JP2008056878A - Thermo-responsive polylysine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a new stimulus-responsive polymer having biodegradability and biocompatibility developing thermo-responsive property under physiologic conditions. <P>SOLUTION: The new polylysine (especially poly(ε-L-lysine)) derivative has a 1,2-epoxyalkane (especially 1,2-epoxybutane) introduced thereto. The aqueous solution composition having thermo-responsive property contains the derivative. The method for concentrating and separating an anionic compound comprises using the polylysine derivative. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a stimulus-responsive polymer (polylysine) that greatly changes its physical properties in response to an external stimulus of temperature.

  Many stimuli-responsive polymers that greatly change their physical properties in response to external stimuli such as temperature, pH, light, and electric field have been studied as biomedical materials such as chromatography carriers and intelligent drug delivery system (DDS) carriers. Has been.

  In recent years, research on stimuli-responsive polymers having biodegradability and biocompatibility has been conducted in Japan and overseas, assuming use in vivo as a high-performance drug carrier. However, the methods reported so far have the following problems: 1) the synthesis process is multistage and complicated, and 2) the safety of decomposition products remains questionable.

  For example, by introducing an appropriate amount of an alkyl group into the carboxyl group of the poly (γ-glutamic acid) (γ-PGA) side chain, which is the main ingredient of natto's stickiness, to control the parent-hydrophobic balance of the entire γ-PGA molecular chain In addition, a propylated γ-PGA that can respond to temperature stimulation has been synthesized (Non-patent Document 1). However, γ-PGA has problems such as that it does not exhibit heat-responsiveness under physiological conditions (the same pH (7.4) and salt concentration (150 mM) environment as in vivo).

In addition, an example in which poly (αL-lysine) is hydrophobized with cholesterol has been reported (Non-patent Document 2). However, this example is a technique for producing nano-sized particles in water with cholesterol as a core, and does not provide a polymer having stimulus responsiveness.
Shimokuri, T .; Kaneko, T .; Akashi, MJ Polym. Sci. Part A: Polym. Chem. 2004, 42, 4492-4501. Akiyoshi, K. et al., Macromolecules 2000, 33, 6752-6756

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel stimulus-responsive polymer having biodegradability and biocompatibility that develops thermosensitive response under physiological conditions.

  As a result of intensive studies by the present inventors, it has been found that the above object can be achieved by amphiphilization of polylysine, and the present invention has been made.

  That is, the present invention relates to a polylysine derivative into which 1,2-epoxyalkane is introduced.

  The lysine, which is a constituent monomer of polylysine used in the present invention, may be any constituent unit of L-form, D-form or a mixture thereof. That is, as polylysine, poly (ε-L-lysine), poly (ε-D-lysine), poly (ε-D, L-lysine), poly (α-L-lysine), poly (α-D-lysine) Poly (α-D, L-lysine) may be used. L-form is a naturally occurring form, and therefore polylysine composed of L-lysine is usually used. Among them, poly (ε-L-lysine) (ε-PL) is a microorganism-derived polyamino acid produced by streptomyces albulus 346, that is, a naturally occurring polyamino acid, is a homopolymer of L-lysine, and can be modified to the side chain. Has a primary amino group. This ε-PL is highly safe to living bodies, such as being used as a food additive.

  The purpose of the present invention is to provide a novel stimulus-responsive polymer having biodegradability and biocompatibility that develops thermosensitive response under physiological conditions. Therefore, polylysine should be soluble in water. . The physiological condition is not limited to the condition of biocompatibility, and it is not necessary to be limited to only those that are soluble in water as long as the purpose is a heat-responsive property.

  The molecular weight of polylysine can be adjusted by adjusting the polymerization degree of lysine, and may be appropriately selected as necessary.

  Usually, the number average molecular weight (Mn) may be several thousand to 200,000, preferably several thousand to 100,000. If a material having a low molecular weight is used, the intermolecular interaction, which is the driving force for expressing the heat-sensitive response, is weak, and it is expected that the response may be difficult to express. If the molecular weight is too high, high molecular weight polylysine may form a complex in the synthesis process, and the hydrophobic group may not be efficiently introduced.

  As a product of polylysine, microorganism-derived poly (ε-L-lysine) (number average molecular weight 4700: trade name polylysine hydrochloride: manufactured by Chisso Corporation) and the like are available.

