We report facile synthesis of the Au10(SG)10 nanoclusters, where SG stands for glutathione, found to be promising as a new class of radiosensitizers for cancer radiotherapy. The homoleptic catenane structure with two Au5SG5 interconnected rings, among different isomer structures, gives the best agreement between theoretical and experimental optical spectra and XRD patterns. This catenane structure exhibits a centrosymmetry-broken structure, resulting in enhanced second harmonic response and new characteristic circular dichroism signals in the spectral region of 250-400 nm. This is the first determination of the nonlinear optical properties of a ligated cluster with an equal Au-to-ligand ratio, thus without a metallic core and therefore zero confined electrons. Insight into the nonlinear and chiroptical efficiencies arising from interplay between structural and electronic properties is provided by the TD-DFT approach.