Phytochemicals such as curcumin have great potential in cancer prevention and treatment. However, instability and low aqueous solubility of free curcumin weaken its anticancer potential. These undesirable problems can be avoided upon loading curcumin into nanoparticles containing biocompatible and biodegradable polymers such as poly lactic-co-glycolic acid (PLGA), liposomes or micelles. The interaction of drugs and release control can be further enhanced upon inclusion of clay minerals into the PLGA containing nanoparticles. Such nanoparticles offer a new way for cancer drug delivery systems. However, the role of the clay mineral in the resulting composite is not fully understood. Therefore, in this study, we carried out systematic adsorption studies of curcumin anticancer drug on montmorillonite (MMT) nanoparticles in the presence of amphiphilic polymer (PLGA) and in an aqueous environment to understand the contribution of the layered clay structure using cluster (B97-D), periodic DFT and molecular dynamics (MD) simulations in acidic and natural pH media. It has been found that MMT has high affinity towards either polymer or drug molecules especially due to vdW interactions. Furthermore, it has been observed that MMT facilitates the release of curcumin. Current findings suggest that a composite consisting of MMT and PLGA might be used to deliver the anticancer agent curcumin.

Organoclays are very important composite materials used in many diverse industries including plastics and paint. In this study, an organoclay was formed using sepiolite and homologs of quaternary amine surfactants of tetradecyl dimethyl ethylbenzyl ammonium chloride (TDEBAC), hexadecyl dimethyl ethylbenzyl ammonium chloride (HDEBAC) and octadecyl dimethyl ethylbenzyl ammonium chloride (ODEBAC). Adsorption isotherms of sepiolite/quaternary amine surfactants show that the surfactant with the longest chain, ODEBAC, is adsorbed at most onto the surface of sepiolite. FTIR spectroscopy of organosepiolite indicated that spectroscopic features related to the surface and tunnel of sepiolite are notably modified in the presence of surfactants. In addition to these experiments, high level ab initio counter-poise corrected binding energy computations at MP2, SCS-MP2, B97-D and B2PLYP-D levels of theory employing the TZVP basis set were also performed. At all levels, basal interaction of the surfactant at the surface of sepiolite was found to exhibit the most favourable configuration. Furthermore, penetration of the surfactant into the intra-crystalline cavities of sepiolite was also found to be plausible.

Sepiolite is a fibrous clay mineral and consists of 2:1 silicate blocks connected at the corners and separated by tunnels (channels on external surfaces) that extend in the direction of fiber length. The tunnels, 3.7 Å × 610.6 Å in cross-section, are responsible for the incorporation of organic and inorganic compounds. The present study aimed to examine the capacity of twelve different organic molecules, such as pyridine, indigo, methylene blue, and quaternary amines, to gain access to the tunnels of sepiolite using quantum chemistry techniques. The interaction energy computations performed at the B97-D/TZVP level showed that all of the considered organic molecules tend to access the tunnels of sepiolite if external water molecules are absent. This finding is in agreement with experimental studies that included pyridine, indigo, 2,2-bipyridyl, and methylene blue. Interestingly, 2,6-dimethyl pyridine preferred to remain in a tunnel rather than an external channel of the sepiolite.

Sepiolite is a hydrated magnesium silicate with a microporous and mesoporous structure. The fibrous morphology and the alternating blocks and tunnels along the fiber direction of sepiolite make it an ideal material to sequester a variety of organic and inorganic contaminants. The adsorption of various surfactants by organo sepiolites have been experimentally investigated. How this hydrophobic material adsorbs dye molecules at the atomic level, however, is a great mystery. For this reason, the present study focused on the adsorption of acid azo 57 dye molecules to modified sepiolite. For this purpose, the amenability of sepiolite to remove the anionic textile dye (acid azo red dye 57) was first studied in detail. Additionally, a typical cationic surfactant, hexadecyltrimethylammonium Br (HTAB), was used to modify sepiolite to increase the adsorption capacity. Zeta potential measurements on the sepiolite and the HTAB modified sepiolite were also carried out. Moreover, Density Functional Theory (DFT) studies were performed to understand the mechanism of the adsorption of dye molecules to natural and modified sepiolite surfaces. On the basis of the experimental studies, three general systems were theoretically examined: (i) HTAB molecules on sepiolite basal surfaces to represent four Si tetrahedra, (ii) neutral or charged acid azo red dye 57 molecules on sepiolite basal surfaces to represent four Si tetrahedra, and (iii) HTAB on the surface of neutral or charged acid azo red dye 57 molecules as a substrate. The results clearly indicated good agreement between the experimental studies and the theoretical computational DFT studies. For example, the double layer structure found in experimental studies was also demonstrated in DFT studies and confirmed increased adsorption in the presence of acid azo dye 57.

The amenability of gold nanoparticles (AuNPs) coating on natural and modified (hexadecyl trimethyl ammonium bromide, CTAB) sepiolite surfaces was studied both experimentally and theoretically. The zeta potential experiments and Fourier transform infrared spectrophotometer (FTIR), environmental scanning electron microscope (ESEM), and transmission electron microscopy (TEM) analyses were carried out with the sepiolite samples in the presence of AuNPs. In addition, the adsorption of three gold-nanoparticles on the sepiolite surface (100) in the absence and presence of CTAB was investigated by molecular dynamics (MD) simulations. The AuNPs showed no significant change in the zeta potential of natural sepiolite surfaces due to negative charges of both the sepiolite and AuNPs at natural pH. The surface charge of modified sepiolite decreased with the increase in AuNPs concentration indicating the significance AuNPs adsorption. FTIR, ESEM, and TEM analyses indicated the coating of AuNPs onto the modified sepiolite surface were higher than that of the natural sepiolite surface. The MD simulation results showed that AuNPs can easily adsorb onto the basal surface of the sepiolite due to its hydrophilicity in the presence and absence of CTAB as indicated in the experimental studies. In short, the modification of sepiolite with CTAB made the charge positive, and in turn considerably increased the AuNPs coating on sepiolite surfaces due to electrostatic attraction.