Medicinal Chemistry:
A chemistry-based discipline, also involving aspects of biological, medical, and pharmaceutical sciences. It is concerned with the invention, discovery, design, identification, and preparation of
biologically active compounds; the study of their METABOLISM; the interpretation of their mode of action at the molecular level; and the construction of STRUCTURE- ACTIVITY RELATIONSHIPs.
Littoral Zone:
The shallow shoreward region of a freshwater body, just beyond the breaker zone, where light penetrates to the bottom sediments, giving rise to a zone that is colonized by rooted plants called helophytes; a region of a lake or pond where the water is
less than 6 meters deep; in oceanography, the line extending from the high-water line to about 200 meters; also called the intertidal zone where submersion of tides is a normal event. The near-surface open water surrounded by the littoral zone is the limnetic
zone, which gets ample light and is dominated by plankton. The littoral system is divided into a eulittoral (lower, middle, and upper) zone and a sublittoral (subtidal or supratidal) zone, the zone exposed to air only at its upper limit by the lowest spring tides. They are separated at a depth of about 50 meters. The term is
also frequently used interchangeably with intertidal zone.
Lipid:
A large group of HYDROPHOBIC (water insoluble) molecules that are the building blocks of cell membranes and liposomes (lipid vesicles) and contain fatty acids; the principal components of fats, oils, waxes, triglycerides, and cholesterol. They are insoluble in
water but soluble in solvents such as alcohol and ether. The phospholipid bilayer of the plasma membrane is a double layer of phospholipid molecules arranged so that the hydrophobic “tails” lie between the HYDROPHILIC “heads.” Also known as fat, they easily store in the body and are an important source of fuel
for the body.
Ligand:
A molecule, ion, hormone or compound that binds to a specific receptor site that binds to another molecule.
The atoms or groups of atoms bound to the CENTRAL
ATOM (see COORDINATION). The root of the word
is sometimes converted into the verb to ligate, meaning
to coordinate as a ligand, and the derived participles,
ligating and ligated. This use should not be confused
with its use to describe the action of LIGASEs (a class of
ENZYMEs). The names for anionic ligands, whether
inorganic or organic, end in -o. In general, if the anion
name ends in -ide, or -ate, the final -e is replaced by -o,
giving -ido and -ato, respectively. Neutral and cationic
ligand names are used without modification. Ligands
bonded by a single carbon atom to metals are regarded
as radical substituents, their names being derived from
the parent hydrocarbon, from which one hydrogen atom has been removed. In general, the final letter -e of the name is replaced by -yl. In biochemistry the term ligand has been used more widely: if it is possible or convenient to regard part of a polyatomic molecular entity as central, then the atoms or groups or molecules bound to that part may be called ligands.
Leveling Effect:
The tendency of a solvent to make all BRONSTED ACIDs whose ACIDITY exceeds a certain value appear equally acidic. It is due to the complete transfer to a PROTOPHILIC SOLVENT of a HYDRON from a dissolved acid stronger than the CONJUGATE ACID of the solvent. The only acid present to any significant
extent in all such solutions is the LYONIUM ION. For example, the solvent water has a leveling effect on the acidities of HClO4, HCl, and HI: aqueous solutions of these acids at the same (moderately low) concentrations have the same acidities. A corresponding leveling effect applies to strong bases in PROTOGENIC SOLVENTs.
Laser:
Acronym for light amplification by stimulated emission of radiation. A device that has mirrors at the ends and is filled with material such as crystal, glass, liquid, gas, or dye that has atoms, ions, or molecules capable of being excited to a metastable state by light,
electric discharge, or other stimulus. The transition from the metastable state back to the normal ground state is accompanied by the emission of photons that form a straight, coherent beam. Laser light is directional and covers a narrow range of wavelengths. It is
more coherent than ordinary light.
Kinetic Energy:
Energy of motion; kinetic energy depends on the object’s mass and velocity and can be described mathematically as K.E. = 1/2 mv2. Moving matter, be it a rolling rock, flowing water, or falling
ball, transfers a portion of its kinetic energy to other matter. For example, an inelastic collision is one in which at least a portion of the kinetic energy of the colliding particles is lost through conversion to some other form of energy. Potential energy, energy stored in a body, can be converted to kinetic energy.
Kilogram:
The basic unit of mass (not of weight or of force). A kilogram is equal to the mass of 1.000028 cubic decimeters of water at the temperature of its maximum density.
Kilocalorie (kcal):
One kilocalorie is equal to 1,000 calories, which is based on the amount of heat energy required to raise the temperature of 1 kilogram of water by 1°C; used to measure the energy value in food
and labor. Usually just called calorie; 1 kilocalorie (kcal) = 1 Calorie (Cal) = 1,000 calories (cal). However, in the International System of Units (ISU), the universal unit of energy is the joule (J). One kilocalorie = 4.184 kilojoules (kJ).
Joule:
The international unit of energy or work. The amount of work done when a force of 1 Newton is applied through a distance of 1 meter. One joule is 1kg·m2/s2 or 0.2390 calorie.
Iron-Sulfur Protein:
Proteins in which non-HEME iron is coordinated with cysteine sulfur and, usually, with inorganic sulfur. Divided into three major categories: RUBREDOXINs; simple iron-sulfur proteins, containing
only IRON-SULFUR CLUSTERs; and complex iron-sulfur proteins, containing additional active redox centers such as FLAVIN, molybdenum, or heme. In most iron-sulfur proteins, the clusters function as ELECTRON TRANSFER groups, but in others they have other functions such as catalysis of hydratase/dehydratase reactions, maintenance of protein structure, or REGULATION
of activity.
Ionization Energy:
Ei (SI unit: kJ mol–1 or J per molecule) The minimum energy required to remove an electron from an isolated MOLECULAR ENTITY (in its vibrational GROUND STATE) in the gaseous phase. If the resulting molecular entity is considered to be in its
vibrational ground state, one refers to the energy as the
“adiabatic ionization energy.” If the molecular entity produced possesses the vibrational energy determined by the Franck-Condon principle (according to which the electron ejection takes place without an accompanying change in molecular geometry), the energy is called the “vertical ionization energy.” The name “ionization energy” is preferred to the somewhat misleading
earlier name “ionization potential.”
Ion Exchange:
A reversible process where ions are released from an insoluble permanent material in exchange for other ions in a surrounding solution. The direction of the exchange depends on (a) the affinities
of the ion exchanger for the ions present and (b) the concentrations of the ions in the solution. In water treatment, this process adds and removes ions from water. In nuclear chemistry, it is a common method for concentrating uranium from a solution. The uranium
solution is passed through a resin bed, where the uranium- carbonate complex ions are transferred to the resin by exchange with a negative ion like chloride. After buildup of the uranium complex on the resin, the uranium is eluted with a salt solution, and the uranium is precipitated in another process.
