Leucine Solubility

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Measurement and Modeling Solubility of Aqueous Multisolute Amino-Acid

Solutions

Jan-Bernd Grosse Daldrup, Christoph Held, Feelly Ruether, Gerhard Schembecker, andGabriele Sadowski*,

Laboratory of Plant and Process Design and Laboratory of Thermodynamics, Department of Biochemical and

Chemical Engineering, Technische UniVersitat Dortmund, Emil-Figge-Strasse 70, 44227 Dortmund, Germany

The solubilities of the ternary mixtures L-alanine/L-leucine,L-alanine/L-valine, andL-leucine/L-valine in waterwere measured at 303 and 323 K. The solubilities of seven binary, eight ternary, and one quaternary amino-acid systems were modeled using the PC-SAFT equation of state. For this purpose, new parameters for L-asparticacid,L-glutamic acid,L-leucine, andL-tyrosine are presented. The model excellently reproduces binary solubilitydata with a linear temperature-dependent binary interaction parameter for the solute-solvent interaction. PC-SAFT allows for a very good prediction of the solubility behavior of ternary mixtures over a wide range oftemperature and concentration. The aqueous mixture with three amino acids is then predicted without anyfurther adjustment with an average relative deviation of 3.34%.

Introduction

The increasing amounts of chemicals produced from biologi-cal feed and by fermentation pose an interesting challenge forthe design of downstream processes due to the high complexityof the mixtures created in the production process. An examplefor the importance of such chemicalssproduced in biotechno-logical processessis the produced amount of amino acids whichincreased from a total amount of approximately 1650 ktons/year in 19961 to 2450 ktons/year in 20062 and 2980 ktons/yearin 2008.3 As most of these amino acids are produced by proteinhydrolysis or fermentation, the solubility, its pH dependence,and the influence of the cosolute concentration (e.g., other aminoacids) are of interest for the design of downstream processes.

Basic solubility data of binary aqueous amino-acid solutionsis readily available in the literature (e.g., several books4,5).

Although the solubility data available for multisolute solutionsare rather sparse, Kuramochi et al.6 gave an overview ofsolutions of two amino acids in water. Most of the citedreferences dealt with racemic mixtures of amino acids and theirsolubility behavior with another amino acid (see Table 1). Inthis work the binary solubilities of L-alanine, L-leucine, andL-valine in water as well as the ternary and quaternary solubilitybehavior of three pairs of amino acids in water were measured.The solubilities were modeled with the PC-SAFT modelproposed by Gross and Sadowski7,8 which was also used byFuchs et al.9 for amino-acid solubilities. To describe thesolubilities measured in this work and given in the literature,the parameters ofL-alanine, L-valine, glycine, L-aspartic acid,

L-glutamic acid,L-leucine, andL-tyrosine were fitted to our ownand literature data. The melting enthalpies and temperatures ofL-alanine andL-valine were determined according to the groupcontribution method by Marrero and Gani10 (see ParameterEstimation).

Measurement of Solubilities

The amino acids used were provided by Evonik AG andMerck KGaA with a purity of>99.0%; they were used without

further purification. Due to divergent data for L-leucine (seeFigure 1) and to ensure the substance purity for L-leucine,L-alanine, and L-valine, the solubilities of the single-solutesystems were measured. For this purpose the amino acids wereplaced in glass vials (20 mL) and purified water was added.These vials were placed in a rotary oven with a temperaturedeviation of(0.3C and allowed to equilibrate for 48 h. Fromthese vials a sample of 2 mL of solution was withdrawn witha preheated syringe with a syringe filter (pore size 0.45 m).The sample was weighed with an accuracy of 0.01 mg, and thesolvent was evaporated in a drying chamber and afterwardweighed again. In order to ensure a total evaporation of thesolvent, the sample was placed back in the drying chamber and

* To whom correspondence should be addressed. Tel.: +49 231 7552635. Fax: +49 231 755 2572. E-mail: [email protected].

Laboratory of Plant and Process Design. Laboratory of Thermodynamics.

Table 1. Literature Dealing with Multisolute Amino Acid Solutions

amino acids reference

glycine, L-leucine, L-tyrosine, L-cystine Carta et al.11

L-isoleucine, L-leucine, L-valine Kurosawa et al.12-14

L-isoleucine, L-leucine, L-valine Givand et al.15

glycine + DL-aspartic acid; glycine +DL-phenylalanine

Soto et al.16

Figure 1.Solubility of leucine in water between 260 and 380 K. Symbols:experimental data (Carta and Tola,28 Kurosawa,12 Dalton and Schmidt,26

Budavari17). Line: PC-SAFT calculation (temperature-dependentkijbetweenwater and L-leucine, see Table 4).

