USE OF HYDROPHOBINS AS ADDITIVES IN THE CRYSTALLIZATION OF SOLIDS
Use of hydrophobins as auxiliaries in the crystallization of solids, in particular the use for producing gypsum from an aqueous phase.
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The present invention concerns to the use of hydrophobins as auxiliaries in the crystallization of solids, in particular the use for producing gypsum from an aqueous phase.
The properties of finely divided solids are very substantially determined by the size and habit of the crystallites making up the solid. Size and habit substantially influence the rheological properties of solid suspensions, the ease of removal of the solids from aqueous suspensions, for example by filtration, the handling of the dried products and the properties of the solids themselves. An example is the color strength or the dispersibility of color pigments, which substantially depend on the size and habit of the individual crystals.
It is known in principle to use suitable inorganic or organic additives to influence the size and habit of the crystallites forming in the course of precipitation or crystallization from solutions. Reference may be made here for example to “Crystallization and Precipitation—4.4 Crystal Habit Modification” in Ullmann's Encyclopedia of Industrial Chemistry, 7th Edition 2006, Electronic Release, Wiley-VCH, Weinheim, New York 2006.
Influencing the size and habit of the crystallites of gypsum is a much studied process (see for example G. A. Bertoldi, Zement-Kalk-Gips, Nr. 12, 1978). Aqueous suspensions of gypsum are these days generated in large volumes in flue gas desulfurization. For further use, the gypsum has to be separated from the aqueous phase. Gypsum typically crystallizes in the form of needles. U.S. Pat. No. 4,183,908 and U.S. Pat. No. 5,246,677 discloses processes for crystallizing gypsum in the form of compact crystals by addition of polyphosphates, organic phosphates or phosphonates to facilitate the removal of the gypsum from the aqueous phase.
Hydrophobins are small proteins of about 100 to 150 amino acids that occur in filamentous fungi, for example Schizophyllum commune. They generally have 8 cysteine units. Hydrophobins can be isolated from natural sources, but they can also be obtained by means of genetic-engineering processes as disclosed for example by
There is a prior art proposing the use of hydrophobins for various applications.
WO 96/41882 proposes the use of hydrophobins as emulgators, thickeners or surfactants, for giving hydrophilic properties to hydrophobic surfaces, for improving water-resistance of hydrophilic substrates, for preparing oil-in-water emulsions or water-in-oil emulsions. Further proposals include pharmaceutical applications such as the preparation of ointments or creams and also cosmetic applications such as skin protection or the production of shampoos or conditioners.
EP 1 252 516 discloses the coating of various substrates with a hydrophobin-containing solution at a temperature of 30 to 80° C.
Further proposals include for example the use as a demulsifier (WO 2006/103251), as an evaporation retarder (WO 2006/128877) or as a soil inhibitor (WO 2006/103215).
The use of hydrophobins as crystallization auxiliaries has hitherto not been disclosed.
It is an object of the present invention to provide novel auxiliaries for influencing the crystallization.
We have found that this object is achieved by the use of hydrophobins as auxiliaries in the crystallization of solids.
A further embodiment of the present invention is a process for producing a solid by crystallizing from an aqueous phase and separating the solid formed from the aqueous phase wherein said aqueous phase has added to it, in an amount of 0.001% to 1% by weight based on the total amount of said aqueous phase, at least one auxiliary soluble in said aqueous phase, at least one of said auxiliaries comprising a hydrophobin.
In one preferred embodiment of the present invention, the process in question is a process for producing gypsum. It is particularly preferable for the process in question to be a step in a flue gas desulfurization process.
A detailed description of the present invention follows:
The term “hydrophobins” as used herein shall hereinbelow refer to polypeptides of the general structural formula (I)
Xn—C1—X1-50—C2—X0-5—C3—X1-100—C4—X1-100—C5—X1-50—C6—X0-5—C7—X1-50—C8—Xm (I)
where X may be any of the 20 naturally occurring amino acids (Phe, Leu, Ser, Tyr, Cys, Trp, Pro, His, Gln, Arg, Ile, Met, Thr, Asn, Lys, Val, Ala, Asp, Glu, Gly). Each X may be the same or different. The indices next to X indicate in each case the number of amino acids, C represents cysteine, alanine, serine, glycine, methionine or threonine subject to the proviso that at least four of the residues identified by C are cysteine, and the indices n and m are independently natural numbers in the range from 0 to 500 and preferably in the range from 15 to 300.
