Solvent-Switched Schiff-Base Macrocycles: Self-Sorting and Self

www.acsnano.org

Solvent-Switched Schiff-Base Macrocycles: Self-Sorting and Self-Assembly-Dependent Unconventional Organic Particles Huaiyu Chen,† Chao Huang,† Yaxin Deng, Qi Sun, Qi-Long Zhang, Bi-Xue Zhu,* and Xin-Long Ni*

ACS Nano Downloaded from pubs.acs.org by IOWA STATE UNIV on 02/04/19. For personal use only.

Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang, Guizhou 550025, China S Supporting Information *

ABSTRACT: Organic reaction is a powerful and versatile tool for the creation of various new substrates and materials. However, there have been few reports of the direct fabrication of organic particles by organic reactions. Herein, we report that water as a co-solvent can efficiently switch a [2 + 2] macrocycle (3) to a [1 + 1] macrocycle (4) in a Schiff-base reaction from the same precursors at room temperature. Unexpectedly, a series of tunable organic micro/nanoparticles, including solid microspheres, core−shell spheres, and vesicles, could be directly precipitated in onestep from the reaction medium with high yield. X-ray structure analysis and other characterizations indicated that social self-sorting and narcissistic self-sorting of the macrocyclic frameworks of 3 and 4 through noncovalent interactions play crucial roles in the formation of such organic particles. Most interestingly, the facile and mild fabrication conditions of the particles allowed us to accurately and in situ monitor their intermediate formation by controlling the reaction time. This work thus provides an advancement of the fabrication of tunable organic particles. KEYWORDS: organic particles, macrocycles, self-assembly, Schiff-base, self-sorting, organic reaction, supramolecular chemistry

M

influence on the geometry and/or topology of the CN-based macrocycles formed.18−20 However, because of the thermodynamic lability of the imine bond in water, establishing stable dynamic covalent assemblies of CN bond derivatives in aqueous media is highly challenging work. In particular, water as a side product is generally considered to inhibit the generation of CN bonds, and it is common to drive the C N equilibrium in the forward direction by removing water as it is formed.14 Additionally, as supramolecular chemistry has become a vastly diverse field, self-assembly involving macrocycles based on noncovalent interactions has emerged as a facile tool for the construction of various micro/nanostructured systems.21−23 In recent years, the general term “self-sorting” has been invoked24,25 to describe the high-fidelity recognition between molecules and ions within a mixture, where their affinities can be either for other species, that is, social self-sorting,26−28 or for themselves, that is, narcissistic self-sorting.29−31 To date, much interest has been directed toward the design of self-sorting structural motifs and the resulting artificial functional architectures and materials based on noncovalent interac-

acrocycles have long captured the imagination of scientists because of their broad potential applications in supramolecular chemistry1−4 and materials 5−8 science. Many chemists have been active in the construction of various macrocycles during the past decades. Various experimental parameters, such as the solvent, concentration, template, pH, temperature, noncovalent bonding interactions, steric hindrance, and electronic factors, can influence the formation of macrocycles, and these have been investigated in detail.9−11 Schiff-base directed reactions,12 because of the facile process and mild reaction conditions, have often been applied for the preparation of macrocycles.13 In particular, as one of the very few covalent bonds with reversible character, iminebased (CN) Schiff-bases have been used to good effect in dynamic covalent chemistry in recent years.14−17 Typically, to synthesize macrocyclic molecules with different topologies or shapes, precursors with different geometries are used.5,9−11 It is relatively rare to see changes in macrocycle geometry and/or topology simply by changing the reaction conditions when employing the same starting materials. Interestingly, rearrangement of CN-based macrocycles in solution to form alternative molecular species is possible because of the dynamic nature of the imine bonds,12 which can allow equilibration of the reaction mixture in response to external stimuli. In particular, studies have indicated that the solvent used for a Schiff-base reaction can have a significant © XXXX American Chemical Society

Received: December 15, 2018 Accepted: January 31, 2019 Published: January 31, 2019 A

DOI: 10.1021/acsnano.8b09478 ACS Nano XXXX, XXX, XXX−XXX

Article

Cite This: ACS Nano XXXX, XXX, XXX−XXX

Article

ACS Nano

Figure 1. (a) Synthetic route to macrocycles 3 and 4. (b1−b4) SEM images, (c1−c4) TEM images, and (d1−d4) HPLC traces of 3, the mixture of 3 and 4, and 4, respectively.