Ind. Eng. Chem. Res. 2010, 49,13951401 1395

10.1021/ie900913c 2010 American Chemical SocietyPublished on Web 12/16/2009


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was reweighed after 24 h. This gravimetric method was usedto determine the amount of amino acid in saturated solutionsin binary mixtures and the total amount of amino acids in ternarymixtures. As a typical example, Figure 1 shows the solubilityofL-leucine versus system temperature. It can be seen that ourdata agree excellently with those of other authors. The data ofBudavari17 do not match the other results, which might indicatethe use ofD- or DL- instead ofL-leucine. In the case of ternarymixtures the ratio of the amino acids was determined by HPLC.For the determination of the ratio of amino acids in multiplemixtures, the dried solutes were dissolved in 15 mL of water.From this solution 100L was taken and diluted with 1 mL ofeluent. HPLC was performed on a Merck automated HPLC

analyzer with an isocratic eluent profile. The solid phase usedwas an amino phase from Macherey & Nagel (EC250/3Nucleosil 100-5-NH2 RP). The eluent was an acetonitrile-watermixture with an potassium phosphate buffer (65.8 wt %acetonitrile (HPLC grade), 34.2 wt % purified water, 0.769 gof potassium hydrogen phosphate, and 1.830 g of potassiumdihydrogen phosphate/kg of solvent, pH 7.2). The pH value wasadjusted by adding concentrated phosphoric acid. For thedetermination of the concentration, 10 L of sample wasinjected. The volume flow of the eluent was varied between0.5 and 1 mL/min. To ensure a pure solid phase, X-raydiffraction measurements were performed with amino acids of99.0% purity and the solid phase after the solubility measurement.

Modeling of Solubilities

Based on the phase equilibrium conditions for solid and liquidphasessassuming pure solid phases and neglecting the influenceof the heat capacitiessthe solubility of component iat atmo-spheric pressure can be calculated according to Prausnitz18 andGmehling et al.:19

xiL)

1

iL

exp[-h0iSL

RT(1 - TT0iSL)] (1)The quantities h0iSL and T0iSL represent the enthalpy and thetemperature of melting of the pure substance i, respectively.However, they are not available for amino acids as they

decompose before melting. Thus, the values were estimated withthe group contribution method proposed by Marrero and Gani10

(see Tables 2 and 4) and adjusted to the solubility curve withinthe given deviation (dev(T0iSL) ) 7.6% and dev(h0iSL) ) 15.7%).The influence of cosolutes on the solubility of component iisexpressed only by the activity coefficients (iL), which changewith different composition and temperature. There are differentpossibilities to calculate activity coefficients of ternary mixtures;e.g., the UNIFAC method was used in the work of Kuramochiet al.6 and Kurosawa et al.,13 and the NRTL,16 the hard spheremodel,16 and the SAFT equation of state were applied by Jiand Feng.20

The model used in the current work is the PC-SAFT equationof state. With this model the residual Helmholtz energy can becalculated as the sum of different contributions such as hard-

chain repulsion, dispersive (van der Waals) interactions, andassociative (hydrogen bonding) interactions.

Aresidual

) Ahard chain

+ Adispersion

+ Aassociation (2)

The equations for hard-chain and dispersion contributions canbe found in refs 7 and 8. The association term was used assuggested in ref 21. To describe an associating compound, fivepure-component parameters are required: the segment number(m), the segment diameter (), the dispersion-energy parameter(/k), the association-energy parameter (hbAiBi), and the associa-tion-volume parameter (hbAiBi).

To describe binary systems, the conventional Berthelot-Lorentzcombining rules are applied, and only one binary parameter isintroduced, correcting the dispersion-energy parameter for themixture of component i and jin eq 4:

ij )12

(i + j) (3)

ij )(1 - kij)ij (4)

kij ) kij,25 C + kij,T(T-298.15 K) (5)

To improve the accuracy of the model, the binary parameterwhich describes the interactions of solvent and solute wasdetermined with a linear temperature dependency if necessary;see eq 5. This procedure is commonly used (see e.g. ref 22)when very accurate fits for low solubility values are desired.We applied linear temperature-dependent binary parameters for

four amino acid-water pairs in this work (see Table 4). Todescribe the unlike solute-solute interactions in ternary mix-

