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Zinc, in commerce also , is a ; it has the symbol Zn and 30. It is the first element of of the . Zinc is, in some respects, chemically similar to , because its is of similar size and its only common is 2. Zinc is the 24th most abundant element in the Earth's crust and has five stable . The most common zinc is (zinc blende), a mineral. The largest mineable amounts are found in , , and the . Zinc production includes of the , , and final using ().

, which is an of and zinc, has been used since at least the 10th century BC in and by the 7th century BC in Ancient Greece. Zinc was not produced in large scale until the 12th century in India, while the metal was unknown to Europe until the end of the 16th century. The mines of have given definite evidence of zinc production going back to 6th Century BC. To date the oldest evidence of pure zinc comes from Zawar, as early as 9th century AD, when distillation process was employed to make pure zinc. burned zinc in air to form what they called "" or "white snow."

The element was probably named by the alchemist after the German word Zinke. German chemist is normally given credit for discovering pure metallic zinc in 1746. Work by and uncovered the electrochemical properties of zinc by 1800. -resistant of iron () is the major application for zinc. Other applications are in , small non-structural castings, and alloys, such as . A variety of zinc compounds are commonly used, such as and (as dietary supplements), (in deodorants), (anti- shampoos), (in luminescent paints), and zinc methyl or in the organic laboratory.

Zinc is an of "exceptional biologic and public health importance". affects about two billion people in the developing world and is associated with many diseases. In children it causes growth retardation, delayed sexual maturation, infection susceptibility, and diarrhea, contributing to the death of about 800,000 children worldwide per year. with a zinc atom in the are widespread in biochemistry, such as in humans. ξ1 electronic-book ISBN 978-94-007-5561-1 electronic- Consumption of excess zinc can cause , and .


Physical properties
Zinc, also referred to in nonscientific contexts as spelter, ξ2 is a bluish-white, lustrous, metal, though most common commercial grades of the metal have a dull finish. It is somewhat less dense than and has a hexagonal .

The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 . Above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a fair . For a metal, zinc has relatively low melting (419.5 °C, 787.1 F) and boiling points (907 °C). Its melting point is the lowest of all the aside from and .

Many contain zinc, including brass, an alloy of and zinc. Other metals long known to form binary alloys with zinc are , , , , , , , , , , , , and . While neither zinc nor are , their alloy exhibits ferromagnetism below 35 .

Zinc makes up about 75  (0.0075%) of the , making it the 24th most abundant element. Soil contains 5–770 ppm of zinc with an average of 64 ppm. has only 30  zinc and the atmosphere contains 0.1–4 µg/m3.

The element is normally found in association with other such as and in . Zinc is a , meaning the element has a low affinity for and prefers to bond with . Chalcophiles formed as the crust solidified under the conditions of the early Earth's atmosphere. , which is a form of zinc sulfide, is the most heavily mined zinc-containing ore because its concentrate contains 60–62% zinc.

Other minerals from which zinc is extracted include (zinc ), (zinc ), (another zinc sulfide), and sometimes (basic ). With the exception of wurtzite, all these other minerals were formed as a result of weathering processes on the primordial zinc sulfides.

Identified world zinc resources total about 1.9 billion . Large deposits are in Australia, Canada and the United States with the largest reserves in . At the current rate of consumption, these reserves are estimated to be depleted sometime between 2027 and 2055. About 346 million tonnes have been extracted throughout history to 2002, and one estimate found that about 109 million tonnes of that remains in use.

Five of zinc occur in nature. 64Zn is the most abundant isotope (48.63% ). This isotope has such a long , at , that its radioactivity can be ignored. Similarly, (0.6%), with a half-life of is not usually considered to be radioactive. The other isotopes found in nature are (28%), (4%) and (19%).

Several dozen have been characterized. , which has a half-life of 243.66 days, is the most long-lived radioisotope, followed by with a half-life of 46.5 hours. Zinc has 10 . 69mZn has the longest half-life, 13.76 h. The superscript m indicates a isotope. The nucleus of a metastable isotope is in an and will return to the by emitting a in the form of a . has three excited states and has two. The isotopes , , and each have only one excited state.

The most common of a of zinc with a lower than 66 is . The resulting from electron capture is an isotope of copper.

The most common decay mode of a radioisotope of zinc with mass number higher than 66 is ), which produces an isotope of .

Compounds and chemistry

Zinc has an of Ar3d104s2 and is a member of the of the . It is a moderately reactive metal and strong . The surface of the pure metal quickly, eventually forming a protective layer of the basic , , by reaction with atmospheric . ξ3 This layer helps prevent further reaction with air and water.

