lee, J.; W., Samal, S.; Selvapalam, N.; Kim, H.-J.; Kim, K. Acc. Chem. Res. 2003, 36, 621− 630. (c) Marquez, C.; Hudgins, R. R.; Nau, W. M. J. Am. Chem. Soc. 2004, 126, 5806−5816. (d) Gerasko, O. A.; Samsonenko, D. G.; Fedin, V. P. Russ. Chem. Rev. 2002, 71, 741−760. (e) Buschmann, Ha.J.; Cleve, E.; Mutihac, L.; Schollmeyer, E. J. Incl. Phenom. Macrocycl. Chem. 2009, 65, 293−297. (2) (a) Uzunova, V. D.; Cullinane, C.; Brix, K.; Nau, W. M.; Day, A. I. Org. Biomol. Chem. 2010, 8, 2037−2042. (b) Hettiarachchi, G.; Nguyen, D.; Wu, J.; Lucas, D.; Ma, D.; Isaacs, L.; Briken, V. PloS ONE 2010, 5, e10515. (d) Wheate, N. J.; Buck, D. P.; Day, A. I.; Collins, J. G. Dalton Trans. 2006, 451−458. (3) (a) Pozo, M.; Hernandez, P.; Hernandez, L.; Quintana, C. J. Mater. Chem. 2011, 21, 13657−13663. (b) Hennig, A.; Bakirci, H.; Nau, W. M. Nat. Methods 2007, 4, 629−632. (c) Walker, S.; Kaur, R.; McInnes, F. J.; Wheate, N. J. Mol. Pharmaceutics 2010, 7, 2166−2172. (d) McInnes, F. J.; Anthony, N. G.; Kennedy, A. R.; Wheate, N. J. Org. Biomol. Chem. 2010, 8, 765−773. (4) Bardelang, D.; Udachin, K.; Leek, D. M.; Margeson, J. M.; Chan, G.; Ratcliffe, C. I.; Ripmeester, J. A. Cryst. Growth Des. 2011, 11, 5598−5614. (5) Zhang, F.; Yajima, T.; Li, Y.-Z.; Xu, G.-Z.; Chen, H.-L.; Liu, Q.T.; Yamauchi, O. Angew. Chem., Int. Ed. 2005, 44, 3402−3407. (6) Danylyuk, O.; Suwinska, K. Chem. Commun. 2009, 5799−5813. (7) Yi, J.-M.; Zhang, Y.-Q.; Cong, H.; Xue, S.-F.; Tao, Z. J. Mol. Struct. 2009, 933, 112−117. (8) Thuery, P. Inorg. Chem. 2011, 50, 10558−10560. (9) Heringa, J.; Argos, P. J. Mol. Biol. 1991, 220, 151−171. (10) Harel, M.; Kleywegt, G. J.; Ravelli, R. B. G.; Silman, I.; Sussman, J. L. Structure 1995, 3, 1355−1366. (11) Katz, B. A. Biochemistry 1995, 34, 15421−15429. (12) Yengo, C. M.; Fagnant, P. M.; Chrin, L.; Rovner, A. S.; Berger, C. L. Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 12944−12949. (13) Versées, W.; Loverix, S.; Vandemeulebroucke, A.; Geerlings, P.; Steyaert, J. J. Mol. Biol. 2004, 338, 1−6. (14) Callis, P. R. Methods Enzymol. 1997, 278, 113−150. (15) The identical complex was obtained with L-Trp, however, usage of D-Trp resulted in better crystal quality and provided a data set with higher resolution. (16) Jeon, Y. M.; Kim, J.; Whang, D.; Kim, K. J. Am. Chem. Soc. 1996, 118, 9790. (17) Synthesis of complex 1: CB6·10H2O (12 mg, 0.01 mmol) and MgCl2·6H2O (80 mg, 0.4 mmol) were dissolved in distilled water (2 mL) upon gentle heating, colourless crystals appeared overnight; 2: CB6·10H2O (12 mg, 0.01 mmol), MgCl2·6H2O (80 mg, 0.4 mmol), and D-Trp (4 mg, 0.02 mmol) were dissolved in distilled water (2 mL) upon gentle heating, yellowish crystals appeared overnight; 3: to the solution of CB6·10H2O (12 mg, 0.01 mmol) and MgCl2·6H2O (80 mg, 0.4 mmol) in 2 mL of distilled water the solution of tryptamine (3.2 mg, 0.02 mmol) in 1 mL of 0.1 M HCl was added, colourless crystals appeared overnight. (18) The X-ray data were collected at 100(2) K on a Nonius KappaCCD diffractometer using MoKα radiation (λ = 0.71073 Ǻ ). The data were processed with HKL2000.25 Structures were solved by direct methods and refined using SHELXL-97.26 The figures were prepared using X-Seed 27 / POV-Ray. Crystal data for 1: C36H46Cl2MgN24O32, Mr = 1414.6, colorless, 0.50 × 0.30 × 0.20, monoclinic, space group P21/c, a = 12.7202(2), b = 15.9032(3), c = 30.5436(7) Å, β = 93.2058(10)°, V = 6169.1(2) Å3, Z = 4, μ = 0.224 mm−1, θmax = 27.5°, 1020 parameters, 10 restraints, 13 945 independent reflections, 11576 with I > 2σ(I). R = 0.073, wR = 0.183 (R = 0.087, wR = 0.192 for all data), GOF = 0.99. Crystal data for 2: C58H83Cl2.5N28O25: Mr = 1654.4, yellow, 0.25 × 0.20 × 0.10, tetragonal, space group I41, a = 31.3812(3), c = 14.7005(1) Å, V = 14476.8(3) Å3, Z = 8, μ = 0.210 mm−1, θmax = 28.3°, 1116 parameters, 14 restraints, 17936 independent reflections, 16406 with I > 2σ(I). R = 0.059, wR = 0.145 (R = 0.068, wR = 0.151 for all data), GOF = 1.09.