Table 2. Assigned Groupsa and Amount of Groups Used for the Determination of the Melting Temperature and Enthalpy with the GroupContribution Method by Marrero and Gani10

group no.a L-Ala L-Asp L-Glu Gly L-Leu L-Tyr L-Val

First Order

CH3 1 1 2 2CH2 2 1 2 1CH 3 1 1C 4aCH 15 4aC-CH

2 21 1

OH 29aC-OH 30 1COOH 31 1 2 2 1 1 1 1CH2NH2 54 1CHNH2 55 1 1 1 1 1 1

Second Order

(CH3)2CH 1 1 1CHm(NHn)COOH (m, n in 0, ..., 0.2) 26 1 1 1 1 1 1 1AROMRINGs1s4 106 1

Third Order

HOOC(CHn)mCOOH-(m > 2, n in 0, ..., 0.2) 1 1 1

a Numbered according to ref 10.

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tures, the binary parameter is assumed to be constant (i.e.,temperature independent) and was fitted to the experimental dataof the solute with the lower solubility.

For cross-association systems in this study, the strength ofcross-associating interactions between two associating sub-stances can be described by applying simple mixing andcombining rules, as suggested by Wolbach and Sandler.23

hbAiBj

)12

(hbAiBi

+ hbAjBj) (6)

hbAiBj

)hbAiBihbAjBj[ iijj(1/2)(ii + jj)]3

(7)

Thus, no adjustable correction parameters have to be intro-duced in the association term. The PC-SAFT parameters usedfor the modeling are given in Tables 3 and 4, where Ndenotesthe number of the association sites acting as proton donatorsand as proton acceptors. Most amino acids are modeled with

two association sites, with the amino group acting as a protonacceptor and the acid group acting as a donor. As amino acidsare zwitterionic molecules, the overall charge is mostly neutraland the ionic character is not regarded in modeling. We used atemperature-dependent segment diameter for water as describedby Cameretti and Sadowski.24 The calculation for the segmentdiameter is given in eq 8, where represents the segmentdiameter and T is the temperature (in kelvin):

(T) )2.7927 +10.11 exp(-0.01775T) -1.417 exp(-0.01146T) (8)

Parameter Estimation

The PC-SAFT parameters of glycine,DL-alanine, andL-valinehave already been determined in previous works by Fuchs etal.9 and Cameretti and Sadowski.24 In this work, the parametersfor glycine,L-alanine,L-valine,L-aspartic acid,L-glutamic acid(-form), L-leucine, and L-tyrosine were fitted to different

experimental data, such as solubilities, binary mixture densities,and amino acid activity coefficients (see Table 4). With theobtained parameters, not only solubilities but also solutiondensities and (water and amino acid) activity coefficients canbe described (see Table 4).L-Aspartic acid andL-glutamic acidwere assumed to exist in a neutrally charged form in aqueoussolution. On the one hand, this differs from the real solutionsas both amino acids are not only present as neutral zwitterionsbut also present as anions and cations (e.g., L-glutamic acid, pI) 3.2175). On the other hand, we describe this by applyingmore than one association site acting as acidic groups. Further-more, some of the former parameters were readjusted as thevalues of the melting properties were unphysically high (e.g.,TL-valine

SL) 1800 K24). Now the values of the melting temperatures

are more reasonable (for L-alanine, TSL ) 692.4 K, and forL-valine,TSL )680.0 K).

The parameters used for the modeling are listed in Tables 3and 4, as are the average absolute deviation (AAD, see eq 9)and the average relative deviation (ARD, see eq 10) of thecalculated binary data to the experimental data.

AAD ) 1NPk)1

NP

|(ykcalc

- ykexp

)| (9)

ARD ) 1NP

k)1

NP

|(1 - ykcalc

ykexp)| (10)

Considered Ternary and Quaternary Mixtures

We considered ternary and quaternary mixtures of aminoacids in water with one pure amino acid in the solid phase.Thus, mixtures forming a solid solution, such as L-leucine-L-isoleucine-water,12 are not included. Furthermore, the solu-bility of amino acids in water is pH-dependent (e.g., refs 9, 28,and 34). This dependency is expressed by an increased solubilityat pH values near the pKavalues of the amino acid. We first donot take into account the pH influence; hence, the consideredamino acids shall possess similar isoelectric points and pKa

