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Effect of Temperature and Concentration on The REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 41, nro. 1 DE 2012 Rev. Colomb. Quím., 2012, 41(1): 123-131 EFFECT OF TEMPERATURE AND CONCENTRATION ON THE VISCOSITY OF AQUEOUS SOLUTIONS OF 3-AMINOPROPANOIC ACID, 4-AMINOBUTANOIC ACID, 5-AMINOPENTANOIC ACID, 6-AMINOHEXANOIC ACID EFECTO DE LA TEMPERATURA Y LA CONCENTRACIÓN EN LA VISCOSIDAD DE SOLUCIONES ACUOSAS DE ÁCIDO 3-AMINOPROPANOICO, ÁCIDO 4-AMINOBUTANOICO, ÁCIDO 5-AMINOPENTANOICO, ÁCIDO 6-AMINOHEXANOICO EFEITO DA TEMPERATURA E A CONCENTRAÇÃO NA VISCOSIDADE DAS SOLUÇÕES AQUOSAS DE ÁCIDO 3-AMINOPROPANOICO, ÁCIDO 4-AMINOBUTANOICO, ÁCIDO 5-AMINOPENTANOICO, ÁCIDO 6-AMINOHEXANOICO Carmen M. Romero1,2, Alejandro Beltrán1. Recibido: 09/04/12 – Aceptado: 30/04/12 ABSTRACT so the contribution of polar and apolar groups was established. The results are In this work we present the effect of tem- interpreted in terms of amino acid hydra- perature on the viscosities of aqueous so- tion. lutions of 3-aminopropanoic acid, 4-ami- nobutanoic acid, 5-aminopentanoic acid Key words: Amino acid; viscosity; and 6-aminohexanoic acid as a function hydrophobic hydration; solute-solvent of concentration. The experimental mea- interactions. surements were done from 293.15 K to 308.15 K. At each temperature the experi- RESUMEN mental data were fi tted to the Tsangaris- Martin equation and the B viscosity coef- En este trabajo se presenta el efecto de fi cient was determined. The dependence la temperatura sobre las viscosidades de of the B coeffi cients on the number of soluciones acuosas de acido 3-aminopro- carbon atoms of the amino acids is linear, panoico, acido 4-aminobutanoico, acido 1 Universidad Nacional de Colombia, sede Bogotá, Facultad de Ciencias, Departamento de Química, Grupo de Ter- modinámica Clásica, Laboratorio de Investigaciones Básicas. Av Cra 30 45-03- Bogotá D.C., Código Postal 111321 - Colombia. 2 [email protected] 123 RCQ41.indd 123 22/06/12 9:57 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 41, nro. 1 DE 2012 5-aminopentanoico, acido 6-aminohexa- Palavras-chave: aminoácidos; vis- noico en función de la concentración. cosidade; hidratação hidrofóbica; intera- Las determinaciones experimentales se ção soluto-solvente. realizaron en un intervalo de temperatura entre 293,15 K hasta 308,15 K. A cada una de las temperaturas trabajadas, los INTRODUCTION datos experimentales se ajustaron a la Amino acids have been considered ecuación de Tsangaris-Martin y se de- model compounds that can give useful terminó el coeficiente B de viscosidad. information to understand the behavior La dependencia del coeficiente B con of proteins and the role of solvent struc- el número de carbonos del aminoácido ture in the denaturation process. For this es lineal lo cual permitió establecer la reason and due to their applications, contribución de los grupos polares y apo- the properties of amino acids in aque- lares del aminoácido. Los resultados se ous solution including their viscometric interpretan en términos de la hidratación properties have been extensively studied de los aminoácidos. (1-18). The information has been used to provide an insight about hydropho- Palabras clave : aminoácidos; visco- bicity, hydration properties and solute- sidad; hidratación hidrofóbica; interac- solvent interactions. However most of ción soluto-solvente. these studies refer to naturally occurring small α-amino acids at 298.15 K and RESUMO very few data are reported in literature for α,ω-amino acids specially at tem- Neste trabalho é apresentado o efeito da peratures different from 298.15 K (5, 8, temperatura sobre as viscosidades das 15, 16). soluções aquosas de ácido 3-aminopro- panoico, ácido 4-aminobutanoico, ácido Although there is much literature on 5-aminopentanoico, ácido 6-aminohe- aqueous solutions of α-amino acids, data xanoico em função da concentração. on the viscosities of solutions of α,ω- As determinações experimentais foram amino acids are limited in particular at feitas em um intervalo de temperatura temperatures different from 298.15 K. In entre os 293,15 K até 308,15 K. Para order to extend the understanding on the cada uma das temperaturas trabalhadas, behavior of aqueous solutions of amino os dados experimentais foram ajustados acids and as continuation of our previous à equação de Tsangaris-Martin, e o coe- experimental studies on viscosity of the ficiente B de viscosidade foi determina- aqueous mixtures of these solutes (11, do. A dependência do coeficiente B com 13, 14), we report here new experimen- o número de carbonos do aminoácido tal viscosity data for aqueous solutions é linear e permitiu estabelecer a contri- of 3-amino propanoic acid, 4-amino bu- buição dos grupos polares e apolares do tanoic acid, 5-amino pentanoic acid and aminoácido. Os resultados foram inter- 6-amino hexanoic acid as a function of pretados em