tions.32 However, few examples have been reported of nanoparticles derived from the self-sorting of supramolecular assemblies. In particular, to the best of our knowledge, the preparation of pure organic nanoparticles by direct precipitation due to the self-sorting of macrocycles in an organic reaction has not hitherto been demonstrated. In this article, as shown in Figure 1, by adjusting the water content in a mixed reaction medium (CH3OH/H2O), we demonstrate that water as a co-solvent can efficiently promote precipitation-driven conversion of a [2 + 2] macrocycle (3) to a [1 + 1] macrocycle (4) in a Schiff-base reaction from the same precursors at room temperature. Macrocycle 3 was directly precipitated from a methanolic solution in high yield. However, when an appropriate amount of water was injected into the methanolic solution, 3 was inhibited, and accompanying 4 was gradually formed from the same precursors. Correspondingly, various uniform tunable organic micro/ nanoparticles, including solid microspheres, core−shell nanospheres, and vesicles, were generated from the one-step reaction. X-ray structure analysis and other characterizations indicated that social self-sorting and narcissistic self-sorting assembly of the macrocyclic frameworks of 3 and 4 through noncovalent interactions played key roles in the formation of such organic particles. Here, due to the facile and mild fabrication conditions of the macrocycle-based organic particles, a kinetic process of particle growth was evidently in operation, leading to the observed series of unconventional intermediate morphologies.

RESULTS AND DISCUSSION Schiff-base [2 + 2] macrocycle 3 and [1 + 1] macrocycle 4 could readily be selectively synthesized through one-pot condensations between N,N′-(6-amino-2-pyridyl)-1,3- dicarboximide (1) and 2,2-bis(5-formyl-2′-furyl)propane (2) in MeOH and the mixed solvent MeOH/H2O, respectively, in the presence of a catalytic amount of concentrated H2SO4. After stirring the reaction solutions at room temperature for about 2 h, large amounts of light-yellow precipitates 3 and 4 were generated, and the pure products were recovered in high yields (80∼90%) simply by washing the precipitates several times with methanol (Figure 1a). The precipitates 3 and 4 were characterized by NMR spectrometry and ESI-HRMS (Figures S1−S3). In particular, the mass spectra clearly confirmed the presence of the species [3 + H ]+ at m/z 1087.3898 (calculated 1087.3885) and [4 + H ]+ at m/z 544.1995 (calculated 544.1979). As shown in Figure 1b1, c1, SEM and TEM images indicated that the precipitates of 3 were composed of a number of micro solid spheres with a remarkably uniform diameter of about 1.3 μm. In contrast, SEM and TEM images revealed that the precipitates of 4 were composed of uniform vesicles with a dramatically decreased diameter of around 380 nm, in which the thickness of the particle shell was determined to be 20−30 nm (Figure 1b4, c4). Surprisingly, it was noted that numerous core−shell spherical organic particles with tunable size from micro- to nanoscale were present in the mixed precipitates of 3 and 4. For example, when the Schiff-base reaction was conducted in CH3OH/H2O (5:1, v/v), the obtained precipitate was B


Article

ACS Nano

Figure 2. Intermediate morphologies of the solid microspheres. SEM images of the precipitates of 3 from a methanolic reaction solution at different times: (a) 2 min, (b) 5 min, (c) 10 min, (d) 1 h. Insert: TEM image of the particles.

composed of particles of uniform size of about 1.075 ± 0.025 μm (Figure 1b2). TEM images indicated that the thicknesses of the solid core and the shell were about 1.0 μm and 20 nm, respectively (Figure 1c2). When the water content of the solvent was increased (CH3OH/H2O, 2:1, v/v), the particle morphology of the precipitate was not significantly changed, according to an SEM image (Figure 1b3), but the mean particle size decreased to around 650 nm. A TEM image revealed that the diameter of the solid core changed significantly to 220−300 nm, but the thickness of the spherical shell remained at around 20−30 nm (Figure 1c3). Evidently, formation of the core−shell organic particles can be attributed to the generation of 4. At first glance, the remarkable decrease in the size of the solid spherical core implies that the shells of the particles were derived from their cores. However, closer inspection raises two questions. The first concerns the compositions of the cores and shells of the particles, that is, whether they were composed of 3 and 4, respectively, or whether both were derived from mixed assemblies of 3 and 4. The second question is whether the [1 + 1] macrocycle 4 was formed by rearrangement of the [2 + 2] macrocycle 3 or was directly generated from the precursors. To answer the first question, high-performance liquid chromatography (HPLC) was applied to elucidate the distributions of [2 + 2] macrocycle 3 and [1 + 1] macrocycle 4 in the organic particles. As shown in Figure 1d1−d4 and Figure S4, retention times of 12.62 and 7.89 min were obtained for the micro solid spheres of 3 (Figure 1d1) and vesicles of 4 (Figure 1d4), respectively. When a solution of the core−shell particles was injected onto the HPLC column, two peaks at 12.62 and 7.89 min with different intensities were obtained (Figure 1d2, d3), which clearly indicated that the core−shell particles were composed of 3 and 4. The intensity ratio of the

