Science - USA (2021-12-03)

growing [n+1]rotaxanes (n= 1 to 5) aligned
on the MOF surfaces, storing increasingly
higher-energy structures as the number of
rings grows. The surface charge density under
oxidizing conditions is +(4n+3) ×c, where the
number density of MPCG33+on the surface
c≈ 1016 /mg. These systems containing robust
MOFs and high-energy oligorotaxanes have
been characterized (figs. S60 to S66) quantita-
tively by^1 H NMR spectroscopy on acid-digested
samples. Almost every pumping cassette of
MPCG33+on the surface of Zr-BTB-MPCG3-
CBPQT(+)-V operates simultaneously and pre-
cisely, affording ~10^16 out-of-equilibrium
[6]rotaxanes, in 1 mg of a high-capacity AMP-
grafted material, wherein each [6]rotaxane car-
ries a charge of +23. The pumping efficiency
decreases slightly with increasing number
of redox cycles (Fig. 5), suggesting a gradual
saturation of PEG chains with rings, most likely
as a result of Coulombic repulsion between
the tetracationic rings. It is worth noting that

active transport ( 56 , 57 ), in which chemical

energy is used to pump materials at high con-

centration into a distinct compartment (e.g.,

a vacuole), is an essential process in biologi-

cal cells.

Summary and outlook

We have demonstrated mechanisorption,

which allows for energy to be stored on sur-

faces in the form of chemical gradients be-

tween the bulk and the surfaces. In the future,

the applicability of mechanisorption could be

generalized by using functionalized rings that

form complexes with other chemicals being

concentrated at the surface. For example, rings

functionalized with azides can be clicked with

alkyne-substituted molecules, polymers, and

nanoparticles so that large concentrations of

these guests can be stabilized at interfaces

andthenreleasedatwill.Wecanthinkofa

chemical capacitor where a nonequilibrium

amount of almost any substance can be stored

under high chemical potential at a surface

and then released and used on demand. The

utility of these chemical capacitors in tech-

nology will be limited only by the creativity

and imagination of chemists and materials

scientists.

