H. D. ELLERTOK, G. REIXFELDS, D. E.
398
l I U L C I H Y , AXD
P.J. DUXLOP
Activity, Density, and Relative Viscosity Data for Several Amino Acids, Lactamide, and Raffinose in Aqueous Solution at 25"
by H. David Ellerton, Gundega Reinfelds, Dennis E. Mulcahy, and Peter J. Dunlop Dppartment of Physical and Inorganic Chemistru, L'nmersity of Adelaide, Adelazde, South Australza (Received August 12, 1963)
Isopiestic vapor pressure measurements, densities, and relative viscosities are reported for aqueous solutions of glycine, glycylglycine, a-amino-n-butyric acid, dl-valine, lactamide, and raffinose a t 2.5'. Osmotic and activity coefficients have been computed from isopiestic vapor pressure measurements and compared where possible with the data preriously published. Apparent and partial molar volume data have been obtained from the density measurements.
The rate at which relative motion of the two components of a binary solution takes place under the influence of chemical potential gradients was first described in terms of a diffusion coefficient, D , by Fick's first law.' It has been pointed out, however, that the diffusion coefficients in both binary and ternary diffusion depend on the frame of reference used, and coefficients on various frames of reference have been defined.2 It has also been shown that the above transport process may be described in terms of a set of mutual frictional coefficients which are independent of the frame of reference sed.^-^ These mutual frictional coefficients may be obtained by combining the diffusion coefficients with certain activity and density data. I t is the purpose of thie paper to report activity data for the binary systems glycine-H20, glycylglycine-HzO, a-amino-n-butyric acid-H20, dl-valiiieHzO, lactamide-HzO, and raffinose-HzO at 23" for uke in computing mutual frictional coefficients for these systems (see companion paper13). Density and relative viscosity data are also reported for four of the above systems. These binary systems were chosen so that comparisons could be made with other data for amino acids, isomers of amino acids. and sugars previously reported in the literature.
Experimental Materials. -411 reagents used, except raffinose, were recrystallized from doubly distilled mater until successire recrystallizations were indistinguishable The Journal of Phgsical Chemistry
by the isopiestic method. l1 The solutions were prepared by weighing and the weights were corrected to weight in vacuo. Doubly distilled water was always used as the solvent. In the case of the activity measurements, the solutions mere prepared so that they were initially reasonably close to their equilibrium values. The densities of the solids used for the vacuum corrections are reported in row 8 of Table 11, and the molecular weights12 used for calculating the solution concentrations are in row 9 of the same table. Sodium chloride (reference solute) was A.R. grade and was recrystallized once from doubly distilled mater, dried in vacuo, and fused in a platinum crucible. Using A. Fick, Pogg. Ann., 94, 59 (1855). J. G. Kirkwood, R. L. Baldwin, P.J. Dunlop, L. J. Gosting, and G. Kegeles, J . Chem. Phys., 33, 1505 (1960). (3) R. P. Wendt and L. J. Gosting, J . P h y s . Chem., 63, 1287 (1959). (4) 0 . Lamm, i b i d . , 61, 948 (1957): Acta Chem. Scand., 11, 362 (1957). (5) R. R . Laity, J . Phys. Chem., 6 3 , 80 (1959). (6) R. J. Benrman. i b i d . , 65, 1961 (1961). (7) .1.Klemm. Z . A7aturforsch., 8a, 397 (1953). (8) S. Ljunggren, T r a n s . Royal I n s t . T ~ c h n o l .Stockholm, No. 172 (1961). (9) P. J. Dunlop, J . P h y s . Chem., 68, 26 (1964). (10) €1. D. Ellerton. G . lieinfelds, D. E. Mulcnhy, and 1'. J. Dunlop. ihid.,68, 403 (1964). (11) R. A. Robinson and R . H. Stokes, "Electrolyte Solut,ions," Butterworths Scientific Publications. London, 1959, pp. 17i-181. (12) Using atomic weights compiled in International Union of Pure and Applied Chemistry, Information Bulletin Yo. 14b (196l), (1) (2)
ACTIVITY,I ~ N S I TAY N D, VISCOSITY OF AMINO ACIDS
