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Solvent effect on uv spectra of 2- and 4-pyrimidinones
JournalofMolecularStructure,143(1986)345-348 El~vierSciencePublishersB.V.,Amsterdam-PPrintedinTheNetherlands
345
SOLVENT EFFECT ON II'.' SPECTRA OF Z- AND 4-PYRIMIDINONES J. TORTAJADA, F. ACCION and D. ESCOLAR Dpto. Espectroscopia, Fat. C. Quimicas, Univ. Complutense, 28040 Madrid (Spain)
ABSTRACT Ultraviolet spectra of 2- and 4-pyrimidinone solutions in several acetonitrile-water and ethanol-water mixtures have been recorded. The observed frequency dispacements have been attributed to hydrogen-bond formation between solute and water molecules. Some expressions to determine solute-solvent association constant have been deduced. These expressions allow to calculate the h-bond complex stoichiometry. Theoretical results seem to indicate hydrogen-bond formation takes place over the oxygen atom of solute. INTRODUCTION Considerable attention has been devoted to the study of tautomerism and molecular interactions (ref.1 and 2) of nitrogen hetero cycles, mainly due to its great importance in biochemistry. In these systems, the solvent play an important role, since tautomeric and self-association equilibria depend markedly on the surrounding medium (ref.3). In addition, the existence of solute-solvent specific interaction is possible (ref.4). In this paper, the influence of water on two representative systems has been investigated. UV absorption spectra of 2- and 4-hydroxypyrimidine-pyrimidinone
(abbreviated 2HP and 4HP) in acetoni-
trile and ethanol solutions show evident changes when different amounts of water are added. It has been assigned to the hydrogenbond formation between solute and water molecules. RESULTS AND DISCUSSION UV absorption spectra of 2HP and 4HP in several acetonitrilewater and ethanol-water mixtures have been recorded. Water concentration used was over the range 0.02-41 M. Figures 1 and 2 show some of the experimental absorption profiles obtained. Frequency displacements, as well as the presence of isosbestic points suggest the existence of solute-water association equilibria. These can be represented by: 0 1986Elsevier Science Publishers B.V. OQ22-2860/86/$03.50
346
S + nD c’ SDn where
S,D and
drogen-bonding Assuming and cDp>c cs
the
(1)
S’ solute
SDn stand
for
complexes,
the
water
has
where
c D represents
one,
the
solute,
water
and solute-water
hy-
respectively.
no absorption
in
the
apparent
molar
the
total
frequency water
range
of
work,
concentration
absortivity
(A/l.cS)
and can
be
4
3
0
3
9
liJ
w
5-
2
0
30
35
40 L).10-3(cm-~)
Fig.1. UV spectra of 2HP (A) water mixtures. a: acetonitrile (E units: liter.mol-1 .cm-1)
Or 35
UV spectra of ethanol
2HP (A) solution.
45
lJ10-3(cm-‘)
and 4HP (B) solution.
0
Fig.2.
40
in several b: water
35
acetonitrilesolution.
40
45
ti.10-3(cm-1
1
and 4HP (B) in several ethanol-water b: water solution. (E units: liter.
347 expressed E-E
+(E
S
where
(ref.
5) as:
respectively;
case
where
only,
the I+l.,n ES
(2)
absortivity
of
n = complex
a frequency last
Es
range
expression
hydrogen-bond
stoichiometry. can
takes
be
complex
In the
assigned
to
thesimplified
and
sol-
particular
solute
absorption
form: (3)
D
Application estimate
+ 1)-l Kc;
= molar
ES~,ES
ute,
1 _= E
- E&(1
SD
of
the
these
expressions
to
experimental
constants,
as
well
equilibrium
as
data
the
allows
complex
to
stoichio
-
metry. If
the
served,
experimental
it
can
be noted
have
no absorption
2HP,
and 533000
rest
of
to
the
the
cm
plex
range data
spectra
in
water
less
than
Then,
the
concentration
only. treated determined
different Figure
absorption
Apparent
be
with
solutions,
cm-’
detected be
in
in
the
assigned at
this
of
ex-
(3). out
The versus
ob-
concentration
absortivities
equation
a plot
2 are
~30000 must
molar
carrying
n-values. 3 shows
1 and
high
water
be
acetonitrile-water
at
range
figures
low
can for
in
4HP.
at
must
stoichiometry.
2HP in
that
shown
a frequency
absorption
The n-value perimental
at -1
solutions
solute
frequency
profiles
of
several
best l/e, CD” at
fit
fits gives
the
com-
corresponding n=l
and 2.
