English

• 0.   Introduction

  Enzyme conformational modification plays a crucial role in regulating biological enzymatic cascades, and the configuration change mechanism by cofactors provides the fundamental principles for artificial catalytic regulation^[1-3]. Exploring external stimuli that can influence the chiral environment of artificial catalysts could provide a deeper understanding of the origin of chirality and the principles of asymmetric catalysis. Actually, anions play an important role in the assembly dynamics and the structural stability of metallo-supramolecular architectures^[4-7]. For instance, with bis-bis urea ligands and phosphate anion as building blocks, a series of well-organized anion assemblies have been obtained, including triple helicate^[8], tetrahedron^[9], bicapped trigonal antiprism^[10], and other architectures. Moreover, anions are critical to the formation of racemic compounds or conglomerates during crystallization^[11]. However, the dynamic regulation of chiral catalyst conformations by anions remains largely unexplored.

  On the other hand, the coordination-driven metal-organic cages with chirality that are obtained by integrating enantiomeric ligands or metal precursor ligands^[12-18] or by inducing chiral host-guest interactions^[19-21], have been considered unique enzyme mimics, and exhibit extensive application in the field of circularly polarized luminescence^[22-24], chiral recognition^[25-29], asymmetric catalysis^[30-33], and potential chiral-induced spin selectivity effects^[34-36] by virtue of their chiral cavity to provided static, geometric, and even asymmetric restriction to the trapped substrates. However, the controllable tuning of the chiral cages catalyst configuration by different effectors is still a steep challenge. The structural regulation process is often elusive, despite the importance of the subsequent modulation of asymmetric catalysis. Salen complexes have garnered significant interest because of their easily tunable stereochemical characteristics, including coordination geometries, conformations, and even supramolecular structures^[37-39]. Furthermore, salen ligands-modified metal-organic cages find extensive utility in asymmetric applications such as epoxidation of olefins, ring-opening reaction of epoxides, and oxidation of sulfides^[40-43]. Therefore, it was considered that the fabrication of an optically informative Zn(Ⅱ)-salen modified cage would allow a state-of-art structural regulation by different anions.

  Herein, a new Zn(Ⅱ)-salen modified heteroleptic metal-organic cage was developed through co-assembly with the other NADH (reduced nicotinamide adenine dinucleotide) mimic modified ligands and kinetically inert square planar Pd(Ⅱ) ions through a 3∶1 complementary coordination approach. By introducing different anions, the conformation of cages was adjustable by the host-guest electrostatic interactions between the allosteric sites of Zn(Ⅱ)-salen moiety on the cage and the anion effectors. Through the complementary spectra analysis, we investigated the selective binding and modulation of various anions at specific locations of the cages, and the incorporation of chloride anion triggered the most significant fluorescence emission enhancement with an exhibited more rigid structure, providing a new insight for structural regulation of chiral catalysts (Scheme 1).

  Scheme 1

  

  Scheme 1.  Precise construction of chiral heteroleptic metal-organic cage and its structural regulation by anions

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  1.   Experimental

  1.1   Materials and methods

  All chemicals were of reagent-grade quality obtained from commercial sources. Unless stated otherwise, all the chemicals and solvents were used without further purification. NMR spectra were measured on a Bruker 400M spectrometer with chemical shifts (in DMSO-d₆ or CDCl₃, TMS as internal standard). ESI-MS spectra were obtained on a Thermo Fisher Q Exactive mass spectrometer using acetonitrile as mobile phase. UV-Vis spectra were measured on a Shimadzu UV3600 spectrometer. The solution fluorescent spectra were measured on a Horiba FL-3 spectrophotometer. Circular dichroism (CD) spectra were measured on a JASCO J-810 spectropolarimeter.

  1.2   Synthesis of the ligands

  The synthetic routes of ligands R^Zn and H₂L^P are shown in Scheme 2.

  Scheme 2

  

  Scheme 2.  Synthetic routes of ligands R^Zn and H₂L^P

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  1.2.1   Synthesis of compound M

  A solution of toluene and ethanol (4∶1, V/V, 25 mL) was degassed with Ar for 30 min. Under Ar, 5-bromo-2-hydroxybenzaldehyde (0.25 g, 1.24 mmol), Cs₂CO₃ (1.0 g, 3.08 mmol), (4-pyridinyl)-boronic acid (0.23 g, 1.84 mmol), and Pd(PPh₃)₄ (0.12 g, 0.10 mmol) were combined and stirred under Ar for 10 min away from light, before being heated at 105 ℃ for 12 h. The solution was filtered through celite and washed with toluene until the washings went colorlessness. The toluene layer was washed with NaOH solution, neutralized, and then extracted into ethyl acetate. The organic layer was washed with saturated NaCl aqueous solution and dried over with Na₂SO₄. The solvent was evaporated and purified via chromatography to afford the product as a light yellow powder. Yield: 87.0 mg, 35%. ¹H NMR (CDCl₃, 400 MHz): δ 11.14 (s, 1H), 10.01 (s, 1H), 8.69-8.63 (m, 2H), 7.90-7.79 (m, 2H), 7.51-7.44 (m, 2H), 7.15 (d, J=8.6 Hz, 1H).

