Indian Journal of Chemistry
Vol. 40A. November 200 I. pp. 1218-1221
Viscosities of amino acid-urea-water ternary
systems from 298.15 to 318.15 K
B N Wari s*, U Hassan & N Shrivastava
water varied from 100 to 200 seconds depending
upon the temperature. The time of fall was recorded
with a stop-watch of least count 0.1 second. Poiseui lles equation
Department of Chem istry, Aligarh Muslim University,
Aligarh 202 002 , India
Received 20 lilli e 2000; revised 16 l illy 2()()}
The vi scos ity B-coe ffici ents for the amino acids valine.
threonine, serine and glycine have been eva luated in ureawater-mi xture in the temperature ran ge 298.15 K to 3 18. 15 K.
The effect of temperature on thi s parameter has also been slUdied. It has bee n found th at the stru clUre of th e hyd rocarbon
ch3in of the 3mino acid plays a predomi nant ro le in determinin g
the sign of the temperalUre depende nce of th e B-coe ffi cient,
i.e .. OBIOT. A positi ve sign of both B-coefficien t and its temperature deri va ti ve i. e. 8Blor indi ca tes a stru ct ure-break in g ion
or molecule and negat ive sign. a structure- mak in g one.
The study of viscous behaviour of macromolec ul es in solution is important in understanding
the mechanism of tran sport processes. Viscosity and
its deri ved parameters provide valuable information
regarding the shapes and sizes of th ese molecules l .
Such meas urements on th e dipolar io ns, particulariy
of th e amino acids, have been carri ed out by a
number of workers 2 -6 . However, th e temperature
effect on th e solution has not bee n exten sively
st udied for amino acids in mixed aq ueo us so lvents.
Therefo re, in th e present case the viscosity Bcoe ffici ent has been evaluated for th e amino-acidurea-water systems in the temperature ran ge of
298.15 to 3 18.1 5 K. The amino acids are L-glycine,
L-serine an d L-valine . Thi s st udy di sc usses the
st ru cture-mak in g or breaking abi li ty of the so lute on
a particu lar so lvent.
Experimental
The amino acids (S LR , Mumbai , India) were ex tra pure and used without further purification , 0. 1 m
aq ueo us urea (Quali gen Co., India) so luti on was
take n as so lvent for the preparation of amino acid
so lutions of different concentrations.
The viscosity measurement has been made with a
Cannon-Ubbelohde viscometer. The viscometer was
calibrated with distilled water. The time of fall for
was employed to calculate the viscosi ty of the amino
acid-urea-water so lutions . Here p is the density of
th e amino acid so lutions, h is th e height of the
column in the viscometer, g is the acce leration due
to gravity, r is the radius of the capi llary, I is th e
length of the capillary, and t is the time of fall of th e
solution of vo lume v. The term h, g, r, I and v are
constant for a given viscometer; therefore these have
been replaced by sing le term B.
The densities of the amino acid-urea-water
solutions were determined by the calibrated pyknometer of 5x lO-6 m3 capacity at each temperature
studied (Table 1). Temperature for both density and
viscosity determination was controlled in constant
temperature bath to ± 0.7° at 25.0, 30.0, 35.0, 40 .0,
and 45 .0°C. The precision in the measurement of
density was approxi mately ± 0.1 %. Due to thi s, th e
error limit in the calculation of viscosity by
Poise uilles
equation
was
approximately
± 0.2% (Table 2) .
The vi scos ity B-coeffici en t of the l ones-Dole
equation has been determined according to th e
.
3
equation
1/ r
11 r= 11'/ 11= 1 +. AC + BC + De
2
... ( I )
where C is the molar concentration (moles dm -3 );
11' and 11 are th e viscosities of the solution and the
solvent, respectively; A-, B- , and D-coefficients are
to be determin ed. A-coeffici ents possess a non-zero
value only for electrolytes where they are observed
to be always positive. B-coeffici ents are positive for
non-electrolytes and either positive or negative for
electrolyte. B-coeffici ents meas ure the structural
modification induced by so lute- solvent interaction 6- 8 . The significance of D-coefficient is not
clearly understood .
NOTES
Results and discussion
The viscosity coefficients for amino acid-ureawater systems have been expressed in terms of JonesDole equation. Amino acids are dipolar ions in solution , and their viscosity measuremen ts display non electrolytic behaviour, therefore, A-coefficient is not
req uired to fit in the data and equation (l) becomes
T] r = T]'/T]
=
1
+. BC tDC2
... (2)
For each dipolar ion, at a fixed temperature a plot of
(T] r - 1)/C vs C was constructed and the B-coefficient
1219
was evaluated from the intercept and the D-coefficient
from the slope. Results obtained for the B- and 0coefficients are tabulated in Table 3.
The increase in concentration of solute in solution
contributes positively to the viscosity B-coefficient.
