Organophosphate Detoxification and Acetylcholinesterase Reactivation Triggered by Zeolitic Imidazolate Framework Structural Degradation

Organophosphate (OP) toxicity is related to inhibition of acetylcholinesterase (AChE) activity, which plays a key role in the neurotransmission process. In this work, we report the ability of different zinc zeolitic imidazolate frameworks (ZIFs) to behave as potential antidotes against OP poisoning. The Zn–L coordination bond (L = purine, benzimidazole, imidazole, or 2-methylimidazole) is sensitive to the G-type nerve agent model compounds diisopropylfluorophosphate (DIFP) and diisopropylchlorophosphate, leading to P–X (X = F or Cl) bond breakdown into nontoxic diisopropylphosphate. P–X hydrolysis is accompanied by ZIF structural degradation (Zn–imidazolate bond hydrolysis), with the concomitant release of the imidazolate linkers and zinc ions representing up to 95% of ZIF particle dissolution. The delivered imidazolate nucleophilic attack on the OP@AChE adduct gives rise to the recovery of AChE enzymatic function. P–X bond breakdown, ZIF structural degradation, and AChE reactivation are dependent on imidazolate linker nucleophilicity, framework topology, and particle size. The best performance is obtained for 20 nm nanoparticles (NPs) of Zn(2-methylimidazolate)2 (sod ZIF-8) exhibiting a DIFP degradation half-life of 2.6 min and full recovery of AChE activity within 1 h. 20 nm sod ZIF-8 NPs are not neurotoxic, as proven by in vitro neuroblastoma cell culture viability tests.


S.1. Synthesis of compounds.
All ZIFs were synthesized as previously reported in literature.

S.1.1. ZIF-20 [Zn(pIm)2]
0.029 g of zinc nitrate hexahydrate (0.10 mmol) were dissolved in 0.40 mL of DMF and 0.06 g of purine (pIm, 0.50 mmol) were dissolved in 0.80 mL of DMF.The two solutions were mixed.Afterwards, 0.80 mL of a triethylamine (TEA) solution in DMF (1.25 mmol of TEA) was added and the mixture was heated in a microwave reactor at 150 ºC during 15 minutes.The resulting precipitate was washed with DMF (3 x 2 mL) and EtOH (3 x 2 mL) and recovered by centrifugation (4000 rpm x 10 min). [1]

S.1.2. ZIF-11 [Zn(bIm)2]
0.12 g of benzimidazole (bIm, 1 mmol) were dissolved in 8.62 mL of EtOH, followed by the addition of 5.31 mL of toluene containing 1 mmol of ammonia.After dissolution, 0.11 g of zinc acetate dyhidrate (0.5 mmol) were added and the solution was stirred during 3 h.The product was washed with EtOH (3 x 10 mL) and recovered by centrifugation (4000 rpm x 10 min). [2]1.3.Zn(Im)2 0.30 g of zinc perchlorate hexahydrate (0.81 mmol) were dissolved in 5 mL of water and 0.11 g of imidazole (Im, 1.61 mmol) were dissolved in 5 mL of water.The two solution were mixed under stirring.Aqueous ammonia was added dropwise until a white precipitate was obtained (pH = 10).The solid was washed with H2O (3 x 10 mL) and EtOH (1 x 10 mL) and recovered by filtration.[3]

Theoretical
Experimental

Figure S2 .
Figure S2.Graphical result of the whole powder pattern refinement carried out with the Le Bail method on the PXRD pattern of as-synthesized sod ZIF-8 particles of decreasing size in terms of observed, calculated and difference traces (blue, red and grey, respectively).The positions of the Bragg reflection are indicated by green ticks.Sod ZIFs-8 particles of 2 μm (a); 1 μm (b); 240 nm (c); and 20 nm (d).

Table S2 .
Cell parameters for sod ZIFs-8 particles determined by PXRD Le Bail analysis.Crystalline domain size was estimated using a Lorentzian-convolution of Bragg peaks performed with the software Topas v3.

Table S4 .
Release of imidazolate linker after sod ZIF-8 degradation exposed to a solution