Molybdenum

Definition

Purpose

Description

Precautions

Interactions

Aftercare

Complications

Parental concerns

Resources

Definition

Molybdenum is a trace element considered a micronutrient, meaning a nutrient needed in very small amounts. It is required by almost all living organisms and works as a cofactor for enzymes that carry out important chemical transformations in the global carbon, nitrogen, and sulfur cycles. Thus, molybdenum-dependent enzymes are not only required for the health of people, but also for the health of ecosystems.

Purpose

Molybdenum is an essential trace mineral considered essential in human nutrition. This is because, as tiny as the required amounts are, the consequences of their absence (deficiency) are severe. The active biological form of molybdenum is known as the molybdenum cofactor. It is found in several tissues of the human body and is required for the activity of enzymes that are involved in eliminating toxic substances, including the catabolism of purines, which produces uric acid, formed primarily in the liver and excreted by the kidney into the urine. In addition to being a cofactor of enzymes involved in purine and pyrimidine detoxification, molybdenum also has therapeutic uses, being used in the treatment of:

• Molybdenum deficiency
• Molybdenum cofactor deficiency, a disease in which deficiency of the molybdenum cofactor causes severe neurological abnormalities, and mental retardation.
• Copper poisoning.
• Improper carbohydrate metabolism.

Recent research findings suggest that molybdenum may also have a role in stabilizing the unoccupied

Molybdenum

mcg=microgram

(Illustration by GGS Information Services/Thomson Gale.)

glucocorticoid receptor. Glucocorticoids are naturally–produced steroid hormones, that inhibit the process of inflammation. Their shape permits them to move across the membrane that surrounds cells in the body, and to be recognized by molecules inside the cell called glucocorticoid receptors.

Description

The body absorbs molybdenum quickly in the stomach and in the small intestine. The mechanism of absorption is uncertain. Following absorption, molybdenum is transported by the blood to the liver and to other tissues of the body. In the molybdate form, it is carried in the blood bound to alpha–macro-globulin and by adsorption to red blood cells. The liver and kidney store the highest amounts of molybdenum. The molybdenum cofactor is made in cells and consists of a molybdenum atom bound to tricyclic pyranopterin molecules, the simplest of which is known as molybdopterin. The cofactor is a component of four main enzymes:

• Sulfite oxidase. This enzyme catalyzes the transformation of sulfite to sulfate, a reaction that is necessary for the metabolism of sulfur-containing amino acids, such as cysteine.
• Xanthine oxidase. This enzyme catalyzes the breakdown of nucleotides (precursors of DNA and RNA) to form uric acid, which contributes to the antioxidant capacity of the blood.
• Aldehyde oxidase. This enzyme is involved in several reactions, including the catabolism of pyrimidines.
• Xanthine dehydrogenase. This enzyme catalyzes the conversion of hypoxanthine to xanthine, and xanthine to uric acid.

Aldehyde oxidase and xanthine oxidase catalyze hydroxylation reactions involving a number of different molecules with similar structures. Xanthine oxidase and aldehyde oxidase also play a role in the metabolism of drugs and toxins. However, according to the Micronutrient Information Center of the Linus Pauling Institute of Oregon State University, only sulfite oxidase is known to be crucial for human health.

Sources of dietary molybdenum include milk, dried beans, peas, nuts and seeds, eggs, liver tomatoes, carrots and meats. The molybdenum contents are per cup:

• Navy beans: 196 μg
• Black-eye peas: 180 μg
• Lentils: 148 μg
• Split peas: 148 μg
• Lima beans: 142 μg
• Kidney beans: 132 μg
• Black beans: 130 μg
• Almonds: 46.4 μg
• Peanuts: 42.4 μg
• Chestnuts: 42.4 μg
• Cashews: 38 μg
• Yogurt: 11.3 μg
• cooked egg: 9 μg
• Green soybeans: 12.8 μg
• Cottage cheese: 10.4 μg
• Milk: 4.9 μg
• Fresh tomatoes: 9 μg
• Veal liver: 8.9 μg per 3.5 oz-serving

The recommended dietary allowance (RDA) for molybdenum was most recently revised in January 2001:

• Infants: (0-6 months): 2 μg
• Infants: (7-12 months): 3 μg.
• Children (1-3 y): 17 μg

KEY TERMS

Acetaminophen —An aspirin substitute that works as a pain killer and fever reducer, but does not have anti–inflammatory properties and does not produce the side effects associated with aspirin, such as stomach irritation.

