Influence of Imidazolium Ionic Liquids on the Interactions of Human

Article pubs.acs.org/jced

Influence of Imidazolium Ionic Liquids on the Interactions of Human Hemoglobin with DyCl3, ErCl3, and YbCl3 in Aqueous Citric Acid at T = (298.15, 303.15, and 308.15) K and 0.1 MPa Dinesh Kumar, Abhishek Chandra, and Man Singh* School of Chemical Sciences, Central University of Gujarat, Gandhinagar, 382030, India S Supporting Information *

ABSTRACT: Density, sound velocity, viscosity, surface tension, and molar conductivity for DyCl3·6H2O, ErCl3·6H2O, and YbCl3·6H2O from (0.002 to 0.012) mol·kg−1 in aqueous solutions of (a) citric acid (0.005 mol·kg−1) (b) citric acid + human hemoglobin (1 g·kg−1) and (c) citric acid + human hemoglobin +1alkyl-3-methylimidazolium chloride (0.001 mol·kg−1) ([RMIMCl], R = ethyl, butyl, and hexyl) at T = (298.15, 303.15, and 308.15) K and 0.1 MPa are reported. Densities were used to calculate the apparent molar volumes. The viscosity data are analyzed and interpreted using the extended Jones−Dole equation for lanthanide chloride to calculate viscosity A- and B-coefficient values. The varying trends of the aforesaid physicochemical parameters have been interpreted in terms of the solute− solute and solute−solvent interactions. An attempt has been made to investigate the influence of ionic liquid alkyl chain length on the interacting activities of lanthanide chloride with citric acid and the critical role being played by human hemoglobin in decoding the dominance of hydrophilic−hydrophobic interactions. 1-Ethyl-3methylimidazolium chloride induced greater conformational changes in the human hemoglobin than 1-butyl-3methylimidazolium chloride and 1-hexyl-3-methylimidazolium chloride due to differences in alkyl chain length with different interacting capabilities. others.3 In view of its water-soluble, well-characterized structure and functions, the human hemoglobin has been selected as a model protein in this study. Currently, lanthanides have attracted significant attention of researchers because of their 4f electrons and their interdisciplinary applications with protein, apart from their optical, luminesce, magnetic,4−10 bioseparation, and biomedical imaging11 properties. As a result of these unique properties, lanthanide complexes could be used as luminescent probes to analyze biological process. For instance, the conformational changes in calcium- and iron-bound proteins have been investigated using Tb3+ and Eu3+ as structural probes.12−14 Also Dy3+ has been used for in vivo imaging, similarly, Er3+ and Yb3+ have been used in the biological imaging, cell culture, and tracking of single cells in vitro and vivo.15−22 Lanthanides are also used to determine the relaxation rate of water protons in tissue.23 Different proteins have been used to modify the surface properties of the lanthanide nanoparticles with allosteric in polypeptides by hydrogen bonds, solvation forces, van der Waals interactions and others, and thus have drawn wider and deeper attentions.24 For ascertaining the biological activity in lanthanide nanoparticles, their sizes25−28 and surface chemistry29−31 are of utmost importance. Thus, it is of considerable

1. INTRODUCTION The structural prerequisites of biomolecules in variable chemical environments, particularly with ionic liquids (ILs), offer a remarkable way to perturb the energetics of biological reactions. Because proteins are biomolecule, altering their structure driven activities by changing the chemical environment can perturb their modes of interaction prevailing in the biological system. These alterations in the activity of proteins can thus play a significant role in biochemistry. For example, protein misfolding or unfolding is a dominant structural factor affecting its function and is responsible for different diseases such as Parkinson’s, Sickle Cell, Prion, Tauopathies, and others. Thus, allosteric regulation of proteins by changing their chemical environment is one example in which such diseases can be controlled by the structural bioengineering of the proteins. Hemoglobin is an iron containing functional protein found in red blood cells of nearly all vertebrates and many invertebrates. It has four polypeptide chains (two alpha and two beta chains), each wrapped in a specific way around its own heme group due to an electrostatic site. Since hemoglobin is an allosteric protein, its interaction with the other subunits in a specific environment can be altered upon binding with high charge density ions such as lanthanides.1,2 Hemoglobin has a wide range of physiological functions such as molecular heat transduction, modulation, and senescence of erythrocyte metabolism, erythrocyte enzymatic activities, and several © 2017 American Chemical Society

Received: August 2, 2016 Accepted: December 30, 2016 Published: January 10, 2017 665

DOI: 10.1021/acs.jced.6b00695 J. Chem. Eng. Data 2017, 62, 665−683

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of Chemical Used

a

name

puritya

waterb %

Mw

source

CAS No.

dysprosium(III) chloride hexahydrate erbium(III) chloride hexahydrate ytterbium(III) chloride hexahydrate citric acid 1-ethyl-3-methylimidazolium chloride 1-butyl-3-methylimidazolium chloride 1-hexyl-3-methylimidazolium chloride hemoglobin human

≥99.9% ≥99.9% ≥99.9% ≥99.5% ≥98% ≥98% ≥98% ≥98%

WCH.63,64 In this study, in comparison to 1-butyl-3-methylimidazolium chloride (BMIMCl) and 1-hexyl-3-methylimidazolium chloride (HMIMCl), 1-ethyl-3-methylimidazolium chloride (EMIMCl), having the shortest alkyl chain length, strongly unfolds the Hgb. In the absence of citric acid, HMIMCl, having the highest hydrophobic character, has a greater ability to dehydrate the charged hemoglobin compartment. Therefore, the unfolding of Hgb is favored by an increment in the interaction between HMIMCl and Hgb.65 Hgb, in aqueous citric acid, acquires a net positive charge in which the NH3+ of the Hgb hydrophilic domain is engaged with the −COO− group of the H3Cit. When, the surface of Hgb is surrounded by water only,

hydration sphere. This resulted in an increase in the overall volume of the solution due to the release of water molecules from the hydration spheres of H3Cit to the bulk with a density of WC > WCH.54 The density being lower for WCH than for WCHILs can be due to three factors: (i) alkyl chain length of ILs; (ii) imidazolium cation, [RMIM]+, of ILs; and (iii) structural reorientation of the functional groups present in Hgb. The inclusion of ILs in WCH (WCHILs) unfolds the structure of Hgb. This results in the availability of more −NH3+, −COOH, and >CO groups present in the Hgb in contact with the bulk water, which were otherwise buried inside the Hgb structure. This unfolding of Hgb thus increases the extent of ion−hydrophilic interaction (IHI) between the [RMIM]+ of IL and hydrophilic domains (−COOH, >CO) of Hgb, with increased density. Furthermore, inclusion of ILs in WCH leads to increased hydrophobic domains of Hgb in WCHILs. The 669