the isopiestic method the once recrystallized material was found to be identical with a sample that had been twice recrystallized. Sucrose was BDH microanalytical grade and was used without further purification. Glyc.ine was obtained from British Drug Houses and this A.11 material was recrystallized once from doubly distilled water. Samples of the first and second recrystallizations were indistinguishable by the isopiestic method. l1 Glycylglycine was obtained from British Drug Houses and was recrystallized four times. a-Amino-n-butyric acid was obtained from the Sigma Chemical Corp., U. S. A., and was recrystallized three times. &Valine was purchased from Kutritional Biochemicals Corp., U. S. A., and was also recrystallized three times. Lactamide was part of a sample prepared for diffusion measurements by Wendt and Gosting3 and had been recrystallized three times. Raffinose was obtained from the Pfanstiehl Laboratories, Inc., U. S. A, and was used without further purification. Osmotic and Activity Coeficients. Osmotic coefficient measurements are of importance since thcy may be combined with density data to obtain the factor (1 C b In y/dC) = (1 (? b In y/de) which is used in the computation of mutual frictional coefficients. Here C and 6 are solute concentrations in moles/cc. and moles/lOOO cc., respectively, and y is the corresponding activity coefficient. The activity data were obtained from the osmotic coefficients determined by the isopiestic vapor pressure method which has been described in detail previously.Il The silver dishes used for containing the solutions had bases which had been ground to a high degree of flatness. These dishes were approximately 3.5 cm. in diameter and 2 cm. in height. Each dish had a close-fitting lid which had been ground so as to fit perfectly. Usually eight dishes were used for each experiment, four containing the reference solution and four containing the solution with unknown osmotic coefficient. Approximately 5 ml. of prepared solution was used per dish. I n order to determine whether any interaction was taking place between the silver dishes and the solutions, several gold-plated silver dishes were used simultaneously in a number of the experiments. S o difference could be detected between the behavior of the solutions in the silver and the gold-plated dishes. The dishes were placed on a flat silver-plated copper block of about %em. thickness which was contained in a glass vacuum desiccator. With the lids removed and the desiccator sealed, evacuation of the apparatus was commenced, and was generally carried out over a period of several hours to avoid splattering caused by
+
+
399
degassing of the solutions. After evacuation, the desiccator and contents were placed in a large thermostat bath, controlled at 2.5' to approximately +0.002", and rocked gently. Stirring of the solutions was effected by 4-mm. stainless steel ball bearings rolling across the bottom of the dishes under the influence of the rocking motion. It was observed that if no ball bearings were used in the dishes, the results were the same as-those in which either one or two ball bearings had been used. However, a much longer time was needed for the solutions to attain equilibrium when the ball bearings were absent. Also, the results were unaffected by whether the ball bearings were wholly or partially immersed in the solutions. The time required for equilibrium to be attained depended on thc concentration of the solution. For the more concentrated solutions, 5 to 7 days was required before the final weights were taken, but for the more dilute ones as much as 2 weeks was sometimes necessary. Sodium chloride was used as the reference solut,e for all systems except in the case of raffinose, for which sucrose was found to be the most suitable reference solute. The experimental values of the equilibrium molalities, m , of all the solutes studied and the molalities of the corresponding reference solutions, rnsacl or rnsucrose, a t 2.5' are given in Table I. To represent the osmotic coefficients, 4, which were computed from the equilibrium solute concentrations and the values of the osmotic coefficients of the reference materials, l 3 , I 4 equations of the form cj5 =
1
+
5 * = 1
Atm'
(1)
mere used and the coefficients A , obtained by the method of least squares.'j Values of the constants for eq. 1, together with the percentage deviations of the experimental points from the equations, are given in Table 11. It can be shown that
and hence using eq. 1
See ref. 11, p. 476. R.A. Robinson and It. H. Stokes, J . Phys. Chem., 6 5 , 1954 (1961). (15) An IBM 7090 electronic computer was used to least squnre all (13) (14)
data.