Table 3. PC-SAFT Parameters for Water24

m /k N hbAiBj/k khbAiBj

1.2047 see eq 8 353.95 2 2425.67 0.0451

Table 4. Pure-Component and Binary PC-SAFT Parameters for Amino Acids, Calculated10 and Adjusted Melting Properties, and Deviationsbetween Correlated and Experimental Data

parameter L-Ala L-Asp L-Glu Gly L-Leu L-Tyr L-Val

m 5.4647 2.9998 3.0248 4.8495 8.3037 8.1390 6.5370 2.5222 3.3668 3.4781 2.3270 2.7000 2.2798 2.7211/k[K] 287.59 207.74 164.54 216.96 330.00 289.37 397.07

N 2 3 3 2 2 3 2hb

AiBi/k[K] 3176.60 3265.67 2536.56 2598.06 3600.00 2500.00 3332.49

hb

AiBi

0.0819 0.0436 0.0160 0.0393 0.0200 0.0400 0.0386TSL [K] 692.4 619.0 586.8 714.3 620.9 542.5 680.0hSL/R[K] 2543.7 2802.7 3022.6 2109.3 4499.8 5000.3 3197.2Tcalc

SL [K] 580.58 595.43 596.0 462.50 582.55 601.67 581.83hcalc

SL/R[K] 2749.4 3241.3 3558.8 3415.7 3330.3 4764.0 3012.8kij,25C(H2O) -6.12 10-2 -1.92 10-4 -1.29 10-1 -6.12 10-2 -6.30 10-2 -2.77 10-4 -6.15 10-2

kij,T(H2O) 2.91 10-4 4.09 10-4 2.90 10-4 3.85 10-4

solution density ref 25 ref 26 this work ref 25 ref 27 ref 28 ref 27Trange [K] 298 298 298.43 298 298 298-318 298ARD [%] 0.20 0.03 0.01 0.09 0.03 0.01 0.02AAD [kg/m3] 0.23 0.25 0.1 0.96 0.25 0.02 0.17

solubility this work ref 5 ref 29 ref 5 this work ref 5 this workTrange [K] 288-346 273-373 278-342 298-373 288-346 273-373 303-346ARD [%] 1.05 5.68 2.23 2.88 1.98 5.68 2.30AAD [mol/kg] 0.02 0.01


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values. The mixtures of amino acids fulfilling these criteria arelisted in Table 5.

Results and Discussion

The experimental solubilities of the considered systems arelisted in Tables 6-9 and in Table 11. In Table 6, our

experimental binary solubilities (one amino acid in water) arepresented. The single-solute solubility ofL-alanine agrees well

with data from the literature (refs 5, 35, and 36), as does thesolubility ofL-valine (refs 5 and 13), whereas the solubility ofL-leucine is difficult to compare to data found in the literatureas these are highly divergent (see Figure 1; refs 11, 12, 17, and

26). Our measured L-leucine solubility does match the data ofKurosawa12 so that thekijbetweenL-leucine and water has beenadjusted to our own experimental data. Figure 2 illustrates thesolubility ofL-tyrosine in water, a very low-soluble amino acid.It can be seen that all the available literature data agree wellwith each other except for the data presented by Carta andTola,28 where small deviations can be observed. Thus, weadjusted the kijbetween water and L-tyrosine to the data fromthe other authors, yielding an excellent modeling result.

The investigated ternary systems consist of two amino acidswhich are L-alanine,L-valine, or L-leucine in water. We focuson these three amino acids as we also present a quaternarysystem consisting of all these molecules later on. In Tables 7-9

all our measured data for these ternary systems are shown. Fromthe solubility behavior of the measured solutions it becomesobvious that these mixtures form eutectic systems. This is alsoaffirmed by the X-ray diffraction measurements, which showno change in the peak positions of the pure substances and thesubstance after solubility measurement. Moreover, also Kuro-sawa12 detected an eutectic for the ternary mixture L-leucine-L-valine-water.

Table 5. Model Mixtures Consisting of at Least Two Amino Acidsin Water

aqueous solutions containing reference

L-Glu andL-Asp Jin and Chao35

L-Leu and Gly Carta11

L-Leu andL-Tyr Carta11

L-Tyr and Gly Carta11

L-Leu andL-Ala this workL-Leu andL-Val Kurosawa et al.;13 this workL-Ala and L-Val this workL-Ala,L-Leu, andL-Val this work

Table 6. Solubility Data: Binary Solutions of L-Alanine, L-Leucine,and L-Valine in Water

T[K] L-Ala [mol/kgwater] L-Leu [mol/kgwater] L-Val [mol/kgwater]

