Heterogeneous ECE processes at channel electrodes: Voltammetric waveshape theory. Application to the reduction of nitromethane at platinum electrodes

Theory is developed for heterogeneous ECE reactions occurring at channel electrode that predicts the voltammetric waveshape, as characterized by the half-wave potential and the Tafel slope as a function of the rate of mass transport and the cell geometry. Working surfaces are reported that allow the ready mechanistic interpretation of experimental data and the deduction of corresponding rate constants. Experiments are reported on the reduction of nitromethane in aqueous buffered solution (7 < PH < 9) at platinum electrodes that is thought to proceed via a heterogeneous ECEEE mechanism. Analysis of both waveshape and limiting current data confirm this mechanistic assignment, allowing the following appropriate kinetic parameters to be reported: heterogeneous rate constant. 0.26 ± 0.07 cm s-1; and standard electrochemical rate constant, 0.13 ± 0.01 cm s-1

Simultaneous measurement of the rates of appearance of palmitic and linoleic acid in critically ill infants

Lipolysis has been measured in humans by means of stable isotope techniques using labeled palmitic acid (PA) or glycerol as tracers. If other fatty acids (FA) such as linoleic acid (LLA) have the same rate of appearance (R(a)) as PA and therefore contribute equally to oxidative and nonoxidative metabolism is unknown. We infused albumin-bound [U-13C]PA and [U-13C]LLA in seven critically ill infants (weight 3.6 \ub1 1.3 kg, age 57 \ub1 64 d) receiving 20.9 \ub1 5.4 kcal \ub7 kg-1 \ub7 d-1 of i.v. glucose only, and measured simultaneously the R(a) of PA and LLA from the isotopic enrichment of plasma FFA by mass spectrometry. A needle biopsy of the s.c. adipose tissue was obtained for FA composition. PA in adipose tissue was higher than LLA (40 \ub1 6.7 versus 5.4 \ub1 3.2 mol %, p < 0.001). The R(a) values of PA and LLA were 5.73 \ub1 2.79 and 1.34 \ub1 0.92 \u3bcmol \ub7 kg-1 \ub7 min-1, respectively (p = 0.005). However, the ratio of the FA's R(a) to their respective mol% values in adipose tissue was lower for PA than for LLA (0.15 \ub1 0.06 versus 0.25 \ub1 0.06, p = 0.02). The R(a) of LLA acid was higher than could be expected from the FA composition of adipose tissue, thus indicating a preferential release of LLA during lipolysis. In critically ill infants receiving only i.v. glucose, the contribution of LLA to the oxidative and nonoxidative metabolism may be larger than what assumed from the FA composition of plasma and adipose tissue