Zinc burns in air with a bright bluish-green flame, giving off fumes of . Zinc reacts readily with , and other non-metals. Extremely pure zinc reacts only slowly at room temperature with acids. Strong acids, such as or , can remove the passivating layer and subsequent reaction with water releases hydrogen gas.

The chemistry of zinc is dominated by the 2 oxidation state. When compounds in this oxidation state are formed the outer s electrons are lost, which yields a bare zinc ion with the electronic configuration Ar3d10. ξ4 In aqueous solution an octahedral complex, is the predominant species. ξ5 The of zinc in combination with zinc chloride at temperatures above 285 °C indicates the formation of , a zinc compound with a 1 oxidation state. No compounds of zinc in oxidation states other than 1 or 2 are known. ξ6 Calculations indicate that a zinc compound with the oxidation state of 4 is unlikely to exist.

Zinc chemistry is similar to the chemistry of the late first-row transition metals and copper, though it has a filled d-shell, so its compounds are and mostly colorless. The of zinc and magnesium happen to be nearly identical. Because of this some of their salts have the same and in circumstances where ionic radius is a determining factor zinc and magnesium chemistries have much in common. ξ7 Otherwise there is little similarity. Zinc tends to form bonds with a greater degree of and it forms much more stable with - and - donors. Complexes of zinc are mostly 4- or 6- although 5-coordinate complexes are known.

See also .

Zinc(I) compounds
Zinc(I) compounds are rare, and requires bulky ligands to stabilize the low oxidation state. Most zinc(I) compounds contains formally the Zn22 core, which is analogous to the Hg22 dimeric cation present in (I) compounds. The nature of the ion confirms its dimeric structure. The first zinc(I) compound containing the Zn—Zn bond, , is also the first . The Zn22 ion rapidly into zinc metal and zinc(II), and has only been obtained as a yellow glass formed by cooling a solution of metallic zinc in molten ZnCl2.

Zinc (II) compounds
of zinc are known for most of the and all the except the . The oxide is a white powder that is nearly insoluble in neutral aqueous solutions, but is , dissolving in both strong basic and acidic solutions. The other (, , and ) have varied applications in electronics and optics. (, , and ), ξ8 the peroxide (), the hydride (), and the carbide () are also known. Of the four , has the most ionic character, whereas the others (, , and ) have relatively low melting points and are considered to have more covalent character.

In weak basic solutions containing ions, the hydroxide forms as a white . In stronger alkaline solutions, this hydroxide is dissolved to form zincates (). The nitrate , chlorate , sulfate , phosphate , molybdate , cyanide , arsenite , arsenate and the chromate (one of the few colored zinc compounds) are a few examples of other common inorganic compounds of zinc. ξ9 One of the simplest examples of an of zinc is the acetate ().

are those that contain zinc–carbon covalent bonds. Diethylzinc () is a reagent in synthetic chemistry. It was first reported in 1848 from the reaction of zinc and , and was the first compound known to contain a metal–carbon .


Ancient use
Various isolated examples of the use of impure zinc in ancient times have been discovered. Zinc ores were used to make the zinc–copper alloy brass many centuries prior to the discovery of zinc as a separate element. Judean brass from the 14th to 10th centuries BC contains 23% zinc. Knowledge of how to produce brass spread to by the 7th century BC but few varieties were made. Ornaments made of that contain 80–90% zinc with lead, iron, , and other metals making up the remainder, have been found that are 2500 years old. A possibly prehistoric statuette containing 87.5% zinc was found in a archaeological site.

The oldest known pills were made of the zinc carbonates hydrozincite and smithsonite. The pills were used for sore eyes, and were found aboard the roman ship , which wrecked in 140 BC.

The manufacture of brass was known to the by about 30 BC. They made brass by heating powdered (zinc or carbonate), charcoal and copper together in a crucible. The resulting was then either cast or hammered into shape and was used in weaponry. Some coins struck by Romans in the Christian era are made of what is probably calamine brass.

, in a passage taken from an earlier writer of the 4th century BC, mentions "drops of false silver", which when mixed with copper make brass. This may refer to small quantities of zinc by-product of smelting ores. ξ10 Zinc in such remnants in melting ovens was usually discarded, as it was thought to be worthless. The is a votive plaque dating to made of an alloy that is mostly zinc.