288 1.7204 ( 0.0109 0.1585 ( 0.0005 -293 1.7774 ( 0.0362 0.1603 ( 0.0005 -298 1.8117 ( 0.0186 0.1644 ( 0.0011 -303 1.9747 ( 0.0103 0.1721 ( 0.0004 0.5179 ( 0.0037308 2.0696 ( 0.0055 0.1773 ( 0.0005 0.5287 ( 0.0034314 2.1989 ( 0.0104 0.1865 ( 0.0003 0.5578 ( 0.0053318 2.3107 ( 0.0056 0.1947 ( 0.0010 0.5741 ( 0.0002324 2.4573 ( 0.0046 0.2057 ( 0.0003 0.6028 ( 0.0009334 2.7455 ( 0.0065 0.2306 ( 0.0014 0.6594 ( 0.0030346 3.0450 ( 0.0117 0.2612 ( 0.0026 0.7300 ( 0.0039

Table 7. Solubility Data: Ternary Solutions of L-Alanine andL-Leucine in Water

T[K] L-Ala [mol/kgwater] L-Leu (solid) [mol/kgwater]

303 0.5621 ( 0.0041 0.1532 ( 0.0035303 0.9478 ( 0.0213 0.1427 ( 0.0005303 1.3861 ( 0.0048 0.1324 ( 0.0021303 1.8320 ( 0.0276 0.1221 ( 0.0017323 1.0957 ( 0.0296 0.1835 ( 0.0040

T[K] L-Ala (solid) [mol/kgwater] L-Leu [mol/kgwater]

303 1.9503 ( 0.0031 0.0819 ( 0.0025303 1.9335 ( 0.0012 0.1214 ( 0.0022323 2.3148 ( 0.0047 0.0905 ( 0.0016323 2.2486 ( 0.0102 0.1789 ( 0.0039323 2.2817 ( 0.0024 0.1359 ( 0.0020

Table 8. Solubility Data: Ternary Solutions of L-Alanine andL-Valine in Water

T[K] L-Ala [mol/kgwater] L-Val (solid) [mol/kgwater]

303 0.1576 ( 0.0039 0.5233 ( 0.0018303 0.3334 ( 0.0028 0.5116 ( 0.0043303 0.8865 ( 0.0018 0.4904 ( 0.0005303 0.2360 ( 0.0128 0.5813 ( 0.0110323 0.4596 ( 0.0061 0.5608 ( 0.0056323 1.1363 ( 0.0111 0.5025 ( 0.0270323 1.7412 ( 0.0066 0.4828 ( 0.0093

T[K] L-Ala (solid) [mol/kgwater] L-Val [mol/kgwater]

303 1.8939 ( 0.0107 0.0926 ( 0.0029303 1.9059 ( 0.0120 0.2323 ( 0.0048303 1.8924 ( 0.0037 0.3296 ( 0.0021303 1.9249 ( 0.0050 0.0458 ( 0.0029323 2.3968 0.1382323 2.3899 ( 0.0189 0.3611 ( 0.0120323 2.4002 ( 0.0044 0.0628 ( 0.0016

Table 9. Solubility Data: Ternary Solutions of L-Alanine andL-Leucine in Water

T[K] L-Val [mol/kgwater] L-Leu (solid) [mol/kgwater]

303 0.0388 ( 0.0020 0.1755 ( 0.0030303 0.0925 ( 0.0049 0.1720 ( 0.0040303 0.2512 ( 0.0045 0.1602 ( 0.0040303 0.3611 ( 0.0003 0.1518 ( 0.0016323 0.1635 ( 0.0124 0.1913 ( 0.0138323 0.0751 ( 0.0083 0.1851 ( 0.0086323 0.4121 ( 0.0035 0.1716 ( 0.0040

323 0.5346(

0.0016 0.1528(

0.0048T[K] L-Val (solid) [mol/kgwater] L-Leu [mol/kgwater]

303 0.5255 ( 0.0021 0.0127 ( 0.0020303 0.5208 ( 0.0016 0.0271 ( 0.0004303 0.5195 ( 0.0011 0.0744 ( 0.0002303 0.5200 ( 0.0046 0.1077 ( 0.0026323 0.6021 ( 0.0018 0.0206 ( 0.0009323 0.6025 ( 0.0024 0.0397 ( 0.0011323 0.6028 ( 0.0061 0.0963 ( 0.0054323 0.5997 ( 0.0061 0.1384 ( 0.0060

Figure 2.Solubility ofL-tyrosine in water between 290 and 360 K. Symbols:

experimental data (Carta and Tola,

28

Drautz,

37

Sober,

5

Hitchcock,

38

Daltonand Schmidt26). Line: PC-SAFT calculation (temperature-dependent kijbetween water and L-tyrosine, see Table 4).

