Leffler’s assumption SeeHAMMOND PRINCIPLE.
left-to-right convention Arrangement of the struc-
tural formulae of the reactants so that the bonds to be
made or broken form a linear array in which the elec-
trons move from left to right.
See alsoLINE FORMULA.
leghemoglobin A monomeric HEMOGLOBINsynthe-
sized in the root nodules of leguminous plants that are
host to nitrogen-fixing bacteria. Has a high affinity
for dioxygen and serves as an oxygen supply for the
bacteria.
See alsoNITROGEN FIXATION.
Leloir, Louis F.(1906–1987) Argentinian/French
Chemist Luis F. Leloir was born in Paris on Septem-
ber 6, 1906, to Argentine parents but lived in Buenos
Aires from the age of two.
He graduated with an M.D. from the University of
Buenos Aires in 1932 and started his scientific career at
the Institute of Physiology researching adrenalin carbo-
hydrate metabolism.
In 1936 he worked at the biochemical laboratory
of Cambridge, England, but returned to Buenos Aires
to conduct research on the oxidation of fatty acids in
the liver.
He was married in 1943 to Amelia Zuberbuhler
and had a daughter.
The following year he moved to the United States
and worked as a research assistant in the laboratory of
Dr. Carl F. Cori in St. Louis, and then with D.E. Green in
the College of Physicians and Surgeons at Columbia Uni-
versity in New York City. He was director of the Instituto
de Investigaciones Bioquímicas, Fundación Campomar in
Argentina and isolated glucose 1,6-diphosphate and uri-
dine diphosphate glucose, uridine diphosphate acetylglu-
cosamine, and guanosine diphosphate mannose.
He received the Nobel Prize in chemistry in 1970
“for his discovery of sugar nucleotides and their role in
the biosynthesis of carbohydrates.” Leloir had eluci-
dated the biosynthesis of glycogen, the chief sugar
reserve in animals and many microorganisms.
He received the following awards: Argentine Scien-
tific Society, Helen Hay Whitney Foundation (United
States), Severo Vaccaro Foundation (Argentina), Bunge
and Born Foundation (Argentina), Gairdner Founda-
tion (Canada), Louisa Gross Horowitz (United States),
and Benito Juarez (Mexico). Leloir was also president
of the Pan-American Association of Biochemical Soci-
eties. He died in 1987.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 SOLVENTof a HYDRONfrom
a dissolved acid stronger than the CONJUGATE ACIDof
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 HClO 4 , 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.levorotatory Refers to an optically active compound
that rotates plane polarized light counterclockwise (to
the left) when viewed in the direction of the light
source. Opposite of DEXTROROTATORY, which rotates it
to the right (clockwise).Lewis acid A molecular entity that is an ELECTRON-
PAIR ACCEPTORand therefore is able to react with a
LEWIS BASEto form a LEWIS ADDUCTby sharing the
electron pair furnished by the Lewis base.Lewis acidity The thermodynamic tendency of a
substrate to act as a LEWIS ACID. Comparative mea-
sures of this property are provided by the equilibrium
constants for LEWIS ADDUCTformation of a series of
Lewis acids with a common reference LEWIS BASE.
See also ACCEPTOR NUMBER; ELECTROPHILICITY;
STABILITY CONSTANT.Lewis adduct The adduct formed between a LEWIS
ACID and a LEWIS BASE. An adduct is formed by the
union of two molecules held together by a coordinate
COVALENT BOND.
See alsoCOORDINATION.Lewis adduct 163