Mercury Uptake by Polyamine-Carbohydrates M. S. Masri and Mendel Friedman’ Western Regional Research Laboratory, Agricultural Research Service, USDA, Berkeley, Calif. 94710
Chitosan (deacetylated chitin), other polyamines derived from cellulose, polyamines derived from dialdehyde starch, and poly(amin0styrene) bind mercury in large amounts from water solutions of HgC12. In contrast, unmodified starch and cellulose adsorb very little mercury, while chitin (with acetylamino groups) binds much less than chitosan. In several instances the adsorbents bound more than one atom of mercury per nitrogen and more than their own weight of mercury. These results show that amino groups in natural and synthetic polymers are effective binding sites for mercuric chloride and point first to the possible utility of such polymers as adsorbents for mercury, and second, to the possible role of naturally occurring polyamine polymers in the distribution of mercury in the environment.
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ne way to immobilize an enzyme on a water-insoluble matrix is to couple the protein to a poly(diazonium salt) derived from a water-insoluble resin such as poly(paminostyrene) or p-amino-benzylcellulose (Goldstein et al., 1970). Recently, Goldstein et al. (1970) described a new, easily prepared, diazotizable carrier matrix made by condensing dialdehyde starch (DAS) with the diamine p,p’-diaminodiphenylmethane (methylene dianiline, MDA) to form a poly (Schiff’s base), which they reduced with NaBH.,. The extent of cross-linking of the polymeric chains of the DAS by the bifunctional diamine and the extent of its one-point attachment (thus leaving one amino group of the diamine free) depend on the proportion of MDA in the reaction mixture. Thus, resins with as much as 48 MDA were prepared, equivalent to about one molecule of MDA per hexose residue. A structure for the resin was proposed (Goldstein et al., 1970). The high nitrogen content of this insoluble resin prompted us to test its ability to remove mercury salts from aqueous solutions. Various agricultural products are being evaluated in this laboratory as possible practical means to recover mercury from wastes and contaminated water (Friedman and Waiss, 1972; Friedman et al., 1971; Webb, 1966). In this paper we compare mercury binding by the DAS derivatives with binding by several natural and modified carbohydrates, by poly(amin0-styrene), and by wool. Results in Table I show the high affinity and capacity of DAS-MDA resin for binding mercury from aqueous solutions of HgCI2. Under some conditions it takes up more than its own weight of mercury. A similar DAS resin, prepared by substituting p,p’-phenylenediamine (PDA) for MDA, behaved similarly. Both DAS-MDA and DAS-PDA resins are more effective in binding mercury from acid than from neutral solution; this pH dependence is minimized if the Schiff‘s base resins are reduced by NaBH4; (RCH=NR’ to RCH,NHR’). In contrast to these diamine-modified dialdehyde starch resins, unmodified potato starch or DAS, itself, adsorb very little mercury under the test conditions. Results are also included in Table I for underivatized celluloses (essentially nil
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To whom correspondence should be addressed.
