Abstract:
A CHTS reactor plate has wells that can be individually heated. The reactor plate includes a substrate with an array of reaction wells and a ferromagnetic material included with the substrate. A CHTS method provides a reactor plate having a substrate with an array of reaction wells and a ferromagnetic material responsive to the application of an electric field included with the substrate. The electric field is energized to control temperature in the proximity of at least one of the reaction wells. Another method comprises providing a reactor plate comprising an array of reaction wells and depositing a ferromagnetic object within at least one of the wells. The object is responsive to the application of an electric field. An electric field is then energized to control temperature in the reaction well.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a reactor plate and method for running multiple parallel screening reactions using multiphase reactant systems. 
     In experimental reaction systems, each potential combination of reactant, catalyst and condition must be evaluated in a manner that provides correlation to performance in a production scale reactor. Since about 1970, combinatorial organic synthesis (COS) has provided an important tool to address the requirements of experimental systems. COS is a systematic and repetitive synthesis that uses sets of chemical “building blocks” to form a diverse set of molecular entities. As with traditional research, COS relies on organic synthesis methodology. However instead of synthesizing a single compound, COS exploits automation and miniaturization to synthesize large libraries of compounds; a procedure that can involve successive stages, each of which produces a chemical modification of an existing molecule of a preceding stage. The synthesis produces large numbers of diverse compounds, which can be screened for various activities. 
     In one approach to COS, arrayed, spatially addressable building blocks are reacted systematically on particle supports. The particles are distributed into a two-dimensional array so that each variant in a combinatorial library can be identified by its position in the array. The array can consist of a set of plates, each having rows and columns of wells, with one particle, or some other predetermined number of particles contained in each well. The particles are typically made of polystyrene. They serve as substrates for different compounds produced in the process of split and combine synthesis. Ultimately, synthesized compounds are stripped from the particles and tested for activity. The identity of an active compound can be determined by spectrographic analysis in the light of the information available concerning the reaction histories of the particles. 
     Combinatorial high throughput screening (CHTS) applies combinatorial chemistry principles of COS to the high throughput screening of materials and processes, particularly industrial materials and processes. A CHTS method can be characterized by parallel reactions at a micro scale. In one aspect, CHTS can be described as a method comprising (A) an iteration of steps of (i) selecting a set of reactants, conditions, catalysts or combinations thereof; (ii) reacting the set and (iii) evaluating a set of products of the reacting step. The CHTS method can further comprise (B) repeating the iteration of steps (i), (ii) and (iii) wherein a successive set of reactants, conditions, catalysts or combinations thereof, selected for a step (i) is chosen as a result of an evaluating step (iii) of a preceding iteration. 
     CHTS reactions are often conducted at elevated temperatures and at pressures both above and below atmospheric. Precise control of temperature can be critical for accurate evaluation of results. Precise control of temperature in each respective well may be part of a screening protocol. In this case, separate temperature control of each well may be required. In some CHTS systems, it may be necessary to repeatedly test within a precise and narrow range of temperatures. In this instance, the temperature ranges must be accurately duplicated in each well of an array as well as in repeated iterations of the CHTS protocol. 
     A uniformly heated array of wells may be obtained by placing a plate in a heated bath, oven or autoclave. But this mechanism does not address the problem of reactions that require different temperatures from well to well and can only poorly match temperatures from iteration to iteration. The wells can be individually wired and controlled with thermocouples or electromechanical or electronic controllers to provide different temperatures in different wells but these solutions are prohibitively expensive. There is a need for a reactor plate and method to provide separate effective and inexpensive heat control of respective plate wells for CHTS. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a reactor plate with wells that can be individually heated or that can be precisely repeatedly heated and a method that can provide individual and reproducible heat control of wells. According to the invention, a reactor plate comprises a substrate with an array of reaction wells and a ferromagnetic material included with the substrate. 
     In another embodiment, a CHTS method comprises providing a reactor plate comprising a substrate with an array of reaction wells and a ferromagnetic material responsive to the application of an electric field. The electric field is energized to control temperature in the proximity of at least one of the reaction wells. 
     In a final embodiment, a CHTS method comprises providing a reactor plate comprising an array of reaction wells and depositing a ferromagnetic object within at least one of the wells. The object is responsive to the application of an electric field. An electric field is then energized to control temperature in the reaction well. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plot of Curie temperature vs. composition; 
     FIG. 2 is another plot of Curie temperature vs. composition; 
     FIG. 3 is a schematic representation of a top view of a preferred reactor plate according to the invention; 
     FIG. 4 is a schematic cut-away front view through line A—A of the reactor plate of FIG. 3; 
     FIGS. 5 to  8  are schematic cut-away representations of various plates and ferromagnetic configurations; 
     FIGS. 9 to  11  are schematic cut-away representations of various RF antenna configurations; and 
     FIG. 12 is a schematic top view and 
