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Cryometry and excess functions of the adduct of light fullerene C60 and arginine -C6o(C6Hi2NaN4O2)8H8 aqueous solutions
M. Yu. Matuzenko1, A. A. Shestopalova1, K.N. Semenov2, N. A. Charykov3,1, V. A. Keskinov1
:St. Petersburg State Technological Institute (Technical University), St. Petersburg, Russia 2St. Petersburg State University, St. Petersburg, Russia 3St. Petersburg State Electro-technical University (LETI), St. Petersburg, Russia
PACS 61.48.+C DOI 10.17586/2220-8054-2015-6-5-715-725
Cryometry investigation of C6o(C6H12NaN4O2)8H8 - H2O solutions was made over concentrations ranging from
0.1.- 10 g of fullerene-arginine adduct per 1 dm3. Freezing point depression was measured for these aqueous solutions. Excess functions for water and fullerene-arginine adduct activities, activity coefficients and excess Gibbs energy of the solutions were calculated. All solutions demonstrate huge deviations from ideality. The last fact, to our opinion, is caused by the very specific - hierarchical type of association of fullerene-arginine adducts in aqueous solution components, which is proved by the results of our visible light scattering analysis. Keywords: cryometry, activities, activity coefficients, fullerene-arginine adduct, water solution.
Received: 11 April 2015 Revised: 15 April 2015
1. Introduction
This article is a continuation in the series of articles devoted to the synthesis, identification and physico-chemical properties investigation of nanoclusters, which represented the fairly water soluble derivatives of light fullerenes C6o and C70 [1-14] - poly-hydroxylated fullerenols (fullerenol-d C60(OH)24±2 and malonic ether - trismalonate C70[=C(COOH)2]3). In previous articles, the authors have reported on the volume, refraction, electrical, transport properties of water soluble nanoclusters and their aqueous solutions. Also, the investigations of solubility in water under poly-thermal conditions as well as in some ternary water-salt systems and complex thermal analysis of nanocluster crystal-hydrates were made.
2. The synthesis of the adduct of light fullerene C60 with arginine C60(C6H13N4O2)8H8
Arginine hydrochloride (L-C6H14N4O2HCl) (5 g) and sodium hydroxide (2.5 g) were dissolved in 30 ml of water and 200 ml CH3CH2OH. In the other vessel fullerene C60 (0.5 g) was dissolved in 80 ml o-C6H4(CH3)2. Then both solutions were combined, mixed and remained at room temperature for 120 hours. A deep-brown exfoliating solution was formed. The colorless organic phase was separated from the aqueous inorganic one. The aqueous phase was salted using excess methanol (CH3OH) over 24 hours. At that time, the sedimentation of the of the light fullerene C60 adduct with arginine was completed. The precipitate was filtered and washed repeatedly with a mix of CH3OH with concentrated HCl. Recrystallization of precipitate was performed 3 times. Finally, the precipitate was dried at 60 °C for 8 hours. Previously, the synthesis of an original ^-alanine C60 adduct was described [18]. Correspondingly, the L-arginine - light fullerene C60 adduct was formed - C60(C6H12NaN4O2)8H8 with a yield « 80 %.
3. Reasons for direct excess functions in fullerene-arginine adduct - water solutions determination
The authors do not know of any direct experimental data concerning the determination of the excess thermodynamic data (primarily activity coefficients) in binary (or more component) solutions of fullerenes or their derivatives in any solutions. This fact may, to our opinion, be explained by the very low solubility of such nanoclusters in the majority of solvents (see, for example [15-17]). For fairly water soluble nanoclusters (e.g.: poly-hydroxylated ffullerenols C60(OH)n, C70(OH)n; some esters - for example: trismalonic esters - trismalonate C6o[=C(COOH)2]3, C70[=C(COOH)2]3, some adducts with amino-acids (for example arginine C60(C6H12NaN4O2)8H8 or alanine [18]), their solubility in water, which depends on the type of nanocluster and temperature, may vary from tens to hundreds grams of nanocluster per dm3 of solvent. This fact permitted us to determine excess functions of the solution by standard methods, for example, cryometry (as described in the present article) or by the determination of water activity by isopiestic method. Such determination is, to our opinion, may be very interesting because of the following reasons.
Visible light scattering analysis in C60(C6H12NaN4O2)8H8 - water solutions (as well as in light fullerenols (trismalonates)-water solutions) at room temperature was provided repeatedly (see [1,5,14]). In all cases, one can observe the following:
- No monomer molecular nanoclusters (with linear dimension diameter d0 ~ 1.5 - 2.0 nm) are seen in all investigated solutions, even in the dilute solution (C = 0.1 g/dm3).
