JP2759716B2 - Method for controlling molecular weight of poly-γ-glutamic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the molecular weight of poly-.gamma.-glutamic acid, and more particularly to poly-.gamma.-glutamic acid (hereinafter abbreviated as PGA) which is easily produced by using a microorganism. , Which is reacted with a nucleophilic reagent in a solution to reduce the molecular weight of PGA
And a molecular weight control method.

[0002]

BACKGROUND OF THE INVENTION The inventors of the present invention have already proposed a compound, a compound in which the γ-carboxyl group and the α-amino group of glutamic acid are linked by an amide bond.
A method for advantageously producing a high polymer of GA using a microorganism has been established (JP-A-1-17497). Also, PGA
The α-carboxyl group of the above is economically esterified with an alkyl group or a benzyl group to obtain an industrially useful poly-γ-glutamic acid α-substituted ester (hereinafter sometimes abbreviated as a PGA esterified product). This has been successful (Japanese Patent Application No. 2-28754).

[0003] However, the above-mentioned properties of PGA that are soluble only in highly polar solvents have hindered the development of a wide range of applications. PGA is inferior in solvent solubility due to PG
The molecular weight of A, the optical isomerism of the constituent amino acids, the inherent properties of the amide bond, and the like are considered.

[0004]

Means for Solving the Problems Accordingly, the present inventors have proposed P
In order to make GA soluble in various solvents, a method of reducing the molecular weight of PGA by reacting a metal salt of PGA with a nucleophilic reagent was repeated. As a result, it has been found that when a metal salt or ammonium salt of PGA produced by a microorganism is dissolved in water, and a nucleophilic reagent is added thereto and heated, the γ-amide bond is decomposed and the molecular weight is reduced. Was completed.

Namely, the present invention in solution of poly -γ- glutamic acid having a repeating unit of the following, the poly -
1.0 to 10.0 of the amide bond of γ-glutamic acid
React with an equivalent ratio of nucleophilic reagent, intrinsic viscosity 0.3-
An object of the present invention is to provide a method for controlling the molecular weight of poly-γ-glutamic acid, which comprises obtaining 0.4 dl / g of poly-γ-glutamic acid .

Embedded image

As the raw material of the present invention, for example, PGA produced by the method described in JP-A-1-17497 can be used. Regarding the molecular weight of PGA, the number average molecular weight as measured by gel filtration-light scattering method generally indicates 1.0 × 10 ⁶ or more, and the degree of polymerization calculated from this analysis value is about 1.0 × 10 ⁴ or more. Is shown. In addition, the intrinsic viscosity commonly used as the molecular weight of a polymer substance is represented by P
Dimethyl sulfoxide (hereinafter referred to as DM
It may be abbreviated as SO. ) Was dissolved at 1% by weight and measured in a thermostat at 30 ° C., and found to be 1.0 dl / g.
The above values are shown. PGA reduced in molecular weight by the present invention
Means those having an intrinsic viscosity of 0.3 to 0.4 dl / g
I do.

In the molecular weight control reaction of PGA according to the present invention, DMSO, dimethylformamide (hereinafter sometimes abbreviated as DMF) which is a PGA (free acid type) soluble solvent, N-methylpyrrolidone, dimethylimidazolidy. Non-protonic highly polar solvents such as non-, PGA (salt type)
Water or the like, which is a soluble solvent, can be used, and it is particularly preferable to use water. The concentration of the PGA solution should be in the range of 0.02 to 20% by weight, and considering the high recovery after the reaction, it is preferable to use the PGA solution at a concentration of 1.0% by weight or more.

Next, examples of the nucleophilic reagent used in the present invention include alkali metal hydroxides and hydrazines. Specifically, sodium hydroxide, potassium hydroxide,
Examples include anhydrous hydrazine and 1,1-dimethylhydrazine. The amount of the nucleophilic reagent to be added is 1.0 to 10.0 equivalents of the amide bond of PGA, preferably 1.1 to 2.0 equivalents.

When water is used as the solvent, the reaction temperature can be from the freezing temperature to the boiling temperature of water.
0 ° C. or higher is preferred. The reaction time varies depending on the reaction temperature and the required molecular weight of PGA.
It may be determined appropriately based on the assumption that PGA is completely decomposed in about 24 hours at 0 ° C. or by measuring the viscosity of the reaction solution.