Amino acid —Organic (carbon–containing) molecules that serve as the building blocks of proteins.

Antioxidant —Any substance that prevents or reduces damage caused by reactive oxygen species (ROS) or reactive nitrogen species (RNS).

Antioxidant enzyme —An enzyme that can counteract the damaging effects of oxygen in tissues.

Catabolism —The metabolic breakdown of large molecules in living organism, with accompanying release of energy.

Chelation therapy —The use of a ring–shaped compound called a chelating agent, that can form complexes with a circulating metal and assisting in its removal from the body.

Cofactor —A compound that is essential for the activity of an enzyme.

Blood brain barrier —A physiological mechanism that alters the permeability of brain capillaries, so that some substances, such as certain drugs, are prevented from entering brain tissue, while other substances are allowed to enter freely.

Detoxification —The process of detoxifying, meaning the removal of toxic substances.

Enzyme —A biological catalyst, meaning a substance that increases the speed of a chemical reaction without being changed in the overall process. Enzymes are proteins and vitally important to the regulation of the chemistry of cells and organisms.

Gout —Painful inflammation of the big toe and foot caused by an abnormal uric acid catabolism resulting in deposits of the acid and its salts in the blood and joints.

Hyperuricemia —Abnormally elevated blood level of uric acid, the breakdown product of purines that are part of many foods we eat.

Inflammation —A response of body tissues to injury or irritation characterized by pain and swelling and redness and heat.

Macro minerals —Minerals that are needed by the body in relatively large amounts. They include sodium, potassium, chlorine, calcium, phosphorus, magnesium.

Macronutrients —Nutrients needed by the body in large amounts. They include proteins, carbohydrates and fats.

Metabolism —The sum of the processes (reactions) by which a substance is assimilated and incorporated

• Children (4-8 y): 22 μg
• Children (9-13 y): 34 μg
• Adolescents (14-18): 43 μg
• Adults: 45 μg
• Pregnancy: 50 μg
• Lactation: 50 μg

Molybdenum in nutritional supplements is available in the form of sodium molybdate or ammonium molybdate. Molybdenum in food is principally in the form of the organic molybdenum cofactors. The efficiency of absorption of nutritional molybdenum in supplements ranges from 88-93%, and the efficiency of absorption of molybdenum from foods ranges from 57-88%.

Precautions

Pregnant women and nursing mothers should be careful not to use supplemental molybdenum in amounts greater than RDA amounts. Those with excess build–up of uric acid in the blood (hyperuricemia) or gout should also exercise caution in the use of supplements. Overall, it is believed that the toxicity of molybdenum compounds appears to be relatively low in humans. The Food and Nutrition Board (FNB) of the Institute of Medicine found little evidence that molybdenum excess was associated with adverse health effects in healthy people. Hyperuricemia and gout–like symptoms have only been reported in occupationally exposed workers in a copper–molybdenum plant and in an Armenian population consuming 10– 15 mg of molybdenum from food daily. Other studies report that blood and urinary uric acid levels were not elevated by molybdenum intakes of up to 1.5 mg/day.

Dietary molybdenum deficiency has never been observed in healthy people. Molybdenum cofactor deficiency and isolated sulfite oxidase deficiency are the only two disorders associated with this trace

into the body or detoxified and excreted from the body.

Micronutrients —Nutrients needed by the body in small amounts. They include vitamins and miberals.