  The 1,2-epoxyalkane introduced into polylysine is 1,2-epoxybutane or 1,2-epoxypentane, more preferably 1,2-epoxybutane, wherein the alkane has 4 or more carbon atoms, preferably 4 or 5. It is. When the carbon number of the alkane is 3 or less, the thermal sensitivity cannot be expressed. In addition, 1,2-epoxyalkane having too many carbon atoms does not dissolve in water, and therefore, a synthetic contrivance is required when introducing it into polylysine.

  The introduction of 1,2-epoxyalkane into polylysine is accomplished by dissolving polylysine in a suitable solvent, adding and dissolving a predetermined amount of 1,2-epoxyalkane, and then nucleophilicity of the polylysine to the epoxy group of the primary amine. This can be done by ring-opening reaction. As a result, a hydroxyalkyl group is introduced into the primary amine of polylysine.

  For example, when poly (ε-L-lysine) is used as polylysine and 1,2-epoxybutane is used as 1,2-epoxyalkane, it can be synthesized in an aqueous solution using water as a solvent. When 1,2-epoxypentane is used as the 1,2-epoxyalkane, 1,2-epoxypentane does not dissolve in water, so once 1,2-epoxybutane is introduced into poly (ε-L-lysine). Thus, hydrophobicity is imparted to such an extent that it can be dissolved in an organic solvent in which 1,2-epoxypentane can be dissolved, and 1,2-epoxypentane may be introduced by reaction in the organic solvent.

  By introducing 1,2-epoxyalkane into polylysine, hydrophobicity can be imparted to polylysine.

  For example, when poly (ε-L-lysine) has an introduction rate of 1.2-epoxybutane (ratio of 1,2-epoxyalkane introduction into the primary amine of polylysine) of more than 14%, DMSO, The solubility of organic solvents such as ethanol is improved. The introduction rate can be adjusted by changing the amount of 1,2-epoxyalkane such as 1.2-epoxybutane in the synthesis.

  Furthermore, thermoresponsiveness can be imparted by controlling the hydrophilicity / hydrophobicity balance of polylysine. In the present invention, “thermosensitive” means a phase separation phenomenon reversibly caused by temperature stimulation. The phase separation temperature can be controlled by changing the hydrophobic group introduction rate of 59% or more, the polymer concentration (0.125 to 2.0 wt%), and the pH (7 or more, preferably 7.4 or more). The phase separation temperature shifts to a lower temperature side as the introduction rate increases. For example, when about 59% or more of 1,2-epoxybutane is introduced into poly (ε-L-lysine), a phase separation temperature is observed in a buffer solution (salt concentration 150 mM) of NaCl (1.0 M) and pH 12. In addition, the composition of the pH 12 buffer solution (salt concentration of 150 mM) used in this example means a disodium hydrogen phosphate / sodium hydroxide aqueous solution, and the salt concentration of 150 mM is close to physiological conditions. .

  The mechanism of thermal sensitivity varies depending on the structure of the main chain. For example, a polylysine derivative (ε-PL-B) in which 1,2-epoxybutane is introduced into poly (ε-L-lysine) exhibits a thermosensitive response due to coacervate, and 1 is added to poly (α-L-lysine). A polylysine derivative into which 2-epoxybutane is introduced exhibits heat-responsiveness due to the coil-globule transition.

  ε-PL-B separates anionic compounds such as anionic dyes, anionic proteins, DNA, RNA, etc., using hydrophobic and electrostatic interactions as driving forces in coacervate droplets formed in a phase-separated state It is possible to concentrate.

  A novel polylysine derivative incorporating a 1,2-epoxyalkane was provided.

(Example 1)
Synthesis of poly [ ^Nα- (2-hydroxybutyl) lysine] (ε-PL-B) Poly (ε-L-lysine) (ε-PL) (trade name: polylysine hydrochloride: manufactured by Chisso Corporation) 820 mg ( 5.0 unit mmol) was dissolved in 25 ml of ultrapure water, a predetermined amount (described in Table 1 below) of butylene oxide was added, and the mixture was reacted at 40 ° C. for 24 hours.

After completion of the reaction, dialysis was performed with distilled water using a dialysis membrane having a molecular weight fraction of 500, and the polymer was purified by lyophilization. The structure of the product was confirmed using ¹ H-NMR and FT-IR.

FIG. 1 shows a ¹ H-NMR chart of ε-PL-B. All peaks are from ε-PL and ε-PL-B.

