{'fraction_non_alphanumeric': 0.052033898305084744, 'fraction_numerical': 0.02497175141242938, 'mean_word_length': 4.832289950576606, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Studies on Volumetric and Viscometric Properties of L- Glutamic Acid in Aqueous Solution of Glucose over a Range of Temperatures (298K to 323K)

In this work, volumetric and viscometric properties of L-glutamic acid in water and aqueous glucose solutions (5%, 10%, 15%, and 20% of glucose, w/w in water) have been measured as a function of molal concentration (0.02 mol.kg to 0.16 mol.kg) of L-glutamic acid at different temperatures T= (293.15, 303.15, 308.15, 313.15 and 323.15) K. By using experimental densities (ρ) and viscosities (η) data, apparent molar volume (φv), experimental slope (Sv), limiting apparent molar volume (φv ), limiting apparent molar volume transfer (Δφv )tra, limiting apparent molar expansibilities (Eφ ), Hepler’s constant (δEφ /δT)p, Falkenhagen coefficient A, and Jones-Dole coefficient B have been computed. Gibbs free energies of activation of viscous flow per mole of solvent (μ1 ) and per mole of solute (μ2 ), hydration number (Hn) is also calculated. The results are discussed based on solute-solute and solutesolvent interactions in these systems. From the results, it is observed that there exists a structure making propensity of L-glutamic acid in water and in the different mass fraction of aqueous glucose solutions, which increases with the increase of glucose concentrations.


Introduction
Macromolecules especially, carbohydrates, lipids, proteins, and nucleic acids, are wellknown biological compounds, which trigger several physiological functions in the human body [1]. Among these, proteins molecules are the most important building block of cytoplasm and cell membranes. The properties of a protein can be well understood by studying the acid-base property of amino acids in aqueous solution [2]. Due to the presence of several non-covalent interactions, including hydrogen-bonding, electrostatic attraction, and hydrophobic interaction, the native structure of a globular protein becomes stable. The stability of protein molecules depends on these non-covalent interactions, which could be affected by the surrounding solute and solvent molecules [3][4][5]. In addition, direct solute-solvent interaction and/or alteration of water molecules may affect the physicochemical properties of proteins [6][7].
Carbohydrates also act as a stabilizing agent for the native conformation of globular proteins and enzymes [8][9]. Among the different types of carbohydrates, glucose is the most abundant monosaccharide that contains both the hydroxyl group (-OH) and the aldehyde group (-CHO). However, glucose plays a pivotal role as an energy source, metabolic intermediary, and important step in cellular respiration [10][11][12][13]. Moreover, glucose acts as receptors for the bioactive structures of enzymes, antibodies, hormones, viruses, etc. [14][15].
The protein-carbohydrates interactions are very important in immunology, biosynthesis, pharmacology, medicine, and the cosmetic industry [16][17]. Therefore, extensive studies of amino acids in aqueous carbohydrate solutions are required for a better understanding of solute-solvent interactions [18][19]. Due to the large size of protein macromolecules, the direct study of the physicochemical properties of proteins is difficult. To overcome this problem, the repeating unit of protein molecules such as amino acids, peptides are considered as a model compound for physicochemical studies [20][21]. Based on the nature of the solutesolute and solute-solvent interaction of amino acid in aqueous solutions, the characteristics of a large size protein molecule are easily understood [22][23][24].
During several decades, researchers are trying to explore new concepts regarding carbohydrate-protein interaction between different solutes and solvents. In a study, Riyazuddeen et al. [25][26] have studied "the interactions in (aqueous sucrose/ aqueous glucose + L-threonine/ L-alanine/) systems at (298.15-323.15) K" and "the densities, viscosities, and speed of sound of L-Proline in aqueous sucrose and glucose solutions". In a similar study, Nain et al. [27][28][29][30][31] have investigated the "solute-solvent and solute-solute interactions of Lserine, L-phenylalanine, L-arginine, L-histidine, and L-threonine in aqueous sucrose, arabinose, and glucose solutions using viscometric and volumetric measurements". Other groups of researchers, Ali et al. [32], have examined "the viscosity, density and refractive index of DL-alanine, glycine, DL-valine, and L-serine in aqueous glucose solution". Being inspired by this research works, Palani and Geetha [33] have determined "the ultrasonic velocity, density, and viscosity of L-asparagine, L-glutamine and L-serine in aqueous glucose solutions".
To date, there is no volumetric and viscometric data available regarding L-glutamic acid in aqueous carbohydrates solution of different mass fractions at different temperatures. This consideration leads us to undertake this study of L-glutamic acid in aqueous glucose solutions. L-Glutamic acid is an important dicarboxylic amino acid that acts as a neurotransmitter [34]. This paper aims to examine the densities (ρ) and viscosities ( ) of Lglutamic acid in water and aqueous glucose (5%, 10%, 15%, and 20% of glucose, w/w in water) at T=(298. 15, 303.15, 308.15, 313.15, 318.15 and 323.15)K. Using the experimental data of (ρ) and ( ) data, the volumetric properties such as apparent molar volume (φv), limiting apparent molar volume (φv 0 ), limiting apparent molar volume transfer (Δφv 0 )tra, limiting apparent molar expansibilities (Eφ 0 ) and Hepler's constant (δEφ 0 /δT)p have been determined and viscometric properties like Falkenhagen coefficient of A and Jones-Dole coefficient B, Gibbs free energies of activation of viscous flow per mole of solvent ( 1 0# ) and per mole of solute ( 2 0# ), hydration number (Hn) is also determined. These parameters have been recognized as being sensitive to structural change due to the use to discuss the solute-solute and solute-solvent interactions in these systems.

