Fluoride is the reduced form of
fluorine. Both organic and inorganiccompounds containing the element fluorine are considered fluorides. As a halogen, fluorine forms a monovalent ion (−1 charge). The range of fluorides is considerable as fluorine forms compounds with all elements except He and Ne [Greenwood&Earnshaw p. 804] [cite journal | last = Khriachtchev | first = Leonid | coauthors = Mika Pettersson, Nino Runeberg, Jan Lundell & Markku Räsänen | date = 24 August 2000| title = A stable argon compound | journal = Nature | volume = 406 | pages = 874–876 | doi = 10.1038/35022551 | url = http://www.nature.com/nature/journal/v406/n6798/abs/406874a0.html ] . Fluorides range from severe toxins such as sarinto life-saving pharmaceuticals such as efavirenzand from refractory materials such as calcium fluorideto highly reactive sulfur tetrafluoride.
Solutions of inorganic fluorides in water contain F− and
bifluorideHF2−. [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.] Few inorganic fluorides are soluble in water without undergoing significant hydrolysis. Examples of inorganic fluorides include hydrofluoric acid(HF), sodium fluoride(NaF), and uranium hexafluoride(UF6). In terms of its reactivity, fluoride differs significantly from chlorideand other halides, and is more strongly solvated due to its smaller radius/charge ratio. Its closest chemical relative is hydroxide. The Si-F linkage is one of the strongest single bonds. In contrast, other silyl halides are easily hydrolyzed.
Many fluoride minerals are known, but paramount in commercial importance are
fluoriteand fluoroapatite. Fluoride is found naturally in low concentration in drinking water and foods. Water with underground sources is more likely to have higher levels of fluoride, whereas the concentration in seawater averages 1.3 parts per million(ppm). [ [http://www.who.int/water_sanitation_health/dwq/chemicals/fluoride.pdf Fluoride in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality] . World Health Organization, 2004, page 2. Page accessed on February 22, 2007.] Fresh water supplies generally contain between 0.01-0.3 ppm, while the ocean contains between 1.2 and 1.5 ppm. [ [http://www.inchem.org/documents/ehc/ehc/ehc227.htm#5.0 Environmental Health Criteria 227: Fluorides] . World Health Organization, 2002, page 38. Page accessed on February 22, 2007.]
Fluorides are pervasive in modern technology.
Hydrofluoric acidis the most important fluoride synthesized. It is principally used in the production of fluorocarbons and aluminium fluorides. Hydrofluoric acid has a variety of specialized applications, including its ability to dissolve glass.Jean Aigueperse, Paul Mollard, Didier Devilliers, Marius Chemla, Robert Faron, Renée Romano, Jean Pierre Cuer, “Fluorine Compounds, Inorganic” in Ullmann’s Encyclopedia of Industrial Chemistry 2005 Wiley-VCH, Weinheim. DOI 10.1002/14356007.a11 307]
Fluoride reagents are significant in synthetic
organic chemistry. Due to the affinity of siliconfor fluoride, and the ability of silicon to expand its coordination number, silyl ether protecting groups can be easily removed by the fluoride sources such as sodium fluorideand tetra-n-butylammonium fluoride(TBAF).
biochemistry, fluoride salts are commonly used to inhibit the activity of phosphatases, such as serine/ threoninephosphatases. [cite journal |author=Nakai C, Thomas JA |title=Properties of a phosphoprotein phosphatase from bovine heart with activity on glycogen synthase, phosphorylase, and histone |journal=J. Biol. Chem. |volume=249 |issue=20 |pages=6459–67 |year=1974 |pmid=4370977 |doi= |url=http://www.jbc.org/cgi/pmidlookup?view=long&pmid=4370977] It may do this by replacing the nucleophilic hydroxyl ionin these enzymes' active sites. [cite journal |author=Schenk G, Elliott TW, Leung E, "et al" |title=Crystal structures of a purple acid phosphatase, representing different steps of this enzyme's catalytic cycle |journal=BMC Struct. Biol. |volume=8 |issue=1 |pages=6 |year=2008 |pmid=18234116 |doi=10.1186/1472-6807-8-6 |url=http://www.biomedcentral.com/1472-6807/8/6] Beryllium fluorideand aluminium fluorideare also used as phosphatase inhibitors, since these compounds are structural mimics of the phosphategroup and can act as analogues of the transition stateof the reaction. [cite journal |author=Wang W, Cho HS, Kim R, "et al" |title=Structural characterization of the reaction pathway in phosphoserine phosphatase: crystallographic "snapshots" of intermediate states |journal=J. Mol. Biol. |volume=319 |issue=2 |pages=421–31 |year=2002 |pmid=12051918 |doi=10.1016/S0022-2836(02)00324-8 |url=http://linkinghub.elsevier.com/retrieve/pii/S0022-2836(02)00324-8] [cite journal |author=Cho H, Wang W, Kim R, "et al" |title=BeF(3)(-) acts as a phosphate analog in proteins phosphorylated on aspartate: structure of a BeF(3)(-) complex with phosphoserine phosphatase |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=98 |issue=15 |pages=8525–30 |year=2001 |pmid=11438683 |doi=10.1073/pnas.131213698 |url=http://www.pnas.org/cgi/pmidlookup?view=long&pmid=11438683]
Sulfur hexafluorideis an inert, nontoxic insulator that is used in electrical transformers. Uranium hexafluorideis used in the separation of isotopes of uranium between the fissile isotope U-235and the non-fissile isotope U-238in preparation of nuclear reactorfuel and atomic bombs. The volatility of fluorides of uranium and other elements may also be used for nuclear fuel reprocessing.