  The introduction rate of 2-hydroxybutyl group was calculated from the ratio of the integrated value of the peak attributed to methine in the ε-PL-B main chain and the peak attributed to the methyl group in the side chain. The introduction rate of 2-hydroxybutyl group was 14 to 93%.

Solubility test The solubility of ε-PL and ε-PL-B in various solvents was tested at a polymer concentration of 0.2 wt%. The results are shown in Table 1.

  ε-PL showed solubility in ultrapure water, but was insoluble in organic solvents. On the other hand, ε-PL-B having an introduction rate of 14 to 93% showed solubility in ultrapure water and improved solubility in ethanol, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). From these results, it can be seen that by introducing a 2-hydroxybutyl group into the ε-PL side chain, it was possible to eliminate the intermolecular interaction of ε-PL and improve the solubility in organic solvents.

Evaluation of heat-sensitive response of ε-PL-B The heat-sensitive response of ε-PL-B was evaluated by measuring the light transmittance of the solution with respect to temperature change using a UV-vis spectrum.

  ε-PL-B is dissolved in ultrapure water, NaCl aqueous solution (1.0 M), pH 7.4, 10, 12 buffer solution (salt concentration 150 mM) (polymer concentration is 1 wt% in ultrapure water and NaCl aqueous solution, The absorbance at a wavelength of 500 nm was measured in a quartz cell having a slit width of 1 mm. The heating / cooling rate was 1 ° C./min, and the phase separation temperature was the temperature at a transmittance of 90%.

Table 2 shows the phase separation temperatures obtained from the measurement of the transmittance of an ε-PL-B aqueous solution having a 2-hydroxybutyl group introduction rate of 14, 37, 59, 73, 80, and 93%.
Change in light rate of ε-PL-B aqueous solution of NaCl aqueous solution (1.0 M) (polymer concentration 1 wt%) and 93% ε-PL-B aqueous solution (pH 7.4, 10, 12) (polymer concentration 0.25 wt%) ) Light transmittance change (phase separation temperature) is shown in FIGS. 2 (a)-(c) and 3 (a)-(c), respectively. 2 (a) and 3 (a) show the transmittance change during the heating process, FIGS. 2 (b) and 3 (b) show the transmittance change during the cooling process, and FIG. 2 (c) shows the phase change. The dependence of the separation temperature on the introduction rate of hydrophobic groups is shown. FIG. 3C shows the dependence of the phase separation temperature on the hydrogen ion concentration.

  All samples of ε-PL-B (14 to 93%) dissolved in ultrapure water did not show thermal sensitivity in ultrapure water. In a NaCl aqueous solution (1.0 M) and a pH 7.4, 10, and 12 buffer solution (salt concentration of 150 mM), ε-PL-B having a 2-hydroxybutyl group introduction rate of 59% or more exhibited heat-responsiveness. Moreover, according to FIG.2 (c), it turns out that the phase-separation temperature has shifted to the low temperature side with the raise of the introduction rate.

  In an aqueous NaCl solution (1.0 M), a change in transmittance with respect to a change in temperature was observed in an ε-PL-B aqueous solution having an introduction rate of 59, 73, 80, and 93%. In addition, reversible changes in transmittance were observed in the ε-PL-B aqueous solutions with introduction rates of 59, 73, 80, and 93% even in pH 7.4, 10, and 12 buffer solutions. FIG. 3C shows that the phase separation temperature can be controlled by changing the pH. Although no data is shown, the phase separation temperature could be controlled by the polymer concentration, pH, ionic strength, and introduction rate.

  In addition, no clear endothermic peak of water near the phase separation temperature was observed by differential scanning thermogravimetry above the phase separation temperature, and droplets due to the concentrated phase were observed from the micrographs. It was suggested that sex was expressed.

  From the above results, 2-hydroxybutyl group is introduced to adjust the hydrophilic / hydrophobic balance of the entire ε-PL molecular chain appropriately, and by adding inorganic salt, the polarity of water is increased or the side chain is increased by increasing pH. It has been clarified that by reducing the electrostatic repulsion of the amino group of ε-PL, heat-responsiveness can be imparted to ε-PL by increasing the hydrophobic interaction of 2-hydroxybutyl.