- The diameters of the first type aggregates (the first order clusters of percolation) have the similar order - tens of nm d1 ~ 20 - 80 nm over the entire concentration range.
- The diameters of the second type aggregates (the second order clusters of percolation) also have a similar order - hundreds nm d2 « 100 - 400 nm.
- The third type associates (the third order clusters of percolation) have not been seen at any concentrations except in the most highly concentrated solution at C > 1 g/dm3, where clusters with extremely huge linear dimension (on the order of microns) are formed: d3 > 1000 nm - the solution 'becomes very heterogeneous' but stable as a colloidal system.
- Thus, to describe such facts in the aggregation process, a stepwise model of particle growth was invoked, in other words, a hierarchical type of association of fullerenols (tris-malonates) components was observed in aqueous solutions. We consider that monomer spherical molecules form the first type of spherical aggregates, then, the first type spherical associates form a second type of spherical associates. Next, the second type of spherical associates form a third type spherical associates (the last ones correspond to a heterogeneous colloidal system). A typical figure of the distribution for C60(C6H12NaN4O2)8H8 nanoclusters in aqueous solutions at comparatively high concentrations is represented below - in Fig. 1 (the third type associates).
4. The possibility of the determination of the excess functions in C60(C6H12NaN4O2)8H8 - water solutions
In order to check the possibility of determining the excess functions in C60(C6H12NaN4O2)8H8 - H2O solutions in the selected concentration range by cryometry method one must be sure of the following:
- Solubility in the binary system C60(C6H12NaN4O2)8H8 - H2O at a temperature of 273.15 K is great enough such that the solution is formally homogeneous, i.e. does not consist of solid C60(C6H12NaN4O2)8H8 crystal hydrates. Preliminary experiments show
Size Dstributicn by Intensity
80
1 60 o k_
OS CL
> 40
tsi n. OS
S 20 0
0.1 1 10 100 1000 10000
Size {d.nrrii
Record 34: Arg60 5,0 g/11 Ffeccrd 35: Arg60 5,0 g/l 2 - Reccrd 36: Arg60 5,0 g/l 3
Fig. 1. The linear dimension of the particles on the base of the adducts C60(C6Hi2NaN4O2)8H8 in aqueous (5) solutions at C = 5 g/dm3 (different curves correspond to the different times of observation (signal integration)
that in both cases, the solubility of C60(C6H12NaN4O2)8H8 nanoclusters at 273.15±1 K is « 70 g/dm3. So, if we set the concentration range at not more than tens g/dm3, we can be sure that no solid crystal hydrates can co-crystallize with water ice during the crystallization.
- Additionally, one must be sure that the nanocluster solutions are really homogeneous -do not delaminate and are not colloidal. In our case, only more or less diluted solutions may satisfy these request (see lower).
- The last condition is that the temperature decrease AT should be more or less significant - hundredths, or even better tenth of a degree K. Fortuitously, this request is easily satisfied.
5. Cryometry investigation in the binary system: C60(C6H12NaN4O2)8H8 - H2O. The decrease of the temperatures of the beginning of the H2O - ice crystallization in C60(C6H12NaN4O2)8H8 - water solutions. Cryometry of water solutions of water soluble fullerene derivatives. Main thermodynamic equations
Let us introduce designation:
A F = FS - FL, AT = Tf - T, (1)
where Tf - melting point of pure solvent, for water Tf = 273.15 K, T - current temperature (K), AF - molar change of thermodynamic function F, FS - molar function F for the solid phase, FL - molar function F for the liquid phase.
The conditions for chemical phase equilibrium liquid (L) - solid (S) for the pure solvent - water (W) were as follows:
= ^W + RT ln aW (2)
where: ^wjf, ^wL - standard chemical potential of the solvent - water, in the solid and liquid phases, correspondingly, aW - water activity in the scale of molar fractions in symmetrical normalization scale. Thus:
-AH,
f + ACp (T - f + T [ASf - ACp ln (t/T7)
RT ln a w ,
ln (T/Tf) = ln (Tf - AT/Tf) = ln (l - AT/Tf) « -AT/Tf,
(3)
(4)
where: AHf, ASf, ACP - molar enthalpy, entropy and change of isobaric heat capacity of water at the temperature Tf. So:
-AHf
1 - T/Tf +ACP T - Tf - T ln (r/Tf^j
RT ln a w ,
-AHf AT/Tf + ACp AT (-1 + T/f = RT ln a w,
ln a W.