Molybdenum cofactor deficiency —An inherited disorder in which deficiency of the molybdenum cofactor causes deficiency of a variety of enzymes, resulting in severe neurological abnormalities, dislocated ocular lenses, mental retardation, xanthinu-ria, and early death.

Molybdopterin —The chemical group associated with the molybdenum atom of the molybdenum cofactor found in molybdenum–containing enzymes.

Nucleotide —A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA).

Plasma —The liquid part of the blood and lymphatic fluid, which makes up about half of its volume. It is 92% water, 7% protein and 1% minerals.

Protein —Biological molecules that consist of strings of smaller units called amino acids, the “building blocks” of proteins. In proteins, amino acids are linked together in sequence as polypeptide chains that fold into compact shapes of various sizes. Proteins are required for the structure, function, and regulation of the body’s cells, tissues, and organs, and each protein has unique functions.

Purines —Components of certain foods that are transformed into uric acid in the body.

Pyrimidine —A nitrogen–containing, double–ring, basic compound that occurs in nucleic acids.

Recommended dietary allowance (RDA —The levels of intake of essential nutrients judged on the basis of scientific knowledge to be adequate to meet the nutrient needs of healthy persons by the Food and Nutrition Board of the National Research Council/National Academy of Sciences. The RDA is updated periodically to reflect new knowledge. It is popularly called the Recommended Daily Allowance.

Toxic —Harmful or poisonous substance.

Toxin —A poisonous substance, especially a protein, that is produced by living cells or organisms and is capable of causing disease.

Trace minerals —Minerals needed by the body in small amounts. They include: selenium, iron, zinc, copper, manganese, molybdenum, chromium, arsenic, germanium, lithium, rubidium, tin.

Vitamin E —A fat–soluble vitamin essential for good health found chiefly in plant leaves, and wheat.

element. Molybdenum cofactor deficiency disorder is severe and usually results in premature death in early childhood since all of the molybdenum cofactor– dependent enzymes are affected. Isolated sulfite oxidase deficiency only affcets sulfite oxidase activity. Together, molybdenum cofactor deficiency and isolated sulfite oxidase deficiency have been diagnosed in more than 100 individuals worldwide. They are, however, both inherited disorders and there are no documented cases of their ever occurring as a result of dietary molybdenum deficiency.

Interactions

Studies have shown that high doses of molybdate inhibit the metabolism of acetaminophen in rats. However, it is not known whether this occurs at clinically relevant doses in humans. High doses of molybdate may also lower the absorption of copper. Likewise, high doses of copper may lower the absorption of molybdenum and decrease overall molybdenum levels.

Aftercare

There is only one report of acute poisoning resulting from intake of a dietary molybdenum supplement. The person consumed a total dose of 13.5 mg of molybdenum over a period of 18 days, at an intake rate of 300–800 μg daily, resulting in visual and auditory hallucinations, several petit mal seizures and one grand mal seizure. The subject was treated with chela-tion therapy to remove the molybdenum from his body and his symptoms disappeared after several hours.

Complications

With molybdenum deficiency being extremely unlikely, molybdenum–related complications are only possible with molybdenum toxicity that may result in gout. High molybdenum levels in people with low copper levels may cause copper deficiency symptoms, but are easily treated with diet readjustments.

Parental concerns

The RDA for molybdenum (17–22 μg for children) is sufficient to prevent deficiency. Although the precise amount of molybdenum required to most likely promote optimum health is not known, there is presently no evidence that intakes higher than the RDA are beneficial. Most people in the United States consume more than sufficient molybdenum in their diets, making supplementation unnecessary. If required, it should be noted that the amount of molybdenum presently found in most multivitamin/mineral supplements is higher than the RDA. It is however well below the tolerable upper intake level of 2,000 μ/day and is generally considered safe.

Resources

BOOKS

Bogden, J., ed. Clinical Nutrition of the Essential Trace Elements and Minerals (Nutrition and Health). Totowa, NJ: Humana Press, 2000.