  1.2.2   Synthesis of ligand R^H

  The compound M (0.13 g, 0.65 mmol) was suspended in methanol (10.0 mL) under an Ar atmosphere. The (1R, 2R)-(+)-1, 2-diaminocyclohexane (37.0 mg, 0.32 mmol) for the ligand R^H was dissolved in methanol (5.0 mL) and added drop by drop before the mixture was heated at 80 ℃ for 2 h. The reaction was cooled and the solvent was evaporated. The product was recrystallized from the CH₂Cl₂/n-hexane solution. Yield: 0.14 g, 90%. ¹H NMR (CDCl₃, 400 MHz): δ 13.54 (s, 2H), 8.62-8.53 (m, 4H), 8.35 (s, 2H), 7.57-7.50 (m, 2H), 7.46-7.41 (m, 2H), 7.39-7.33 (m, 4H), 7.01 (d, J=8.6 Hz, 2H), 3.44-3.33 (m, 2H), 2.05-1.88 (m, 4H), 1.84-1.71 (m, 2H), 1.56-1.47 (m, 2H).

  1.2.3   Synthesis of ligand R^Zn

  The ethanol (5.0 mL) dissolved with Zn(AcO)₂ (18.4 mg, 0.1 mmol) was added to the ethanol (10.0 mL) solution of ligand R^H (47.7 mg, 0.1 mmol). The solution was stirred at 85 ℃ for 6 h, after which the solvent was filtered. The white powder was collected, washed with ethanol, and then dried under reduced pressure to obtain pure ligand R^Zn. Yield: 5.70 mg, 95%. ESI-MS(C₃₀H₂₆N₄O₂Zn): m/z=539.142 0 [R^Zn+H]⁺.

  1.2.4   Synthesis of ligand H₂L^P

  Ligand H₂L^P was synthesized according to the literature^[44]. 1-Benzyl-4-phenyl-1, 4-dihydro-pyridine-3, 5-dicarbohydrazide (0.91 g, 1.0 mmol) was added to an ethanol solution (50 mL) containing 2-(diphenylphosphino)benzaldehyde (0.58 g, 2.0 mmol). After three drops of acetic acid were added, the mixture was heated at 85 ℃ for 12 h according to the reference. The yellow solid was collected by filtration, washed with methanol, and dried in a vacuum. Yield: 1.10 g, 75.8%. ¹H NMR (400 MHz, DMSO-d₆): δ 11.26 (s, 2H), 8.89 (s, 2H), 7.92 (s, 2H), 7.45-7.31 (m, 28H), 7.45-7.35 (m, 8H), 6.81-6.78 (m, 2H), 5.25 (s, 1H), 4.71 (s, 2H).

  1.3   Synthesis of cage Pd-R(Zn)

  The ligand R^Zn (26.9 mg, 0.05 mmol), ligand H₂L^P (45.4 mg, 0.05 mmol), and Pd(NO₃)₂·2H₂O (26.6 mg, 0.10 mmol) were dissolved in DMF to give a dark red solution. The product could be obtained by precipitation with diethyl ether. Yield: 65%. ESI-MS (Pd₄Zn₂C₁₇₆H₁₄₂N₁₈O₈P₄): m/z=829.374 3 [Pd₄(L^PR^Zn)₂]⁴⁺.

  2.   Results and discussion

  2.1   Characterization of metal-organic cage

  Through a symmetry interaction strategy using 3∶1 complementary denticity in symmetry interaction^[44-45], chiral metal-organic cage Pd-R(Zn) was developed through co-assembly of Zn(Ⅱ)-salen-based ligand R^Zn with monodentate pyridine N coordination site, the secondary ligand H₂L^P with NOP tridentate coordinating sites, and kinetically inert square planar Pd(Ⅱ) salt (palladium nitrate) at a ratio of 1∶1∶2 in DMF solution at room temperature according to the reported method (Fig. 1a). Thereinto, the Zn-salen ligand R^Zn was obtained by the Schiff base reaction of 2-hydroxy-5-(pyridin-4-yl)benzaldehyde and (1R, 2R)-(+)-1, 2-diaminocyclohexane followed by zinc metallization, while the ligands H₂L^P was easily obtained through the Schiff base reaction of 2-(diphenylphosphino)benzaldehyde and 1-benzyl-4-phenyl-1, 4-dihydropyridine-3, 5-di-carbohydrazide.