two peaks in the HPLC trace corresponded to the areas of the shell and core in the TEM images. This result thus provided unequivocal proof that the shell was assembled by narcissistic self-sorting of 4, whereas the core was assembled by narcissistic self-sorting of 3. In addressing the second question, we first noted that [2 + 2] macrocycle 3 and [1 + 1] macrocycle 4 have limited solubility in CH3OH and a mixture of CH3OH/H2O. Indeed, both of the macrocycles were precipitated from these media. Therefore, conversion of the [2 + 2] macrocycle 3 to the [1 + 1] macrocycle 4 is likely driven by competitive precipitation. Specifically, we propose that a larger amount of water, acting as a poor solvent, promotes the reaction through rapid precipitation of the product 4. In an effort to gain more detailed information on the role of macrocycles 3 and 4 in the construction of these organic particles, the kinetic process of particle growth at different stages was carefully evaluated. Fortunately, the facile and mild fabrication conditions of the particles allowed us to accurately monitor their intermediate formation simply by controlling the reaction time. Actually, the Schiff-base reaction proceeded very rapidly. As shown in Video S1 (Supporting Information), starting from substrates 1 and 2, a light-yellow precipitate appeared almost immediately when the mixture was stirred at room temperature in the presence of a catalytic amount of sulfuric acid. As a result, it was very convenient to collect precipitates in situ from the reaction solution at different times and subject them to SEM analysis. Figure 2 shows the SEM morphologies of the evolving solid microsphere products, composed of macrocycle 3, as directly precipitated from a solution in CH3OH. Unexpectedly, no microspheres or other particle shapes were seen in the image when the reaction time was restricted to 2 min; rather, a large amount of burr-like C


Article

ACS Nano

Figure 3. Intermediate morphologies of the spherical vesicles. SEM images of the precipitates of 4 from CH3OH/H2O (1:2, v/v) at different times: (a) 1 min, (b) 5 min, (c) 10 min, (d) 1 h. Insert: TEM images of the particles.

blocks of size >20 μm appeared (Figure S5). Closer inspection revealed that these blocks were composed of “burr flower balls” with multiple petal layers (Figure 2a). Interestingly, as the reaction time increased, some small microspheres with uniform size (∼1.3 μm) appeared on the “mother” flowers (Figure 2b and Figure S6), resembling fruits generated from the petals of the burr flower. The burr flowers were fully converted into microsphere “fruits” after a reaction time of 10 min (Figure 2c and Figure S7). Further observation revealed that the solid microsphere “fruits” required more than 1 h to separate from the “mother flower balls” as uniform individual spheres (Figure 2d). In contrast to the solid microsphere formation from macrocycle 3 in pure CH3OH solution, for vesicle formation from macrocycle 4 in a mixed solvent of CH3OH/H2O (1:2, v/v), it was found that spherical particles were quantitatively formed and agglomerated within a reaction time of 1 min. The organic particles were of uneven size (Figure 3a), with diameters mainly distributed around 380 and 130 nm, respectively. Particle diameter statistics showed that the smaller particles (130 nm) accounted for the vast majority (more than 80%). TEM images revealed that all of the particles were vesicles (Figure S8). Notably, as the reaction time was increased to 10 min, we observed that the small particles fused together (Figure 3b, c). When the reaction was carried out over 1 h, the small particles were completely consumed, and larger vesicle particles were stably formed with a uniform diameter of about 380 nm (Figure 3d and Figures S9−S10). Thus, the larger particles were clearly assembled from the smaller particles rather than directly precipitated from the reaction mixture. Our recent work has suggested that tunable core−shell organic particles can be fabricated from a twisted [2 + 2] macrocycle33 by condensation of the same substrate 1 with

5,5′-methylene-bis-salicylaldehyde under similar reaction conditions as described for 3 and 4. Thus, how macrocycles 3 and 4 assemble to form solid microspheres and vesicles has greatly attracted our attention. Fortunately, crystals of 3 were successfully obtained by evaporation of the volatiles from a solution in THF. Singlecrystal X-ray analysis revealed that the macrocycle 3 adopts a C2-symmetric twisted structure, and enantiomeric conformers can be observed in the unit cell (Figure 4a−e), similar to our previous observations.33 The difference is that a series of intramolecular CH···π interactions (dH···π‑center = 2.9−3.16 Å) is established in macrocycle 3. From a structural viewpoint, these noncovalent interactions should contribute to stabilizing the twisted conformation of 3. Essentially, social self-sorting of the twisted enantiomeric conformations (M- and P-handed) plays a significant role in the assembly of 3 to 3D superstructures. For example, the selfsorting-based complementary enantiomers become alternately linked to form 1D single-strand chains through intermolecular CH···N hydrogen-bonding between the imine nitrogen (N4) and a carbon atom (C21) of the furan ring with a distance 2.694 Å (Figure 4f). As a result, the macrocycles become stacked in 1D solid quadrilateral columns when viewed along the c-axis (Figure 4g−j). These 1D single quadrilateral columns are then further interlinked to form 2D and 3D networks through alternating intermolecular CH···π interactions between the protons of the central pyridine ring (C4) and the phenyl rings (dH···π‑center = 3.002 Å) and CH···O bonding interactions between the carbonyl oxygen (O4) and a carbon atom (C10) of the phenyl ring (bond distance 2.486 Å) (Figure 4k). Comparing the X-ray structure of our recently synthesized [2 + 2] macrocycle33 with that of 3, the main difference is that the former revealed that CH···π interactions between D


