Compatibility of mixtures of deoxyribonucleic acid with hydroxypropylcellulose in concentrated aqueous solutions

Abstract

In order to obtain information about the compatibility between biopolymeric substances and water-soluble polymers, the phase states of mixtures of DNA with hydroxypropylcellulose (HPC) in concentrated aqueous solutions were studied by simultaneous measurement of differential thermal analysis (DTA) and laser transmittance (He-Ne gas laser; λ 0 = 633 nm), and by means of a polarization microscope and a refractometer. From the results obtained, the phase states in mixture I exhibit an isotropic phase. Mixture II exhibits an anisotropic phase with a slight birefringence from the measurement of the refractive index at 298 K, suggesting that an anisotropic phase in this region corresponds to a quasi-liquid crystal similar to that found previously in the concentration range 3.00–5.00 wt.% of DNA solutions. The phase states in mixture III exhibit birefringence from the measurement of refractive index at 298 K, suggesting that these phase states form stable liquid crystals which are essentially different from an already known liquid crystal of HPC or DNA in concentrated solutions. It is suggested that these liquid crystals are formed by the interaction between DNA and HPC. In order to obtain information about the enthalpy change associated with the liquid crystal formation, the phase states of mixtures I, II and III were also studied using a DTA instrument equipped with a laser, under the same experimental conditions as observed with the polarization microscope. From the thermal and optical properties obtained, the degree of formation α of liquid crystal phases of the mixture formed by the interaction between DNA and HPC is estimated, making use of the degree of precipitation accompanying the phase separation of HPC corresponding to the difference in intensity Δ Iof the transmitted laser light before and after the change in the laser with increasing temperature. From the α value, the net heat of fusion of liquid crystal phases of the mixture formed by the interaction of DNA with HPC is estimated to be about 2.4 kJ per mol of nucleotide.