  Figure 1

  

  Figure 1.  (a) Construction of the heteroleptic metal-organic cage Pd-R(Zn) with both NADH model ligand and Zn(Ⅱ)-salen modified ligand through coordination self-assembly; (b) ¹H NMR and ¹H DOSY spectra of Pd-R(Zn) (1.0 mmol·L^-1) in DMSO-d₆ solution; (c) ESI-MS spectra of Pd-R(Zn) (1.0 mmol·L^-1) in DMF solution

  The inset shows the measured and simulated isotopic patterns at The inset shows the measured and simulated isotopic patterns at m/z=829.374 3.

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  ¹H NMR spectra of Pd-R(Zn) showed the characteristic signals of both ligand R^Zn and H₂L^P (Fig. 1b). Moreover, the formation of a sole species during the multi-component self-assembly was intuitively confirmed by the diffusion-ordered NMR spectrum with a diffusion coefficient of 1.32×10^-10 m²·s^-1. The ESI-MS analysis of Pd-R(Zn) exhibited an intense peak at m/z=829.374 3 assigned to [Pd₄(L^PR^Zn)₂]⁴⁺ via a comparison with the simulation result with the isotopic distribution patterns separated by 0.25 Da (Fig. 1c), validating the formation of M₄L^A₂L^B₂ tetranuclear macrocyclic capsules and bivalent zinc ions within the Zn-salen modified cage. Meanwhile, the intensive ESI-MS outcome suggested their suitable stability in solution.

  UV-Vis absorption spectrum of Pd-R(Zn) (10.0 μmol·L^-1) contained the characteristic peaks of Zn(Ⅱ)-salen moiety and ligand H₂L^P, implying the maintenance of the photophysical property of both functional units (Fig. 2a). Specifically, CD mesurement of Pd-R(Zn) in CH₃CN solution showed two absorption bands at 260 and 294 nm originating from the phenolates, and peaks at 340, 384, and 488 nm assigned to the azomethine moiety absorption, the salen conjugate skeleton, and phenolate-to-Zn(Ⅱ) charge transfer band^[46], respectively, in consistent to ligand R^Zn exhibiting the 278, 305, 356, 408, and 530 nm peaks in the CD spectrum (Fig. 2b). The luminescence spectra of ligand R^Zn showed a strong fluorescence emission at around 480 nm upon the excitation of the π-π* charge transfer band (at 325 nm) (Fig. 2c), while showing a blue-shifted emission peak of Pd-R(Zn) at around 450 nm upon the same light excitation, which might be due to the coordination effect.

  Figure 2

  

  Figure 2.  (a) UV-Vis spectra of 10.0 μmol·L^-1 Pd-R(Zn), and ligands R^Zn and H₂L^P, respectively, in CH₃CN solution; (b) CD spectra of 10.0 μmol·L^-1 Pd-R(Zn) and ligand R^Zn, respectively, in CH₃CN solution; (c) Luminescence spectra of 10.0 μmol·L^-1 Pd-R(Zn) and ligand R^Zn, respectively, in CH₃CN solution

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  2.2   Selective binding anions by the cages

  On account of the measurable and informative spectral properties of Pd-R(Zn), we thought that it was feasible to investigate the structural regulation of cage catalysts by effectors through optical spectroscopy. Given the potential template role of counter ions in supramolecular assembly processes, we attempted to modulate the cage conformation by introducing anions. The addition of different anions, respectively, to a CH₃CN solution of Pd-R(Zn) (10.0 μmol·L^-1) caused obvious and distinct variation in the absorption bands with several isosbestic points in the UV-Vis spectra, indicating the combination of anions with Pd-R(Zn) via the potential host-guest electrostatic interactions and the changes of Pd-R(Zn) structure (Fig. 3)^[47-48]. The spectral changes induced by anions were mainly divided into three regions: the range of 295 to 335 nm assignable to the ON two chelate sites with Zn(Ⅱ), around 380 nm attributable to the salen conjugate backbone, and around 490 nm corresponding to the phenolate-to-Zn(Ⅱ) charge transfer band. For the six anions, Cl^-, PO₄^3-, BF₄^-, PF₆^-, F^-, and ClO₄^-, all decreased the 380 nm absorbance except ClO₄^- (Fig. 3), and F^- and Cl^- showed significant peak decrease (Fig. 3a and 3d). These results demonstrated that these anions induced a change in the salen conjugate skeleton when they interacted with a Zn-salen-modified cage. Specifically, PO₄^3-, BF₄^-, PF₆^-, and F^- made obvious changes in peaks at around 320 nm (Fig. 3b-3e), indicating a proximity between these anions with the ON two chelate sites. Regarding the UV-Vis absorption at 490 nm, PO₄^3- showed some decrease effect on this peak, while Cl^- and BF₄^- exhibited a trend towards blue shift, indicating the direct interactions between Zn(Ⅱ) metal sites and these three anions in different modes (Fig. 3a-3c). Interestingly, ClO₄^- maintained a consistent signal throughout the spectrum, despite the existence of electrostatic interactions (Fig. 3f). These results indicated that different anions interacted with the salen-modified framework through electrostatic interactions at different binding sites with divergent strengths. Therefore, cage conformation could be changed by selective binding of anions in different ways.