     FIG. 13 is a schematic side view of a reactor plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Combinatorial synthesis may require that samples be heated to a reproducible high and constant temperature. The present invention is based on Curie point heating of ferromagnetic materials to provide accurate and reproducible temperature. Ferromagnetic materials display a hysteresis effect of polarization with an applied electrical field. A hysteresis loop is generated by the existence of permanent electric dipoles that spontaneously develop in the ferromagnetic material below the Curie temperature. A ferromagnetic material cation can be off center by a small fraction of an angstrom with respect to an anion to create an electric dipole. Energy barrier between possible cation positions is sufficiently low to permit motion of the cation between sites through coercion of an electric field. Hence, the material is easily polarized to a magnet. If the direction of the current is changed, the polarity of the magnet is reversed, i.e., N→S is reversed to S→N. When polarity of the coil is changed rapidly, heat is generated. The heat causes the ferromagnetic material to reach its Curie point temperature, where the magnetic property is lost and the temperature is maintained constant. The time to reach the Curie point temperature can be less than 0.2 second. 
     A radio frequency (RF) coil can provide one arrangement for applying an electric field to a ferromagnetic material to provide a heating system. In an RF heating system, a generator creates an alternating electric field between two electrodes or in the interior of a coil or between two plates. The electrodes are placed to oppose one another across a material to be heated. Alternating electric fields cause polar molecules in the material to continuously reorient themselves to face opposite poles much like the way bar magnets behave in an alternating electric field. The reorienting interaction causes the material to rapidly heat throughout its entire mass. 
     The application of the electric field can be through an antenna coil mounted in close proximity to the ferromagnetic material or surrounding the reaction plate. In the case of a flat antenna coil or a coil surrounding the reaction plate, the electrical properties of the antenna are adjusted to minimize the RF power reflected by the apparatus and coil. This is typically carried out by providing a matching element such as a variable capacitor in the RF power output to the antenna. Commercial RF power sources such as the RF200W from Plasma Sciences, Inc. 12 Columbus St., New Windsor, N.Y. 12553, contain the necessary electrical components to minimize reflected power and maximize energy transfer to the ferromagnetic material. An alternative method of excitation of the ferromagnetic material is by the application of microwave radiation. Commercial microwave ovens with controllable power levels such as the MDS-2100 Microwave Digestion System or the MARS-5 Microwave Accelerated Reaction System, both from CEM Corp. Mathews, N.C. 28106 are examples of suitable microwave sources. 
     The applied power, which in an RF system is the transmitter power minus the reflected power, is chosen to suit the desired rate of temperature rise. This in turn is dependent on the mass of the ferromagnetic material, the magnetic susceptibility of the ferromagnetic material, the heat capacity of the reactor plate and the reactants, heat losses due to convection, conduction and thermochemistry (such as heats of melting, vaporization, dissociation), a shape factor for the ferromagnetic articles and field strength at the ferromagnetic objects. The rate of temperature rise can be experimentally determined for a given system. Typically for ferromagnetic materials of several milligrams weight in an air atmosphere and well coupled to a 500 watt RF source the heating time to Curie temperature is on the order of less than 0.2 seconds. On reaching the Curie temperature, the amount of power may be maintained since the Curie point of the ferromagnetic object limits the temperature. Energy can be conserved, however, by lowering the applied power to just maintain the wells in the reactor plate at the desired temperature or temperatures. 
     RF generators can be used with output powers of many kilowatts, however antenna cooling, safety and shielding become problematic at higher power levels. An output power range can be 200 W to less than about 2000 W for an insulated single reactor array plate of approximately 3 inch by 5 inch dimension. Desirably, the range can be about 250 W to less than about 1000 W, which can be sufficient to reach temperatures of less than 1000° C. 
     The ferromagnetic material should have a Curie temperature in the desired temperature range, have high coercivity, should be castable or formable or able to be incorporated into composites, should be unreactive if in contact with a reaction medium or able to be coated or encapsulated. The materials can be prepared and formed using standard metallurgical methods. The Curie point of the particular form or shape of material can be confirmed before use in the CHTS method. 
     Different and accurate temperatures can be chosen by varying the composition of the ferromagnetic material. Several major families of ferromagnetic materials are commercially available. These include metals, alloys, ceramics and inorganic substances. T. R. Connolly and Emily D. Copenhaver, Bibliography of Magnetic Materials and Tabulation of Magnetic Transition Temperatures, Solid State Physics Literature Guides, 1972, 5, includes numerous suitable materials. The materials range from ferrite, which is low cost and low energy, to rare earth materials, which are high cost and high energy. The disclosure of the T. R. Connolly and Emily D. Copenhaver compilation is incorporated into this application by reference. 
     Pure metals such as nickel and iron with Curie temperatures of 358° C. and 770° C., respectively can be used as well as binary and higher multiplicity alloys. Examples of binary alloys are Gd/Co and Fe/Ni and an example of a ternary alloy is GdYFe 2  with a Curie temperature of 407° C. Ceramic materials such as 5Fe 2 O 3 .3Y 2 O 3  with a Curie temperature of 290° C., are also useful. 
     There are a number of alloy series that have a range of Curie points in the temperature ranges applicable to organic and polymer chemistry. A particular alloy series with this property is the Gd/Co system. A plot of Curie temperature vs. composition for the Gd/Co system is shown in FIG.  1 . The plot shows a straight line that is represented by: 
     