Challem, J., Brown, L. User’s Guide to Vitamins & Minerals. Laguna Beach, CA: Basic Health Publications, 2002.

Garrison, R., Somer, E. The Nutrition Desk Reference. New York, NY: McGraw–Hill, 1998.

Griffith, H. W. Minerals, Supplements & Vitamins: The Essential Guide. New York, NY: Perseus Books Group, 2000.

Larson Duyff, R. ADA Complete Food and Nutrition Guide, 3rd ed.Chicago, IL: American Dietetic Association, 2006.

Newstrom, H. Nutrients Catalog: Vitamins, Minerals, Amino Acids, Macronutrients—Beneficials Use, Helpers, Inhibitors, Food Sources, Intake Recommendations. Jefferson, NC: McFarland & Company, 1993.

Quesnell, W. R. Minerals : The Essential Link to Health. Long Island, NY: Skills Unlimited Press, 2000.

Wapnir, R. A. Protein Nutrition and Mineral Absorption. Boca Raton, FL: CRC Press, 1990.

ORGANIZATIONS

American Dietetic Association (ADA). 120 South Riverside Plaza, Suite 2000, Chicago, IL 60606-6995. 1-800/877-1600. <www.eatright.org>.

American Society for Nutrition (ASN). 9650 Rockville Pike, Bethesda, MD 20814. (301) 634-7050. <www.nutrition.org>.

Office of Dietary Supplements, National Institutes of Health. National Institutes of Health, Bethesda, Maryland 20892 USA. <ods.od.nih.gov>.

U.S. Department of Agriculture, Food and Nutrition Information Center. National Agricultural Library,10301 Baltimore Avenue, Room 105, Belts-ville, MD 20705. (301) 504-5414. <www.nal.usda.gov>.

Monique Laberge, Ph.D.

MSUD seeMaple syrup urine disease

MyPyramid seeUSDA Food Guide Pyramid (MyPyramid)

MOLYBDENUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Molybdenum was one of the first metals to be discovered by a modern chemist. It was found in 1781 by Swedish chemist Peter Jacob Hjelm (1746-1813). Hjelm's work on the element was not published, however, until more than a century later.

Molybdenum is a transition metal, placing it in the center of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another.

Molybdenum is a hard, silvery metal with a very high melting point. It is used primarily to make alloys with other metals. An alloy is a mixture of two or more metals. The mixture has properties different from those of the individual metals. The most common alloys of molybdenum are those with steel. Molybdenum improves the strength, toughness, resistance to wear and corrosion, and ability to harden steel.

SYMBOL
Mo

ATOMIC NUMBER
42

ATOMIC MASS
95.94

FAMILY
Group 6 (VIB)
Transition metal

PRONUNCIATION
muh-LIB-duh-num

Discovery and naming

The most common ore of molybdenum is called molybdenite. Molybdenite contains a compound of molybdenum and sulfur, molybdenum disulfide (MoS₂). Molybdenum disulfide is a soft black powder that looks like graphite. Graphite is pure carbon; it makes up the "lead" in ordinary pencils. In fact, earlier chemists thought that graphite and molybdenum disulfide were the same material.

The soft "squishy" character of molybdenum disulfide frustrated early researchers of the compound. Chemists often grind up a material before trying to dissolve it in acids or other liquids. But molybdenum disulfide cannot be ground up. The material just slides out of the way.

It was not until 1781 that Hjelm found a way to work with the compound. He discovered that it was very different from graphite. In fact, he found that it contained an entirely new element. The name chosen for the new element illustrates a further confusion. In Greek, the word for lead is molybdos. The name chosen for the new element, molybdenum, is actually the Greek word for lead!

Hjelm's work was known to his fellow chemists because of letters they had written each other. But the report of his discovery was not actually printed for all chemists to read until 1890. Between 1791 and 1891, Hjelm's research was repeated by other chemists. They confirmed what he discovered, and he is recognized today as the discoverer of molybdenum.

