Thermodynamic Difference between Protocatechualdehyde and p

Article pubs.acs.org/jced

Thermodynamic Difference between Protocatechualdehyde and p‑Hydroxybenzaldehyde in Aqueous Sodium Chloride Solutions Jimin Xie,† Min Liu,*,†,‡ Guiqin Liu,‡ Lixia Yuan,† Dacheng Li,‡ Zhiping Fan,‡ Zhengping Wang,‡ Bingquan Wang,‡ and Jun Han‡ †

School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, China Institute of BioPharmceutical Research, Liaocheng University, Liaocheng 252059, China

‡

S Supporting Information *

ABSTRACT: The enthalpies of dilution of protocatechualdehyde and p-hydroxybenzaldehyde in the aqueous sodium chloride solutions were measured by using a mixing-flow microcalorimeter at 298.15 K. Densities of the ternary homogeneous systems at different temperatures (293.15, 298.15, 303.15, 308.15, and 313.15 K) were also measured with a quartz vibratingtube densimeter. The homogeneous enthalpic interaction coefficients (h2, h3, and h4) were calculated according to the excess enthalpy concept based on the calorimetric data. The apparent molar volumes (Vϕ) and standard partial molar volumes (V0ϕ) of the investigated system were computed from their density data. The variation trends in h2 and V0ϕ with increasing salt molality were obtained and discussed in terms of the (solute + solute) and (solute + solvent) interactions. The experimental results showed that the molecular structures of protocatechualdehyde and p-hydroxybenzaldehyde, especially the number of hydroxyl groups, have evident influence on their thermodynamic properties. The thermodynamic data obtained in this work may be helpful for exploring the structure−function relationship of protocatechualdehyde and p-hydroxybenzaldehyde. verified to have anticancer effects.7,11,12 For example, it was suggested that PAL is likely to inhibit oncogenic disease through the inhibition of protein kinase CKII activity.7 p-Hydroxybenzaldehyde (4-hydroxybenzaldehyde, PHBA; Scheme 1b), a major active constituent of Gastrodiae rhizoma13 and vanilla bean,14 is an important intermediate for the production of fine chemicals and is extensively applied in medicine, perfume, cosmetic, and agrochemical industries.15,16 The molecular structures of PHBA and PAL are similar to the characteristics of a hydroxyl group and an aldehyde group attached to the C4 and C1 positions of a benzene ring, respectively. The difference is that PAL has an additional hydroxyl group at the C3 position. In comparison with PAL, PHBA is known mainly for its use as an intermediate. It is less known for its antioxidant activity.17,18 This difference of activity may be caused by their different structures, such as the number and position of the functional groups. The investigation of the physicochemical properties of phenolic compounds is helpful to understand both their efficacies and the role of each functional group. In recent years, several studies have been performed to determine the solubility, density, refractive index, and standard molar enthalpy of formation of PAL and PHBA.16,19−23 The equilibrium solubility of PHBA at different temperature, pressure, and solvent conditions were measured by Wu et al.16,19,20 The solubility of PAL in

1. INTRODUCTION Phenolic compounds have drawn increasing attention due to their great abundance in our diet, their antioxidant properties, and their effective prevention of oxidative stress associated diseases such as cancer and cardiovascular diseases.1,2 Phenolic compounds possess one or more aromatic rings with one or more hydroxyl groups. It has been reported that their antioxidant activity seems to be related to their molecular structure. More precisely, it is related to the presence and number of hydroxyl groups.3,4 Protocatechualdehyde (3,4-dihydroxybenzaldehyde, PAL; Scheme 1a) is a phenolic compound present in Salvia miltiorrhiza,5 barley tea6 and Xanthium strumarium and so on.7 A great deal of research has proven that PAL has antioxidant, anti-inflammatory, antihepatitis B virus, and antiatherosclerosis effects.5,8−10 More importantly, PAL has also been Scheme 1. Molecular Structures of PAL (a) and PHBA (b)

Received: June 5, 2016 Accepted: February 8, 2017 Published: February 21, 2017 © 2017 American Chemical Society

902

DOI: 10.1021/acs.jced.6b00458 J. Chem. Eng. Data 2017, 62, 902−912

Journal of Chemical & Engineering Data

Article

Table 1. Specification of the Chemical Samples chem name a

PHBA PALb sodium chloride a

CAS no.

source

mass fraction purity (%)c

123-08-0 139-85-5 7647-14-5

J&K Chemical Ltd. (Beijing) J&K Chemical Ltd. (Beijing) Aladdin Bio-Chem Technology Co., Ltd. (Shanghai)

≥99.0 ≥99.0 99.8

p-Hydroxybenzaldehyde. bProtocatechualdehyde (3,4-dihydroxybenzaldehyde). cStated by the supplier.

supercritical carbon dioxide was measured by Beltrán et al.21 In our previous work, the influence of temperature and pH on the densities and refractive indices of PAL in aqueous phosphate buffer solutions was discussed in detail.24 The enthalpy of dilution, which can embody important information about (solute + solute) and (solute + solvent) interactions, is one of the basic thermodynamic properties.25−27 Volumetric property, especially standard partial molar volume, is very useful to explain the intermolecular interaction occurring in the investigated system.28−30 It is well-known that biological fluids of living organisms contain a specified quantity of ions, especially sodium, potassium, and chloride ions, which are indispensable for the metabolic processes of a living organism to proceed. Among various inorganic salts, sodium chloride is especially essential to our life. It is required for blood, sweat, digestive juices, and efficient nerve transmission. For example, sodium coupled neurotransmitter transporters cooperate with postsynaptic receptors to detect signaling by the presynaptic nerve cell in the form of exocytotically released transmitters.31 Therefore, the research of thermodynamic properties of PHBA and PAL in aqueous sodium chloride solutions is very important and necessary. Until now, however, there has been a paucity of information on the dilution enthalpy and volumetric property of PAL and PHBA in the aqueous salt solutions. In this work, and continuing our previous study, the enthalpies of dilution PHBA and PAL in the aqueous sodium chloride solutions were measured at 298.15 K. In addition, the densities of PHBA (PAL) + NaCl + H2O at different temperatures (293.15, 298.15, 303.15, 308.15, and 313.15 K) were also measured. The enthalpic interaction coefficients and standard partial molar volumes were obtained based on the values of the enthalpies of dilution and densities, respectively. The results were discussed in light of (solute + solute) and (solute + solvent) interactions. The resulting parameters may provide fundamental information for exploring the structure−function relationship of PHBA and PAL.

