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Sci.Rep_Fukushima Univ.,Na67 (2003) 39

Adsorption of Organic Compounds byProteins and Synthetic Polypeptides

Hitoshi Kanazawa

Faculty of Education,Fukushima University,Kanayagawa_1,Fukushima 960-1296,Japan

Recieved April 16,2003

Synopsis

Adsorption of organic compounds by proteins and synthetic polypeptides was investigated. Each of the polypeptides gave its own adsorptivity of the organic compounds. The results suggested that the difference in the component amino acid residue in each adsorbent is an important factor to decide the adsorption of the compounds. This simple adsorption experiment is useful for the analysis of the molecular structure of the polymer as an adsorbent.

1. INTRODUCTION

In general,it is known that proteins such as hair and wool fiber can adsorb some odor substances. The adsorption of organic compounds on materials is a very important phenomenon in science or even in our life but the mechanism does not seem to be considered well. This study aimed to reveal the mechanism of the adsorption of usual organic compounds,dyes and amino acids,etc. by proteins. Several synthetic polypeptides with simple structure were prepared to discuss essentially the adsorption mechanism. The final aim of this study is to consider the desigT1of a material with an adsorption selectivity of organic compounds.

The adsorption of vapor of organic compounds by silk fibroin and synthetic polypeptides was investigated in this article. In addition, the adsorption of organic compounds contained in water by silk fibroin was examined.

2. EXPERIMENTAL

Fibroin powder (Fib micro crystals) was prepared by dissolving silk fibroin fiber with calcium chloride solution,dialyzing, concentrating, gelling, and freeze-drying. Fibroin- covered silica was prepared from fibroin solution and silica gel particles (diameter.5 ｵm). Powder silk fibroin (Fib) was prepared as micro crystals by the following successive

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40 Hitoshi Kanazawa:Adsorption of Organic Compounds by Proteins and Synthetic Polypeptides

processes; dissolving silk fibroin fiber in calcium chloride solution, dialyzing to water, concentrating,gelling,and freeze-drying.

Polypeptides were obtained by the synthesis of N;carboxy anhydrates (NCA) of amino acids in the solid state so that the number-average degree of polymerization was 200.1-3 Prepared polypeptides are as follows;poly(7,-benzyl-L-glutamate) (BLG in Fig.1), poly(β一benzyl_L_aspartate) (BLA in Fig.1),poly(glycine),poly(L-alanine),poly(L-valina),poly(L- leucine) and po]y(L_phenylalanine).

Adsorption of vapor of organic compounds:The polymer (proteins and pc]ypeptides)was exposed to vapor of organic compounds in a sealed glass vessel at mainly 25℃ and 40℃under a given vapor pressure. Adsorbed compounds by the adsorbent were extracted with ethyl acetate and the extract solution was analyzed by GC. The adsorption of compounds was examined by two methods;the adsorption from vapor mixture of several compounds and that from a vapor of single compound.

An aqueous solution or mixture of organic compounds was passed through a glass tube packed with fibroin and the solution passed through the column was analyzed by GC. A Shimadzu Ge l4 system (Shimadzu Co. Ltd.)was used for the GC analysis.

3. RESULTS AND DISCUSSION

1) Adsorption of vapor of organic compoundsFigure l gives the adsorption of vapor of eight kinds of organic compounds by seven

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Fig.1 Adsorption of each organic compound from their mixture by silk fibroin andsynthetic polypeptides. Adsorption was carried out for 24 h at 25℃.

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Sci。Rep.Fukushima Univ_,Na67 (2003) 41

kinds of synthetic polypeptides and silk fibroin.In this experiment, all of the compounds were adsorbed from their vapor mixture.

Therefor゙e,the adsorption of each compound should be affected by each vapor pressure. The compounds as adsorbents are arranged in the order that vapor pressure is high as follows; methanol,acetonitrile,dioxane;.p_xylene,anisole,decane and o-dichlorobenzene.Figure 1 indicates that the amount of compounds adsorbed by each material is very different from each other. It is remarkable that the order of high vapor pressure is not in accordance with the order of amount of adsorbed compounds.

It is apparent that the property of proteins or polypeptides which adsorb organic compounds depends on the molecular structure of the amino acid residues in an adsorbent, polymer. Polar compounds such as alcohol and acetonitrile seemed to be adsorbed well by the protein or polypeptides as compared with non-polar compounds such as xylene.

