Embed Size (px)
Citation preview
71
CHAPTER 4
PARTIAL MOLAL VOLUMES, PARTIAL MOLAL
COMPRESSIBILITIES AND VISCOSITY
B-COEFFICIENTS OF SALBUTAMOL SULPHATE IN
AQUEOUS METHANOL SOLUTIONS AT 303.15 K,
308.15 K, 313.15 K AND 318.15 K
4.1 INTRODUCTION
Solute-solvent interactions play an important role in a variety of
phenomena. In bio-physical chemistry, drug interaction is a subject of
intensive studies, involving complex molecular mechanisms. Despite years of
investigations, many important drug actions and their mechanisms are not
fully understood. Structure activity relationship is one of the most common
rationale presented for explaining drug reactions.
One of the precise features that confer the solution properties of
drug molecules is the implication of hydrophobic and charge contributions.
In water, however, since the polar groups are hydrated, the intermolecular
aggregation of drug molecules through their hydrophobic parts is expected to
occur in a way analogous to miscillization, favouring their limited aqueous
solubilization. However, this aggregating tendency is affected with the
addition of the non-aqueous component. Alcohol molecules contain both
hydrophilic groups and hydrophobic tails. This unique quality towards an
aqueous environment leads to a complex self association behaviour which is
72
not exhibited in non aqueous solvents. The solution behaviour of alcohol
molecules in the water region is largely established by the phenomenon of a
polar or hydrophobic hydration. There are some reports available in literature
on the volumetric and transport properties of some drugs in aqueous methanol
solution system. Sharma et al (2008) have reported the values of ultrasonic
velocity and viscosity studies of narcotic drugs Parvodex and Tramacip in
binary mixtures of water +alcohol at 25oC. They have calculated free volume,
internal pressure and molar cohesive energy, from these results they
characterized the systems of hydrogen bonding in aqueous alcohol. The
studied drugs behave as structure promoter and enhance the presence of
interactions in the aqueous alcohol system.
Syal et al (2005) determined ultrasonic velocity values of Drug
Parvon–spas in mixed alcohol-water solvent systems at 25oC, and they have
characterized by hydrogen bonding in methanol, ethanol and propan-1-ol,
solute-solvent interactions .Further the studied drugs behave as structure
promoter in the aqueous alcohol systems. Sharma et al (2008a) have
determined partial molar volumes of the drugs namely Parvon-spas,
Parvon-Forte, Tramacip, Parvodex in various aqueous mixtures of alcohols at
25oC. Furthermore, the results are correlated to understand the solution
behaviour of drugs in aqueous-alcoholic systems, as a function of the nature
of the alcohol and solutes.
Sharma et al (2007) have reported viscosity values of drugs namely
Parvon-spas, Parvon-Forte, Tramacip, Parvodex in various aqueous mixtures
of alcohols (methanol, ethanol and 1-prapanol) at 25oC. The viscosity data
have been analyzed for the evaluation of A and B coefficients using
Jones-Dole equation. B-coefficients were found to be positive thereby
showing drug-solvent interactions. From these studies they concluded that all
73
the drug cations can be regarded as structure-makers due to hydrophobic
hydration of the drug molecules.
The partial molal volume is a characteristic parameter which is
indicative of molecular interactions in the solution phase. The transport
properties of drug molecules have important implications for the permeation
of the drug molecules through biological membranes. Thus, the behaviour of
the drugs in solutions may be of importance from a pharmacological point of
view. Further, alcohols are often present in drug delivery formulation.
Literature survey shows that thermodynamic and transport
properties of salbutamol sulphate in aqueous methanol solutions have not
been attempted. This chapter highlights the molecular interaction studies of
the drug salbutamol sulphate in water-methanol mixtures at different
temperatures. The data on density ( ), ultrasonic speed (u) and viscosity ( )
of salbutamol sulphate in different concentrations of aqueous methanol
solution are presented at four different temperatures. From these
experimental data, several thermodynamic and transport parameters like
apparent molal volume V , partial molal volume 0V , molal expansivity 0
2E ,
isobaric thermal expansion coefficient ( 2 ), second derivative of infinite
dilution of apparent molal volume with temperature 202 / TV , isentropic
compressibility sk , change in isentropic compressibility s , relative change
in isentropic compressibility ( 0/ ss kk ), apparent molal compressibility K ,
partial molal compressibility 0K , viscosity B-coefficient, variation of B-
coefficient with temperature, i.e., dB/dT, free energy of activation per mole of
solvent *01 and solute *0
2 are computed. The thermodynamic and
transport properties are discussed in terms of drug-solvent interaction and
structure making ability of the drug in the aqueous methanol solution.
74
4.2 EXPERIMENTAL
The densities, ρ, ultrasonic speeds, u and viscosities, η, of
salbutamol sulphate in aqueous methanol volume by volume ratio are
measured at temperatures, 303.15, 308.8.15, 313.15 and 318.15 K, using a
single capillary pycnometer, a single-crystal variable-path multifrequency
ultrasonic interferometer operating at 2 MHz and a Ubbelohde type suspended
level viscometer which are discussed in detail in Chapter 2.
4.3 RESULTS
The experimentally measured density values for the of salbutamol
sulphate in aqueous methanol solution at T = 308.15, 313.15 and 318.15 K are
shown in Table 4.1. The Uncertainty values with density are also given in
the same Table 4.1.