Article

ACS Nano

Figure 4. Structure of 3 determined by single-crystal X-ray diffraction. (a) Structure of 3 in left-handed twisted conformation (M); (b−e) side and top views of M- and P-structures of 3; (f) CH···N interactions between the enantiomeric forms; (g−j) top and side views of the 1D assembly of 3; and (k) 2D and 3D superstructures of 3 based on CH···π and CH···O interactions. Water molecules and hydrogen atoms have been omitted for clarity.

Scheme 1. Proposed Particle Growth Process of the Solid Microspheres of 3

particles, whereas the latter indicated that all of the noncovalent interactions stemmed from the social self-sorting of twisted enantiomeric forms (Figures S11 and S12). For

enantiomeric forms in 1D circular column assemblies and hydrogen-bonding between solvent molecules and these 1D assemblies play key roles in the formation of core−shell E


Article

ACS Nano

Figure 5. Structures of 4 and 5. (a) Top and (b) side views of the DFT structure of 4; (c) top and (d) side views of the X-ray structure of 5; and (e−g) self-assembly of 5 in the solid state.

Scheme 2. Proposed Particle Growth Process of the Vesicles of 4

arising from social self-sorting of the enantiomeric forms, allow the 2D and 3D assemblies to aggregate compactly, contributing to the formation of solid microspheres of the particles. Numerous attempts have been made to obtain an X-ray structure of macrocycle 4, but without success. To obtain more information on the molecular structure, the energy-minimized structure of 4 was evaluated by DFT calculation (B3LYP/631G(d)). As illustrated in Figure 5a, b, the calculated result suggests that the framework of 4 adopts a saddle-shaped 1,3alternating conformation with a deep cavity. The longest distances of the portals between the 1,3-alternating walls are 10.86 and 6.95 Å, respectively. To obtain further evidence, a single-crystal structure of macrocycle 5,36 which was reported by Sessler in 2004 and has a very similar molecular structure to that of 4, was successfully obtained. X-ray analysis revealed that 5 adopts a molecular framework akin to the calculated structure of 4 (Figure 5c, d). As shown in Figure 5e, f, individual macrocycles of 5 were alternately assembled into 1D hollow quadrilateral column structures through unusual CH···π interactions between a methyl group (C12) and the pyrrole moieties and between another methyl group (C13) and the CN bonds when viewed along the a-axis. The 1D hollow quadrilateral columns are further linked to form hollow 2D and 3D layers through multiple CH···O bonding between the methylene units and carbonyl groups (Figure 5g). From a structural viewpoint, the assembly modes of 4 for the formation of vesicles can be illustrated by the assembly of 5 in the solid state. Indeed, recent results from Tominaga et al. also suggested that organic vesicles can be generated from hollow 2D and 3D assemblies of nonamphiphilic macrocycles.37 Therefore, a mechanism for the formation of vesicles

example, the construction of 1D quadrilateral columns of 3 was induced by CH···N bonding between the enantiomeric species, and the 2D and 3D column networks were tightly linked by intermolecular CH···π interactions and CH···O bonds, which were also derived from social self-sorting of the enantiomeric forms. We thus surmise that these noncovalent interactions should be the crucial factor in the formation of solid microspheres from 3. Taking together all of our observations, a model for the formation of solid microspheres by the assembly of 3 is proposed in Scheme 1. The Schiff-base reaction proceeded very rapidly, so that macrocycle 3 was generated at an early stage. Social self-sorting based on CH···N hydrogen-bonding between the enantiomeric species is considered to be the dominant driving force during this period, leading to a large amount of 1D quadrilateral columns. In principle, these 1D assemblies are more favorable for the formation of spheres as opposed to infinite 1D growth.34 This is because, in a closed sphere, the energetically unfavorable edges are eliminated at a finite aggregation number, which is also entropically favored.35 However, the growth of self-sorting 1D assemblies is faster than sphere formation at this stage. As a result, numerous large spherical cluster-like “burr flower balls” are generated. With increasing reaction time, noncovalent interactions between the 1D assemblies gradually become the dominant driving force, leading to the formation of 2D and 3D networks. Under certain conditions, 2D and 3D aggregates of a certain size bend to form solid spherical particles with the assistance of continued self-sorting of 1D assemblies in the remaining reaction mixture. Finally, because of the dynamic properties and reversibility of the noncovalent interactions, a series of uniform individual solid microsphere particles is fabricated. Here, the CH···π interactions and CH···O bonds, F


Article

ACS Nano

Figure 6. Intermediate morphologies of the core−shell-shaped particles. SEM images of the mixture precipitates of 3 and 4 from CH3OH/ H2O (5:1, v/v) at different times: (a) 5 min and (b) 10 min. SEM images of the mixture precipitates of 3 and 4 from CH3OH/H2O (2:1, v/v) at different times: (c) 5 min and (d) 10 min.

