Preparation of Au102(p-MBA)44. Following the method of
Brust et al.,19 the synthesis of Au102(p-MBA)44 is performed in
two steps: p-MBA and HAuCl4 (3:1 ratio of p-MBA:gold) are
combined in water and 47% methanol at a final gold concentration
of 3 mM; NaBH4 is added (2:1 ratio of BH4
-:gold), and the
reaction is allowed to proceed from a minimum of 5 h to as long
as overnight at room temperature. The product is purified by
fractional precipitation with methanol. PAGE gave a single band
(Figure 1A) of the same mobility as observed for Au102(p-MBA)44
in the past.4 Crystallization led to the growth of large black rods,
a few micrometers in width and few tens of micrometers in length
(Figure 1B,C), which gave X-ray diffraction identical to that
obtained from Au102(p-MBA)44 in the past. The yield was 50-
70% (conversion of Au from HAuCl4 to Au102(p-MBA)44). The
product was stable in aqueous solution at 4 C for at least 6 months
and could be dried and resuspended at will.