Adsorption Mechanism,Sensing Application Of ZIF-8 And Interaction Between DNA Bases And The Degradation Products Of ZIF-8

Metal–organic frameworks?MOFs?are a kind of porous crystal materials,which are three-dimensional framework structures composed of transition metals and organic ligands.In recent years,researchers have designed and synthesized a large number of MOFs,which have broad application prospects in gas storage and separation,surface catalysis,photoelectric sensing,drug sustained release and other aspects.In the study of MOFs materials,theoretical simulation analysis of computational chemistry plays an increasingly important role in understanding,predicting and discovering new phenomena and their essence.The combination of theoretical simulation and traditional experiment can theoretically analyze the properties that are difficult to be characterized by experiment and promote the development of materials science.In this work,theoretical simulation and experimental determination are combined to investigate the gas adsorption,catalytic activity and biological safety of zeolite imidazole framework?ZIF?,a typical MOFs material.The details are as follows:1.Adsorption process and mechanism of VOCs on ZIF-8 filmIn this work,zeolite imidazole framework 8?ZIF-8?,a typical MOFs material,is selected as the adsorbent.The dynamic processes of volatile organic compounds?VOCs?such as CH₂Cl₂,CHCl₃ and CCl₄ adsorption on ZIF-8 film are monitored in real time using a quartz crystal microbalance sensor.The microcosmic changes of the pore aperture in the cage unit of ZIF-8 on thermodynamics are studied by density functional theory?DFT?.Experimental results show that the adsorption rate of CH₂Cl₂ on ZIF-8 film is significantly faster than that of CHCl₃ and CCl₄.Simulation results show that the different adsorption rates are due to the different rotation angles of 2-methylimidazole?mIms?in the pore aperture to different guest molecules.The adsorption of CH₄ and CH₃Cl,not easy to be carried out in the experiment for the sake of safety,are also included in the simulation.Diffusion energy barriers?kJ/mol?of all VOCs are in the order of CH₄?3.3?<CH₂Cl₂?6.5?<CH₃Cl?13.5?<CHCl₃?56.9?.The changes of experimental phenomena can be explained well by theoretical simulation.2.Adsorption processes and mechanism of Cl₂,Br₂,I₂ on ZIF-8 filmA DFT computational approach is used for characterizing the detailed adsorption and desorption processes of Cl₂,Br₂ and I₂ on ZIF-8.Attachment energies?kJ/mol?of Cl₂,Br₂and I₂ are-55.2,-48.5 and-43.0,respectively.Cl₂ has the highest adhesion capacity and two Cl₂ molecules can be accommodated at the same time on each pore aperture.Cl₂ can react with Zn on the surface and in the cage,resulting in the decomposition of the pore apertures.A framework deformation on the surface of ZIF-8 can be caused by the attachment of Br₂,while I₂ only causes the reorientation of mIms.All the halogen vapors tend to enter the ZIF-8 cages in a vertical configuration followed with swing effect implemented by the reorientation of mIms.Each cage can accommodate a maximum of 7 Br₂ or 5 I₂ molecules.Br₂ are clinging to mIms and I₂ arranged as crystal layout in the cages,therefore in desorption some vapors remained while molecules on the surface and free molecules inside desorbed.The experimental results show that each cage can hold 5.2 I₂ molecules,which confirms that the choice of the simulation method is reasonable and the simulation result is accurate.3.A PEC sensor to H₂O₂ based on catalytic activity difference betweenZIF-8&ZIF-67ZIF-67 exhibits excellent catalytic effect to H₂O₂ and can catalyze the decomposition of H₂O₂ to produce free radicals.Here,a photoelectrochemical?PEC?sensor to H₂O₂ is proposed based on the catalytic activity difference between two ZIFs surface coatings.In the sensing and reference photoelectrodes,ZIF-67 and ZIF-8 films are grown on the surface of CNTs-g-C₃N₄/TiO₂ NTs array,respectively.The diffusion of molecules with size larger than the pore apertures in coating