Microrheology study of semidiluted deoxyribonucleic acid solutions
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Microrheology study of semidiluted deoxyribonucleic acid solutions F. Carvajal1, J. G. Alvarez1, E.R. Macías1, V.V.A. Fernández2, E. Robles-Avila3, R. GámezCorrales4, J.F.A. Soltero1,* 1 Departamenteo de Ingeniería Química, Universidad de Guadalajara, M. García Barragán 1451, Guadalalajara, Jal. 44430, México. 2 Departamento de Ciencias Tecnológicas, Universidad de Guadalajara, Av. Universidad # 1115, Ocotlán, Jal. 47810, México. 3 Departamento de Investigación en Polimeros y Materiales, Universidad de Sonora, Apdo. Postal # 130, Hermosillo, Sonora 83000, México. 4 Departamento de Física, Universidad de Sonora, Apdo. Postal # 130, Hermosillo, Sonora 83000, México. *Corresponding author: [email protected] [email protected] Telephone and fax number: (52) 33-13-78-59-00 ext 7590
ABSTRACT Linear rheological behavior and Microrheology measurements of sodium salt calf-thymus DNA aqueous solutions as a function of concentration are reported here. The microrheological behavior was obtained by a combination of experimental techniques: mechanical Rheometry and Dynamic light scattering (DLS). The viscoelastic properties of DNA in water as a function of concentration were performed at 20 ºC and rheological and microrhelogical curves were performed. The result indicated that for concentrations lower than the entanglement concentration (Ce) the system exhibits a predominantly viscous behavior, whereas for higher concentrations exhibits a predominantly elastic behavior. The plateau modulus (G0) and the zero 2.3 complex viscosity ( ) follow a power law concentration dependence of the form: G0 CDNA 3.6
and 0* CDNA , respectively The microrheology results overlap perfectly in a single line with the mechanical rheology results, extending the time resolution to faster breathing modes. INTRODUCTION Deoxyribonucleic acid (DNA) is a linear, double stranded, charged and semiflexible biomolecule that contains the genetic information for the biological development of living cells [1]. At certain concentration, the DNA molecules can be entangled and so the system exhibits a rich rheological behavior [2]. A detailed structural and rheological characterization of DNA in aqueous or salt solution is essential for gene therapy applications [3]. The microrheological measurements have been obtained using the generalized StokesEinstein relationship (GSER), which allows the measurement of the dynamics of colloids dispersed in DNA solutions describing the rheology of DNA suspensions. We calculated the frequency-dependent modulus amplitude from the particle mean-squared displacements measured using light scattering technique recently developed by Mason et al. [2] as an alternative method of obtaining the viscoelastic moduli. In the method of Mason, the complex shear modulus is estimated algebraically by using a local power law to describe the mean square displacement of the testing colloidal particles in the complex fluid, where a power law behavior is determined from the logarithmic time derivative of the MSD (Mean Square Displacement). For a
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