       
         Curie temperature (° C.)=Atom % Co×30−1748. 
       
     
     Thus, 68.3 atom % Cobalt in Gadolinium provides a Curie point of about 300° C. 
     The Curie temperature for Fe/Ni alloys ranges from less than 100° C. to over 450° C. A plot of known data is shown in FIG.  2 . Here, the straight line is described by 
     
       
         Curie Temperature (° C.)=Atom % Ni×22.9−559. 
       
     
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Curie Pt. 
                 Magnetic 
                   
                 Resistance to 
               
               
                 Material 
                 Temperature 
                 Energy 
                 Cost 
                 Demagnetization 
               
               
                   
               
             
             
               
                 NdFeB 
                 150° C. 
                 48 MGOe 
                 High 
                 High 
               
               
                 SmCo 
                 300° C. 
                 32 MGOe 
                 Very High 
                 Very High 
               
               
                 NeoForm-B 
               
               
                 Bonded 
                 150° C. 
                 10 MGOe 
                 High 
                 High 
               
               
                 NdFeB 
               
               
                 Alnicc 
                 550° C. 
                 7.5 MGOe  
                 Moderate 
                 Low 
               
               
                 Ceramic 
                 300° C. 
                    4 MGOe 
                 Very Low 
                 Moderate 
               
               
                 Ferrite 
               
               
                   
               
             
          
         
       
     