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HMIMCl would have easily dehydrated the Hgb surface, and as a result, the Hgb would have easily unfolded. Interestingly, in the presence of H3Cit, the water molecule surrounding the Hgb are engaged in the hydration sphere of the H3Cit and as a result, HMIMCl cannot replace the water molecules, and thus, is ineffective in unfolding the Hgb. Since, EMIMCl has the lowest +I effect (least neutralizing of the positive charge of the imidazolium ring) and least hydrophobic character, it can easily approach the Hgb surface and could interact with the carbonyl oxygen of the peptide linkage of the Hgb through ionhydrophilic interaction. This in-turns, releases out the hydrogen-bonded water molecules from the Hgb surface to the bulk, thereby unfolding the Hgb, with lowest density. For WCHL6, the hexyl chain of HMIMCl is amenable for its lower density value than WCHL4 because its large surface area attributes to greater hydrophobic interactions.66 From Table 2, it is evident that upon the addition of LnCl3 to WC, WCH, WCHL2, WCHL4, and WCHL6, the density increased at all the investigated temperatures. Table 2 also shows a higher increase in density values for LnCl3 with WC and WCHL2 than with WCH, WCHL4, and WCHL6. With WC, the Ln3+ ions due to their higher charge density, interact strongly with excess water released to the bulk solution due to the disruption of structured water by H3Cit. The disrupted water further realigned and form hydration spheres around the Ln3+ as per the Hofmeister series. In the case of WCHL2, EMIMCl unfolds the Hgb and leads to the exposure of more hydrophobic groups of Hgb, repelling out more water molecules to the bulk. These repelled out water molecules noted as excess water molecules interact strongly with Ln3+ ions with increased density. The densities of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at 298.15, 303.15, and 308.15 K are in the order: YbCl3 > ErCl3 > DyCl3. This trend indicates that Yb3+ with highest charge density (Dy3+ = 5.27 nC·m−1, Er3+ = 5.40 nC·m−1, and Yb3+ = 5.53 nC·m−1)67 develops the strongest ion−ion and ion−hydrophilic interaction (IHI) with the −COO−, −OH, −COOH, and >CO groups present in WC, WCH, and WCHILs and also with the bulk water molecules, while Dy3+ with the lowest charge density develops the weakest IHI. As the charge density of Ln3+ increases, the hydrophilic groups (−COO−, −OH, and >CO) are able to approach the Ln3+ ions more closely with increasing propensity of the hydrophobic domains to aggregate. This leads to the highest compact arrangement for Yb3+ ions with the highest density. The development of stronger IHI tends to increase the internal pressure of the system with higher density, while development of weaker IHI leads to weaker internal pressure with lower density. The density values of all the reported systems decreased on increasing temperature (Table 2) because, the molecules on gaining kinetic energy oscillate very strongly, thereby weakening their intermolecular interactions. 3.2. Apparent Molar Volume (Vϕ/m3·mol−1). The densities of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at T = (298.15, 303.15, and 308.15 K) K have been used to calculate the apparent molar volume, Vϕ of LnCl3 (Table 3 and Figures 1 to 5) from eq 1:54,55 Vϕ =

1000(ρ0 − ρ) mρ0 ρ

+

M ρ

Figure 1. Apparent molar volume of DyCl3, ErCl3, and YbCl3 with WC at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond), respectively.

Figure 2. Apparent molar volume of DyCl3, ErCl3, and YbCl3 with WCH at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond), respectively.

Figure 3. Apparent molar volume of DyCl3, ErCl3, and YbCl3 with WCHL2 at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond), respectively.

mol−1) is molar mass of LnCl3. In the case of molal solutions, the weight of the solvent is fixed, hence with increasing solute concentration, the mole fraction of the solvent decreases while that of solute increases. In ionic salt systems, because of their electric neutrality, cations cannot be independent of anions. Hence, there is always a presence of interionic forces between the Ln3+ and Cl− ions (solute−solute interactions). At very low LnCl3 concentration (higher solvent mole fraction), the solute−solvent interactions dominate while solute−solute interactions can be ignored. As the concentration of LnCl3 increases (solvent mole fraction decreases), there is a

(1)

where m (mol·kg−1) is the molality of LnCl3, ρ0 and ρ are the densities of the solvent and solution, respectively, and M (kg· 670



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>CO, −COOH, and [RMIM]+) of H3Cit, Hgb, and ILs. This weakens electrostriction with increased Vϕ0 values54 (b) Ion−hydrophobic interactions (IHbI) among Ln3+ and Cl− and nonpolar groups of solvent (hydrophobic side chain of amino acids present in Hgb peptide chain and alkyl chain of ILs). This strengthens electrostriction with lower V0ϕ values54 The addition of LnCl3 in solvent develops IHI with the hydrophilic groups of H3Cit (−COO−, −OH), Hgb (−NH3+, >CO,−COOH) and ILs ([RMIM]+), thereby reducing the HHI prevailing between the solvent molecules. The trend for V0ϕ values of LnCl3 with the solvent follows the order (WCH and WCHL2) < (WC, WCHL4, and WCHL6) (Table 4). This infers that the IHI prevailing between Ln3+ and (WCH, WCHL2) is weaker than with (WC, WCHL4, WCHL6). These results indicate that the presence of Hgb in WCH shields the IHI prevailing between the Ln3+ ions and WC by developing HHI with WC and as a result, decreases the V0ϕ values, with WCH < WC. Since, with increasing alkyl chain length, the +I effect increases, this in turn decreases the positive charge on the imidazolium cation ([RMIM]+) of the ILs. As a result, the presence of ILs:BMIMCl and HMIMCl in WCHL4 and WCHL6 poorly shields the IHI prevailing between the Ln3+ ions and WCH by developing weaker HHI with WCH and as a result, increases the V0ϕ values, with WCHL2 < WCHL4 < WCHL6. Additionally, the higher value of V0ϕ indicates stronger solute−solvent interaction in which the IHI is dominant over IHbI. The presence of ILs increases IHI due to the additional hydrophilicity generated by the imidazolium cation of the ILs. Therefore, in the presence of ILs, it seems that the IHI dominates over IHbI for WCHL2, WCHL4, and WCHL6, with V0ϕ as WCH < WCHL2 < WCHL4 < WCHL6. Probably, the IHI attenuates the electrostriction of water molecules, where Ln3+ attracts some more water molecules from the bulk with decrease in volume. The V0ϕ trend for LnCl3 with WC is YbCl3 > ErCl3 > DyCl3, depicting the strongest IHI for YbCl3 due to the highest charge density of the Yb3+ ions for ErCl3 and DyCl3, in which the water electrostriction is weakened most efficiently, subsequently leading to the strongest solute−solvent and weakest solute−solute interactions. Further, for LnCl3, the V0ϕ values with WCHILs are as DyCl3 > ErCl3 > YbCl3. The working mechanism behind this trend is the development of the strongest IHbI with Yb3+ ions, whereas the weakest IHI for the Dy3+ ions has the lowest charge density. Hence, there is an extensive strengthening of electrostriction with YbCl3 in the presence of the ILs. The lower V0ϕ values for LnCl3 with WCH at 298.15 K and for YbCl3 with WCHL2 at T = (298.15, 303.15, and 308.15) K, predict weaker solute−solvent interactions70 attributed to increased electrostriction.71,72 Initially, on increasing the temperature from 298.15 to 303.15 K, the V0ϕ values of LnCl3 with WC decreased, but eventually increased on increasing the temperature to 308.15 K. It is probably due to the perturbation of the water molecules arrangement in the bulk water by the electric field of the Ln3+. For LnCl3, the V0ϕ values increases with increasing temperature and could be due to the reduced solvation and increased intrinsic volumes of the Ln3+.73 The higher thermal energy induces additional oscillation that attenuates the strength of van der Waals forces and expansion in volume. It is obvious from the Sv sign that ion−ion interactions for LnCl3 are higher and more positive than V0ϕ at the experimental



development of stronger interionic interactions (solute−solute interactions) resulting in a dominancy competition between the solute−solvent and solute−solute interactions. Interestingly, the Vϕ values with WCH and WCHL2, increased on increasing LnCl3 concentration whereas, with WC, WCHL4, and WCHL6, decreased with increasing LnCl3 concentration. This may be due to the slight difference in the Ln3+ ions solvation by the solvents (WC, WCH, WCHL2, WCHL4, and WCHL6). The hydration sphere of the Ln3+ and Cl− ions seems to accommodate the H3Cit, Hgb, and ILs, maintaining the electrostatic force. On the other hand, the increased Vϕ values upon increasing temperature may be due to the attenuation of the solute−solvent binding energy between the Ln3+ and −COO−/−OH/−NH3+/[RMIM]+ of Hgb, H3Cit, and imidazolium cation.68,69 The concentration independence of the apparent molar volume at infinite dilution, V0ϕ, of LnCl3 is obtained by fitting the Vϕ values in the Redlich−Rosenfeld− Meyer eq 2:54,55 Vϕ = V ϕ0 + Svm1/2 + Bv m

(2)

−1

where (m ·mol ) is the apparent molar volume at infinite dilution of LnCl3, depicting the nature of solute−solvent interaction while, Sv (kg1/2·m3·mol−3/2) and Bv (kg·m3·mol−2) are the empirical parameters used to interpret solute−solute (interionic) interactions (Table 4). The following interactions are responsible for variation in V0ϕ values: (a) Ion−hydrophilic interaction (IHI) among the Ln3+ and Cl− and hydrophilic groups (−COO−, −OH, −NH3+, V0ϕ

