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THE DISTRIBUTION OF NOR-α-AMINOACIDS IN LIQUIDTWO-PHASE TERNARY SYSTEMS FORMED BY SALTING-OUT OF LOW ALIPHATIC ALCOHOLS FROM AQUEOUSSOLUTIONS.E.S. VAISERMAN a , V.Yu. RYASHENTSEV* a & S.V. ROGOZHIN aa A.N. Nesmeyanov Institute of Organoelement Compounds, Academy of Sciences of USSR ,Vavilov st., 28, Moscow, 117813, USSRPublished online: 27 Apr 2007.
To cite this article: E.S. VAISERMAN , V.Yu. RYASHENTSEV* & S.V. ROGOZHIN (1990) THE DISTRIBUTION OF NOR-α-AMINOACIDSIN LIQUID TWO-PHASE TERNARY SYSTEMS FORMED BY SALTING-OUT OF LOW ALIPHATIC ALCOHOLS FROM AQUEOUS SOLUTIONS.,Solvent Extraction and Ion Exchange, 8:1, 35-47, DOI: 10.1080/07366299008917985
To link to this article: http://dx.doi.org/10.1080/07366299008917985
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SOLVENT EXTRACTION AND ION EXCHANGE, 8(1), 35-47 (1990)
THE DISTRIBUTION OF NOR-M-AMINOACIDS IN LIQUID TWO-PHASE TERNARY
SYSTEMS FORMED BY SALTINC-OUT OF LOW ALIPHATIC ALCOHOLS FROM
AQUEOUS SOLUTIONS.
E.S.VAIKERMAN, V.Y~.RIASHENTSEV', S.V.ROGOZHIN
il. iV. ,Vesme.vanov Ins ti tote of Organoelement Compounds, ;lcademy
of Sciences of LSSR, 11 i8l3 Moscow, L'avilov st., 28, USSR.
ABSTRACT
It is shown that the distribution of homologous series of nor-a-aminoacids in liquid two-phase three-component systems formed by salting-out of low aliphatic alcohols from their aqueous solutions by sodium chloride can be described by the folloving relation:
& I D = a + b h 9 , vhere: D is the distribution coefficient expressed as the
ratio of concentration of aminoacid in the upper and lover phases, respectively; 9 is the ratio of alcohol concentration expressed in molar percent in the same phases; a and b are constants related to activity coefficients and salting-out constants of aminoacid and alcohol by sodium chloride.
INTRODUCTION
The liquid two-phase ternary systems (TPTS) formed by
salting-out of polar organic solvents from their aqueous
Copyright 8 1990 by Marcel Dckker, Inc
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36 VAINERMAN, RYASHENTSEV, AND ROGOZHIM
solutions, the so-called Timmermans' systems, are promising with
respect to separation of various bioorganic substances (1,2). Due
to this fact the origin of fractionating action in these systems
is of primary importance.
It was shown (31, that the distribution coefficient of
3-aminophtalimide (API) in such a typical Timmermans' system as
11-PrOH - H20 - NaCl is directly dependent on the relative
concentration of alcohol in coesisting phases. Qualitatively, it
can be interpreted as the result of the difference in the
solvating strength of these phases. The experimental data on
fluorescence spectra and reversed phase HPLC enables one to assume
that the solvating strength of mised three-component solvents
comprising alcohol, salt and water out of the demising zone is
mainly determined by the water/alcohol ratio, since the salt does
not effect the solvation of API.
Due to this fact the distribution coefficient of API is
likely to depend on the ratio of alcohol concentration in the
coexisting phases. Further thorough treatment of experimental data
on distribution of API showed that the following relation is
valid:
here: D is the distribution coefficient espressed as the ra-
tio of the concentration of API (mg/ml) in the upper
and lower phases, respectively;
O is the ratio of alcohol concentration expressed in
molar percent in the same phases;
a,b are constants.
It was interesting to find out to vhat extent this relation
was applicable and to give a phisical meaning of constants a and b.
Bearing this in mind we studied esperimentally the distribution of
homologous series of nor-a-aminoacids ( Gly, Ala, .lBL', Val, Leu )
in TPTS formed by salting-out of low aliphatic alcohols
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( n-PrOH, i-PrOH, t-BuOH ) from their aqueous solutions in the
presence of sodium chloride. We also attempted to derive
theoretically the equation for this distribution.
Nor-a-aminoacids are difile molecules which are soluble in
water, alcohols and mixed aqueous organic solvents. The properties
of these aminoacids in solutions have been studied well enough.
The use of a homologous series makes it possible to compare the
results of distribution of aminoacids which differ only in the
number of CH -groups in the hydrocarbon chain. From this point of 2
view the nor-a-aminoacids are a convenient object to carry out
experiments of this kind.
EXPERIMENTAL
Materials. We used n-propanol, i-propanol, t-butanol purified
according to the method given in ( 4 ) and distilled on a rectifying
column supplied with a stainless steel spiral-prismatic nozzle
(3~3~0.2 mm.), layer height - 70 cm. The water content in alcohols was less than 0.05 X . We used deionized water having resistivity
215 &/cm, sodium chloride of hiqh purity grade ("Reakhim", USSR),
aminoacids (all racemic) of pure grade ("Reanal",C.zechoslovakia)
were used without further purification.