On the other hand, the breaking of the solvent structure by solutes causes a decrease in the viscosity. This
contributes negatively to the B-coefficient. Thus
B-coefficient is the resultant of these two opposite
forces 2• Therefore the moleculeslions exhibiting
negative B-coefficient have been assumed to exert a
structure-breaking effect. On the solvent, while the
Table I-Density (kg m') of amino acid-urea-water systems as functions of concentration and temperature
Glycine
298 .15
303.15
Temperature (K)
308.15
313.15
318.15
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
998.8
1002.1
1005. 1
1009.2
1013.3
1015.7
1021.0
1024.6
1026.0
1031.0
1034.5
997.1
1000.7
1003.6
1007.6
1011.7
1014.0
1019.4
1022.9
1024.3
1029.2
1032.8
995.4
999.0
1001.9
1005.8
1010.0
1012.2
1017.6
1021.1
1022.5
1027.3
1030.9
993.4
997 .2
1000.0
1003.9
1008.0
1010.3
1015.6
1019.1
1020.5
1025.3
1028.8
991.3
995. 1
997.9
1001.8
1005.9
1008.2
1013.4
1016.9
101 8.4
1023. 1
1026.6
0.10
0.16
0.24
0.32
0.43
0.48
0.56
0.64
0.72
0.86
1004.6
1009.6
1013.9
1017.8
1021.8
1026.1
1029.6
1034.0
1037.5
1041.1
1003.9
1008.5
1012.8
1016.8
1020.8
1024.9
1028.6
1032.8
1036.5
1040.8
1002.7
1007.1
1011.3
1015.3
1019.4
1023.4
1027.2
1031.2
1035.0
1038.8
1001.0
1005.2
1009.4
10 13.4
1017.6
1021.5
1025.3
1029.2
1033. 1
1036.9
998 .9
1002.9
1007.1
1011.2
1015.3
1019. 1
1023.0
1026.9
1030.7
1034.5
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1003.8
1007.6
1014. 1
1017.4
1022.9
i027.2
1030.0
1036.4
1002.2
1006.2
1012.5
1015.9
1021.3
1025.5
1028.3
1034.6
1000.5
1004.5
1010.8
1014.1
1019.6
1023.6
1026.5
1032.7
998.6
1002.7
1008.8
1012.2
1017.6
1021.6
1024.5
1030.7
996.6
1000.6
1006.7
1010.2
1015.4
10.19.4
1022.3
1028.6
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
1002.1
1003.3
1004.4
1006.0
1007.6
1009.0
1010.6
1012.2
1000.4
1001.7
1002.9
1004.4
1006.0
1007.4
1008.9
1010.5
998.6
999.9
1001.1
1002.6
1004.2
1005.6
1007.1
1008.7
996.7
998.0
999 .3
1000.7
1002.2
1003.6
1005.2
1006.7
994.5
995.8
997.2
998.6
1000. 1
1001.5
1003.0
1004.5
Serine
Threonine
Valine
INDIAN J CHEM, SEC A, NOVEMBER 2001
1220
Table 2-Viscosity (11 x 10 4 Nm·2 s) of amino acid-urea-water systems as function s of concentration and temperature
C (mol/dm·3)
298.15
303.15
9.02
9.09
9.20
9.32
8.06
8.16
8.26
8.37
Temperature (K)
308.15
313.15
318.15
7.53
7.62
7.70
7.77
7.87
7.98
8.05
8.14
8.23
6.54
6.75
6.85
6.97
7.06
7. 15
7.25
7.35
7.46
7.5 5
7.64
5.99
6.20
6.31
6.41
6.52
6.60
6.71
6.79
6.89
7.00
7. 10
6.65
6.82
7.0 1
7. 16
7.33
7.5 1
7.67
7.88
8.04
8.22
6.08
6.25
Glycine
0.0
0.10
0.20
0.30
7.23
7A5
OAO
9A4
8A9
0.50
0.60
0.70
0.80
0.90
1.00
9.54
9.67
9.79
9.88
10.0 1
10.12
8.59
8.75
8.82
8.91
9.05
9.16
0.10
0.16
0.24
0.32
9.07
9.35
9.60
9.82
10.05
10.32
10.60
10.79
11.07
11.34
8.17
9.70
9.93
10.16
7.36
7.59
7.76
7.94
8.11
8.32
8.51
8.72
8.92
9.12
9.10
9.42
9.74
10.02
10.42
10.75
10.96
11.47
8.39
8.65
8.95
9.20
9.75
9.84
10.13
IOA3
7.53
7.76
8.04
8.25
8.75
8.81
9.07
9.35
6.87
7.07
7.32
7.50
7.79
7.99
8.36
8.64
6.22
6.36
6.59
6.75
7.01
7.19
7. 37
7.60
9.13
9.29
9.55
9.73
9.94
10.19
10.44
10.70
8.18
8.30
8.53
8.69
8.89
9. 10
9.32
9.54
7.34
6.64
6.76
6.89
7.04
7.19
7.33
6. 10
6. 17
6.31
6.44
6.56
6.69
6.82
6.96
Serine
OA3
OA8
0.56
0.64
0.72
0.86
8A2
8.63
8.82
9.02
9.26
9A9
6AO
6.55
6.71
6.86
7.00
7.18
7.34
7.5 1
Threonine
0.10
0.20
0.30
OAO
0.50
0.60
0.70
0.80
Va line
0.05
0. 10
0.15
0.20
0.25
0.30
0.35
OAO
7A5
7.64
7.79
7.96
8.13
8.3 1
8.50
Table 3-Viscosity B-coefficients (M .,) and D-coeffi cients
{M·2. )
Amino acid
Temperature (K)
303.15
308. 15
298 .15
7A8
7.63
as function s of temperature for amino acids-urea-water systems
313.15
318.15
Glycine
BD-
0.1163
0.01 15
0. 1444
-0.0066
0.1829
-0.0675
0.1325
O. 0494
0.2729
-0. 1127
Serine
BD-