After completion of the reaction, the molecular weight-controlled PGA is
When water is used as the solvent, the pH of the reaction solution is adjusted to 1.0 to 1.5 with an inorganic acid such as hydrochloric acid, sulfuric acid, and the like.
It can be precipitated by leaving it at a temperature of 2 to 3 days. When an organic solvent is used, 1 to 6 of the reaction solution is used.
By pouring the reaction solution into twice as much diethyl ether, low molecular weight PGA can be recovered in high yield.

[0011]

Next, the present invention will be described in detail with reference to examples. Example 1 After 8.0 g of PGA was suspended in 190 ml of deionized water, 2.06 g of sodium hydroxide was added thereto, and the suspension was added at room temperature.
Stir for 7 hours to completely dissolve. The solution temperature was raised to 60 ° C., and after the temperature reached 60 ° C., 10 ml of a solution containing 3.72 g of sodium hydroxide was added to the reaction solution to start the reaction. The intrinsic viscosity was measured as a 1.0% by weight solution of DMSO as an index of the molecular weight of the purified PGA having a reduced molecular weight, and the relationship with the reaction time was examined. The results are shown in FIG.
FIG. 1 also shows the results when the reaction was carried out in the same manner except that the reaction was carried out at 25 ° C. as a control.

As is apparent from the figure, in the case of the control, the molecular weight of PGA is hardly reduced irrespective of the reaction time, but in the case of the present invention, the molecular weight of PGA is reduced with the lapse of the reaction time. After the reaction for 58 hours, the pH of the reaction solution was adjusted to a range of 1.0 to 2.0 using 2N hydrochloric acid, and then adjusted to 4 ° C at 4 ° C.
PGA was precipitated by standing for 8 hours. The precipitated PGA was separated by filtration, washed with a small amount of methanol, and dried under reduced pressure at 40 ° C. for 4 hours to obtain 5.6 g of powder (yield: 70%). The elemental analysis values of this powder are shown below. 45.52 carbon
%; Hydrogen 5.57%; nitrogen 10.42%; inorganics
0%

Example 2 After 8.0 g of PGA was suspended in 190 ml of deionized water, 7.81 g of anhydrous hydrazine was added and stirred at room temperature for 2 hours to completely dissolve. The reaction was started by raising the solution temperature to 60 ° C. The intrinsic viscosity was measured as a 1.0% by weight solution of DMSO as an index of the molecular weight of the purified PGA having a reduced molecular weight, and the relationship with the reaction time was examined. The results are shown in FIG. FIG. 2 also shows the results when the reaction was carried out at 25 ° C. as a control.

As is apparent from the figure, in the case of the control, the reduction of the molecular weight of PGA is hardly recognized irrespective of the reaction time, but in the case of the present invention, the molecular weight of PGA is reduced with the lapse of the reaction time. After completion of the reaction, the pH of the reaction solution was adjusted to 1.5 using 2N hydrochloric acid, and then left at 4 ° C. for 48 hours to obtain PG.
A was precipitated. The precipitated PGA was filtered off to give powder 6.8.
g (85% yield).

[0015]

According to the present invention, a low molecular weight PG is obtained from PGA which is commercially stable and can be obtained at low cost.
A can be manufactured efficiently.

[0016]

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the reaction time and the molecular weight of PGA in Example 1.

FIG. 2 is a graph showing the relationship between the reaction time and the molecular weight of PGA in Example 2.

──────────────────────────────────────────────────続 き Continued on the front page (56) Reference “Yoshiharu Toi” edited by “Biodegradable Polymer Materials” (1990-11-9) 124-126 (58) Field surveyed (Int. Cl. ⁶ , DB name) C08G 69/46 C07C 231/08 C07C 237/22

Claims (2)

(57) [Claims] 1. Poly-γ- having the following repeating unit:
Glutamic acid in solution, the poly-γ-glutamic acid
Of amide bond having a ratio of 1.0 to 10.0 equivalents
React with the reagent to obtain a powder with an intrinsic viscosity of 0.3 to 0.4 dl / g.
Poly-γ characterized by obtaining ly-γ-glutamic acid
-A method for controlling the molecular weight of glutamic acid. Embedded image 2. The method according to claim 1, wherein the nucleophile is an alkali metal hydroxide or hydrazine.