layers,e.g.ascorbic acid,can be prevented by the molecular sieve effect of ZIF-8 and ZIF-67.That improves the selectivity of the PEC sensor to H₂O₂and offers higher sensitivity than the reference one due to the excellent catalytic activity of ZIF-67.The sensing and reference photoelectrodes interference can be eliminated effectively by the differential strategy.The selectivity,reliability and stability of the sensor are further enhanced.Under the optimized condition,the linear range to the detection of H₂O₂ of the sensor is 0.003¹0mM and the limit of detection is 1.5 nM.4.Effect of Zn²⁺from decomposed ZIF-8 on Thymine tautomerizationZn²⁺is one of the important metal cations that maintain the basic physiological functions of human bodies.A certain amount of Zn²⁺can be released from ZIF-8 when ZIF-8 is used as a drug delivery system.Metal cations can easily lead to base tautomerization,i.e.intramolecular proton transfer.In this work,the influence of isolated and penta-hydrated Zn²⁺on some of the Thymine?T?intramolecular proton-transfer processes are investigated by DFT method.In vacuum,the binding energy between Zn²⁺and T is exothermic.Zn²⁺increases the stability of T tautomer by 28.7 kcal/mol compared to canonical T structure,promoting the intramolecular proton transfer.In a micro-water environment,the attachments of Zn²⁺to T hydrates,penta-hydrated Zn²⁺to T and penta-hydrated Zn²⁺to T hydrates lead to the molecules rearrangement and the charges redistribution.Results reveal that the canonical T structure is still the most stable form.The influence of Zn²⁺is much reduced by water cluster and the processes of proton transfer are thermodynamically unfavored.5.Effect of hydrolyzed fragments from ZIF-8 on Thymine tautomerizationWhen ZIF-8 is used as a drug carrier,it is easy to degrade in the complex humoral environment of human body.That could result in various fragments such as neutral mIms monomer?M?and negative mIms monomer?M^-?,which may promote the mutation of the base.Therefore in this work,the intramolecular proton transfer processes of T affected by M and M^-in water environment are investigated by DFT method.It is shown that with the number of water?w?molecules which assist the proton transfer processes increasing from 1to 4,the order of the tautomeric energy barriers?in kcal/mol?is T-2w?16.3?<T-1w?17.6?<T-3w?17.8?<T-4w?20.5?.In the presence of M,the energy barriers are in the order of MT-2w?16.6?<MT-1w?17.7?<MT-3w?18.9?<MT-4w?20.8?.The presence of M has little effect on the energy barriers of proton transfer while M^-has a catalysis effect.The attachment of M^-slightly promotes the proton transfers in some instances.In general,all proton transfer processes encounter high energy barriers,therefore,proton transfer of T base is not favorable when surrounded by water.Hopefully this investigation work is helpful to understand the genotoxicity of ZIF-8 during the drug delivery applications.6.Effect of charged particles from ZIF-8 on proton transfer processes ofGuanine-Cytosine base pairZIF can be decomposed into various fragments including metal cations,negative or positive charges when used as drug delivery materials.To evaluate the safety of ZIF materials,mechanisms of intermolecular proton transfer processes in Guanine-Cytosine?GC?base pair,under the influence of fragments stated above,are investigated by DFT method.In vacuum,simulation result shows that it is the additional electron assists proton transfer in the anionic GC radical with a small energy barrier?0.5 kcal/mol?.The positive charge attaches to the base pair to form a"hole"promotes the proton transfer and the energy barrier is 2.4 kcal/mol.When surrounded by water molecules,the averaged energy barrier of proton transfer increases by 2.8 kcal/mol because of the charges redistribution.Therefore,the micro-water environment plays a very important buffering role and the influence of charge or metal cation on the proton transfer of the GC base pair is weakened,correspondingly,the probability of proton transfer is reduced.