Influence of Phosphate-Based Salts on Enthalpy of Dilution and

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Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Influence of Phosphate-Based Salts on Enthalpy of Dilution and Isentropic Compressibility Properties of Saccharides and Their Derivatives in Aqueous Solutions Neha Aggarwal,*,† Mousmee Sharma,‡ Tarlok S. Banipal,‡ and Parampaul K. Banipal‡ †

Department of Chemistry, Gandhi Memorial National College, Ambala Cantt 133001, Haryana, India Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, Punjab, India

‡

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S Supporting Information *

ABSTRACT: The standard enthalpies of dilution (ΔdilH°) and isentropic compressibilities (K°s,2) of some saccharides and their derivatives; (−)-D-ribose, (+)-D-glucose, 2-deoxy-D-glucose, (+)-methyl α-D-glucopyranoside, (+)-maltose monohydrate, and (+)-raffinose pentahydrate (solutes) were determined from heat change (q) and speed of sound (u) data measured, respectively, in (0.05, 0.15, 0.25, and 0.35) mol·kg−1 and (0.5, 1.0, 1.5 and 2.0) mol·kg−1 aqueous solutions of sodium phosphate (NaH2PO4), ammonium phosphate (NH4H2PO4) monobasic salts, and potassium phosphate (K3PO4) tribasic salt at T = 288.15− 318.15 K at P = 0.1 MPa. Other parameters such as transfer values (Δt(ΔdilH°), ΔtK°s,2), change in heat capacity (ΔdilC°p,2,m), and hydration numbers (nw) were also derived to rationalize the molecular interactions in mixtures of saccharide and derivative and phosphate-based salts.These studies are important to understand various interactions in terms of changing cation (Na+, NH4+, and K+) and anion (H2PO4− and PO43−) size, ionic strength, and influence of salts on water structure.

1. INTRODUCTION Saccharides being integral parts of biomacromolecules (glycoproteins, glycolipids, nucleic acids, polysaccharides, etc.) play key roles in control of various life processes like cell−cell communication, biosynthesis, protein folding, immunology, fertilization, etc. A number of important polymers that occur in the living cells are composed of glucose, hyaluronic acid, and other saccharides.1−4 Thermodynamic studies of these saccharides in electrolyte solutions have importance in several fields of catalysis, biology, medicine, and environment.5−8 The phosphate salts being components of adenosine diphosphate (ADP), adenosine triphosphate (ATP), nucleic acids, etc., play important roles in biological processes. Therefore, the study of interactions of saccharides and their derivatives with metal ions and H2PO4−/PO43− ions in water is of major importance. Very few studies9−11 on the solution behavior of saccharides in the presence of monobasic salts, that is, NaH2PO4, NH4and H2PO4, and tribasic salts, that is, K3PO4, are available in the literature. Therefore, to elucidate the interactions among saccharides and phosphate salts, various physicochemical techniques12−15 such as densimetry, viscometry, calorimetry, and sound velocity measurements are being employed. There is only single report on K°s,2 values of 2de-Glc at 298.15 K.16 The studied properties are useful in understanding the basic taste quality of aqueous saccharide and their derivative © XXXX American Chemical Society

solutions, which gets affected by the presence of salts. The hydration behavior of these solutes is a key feature to understand their structural and functional properties, as well as their mechanism of taste chemoreception. The literature survey reveals no calorimetric and compressibility studies of saccharides and their derivatives in the presence of aqueous mono- and tribasic phosphate-based salt solutions as a function of temperature. The present work deals with the study on the interactions of various saccharides and their derivatives with ions in water to rationalize the hydration characteristics of solute molecules. Therefore, we hereby report the standard enthalpies of dilution and isentropic compressibilities of some saccharides and their derivatives in aqueous solutions of NaH2PO4, NH4H2PO4, and K3PO4 salts at different temperatures and compare the results with those reported in the presence of KH2PO4.12,13

2. EXPERIMENTAL SECTION 2.1. Materials. The details of the chemicals used in the present study are given in Table 1 along with C, H, N, S analysis data that were used to analyze the purity and water content. There is no loss of the bound water; only nonhydrate Received: August 1, 2018 Accepted: January 23, 2019

A

DOI: 10.1021/acs.jced.8b00681 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of the Chemicals Used C,H,N,S analysis compound/(symbol)/molecular formula

source

CAS No.

mass fraction puritya

(−)-D-ribose (Rib) [C5H10O5]

Sigma Chemical Co.

50-69-1

0.99

2-deoxy-D-glucose (2de-Glc) [C6H12O5]

Sisco Research Lab.

154-17-6

0.99

(+)-methyl α-D-glucopyranoside (Me α-Glc) [C7H14O6]

Sigma Chemical Co.

97-30-3

≥0.99

(+)-D-glucose(Glc) [C6H12O6]

Sigma Chemical Co.

50-99-7

≥0.99

(+)-maltose monohydrate (Mal) [C12H22O11·H2O]

Sigma Chemical Co.

6363-53-7

0.99

(+)-raffinose pentahydrate (Raf) [C18H32O16·5H2O]

Fluka

17629-30-0

≥0.99

sodium phosphate monobasic (NaH2PO4) ammonium phosphate monobasic (NH4H2PO4) potassium phosphate tribasic (K3PO4)

Sigma Chemical Co. Sigma Chemical Co. Sigma Chemical Co.

7558-80-7 7722-76-1 7778-53-2

≥0.99 ≥0.98 ≥0.98

calcd %

obsvd %

C = 40.00 H = 6.71 C = 43.90 H = 7.37 C = 43.30 H = 7.27 C = 40.00 H = 6.71 C = 40.00 H = 6.71 C = 36.36 H = 7.12

C = 39.98 H = 6.69 C = 43.88 H = 7.39 C = 43.27 H = 7.25 C = 40.03 H = 6.69 C = 40.02 H = 6.69 C = 36.34 H = 7.15

a

Declared by supplier.