3

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Table 4. Limiting Apparent Molal Volume V0ϕ (10−6m3·mol−1), Slope Bv(10−6 kg1/2·m3·mol−3/2), and Bv (10−6 kg·m3·mol−2) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1-Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3-methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, 308.15) K V0ϕ

T −6

K

DyCl3

298.15 303.15 308.15 298.15 303.15 308.15 298.15 303.15 308.15

42.78 40.16 48.76 44.79 40.67 60.37 44.54 40.73 56.18

± ± ± ± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15 298.15 303.15 308.15

−5.73 1.78 15.02 −7.49 1.72 9.80 −1.65 5.25 19.07

± ± ± ± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15 298.15 303.15 308.15

14.97 17.76 22.56 1.29 −0.48 4.46 −10.09 −4.52 −3.65

± ± ± ± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15 298.15 303.15 308.15

89.82 113.63 133.07 83.43 105.68 138.88 85.04 85.57 87.73

± ± ± ± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15 298.15 303.15 308.15

123.97 137.19 138.79 145.77 126.88 134.70 123.27 111.86 119.02

± ± ± ± ± ± ± ± ±

ErCl3

YbCl3

DyCl3

ErCl3

YbCl3

DyCl3

ErCl3

YbCl3

DyCl3

ErCl3

YbCl3

DyCl3

ErCl3

YbCl3

10

m3·mol−1

chloride salts

WC 0.12 0.14 0.13 0.11 0.08 0.03 0.11 0.12 0.14 WCH 0.09 0.06 0.12 0.08 0.03 0.05 0.02 0.08 0.11 WCHL2 0.07 0.09 0.11 0.05 0.04 0.08 0.11 0.08 0.03 WCHL4 0.09 0.11 0.18 0.20 0.11 0.13 0.12 0.14 0.16 WCHL6 0.09 0.07 0.12 0.14 0.12 0.16 0.20 0.12 0.11

Sv

Bv

10−6 kg1/2·m3·mol−3/2

10−6 kg·m3·mol−2

−468.79 −357.14 −461.98 −505.05 −361.45 −777.24 −486.52 −338.39 −636.68

± ± ± ± ± ± ± ± ±

0.21 0.11 0.22 0.13 0.11 0.13 0.17 0.20 0.19

2352.02 1940.18 2424.45 2536.78 1974.15 4418.55 2405.20 1773.23 3470.86

± ± ± ± ± ± ± ± ±

0.22 0.14 0.12 0.21 0.17 0.11 0.13 0.23 0.25

626.90 522.73 261.80 788.38 637.34 490.02 708.77 603.45 256.20

± ± ± ± ± ± ± ± ±

0.21 0.13 0.16 0.23 0.12 0.14 0.11 0.16 0.12

−2204.81 −1782.25 −256.53 −3331.63 −2610.47 −1627.69 −2975.87 −2442.27 −24.27

± ± ± ± ± ± ± ± ±

0.02 0.09 0.04 0.09 0.04 0.03 0.11 0.13 0.15

379.51 335.38 271.56 517.72 616.32 508.25 666.72 571.41 566.74

± ± ± ± ± ± ± ± ±

0.13 0.12 0.09 0.08 0.23 0.21 0.12 0.17 0.13

−1771.64 −1550.01 −1244.44 −2607.97 −3166.32 −2322.76 −3388.03 −2870.64 −2775.43

± ± ± ± ± ± ± ± ±

0.12 0.17 0.15 0.21 0.09 0.11 0.08 0.12 0.14

−805.22 −787.87 −1011.75 −861.33 −1201.45 −1645.66 −1234.95 −966.67 −672.97

± ± ± ± ± ± ± ± ±

0.23 0.19 0.21 0.16 0.21 0.12 0.12 0.15 0.23

3302.20 1803.23 2645.25 3860.61 5672.11 7454.07 6143.77 4639.20 2257.46

± ± ± ± ± ± ± ± ±

0.14 0.11 0.23 0.25 0.24 0.22 0.15 0.12 0.09

−725.70 −1025.10 −962.92 −1773.36 −983.03 −1038.75 −1638.37 −806.60 −809.41

± ± ± ± ± ± ± ± ±

0.11 0.21 0.25 0.14 0.16 0.11 0.13 0.16 0.13

412.46 2568.01 2211.56 7165.20 1711.66 2090.26 7281.09 880.53 806.27

± ± ± ± ± ± ± ± ±

0.21 0.11 0.31 0.21 0.32 0.11 0.23 0.34 0.26

unfolding of Hgb by EMIMCl. The Sv value for LnCl3 decreases with WC, WCHL4, and WCHL6, and infers stronger solute− solvent interactions due to IHI. The Sv values decreased with

temperature with WCH and WCHL2. This infers weaker solute−solvent interactions induced by the hydrophobic domain of Hgb and H3Cit, which further increases due to the 672



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Table 5. Sound Velocity (u/m·s−1) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K and p = 0.1 MPaa m