Thermometric 2277 thermal activity monitor (Thermometric, Jarfalla, Sweden) at 298.15 K. The molality ranges of the aqueous PAL and PHBA solutions were 0.0250−0.0900 and 0.0250−0.0800 mol·kg−1, respectively. Both PAL and PHBA solutions were prepared with water or aqueous sodium chloride solution of a certain molality as solvent. With the aid of a VS2-10R MIDI dual-channel pump, the PAL and PHBA solutions and the corresponding solvent were simultaneously pumped through the mixing-flow vessel and the reference vessel connected in sequence. The masses of the samples delivered in 6 min were collected and weighed to determine their flow rates. The uncertainties in the thermal power, the molality of solute, and the flow rate were ±0.2 μW, ±0.0001 mol·kg−1, and ±0.002 mg·s−1, respectively. The detailed description of the instrument and the measurement procedure for dilution enthalpy determination were set forth elsewhere.32 2.3. Density Measurement. Densities of the investigated binary and ternary solution systems were measured with an Anton Paar DMA-5000 vibrating-tube densimeter (Graz, Austria) in the temperature range from 293.15 to 313.15 K with an interval of 5 K. The density measurements were performed at atmospheric pressure. The precision of this densimeter was ±2 × 10−6 g·cm−3, and its temperature accuracy was ±0.01 K. Calibration was performed periodically under atmospheric pressure using deionized water and dry air according to the specifications provided by the manufacturer. The molality ranges of the aqueous PAL and PHBA solutions for the density measurement were 0.0100−0.0900 and 0.0100− 0.0500 mol·kg−1, respectively, owning to their solubility. During the measurements, the sample (ca. 5 cm3) was transferred to a syringe and some of the contents of the syringe were injected into the densimeter. Precautions were taken to avoid evaporation losses and air dissolved during the experiment. Triplicate measurements of each sample were conducted to obtain the average value of density. After each measurement, distilled water and anhydrous ethanol were used to clean the vibrating tube.

2. EXPERIMENTAL SECTION 2.1. Materials. Protocatechualdehyde (PAL), p-hydroxybenzaldehyde (PHBA), and sodium chloride used in this work were of the highest purity that were commercially available and used as supplied without further purification. The list of chemicals used along with their suppliers and mass fraction purities were given in Table 1. Deionized, doubly distilled, and degassed water prepared with a quartz sub-boiling purifier was used for preparation of all of the solutions. The solutions were prepared on a mass basis by using a Mettler Toledo AG 135 analytical balance with a precision of ±0.00001g. Aqueous sodium chloride solutions with the molality of 0.00−0.60 mol·kg−1 were prepared and then were used as solvent to prepare the ternary mixtures. All of the reagents were stored over P2O5 in a vacuum drier before use. 2.2. Calorimetric Measurements. The enthalpies of dilution for PAL and PHBA in sodium chloride solutions were performed with a 2277-204 measuring cylinder supported by a

3. RESULTS AND DISCUSSION 3.1. Enthalpy of Dilution. The enthalpic interaction coefficients, derived from McMillan−Mayer’s theory,33 and modified by Franks et al.,34 characterize the total energetic effects of interactions between the investigated solute molecules with the competitive participation of solvent molecules.35 Therefore, these coefficients can contribute to a better understanding of the effects of the molecular structures of solute molecules on their hydrophobic/hydrophilic properties. The enthalpic interaction coefficients (hn) can be obtained from multiple linear regression analyses by fitting the data of dilution enthalpy ΔdilHm to eq 1:36 Δdil Hm = HmE(mf ) − HmE(m i ) = h2(mf − m i) + h3(mf2 − m i2) + h4(mf3 − m i3) + ... (1) 903



Article

Table 2. Enthalpies of Dilution of PHBA and PAL in Aqueous Sodium Chloride Solutions at 298.15 K and Atmospheric Pressure of 0.1 MPaa mi/(mol·kg−1)

mf/(mol·kg−1)

ΔdilHm/(J·mol−1)

0.0250 0.0300 0.0400 0.0450 0.0500

0.0110 0.0132 0.0177 0.0199 0.0221

150.99 176.66 226.19 250.46 274.61

0.0250 0.0300 0.0400 0.0450 0.0500

0.0112 0.0136 0.0181 0.0203 0.0227

164.02 190.49 243.81 271.18 294.68

0.0250 0.0300 0.0400 0.0450 0.0500

0.0109 0.0131 0.0175 0.0195 0.0219

140.46 164.92 209.49 232.56 252.03

0.0250 0.0300 0.0400 0.0450 0.0500

0.0105 0.0123 0.0167 0.0188 0.0209

163.14 197.04 248.61 274.79 298.96

0.0250 0.0300 0.0400 0.0450 0.0500

0.0114 0.0136 0.0182 0.0205 0.0227

162.93 193.03 249.08 275.74 303.53

0.0250 0.0300 0.0400 0.0450 0.0500

0.0107 0.0131 0.0176 0.0199 0.0219

178.55 206.27 259.10 283.70 309.73

0.0250 0.0300 0.0400 0.0450 0.0500

0.0106 0.0127 0.0168 0.0189 0.0212

166.57 197.73 257.49 283.98 307.28

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0120 0.0141 0.0185 0.0206 0.0237 0.0254

337.59 389.92 492.11 547.77 577.60 633.28

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0119 0.0143 0.0193 0.0217 0.0239 0.0263

354.44 405.21 499.24 546.81 596.59 640.46

δ/(J·mol−1) mNaCl = 0.01 −0.02 0.02 0.01 0.01 mNaCl = 0.03 −0.02 0.01 0.02 −0.03 mNaCl = 0.04 −0.04 −0.01 0.03 0.02 mNaCl = 0.02 −0.03 0.01 0.01 0.02 mNaCl = 0.01 −0.02 0.01 0.03 0.01 mNaCl = 0.03 −0.04 −0.01 0.02 0.02 mNaCl = 0.02 −0.05 −0.03 0.03 0.04 mNaCl = −0.02 −0.03 0.04 −0.01 0.01 −0.02 mNaCl = −0.01 −0.02 0.03 −0.03 0.04 −0.01

mi/(mol·kg−1)

PHBA 0.0000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.1000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.2000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.3000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.4000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.5000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 0.6000 mol·kg−1 0.0550 0.0600 0.0650 0.0700 0.0800 PAL 0.0000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900 0.1000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900

904

mf/(mol·kg−1)


δ/(J·mol−1)

0.0243 0.0264 0.0288 0.0310 0.0351

297.49 321.93 342.19 364.53 411.69

−0.01 0.01 −0.02 −0.03 −0.02

0.0247 0.0272 0.0293 0.0316 0.0362

322.51 343.81 368.52 391.39 435.42

−0.01 0.03 −0.04 −0.02 0.01

0.0240 0.0261 0.0282 0.0305 0.0349

272.38 293.32 314.80 334.20 376.03

−0.01 −0.02 −0.02 −0.01 −0.01

0.0230 0.0250 0.0272 0.0291 0.0335

323.28 347.87 369.96 394.97 437.30

0.03 −0.02 −0.02 −0.03 0.01

0.0249 0.0273 0.0296 0.0318 0.0360

330.31 353.83 377.84 404.60 458.45

−0.02 −0.01 0.03 −0.01 −0.01

0.0241 0.0262 0.0284 0.0306 0.0354

333.95 358.50 381.82 404.95 449.15

0.03 −0.02 −0.01 −0.02 −0.02

0.0229 0.0252 0.0274 0.0293 0.0337

336.96 358.49 381.47 408.73 459.85

0.02 0.04 0.03 −0.05 0.02

0.0274 0.0300 0.0322 0.0348 0.0377 0.0410

669.19 723.20 759.00 797.80 815.77 893.43

−0.02 −0.02 0.01 −0.01 0.03 −0.03

0.0282 0.0309 0.0336 0.0357 0.0374 0.0425

692.32 727.10 759.13 800.46 848.43 899.82

−0.04 −0.01 0.04 0.02 −0.05 0.02



Article

Table 2. continued mi/(mol·kg−1)

mf/(mol·kg−1)