3. RESULTS AND DISCUSSION

water or free water is removed while drying in vacuum desiccators. The carbon and hydrogen percentages obtained in the analysis suggest that the samples were completely dried. 2.1.1. Preparation of Sample. The solutions were prepared afresh on mass basis in water that was degassed before use to avoid microbubbles in solutions. Mettler balance with a precision of ±0.01 mg was used in the present study. 2.2. Isothermal Titration Calorimetry. The heat of dilution was measured using MicroCal ITC200 calorimeter over the temperature range from 288.15 to 318.15 K. The working conditions and experimental details of isothermal titration calorimeter are the same as those mentioned in an earlier publication.12 The calorimeter was calibrated through a complexation reaction with 5 mM CaCl2 solution in the syringe and 0.4 mM ethylenediaminetetraacetic acid (EDTA) solution in the sample cell with 2-(N-morpholino)ethanesulfonic acid (MES) buffer of pH = 5.6. The resultant value of enthalpy of binding was comparable with the data provided with the isothermal titration calorimetry (ITC) kit ensuring the accurate functioning of the instrument (Figure S1a). Also the enthalpy values for the reactions between AgNO3 and NaI17 [ΔH (AgNO3 and NaI) = 109.18 kJ·mol−1 Figure S1b] and 18-crown-6 and BaCl218 [ΔH (18-C-6 and BaCl2) = 32.08 kJ· mol−1 Figure S2a] agreed well with the reported data. The standard molar enthalpies of dilution ΔdilH° values were determined for aqueous solutions of glycine at 298.15 K (Figure S2b), which agreed well with the literature values.19 2.3. Speed of Sound Measurement. The speed of sound was measured with the maximum uncertainty of ±0.50 m·s−1 using multifrequency ultrasonic interferometer, which was calibrated by measuring the speed of sound of pure water at various temperatures. The measured values of speed of sound u in water at (288.15, 298.15, 308.15 and 318.15) K are in good agreement with the literature values20−27(comparison given in Table S1). The average of at least 10 readings was taken as a final value of speed of sound. The temperature of the solution was controlled by a unit of Julabo F-25, a constant temperature bath whose thermal stability was within ±0.01 K.

3.1. Enthalpy of Dilution. The heat change (q) for saccharides and their derivatives was measured in mB (molality of salts in water) = (0.05, 0.15, 0.25 and 0.35) mol·kg−1 aqueous solutions of NaH2PO4, NH4H2PO4, and K3PO4 using isothermal titration microcalorimeter at T = (288.15, 298.15, 308.15 and 318.15) K (Table S2). The process of titration is exothermic for the injection of the titrant. The amount of heat evolved for same solute in different salts varies, obviously due to specific interactions of cations (Na+, NH4+, and K+) and anions (H2PO4− and PO43−) with solutes. It is evident from Figure 1 and Table S2 that enthalpy change is more exothermic for all the studied solutes in K3PO4, since the ionic strength of tribasic phosphate salt is more than those of monobasic phosphate salts. In most cases, a linear dependence of data was found; hence, the standard enthalpies of dilution ΔdilH° of the solutes were

Figure 1. Plot of heat change (q) vs molality (mA) of (+)-maltose monohydrate in mB = 0.35 mol·kg−1 aqueous solutions of phosphate based salts; i.e., (◆) NaH2PO4; (■) NH4H2PO4; (▲) KH2PO4; and (×) K3PO4 at T = 298.15 K (reference data for (+)-maltose monohydrate in mB = 0.35 mol·kg−1 aqueous solutions of ▲, KH2PO4 are included). B



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Table 2. Standard Enthalpies of Dilution (ΔdilH°) of Various Saccharides and Their Derivativesa ΔdilH° (J·mol−1) mBb

−1

(mol·kg )

T (K) = 288.15

298.15

308.15

318.15

288.15

298.15

308.15

318.15

NaH2PO4 0.00 0.05 0.15 0.25 0.35 0.00 0.05 0.15 0.25 0.35 0.00 0.05 0.15 0.25 0.35

0.05 0.15 0.25 0.35 0.05 0.15 0.25 0.35 0.05 0.15 0.25 0.35

(−)-D-ribose −151 −136 −230 −191 −436 −351 −639 −468 −882 −588 (+)-methyl α-D-glucopyranoside −501 −474 −521 −438 −571 −429 −552 −428 −660 −415 (+)-maltose monohydrate −66 −75 −92 −62 −234 −190 −520 −378 −1015 −666 (−)-D-ribose −178 −158 −293 −207 −398 −275 −487 −337 (+)-methyl α-D-glucopyranoside −569 −521 −584 −525 −577 −536 −597 −544 (+)-maltose monohydrate −90 −81 −136 −102 −297 −212 −437 −291

−66 −109 −253 −380 −428

−38 −68 −126 −228 −318

−285 −312 −409 −400 −518

−446 −400 −366 −361 −348

−430 −366 −320 −297 −221

−152 −208 −329 −481 −757

−95 −55 −170 −330 −565

−187 −119 −230 −372 −547 NH4H2PO4

−63 −217 −681 −997 −1532

−79 −122 −184 −260

−40 −79 −134 −183

−407 −432 −467 −502

−471 −480 −489 −504

−445 −453 −464 −477

−225 −322 −469 −469

−56 −74 −108 −170

−124 −139 −173 −209

−147 −447 −747 −958

−1683 −1978 −2213 −2265

−1903 −2766 −2481 −2293

−1988 −3053 −3453 −3484

−1562 −2956 −3772 −4676

−1153 −2119 −3182 −3730

−1016 −2563 −4897 −6096

−1895 −2111 −6314 −5587

−1273 −1778 −5273 −5045

−2654 −7372 −11 528 −13 687

2-deoxy-D-glucose −278 −229 −293 −242 −332 −268 −304 −221 −320 −163 (+)-D-glucose −175 −180 −191 −183 −294 −247 −384 −330 −489 −379 (+)-raffinose pentahydrate −175 −194 −278 −276 −662 −506 −869 −650 −1016 −724 2-deoxy-D-glucose −324 −268 −350 −294 −363 −270 −369 −235 (+)-D-glucose −224 −210 −269 −249 −323 −235 −355 −255 (+)-raffinose pentahydrate −141 −136 −385 −342 −528 −450 −652 −552

