Encyclopedia of Chemistry

levels. The band is not filled, and electrons are free to
move in an electric field, giving typical metallic conduc-
tivity. Sometimes this is modeled as ions surrounded by
a “sea” of electrons.

metallic conduction The conduction of an electrical
current through a METALor along a metallic surface.

metalloenzyme An ENZYMEthat, in the active state,
contains one or more METALions that are essential for
its biological function.

metalloids Elements with properties intermediate
between METALs and nonmetals: boron, silicon, germa-
nium, arsenic, antimony, tellurium, and polonium.

metallo-immunoassay A technique in which ANTI-
GEN-ANTIBODYrecognition is used, with attachment of
a METALion or metal complex to the antibody. The
specific absorption or (radioactive) emission of the
metal is then used as a probe for the location of the
recognition sites.
See alsoIMAGING; RADIONUCLIDE.

metallothionein A small, cysteine-rich protein that
binds heavy METALions such as zinc, cadmium, and
copper in the form of CLUSTERs.

metallurgy The science of METALs and their proper-
ties at the macroscopic and atomic level; overall pro-
cesses by which metals are extracted from ores.

metastable SeeSTABLE.

metastable (chemical) species See TRANSIENT

(CHEMICAL) SPECIES.

metathesis A bimolecular process formally involving

the exchange of a BOND(or bonds) between similar

interacting CHEMICAL SPECIESso that the bonding affili-

ations in the products are identical (or closely similar)

to those in the reactants. For example:

(The term has its origin in inorganic chemistry with

a different meaning, but this older usage is not applica-

ble in physical organic chemistry.)

See alsoBIMOLECULAR REACTION.

meter A unit of metric measure that equals 39.37 in.

methane hydrate A frozen latticelike substance

formed when water and methane, CH 4 , are combined

under low temperatures and high pressures. It is a crys-

talline combination of a natural gas and water, called a

CLATHRATE, and looks like ice but burns like a candle.

methane monooxygenase A METALLOENZYMEthat

converts methane and dioxygen to methanol using

NADHas co-SUBSTRATE. Two types are known, one con-

taining a dinuclear oxo-bridged iron center, the other a

copper protein.

See alsoNUCLEARITY.

methanogen Strictly ANAEROBIC ARCHAEA, able to

use a variety of SUBSTRATEs (e.g., dihydrogen, formate,

methanol, methylamine, carbon monoxide, or acetate)

as ELECTRON DONORs for the reduction of carbon

dioxide to methane.

methylene SeeCARBENE.

methylene 177

The bonding in metallic elements