The experiment given in Fig.1 was carried out te sco the tendency of the adsorption property of various compounds by a rather simple method. In this experiment, the molecular interaction in the organic compounds should influence the results。 Thus,the adsorption experiment was carried out at a defined vapor pressure of a compound. The vessel for the adsorption was evacuated and vapor of a compound was introduced in lt. The vapor pressure was measured with a manometer.

Figure 2 gives the relation between adsorption of methanol and its vapor pressure in the

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Fig.2 Relation between vapor pressure and adsorbed amount in the adsorption ofmethanol by poly(L-alanine),poly(L-valline)and fibroin at 40℃.

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42 Hitoshi Kanazawa :Adsorption of Organic Compounds by Proteins and Synthetic Polypeptides

adsorption by poly(L-valine),poly(L-alanine) and silk fibroin. Fibroin showed a similar behavior with poly(L-alanine). This is explained by the high content of L_alanine residues (about 31 met.%). ・Figure3 gives the relation between adsorption of p_xylene arid its vapor pressure in the

adsorption by poly(glycine),poly(L-alanine),and poly(L_valine). Poly(L_valine) adsorbed more p-xylene than the other two polypeptides. Poly(L-valine)has larger hydrophobic side chain as compared with poly(L-alanine) and poly(glycine). The hydrophobic side chain should have an interaction between an hydrophobic compound,p_xylene. .

These results suggest that the adsorption was dependent on the interaction between the organic compounds (adsorbates) and the side chain of amino acid residues in the polypeptides (adsorbents). The formation of peptide bonds and hydrogen bonds between the hydroxyl group of the adsorbent and the polypeptide is also important.N

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Fig.3 Relation between vapor pressure and adsorbed amount irl the adsorption ofp-xylene by poly(glycine).,.poly(L-alanine),poly(L-valline) and fibroin at 40℃.

2) Adsorption of organic compounds in liquids by fibroinWe found that fibroin and synthetic pc]ypeptides selectively adsorb organic compounds

that are scarcely contained in water_ Figure 4 gives a plot of the flow volume of a water solution of organic compounds against the amount of a compound adsorbed by fibroin. The line represents the amount of organic compounds flowed at each flow volume. When all amount of a compound is adsorbed by fibroin at a given flow volume,the adsorbed

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Sci.Rep.Fukushima Univ.,Na67 (2003) 43

amount should be plotted on the line. As each of the adsorption amount is close to the straight line until the flow volume 7m1, the compounds in water is considered to be adsorbed well by fibroin. This result indicates that fibroin is very effective for the purification of water containing organic compounds.

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Fig.4 Adsorption of organiccompounds in water by silk fibroin. Straight 「me givesthe amount of each compound contained in each flow volume.

4. CONCLUSION

The adsorptivity of vapor of organic compounds by polypeptides or proteins was dependent on the molecular structure of the adsorbent.; which suggests that the investigation of the adsorption gives a useful information for the molecular structure of the adsorbent.

Organic compounds contaminated in water was removed by the adsorption by fibroin. This should give a useful method to clean water. We should examine if this property is specific only for fibroin or not by further investigations.

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44 Hitoshi Kana2awa :Adsorption of Organic Compounds by Proteins and Synthetic Polypeptides

REFERENCES

1)H.Kanazawa,Polymer,33;pp.2557_2566(1992).2)H。Kanazawa,Acta Crysta11ographica Sec.c,c56f pp.469_470 (2000).3)H.Kana2awa and J.Magoshi,Acta Crystal1ographica Sec.c c59 pp.323_327(2003).4) Takashima, Shogenji and Nemoto, UT. Vickerstaff Senshoku no Butsuri Kagaku'', p.88;Maruzen (1957);Original:T.Vickerstaff,''The Physical Chemistry of Dyeing".Copyright;1954,by I.C.I.Great Britain,published by Oliver and Bord,London.

5)H。Kanazawa,52th Annual Conference of Home Ecomomics Japan,Tokyo,Preprint,52,p.218(2000).

6) H.Kana2;awa,2000 the Annual Conference of the Society of Fiber Science, Kyoto Japan,Preprint,55,No.1,p.152,and p.160 (2000)。

7)H.Kanazawa,44th Annual Conference of Home Economics;Tohoku_Hokkaido,Japan,Preprintp.29 (2000).

8)H.Kanazawa,2001 the Annual Conference of the Society of Fiber Science,Hamamatsu Japan,Preprint 56,No.1,p。118 (2001).