−217 −227 −237 −134 −113 −185 −165 −192 −246 −299 −201 −248 −425 −514 −576

−232 −243 −201 −156 −196 −193 −195 −160 −124 −256 −334 −420

K3PO4 0.05 0.15 0.25 0.35 0.05 0.15 0.25 0.35 0.05 0.15 0.25 0.35

(−)-D-ribose −680 −1084 −1689 −1662 −2446 −2288 −2806 −2367 (+)-methyl α-D-glucopyranoside −2044 −1699 −4306 −3528 −5596 −4601 −6284 −5688 (+)-maltose monohydrate −1030 −1186 −3494 −2599 −7247 −6918 −8145 −6362

2-deoxy-D-glucose −1956 −2759 −2723 −3101 −2957 −3151 −2940 −3079 (+)-D-glucose −1492 −1655 −2416 −2297 −3846 −3233 −4837 −3771 (+)-raffinose pentahydrate −2721 −2558 −5593 −4780 −9628 −6720 −11 175 −8980

−2918 −2961 −3044 −3077 −1408 −1983 −2786 −2889 −2060 −4002 −5578 −6108

a

In water and in aqueous phosphate-based inorganic salt solutions at T = (288.15 to 318.15) K and P = 0.1 MPa. bmB is molality of phosphatebased inorganic salts in water. Standard uncertainties (u) are u(mB) = 0.01 mol·kg−1, ur(ΔdilH) = 0.10, u(T) = 0.01 K, u(P) = 0.5 kPa (level of confidence is 0.68).

determined by least-squares fit of the following equation to the

where mA is the molality of the solute in solution, and Ss is the empirical slope. In some cases, the ΔdilH° values were calculated by using a second-order polynomial equation. The ΔdilH° values are negative accompanied by exothermic process,

measured heat q as q = Δdil H o + mA Ss

(1) C



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Figure 2. continued

D



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Figure 2. Standard enthalpies of dilution of transfer (Δt(ΔdilH°)) vs molalities (mB) of phosphate-based salts for (a) (+)-D-glucose, (b) (+)-methyl α-D-glucopyranoside, (c) 2-deoxy D-glucose, (d) (+)-maltose monohydrate in NaH2PO4, (e) (+)-D-glucose, (f) 2-deoxy-D-glucose, (g) (+)-methyl α-D-glucopyranoside, (h) (+)-raffinose pentahydrate in NH4H2PO4, (i)(+)-methyl α-D-glucopyranoside, (j) 2-deoxy-D-glucose, and (k) (+)-maltose monohydrate in K3PO4 at (◆) 288.15 K; (■) 298.15 K; (▲) 308.15 K; (×) 318.15 K.

exothermicity is more in NaH2PO4(aq) than in NH4H2PO4(aq), except for Glc and its derivatives at low concentrations and temperatures. Also, the exothermicity is more in K3PO4(aq) than in monobasic salts solutions. This indicates that anion charge, ionic strength of the salts, and the alteration in water structure are key factors governing the interactions between solute and salt. This also shows that water−K3PO4 interactions are stronger than those for water−NaH2PO4/NH4H2PO4, which cannot be easily disrupted by the solutes. Hence the studied saccharides behave as stronger structure makers in aqueous K3PO4 solutions than in monobasic salt solutions. The standard enthalpies of dilution of transfer Δt(ΔdilH°) of solutes from water to aqueous salts solutions were determined as

and generally their magnitudes increase with increase in concentration of salt but decrease with rise of temperature except for (+)-maltose monohydrate (Mal) in NaH2PO4(aq) and NH4H2PO4(aq) solutions and (−)-D-ribose (Rib) and 2deoxy-D-glucose (2de-Glc) in K3PO4(aq) solutions (Table 2). The exothermic or endothermic processes taking place in solutions depend on interactions between solute and salt and their influences on water structure.28,29 The exothermic contribution is provided by structure-making solute and endothermic contribution is provided by structure-breaking solute to the overall heat of interaction.19,30,31 This may be attributed to the changes in the structure of solvent when a solute is introduced into it. The negative ΔdilH° values suggest that hydrophilic−ionic interactions between the hydrophilic (−OH, −CO, −O−) sites of the saccharide and derivative and ions of the salt predominate in the present systems. The magnitude of ΔdilH° values vary as (+)-raffinose pentahydrate (Raf) > Mal > Rib > (+)-D-glucose (Glc) in NaH2PO4(aq), as Raf > Glc > Rib > Mal in NH4H2PO4(aq), and as Raf > Mal > Glc > Rib in K3PO4(aq) solutions. This indicates that the exothermicity in enthalpy change increases systematically with the complexity of solutes in tribasic salt solutions. The highly exothermic ΔdilH° values in cases of studied di- and trisaccharides suggest the enhanced structure-making capabilities of these solutes. In all the studied salts, Glc and its derivatives obey the following order: (+)-methyl α-Dglucopyranoside (Me α-Glc) > 2de-Glc > Glc. The comparison shows less exothermicity in NaH2PO4(aq) and NH4H2PO4(aq) than in KH2PO4(aq) solutions,12 which reflects the distinct nature of cations (K+, Na+, and NH4+). Further the

