ADSORPTION AND DESORPTION OF METAL IONS BY SYSTEMS BASED ON CELLULOSE DERIVATIVES THAT CONTAIN AMINO ACID RESIDUES"

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1 (41) Vol. 41, No.6 (1985) T-235 (Received May 24, 1984) ADSORPTION AND DESORPTION OF METAL IONS BY SYSTEMS BASED ON CELLULOSE DERIVATIVES THAT CONTAIN AMINO ACID RESIDUES" By Toshihiko Sato, Shigenori Motomura and Yasuo Ohno (Department of Industrial Chemistry, Faculty of Technology, Tokyo University of Agriculture and Technology, Nakamachi, Koganei, Tokyo 184 Japan) A reactive cellulose intermediate having free isocyanate groups (isocyanate cellulose) was prepared by the treatment of cellulose with 2, 4-tolylene diisocyanate (2, 4-TDI). The reactions of the isocyanate cellulose with amino acids in organic solvents gave cellulose derivatives containing amino acid residues. The amounts of amino acids bound to the isocyanate cellulose through the urea linkage were `0.747 mmol/g. The adsorption and desorption of metal ions by systems based on the cellulose derivatives were investigated. The cellulose derivatives could adsorb various kinds of metal ions from aqueous solution with relatively high adsorption values for copper (II) and iron (III) than zinc (II), cadmium (II), chromium (III) and mercury (II) ions. The cellulose derivative containing cysteine was especially effective for the adsorption of mercury (II) ion with the distribution coefficient, [Kd]=1.63 ~103. The desorption of copper (II), zinc (II) and cadmium (II) ions from the derivatives were effected completely with 2N HCl and that of iron (III), with 4N HCI. These derivatives could readsorb metal ions. 1. Introduction A few studies of the preparation of reactive cellulose intermediate having a free isocyanate group (isocyanate cellulose) have been reported1, 2). However, no study of the reaction of isocyanate cellulose with amino acids has appeared so far. In previous papers3, 4), we have reported the synthesis of cellulose derivatives containing amino acid and amino acid ester residues in buffer solu tion or in organic solvents. In dimethylsulfoxid (DMSO), because of the high solubility of amino acid esters, large amounts of amino acid esters reacted with isocyanate cellulose at low tempera ture. Since many cellulose derivatives have been studied as chelate resins5 `11), it is of interest to test the present products as metal adsorbing agents. In this paper, we report the synthesis of cellu lose derivatives containing amino acid residues in organic solvents and their abilities to adsorb and *1 Studies on Synthesis of Functional Cellulose Derivatives and their Application (Part 3) desorb various metal ions. 2. Experimentals Materials Microcrystalline cellulose used as a starting material was supplied by Asahi Kasei Kogyo Co. Ltd. The cellulose was dried in a vacuum oven at 80 Ž for more than 4 hrs. 2, 4-TDI was distilled just before its use under nitrogen atmosphere at reduced pressure (b. p.: 92 `93 Ž/5 mmhg). N, N- dimethylformamide (DMF) was dried over molecu lar sieve and DMSO was dried by refluxing on a calcium hydride. These solvents were distilled under nitrogen atmosphere at reduced pressures. Dioxane was stored over molecular sieve for 5 days and then distilled. The amino acids used for the reaction with the isocyanate cellulose were glycine (Gly), L-alanine (Ala), L-valine (Val), L- leucine (Leu), L-serine (Set), L-tyrosine (Tyr), L- glutamine (Glu), L-lysine (Lys), L-histidine (His), L-glutamic acid (Glu. acid), L-cysteine (Cys) and L-methionine (Met).

