Lyophilisation: difference between revisions
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| 11 | The process is used because peptides in aqueous solution degrade by hydrolytic routes — [[deamidation]] of asparagine and glutamine, backbone cleavage, [[Peptide aggregation|aggregation]] — whose rates depend strongly on molecular mobility and on the availability of water. Removing water and holding the residue in an amorphous glass suppresses those routes by orders of magnitude, converting a product with a shelf life of days at ambient temperature into one with a shelf life measured in years.{{r|wang2000,chang2009}} | 11 | The process is used because peptides in aqueous solution degrade by hydrolytic routes — [[deamidation]] of asparagine and glutamine, backbone cleavage, [[Peptide aggregation|aggregation]] — whose rates depend strongly on molecular mobility and on the availability of water. Removing water and holding the residue in an amorphous glass suppresses those routes by orders of magnitude, converting a product with a shelf life of days at ambient temperature into one with a shelf life measured in years.{{r|wang2000,chang2009}} |
| 12 | 12 | ||
| + | 13 | == Physical basis == | |
| + | 14 | Water can pass directly from solid to vapour only at pressures below its triple point, which lies at 611.657 Pa and 0.01 °C. Above that pressure, warming ice produces liquid; below it, warming ice produces vapour. Every lyophilisation cycle therefore operates at a chamber pressure well beneath 611 Pa, typically between 5 and 20 Pa, so that heat supplied to the product drives sublimation rather than melting.{{r|nail2002}} | |
| + | 15 | ||
| + | 16 | The driving force for sublimation is the difference between the vapour pressure of ice at the product temperature and the partial pressure of water vapour in the chamber. Because the vapour pressure of ice falls steeply with temperature, small changes in product temperature produce large changes in drying rate. | |
| + | 17 | ||
| + | 18 | |+ Vapour pressure of ice | |
| + | 19 | | !Temperature | Vapour pressure | Ratio to 0 °C | | |
| + | 20 | |---|---|---| | |
| + | 21 | | 0 °C | 611.2 Pa | 1.00 | | |
| + | 22 | | −10 °C | 259.9 Pa | 0.43 | | |
| + | 23 | | −20 °C | 103.2 Pa | 0.17 | | |
| + | 24 | | −30 °C | 38.0 Pa | 0.062 | | |
| + | 25 | | −40 °C | 12.84 Pa | 0.021 | | |
| + | 26 | | −50 °C | 3.94 Pa | 0.0064 | | |
| + | 27 | ||
| 13 | == References == | 28 | == References == |
| 14 | {{reflist}} | 29 | {{reflist}} |