Fig.3. Diagram showing relationship between 1,‘~ and water tration (c ) for n-l and 2. (Experimental data correspond in acetoni .P rile-water mixtures). .
to In
concento 2HP
TABLE 1 Solute-water
association
equilibrium
constants
K
Solute
Stoichiometry
2HP
(3.0
+ 0.7).10_’
1:l
4HP
(5.0
+ 3.0)*lo-2
1:1
this
case
the
Equation any
best
(2)
frequency,
ferent
but
is
be it
The
of
both
n=l. experimental
requires
to
accomplish
However,
today
it
absorption several
can
be
data
fits
carried
for out
at dif-
easily
program.
obtained
equations
to to
a computer
results
due
applied
K and n values.
by means using
fit
can
with have
various
shown
in
sets all
indicating
experimental
data
formation.
Table
the
solute-water
carried
out
1 show
adjust
of
cases
to
1:l
experimental a good
data
hydrogen-bond
equilibrium
and
correlation, complex
constants
ob-
tained. CNDO/S calculations plexes
(ref.6)
ute-solvent Then, where
frequency
hydrogen-bond
we can
be mainly
indicate conclude
attributed
solute
acts
as
formation
water to
for
1:l
acceptor
several
solute-solvent
displacements over
influence solute-water and water
on
the 2-
must oxygen
com-
be
due
atom
of
and 4-pyrimidinone
h-bond
complex
to
sol-
solute. can
formation,
as donor.
REFERENCES 1 2 3 4 5 6
J. Elguero, C. Marzin, A.R. Katritzky and P. Linda, The Tautomerism of Heterocycles, A.R. Katritzky and A.J. Boulton, Eds., Academic Press, New York, 1976. Intermolecular Interaction: From diatomics to bioB. Pullman, polymers, John Wiley 8, Sons? Chichester, 1978 C. Krebs, W. Forster, C. Weiss and H.J. Hofmann, J. Prakt. Chem. 324(3) (1982) 369-378, and ref. cited therein. P. Beak, J.B. Covington and J.M. White, J. Org. Chem. 45(8) (1980) 1347-1353, and ref. cited therein. J. Tortajada, Ph. D. Thesis, Univ. Complutense, Madrid, 1985 J. Tortajada and F. Action, to be published.
345
SOLVENT EFFECT ON II'.' SPECTRA OF Z- AND 4-PYRIMIDINONES J. TORTAJADA, F. ACCION and D. ESCOLAR Dpto. Espectroscopia, Fat. C. Quimicas, Univ. Complutense, 28040 Madrid (Spain)
ABSTRACT Ultraviolet spectra of 2- and 4-pyrimidinone solutions in several acetonitrile-water and ethanol-water mixtures have been recorded. The observed frequency dispacements have been attributed to hydrogen-bond formation between solute and water molecules. Some expressions to determine solute-solvent association constant have been deduced. These expressions allow to calculate the h-bond complex stoichiometry. Theoretical results seem to indicate hydrogen-bond formation takes place over the oxygen atom of solute. INTRODUCTION Considerable attention has been devoted to the study of tautomerism and molecular interactions (ref.1 and 2) of nitrogen hetero cycles, mainly due to its great importance in biochemistry. In these systems, the solvent play an important role, since tautomeric and self-association equilibria depend markedly on the surrounding medium (ref.3). In addition, the existence of solute-solvent specific interaction is possible (ref.4). In this paper, the influence of water on two representative systems has been investigated. UV absorption spectra of 2- and 4-hydroxypyrimidine-pyrimidinone
(abbreviated 2HP and 4HP) in acetoni-
trile and ethanol solutions show evident changes when different amounts of water are added. It has been assigned to the hydrogenbond formation between solute and water molecules. RESULTS AND DISCUSSION UV absorption spectra of 2HP and 4HP in several acetonitrilewater and ethanol-water mixtures have been recorded. Water concentration used was over the range 0.02-41 M. Figures 1 and 2 show some of the experimental absorption profiles obtained. Frequency displacements, as well as the presence of isosbestic points suggest the existence of solute-water association equilibria. These can be represented by: 0 1986Elsevier Science Publishers B.V. OQ22-2860/86/$03.50
346
S + nD c’ SDn where
S,D and
drogen-bonding Assuming and cDp>c cs
the
(1)
S’ solute
SDn stand
for
complexes,
the
water
has
where
c D represents
one,
the
solute,
water
and solute-water
hy-
respectively.
no absorption
in
the
apparent
molar
the
total
frequency water
range
of
work,
concentration
absortivity
(A/l.cS)
and can
be
4
3
0
3
9
liJ
w
5-
2
0
30
35
40 L).10-3(cm-~)
Fig.1. UV spectra of 2HP (A) water mixtures. a: acetonitrile (E units: liter.mol-1 .cm-1)
Or 35
UV spectra of ethanol
2HP (A) solution.