The , thought to have been written in 500 BC or before, mentions a metal which, when oxidized, produces pushpanjan, thought to be zinc oxide. ξ10 Zinc mines at Zawar, near in India, have been active since the . The smelting of metallic zinc here however appears to have begun around the 12th century AD.p. 46, Ancient mining and metallurgy in Rajasthan, S. M. Gandhi, chapter 2 in Crustal Evolution and Metallogeny in the Northwestern Indian Shield: A Festschrift for Asoke Mookherjee, M. Deb, ed., Alpha Science Int'l Ltd., 2000, ISBN 1-84265-001-7. One estimate is that this location produced an estimated million tonnes of metallic zinc and zinc oxide from the 12th to 16th centuries. Another estimate gives a total production of 60,000 tonnes of metallic zinc over this period. The , written in approximately the 13th century AD, mentions two types of zinc-containing ores; one used for metal extraction and another used for medicinal purposes.

Early studies and naming
Zinc was distinctly recognized as a metal under the designation of Yasada or Jasada in the medical Lexicon ascribed to the Hindu king and written about the year 1374. (public domain text) Smelting and extraction of impure zinc by reducing calamine with wool and other organic substances was accomplished in the 13th century in India. The Chinese did not learn of the technique until the 17th century.

burned zinc metal in air and collected the resulting zinc oxide on a . Some alchemists called this zinc oxide lana philosophica, Latin for "philosopher's wool", because it collected in wooly tufts while others thought it looked like white snow and named it nix album.

The name of the metal was probably first documented by , a Swiss-born German alchemist, who referred to the metal as "zincum" or "zinken" in his book Liber Mineralium II, in the 16th century. ξ11 The word is probably derived from the German zinke, and supposedly meant "tooth-like, pointed or jagged" (metallic zinc crystals have a needle-like appearance). ξ12 Zink could also imply "tin-like" because of its relation to German zinn meaning tin. ξ13 Yet another possibility is that the word is derived from the word سنگ seng meaning stone. ξ14 The metal was also called Indian tin, tutanego, calamine, and spinter.

German metallurgist received a quantity of what he called "calay" of Malabar from a cargo ship captured from the Portuguese in 1596. ξ15 Libavius described the properties of the sample, which may have been zinc. Zinc was regularly imported to Europe from the Orient in the 17th and early 18th centuries, but was at times very expensive.An ship carrying a cargo of nearly pure zinc metal from the Orient sank off the coast in 1745.

The isolation of metallic zinc in the West may have been achieved independently by several people. Universal Dictionary, a contemporary source giving technological information in Europe, did not mention zinc before 1751 but the element was studied before then.

Flemish metallurgist P.M. de Respour reported that he extracted metallic zinc from zinc oxide in 1668. By the start of the 18th century, described how zinc oxide condenses as yellow crystals on bars of iron placed above zinc ore being smelted. In Britain, is said to have carried out experiments to smelt zinc, probably at , prior to his bankruptcy in 1726.

In 1738, patented in Great Britain a process to extract zinc from calamine in a vertical style smelter. ξ16 His technology was somewhat similar to that used at Zawar zinc mines in but there is no evidence that he visited the Orient. Champion's process was used through 1851.

German chemist normally gets credit for discovering pure metallic zinc even though Swedish chemist Anton von Swab distilled zinc from calamine four years before. In his 1746 experiment, Marggraf heated a mixture of calamine and charcoal in a closed vessel without copper to obtain a metal. This procedure became commercially practical by 1752.

Later work
William Champion's brother, John, patented a process in 1758 for zinc sulfide into an oxide usable in the retort process. Prior to this only calamine could be used to produce zinc. In 1798, improved on the smelting process by building the first horizontal retort smelter. ξ17 Jean-Jacques Daniel Dony built a different kind of horizontal zinc smelter in Belgium, which processed even more zinc.

Italian doctor discovered in 1780 that connecting the of a freshly dissected frog to an iron rail attached by a brass hook caused the frog's leg to twitch. ξ18 He incorrectly thought he had discovered an ability of nerves and muscles to create and called the effect "". The galvanic cell and the process of galvanization were both named for Luigi Galvani and these discoveries paved the way for , galvanization and .

Galvani's friend, , continued researching this effect and invented the in 1800. The basic unit of Volta's pile was a simplified , which is made of a plate of copper and a plate of zinc connected to each other externally and separated by an . These were stacked in series to make the Voltaic cell, which in turn produced electricity by directing from the zinc to the copper and allowing the zinc to corrode.

The non-magnetic character of zinc and its lack of color in solution delayed discovery of its importance to biochemistry and nutrition. This changed in 1940 when , an enzyme that scrubs carbon dioxide from blood, was shown to have zinc in its . The digestive enzyme became the second known zinc-containing enzyme in 1955.


Mining and processing
Top zinc output countries 2010

Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper with an annual production of about 12 million tonnes. The world's largest zinc producer is , a merger of the Australian and the Belgian . About 70% of the world's zinc originates from mining, while the remaining 30% comes from recycling secondary zinc. Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure.