Table 4.1 Densities, , of Salbutamol Sulphate in Aqueous Methanol
Solution at different temperatures
mS / mol kg-1
10-3 / kg m-3
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-90%W+10%M)
0.0000 0.9858 0.9856 0.9830 0.9804
0.0500 0.9930 0.9922 0.9886 0.9852
0.0750 0.9976 0.9965 0.9922 0.9885
0.1000 1.0026 1.0015 0.9963 0.9923
0.1250 1.0088 1.0071 1.0006 0.9965
0.1500 1.0141 1.0124 1.0051 1.0012
75
Table 4.1 (Continued)
mS / mol kg-1
10-3 / kg m-3
303.15 K 308.15 K 313.15 K 318.15 K =4.2010-4 =4.0110-4 =3.2910-4 =3.0910-4 (V/V-80%W+20%M)
0.0000 0.9781 0.9747 0.9727 0.9694 0.0500 0.9851 0.9812 0.9782 0.9742 0.0750 0.9889 0.9854 0.9816 0.9774 0.1000 0.9939 0.9902 0.9854 0.9811 0.1250 0.9989 0.9954 0.9896 0.9849 0.1500 1.0039 1.0002 0.9938 0.9893
=3.8310-4 =3.8210-4 =3.1310-4 =2.9510-4 (V/V-70% W + 30% M)
0.0000 0.9588 0.9585 0.9582 0.9534 0.0500 0.9652 0.9647 0.9635 0.9582 0.0750 0.9693 0.9689 0.9669 0.9613 0.1000 0.9751 0.974 0.9709 0.9650 0.1250 0.9798 0.9792 0.9749 0.9689 0.1500 0.9859 0.9847 0.9792 0.9731
=4.0410-4 =3.9210-4 =3.1210-4 =2.9310-4 (V/V-60% W+40%M)
0.0000 0.9438 0.9432 0.9410 0.9386 0.0500 0.9500 0.9492 0.9459 0.9432 0.0750 0.9545 0.9533 0.9489 0.9461 0.1000 0.9594 0.9583 0.9522 0.9494 0.1250 0.9645 0.9634 0.9558 0.9528 0.1500 0.9704 0.9688 0.9595 0.9564
=3.9610-4 =3.8410-4 =2.7410-4 =2.6510-4 (V/V-50% W+50%M)
0.0000 0.9315 0.9301 0.9279 0.9241 0.0500 0.9373 0.9357 0.9326 0.9286 0.0750 0.9412 0.9393 0.9354 0.9314 0.1000 0.9453 0.9435 0.9385 0.9347 0.1250 0.9502 0.9481 0.9424 0.9385 0.1500 0.9556 0.9526 0.9462 0.9432
=3.5610-4 =3.3610-4 =2.7110-4 =2.8110-4 mS- stands for molal concentration of salbutamol sulphate:
-uncertainty in density values
76
Density values are used to calculate the apparent molal volumes of
salbutamol sulphate in aqueous methanol solution using equation 1.1 and are
given in Table 4.2. The error values for apparent molal volume are evaluated
using equation 1.2 and are given in Table 4.2 within parenthesis.
Table 4.2 Apparent Molal Volume V of Salbutamol Sulphate in
Aqueous Methanol Solution at Different Temperatures
mS / mol kg-1
V 610 /m3 mol-1
308.15 K 308.15 K 313.15 K 318.15 K
(V/V-90%W+10%M)
0.0500 433.7(2.17) 446.2(2.06) 468.1(1.70) 485.9(1.61)
0.0750 418.1(1.08) 430.7(1.06) 455.5(0.85) 471.9(0.81)
0.1000 405.2(0.72) 414.7(0.68) 443.0(0.57) 458.8(0.54)
0.1250 386.6(0.54) 399.4(0.51) 433.2(0.42) 446.9(0.40)
0.1500 380.9(0.43) 390.6(0.41) 424.6(0.34) 434.7(0.32)
(V/V-80%W+20%M)
0.0500 440.1(1.99) 451.7(2.00) 473.9(1.65) 490.3(1.57)
0.0750 434.3(1.00) 436.6(1.00) 463.2(0.83) 477.5(0.79)
0.1000 417.7(0.66) 421.7(0.67) 452.8(0.55) 464.8(0.52)
0.1250 407.0(0.50) 408.6(0.50) 442.3(0.41) 455.7(0.39)
0.1500 399.3(0.40) 402.1(0.40) 434.8(0.33) 444.6(0.31)
(V/V-70%W+30%M)
0.0500 459.2(2.19) 463.6(2.13) 483.7(1.70) 496.8(1.61)
0.0750 444.3(1.10) 445.8(1.06) 471.2(0.85) 484.9(0.81)
0.1000 417.1(0.73) 425.9(0.71) 457.5(0.57) 471.5(0.54)
0.1250 409.8(0.55) 412.4(0.53) 448.5(0.43) 460.9(0.40)
0.1500 393.8(0.44) 400.5(0.42) 439.7(0.34) 451.1(0.32)
77
Table 4.2 (Continued)
mS / mol kg-1
V 610 /m3 mol-1
308.15 K 308.15 K 313.15 K 318.15 K
(V/V-60%W+40%M)
0.0500 468.7(2.22) 473.4(2.15) 499.6(1.55) 507.5(1.50)
0.0750 445.8(1.11) 455.1(1.07) 489.8(0.77) 496.9(0.75)
0.1000 428.8(0.74) 434.6(0.72) 480.6(0.52) 486.2(0.50)
0.1250 416.0(0.55) 420.7(0.54) 471.7(0.39) 478.2(0.38)
0.1500 400.7(0.44) 408.4(0.43) 464.4(0.31) 470.8(0.30)
(V/V-50%W+50%M)
0.0500 482.4(2.05) 487.5(1.94) 509.7(1.57) 516.2(1.64)
0.0750 465.2(1.03) 473.4(0.97) 501.3(0.79) 506.0(0.82)
0.1000 453.3(0.68) 458.4(0.65) 492.8(0.53) 494.3(0.55)
0.1250 437.9(0.51) 444.9(0.48) 479.3(0.39) 481.7(0.41)
0.1500 423.0(0.41) 435.9(0.39) 470.5(0.32) 465.3(0.33)
mS- stands for molal concentration of salbutamol sulphate
Partial molal volume 0V of salbutamol sulphate are evaluated from
linear plot of V Vs m are shown in Figure 4.1 using the least squares method
of the following general equation (1.3). The evaluated values of 0V and slope
Sv are given in Table 4.3.