0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0121 0.0148 0.0194 0.0221 0.0243 0.0269

367.42 412.47 513.03 552.21 601.50 640.21

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0120 0.0143 0.0194 0.0216 0.0243 0.0265

356.43 411.65 509.51 557.22 597.41 645.62

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0124 0.0147 0.0195 0.0222 0.0242 0.0270

360.88 419.73 526.48 570.43 627.30 661.55

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0117 0.0141 0.0183 0.0213 0.0232 0.0260

373.26 429.08 545.92 580.91 636.08 669.08

0.0250 0.0300 0.0400 0.0450 0.0500 0.0550

0.0122 0.0144 0.0191 0.0215 0.0238 0.0264

362.75 428.10 536.21 583.24 631.75 671.37

δ/(J·mol−1) mNaCl = 0.03 −0.02 0.01 −0.01 −0.03 0.03 mNaCl = 0.02 −0.03 −0.01 0.02 0.02 0.03 mNaCl = −0.01 −0.02 −0.03 0.03 0.05 0.00 mNaCl = −0.01 −0.03 −0.02 0.04 −0.03 0.03 mNaCl = −0.02 0.01 0.02 −0.02 −0.01 0.05

mi/(mol·kg−1)

mf/(mol·kg−1)


δ/(J·mol−1)

0.0291 0.0321 0.0345 0.0369 0.0396 0.0444

686.75 713.32 750.25 785.91 814.51 874.67

0.04 −0.02 0.01 0.04 −0.03 0.01

0.0288 0.0311 0.0333 0.0355 0.0384 0.0434

688.06 729.84 769.66 807.62 830.05 880.23

0.02 0.01 0.01 −0.02 0.01 0.02

0.0288 0.0313 0.0345 0.0366 0.0381 0.0438

718.84 756.35 774.23 816.58 867.05 902.46

−0.01 −0.03 0.02 0.04 −0.05 0.01

0.0283 0.0300 0.0330 0.0354 0.0375 0.0424

712.03 764.03 783.10 812.93 847.22 889.93

0.02 −0.02 0.03 0.02 −0.03 0.01

0.0280 0.0306 0.0332 0.0353 0.0376 0.0428

730.98 765.36 796.98 839.55 877.95 931.94

−0.03 −0.02 0.02 0.02 −0.02 0.01

−1

0.2000 mol·kg 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900 0.3000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900 0.4000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900 0.5000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900 0.6000 mol·kg−1 0.0600 0.0650 0.0700 0.0750 0.0800 0.0900

mi and mf represent the initial and final molalities of PHBA and PAL, respectively; the symbol δ is defined as δ = ΔdilHm − ΔdilHm(calcd), where ΔdilHm(calcd) was calculated using eq 1 with coefficients obtained by fitting the data at the corresponding molality. Standard uncertainties u for each variable are u(T) = 0.01 K, u(P) = 10 kPa, u(mNaCl) = 0.0001 mol·kg−1, and u(mi) = 0.0001 mol·kg−1, and the relative standard uncertainty ur is ur(ΔdilHm) = 0.05. a

where HEm(mi) and HEm(mf) are the molar excess enthalpies of a solute (PAL or PHBA in this work) in the solvent (sodium chloride solutions in this work) before and after dilution, respectively. mi and mf represent the initial and final solute molalities. The calculation of ΔdilHm has been described elsewhere by us and others,37−39which is expressed as Δdil Hm = −P(1 + m i M )/m i f2

(2)

where P is the dilution thermal power of PAL or PHBA, M is the molar mass of the solute, and f 2 is the flow rate of PAL or PHBA solution. The relative mean deviation of ΔdilHm values owing to duplicate runs at each initial molality was within 1%. The final molality mf, an important parameter in data processing, can be obtained from the equation mf = m i f2 /[f1 (1 + m i M ) + f2 ]

Figure 1. Variation of the enthalpic pairwise interaction coefficients h2 of PAL (●) and PHBA (■) versus the molality m of sodium chloride solutions.

(3)

in which f1 is the flow rate of solvent. Table 2 gives the experimental ΔdilHm values of PHBA and PAL diluted from mi to mf in the aqueous sodium chloride solutions, together with the differences between the experimental values and the

corresponding calculated values. The enthalpic interaction coefficients in eq 1 obtained from the values of ΔdilHm are listed in 905



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Table 3. Values of Density (ρ) and Apparent Molar Volumes (Vϕ) of PHBA in Aqueous Sodium Chloride Solutions at Temperatures between 293.15 and 313.15 K and Atmospheric Pressure of 0.1 MPaa 293.15 K mPHBA/ (mol·kg−1)

10−3/ −3

ρ× (kg·m )

298.15 K 10−3/ −3

Vϕ × (m3·mol )

ρ× kg·m

106/ −1

303.15 K

Vϕ × (m3·mol ) 106/ −1

10−3/ −3

308.15 K

Vϕ × (m3·mol )

ρ× kg·m

106/ −1

10−3/ −3

ρ× (kg·m )

313.15 K

Vϕ × (m3·mol ) 106/ −1

10−3/ −3

ρ× (kg·m )

Vϕ × 106/ (m3·mol−1)