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As an example, the solubility behavior of the mixtureL-alanine-L-leucine-water is illustrated in Figure 3. It can beobserved that for this system the measured solubility of theprecipitating amino acid decreases with increasing amount ofthe cosolute. As the amino acid parameters are already fixed(Table 4), the solubility behavior of the ternary system candirectly be predicted with PC-SAFT. Although the prediction(with no additional interaction parameters) already yields goodresults, we applied a constantkij(betweenL-alanine andL-valine,fitted to one solubility point at 313 K) to this system to improvethe modeling. Moreover, the temperature extrapolation to 333

K can be safely performed, as shown in Figure 3. Thedeteriorative effect of both solutes on the solubility of the otheramino acid can thus be described satisfactorily. The deviationbetween modeled and measured data is given in Table 10 (AADand ARD), where the binary kijparameter between two solutesused for the calculations is also given.

Figure 4 illustrates the solubility data for the system L-valine-L-leucine-water. Our experimental work compares well withthe data presented by Kurosawa.12 As forL-alanine-L-leucine-water, the measured data show a decrease in solubility withincreasing amount of cosolute. This behavior can be predictedwith PC-SAFT (kij ) 0); i.e., no additional adjustment isnecessary to describe the experimental data. The AADs and theARDs for this system are summarized in Table 10. Again, the

model is able to predict the solubility at different temperatureswithout applying any temperature-dependent ternary parameters.

The mixture L-valine-L-alanine-water (results are not shown here)has a similar solubility behavior as described above. PC-SAFT is

able to predict the solubilities without using additional kijparam-eters. The AAD and ARD are listed in Table 10.

Beside the solubilities measured in this work, experimentaldata from literature was also modeled with PC-SAFT. One dataset used was measured by Carta.11 Figures 1 and 2 (solubilitiesofL-leucine andL-tyrosine in water) already reveal that the datafrom Carta and Tola28 differ from other data.5,26,37 The same isvalid for glycine. ComparingL-leucine (our data at 298 K) withdata presented by Carta and Tola gives an ARD of 8.37%,comparing data for L-tyrosine (Drauz et al.37 at 298 K) withdata from Carta and Tola gives an ARD of 37.83%, andcomparing data for glycine (Sober5 at 298 K) with data fromCarta and Tola gives an ARD of 5.17%. These differences in

the single-solute data can also be observed in the ternarysystems. To test whether the model can predict solubilitybehavior qualitatively, we readjusted the two-solute solubilitydata from Carta and Tola to the single-solute solubilities; i.e.,the difference of the single-solute data supplied by Carta andTola to the binary data used for parameter fitting was calculatedfor each temperature. This calculated difference was subtractedfrom the ternary data, thus shifting the ternary data but leavingit with the same slope. The result can be seen in Figures 5 and6, where the original data and the adjusted data of the mixtureL-leucine-L-tyrosine-water and the PC-SAFT calculations areillustrated. It can be observed that the solubility behavior differsfrom the systems shown previously: Whereas the solubility of

L-leucine slightly decreases with increasing amount of cosolute,the solubility ofL-tyrosine increases with increasing amount ofcosolute. Despite this opposite solubility influence of bothcosolutes, this behavior can be predicted well with PC-SAFTwithout applying additional ternary parameters (Figure 6).Temperature extrapolation is also possible within the showntemperature range (298-318 K). This is also valid for the otherternary mixtures. The AAD and the ARD of all modeledmixtures are shown in Table 10, where the deviation betweenmodel and adjusted values is given and the deviation betweenmodel and original values is given in parentheses.

In Figure 7, the mixture L-glutamic acid-L-asparticacid-water measured by Jin and Chao35 is illustrated. In thissystem, both amino acids exist beside the neutral form as

anions and cations. In the modeling they are treated equallywith two acidic and one basic association sites. Obviously,

Figure 3. Ternary mixture L-alanine-L-leucine-water. Symbols: experi-mental data (this work). Line: PC-SAFT calculation (kijbetween L-alanineand L-leucine set to 0.02).