78
350
370
390
410
430
450
470
490
510
0.04 0.06 0.08 0.10 0.12 0.14 0.16
m / (mol.kg-1)
V
10
-6m
3 mol
-1)
Figure 4.1 Plot of apparent molal volume ( V ) against molal
concentration (m) of salbutamol sulphate in (♦) 303.15
K, (■) 308.15 K, (▲) 313.15 K, (Δ) 318.15 K of (90% W +
10% M)
79
Table 4.3 Partial Molal Volume 0V , Experimental Slopes SV, Limiting
Molal Expansivity 02E , Isobaric Thermal Expansion
Coefficient 2 and Hepler’s Constant ( 2 0V /T2) of
Salbutamol Sulphate in Aqueous Methanol Solution at Different Temperatures
T/K 0V 106
(m3mol-1) SV106
(m3l1/2mol-3/2)
02E 106
(m3mol-1k-1) 2 103
(k-1)
202 / TV
(m6mol-2k-2) (V/V-90%W+10%M)
303.15 459.6(4.56) -547.5
3.308
7.196
0.0857 308.15 473.2(3.42) -569.6 6.989 313.15 488.5(2.23) -436.6 6.771 318.15 510.7(1.05) -510.2 6.476
(V/V-80%W+20%M) 303.15 463.3(3.84) -435.7
3.272
7.062 0.0700 308.15 475.0(4.25) -508.9 6.888 313.15 493.1(1.51) -396.9 6.635 318.15 511.8(1.76) -452.9 6.393
(V/V-70%W + 30%M) 303.15 490.9(6.78) -661.1
1.916
3.902 0.1228 308.15 493.5(4.02) -638.3 3.882 313.15 504.4(2.74) -442.7 3.798 318.15 519.2(1.62) -461.6 3.690
(V/V-60%W + 40%M) 303.15 498.9(4.53) -663.9 1.802 3.612 0.0291 308.15 504.2(4.15) -657.8 3.573 313.15 516.6(1.12) -353.4 3.488 318.15 524.8(1.19) -368.5 3.437
(V/V-50%W + 50%M) 303.15 510.8(1.70) -584.3 2.302 4.507 0.0103 308.15 512.7(2.81) -526.6 4.490 313.15 530.9(2.12) -401.8 4.336 318.15 543.1(2.81) -504.3 4.238
W - stands for Water M – stands for methanol
Parenthesis indicates standard error
80
The values of molal expansivity are calculated (Rudan-Tasic 1998)
from the partial molal volume using the following relation (4.1)
02E = PTV )/( 0 (4.1)
The evaluated values of 02E are also given in Table 4.3.
From the partial molal volume 0V the isobaric thermal expansion
coefficient of the solute at infinite dilution, 2 is evaluated using the
following equation (Iqbal and Siddiquah 2006)
2 = PTVV )/)(/1( 00 = 002 / VE (4.2)
and the calculated values are included in Table 4.3.
The partial molal volume values, 0V , are related to temperature ‘T’
using the quadratic equation given by 1.16. The values of 202 / TV are
evaluated and given in Table 4.3.
The experimental data on ultrasonic speed of salbutamol sulphate in
aqueous methanol solutions are given in Table 4.4. The uncertainty u values
for ultrasonic speed are calculated and also given in Table 4.4.
81
Table 4.4 Ultrasonic Speed u , of Salbutamol Sulphate in Aqueous Methanol Solution at Different Temperatures
mS / mol kg-1
u / m s-1 303.15 K 308.15 K 313.15 K 318.15 K
(V/V-90% W + 10%M) 0.0000 1535.0 1539.8 1545.0 1548.6 0.0500 1546.8 1552.6 1559.0 1563.7 0.0750 1550.9 1556.8 1564.4 1569.7 0.1000 1554.3 1559.4 1568.8 1574.6 0.1250 1555.3 1562.5 1572.5 1578.7 0.1500 1555.7 1564.9 1576.0 1582.0
u = 3.2310-4 u = 3.6810-4 u = 4.5610-4 u = 4.9510-4 (V/V-80% W + 20% M)
0.0000 1554.3 1556.8 1561.6 1565.0 0.0500 1567.9 1569.6 1575.8 1580.2 0.0750 1572.8 1574.1 1581.5 1585.9 0.1000 1576.5 1577.4 1586.3 1590.4 0.1250 1579.8 1580.2 1590.1 1595.1 0.1500 1583.3 1583.5 1594.0 1598.7
u =4.2410-4 u =3.8910-4 u =4.7610-4 u =4.9510-4
(V/V-70%W + 30% M) 0.0000 1566.1 1560.2 1556.0 1549.8 0.0500 1578.8 1573.3 1570.6 1564.6 0.0750 1583.5 1577.4 1575.8 1570.6 0.1000 1585.3 1579.8 1579.4 1575.4 0.1250 1588.8 1581.8 1584.6 1579.8 0.1500 1589.6 1583.2 1588.5 1583.6
u = 3.5510-4 u = 3.4510-4 u = 4.7210-4 u = 4.9810-4
(V/V-60% W + 40% M) 0.0000 1549.6 1544.3 1541.6 1538.2 0.0500 1562.8 1557.1 1556.1 1553.1 0.0750 1566.8 1561.5 1562.1 1559.1 0.1000 1569.9 1564.3 1567.3 1564.2 0.1250 1572.7 1566.8 1572.2 1569.2 0.1500 1574.1 1568.7 1576.6 1573.8
u = 3.6710-4 u = 3.6410-4 u = 5.1410-4 u = 5.2110-4
(V/V-50%W + 50% M) 0.0000 1528.4 1517.6 1506.5 1493.6 0.0500 1542.4 1530.6 1520.8 1508.0 0.0750 1546.9 1535.3 1526.6 1513.9 0.1000 1551.4 1538.7 1531.9 1518.7 0.1250 1554.4 1541.6 1536.0 1522.8 0.1500 1556.5 1544.6 1540.0 1525.4
u = 4.2010-4 u = 3.9610-4 u = 4.9410-4 u = 4.7610-4
mS - stands for molal concentration of salbutamol sulphate u - stands for uncertainty in ultrasonic speed
82
The data on ultrasonic speed and density are used to calculate the
isentropic compressibility Sk using the equation 1.17 and the values are given
in Table 4.5. The uncertainty in Sk values are calculated using the equation
1.18 and are given in parenthesis of Table 4.5.