45
lJ10-3(cm-‘)
and 4HP (B) solution.
0
Fig.2.
40
in several b: water
35
acetonitrilesolution.
40
45
ti.10-3(cm-1
1
and 4HP (B) in several ethanol-water b: water solution. (E units: liter.
347 expressed E-E
+(E
S
where
(ref.
5) as:
respectively;
case
where
only,
the I+l.,n ES
(2)
absortivity
of
n = complex
a frequency last
Es
range
expression
hydrogen-bond
stoichiometry. can
takes
be
complex
In the
assigned
to
thesimplified
and
sol-
particular
solute
absorption
form: (3)
D
Application estimate
+ 1)-l Kc;
= molar
ES~,ES
ute,
1 _= E
- E&(1
SD
of
the
these
expressions
to
experimental
constants,
as
well
equilibrium
as
data
the
allows
complex
to
stoichio
-
metry. If
the
served,
experimental
it
can
be noted
have
no absorption
2HP,
and 533000
rest
of
to
the
the
cm
plex
range data
spectra
in
water
less
than
Then,
the
concentration
only. treated determined
different Figure
absorption
Apparent
be
with
solutions,
cm-’
detected be
in
in
the
assigned at
this
of
ex-
(3). out
The versus
ob-
concentration
absortivities
equation
a plot
2 are
~30000 must
molar
carrying
n-values. 3 shows
1 and
high
water
be
acetonitrile-water
at
range
figures
low
can for
in
4HP.
at
must
stoichiometry.
2HP in
that
shown
a frequency
absorption
The n-value perimental
at -1
solutions
solute
frequency
profiles
of
several
best l/e, CD” at
fit
fits gives
the
com-
corresponding n=l
and 2.
Fig.3. Diagram showing relationship between 1,‘~ and water tration (c ) for n-l and 2. (Experimental data correspond in acetoni .P rile-water mixtures). .
to In
concento 2HP
TABLE 1 Solute-water
association
equilibrium
constants
K
Solute
Stoichiometry
2HP
(3.0
+ 0.7).10_’
1:l
4HP
(5.0
+ 3.0)*lo-2
1:1
this
case
the
Equation any
best
(2)
frequency,
ferent
but
is
be it
The
of
both
n=l. experimental
requires
to
accomplish
However,
today
it
absorption several
can
be
data
fits
carried
for out
at dif-
easily
program.
obtained
equations
to to
a computer
results
due
applied
K and n values.
by means using
fit
can
with have
various
shown
in
sets all
indicating
experimental
data
formation.
Table
the
solute-water
carried
out
1 show
adjust
of
cases
to
1:l
experimental a good
data
hydrogen-bond
equilibrium
and
correlation, complex
constants
ob-
tained. CNDO/S calculations plexes
(ref.6)
ute-solvent Then, where
frequency
hydrogen-bond
we can
be mainly
indicate conclude
attributed
solute
acts
as
formation
water to
for
1:l
acceptor
several
solute-solvent
displacements over
influence solute-water and water
on
the 2-
must oxygen
com-
be
due
atom
of
and 4-pyrimidinone
h-bond
complex
to
sol-
solute. can
formation,
as donor.
REFERENCES 1 2 3 4 5 6
J. Elguero, C. Marzin, A.R. Katritzky and P. Linda, The Tautomerism of Heterocycles, A.R. Katritzky and A.J. Boulton, Eds., Academic Press, New York, 1976. Intermolecular Interaction: From diatomics to bioB. Pullman, polymers, John Wiley 8, Sons? Chichester, 1978 C. Krebs, W. Forster, C. Weiss and H.J. Hofmann, J. Prakt. Chem. 324(3) (1982) 369-378, and ref. cited therein. P. Beak, J.B. Covington and J.M. White, J. Org. Chem. 45(8) (1980) 1347-1353, and ref. cited therein. J. Tortajada, Ph. D. Thesis, Univ. Complutense, Madrid, 1985 J. Tortajada and F. Action, to be published.