2 Synthesis of isocyanate cellulose Isocyanate cellulose was obtained by heating a mixture of microcrystalline cellulose (2.0 g) and 2, 4-TDI (5 ml) in DMSO (30 ml) at 60 Ž for 4 hrs under nitrogen atmosphere. The reaction resulted in a reactive cellulose intermediate containing linked TDI (content: `0.356 mol/glucose unit), in which `0.252 mol/g. u. of intact isocyanate groups were contained. Synthesis of cellulose derivatives containing amino acid residues The reaction was carried out by stirring mixture of the isocyanate cellulose (isocyanate group content: `1.16 mmol/g) (1.0 g) and an amino acid (5.3 mmol) in organic solvent (20 ml) such as, DMF, DMSO and dioxane at 30 Ž for 24 hrs. The amounts of incorporated amino acid were determined by the back titration'). Adsorption and desorption of metal ions by cellulose derivatives containing amino acid residues The adsorption was performed by stirring a suspension of the cellulose derivatives (300 mg) in various metal ion solutions (initial concentra tion: 1.0 mmol/1) (50 ml) at room temperature for 3 hrs. The amounts of metal ions adsorbed were determined by atomic absorption spectrometry for copper (II), zinc (II), iron (III), cadmium (II) and chromium (III) ions, and by chelate titration for mercury (II) ion. All metal ions used for the adsorption were hydrochloride complex. Adsorp tion value was obtained by the following equation. tration of the ion in the solution. The desorption of copper (II), zinc (II) and cadmium (II) ions was performed by stirring a suspension of the adsorbent incorporated metal ion in 2N HC1 (50 ml) at room temperature for 3 hrs and the desorption of iron (III), in 4N HCI. 3. Results and discussion 1) Synthesis of cellulose derivatives containing amino acid residues The reaction of isocyanate groups with com pounds having an active hydrogen, such as amine, alcohol, mercapto group and carboxylic acid, have been achieved easily. In order to obtain cellulose derivatives containing amino acid residues, the reaction of the isocyanate cellulose with various amino acids in organic solvents under nitrogen atmosphere were investigated. Table 1 shows the effects of reaction time on the reactions of the isocyanate cellulose with Gly and Ser at 30 Ž in DMSO. On the reaction of the isocyanate cellulose with Gly and Ser, the amount of incorporated amino acids reaches a saturation after 24 hrs. The time course of the conversion indicates that an amino group reacted with the isocyanate group is much more than that reacted with the other functional groups, because the rate of conversion at 6 48 hrs is very slow. Table 2 shows the effects of the amount of Gly on the reaction with the isocyanate cellulose. The amount of incorpo rated Gly does not significantly increase with the increasing amount used for the reaction. These results suggest the optimum reaction conditions on the synthesis of cellulose derivatives containing where, A is the initial concentration of metal ion in the solution (mmol/1), B is the residual concen- amino acid residues as isocyanate cellulose, 1.0 g; amino acid, 5.3 mmol; DMSO, 20 ml; reaction temperature, 30 Ž; reaction time, 24 hrs. Table 1. Effect of reaction time on the reaction of isocyanate cellulose with amino acids. *) Cellulose derivative containing amino acid. Reaction conditions: Isocyanate cellulose, 1.0 g; Amino acid, 5.3 mmol; DMSO, 20 ml; Reaction temperature, 30 Ž

3 (43) Vol. 41, No.6 (1985) T-237 Table 2. Effect of an amount of Glycine on the reaction with isocyanate cellulose. Reaction conditions: Isocyanate cellulose, 1.0 g; DMSO, 20 ml; Reaction time, 24 hr; Reaction temperature, 30 Ž The effects of solvents and substituent groups of amino acids on the reactions with the isocyanate cellulose were examined in DMSO, DMF and dioxane. In DMSO, the highest conversion of Gly and Glu. acid incorporation was achieved (Table 3). Gly content is mmol/cell-der.g and the conversion, 60%. Glu.acid is mmol/cell-der.g and the conversion, 26.9%. These results suggest that the solubility of amino acids in the three organic solvents has a decisive effect on the con version. The reactivities of the isocyanate cellulose with amino acids in DMSO are shown by the conversion rates: Cys (75.4%), Gly (60.0%), Met (56.1%), Ala (52.7%), Tyr (48.2%), Val (46.7%), Leu (42.3%), Glu (38.3%), Lys (36.2%), His (33.4%) and Glu. acid (26.9%). These results indicated that Cys and Met having a mercapto and a sulfhydryl group, respectively, are effective for the reaction with the isocyanate cellulose in DMSO and that the low conversions of Glu, Lys and His in DMSO are due to the hydrolysis of the iso cyanate group by some active functional groups followed by crosslinking through urea linkage. 2) Adsorption and desorption of metal ions by systems based on cellulose derivatives con taining amino acid The cellulose derivatives containing amino acid residues shown in Tables 4 9 were prepared by the reaction of isocyanate cellulose with amino acids in DMSO under nitrogen atmosphere. The effect of the kinds of amino acid residues bound to the cellulose derivatives on the adsorption of metal ions was studied in the aqueous solution of ions such as copper (II), zinc (II), iron (III), cadmium (II), chromium (III) and mercury (II) at various ph's. The ratio of COOH group of cellu lose derivatives bound to metal ion and the distribution coefficient [Kdl were also determined. The distribution coefficient was obtained by following equation. Table 3. The amounts of incorporated amino acid on the reaction of isocyanate cellulose with amino acids. Table 4 shows the adsorption value of copper (II) ion by the cellulose derivatives. Most of the cellulose derivatives adsorb copper (II) ion more than 80% at ph 7 in 50 ml of 60 ppm solution of copper (II) ion. The desorption of copper (II) ion were effected completely with 2N HCI. The cellulose derivatives containing Gly, Ala, Val, Leu, Glu, Lys and Cys are highly copper ion readsorptive at ph 7. The ratio of COOH group of the cellulose derivatives to bind copper (II) ion is 10 `48%. The distribution coefficient value of the cellulose derivative containing His is 11.3 ~102, which is the highest in all of the cellulose deriva tives. Table 5 shows that all of the cellulose derivatives have low adsorption values for 60 ppm solution of zinc (II) ion and the readsorption values are low after the desorption with 2N HCI. Table 6 shows that cellulose and cellulose deriva tives have high adsorption values for iron (III) ion and high readsorption values at ph 5. The Kd