mNaCl = 0.1000 mol·kg−1 0.0000

1.002423

1.001209

0.999767

0.998116

0.996272

0.0100

1.002652

99.06 ± 0.28

1.001434

99.47 ± 0.28

0.999990

99.80 ± 0.28 0.998338 100.03 ± 0.28 0.996491 100.48 ± 0.29

0.0150

1.002763

99.24 ± 0.19

1.001543

99.73 ± 0.19

1.000099

99.97 ± 0.19 0.998447 100.19 ± 0.19 0.996598 100.64 ± 0.19

0.0200

1.002872

99.41 ± 0.14

1.001652

99.81 ± 0.14

1.000206

100.13 ± 0.14 0.998554 100.35 ± 0.14 0.996704 100.79 ± 0.14

b

0.0250

1.002980

99.59 ± 0.11

1.001759

99.98 ± 0.11

1.000312

100.29 ± 0.11 0.998660 100.45 ± 0.11 0.996807 100.94 ± 0.11

0.0300

1.003084

99.83 ± 0.09

1.001863 100.15 ± 0.09

1.000417

100.41 ± 0.09 0.998762 100.66 ± 0.09 0.996911 101.05 ± 0.10

0.0350

1.003190

99.94 ± 0.08

1.001966 100.32 ± 0.08

1.000518

100.61 ± 0.08 0.998864 100.82 ± 0.08 0.997010 101.25 ± 0.08

0.0400

1.003292 100.12 ± 0.07

1.002067 100.49 ± 0.07

1.000618

100.78 ± 0.07 0.998964 100.98 ± 0.07 0.997109 101.40 ± 0.07

0.0450

1.003392 100.29 ± 0.06

1.002166 100.66 ± 0.06

1.000717

100.94 ± 0.06 0.999063 101.13 ± 0.06 0.997207 101.55 ± 0.06

0.0500

1.003491 100.47 ± 0.06

1.002263 100.83 ± 0.06

1.000814

101.10 ± 0.06 0.999160 101.29 ± 0.06 0.997303 101.71 ± 0.06

mNaCl = 0.2000 mol·kg−1 0.0000

1.006570

1.003825

1.002141

1.000267

0.0100

1.006810

97.62 ± 0.28

1.005547

1.005309 97.92 ± 0.28

1.004061

98.24 ± 0.28 1.002375

98.56 ± 0.28 1.000500

98.78 ± 0.28

0.0150

1.006927

97.82 ± 0.19

1.005663

98.12 ± 0.19

1.004175

98.43 ± 0.19 1.002489

98.75 ± 0.19 1.000614

98.96 ± 0.19

0.0200

1.007040

98.08 ± 0.14

1.005776

98.31 ± 0.14

1.004288

98.63 ± 0.14 1.002601

98.91 ± 0.14 1.000726

99.10 ± 0.14

0.0250

1.007154

98.23 ± 0.11

1.005889

98.46 ± 0.11

1.004399

98.82 ± 0.11 1.002710

99.13 ± 0.11 1.000835

99.32 ± 0.11

0.0300

1.007264

98.43 ± 0.09

1.005997

98.71 ± 0.09

1.004508

98.99 ± 0.09 1.002818

99.32 ± 0.09 1.000943

99.51 ± 0.09

0.0350

1.007372

98.63 ± 0.08

1.006104

98.91 ± 0.08

1.004614

99.21 ± 0.08 1.002924

99.51 ± 0.08 1.001049

99.69 ± 0.08 99.87 ± 0.07

0.0400

1.007478

98.84 ± 0.07

1.006210

99.11 ± 0.07

1.004719

99.39 ± 0.07 1.003028

99.70 ± 0.07 1.001153

0.0450

1.007581

99.04 ± 0.06

1.006313

99.31 ± 0.06

1.004821

99.60 ± 0.06 1.003131

99.85 ± 0.06 1.001255 100.05 ± 0.06

0.0500

1.007683

99.24 ± 0.06

1.006414

99.50 ± 0.06

1.004921

99.79 ± 0.06 1.003229 100.08 ± 0.06 1.001355 100.24 ± 0.06

mNaCl = 0.3000 mol·kg−1 0.0000

1.010635

1.007803

1.006083

1.004184

0.0100

1.010886

96.20 ± 0.28

1.009575

1.009326 96.48 ± 0.28

1.008050

96.83 ± 0.28 1.006328

97.12 ± 0.28 1.004429

97.33 ± 0.28

0.0150

1.011008

96.42 ± 0.18

1.009697

96.70 ± 0.19

1.008171

96.98 ± 0.19 1.006449

97.24 ± 0.19 1.004548

97.54 ± 0.19

0.0200

1.011129

96.60 ± 0.14

1.009816

96.90 ± 0.14

1.008288

97.26 ± 0.14 1.006565

97.54 ± 0.14 1.004665

97.71 ± 0.14

0.0250

1.011245

96.87 ± 0.11

1.009932

97.15 ± 0.11

1.008403

97.48 ± 0.11 1.006679

97.75 ± 0.11 1.004779

97.96 ± 0.11

0.0300

1.011360

97.09 ± 0.09

1.010046

97.37 ± 0.09

1.008516

97.70 ± 0.09 1.006792

97.97 ± 0.09 1.004891

98.16 ± 0.09

0.0350

1.011473

97.32 ± 0.08

1.010158

97.59 ± 0.08

1.008627

97.91 ± 0.08 1.006902

98.18 ± 0.08 1.005001

98.37 ± 0.08

0.0400

1.011583

97.54 ± 0.07

1.010268

97.78 ± 0.07

1.008737

98.09 ± 0.07 1.007010

98.39 ± 0.07 1.005109

98.58 ± 0.07

0.0450

1.011691

97.76 ± 0.06

1.010374

98.03 ± 0.06

1.008842

98.34 ± 0.06 1.007116

98.60 ± 0.06 1.005215

98.79 ± 0.06

0.0500

1.011796

97.99 ± 0.06

1.010479

98.25 ± 0.06

1.008946

98.56 ± 0.06 1.007220

98.81 ± 0.06 1.005319

98.99 ± 0.06

mNaCl = 0.4000 mol·kg−1 0.0000

1.014732

1.011817

1.010066

1.008139

0.0100

1.014996

94.70 ± 0.27

1.013640

1.013378 95.00 ± 0.28

1.012076

95.34 ± 0.28 1.010324

95.58 ± 0.28 1.008395

95.93 ± 0.28

0.0150

1.015124

94.95 ± 0.18

1.013767

95.25 ± 0.18

1.012202

95.58 ± 0.18 1.010449

95.81 ± 0.18 1.008519

96.16 ± 0.19

0.0200

1.015250

95.15 ± 0.14

1.013891

95.50 ± 0.14

1.012326

95.79 ± 0.14 1.010572

96.05 ± 0.14 1.008641

96.39 ± 0.14

0.0250

1.015371

95.46 ± 0.11

1.014011

95.79 ± 0.11

1.012446

96.06 ± 0.11 1.010692

96.29 ± 0.11 1.008761

96.59 ± 0.11

0.0300

1.015491

95.71 ± 0.09

1.014131

95.99 ± 0.09

1.012564

96.30 ± 0.09 1.010811

96.49 ± 0.09 1.008877

96.86 ± 0.09

0.0350

1.015608

95.96 ± 0.08

1.014247

96.24 ± 0.08

1.012680

96.53 ± 0.08 1.010925

96.77 ± 0.08 1.008991

97.09 ± 0.08

0.0400

1.015722

96.21 ± 0.07

1.014361

96.48 ± 0.07

1.012792

96.79 ± 0.07 1.011037

97.01 ± 0.07 1.009102

97.35 ± 0.07

0.0450

1.015834

96.46 ± 0.06

1.014472

96.73 ± 0.06

1.012903

97.03 ± 0.06 1.011147

97.24 ± 0.06 1.009213

97.56 ± 0.06

0.0500

1.015943

96.72 ± 0.06

1.014580

96.98 ± 0.06

1.013010

97.27 ± 0.06 1.011255

97.48 ± 0.06 1.009319

97.79 ± 0.06

mNaCl = 0.5000 mol·kg 1.017375

−1

0.0000

1.018778

1.015775

1.013992

1.012038

0.0100

1.019054

93.28 ± 0.27

1.017649

93.57 ± 0.27

1.016046

93.89 ± 0.27 1.014262

94.19 ± 0.28 1.012306

94.51 ± 0.28

0.0150

1.019187

93.55 ± 0.18

1.017782

93.78 ± 0.18

1.016178

94.16 ± 0.18 1.014392

94.45 ± 0.18 1.012436

94.72 ± 0.18

906



Article

Table 3. continued 293.15 K mPHBA/ (mol·kg−1)

