SRC="/isubscribe/journals/joceah/73/i03/figures/jo701926rn00001.gif" ALIGN="left" HSPACE=5> |
Can a benzene molecule differentiate between two i
someric carbohydrate
s? It i
s generally accepted thattwo factor
s govern molecular recognition: complementarity and preorganization. Preorganization require
sthe pre
sence of cavitie
s for po
sitioning the ho
st'
s group
s of complementary nature to tho
se of the gue
st.Thi
s study
show
s that, in fact, group
s should be complementary to recognize each other (for the ca
sepre
sented here, it i
s controlled by the CH/
s/gifchar
s/pi.gif" BORDER=0 > interaction) but preorganization i
s not e
ssential. Since weakinteraction
s have their origin in di
sper
sion force
s, they al
so have impact on the enthalpic term of the freeenergy,
so it wa
s con
sidered that their participation can be demon
strated by mea
suring the energy involved.For recognition to happen, two condition
s mu
st be
sati
sfied:
specificity and a
ssociated
stabilizing energy.In thi
s study we evaluated the heat of di
ssolution of different carbohydrate
s such a
s methyl 2,3,4,6-tetra-
O-methyl-
s/gifchar
s/alpha.gif" BORDER=0>-
D-mannopyrano
side and methyl 2,3,4,6-tetra-
O-methyl-
s/gifchar
s/beta2.gif" BORDER=0 ALIGN="middle">-
D-galactopyrano
side u
singdifferent aromatic
solvent
s. The
solvation enthalpie
s in benzene were -78.8 ± 3.9 and -88.7 ± 5.5 kJmol
-1 for each carbohydrate, re
spectively; and the
se value
s yielded a CH/
s/gifchar
s/pi.gif" BORDER=0 > energy of interaction of 9.9kJ mol
-1. In addition, NMR
studie
s of the effect of the addition of benzene to ch
loroform
solution
s ofthe two carbohydrate
s showed that benzene
specifically interact
s with the hydrogen atom
s of the pyrano
sering at po
sition
s 3, 4, and 5 located on the
s/gifchar
s/alpha.gif" BORDER=0> face of the methyl-
s/gifchar
s/beta2.gif" BORDER=0 ALIGN="middle">-galacto
side,
so it i
s, in fact, able torecognize it. Thu
s, the interaction
s between carbohydrate
s and the aromatic re
sidue
s of protein
s occur inthe ab
sence of the confinement generated by the protein
structure. By experimentally mea
suring theenergy a
ssociated with thi
s interaction and comparing it to theoretical calculation
s, it wa
s al
so po
ssibleto unequivocally determine the exi
stence of CH/
s/gifchar
s/pi.gif" BORDER=0 > interaction
s between carbohydrate
s and protein
s.