Fluoropolymerssuch as polytetrafluoroethylene, Teflon, are used as chemically inert and biocompatiblematerials for a variety of applications, including as surgical implants such as coronary bypassgrafts, [cite journal |author=Kannan RY, Salacinski HJ, Butler PE, Hamilton G, Seifalian AM |title=Current status of prosthetic bypass grafts: a review |journal=J. Biomed. Mater. Res. Part B Appl. Biomater. |volume=74 |issue=1 |pages=570–81 |year=2005 |pmid=15889440 |doi=10.1002/jbm.b.30247] and a replacement for soft tissuein cosmetic and reconstructive surgery. [cite journal |author=Singh S, Baker JL |title=Use of expanded polytetrafluoroethylene in aesthetic surgery of the face |journal=Clin Plast Surg |volume=27 |issue=4 |pages=579–93 |year=2000 |pmid=11039891] These compounds are also commonly used as non-stick surfaces in cookware and bakeware, and the fluoropolymer fabric Gore-Texused in breathable garments for outdoor use.
Fluoride-containing compounds are used in topical and systemic
fluoride therapyfor preventing tooth decay. They are used for water fluoridationand in many products associated with oral hygiene.cite journal|author=McDonagh M S, Whiting P F, Wilson P M, Sutton A J, Chestnutt I, Cooper J, Misso K, Bradley M, Treasure E, & Kleijnen J.|date=2000 |title=Systematic review of water fluoridation |journal= British Medical Journal|volume=321 |issue=7265| pages=855–859|doi=10.1136/bmj.321.7265.855 |pmid=11021861] Originally, sodium fluoridewas used to fluoridate water, however, hexafluorosilicic acid(H2SiF6) and its salt sodium hexafluorosilicate (Na2SiF6) are more commonly used additives, especially in the United States. The fluoridation of water prevents tooth decay [cite journal |author=Griffin SO, Regnier E, Griffin PM, Huntley V |title=Effectiveness of fluoride in preventing caries in adults |journal=J. Dent. Res. |volume=86 |issue=5 |pages=410–5 |year=2007 |pmid=17452559] [cite journal |author=Winston AE, Bhaskar SN |title=Caries prevention in the 21st century |journal=J Am Dent Assoc |volume=129 |issue=11 |pages=1579–87 |year=1998 |pmid=9818575 |url=http://jada.ada.org/cgi/pmidlookup?view=long&pmid=9818575] and is considered by the U.S. Centers for Disease Control and Preventionas "one of 10 great public health achievements of the 20th century". [ [http://www.cdc.gov/fluoridation/ Community Water Fluoridation - Oral Health ] ] In some countries where large, centralized water systems are uncommon, fluoride is delivered to the populace by fluoridating table salt. Fluoridation of water is not without critics, however (see water fluoridation opposition). [cite journal |author=Newbrun E |title=The fluoridation war: a scientific dispute or a religious argument? |journal=J Public Health Dent |volume=56 |issue=5 Spec No |pages=246–52 |year=1996 |pmid=9034969 |doi=10.1111/j.1752-7325.1996.tb02447.x]
Positron emission tomographyis commonly carried out using fluoride-containing pharmaceuticals such as fluorodeoxyglucose, which is labelled with the radioactive isotope fluorine-18that emits positrons when it decays into 18O.