10−3/ −3

ρ× (kg·m )

298.15 K

Vϕ × (m3·mol ) 106/ −1

10−3/ −3

ρ× kg·m

303.15 K

Vϕ × (m3·mol ) 106/ −1

10−3/ −3

308.15 K

Vϕ × (m3·mol )

ρ× kg·m

106/ −1

10−3/ −3

ρ× (kg·m )

313.15 K

Vϕ × (m3·mol ) 106/ −1

10−3/ −3

ρ× (kg·m )

Vϕ × 106/ (m3·mol−1)

mNaCl = 0.5000 mol·kg−1 0.0200

1.019319

93.76 ± 0.14

1.017911

94.11 ± 0.14

1.016307

94.39 ± 0.14 1.014521

94.66 ± 0.14 1.012562

95.02 ± 0.14

0.0250

1.019445

94.10 ± 0.11

1.018037

94.39 ± 0.11

1.016432

94.69 ± 0.11 1.014645

94.97 ± 0.11 1.012687

95.27 ± 0.11

0.0300

1.019569

94.38 ± 0.09

1.018161

94.66 ± 0.09

1.016556

94.92 ± 0.09 1.014767

95.24 ± 0.09 1.012808

95.53 ± 0.09

0.0350

1.019691

94.65 ± 0.08

1.018281

94.93 ± 0.08

1.016675

95.22 ± 0.08 1.014886

95.50 ± 0.08 1.012927

95.78 ± 0.08

0.0400

1.019810

94.93 ± 0.07

1.018399

95.20 ± 0.07

1.016792

95.49 ± 0.07 1.015003

95.76 ± 0.07 1.013043

96.03 ± 0.07

0.0450

1.019925

95.20 ± 0.06

1.018514

95.48 ± 0.06

1.016907

95.74 ± 0.06 1.015116

96.03 ± 0.06 1.013157

96.29 ± 0.06

0.0500

1.020038

95.48 ± 0.05

1.018626

95.75 ± 0.05

1.017018

96.02 ± 0.05 1.015227

96.29 ± 0.06 1.013267

96.54 ± 0.06

mNaCl = 0.6000 mol·kg−1 0.0000

1.022598

0.0100

1.022886

1.021155 91.82 ± 0.27

1.021441

92.14 ± 0.27

1.019517

1.017705

1.015725

1.019801

92.46 ± 0.27 1.017987

92.70 ± 0.27 1.016006

92.92 ± 0.27

0.0150

1.023027

92.03 ± 0.18

1.021580

92.38 ± 0.18

1.019938

92.75 ± 0.18 1.018125

92.92 ± 0.18 1.016144

93.12 ± 0.18

0.0200

1.023162

92.42 ± 0.14

1.021714

92.73 ± 0.14

1.020072

93.04 ± 0.14 1.018258

93.25 ± 0.14 1.016276

93.48 ± 0.14

0.0250

1.023294

92.72 ± 0.11

1.021846

93.02 ± 0.11

1.020204

93.28 ± 0.11 1.018388

93.56 ± 0.11 1.016406

93.76 ± 0.11

0.0300

1.023424

93.03 ± 0.09

1.021975

93.30 ± 0.09

1.020330

93.62 ± 0.09 1.018515

93.85 ± 0.09 1.016533

94.04 ± 0.09

0.0350

1.023550

93.33 ± 0.08

1.022100

93.61 ± 0.08

1.020455

93.91 ± 0.08 1.018640

94.12 ± 0.08 1.016657

94.32 ± 0.08

0.0400

1.023673

93.63 ± 0.07

1.022223

93.90 ± 0.07

1.020576

94.20 ± 0.07 1.018761

94.42 ± 0.07 1.016779

94.60 ± 0.07

0.0450

1.023792

93.93 ± 0.06

1.022342

94.19 ± 0.06

1.020695

94.49 ± 0.06 1.018879

94.71 ± 0.06 1.016897

94.88 ± 0.06

0.0500

1.023909

94.24 ± 0.05

1.022458

94.48 ± 0.05

1.020810

94.78 ± 0.05 1.018994

94.99 ± 0.05 1.017012

95.16 ± 0.05

Standard uncertainties u for each variable are u(T) = 0.01 K. u(P) = 10 kPa, u(mNaCl) = 0.0001 mol·kg−1, and u(mPHBA) = 0.0001 mol·kg−1, and the combined expanded uncertainty Uc (level of confidence = 0.95, k = 2) is Uc(ρ) = 0.5 kg·m−3. bThe “±” symbols for Vϕ represent the 95% confidence interval. a

Table 4. Values of Density (ρ) and Apparent Molar Volumes (Vϕ) of PAL in Aqueous Sodium Chloride Solutions at Temperatures between 293.15 and 313.15 K and Atmospheric Pressure of 0.1 MPaa 293.15 K −3

ρ × 10 / mPAL/ (mol·kg−1) (kg·m−3

298.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

303.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

308.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

313.15 K −3

Vϕ × 10 / (m3·mol−1)

ρ × 10 / (kg·m−3)

6

Vϕ × 106/ (m3·mol−1)