     These and other features will become apparent from the drawings and following detailed discussion, which by way of example without limitation describe preferred embodiments of the present invention. 
     FIG. 3 shows a top view of a preferred reactor plate and FIG. 4 shows a cut-away front view through line A—A of the plate of FIG.  3 . FIG.  3  and FIG. 4 show reactor plate  10  that includes an array  12  of reaction wells  14  embedded into a supporting substrate  16  of the plate  10 . The plate  10  further includes electric field generator  18 . The walls and base of the wells  14  of the reactor plate  10  are constructed of the desired ferromagnetic material. 
     FIG. 3 shows that electric field generator  18  is Operatively connected via leads  20  and  22  to a flat RF antenna coil  24 , which is embedded within supporting substrate  16 . In the embodiment shown in FIG.  3  and FIG. 4, reaction wells  14  are lined with a ferromagnetic material  28 . While the FIGS. show than all wells  24  are lined, in other embodiments, one or more wells can be lined and one of more wells can be lined with the same or with a different ferromagnetic material. The lined well can provide reaction wells for beads for COS, which can be used directly to carry out reactions. Or, the wells  14  can provide cavities  32  to accept reaction vials as exemplified by reaction vial  30  as shown in FIG.  4 . The ferromagnetic material  28  can be an integral part of the supporting substrate  16  or the material  28  can form separate shaped inserts that can be replaceably fitted within the cavities  32  of the wells  14 . 
     FIGS. 5 to  8  illustrate other embodiments of the reactor plate designated  40 . 
     In FIG. 5, reactor plate  40  includes an array  42  of reaction wells  44  embedded into a supporting substrate  46  of the plate  40 . The plate  40  includes ferromagnetic discs  58  that are respectively associated with reaction wells  44 . Wells  44  can directly contain reagent or vials or other containers can be inserted into wells  44  to provide replaceable reaction sites. The ferromagnetic discs  58  can have the same Curie temperature to provide a constant temperature across the array  42  or the Curie temperature of the discs can be chosen to provide a stepped temperature gradient. For example, the first row of 8-wells of a 96-well plate can be associated with ferromagnetic discs  58  with a Curie point of 100° C., a second row with discs  58  having a Curie point of 110° C. and so on until the last row of the well plate contains discs with a Curie point of 210° C. Adjacent rows or columns of wells can be associated with ferromagnetic discs of any desired Curie point according to the constraints or requirements of the CHTS methodology. The T c  of discs  58  in adjacent rows or columns of an array may be widely different as long as thermal conductivity of the substrate  46  construction material prevents thermal cross-talk among wells  44 . 
     FIG. 6 shows a reactor plate  40  with discrete ferromagnetic objects  68  added directly into each well cavity  32 . The objects can be beads, bars, discs, cylinders, flakes or particles or any shape conducive to good heat transfer to the reaction medium. The objects can have the same Cure temperature to provide a constant temperature across the array or the objects can be chosen with respect to Curie temperature to provide a stepped gradient with different reaction temperatures in one or more wells. For example, a 96-well plate can have a first row of 8-wells containing 100° C. Curie point objects. A second row can have 110° C. Curie point objects and so on, with the last row of the well plate containing 210° C. Curie point objects. Adjacent rows or columns can contain ferromagnetic objects with any accessible Curie point. 
     The ferromagnetic objects can comprise metals, alloys, ceramics and inorganics and can be present in the shapes described above. The objects can be encapsulated in vitreous substances, encapsulated in polymers stable at the T c , encapsulated by a plating or coating or the objects can be used without encapsulation if the ferromagnetic material is unreactive with the reaction medium. Suitable encapsulants include polymers, fluoropolymers, glass and other vitreous materials, ceramics, foamed materials and so-called syntactic foams. The encapsulants are preferably vitreous materials and more preferably quartz to avoid chemical interactions with the ferromagnetic material. Metals can also be used for plating or encapsulating if they have Curie points below operating temperatures of the CHTS protocol and do not interfere with RF penetration to the ferromagnetic material. 
     Intervals of the Curie point differences can be whatever are suitable for the particular CHTS system as long as thermal conductivity of the array plate substrate  16  does not permit heat cross-talk among wells. The difference can-be less than about 50° C. between adjacent wells. Desirably, the difference is less than about 25° C. between adjacent wells and preferably the difference is less than 10° C. between adjacent wells. 
     When the ferromagnetic objects have the same T c , the substrate  16  can comprise any material that will not interact with the RF field and that has high thermal conductivity. In the embodiment with variable temperatures across the array plate, the substrate  16  material should have low thermal conductivity to avoid cross-talk between adjacent wells. Examples of suitable substrate  16  materials include polymers, either thermoplastics or thermosets, fluoropolymers such as polytetrafluoroethylene and others, glass, quartz and other vitreous materials, ceramics, foamed ceramics and syntactic foams. The substrate  16  materials can be filled with low thermal conductivity additives such as hollow beads, bubbles and voids or particles of low conductivity material. 
