Carbon Dioxide Utilisation—The Formate Route

Abstract

The relentless rise of atmospheric CO2 is causing large and unpredictable impacts on the Earth climate, due to the CO2 significant greenhouse effect, besides being responsible for the ocean acidification, with consequent huge impacts in our daily lives and in all forms of life. To stop spiral of destruction, we must actively reduce the CO2 emissions and develop new and more efficient “CO2 sinks”. We should be focused on the opportunities provided by exploiting this novel and huge carbon feedstock to produce de novo fuels and added-value compounds. The conversion of CO2 into formate offers key advantages for carbon recycling, and formate dehydrogenase (FDH) enzymes are at the centre of intense research, due to the “green” advantages the bioconversion can offer, namely substrate and product selectivity and specificity, in reactions run at ambient temperature and pressure and neutral pH. In this chapter, we describe the remarkable recent progress towards efficient and selective FDH-catalysed CO2 reduction to formate. We focus on the enzymes, discussing their structure and mechanism of action. Selected promising studies and successful proof of concepts of FDH-dependent CO2 reduction to formate and beyond are discussed, to highlight the power of FDHs and the challenges this CO2 bioconversion still faces.

How a Formate Dehydrogenase Responds to Oxygen: Unexpected O2 Insensitivity of an Enzyme Harboring Tungstopterin, Selenocysteine, and [4Fe–4S] Clusters

“…Formate oxidation and CO 2 reduction are interconvertible processes that are carried out by prokaryotic formate dehydrogenases (FDHs) (reaction ). , …”

Second and Outer Coordination Sphere Effects in Nitrogenase, Hydrogenase, Formate Dehydrogenase, and CO Dehydrogenase

“…Formate dehydrogenases (FDHs) are a diverse group of enzymes in bacteria, archaea, and eukaryotes that catalyze the reversible two electron and one proton abstraction of formate (HCOO – ) to produce CO 2 (eq ). , In general, these enzymes are involved in diverse metabolic pathways but mostly in the production of CO 2 from formate . On the basis of the low standard potential of formate oxidation ( E ° = −420 mV vs SHE) prokaryotes derive energy by coupling it to the reduction to one of several terminal electron acceptors .…”

“…FDHs are divided into two major classes, into the metal-dependent and metal-independent FDH enzymes . The metal-independent FDHs generally are NAD + -dependent and distributed from bacteria to yeast, fungi, and plants .…”

“…In organisms that catalyze the oxidation of formate, this reaction is a key process for obtaining energy and reducing equivalents . The CO 2 formed is usually incorporated predominantly into the Calvin-Benson cycle, as in autotrophic organisms . Formate is a key metabolite for bacteria, arising as a metabolic product of bacterial fermentations and functioning as a growth substrate for many microorganisms (e.g., methanogens and sulfate-reducing bacteria). − …”

Purification and concentration of formic acid from formic acid/gluconic acid mixtures by two successive steps of nanofiltration and reactive liquid-liquid extraction

“…One of the most interesting chemicals that can be obtained from CO 2 is formic acid (FA), a chemical with many current uses [3] and a great potential as hydrogen storage compound and building block [4]. Several chemo-catalytic methods have been reported to carry out the conversion of CO 2 and H 2 to FA [3], but they are energy-intensive processes that usually show low selectivity and yields [5]. An interesting alternative to the chemical methods is based on biotechnology and involves the use of microorganisms or enzymes to catalyse that conversion.…”