Nanozymes are nanomaterials with enzyme-like properties. These artificial enzymes have emerged more robust than the natural enzymes and find applications in biotechnology.
Cyclodextrin’s cavity mimicking the hydrophobic receptor of an enzyme can bind a substrate and the several OH groups at the rim of the cavity can serve as catalytic groups in various reactions. The first studies in the sixties and seventies proved the hydrolytic activity of cyclodextrins. For instance, deacetylation of m-t-butyl phenyl acetate was enhanced by a factor of 13000 in 60% DMSO as observed by Siegel and Breslow (1975).
In addition to hydrolases several other enzymes were mimicked by introducing catalytic moieties to the cyclodextrin. Some early examples are shown in Table 1.
Table 1 Some early examples for enzyme modeling
|Enzyme model||Catalytic group||Reaction||Reference|
|Decarboxylase||OH||Hennrich & Cramer 1965|
|Hydrolase||imidazole||ester hydrolysis||Cramer and Mackensen 1966|
|pyridinealdoxime-Ni||ester hydrolysis||Breslow 1971|
|Ribonuclease (see the featured image)||bis-imidazole||degradation of RNA||Breslow et al. 1978|
|Photoisomerase||benzophenone||Tabushi et al. 1976|
|Transaminase||piridoxine||transamination||Breslow et al. 1980|
Nowadays “nanozymes” are mentioned instead of traditional expressions such as enzyme modeling, inclusion catalysis, cyclodextrin-based artificial enzymes (Li et al. 2008; Wei & Wang 2013).
The topic is still interesting. The cyclodextrin nanoreactors as host structures in artificial enzymes have attracted special attention over the last years. Several research groups have been working on the synthesis of novel supramolecular enzyme mimics, including metal free cyclodextrin-based artificial enzymes and artificial metalloenzymes consisting of cyclodextrin which accommodates the organometallic factor (Aghahosseini and Ramazani 2016; Hapiot et al. 2011; Okamoto and Ward 2017). These cyclodextrin-based catalysts mimic enzymes such as oxidase, reductase, dehydrogenase, esterase, aminotransferase, glycosidase, protease, nuclease etc. For instance, artificial metallooxidases were made from cyclodextrin diacids with copper, zinc and iron (Wang and Bols 2017), glycosidases with phenol as catalytic group (Lindback et al. 2012) and glutathione peroxidases, such as 2,2′-seleno-(2-deoxy-β-cyclodextrin) (Wang et al. 2017). Another recently published example is a manganese porphyrin-α-cyclodextrin conjugate used as an artificial enzyme for the catalytic epoxidation of polybutadiene (Zhang et al. 2018).
Aghahosseini, H., Ramazani, A. (2016) General overview on cyclodextrin-based artificial enzymes’ activity. Curr. Org. Chem. 20(26), 2817-2836
Breslow, R. (1971) Enzyme models. Adv. Chem. Ser., No. 100, 21-43
Breslow, R., Hammond, M., Lauer, M. (1980) Selective Transamination and Optical Induction by a β-Cyclodextrin-Pyridoxamine Artificial Enzyme. J. Am. Chem. Soc., 102(1), 421-422
Cramer, F., Mackensen, G. (1966) A model for the action of chymotripsin. Angew. Chem. 78, 641
Hapiot, F., Ponchel, A., Tilloy, S., Monflier, E. (2011) Cyclodextrins and their applications in aqueous-phase metal- catalyzed reactions. Comptes Rendus Chimie, 14(2-3), 149-166
Hennrich, N., Cramer, F. (1961) Catalytic action of cyclodextrins in the fission of pyrophosphates. Chem. Ind. 31, 1224
Li, X., Qi, Z., Liang, K., Bai, X., Xu, J., Liu, J., Shen, J. (2008) An artificial supramolecular nanozyme based on β-cyclodextrin-modified gold nanoparticles. Catal. Lett. 124(3-4), 413-417
Lindback, E.Z., You Pedersen, C.M., Bols, M. (2012) Artificial enzymes based on cyclodextrin with phenol as the catalytic group. Tetrahedr. Lett. 53(37), 5023-5026
Okamoto, Y., Ward, T.R. (2017) Supramolecular Enzyme Mimics. In: Atwood, J.L., Gokel, G.W., Bartour, L. (eds.) Comprehensive Supramolecular Chemistry II, 4, pp. 459-510, Elsevier
Siegel, B., Breslow, R. (1975) Lyophobic binding of substrates by cyclodextrins in nonaqueous solvents. J. Am. Chem. Soc., 97(23), 6869-6870
Tabushi, I., Shimokawa, K., Shimizu, N., Shirakata, H., Fujita, K. (1976) Capped cyclodextrin. J. Am. Chem. Soc., 98(24), 7855-7856
Wang, L., Qu, X., Xie, Y., Lv, S. (2017) Study of 8 types of glutathione peroxidase mimics based on β-Cyclodextrin. Catalysts 7(10), 289
Wei, H., Wang, E. (2013) Nanomaterials with enzyme-like characteristics (nanozymes): next- generation artificial enzymes. Chem. Soc. Rev. 42, 6060-6093
Zhang, Q.-W., Elemans, J.A.A.W., White, P.B., Nolte, R.J.M. (2018) A manganese porphyrin-α-cyclodextrin conjugate as an artificial enzyme for the catalytic epoxidation of polybutadiene. Chem. Commun. 54(44), 5586-5589