4 values of cellulose, Val-cellulose and His-cellulose are especially higher than those of the other cellulose derivatives for 50 ml of 60 ppm solution of iron (III) ion. Iron (III) ion precipitated in the solution at ph's higher than 5. Table 7 shows that the cellulose derivatives containing Gly, Ser, Glu, Glu.acid, Cys and Met adsorb cadmium (II) ion about 50% of the 100 ppm solution. The desorp tion values of cadmium (II) ion for all of the cellulose derivatives are 100% with 2N HCl and the desorption of iron (III) ion is achieved com pletely with 4N HCI. Table 8 shows that adsorp tion values of chromium (III) ion by the cellulose derivatives are less than 50%. Although it is not listed in the tables, the ratio of COOH group to bind chromium (III) ion is about 10%, which is fairly lower than the ratio of other metal ions. The adsorption of chromium (III) ion were not Table 4. The adsorption values (%) of copper (II) ion by cellulose derivatives containing amino acid residues. Table 5. The adsorption values (%) of zinc (II) ion by cellulose derivatives containing amino acid residues.

5 (45) Vol. 41. No.6 (1985) T-239 completely effected-with 6N HCI. Table 9 shows that the cellulose derivative containing Cys can remove 90% of mercuric (II) ion from 50 ml of 200 ppm solution at ph 7. Its Kd is 1.6 ~103. In case of the cellulose derivatives containing Cys and Met, they showed a good removal of mercury (II) ion. This implies that mercapto and sulfhydryl groups are especially effective though the ratio of COOH group to bind mercury (II) ion is small. The desorption of mercury (II) ion can not be achieved with H2SO4. These results indicate that functional groups suitable for the adsorption of metal ions are amino, carboxyl, imidazol and sulfydryl groups. In conclusion, the present study reveals that the reactions of the isocyanate cellulose with various Table 6. The adsorption values (%) of iron (III) ion by cellulose derivatives containing amino acid residues. b) determined at ph 5 Table 7. The adsorption values (%) of cadmium (II) ion by cellulose derivatives contain ing amino acid residues. Table 8. The adsorption values (%) of chromium (III) ion by cellulose derivatives con taining amino acid residues. b) determined at ph 5

6 Table 9. The adsorption values (%) of mercury (II) ion by cellulose derivatives containing amino acid residues. amino acids in organic solvents under specified conditions give urea linkage in high conversion to result in cellulose derivatives containing Cys, Gly, Met, Ala and Tyr. All of the cellulose derivatives adsorb large quantities of copper (II) and iron (III) ions among various metal ions. Cys-cellulose can adsorb completely mercury (11) ion from the 200 ppm solution (50 ml) at ph 7. Suitable functional groups for the adsorption of metal ions by cellulose derivatives containing amino acid residues are amino, carboxyl, imidazole and sulfhydryl groups. The desorption of copper (II), zinc (II), cadmium (II) and iron (III) can be achieved by treating with 2N HCI or 4N HCl. References 1) L. F. Chen and G. T. Tsao, Biotech. and Bioeng., 19, 1463 (1977) 2) J. Augustin, L. Drobnica and P. Gemeiner, Carbohydr. Res., 53, 217 (1976) 3) T. Sato, K. Karatsu, H. Kitamura and Y. Ohno, Kobunshi Ronbunshu, 39, 699 (1982) 4) T. Sato, K. Karatsu, H. Kitamura and Y. Ohno, Sen-i Gakkaishi, 39, T-519 (1983) 5) K. Goldbach and K. Lieser, Anal. Chem., 311, 183 (1982) 6) W. Wegscheider and G. Knapp, Anal, Chem., 11, 79 (1981) 7) P. burba and G. Willmer, Talanta, 30, 381 (1983) 8) R. bulman, Starch, 35, 96 (1983) 9) T. Tashiro and Y. Shimura, J. Appl. Poly. Sci., 27, 747 (1982) 10) J. Kahovec and F. Svec, Polm. Bull., 9, 139 (1983) 11) K. Lieser and B. Gleitsmann, Fresenius Z. Anal. Chem., 314, 391 (1983)