Molecular design of coordination bonding architecture in mesoporous nanoparticles for rational pH-responsive delivery

Abstract

pH-responsive release profiles have been investigated from the perspective of “guest” molecules in a “NH2–metal–guest” coordination bonding architecture on pore surface of mesoporous silica. Guest molecules can be released by the cleavage of either the “NH2–metal” or the “metal–guest” coordinate bonding in response to pH variations. The strengths of coordination bondings between “metal” ions and “guest” molecules have been designed and fabricated from the aspects of the arrangement of functional groups, the number of functional groups and the steric conformation of “guest” molecules. It has been found that (i) reducing the distance of functional group in the order of 1,5-diaminonaphthalene and 1,8-diaminonaphthalene resulted in an increase of coordination bonding stability; (ii) the physiological stabilities of “NH2–metal–guest” architectures formed by various number of functional groups of fluorescein isothiocyanate–oligoarginine (FITC–Rn, where n is the number of arginine) are in the increasing order of FITC–R2<FITC–R4<FITC–R8, indicating that the increase of the number of functional groups led to an increase in “metal–guest” stability due to more coordination bonding sites; (iii) different steric conformation of “guest” molecules gave rise to different pH-sensitivity due to different coordination bonding strengths of the architectures. This report leads to a deeper understanding of the influence of guest molecules in “NH2–metal–guest” architectures and provides a feasible approach to the pH-sensitivity design of this system.