DyCl3

ErCl3

mol·kg-1

298.15 K

303.15 K

308.15 K

298.15 K

0.000 0.002 0.004 0.006 0.008 0.010 0.012

1494.60 1494.63 1494.66 1494.69 1494.73 1494.77 1494.83

1504.71 1504.73 1504.74 1504.76 1504.77 1504.79 1504.80

1516.25 1516.26 1516.29 1516.31 1516.33 1516.36 1516.38

1494.60 1494.62 1494.64 1494.68 1494.72 1494.76 1494.81

0.000 0.002 0.004 0.006 0.008 0.010 0.012

1491.49 1491.52 1491.55 1491.59 1491.63 1491.67 1491.73

1501.60 1501.62 1501.64 1501.66 1501.68 1501.69 1501.71

1515.26 1515.29 1515.32 1515.36 1515.40 1515.44 1515.48

1491.49 1491.51 1491.54 1491.57 1491.62 1491.66 1491.72

0.000 0.002 0.004 0.006 0.008 0.010 0.012

1495.78 1495.92 1496.03 1496.18 1496.36 1496.54 1496.76

1509.15 1509.29 1509.40 1509.53 1509.65 1509.77 1509.88

1519.84 1519.91 1520.02 1520.14 1520.25 1520.37 1520.49

1495.78 1495.86 1495.97 1496.11 1496.30 1496.48 1496.71

0.000 0.002 0.004 0.006 0.008 0.010 0.012

1497.39 1497.48 1497.59 1497.72 1497.84 1497.98 1498.09

1509.63 1509.68 1509.81 1509.94 1510.03 1510.18 1510.29

1520.20 1520.26 1520.36 1520.47 1520.57 1520.68 1520.79

1497.39 1497.46 1497.57 1497.68 1497.81 1497.92 1498.07

0.000 0.002 0.004 0.006 0.008 0.010 0.012

1496.53 1496.62 1496.73 1496.87 1496.98 1497.11 1497.23

1507.73 1507.87 1507.98 1508.12 1508.22 1508.35 1508.46

1518.26 1518.33 1518.43 1518.57 1518.66 1518.79 1518.92

1496.53 1496.59 1496.71 1496.83 1496.95 1497.08 1497.19

YbCl3

303.15 K

308.15 K

298.15 K

303.15 K

308.15 K

1504.71 1504.72 1504.73 1504.75 1504.76 1504.78 1504.79

1516.25 1516.25 1516.28 1516.30 1516.32 1516.35 1516.37

1494.60 1494.61 1494.63 1494.67 1494.71 1494.75 1494.81

1504.71 1504.71 1504.73 1504.74 1504.76 1504.77 1504.79

1516.25 1516.25 1516.26 1516.29 1516.31 1516.33 1516.36

1501.60 1501.61 1501.63 1501.65 1501.67 1501.68 1501.70

1515.26 1515.28 1515.30 1515.35 1515.39 1515.43 1515.47

1491.49 1491.49 1491.52 1491.56 1491.61 1491.65 1491.71

1501.60 1501.59 1501.61 1501.63 1501.65 1501.67 1501.69

1515.26 1515.27 1515.28 1515.33 1515.37 1515.40 1515.45

1519.84 1519.86 1519.97 1520.09 1520.21 1520.33 1520.45

1495.78 1495.80 1495.92 1496.08 1496.27 1496.45 1496.68

1509.15 1509.17 1509.29 1509.43 1509.56 1509.68 1509.80

1519.84 1519.85 1519.91 1520.04 1520.15 1520.26 1520.39

1520.20 1520.22 1520.32 1520.43 1520.54 1520.65 1520.76

1497.39 1497.41 1497.55 1497.64 1497.75 1497.88 1498.02

1509.63 1509.64 1509.65 1509.67 1509.70 1509.71 1509.73

1520.20 1520.21 1520.26 1520.38 1520.48 1520.58 1520.70

1518.26 1518.29 1518.38 1518.52 1518.62 1518.76 1518.88

1496.53 1496.55 1496.67 1496.79 1496.90 1497.04 1497.15

1507.73 1507.75 1507.88 1508.01 1508.13 1508.25 1508.39

1518.26 1518.27 1518.34 1518.47 1518.58 1518.67 1518.82

WC

WCH

WCHL2 1509.15 1509.23 1509.34 1509.46 1509.59 1509.71 1509.83 WCHL4 1509.63 1509.65 1509.66 1509.68 1509.70 1509.72 1509.74 WCHL6 1507.73 1507.81 1507.93 1508.05 1508.17 1508.29 1508.42

m is the molality (mol·kg−1) of DyCl3, ErCl3, and YbCl3, in the solvent (WC, WCH, WCHL2, WCHL4, and WCHL6). Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, u(m) = 0.00001 mol·kg−1, and the expanded uncertainties Uc (0.95 level of confidence) is Uc(u) = 0.52 m·s−1.

a

0.005 mol·kg−1 aqueous citric acid concentration, using linear regression analysis of the earlier reported values. Our reported sound velocity differs by 0.046%, 0.180%, and 0.070%, at 298.15, 303.15, and 308.15 K, respectively, when compared with the reported values by Apelblat et al.75 Interestingly, at 303.15 K, Bhat et al.76 have also reported the sound velocities, and when Bhat76 and Apelblat et al.75 values were regressed and compared at 0.005 mol·kg−1, they differ by 0.081%. Thus, there are discrepancies in the reported sound velocity of aqueous citric acid, due to very limited literature, and our reported value is well within these discrepancies, and are thus in good agreement with the literature values.

increasing temperature due to a decrease in interionic attraction (LnCl3 ionizes to a greater extent). This suggests that a greater population of Ln3+ ions are accommodated within the void spaces left in the packing of the large associated solvent molecules. The Bv values (Table 4) for LnCl3 with WC, WCHL4, and WCHL6 are as YbCl3 > ErCl3 > DyCl3, indicating stronger electrostatic interactions (IHI) for Yb3+, while the reverse trend with WCH and WCHL2 infers weakest nonelectrostatic interactions (IHbI) for Dy3+.74 3.3. Sound Velocity (u/m·s−1). Table S3 of the Supporting Information compares the sound velocity of WC in this work with the earlier reported values. The comparison was done at 673



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Table 6. Viscosity (η/ 10−3kg·m−1·s−1) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3Methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K and p = 0.1 MPaa m

DyCl3

ErCl3

mol·kg−1

298.15 K

303.15 K

308.15 K

298.15 K

0.000 0.002 0.004 0.006 0.008 0.010 0.012

0.9011 0.9060 0.9127 0.9198 0.9273 0.9343 0.9449

0.8009 0.8026 0.8060 0.8081 0.8110 0.8140 0.8168

0.7225 0.7245 0.7260 0.7274 0.7292 0.7309 0.7327

0.9011 0.9147 0.9244 0.9317 0.9389 0.9478 0.9544

0.000 0.002 0.004 0.006 0.008 0.010 0.012

0.9167 0.9254 0.9280 0.9303 0.9332 0.9358 0.9377

0.8217 0.8240 0.8267 0.8318 0.8369 0.8398 0.8452

0.7343 0.7364 0.7386 0.7404 0.7421 0.7443 0.7468

0.9167 0.9226 0.9249 0.9270 0.9290 0.9313 0.9345

0.000 0.002 0.004 0.006 0.008 0.010 0.012

0.9418 0.9706 0.9727 0.9750 0.9776 0.9820 0.9871

0.8389 0.8656 0.8681 0.8717 0.8748 0.8786 0.8819

0.7636 0.7719 0.7802 0.7848 0.7914 0.7999 0.8148

0.9418 0.9503 0.9531 0.9565 0.9599 0.9646 0.9695

0.000 0.002 0.004 0.006 0.008 0.010 0.012

0.9652 0.9698 0.9709 0.9725 0.9742 0.9759 0.9784

0.8618 0.8665 0.8674 0.8685 0.8698 0.8712 0.8727

0.7850 0.8433 0.8441 0.8451 0.8462 0.8476 0.8490

0.9652 0.9662 0.9670 0.9679 0.9690 0.9703 0.9722

0.000 0.002 0.004 0.006 0.008 0.010 0.012

0.9899 1.2702 1.2739 1.2786 1.2830 1.2885 1.2943

0.8828 1.1046 1.1067 1.1090 1.1112 1.1148 1.1183

0.8080 0.8232 0.8239 0.8248 0.8258 0.8271 0.8284

0.9899 1.2573 1.2616 1.2670 1.2725 1.2775 1.2842

YbCl3

303.15 K

308.15 K

298.15 K

303.15 K

308.15 K

0.8009 0.8051 0.8086 0.8116 0.8147 0.8178 0.8225

0.7225 0.7259 0.7276 0.7289 0.7307 0.7322 0.7336

0.9011 0.9255 0.9342 0.9417 0.9484 0.9571 0.9677

0.8009 0.8082 0.8127 0.8164 0.8204 0.8238 0.8288

0.7225 0.7289 0.7309 0.7328 0.7344 0.7365 0.7385

0.8217 0.8229 0.8251 0.8303 0.8356 0.8385 0.8441

0.7343 0.7351 0.7365 0.7387 0.7404 0.7427 0.7450

0.9167 0.9207 0.9225 0.9245 0.9264 0.9286 0.9325

0.8217 0.8223 0.8244 0.8287 0.8345 0.8377 0.8429

0.7343 0.7347 0.7357 0.7368 0.7389 0.7404 0.7424

0.8389 0.8492 0.8544 0.8580 0.8618 0.8665 0.8720

0.7636 0.7670 0.7725 0.7792 0.7857 0.7918 0.8068

0.9418 0.9455 0.9482 0.9514 0.9550 0.9587 0.9640

0.8389 0.8448 0.8504 0.8555 0.8581 0.8620 0.8652

0.7636 0.7648 0.7701 0.7731 0.7772 0.7865 0.7997

0.8618 0.8642 0.8650 0.8658 0.8671 0.8681 0.8700

0.7850 0.8420 0.8427 0.8437 0.8447 0.8459 0.8476

0.9652 0.9654 0.9661 0.9670 0.9677 0.9684 0.9698

0.8618 0.8624 0.8631 0.8640 0.8652 0.8662 0.8679

0.7850 0.8408 0.8415 0.8423 0.8434 0.8445 0.8461

0.8828 1.1009 1.1034 1.1052 1.1076 1.1117 1.1153

0.8080 0.8212 0.8220 0.8233 0.8244 0.8253 0.8266

0.9899 1.2499 1.2534 1.2579 1.2629 1.2681 1.2736

0.8828 1.0923 1.0952 1.0979 1.1011 1.1050 1.1095

0.8080 0.8206 0.8213 0.8222 0.8231 0.8242 0.8256

WC

WCH

WCHL2

WCHL4

WCHL6

m is the molality (mol·kg−1) of DyCl3, ErCl3, and YbCl3, in the solvent (WC, WCH, WCHL2, WCHL4, and WCHL6). Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, u(m) = 0.00001 mol·kg−1, and the combined expanded uncertainties Uc (0.95 level of confidence) is Uc(η) = 0.0023 × 10−3 kg·m−1·s−1. a

solvent−solvent interactions. The sound velocity increased with increasing Ln3+ concentration and temperature both. Upon increasing the Ln3+ concentration, the intermolecular force strengthens, and the Ln3+ and hydrophilic sites (−NH3+, −COOH, >CO, −COO−, −OH, [RMIM]+) of Hgb, H3Cit, and ILs become closer with greater kinetic energy transfer, thereby increasing u with higher density. With the rise in temperature, the interacting groups (−NH3+, −COOH of Hgb) and (−COO−, −OH of H3Cit), and imidazolium cation [RMIM]+ of ILs with Ln3+ acquire more energy with greater vibration, causing faster sound wave propagation. This