Table 4.5 Isentropic Compressibilities Sk of Salbutamol Sulphate in
Aqueous Methanol Solution at Different Temperatures
mS / mol kg-1
Sk 1011 (Pa-1)
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-90%W + 10%M) 0.0000 43.05(1.98) 42.79(1.89) 42.61(1.65) 42.53(1.59)
0.0500 42.09(1.93) 41.81(1.84) 41.61(1.60) 41.51(1.54)
0.0750 41.67(1.89) 41.40(1.81) 41.18(1.58) 41.05(1.52)
0.1000 41.28(1.87) 41.06(1.79) 40.78(1.55) 40.64(1.50)
0.1250 40.97(1.84) 40.67(1.76) 40.41(1.53) 40.26(1.48)
0.1500 40.68(1.82) 40.33(1.74) 40.05(1.51) 39.90(1.46)
(V/V-80%W + 20%M) 0.0000 42.32(1.83) 42.33(1.82) 42.15(1.59) 42.11(1.53)
0.0500 41.29(1.78) 41.36(1.77) 41.16(1.54) 41.10(1.49)
0.0750 40.87(1.75) 40.95(1.74) 40.73(1.52) 40.68(1.47)
0.1000 40.48(1.73) 40.58(1.72) 40.32(1.50) 40.29(1.45)
0.1250 40.11(1.70) 40.23(1.70) 39.96(1.48) 39.90(1.43)
0.1500 39.73(1.68) 39.87(1.67) 39.60(1.46) 39.54(1.41)
(V/V-70%W + 30%M) 0.0000 42.52(1.93) 42.86(1.89) 43.10(1.64) 43.66(1.61)
0.0500 41.56(1.87) 41.87(1.84) 42.07(1.59) 42.63(1.56)
0.0750 41.14(1.85) 41.48(1.79) 41.65(1.57) 42.17(1.54)
0.1000 40.80(1.82) 41.13(1.77) 41.29(1.55) 41.75(1.52)
0.1250 40.43(1.80) 40.81(1.74) 40.85(1.53) 41.35(1.50)
0.1500 40.14(1.77) 40.51(1.72) 40.47(1.51) 40.97(1.48)
83
Table 4.5 (Continued)
mS / mol kg-1
Sk 1011(Pa-1)
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-60%W + 40%M)
0.0000 44.12(2.00) 44.45(1.96) 44.71(1.60) 45.02(1.58)
0.0500 43.09(1.94) 43.45(1.91) 43.66(1.55) 43.95(1.53)
0.0750 42.67(1.91) 43.02(1.88) 43.18(1.53) 43.48(1.51)
0.1000 42.29(1.89) 42.64(1.85) 42.75(1.51) 43.04(1.49)
0.1250 41.91(1.86) 42.28(1.83) 42.32(1.49) 42.62(1.47)
0.1500 41.59(1.84) 41.94(1.81) 41.92(1.47) 42.21(1.45)
(V/V-50%W + 50%M)
0.0000 45.95(1.96) 46.68(1.89) 47.48(1.70) 48.50(1.78)
0.0500 44.84(1.90) 45.61(1.84) 46.36(1.65) 47.35(1.73)
0.0750 44.40(1.87) 45.16(1.81) 45.87(1.63) 46.84(1.70)
0.1000 43.95(1.85) 44.76(1.79) 45.40(1.60) 46.38(1.68)
0.1250 43.55(1.82) 44.38(1.77) 44.97(1.58) 45.94(1.66)
0.1500 43.19(1.80) 44.00(1.74) 44.56(1.56) 45.56(1.64)
mS - stands for molal concentration of salbutamol sulphate
Parenthesis indicates uncertainty of ks.
The change Sk and relative change ( 0/ SS kk ) in isentropic
compressibility are calculated by using the equations from 1.19–1.22 and are
listed in Tables 4.6 and 4.7.
