Abstract:
A multi-well plate is disclosed for holding chemical compounds for heating in a microwave oven. The plate is a substantially planar member having wells arranged in an array of rows and columns in its upper surface. The plate has heat reservoirs in the form of fluid filled channels or elongated solid bodies positioned lengthwise along the side portions of the plate to reduce temperature gradients among the wells across the length and width of the plate. The heat reservoirs prevent or mitigate heat loss from the wells near the side portions of the plate and ensure that the compounds in all of the wells have a uniform temperature.

Description:
FIELD OF THE INVENTION 
     This invention concerns multi-well plates for organic chemical synthesis testing, and especially to multi-well plates useable in a microwave. 
     BACKGROUND OF THE INVENTION 
     Organic chemical synthesis concerns the chemistry of the compounds of carbon and is fundamental to a broad range of industrial and research activities, notably pharmaceuticals, but also including polymer chemistry, the chemistry of food additives, flavor chemistry, as well as biochemistry. 
     Synthesis testing involves the determination of percentage yield of product from starting reagents. Synthesis testing may be performed in either the solid or liquid phases and is conveniently accomplished using a multi-well plate, wherein reagents of various concentrations in each well are permitted to react and form product compounds. The percentage yield for the various starting concentrations is measured and compared to determine the optimum reagent ratios which will yield the largest percentage of product. 
     When the reaction is endothermic or when heat is a catalyst, it is convenient to heat the reagents in a microwave oven. Microwave heating works by exciting molecules having a dipole moment at or near the resonant frequency of the dipole and, hence, is very selective in what is heated within the oven. For example, the microwaves bombarding a multi-well plate will heat the reagents within the wells but will not heat the plate or the air within the oven. While this is economical, because energy is not wasted heating items other than the constituents, there is a drawback in that temperature differences are present between items within the oven, such as between the reagents and the plate, as well as between the plate and the ambient air. Such temperature differences inevitably cause heat transfer to occur. For example, heat is transferred from the reagents to the plate and from the plate to the ambient air within the microwave chamber. The heat transfer leads to transient and static temperature gradients across the plate. Relatively lower temperatures are found in the wells near the edges of the plate where the heat transfer from the plate to the air is greatest due to the relatively large surface area of the side portions of the plate in contact with the air. Relatively higher temperatures are present in the wells near the center of the plate where the heat transfer is not as great because there is less surface area from which heat is lost. 
     The temperature gradients cause uneven results to occur, thereby biasing the testing and providing false results since all of the samples are not being tested at the same temperature due to the gradients formed across the plate. There is clearly a need for a multi-well plate useable in a microwave oven which does not suffer from the disadvantages of temperature gradients and which will yield consistent, uniform results in testing. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention concerns a multi-well plate for holding a compound for testing. The plate is formed from a substantially planar member having an upper surface and a plurality of side portions bounding the planar member. A plurality of wells are positioned in the planar member and are adapted to hold samples of the compound. Each of the wells has an opening located on the upper surface. A first group of the wells are arranged adjacent to one of the side portions. A first elongated body extends lengthwise along the one side portion adjacent to the first group of wells. The body has a capacity to act as a heat reservoir to resist temperature changes of the samples in the first group of wells relative to the samples in others of the wells. Preferably, the body extends substantially continuously around the planar member and serves as a heat reservoir to resist temperature changes of samples in any other adjacent wells. 
     In its preferred embodiment, the substantially planar member is bounded by downwardly depending side portions. The first group of wells is arranged adjacent to one of the side portions. The elongated body comprises a first elongated chamber which extends within the plate lengthwise along the one side portion and is positioned between the one side portion and the first group of wells. The first chamber is adapted to contain a fluid which has a capacity to act as a heat reservoir and resist temperature changes of the samples in the first group of wells relative to the samples in others of the wells. 
     In the preferred embodiment, the first chamber is filled with a liquid and is sealed to isolate it from the ambient. In an alternate embodiment, the chamber is initially air-filled and there is a port in the planar member in fluid communication with the first chamber. The port is adapted to receive the fluid, preferably a liquid which may be poured through the port to fill the first chamber. Preferably, the port is positioned on the upper surface. 