Materials and Methods
Highly purified (mass fraction ≥ 99%) L-glutamic acid and glucose were purchased from E. Merck (India) (table 1). Using ethanol and water mixture, L-glutamic acid was recrystallized, and after drying at 383.15K, it was placed for at least 72 h in a vacuum desiccator over P2O5. Solvent, aqueous glucose (5, 10, 15 and 20% of glucose, w/w in water) solutions were prepared through doubly distilled water (conductivity less than 1× 10 -6 S/cm) and these solvents were used to make different molal concentrations (0.02mol/kg to 0.16mol/kg) of Lglutamic acid solutions [30]. Moreover, all the mass measurements were carried out by electronic balance with uncertainty ±0.0001g. For density measurement, a double-arm Ostwald-Sprengel type pycnometer of about 25 cm 3 capacity was used, which were calibrated with distilled water at different temperatures. After reaching thermal equilibrium (temperatures 298.15 to 323.15K) of the water bath, the densities of the prepared solutions were determined from the mass of the solution in the density bottle.
To measure viscosity, calibrated British standard U-type Ostwald viscometer was used. The test solution containing a viscometer was placed vertically in the water bath. An electronic watch with an accuracy of ±0.1s was used to record the efflux times of flow after the stability of the desired temperature of the water bath. The final efflux time was taken from the average of at least three readings reproducible within ±0.1s, and the viscosity (η) was calculated by using the following equation, Where A = πr 4 hg 8lv is the viscometer, ρ is density, and is the final efflux time. However, water viscosities were taken from the literature [35] for calibration purposes.