Complexing Behavior of ε-PL-B Aqueous Solution with Ionic Dye ε-PL-B that expresses thermal sensitivity by coacervate has an amino group remaining in the side chain. Therefore, the complexing behavior of the ε-PL-B aqueous solution before and after the phase separation temperature was observed using trypan blue (TB: anionic) and methylene blue (MB: cationic) which are ionic dyes.

  TB and MB were each added to an aqueous solution of 93% ε-PL-B (ε-PL-B93) (pH 7.4, LCST (phase separation temperature) 45 ° C.) to a concentration of 10 μM, and the phase separation temperature. The formation of ion complexes before and after was observed.

  It was confirmed that both TB and MB were uniformly dissolved in the ε-PL-B93 aqueous solution at 20 ° C., which is lower than the phase separation temperature. On the other hand, at 50 ° C., which is higher than the phase separation temperature, it was confirmed that TB, which is an anionic dye, was concentrated and precipitated in coacervate droplets. Above this phase separation temperature, ε-PL-B93 associates with a hydrophobic interaction as a driving force to form a concentrated phase by coacervate, and only TB, which is an anionic dye, is concentrated in the droplet by electrostatic interaction. It is thought that it happened because of it.

  When the absorbance at 570 nm, which is the absorption wavelength of TB, was measured, no TB absorption was observed from the supernatant of the 50 ° C. aqueous ε-PL-B93 solution.

  From the above results, it is expected that ε-PL-B93 can capture anionic compounds such as anionic proteins and DNAs via electrostatic interaction in coacervate droplets formed by thermal response, and separation using temperature stimulation. Use as a material is expected.

CD spectrum measurement of ε-PL-B aqueous solution The CD spectrum of ε-PL-B (introduction rate: 93%) was measured under the conditions of pH 7.4, 10, 12, polymer concentration 0.005 wt%, buffer concentration 150 mM. . The results are shown in FIG.

  It was revealed that ε-PL and ε-PL-B have a β-sheet structure under the conditions of pH 7.4 and 12. Furthermore, it turns out that the beta structure of (epsilon) -PL-B is stabilized by heating.

DLS measurement of ε-PL-B aqueous solution ε-PL-B (introduction rate 93%), pH 7.4, phase separation temperature 44 ° C., polymer concentration 0.5 wt%, buffer concentration 150 mM was used. DLS of B (introduction rate 93%) was measured under 20, 40, and 60 ° C conditions. The results are shown in FIG.

  The ε-PL-B aqueous solution formed an aggregate having a particle size of about 400 nm at a temperature equal to or higher than the phase separation temperature and using the hydrophobic interaction of 2-hydroxybutyl groups as a driving force.

Synthesis of poly [N ^ε- (2-hydroxybutyl) lysine] (α-PL-B) Poly [N ^α- (2-hydroxybutyl) lysine] (ε-PL-B) ^[epsilon] -(2-hydroxybutyl) lysine] ([alpha] -PL-B) was synthesized. Table 3 shows the synthesis results and water solubility.

  The introduction rate of 2-hydroxybutyl group was 50, 72, 83, 95%. Α-PL-B having an introduction rate of 50% and 72% was dissolved in ultrapure water, but α-PL-B having an introduction rate of 83% was dispersed in ultrapure water, and 95% α-PL-B was dissolved. Was insoluble in ultrapure water.

  In addition, α-PL-B having an introduction rate of 50, 72% showed solubility in a buffer solution having a pH of 7.4, whereas α-PL-B having an introduction rate of 83% was precipitated in the buffer solution having a pH of 7.4. As α-PL-B was introduced, the solubility in water decreased. It has been clarified that the synthesized α-PL-B has a lower solubility in water in the case of the same introduction rate as compared with ε-PL-B. This is considered to be due to the fact that α-PL-B has a strong hydrophobic interaction as compared with ε-PL-B because the side chain has a long chain length.

  The thermal responsiveness of α-PL-B having an introduction rate of 50,72% showing solubility in a buffer solution of pH 7.4 was examined, and dynamic light scattering (DLS) measurement with an introduction rate of 83% dispersed in water was performed. went.

  FIG. 6 shows the light transmittance with respect to temperature change of an α-PL-B aqueous solution (pH 7.4) having an introduction rate of 50% (polymer concentration: 1 wt%) and an introduction rate of 72% (polymer concentrations: 1 wt%, 0.2 wt%). The measurement results are shown.

  Only the sample with an introduction rate of 72% was confirmed to exhibit a sensory response, but a disturbance in transmittance change was observed. When the α-PL-B aqueous solution above the phase separation temperature was observed, polymer precipitation and precipitation were observed.