Δt (Δdil H °) = Δdil H °(in aqueous phosphate salt solutions) − Δdil H °(in water)

(2)

Generally, the Δt(ΔdilH°) values are negative for solutes studied in all the phosphate-based salts. The magnitude of Δt(ΔdilH°) values increase with increase in concentration of salt and decrease with rise of temperature (Figure 2), except for 2de-Glc in the presence of K3PO4(aq) solution. This suggests that the interactions between the hydrophilic sites of the saccharide and their derivative and ions of the phosphate salts become stronger with increase in the concentration of salt but decrease with temperature. In case of NaH2PO4(aq), for Me α-Glc, the Δt(ΔdilH°) values are negative at only T = 288.15 K and shift to endothermic change as the temperature is raised from 288.15 to 318.15 K (Figure 2b). The endothermic E



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Table 3. Values of ΔdilC°p,2,m for Saccharides and Their Derivativesa ΔdilC°p,2,m (J·K−1·mol−1) b

−1

mB (mol·kg )

T (K) = 288.15

298.15

308.15

318.15

288.15

298.15

308.15

318.15

NaH2PO4

0.05 0.15 0.25 0.35

(−)-D-ribose 5.63 5.75 9.25 11.33 13.67 12.72 23.10 13.93 (+)-methyl α-D-glucopyranoside 8.95 6.21 3.47 15.37 10.55 5.74 12.84 9.82 6.81 22.66 16.79 10.91 (+)-maltose monohydrate 5.03 1.09 −2.85 7.61 2.99 −1.63 16.01 8.91 1.80 39.85 23.32 6.79

0.05 0.15 0.25 0.35

3.41 10.46 14.28 15.41

0.05 0.15 0.25 0.35

5.85 6.77 5.09 5.94

0.05 0.15 0.25 0.35

5.01 7.54 16.01 21.99

0.05 0.15 0.25 0.35 0.05 0.15 0.25 0.35

5.52 7.17 14.62 32.27

5.86 13.41 11.77 4.76

3.30 9.31 9.44 24.79

0.74 0.92 3.79 5.04

1.31 3.11 8.52 29.02

−6.78 −6.25 −5.30 −9.74 NH4H2PO4

13.26 4.54 15.98 59.23

6.47 4.03 3.38 4.34

9.35 8.56 11.47 15.74

2.62 2.00 2.60 2.07

1.97 3.83 17.06 11.79

−6.54 −7.14 −6.45 −5.89

0.22 4.30 20.94 30.09

−203.62 507.77 −17.47 119.32

514.74 387.62 518.24 247.29

−44.11 −11.47 441.61 −282.68

−639.34 −128.58 567.45 391.04

−758.77 578.14 −592.72 1261.73

−249.44 937.83 781.72 −171.31

(−)-D-ribose 4.43 5.45 8.32 6.18 10.65 7.02 11.72 8.03 (+)-methyl α-D-glucopyranoside 4.77 3.70 5.18 3.59 4.26 3.43 4.65 3.36 (+)-maltose monohydrate 1.16 −2.69 2.65 −2.25 8.53 1.04 12.70 3.40

2-deoxy-D-glucose 3.13 2.96 6.98 4.65 9.02 8.60 17.41 10.04 (+)-D-glucose 1.35 1.39 4.10 5.09 7.90 7.28 19.57 10.11 (+)-raffinose pentahydrate −6.47 −26.20 7.67 10.80 16.45 16.92 40.81 22.38 2-deoxy-D-glucose 7.00 4.65 7.02 5.47 9.75 8.04 13.05 10.36 (+)-D-glucose 1.65 1.33 4.00 4.17 11.74 6.42 10.77 9.76 (+)-raffinose pentahydrate 0.55 0.88 5.54 6.78 15.78 10.62 21.45 12.82

2.79 2.32 8.18 2.66 1.42 6.08 6.67 0.65 −45.92 13.93 17.39 3.96

2.30 3.93 6.32 7.68 1.01 4.34 1.10 8.74 1.21 8.01 5.46 4.18

K3PO4 0.05 0.15 0.25 0.35

−184.42 459.89 −15.82 108.06

0.05 0.15 0.25 0.35

−39.95 −10.39 399.97 −256.03

0.05 0.15 0.25 0.35

−687.23 523.62 −536.83 1142.76

(−)-D-ribose −190.82 −197.22 475.85 491.81 −16.37 −16.92 111.81 115.56 (+)-methyl α-D-glucopyranoside −41.34 −42.73 −10.75 −11.11 413.85 427.73 −264.91 −273.80 (+)-maltose monohydrate −711.08 −734.93 541.80 559.97 −555.46 −574.09 1182.42 1222.08

2-deoxy-D-glucose 532.61 550.47 401.08 414.53 536.22 554.21 255.87 264.45 (+)-D-glucose −661.53 −683.72 −133.04 −137.51 587.14 606.84 404.61 418.18 (+)-raffinose pentahydrate −258.10 −266.76 970.38 1002.93 808.85 835.98 −177.25 −183.20

568.33 427.98 572.19 273.03 −705.90 −141.97 626.53 431.75 −275.41 1035.48 863.11 −189.14

In phosphate-based inorganic salts at T = (288.15 to 318.15) K and P = 0.1 MPa. bmB (mol·kg−1) is molality of phosphate-based inorganic salts in water. Standard deviations in the heat capacity change lie in the range of 5.49−6.21 J·K−1·mol−1. Standard uncertainties (u) are u(T) = 0.01 K, u(P) = 0.5 kPa (level of confidence = 0.68). a