The sound velocity of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 as a function of LnCl3 molalities are summarized in Table 5, visualized in Figures S4 to S18 of Supporting Information. The sound velocities of solvent follow the order WCHL4 > WCHL6 > WCHL2 > WC > WCH (Table 5). The trend suggests that the number of interacting molecules per unit volume increases, and the molecules become tightly packed in the presence of ILs, resulting in faster sound wave propagation. The u values were found to increase on increasing the temperature. This illustrates that the molecules upon gaining kinetic energy oscillate very strongly, weakening the 674



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Table 7. Viscosity B-Coefficients and A-Coefficients for Dysprosium(III) chloride (DyCl3), Erbium(III) chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1-Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3-methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K T/K B/kg·mol−1

A/kg1/2·mol−1/2

B/kg·mol−1

A/kg1/2·mol−1/2

B/kg·mol−1

A/ kg1/2·mol−1/2

B/kg·mol−1

A/kg1/2·mol−1/2

B/kg·mol−1

A/kg1/2·mol−1/2

DyCl3

298.15 303.15 308.15 298.15 303.15 308.15

2.2569 2.7316 −0.0637 −0.0100 −0.0616 0.0514

± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15

−2.4336 2.3527 0.6612 0.2878 0.0592 0.0293

± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15

−19.4911 −16.6792 −4.6476 1.3477 1.2810 0.3457

± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15

−2.5131 2.7872 −45.3297 0.1814 0.2109 3.2682

± ± ± ± ± ±

298.15 303.15 308.15 298.15 303.15 308.15

−171.3397 −153.7331 −11.1701 12.4099 11.0792 0.8075

± ± ± ± ± ±

ErCl3 WC 0.0275 0.0159 0.0177 0.0022 0.0085 0.0094 WCH 0.0125 0.0109 0.0111 0.0065 0.0067 0.0058 WCHL2 0.0113 0.0242 0.0221 0.0023 0.0013 0.0015 WCHL4 0.0224 0.0124 0.0135 0.0034 0.0023 0.0034 WCHL6 0.0124 0.0187 0.0187 0.0025 0.0087 0.0076

subsequently increases the u while decreasing the ρ values (Table 2). The u values increase linearly with LnCl 3 concentration, inferring stronger association of Hgb, H3Cit, ILs, and water molecules with LnCl3. The slopes for ρ are steeper than those for u (Figures S4 to S18) which mutually supports the first order of interaction with increasing LnCl3 concentration. The less steeper slope for u infers an acoustic resonance of the acoustic system which absorbs more energy with increasing LnCl3 concentration, thereby reducing the impact of LnCl3 concentration on u. 3.4. Viscosity (η/10−3 kg·m−1·s−1). Table S3 of Supporting Information compares the viscosity of 0.005 mol·kg−1 aqueous anhydrous citric acid with that of aqueous citric acid monohydrate, reported by Roy et al.,59 using linear regression analysis, The viscosity value differs from our value by 4.53% and 0.02% at 298.15 and 308.15 K respectively, which may be due to the water of crystallization present in the citric acid monohydrate, thereby changing the behavior of citric acid in the solution.60 Viscosity is a flow property of liquid, which directly reflects the interacting strength of LnCl3 with H3Cit,

YbCl3

3.0734 0.2746 −0.3795 0.2047 0.0885 0.1115

± ± ± ± ± ±

0.0219 0.0131 0.0180 0.0094 0.0073 0.0094

−8.2369 0.1249 −2.5524 0.8586 0.1818 0.2788

± ± ± ± ± ±

0.0129 0.0137 0.0116 0.0025 0.0068 0.0072

−1.9541 1.9601 0.9334 0.1963 −0.0800 −0.0278

± ± ± ± ± ±

0.0123 0.0217 0.0126 0.0065 0.0117 0.0025

1.5533 1.5626 0.1018 0.1522 −0.0840 −0.0096

± ± ± ± ± ±

0.0122 0.0324 0.0225 0.0023 0.0037 0.0022

−4.3429 −2.1197 −1.6679 0.3257 0.3309 0.0821

± ± ± ± ± ±

0.0123 0.0267 0.0245 0.0016 0.0014 0.0023

−1.2522 5.8497 −5.7248 0.1045 −0.0510 0.1657

± ± ± ± ± ±

0.0154 0.0165 0.0245 0.0024 0.0056 0.0015

−0.7191 −1.6104 −44.6040 0.0396 0.1080 3.2031

± ± ± ± ± ±

0.0174 0.0165 0.0155 0.0035 0.0040 0.0015

0.3647 −0.1033 −43.7639 −0.0140 0.0081 3.1395

± ± ± ± ± ±

0.0185 0.0185 0.0185 0.0035 0.0024 0.0021

−161.0429 −151.2287 −8.8122 11.7859 10.8945 0.6702

± ± ± ± ± ±

0.0254 0.0265 0.0285 0.0026 0.0078 0.0067

−158.6311 −144.2101 −9.2621 11.4956 10.4248 0.6709

± ± ± ± ± ±

0.0135 0.0185 0.0187 0.0087 0.0025 0.0056

Hgb, and ILs in aqueous medium. Stronger interactions infer higher opposing or higher frictional force with higher viscosity, whereas weaker interactions infer lower frictional forces with lower η. The viscosities of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 as a function of their molalities are presented in Table 6 and shown in Figures S19 to S33. The η values of solvents are as WCHL6 > WCHL4 > WCHL2 > WCH > WC at the investigated temperatures. The hydrophilic and hydrophobic groups of Hgb are better solvated by the hydrophilic (−OH/−COO−) and hydrophobic groups of H3Cit, respectively, causing a compact polymeric structure, reflected through WCH > WC viscosity values. The intermolecular interactions of ILs with WCH lead to dimeric or polymeric association depending on the IL alkyl chain length. For the ILs, their alkyl chain having −CH2− groups provides an opportunity for extensive intermolecular association, whereas −CH2− groups, due to their hydrophobic interactions with hydrophobic domains of Hgb and H3Cit, result in a three-dimensional solvent structure with higher η values. Thus, H3Cit acts as an interlocutor. This effect increases 675



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Table 8. Surface Tension (γ/mN·m−1) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K and p = 0.1 MPaa m