Physical properties

As a solid, molybdenum has a silvery-white metallic appearance. It more commonly occurs as a dark gray or black powder with a metallic luster. Its melting point is about 2,610°C (about 4,700°F) and the boiling point is 4,800 to 5,560°C (8,600 to 10,000°F). Its density is 10.28 grams per cubic centimeter.

Chemical properties

Molybdenum does not dissolve in most common chemical reagents. A chemical reagent is a substance used to study other substances, such as an acid or an alkali. For example, molybdenum does not dissolve in hydrochloric acid, hydrofluoric acid, ammonia, sodium hydroxide, or dilute sulfuric acid. These chemicals are reagents often used to test how reactive a substance is. Molybdenum does dissolve in hot strong sulfuric or nitric acids, however. The metal does not react with oxygen at room temperatures, but does react with oxygen at high temperatures.

Occurrence in nature

Molybdenum never occurs free in nature. Instead, it is always part of a compound. In addition to molybdenite, it occurs commonly as the mineral wulfenite (PbMo0₄). Its abundance in the Earth's crust is estimated to be about 1 to 1.5 parts per million. That makes it about as common as tungsten and many of the rare earth (lanthanide) elements. About two-thirds of all the molybdenum in the world comes from Canada, Chile, China, and the United States. In the United States, molybdenum ores are found primarily in Alaska, Colorado, Idaho, Nevada, New Mexico, and Utah.

Isotopes

Seven naturally occurring isotopes of molybdenum exist: molybdenum-92, molybdenum-94, molybdenum-95, molybdenum-96, molybdenum-97, molybdenum-98, and molybdenum-100. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

None of the seven naturally occurring molybdenum isotopes is radioactive. However, about a dozen artificial radioactive isotopes have been produced. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

One radioactive isotope of molybdenum is commonly used in medicine, molybdenum-99m. (The "m" in this instance stands for "metastable," which means the isotope does not last very long.) This isotope is not used directly, however. Instead, it is used in hospitals to make another radioactive isotope technetium-99m. This isotope of technetium (atomic number 43) is widely used as a tracer for diagnostic studies of the brain, liver, spleen, heart, and other organs and body systems.

Molybdenum disulfide is soft and squishy.

A radioactive tracer is an isotope whose movement in the body can be followed because of the radiation it gives off. The radiation can be "traced" with special equipment held above the body. The pattern produced by the radiation allows a doctor to diagnose any unusual functioning (behavior) of the organ or body part.

Technetium-99m cannot be used for this purpose all by itself. It changes very quickly into a new isotope. Hospitals prepare molybdenum-99m first. This isotope can be stored for short periods of time. It slowly gives off radiation and changes into technetium-99m. The technetium-99m is captured as it is formed from molybdenum-99m and injected into the body for tracer studies. Because it is used to produced technetium-99m, the isotope molybdenum-99m is sometimes referred to as a "molybdenum cow.

Extraction

Pure molybdenum metal can be obtained from molybdenum trioxide (Mo0₃) in a variety of ways. For example, hot hydrogen can be passed over the oxide to obtain the metal:

Uses

About 75 percent of the molybdenum used in the United States in 1996 was made into alloys of steel and iron. Nearly half of these alloys, in turn, were used to make stainless and heat-resistant steel. A typical use is in airplane, spacecraft, and missile parts. Another important use of molybdenum alloys is in the production of specialized tools. Spark plugs, propeller shafts, rifle barrels, electrical equipment used at high temperatures, and boiler plates are all made of molybdenum steel.

Another important use of molybdenum is in catalysts. A catalyst is a substance used to speed up or slow down a chemical reaction. The catalyst does not undergo any change itself during the reaction. Molybdenum catalysts are used in a wide range of chemical operations, in the petroleum industry, and in the production of polymers and plastics.