Volume 613,Number 2
February, 1964
I€. D. ELLERTON, G. REINFELDS, D. E . MULCAHY, AXD P. J. D V N L O P
400
.-
Table I : Summary of Tsopiestic Results at 25"
--Glycine-m
mNaCl
0.2064
0.1088 0 1718 0 1732 0 1747 0.2720 0 3969 0.4232 0 5616 0 5705 0 8429 0 9382 1 ,0286 1 0365 1.1414 1.3014 1 3155 1 4313 1.4433
0 3272 0.3298
0.3327 0.5290 0.7757 0,8282 1 1174 l.l;&? 1.7304 1.9424 2 , 1476 2 1657 2 4059 2.7772 2.80!24 3.0854 3.1139
Table T I :
-Glycyl m
glycine-
-Glycylglycine--
mNnci
0,1030 0.1047 0 2093 0.2127 0 3061 0.3121 0 4035
0.05328 0.05416 0 . 1071 o 1088 0 1549 0.1580 0.2021 0.4090 0 2045 o 5096 0.2517 0 5151 0 2544 0 6124 0 2996 0 . 6 2 3 8 0 3048 0.7100 0.3441 0.7229 0 3498 0 8183 0 39:3.4 0 . 8 3 5 ~ 0.4011 1.0213 0 , 4 8 4 5 1.0368 0 . 4 9 1 1
mxac1
1.1792 1.1942 1.3318 1 3468 I . 0744 1.3967 1 ,4897 1 5057 1.6038 1.62?(1 1 ,6255
0.5548 0.5614 0.6229 0.6291 0.6417 0 6513 O,69:33 0.7003 0.7447 0.7521 0.7,543
0.2191 0.3792 0.(;107 0.9586
1.0619 1.3925 1 6644 2 0796
0.1184 0.2072 0.3382 0.5357 0.5980 0.7855 0 0426 1 1860
--dl-Valinem mNnrl 0 09997 1016 0 3040 0 3089 0 3869 0 3909 0 4363 0 5196 0 5124 0 6033 0 5977
o
--Lact,arnide-
0 05328 0541~
0.2039 0.3216 0 3243 0.5098 0 7464 1 ,2902 1.600~ 1.6357 1.8370
o
0 0 0 0
0 0
0 0 0
mNnci
nt
1662
1688 2134 2156 2412 2896 2856 3386 3.352
2 4089 2 6009
3.0295 4.0940 4.0065
4.7473
0 1088 0.1718 0.1732 0 2720 0 3969 0.6729 0.8254 0.8429
0.9382 1.2049 1.2814
-RaHinosem m8Llcr0Se
0 1212 0 1263 0 1299 0 1837 0 1868 o 1901 0 2287 0 2330 o 2243 o ?.do1
1222 1273 1306 18.57 1891 o 1924 0 2312 0 2359 o 2275 o 2329 0 0 0 0 0
1.4814 1 ,9253
2.1247 2.1792
Coilstants for the Least-Squared Equations of Osmotic Coefficients us. Molarity a t 25"
Glycine
AI X A, X A~ x A &x A, X
m
a-Amino-n-butyric acid m mNRw
10 10' 103
Glycylglycine
a-Aminon-butyric acid
-2.682 0.251 27.595 0.876 -228.8 -1.76 104 1214.4 ... 10' ... -2.630 ... 70deviation f0 . 0 5 + O , 03 f0 . 0 3 Range 3.1 1.6 2.0 Solid density" 1.601 1.561 1.231 Molecular weightb 75.068 132.120 103.122 a The density of solid Sac1 was taken as 2.365 g./cc. and sucrose as 1.588 g./cc. taken as 58.443 and 342.303, respectively.