84
Table 4.6 Sk –Change in Isentropic Compressibility of Salbutamol
Sulphate in Aqueous Methanol Solution at Different
Temperatures
mS / mol kg-1
Sk 1011(Pa-1)
303.15 K 308.15 K 313.15 K 318.15 K (V/V-90%W+10%M)
0.0500 0.961 0.982 0.999 1.021 0.0750 1.377 1.387 1.436 1.475 0.1000 1.766 1.731 1.835 1.886 0.1250 2.077 2.122 2.201 2.268 0.1500 2.372 2.458 2.561 2.624
(V/V-80%W+20%M) 0.0500 1.027 0.963 0.989 1.010 0.0750 1.441 1.375 1.427 1.439 0.1000 1.837 1.744 1.829 1.821 0.1250 2.208 2.099 2.192 2.213 0.1500 2.584 2.459 2.555 2.569
(V/V-70%W+30%M) 0.0500 0.958 0.981 1.030 1.037 0.0750 1.380 1.380 1.455 1.498 0.1000 1.718 1.722 1.815 1.916 0.1250 2.092 2.044 2.254 2.315 0.1500 2.383 2.344 2.633 2.691
(V/V-60%W+40%M) 0.0500 1.025 1.004 1.057 1.075 0.0750 1.447 1.435 1.529 1.547 0.1000 1.833 1.812 1.963 1.980 0.1250 2.206 2.173 2.389 2.406 0.1500 2.535 2.511 2.788 2.815
(V/V-50%W+50%M) 0.0500 1.110 1.064 1.124 1.153 0.0750 1.555 1.517 1.613 1.662 0.1000 2.004 1.916 2.080 2.122 0.1250 2.399 2.301 2.509 2.558 0.1500 2.762 2.682 2.922 2.943
mS- stands for molal concentration of salbutamol sulphate
85
Table 4.7 0/ SS kk -Relative Change in Isentropic Compressibility of
Salbutamol Sulphate in Aqueous Methanol Solution at
Different Temperatures
mS / mol kg-1
0/ SS kk 102
303.15 K 308.15 K 313.15 K 318.15 K (V/V-90%W+10%M)
0.0500 2.285 2.350 2.401 2.459 0.0750 3.304 3.351 3.487 3.592 0.1000 4.278 4.217 4.500 4.641 0.1250 5.068 5.216 5.446 5.632 0.1500 5.831 6.095 6.393 6.574
(V/V-80%W+20%M) 0.0500 2.486 2.329 2.403 2.457 0.0750 3.525 3.357 3.503 3.536 0.1000 4.539 4.297 4.536 4.519 0.1250 5.505 5.217 5.485 5.545 0.1500 6.504 6.166 6.453 6.495
(V/V-70%W+30%M) 0.0500 2.307 2.344 2.449 2.432 0.0750 3.354 3.326 3.492 3.553 0.1000 4.209 4.186 4.396 4.588 0.1250 5.174 5.008 5.517 5.598 0.1500 5.936 5.785 6.505 6.567
(V/V-60%W+40%M) 0.0500 2.379 2.311 2.421 2.446 0.0750 3.391 3.335 3.539 3.557 0.1000 4.334 4.250 4.592 4.599 0.1250 5.263 5.140 5.645 5.646 0.1500 6.095 5.986 6.649 6.668
(V/V-50%W+50%M) 0.0500 2.474 2.333 2.424 2.434 0.0750 3.502 3.359 3.516 3.548 0.1000 4.559 4.281 4.582 4.575 0.1250 5.508 5.185 5.579 5.568 0.1500 6.394 6.096 6.558 6.459
mS- stands for molal concentration of salbutamol sulphate
86
The apparent molal compressibility k values of salbutamol
sulphate in aqueous methanol solution are obtained using the equation 1.23
and are listed in Table 4.8. The error values for apparent molal
compressibility are evaluated using equation 1.2 and are given in Table 4.8
within parenthesis.
Table 4.8 Apparent Molal Compressibility, K of Salbutamol
Sulphate in Aqueous Methanol Solution at Different
Temperatures
mS / mol kg-1
K 1015 (m3 mol-1 Pa-1 )
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-90%W+10%M)
0.0500 12.60(0.06) 12.82(0.09) 8.455(0.10) 6.487(0.10)
0.0750 12.01(0.03) 9.334(0.04) 7.191(0.05) 6.817(0.05)
0.1000 11.86(0.02) 5.363(0.03) 5.998(0.03) 5.901(0.03)
0.1250 10.44(0.01) 9.784(0.02) 4.055(0.02) 5.099(0.03)
0.1500 10.42(0.01) 8.756(0.02) 3.560(0.02) 4.909(0.02)
(V/V-80%W+20%M)
0.0500 28.16(0.08) 10.79(0.08) 8.26(0.09) 6.79(0.10)
0.0750 18.91(0.04) 9.22(0.04) 6.92(0.05) 3.62(0.05)
0.1000 18.76(0.02) 7.71(0.02) 5.46(0.03) 5.44(0.03)
0.1250 17.35(0.02) 7.84(0.02) 3.51(0.02) 0.76(0.03)
0.1500 17.48(0.01) 7.79(0.01) 2.96(0.02) 0.82(0.02)
(V/V-70%W+30%M)
0.0500 9.14(0.07) 10.64(0.07) 11.54(0.10) 5.72(0.10)
0.0750 9.09(0.04) 6.96(0.04) 6.13(0.05) 5.03(0.05)
0.1000 8.93(0.02) 4.39(0.02) 0.53(0.03) 4.05(0.03)
0.1250 8.87(0.02) 2.23(0.02) 4.94(0.02) 3.62(0.03)
0.1500 7.57(0.01) 0.70(0.01) 5.20(0.02) 3.32(0.02)
87
Table 4.8 (Continued)
mS / mol kg-1
K 1015 (m3 mol-1 pa-1 )
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-60%W+40%M)
0.0500 15.26(0.08) 7.19(0.08) 6.49(0.11) 6.05(0.11)
0.0750 14.20(0.04) 6.98(0.04) 5.05(0.05) 3.62(0.06)
0.1000 12.84(0.03) 6.74(0.03) 3.14(0.04) 1.61(0.04)
0.1250 12.61(0.02) 6.41(0.02) 3.47(0.03) 1.26(0.03)
0.1500 12.43(0.02) 6.11(0.02) 2.76(0.02) 1.17(0.02)
(V/V-50%W+50%M)
0.0500 21.92(0.09) 6.40(0.09) 5.91(0.11) 5.02(0.11)
0.0750 16.02(0.05) 3.57(0.04) 1.85(0.05) 2.75(0.05)
0.1000 15.84(0.03) 0.78(0.03) 0.50(0.04) 0.38(0.04)
0.1250 15.29(0.02) 0.44(0.02) 0.82(0.03) 0.17(0.03)
0.1500 14.95(0.02) 0.36(0.02) 0.32(0.02) 0.29(0.02)
mS- stands for molal concentration of salbutamol sulphate
Parenthesis indicates standard errors
The partial molal compressibility 0k of homologous amino acids
are evaluated using the least square fit of equation 1.24. The evaluated values
of 0k and SK are listed in Table 4.9.