uptake), ion-exchange celluloses (moderate uptake) and wool fiber for comparison. The high uptake by the chitosan (deacetylated chitin), point to the efficacy of the free amino groups for mercury binding. The binding of Hg to chitosan is about five times higher than to chitin, which is a linear polymer of N-acetyl-2-deoxy-2-amino glucose with a 1,4 P-linkage between the monomer units as in cellulose. Although we do not know the structure of the mercury resin complexes, data in Table I show that the ratio of gramatom Hg bound/gram-atom nitrogen ranges from 0.18 to 2.26. (The ratios were calculated for the experiments at the higher initial level of 40 mg Hg/ml and the experimental nitrogen values of the resins.) These results suggest that the extent of binding is related to the nature of the substituent on nitrogen; evidently, nitrogen tied by acetylation or as a Schiff‘s base is a less effective binding site than primary or secondary amino nitrogen. Nitrogen combined as a Schiff’s base is less effective in “water” than the reduced (secondary amine) form, although equally effective in strong acid. The greater binding capacity of the reduced DAS resins is presumably the result of the enhanced basicity of the nitrogen atom in the reduced form. We used mercuric chloride for most of this work. However, a few experiments were done with the more toxic and less water-soluble methyl mercuric chloride. Chitosan, poly(p-aminostyrene), and DAS-MDA were equilibrated 24 hr at 25°C with solutions containing 4 mg of methyl mercuric chloride per ml in aqueous methanol (1 :1 v/v). The liquidpolymer ratio was 25 ml/gram. Polymer samples were recovered by filtration, then rinsed with methanol and airdried. Weighed samples were then oxidized with K M n 0 4 in sulfuric acid, and mercury contents determined by atomic absorption. Observed uptakes were 28, 36, and 26 mg of Hg per gram of chitosan, poly(p-aminostyrene), and DAS-MDA, respectively, corresponding to 35, 45, and 32 of the amount of Hg initially present. It appears that these polymers bind about one third as much mercury from methyl mercuric chloride in 1 :1 methanol-water as from aqueous mercuric chloride under similar conditions. For wool this ratio is about one fifth (Friedman et al., 1971). In summary, these results suggest that polyamino derivatives of carbohydrates may be useful to remove and recover mercury compounds from water. They suggest also that free amino groups and possibly other basic groups in proteins and other biological materials are important in the natural accumulation and distribution of mercury in the biosphere. Finally, the natural occurrence of mucopolysaccharides in the N-acetylated or N-sulfated forms-e.g., chitin, chondroitin, hyaluronic acid, heparin-may provide a mechanism for the exclusion of nitrogen-metal complex formation in certain biological structures and functions.
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Experimental Materials. Dialdehyde starch, a 100% periodate-oxidized preparation was originally obtained from the Northern Regional Research Laboratory, Peoria, Ill. Methylenedianiline was prepared by condensing aniline and formaldehyde in hydrochloric acid according to Scanlon (1935). p-Phenylenediamine was from Eastman Kodak; the ion-exchange celluloses (aminoethylcellulose, N = 0.4 ; DEAE-CellUlOSe, Volume 6, Number 8, August 1972 745
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Table I. Mercury Uptake by Carbohydrates and Derivativesa Aqueous medium HgCll solution Hg removed Initial Hg Initial concn, Solid polymer tested ml/g polymer mg Hg/ml mg Hg/g polymer in medium, Cellulose, starch, or DAS 25 4 5-12 5-12 DAS-MDA 17 4 64 94 DAS-MDA 25 40 280 28 DAS-MDA (0.1N HC1) 25 40 970 97 DAS-MDA ( 0 , l N HCl) 50 40 1,050 52 DAS-MDA, reduced 25 40 617 62 DAS-MDA, reduced (0.1N HCl) 25 40 830 83 DAS-PDA 25 4 96 96 DAS-PDA 30 40 705 59 DAS-PDA (0.1N HC1) 30 40 999 83 DAS-PDA, reduced 33 40 1,033 78 DAS-PDA, reduced (0.1N HC1) 33 40 993 75 DEAE-CellUlOSe , 25 40 290 29 Aminoethyl cellulose 25 40 55 5 25 40 128 13 Aminoethyl cellulose (0.1N HC1) p-Aminobenzyl cellulose 25 40 90 9 120 12 p-Aminobenzyl cellulose (0.1N HC1) 25 40 Chitin 25 4 33 33 Chitin 25 40 175 17 Chitosan 25 4 100 100 Chitosan 25 40 948 95 Chitosan 50 40 1,425 71 Poly(p-aminostyrene) 25 4 100 100 Poly(p-aminostyrene) 25 40 912 91 50 40 1,450 72 Poly(p-aminostyrene) Wool fiber 50 4 116 58 Wool fiber 50 40 510 25
g-atom Hg/ g-atom N
0.23 0.80 0.86 0.55 0.69 0.46 0.65 0.68 0.65 2.26 0.98 2.25 1.58 2.11 0.17 0.76 1.15 0.54 0.86 b
a Unmodified celluloses used were absorbent cotton and chromatography grade cellulose powder; starch was purified from potato, DAS was the same used to prepare DAS-MDA and DAS-PDA resins. Mercury concentrations or uptake are on basis of Hg, not HgClz; thus 4 mg Hg/ml refers to 0.02kf H g C h The medium was prepared by dissolving HgCh in H20 or, when indicated, in 0.1N HCl (aqueous). Usually tests were performed in both media (HzO or 0.1N HC1) but results in 0.1N HCl are listed only when they appeared different from those in HzO. * -3 g-atom Hg/g-atom N of basic amino acid residues (arginine, histidine, lysine); 0.75 g-atom Hg/g-atom N of lysine.