     FIGS. 7 and 8 show further embodiments of the reactor plate  40 . FIG. 7 shows a separable substrate  46  comprising top section  60  and bottom section  62 . In this embodiment, the two sections  60  and  62  can be separated to receive removable ferromagnetic discs  58 . FIG. 7 shows substrate  46  separated into two sections,  60  and  62  and FIG. 8 shows the same substrate  46  assembled. 
     FIGS. 9 to  13  illustrate various RF antenna and coil arrangements according to the invention. FIG. 9 shows a reactor plate  40  with integral ferromagnetic discs  58  and an RF antenna coil  54  embedded in substrate  46 . The coil  54  is located in close proximity to the ferromagnetic discs  58 . FIG. 10 shows a well plate  40  with integral ferromagnetic discs  58  and opposing RF antenna coils  54  and  56  above and below the array  42  of reaction wells  44 . FIG. 11 shows a reactor plate  40  with integral ferromagnetic discs  58  and surrounding RF antenna coil  54 . FIG. 12 is a top view and FIG. 13 is a side view of a 96-well reactor plate  40  and a sinuous antenna  54  that winds along rows of the array  42  wells  44 . The antenna is attached to an electric field generator (not shown) by means of leads  50 . 
     In any of FIGS. 5-13, application of RF power heats the contents of wells  44  to the T c  of the associated discs  58  and holds that temperature until the power is terminated. The contents of the wells  44  are then analyzed by serial or parallel analytical means. A video camera and a CCD imager to obtain images of the plate are examples of parallel analytical means. Image analysis can then determine color levels from the imaged signals of each well location. An image analysis program can then transfer the results to a computer for evaluation. In a serial analysis, a robotic device can address each well  44  in sequence with a fiber optic sampling probe connected to a spectrograph. In this case, individual spectra or derived color values can be transferred to a computer for evaluation. 
     These and other features will become apparent from the following detailed discussion, which by way of example without limitation describes preferred embodiments of the present invention. 
     EXAMPLE 1 
     A glass 96 well plate with flat bottom wells is placed on a substrate as in FIG. 5, containing ferromagnetic discs in rows of  8 . Pairs of the rows have identical compositions so that 6 different ferromagnetic disc compositions are provided in all. Adjacent pairs of rows have discs of different composition such that there is a 15° C. increase in T c  of the disc materials across the 6 pairs of rows of the 96 well plate. The discs are prepared from Fe/Ni alloys that vary in composition by about 0.5 atom % in the range of 36 to 38.5 atom % Ni. Thus, target temperatures across the reaction array range from 265° C. to 322° C. 
     A varying combinatorial array of bisphenol-A polycarbonate and a selection of experimental and commercial stabilizers at known concentrations are loaded into the array wells by means of a robotic fluid handling device and the transfer solvents are evaporated. Thus, an array consisting of 6 replicates of 16 elements of polycarbonate resins with varying stabilizer compositions and amounts are generated. The wells are capped with an oxygen permeable membrane and the reaction plate is attached to an RF generator. Application of RF power heats the reaction wells to the T c  of the discs and holds that temperature until the power is discontinued. The contents of the reactor plate are then analyzed by a CCD imager to obtain an image of the entire plate. Image analysis then determines color levels from the red, green and blue signals of the image at each well location. An image analysis program then transfers the imaging data to a computer for analysis. Effectiveness of the various stabilizers as a function of temperature for each polycarbonate/stabilizer composition is determined by measuring the amount of thermal yellowing of the resin. 
     EXAMPLE 2 
     The following example illustrates the invention as carried out in the reactor plate  10  of FIG. 6. A 96-well plate  10  is provided that is constructed of quartz. A 25 milligram disc of an alloy containing 38.6 atom % nickel is placed in each well  14 . Then, to each well a robotic fluid delivery system adds diphenyl carbonate and bisphenol-A reactants. Subsequently, a range of different basic catalysts are added by a fluid robotic delivery system so that individual wells or groups of wells have chemically distinct catalysts or identical catalysts with varying concentrations. The array plate  10  is placed inside an antenna coil and excited by a 200 watt RF field. The reaction temperature rises rapidly to 325° C. and holds steady while the RF field is maintained. At the end of a reaction time, the array plate  10  is cooled and the resulting polycarbonate resins are analyzed. 
     While a preferred embodiment of the invention has been described, the present invention is capable of variation and modification and therefore should not be limited to the precise details of the Example. For example, the procedure of Example 1 can be carried out in the array plate  10  or  40  of any of FIGS. 3 to  5  or  7  to  8  with any of the RF coil arrangements illustrated in FIGS. 9 to  13 . The invention includes changes and alterations that fall within the purview of the following claims.