2c). The −CHOH group in Glc is being replaced by −CH2 and −CH 2 OCH 3 groups in 2de-Glc and Me α-Glc, respectively; hence, they introduce a hydrophobic hydration in the system and cause the shift of Δt(ΔdilH°) values from exo- to endothermic change.31,32 In the cases of Glc (Figure 2a) and Mal (Figure 2d), the Δt(ΔdilH°) values are positive at

change to the observed heat suggests that hydrophobic−ionic interactions between the hydrophobic alkyl groups (R = CH, CH2, CH3) of the saccharide and their derivative and ions of the salt becomes predominant in the case of Me α-Glc at higher temperatures. Similar type of interactions are responsible for endothermic change in the case of 2de-Glc at mB ≈ (0.25 and 0.35) mol·kg−1 and (308.15 and 318.15) K (Figure F



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lower concentration (mB ≈ 0.05 mol·kg−1) of NaH2PO4 salt and at higher temperatures. In NH4H2PO4(aq) solutions, the Δt(ΔdilH°) values are negative, except for Glc and 2de-Glc at higher concentrations {mB ≈ (0.25 and 0.35) mol·kg−1} at 318.15 K (Figure 2e,f), while in the cases of Mal and Raf (representative Figure 2h), the Δt(ΔdilH°) values are positive at low concentration (mB ≈ 0.05 mol·kg−1) and at higher temperatures. The Δt(ΔdilH°) values of Glc are higher than its derivatives, and Raf being a trisaccharide has higher Δt(ΔdilH°) values than mono- and disaccharides in both the studied monobasic salts (Figure 2a− h). In K3PO4(aq) solutions, the magnitude of Δt(ΔdilH°) values decrease with increase in temperature for most of the solutes, except for Rib and 2de-Glc, where the influence of temperature is reverse. In the latter cases (representative Figure 2j), the negative values show minima at mB ≈ (0.05 or 0.15) mol·kg−1 and leveling off effect at higher concentrations of salt. The magnitude of Δt(ΔdilH°) values is higher for Me α-Glc (Figure 2i) than for Glc and 2de-Glc. The magnitudes of Δt(ΔdilH°) values increase systematically with the complexity of saccharides, that is, from mono- to di- to trisaccharides in K3PO4. The comparison shows that the magnitude of Δt(ΔdilH°) values of solutes is higher in NaH 2 PO 4(aq) than in NH4H2PO4(aq) solutions, except for Glc and its derivatives at low concentrations and temperatures. Generally, the Δt(ΔdilH°) values of solutes follow the order K3PO4 > KH2PO4 > NaH2PO4 > NH4H2PO4, which suggests strong interactions between solute and PO43− anion compared to H2PO4− anion. Since the H2PO4− anion is the same in monobasic salts, this clearly indicates the influence of cation (K+/Na+/NH4+) on the properties of solute solutions. The size of ions is an important factor influencing the properties of solutes in different salt solutions. The Na+ ion, having a small size (crystal radius = 0.95 Å) and high surface charge density, undergoes strong hydration through electrostatic ordering of nearby waters.This is consistent with a structure-making effect on water structure, while the NH4+ ion being large in size (crystal radius = 1.48 Å) exhibits a structure-breaking effect on water. The K+ ion having an intermediate size (crystal radius = 1.33 Å) acts as “slightly structure breaking”. The effective radii of hydrated ions {Na+(aq) = 2.80 Å, K+(aq) = 1.87 Å, NH4+(aq) = 2.77 Å} in solution suggests more hydration of sodium ions than potassium and ammonium ions. This may be the reason for the difference in the influence of different phosphate salts on the Δt(ΔdilH°) results. Our earlier studies13,14 of the present systems show that positive standard partial molar volumes of transfer ΔtV2° increase with increase in complexity of solutes. These results indicate that phosphate salts enhance the overall structural order due to the hydrophilic−ionic type of interactions between polar sites of the saccharide molecules and ions of the salts. The volumetric and viscometric properties13−15 also suggest that the saccharides and their derivatives behave as structure makers in mixed aqueous solvent. These studies also support the view of higher structure-making nature of K3PO4 due to more hydration of triply charged PO43− anions than singly charged H2PO4− anions. These observations are in line with the present results. The change in heat capacity (ΔdilC°p,2,m) accompanying the dilution of solutes in aqueous salt solutions was determined from temperature dependence of enthalpy of dilution (ΔdilH°) by fitting the following equations to ΔdilH° data:

Δdil H o = A + BT

(3)

Δdil H o = A + B1T + B2 T 2

(4)

The values of A, B, B1, and B2 coefficients are given in Table S3. Overall the B coefficients are positive for the systems that show linear variation of ΔdilH° with temperature, while B1 coefficients are positive and B2 coefficients are negative for those systems that show nonlinear variation. The ΔdilC°p,2,m values correspond to values of B coefficients in case of linear fit (given by eq 3), whereas for nonlinear fit,19,31 the ΔdilC°p,2,m values are calculated from eq 4, at different temperatures given in Table 3. Overall the ΔdilC°p,2,m values are positive, except for a few solutes in K3PO4. The positive ΔdilC°p,2,m values indicate that saccharides and their derivatives act as structure makers in the studied phosphate based salts, but negative ΔdilC°p,2,m values indicate that these solutes act as structure breakers in tribasic phosphate salt. The ΔdilC°p,2,m values increase with increase in molalities of salts and rise of temperature in most cases. This indicates an increase in the dominance of hydrophilic−ionic interactions between the solute molecules and the ions of the salts leading to an increase in the structural order of solution due to alternation in water structure. Generally, the magnitude of ΔdilC°p,2,m values is higher in NaH2PO4(aq) than in NH4H2PO4(aq), which suggests the strong structure-enhancing capabilities of saccharides and derivatives in NaH2PO4(aq) solutions. 3.2. Apparent Molar Isentropic Compressibility (Ks,2,ϕ). The Ks,2,ϕ values for saccharides and their derivatives were determined in mB = (0.5, 1.0, 1.5, and 2.0) mol·kg−1 aqueous solutions of NaH2PO4, NH4H2PO4, and K3PO4 from the isentropic compressibility (κs = 1/u2ρ) and density data14 at T = (288.15, 298.15, 308.15, and 318.15) K using the following relation: K s,2, ϕ = (κsM /ρ) − {(κsoρ − κsρo )/(mA ρρo )}