DSC measurement ε-PL-B (introduction rate 93%), α-PL-B (introduction rate 72%), pH 7.4, polymer concentration 0.5 wt%, buffer concentration 150 mM, heating / cooling rate 2 ° C./min DSC measurement was performed under the conditions of The results are shown in FIG.

  From the results of DSC measurement, ε-PL-B expresses thermal sensitivity by coacervate which is liquid-liquid phase separation, and α-PL-B has thermal response by coil-globule transfer which is liquid-solid phase separation. It was confirmed to express sex. Further, FIG. 7 shows that the phase separation temperature of the α-PL-B aqueous solution (pH 7.4) is about 65 ° C.

  In the phase separation state of ε-PL-B, since the liquid-liquid phase separation was performed, polymer precipitation was not confirmed. However, since α-PL-B has a long chain length of the hydrophobic group, ε- Compared with PL-B, a strong hydrophobic interaction acts, and in the α-PL-B72 aqueous solution, it is considered that a polymer association was caused by the hydrophobic interaction as a driving force in response to temperature stimulation and precipitated.

  In FIG. 8, the result of the DLS measurement of (alpha) -PL-B83 which showed water dispersibility was shown. The average particle diameters of α-PL-B83 measured at 20 ° C. and 50 ° C. were 177 nm and 183 nm, respectively. It was confirmed that α-PL-B83 forms a relatively monodisperse aggregate in water using the hydrophobic interaction of 2-hydroxybutyl groups as a driving force. Further, when the zeta potential of α-PL-B83 in a dispersed state was measured, the surface potential was 35 mV, and it was revealed that an aggregate in which amino groups were accumulated on the surface was formed.

  In this example, poly (ε-L-lysine) and poly (α-L-lysine) are used as polylysine. However, poly (ε-D-lysine), poly (ε- D, L-lysine) (a mixture of D and L lysine monomer units), poly (α-D-lysine), and poly (α-D, L-lysine) are also considered to be usable.

  The polylysine derivative of the present invention is considered to be applicable to a novel biodegradable separation material, an anionic drug carrier.

¹ H-NMR chart of ε-PL-B. The figure which shows the temperature dependence (heating process) of the transmittance | permeability of (epsilon) -PL-B aqueous solution. The figure which shows the temperature dependence (cooling process) of the transmittance | permeability of (epsilon) -PL-B aqueous solution. The figure which shows the introduction rate dependence of the phase separation temperature of (epsilon) -PL-B aqueous solution. The figure which shows the temperature dependence (heating process) of the transmittance | permeability of (epsilon) -PL-B93 aqueous solution. The figure which shows the temperature dependence (cooling process) of the transmittance | permeability of (epsilon) -PL-B93 aqueous solution. The figure which shows the hydrogen ion concentration dependence of the phase-separation temperature of (epsilon) -PL-B93 aqueous solution. The figure which shows CD spectrum of (epsilon) -PL-B93. The figure which shows the result of the DLS measurement of (epsilon) -PL-B93. The figure which shows the light transmittance with respect to the temperature change of alpha-PL-B aqueous solution. The figure which shows the DSC measurement result of (epsilon) -PL-B93% and (alpha) -PL-B72%. The figure which shows the result of the DLS measurement of (alpha) -PL-B83.

Claims (8)

  Polylysine derivative introduced with 1,2-epoxyalkane.   The polylysine derivative according to claim 1, wherein the polylysine is poly (ε-L-lysine) or poly (α-L-lysine).   The polylysine derivative according to claim 1, wherein the polylysine is poly (ε-L-lysine).   The polylysine derivative according to claim 1 or 2, wherein the 1,2-epoxyalkane is 1,2-epoxybutane.   The polylysine derivative according to any one of claims 1 to 4, wherein 1,2-epoxyalkane is introduced in an amount of 14% or more based on the primary amine of the polylysine derivative.   The polylysine derivative according to any one of claims 1 to 4, wherein 1,2-epoxyalkane is introduced in an amount of 14% or more based on the primary amine of the polylysine derivative.   An aqueous solution composition comprising the polylysine derivative according to any one of claims 1 to 6 and having a heat-responsive property and having a pH maintained at 7 or more.   A method for concentrating and separating an anionic compound, wherein the polylysine derivative according to any one of claims 1 to 6 is used.

Images