Scheme 3. Proposed Growth Process of the Core−Shell-Shaped Particles from the Mixture of 3 and 4

they were heated at 180 °C (Figures S13−S15), apart from vesicles from the assembly of 4 where broken vesicles and larger fused vesicles were observed around 160 °C, and finally merged into a block morphology at 180 °C (Figure S16).

by the assembly of 4 is proposed in Scheme 2. The large amount of smaller vesicles is believed to be formed as the kinetic product of the assembly of 4, which may be attributed to the rapid and quantitative generation of 4 in the early stage of the Schiff-base reaction. The expanded vesicles, derived from fusion of the smaller vesicles, are considered to be the thermodynamic products. The driving forces for agglomeration of the smaller spheres mostly arose from multiple noncovalent interactions between the surfaces of the spheres. In addition, SEM images of the mixtures of 3 and 4, which were precipitated from the medium of CH3OH/H2O solution at different reaction time, indicate that the shell and core were simultaneously formed (Figure 6). As shown in Scheme 3, we proposed that the hydrophobic effect between the solid microspheres of 3 and the bowl-shaped shells of 4 in the presence of water should be the driving force for the formation of the core−shell-shaped spherical particles. Last but not the least, the noncovalent interactions derived organic particles exhibited excellent thermal stability, as no change was observed in regard to their size and shape after

CONCLUSIONS In summary, water has been introduced as a co-solvent in a Schiff-base reaction, which efficiently promoted the conversion of one precipitation-derived macrocycle to another. Notably, a series of uniform organic micro/nanoparticles, including solid microspheres, core−shell spheres, and vesicles, could be directly precipitated from the same reaction mixture in high yields through simple, facile, and mild operations. X-ray structure analysis and other characterizations have revealed that the social self-sorting and narcissistic self-sorting of macrocyclic molecular frameworks of 3 and 4 play crucial roles in the formation of such organic particles. Most interestingly, the facile and mild fabrication conditions of the particles allowed us to accurately and in situ monitor their intermediate formation simply by controlling the reaction time. G


Article

ACS Nano

X-ray Structure of 5. Pale-yellow single crystal was obtained from a crystal grown of 5 (30.0 mg) in DMF solution (6.0 mL) within 2 weeks. Crystal data for 5: (C32H25N5O4)·C3H7NO, Mr = 614.70, orthorhombic, space group P212121, a = 11.686(7) Å, b = 12.036(7) Å, c = 22.607(13) Å, α = 90.00°, β = 90.00° (4), γ = 90.00°, V = 3180(3) Å3, Z = 4, Dc = 1.284 g cm−3, R1 = 0.0655 (I > 2σ(I)), wR2 = 0.1715 (all data), GoF = 0.771. CCDC 1878653.

Whereas a plethora of methods have been developed for the scalable synthesis and preparation of inorganic metal and inorganic−organic hybrid nanoparticles, only a few specialized techniques have been reported for the preparation of organic nanoparticles. This work thus provides a perspective insight for the tunable self-assembly of organic species with increased complexity and unusual functionality and may advance the design of organic particles.

ASSOCIATED CONTENT S Supporting Information *

METHODS

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.8b09478. Crystallographic data (CIF) Crystallographic data (CIF) Video S1 (AVI) Video S2 (AVI) Full experimental details, NMR, SEM and TEM experiments (PDF)