mNaCl = 0.1000 mol·kg−1 0.0000

1.002423

0.0100

1.002788

101.44 ± 0.28b

1.001572

1.001209 101.70 ± 0.28

1.000129

0.999767 101.90 ± 0.28

0.998477

0.998116 102.07 ± 0.28

0.996633

102.23 ± 0.29

0.0250

1.003323

101.87 ± 0.11

1.002106

102.06 ± 0.11

1.000662

102.23 ± 0.11

0.999010

102.39 ± 0.11

0.997168

102.44 ± 0.11

0.0300

1.003501

101.92 ± 0.09

1.002284

102.10 ± 0.09

1.000838

102.34 ± 0.09

0.999185

102.49 ± 0.09

0.997341

102.63 ± 0.10

0.0400

1.003849

102.17 ± 0.07

1.002628

102.41 ± 0.07

1.001186

102.52 ± 0.07

0.999532

102.71 ± 0.07

0.997688

102.83 ± 0.07

0.0550

1.004361

102.53 ± 0.05

1.003139

102.76 ± 0.05

1.001695

102.89 ± 0.05

1.000041

103.06 ± 0.05

0.998200

103.13 ± 0.05

0.0650

1.004695

102.77 ± 0.04

1.003472

102.99 ± 0.04

1.002028

103.11 ± 0.04

1.000377

103.23 ± 0.04

0.998535

103.33 ± 0.04

0.0750

1.005024

103.01 ± 0.04

1.003800

103.23 ± 0.04

1.002357

103.34 ± 0.04

1.000706

103.45 ± 0.04

0.998865

103.53 ± 0.04

0.0800

1.005186

103.13 ± 0.04

1.003962

103.35 ± 0.04

1.002520

103.45 ± 0.04

1.000869

103.55 ± 0.04

0.999029

103.63 ± 0.04

0.0900

1.005507

103.37 ± 0.03

1.004281

103.58 ± 0.03

1.002841

103.67 ± 0.03

1.001191

103.76 ± 0.03

0.999353

103.83 ± 0.03

mNaCl = 0.2000 mol·kg 1.005309

0.996272

−1

0.0000

1.006570

0.0100

1.006941

100.60 ± 0.28

1.005678

100.84 ± 0.28

1.003825 1.004193

101.04 ± 0.28

1.002508

101.23 ± 0.28

1.000635

101.27 ± 0.28

0.0250

1.007486

100.96 ± 0.11

1.006220

101.26 ± 0.11

1.004733

101.45 ± 0.11

1.003048

101.63 ± 0.11

1.001178

101.57 ± 0.11

0.0300

1.007662

101.18 ± 0.09

1.006395

101.46 ± 0.09

1.004910

101.59 ± 0.09

1.003224

101.76 ± 0.09

1.001354

101.78 ± 0.09

0.0400

1.008013

101.47 ± 0.07

1.006747

101.69 ± 0.07

1.005261

101.82 ± 0.07

1.003574

102.02 ± 0.07

1.001704

102.03 ± 0.07

0.0550

1.008527

101.91 ± 0.05

1.007260

102.11 ± 0.05

1.005772

102.27 ± 0.05

1.004090

102.35 ± 0.05

1.002219

102.42 ± 0.05

0.0650

1.008861

102.20 ± 0.04

1.007593

102.39 ± 0.04

1.006105

102.55 ± 0.04

1.004420

102.67 ± 0.04

1.002555

102.67 ± 0.04

0.0750

1.009189

102.49 ± 0.04

1.007921

102.67 ± 0.04

1.006433

102.82 ± 0.04

1.004749

102.94 ± 0.04

1.002885

102.93 ± 0.04

0.0800

1.009350

102.64 ± 0.03

1.008082

102.81 ± 0.04

1.006595

102.96 ± 0.04

1.004911

103.07 ± 0.04

1.003048

103.06 ± 0.04

0.0900

1.009668

102.93 ± 0.03

1.008400

103.09 ± 0.03

1.006913

103.23 ± 0.03

1.005230

103.33 ± 0.03

1.003369

103.31 ± 0.03

907

1.002141

1.000267



Article

Table 4. continued 293.15 K −3

ρ × 10 / mPAL/ (mol·kg−1) (kg·m−3

298.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

303.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

308.15 K

Vϕ × 10 / (m3·mol−1) 6

−3

ρ × 10 / (kg·m−3)

313.15 K −3

Vϕ × 10 / (m3·mol−1)

ρ × 10 / (kg·m−3)

6

Vϕ × 106/ (m3·mol−1)

