Biologically active fullerene derivatives: Computations of structures, energetics, and vibrations of C-60(OH)(x) and C-60(NO2)(y)

This article reports quantum-chemical semiempirical computations of selecte d multihydroxy and multinitro derivatives of C-60. Polyhydroxylated fullere nes have been known for their efficient free-radical scavenging activity an d promising results in reducing the concentration of free radicals in patho logical blood and in inhibiting the growth of abnormal cells. Nitro-fullere nes are directly linked to hydroxy-fullerenes as polyhydroxylated fullerene s can be produced through hydrolysis of polynitro-fullerenes. In spite of t his considerable biological application potential, microscopic knowledge of the systems is very Limited. This study thus supplies' quantum-chemical se miempirical (primarily PM3) calculations of the structure and energetics fo r selected hydroxy- and nitro-fullerenes. The configurational sampling of C -60(OH)(x) extends from x = 2 to x = 36. The computations offer a useful in sight into the molecular structure, energetics, and possible stability meas ures. It is suggested that thermodynamic stability could be measured throug h a partial dissociation heat. Among the computed structures, C-60(OH)(6) a nd C-60(OH)(18) exhibit the best value of the partial dissociation heat. Wi th nitro-fullerenes, tetra-nitro derivatives were computed here. The comput ations follow the finding for dinitro derivatives that low-energy structure s have either the two nitro groups placed in the para position on one hexag on or added to one 6/6 (double) bond of the cage. The lowest tetra-nitro sp ecies found has the para-pal a arrangement applied to two hexagons separate d by one pentagon. Hydroxy- and nitro-fullerenes do not exhibit the highest topologically possible symmetry, that is, symmetry is lowered due to nonbo nding interactions. (C) 1999 John Wiley & Sons, Inc.