The polypeptides of formula (I) are further characterized by the property (after coating of a glass surface) of increasing the contact angle of a drop of water by at least 20°, preferably at least 25° and more preferably at least 30°, compared with the contact angle formed by a drop of water of the same size with the uncoated glass surface, each measurement being carried out at room temperature.
The amino acids denoted C1 to C8 are preferably cysteines; but they may also be replaced by other amino acids of similar bulk, preferably by alanine, serine, threonine, methionine or glycine. However, at least four, preferably at least 5, more preferably at least 6 and especially at least 7 of the C1 to C8 positions shall consist of cysteines. Cysteines in proteins used according to the present invention may be present in reduced form or form disulfide bridges with one another. Particular preference is given to intramolecular formation of C-C bridges, in particular that involving at least one, preferably 2, more preferably 3 and most preferably 4 intramolecular disulfide bridges. In the case of the above-described exchange of cysteines for amino acids of similar bulk, it is advantageous for such C-positions to be involved in a pairwise exchange as are able to form intramolecular disulfide bridges with each other.
When cysteines, serines, alanines, glycines, methionines or threonines are used in the positions designated X, the numbering of the individual C-positions in the general formulae may change accordingly.
Preference for embodying the present invention is given to using hydrophobins of the general formula (II)
Xn—C1—X3-25—C2—X5-50—C4—X2-35—C5—X2-15—C8—X0-2—C7—X3-35—C8—Xm (II)
where X, C and the indices next to X and C are each as defined above, the indices n and m represent numbers in the range from 0 to 350 and preferably from 15 to 300, and the proteins are further distinguished by the abovementioned contact angle change, and at least 6 of the residues denoted C comprise cysteine. It is particularly preferable for all the C residues to comprise cysteine.
Particular preference is given to using hydrophobins of the general formula (III)
Xn—C1—X5-9—C2—C3—X11-39—C4—X2-23—C8—X5-9—C6—C7—X6-18—C8—Xm (III)
where X, C and the indices next to X are each as defined above, the indices n and m represent numbers in the range from 0 to 200, the proteins are further distinguished by the abovementioned contact angle change and furthermore at least six of the residues denoted C are cysteine. It is particularly preferable for all residues denoted C to be cysteine.
The residues Xn and Xm may be peptide sequences which may be naturally linked to a hydrophobin. However, either or both of the residues Xn and X. may be peptide sequences which are not naturally linked to a hydrophobin. This also includes Xm, and/or Xm residues in which a peptide sequence naturally occurring in a hydrophobin is extended by a peptide sequence not naturally occurring in a hydrophobin.
When Xn and/or Xm are peptide sequences which are not naturally linked to hydrophobins, the length of such sequences is generally at least 20 amino acids, preferably at least 35 amino acids. These may be sequences of from 20 to 500, preferably 30 to 400 and particularly preferably 35 to 100 amino acids, for example. A residue of this kind, which is not naturally linked to a hydrophobin, will also be referred to as a fusion partner hereinbelow. This is intended to articulate the fact that the proteins consist of at least one hydrophobin portion and a fusion partner portion which do not occur together in this form in nature. Fusion hydrophobins composed of a fusion partner and a hydrophobin portion are disclosed for example in WO 2006/082251, WO 2006/082253 and WO 2006/131564.
The fusion partner portion may be selected from a multiplicity of proteins. It is possible for only one fusion partner to be linked to the hydrophobin portion or it is only possible for a plurality of fusion partners to be linked to one hydrophobin portion, for example to the amino terminus (Xn.) and to the carboxy terminus (Xm) of the hydrophobin portion. But it is also possible, for example, to link two fusion partners to one position (Xn or Xm) of the protein according to the present invention.