Worldwide, 95% of the zinc is mined from ore deposits, in which sphalerite ZnS is nearly always mixed with the sulfides of copper, lead and iron. There are zinc mines throughout the world, with the main mining areas being China, Australia and Peru. China produced 29% of the global zinc output in 2010.

Zinc metal is produced using . ξ19 After grinding the ore, , which selectively separates minerals from by taking advantage of differences in their , is used to get an ore concentrate. A final concentration of zinc of about 50% is reached by this process with the remainder of the concentrate being sulfur (32%), iron (13%), and (5%).

converts the zinc sulfide concentrate produced during processing to zinc oxide: ξ20

2 ZnS 3 → 2 ZnO 2

The sulfur dioxide is used for the production of sulfuric acid, which is necessary for the leaching process. If deposits of zinc carbonate, zinc silicate or zinc spinel, like the in Namibia are used for zinc production the roasting can be omitted.

For further processing two basic methods are used: or . Pyrometallurgy processing reduces zinc oxide with or at into the metal, which is distilled as zinc vapor. ξ21 The zinc vapor is collected in a condenser. The below set of equations demonstrate this process:

2 ZnO C → 2 Zn
ZnO CO → Zn

Electrowinning processing leaches zinc from the ore concentrate by : ξ22

ZnO →

After this step is used to produce zinc metal.

2 2 → 2 Zn 2

The sulfuric acid regenerated is recycled to the leaching step.

Environmental impact
The production for sulfidic zinc ores produces large amounts of sulfur dioxide and vapor. Smelter and other residues of process also contain significant amounts of heavy metals. About 1.1 million tonnes of metallic zinc and 130 thousand tonnes of lead were mined and smelted in the Belgian towns of and between 1806 and 1882. The dumps of the past mining operations leach significant amounts of zinc and cadmium, and, as a result, the sediments of the contain significant amounts of heavy metals. About two thousand years ago emissions of zinc from mining and smelting totaled 10 thousand tonnes a year. After increasing 10-fold from 1850, zinc emissions peaked at 3.4 million tonnes per year in the 1980s and declined to 2.7 million tonnes in the 1990s, although a 2005 study of the Arctic troposphere found that the concentrations there did not reflect the decline. Anthropogenic and natural emissions occur at a ratio of 20 to 1.

Levels of zinc in rivers flowing through industrial or mining areas can be as high as 20 ppm. Effective greatly reduces this; treatment along the , for example, has decreased zinc levels to 50 ppb. Concentrations of zinc as low as 2 ppm adversely affects the amount of oxygen that fish can carry in their blood. ξ23

with zinc through the mining of zinc-containing ores, refining, or where zinc-containing sludge is used as fertilizer, can contain several grams of zinc per kilogram of dry soil. Levels of zinc in excess of 500 ppm in soil interfere with the ability of plants to absorb other , such as iron and . Zinc levels of 2000 ppm to 180,000 ppm (18%) have been recorded in some soil samples.

Major applications of zinc include (numbers are given for the US)
  1. (55%)
  2. Alloys (21%)
  3. and (16%)
  4. Miscellaneous (8%)

Anti-corrosion and batteries
The metal is most commonly used as an anti-corrosion agent. Galvanization, which is the coating of or to protect the metals against , is the most familiar form of using zinc in this way. In 2009 in the United States, 55% or 893 thousand tonnes of the zinc metal was used for galvanization.

Zinc is more reactive than iron or steel and thus will attract almost all local oxidation until it completely corrodes away. A protective surface layer of oxide and carbonate ( forms as the zinc corrodes. This protection lasts even after the zinc layer is scratched but degrades through time as the zinc corrodes away. The zinc is applied electrochemically or as molten zinc by or spraying. Galvanization is used on chain-link fencing, guard rails, suspension bridges, lightposts, metal roofs, heat exchangers, and car bodies.

The relative reactivity of zinc and its ability to attract oxidation to itself makes it an efficient in (CP). For example, cathodic protection of a buried pipeline can be achieved by connecting anodes made from zinc to the pipe. Zinc acts as the (negative terminus) by slowly corroding away as it passes electric current to the steel pipeline.Electric current will naturally flow between zinc and steel but in some circumstances inert anodes are used with an external DC source. Zinc is also used to cathodically protect metals that are exposed to sea water from corrosion. A zinc disc attached to a ship's iron rudder will slowly corrode while the rudder stays unattacked. Other similar uses include a plug of zinc attached to a propeller or the metal protective guard for the keel of the ship.