-AHf AT - ACPAT2
R I Tf - AT) Tf
(5.1)
(5.2)
(5.3)
Later, we shall use formula (5.3) as the basis for calculating the excess solution functions. In all calculations, we will use symmetrical normalization of the excess functions, as if nanoclusters are very weak electrolytes - practically non-electrolytic (see nanocluster-water systems close to our system, for example [4,6,12]). Accordingly, we assume that:
aH2o(xH2O = 1) = YH2o(xH2O = 1) = 1, (6.1)
ananocluster (xnanocluster 1) Tnanocluster (xnanocluster 1) 11, (6.2)
where: a^, ji - activity and activity coefficients of i-th solution component.
Experimental data were obtained with the help of metastatic Beckman thermometer. Data are represented in the Fig. 2 and Table 1. Arrow in the Fig. 2 shows the temperature decrease in the case of an ideal non-electrolyte solution. Thus, one can see the huge temperature decrease we observed for our water soluble nanoclusters solutions.
Fig. 2. The decrease of the temperatures of the beginning of the H2O - ice crystallization in C60(C6H^NaN4O2)8H8 - water solutions (AT = 273.15 - T)
Table 1. Cryometry data and excess function in the binary C60(C6H12NaN4O2)8H8 - H2O solutions at 273.15 K
Number Molar fraction of C60(C6H13N4O2)8H8 in solution XC60(C6H13N402)8H8 (rel.un.) Temperature of water crystallization decrease AT (K) ln amo (water activity) (rel.un.) aH2O (water activity) (rel.un.)
1 0.000 0.000 0.000 1.00000
2 7.868 ■ 10-8 0.099 -9.561 ■ 10-4 0.99904
3 7.868 ■ 10-7 0.151 -0.00146 0.99854
4 3.923 ■ 10-6 0.179 -0.00172 0.99827
5 7.828 ■ 10-6 0.210 -0.00202 0.99797
6 1.949 ■ 10-5 0.254 -0.00245 0.99755
7 3.887 ■ 10-5 0.308 -0.00297 0.99703
8 5.821 ■ 10-5 0.354 -0.00341 0.99658
9 7.758 ■ 10-5 0.401 -0.00387 0.99613
Number ln YH2O (water activity coefficient) (rel.un.) derivative d ln yh2o derivative d ln YC60(C6H13N4O2)8H8 ln YC60(C6H13N4O2)8H8 (rel.un.)
dxC60(C6H13N4O2)8H8 (rel.un.) dxC60(C6H13N4O2)8H8 (rel.un.)
1 0.000 -12000 4.2 ■ 1010
2 -9.561 ■ 10-4 -6300 1.3 ■ 1010 9.2 ■ 106
3 -0.00146 -410 5.2 ■ 108 3750
4 -0.00172 -81 2.1 ■ 107 4100
5 -0.00202 -55 7.0 ■ 106 4130
6 -0.00243 -31 1.6 ■ 106 4150
7 -0.00293 -24 6.2 ■ 105 4170
8 -0.00336 -22 3.8 ■ 105 4180
9 -0.00379 -22 2.8 ■ 105 4200
Number In aC60(C6H13N4O2)8H8 (rel.un.) Gex/RT (rel.un.) Gmix/RT (rel.un.)
1 0.00000 0.00000 0.00000
2 9.2 ■ 106 -8.83 -8.83
3 3740 0.00149 0.00148
4 4090 0.0143 0.0143
5 4120 0.0303 0.0302
6 4140 0.0784 0.0782
7 4160 0.159 0.158
8 4170 0.239 0.239
9 4190 0.322 0.321
6. Excess partial functions of water C6o(C6Hi2NaN4O2)8H8 components in the binary system: C6o(C6Hi2NaN4O2№ - H2O
The graph of the dependence ln of water activity (ln aH2O), ln of water activity coefficient (ln YH2O), against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions are represented in Figs. 3, 4 and in Table 1. The dependence of the derivative of ln of water (nanocluster) activity coefficients (d ln YH2O/dxnanocluster) and (d ln Ynanocluster/dxnanocluster) in C60(C6H12NaN4O2)8H8 - water solutions against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions are also represented in Figs. 5, 6 (curves - approximation, points - experimental data). The approximation is represented in the Figs. 5, 6 also. For calculation, we have used the Gibbs-Duheim equation:
dln Qnanocluster \ _ xH2O /d ln aH2O \ (7)
T xnanocluster \ d ln xH2O / y
d In Xnanoc!uster
Fig. 3. The dependence of ln of water C60(C6H12NaN4O2)8H8 - water solutions against C60(C6H12NaN4O2)8H8 in aqueous solutions
activity (ln aH2O) in the molar fraction of
The dependence of the ln of C60(C6H12NaN4O2)8H8 activity coefficients (ln Ynanociuster) and ln of C60(C6H12NaN4O2)8H8 activity (ln awnocluster) in C60(C6H12NaN4O2)8H8 - water solutions against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions are represented in Figs. 7, 8 and Table 1.