(5)

where M is the molar mass of the solute; mA is the molality of solute. The quantities ρ, ρ° and κs, κs° are the densities and isentropic compressibilities of solution and solvent, respectively. The speed of sound u (Table S4) values for studied solutes increase with increase in molalities of solute and cosolute as well with increase in temperature. The molality corrections were applied to the hydrated solutes, that is, (+)-maltose monohydrate and (+)-raffinose pentahydrate, in all the studied cosolutes, and the corresponding data for the anhydrous solutes are given in Table S5. The present values of speed of sound u for salts in water and saccharides in water were compared graphically with the literature values33−45 and are given as a part of Supporting Information (Figures S3 and S4). The present data of speeds of sound u of salts in water {(NaH2PO4 + H2O), (NH4H2PO4 + H2O), and (K3PO4 + H2O)} systems are consistent with the literature data33−35 available at temperatures T = (288.15, 298.15, and 308.15) K. The u values for NaH2PO4 in water at T = 298.15 K are comparable with those reported by Ameta et al.,33 but the present values are slightly higher than the values reported by Sadeghi et al.34 at higher concentrations. The present values of u for (+)-D-ribose in water are in good agreement with the literature values36−39{Figure S4a,b,d} except at 308.15 K {Figure S4c}. The u values for (+)-D-glucose reported by various workers36,37,39−45{Figure S4e−h} are in good agreement with the present u values at all the studied temperatures. Chauhan et al.38 reported the u values for (+)-maltose G



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Figure 3. Partial molar isentropic compressibilities of transfer (ΔtK°S,2) vs molalities (mB) of phosphate-based salts for (a) (−)-D-ribose, (b) (+)-raffinose (anhydrous) in NaH2PO4, (c) 2-deoxy-D-glucose, (d) (+)-maltose (anhydrous) in NH4H2PO4, (e) (+)-methyl α-D-glucopyranoside in K3PO4 at (◆) 288.15 K; (■) 298.15 K; (▲) 308.15 K; (×) 318.15 K.

monohydrate at (298.15 and 308.15) K, which agreed well with the present u values {Figure S4i,j}. However, the present u values for (+)-raffinose pentahydrate are higher than those reported by Chauhan et al.38 at (298.15 and 308.15) K {Figure S4k,l}. These discrepancies in the u values may be assigned to the purity of materials, solution preparation, and experimental methods employed. The acoustic impedance (Z) was determined from the density and sound velocity (u) data using the relation

Z = ρ·u

The acoustic impedance increases with an increase in molality as well as temperature as seen in the values of speed of sound (Table S4). The increasing value in these parameters suggests the strengthening of solute−solvent interactions among the components. Overall the apparent molar isentropic compressibility Ks,2,ϕ values are negative, and their magnitudes decrease with increase in temperature and molality of solute as well as salt (Table S4). At infinite dilution, Ks,2,ϕ becomes equal to K°s,2 (standard partial molar isentropic compressibility). The standard partial molar isentropic compressibility K°s,2 values

(6) H



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Table 4. Hydration Numbers (nW) of Saccharides and Their Derivativesa nW mB (mol·kg−1)

T (K) = 288.15

298.15

308.15

318.15

288.15

0.7 0.4 0.2

2.7 2.1 1.9 1.8 1.4

298.15

308.15

318.15

NaH2PO4 (−)-D-ribose 0.0 0.5 1.0 1.5 2.0

2.5 2.1 1.8 1.6 1.3

0.0 0.5 1.0 1.5 2.0

1.3 0.5 0.01

0.0 0.5 1.0 1.5 2.0

1.5 1.1 0.8 0.6 0.3 2-deoxy-D-glucose 0.6 0.01

(+)-maltose monohydrate 3.4 3.1 1.9 1.8 1.5 1.4 1.1 0.9 0.7 0.5

1.1 0.7 0.5 0.2 0.1 0.2

2.9 2.0 1.7 1.6 1.4

2.4 1.2 0.9 0.4

2.0 1.0 0.7 0.2

4.8 2.2 1.5 0.9 0.1

0.2

2.0 1.7 1.4 1.1

(+)-methyl α-D-glucopyranoside 1.8 1.3 1.2 0.7 1.0 0.5 0.8 0.3 0.4 (+)-D-glucose 2.2 2.0 1.3 1.1 1.2 1.0 0.9 0.8 0.7 0.5 (+)-raffinose pentahydrate 4.4 3.9 2.0 1.7 1.4 1.2 0.7 0.4 0.03

1.1 0.5 0.3 0.02

1.4 0.7 0.5 0.3 0.1 3.5 1.4 1.0 0.2

NH4H2PO4 (−)-D-ribose 0.5 1.0 1.5 2.0

1.9 1.6 1.3 1.1

0.5 1.0 1.5 2.0

0.3

0.9 0.5 0.2

0.5 0.2

2-deoxy-D-glucose

0.5 1.0 1.5 2.0

1.8 1.4 1.3 0.94

(+)-maltose monohydrate 1.7 1.5 1.1 1.0 0.5 0.4 0.1

1.0 0.5

0.8 0.3

2.1 1.1 0.6

0.3 0.02

2.5 2.7 2.7 2.2

(+)-methyl α-D-glucopyranoside 1.1 0.7 0.7 0.3 0.4 0.1 (+)-D-glucose 1.1 1.0 0.8 0.7 0.5 0.5 0.17 0.13 (+)-raffinose pentahydrate 2.0 1.8 1.1 0.9 0.5 0.2