With a (SEP) of −0.76 , zinc is used as an anode material for batteries. (More reactive lithium (SEP −3.04 V) is used for anodes in ). Powdered zinc is used in this way in and sheets of zinc metal form the cases for and act as anodes in . ξ24 Zinc is used as the anode or fuel of the /fuel cell. ξ25

A widely used alloy which contains zinc is brass, in which copper is alloyed with anywhere from 3% to 45% zinc, depending upon the type of brass. Brass is generally more and stronger than copper and has superior . These properties make it useful in communication equipment, hardware, musical instruments, and water valves.

Other widely used alloys that contain zinc include , typewriter metal, soft and aluminium , and commercial . Zinc is also used in contemporary pipe organs as a substitute for the traditional lead/tin alloy in pipes. ξ26 Alloys of 85–88% zinc, 4–10% copper, and 2–8% aluminium find limited use in certain types of machine bearings. Zinc is the primary metal used in making since 1982. The zinc core is coated with a thin layer of copper to give the impression of a copper coin. In 1994, of zinc were used to produce 13.6 billion pennies in the United States.

Alloys of primarily zinc with small amounts of copper, aluminium, and magnesium are useful in as well as , especially in the automotive, electrical, and hardware industries. These alloys are marketed under the name . An example of this is . The low melting point together with the low of the alloy makes the production of small and intricate shapes possible. The low working temperature leads to rapid cooling of the cast products and therefore fast assembly is possible. Another alloy, marketed under the brand name Prestal, contains 78% zinc and 22% aluminium and is reported to be nearly as strong as steel but as malleable as plastic. ξ27 This of the alloy allows it to be molded using die casts made of ceramics and cement.

Similar alloys with the addition of a small amount of lead can be cold-rolled into sheets. An alloy of 96% zinc and 4% aluminium is used to make stamping dies for low production run applications for which ferrous metal dies would be too expensive. In building facades, roofs or other applications in which zinc is used as and for methods such as , or , zinc alloys with and copper are used. ξ3 Unalloyed zinc is too brittle for these kinds of manufacturing processes.

As a dense, inexpensive, easily worked material, zinc is used as a replacement. In the wake of , zinc appears in weights for various applications ranging from fishing ξ28 to and flywheels.

(CZT) is a alloy that can be divided into an array of small sensing devices. These devices are similar to an and can detect the energy of incoming photons. When placed behind an absorbing mask, the CZT sensor array can also be used to determine the direction of the rays. ξ29

Other industrial uses
Roughly one quarter of all zinc output in the United States (2009), is consumed in the form of zinc compounds; a variety of which are used industrially. Zinc oxide is widely used as a white pigment in paints, and as a in the manufacture of rubber. It is also used as a heat disperser for the rubber and acts to protect its polymers from (the same UV protection is conferred to plastics containing zinc oxide). The properties of zinc oxide make it useful in and photocopying products. ξ30 The is a two step process based on zinc and zinc oxide for .

is often added to lumber as a and can be used as a wood . It is also used to make other chemicals. () is used in a number of organic . (ZnS) is used in pigments such as on the hands of clocks, and television screens, and . Crystals of ZnS are used in that operate in the mid- part of the spectrum. ξ31 is a chemical in and pigments. is used in paints.

Zinc powder is sometimes used as a in . When a compressed mixture of 70% zinc and 30% powder is ignited there is a violent chemical reaction. This produces zinc sulfide, together with large amounts of hot gas, heat, and light. Zinc sheet metal is used to make zinc .

, the most abundant isotope of zinc, is very susceptible to , being into the highly radioactive , which has a half-life of 244 days and produces intense . Because of this, Zinc Oxide used in nuclear reactors as an anti-corrosion agent is depleted of before use, this is called . For the same reason, zinc has been proposed as a material for ( is another, better-known salting material). A jacket of would be irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, forming a large amount of significantly increasing the radioactivity of the weapon's . Such a weapon is not known to have ever been built, tested, or used. is also used as a to study how alloys that contain zinc wear out, or the path and the role of zinc in organisms. ξ32

Zinc dithiocarbamate complexes are used as agricultural ; these include , Metiram, Propineb and Ziram. ξ33 Zinc naphthenate is used as wood preservative. ξ34 Zinc, in the form of , is also used as an anti-wear additive for metal parts in engine oil.

Dietary supplement
Zinc is included in most single tablet over-the-counter daily vitamin and supplements. ξ35 Preparations include zinc oxide, zinc acetate, and . It is believed to possess properties, which may protect against accelerated aging of the skin and muscles of the body; studies differ as to its effectiveness. ξ36 Zinc also helps speed up the healing process after an injury. It is also suspected of being beneficial to the body's immune system. Indeed, zinc deficiency may have effects on virtually all parts of the human immune system.