     The plate preferably has a second group of the wells arranged adjacent to another of the side portions and a second elongated chamber extending within the plate lengthwise along the other side portion. The second chamber is positioned between the other side portion and the second group of wells. Similar to the first chamber, the second chamber is also adapted to contain a fluid having a capacity to act as a heat reservoir and resist temperature changes of the samples in the second group of the wells relative to the samples in others of the wells. Preferably, the first and the second chambers are in fluid communication with each other. 
     In another embodiment, the elongated body is a solid material which may be heated by the microwaves and preferably extends continuously around the planar member. The solid material may be considered to form the side portions or it may be positioned within the elongated chamber. 
     It is an object of the invention to provide a multi-well plate suitable for use in a microwave oven. 
     It is another object of the invention to provide a multi-well plate in which temperature differences between wells is minimized. 
     It is another object of the invention to reduce or eliminate the presence of temperature gradients across the plate. 
     These and other objects of the invention will become apparent from consideration of the following drawings and detailed description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a multi-well plate according to the invention; 
     FIG. 2 is a plane sectional view of the plate shown in FIG. 1 taken along lines  2 — 2 ; 
     FIG. 3 is a cross-sectional view of the plate shown in FIG. 1 taken along lines  3 — 3 ; 
     FIG. 4 is a perspective view of another embodiment of a multi-well plate according to the invention; 
     FIG. 5 is a plane sectional view of the multi-well plate shown in FIG. 4 taken along lines  5 — 5 ; 
     FIG. 6 is a partial cross-sectional view of the multi-well plate taken along lines  6 — 6  in FIG. 4; 
     FIG. 7 is a partial cross-sectional view of an alternate embodiment of a multi-well plate according to the invention similar to FIG. 6; 
     FIG. 8 is a cross-sectional view of another alternate embodiment of a multi-well plate according to the invention similar to FIG. 3; 
     FIG. 9 is a cross-sectional view of another alternate embodiment of a multi-well plate according to the invention similar to FIG. 3; and 
     FIG. 10 is a perspective view of multi-well plates in use. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a multi-well plate  10  according to the invention. Plate  10  is a substantially planar member  12  bounded by downwardly depending side portions  14 . The plate has an upper surface  16  and a plurality of wells  18 , each well having an opening  20  on the upper surface  16 . The wells are preferably arranged in a regular array of rows and columns and are adapted to hold samples of compounds for heating in an experiment, for example, one involving solid phase synthesis. 
     As best shown in FIGS. 2 and 3, an elongated chamber  22  extends lengthwise within the planar member  12  between one of the side portions  14  and a row or group of wells  24  proximal to the side portion. In the preferred embodiment, the chamber extends continuously around the entire planar member  12  between the outermost rows of wells and the proximal side portions  14 . Preferably, the chamber is permanently sealed and isolated from the ambient and contains a substance  26 , which has a capacity to act as a heat reservoir, i.e., the substance is heatable by microwave radiation and has the ability to store and transfer heat. The preferred substance  26  is a liquid and has a higher boiling point than the temperature at which the experiment is designed to run for reasons described below. 
     The plate illustrated in FIG. 1 is preferably made of polytetrafluoroethylene or another relatively inert substance which is transparent to microwaves (i.e., will not heat up significantly when subjected to microwave radiation), will not react with the compound in the wells and which can withstand relatively high temperatures, at least in excess of the experiment temperature. The plate may be machined from a solid block, the channel filled with the substance  26  and then sealed with the bottom plate  28 , attached with adhesives or fasteners or other appropriate means. 
     FIG. 4 shows another embodiment of a multi-well plate  30  wherein one or more chambers  22  are drilled into the planar member  12 , each chamber being positioned between a respective row of wells  34  and a side portion  14 . As shown in FIG. 5, chambers  22  preferably surround the entire planar member  12  and are in fluid communication with one another. One or more plugs  36 , as necessary, are used to seal the chambers to prevent the fluid contents from escaping. A fill port  38 , in fluid communication with a chamber  22 , is preferably located on the upper surface  16  of the planar member  12  to permit a liquid to be poured into the chambers. It is convenient to use two fill ports  38  as shown in FIG. 4, one of the ports allowing air to escape from the chamber or chambers as fluid is poured into the other. 
