The molecular structures of a series of 1,3-propanedithiols that contain
carboxylic acid groups, namely rac- and
meso-2,4-dimercaptoglutaric acid (H4DMGA) and
2-carboxy-1,3-propanedithiol (H3DMCP), have been determined by X-ray
diffraction. Each compound exhibits two centrosymmetric intermolecular hydrogen
bonding interactions between pairs of carboxylic acid groups, which result in a
dimeric structure for H3DMCP and a polymeric tape-like structure for
rac- and meso-H4DMGA.
Significantly, the hydrogen bonding motifs observed for rac-
and meso-H4DMGA are very different to those observed
for the 1,2-dithiol, rac-2,3-dimercaptosuccinic acid
(rac-H4DMSA), in which the two oxygen atoms of
each carboxylic acid group hydrogen bond to two different carboxylic acid
groups, thereby resulting in a hydrogen bonded sheet-like structure rather than
a tape. Density functional theory calculations indicate that 1,3-dithiolate
coordination to mercury results in larger S–Hg–S bond angles than
does 1,2-dithiolate coordination, but these angles are far from linear. As such,
κ2-S2 coordination of these dithiolate ligands
is expected to be associated with mercury coordination numbers of greater than
two. In vivo studies demonstrate that both
rac-H4DMGA and
H3DMCP reduce the renal burden of mercury in rats, although the
compounds are not as effective as either 2,3-dimercaptopropane-1-sulfonic acid
(H3DMPS) or meso-H4DMSA.