Zinc deficiency has been associated with (MDD) and may be an effective treatment.

Zinc serves as a simple, inexpensive, and critical tool for treating diarrheal episodes among children in the developing world. Zinc becomes depleted in the body during , but recent studies suggest that replenishing zinc with a 10- to 14-day course of treatment can reduce the duration and severity of diarrheal episodes and may also prevent future episodes for up to three months.

The determined that zinc can be part of an effective treatment for . Zinc supplementation is an effective treatment for , a genetic disorder affecting zinc absorption that was previously fatal to babies born with it.

is strongly attenuated by ingestion of zinc, and this effect could be due to direct antimicrobial action of the zinc ions in the , or to the absorption of the zinc and re-release from immune cells (all secrete zinc), or both. In 2011, researchers at reported that dietary zinc supplements can mask the presence of drugs in urine. Similar claims have been made in web forums on that topic.

Although not yet tested as a therapy in humans, a growing body of evidence indicates that zinc may preferentially kill prostate cancer cells. Because zinc naturally homes to the prostate and because the prostate is accessible with relatively non-invasive procedures, its potential as a chemotherapeutic agent in this type of cancer has shown promise. However, other studies have demonstrated that chronic use of zinc supplements in excess of the recommended dosage may actually increase the chance of developing prostate cancer, also likely due to the natural buildup of this heavy metal in the prostate.

Zinc lozenges and the common cold
There is strong evidence that zinc lozenges shorten the duration of colds. The most positive results have been found in studies in which was used, apparently because acetate does not bind zinc ions. Three high dose trials which used zinc acetate found an average 42% reduction in the duration of colds.

There is no concern of in the dosages that were used in the zinc acetate trials with 80–100 mg/day of elemental zinc. The effect of zinc lozenges seems to take place locally in the so that it is not a systemic effect, i.e., the effect is not a dietary supplement effect.

Topical use
of zinc preparations include ones used on the skin, often in the form of . Zinc preparations can protect against in the summer and in the winter. Applied thinly to a baby's diaper area () with each diaper change, it can protect against .

Zinc lactate is used in toothpaste to prevent . is widely applied in shampoos because of its anti-dandruff function. Zinc ions are effective even at low concentrations.

Organic chemistry
There are many important . Organozinc chemistry is the science of organozinc compounds describing their physical properties, synthesis and reactions. ξ37 ξ38 ξ39 ξ40 Among important applications is the Frankland-Duppa Reaction in which an (ROCOCOOR) reacts with an R'X, zinc and to the α-hydroxycarboxylic esters RR'COHCOOR, the which converts α-halo-esters and aldehydes to β-hydroxy-esters, the in which the carbenoid (iodomethyl)zinc iodide reacts with alkene(or alkyne) and converts them to cyclopropane, the of organozinc compounds to compounds. The (1899) which is the zinc equivalent of the magnesium and is better of the two. In presence of just about any water the formation of the organomagnesium halide will fail whereas the Barbier reaction can even take place in water. On the downside organozincs are much less nucleophilic than Grignards, are expensive and difficult to handle. Commercially available diorganozinc compounds are , and diphenylzinc. In one studyIn this is converted to by reaction with 4 equivalents of , then transmetalation with forms diphenylzinc which continues to react in an first with the and then with 2-naphthylaldehyde to the . In this reaction formation of diphenylzinc is accompanied by that of , which unchecked, catalyses the reaction without MIB involvement to the . The salt is effectively removed by with (TEEDA) resulting in an of 92%. the active organozinc compound is obtained from much cheaper precursors:

The is also an important reaction for the formation of new carbon carbon bonds between unsaturated carbon atoms in alkenes, arenes and alkynes. The catalysts are nickel and palladium. A key step in the is a in which a zinc halide exchanges its organic substituent for another halogen with the palladium (nickel) metal center. The is another coupling reaction but this one with a thioester as reactant forming a ketone.

Biological role
Zinc is an essential , necessary for plants, animals, and .Zinc's role in microorganisms is particularly reviewed in: Zinc is found in nearly 100 specific (other sources say 300), serves as structural ions in and is stored and transferred in . It is "typically the second most abundant transition metal in organisms" after iron and it is the only metal which appears in all .

In proteins, Zn ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult.

There are 2-4 grams of zinc distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. ξ41 Semen is particularly rich in zinc, which is a key factor in function and growth. ξ42

In humans, zinc plays "ubiquitous biological roles". It interacts with "a wide range of organic ", and has roles in the metabolism of RNA and DNA, , and . It also regulates . A 2006 study estimated that about 10% of human proteins (2800) potentially bind zinc, in addition to hundreds which transport and traffic zinc; a similar study in the plant Arabidopsis thaliana found 2367 zinc-related proteins.

