The average hydrocarbon chain length is 1.16 and 1.17 nm for AuNP+ and AuNP–, respectively, measured as the distance between the first carbon (connected to S) and the amine nitrogen or carboxylic carbon, respectively. Correspondingly, for a single unit of the alkyl chain, CH2, the segment length is 0.096 nm for both AuNPs. The radius of gyration is Rg = 0.946 ± 0.004 nm and Rg = 0.995 ± 0.005 nm for AuNP+ and AuNP–, respectively. These values are biased toward the Au core because of the large atomic mass of gold.