APPARATUS FOR THE STEPWISE PERFORMANCE OF CHEMICAL REACTIONS

Abstract: An apparatus for the stepwise performance of chemical reactions comprises a cup-shaped reactor vessel (1) spinning around its longitu­ dinal axis and a pipette (11) for applying sample, reagents and sol­ vents onto the inner wall of the vessel. The pipette (11) is slewable around an axis (23) and can be positioned at a location (17) from which it can be lowered into reservoirs (51, 5b) for drawing in or for ejecting liquid; the pipette (11) can furthermore be positioned at a location (19) from which it can be lowered into the vessel (1) for applying sample, reagents or solvents onto its inner wall or it can be positioned at a location (18) from which it can be lowered to remove reaction products and excess products from the bottom of the vessel (1). The apparatus can be used for automatically sequencing proteins or peptides (Fig. 1).

Description: The invention relates to an apparatus for the stepwise performance of chemical reactions according to the preamble of claim 1, in particular to an apparatus for the sequencing of proteins or peptides. The sequence of amino acids in a protein, i.e. the linear succession of the individual amino acids, is a deciding criterion for its higher structures which in turn are deciding for the biological function of the protein. The sequence of proteins is thus of considerable importance in biochemical research and industry, for example in genetic engineering. In the following description, no difference is made between porteins, peptides and polypeptides: the whole group of these substances is addressed when the term "protein" is used. A protein sequenator for the automatic determination of amino acid sequences in proteins is known from P. Edman and G. Begg , European Journal of Biochemistry, Vol. 1, 1967, pages 80-91. This sequenator operates on the principle of the phenylisothiocyanate degradation scheme. According to this degradation process, the free N-terminal alpha-amino group is first converted in a coupling step in a basic environment with phenylisothiocyanant (PITC) into a phenylthiocarbamyl (PTC) derivative. The phenylthiocarbamyl derivative is cleaved in a strongly acidic environment and is cyclisized under formation of a thiazolinone derivative (ATZ) which can be converted by treatment with aqueous acid into the more stable phenylthiohydantoin (PTH) derivative. The alpha-amino group of the following amino acid in the chain of amino acids is thus set free and can be subject to a further degradation step similar to the one described. The PTH amino acid can be identified using the liquid chromatography. The sequenator known from the above-mentioned article by Edman and Begg which is also known from US-A-3 725 010, comprises a reaction vessel wherein the degradation of proteins to be determined takes place and a plurality of reservoirs for storing reagents and solvents. The reservoirs are under constant pressure and by opening appropriate valves a liquid or gas stream can be fed to the reaction vessel. The reaction vessel is a cylindrical glass cup which spins continuously around its longitudinal axis. The protein is applied as a thin film on the inner wall of the cup. Reagents and solvents entering through a feed line at the bottom of the cup climb up the inner wall due to centrifugal forces and accumulate in a circular groove near the upper rim of the cup. The accumulated liquids are scooped off with a bilge pipe and leave through an effluent line. In this known sequenator, the application of the protein layer and the guiding of the liquid film of reagents and solvents across the protein layer are not very precise and comparatively high quantities of protein and liquid are required in order to obtain acceptable reaction yields. Furthermore, as the reagents wherein the proteins are soluble slide across the protein layer towards the circular groove at the rim of the vessel they gradually wash away the proteins. From US-A- 4 252 769 , a further development of the sequenator disclosed in the above-mentioned patent US-A- 3 725 010 is known. The sequenator according to US-A- 4 252 769 is based on the same principle as the sequenator according to US-A- 3 725 010 in that it also comprises a spinning reaction vessel, a stationary feed line for introduction of solvents and reagents near the bottom of the vessel, a circular groove near the upper rim of the vessel wherein liquid can accumulate , and a pick-up conduit the end of which can be positioned in the groove to remove liquid therefrom. The introduction of liquids into the reaction vessel is controlled by opening appropriate valves so that the liquids from pressurized reservoirs are fed to the vessel. The prior art according to US-A-4 252 769 is primarily concerned with the accurate adjustment of the conduit for removing liquid relative to the circular groove of the reaction vessel, and with the avoiding of contamination in the reaction vessel. For this purpose, the known device comprises special designs for the pick-up conduit and the sealing of the various conduits extending into the reaction vessel. From US-A-3 892 531 and from US-A-4 065 412 devices for sequencing proteins are known which tend to avoid the washing away of the proteins by the solvents and reagents. In these devices, the protein is deposited on a porous surface, for example on a paper strip or on a fibre glass web, and the reagents are applied as vapour.The reaction velocity and the completeness of the reaction, however, are reduced when using the reagents in gaseous or vapour state relative to the liquid state in the Edman process. Furthermore, the protein agglomerates in the cavities of the porous material causing a decrease of the surface of the protein sample and it depends on the properties of the specific protein and on other unforeseen occurrences in which way the protein spreads on the