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The hydrophobic effect depends on the temperature, which leads to "cold denaturation" of proteins. [19] The hydrophobic effect can be calculated by comparing the free energy of solvation with bulk water. In this way, the hydrophobic effect not only can be localized but also decomposed into enthalpic and entropic contributions. [3]
Water on hydrophobic surfaces will exhibit a high contact angle. Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds. [2]
In some cases, both hydrophilic and hydrophobic properties occur in a single molecule. An example of these amphiphilic molecules is the lipids that comprise the cell membrane . Another example is soap , which has a hydrophilic head and a hydrophobic tail, allowing it to dissolve in both water and oil.
A table comparing four different scales for the hydrophobicity of an amino acid residue in a protein with the most hydrophobic amino acids on the top. A number of different hydrophobicity scales have been developed. [3] [1] [7] [8] [9] The Expasy Protscale website lists a total of 22 hydrophobicity scales. [10]
Phospholipids, a class of amphiphilic molecules, are the main components of biological membranes. The amphiphilic nature of these molecules defines the way in which they form membranes. They arrange themselves into lipid bilayers, by forming a sheet composed of two layers of lipids. Each layer forms by positioning their lypophilic chains to the ...
Substances that are hydrophobic ('water-fearing') do not dissolve well in water, whereas those that are hydrophilic ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions (H +) and hydroxide ions (OH −) are in Arrhenius balance ([H +] [OH −] = K w = 1 x 10 −14 at 298 K).
Most lipids consist of a polar or hydrophilic head (typically glycerol) and one to three non polar or hydrophobic fatty acid tails, and therefore they are amphiphilic. Fatty acids consist of unbranched chains of carbon atoms that are connected by single bonds alone ( saturated fatty acids) or by both single and double bonds ( unsaturated fatty ...
Sterols have a hydrophobic four-membered fused ring rigid structure, and a small polar head group. Cholesterol is bio-synthesised from mevalonate via a squalene cyclisation of terpenoids . Cell membranes require high levels of cholesterol – typically an average of 20% cholesterol in the whole membrane, increasing locally in raft areas up to ...