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Concept
Electron acceptor
Résumé
An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mistakenly called electron receptors.
The electron accepting power of an acceptor molecule is measured by its electron affinity (A) which is the energy released when filling the lowest unoccupied molecular orbital (LUMO). The energy required to remove one electron from the electron donor is its ionization potential (I). The overall system energy change (ΔE), i.e. the energy gained or lost, for the charge transfer is
While oxidizing agents undergo permanent chemical alteration through covalent or ionic reaction chemistry, resulting in the irreversible transfer of one or more electrons, in many systems, the transfer of electronic charge from an electron donor may only appear fractional due to resonance and equilibrium between the initial configuration before transfer and the resulting configuration. This leads to the formation of charge transfer complexes in which the components largely retain their chemical identities.
A class of electron acceptors that acquire not just one, but a set of two paired electrons that form a covalent bond with an electron donor molecule, is known as a Lewis acid. This phenomenon gives rise to the wide field of Lewis acid-base chemistry. The driving forces for electron donor and acceptor behavior in chemistry is based on the concepts of electropositivity (for donors) and electronegativity (for acceptors) of atomic or molecular entities.
Examples of electron acceptors include oxygen, nitrate, iron (III), manganese (IV), sulfate, carbon dioxide, or in some microorganisms the chlorinated solvents such as tetrachloroethylene (PCE), trichloroethylene (TCE), dichloroethene (DCE), and vinyl chloride (VC). These reactions are of interest not only because they allow organisms to obtain energy, but also because they are involved in the natural biodegradation of organic contaminants.
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Light-dependent reactions
Light-dependent reactions is jargon for certain photochemical reactions that are involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions, the first occurs at photosystem II (PSII) and the second occurs at photosystem I (PSI), PSII absorbs a photon to produce a so-called high energy electron which transfers via an electron transport chain to cytochrome b_6f and then to PSI. The then-reduced PSI, absorbs another photon producing a more highly reducing electron, which converts NADP^+ to NADPH.
Electron donor
In chemistry, an electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. Typical reducing agents undergo permanent chemical alteration through covalent or ionic reaction chemistry. This results in the complete and irreversible transfer of one or more electrons. In many chemical circumstances, however, the transfer of electronic charge to an electron acceptor may be only fractional, meaning an electron is not completely transferred, but results in an electron resonance between the donor and acceptor.
Bactérie
Le terme bactérie est un nom vernaculaire qui désigne certains organismes vivants microscopiques et procaryotes présents dans tous les milieux. Le plus souvent unicellulaires, elles sont parfois pluricellulaires (généralement filamenteuses), la plupart des espèces bactériennes ne vivant pas individuellement en suspension, mais en communautés complexes adhérant à des surfaces au sein d'un gel muqueux (biofilm). vignette|200px|Coques à gauche, Spirillum au centre, bacille à droite.