  Figure 3

  

  Figure 3.  UV-Vis spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon the addition of NaCl (total 0.1 mmol·L^-1) (a), NaBF₄ (total 3.5 mmol·L^-1) (b), K₃PO₄ (total 5.0 mmol·L^-1) (c), NaF (total 0.2 mmol·L^-1) (d), NaPF₆ (total 2.0 mmol·L^-1) (e), and NaClO₄ (total 5.0 mmol·L^-1) (f)

  Inset: the differential UV-Vis spectra as a function of anions concentration.

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  Furthermore, the fluorescence spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN solution upon the addition of different anions (150 μmol·L^-1) showed that introduction of Cl^- resulted in a most significant increase in the fluorescence intensity around 450 nm (Fig. 4a). It was found that the addition of PO₄^3- and F^- only led to low-amplitude enhancement effect, whereas the introduction of BF₄^- and ClO₄^- exhibited trace effect on the cage fluorescence. Notably, PF₆^- caused cage fluorescence quenching. Fluorescence titration experiments between Pd-R(Zn) and Cl^- showed that the fluorescence signal around 450 nm exhibited a linear increase dependent on the Cl^- concentration (0 to 100 μmol·L^-1, Fig. 4b), and a 2.5-fold fluorescence enhancement was achieved when the Cl^- reached 150 μmol·L^-1.

  Figure 4

  

  Figure 4.  (a) Fluorescence intensity change of Pd-R(Zn) (10.0 μmol·L^-1) upon the addition of different anions (150 μmol·L^-1); (b) Fluorescence spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon the addition of NaCl (total 150 μmol·L^-1)

  Inset: the linear fitting of fluorescence intensity vs the concentration of NaCl at 428 nm.

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  As the introduction of Cl^- caused a more sensitive UV-Vis spectral variation and stronger fluorescence response, fine changes of the Pd-R(Zn) conformation were further determined through CD spectra (Fig. 5a). Upon the addition of Cl^- (total 100 μmol·L^-1) to the solution of Pd-R(Zn) (10.0 μmol·L^-1), the CD absorption bands around 260 and 294 nm attributed to the phenolic module shifted from negative to positive Cotton effect, accompanied with an increase in signal intensity. Conversely, the absorption bands at 340 nm originating from the azomethine moiety underwent an opposite change, indicating a potential change of a slack cage scaffold to a rigid salen-modified framework by limiting the structural torsion of cages. ¹H NMR spectra showed that the splitting of Pd-R(Zn) became clearer from a previously indistinguishable state with the addition of Cl^- into cage solution (Fig. 5b), implying that the relaxed Pd-R(Zn) might allow ligands to have a higher degree of freedom of movement, resulting in a less restricted and more varied cage conformation and broadening ¹H NMR signals^[49]. In contrast, Cl^- could stiffen cage conformations and lead to uniform proton resonances in line with CD results, to provide catalytic regulation.

  Figure 5

  

  Figure 5.  (a) CD spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon addition of NaCl (total 100 μmol·L^-1); (b) ¹H NMR of Pd-R(Zn) (1.0 mmol·L^-1) in DMSO-d₆ with different NaCl concentrations.

  Inset: the differential spectra as a function of the concentration of NaCl.

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  3.   Conclusions

  In summary, the Zn-salen-modified chiral metal-organic cage with adjustable conformational characteristics was successfully assembled by a unique 3∶1 complementary coordination approach. A novel approach was provided to regulate chiral cage structure by introducing anions. The rigid cage scaffold was obtained when the relaxed state of the cage encountered Cl^- anions, providing a potential strategy to modify chiral catalyst for future chiral catalysis regulation.

  
  
• 1. [1]

     Goodey N M, Benkovic S J. Allosteric regulation and catalysis emerge via a common route[J]. Nat. Chem. Biol., 2008, 4:  474-482. doi: 10.1038/nchembio.98

  2. [2]

     Nussinov R, Tsai C J. Allostery in disease and in drug discovery[J]. Cell, 2013, 153:  293-305. doi: 10.1016/j.cell.2013.03.034

  3. [3]

     Cong Z Q, Shoji O, Kasai C, Kawakami N, Sugimoto H, Shiro Y, Watanabe Y. Activation of wild-type cytochrome P450BM3 by the next generation of decoy molecules: Enhanced hydroxylation of gaseous alkanes and crystallographic evidence[J]. ACS Catal., 2015, 5:  150-156. doi: 10.1021/cs501592f

  4. [4]

     Zhang Z, Li Y, Song B, Zhang Y, Jiang X, Wang M, Tumbleson R, Liu C L, Wang P S, Hao X Q, Rojas T, Ngo A T, Sessler J L, Newkome G R, Hla S W, Li X P. Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid[J]. Nat. Chem., 2020, 12:  468-474. doi: 10.1038/s41557-020-0454-z