Particularly suitable fusion partners are proteins which occur naturally in microorganisms, in particular in E. coli or Bacillus subtilis. Examples of such fusion partners are the sequences yaad (SEQ ID NO: 16 in WO 2006/082251), yaae (SEQ ID NO: 18 in WO 2006/082251) and thioredoxin. Also highly suitable are fragments or derivatives of the aforementioned sequences which comprise only a portion, for example 70% to 99%, preferably 5% to 50% and more preferably 10% to 40%, of said sequences, or in which individual amino acids or nucleotides have been altered compared with the sequence mentioned, the percentages each being based on the number of amino acids.
In a further preferred embodiment, the fusion hydrophobin has not only the fusion partner mentioned but also, as one of the groups Xn or Xmor as a terminal constituent of such a group, an “affinity domain” in the form of an affinity tag/tail. Affinity tags or tails, as will be known in principle, comprise anchor groups which can interact with certain complementary groups and can serve to facilitate workup and purification of the proteins. Examples of such affinity domains comprise (His)k, (Arg)k, (Asp)k, (Phe)k or (Cys)k groups, where k is generally a natural number from 1 to 10. A (His)k group may be preferable, in which case k is from 4 to 6. The Xn and/or Xm group may consist exclusively of such an affinity domain, or else an Xn or Xm residue which is naturally linked or not naturally linked to a hydrophobin is extended by a terminally disposed affinity domain.
The proteins used according to the present invention as hydrophobins or derivatives thereof may additionally be modified in their polypeptide sequence, for example by glycosilation, acetylation or else by chemical crosslinking, for example with glutaraldehyde.
One property of the hydrophobins used according to the present invention, or of their derivatives, is the change in surface properties when the surfaces are coated with the proteins. The change in surface properties can be determined experimentally, for example, by measuring the contact angle of a drop of water before and after coating of the surface with the protein and determining the difference between the two measurements.
A person skilled in the art will know in principle how to perform contact angle measurements. The measurements relate to room temperature and water droplets of 5 I and the use of glass plates as substrate. The precise experimental conditions for a method suitable by way of example measuring the contact angle are described in the experimental portion. Under the conditions mentioned there, the fusion proteins used according to the present invention have the property of increasing the contact angle by at least 20°, preferably at least 25° and particularly preferably at least 30° in each case compared with the contact angle of an identically sized water droplet with the uncoated glass surface.
Particularly preferred hydrophobins for embodying the present invention are the hydrophobins of the type dewA, rodA, hypA, hypB, sc3, basf1, basf2. These hydrophobins including their sequences are disclosed for example in WO 2006/82251. Unless otherwise stated, the sequences referred to hereinbelow relate to the sequences disclosed in WO 2006/82251. An overview table featuring the SEQ-ID numbers is to be found in WO 2006/82251 at page 20.
Particularly suitable according to the present invention are the fusion proteins yaad-Xa-dewA-his (SEQ ID NO: 20), yaad-Xa-rodA-his (SEQ ID NO: 22) or yaad-Xa-basfl-his (SEQ ID NO: 24) having the polypeptide sequences placed between parentheses and also the nucleic acid sequences which code therefor, especially the sequences according to SEQ ID NO: 19, 21, 23. It may be particularly preferable to use yaad-Xa-dewA-his (SEQ ID NO: 20). Similarly, proteins which, proceeding from the polypeptide sequences shown in SEQ ID NO. 20, 22 or 24, result through exchange, insertion or deletion of at least one, up to 10, preferably 5 and more preferably 5% of all amino acids and which still have the biological property of the starting proteins to an extent of at least 50% are particularly preferred embodiments. A biological property of the proteins is herein to be understood as meaning the already described change in the contact angle by at least 20°.
Derivatives particularly suitable for embodying the present invention are derivatives derived from yaad-Xa-dewA-his (SEQ ID NO: 20), yaad-Xa-rodA-his (SEQ ID NO: 22) or yaad-Xa-basfl-his (SEQ ID NO: 24) by truncating the yaad fusion partner. Instead of the complete yaad fusion partner (SEQ ID NO: 16) having 294 amino acids, it may be advantageous to use a truncated yaad residue. However, the truncated residue should comprise at least 20, preferably at least 35 amino acids. For example, a truncated residue having 20 to 293, preferably 25 to 250, more preferably 35 to 150 and for example 35 to 100 amino acids can be used. One example of such a protein is yaad40-Xa-dewA-his (SEQ ID NO: 26 in PCT/EP2006/064720), which has a yaad residue truncated to 40 amino acids.