0.1643
0.22 17
0.2250
0.1383
0.2590
0.0891
0.2326
0.1 188
0.2191
0.13 17
Threoni ne
BD-
0.2350
0.1363
0.3800
-0.0277
0.3201
0.0436
0.2500
0.1407
0.2980
0.0357
Valine
BD-
0.3390
0.0556
0.3325
0.0474
0.3400
0.0346
0.3320
0.0303
0.3310
0.0254
NOTES
ions with posItIve B-coefficient exert a structuremaking effect on the solvent. In the present case, glycine and valine belong to the category of amino acids
having hydrocarbon chains, threonine and serine belong to the group containing a hydroxyl group attached to the hydrocarbon chain the amino acids. But,
when the data was compared, it was found that in determining the viscosity of an amino acid, the charge
distribution is less important than the size and structure of the hydrocarbon chain. Due to the large size
and non-electrolytic nature all the amino acids, irrespective of the structure, show significant positive
core contribution to the B-coefficient, which exceed
any negative contribution . All the dipolar ions including amino acids will exhibit a poslttve
B-coefficient. Therefore the sign of 881& appears to
be a more straightforward indicator of the structurebreaking or making ability than the sign or the size of
the B-coefficient3 .
In the present case, the B-value of glycine increases with increase in temperature since
B-coefficient and its derivative of temperature 3
(i.e. 8818
is positive. We can classify glycine as a
structure-breaker in urea-water mixture. Therefore,
glycine, being polar in nature, is involved in hydrogen
binding with the solvent components resulting in the
breaking of the solvent structure. Another amino acid
valine, belonging to the same category as that of glycine, shows negative 881&. Since B-value decreases
with temperature indicating structure making properties. This property is due to the presence of hydrophobic (or polar) R group which stabilizes the structure of the solvent through hydrophobic hydration
with the solvent components. In this case the probability of hydrogen bonding between the molecules of
the solvent is increased by forming solvent clathrate
around the hydrophobic moiety. The B-value for serine increases up to 308.15 K, then decreases and
negative values of 8818T are observed at 313.15 K
and 318.15 K. This might be the effect of decrease in
solvation at higher temperature. Threonine, also having a polar OH group attached to hydrocarbon chain,
n
1221
0 .4 , . - . - - - - - - - - - - - - ,
0 .3
.. 0 .2
"0
E
o
o
0.1
o Glycinl2
.Sl2rinl2
/; Thrl2oninl2
• Valinl2
o . o~----,._';,_,;_~~----,.-;~__::;o~~
295
300 305
310
315
320
Tl2mpl2raturl2 (K)
Fig. I-Plots of B-coefficients versus temperature for amino ac idurea-water systems
shows a positive 8818 T upto 303.15 K and after that
there is decrease in the value of B-coefficient. This
decrease is most pronounced in the case of threonine
which may be due to the additional effect of a polar
CH 3 group attached to the side chain of the amino
acid. The magnitude of the B-coefficient is larger in
the case of threonine as compared to that of serine due
to its large size. After 313.15 K, the effect of CH 3
group is suppressed by the effect of OH group. The
results are illustrated in Fig. 1.
References
I
2
3
4
5
6
7
8
Stokes R H & Mills R, Viscosity of electroLytes and related
properties (Pergamon, London), 1965.
Mason L S, Kampmeyer P M & Robinson A L, J Alii chem
soc, 74 (1952) 1287.
Tsangaris J N & Martin R B, Arch Biochem Biophys, 112
(1965) 267.
Tynel H J V & Kennerly M, J chern soc A, (1968) 2724.
Devine W & Lowe B M, J chern soc A, (1971) 2113.
Dey N C, Saikia B K & Haque I, Call J chern , 58 ( 1980)
1512.
Pandey J D, Misra K & Mushran V, Accust Lett, 15 ( 1992)
231.
Nikam P S & Saw ant A B, BuLL chern Soc Japan , 71 (1998)
2055 .