0.6 0.3 0.01

0.5 0.3 0.01

1.6 0.7

K3PO4 (−)-D-ribose 0.5 1.0 1.5 2.0

2.5 2.6 2.5 2.1

0.5 1.0 1.5 2.0

0.4

0.5 1.0 1.5 2.0

1.2 1.0 0.7 0.2 2-deoxy-D-glucose

(+)-maltose monohydrate 1.9 1.6 1.5 1.3 1.1 0.9 0.4 0.1

0.7 0.5 0.02

2.5 2.3 2.3 2.1 0.9 0.4 0.1

1.8 1.0 0.6

(+)-methyl α-D-glucopyranoside 1.3 0.8 1.1 0.6 0.9 0.3 0.2 (+)-D-glucose 1.7 1.5 1.3 1.2 1.1 1.1 0.7 0.6 (+)-raffinose pentahydrate 1.7 1.4 0.7 0.5 0.1

0.6 0.4 0.01

1.0 0.5 0.2

1.4 0.5

a

In aqueous phosphate-based inorganic salts solutions at T = (288.15 to 318.15) K and P = 0.1 MPa. Standard uncertainties (u) are u(T) = 0.01 K, u(P) = 0.5 kPa (level of confidence is 0.68).

were determined by least-squares fitting of the following

where SK is the experimental slope. The K°s,2 values for the studied solutes in aqueous solutions of salts are given in Table S3. The K°s,2 values for the studied solutes in the presence of water were compared with the literature data,16,36,46−51 and the values show good agreement except for few cases16,50 (Table

equation to the corresponding Ks,2,ϕ data: o K s,2, ϕ = K s,2 + SK m

(7) I



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Table 5. Range of Apparent Specific Isentropic Compressibility Values (Kϕ,m) for Saccharide and Their Derivativesa solute

cosolute Kϕ,m·10−8 (m3·kg−1·Pa−1) −6

(−)-D-ribose

(+)-methyl α-D-glucopyranoside

2-deoxy-D-glucose

cosolute Kϕ,m·10−8 (m3·kg−1·Pa−1)

solute

−5

KH2PO4 (3.437·10 to −1.157·10 ) NaH2PO4 (−0.142 to −1.745)·10−6 NH4H2PO4 (−4.649 to 3.450)·10−6 K3PO4 (−1.037·10−5 to 3.237·10−6) KH2PO4 (−7.522 to −9.269)·10−6 NaH2PO4 (−8.126 to 1.365)·10−6 NH4H2PO4 (−4.130 to 1.447)·10−6 K3PO4 (−1.037·10−5 to 3.237·10−6) KH2PO4 (−1.901·10−7 to −1.140·10−6) NaH2PO4 (−2.015 to 7.420)·10−6 NH4H2PO4 (−1.096 to 9.424)·10−6 K3PO4 (−1.292·10−6 to 9.219·10−7)

(+)-D-glucose

(+)-maltose monohydrate

(+)-raffinose pentahydrate

KH2PO4 (3.437·10−6 to −1.157·10−5) NaH2PO4 (−8.302 to −0.066)·10−6 NH4H2PO4 (−1.965 to 1.599)·10−6} K3PO4 (−1.037·10−5 to 3.237·10−6) KH2PO4 (−1.901·10−7 to −1.140·10−6) NaH2PO4 (−3.858 to 0.927)·10−6 NH4H2PO4 (−3.588 to 1.723)·10−6 K3PO4 (−1.037·10−5 to 3.237·10−6) KH2PO4 (−1.901·10−7 to −1.140·10−6) NaH2PO4 (−2.732 to 0.375)·10−6 NH4H2PO4 (−2.723 to 0.971)·10−6 K3PO4 (−1.292·10−6 to 9.219·10−7)

a

In aqueous solutions of phosphate-based inorganic salts at T = (288.15 to 318.15) K.

into the bulk water, hence exhibiting the positive ΔtK°s,2 values. The ΔtK°s,2 values increase sharply below mB ≈ 0.5 mol·kg−1 of salts, and the values increase almost linearly afterward (Figure 3). In cases of Raf in NaH2PO4(aq) and Me α-Glc in K3PO4(aq), the ΔtK°s,2 values show some level off effect from mB ≈ (0.5 to 1.0) mol·kg−1, and then values again increase sharply with the increase in mB values (Figure 3b,e). The ΔtK°s,2 values increase systematically with complexity of solutes as Rib < Glc < Me α-Glc < 2de-Glc < Mal < Raf. In most of the solutes (except for Raf), the ΔtK°s,2 values in various salts follow the order NH4H2PO4 > K3PO4 > NaH2PO4 > KH2PO4 > CH3COONa (organic salt), indicating that phosphate anions undergo higher hydration as compared to acetate anions.36 The ΔtK°s,2 results are in line of volumetric,13,14 viscometric,15 and calorimetric12 studies that saccharides and their derivatives act as structure makers in mixed aqueous solutions. Hydration numbers (nw) of solutes were determined using the method reported by Millero et al.52

S6). In cases of (+)-maltose monohydrate and (+)-raffinose pentahydrate, the K°s,2 values were also calculated using the corrected molalities. This approach provides reliable K°s,2 values for these solutes in the anhydrous state from the studies of hydrated solutes ensuring better comparison of results. No literature data are available for the comparison of K°s,2 values of the studied solutes in the presence of phosphatebased salts. The K°s,2 values provide information about the solute− solvent interactions and by using the model of Millero et al.52 as follows: o o o K s,2 = K s,2 (int) + K s,2 (elect)

(8)

