Negatively charged nanoparticles are known to inhibit the fibrillation of amyloidogenic protein amyloid β (Aβ40), though the overall charge on the protein is negative. In this work a molecular dynamics(MD) study is reported to investigate the interaction of Aβ40 on negatively charged gold nanoparticles (3 - 5 nm) and charged (positive and negative) and neutral gold slabs. The equilibrium structure of Aβ40 on gold surfaces are characterized using residue-specific contacts on gold surface, secondary structure analysis and binding free energy calculations. Simulation results reveal that Aβ40 protein in water interconverts into β-sheets, which are building blocks of the mature fibrils, whereas on gold nanoparticles Aβ40 unfolds and adsorbs. Both negatively charged gold nanoparticles and gold slabs arrest the formation of β-sheets in Aβ40, whereas positively charged gold slab does not inhibit the formation of β-sheet. The residue-specific interactions between Aβ40 and gold surfaces are far more important in governing the adsorption of Aβ40 on charged surfaces.

Self-assembly of (cetyl-tri-methyl ammonium bromide, cationic surfactant) CTAB on gold nanoparticles MD simulation have been performed in order to obtain functionalized nanoparticles which can be latter used to study the conformational changes of amyloid proteins. Generally, it is hypothesized that CTAB forms bilayer around nanoparticle surface at a concentrations above its CMC. Yet, no clear evidence either experimental or theoretical proof for the bilayer hypothesis exists. However, there could be monolayer formation of CTAB with AuNPs. In this work we report, the CTAB surfactant self assembles and forms uniform monolayer around AuNP surface. The surfactants hydrophobic tail group adsorbed around AuNP surface with head group projecting outwards to aqueous phase. Packing density, absolute charge of self-assembled nanoparticles and CTAB chain orientation on nanoparticle surface have been investigated.