88
Table 4.9 Partial Molal Compressibility, 0K and Experimental
Slope, SK, of Salbutamol Sulphate in Aqueous Methanol
Solution at Different Temperatures
T/K 0K 1015
(m3 mol-1 Pa-1)
SK1017
(m3 mol-2 kg Pa-1)
(V/V-90%W+10%M) 303.15 13.83(0.43) 2.37 308.15 12.29(0.36) 3.01 313.15 11.02(0.46) 5.17 318.15 7.79(0.50) 1.95
(V/V-80%W+20%M) 303.15 29.30(0.40) 9.17 308.15 11.62(0.10) 2.95 313.15 11.03(0.48) 5.61 318.15 8.44(0.21) 5.92
(V/V-70%W + 30%M) 303.15 10.07(0.58) 1.34 308.15 14.83(0.98) 9.84 313.15 12.22(0.05) 5.54 318.15 6.84(0.31) 2.48
(V/V-60%W + 40%M) 303.15 16.36(0.64) 2.89 308.15 7.79(0.059) 1.10 313.15 7.81(0.95) 3.62 318.15 7.59(0.13) 4.84
(V/V-50%W+50%M) 303.15 22.67(0.26) 5.86 308.15 8.39(0.17) 6.08 313.15 6.77(0.20) 4.88 318.15 6.54(0.14) 4.81
W - stands for Water M - stands for methanol
Parenthesis indicates standard error
89
In order to support the results obtained from volumetric and
compressibility data, the viscosity data have been obtained for all binary
solutions at the reported temperatures and values are given in Table 4.10. The
uncertainty values for viscosity are evaluated and are given in the same
Table 4.10.
Table 4.10 Viscosities of Salbutamol Sulphate in Aqueous Methanol
Solution at Different Temperatures
mS / mol kg-1
(mPa s)
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-90% W + 10%M)
0.0000 0.961 0.853 0.764 0.691
0.0500 1.009 0.969 0.812 0.762
0.0750 1.050 1.011 0.874 0.792
0.1000 1.094 1.051 0.909 0.820
0.1250 1.142 1.099 0.943 0.861
0.1500 1.200 1.137 0.965 0.896
=3.310-3 =4.110-3 =3.110-3 =2.910-3
(V/V-80% W + 20%M)
0.0000 1.091 0.991 0.885 0.790
0.0500 1.140 1.114 0.977 0.864
0.0750 1.188 1.160 1.016 0.898
0.1000 1.245 1.209 1.057 0.931
0.1250 1.305 1.259 1.105 0.967
0.1500 1.353 1.309 1.151 1.021
=4.110-3 =4.610-3 =3.810-3 =3.210-3
90
Table 4.10 (Continued)
mS / mol kg-1
(mPa s)
303.15 K 308.15 K 313.15 K 318.15 K
(V/V-70%W + 30%M)
0.0000 1.211 1.108 0.978 0.871
0.0500 1.246 1.216 1.073 0.948
0.0750 1.285 1.268 1.114 0.983
0.1000 1.344 1.328 1.161 1.023
0.1250 1.421 1.387 1.210 1.070
0.1500 1.482 1.435 1.265 1.116
=4.210-3 =4.810-3 =4.110-3 =3.510-3
(V/V-60%W+40%M)
0.0000 1.317 1.227 1.056 0.965
0.0500 1.352 1.290 1.102 1.003
0.0750 1.359 1.356 1.151 1.045
0.1000 1.450 1.412 1.202 1.091
0.1250 1.553 1.482 1.240 1.137
0.1500 1.582 1.528 1.314 1.189
=4.510-3 =4.610-3 =3.810-3 =3.210-3
(V/V-50%W+50%M)
0.0000 1.370 1.305 1.135 1.014
0.0500 1.396 1.328 1.153 1.033
0.0750 1.418 1.398 1.213 1.077
0.1000 1.496 1.460 1.266 1.130
0.1250 1.568 1.516 1.311 1.174
0.1500 1.659 1.584 1.376 1.225
=4.510-3 =4.410-3 =3.810-3 =3.310-3
mS- stands for molal concentration of salbutamol sulphate
91
Using the linear plots of r versus C (Figure 4.2) the viscosity
B-coefficients are evaluated by the least squares method of equation 1.28.
