Figure 5. Distribution of isotopologues of isoprene at 30 and 40°C.

The number on each slice is the number of ¹³C atoms. The unlabeled isotopologue was 6.5 ± 0.8% of the total at 30°C and 7.4 ± 1.2% at 40°C. The difference was not statistically significant (two-tailed t-test with unequal variance P = 0.23, n = 5). If the difference were real it would add 0.9% times 5 carbons of ¹²C for an effect of 4.5% reduction in label compared with the observed 17.2% decline in label in isoprene at 40°C or about one quarter of the effect if all of the isotopologue zero isoprene at 40°C is from MEcDP. Isotopologue +1 increased from 2.7% at 30°C to 7.0% of total isoprene at 40°C so some of the isotopologue zero isoprene may have resulted from the reduced labeling independent of the MEcDP effect.