Chemistry Reference
In-Depth Information
$F\O'RQRU
Fig. 6.4
The apparent rate constant for the N435-catalyzed polymerizations of several dimethyl
esters with 1,8-octanediol at 100 °C. Each bar represents the average of three individual trial ± the
standard deviation
Furthermore, dimethyl phthalate was also not a suitable acyl donor even though di-
methyl terephthalate could be polymerized using N435 as a catalyst [
10
,
11
]. These
results can be attributed to the geometric arrangement of the reactive groups around
the
sp
2
hybridized carbons which prevent the acyl donor from binding to the active
serine residue in the active site.
CPr-TMDS-DME is comparable in length to a C11 ester. Furthermore, silox-
anes are some of the most hydrophobic materials that are known, which should
prove to be beneficial for the functioning of N435. Generally speaking, lipases have
adapted to function in hydrophobic environments. Despite this observation, N435
did not demonstrate a capacity for producing polyoctylene esters containing a si-
loxane block with the same proficiency as it could when charged with C4, C6 or
C12 aliphatic esters. When this is taken together with the poor performance of the
enzyme-catalyst with the smaller, and more geometrically constrained acyl donors,
the conclusion that can be drawn is that the geometry of the acyl donor affects the
proficiency with which it can be processed by N435. While CPr-TMDS-DME is not
constrained by a π-system of electrons in the same manner as the fumarate, maleate,
or phthalate methyl esters, the carbon-carbon single bond next to the dimethylsiloxy
group is rotationally constrained as evident by the complex splitting pattern that is
observed in its
1
H NMR spectrum. It is possible that this rotational restriction may