     While a single chamber  22  may be used per side of the plate as shown in FIG. 6, the invention contemplates using multiple chambers  22  arranged one above the other along one or more sides of a plate as shown in FIG.  7 . This embodiment will allow more fluid to be positioned between a row of wells and a side portion  14  of the plate, thereby increasing the effectiveness of the chambers as a heat reservoir as described below. 
     Chambers  22 , when filled with an appropriate substance  26 , act as heat reservoirs to slow or prevent heat loss from the sides  14  to the cooler ambient air within the microwave oven. The substance acts as a buffer which does not allow significant heat transfer from wells  24  positioned adjacent to the sides, thus, allowing all of the wells to maintain substantially the same temperature and avoid any significant temperature gradient between wells at the center of the plate and wells nearer to the sides  14 . By avoiding significant temperature gradients, the integrity of the experimental results will not be compromised and meaningful results will be obtained for all of the reactants in all of the wells of the multi-well plate according to the invention. 
     To ensure effective operation of the multi-well plate, it is preferred that a liquid within chambers  22  have a boiling point relatively higher than the temperature at which the experiment is to be run. This will ensure that the chambers remain fluid filled and continue to act as a heat reservoir to reduce or eliminate temperature gradients, and also do not form a vapor which may contaminate the atmosphere within the oven, possibly compromising the integrity of the experiment. Safety is also an issue since liquid, heated to its boiling point within a sealed chamber, may achieve significant pressure before the chamber bursts and spews the hot liquid and vapor into the oven. 
     For example, for an experiment designed to heat the samples within the wells to a constant temperature of about 130° C., the preferred liquid  26  within chambers  22  is N-methylpyrrolidinone, which has a boiling point of 202° C. at one atmosphere of pressure. A boiling point for the liquid substance  26  of at least 50° C. above the temperature of the experiment provides an adequate safety margin for most applications. 
     For a standard multi-well plate made of polytetrafluoroethylene having 96 wells and dimensions of 124×85×27 mm, it is found that about 7 mL of liquid is sufficient to form an effective heat reservoir around the plate and reduce the temperature gradients to relative insignificance. A greater volume of liquid is preferred however to provide even more effective gradient smoothing. 
     In another embodiment, shown in FIG. 8, a heat reservoir  40  is formed around the planar member  12  by positioning an elongated body  44  of solid material lengthwise along the sides  46  directly adjacent to the wells  18 . The elongated body  44  may be considered to form the side portions  14  and preferably extends continuously around the entire planar member. The material comprising body  44  is readily heatable by the microwave to the temperature of the experiment and thereby acts as a heat reservoir to prevent heat loss from the adjacent wells  18  to the cooler atmosphere within the microwave oven. The presence of the solid body surrounding the planar member  12  prevents any significant temperature gradients from forming between the center wells and the wells adjacent to the sides  46 . Any gradients which would form would likely be confined to the elongated body  44  itself. The body  44  may be formed of ceramic material, as well as other solid materials. If the body  44  is a gelatinous material, it may be placed within the chamber  22  between the sides  46  and the side portion  14  as shown in FIG. 9 before the bottom plate  28  is attached to seal the chamber. This is similar to the embodiment shown in FIG.  3 . 
     FIG. 10 shows multi-well plates  10  according to the invention being used on a turntable  48  which is positioned within a microwave oven, not shown. Preferably, the plates  10  resides in a tray  50  which is situated on turntable  48 , preferably within a recess  52  to ensure proper positioning of the plate. A rotating arm  54  permits a measuring device, such as a thermometer, to be brought to bear on the plates to monitor the temperature of the compound samples in the wells. The turntable is powered and turns within the oven about vertical axis  56  to ensure even heating to all of the wells within all of the plates by the microwaves. 
     Experimental results achieved prove the effectiveness of the multi-well plate according to the invention when used in a microwave oven in chemical synthesis testing. For such a plate, 90% to 100% of the reactants in all wells go to product. This contrasts with multi-well plates according to the prior art wherein the reactants in the wells adjacent to the periphery see only 10% to 20% of the reactants going to product.