DyCl3

ErCl3

mol·kg−1

298.15 K

303.15 K

308.15 K

298.15 K

0.000 0.002 0.004 0.006 0.008 0.010 0.012

71.60 72.04 72.08 72.11 72.15 72.18 72.22

70.84 71.27 71.31 71.34 71.38 71.41 71.44

70.06 70.48 70.52 70.55 70.59 70.62 70.65

71.60 72.45 72.49 72.52 72.56 72.60 72.63

0.000 0.002 0.004 0.006 0.008 0.010 0.012

69.24 72.84 71.24 69.72 68.26 67.21 66.54

68.54 68.21 66.46 64.15 62.00 60.85 59.74

67.08 66.76 63.77 61.63 59.91 58.83 58.32

69.24 71.61 69.69 68.59 67.18 65.83 64.85

0.000 0.002 0.004 0.006 0.008 0.010 0.012

71.62 70.47 69.73 68.64 66.87 65.87 64.57

70.47 68.98 68.27 67.23 65.87 65.23 63.95

69.31 68.59 67.53 65.14 63.86 62.94 61.44

71.62 69.70 68.61 66.50 65.17 63.90 62.68

0.000 0.002 0.004 0.006 0.008 0.010 0.012

70.05 66.09 65.10 63.83 62.61 61.73 60.88

69.34 65.12 63.84 62.93 61.74 60.89 59.78

67.85 63.78 62.55 61.67 60.52 59.14 58.35

70.05 66.78 65.78 64.48 63.23 62.34 61.47

0.000 0.002 0.004 0.006 0.008 0.010 0.012

69.66 65.40 64.76 64.46 63.85 63.24 62.65

68.96 61.95 61.68 61.41 61.14 60.88 60.62

67.12 59.30 59.05 58.80 58.55 58.31 58.07

69.66 68.20 67.51 67.18 66.52 65.86 65.22

YbCl3

303.15 K

308.15 K

298.15 K

303.15 K

308.15 K

70.84 71.67 71.71 71.74 71.78 71.81 71.85

70.06 70.88 70.91 70.95 70.98 71.02 71.05

71.60 72.86 72.90 72.94 72.98 73.02 73.05

70.84 72.08 72.11 72.15 72.19 72.22 72.26

70.06 71.28 71.31 71.35 71.38 71.42 71.46

68.54 67.84 65.44 63.52 61.70 60.56 59.46

67.08 66.06 63.14 61.33 59.63 58.56 58.05

69.24 70.81 69.31 68.23 66.83 65.49 64.53

68.54 66.78 64.78 62.89 61.11 60.28 59.19

67.08 65.05 62.51 60.75 59.08 58.29 57.79

70.47 67.52 66.85 65.84 64.55 63.30 62.40

69.31 66.44 64.78 63.20 61.99 60.55 59.72

71.62 68.58 67.52 65.48 64.19 62.96 61.78

70.47 66.47 65.82 64.85 63.91 62.38 61.81

69.31 65.41 64.13 62.58 61.40 59.98 58.90

69.34 65.79 64.49 63.56 62.35 61.48 60.64

67.85 64.43 63.18 62.28 61.11 59.98 59.17

70.05 67.49 66.47 65.15 63.88 62.96 62.08

69.34 66.83 65.83 64.53 63.28 62.39 61.52

67.85 65.43 64.14 62.90 61.71 60.56 59.74

68.96 65.11 64.48 63.87 63.27 62.68 62.41

67.12 62.21 61.63 60.77 60.23 59.69 59.16

69.66 70.85 70.49 70.14 69.42 69.08 68.37

68.96 68.99 68.65 67.95 67.27 66.61 65.95

67.12 66.44 65.78 64.81 63.86 63.26 62.36

WC

WCH

WCHL2

WCHL4

WCHL6

m is the molality (mol·kg−1) of DyCl3, ErCl3, and YbCl3, in the solvent (WC, WCH, WCHL2, WCHL4, and WCHL6). Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, u(m) = 0.00001 mol·kg−1, and the combined expanded uncertainties Uc (0.95 level of confidence) is Uc(γ) = 0.34 mN·m−1.

a

with increasing −CH2− groups resulting in WCHL6 > WCHL4 > WCHL2 viscosity values, that is, the main factor contributing to enhancement of viscosity in the presence of ILs is the hydrophobic domain concentration. On every successive addition of LnCl3, the η values increased for all the investigated temperatures (Table 6 and Figures S19 to S33 of the Supporting Information). For increasing LnCl3 concentration with WC, WCH, WCHL2, WCHL4, and WCHL6, the linear increase in the η values depicts enhancement of the intermolecular interactions of Ln3+ ions with solvent molecules where, water molecules are tetrahedrally arranged around Ln3+

with stronger water cluster. Conversely, η values of LnCl3 solutions decreases sharply on increasing temperatures. Thus, the trend of η is complementary to other physicochemical properties. For instance, on increasing temperature, the η and ρ values decreased whereas, the u values increased. This effect supports the generation of oscillatory effects within the system. At higher temperature, molecules gain high kinetic energy, can overcome the strong IMF within the system, and can slip faster over one another. However, stronger interacting activities slow down the faster slipping of liquid laminar flow with higher η values. Such concentration dependence can decide the order of 676



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change in the η values, explained by the A- and B-coefficients. These coefficients also determine the transitional changes of the molecules within the system. Relative viscosity (ηr) of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 is used to calculate the viscosity A- and B-coefficients values using the extended Jones−Dole eq 3:56,77 nr − 1 = A + B m + Dm m

structure breaking tendency of LnCl3 is as YbCl3 > ErCl3 > DyCl3 with WC and WCH, whereas with WCHILs it is as YbCl3 < ErCl3 < DyCl3. 3.5. Tensiometry (γ/mN·m−1). The surface tension or surface energy defines involvement of solvent with LnCl3 activities where the cohesive force or surface energy of solvent decreases to interact with LnCl3. Stronger LnCl3−solvent interactions reflect a weaker cohesive force with disruption of the hydrogen bonding network, with lower γ and vice versa. The hydrophobic alkyl chain of the ILs accumulates on the solvent surface, thereby decreasing the γ value. The γ values of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 are listed in Table 8 and illustrated in Figures S34 to S48 of the Supporting Information. The surface tension of the solvent trends as WC > WCHL2 > WCHL4 > WCHL6 > WCH at T = (298.15, 303.15, and 308.15) K. The high surface active Hgb with WC increases the hydrophobicity which attenuates the hydrogen bonding network and HHI acting between H3Cit and water, amenable for γ as WC > WCH. The ILs with WCH (WCHILs) show lower γ values than WC, inferring attenuation of IMF acting among water, H3Cit, and Hgb molecules. The addition of hydrophobic groups in the form of −CH2− of ILs and Hgb, reduce the net inward force with decreasing surface energy, amenable for lower γ. The γ of ILs are as WCHL2 > WCHL4 > WCHL6 which is the inverse trend of η, and correlates to the hydrophobicity of the alkyl chain length. For ILs with alkyl chains (n ≤ 8), the γ strongly decreases with increasing −CH2− groups of the alkyl chain, and shows a linear relationship between γ and number of carbon atoms in the alkyl chain. Zhou et al. ascribe such behavior to the attenuation of the Coulombic interactions, when the alkyl chain length of ILs is increased.79 Since ILs, Hgb, and H3Cit already weaken the Coulombic interaction and electrostatics of water, the Ln3+ ions realign the water. The γ of LnCl3 with WC increased with concentration and decreased with temperature as YbCl3 > ErCl3 > DyCl3 (Figures S34 to S36 of Supporting Information). The Yb3+ with highest charge density shows stronger IHI with water, strengthening the IMF with highest γ, whereas Dy3+ with lowest charge density is amenable for the weaker IMF with lowest γ values. Upon increasing the LnCl3 concentration with WC, the γ increased owing to the increased IMF due to increased IHI with water. Interestingly, the γ of LnCl3 with WCH, WCHL2, WCHL4, and WCHL6 decreased with increasing concentration and temperature (Figures S34 to S45 of Supporting Information) due to the increased IHI with hydrophilic groups of Hgb by disrupting the hydrogen bonding network and Coulombic interactions (between −COO− and −NH3+) acting within the hydrophilic groups of Hgb and H3Cit. Such mechanism leads to the dominance of IHbI over IHI with Hgb, with decreased γ and increased η values.54 The γ of LnCl3 with WCH and WCHL2 are as DyCl3 > ErCl3 > YbCl3 and is due to the presence of the weakest IHbI prevailing between the Dy3+ ions and hydrophobic domain of Hgb, as EMIMCl induces the highest unfolding of Hgb with increased hydrophobic domains. The molecular orientation of BMIMCl and HMIMCl on the solvent surface is influenced by the increased alkyl chain length where they form a stable adsorbed film in the presence of LnCl3 with the order YbCl3 > ErCl3 > DyCl3. With increasing temperature, the kinetic energy of the molecules increases which attenuates the effectiveness of the intermolecular attraction. This increased molecular motion thus make it easier to stretch the solvent surface with lower γ.80