A cleavage site between the hydrophobin and the fusion partner or partners can be utilized to detach the fusion partner and to release the pure hydrophobin in underivatized form (for example by BrCN cleavage at methionine, factor Xa cleavage, enterokinase cleavage, thrombin cleavage, TEV cleavage, etc).
The hydrophobins used according to the present invention as a crystallization auxiliary can be prepared chemically by known methods of peptide synthesis, for example by Merrifield solid-phase synthesis.
Naturally occurring hydrophobins can be isolated from natural sources by means of suitable methods. Reference may be made by way of example to Wösten et al., Eur. J Cell Bio. 63, 122-129 (1994) or WO 96/41882.
A genetic-engineering production process for hydrophobins without fusion partners from Talaromyces thermophllus is described by US 2006/0040349.
Fusion proteins may preferably be prepared by genetic-engineering processes wherein a nucleic acid sequence coding for the fusion partner and a nucleic acid sequence coding for the hydrophobin portion, in particular a DNA sequence, are combined such that the desired protein is generated in a host organism as a result of gene expression of the combined nucleic acid sequence. Such a production process is disclosed for example by WO 2006/082251 or WO 2006/082253. The fusion partners greatly facilitate the production of the hydrophobins. Fusion hydrophobins are produced in the genetic-engineering processes in distinctly better yields than hydrophobins without fusion partners.
The fusion hydrophobins produced by the genetic engineering method from the host organisms can be worked up in a manner known in principle and be purified by means of known chromatographic methods.
One preferred embodiment may utilize the simplified workup and purification process disclosed in WO 2006/082253 at pages 11/12. To this end, the fermented cells are initially separated from the fermentation broth, disrupted and the cell debris separated from the inclusion bodies. The latter may advantageously be done by centrifugation. Finally, the inclusion bodies can be disrupted in a manner known in principle, for example by means of acids, bases and/or detergents, to release the fusion hydrophobins. The inclusion bodies with the fusion hydrophobins used according to the present invention can generally be completely dissolved within about 1 h even when using 0.1 M NaOH.
The solutions obtained can be used without further purification to embody this invention. The fusion hydrophobins, however, can also be isolated from the solutions as a solid. It may be preferable to isolate by means of spray drying, as described in WO 2006/082253 at page 12. The products obtained by the simplified workup and purification process generally comprise about 80% to 90% by weight of proteins as well as remnants of cell debris. The amount in terms of fusion hydrophobins generally ranges from 30% to 80% by weight, based on the amount of all the proteins, depending on the fusion construct and the fermentation conditions.
The isolated products comprising fusion hydrophobins can be stored as solids and for use be dissolved in the particular desired media.
The fusion hydrophobins can be used as such or also after cleavage and removal of the fusion partner as “pure” hydrophobins for carrying out this invention. A cleavage is undertaken advantageously following isolation of the inclusion bodies and their dissolution.
In accordance with the present invention, the hydrophobins are used as auxiliaries in the crystallization of solids by effecting the crystallization in the presence of hydrophobins.
One preferred embodiment of the present invention comprises a crystallization of solids from liquid phases. The liquid phases comprise one or more solvents, dissolved solid and/or starting materials for their production, the hydrophobins and also optionally further components, for example further auxiliary materials. The choice of solvent or solvent mixture is not restricted in principle, provided the solids to be crystallized and the hydrophobins have sufficient solubility therein. A person skilled in the art will make suitable choice depending on the solid to be crystallized.
The liquid phases preferably comprise aqueous phases. The term “aqueous phase” is to be understood as meaning that the solvents used comprise at least 50% by weight of water, based on the total amount of all solvents used. The water content is preferably at least 70% by weight and more preferably at least 90% by weight. Possible cosolvents include water-miscible solvents, for example alcohols such as methanol, ethanol or propanol. It is very particularly preferred for the solvent to comprise exclusively water.
