Phase Separation of Carboxylated Poly-L-lysine
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Phase Separation of Carboxylated Poly-L-lysine Esha Das1, 2 and Kazuaki Matsumura1 1 School of Material Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1211 2 M.Tech (CSPT), Department of Chemistry, University of Delhi-110007, India ABSTRACT Stimuli-responsive materials are capable of reversibly altering their properties depending on the environmental conditions or external stimuli. External stimuli typically include thermal, pH, electric fields, optical, magnetic fields, mechanical forces and chemical interactions. There are many instances in nature where responsive surfaces have been observed. Temperature is the most widely used stimulus in environmentally responsive polymer systems. The change of temperature is not only relatively easy to control, but also easily applicable both in vitro and in vivo. Temperature responsive polymers exhibit a phase transition at a certain temperature, which causes a sudden change in the solvation state. Polymers that become insoluble upon heating have a so-called lower critical solution temperature (LCST). One example of these polymers is poly (N-isopropyl acrylamide), which shows LCST at about 32 oC, close to the physiological temperature. In this study, we report the developing of novel polyampholytes which shows thermo-, salt-responsive liquid-liquid phase separation in aqueous solution. INTRODUCTION Polymers exhibit innumerable achievements in phase separation. The progress has been acquired by enormous efforts. A polymer solution being polar or non-polar separates into two phases when the temperature is reached to the phase separation temperature [1]. Phase separation is ascribed by the presence of specific unstable interactions between the polymer and solvent. The phase separation temperature is therefore below the boiling point of the liquid. Lower critical solution temperatures (LCSTs) are found in many polymer solutions which is having strong hydrogen bonds [2]. Polyampholytes are those macromolecules which have both positively and negatively charged groups. We found a polyampholyte which consist of amino and carboxyl groups in one polymer chain showed clear liquid-liquid phase separation responsive to temperature and salt concentration. There are many reports about phase separation of polypepotides [3] but our polymer has highly density of the charged groups so the phase separation behavior was quite unique. Here we report that the phase separation temperature in the liquid- liquid phase separation of carboxylated poly-lysine (polyampholyte) are highly effected by the polymer concentration, salt effect and hydrophobicity. Thermoresponsive polymer systems are intensively applied in tissue engineering, drug delivery, protein chromatography or controlled bioadhesion [4]. EXPERIMENTAL Preparation of polyampholytes: To synthesize polyampholytes, poly-L-lysine (25%) (w/v) and anhydride has been used to convert the amino groups to carboxyl groups.
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Poly-L-lysine (PLL) aqueous solution (25%) (w/w) (JNC Corp., Tokyo, Japan) and
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