In the brain, zinc is stored in specific by neurons and can "modulate brain excitability". It plays a key role in and so in learning. However it has been called "the brain's dark horse" since it also can be a , suggesting zinc plays a critical role in normal functioning of the brain and .

Zinc is an efficient , making it a useful catalytic agent in and other enzymatic reactions. The metal also has a flexible , which allows proteins using it to rapidly shift to perform biological reactions. ξ43 Two examples of zinc-containing enzymes are and , which are vital to the processes of () regulation and digestion of proteins, respectively.

In vertebrate blood, carbonic anhydrase converts into bicarbonate and the same enzyme transforms the bicarbonate back into for exhalation through the lungs. ξ44 Without this enzyme, this conversion would occur about one million times slower at the normal blood of 7 or would require a pH of 10 or more. The non-related β-carbonic anhydrase is required in plants for leaf formation, the synthesis of indole (auxin) and .

Carboxypeptidase cleaves peptide linkages during digestion of proteins. A is formed between the terminal peptide and a C=O group attached to zinc, which gives the carbon a positive charge. This helps to create a pocket on the enzyme near the zinc, which attracts the non-polar part of the protein being digested.

Other proteins
Zinc serves a purely structural role in , twists and clusters. Zinc fingers form parts of some , which are proteins that recognize during the replication and transcription of . Each of the nine or ten ions in a zinc finger helps maintain the finger's structure by coordinately binding to four in the transcription factor. The transcription factor wraps around the DNA helix and uses its fingers to accurately bind to the DNA sequence.

In , zinc is bound to and transported by (60%, low-affinity) and (10%). Since transferrin also transports iron, excessive iron reduces zinc absorption, and vice-versa. A similar reaction occurs with copper. ξ45 The concentration of zinc in blood plasma stays relatively constant regardless of zinc intake. Cells in the salivary gland, prostate, immune system and intestine use as one way to communicate with other cells.

Zinc may be held in reserves within microorganisms or in the intestines or liver of animals. Metallothionein in intestinal cells is capable of adjusting absorption of zinc by 15–40%. ξ46 However, inadequate or excessive zinc intake can be harmful; excess zinc particularly impairs copper absorption because metallothionein absorbs both metals.

Dietary intake
In the U.S., the (RDA) is 8 mg/day for women and 11 mg/day for men. ξ47 Median intake in the U.S. around 2000 was 9 mg/day for women and 14 mg/day in men. Oysters, lobster and red meats, especially , and have some of the highest concentrations of zinc in food.

Zinc supplements should only be ingested when there is zinc deficiency or increased zinc necessity (e.g. after , or ).Colin Tidy: Zinc Supplements. 2010-03-22. Retrieved on 2013-11-02. Burgerstein Zinktabletten 15 mg. In: Arzneimittel-Kompendium der Schweiz. 2009-09-07. Retrieved on 2013-11-02. (German) Persistent intake of high doses of zinc can cause copper deficiency.

The concentration of zinc in plants varies based on levels of the element in soil. When there is adequate zinc in the soil, the food plants that contain the most zinc are wheat (germ and bran) and various seeds (, , , , ). ξ48 Zinc is also found in , , , , , and .

Other sources include and , which come in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body. This review cited studies which found low plasma zinc concentrations after zinc oxide and zinc carbonate were consumed compared with those seen after consumption of zinc acetate and sulfate salts. However, harmful excessive supplementation is a problem among the relatively affluent, and should probably not exceed 20 mg/day in healthy people, although the U.S. National Research Council set a Tolerable Upper Intake of 40 mg/day.

For fortification, however, a 2003 review recommended zinc oxide in cereals as cheap, stable, and as easily absorbed as more expensive forms. A 2005 study found that various compounds of zinc, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortificants to maize tortillas. A 1987 study found that zinc picolinate was better absorbed than zinc gluconate or zinc citrate. However, a study published in 2008 determined that is the best absorbed of the four dietary supplement types available.

Zinc deficiency is usually due to insufficient dietary intake, but can be associated with , , chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses. Symptoms of mild zinc deficiency are diverse. Clinical outcomes include depressed growth, diarrhea, impotence and delayed sexual maturation, , eye and skin lesions, impaired appetite, altered cognition, impaired host defense properties, defects in carbohydrate utilization, and reproductive teratogenesis. Mild zinc deficiency depresses immunity, although excessive zinc does also. Animals with a diet deficient in zinc require twice as much food in order to attain the same weight gain as animals given sufficient zinc.