38

N,N′-(6-amino-2-pyridyl)-1,3-dicarboximide (1) and 2,2-bis(5formyl-2′-furyl)propane (2)39 were synthesized according to methods described in the literature. Synthesis of Macrocycle (3) and Organic Particles. 1 (174 mg, 0.5 mmol) and 2 (116 mg, 0.5 mmol) were dissolved in methanol solution (30 mL) in round-bottomed flask for 5 min, and conc. H2SO4 (10.0∼20.0 μL) was added to the solution. The resulting mixture was stirred at room temperature for 2 h. Then, the reaction mixture was filtered to give the crude solid product, and the residue was washed with methanol three times to afford a light yellow solid compound 3 (246 mg, 91%). SEM and TEM images confirmed that the yellow solid is solid microspheres (∼1.30 μm). Mp > 200 °C. 1H NMR (400 MHz, d6-DMSO) δ10.79 (s, 4H, OC-NH), 8.57 (d, J = 8 Hz, 4H, Py−H), 8.47 (d, J = 8 Hz, 2H, Py−H), 8.41 (t, J = 8 Hz, 4H, Ar−H), 8.08 (s, 4H, NCH), 7.33 (t, J = 16 Hz, 4H, Ar−H), 6.96 (t, J = 16 Hz, 4 H, Ar−H), 6.92 (d, J = 4 Hz, 4H, Ar−H), 6.82 (d, J = 12 Hz, 8H, Fu-H), 5.60 (d, 8H, Fu-H), 1.39 (s, 12H, CH3). 13 C NMR of 3 could not be determined due to its low solubility. ESIMS (m/z): calcd for [M + H]+ [C64H51N10O8]+ m/z = 1087.3885; found m/z = 1087.3898. Synthesis of macrocycle (4) and organic particles. 1 (174 mg, 0.5 mmol) and 2 (116 mg, 0.5 mmol) were dissolved in a mixed solvent MeOH/H2O (30 mL, 1:2, v/v) in round-bottomed flask for 5 min, conc. H2SO4 (10.0∼20.0 μL) was added to the solution. The resulting mixture was stirred at room temperature for 2 h. Then, the reaction mixture was filtered to give the crude solid product, the residue was washed with methanol three times to afford a light yellow solid compound 4 (225 mg, 83%). SEM and TEM images confirmed that the yellow solid is vesicles (∼380 nm). Mp > 200 °C. 1H NMR (400 MHz, d6-DMSO) δ (ppm) 10.74 (s, 2H, OC−NH), 8.54 (d, J = 4 Hz, 2H, Py−H), 8.42 (d, J = 8 Hz, 1H, Py−H), 8.37 (t, J = 16 Hz, 2H, Ar−H), 8.05 (s, 2H, NCH), 7.27 (t, J = 8 Hz, 2H, Ar−H), 6.91 (d, J = 4 Hz, 2H, Ar−H), 6.89 (d, J = 4 Hz, 2H, Ar−H), 6.82 (d, J = 8 Hz, 2H, Fu−H), 5.51 (4H, Fu−H), 1.35 (s, 12H, CH3). 13C NMR (100 MHz, CDCl3) δ 162.97, 162.23, 152.53, 150.37, 148.86, 139.97, 133.53, 127.92, 125.79, 124.73, 119.91, 116.71, 113.23, 107.53, 37.72, 26.44. ESI-MS (m/z): calcd for [M + H] + [C32H26N5O4]+ m/z = 544.1995; found m/z = 544.1979. Synthesis Organic Particles from the Mixture of 3 and 4. 1 (174.0 mg, 0.5 mmol) and 2 (116 mg, 0.5 mmol) were dissolved in mixed solvent MeOH/H2O (30 mL, 5:1, v/v) in round-bottomed flask for 5 min, and conc. H2SO4 (10.0∼20.0 μL) was added to the solution. The resulting mixture was stirred at room temperature for 2 h. Then, the reaction mixture was filtered to give the crude solid product, and the residue was washed with methanol three times to afford a light yellow solid precipitates (235 mg). SEM and TEM images confirmed that the yellow solid is core−shell spheres (∼1.0 μm). A similar experiment procedure for preparation of another core−shell spheres (∼650 nm) by just modifying the reaction medium of MeOH/H2O forms 5:1 to 2:1 (30 mL, v/v). X-ray Structure of 3. Pale-yellow single crystal was obtained from a crystal grown by evaporation of 3 (10.0 mg) in CH3OH solution (10.0 mL) within 1 week. Crystal data for 3: (C64H50N10O8)·2H2O, Mr = 1122.38, monoclinic, space group C2/c, a = 27.968(9) Å, b = 12.231(4) Å, c = 23.163(12) Å, α = 90.00°, β = 121.823° (4), γ = 90.00°, V = 6733(5) Å3, Z = 4, Dc = 1.556 g cm−3, R1 = 0.1024 (I > 2σ(I)), wR2 = 0.2940 (all data), GoF = 1.030. CCDC 1878652.

