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Molecular simulation methods were used to describe the spiral-structure of halloysite (7 Å) loaded with irinotecan in Materials Studio modeling environment. Halloysite is a clay mineral commonly used as a drug delivery system for a variety of molecules due to its suitable characteristics and its morphology. Irinotecan is a semi-synthetic drug used in the treatment of colorectal cancer and exists in an active lactone form and an inactive hydroxyl-acid anion form. In this work, the anionic form of the irinotecan is tested for the interaction with the halloysite nanotubes in different geometrical conformations and mutual arrangements when the anionic drug is loaded on the inner part of halloysite nanotubes. The optimized model of anionic irinotecan was used in various concentrations/amounts related to the experimental data to determine the most probable drug loaded halloysite system. The atomic coordinates for the creation and construction of the spiral-shape halloysite nanotubes were based on previously published paper. The halloysite (7 Å) spiral ring nanotube was built and subsequently sets of models with various amount of drug anions loaded in the halloysite nanotube were created. Except of the irinotecan anions, water molecules were included into the optimized system and different concentrations of them were tested. The mutual interactions between the water molecules, the irinotecan anions and the halloysite nanotube were investigated in detail by using molecular mechanics and molecular dynamics calculations. [ABSTRACT FROM AUTHOR]

The atomic motion is coupled by the fast and slow components due to the high frequency vibration of atoms and the low frequency deformation of atomic lattice, respectively. A two-step approximate method was presented to determine the atomic slow motion. The first step is based on the change of the location of the cold potential well bottom and the second step is based on the average of the appropriate slow velocities of the surrounding atoms. The simple tensions of one-dimensional atoms and two-dimensional atoms were performed with the full molecular dynamics simulations. The conjugate gradient method was employed to determine the corresponding location of cold potential well bottom. Results show that our two-step approximate method is appropriate to determine the atomic slow motion under the low strain rate loading. This splitting method may be helpful to develop more efficient molecular modeling methods and simulations pertinent to realistic loading conditions of materials. [ABSTRACT FROM AUTHOR]