The pH of the aqueous phase can be chosen by one skilled in the art according to the identity of the solid to be crystallized and according to the properties desired for the solid. According to the present invention, the hydrophobins, preferably fusion hydrophobins can advantageously be used at a pH≧4, in particular 4 to 13. The pH range is preferably from 5 to 13, more preferably from 6 to 12 and most preferably from 7 to 11.
The amount of the hydrophobins to be used can be chosen by one skilled in the art according to the identity of the solid to be crystallized and according to the properties desired for the solid. In general an amount of less than 1% by weight based on the sum total of all the constituents of the aqueous phase will be found advantageous. The hydrophobins may preferably be used in an amount of 0.001% by weight to 1% by weight, more preferably 0.001% to 0.2% by weight.
All manner of crystallization processes from liquid phases are possible in principle. One possibility for example is a crystallization process wherein a saturated solution of the solid is used and the crystallization of the solid is induced by evaporating the solvent, cooling or admixing a further solvent in which the solid is not soluble. Another possibility is a reactive precipitation wherein the solid is only formed in the aqueous phase as a result of the reaction of soluble components with each other.
One particularly preferred embodiment of the present invention utilizes the abovementioned fusion hydrophobins. For example, yaad-Xa-dewA-his (SEQ ID NO: 20) can be used and also, in particular, proteins having a truncated yaad residue, for example yaad40-Xa-dewA-his. It is advantageous to use the products obtained by the simplified purification process described above.
The hydrophobins are useful as auxiliaries for crystallizing both inorganic and organic solids from liquid phases. The hydrophobins are particularly useful as auxiliaries for crystallizing gypsum (CaSO4*2H2O). instead of acicular crystallites, more compact crystallites having a distinctly smaller length/thickness ratio are obtained which are easier to separate from the aqueous phase.
The hydrophobins are further very useful for crystallizing calcium carbonate.
In one preferred embodiment of the present invention, the hydrophobins can be used in a process for producing solids by crystallizing from an aqueous phase and removing the solid formed from the aqueous phase. The process in question may particularly preferably be a process for removal of gypsum.
The step of crystallizing and preferred conditions were described above. The solids, preferably the gypsum, can be removed by methods known to one skilled in the art, for example by filtration or by a combination of various measures to separate liquids from solids. After separation, the moist solid can be dried and further processed.
The process of the present invention may particularly comprise a step of a flue gas desulfurization process. In a flue gas desulfurization process, a first stage comprises gaseous SO2 present in the flue gas being reacted in a washers known to one skilled in the art with an aqueous CaCO3 suspension to form CaSO3 which is oxidized with O2 to form CaSO4, which crystallizes out as CaSO4*2H2O. Thus, gypsum is formed continuously in the aqueous phase by reaction. To control the crystal form, the hydrophobins are added to the process water in the above-stated concentrations.
Flue gas desulfurization processes are known to those skilled in the art. The reaction of SO2 and CaCO3 may be carried out coutercurrently for example. The gypsum crystals formed can initially be separated off, as a concentrated gypsum suspension, in a hydrocyclone and then be recovered as a solid by filtration, washing and drying. For further details reference may be made to “Calcium Sulfate—3.2 Flue Gas Desulphokation (FOG) Gypsum” in Ullmann's Encyclopedia of Industrial Chemistry, 7th Edition 2006, Electronic Release, Wiley-VCH, Weinheim, New York 2006, and also the references cited therein. The gypsum formed can subsequently be burned (anhydride) and be used for example in a known manner in the building materials industry.
The examples which follow illustrate the invention:
Providing the HydrophobinsThe examples utilized a fusion hydrophobin with the complete fusion partner yaad (yaad-Xa-dewA-his; hereinafter referred to as hydrophobin A) and also a fusion hydrophobin having a fusion partner truncated to 40 amino acids, yaad40-Xa-dewA-his (hydrophobin B). They were prepared as per the procedure described in WO 2006/082253.
The products were worked up by the simplified purification process of Example 9 of WO 2006/82253 and spray dried according to Example 10 of the same reference. The total protein content of the dried products obtained was in each case about 70% to 95% by weight, and the hydrophobin content was about 40% to 90% by weight based on the total protein content. The products were used as such for the experiments.