Volumetric properties.
The experimentally measured density (ρ), and viscosity (η) for a binary and ternary system of L-glutamic acid in water and aqueous-glucose solution as a function of the molal concentration of L-glutamic acid and temperature: (298.15K, 303.15K, 308.15K, 313.15K, 318.15K, and 323.15K) are listed in table 2.
By using experimental densities, the apparent molar volume (φv), the apparent molar volumes at infinite dilution (φv 0 ), and the limiting apparent molar volume transfer (Δφv 0 )tra of L-glutamic acid were calculated in solutions with different percentage of aqueous glucose. The apparent molar volume (φv), of L-glutamic acid, was calculated by using the relation, From this figure, it is seen that the curves of φv vs. m are linear for L-glutamic acid in water and in all the four aqueous-glucose solvents in the studies concentration range and at each investigated temperature. Moreover, the φv for L-glutamic acid increase with arising the concentration of L-glutamic acid and increasing temperature, but these values are reduced by increasing the percentage of glucose. A similar phenomenon is noticed in the case of L-proline in aqueous metformin hydrochloride solutions [36]. These types of results indicate the presence of strong interaction between L-glutamic acid and glucose molecules. The limiting apparent molar volumes or apparent molar volumes at infinite dilution (φv 0 ) were calculated using the Masson equation [37].     The Limiting apparent molar volume transfer (Δφv 0 )tra for L-glutamic acid from water to the aqueous glucose mixture can be calculated from the following equation, [42]: (Δφv 0 )tra = φv 0 (L-glutamic acid in aq. glucose solution) -φv 0 (L-glutamic acid in water) (4) The (Δφv 0 )tra is free from solute-solute interactions but only depends on the solute-solvent interactions [43]. In this study, the interaction occurring between L-glutamic acid and aqueous glucose solution could be categorized as follows [30,44,45]: I. -OH groups of glucose interact with zwitterions (NH3 + , COO -) of amino acids through ionic-hydrophilic interaction. II. Hydrophilic-hydrophilic interactions present in OH groups of glucose and side-chain OH groups of L-glutamic acid through H-bonding. III. Non-polar groups of glucose (alkyl chain) and zwitterionic groups (NH3 + , COO -) of Lglutamic acid interrelate with hydrophobic-ionic interaction. IV. Hydrophobic-hydrophobic interactions link-up between non-polar (-CH3) in the side chain of L-glutamic acid and alkyl chain of glucose. V. Hydrophobic-hydrophilic interactions linkage between non-polar groups of L-glutamic acid and the -OH groups of glucose. Type (I) and (II) interaction are responsible for a positive contribution to the (Δφv 0 )tra, since the overlap of the hydration co-sphere of charged ions (NH3 + , COO -), hydrophilic groups (-NH2, -OH) and -OH groups could lead to the reduction of electrostriction of water molecules lying in the proximity of these amino acids and type (III), (IV), and (V) contribute negatively to the (Δφv 0 )tra due to disruption of side group hydration by that of the charged end [45]. The variation of φv 0 with the temperature at infinite dilution can be represented by the following polynomial equation [46]: 0 = a + b (T-Tm) + c (T-Tm) 2 (5) Where T = temperature (Kelvin), Tm = the average temperature (Kelvin), and a, b, and c = the empirical constants. The limiting apparent molar expansibilities or first derivatives of the temperature dependence of limiting apparent molar volumes are obtained as follows: The calculated values of Eφ 0 are listed in table 3. The values of Eφ 0 of any solute expose the solute-solvent interaction [47]. From this table, the values of Eφ 0 are positive for L-glutamic acid in water and all four systems of aqueous solutions of glucose, suggesting the presence of solute-solvent interactions in these systems, as already indicated by apparent molar volume data. Yan et al. [48] have found a similar trend of Eφ 0 in some amino acids and a pharmaceutically active ionic liquid domiphen DL-mandelic acid in aqueous medium at temperatures from 293.15 K to 313.15 K.
Hepler [49] developed the general thermo-dynamic expression to determine the capacity of solute as a structure maker or structure breaker in a mixed solvent system using the general thermodynamic expression: Solute acts as structure-maker when the values of (δEφ 0 /δT)p are positive, whereas a solute acts as structure-breaker when the values of (δEφ 0 /δT)p are negative [50]. In this work, the values of (δEφ 0 /δT)p are positive, which are indexed in table 3, and that indicates the structure-maker property of L-glutamic acid in water and aqueous glucose solutions.