  5. [5]

     Leigh D A, Pritchard R G, Stephens A J. A star of David catenane[J]. Nat. Chem., 2014, 6:  978-982. doi: 10.1038/nchem.2056

  6. [6]

     Marcos V, Stephens A J, Jaramillo-Garcia J, Nussbaumer A L, Woltering S L, Valero A, Lemonnier J F, Vitorica-Yrezabal I J, Leig D A. Allosteric initiation and regulation of catalysis with a molecular knot[J]. Science, 2016, 352:  1555-1559. doi: 10.1126/science.aaf3673

  7. [7]

     Liang L, Zhao W, Yang X J, Wu B. Anion-coordination-driven assembly[J]. Acc. Chem. Res., 2022, 55:  3218-3229. doi: 10.1021/acs.accounts.2c00435

  8. [8]

     Li S G, Jia C D, Wu B, Luo Q, Huang X J, Yang Z W, Li Q S, Yang X J. A triple anion helicate assembled from a bis(biurea) ligand and phosphate ions[J]. Angew. Chem. Int. Ed., 2011, 50:  5721-5724. doi: 10.1002/anie.201180593

  9. [9]

     Bai X M, Jia C D, Zhao Y X, Yang D, Wang S C, Li A Y, Chan Y T, Wang Y Y, Yang X J, Wu B. Peripheral templation-modulated interconversion between an A₄L₆ tetrahedral anion cage and A₂L₃ triple helicate with guest capture/release[J]. Angew. Chem. Int. Ed., 2018, 57:  1851-1855. doi: 10.1002/anie.201712080

  10. [10]

      Li B Y, Zhang W Y, Lu S, Zheng B, Zhang D, Li A Y, Li X P, Yang X J, Wu B. Multiple transformations among anion-based A_2nL_3n assemblies: Bicapped trigonal antiprism A₈L₁₂, tetrahedron A₄L₆, and triple helicate A₂L₃ (A=anion)[J]. J. Am. Chem. Soc., 2020, 142:  21160-21168. doi: 10.1021/jacs.0c10346

  11. [11]

      Xu C, Lin Q J, Shan C, Han X, Wang H, Wang H, Zhang W J, Chen Z, Guo C X, Xie Y H, Yu X J, Song B, Song H, Wojtas L, Li X P. Metallo-supramolecular octahedral cages with three types of chirality towards spontaneous resolution[J]. Angew. Chem. Int. Ed., 2022, 61:  e202203099. doi: 10.1002/anie.202203099

  12. [12]

      Li Y G, Dong J Q, Gong W X, Tang X H, Liu Y H, Cui Y, Liu Y. Artificial biomolecular channels: Enantioselective transmembrane transport of amino acids mediated by homochiral zirconium metal-organic cages[J]. J. Am. Chem. Soc., 2021, 143:  20939-20951. doi: 10.1021/jacs.1c09992

  13. [13]

      Pan M, Wu K, Zhang J H, Su C Y. Chiral metal-organic cages/containers (MOCs): From structural and stereochemical design to applications[J]. Coord. Chem. Rev., 2019, 378:  333-349. doi: 10.1016/j.ccr.2017.10.031

  14. [14]

      Bierschenk S M, Pan J Y, Settineri N S, Warzok U, Bergman R G, Raymond K N, Toste F D. Impact of host flexibility on selectivity in a supramolecular host-catalyzed enantioselective aza-darzens reaction[J]. J. Am. Chem. Soc., 2022, 144:  11425-114331. doi: 10.1021/jacs.2c04182

  15. [15]

      Chen L J, Yang H B, Shionoya M. Chiral metallosupramolecular architectures[J]. Chem. Soc. Rev., 2017, 46:  2555-2576. doi: 10.1039/C7CS00173H

  16. [16]

      Schulte T R, Holstein J J, Clever G H. Chiral self-discrimination and guest recognition in helicene-based coordination cages[J]. Angew. Chem. Int. Ed., 2019, 58:  5562-5566. doi: 10.1002/anie.201812926

  17. [17]

      吴大雨, 黄薇, 李庚, 谢黎霞, 段春迎, 孙巧珍, 孟庆金. 镍螺旋化合物及其杂银配位聚合物的设计合成与结构[J]. 无机化学学报, 2007,23,(7): 1129-1136. doi: 10.3321/j.issn:1001-4861.2007.07.001WU D Y, HUANG W, LI G, XIE L X, DUAN C Y, SUN Q Z, MENG Q J. Nickel helicates and hybrid silver coordination polymer: Design, synthesis and structure characterization[J]. Chinese J. Inorg. Chem., 2007, 23(7):  1129-1136. doi: 10.3321/j.issn:1001-4861.2007.07.001

  18. [18]

