Solid-phase peptide synthesis (SPPS) is now the accepted method for creating peptides and proteins in the laboratory in a synthetic manner. Small porous solid beads (typically resin) are treated with functional units, or linkers, on which peptide chains can be built. The peptide will remain covalently attached to the bead until cleaved from it by a reagent, such as trifluoroacetic acid.
The general principle of solid-phase peptide synthesis involves repeated cycles of coupling, wash, deprotection, and wash steps (Chan and White, “Fmoc solid phase peptide synthesis: A practical approach”, Oxford University Press, Oxford, England, 2000). The free N-terminal amine of a solid-phase attached peptide is coupled to a single N-protected amino acid unit. The formed unit is then deprotected, revealing a new N-terminal amine to which a further amino acid may be attached. The superiority of this technique partially lies in the ability to perform wash cycles after each reaction, removing excess reagent with all of the growing peptide of interest remaining covalently attached to the insoluble beads.
The use of microwave irradiation in peptide synthesis has reduced coupling reaction times substantially, and also permitted preparation of long peptide sequences with high degrees of yield and low degrees of racemization (Pedersen, S. L., et al. Microwave heating in solid-phase peptide synthesis. Chem. Soc. Rev. 2012, 41, 1826-1844).
In solid phase synthesis, the mass transfer around the resin beads is of great importance. To achieve this, different kinds of mixing techniques are used in today's solid phase peptide synthesis instruments, including, for instance, vortex mixers (sometimes described as variable oscillating mixers), N2 bubbling, recirculation, and inversion mixers.
In a microwave based instrument for peptide synthesis, the microwave cavity of the instrument has a limited volume which determines the maximum size of the reaction vial, the filling degree of which is in turn determined by the mixing technique used.
Since using a magnetic stirrer, a paddle or some other mechanical device for mixing might damage the peptide synthesis resin beads, vortex mixing has typically been used in commercial instruments.
WO 99/56863 discloses a mixing device for mixing liquids and/or solids wherein a container, typically a cylindrical vessel, which is received in a holder can be rotated alternately in clockwise and anti-clockwise direction about the axis of the container by means of a drive mechanism. The angular displacement of the container is regulated by a control unit. In addition to providing for efficient mixing, the device enables the meniscus deflection to be kept small such that mixing is also possible in almost completely filled vessels without a closure.