Table 10. Binary Interaction Parameterk ij, AAD, and ARD of theTreated Systems

mainsolute/cosolute data kij ARD [%] AAD [mol/kg]

Ala/Val this work 0 1.60 0.03Ala/Leu this work 0.02 2.44 0.06Asp/Glu Jin35 0 6.67


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Symbols

A )Helmholtz energy [J])segment diameter []/kB )energy parameter, dispersion [K]m )number of segmentsN)number of association siteshb

AiBj/k)energy parameter, association [K]hb

AiBi )association volumeT)temperature [K]hSL/R )melting enthalpy [K]kij,25 C(H2O) )binary interaction parameter at 25Ckij,T(H2O) ) temperature-dependent interaction parameter [1/K]NP )number of measured valuesR )ideal gas constant [J/mol K]x)mole fraction )activity coefficientdev( ) )deviation of a value [%]

Superscripts

L )liquid phaseSL )melting/phase changecalc )calculated

exp )experimental

Subscripts

0 )reference state0i )pure substance ii )substance isolute-solute )solute-solute interaction

Literature Cited

(1) Scheper, T. Microbial Production of L-Amino-Acids; Advances inBiochemical Engineering/Biotechnology 79; Springer: Berlin, 2002.

(2) Eggeling, L.; Pfefferle, W.; Sahm, H. Amino Acids. In Basicbiotechnology; Ratledge, C.; Kristiansen, B., Eds.; Cambridge University

Press: New York, 2006; p 666.(3) Sanchez, S.; Demain, A. L. Metabolic regulation and overproduction

of primary metabolites. Microb. Biotechnol. 2008, 1 (4), 283319.(4) Greenstein, J. P.; Milton, W.Chemistry of Amino Acids; Wiley: New

York, 1961.(5) Sober, H. A.Handbook of biochemistry: selected data for molecular

biology, 3rd ed.; CRC Press: Cleveland, OH, 1973.(6) Kuramochi, H.; Noritomi, H.; Hoshino, D.; Nagahama, K. Measure-

ments of solubilities of two amino acids in water and prediction by theUNIFAC model. Biotechnol. Prog. 1996, 12 (3), 371379.

(7) Gross, J.; Sadowski, G. Perturbed-chain SAFT: An equation of statebased on a perturbation theory for chain molecules. Ind. Eng. Chem. Res.2001, 40 (4), 12441260.

(8) Gross, J.; Sadowski, G. Application of the perturbed-chain SAFTequation of state to associating systems. Ind. Eng. Chem. Res. 2002, 41(22), 55105515.

(9) Fuchs, D.; Fischer, J.; Tumakaka, F.; Sadowski, G. Solubility ofamino acids: Influence of the pH value and the addition of alcoholiccosolvents on aqueous solubility. Ind. Eng. Chem. Res. 2006,45(19), 65786584.

(10) Marrero, J.; Gani, R. Group-contribution based estimation of purecomponent properties. Fluid Phase Equilib. 2001, 183, 183208.

(11) Carta, R. Solubilities of L-cystine, L-tyrosine, L-leucine, and glycinein their water solutions. J. Chem. Eng. Data 1999, 44 (3), 563567.

(12) Kurosawa, I. Solid-Liquid Equilibrium in multi solute systems.Ph.D. Dissertation, Georgia Institute of Technology, 2004.

(13) Kurosawa, I.; Teja, A. S.; Rousseau, R. W. Solid-liquid equilibriain L-leucine plus L-valine plus water. Fluid Phase Equilib. 2004, 224 (2),245249.

(14) Kurosawa, I.; Teja, A. S.; Rousseau, R. W. Solubility measurementsin the L-isoleucine plus L-valine plus water system at 298 K. Ind. Eng.Chem. Res. 2005, 44, 32843288.

(15) Givand, J.; Chang, B. K.; Teja, A. S.; Rousseau, R. W. Distributionof isomorphic amino acids between a crystal phase and an aqueous solution.

Ind. Eng. Chem. Res. 2002, 41 (7), 18731876.(16) Soto, A.; Arce, A.; Khoshkbarchi, M. K.; Vera, J. H. Measurements

and modelling of the solubility of a mixture of two amino acids in aqueoussolutions. Fluid Phase Equilib. 1999, 160, 893901.

(17) Budavari, S.The Merck Index, 12th ed.; Merck: Whitehouse Station,NJ, 1996.

(18) Prausnitz, J. M. Molecular thermodynamics of fluid-phase equi-libria; Prentice-Hall: Englewood Cliffs, NJ, 1969; pp xiii, 523.

(19) Gmehling, J. G.; Anderson, T. F.; Prausnitz, J. M. Solid-Liquid

Equilibria Using Unifac. Ind. Eng. Chem. Fundam. 1978, 17, 269273.(20) Ji, P. J.; Feng, W. Solubility of amino acids in water and aqueoussolutions by the statistical associating fluid theory. Ind. Eng. Chem. Res.2008, 47(16), 62756279.