Viscosity coefficient-B and A.
Viscosities of L-glutamic acid in aqueous and in aqueous glucose solutions are measured at 293.15, 298.15, 303.15, 308.15, and 313.15 K respectively and indexed in table 2. It is observed that the viscosities increase with increasing the concentration of L-glutamic acid and decrease with increasing the temperature. When a solute is subjected to dissolved in a solvent, some of the solvents molecules interact with the solutes, as the result of solute-solvent interaction that slows down the mobility of the liquid for this the value of viscosities are increased with increasing the concentration of L-glutamic acid [51]. As the temperature increasing, the kinetic energy of the molecule is increased, which increases the mobility of the liquid; therefore, the values of viscosities are decreased with increasing temperature. Increasing the viscosities by adding the solute indicates the structure making ability of the solute [52]. The detailed information about solute-solute and solute-solvent interaction of the system is provided by the resulting Falkenhagen and Jones-Dole viscosity B-coefficients [53][54]. There is a linear relationship between the viscosity and the molality of the L-glutamic acid in aqueous glucose system. So, the coefficient A (Falkenhagen coefficient) and Jones-Dole viscosity Bcoefficient are calculated from the Jones-Dole equation that is given below: Where, r = the relative viscosity of the solution and m molality of L-glutamic acid, A and B = the Falkenhagen and Jones-Dole coefficients, respectively. From the intercept and slope of the plots of (r -1)/m 1/2 versus m 1/2 , the values of A and B coefficient is measured and displayed in table 4. The positive value of B-coefficient is associated with strong solute-solvent interaction and also with structure making ability of solute, while a negative value of Bcoefficient is associated with structure-breaking properties between solute and solvent [55][56].
The coefficient-A represents the solute-solute interaction associated with the size and shape of the solute. The negative values of the A coefficient indicate the presence of very weak solutesolute interactions; the positive values of the A coefficient indicate the presence of significant solute-solute interactions [57]. The hydration number, (Hn) values of L-glutamic acid in aqueous-glucose solutions are also determined by using the equation [30,[59][60][61], The values of Hn are indexed in table 4. The table discloses that the values of Hn raise with raising glucose concentration for most of the studied systems, which indicates the enhancement of hydration of L-glutamic acid in the studied solution. Actually, the water molecules are substituted by glucose and act as a structure-maker by H-bonding. Hn values also increase with increasing temperature indicates the presence of solute-solvent interaction in these studied systems. Jones-Dole coefficient-B and 0 values also support the trend of hydration number, Hn values.

Thermodynamics of viscous flow.
Gibbs free energy of activation for a per mole of solute (∆μ 2 0≠ ) and solvent (∆μ 1 0≠ ) was calculated based on the transition state theory of the relative viscosity proposed by Feakins et al. [62][63][64][65][66][67]. According to this theory, the B-coefficient could be express by the relation, Where, 1 0 ̅̅̅̅ = the apparent molar volume of the solvent (aqueous-sucrose) and 2 0 ̅̅̅̅ = the limiting apparent molar volume of the solute, respectively. h and N are Planck's constant and Avogadro number, respectively. The (∆ 1 0≠ ) and (∆ 2 0≠ ) values are listed in table 5. It is observed that the value of (∆ 1 0≠ ) and (∆ 2 0≠ ) for L-glutamic acid are positive and the ( ∆ 2 0≠ ) values are much higher than (∆ 1 0≠ ) in aqueous glucose solutions. This indicates the presence of strong interaction between L-glutamic acid and solvent (5, 10, 15, 20% w/w, aqueous glucose), and the interaction is greater in the ground state than in the transition state. So, it is evident that the solvation of the L-glutamic acid molecule is not as much preferred in free energy terms in the transition state [68]. The (∆ 2 0≠ ) values increase with an increase in temperature for most of the systems as well as increase the solute-solvent interaction that makes it hard to flow the solute molecules.

Conclusions
This work represents the temperature based volumetric and viscometric properties of L-glutamic acid solution in water and in aqueous glucose solutions (5, 10, 15, and 20% of glucose, w/w in water). Various volumetric and viscometric parameters like φv, φv 0 , (Δφv 0 )tra, Eφ 0 , (δEφ 0 /δT)p, coefficients-A, B, Hn, (∆ 1 0≠ ) and (∆ 2 0≠ ) were calculated from experimental data. The results narrate the presence of strong solute-solvent interactions in these studied systems. Hence, it is concluded from Hepler constant (δEφ 0 /δT)p, and Jones-Dole coefficient-B values that L-glutamic acid act as a structure-maker in aqueous glucose solutions as well as in water.

Funding
The authors are thankful to Research Cell, Khulna University, Khulna-9208, Bangladesh, for the financial support in form of research project (No. KU/Research Cell-04/2000-228).