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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 protonated), classifying it as a ...
Aromatic amino acid. Histidine. Tryptophan. Tyrosine. An aromatic amino acid is an amino acid that includes an aromatic ring. Phenylalanine. Among the 20 standard amino acids, histidine, phenylalanine, tryptophan, tyrosine, are classified as aromatic.
Most surfactants are organic compounds with hydrophilic "heads" and hydrophobic "tails." The "heads" of surfactants are polar and may or may not carry an electrical charge. The "tails" of most surfactants are fairly similar, consisting of a hydrocarbon chain, which can be branched, linear, or aromatic. Fluorosurfactants have fluorocarbon chains.
Chemical polarity. A water molecule, a commonly used example of polarity. Two charges are present with a negative charge in the middle (red shade), and a positive charge at the ends (blue shade). In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a ...
In nonpolar solvents contact ion pairs with very high association constants are formed; [3] [4] in the gas phase the association energies of e.g. alkali halides reach up to 200 kJ/mol. [5] The Bjerrum or the Fuoss equation describe ion pair association as function of the ion charges zA and zB and the dielectric constant ε of the medium; a ...
Amine. In chemistry, amines (/ ə ˈ m iː n, ˈ æ m iː n /, [1] [2] UK also / ˈ eɪ m iː n / [3]) are compounds and functional groups that contain a basic nitrogen atom with a lone pair.Formally, amines are derivatives of ammonia (NH 3), wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group [4] (these may respectively be called alkylamines ...
Hydrophobicity scales. Hydrophobicity scales are values that define the relative hydrophobicity or hydrophilicity of amino acid residues. The more positive the value, the more hydrophobic are the amino acids located in that region of the protein. These scales are commonly used to predict the transmembrane alpha-helices of membrane proteins.
An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of local structure, and it is the local structure that is most easily predicted from a sequence of amino ...