mNaCl = 0.3000 mol·kg−1 0.0000

1.010635

0.0100

1.011012

99.69 ± 0.28

1.009326 1.009702

99.91 ± 0.28

1.007803 1.008178

100.09 ± 0.28

1.006457

1.006083 100.28 ± 0.28

1.004558

1.004184 100.40 ± 0.28

0.0250

1.011566

100.12 ± 0.11

1.010252

100.40 ± 0.11

1.008727

100.57 ± 0.11

1.007005

100.75 ± 0.11

1.005105

100.92 ± 0.11

0.0300

1.011744

100.37 ± 0.09

1.010433

100.51 ± 0.09

1.008906

100.73 ± 0.09

1.007186

100.85 ± 0.09

1.005286

101.01 ± 0.09

0.0400

1.012098

100.71 ± 0.07

1.010785

100.90 ± 0.07

1.009263

100.97 ± 0.07

1.007537

101.22 ± 0.07

1.005640

101.31 ± 0.07

0.0550

1.012615

101.22 ± 0.05

1.011301

101.40 ± 0.05

1.009776

101.54 ± 0.05

1.008054

101.68 ± 0.05

1.006158

101.76 ± 0.05

0.0650

1.012950

101.56 ± 0.04

1.011636

101.73 ± 0.04

1.010111

101.86 ± 0.04

1.008390

101.99 ± 0.04

1.006494

102.07 ± 0.04

0.0750

1.013278

101.91 ± 0.04

1.011963

102.06 ± 0.04

1.010439

102.18 ± 0.04

1.008718

102.30 ± 0.04

1.006824

102.37 ± 0.04

0.0800

1.013438

102.08 ± 0.03

1.012124

102.23 ± 0.03

1.010601

102.34 ± 0.04

1.008880

102.46 ± 0.04

1.006987

102.52 ± 0.04

0.0900

1.013754

102.42 ± 0.03

1.012440

102.56 ± 0.03

1.010918

102.66 ± 0.03

1.009198

102.77 ± 0.03

1.007306

102.82 ± 0.03

mNaCl = 0.4000 mol kg−1 0.0000

1.014732

1.013378

1.011817

1.010066

0.0100

1.015117

98.71 ± 0.27

1.013762

98.91 ± 0.28

1.012199

99.12 ± 0.28

1.010447

99.33 ± 0.28

1.008520

99.49 ± 0.28

0.0250

1.015675

99.39 ± 0.11

1.014321

99.49 ± 0.11

1.012757

99.68 ± 0.11

1.011004

99.88 ± 0.11

1.009075

100.08 ± 0.11

0.0300

1.015860

99.49 ± 0.09

1.014505

99.61 ± 0.09

1.012939

99.86 ± 0.09

1.011185

100.06 ± 0.09

1.009258

100.19 ± 0.09

0.0400

1.016218

99.88 ± 0.07

1.014860

100.06 ± 0.07

1.013298

100.19 ± 0.07

1.011542

100.42 ± 0.07

1.009615

100.54 ± 0.07

0.0550

1.016740

100.47 ± 0.05

1.015381

100.63 ± 0.05

1.013817

100.79 ± 0.05

1.012061

101.00 ± 0.05

1.010137

101.07 ± 0.05

0.0650

1.017076

100.86 ± 0.04

1.015717

101.02 ± 0.04

1.014154

101.16 ± 0.04

1.012399

101.33 ± 0.04

1.010474

101.42 ± 0.04

0.0750

1.017404

101.26 ± 0.04

1.016045

101.40 ± 0.04

1.014482

101.53 ± 0.04

1.012728

101.69 ± 0.04

1.010804

101.77 ± 0.04

0.0800

1.017564

101.45 ± 0.03

1.016206

101.59 ± 0.03

1.014643

101.72 ± 0.03

1.012889

101.87 ± 0.03

1.010966

101.95 ± 0.03

0.0900

1.017879

101.84 ± 0.03

1.016521

101.97 ± 0.03

1.014959

102.09 ± 0.03

1.013206

102.23 ± 0.03

1.011284

102.30 ± 0.03

mNaCl = 0.5000 mol·kg 1.017375

1.008139

−1

0.0000

1.018778

1.015775

1.013992

1.012038

0.0100

1.019170

97.77 ± 0.27

1.017766

97.97 ± 0.27

1.016162

98.40 ± 0.27

1.014380

98.40 ± 0.28

1.012426

98.53 ± 0.28

0.0250

1.019741

98.37 ± 0.11

1.018334

98.62 ± 0.11

1.016726

99.03 ± 0.11

1.014946

99.01 ± 0.11

1.012990

99.21 ± 0.11

0.0300

1.019924

98.66 ± 0.09

1.018516

98.91 ± 0.09

1.016909

99.25 ± 0.09

1.015130

99.22 ± 0.09

1.013176

99.33 ± 0.09

0.0400

1.020286

99.10 ± 0.07

1.018880

99.26 ± 0.07

1.017270

99.61 ± 0.07

1.015490

99.63 ± 0.07

1.013537

99.74 ± 0.07

0.0550

1.020811

99.77 ± 0.05

1.019405

99.91 ± 0.05

1.017789

100.30 ± 0.05

1.016013

100.28 ± 0.05

1.014063

100.34 ± 0.05

0.0650

1.021148

100.21 ± 0.04

1.019742

100.34 ± 0.04

1.018124

100.72 ± 0.04

1.016352

100.66 ± 0.04

1.014401

100.74 ± 0.04

0.0750

1.021475

100.66 ± 0.04

1.020070

100.77 ± 0.04

1.018450

101.14 ± 0.04

1.016681

101.07 ± 0.04

1.014731

101.15 ± 0.04

0.0800

1.021635

100.88 ± 0.03

1.020231

100.99 ± 0.03

1.018610

101.35 ± 0.03

1.016842

101.28 ± 0.03

1.014893

101.35 ± 0.03

0.0900

1.021948

101.32 ± 0.03

1.020545

101.42 ± 0.03

1.018922

101.77 ± 0.03

1.017157

101.69 ± 0.03

1.015210

101.75 ± 0.03

mNaCl = 0.6000 mol·kg−1 0.0000

1.022598

1.021155

1.019517

1.017705

1.015725

0.0100

1.022997

96.85 ± 0.27

1.021553

97.02 ± 0.27

1.019914

97.23 ± 0.27

1.018101

97.41 ± 0.27

1.016120

97.61 ± 0.27

0.0250

1.023573

97.68 ± 0.11

1.022131

97.74 ± 0.11

1.020490

97.94 ± 0.11

1.018677

98.10 ± 0.11

1.016693

98.36 ± 0.11

0.0300

1.023763

97.83 ± 0.09

1.022316

98.04 ± 0.09

1.020677

98.18 ± 0.09

1.018863

98.33 ± 0.09

1.016881

98.52 ± 0.09

0.0400

1.024129

98.33 ± 0.07

1.022684

98.46 ± 0.07

1.021044

98.60 ± 0.07

1.019229

98.79 ± 0.07

1.017246

98.98 ± 0.07

0.0550

1.024658

99.07 ± 0.05

1.023213

99.19 ± 0.05

1.021570

99.37 ± 0.05

1.019760

99.45 ± 0.05

1.017775

99.66 ± 0.05

0.0650

1.024996

99.56 ± 0.04

1.023551

99.67 ± 0.04

1.021909

99.84 ± 0.04

1.020097

99.95 ± 0.04

1.018115

100.11 ± 0.04

0.0750

1.025323

100.05 ± 0.04

1.023880

100.15 ± 0.04

1.022237

100.31 ± 0.04

1.020427

100.41 ± 0.04

1.018445

100.56 ± 0.04

0.0800

1.025483

100.30 ± 0.03

1.024040

100.39 ± 0.03

1.022398

100.55 ± 0.03

1.020588

100.64 ± 0.03

1.018606

100.79 ± 0.03

0.0900

1.025794

100.79 ± 0.03

1.024352

100.87 ± 0.03

1.022710

101.02 ± 0.03

1.020902

101.11 ± 0.03

1.018921

101.25 ± 0.03

Standard uncertainties u for each variable are u(T) = 0.01 K, u(P) = 10 kPa, u(mNaCl) = 0.0001 mol·kg−1, and u(mPAL) = 0.0001 mol·kg−1, and the combined expanded uncertainty Uc (level of confidence = 0.95, k = 2) is Uc(ρ) = 0.5 kg·m−3. bThe “±” symbols for Vϕ represent the 95% confidence interval. a

908



Article

under most conditions. In fact, the contribution of three-body and higher order interactions is small compared with that of two-body interactions. Besides, the McMillan−Mayer’s theory assumes higher order coefficients also have the contribution from h2; therefore it is difficult to interpret h3 and h4.43 3.2. Volumetric Properties. Partial molar volume is another important thermodynamic parameter to study the intermolecular interactions between solute and solvent molecules. The data of standard partial molar volume that numerically coincide with the infinite dilution apparent molar volume can be calculated from determined densities. The density data measured for PHBA + NaCl + H2O and PAL + NaCl + H2O at different temperatures are given in Tables 3 and 4, respectively. Apparent molar volumes Vϕ of PAL and PHBA in sodium chloride solutions were calculated from densities of solution (ρ) using the following equation:44

Table S1 in the Supporting Information. It is interesting to observe that the ΔdilHm value of PAL is slightly more than double the value for PHBA when diluted from the same initial molality in the aqueous sodium chloride solutions of the same molality. This is caused by the different molecular structures between PHBA and PAL. PAL molecule has an additional hydroxyl group at the C3 position of the benzene ring compared with PHBA molecule. Therefore, more energy will be needed to disrupt the hydrogen bond interactions between hydrated PAL molecules when they are diluted, resulting in a more positive ΔdilHm value of PAL than that of PHBA. The enthalpic pairwise interaction coefficients h2 reflect the summary process of interaction between two PHBA or PAL molecules in solution proceeding with the participation of the solvent molecules. The variation tendency of h2 is shown in Figure 1. From Figure 1, we can see that the values of h2 for both PHBA and PAL in pure water and aqueous sodium chloride solutions of different molalities are all negative. These results indicate that the electrostatic and hydrogen bond interactions (negative contribution to h2) are stronger than the hydrophobic−hydrophobic and hydrophobic−hydrophilic interactions (positive contribution to h2)40 as well as partial desolvation of solvation shells of solute and solvent molecules (positive contribution to h2).41 In the above interactions, the electrostatic and hydrogen bond interactions are present between solvent-mediated solute (PAL or PHBA) molecules. The hydrophobic−hydrophobic interactions occur between the benzene ring of PHBA or PAL molecules. The hydrophobic− hydrophilic interactions take place between the benzene ring of the solute molecule and the hydrophilic group of the solute molecule or solvent ion. From Table S1 (Supporting Information) and Figure 1, we know that the values of h2 become more negative with an increase in the molality of sodium chloride solutions for both PHBA and PAL. This may be explained as follows. With the increasing molality of sodium chloride solutions, the partial desolvation of solvation shells makes more positive contribution to h2. However, the negative contribution of the electrostatic and hydrogen bond interactions to h2 surpasses the positive contribution of the hydrophobic−hydrophilic interaction and partial desolvation effects, resulting in the more negative values of h2. This further verifies the dominant role of the electrostatic and hydrogen bond interactions in the examined systems. It can be clearly seen from Figure 1 that the value of h2 for PHBA is less negative than that for PAL in sodium chloride solution at the same molality. This difference is caused by the different molecular structures between PHBA and PAL. As discussed above, PAL molecule has two hydroxyl groups while PHBA molecule has only one. The stronger electrostatic interactions between the hydroxyl group of PAL molecule and solvent ions make a more negative contribution to h2. In addition, the intramolecular hydrogen bonding existing in PAL molecule will attenuate the intermolecular hydrogen bonding between them. However, the more negative value of h2 for PAL than that for PHBA suggests that the intermolecular hydrogen bonding and electrostatic interactions are dominant over the intramolecular hydrogen bonding. This indicates that the molecular structure of drugs has an important influence on the intermolecular interaction and the efficacy of the drugs.42 As for enthalpic triplet and quartet interaction coefficients (h3 and h4), the values of them listed in Table S1 (Supporting Information) are irregular although the values of h3 are positive

