CRYSTALLIZATION TRAY

Specification

Technical field

The invention deals with the crystallization of molecules, especially macromole- cules, by a so-called sitting drop vapor diffusion technique. The invention relates to a crystallization tray with one or more crystallization units. The invention can be used for example in the preparation and research of proteins.

Technical background

In the crystallization of macromolecules, in particular, a so-called vapor diffusion technique is used. It comprises placing a small drop of dissolved substance to be crystallized into a chamber, which contains separately from the drop a solution of the same liquid, the vapor pressure of the liquid in the solution being lower than that of the solution in the drop. When the solutions are contained in a common sealed chamber, the liquid of the drop gradually concentrates, thus leading to the crystallization of the dissolved substance. The size of a crystallization drop is typically 0.1 - 4 μl. In a so called sitting drop technique, the drop is placed in a small dish.

Vapor diffusion crystallizations are often conducted in large series, and the progress of crystallization can be traced automatically by means of a camera. For sitting drop crystallization, various types of trays are available, provided with an array of crystallization units. The crystallization unit usually includes a larger solution dish and one or more small crystallization dishes thereabove. The unit can be tightly sealed. Patent publication EP 1119654 Bl, for example, discloses one such crystallization tray. Its crystallization unit contains a central reservoir with four drop chambers above and around it, each with a diffusion channel extending from its upper part to the upper part of the central reservoir.

General description of the invention

What is invented now, as set forth in the independent claims, is a crystallization tray, a crystallization method, and use of those for the crystallization of macro- molecules. The dependent claims present some preferred embodiments of the in- vention.

The crystallization unit of a crystallization tray includes a solution well and separated therefrom a horizontal crystallization plane. The crystallization plane does not include wells or bulges. On the upper surface of the crystallization plane there is at least one crystallization zone whose adsorptivity to the liquid used in crystalli- zation is higher than that of the surrounding area. Thus, a drop of liquid administered onto the plane settles within the crystallization zone.

Since the crystallization liquid is generally aqueous, the crystallization zone is usually most conveniently more hydrophilic than the surrounding area.

A benefit of the invention is, among others, that the trays can be manufactured by injection molding more conveniently than the prior known trays.

Drawings

The accompanying drawings constitute a portion of the written description and relate to the subsequent detailed description of the invention. The drawings illus- trate one crystallization tray according to the invention. Fig. 1 shows the tray in a side view section and fig. 2 shows the tray in a plan view.

Detailed description of the invention

The crystallization unit according to the invention is provided with a crystalliza- tionplane, which includes at least one crystallization zone whose adsorptivity to the liquid in question is higher than that of the surrounding area. The crystallization plane is most preferably a ledge on the wall of a solution well.

According to one preferred embodiment, the crystallization unit includes a solution well with a substantially rectangular cross-section and with a ledge on one side thereof.

The crystallization shoulder includes most preferably several crystallization zones, for example 2 - 4.

Most preferably, the crystallization zone is circular and has a cross-section which is smaller than that of an administered drop. Thus, the drop strives to uphold as round a shape as possible and the drop sort of anchors itself to the surface.

Since the crystallization liquid is generally aqueous, the crystallization zone is usually most conveniently more hydrophilic than the surrounding area.

Most preferably, the crystallization tray contains an array of crystallization units, for example 96 specimens in a 12x8 microtitration plate format. The manufacture of trays of the invention by injection molding is easier than prior known trays. The attainment and management of a required optical quality are easier. The molding tool costs are also lower.

One and the same basic tray can be readily formed into trays modified for various applications as the number, shape and adsorptivity of crystallization zones can be varied.

From a smooth surface, a crystal is easily picked up to be carried away. For example, X-ray investigations often require an absolutely intact crystal.

Likewise, the tracing of crystal growth automatically with a camera is easy. From a smooth surface, the camera finds and focuses a crystal easily. Imaging is as reli- able as possible as the shoulder does not have light-refracting angles. The shoulder is also easier to manufacture for a consistent optical quality.

The administration of a drop need not be perfectly spot-on. The drop is inherently attracted to the crystallization zone as long as just a fraction of the drop touches the zone. The drop also releases easier from an administration instrument.

The surfaceEs adsorptivity can be changed, for example by treating with some suitable chemical, by coating (e.g. with an appropriate lacquer, sol-gel or film) or by a plasma treatment. In plasma treatment, the surface undergoes chemical changes, for example repolymerization. Another possibility is to apply an appropriate treatment to the surface of a mold for providing the molded product with ar- eas of unequal adsorptivity. The invention can be implemented either by making the crystallization zone more adsorptive or the surrounding area less adsorptive. Regarding the treatment, it is naturally necessary to make sure that the employed

chemical, for example, does not interfere with crystallization or that the trayEs p- tical qualities are at a required level even after the treatment.

In reference to the drawings, one more example of a crystallization tray according to the invention will now be described.

Regarding its dimensions, the crystallization tray of figs. 1 and 2 is consistent with a vertical row present on a standard 8x12 microtitration plate. The tray contains 8 crystallization units 1, each having a liquid well 2. The liquid well is basically rectangular by shape and it has a diameter which is longer in a direction transverse to the row than in a direction lengthwise of the row. The well has its edges rounded. The well has one of its row-directed sides provided with a horizontal ledge 3, featuring two crystallization spots 4 which are more hydrophilic than the ledge surface surrounding them. The spots are formed for example by coating with an appropriate hydrophilic agent. The crystallization unit has a smooth and flat top edge, making the units tightly sealable with a cover. The tray and the cover are manufactured from an appropriate transparent plastic material by injection molding.

The substance to be crystallized is dissolved in the aqueous solution. A small drop of the solution (e.g. appr. 2 μl) is administered onto the crystallization spot 4. Because of the zoneEs hydrophilicity, the drop centers and anchors itself onto the zone. Into the liquid well is administered some strong aqueous solution, the water of which has a vapor pressure which is lower than that of the drop. The crystallization unit is closed with a transparent cover. Thus, water starts to evaporate from the drop and that is absorbed in a liquid phase present in the liquid well. When the dropEs solution concentrates, the substance crystallizes. The crystallia- tion can be monitored through the cover.