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The pK a values of an amino acid side chain in solution is typically inferred from the pK a values of model compounds (compounds that are similar to the side chains of amino acids). See Amino acid for the pK a values of all amino acid side chains inferred in such a way. There are also numerous experimental studies that have yielded such values ...
The Van Slyke determination is a chemical test for the determination of amino acids containing a primary amine group. It is named after the biochemist Donald Dexter Van Slyke (1883-1971). [1] One of Van Slyke's first professional achievements was the quantification of amino acids by the Van Slyke determination reaction. [2]
The higher the proton affinity, the stronger the base and the weaker the conjugate acid in the gas phase.The (reportedly) strongest known base is the ortho-diethynylbenzene dianion (E pa = 1843 kJ/mol), [3] followed by the methanide anion (E pa = 1743 kJ/mol) and the hydride ion (E pa = 1675 kJ/mol), [4] making methane the weakest proton acid [5] in the gas phase, followed by dihydrogen.
Using Gibbs free energy: ΔG = −RT ln(K eq), where R is the universal gas constant, T is the temperature in kelvins, and K eq is the equilibrium constant of a reaction in equilibrium. The deprotonation of His31 is an acid equilibrium reaction with a special K eq known as the acid dissociation constant, K a: His31-H + ⇌ His31 + H +.
Acetic acid, a weak acid, donates a proton (hydrogen ion, highlighted in green) to water in an equilibrium reaction to give the acetate ion and the hydronium ion. Red: oxygen, black: carbon, white: hydrogen. Brønsted and Lowry generalised this further to a proton exchange reaction: [6] [7] [8]
Histidine ball and stick model spinning. Histidine (symbol His or H) [2] is an essential amino acid that is used in the biosynthesis of proteins.It contains an α-amino group (which is in the protonated –NH 3 + form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO − form under biological conditions), and an imidazole side chain (which is partially ...
Theoretical calculations have been used to show that zwitterions may also be present in the gas phase for some cases different from the simple carboxylic acid-to-amine transfer. [6] The pK a values for deprotonation of the common amino acids span the approximate range 2.15 ± 0.2. This is also consistent with the zwitterion being the ...
Often general acid or base catalysis is employed to activate nucleophile and/or electrophile groups, or to stabilize leaving groups. Many amino acids with acidic or basic groups are this employed in the active site, such as the glutamic and aspartic acid, histidine, cystine, tyrosine, lysine and arginine, as well as serine and threonine.