      谢黎霞, 吴大雨, 段春迎, 张丙广, 孟庆金. 含潜在异构手性双臂配体的螺旋组装和手性聚集[J]. 无机化学学报, 2007,23,(2): 191-199. doi: 10.3321/j.issn:1001-4861.2007.02.001XIE L X, WU D Y, DUAN C Y, ZHANG B G, MENG Q J. Helical assembly and chiral aggregations based on atropisomeric molecular clips[J]. Chinese J. Inorg. Chem., 2007, 23(2):  191-199. doi: 10.3321/j.issn:1001-4861.2007.02.001

  19. [19]

      Howlader P, Mondal S, Ahmed S, Mukherjee P S. Guest-induced enantioselective self-assembly of a Pd₆ homochiral octahedral cage with a C₃-symmetric pyridyl donor[J]. J. Am. Chem. Soc., 2020, 142:  20968-20972. doi: 10.1021/jacs.0c11011

  20. [20]

      Zhang D, Ronson T K, Greenfield J L, Brotin T, Berthault P, Léonce E, Zhu J L, Xu L, Nitschke J R. Enantiopure [Cs⁺/Xe⊂Cryptophane]⊂Fe^Ⅱ₄L₄ hierarchical superstructures. J. Am. Chem. Soc., 2019, 141: 8339-8345

  21. [21]

      Li B Y, Zheng B, Zhang W Y, Zhang D, Yang X J, Wu B. Site-selective binding of peripheral chiral guests induces stereospecificity in A₄L₆ tetrahedral anion cages[J]. J. Am. Chem. Soc., 2020, 142:  6304-6311. doi: 10.1021/jacs.0c00882

  22. [22]

      Yeung C T, Yim K H, Wong H Y, Pal R, Lo W S, Yan S C, Wong M Y M, Yufit D, Smiles D E, McCormick L J, Teat S J, Shuh D K, Wong W T, Law G L. Chiral transcription in self-assembled tetrahedral Eu₄L₆ chiral cages displaying sizable circularly polarized luminescence[J]. Nat. Commun., 2017, 8:  1128. doi: 10.1038/s41467-017-01025-1

  23. [23]

      Zhou Y Y, Li H F, Zhu T Y, Gao T, Yan P F. A highly luminescent chiral tetrahedral Eu₄L₄(L')₄ cage: Chirality induction, chirality memory, and circularly polarized luminescence[J]. J. Am. Chem. Soc., 2019, 141:  19634-19643. doi: 10.1021/jacs.9b07178

  24. [24]

      Tang X H, Jiang H, Si Y B, Rampal N, Gong W, Cheng Ch, Kang X, David F J, Cui Y, Liu Y. Endohedral functionalization of chiral metal-organic cages for encapsulating achiral dyes to induce circularly polarized luminescence[J]. Chem, 2021, 7:  2771-2786. doi: 10.1016/j.chempr.2021.07.017

  25. [25]

      Fiedler D, Leung D H, Bergman R G, Raymond K N. Enantioselective guest binding and dynamic resolution of cationic ruthenium complexes by a chiral metal-ligand assembly[J]. J. Am. Chem. Soc., 2004, 126:  3674-3675. doi: 10.1021/ja039225a

  26. [26]

      Xuan W M, Zhang M N, Liu Y, Chen Z J, Cui Y. A chiral quadruple-stranded helicate cage for enantioselective recognition and separation[J]. J. Am. Chem. Soc., 2012, 134:  6904-6907. doi: 10.1021/ja212132r

  27. [27]

      Zhao C, Toste F D, Raymond K N, Bergman R G. Nucleophilic substitution catalyzed by a supramolecular cavity proceeds with retention of absolute stereochemistry[J]. J. Am. Chem. Soc., 2014, 136:  14409-14412. doi: 10.1021/ja508799p

  28. [28]

      Wu K, Li K, Hou Y J, Mei Pan, Zhang L Y, Chen L, Su C Y. Homochiral D₄-symmetric metal-organic cages from stereogenic Ru(Ⅱ) metalloligands for effective enantioseparation of atropisomeric molecules[J]. Nat. Commun., 2016, 7:  10487. doi: 10.1038/ncomms10487

  29. [29]

      Hou Y J, Wu K, Wei Z W, Li K, Lu Y L, Zhu C Y, Wang J S, Pan M, Jiang J J, Li G Q, Su C Y. Design and enantioresolution of homochiral Fe(Ⅱ)-Pd(Ⅱ) coordination cages from stereolabile metalloligands: Stereochemical stability and enantioselective separation[J]. J. Am. Chem. Soc., 2018, 140:  18183-18191. doi: 10.1021/jacs.8b11152

  30. [30]

      Nishioka Y, Yamaguchi T, Kawano M, Fujita M. Asymmetric [2+2] olefin cross photoaddition in a self-assembled host with remote chiral auxiliaries[J]. J. Am. Chem. Soc., 2008, 130:  8160-8161. doi: 10.1021/ja802818t

  31. [31]

