Biohydrogen production from arabinose and glucose using extreme thermophilic anaerobic mixed cultures

Table 3 Gibbs free energy changes for some of the glucose and arabinose oxidation reactions.

Equation		ΔG⁰'^a (kJ reaction^-1)	ΔG'^b (kJ reaction^-1)
*Fermentative reactions*
NADH + H ⁺ + pyruvate ^- → NAD ⁺ + lactate ^-	(1)	-25
2 ferredoxin(red) + 2H ⁺ → 2 ferredoxin(ox) + H ₂	(2)	+3	-25
*Glucose oxidation reactions*
1 glucose + 2H ₂ O → 2 acetate ^- + 2CO ₂ + 2H ⁺ + 4H ₂	(3)	-216
1 glucose → 1 butyrate ^- + 2CO ₂ + 2H ⁺ + 2H ₂	(4)	-264
1 glucose → 2 lactate ^- + 2H ⁺	(5)	-197
1 glucose → 2ethanol ^- + 2CO ₂ + 2H ⁺	(6)	-315
*Arabinose oxidation reactions*
1 arabinose+ 1.67H ₂ O → 1.67 acetate ^- + 1.67CO ₂ + 1.67H ⁺ + 3.33H ₂	(7)	-192
1 arabinose → 0.83 butyrate ^- + 1.66CO ₂ + 0.83H ⁺ + 1.66H ₂	(8)	-228
1 arabinose → 1.66 lactate ^- + 1.66H ⁺	(9)	-172
1 arabinose → 1.66 ethanol ^- + 1.66CO ₂ + 1.66H ⁺	(10)	-269

Standard Gibbs energies of formation of arabinose (in aqueous solution, pH 7 and 25°C) were estimated from the structures of the compounds, using a group contribution method described by [19]; standard Gibbs energies of formation of other compounds involved in the reactions were obtained from [20]
^a Gibbs free energies (at 25°C) calculated at standard conditions (solute concentrations of 1 M and gas partial pressure of 10⁵ Pa).
^b Gibbs free energies (at 25°C) calculated at standard conditions (solute concentrations of 1 M and gas partial pressure of 1 Pa).

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