-0,960 3.334 -6.08 4.55
Thus, without, any graphical integration, molal activity coefficients, y, may be calculated using eq. 2a and the parameters A I in Table 11. Molar activity coefficients, y, may be computed with the aid of the density data for each system. It is believed that the activity coefficients computed by eq. 2a are accurate to within 0.1%. Denszty dfeasurements. All density measurements were performed in triplicate or quadruplicate with singlc stem pycnometers, each having a volume of approximately 30 cc. These pycnometers were calibrated a t 23" assuming the density of water, do, to be 0.997048 g./cc. They were cleaned before use with chromic acid, and over a period of about a year the volumes changed by less than 0 . 0 0 4 ~ 0 . The density values for each system were fitted to equations of the form The Journal of Phusical Chemistru
&Valine
0 383 0 48 40 6
Lactarnide
-0 0 -0 0
3202 4954 6771 521
Raffinose
1 333
f O 07
'
f 0 06 f O 12 0 6 4 7 0 23 1 316 1 138 1 465 117 149 89 095 504 446 The molecular weights o[ S a C l and sucrose were
by the method of least squares. The densities, d , are in g./cc. The values of the constants, B,, in eq. 3, together with the concentration limits and the percentage deviations of the experimental points from the equations, are given in Table 111. Apparent molar volumes for the solutes, a,, are given by the relation
where M is the molecular weight of the solute. By combining eq. 1 and 2, the apparent molar volumes may be expressed by equations of the form
ACTIVITY,DENSITY, A N D VISCOSITY OF AMINOACIDS
Apparent Molar Volume us. Concentration a t 25""
Glycylglycine
a-Aminon-butyric acid
B1
x
B~ x 103 B~ x 104
102
3.1978 -1,044 0.964
5 6007 - 2 165 2 63 1 0 003
2,7718 -0,460 ... 50.0005
% deviation
* O . 0007
5 0.0002
76,338 2 1713 -0 2643 1.4
75 628 0 4613
90.77[; 0.2501
...
...
1.1
0.5
dlValine
2.6642 -0.249
...
of densities 43,217 1 ,0473
910
DI DZ
- 0.0967
Range
2.1
Density data for lactsmide and raffinose solutions have been reported previously: F. T. Gucker, Jr., and T. W. Allen, J . Am. Chem. Soc., 64, 191 (1942); P. J. Dunlop, J . Phys. Chem., 60, 1464 (1956). a
@1
+
= @lo
2
i = l
DCi
(5)
qr =
1
(54
and the constants D, are given by D1
I
-(lOOOBz)/&
(5b)
D,
= - (1000B3)/d~
(5c)
Values for @lo,D1, and D2 are given in Table 111. Partial molar volurnes of the solute, 71, and of the solvent, To, may be computed using the equations of Geffcken16and the values of (Plo, D1, and Dz.
voo
where is the partial molar volume of the pure solvent, The partial molar volumes of the solvent are given in a, companion paper10 where they are used to compute mutual frictional coefficients. Viscosity Measurements. Two Ubbelohde viscorneters with water flow times of 288.7 and 328.5 sec., respectively, were 'used for the measurements. A small kinetic energy correction was applied to each result. It can be shown that
3 i = l
Fie$
(8)
Table IV : Constants for the Least-Squared Equations of Relative Viscosity us. Concentration a t 25" Glycylglycine
( M - 1000Bl)/&
+
by the method of least squares. The viscosity data, together with the concentration limits and percentage deviations of the experimental points from eq. 8, are given in Table IV.
where @io =
A - (B/t2)
(7) where 7 , d. and t are the viscosity, density, and flow time for a given solution, and A and B are constants. The kinetic energy correction, K , is given by K = ( B / A ) . The values of ( v / d t ) vs. (l/t2)for water were plotted a t 20, 25, and 30" to obtain A and B and hence K for each viscomleter. The value obtained was 530 sec. in each case. The experimental relative viscosity values were fitted to equations of the form (q/dt) =
Table I11 : Constants for the Equations of Density and
Glycine
401
FI X 10 Fz x 10% F~x 103 Range yo deviation
3.151 5.45 36.7 1.4 10.13
a-Aminon-butyric acid
3.606
0.89 67.8 1.0 50.07
dlValine
Lactamide
4.052 14.09 98.0 0.4
10.06
1.984 2.668 3.97 2.1 50.12
Discussion Osmotic coefficients for the systems glycine-H20, glycylglycine-€120, a-amino-n-butyric acid-H20, and dl-valine-HzO have been reported previously. l 7 -19 These measurements depended on the use of osmotic coefficients of sucrose solutions as a reference, as determined from earlier vapor pressure measurements. However, in order to achieve the maximum accuracy in computation of the frictional coefficients (see companion paper), a completely new series of measurements has been made using as the reference recently published osmotic coefficient data for sodium chlorideI3 and sucrose14solutions. When the osmotic coefficients calculated from this work were plotted as a function of molality, it was found that the points lay on smooth curves of a similar type to those obtained earlier b,y (16) W. Geffcken, 2. physik. Chem., A155, 1 (1931). (17) E. R. B. Smith and P. K. Smith, J . Bid. Chem., 117, 209 (1937). (18) P. K. Smith and E. R. B. Smith, ibid., 121, 607 (1937). (19) E. R. B. Smith and f.K. Smith, i b i d . , 135, 273 (1940).
