The differential quantum yield is
φ= d[X]/dt
nwhere d[X]/dtis the rate of change of the amount of
(substance) concentration of a measurable quantity,
and nis the amount of photons (mol or its equivalent
einsteins) absorbed per unit time. φcan be used for
photophysical processes or photochemical reactions.
quartz A crystalline mineral found worldwide in
many forms, including amethyst, aventurine, citrin,
opal, rock crystal, tiger’s eye, rose quartz,and others.
Quartz has a hardness of 7.0. It is a form of silica,
SiO 2.
quaternary ammonium salts (quats) Substances
that are used extensively as surfactants and antimicro-
bial agents. They contain at least one nitrogen atom
linked to four alkylor ARYL GROUPs.
quaternary nitrogen A quaternary nitrogen is one
that is attached to four other carbon atoms.quaternary structure There are four levels of struc-
ture found in POLYPEPTIDEs and PROTEINs. The first or
primary structure of a polypeptide of protein deter-
mines its secondary, tertiary, and quaternary structures.
The primary structure is the AMINO ACIDsequence. This
is followed by the secondary structure, how the amino
acids adjacent to each other are organized in the struc-
ture. The tertiary or third structure is the folded three-
dimensional protein structure that allows it to perform
its role, and the fourth or quaternary is the total protein
structure that is made when all the SUBUNITs are in
place. Quaternary structure is used to describe proteins
composed of multiple subunits or multiple polypeptide
molecules, each called a MONOMER. The arrangement
of the monomers in the three-dimensional protein is the
quaternary structure. A considerable range of quater-
nary structure is found in proteins.226 quartz