(3)

where η and η0 are the viscosities of solution and solvent, respectively, and m is the molarity of the solution. The viscosity A- and B-coefficients for LnCl3 solutions are derived by leastsquares analysis using ηr − 1/√m versus √m plot (Table 7). The term D depicts those solute−solvent and solute−solute structural interactions that were not accounted by A and B coefficients at higher LnCl3 concentrations. Here, A (m3/2· mol−1/2) is the Falkenhagen constant, specific for solute−solute interactions, reflecting long-range interionic forces (Columbic forces) at infinite dilution54,55 and B is the viscosity Bcoefficient (m3·mol−1) manifesting solute−solvent interactions at infinite dilution. These coefficients quantify the structural modifications induced by solute−solvent interactions, influencing the fluid dynamics.54,55 The B-coefficient values could be interpreted with specified viscosity effects as Columbic interactions, size, shape, alignment, or orientation of polar molecules by LnCl3 ionic field, and distortion of the solvent structure. These effects govern the viscosity behavior of LnCl3 solutions. The positive or negative sign of B-coefficient depends on the degree of solvent structuring induced by the LnCl3. A positive viscosity B-coefficient is associated with structuremaking efficiency of Ln3+ ions (enhancement of solvent association and ordering by Ln3+, with higher viscosity at infinite dilution). A negative B-coefficient value is associated with structure-breaking activity of Ln3+ ions, attributed to attenuation of the hydrogen bonding network within the solvent molecules (disordering, lower viscosity at infinite dilution).77,78 As the structural configuration seriously affect the laminar flow of such liquids, the B-coefficient values become less positive with decreasing surface charge density of the Ln3+ ions. This is in good agreement with the behavior found in different solvents. The A-coefficient values for LnCl3 solutions linearly decreased with increasing temperature for WC and WCH whereas, it increased for WCHL2, WCHL4, and WCHL6. Interestingly, on increasing the temperature from T = (298.15 to 303.15) K, the B-coefficients increased, whereas with further increase in temperature, the B-coefficients decreased. Additionally, the viscosity B-coefficient values increased with increasing charge density of the Ln3+ ions with WCHILs, whereas they decreased with WC and WCH (Table 7). Findings from V0ϕ illustrate that with increasing Ln3+ charge density, the inclusion of ILs in WCH increases the IHbI due to the interactions among the alkyl chain of the IL and the hydrophilic groups of Hgb. Thus, the weaker solute−solvent interactions prevailing between the Ln3+ and solvent decreased the B values in the presence of ILs. The lowest B values for Yb3+ with WCH indicate the presence of stronger IHbI with the hydrophobic domains of H3Cit and Hgb. The highest B values of Yb3+ with WCHILs infer the dominance of IHI prevailing between Yb3+ and hydrophilic groups of H3Cit, Hgb, and ILs (−COO−/−OH/−NH3+/−COOH/ >CO/[RMIM]+). This is due to the +I effect of the alkyl chain of the ILs which leads to weaker HHI with WCH, and thereby causes poor shielding to the IHI prevailing between the Ln3+ ions and WCH. The 677



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Table 9. Molar conductivity (Λm/mS·cm−1·mol−1) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1-Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3-methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K and p = 0.1 MPaa m

DyCl3

ErCl3

mol·kg−1

298.15 K

303.15 K

308.15 K

298.15 K

0.002 0.004 0.006 0.008 0.010 0.012

58.03 29.96 20.83 21.03 17.51 15.52

108.71 54.64 40.98 33.21 26.94 24.72

153.05 76.66 57.83 43.65 35.48 32.69

50.22 25.88 17.63 18.71 15.64 13.91

0.002 0.004 0.006 0.008 0.010 0.012

32.62 20.76 15.61 14.41 13.01 11.39

87.37 46.00 34.06 25.85 21.41 18.73

149.33 79.41 55.12 42.65 34.58 29.69

41.24 24.55 19.48 17.48 15.18 13.72

0.002 0.004 0.006 0.008 0.010 0.012

28.25 16.36 12.21 10.08 8.44 7.78

51.20 31.60 23.23 19.82 16.11 14.22

96.01 49.56 34.35 25.99 21.20 18.35

32.94 19.17 14.20 11.23 9.73 8.59

0.002 0.004 0.006 0.008 0.010 0.012

24.38 14.58 11.51 9.91 9.06 7.80

55.85 32.49 22.47 19.41 16.33 14.06

117.54 62.55 42.33 32.43 26.13 22.87

31.34 17.59 14.38 12.69 10.95 9.30

0.002 0.004 0.006 0.008 0.010 0.012

21.58 13.18 10.67 9.48 8.61 7.94

66.01 34.58 23.91 19.75 16.63 14.55

95.46 49.22 33.51 26.52 22.05 18.87

33.72 18.65 13.24 10.69 9.95 8.81

YbCl3

303.15 K

308.15 K

298.15 K

303.15 K

308.15 K

100.53 50.46 37.44 30.68 24.96 22.71

142.22 72.45 53.32 40.67 33.04 30.38

40.40 20.61 13.97 16.87 13.51 11.92

91.60 46.75 33.34 28.47 23.11 20.92

134.90 68.24 48.92 38.55 32.02 28.75

100.29 54.29 39.35 30.54 27.00 23.16

153.05 81.27 56.17 43.28 35.68 30.32

50.25 29.11 23.03 20.56 18.33 17.01

110.25 61.94 43.72 34.23 29.78 25.82

160.93 83.04 57.36 44.26 36.38 31.06

60.94 34.30 26.31 22.07 17.88 15.75

100.17 51.55 35.29 27.43 22.14 18.95

39.81 21.94 16.01 12.55 10.80 9.49

72.51 39.06 27.97 23.14 19.13 17.04

103.70 52.87 36.11 28.06 22.97 19.83

69.43 38.19 25.81 22.99 18.77 15.99

97.35 52.99 36.29 27.77 23.09 20.07

37.45 21.92 16.97 14.30 12.41 11.21

72.06 40.06 27.36 23.75 19.54 16.89

107.45 57.62 38.83 29.86 24.76 21.36

69.49 36.28 26.35 21.32 18.48 15.81

101.14 51.95 35.93 27.78 23.43 20.11

41.57 21.84 16.07 12.72 10.99 9.69

74.40 39.47 28.45 22.63 19.39 16.51

103.55 53.58 37.29 28.65 24.15 20.69

WC

WCH

WCHL2

WCHL4

WCHL6

m is the molality (mol·kg−1) of DyCl3, ErCl3, and YbCl3, in the solvent (WC, WCH, WCHL2, WCHL4, and WCHL6). Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.01 MPa, u(m) = 0.00001 mol·kg−1, and the expanded uncertainties Uc(0.95 level of confidence) is Uc(Λm) = 0.60 mS·cm−1· mol−1.

a

3.6. Molar Conductivity (Λm/mS·cm−1·mol−1). The molar conductivities of DyCl3, ErCl3, and YbCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 as solvent are reported in Table 9. For the calculation ofΛm, density values were used for the conversion of molality into molarity. The Λm values are evaluated as follows: Λm =

κ − κ0 c

increased microscopic viscosity of the medium, retarding the Ln3+ and Cl− ions mobility (ii) increased hydrodynamic radii of Ln3+ ions due to enhanced electrostatic attraction among Ln3+ and −COO−, −OH, −NH3+, and [RMIM]+, of solvent molecules, causing presolvation of Ln3+ ions by −COO−, − OH, − NH3+, and [RMIM]+, retarding the Ln3+ and Cl− ions mobility. Further, with an increase in temperature, the electrostatic forces existing among the solvent molecules weakens due to increased thermal energy, resulting in higher Ln3+ and Cl− ions mobility. The Λm values of LnCl3 with WCHILs as solvent follows the order WCHL2 > WCHL4 > WCHL6. This is because the longer is the alkyl chain length of the ionic liquid, the greater will be the hindrance it will cause to the ionic mobility of the Ln3+/Cl− ions. The limiting molar conductivity (Λ0) is obtained by fitting the Λm values in eq 5 given below:

(4)

where κ (S·cm−1) and κ0 (S·cm−1) are the specific conductance or electrical conductivities of solution and solvent (WC, WCH, WCHL2, WCHL4, and WCHL6), respectively, while c (mol· cm−3) is the molar concentration of the electrolytes: DyCl3, ErCl3, and YbCl3 (Table S4 of Supporting Information file). Figures 6 to 10 show decreased Λm values for solutions with increasing LnCl3 concentration. This may be due to (i) 678



Article

Figure 6. Molar conductivity of DyCl3, ErCl3, and YbCl3 with WC at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond) respectively.