N = 0.9%; p-aminobenzylcellulose, N = 0 . 4 x ) from Biorad Laboratories, Richmond, Calif.; poly(p-aminostyrene) from Polysciences Inc., Rydal, Pa. ; chitin (shellfish) from Nutritional Biochemical Co., Cleveland, Ohio ; chitosan by alkali deacetylation of chitin (Peniston and Johnson, 1970). Dialdehyde Starch-Methylenedianiline (DAS-MDA) Resin. This was prepared according to Goldstein et al. (1970) using 10 grams DAS and 30 grams of MDA; after about two days at room temperature with stirring, the precipitated dark yellow orange resin was collected, filtered, and washed with water and methanol (yield about 18 grams; N = 8.46%). This resin was tested for mercury uptake both as prepared and after reduction with sodium borohydride. Dialdehyde Starch-p-phenylenediamine (DAS-PDA) Resin, This was prepared in a similar manner as DAS-MDA but with 5 grams DAS and 10 grams PDA in the carbonate buffermethanol. After about three days of stirring at room temperature, the purple-black precipitate was collected, washed, and dried (yield 4.5 grams; N = 10.7). This resin was similarly tested for mercury uptake as prepared and after reduction with sodium borohydride. Measurement of Mercury Uptake. This was done by equilibrating a weighed sample of adsorbent in a measured volume of HgClz solution of known initial concentration for one day at room temperature (25°C) with a mechanical shaker. The concentration in the mother liquor was then measured. The difference between this and the initial concentration was used to calculate the amount of mercury taken 746 Environmental Science & Technology
up by the solid. Mercury concentrations were determined by atomic absorption using a Perkin-Elmer Model 303 spectrometer with an acetyleneair burner. In most tests showing high mercury uptake, the measurements were corroborated by weighing-Le., compatible weight increases were observed with polymers that were equilibrated with HgClz solutions, then rinsed with HzO followed by methanol, and air-dried. Acknowledgment Thanks are given to W. H. Ward for constructive contributions to this manuscript. Literature Cited Friedman, M., Waiss, A. C., Jr., ENVIRON. SCI. TECHNOL., 6 (5), 457 (1972). Friedman, M., Harrison, C.,S., Ward, W. H., Lundgren, H. P.. Presented at the Division of Water, Air, and Waste Chemistry, 161st National Meeting, ACS, Los Angeles, Calif., March 28-April 2, 1971, Abstracts, p WATR 052; Preprints, 11 (l), 109-14 (1971). Goldstein, L., Pecht, M., Blumberg, S., Atlas, D., Levin, Y., Biochemistry, 9, 2322 (1970). Peniston, Q. P., Johnson, E, L., U.S. Patent 3,533,940 (1970). Scanlon, J. T., J. Amer. Chem. Soc., 57, 887 (1935). Webb, J. L., “Enzyme and Metabolic Inhibitors,” Vol 2, Chap. 7, p 729, Academic Press, New York, N.Y., 1966. Receiced for reciew January 12, 1972. Accepted May 24, 1972. Reference to a company or product name does not imply approcal or recommendation of the product by the U S .Department o f Agriculture to the exclusion of others that may be wituble.