      Li G, Yu W B, Ni J, Liu T F, Liu Y, Sheng E H, Cui Y. Self-assembly of a homochiral nanoscale metallacycle from a metallosalen complex for enantioselective separation[J]. Angew. Chem. Int. Ed., 2008, 47:  1245-1249. doi: 10.1002/anie.200704347

  32. [32]

      Guo J, Xu Y W, Li K, Xiao L M, Chen S, Wu K, Chen X D, Fan Y Z, Liu J M, Su C Y. Regio- and enantioselective photodimerization within the confined space of a homochiral ruthenium/palladium heterometallic coordination cage[J]. Angew. Chem. Int. Ed., 2017, 56:  3852-3856. doi: 10.1002/anie.201611875

  33. [33]

      Ji J C, Wu WH, Liang W T, Cheng G, Matsushita R, Yan Z Q, Wei X Q, Rao M, Yuan D Q, Fukuhara G, Mori T, Inoue Y, Yang C. An ultimate stereocontrol in supramolecular photochirogenesis: Photocyclodimerization of 2-anthracenecarboxylate mediated by sulfur-linked β-cyclodextrin dimers[J]. J. Am. Chem. Soc., 2019, 141:  9225-9238. doi: 10.1021/jacs.9b01993

  34. [34]

      Göhler B, Hamelbeck V, Markus T Z, Kettner M, Hanne G F, Vager Z, Naaman R, Zacharias H. Spin selectivity in electron transmission through self-assembled monolayers of double-stranded DNA[J]. Science, 2011, 331:  894-897. doi: 10.1126/science.1199339

  35. [35]

      Kulkarni C, Mondal A K, Das T K, Grinbom G, Tassinari F, Mabesoone M F J, Meijer E W, Naaman R. Highly efficient and tunable filtering of electrons' spin by supramolecular chirality of nanofiber-based materials[J]. Adv. Mater., 2020, 32:  1904965. doi: 10.1002/adma.201904965

  36. [36]

      Mondal A K, Preuss M D, Ślęczkowski M L, Das T K, Vantomme G, Meijer E W, Naaman R. Spin filtering in supramolecular polymers assembled from achiral monomers mediated by chiral solvents[J]. J. Am. Chem. Soc., 2021, 143:  7189-7195. doi: 10.1021/jacs.1c02983

  37. [37]

      Wang Y, DuBois J L, Hedman B, Hodgson K O, Stack T D P. Catalytic galactose oxidase models: Biomimetic Cu(Ⅱ)-phenoxyl-radical reactivity[J]. Science, 1998, 279:  537-5401. doi: 10.1126/science.279.5350.537

  38. [38]

      Kim H J, Kim W, Lough A J, B. Kim M, Chin J. A cobalt(Ⅲ)-salen complex with an axial substituent in the diamine backbone: Stereoselective recognition of amino alcohols[J]. J. Am. Chem. Soc., 2005, 127:  16776-16777. doi: 10.1021/ja0557785

  39. [39]

      张奇龙, 王家忠, 杨小生, 朱必学. 不对称Salen配体的Ni(Ⅱ)/Cu(Ⅱ)/Mn(Ⅲ)配合物的合成及其晶体结构[J]. 无机化学学报, 2020,36,(1): 132-138. ZHANG Q L, WANG J Z, YANG X S, ZHU B X. Synthesis and crystal structure of Ni(Ⅱ)/Cu(Ⅱ)/Mn(Ⅲ) complexes with asymmetric salen ligand[J]. Chinese J. Inorg. Chem., 2020, 36(1):  132-138.

  40. [40]

      Shaw S, White J D. Asymmetric catalysis using chiral salen-metal complexes: Recent advances[J]. Chem. Rev., 2019, 119:  9381-9426. doi: 10.1021/acs.chemrev.9b00074

  41. [41]

      Yuan Y C, Mellah M, Schulz E, David O R P. Making chiral salen complexes work with organocatalysts[J]. Chem. Rev., 2022, 122:  8841-8883. doi: 10.1021/acs.chemrev.1c00912

  42. [42]

      邹晓川, 石开云, 王存, 王跃, 邓朝芳, 任彦荣, 王贵凤, 谭脂文, 傅相锴. 苯氧基修饰的聚(苯乙烯-异丙烯膦酸)磷酸氢锆固载手性Mn^Ⅲ(Salen)及其催化苯乙烯环氧化. 无机化学学报, 2016, 32(9): 1585-1595ZOU X C, SHI K Y, WANG C, DENG C F, REN Y R, WANG G F, TAN Z W, FU X K. Immobilization of chiral Mn^Ⅲ(salen) on phenoxyl group modified zirconium poly (styrene-isopropenyl phosphonate)-phosphate and catalytic performance for epoxidation of styrene. Chinese J. Inorg. Chem., 2016, 32(9): 1585-1595

  43. [43]

      罗云飞, 傅相锴, 邹晓川, 王长炜, 胡小艳, 贾紫永, 张怀志. 链接基团对固载手性Salen Mn(Ⅲ)催化不对称环氧化反应的影响[J]. 无机化学学报, 2011,27,(7): 1302-1308. LUO Y F, FU X K, ZOU X C, WANG C W, HU X Y, JIA Z Y, ZHANG H Z. Effect of axial linker group on heterogeneous chiral salen Mn(Ⅲ) catalyzed enantioselective epoxidation of unfunctionalized olefins[J]. Chinese J. Inorg. Chem., 2011, 27(7):  1302-1308.