52

Millero et al. further made an approximation to the intrinsic partial molar isentropic compressibility as K°s,2(int) ≈ 0, since one would expect K°s,2 (int) to be very small. Therefore, the K°s,2 may be thought to represent the electrostriction partial molar isentropic compressibility, K°s,2 (elect). It is known53,54 that the values of K°s,2 in aqueous solutions are (i) positive for mainly hydrophobic solutes, (ii) large and negative for ionic compounds, and (iii) small and intermediate for hydrophilic solutes. In the present study, the K°s,2 values are negative and increase with increase in salt concentration and temperature except for 2de-Glc, where the K°s,2 values are positive in the studied three salts. The negative K°s,2 values of solutes (except for few cases) are attributed to the strong attractive interactions between solute and cosolute. Further, the values of K°s,2 are less for Me α-Glc than Glc indicating the hydrophobic hydration due to methoxy (−OCH3) group in methyl derivative leading to lesser K°s,2 values. The K°s,2 values show an increasing order of hydration from mono- to di- to trisaccharides. Partial molar isentropic compressibilities of transfer (ΔtK°s,2) were determined using the following equation.

o nw = −K s,2 (elect)/(κsoV1o)

(10)

where κs° and V°1 are the compressibility and molar volume of bulk water or solvent, respectively. K°s,2(elect) is considered approximately equal to K°s,2(saccharide), as K°s,2(int) ≈ 0. The hydration numbers are mostly positive (except for a few cases) and decrease with rise of temperature (Table 4). This suggests that extent of the cosphere water around the ions decreases with increased temperature. The exclusion of water molecules out of the hydration sphere is a consequence of increased solute−solute interactions at higher temperature.55 3.2.1. Apparent Specific Isentropic Compressibility (Kϕ,m). The Kϕ,m values were determined using the relation Kϕ,m = Ks,2,ϕ/M, where M is the molar mass of the solute. The Kϕ,m values suggest the influence of salts on the taste quality of saccharides and are divided into four basic tastes,56 namely, salt; Kϕ,m = (−2.332·10−5 to −8.064·10−5)·10−8 m3·kg−1·Pa−1, sweet; Kϕ,m = (−3.383·10−7 to −2.335·10−5)·10−8 m3·kg−1· Pa−1, sour; Kϕ,m= (6.131·10−6 to −2.991·10−5)·10−8 m3·kg−1· Pa−1, and bitter; Kϕ,m= (−1.993·10−8 to −2.487·10−6)·10−8 m3· kg−1·Pa−1. The Kϕ,m values of studied saccharides and their derivatives in water at (288.15, 298.15, 308.15, and 318.15) K lie in the sweet taste range (−9.269·10−7 to−6.149·10−6)·10−8 m3·kg−1·Pa−1 (Table 5). The Kϕ,m values for 2de-Glc and Raf lie in sour taste range at all temperatures in these phosphate salts, whereas for the rest of the solutes (Rib, Glc, Me α-Glc, and Mal), the values lie in sour taste range at only higher

o o o Δt K s,2 = K s,2 (in aqueous salt solutions) − K s,2 (in water)

(9)

The ΔtK°s,2 values are positive for solutes in the studied phosphate salts. Their magnitudes increase with increasing molality of salt but decrease with the rise of temperature in all the cases (Figure 3). It indicates the strengthening of hydrophilic−ionic interactions over the hydrophobic−ionic interactions for the entire range of concentration studied. Because of the interactions among the hydrophilic sites of solute molecules and ions of salt, the less compressible water present in the hydration shells of solute molecules comes out J



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temperatures (308.15 and 318.15) K. This indicates that phosphate anions and cations change the sweet taste of saccharides and their derivatives to sour/bitter when transferred from water to aqueous solutions of phosphate salts. Earlier from the volumetric studies13,14 it was reported that sweet taste of saccharides and sweet−bitter taste of their derivatives was concluded not only in water but also in the presence of KH2PO4(aq). Kϕ,m correlates results better than vϕ; hence, rationalization based on compressibility studies is more preferred.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00681. Comparison of speed of sound values for pure water, heat effect, coefficients (A, B, B1, and B2), speeds of sound (u), apparent molar isentropic compressibilities (Ks,2,ϕ), acoustic impedance (Z), partial molar isentropic compressibilities (K°s,2), ITC profile showing titrations and comparison plots (PDF)

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REFERENCES

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4. CONCLUSIONS The heat change (q) of various saccharides and their derivatives was measured in aqueous NaH2PO4, NH4H2PO4, and K3PO4 solutions by calorimetric studies at T = (288.15, 298.15, 308.15, and 318.15) K. The negative values of ΔdilH° suggest the predominance of hydrophilic−ionic interactions over the hydrophobic−ionic interactions. The larger magnitudes of ΔdilH° for the studied solutes in K3PO4(aq) solutions than in monobasic salt solutions have been attributed to more ionic strength and charge of PO43− than H2PO4− anions. The Δt(ΔdilH°) values of solutes in various monobasic salts follows the order KH2PO4 > NaH2PO4 > NH4H2PO4. This shows the influence of the cations (K+, Na+, NH4+) in the same order, since the anion (H2PO4−) is same. The ΔtK°s,2 values are positive for the solutes and increase with molalities of salts, hence suggesting the predominance of hydrophilic−ionic interactions over hydrophobic−ionic interactions. The Kϕ,m values indicate that the phosphate salts influence the sweet taste of saccharides and their derivatives. The ΔdilC°p,2,m values indicate that dilution of saccharides and their derivatives in the aqueous salt solutions is the structure-making phenomenon as also observed from isentropic compressibility and previously reported volumetric and viscometric studies.

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Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Neha Aggarwal: 0000-0002-6025-8471 Tarlok S. Banipal: 0000-0002-6239-2543 Parampaul K. Banipal: 0000-0001-5467-843X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Guru Nanak Dev University, Amritsar, is acknowledged for the research facility, and CSIR is acknowledged for the fellowship. K



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Influence of Phosphate-Based Salts on Enthalpy of Dilution and

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