The evaluated values of B- coefficients are given in Table 4.11.
0.9
1
1.1
1.2
1.3
1.4
0.00 0.05 0.10 0.15
C / (mol.dm-3)
η r
Figure 4.2 Plot of Relative Viscosity ( r ) Against Molarity (C) of
Salbutamol Sulphate in Aqueous Methanol (90%W+10%
M) at (♦) 303.15 K, (■) 308.15 K
The data of B-coefficient of the solutions are used to estimate mean
volume of the solvent, the free energy of activation per mole of the solute
)( *02 and solvent )( *0
1 using equations 1.29, 1.31 and 1.32 and values are
given in Table 4.11.
92
Table 4.11 Viscosity B-Coefficients, Mean Volume of Solvent 01V
Activation Free Energy of Solvent *01
and Solute *02 of
Salbutamol Sulphate in Aqueous Methanol Solution at Different Temperatures
T/K B- Coeff 103
(m3 mol-1)
01V 106
(m3 mol-1)
*01
(kJ mol-1)
*02
(kJ mol-1)
(V/V-90%W+10%M) 303.15 2.184(0.079) 18.27 26.949 325.733 308.15 2.179(0.039) 18.28 27.087 330.033 313.15 2.171(0.227) 18.33 27.247 333.093 318.15 2.169(0.100) 18.37 27.425 337.099
(V/V-80%W+20%M) 303.15 2.191(0.052) 18.42 27.288 324.804 308.15 2.187(0.030) 18.48 27.501 328.183 313.15 2.180(0.070) 18.52 27.658 331.605 318.15 2.176(0.136) 18.58 27.809 335.037
(V/V-70%W+30%M) 303.15 2.232(0.140) 18.79 27.602 324.570 308.15 2.230(0.048) 18.79 27.830 330.161 313.15 2.229(0.086) 18.80 27.958 334.127 318.15 2.210(0.088) 18.89 28.114 334.855
(V/V-60%W+40%M) 303.15 2.254(0.333) 19.08 27.853 323.052 308.15 2.240(0.073) 19.09 28.133 326.389 313.15 2.237(0.140) 19.14 28.205 329.908 318.15 2.226(0.055) 19.19 28.425 332.648
(V/V-50%W+50%M) 303.15 2.282(0.250) 19.34 27.986 322.956 308.15 2.242(0.044) 19.37 28.326 322.539 313.15 2.241(0.071) 19.41 28.428 326.445 318.15 2.229(0.042) 19.49 28.595 328.552
W - stands for Water M – stands for methanol
Parenthesis indicates standard error
93
4.4 DISCUSSION
It is observed from Table 4.1, that the density of ternary system
increases with an increase in concentration of salbutamol sulphate. This may
be attributed to the shrinkage in the volume which in turn is due to the
presence of the solute / drug. In other words, the increase in density may be
interpreted due to the enhanced structure of the solvent mixture due to the
added drug (Sharma et al. 2008). Partial molal volume 0V (Table 4.3) are
positive in aqueous methanol solution indicating the presence of strong
drug-solvent interactions between the molecules, and the structure making
effect of salbutamol sulphate in aqueous methanol solution (Sharma et al.
2008). Further it is seen from Table 4.3, that 0V values increase with increase
in temperature. The variation of 0V values with temperature may be
explained based on scaled particle theory (Gurney 1954) as discussed in
Chapter 3.
It is further seen from Table 4.3, that sV shows negative values at all
the studied temperatures. sV is the measure of solute-solute interaction and
depends on charge, nature of solute and solvent respectively. The negative
values of sV indicate the presence of weak solute-solute interactions in the
solution (Ali et al 2002).
It is further attributed to the fact that in solvent of high dielectric
constant like water, the solutes remain completely ionized even at fairly high
concentration. Similar observations have been reported by Parmar et al
(2004) of Citric acid and Tartaric acid in binary aqueous mixtures of ethanol
at various temperatures using the negative Sv values. However, at a particular
temperature, with the increase of methanol content in aqueous methanol
solution, 0V increases thereby showing that solute-solvent interactions
improve on the addition of more and more methanol in water
94
(Parmar et al 2004). From Table 4.3, it is seen that the values of partial molal
expansivity 02E are positive indicating that the drug acts as a structure maker
(Iqbal and Chaudhry 2009a). Further they indicate the predominance of
hydrophobic hydration over the electrostriction of water methanol molecules
around the solute molecules.
Furthermore, the isobaric thermal expansion coefficient )( 2
(Table 4.3) shows a decreasing behaviour with increasing temperature in
aqueous methanol solution studied in the present work, because when the
temperature is increased the density of the solution decreased (Table 4.1),
resulting in a decrease in partial molal expansivity coefficient )( 2 . A similar
trend was reported by Iqbal and Siddiquah (2006) in mafenamic acid alcohol.
The positive values of Hepler’s constant i.e., 202 / TV (Table 4.3)
indicate the structure making ability of the solute in aqueous methanol
solution (Iqbal and Chaudhry 2009b). From Table 4.4 it is observed that
ultrasonic speed increases with increase in temperature. An increase in the
ultrasonic velocity in any solution with the addition of a solute is indicative of
greater association of molecules due to effective solute-solvent interactions
(Syal et al 1998). Isentropic compressibility Sk decreases with increase in
concentration of methanol and temperature. This decrease in compressibility
values may be viewed as follows. Water is regarded as an equilibrium mixture
of two structures such as an ice –like structure and a close packed structure
(Hall 1948, Arakawa and Sasaki 1969).Compressibility of liquid water is
given by sk = k + )1/( 22Tk relax , where k is an instantaneous part of
compressibility and relaxk , a relaxational part of compressibility (Hall 1948).