Performance Testing: Characterization of Fusion Hydrophobins Via Contact Angle Change of a Water Droplet on Glass Substrate:glass (window glass, Süddeutsche Glas, Mannheim)
For the tests, the spray-dried products comprising fusion hydrophobins were dissolved in water in the presence of 50 mm sodium acetate pH 4 and 0.1% by weight of polyoxyethylene(20) sorbitan monolaurate (Tween® 20). Concentration of product: 100 μg/mL in aqueous solution.
Procedure:
-
- incubation of glass slides overnight (temperature 80° C.), then coating wash in distilled water,
- thereafter incubation 10 min/80° C./1% sodium dodecylsulfate (SDS) solution in distilled water,
- washing in distilled water
The samples are air dried and subjected at room temperature to a determination of the contact angle (in degrees) of a droplet of 5 μl of water.
The contact angle measurement was determined on a Dataphysics Contact Angle System OCA 15+, Software SCA 20.2.0. (November 2002). The measurement was carried out in accordance with the manufacturer's instructions.
Untreated glass gave a contact angle of 15° to 30°±5°. A coating with the fusion hydrophobin yaad-Xa-dewA-his6 gave a contact angle increase of more than 30°; a coating with the fusion hydrophobin yaad40-Xa-dewA-his likewise gave a contact angle increase of more then 30°.
Tests for crystallization of gypsum
General Working PrescriptionA saturated solution of CaSO4×2H2 in completely ion-free water was prepared (concentration about 2 g/l). The solutions were each admixed with hydrophobin A and hydrophobin B respectively, so that the gypsum solution had a concentration of about 0.1 g/l of the spray-dried product. The pH of the solution was adjusted with HCl and NaOH respectively. The aqueous solutions/dispersions were filtered through a pleated filter (about 10 μm). Thereafter, about 25 ml of each solution were transferred into a Petri dish and the water was allowed to evaporate at room temperature in the course of about 24 hours. A solution was left for comparison without added hydrophobin.
The forms of the gypsum crystals formed were compared with a BH-2 microscope from Olympus.
The needle length is truncated by the hydrophobins at all pH values (
Claims
1-8. (canceled)
9. A process for producing a solid, the process comprising the steps of crystallizing the solid from an aqueous phase by adding an auxiliary in an amount of 0.001% to 1% by weight based on the total amount of the aqueous phase, and separating the solid from the aqueous phase, wherein the auxiliary comprises a hydrophobin.
10. The process of claim 9 wherein the pH of the aqueous phase is about pH 7 to about pH 11.
11. The process of claim 9 wherein the solid comprises gypsum.
12. The process of claim 9 wherein the solid comprises calcium carbonate.
13. The process of claim 9 wherein the solid comprises a compound selected from the group consisting of gypsum and calcium carbonate, and wherein the process further comprises a flue gas desulfurization process.
14. The process of claim 9 wherein the hydrophobin comprises a hydrophobin fusion.
15. A method for crystallizing a solid wherein a hydrophobin is incorporated as an auxiliary soluble.
16. The method of claim 15 wherein the solid is crystallized from a liquid phase.
17. The method of claim 16 wherein the hydrophobin comprises 0.001% to 1% by weight based on the total amount of the liquid phase.
18. The method of claim 15 wherein the liquid phase comprises an aqueous phase.
19. The method of claim 18 wherein the pH of the aqueous phase is about pH 7 to about pH 11.
20. The method of claim 18 wherein the solid comprises gypsum.
21. The method of claim 18 wherein the solid comprises calcium carbonate.
22. The method of claim 15 wherein the hydrophobin comprises a hydrophobin fusion.
Type: Application
Filed: May 21, 2008
Publication Date: Jul 1, 2010
Applicant: BASF SE (Ludwigshafen)
Inventors: Ulf Baus (Dossenheim), Thorsten Montag (Dudenhofen), Stefan Becker (Mannheim), Stephan Nied (Neustadt/Wstr.), Claus Bollschweiler (Heidelberg), Thomas Subkowski (Ladenburg), Marvin Karos (Schwetzingen)
Application Number: 12/601,281
International Classification: C22B 26/20 (20060101);