Figure 9. Molar conductivity of DyCl3, ErCl3, and YbCl3 with WCHL4 at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond) respectively.

Figure 7. Molar conductivity of DyCl3, ErCl3, and YbCl3 with WCH at T/K = 298.15 (○, △, and □), 303.15 (●, ▲, and ■), and 308.15 (◇, ◆, and gray diamond) respectively.



conductivity for LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 is the reverse of the trend obtained for the viscosities (η) (Table 6) and limiting apparent molar volumes (V0ϕ) (Table 4), and follows the Walden rule.79 For Yb3+ ions with WC, the IHI is strongest due to the highest charge density of the Yb3+ ions, while weakest for Dy3+ ions, with lowest charge density. This results in the highest viscosity value for YbCl3 with WC, but the lowest value for DyCl3 (Table 6). The inclusion of Hgb and ILs in WC induces IHbI in the Ln3+ ionic systems owing to the presence of the hydrophobic side chains of the amino acids present in Hgb and the alkyl chain of the ILs. The Yb3+ ions because of their highest charge density cause the strongest IHbI, whereas the Dy3+ ions cause the weakest. This increased IHbI for Yb3+ ions with WCH, WCHL2, WCHL4, and WCHL6 causes the highest decrease in the viscosity of the system, with the least hindrance for the movement of the Yb3+ ions in these systems, and highest Λ0 values. With WCH, WCHL2, WCHL4, and WCHL6; for Dy3+ ions, the presence of weakest IHbI causes IHI to dominate, resulting for the development of strongest solute−solvent interaction. This intern leads to the highest viscosity values for DyCl3 with WCH, WCHL2, WCHL4, and WCHL6 (Table 6) and thereby causing the highest hindrance for the movement of Dy3+ ions in these systems. Thus, the results of the limiting molar conductivity and limiting apparent molar volume complement each other.

Λ m = Λ 0 + Am + Bm2

(5)

where Λ0 (S·cm−1·mol−1) is the limiting molar conductivity of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 as solvent, depicting the nature of solute−solvent interaction (Table 10) while, A (S·cm2·mol−2) and B (S·cm5·mol−3) are empirical parameters used to interpret solute−solute (interionic) interactions. As observed in Table 10, the trend of variation in Λ0 values for LnCl3 with WC is DyCl3 > ErCl3 > YbCl3, while with WCH, WCHL2, WCHL4, and WCHL6 is DyCl3 < ErCl3 < YbCl3. This trend of limiting molar 679


124.53 149.91 98.192 97.50 100.92

± ± ± ± ±

0.05 0.06 0.05 0.04 0.06

184.89 221.42 143.16 148.27 142.3

± ± ± ± ±

0.06 0.08 0.06 0.05 0.04

4. CONCLUSION The higher V0ϕ values for YbCl3, ErCl3, and DyCl3 with WC, WCHL2, WCHL4, and WCHL6 infer the dominance of IHI over IHbI. The V0ϕ values are found to be affected by the charge density of Ln3+ ions and follow the order YbCl3 > ErCl3 > DyCl3 with WC, WCHL4, and WCHL6, whereas DyCl3 > ErCl3 > YbCl3 with WCH and WCHL2. These findings are in good agreement with the viscosity B-coefficient values for which the order is the same as for the limiting apparent molar volumes. The structure breaking tendency of LnCl3 is as YbCl3 > ErCl3 > DyCl3 with WC and WCH, whereas with WCHILs it is as YbCl3 < ErCl3 < DyCl3. The viscosity confirms the prevalence of strong ion−hydrophilic interactions between LnCl3 and WC, WCHL4, and WCHL6 as solvents. The higher surface tension values of YbCl3, ErCl3, and DyCl3 with WCHL2 than with WCHL4 and WCHL6 gives strong evidence that a longer alkyl chain imparts less Coulombic interactions with lower surface tension, as compared to the shorter alkyl chain. The limiting molar conductivity values for LnCl3 with WC follow the order DyCl3 > ErCl3 > YbCl3, while with WCH, WCHL2, WCHL4, and WCHL6, the order is reversed, further complementing the V0ϕ values. The lowest Λ0 and highest viscosity values for YbCl3 with WC confirm the dominance of IHI in the absence of Hgb and ILs. The lowest Λ0 and highest viscosity values for YbCl3 in the presence of Hgb and ILs confirm increased solute−solute interaction with increasing charge density of the Ln3+ ions.

± ± ± ± ± 194.61 209.98 137.98 133.85 139.28

0.08 0.08 0.05 0.05 0.06

52.98 65.57 53.87 49.27 56.40 ± ± ± ± ±

0.04 0.05 0.03 0.03 0.04

308.15 K

Article

0.08 0.06 0.03 0.04 0.03

■

ASSOCIATED CONTENT

S Supporting Information *

136.42 136.14 80.45 93.85 94.15

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

YbCl3

303.15 K 298.15 K 308.15 K

ErCl3

303.15 K

0.07 0.04 0.08 0.03 0.02

147.42 118.66 67.37 75.02 90.26

0.08 0.07 0.07 0.02 0.04

208.95 204.65 132.36 162.28 131.46

0.09 0.08 0.06 0.05 0.08

67.08 53.25 44.12 40.29 45.89

± ± ± ± ±

0.05 0.04 0.02 0.03 0.02

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00695. Table S1 comparison of density, sound velocity, viscosity of 1.27 mol·kg−1 aqueous sucrose solution and surface tension of dimethyl sulfoxide with literature values at T = (298.15, 303.15, and 308.15) K and 0.1 MPa. Table S2 reports the density of aqueous solutions of citric acid (0.005 mol·kg−1), human hemoglobin (1 g·kg−1), and LnCl3 (0.004 mol·kg−1) with and without ILs (0.001 mol·kg−1): 1-ethyl-3-methylimidazolium chloride, 1butyl-3-methylimidazolium chloride, and 1-hexyl-3-methylimidazolium chloride at T = 298.15 K and 0.1 MPa. Table S4 illustrate the electrical conductivity of DyCl3, ErCl3, and YbCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at T = (298.15, 303.15, and 308.15) K and p = 0.1 MPa. Figures S1 to S15 show the density and sound velocity of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at T = (298.15, 303.15, and 308.15) K. Figures S16 to S30 illustrate the viscosity of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at T = (298.15, 303.15, and 308.15) K. Figures S31 to S45 show the surface tension of LnCl3 with WC, WCH, WCHL2, WCHL4, and WCHL6 at T = (298.15, 303.15, and 308.15) K (PDF)

77.59 42.06 37.71 31.58 27.76

± ± ± ± ±

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

WC WCH WCHL2 WCHL4 WCHL6

298.15 K 308.15 K DyCl3

303.15 K 298.15 K

Table 10. Limiting Molar Conductivity (Λ0/mS·cm−1·mol−1) of Dysprosium(III) Chloride (DyCl3), Erbium(III) Chloride (ErCl3), and Ytterbium(III) Chloride (YbCl3) with Aqueous Citric Acid (WC), Aqueous Citric Acid + Human Haemoglobin (WCH), Aqueous Citric Acid + Human Haemoglobin +1-Ethyl-3-methylimimdazolium Chloride (WCHL2), Aqueous Citric Acid + Human Haemoglobin +1-Butyl-3-methylimimdazolium Chloride (WCHL4), and Aqueous Citric Acid + Human Haemoglobin +1-Hexyl-3methylimimdazolium Chloride (WCHL6) at T = (298.15, 303.15, and 308.15) K


Man Singh: 0000-0002-0706-3763 Notes

The authors declare no competing financial interest. 680



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ACKNOWLEDGMENTS Authors thank the Central University of Gujarat, Gandhinagar, for financial and infrastructural support and experimental facilities.

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