Multi-scale computational investigation of Ag-doped two-dimensional Zn-based MOFs for storage and release of small NO and CO bioactive molecules.

Abstract

Nitric oxide (NO) and carbon monoxide (CO) are two important gasotransmitters with critical biological roles in the human body. Due to their short lifetime and dangerous side effects at high concentrations, it is essential to find safe storage and slow release methods of these two gases. Herein, we report the multi-scale simulations of two-dimensional (Zn)MOF-470 doped with antimicrobial Ag atoms to evaluate the degree of enhancement of adsorption and dynamics of NO and CO. The results show that NO binds to Ag stronger than CO. In addition, the decoration of the benzene ring with Ag atoms on both sides has led to the effective adsorption of NO and CO with binding energies of -26.34 and -21.71 kcal mol-1, respectively. The GCMC results show that Ag can significantly improve NO and CO storage capacity, especially in low-pressure ranges. The storage capacity of NO in (Zn)MOF-470 and Ag-doped MOFs is 6.12 and 7.21 mol kg-1, respectively. This storage capacity for CO is 4.09 and 5.48 mol kg-1, respectively. The heat of adsorption for NO and CO was obtained to be 31.72 and 25.64 kJ mol-1 for (Zn)MOF-470, and 36.5 and 31.12 kJ mol-1 for Ag-(Zn)MOF-470 at 298 K and 1 bar. Besides, the MD results indicate that when Ag is doped into the structure of MOFs, the dynamics of gases within the pores of MOFs significantly decrease. When Ag atoms are considered mobile, the dynamics of guest molecules increase and it shows that the structural and dynamical behavior of NO and CO strongly depends on the mobility or immobility of doped Ag atoms. The result from the MSD directions (x, y, and z components) indicates that the diffusion of NO and CO within the pores of (Zn)MOF-470 is anisotropic and this may be due to the 2D structural characteristics of the MOF, the dipolar nature of NO and CO molecules, and the very narrow and layered pores of (Zn)MOF-470. These promising results from the simulations suggest that (Zn)MOF-470 and doping Ag atoms into this MOF can improve the storage capacity and slow release of bioactive NO and CO along with utilization of the antimicrobial nature of Ag atoms in medical applications.