The relaxation time corresponding to relaxk is of the order of 10-11s. The
relation <<1 holds good in the present experiment, where is the
95
angular frequency. Thus the isentropic compressibility obtained is equal to
( k + relaxk ). With rise in temperature, k increases due to thermal expansion,
and relaxk , decreases due to thermal rupture of the ice-like structure. Thus the
decrease in isentropic compressibility values with increase in temperature
may be attributed to the corresponding decrease in relaxk , which is dominant
over the corresponding increase in k . Hirata and Arakawa (1972) gave
similar conclusion for aqueous solutions of Tetraalkylammonium salts.
From Tables 4.6 and 4.7, it is seen that sk and 0/ ss kk increases
with increase in drug concentration and temperature (Figures 4.3 and 4.4
respectively). This may be attributed to an increase in the incompressible part
in the solution. The variation of the change and relative change in isentropic
compressibility values with temperature may be attributed to thermal rupture
of water structure. A close observation of plots of sk and 0/ ss kk versus
salbutamol sulphate concentration (Figures 4.3 and 4.4) indicate that the
intercept values for all the systems (% of methanol) are zero or close to
zero.Such a behaviour supports the strong solute – solvent intermolecular /
interionic interactions in these systems. Similar trends were reported in
electrolyte systems (Riyazudeen and Bansal 2006).
96
0
0.5
1
1.5
2
2.5
3
0.04 0.06 0.08 0.10 0.12 0.14 0.16m / (mol.kg-1)
βS(1
0-11 P
a-1)
Figure 4.3 Plot of Change in Isentropic Compressibility ( sk ) against
Molal Concentration ( m ) of salbutamol Sulphate in
(♦) 303.15K, (■) 308.15 K, (▲) 313.15 K, (Δ) 318.15 K of
(90%W + 10%M)
97
0
1
2
3
4
5
6
7
0.04 0.06 0.08 0.10 0.12 0.14 0.16
m / (mol.kg-1)
Δβ s
/ β
S0 (1
0-2)
Figure 4.4 Plot of Relative Change in Isentropic Compressibility
( 0/ ss kk ) Against Molal Concentration ( m ) of SBS in
(♦) 303.15 K, (■) 308.15 K, (▲) 313.15 K, (Δ) 318.15 K of
(90%W + 10%M)
It is well known that ionic groups of solute attract strongly
surrounding water molecules called electrostriction which causes a large
decrease both in volume and incompressibility of the aqueous methanol
solutions. Since the partial molal compressibility is a more sensitive measure
of solute - solvent interactions than in the partial molal volume (Hoiland
1986), the effect of electrostriction is more obvious for the former
thermodynamic property. As seen from Table 4.9, the values of partial molal
98
compressibilities 0K are negative at all mixed volume systems and
temperatures studied, thereby showing the presence of strong solute-solvent
interactions. Further the compressibility decreases steeply with decrease of
temperature, that is the characteristic for dilute aqueous solutions regardless
of whether they are hydrophilic or hydrophobic solutes (Kikuchi 1995).
Similar conclusions were drawn by Yasuda et al (1988) for several aqueous
mono hydrochlorides. The positive values of sk further support the weak
solute-solute interaction in mixed solutions.
It is further seen from Table 4.10, that viscosity values increase
with increase in concentration of salbutamol sulphate, when a solute is
dissolved in a solvent some of the solvent molecules are attracted to the solute
as the result of solute-solvent interaction and thus increase the solution
viscosity. Generally, the increase in viscosity of the solution on addition of
solute indicates the structure-making aspects of solutes (Iqbal and Chaudhry
2008). The relative viscosity values of the solutions decrease with an increase
in temperature. The increase in temperature may have caused the increase in
the kinetic energy of molecules and ions present in the solution, which in turn,
decreases, the solute-solvent interactions (Riyazuddeen and Imrankhan 2008).
The viscosity B-coefficients provide information about the salvation of the
solutes and their effects on the structure of the solvent in the near
environment of the solute molecule. Further some activation parameters of
viscous flow can be obtained using B-coefficients (Jenkins and Marcus 1995).
The viscosity B-coefficients (Table 4.11) originally introduced as an
empirical term has been found to depends upon solute-solvent interactions
and on the relative size of the solute and solvent molecules, are positive
indicating the strong solute-solvent interactions in addition to the
structure-making ability of the solute (Sharma and Ahluwalia 1973).
Furthermore, from Table 4.11, it is clear that with increase of temperature the
99
values of B-coefficient of the solution decrease (Figure 4.5). Thus dB/dT is
negative in the case of salbutamol sulphate and acts a structure maker in these
solutions, thereby, complimenting the volumetric and compressibility
conclusions.
2.165
2.17
2.175
2.18
2.185
2.19
2.195
300.00 305.00 310.00 315.00 320.00
T / K
B-c
oeff
/(10-3
m3 .m
ol-l )
Figure 4.5 Variation of Viscosity B-Coefficient against Temperature of
SBS in (♦)10%,(■)20% of Aqueous Methanol
From Table 4.11, it is clear that *02 and *0
1 increases with
increase in concentration of methanol content in aqueous methanol solution. It
is further seen that *02 > *0
1 thus indicating the structure-making ability of
the solute and strong solute-solvent interactions (Ali et al 2002, Mishra et al
2001). In other words the formation of the transition state is accompanied by
the rupture and distortion of intermolecular forces in solvent structure.