Figure 7. The packing of adjacent supramolecular columns through stacking interactions with tryptamine molecules viewed from the c axis in complex 3.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: + 48 22 343 3232. E-mail: [email protected].

ACKNOWLEDGMENTS This research was supported by the Polish Ministry of Science and Higher Education (Grant Iuventus Plus Nr IP2010 029170). O.D. is grateful to the Foundation for Polish Science for a START stipend for young researchers. We thank Dr. Denis Samsonenko for helpful discussion. 554



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Crystal data for 3: C56H62Cl2N28O29: Mr = 1658.2, colourless, 0.55 × 0.45 × 0.40, monoclinic, space group C2/c, a = 27.1196(6), b = 16.1001(4), c =- 34.3202(7) Å, β = 97.7838(7)°, V = 14847.1(6) Å3, Z = 8, μ = 0.190 mm−1, θmax = 27.5°, 1314 parameters, 306 restraints, 16 882 independent reflections, 11766 with I > 2σ(I). R = 0.096, wR = 0.253 (R = 0.132, wR = 0.287 for all data), GOF = 1.05. (19) Heo, J.; Kim, J.; Whang, D.; Kim, K. Inorg. Chim. Acta 2000, 297, 307−312. (20) Freeman, W. A.; Mock, W. L.; Shih, N.-Y. J. Am. Chem. Soc. 1981, 103, 7367−7368. (21) Chen, W.-J.; Yu, D.-H.; Xiao, X.; Zhang, Y.-Q.; Zhu, Q.-J.; Xue, S.-F.; Tao, Z.; Wei, G. Inorg. Chem. 2011, 50, 6956−6964. (22) Samsonenko, D. G.; Virovets, A. V.; Lipkowski, J.; Gerasko, O. A.; Fedin, V. P. J. Struct. Chem. 2002, 43, 664−668. (23) Orr, G. W.; Barbour, L. J.; Atwood, J. L. Science 1999, 285, 1049−1052. (24) Heitmann, L. M.; Taylor, A. B.; Hart, P. J.; Urbach, A. R. J. Am. Chem. Soc. 2006, 128, 12574−12581. (25) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307− 326. (26) Sheldrick, G. M. Acta Crystallogr. 2008, 64A, 112−122. (27) Barbour, L. J. J. Supramol. Chem. 2001, 1, 189−191.

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Solid-State Supramolecular Assemblies of Tryptophan and

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