Groups at risk for zinc deficiency include the elderly, children in developing countries, and those with renal insufficiency. The zinc , found in seeds and , can contribute to zinc malabsorption.

Despite some concerns,"Position of the American Dietetic Association and Dietitians of Canada: Vegetarian diets". Journal of the American Dietetic Association, 2003, 06. Retrieved 4 January 2007. western vegetarians and vegans have not been found to suffer from overt zinc deficiencies any more than meat-eaters. Major plant sources of zinc include cooked dried beans, sea vegetables, fortified cereals, soyfoods, nuts, peas, and seeds. However, phytates in many whole-grains and fiber in many foods may interfere with zinc absorption and marginal zinc intake has poorly understood effects. There is some evidence to suggest that more than the US RDA (15 mg) of zinc daily may be needed in those whose diet is high in phytates, such as some vegetarians. These considerations must be balanced against the fact that there is a paucity of adequate zinc , and the most widely used indicator, plasma zinc, has poor . Diagnosing zinc deficiency is a persistent challenge.

Nearly two billion people in the developing world are deficient in zinc. In children it causes an increase in infection and diarrhea, contributing to the death of about 800,000 children worldwide per year. The World Health Organization advocates zinc supplementation for severe malnutrition and diarrhea. Zinc supplements help prevent disease and reduce mortality, especially among children with low birth weight or stunted growth. However, zinc supplements should not be administered alone, since many in the developing world have several deficiencies, and zinc interacts with other micronutrients.

Soil remediation
The Ericoid Mycorrhizal Fungi Calluna, Erica and Vaccinium can grow in zinc metalliferous soils.

Zinc deficiency is crop plants' most common micronutrient deficiency; it is particularly common in high-pH soils. Zinc-deficient is in the cropland of about half of Turkey and India, a third of China, and most of Western Australia, and substantial responses to zinc fertilization have been reported in these areas. Plants that grow in soils that are zinc-deficient are more susceptible to disease. Zinc is primarily added to the soil through the weathering of rocks, but humans have added zinc through fossil fuel combustion, mine waste, phosphate fertilizers, limestone, manure, sewage sludge, and particles from galvanized surfaces. Excess zinc is toxic to plants, although zinc toxicity is far less widespread.


Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption. The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish. The Free Ion Activity Model is well-established in the literature, and shows that just amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all in water.

The free zinc ion is a powerful up to the point of being . Stomach acid contains , in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post-1982 American one piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.

There is evidence of induced at low intakes of 100–300 mg Zn/day; a recent trial had higher hospitalizations for urinary complications compared to placebo among elderly men taking 80 mg/day. The is 11 and 8 mg Zn/day for men and women, respectively. Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or adversely affect cholesterol. Levels of zinc in excess of 500 ppm in soil interfere with the ability of plants to absorb other essential metals, such as iron and manganese. There is also a condition called the or "zinc chills" that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of materials. Zinc is a common ingredient of cream which may contain between 17 and 38 mg of zinc per gram. There have been cases of disability or even death due to excessive use of these products.

The U.S. (FDA) has stated that zinc damages nerve receptors in the nose, which can cause . Reports of anosmia were also observed in the 1930s when zinc preparations were used in a failed attempt to prevent infections. ξ49 On June 16, 2009, the FDA said that consumers should stop using zinc-based intranasal cold products and ordered their removal from store shelves. The FDA said the loss of smell can be life-threatening because people with impaired smell cannot detect leaking gas or smoke and cannot tell if food has spoiled before they eat it. Recent research suggests that the topical antimicrobial zinc pyrithione is a potent response inducer that may impair genomic integrity with induction of -dependent energy crisis in cultured human and .

In 1982, the began minting coated in copper but made primarily of zinc. With the new zinc pennies, there is the potential for zinc toxicosis, which can be fatal. One reported case of chronic ingestion of 425 pennies (over 1 kg of zinc) resulted in death due to gastrointestinal bacterial and fungal , while another patient, who ingested 12 grams of zinc, only showed and (gross lack of coordination of muscle movements). Several other cases have been reported of humans suffering zinc intoxication by the ingestion of zinc coins.

Pennies and other small coins are sometimes ingested by dogs, resulting in the need for medical treatment to remove the foreign body. The zinc content of some coins can cause zinc toxicity, which is commonly fatal in dogs, where it causes a severe , and also liver or kidney damage; vomiting and diarrhea are possible symptoms. Zinc is highly toxic in and poisoning can often be fatal. The consumption of fruit juices stored in galvanized cans has resulted in mass parrot poisonings with zinc.

See also



External links

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