Electron donor in the context of "Charge transfer complex"

A chemotroph is an organism that obtains energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which use photons. Chemotrophs can be either autotrophic or heterotrophic. Chemotrophs can be found in areas where electron donors are present in high concentration, for instance around hydrothermal vents.

Examples of substances that are common reducing agents include hydrogen, carbon monoxide, the alkali metals, formic acid, oxalic acid, and sulfite compounds.

Denitrification is a microbially facilitated process where nitrate (NO₃) is reduced and ultimately produces molecular nitrogen (N₂) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter. The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO−3), nitrite (NO−2), nitric oxide (NO), nitrous oxide (N₂O), finally resulting in the production of N₂, completing the nitrogen cycle. Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO−3, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N₂O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.

The process is performed primarily by heterotrophic bacteria (such as Paracoccus denitrificans and various pseudomonads), although autotrophic denitrifiers have also been identified (e.g., Thiobacillus denitrificans). Denitrifiers are represented in all main phylogenetic groups. Generally, several species of bacteria are involved in the complete reduction of NO−3 to N₂, and more than one enzymatic pathway has been identified in the reduction process. The denitrification process does not only provide energy to the organism performing nitrate reduction to dinitrogen gas, but also some anaerobic ciliates can use denitrifying endosymbionts to gain energy similar to the use of mitochondria in oxygen respiring organisms.

An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H ions) across a membrane. Many of the enzymes in the electron transport chain are embedded within the membrane.

The flow of electrons through the electron transport chain is an exergonic process. The energy from the redox reactions creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP). In aerobic respiration, the flow of electrons terminates with molecular oxygen as the final electron acceptor. In anaerobic respiration, other electron acceptors are used, such as sulfate.

In coordination chemistry, denticity (from Latin dentis 'tooth') refers to the number of donor groups in a given ligand that bind to the central metal atom in a coordination complex. In many cases, only one atom in the ligand binds to the metal, so the denticity equals one, and the ligand is said to be unidentate or monodentate. Ligands with more than one bonded atom are called multidentate or polydentate. The denticity of a ligand is described with the Greek letter κ ('kappa'). For example, κ-EDTA describes an EDTA ligand that coordinates through 6 non-contiguous atoms.

Denticity is different from hapticity because hapticity refers exclusively to ligands where the coordinating atoms are contiguous. In these cases the η ('eta') notation is used. Bridging ligands use the μ ('mu') notation.

The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle, or the reductive tricarboxylic acid cycle, or the reductive TCA cycle) is a sequence of chemical reactions that are used by some bacteria and archaea to produce carbon compounds from carbon dioxide and water by the use of energy-rich reducing agents as electron donors.

The reaction is the citric acid cycle run in reverse. Where the Krebs cycle takes carbohydrates and oxidizes them to CO₂ and water, the reverse cycle takes CO₂ and H₂O to make carbon compounds.This process is used by some bacteria (such as Aquificota) to synthesize carbon compounds, sometimes using hydrogen, sulfide, or thiosulfate as electron donors. This process can be seen as an alternative to the fixation of inorganic carbon in the Calvin cycle which occurs in a wide variety of microbes and higher organisms.