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Protonation
 
 
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In chemistry, protonation is the addition of a proton (H
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
+) to an atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
, molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
, or ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
. Protonation is possibly the most fundamental chemical reaction and is a step in many stoichiometric
Stoichiometry

Stoichiometry is the calculation of quantitative relationships of the reactants and Product in a balanced chemical reaction .Etymology...
 and catalytic processes
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
. Some ions and molecules can undergo more than one protonations or deprotonations; such species are labeled polybasic. Most biological macromolecules are polybasic.

Upon protonating a substrate, the mass and the charge of the species each increase by one unit.






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Encyclopedia


In chemistry, protonation is the addition of a proton (H
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
+) to an atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
, molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
, or ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
. Protonation is possibly the most fundamental chemical reaction and is a step in many stoichiometric
Stoichiometry

Stoichiometry is the calculation of quantitative relationships of the reactants and Product in a balanced chemical reaction .Etymology...
 and catalytic processes
Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
. Some ions and molecules can undergo more than one protonations or deprotonations; such species are labeled polybasic. Most biological macromolecules are polybasic.

Upon protonating a substrate, the mass and the charge of the species each increase by one unit. Protonating or deprotonating a molecule or ion alters many chemical properties beyond the change in the charge and mass: hydrophilicity
Hydrophile

Hydrophile, from the Greek language ' "water" and f???a ' "friendship," refers to a physical property of a molecule that can transiently bond with water through hydrogen bonding....
, reduction potential
Reduction potential

Reduction potential is the tendency of a chemical species to acquire electrons and thereby be redox. Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced....
, optical properties
Ultraviolet-visible spectroscopy

Ultraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry involves the spectroscopy of photons in the UV-visible region....
, among others. Protonation is also an essential step in certain analytical procedures such as electrospray mass spectrometry
Mass spectrometry

Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds....
.

Protonation and deprotonation occur in most acid-base reactions; they are the core of most acid-base reaction theories. A Bronsted-Lowry acid is defined as a chemical substance
Chemical substance

A chemical substance is a material with a specific Empirical formula. It is a concept that became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate....
 that protonates another substance.

Rates of protonation and deprotonation

Protonations are often rapid, in part because of the high mobility of protons in water. The rate
Reaction rate

The reaction rate or rate of reaction for a reactant or product in a particular chemical reaction is intuitively defined as how fast a reaction takes place....
 of protonation is related to the acidity of the protonated species. Weak acids protonate more slowly than strong acids. The rates of protonation and deprotonation can be especially slow when protonation induces significant structural changes.

Reversibility and catalysis

Usually, protonations are reversible and the conjugate base is unchanged by being protonated. In some cases, however, protonation causes isomerization. Cis-alkene
Alkene

In organic chemistry, an alkene, olefin, or olefine is an Saturation chemical compound containing at least one carbon-to-carbon double bond....
s can be converted to trans-alkenes using a catalytic amount of protonating agent. Many enzymes, such as the serine hydrolase
Serine hydrolase

The serine hydrolase superfamily is one of the largest known enzyme families comprising approximately 1% of the genes in the human genome. This family includes:...
s operate by mechanisms that involve reversible protonations of substrates.

IUPAC recommendation

Formally, the term "hydronation" is recommended by the IUPAC, just as "hydron
Hydron (chemistry)

In chemistry, hydron is the general name for the positive hydrogen H+ cation.Hydron is the name for positive hydrogen ions without regard to nuclear mass, or positive ions formed from natural hydrogen ....
" is recommended in place of "proton" because only 99.999% of natural hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 nuclei are proton
Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s; the rest are deuterons and rare tritons (tritium
Tritium

Tritium is a radioactive isotope of hydrogen. The atomic nucleus of tritium contains one proton and two neutrons, whereas the nucleus of Hydrogen atom contains one proton and no neutrons....
). In fact, few chemists actually use the terms "hydron", "hydronation", and "dehydronation". (However all chemists use the term "hydride
Hydride

Hydride is the name given to the Electric charge ion of hydrogen, H-. Although this ion does not exist except in extraordinary conditions, the term hydride is widely applied to describe Chemical compound of hydrogen with other chemical element, particularly those of Periodic table group 1–16....
", which could be considered inconsistent.)

See also

  • Deprotonation
    Deprotonation

    Deprotonation is a chemistry term that refers to the removal of a proton from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value....