mineral A naturally occurring homogeneous solid,
inorganically formed, with a definite chemical composi-
tion, usually crystalline in form, and an ordered atomic
arrangement, e.g., quartz. Also a naturally occurring
inorganic element or compound having an orderly
internal structure and characteristic chemical composi-
tion, crystal form, and physical properties. The impor-
tant point is that while a mineral has a characteristic
composition, it is not always definite.
minimum structural change, principle of See
MOLECULAR REARRANGEMENT.
miscibility The ability of one liquid to mix with or
dissolve in another liquid to form a uniform blend.
mitochondria CYTOPLASMIC organelles of most
eukaryotic cells, they are surrounded by a double mem-
brane and produce ADENOSINE 5 ′-TRIPHOSPHATE(ATP)
as useful energy for the cell by oxidative PHOSPHORYLA-
TION. The proteins for the ATP-generating electron
transport of the respiration chain are located in the
inner mitochondrial membrane. Mitochondria contain
many ENZYMEs of the citric acid cycle and for fatty-
acid β-oxidation. They also contain DNA, which
encodes some of their proteins, the remainder being
encoded by nuclear DNA.
See alsoEUKARYOTE.
mitosis The cell-division process in eukaryotic cells
that replicates chromosomes so that two daughter cells
get equally distributed genetic material from a parent
cell, making them identical to each other and the par-
ent. It is a five-step process that includes prophase,
prometaphase, metaphase, anaphase, and telophase.
Interphase is the time in the cell cycle when DNAis
replicated in the nucleus.
See alsoEUKARYOTE.
mixed valency This is one of several names, such as
“mixed oxidation state” or “nonintegral oxidation
state,” used to describe COORDINATION compounds
and CLUSTERs, in which a METAL is present in more
than one level of OXIDATION. The importance in biol-
ogy is due to the often-complete DELOCALIZATIONof
the valence electrons over the cluster, allowing efficient
ELECTRON-TRANSFERprocesses.
See alsoOXIDATION NUMBER.mixing control The experimental limitation of the
RATE OF REACTIONin solution by the rate of mixing of
solutions of the two reactants. It can occur even when
the reaction rate constant is several powers of 10 less
than that for an ENCOUNTER-CONTROLLEDrate. Analo-
gous (and even more important) effects of the limita-
tion of reaction rates by the speed of mixing are
encountered in heterogeneous (solid-liquid, solid-gas,
liquid-gas) systems.
See also MICROSCOPIC DIFFUSION CONTROL;
STOPPED FLOW.mixture Matter composed of two or more substances,
each of which retains its identity and properties.mobile phase Part of an analytical method in GC
(GAS CHROMATOGRAPHY) in which a sample is vapor-
ized and injected into a carrier gas (called the mobile
phase, usually helium) moving through a column.Möbius aromaticity A monocyclic array of ORBITALs
in which a single out-of-phase overlap (or, more gener-
ally, an odd number of out-of-phase overlaps) reveals the
opposite pattern of AROMATICcharacter to Hückel sys-
tems; with 4n electrons it is stabilized (aromatic),
whereas with 4n + 2 it is destabilized (antiaromatic). In
the excited state 4n + 2, Möbius pi-electron systems are
stabilized, and 4n systems are destabilized. No examples
of GROUND-STATEMöbius pi systems are known, but the
concept has been applied to TRANSITION STATEs of PERI-
CYCLIC REACTIONs (seeAROMATIC[3]).
The name is derived from the topological analogy
of such an arrangement of orbitals to a Möbius strip.
See alsoHÜCKEL( 4 N+ 2 )RULE.180 mineral