Polyethylene glycol
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| Polyethylene glycol | |
|---|---|
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| Chemical name | Polyethylene glycol |
| Chemical formula | C2nH4n+2On+1 |
| Molecular mass | 44n+18 g/mol |
| CAS number | [25322-68-3] |
| Density | 1.1 - 1.2 g/cm³ |
| Melting point | varies |
| Boiling point | xx.x °C |
| Flash Point | 182 - 287 °C |
| SMILES | xxxx |
| Disclaimer and references | |
Polyethylene glycol (PEG) and polyethylene oxide (PEO) are polymers composed of repeating subunits of identical structure, called monomers, and are the most commercially important polyethers. Poly (ethylene glycol) or poly (ethylene oxide) refers to an oligomer or polymer of ethylene oxide. The two names are chemically synonymous, but historically PEG has tended to refer to shorter polymers, PEO to longer.[1] PEG and PEO are liquids or low-melting solids, depending on their molecular weights. Both are prepared by polymerization of ethylene oxide. While PEG and PEO with different molecular weights find use in different applications and have different physical properties (e.g. viscosity) due to chain length effects, their chemical properties are nearly identical. Derivatives of PEG and PEO are in common use, the most common derivative being the methyl ether (methoxypoly (ethylene glycol)), abbreviated mPEG.
Their melting points vary depending on the Formula Weight of the polymer. PEG or PEO has the following structure:
- HO-(CH2-CH2-O)n-H
The numbers that are often included in the names of PEGs and PEOs indicate their average molecular weights, e.g. a PEG with n=80 would have an average molecular weight of approximately 3500 Daltons and would be labeled PEG 3500. Most PEGs and PEOs include molecules with a distribution of molecular weights, i.e. they are polydisperse. The size distribution can be characterized statistically by its weight average molecular weight (Mw) and its number average molecular weight (Mn), the ratio of which is called the polydispersity index (Mw/Mn). Mw and Mn can be measured by mass spectroscopy.
PEGylation is the act of covalently coupling a PEG structure to another larger molecule, for example, a therapeutic protein (which is then referred to as PEGylated). PEGylated interferon alfa-2a or -2b is a commonly used injectable treatment for Hepatitis C infection.
PEG is soluble in water, methanol, benzene, dichloromethane and is insoluble in diethyl ether and hexane. It is coupled to hydrophobic molecules to produce non-ionic surfactants.
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[edit] Clinical uses
Poly (ethylene glycol) is non-toxic and is used in a variety of products. It is the basis of a number of laxatives (e.g. macrogol-containing products such as Movicol® and polyethylene glycol 3350, or MiraLax® or GlycoLax). It is the basis of many skin creams, as cetomacrogol, and sexual lubricants, frequently combined with glycerin. Whole bowel irrigation (polyethylene glycol with added electrolytes) is used for bowel preparation before surgery or colonoscopy and drug overdoses. It is sold under the brand names GoLYTELY, GlycoLax and Colyte. When attached to various protein medications, poly (ethylene glycol) allows a slowed clearance of the carried protein from the blood. This makes for a longer acting medicinal effect and reduces toxicity, and it allows longer dosing intervals. Examples include PEG-interferon alpha which is used to treat hepatitis C and PEG-filgrastim (Neulasta®) which is used to treat neutropenia. It has been shown that poly (ethylene glycol) can improve healing of spinal injuries in dogs [2]. One of the earlier findings that poly (ethylene glycol) can aid in nerve repair came from the University of Texas (Krause and Bittner) [3]. Poly (ethylene glycol) is commonly used to fuse B-cells with myeloma cells in monoclonal antibody production.
[edit] Research for New Clinical Uses
- High-molecular weight PEG, e.g., PEG 8000, is a strikingly potent dietary preventive agent against Colorectal cancer in animal models [4]. The Chemoprevention Database shows it is the most effective agent to suppress chemical carcinogenesis in rats. Cancer prevention in humans has not yet been tested in clinical trials.
- The injection of PEG 2000 into the bloodstream of guinea pigs after spinal cord injury leads to rapid recovery through molecular repair of nerve membranes. [5] The effect of this treatment to prevent Paraplegia in humans after an accident is not known yet.
- Research is being done in the use of PEG to mask antigens on red blood cells. Various research institutes have reported that using PEG can mask antigens without damaging the functions and shape of the cell.
[edit] Other uses
PEG is used in a number of toothpastes as a dispersant; it binds water and helps keep gum uniform throughout the toothpaste. It is also under investigation for use in body armor [6] and tattoos to monitor diabetes[7]. Functional groups of PEG give polyurethane elastomers their "rubberiness", for applications such as foams (foam rubber) and fibers (spandex). Its backbone structure is analogous to that of silicone, another elastomer.
Since PEG is a flexible, water-soluble polymer, it can be used to create very high osmotic pressures (tens of atmospheres). It also is unlikely to have specific interactions with biological chemicals. These properties make PEG one of the most useful molecules for applying osmotic pressure in biochemistry experiments, particularly when using the osmotic stress technique. [8]
PEO (poly (ethylene oxide)) can serve as the separator and electrolyte solvent in lithium polymer cells. Its low diffusivity often requires high temperatures of operation, but its high viscosity even near its melting point allows very thin electrolyte layers. While crystallization of the polymer can degrade performance, many of the salts used to carry charge can also serve as a kinetic barrier to the formation of crystals. Such batteries carry greater energy for their weight than other lithium ion battery technologies.
Poly (ethylene glycol) is also commonly used as a polar stationary phase for gas chromatography, as well as a heat transfer fluid in electronic testers.
PEG is included in many or all formulations of the soft drink Dr Pepper, purportedly as an anti-foaming agent.
PEG has also been used to preserve objects which have been salvaged from underwater, as was the case with the warship Vasa in Stockholm. It replaces water in wooden objects to prevent them from shrinking when dried. [9]
PEG is often seen (as a side effect) in mass spectrometry experiments with characteristic fragmentation patterns [[10]].
In the field of Microbiology PEG precipitation is used to concentrate viruses.
PEG is also used in lubricant eye drops such as Visine.
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