Fluorine is also part of a large variety of drugs including:
antipsychotics such as fluphenazine, HIV protease inhibitors such as tipranavir, antibiotics such as ofloxacinand trovafloxacin, and anesthetics such as halothane. [cite journal |author=Park BK, Kitteringham NR, O'Neill PM |title=Metabolism of fluorine-containing drugs |journal=Annu. Rev. Pharmacol. Toxicol. |volume=41 |issue= |pages=443–70 |year=2001 |pmid=11264465 |doi=10.1146/annurev.pharmtox.41.1.443] These atoms are incorporated in the drug structures to reduce drug metabolism, as the strong C-F bond resists deactivation in the liver by cytochrome P450 oxidases. [cite journal |author=Fisher MB, Henne KR, Boer J |title=The complexities inherent in attempts to decrease drug clearance by blocking sites of CYP-mediated metabolism |journal=Curr Opin Drug Discov Devel |volume=9 |issue=1 |pages=101–9 |year=2006 |pmid=16445122]
Fluoride-containing compounds are so diverse that it is not possible to generalize on their
toxicity, which depends on their reactivity and structure, and in the case of salts, their solubility and ability to release fluoride ions.Soluble fluoride salts, of which NaFis the most common, are mildly toxic but have resulted in both accidental and suicidal deaths from acute poisoning. While the minimum fatal dose in humans is not known, a case of a fatal poisoning of an adult with 4 grams of NaF is documented. Sodium fluorosilicate, Na2SiF6 with its higher fluorine content, can cause death with as little as 0.2 g. The fatal period ranges from 5 min to 12 hours. The mechanism of toxicity involves the combination of the fluoride anion with the calcium ions in the blood to form insoluble calcium fluoride, resulting in hypocalcemia; calcium is indispensable for the function of the nervous system, and the condition can be fatal. Treatment may involve oral administration of dilute calcium hydroxideor calcium chlorideto prevent further absorption, and injection of calcium gluconateto increase the calcium levels in the blood.I. M. Rabinowitch. Acute Fluoride Poisoning. "Can Med Assoc J." 1945, "52", 345–349. [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1581810] ] Hydrogen fluorideis more dangerous than salts such as NaF because it is corrosive and volatile, and can result in fatal exposure through inhalation or contact with the skin; calcium gluconate gel is the usual antidote. [Muriale L, Lee E, Genovese J, Trend S. Fatality due to acute fluoride poisoning following dermal contact with hydrofluoric acid in a palynology laboratory. "Ann Occup Hyg." 1996 "40", 705-710. PMID 8958774.]
A few organofluorine compounds are extremely toxic, such as
organophosphates like sarinand diisopropylfluorophosphatethat react with the cholinesterase enzymeat neuromuscular junctions and thus block the transmission of nerve impulses to the muscles. [cite journal |author=Marrs TC |title=Organophosphate poisoning |journal=Pharmacol. Ther. |volume=58 |issue=1 |pages=51–66 |year=1993 |pmid=8415873 |doi=10.1016/0163-7258(93)90066-M] Here, a reactive fluorine-phosphorous bond in the inhibitor is the site of nucleophilic attack by a serineresidue in the enzyme's active site, causing the loss of a F- ion and alkylationand inactivation of the enzyme.
While PTFE itself is chemically inert and non-toxic, it begins to deteriorate after the temperature of cookware reaches about 500 °F (260 °C), and decompose above 660 °F (350 °C).DuPont, [http://www.teflon.com/Teflon/teflonissafe/keyquestions.html#q3 Key Questions About Teflon®] , accessed on 03 Dec 2007.] These degradation products can be lethal to
birds, and can cause flu-like symptoms in humans. In comparison, cooking fats, oils, and butter will begin to scorch and smoke at about 392 °F (200 °C), and meat is usually fried between 400–450 °F (200–230 °C), but empty cookware can exceed this temperature if left unattended on a hot burner.
A 1959 study, (conducted before the
Food and Drug Administrationapproved the material for use in food processing equipment) showed that the toxicity of fumes given off by the coated pan on dry heating was less than that of fumes given off by ordinary cooking oils. [cite web
url=http://www.fda.gov/bbs/topics/CONSUMER/CON00036.html |title=Is That Newfangled Cookware Safe? |publisher=Food and Drug Administration |author=Dale Blumenthal |accessdate=2006-05-20 ]
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