phosphate solvent. The strands are antiparallel, thus
the phosphodiester bonds run in opposite directions.
As a result, the structure has major and minor grooves
at the surface. Each adenine in one strand of DNA is
hydrogen-bonded to a thymine in the second strand;
each guanine is hydrogen-bonded to a cytosine.
See alsoDNA.
double prodrug(pro-prodrug) A biologically inac-
tive molecule that is transformed in vivo in two steps
(enzymatically or chemically) to the active species.
double salt A compound of two salts. That is, the
ions in solution appear to come from two salts, but a
single substance is formed on crystallization. Examples
are alum, potassium aluminum sulfate, and zinc ammo-
nium chloride.
downfield SeeCHEMICAL SHIFT.
Downs cell Electrolytic cell used for the commercial
electrolysis of molten sodium chloride to produce com-
mercial-grade sodium.
DP number The number of MONOMERunits jointed
together in a polymer; the degree of polymerization; the
average number of monomer units per polymer unit.
driving force(affinity of a reaction), (SI unit: kJ mol–1)
The decrease in Gibbs energy on going from the reac-
tants to the products of a chemical reaction (–∆G).
See alsoGIBBS FREE ENERGY.
drug Any substance presented for treating, curing, or
preventing disease in human beings or in animals. A
drug may also be used for making a medical diagnosis,
managing pain, or for restoring, correcting, or modify-
ing physiological functions (e.g., the contraceptive pill).
drug disposition Refers to all processes involved in
the absorption, distribution, METABOLISM, and excre-
tion of DRUGs in a living organism.
drug latentiation The chemical modification of a
biologically active compound to form a new com-
pound that in vivo will liberate the parent compound.
Drug latentiation is synonymous with PRODRUG
design.drug targeting A strategy aiming at the delivery of a
compound to a particular tissue of the body.dry cells The term used for ordinary batteries
(voltaic cells) that are used in everyday flashlights, etc.
A dry-cell battery contains electrolytes that are in the
form of paste rather than liquid; the electrolyte is
absorbed in a porous medium or is otherwise
restrained from flowing. Also known as a Leclanché
cell, which is the common commercial type.dry ice A solid form of the gas carbon dioxide
(CO 2 ), used for keeping items cold or transporting
food materials over long distances. At –78.5°C and
ambient pressure, it changes directly to a gas as it
absorbs heat.dry ice 85A dry-cell battery contains electrolytes that are in the form of
paste rather than liquid.