termos da hidratação dos concentration at 293.15, 298.15, 303.15 aminoácidos. and 308.15 K. The amino acids were 124 RCQ41.indd 124 22/06/12 9:57 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 41, nro. 1 DE 2012 chosen to examine the effect of increase Merck purity ≥ 99 %, 4-aminobuta- in the number of CH2 groups. noic acid (γ-aminobutyric acid) Merck purity ≥ 98 %, 5-aminopentanoic acid The behavior of the viscosity of (δ-aminovaleric acid) Aldrich puri- solutions is a consequence of the different ty ≥ 97 % and 6-aminohexanoic acid interactions between solute and the solvent (ε-aminocaproic acid) Merck purity ≥ molecules. For this reason it depends on 99 %. The amino acids were dried under the nature of solvent and solute nature, the vacuum at room temperature and kept in size and shape of the latter, concentration, desiccator at least 48 h before use. Water and is affected by external factors was doubly distilled and deionized ac- such as temperature. Several industrial cording to literature and degassed before applications are very sensitive to fl ow use obtaining a product with conductiv- behavior and are specially affected by the ity less than 2 μS m-1 (19, 20). All solu- behavior of viscosity with temperature. tions were prepared by weight using a In this regard, information about the fl ow Mettler balance AT 261 dual range with properties of aqueous solutions of α,ω- sensitivity of 10–5 g in the lower range. amino acids is important. Of particular interest is the behavior of the relative Viscosity h was determined using viscosity as a function of concentration, two Ubbelohde viscometers with effl ux since it gives important information about times t near 500 s for water that were cal- solute hydration. ibrated with water at the selected temper- atures. Reproducibility of effl ux times In this work the relative viscosity results was in all cases better than 0.05 %. Effl ux were used to determine the B-coeffi cients times were determined at 293.15, 298.15, of amino acids at the selected temperatures. 303.15 and 308.15 K for the amino acid The dependence of the B coeffi cient aqueous solutions. All measurements with temperature was used to discuss the were carried out in a constant tempera- effect of the hydrocarbon chain on water ture bath with temperature controlled to structure and the hydration properties of + 0.005 K. Reported values are the av- the solutes. A comparison between the B erage of at least three independent mea- coeffi cients of α-amino acids and α,ω- surements in each viscometer. Densities amino acids is presented. The results ρ of the solutions at the selected temper- show that the coeffi cients for α,ω-amino atures were taken from a previous work acids are smaller than the corresponding (21). They were measured at the same values for α-amino acids at the same temperatures using pycnometers of the temperatures suggesting that solute– Wood-Brusie type, in a constant temper- solvent hydrophobic interactions are larger ature bath with temperature controlled to for α-amino acids due to the more exposed ± 0.01 K. Density values are the average aliphatic chain to the solvent. of three independent measurements and uncertainty in the density measurements -5 -3 MATERIALS AND METHODS is estimated to be ± 5·10 g cm The materials used in this work were: The viscosity data were obtained 3-aminopropanoic acid (β-alanine) from the general equation: 125 RCQ41.indd 125 25/06/12 12:07 REVISTA COLOMBIANA DE QUÍMICA, VOLUMEN 41, nro. 1 DE 2012 h = αρt - βρ / t [1] At all temperatures, solution viscosity increases with amino acid concentration where a and b are the viscometer con- and the effect is more pronounced as the stants obtained by calibration with water length of the hydrocarbon chain becomes at each temperature, ρ is the density and larger. From Tables 1-4 it can be seen t the efflux time. The relative viscosities that for each amino acid, the viscosity h ηr = /ηo were calculated from the solu- decreases as temperature increases. tion and solvent viscosities respectively. The relative viscosity values were calculated and adjusted by least-squares RESULTS AND DISCUSSION to a second order equation as proposed Tables 1-4 show the experimental results by Tsangaris-Martin (3). for density and viscosity of the aque- 2 ous solutions of 3-aminopropanoic acid, ηr = 1 + Bm + Dm [2] 4-aminobutanoic acid, 5-aminopenta- noic acid, and 6-aminohexanoic acid as In this equation B and D are empirical a function of molality at 293.15, 298.15, coefficients; however it has been sug- 303.15 and 308.15 K. The density data gested that the B coefficient depends on were obtained adjusting the values re- the size, shape and charge of the solute ported in literature from a previous work molecule and is sensitive to solute sol- at the same temperatures considered in vent interactions (4, 15-18). The effect of this work (21).
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