porous surface. As a consequence thereof, there are regions where the protein accumulates so that the accessibility of reagents and solvents is reduced, whereas in other regions there is little or no protein so that the reagents pass there without reaction. These are the main reasons that such gaseous phase methods have comparatively low reaction yields. In view of the mentioned prior art it is the object of the invention to provide an apparatus for the stepwise performance of chemical reactions which permits higher reaction yields and a better control of the reaction process, which permits the use of smaller amounts of sample, reagents and solvents and which has an uncomplicated construction. According to the invention, this object is solved for an apparatus as defined in the preamble by the characterizing features of claim 1. The apparatus of the invention thus comprises a cup-shaped reactor vessel spinning around its axis with a feed system for successively introducing into the reactor vessel the sample as well as various reagents and solvents, and an outtake system for removing reaction products and excess products wherein the feed system comprises a feed tube the opening of which can be arranged close to the inner wall of the reactor vessel such that reagents and solvents can be applied on to the sample substance and wherein the outtake system comprises an outtake tube for removing reaction products and excess products from the bottom of the reactor vessel. The invention permits the deposition of the reagents as a film on to the sample substance, for example on a protein to be analyzed. Consequently, relative motion between the sample substance and the reagents causing the washing away of the protein is avoided. Since the protein and the reagents are applied as liquid films on each other they have a large contact area which also contributes to a high reaction yield. In order to produce a still more uniform liquid film, the feed tube can, according to claim 2, be moved up and down during the application of the film on the wall of the rotating cup. According to claim 3, the same movable tube is used as a feed tube and as an outtake tube. According to claim 4, the rotational speed of the reactor vessel can be reduced while solvents are delivered to the wall so that reaction products or solutions run down the wall in spirals and gather at the bottom of the vessel. This is done in a protein sequencing process for washing out reaction excess products and for extracting ATZ amino acids. When the rotation of the vessel is stopped the collected liquid can easily be removed from the bottom. According to claim 5, the movable tube for introducing liquid into and for removing liquid from the reactor vessel forms one end of a tube system, the other end of which is connected to a reversible pump which can be operated to draw in or to eject liquid through the movable tube. Thereby, precise metering of the reagents and solvents is permitted ensuring well-defined reaction conditions. The tube system forms an arm slewable around an axis whereby the circle described by the movable tube comprises a first point above the center of the reactor vessel, a second point near the periphery of the vessel and a third point above a position where a reservoir can be positioned. According to claim 6, reservoirs, waste containers and other containers are arranged on a plate. The containers with the liquid needed in a certain reaction step or the containers for accepting waste liquid can thus be positioned at a place where the movable tube can be dipped into the container. This also contributes to the simple design of the apparatus and easy automation. The invention has the additional advantages that solvents and reagents reach the reactor vessel and other vessels on very short paths without contacting movable parts or seals. Thus, the problems of prior art devices are avoided wherein the delivered substances come into contact with the surfaces of the feeding tubes and with the movable parts of the valves and be absorbed there resulting in contamination of the liquids which flow through the tube at a later point in time or resulting in leakage. Furthermore, the invention permits precise metering of small amounts of liquid and makes it possible to use smallest amounts of sample substance, e.g. less than 100 picomoI of a protein. The required quantities of reagents and solvents and the quantities of excess products are small. Due to the intense contact between the sample substance on one hand and the reagents and solvents on the other hand, the reaction times are short which is particularly advantageous when the number of reactions to be performed is very large as, for example, in protein sequencing. Since the design of the apparatus according to the invention is simple, it is less susceptible to faults than the more complicated prior art systems. A further advantage of the invention is that the initial yield and the repetitive yield of the reactions performed with the apparatus can be increased compared to prior art devices and that the reaction products, for example the PTH amino acids in a protein sequencing process, are obtained in concentrated form with little impurities, thus leading to a low detection limit for the subsequent chromatographic anaysis. It is understood that the apparatus according to the invention cannot only be used for the analysis of proteins but also for other sequential chemical reaction processes, e.g. for the synthesis of oligonucleotides or peptides. Subsequently, an embodiment of the invention is explained in more detail with reference to the drawing. Figure 1 schematically shows an apparatus according to the invention which can be used as a protein sequenator. Figure 2 is a cross-sectional view of a reactor vessel in an apparatus according to the invention. Figures 3A to 3B show the reactor vessel and a pipette for