Polycondensation of organic silicon compounds

Details Polycondensation of organic silicon compounds Polycondensation of organic silicon compounds

2000-11-22

2003-09-09

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S012000

Reexamination Certificate

active

06617411

ABSTRACT:

The invention relates to a process for polycondensation of organic silicon compounds in the presence of an enzyme.
Silicones and silicates are of industrial-scale importance. Silicates are employed, for example, as phase material in chromatography. There are numerous processes for their preparation. Processes leading to amorphous silicates, for example, start from orthosilicic acid which is condensed in aqueous solution with acid or base catalysis (A. F. Holleman, E. Wiberg, Lehrbuch der Anorganischen Chemie [Textbook of Inorganic Chemistry], Walter de Gruyter Verlag, Berlin N.Y. 1985, 91st-100th edition, pp. 757-764). Silicones can be prepared by condensation of silanols, silanediols and silanetriols (A. F. Holleman, E. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter Verlag, Berlin N.Y. 1983, 91st-100th edition, pp.786-788). In novel processes developed in the last few years it is possible to condense organic silicon compounds under mild conditions. Enzymes are employed as catalysts. The reactions can be carried out at from pH 6 to pH 8. In 1998 a suitable enzyme has been isolated for the first time from a marine sponge, as described in J. N. Cha, K. Shimizu, Y. Zhou, S. C. Christiansen, B. F. Chmelka, G. D. Stucky, D. E. Morse, Proc. Natl. Acad. Sci. USA 1999, 96, 361-365. The enzyme is composed of three subunits, the so-called silicateins. Extracting the enzyme is relatively costly. Besides polycondensation in buffer solution, the organic silicon compounds (EtO)
4
Si and (EtO)
3
SiPh have been converted directly using air-dried enzyme. Moreover, WO 00/35993 describes employing synthetic homopolymers composed of cysteine and block polypeptides composed of lysine and cysteine for polycondensation of silicon alkoxides, metal alkoxides and derivatives thereof into silicates, polysiloxanes and polymetaloxanes.
It is an object of the present invention to provide a further process for the polycondensation of organic silicon compounds, which can be carried out at from pH 6 to 8, and to find a suitable catalyst for this reaction.
The object is achieved by starting from the known process for the polycondensation of organic silicon compounds in solution at from pH 6 to 8 in the presence of an enzyme. The process of the invention comprises employing a lipase as the enzyme. This is surprising because lipases possess no structural similarity to previously employed enzymes such as silicateins.
In general, all lipases are suitable for the process of the invention; preferred are lipases from
Pseudomonas
species, particularly preferred are
Burkholderia plantarii
lipase (EC 3.1.1.3; SWISS-PROT: Q05489; L. G. J. Frenken, M. R. Egmond, A. M. Batenburg, J. W. Bos, C. Visser, C. T. Verrips, Appl. Environ. Microbiol. 1992, 58, 3787-3791),
Burkholderia cepacia
lipase A (EC 3.1.1.3; SWISS-PROT: P22088; S. Joergensen, K. W. Skov, B. Diderichsen, J. Bacteriol. 1991, 173, 559-567) and
Pseudomonas aeruginosa
lipase A (EC 3.1.1.3; SWISS-PROT: P26876; S. Wohlfarth, C. Hoesche, C. Strunk, U. K. Winkler, J. Gen. Microbiol. 1992, 138, 1325-1335), and very particularly preferred is
Burkholderia plantarii
lipase.
It is advantageous and possible to produce lipases on a large scale by fermentation processes. A bacterial lipase, for example, can be produced by fermentation of bacteria secreting the desired lipase in a nutrient medium containing yeast extract, soybean oil and usual additives such as mineral salts and trace elements and, where appropriate, buffer substances. After completion of the fermentation, the lipase may be removed from the bacterial cells and cell constituents, for example by centrifugation or filtration, and be purified by processes such as ion exchange chromatography, molecular sieve chromatography, hydrophobic chromatography and precipitation methods. Purification of the lipase is not necessary if the lipase is immobilized on carriers such as polyolefin particles and polyurethane foams after removal from the bacterial cells and cell constituents. Immobilization means that enzymes from anhydrous or aqueous solutions are bonded to, in particular, nonpolar matrices having a large surface area permanently and with retention of the catalytic activity. Immobilization reduces the loss in lipase during working-up and allows polycondensation of organic silicon compounds to be carried out even in organic solvents in which free lipase is insoluble. In addition, the polycondensation products may grow on the carrier, thus resulting in possible novel applications for producing components in microelectronics.
When employing polyurethane foams as carriers, the enzymes are immobilized on the carrier by reacting the enzymes with reactive groups on the surface of the polyurethane foam. The enzymes are covalently bonded to the surface. Such reactive groups may be NCO groups, epoxide groups, CO
2
H groups and/or phenolic OH groups which, where appropriate, were attached to the polyurethane foam surface only after polymerization.
When employing polyolefin particles as carriers, the bond between enzyme and carrier is based inter alia on hydrophobic interactions. Suitable polyolefins are homopolymers and copolymers composed of unsubstituted or substituted olefins such as ethylene, propylene, butadiene, butene, octene or styrene; preference is given to employing polypropylene as a carrier.
Lipases which are present in solutions obtained by fermentation of bacteria, fermenter solutions, are usually immobilized on polyolefin particles as follows: bacterial cells and cell constituents are removed from the fermenter solution, for example by centrifugation. The remaining solution is diluted with water and the polyolefin particles are contacted with this solution which contains the lipase. The contacting takes place, for example, by adding the polyolefin particles to the lipase-containing solution. When the lipase-containing solution is contacted with the polyolefin particles, the lipase is adsorbed onto the polyolefin particles. The polyolefin particles have a very high selectivity for lipases. Only the lipase and, where appropriate, its fragments are predominantly adsorbed onto the polyolefin particles. The proportion of other proteins adsorbed from the lipase-containing solution onto the polyolefin particles is normally below 2% by weight. The adsorption is thus also a step to purify the lipase from the other proteins and enzymes in the lipase-containing solution.
The particle size and the void fraction of the polyolefin particles is not critical. Preferred polyolefin particles have a particle size of from 100 &mgr;m to 2000 &mgr;m, particularly preferred polyolefin particles have a particle size of from 200 &mgr;m to 1000 &mgr;m. The void fraction of the polyolefin particles is preferably 40% to 80%, particularly preferably 60% to 70%, very particularly preferably 65%. The pore size of the polyolefin particles is preferably 0.01 &mgr;m to 1 &mgr;m, particularly preferably 0.05 to 0.5 &mgr;m.
In one embodiment of the invention, propylene carriers Accurel® from Akzo are employed as carriers having particle sizes of <400 &mgr;m (Accurel 1004), of from 400 to 1000 &mgr;m (Accurel 1001) and of >1000 &mgr;m (in pellet form); preference is given to employing Accurel 1004 and Accurel 1001.
The optimal duration of lipase immobilization on polyolefin particles depends on the lipase and on the type of polyolefin particles and can be determined by routine tests. Normally, the immobilization lasts for 10 min to 24 h, preferably 4 to 24 h, particularly preferably 4 to 6 h.
Normally, the immobilization takes place at from pH 4.0 to 8.8, preferably from 4.5 to 7.8, particularly preferably from 4.5 to 6.0.
The ionic strength, which may be determined by conductivity measurement, should normally be <0.5 M, preferably <0.3 M.
Immobilizing the lipase on the polyolefin particles is also called loading the polyolefin particles with the lipase. A preferred loading at which a maximum amount of lipase is adsorbed and a minimum amount of lipase remains in the solution is dependent on the type of

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