  44. [44]

      Cai J K, Zhao L, Li Y N, He C, Wang C, Duan C Y. Binding of dual-function hybridized metal-organic capsules to enzymes for cascade catalysis[J]. JACS Au, 2022, 2:  1736-1746. doi: 10.1021/jacsau.2c00322

  45. [45]

      Preston D, Inglis A R, Garden A L, Kruger P E. A symmetry interaction approach to [M₂L₂]⁴⁺ metallocycles and their self-catenation[J]. Chem. Commun., 2019, 55:  13271-13274. doi: 10.1039/C9CC07130J

  46. [46]

      Kurahashi T, Hada M, Fujii H. Critical role of external axial ligands in chirality amplification of trans-cyclohexane-1, 2-diamine in salen complexes[J]. J. Am. Chem. Soc., 2009, 131:  12394-12405. doi: 10.1021/ja904635n

  47. [47]

      Spenst P, Würthner F. A perylene bisimide cyclophane as a "turn-on" and "turn-off" fluorescence probe[J]. Angew. Chem. Int. Ed., 2015, 54:  10165-10168. doi: 10.1002/anie.201503542

  48. [48]

      He C, Lin Z H, He Z, Duan C Y, Xu C H, Wang Z M, Yan C H. Metal-tunable nanocages as artificial chemosensors[J]. Angew. Chem. Int. Ed., 2008, 47:  877-881. doi: 10.1002/anie.200704206

  49. [49]

      Lu Y L, Qin Y H, Zheng S P, Ruan J, Huang Y H, Zhang X D, Liu C H, Hu P, Xu H S, Su C Y. Anion-mediated allosteric catalysis of [2+2] photocycloaddition based on a flexible metallo-amine cage for high diastereoselectivity[J]. ACS Catal., 2024, 14:  94-103. doi: 10.1021/acscatal.3c04593

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  Scheme 1  Precise construction of chiral heteroleptic metal-organic cage and its structural regulation by anions

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  Scheme 2  Synthetic routes of ligands R^Zn and H₂L^P

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  Figure 1  (a) Construction of the heteroleptic metal-organic cage Pd-R(Zn) with both NADH model ligand and Zn(Ⅱ)-salen modified ligand through coordination self-assembly; (b) ¹H NMR and ¹H DOSY spectra of Pd-R(Zn) (1.0 mmol·L^-1) in DMSO-d₆ solution; (c) ESI-MS spectra of Pd-R(Zn) (1.0 mmol·L^-1) in DMF solution

  The inset shows the measured and simulated isotopic patterns at The inset shows the measured and simulated isotopic patterns at m/z=829.374 3.

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  Figure 2  (a) UV-Vis spectra of 10.0 μmol·L^-1 Pd-R(Zn), and ligands R^Zn and H₂L^P, respectively, in CH₃CN solution; (b) CD spectra of 10.0 μmol·L^-1 Pd-R(Zn) and ligand R^Zn, respectively, in CH₃CN solution; (c) Luminescence spectra of 10.0 μmol·L^-1 Pd-R(Zn) and ligand R^Zn, respectively, in CH₃CN solution

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  Figure 3  UV-Vis spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon the addition of NaCl (total 0.1 mmol·L^-1) (a), NaBF₄ (total 3.5 mmol·L^-1) (b), K₃PO₄ (total 5.0 mmol·L^-1) (c), NaF (total 0.2 mmol·L^-1) (d), NaPF₆ (total 2.0 mmol·L^-1) (e), and NaClO₄ (total 5.0 mmol·L^-1) (f)

  Inset: the differential UV-Vis spectra as a function of anions concentration.

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  Figure 4  (a) Fluorescence intensity change of Pd-R(Zn) (10.0 μmol·L^-1) upon the addition of different anions (150 μmol·L^-1); (b) Fluorescence spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon the addition of NaCl (total 150 μmol·L^-1)

  Inset: the linear fitting of fluorescence intensity vs the concentration of NaCl at 428 nm.

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  Figure 5  (a) CD spectra of Pd-R(Zn) (10.0 μmol·L^-1) in CH₃CN upon addition of NaCl (total 100 μmol·L^-1); (b) ¹H NMR of Pd-R(Zn) (1.0 mmol·L^-1) in DMSO-d₆ with different NaCl concentrations.

  Inset: the differential spectra as a function of the concentration of NaCl.

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