intramolecular (1) Descriptive of any process that
involves a transfer (of atoms, GROUPS, electrons, etc.)
or interactions between different parts of the same
MOLECULAR ENTITY.
(2) Relating to a comparison between atoms or
groups within the same molecular entity.
See alsoINTERMOLECULAR.
intramolecular catalysis The acceleration of a
chemical transformation at one site of a MOLECULAR
ENTITY through the involvement of another FUNC-
TIONAL (“catalytic”) GROUP in the same molecular
entity, without that group appearing to have undergone
change in the reaction product. The use of the term
should be restricted to cases for which analogous
INTERMOLECULAR CATALYSIS by CHEMICAL SPECIES
bearing that catalytic group is observable. Intramolecu-
lar catalysis can be detected and expressed in quantita-
tive form by a comparison of the reaction rate with
that of a comparable model compound in which the
catalytic group is absent, or by measurement of the
EFFECTIVE MOLARITYof the catalytic group.
See alsoCATALYSIS; NEIGHBORING-GROUP PARTICI-
PATION.
intrinsic activity The maximal stimulatory response
induced by a compound in relation to that of a given
reference compound.
This term has evolved with common usage. It was
introduced by Ariëns as a proportionality factor
between tissue response and RECEPTORoccupancy. The
numerical value of intrinsic activity (alpha) could range
from unity (for full AGONISTs, i.e., agonists inducing
the tissue maximal response) to zero (for ANTAGO-
NISTs), the fractional values within this range denoting
PARTIAL AGONISTs. Ariëns’s original definition equates
the molecular nature of alpha to maximal response
only when response is a linear function of receptor
occupancy. This function has been verified. Thus,
intrinsic activity, which is a DRUGand tissue parameter,
cannot be used as a characteristic drug parameter for
classification of drugs or drug receptors. For this pur-
pose, a proportionality factor derived by null methods,
namely, relative EFFICACY, should be used.
Finally, the term intrinsic activityshould not be
used instead of intrinsic efficacy.A “partial agonist”
should be described as “agonist with intermediate
intrinsic efficacy” in a given tissue.
See alsoPARTIAL AGONIST.intrinsic barrier The GIBBS ENERGY OF ACTIVATION
(∆‡G) in the limiting case where ∆Go= 0, i.e., when the
effect of thermodynamic driving force is eliminated.
According to the MARCUS EQUATION, the intrinsic bar-
rier is related to the REORGANIZATION ENERGY, λ, of
the reaction by the equation
∆‡G = λ/4intron An intervening section of DNA that occurs
almost exclusively within a eukaryotic GENE, but which
is not translated to amino-acid SEQUENCEs in the gene
product. The introns are removed from the pre-mature
mRNA through a process called splicing, which leaves
the EXONs untouched, to form an active mRNA.
See alsoEUKARYOTE.inverse agonist A DRUGthat acts at the same RECEP-
TORas that of an AGONIST, yet produces an opposite
effect. Also called negative ANTAGONIST.inverse kinetic isotope effect SeeISOTOPE EFFECT.inverted micelle The reversible formation of associa-
tion colloids from surfactants in nonpolar solvents leads
to aggregates termed inverted (or inverse, reverse, or
reversed) MICELLEs. Such association is often of the type
Monomer Dimer Trimer ... n-mer
and the phenomenon of CRITICAL MICELLE CONCEN-
TRATION(or an analogous effect) is consequently not
observed.
In an inverted micelle, the polar GROUPs of the sur-
factants are concentrated in the interior, and the
LIPOPHILICgroups extend toward and into the nonpo-
lar solvent.ion An atom or group of atoms that acquires a
charge by either gaining or losing one or more elec-
trons. 142 intramolecular