Methods. The distribution of aminoacids in TPTS having
different contents of equilibrium phases (Table 1) was carried out
in the following manner. A certain amount of aminoacid was
dissolved in the required amount of water. The needed amount of
salt was added to this solution on stirring, and then required
amount of alcohol was added. The formed two-phase system was
stirred for 2-3 hours at temperature 2 5 f 0.1 OC. When the
stirring was completed, the system was thermostated fir 2-3 hours
to ensure the complete separation of the layers formed. The
aliquotes of the co-existing phases *ere taken to assess the
aminoacid concentration by the reaction with o-phthalic aldehyde
described in ( 5 ) .
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TABLE 1
Composition of equilibrium phases (weight percent) at 25'~.
System : n-PrOH - H20 - NaCl
Top phase z-p-pz 1.00 17.00 82.00
1.20 21.80 77.00
2.25 32.50 65.25
2.50 37.50 60.00
System : i-PrOH - H20 - NaCl
System: t-BuOH - H20 - NaCl (6)
AC
32.73 7.19
19.37 5.48
9.23 2.99
5.37 2.30
Bottom phase
The distribution coefficient was'calculated according to the
equation: D = Clj/C2, where CI and C . are concentrations of 2 aminoacids in mg/ml in the upper and lower. phases, respectively. . In preliminary experiments we found that when the aminoacid
content is less then 2.5 mg/ml in TPTS 'the value of the '
distribution coefficient does not depend on its concentration. The
NaCl
21.10 74.00 4.90
17.00 75.70 7.30
11.75 77.00 11.25
9.75 74.00 16.25
H20 n-PrOH
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THE DISTRIBUTION OF NOR-CI-AMINOACIDS 39
value of D was determined as the average result of three or more
independent experiments. The experimental error in determination
of D was less than 5%.
The content of equilibrium phases presented in Table 1 was
determined by analysing the alcohol and salt concentration in the
coexisting phases. The alcohol content was determined by GLC and
the content of salt was obtained gravimetrically according to the
method described in (1). The experimental data on the t-BuOH - H20 - NaCl system were borrowed from paper (6).
The programmable calculator HP-9815s (USA) was used to
process experimental data.
RESULTS AND DISCUSSION
It was found in agreement with the results obtained for API
that the distribution of aminoacids in TPTS can be described by
equation [ 1 I. The experimental data on distribution of aminoacids in TPTS
comprising n-PrOH - H 0 - NaCl plotted as h D versus h @ are 2 presented in Fig.1. The constants a and b calculated by least
square fitting are given in Table 2.
The analysis of the experimental data enables one to conclude
that equation [I] has a sufficiently universal character. The
distributed substances mainly affect the value of constant b. Thus
in the series Gly - Leu the value of constant b drops aproximately 7 times and the value of constant a is almost constant and equals
zero within the experimental error. The value of constant b
correlates with the number of CH2-groups of the aminoacid
molecule. The profile of this dependence is given in Fig.2.
Qualitatively, this means that the higher hydrophobicity of
the distributed compounds (i.e. the higher degree of its alcohol
solvation), the more their trend to concentrate in the upper
organic phase.
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V A I N E M A N , RYASHENTSEV, AND ROGOZHIN
1 . 0 2 . 0 3.0 $
FIGURE 1. The distribution of nor-a-aminoacids in TFTS n-PrOH - H20 - NaCl.
TABLE 2
The least-square coefficients for aminoacids distribution.
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THE DISTRIBUTION OF NOR-a-AHINOACIDS
0 1 2 3 4 "CH,
FIGURE 2. The value of b constant versus number of CH - groups in aliphatic chain of aminoacid. 2
The same behaviour was observed for the distribution of Cly
and Val in TPTS formed by salting-out of i-propanol and t-butanol.
The corresponding calculated values of the constants of
equation [ I ] for these systems are given in Table 3 (the results
for system n-PrOH - H20 - NaCl are presented for compa-
rison).
We can deduce that the decrease in alcohol polarity in the
i-PrOH - n-PrOH - t-BuOH series results in the decrease in the distribution coefficient of the given aminoacid, which is
reflected in constant b of equation [ I ] . This fact proves that the
value of constant b is not only defined by the properties of the
distributed substance but also by the origin of alcohol.
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VAINERMAN, RYASHENTSEV, AND ROGDZHIN
TABLE 3
The least-square coefficients for Gly and Val distribution.
I aminoacid ( alcohol
It is known that the equilibrium condition for any two-phase
system occurs when the value of chemical potentials of all its
components in the coexisting phases are equal:
Here, lpi, 2pi are the chemical potentials of the i-th
component in the upper (1) and lower ( 2 ) phases, respectively.
~xpressing the chemical potentials through activity values,
one bbtains:
after rearrangement:
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THE DISTRIBUTION OF NOR-a-AMINOACIDS 43
0 0 Here lai and 2ai are the activities, lpi and 2pi the
standard chemical potentials of the i-th component in each
phase.