Vϕ = M /ρ − 1000(ρ − ρ0 )/(mρρ0 )

(4)

in which M is the molar mass of PAL or PHBA, m is its molality, and ρ0 is the density of the solvent (NaCl + H2O). The values of the calculated apparent molar volumes of PAL and PHBA are also given in Tables 3 and 4, respectively. From Tables 3 and 4, we can see that the apparent molar volumes increase with the ascent of temperature and the increasing molalities of PAL and PHBA. The standard partial molar volume V0ϕ was calculated by correlating Vϕ with m using eq 5:28

Figure 2. Variation of apparent molar volumes (Vϕ) of PHBA (a) and PAL (b) versus their molalities at 298.15 K in the aqueous sodium chloride solutions of different molalities (0.1 (■), 0.2 (●), 0.3 (▲), 0.4 (▼), 0.5 (◀), and 0.6 mol·kg−1 (Δ)). 909



Vϕ = V ϕ0 + S Vm

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(5)

where SV is obtained from the slope of the straight line. Figure 2 shows the variation of apparent molar volumes (Vϕ) of PHBA and PAL versus their molalities in the aqueous sodium chloride solutions of different molalities at 298.15 K. The corresponding plots at 293.15, 303.15, 308.15, and 313.15 K are provided in Figures S1−S4 in the Supporting Information, respectively. All of the plots of Vϕ versus m showed a good linear relation (R2 > 0.99). The values of V0ϕ and SV of PAL and PHBA are summarized in Table S2 in the Supporting Information, and the change tendencies of V0ϕ and SV with increasing sodium chloride concentration are shown in Figures 3 and 4, respectively. The

Figure 4. Variation of experimental slope (SV) of PHBA (a) and PAL (b) versus the molality m of sodium chloride in aqueous solutions at T = 293.15 (■), 298.15 (●), 303.15 (▲), 308.15 (▼), and 313.15 K (◀).

both PAL and PHBA, while the change trend in the values of V0ϕ is contrary. The rising temperature may facilitate the partial desolvation of solvation shells of solute and solvent species. The release of some water molecules from the hydrophilic solvation layer around solvent molecules into the bulk of the solvent may be responsible for the increase of V0ϕ. In contrast, the release of some water molecules from the hydrophobic hydration shells of solute molecules will lead to a negative contribution to SV. From Figures 3 and 4 we can see that the values of V0ϕ decrease with the increase of salt concentration, while the change trend in the values of SV is contrary. This phenomenon might be mainly caused by interaction of PAL or PHBA molecule with the coexisting ions.36 With the elevation of the molality of sodium chloride, the degree of disruption of the hydration shells of solvent ions is intensified, resulting in tighter hydration layers around solute molecules. Therefore, the dipole−dipole and hydrogen bond interactions between solvated solute molecules release more water molecules into the bulk medium, making a positive contribution to SV. At the same time, the disruption effect attenuates the electrostatic and hydrogen bond interactions between solute and solvent molecules, resulting in the decrease of V0ϕ. It can also be seen from Table S2 (Supporting Information) that the values of V0ϕ and SV of PAL are slightly larger and smaller than those of PHBA in sodium chloride solution at the same molality, respectively. This is also caused by the structure difference between PHBA and PAL. On one side, the stronger solute−solvent electrostatic and hydrogen bond interactions between PAL molecule and solvent ion increase the values of

Figure 3. Variation of standard partial molar volume (V0ϕ) of PHBA (a) and PAL (b) versus the molality m of sodium chloride in aqueous solutions at T = 293.15 (■), 298.15 (●), 303.15 (▲), 308.15 (▼), and 313.15 K (◀).

values of V0ϕ and SV show the nature of (solute + solvent) and (solute + solute) interactions, respectively. It can be seen from Table S2 (Supporting Information) that the values of V0ϕ and SV are all positive. The positive V0ϕ indicates that (solute + solvent) electrostatic and hydrogen bond interactions (positive contribution to V0ϕ) surpass hydrophobic−hydrophilic interactions (negative contribution to V0ϕ).29 The positive SV may be interpreted from the fact that dipole−dipole and hydrogen bond interactions between solute molecules themselves (positive contribution to SV) surpass hydrophobic−hydrophobic and hydrophobic−hydrophilic interactions between them. This conclusion agrees well with the effect of different interactions on enthalpic interaction coefficient h2. The data in Table S2 (Supporting Information) also show that the values of SV decrease with a rise in temperature for 910



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V0ϕ. On the other side, the stronger hydrophilic−hydrophobic interactions between PAL molecules decrease the values of SV.

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4. CONCLUSIONS The enthalpies of dilution of PAL and PHBA in aqueous sodium chloride solutions at 298.15 K and the densities of the ternary homogeneous systems at different temperatures (293.15, 298.15, 303.15, 308.15, and 313.15 K) have been determined. The enthalpic interaction coefficients (h2, h3, and h4), apparent molar volumes (Vϕ), standard partial molar volumes (V0ϕ), and experimental slope (SV) for the investigated systems have been obtained from the experimental data. The following conclusions can be drawn from the above results and discussion. (1) The enthalpic pairwise interaction coefficients h2 of PAL and PHBA in aqueous sodium chloride solutions are all negative and decrease with the increase in the molality of sodium chloride. (2) The value of h2 for PHBA is less negative than that for PAL at the same sodium chloride molality. (3) The values of V0ϕ and SV of PAL and PHBA are all positive and have different variation trends with the increasing temperature and molality of sodium chloride. (4) The value of V0ϕ of PAL is larger than that of PHBA in aqueous sodium chloride solutions at the same molality, while the value of SV is contrary. (5) The thermodynamic difference between PAL and PHBA is caused by their different molecular structures, especially the number of hydroxyl groups.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.6b00458. Apparent molar volumes at different temperatures (Figures S1−S4), enthalpic interaction coefficients (Table S1), and standard partial molar volumes and experimental slope (Table S2) (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86-635-8239136. ORCID

Min Liu: 0000-0002-1918-9072 Funding

This work was supported by the National Natural Science Foundation of China (Grant No. 21473085), the Key Research and Development Program of Shandong Province of China (Grant No. 2015GGB01567), and the Tai-Shan Scholar Research Fund of Shandong Province of China. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was technically supported by Shandong Collaborative Innovation Center for Antibody Drugs and Engineering Research Center for Nanomedicine and Drug Delivery Systems.

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REFERENCES

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Thermodynamic Difference between Protocatechualdehyde and p

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