Compounds

A number of molybdenum compounds are used in industry and research. Interestingly, molybdenum disulfide is still used as a lubricant, as it was over two hundred years ago. The slippery black powder looks and behaves much like graphite. Molybdenum is used in industrial operations to reduce the friction between sliding or rolling parts. It does not break down when heated or used for very long periods of time.

Other compounds of molybdenum are used as protective coatings in materials used at high temperatures; as solders; as catalysts; as additives to animal feeds; and as pigments and dyes in glasses, ceramics, and enamels.

Health effects

Molybdenum is relatively safe for humans and animals. No studies have shown it to be toxic. In fact, it is regarded as a necessary trace element for the growth of plants. A trace element is one that is needed in very small amounts for the proper growth of a plant or animal.

Molybdenum

melting point: 2,623°C
boiling point: 4,639°C
density: 10.22 g/cm ³
most common ions: Mo ³⁺, Mo ₂(OH) ₂⁴⁺, M ₂O ₄²⁺

Molybdenum is a hard, silver-white metal discovered by Swedish chemist Carl Wilhelm Scheele in 1778. Scheele had been researching a mineral called molybdenite, which many suspected of containing lead (the Greek word molybdos means "lead"). He instead found that it contained a new element which he named "molybdenum" after the mineral. Molybdenum was first isolated by Swedish mineralogist Peter Jacob Hjelm in 1782.

Molybdenum has an abundance in Earth's crust of approximately 1.1 parts per million (ppm) or 1.2 milligrams per kilogram. Its chief source is the mineral molybdenite (MoS₂), but it is also found in the ores wulfenite (PbMoO₄) and powellite (CaMoO₄) or obtained as a by-product of copper mining. The leading producers of molybdenum are the United States, Canada, Chile, Mexico, Peru, China, Russia, and Mongolia.

There are seven known isotopes of molybdenum that occur naturally: ⁹²Mo, ⁹⁴Mo, ⁹⁵Mo, ⁹⁶Mo, ⁹⁷Mo, ⁹⁸Mo, and ¹⁰⁰Mo. Their natural abundances range from 9.25 percent (⁹⁴Mo) to 24.13 percent (⁹⁸Mo). Common compounds of molybdenum include molybdenum disulfide (MoS₂), molybdenum trioxide (MoO₃), molybdic acid (H₂MoO₄), molybdenum hexafluoride (MoF₆), and molybdenum phosphide (MoP₂).

Molybdenum's melting point (2,623°C, or 4,753.4°F) exceeds that of steel by 1,000°C (1,832°F) and that of most rocks by 500°C (932°F). For this reason, the element is used in various alloys to improve strength, particularly at high temperatures. Approximately 75 percent of molybdenum produced is used by the iron and steel industries. The element is also utilized to make parts for furnaces, light bulbs, missiles, aircraft, and guns. Molybdenum disulfide is used as a high temperature lubricant.

see also Coordination Compounds; Inorganic Chemistry; Scheele, Carl.

Stephanie Dionne Sherk

Bibliography

Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.

Other Resource

Powell, Darryl. "Molybdenum." Mineral Information Institute. Available from <http://www.mii.org/Minerals/photomoly.html>.

molybdenum (symbol Mo) Silvery-white metallic element; one of the transition elements. It was first isolated in 1781 by the Swedish chemist Karl Scheele. Its chief ore is molybdenite. Hard but malleable and ductile, it is used in alloy steels, X-ray tubes and missile parts; molybdenum compounds are used as catalysts and lubricants. It is one of the essential trace elements for plant growth. Properties: at.no. 42; r.a.m. 95.94; r.d. 10.22; m.p. 2610°C (4730°F); b.p. 5560°C (10,040°F); most stable isotope Mo⁹⁸ (23.78%).

mo·lyb·de·num / məˈlibdənəm/ • n. the chemical element of atomic number 42, a brittle silver-gray metal of the transition series, used in some alloy steels. (Symbol: Mo)