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Xin-Long Ni: 0000-0002-5557-1631 Author Contributions †

H.C. and C.H. contributed equally to this work.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (nos. 21061003, 21871063), the Science and Technology Fund of Guizhou Province (nos. 20165656, 20175788, and 20181033). REFERENCES (1) Liu, Z.; Nalluri, S. K. M.; Stoddart, J. F. Surveying Macrocyclic Chemistry: from Flexible Crown Ethers to Rigid Cyclophanes. Chem. Soc. Rev. 2017, 46, 2459−2478. (2) Murray, J.; Kim, K.; Ogoshi, T.; Yao, W.; Gibb, B. C. The Aqueous Supramolecular Chemistry of Cucurbit[n]urils, Pillar[n]arenes and Deep-Cavity Cavitands. Chem. Soc. Rev. 2017, 46, 2479− 2496. (3) Chen, Y.; Huang, F.; Li, Z.-T.; Liu, Y. Controllable Macrocyclic Supramolecular Assemblies in Aqueous Solution. Sci. China: Chem. 2018, 61, 979−992. (4) Zhu, H.; Shangguan, L.; Shi, B.; Yu, G.; Huang, F. Recent Progress in Macrocyclic Amphiphiles and Macrocyclic Host-Based Supra-Amphiphiles. Mater. Chem. Front. 2018, 2, 2152−2174. (5) Hasell, T.; Cooper, A. I. Porous Organic Cages: Soluble, Modular and Molecular Pores. Nat. Rev. Mater. 2016, 1, 16053. (6) Xue, M.; Yang, Y.; Chi, X.; Yan, X.; Huang, F. Development of Pseudorotaxanes and Rotaxanes: from Synthesis to StimuliResponsive Motions to Applications. Chem. Rev. 2015, 115, 7398− 7501. (7) Yang, Y.; He, P.; Wang, Y.; Bai, H.; Wang, S.; Xu, J.-F.; Zhang, X. Supramolecular Radical Anions Triggered by Bacteria In Situ for Selective Photothermal Therapy. Angew. Chem., Int. Ed. 2017, 56, 16239−16242. (8) Hua, B.; Zhou, W.; Yang, Z.; Zhang, Z.; Shao, L.; Zhu, H.; Huang, F. Supramolecular Solid-State Microlaser Constructed from Pillar[5]arene-Based Host−Guest Complex Microcrystals. J. Am. Chem. Soc. 2018, 140, 15651−15654. H


Article

ACS Nano (9) Morohashi, N.; Narumi, F.; Iki, N.; Hattori, T.; Miyano, S. Thiacalixarenes. Chem. Rev. 2006, 106, 5291−5316. (10) Assaf, K. I.; Nau, W. M. Cucurbiturils: from Synthesis to HighAffinity Binding and Catalysis. Chem. Soc. Rev. 2015, 44, 394−418. (11) Ogoshi, T.; Yamagishi, T.; Nakamoto, Y. Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry. Chem. Rev. 2016, 116, 7937−8002. (12) Schiff, H. Mittheilungen aus dem Universitätslaboratorium in Pisa: eine neue Reihe organischer Basen. Justus Liebigs Ann. Chem. 1864, 131, 118. (13) Borisova, N. E.; Reshetova, M. D.; Ustynyuk, Y. A. Metal-Free Methods in the Synthesis of Macrocyclic Schiff Bases. Chem. Rev. 2007, 107, 46−79. (14) Belowich, M. E.; Stoddart, J. F. Dynamic Imine Chemistry. Chem. Soc. Rev. 2012, 41, 2003−2024. (15) Hasell, T.; Wu, X.; Jones, J. T. A.; Bacsa, J.; Steiner, A.; Mitra, T.; Trewin, A.; Adams, D. J.; Cooper, A. I. Triply Interlocked Covalent Organic Cages. Nat. Chem. 2010, 2, 750−755. (16) Vitaku, E.; Dichtel, W. R. Synthesis of 2D Imine-Linked Covalent Organic Frameworks Through Formal Transimination Reactions. J. Am. Chem. Soc. 2017, 139, 12911−12914. (17) Ma, T.; Kapustin, E. A.; Yin, S. X.; Liang, L.; Zhou, Z.; Niu, J.; Li, L.-H.; Wang, Y.; Su, J.; Li, J.; Wang, X.; Wang, W. D.; Wang, W.; Sun, J.; Yaghi, O. M. Single-Crystal X-ray Diffraction Structures of Covalent Organic Frameworks. Science 2018, 361, 48−52. (18) Katayev, E. A.; Pantos, G. D.; Reshetova, M. D.; Khrustalev, V. N.; Lynch, V. M.; Ustynyuk, Y. A.; Sessler, J. L. Anion-Induced Synthesis and Combinatorial Selection of Polypyrrolic Macrocycles. Angew. Chem., Int. Ed. 2005, 44, 7386−7390. (19) Liu, X.; Warmuth, R. Solvent Effects in Thermodynamically Controlled Multicomponent Nanocage Syntheses. J. Am. Chem. Soc. 2006, 128, 14120−14127. (20) Li, H.; Zhang, H.; Lammer, A. D.; Wang, M.; Li, X.; Lynch, V. M.; Sessler, J. L. Quantitative Self-Assembly of a Purely Organic Three-Dimensional Catenane in Water. Nat. Chem. 2015, 7, 1003− 1008. (21) Liu, M.; Zhang, L.; Wang, T. Supramolecular Chirality in SelfAssembled Systems. Chem. Rev. 2015, 115, 7304−739. (22) Jie, K.; Zhou, Y.; Yao, Y.; Huang, F. Macrocyclic Amphiphiles. Chem. Soc. Rev. 2015, 44, 3568−3587. (23) Kai, S.; Maddala, S. P.; Kojima, T.; Akagi, S.; Harano, K.; Nakamura, E.; Hiraoka, S. Flexibility of Components Alters the SelfAssembly Pathway of Pd2L4 Coordination Cages. Dalton Trans. 2018, 47, 3258−3263. (24) Wu, A.; Isaacs, L. Self-Sorting: The Exception or the Rule? J. Am. Chem. Soc. 2003, 125, 4831−4835. (25) Northrop, B. H.; Zheng, Y.-R.; Chi, K.-W.; Stang, P. J. SelfOrganization in Coordination-Driven Self-Assembly. Acc. Chem. Res. 2009, 42, 1554−1563. (26) Shivanyuk, A.; Rebek, J. Social Isomers in Encapsulation Complexes. J. Am. Chem. Soc. 2002, 124, 12074−12075. (27) Mukhopadhyay, P.; Wu, A.; Isaacs, L. Social Self-Sorting in Aqueous Solution. J. Org. Chem. 2004, 69, 6157−6164. (28) Joseph, R.; Nkrumah, A.; Clark, R. J.; Masson, E. Stabilization of Cucurbituril/Guest Assemblies via Long-Range Coulombic and CH•••O Interactions. J. Am. Chem. Soc. 2014, 136, 6602−6607. (29) Johnson, A. M.; Wiley, C. A.; Young, M. C.; Zhang, X.; Lyon, Y.; Julian, R. R.; Hooley, R. J. Narcissistic Self-Sorting in Self− Assembled Cages of Rare Earth Metals and Rigid Ligands. Angew. Chem., Int. Ed. 2015, 54, 5641−5645. (30) Yan, L.-L.; Tan, C.-H.; Zhang, G.-L.; Zhou, L.-P.; Bünzli, J.-C.; Sun, Q.-F. Stereocontrolled Self-Assembly and Self-Sorting of Luminescent Europium Tetrahedral Cages. J. Am. Chem. Soc. 2015, 137, 8550−8555. (31) Gidron, O.; Jirásek, M.; Trapp, N.; Ebert, M.-O.; Zhang, X.; Diederich, F. Homochiral [2]Catenane and Bis[2]catenane from Alleno−Acetylenic Helicates−a Highly Selective Narcissistic SelfSorting Process. J. Am. Chem. Soc. 2015, 137, 12502−12505.