7. Excess and Mixing Gibbs energy in the binary system: C60(C6H12NaN4O2)8H8 -H2O. Miscibility gap and micro-heterogeneous behavior of the solutions
We have also calculated the dependence of the excess Gibbs energy of the solutions (Gex) in C60(C6H12NaN4O2)8H8 - water solutions against the logarithm of the C60(C6H12NaN4O2)8H8 molar fraction in aqueous solutions (Fig. 9) and the dependence of the Gibbs energy mixing for solutions (Gmix) and the miscibility gap in C60(C6H12NaN4O2)8H8 - water solutions against the logarithm of the C60(C6H12NaN4O2)8H8 molar fraction (Fig. 10) and also Table 1:
GeX = RT [ln Ynanociuster + xH2O ln YH2o]
(8)
Fig. 4. The dependence of ln of water activity coefficients (lnyh2o) in C60(C6Hi2NaN4O2)8H8 - water solutions against the molar fraction of C60(C6Hi2NaN4O2)8H8) in aqueous solutions
Fig. 5. The dependence of the derivative of ln of water activity coefficients (d ln YH2o/dxnanccluster) in C6o(C6Hi2NaN4O2)8H - water solutions against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions (curves - approximation, points - experimental data)
Fig. 6. The dependence of the derivative of ln of C60(C6H12NaN4O2)8H8 activity coefficients (d ln Ynanocluster/dxnanocluster) in C60(C6H12NaN4O2)8H - water
solutions against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions
Fig. 7. The dependence of ln of C60(C6H12NaN4O2)8H8 activity coefficients (ln Ynanocluster) in C6 (C6H12NaN4O2)8H8 - water solutions against the molar fraction of C6 (C6H12NaN4O2)8H8 in aqueous solutions
Fig. 8. The dependence of ln of C60(C6H12NaN4O2)8H8 activity (lnananoclus-ter) in C60(C6H12NaN4O2)8H8 - water solutions against the molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions
G [xnanocluster ln ananocluster + xH2O ln aH2O] .
(9)
Fig. 9. The dependence of the excess Gibbs energy for solutions (Gex) in C60(C6H12NaN4O2)8H8 - water solutions against logarithm of molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions
One can see the inflection points in the Figs. 9, 10 where the second derivatives:
G /dxnanocluster] T P
and
[d G /dxnanocluster]T,P
change signs or derivatives
[d'G^/dlnx
CWKCp^O^HS J
,,, =-14.8 rel.un.
]=0
lnx
OÏOiCH^lOJHl
Miscibility Gap
-10
-21
-18
-15
-12
-9
ln[Molar fraction of C (C H N O ) H in water solutionl - lnx
L 60v 6 13 4 ZyS S J I
'CWXCHN^H
(rel.un.)
Fig. 10. The dependence of the Gibbs energy mixing for solutions (Gmix) and the miscibility gap in C6o(C6Hi2NaN4O2)8H8 - water solutions against logarithm of molar fraction of C60(C6H12NaN4O2)8H8 in aqueous solutions
[52GmiX/dX2an0c1uster]T, P and [d^V^LoclusteJT, P Cross through zero Naturally, this fact takes place together with the crossing through zero of such functions: [52Gmix/d ln(xnanocluster)2] Tp and [52Gex/d ln(xnanocluster)2]T P. Geometrically, this means that the convexity in the graph Gex(xnanocluster) and Gmix(xnanocluster) is replaced by concavity. And, if the behavior of the first function - Gex is arbitrarily, the sign of the derivation, [52Gmix/dx2anocluster] T p, over the concentration range of diffusion stability, should be positive. Thus, we can consider that in the region xnanocluster > 4 ■ 10-7 rel.un. homogeneous solutions exfoliate and becomes micro-heterogeneous. Light scattering experiments show us that this occurs at the concentration region of the transition from the first type aggregates (the first order clusters of percolation) with the linear dimensions d1 & 20 - 80 nm to that of the second type aggregates (the second order clusters of percolation) with the linear dimensions d2 ~ 100 - 400 nm. In other words, there are the concentrations where the system transitions from a nano-heterogeneous one to that of a micro-heterogeneous
type.
Acknowledgements
Investigations were supported by Russian Found of Basic Research - RFBR (Project No. 15-08-08438) and with the help of the equipment of Resource Center 'Geomodel' (St. Petersburg State University).
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[2] K.N. Semenov, N.A. Charykov, I.V. Murin, Yu.V. Pukharenko. Physico-chemical properties of the fullerenol-70 water solutions. J. of Molecular Liquids, 2015, 202, P. 1-8.
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