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A palladium diphosphine pincer complex H3(PNNNP-PdI) has been encapsulated in the benzotriazolate metal-organic framework MFU-4l-OH ([Zn5(OH)4(btdd)3], btdd2− = bis(1,2,3-triazolo)dibenzodioxin), and the resulting materials were investigated as Lewis acid catalysts for cyclization of citronellal to isopulegol. Rapid catalyst immobilization is facilitated by a Brønsted acid–base reaction between the H3(PNNNP-PdI) benzoic acid substituents and Zn–OH groups at the framework nodes. Catalyst loading can be controlled up to a maximum of 0.5 pincer complexes per formula unit [PdI-x, Zn5(OH)4−nx(btdd)3(H3−nPNNNP-PdI)x x = 0.06–0.5, n ≈ 2.75]. Oxidative ligand exchange was used to replace I− with weakly coordinating BF4− anions at the Pd–I sites, generating the activated PdBF4-x catalysts (x = 0.06, 0.10, 0.18, 0.40). The Lewis acid catalytic activity of the PdBF4-x series decreases with increasing catalyst density as a result of the appearance of mass transport limitations. Initial catalytic rates show that the activity of PdBF4-0.06 approaches the intrinsic activity of a homogeneous PNNNP-PdBF4 catalyst analogue. In addition, PdBF4-0.06 exhibits better catalytic activity than the metallolinker-based MOF Zr-PdBF4 and was not subject to leaching or catalyst degradation processes observed for the homogeneous analogue.
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This content will become publicly available on April 1, 2026
Design of a halogen bond catalyzed DNA endonuclease
In this study, we expand the repertoire of biological catalysts by showing that a halo- gen bond (X-bond) can functionally replace the magnesium (Mg2+) cofactor in mouse endonuclease G (mEndoG). We mutated the metal coordinating glutamate E136 in mEndoG to a meta-halotyrosine (mXY, X = chlorine or iodine) to form a mXY-mEndoG construct that is both acid and base catalyzed. Under basic conditions, the enzyme is inactivated by the metal chelator ethylene diamine tetraacetic acid (EDTA), indicating that the halogen substituent facilitates deprotonation of the tyrosyl hydroxyl group, allowing recruitment of Mg2+ to restore the metal-dependent catalytic center. At low pHs, we observe that the mXY-mEndoG is resistant to EDTA inactivation and that the iodinated constructed is significantly more active than the chlorinated analogue. These results implicate a hydrogen bond (H-bond) enhanced X-bond as the catalyst in the mXY-mEndoG, with asparagine N103 serving as the H-bond donor that communicates the protonation state of histidine H104 to the halogen. This model is supported by mutation studies and electrostatic potential (ESP) calculations on models for the protonated and unprotonated mXY···N103···H104 system compared to the Mg2+ coor- dination complex of the wild type. Thus, we have designed and engineered an enzyme that utilizes an unnatural catalyst in its active site—a catalytic X-bonding enzyme, or cX-Zyme—by controverting what constitutes a metal catalyst in biochemistry.
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- Award ID(s):
- 2203161
- PAR ID:
- 10613845
- Publisher / Repository:
- National Academy of Science
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences of the United States of America
- ISSN:
- 1091-6490
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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