imidonium ion SeeNITRENIUM ION.
imin SeeNITRENE.
imine radical SeeNITRENE.
immiscibility When two or more substances or liquids
do not dissolve into one another, e.g., oil and water.
immune response The process by the body of an
organism to recognize and fight invasion of microor-
ganisms, viruses, and other substances (antigens) that
may be harmful to the body; the total time from recog-
nition of the intrusion to attack or tolerance of the
antigen.
immunoglobulin(Ig) Also known as antibodies,
these are proteins created by plasma cells and B cells
that are designed to control the body’s immune
response by binding to antigens. There are more than
1,000 possible ANTIBODY variations and five major
types, and each is specific to a particular antigen. Of
the five main types, IgA, IgD, IgE, IgG, and IgM, the
most common are IgA, IgG, and IgM.
immunogold A method for visualizing proteins in
electron microscopy within a cell using gold particles
attached to an ANTIBODYthat binds specifically to that
protein.
inclusion compound (inclusion complex) A COM-
PLEXin which one component (the HOST) forms a cav-
ity or, in the case of a crystal, a crystal lattice
containing spaces in the shape of long tunnels or chan-
nels in which molecular entities of a second CHEMICAL
SPECIES(the GUEST) are located. There is no covalent
bonding between guest and host, the attraction being
generally due to VAN DERWAALS FORCES. If the spaces
in the host lattice are enclosed on all sides so that the
guest species is “trapped” as in a CAGE, such com-
pounds are known as clathrates or cage compounds.
IND(investigational new drug) Regulations define
IND as a new drug, antibiotic drug, or biological drug
that is used in clinical investigation. The term also
includes biological products used in vitro for diagnostic
purposes. Required when a new indication or market-
ing/labeling change of an approved drug is being
sought.indicators Compounds that exhibit different colors
in solutions of different acidities or bases. Compounds
whose color depends upon the pH; typically, they
change color over a narrow pH range and are useful in138 imidonium ion
Demonstration of an acid-base titration that uses the indicator
phenolphthalein. An alkaline solution is in the flask, with a few
drops of the indicator added to give a purple color. Acid is slowly
added from the burette above. When the acid has completely neu-
tralized the alkali in the solution, the indicator turns colorless.
This technique is used to gather data for many investigations,
such as determining the concentration of the acid or alkali.
(Courtesy of Jerry Mason/Science Photo Library)