(21) Kleiner, M.; Tumakaka, F.; Sadowski, G.; Latz, H.; Buback, M.Phase equilibria in polydisperse and associating copolymer solutions: Poly(ethene-co-(meth)acrylic acid)-monomer mixtures. Fluid Phase Equilib.2006, 241 (1-2), 113123.

(22) Ruether, F.; Sadowski, G. Modeling the solubility of pharmaceu-ticals in pure solvents and solvent mixtures for drug process design.

J. Pharm. Sci. 2009, 98, 42054215.(23) Wolbach, J. P.; Sandler, S. I. Using molecular orbital calculations

to describe the phase behavior of cross-associating mixtures. Ind. Eng. Chem.Res. 1998, 37(8), 29172928.

(24) Cameretti, L. F.; Sadowski, G. Modeling of aqueous amino acidand polypeptide solutions with PC-SAFT. Chem. Eng. Process. 2008, 47,10181025.

(25) Ninni, L.; Meirelles, A. J. A. Water activity, pH and density ofaqueous amino acids solutions. Biotechnol. Prog. 2001, 17, 703711.

(26) Dalton, J. B.; Schmidt, C. L. A. The solubilities of certain aminoacids in water, the densities of their solutions at twenty-five degrees, andthe calculated heats of solution and partial molal volume. J. Biol. Chem.1933, 103, 549577.

(27) Kikuchi, M.; Sakurai, M.; Nitta, K. Partial Molar Volumes andAdiabatic Compressibilities of Amino-Acids in Dilute Aqueous-Solutions at5, 15, 25, 35, and 45-Degrees-C. J. Chem. Eng. Data1995,40 (4), 935942.

(28) Carta, R.; Tola, G. Solubilities of L-cystine, L-tyrosine, L-leucine,and glycine in aqueous solutions at various pHs and NaCl concentrations.

J. Chem. Eng. Data 1996, 41 (3), 414417.(29) Manzurola, E.; Apelblat, A. Solubilities of L-glutamic acid,

3-nitrobenzoic acid, p-toluic acid, calcium-L-lactate, calcium gluconate,magnesium-DL-aspartate, and magnesium-L-lactate in water. J. Chem.Thermodyn. 2002, 34, 11271136.

(30) Robinson, R. A. The vapor pressure of aqueous solutions of alanine.J. Biol. Chem. 1952, 199, 7173.

(31) Tsurko, E. N.; Neueder, R.; Kunz, W. Water activity and osmoticcoefficients in solutions of glycine, glutamic acid, histidine and their saltsat 298.15 and 310.15 K. J. Solution Chem. 2007, 36(5), 651672.

(32) Barrett, G. C.; Lilley, T. H. Physical Properties of Amino AcidSolutions. In Chemistry and Biochemistry of the Amino Acids; Chapmanand Hall: London, 1985; pp 591-624.

(33) Kuramochi, H.; Noritomi, H.; Hoshino, D.; Nagahama, K. Measure-ments of vapour pressures of aqueous amino acid solutions and determi-nation of activity coefficients of amino acids. J. Chem. Eng. Data 1997,42, 470474.

(34) Brown, M. G.; Rousseau, R. W. Effect of Sodium-Hydroxide onthe Solubilities of L-Isoleucine, L-Leucine, and L-Valine.Biotechnol. Prog.1994, 10 (3), 253257.

(35) Jin, X. Z.; Chao, K. C. Solubility of 4 Amino-Acids in Water and

of 4 Pairs of Amino-Acids in Their Water Solutions. J. Chem. Eng. Data1992, 37(2), 199203.(36) Amend, J. P.; Helgeson, H. C. Solubilities of the common L-alpha-

amino acids as a function of temperature and solution pH. Pure Appl. Chem.1997, 69 (5), 935942.

(37) Drauz, K.; Grayson, I.; Kleemann, A.; Krimmer, H.-P.; Leuchten-berger, W.; Weckbecker, C. Amino Acids. In Ullmanns Encyclopediae of

Industrial Chemistry; Wiley VCH: New York, 2007.(38) Hitchcock, D. I. The solubility of tyrosine in acid and alkali.J. Gen.

Physiol. 1924, 6, 747575.

ReceiVed for reViewJune 3, 2009ReVised manuscript receiVedOctober 9, 2009

AcceptedNovember 19, 2009

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