The equation similar to [31 can be written if both the phases
are in equilibrium with the i-th component in its saturated
solution:
Here a* and at are the activities of the i-th component in 1 1 2 i
saturated solution of each phase.
Thus, we can deduce that
If we assume that a = fC (where f is the activity
coefficient, C the concentration), and a = f * ~ (where f* is the,
activity coefficient in saturated solution, S the solubility),
the equation [ 5 ] after rearrangement can be rewritten:
Denoting h 1Ci/2Ci = Ki, where K. is the distribution coef- 1
ficient of the i-th component one obtains:
where and ?S. are the solubilities of the i-th compo- - 1
nent defined as the concentrations of its saturated solutions in
ihe upper and lower phases, respectively.
It is well known that the relation between the solubility of
a compound (e.g. alcohol) and the concentration of the salt in
aqueous-salt systems is described by Setschenov's equation (7):
Here ?and S are, respectively, the solubilities of the
compound in water and aqueous-salt solution with the salt
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44 V A I N E R M N , RYASHENTSEV, AND ROGOZHIN
concentration Cs; k is the saltig-out constant defined by the S
origin of the compound and salt.
Here one con write for each coexisting phase:
6 1 so/ S. = ki LCs 1 1 1
[91
8.n .$/?si = k; ,cs [ 101
where C and ,C: are the concentrations of salt in the upper I s - S and lower phases.
Subtracting equation (31 from [lo], one obtains:
fh lsi/2Si = ( ,ci - ,ci ) [Ill
This equation represents the relation between the solubility
of a component ill the coexisting phases and the difference of salt
concentrat ion in these phases.
Substituting the value of 1Si/2Si taken from equation [I11
into equation [ 7 ] , I;e obtain:
h K. 1 = ki s ( 2Cs - lCs ) + Pin 1f;~2fi/2f;~lfi [I21
I f we denote I C 2 s
the equation [ I 2 1
can be rewritten:
- C ) - ACs and {& f*x f./ ffx f . 1 - mi' 1 s l i 2 1 2 1 1 1
a. L
[I31
Let us consider this equation with respect to an organic sol-
vent (A]. Denoting its distribution coefficient as K = +, we A obtain:
I f one assumes that the substance ( R l introduced in the sys-
tem does not affect the content of the coexisting phases (which
seems to be true in view of its small concentrations) then,
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VAINERMN, RYASHENTSEV, AND ROGOZHIN
0.1 0.2 0.3 k: (lit.)
I r Leu 0 Val
.I 0 Ala
FIGURE 3. The comparison of calculated salting-out cons- tants of aminoacids with published data (8).
equation of the first order as a function of the difference of
salt concentration in the coexisting phases.
Table 4 represents the results of processing the experimen-
tal data on the distribution of aminoacids and n-PrOH in TPTS
comprising n-PrOH - H20 - NaCl in coordinates &% @ - PCs.
The analysis of these data proves that 'the above assumption
is valid. The comparison of the values of constants kR for S
aminoacids 'in equation [I51 which, according to our derivation,
are equal to the salting-out constants, shows that they correlate
satisfactorily with the values given in liteterature (8) (Fig. 3).
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THE DISTRIBUTION OF NOR-a-AMINOACIDS 47
This proves the validity of the proposed approach for analy-
sing the substance distribution in TPTS of this type.
It is necessary to point out that the distribution of organic
solvents as well as that of aminoacids is described by the similar
equations which put the relations between the distribution
coefficient and the difference of salt concentration in the
coexisting phases through the salting-out constant value.
It can be assumed that the established relations can be
useful both for further investigations of the nature of formation
of two-phase liquid systems and for analysis of the distribution
of various substances.
REFERENCES
(1) V.Yu Ryashentsev, M.A. Voskoboinikov, E.S. Vainerman and
S.V.Rogozhin, J.Chromatogr., 216, 346 (1981). ( 2 ) V.Yu.Ryashentsev, E.S.Vainerman and S.V.Rogozhin, in VII All-
Union Conference for Extraction Chemistrx, Nauka, Moscow,
1984, p. 50 (in Russian)
(3) V.Yu.Ryashentsev, E.S.Vainerman and S.V.Rogozhin, J.Chroma-
togr., 288, 43 (1984). ( 4 ) A . J .Gordon and R.A. Ford, The Chemist's Companion, Mir, Moscow,
1973 (in Russian).
( 5 ) V.Y.K.Shvyadas, 1.V.Galaev and I.V.Berezin, Bioorg.Chem.,i, 19
(1978) (in Russian).
(6) T.V.Kuporova and I.L.Krupatkin, in Phase Eauilibria, Kalinin-
grad university, Kaliningrad, 1974, p. 118 (in Russian).
( I ) I.Setschenov, Z. Phys. Chem., 4, 117 (1889). (8) P.K.Nnndi and D.R.Robinson, JACS, 94, 1308 (1972).
Received by Editor
May 30, 1989
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