introducing and removing liquid at different steps of a chemical process. The apparatus according to the invention comprises a reactor vessel 1 wherein the chemical reactions, for example the degradation of proteins as described above, take place. The generally cylindrical reactor vessel 1 is secured to a rotatable shaft 2 which is driven by a motor 3. Details of the reactor vessel 1 are described below with reference to Fig. 2. The reactor vessel 1 is arranged in a chamber formed by a cylinder 4 which is sealed off at its top and at its bottom. The apparatus further comprises several supply reservoirs 5a, 5b for reagents and for solvents arranged on a carrousel 7 which can be rotated by means of a motor 6. The supply reservoirs 5a, 5b including the carrousel 7 are located in a sealed chamber formed by a cylinder 8, a plate 9 and a central plate 10. The reservoirs 5a, 5b can also be used for receiving cleaning or rinsing liquid and as a waste container. A micropipette 11 is connected via a movable capillary tube 12 with a pump 13 which is operated by a motor 14. The pump can be, for example, a syringe. The pipette 11 , the capillary tube 12 and the pump 13 form a dispensing system which allows liquid to be drawn in and metered. The pipette 11 with the tube 12 are mounted on a pipette holder 15 which can be rotated about the axis 23 and which can be lowered and raised. A drive element 16 is provided for performing these movements. The pipette 11 can dip into one of the reservoirs 5a, 5b through the bore 17 or it can dip into the center of the reaction vessel 1 through the bore 18. A second bore 19 in the plate covering the reaction vessel 1 is located outside the center of the vessel close to its wall. The bores 17, 18, and 19 are located on a single circle described by the tip of pipette 11 when rotating around the axis 23. The bore 19 indicated in Fig. 1 is therefore not exactly located in the cutting plane containing bores 17 and 18 but somewhat out of this plane. As a practical example, the pipette 11 may have an inner diameter of 0.8 mm and an outer diameter of 1.6 mm. When the pipette 11 is lowered through the off-centre bore 19 the tip of the pipette 11 comes into close proximity of the inner wall of the reaction vessel without contacting it. In that way, liquids and substances solved therein can be deposited directly on the wall of the reactor vessel 1. Additional openings on the circle described by the tip of the pipette 11 can be provided which permit access to further containers, for example to converting vessels or a fraction collector. Such openings have appropriate locks. Each chamber of the system comprises connections which permit a continuous purge with inert gas. In that way, and by the inherent sealing-off of the apparatus the access of ambient air is prohibited and the exchange of substances between the various regions of the apparatus is reduced to a minimum. Particularly in protein sequencing, some of the reactions are extremely sensitive to oxygen and water so that the whole system has to be operated under an inert gas atmosphere. Furthermore, the reagents required for protein sequencing are corrosive (pH value: 0-9) and ill-smelling so that the sealing of the containers wherein they are stored and the chambers of the protein sequenator is important. An embodiment of the reactor vessel 1 is shown in more detail in Figure 2. The reactor vessel 1 has the shape of a cup with a cylindrical upper portion 30 and a lower portion narrowing at the bottom. The bottom of the cup has the form of a hemisphere 31 and comprises at its lowest point a recess 32 wherein liquid can accumulate and which is accessible to the pipette 11. The reactor vessel 1 is secured with its lower portion to the shaft 2 (Fig. 1). In operation, the vessel 1 spins around the axis 33. The vessel 1 can be made, for example, of glass or ceramics. As a practical example, the inner diameter of the cup may be 15 millimetres and the height from the bottom of the cup to its upper rim 43 may be 22.5 millimetres. The operation of the apparatus according to the invention is now further explained with reference to Figures 3A to 3C. According to Figure 3A, the protein to be analysed is pipetted onto the inner wall 40 by means of pipette 11 when the cup 11 is rapidly spinning. A typical rotational speed can be, for example, 6000 revolutions per minute. The tip 41 of the pipette 11 can be inclined as shown in the drawing to ensure easy application of the protein onto the wall. The resulting protein strip has a width of a few millimeters and forms a very uniform film which is easily accessible. When the pipette is moved up and down during the application of the protein, the resulting film is even more uniform. In Fig. 3A, the lower extreme position of the tip of the pipette 11 during its up and down movement is indicated by dashed lines 42. In a next step, the pipette 11 is raised above the upper rim 43 of the cup 1, and the whole pipette-tube assembly 11,12,15 (Fig.1) is rotated around axis 23 so that the pipette tip is located above the bore 17 (Fig.1). After a reservoir with the reagent needed in this reaction step has been positioned below the bore 17 by turning the carrousel 7, pipette 11 is lowered and a predetermined amount of liquid is drawn in by controlling the pump 13 appropriately. Then, the pipette 11 is raised, rotated back until the tip is positioned above the bore 19 and lowered into the cup 1. The pump 13 is then controlled to discharge the liquid from the pipette 11 onto the wall. Thus, the reagent is placed as a uniform layer upon the protein film. If desired, the pipette can be moved up and down during the discharge of the reagent, similarly as in the application of the protein film in a previous step. It is an important feature of the invention that in this way the reagents are brought into contact with the protein film without