Volume 68, n'umber 2
February, 1964
402
H. D. ELLERTON, G. REINFELDS, D. E. MULCAHY, AND P. J. DUNLOP
Smith and Smith.n-19 Their poin s, however, showed considerable scatter, and in some regions their values, after correction to the new standard, differed by as much as 1.5% for glycine, 1.3% for glycylglycine, 1.7% for a-amino-n-butyric acid, and 0.4% for dl-valine, from the values obtained in this work. It is of interest to compare the osmotic coefficients of lactamide with those of glycolamide. 2o The additional methyl group on the lactamide molecule seems to have little effect on the vapor pressure of the solutions, as the osmotic coefficients are almost identical with those of glycolamide solutions. However, the relative viscosities of lactamide solution,s showed greater concentration dependence than those of glycolamide.21 The densities of glycine solutions have been reported previously.22 The results of this work show an average deviation from eq. 3 of +0.000770 while those of the previous workers showed an average deviation from Fheir least-squared equation of kO.0097,. The two gets of results agree very closely at low and high concentrations but differ by as much as 0.012% in the region of 6 = 1. The densities and relative viscosities of glycylglycine solutions and a-amino-n-butyric acid solutions a t several concentrations have also been reported p r e v i o ~ s l y . ~The ~ densities agree with this work to within 0.003010 for glycylglycine solutions, and 0.007% for a-amino-n-butyric acid solutions, whereas the relative viscosities agree to within 0.5 and 0.3010, respectively. It is of interest to compare the apparent molar volumes of glycylglycine with those of two isomers, asparagine and methylhydantoic acid. The limiting apparent molar volume, for glycylglycine obtained from this work was 76.33 cc./mole, whereas values of apparent molar volumes of 78.0 and 94.2 cc. per mole
The .Journal of Phunirnl f'hemistry
have been quoted for asparagine24and methylhydantoic a t unspecified concentrations. Of the three isomers, glycylglycine has a much greater dipole moment than asparagine, which is an a-amino acid, whereas the methylhydantoic acid molecule, according to McMeekin, et ~ l . , ?bears ~ no electric charge. The charged condition of the first two molecules results in electrostriction of the solvent, and the apparent molar volumes are smaller than that of the uncharged methylhydantoic acid, whose volume is close t o that expected from empirical calculations. 26 The somewhat larger molecular volume of asparagine compared to glycylglycine has been attributedz7to the closer proximity of its -NH,+ and -COO- groups. Acknowledgments. The authors wish to thank Mr. E. W. Gooden for performing some of the experiments with a-amino-n-butyric acid and Dr. B. J. Steel for many helpful discussions and his criticism of the manuscript. This work was supported in part by grants from the Colonial Sugar Refining Co. Ltd. of Australia and the United States Institutes of Health (AM06042-02). (20) R. H. Stokes, T r a n s . Faraday SOC.,50, 565 (1954). (21) P. J. Dunlop and L. J. Gosting, J . Am. Chem. Soc., 7 5 , 5073 (1953). (22) F. T. Gucker, Jr., 1%'. L. Ford, and C. E. Moser, J . Phys. Chem., 43, 153 (1939). (23) J. Daniel and E. J. Cohn, J . Am. Chem. Soc., 5 8 , 415 (1936). (24) J. P. Greenstein and J. Wyman, ibid., 5 8 , 463 (1936). (25) T. L. McMeekin, E. J. Cohn, and J. H. Weare, ibid., 57, 626 (1935). (26) E. J. Cohn and J. T. Edsall, "Proteins, Amino Acids and Peptides," Reinhold Publishing Corporation, New York, N. Y., 1943, p. 157. (27) E. J. Cohn, T. L. McMeekin, J. T. Edsall, and M .H. Blanchard, J . Am. Chem. Soc., 56, 784 (1934).