(32) Safont-Sempere, M. M.; Fernández, G.; Würthner, F. SelfSorting Phenomena in Complex Supramolecular Systems. Chem. Rev. 2011, 111, 5784−5814. (33) Chen, H.; Huang, C.; Ding, Y.; Zhang, Q.-L.; Zhu, B.-X.; Ni, X.-L. Organic Core−Shell-Shaped Micro/Nanoparticles from Twisted Macrocycles in Schiff Base Reaction. Chem. Sci. 2019, 10, 490−496. (34) Israelachvili, J. N. Intermolecular and Surface Forces; Academic Press: London, 2011. (35) Shioi, A.; Hatton, T. A. Model for Formation and Growth of Vesicles in Mixed Anionic/Cationic (SOS/CTAB) Surfactant Systems. Langmuir 2002, 18, 7341−7348. (36) Sessler, J. L.; Katayev, E. G.; Pantos, D.; Ustynyuk, Y. A. Synthesis and Study of a New Diamidodipyrromethane Macrocycle. An Anion Receptor with a High Sulfate-to-Nitrate Binding Selectivity. Chem. Commun. 2004, 1276−1277. (37) Tominaga, M.; Takahashi, E.; Ukai, H.; Ohara, K.; Itoh, T.; Yamaguchi, K. Solvent-Dependent Self-Assembly and Crystal Structures of a Salen-Based Macrocycle. Org. Lett. 2017, 19, 1508− 1511. (38) Sessler, J. L.; Katayev, E.; Pantos, G. D.; Scherbakov, P.; Reshetova, M. D.; Khrustalev, V. N.; Lynch, V. M.; Ustynyuk, Y. A. Fine Tuning the Anion Binding Properties of 2,6-Diamidopyridine Dipyrromethane Hybrid Macrocycles. J. Am. Chem. Soc. 2005, 127, 11442−11446. (39) Ackman, R. G.; Brown, W. H.; Wright, G. F. The Condensation of Methyl Ketones with Furan. J. Org. Chem. 1955, 20, 1147−1158.

I


Solvent-Switched Schiff-Base Macrocycles: Self-Sorting and Self

Recommend Documents