relative movement between the proteins and the reagents. Since there is no relative movement, washing away of the protein is avoided. This is a substantial difference to the prior art wherein the reagents flow across the protein and wash away a portion of it. In contrast thereto, according to the invention, the reagent layer is put onto the protein layer ensuring intimate contact between the two layers and avoiding the flushing away of the protein layer. When the reagent layer has been applied on the protein layer, the water and the volatile components contained therein are removed from the protein film by evaporation and the non-volatile components are washed out with organic solvents. For washing out surplus liquid and for extracting the ATZ amino acids the pipette 11 is raised again, rotated until it is positioned above bore 17 and lowered into a container with the appropriate solvent which has been placed below bore 17. When the desired amount of solvent has been drawn in, the pipette is rotated back to the position above bore 19 and lowered until the tip 41 of the pipette is positioned above the upper rim of the protein film, as shown in Fig. 3B. The rotation velocity of the reactor vessel 1 is reduced such that the solvents pipetted onto the wall above the protein film run across the protein film on helical paths and are finally collected at the bottom of the reactor. The speed of revolution for this step can be, for example, 600 revolutions per minutes. When the cup 1 is at rest, and after the pipette 11 has been moved through the central bore 18 in the position shown in Figure 3C, the solvent containing the ATZ amino acid or a waste product is drawn in by the pipette 11 and supplied either to a converting vessel or to a waste container. The determination of the cleaved off amino acid can be performed using liquid chromatography on the basis of the different retention times of the amino acids. Then, the above described steps can be repeated to cleave off the next amino acid in the amino acid chain of the protein. The protein layer deposited on the inner wall of the reactor vessel 1 can be heated contactlessly with a resistance heating. The protein layer can be dried with inert gas supplied through a port in its immediate neighbourhood.

Claims: An apparatus for the stepwise performance of chemical reactions with a sample substance which is applied on the inner wall (40) of a cup-shaped reactor vessel (1) spinning around its longitudinal axis (33), comprising a feed system for successively introducing into the reactor vessel (1) various reagents and solvents and an outtake system for removing reaction products and excess products, characterized in that a) the feed system comprises a movable feed tube (11) with an opening (41) through which liquids can leave the feed system , said feed tube (11) being movable by a drive element (16) such that the opening (41) can be positioned close to the inner wall (40) of the reactor vessel (1) for applying the sample substance on the inner wall (40) of the reactor vessel (1), and applying reagents and solvents onto the sample substance which has previously been applied on the inner wall (40) of the reactor vessel (1), b) the outtake system comprises an outtake tube for removing reaction products and excess products from the bottom (31) of the reactor vessel (1). An apparatus according to claim 1, characterized in that for laying a uniform film of reagents over the sample substance the feed tube (11) is moved up and down during the application of the reagents when the reactor vessel (1) is spinning. An apparatus according to claim 1 or 2, characterized in that the feed tube and the outtake tube are formed by the same movable tube (11) the opening (41) of which can be positioned a) close to the wall (40) of the reactor vessel (1) for applying reagents on the sample substance or for applying the sample substance on the wall (40), and b) close to the bottom (31) of the reactor vessel (1) for removing liquid collected at the bottom. An apparatus according to any of the claims 1 to 3, characterized in that the rotational speed of the reactor vessel (1) is reduced while solvents are being applied, thus causing the dissolved reaction or excess products to flow down the wall and to gather at the bottom (31) wherefrom they can be removed after the rotation of the reactor vessel (1) has been stopped. An apparatus according to any of the claims 2 to 4, characterized in that the movable feed tube (1 1) is connected to a capillary tube (12) with the feed tube (11) and the capillary tube (12) forming an arm which is slewable around an axis (23) such that it can be positioned at a position above the center of the reactor vessel (1) or at a position above the reactor vessel (1) close to the periphery of the vessel or at a position above a chamber contained reservoirs and containers (5a, 5b), and that a controllable pump (13) is provided for drawing in or for ejecting adjustable amounts of liquid through the opening (41) of the feed tube (11). An apparatus according to claim 5, characterized in that the reservoirs and containers (5a, 5b) are arranged on a rotatable plate (7) which can be rotated to a position where the movable feed tube (11) can be lowered into the respective reservoir or container. An apparatus according to any of the preceding claims, characterized in that the inner surfaces of the reactor vessel (1) form a rotationally symmetrical body with a cylindrical upper portion (30) and with a hemispherical bottom (31) having a recess (32) for collecting liquid. Use of an apparatus according to any of the preceding claims for automatically sequencing proteins or for synthesizing oligonucleotides and/or peptides.

Inventors: HUPE, KLAUS-PETER, DR., STROHMEIER, FRED
Applicants: HEWLETT-PACKARD GMBH
Application year: 1987
Main classification: G01N33
IPC codes: C40B60, B01J19, G01N33, C40B40