REFERENCESANDNOTES

1. I. Langmuir,Chem. Rev. 6 , 451–479 (1930).


2. J. Lennard-Jones,Trans. Faraday Soc. 28 , 333– 359
   (1932).


3. D. Borodinet al.,Science 369 , 1461–1465 (2020).


4. D. E. Brown, D. J. Moffatt, R. A. Wolkow,Science 279 , 542– 544
   (1998).


5. Z. Li, J. C. Barnes, A. Bosoy, J. F. Stoddart, J. I. Zink,Chem.
   Soc. Rev. 41 , 2590–2605 (2012).


6. X. Meng, B. Gui, D. Yuan, M. Zeller, C. Wang,Sci. Adv. 2 ,
   e1600480 (2016).


7. L.-L. Tanet al.,Chem. Sci. 6 , 1640–1644 (2015).


8. J. H. van Esch, R. Klajn, S. Otto,Chem. Soc. Rev. 46 ,
   5474 – 5475 (2017).


9. C. Pezzato, C. Cheng, J. F. Stoddart, R. D. Astumian,Chem.
   Soc. Rev. 46 , 5491–5507 (2017).


10. R. D. Astumian, B. Robertson,J. Am. Chem. Soc. 115 ,
    11063 – 11068 (1993).


11. P. R. Ashton, D. Philip, N. Spencer, J. F. Stoddart,J. Chem. Soc.
    Chem. Commun. 1991 , 1677–1679 (1991).


12. C. Chenget al.,Nat. Nanotechnol. 10 , 547– 553
    (2015).


13. C. Pezzatoet al.,Tetrahedron 73 , 4849– 4857
    (2017).


14. Y. Qiuet al.,J. Am. Chem. Soc. 141 , 17472– 17476
    (2019).


15. Y. Qiuet al.,Science 368 , 1247–1253 (2020).


16. Q.-H. Guoet al.,J. Am. Chem. Soc. 142 , 14443– 14449
    (2020).


17. Y. Qiu, Y. Feng, Q.-H. Guo, R. D. Astumian, J. F. Stoddart,
    Chem 6 , 1952–1977 (2020).


18. Y. Fenget al.,J. Am. Chem. Soc. 143 , 5569– 5591
    (2021).


19. K. Cai, L. Zhang, R. D. Astumian, J. F. Stoddart,Nat. Rev.
    Chem. 5 , 447–465 (2021).


20. C. Cheng, P. R. McGonigal, J. F. Stoddart, R. D. Astumian,
    ACS Nano 9 , 8672–8688 (2015).


21. J.F.Stoddart,Angew. Chem. Int. Ed. 56 , 11094– 11125
    (2017).
    22.S.Erbas-Cakmak,D.A.Leigh,C.T.McTernan,
    A. L. Nussbaumer,Chem. Rev. 115 , 10081– 10206
    (2015).


22. V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart,Angew. Chem.
    Int. Ed. 39 , 3348–3391 (2000).


23. G. Ragazzon, M. Baroncini, S. Silvi, M. Venturi, A. Credi,
    Nat. Nanotechnol. 10 , 70–75 (2015).


24. S. Erbas-Cakmaket al.,Science 358 , 340– 343
    (2017).


25. S. Amano, S. D. P. Fielden, D. A. Leigh,Nature 594 , 529– 534
    (2021).


26. H. Deng, M. A. Olson, J. F. Stoddart, O. M. Yaghi,Nat. Chem. 2 ,
    439 – 443 (2010).


27. S. Horike, S. Shimomura, S. Kitagawa,Nat. Chem. 1 , 695– 704
    (2009).


28. H. Furukawa, K. E. Cordova, M. O’Keeffe, O. M. Yaghi,Science
    341 , 1230444 (2013).


29. H. Li, M. Eddaoudi, M. O’Keeffe, O. M. Yaghi,Nature 402 ,
    276 – 279 (1999).


30. A. M. Riceet al.,Chem. Rev. 120 , 8790– 8813
    (2020).


31. M. Eddaoudiet al.,Science 295 , 469–472 (2002).


32. L. Feng, K.-Y. Wang, J. Willman, H.-C. Zhou,ACS Cent. Sci. 6 ,
    359 – 367 (2020).


33. S. H. Loet al.,Nat. Chem. 12 , 90–97 (2020).


34. J. Peregoet al.,Nat. Chem. 12 , 845–851 (2020).


35. S. L. Gould, D. Tranchemontagne, O. M. Yaghi,
    M. A. Garcia-Garibay,J. Am. Chem. Soc. 130 , 3246– 3247
    (2008).


36. Y.-S. Suet al.,Nat. Chem. 13 , 278–283 (2021).


37. V. N. Vukotic, K. J. Harris, K. Zhu, R. W. Schurko, S. J. Loeb,
    Nat. Chem. 4 , 456–460 (2012).

1220 3 DECEMBER 2021¥VOL 374 ISSUE 6572 science.orgSCIENCE

Fig. 5. Sequential and quantitative mechanisorption on the surfaces of a high-capacity Zr-BTB-MPCG3.
The relationship between the number of redox cycles and the number of CBPQT4+rings threaded
per MPCG33+. Sequential redox reactions drive the formation of a series of highly nonequilibrium robust
dynamic systems—robust MOFs decorated with mechanically interlocked oligorotaxanes containing
highly controlled numbers of rings threaded onto a PEG collecting chain—that can adsorb incoming
guests sequentially and quantitatively upon stimuli. The conformations and arrangements of MPCG33+
are idealized for the sake of clarity. I, II, III, IV, and V refer to the one, two, three, four, and five redox
cycles conducted on the surfaces, respectively.

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