If you have been reading about Sublimation and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-06-17. Where a claim depends on a specific study, the study is described rather than over-claimed.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization, also called freeze-drying, removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts free water into ice and may also produce a glassy phase. Primary drying then lowers chamber pressure so ice sublimes directly to vapor without passing through a liquid stage. Secondary drying raises the temperature modestly to remove bound water. The result is a porous, dry solid that usually reconstitutes quickly. Each stage influences pore structure, residual moisture, and stability.
The physics of lyophilization depends on phase boundaries and heat and mass transfer. During primary drying, heat supplied to the product must equal the latent heat of sublimation, while water vapor moves through the drying cake to the condenser. If shelf temperature or pressure is set too high, the ice front can exceed the collapse temperature, causing meltback or pore collapse. If conditions are too cold, drying slows and costs rise. Formulation excipients, vial geometry, and freezing rate alter these limits.
| Property | Value | Notes |
|---|---|---|
| Common name | Freeze-drying | Process removes water by sublimation under vacuum. |
| Typical primary drying shelf temperature | -40 C to -10 C | Set below the formulation's collapse temperature. |
| Typical chamber pressure | 0.05-0.3 mbar | Low pressure allows ice to sublime below its triple point. |
| Water content after drying | 0.5-3% by weight | Higher values may reduce storage stability for some materials. |
| Key thermal parameter | Collapse temperature | Measured by freeze-drying microscopy or differential scanning calorimetry. |
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
The process usually has three stages: freezing, primary drying, and secondary drying. Freezing sets the ice crystal structure and can determine pore size in the final cake. Primary drying removes free ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, although some water may remain as part of the solid. Cycle parameters depend on formulation, fill volume, vial type, and equipment performance.
The physical chemistry of freezing influences whether a formulation forms an amorphous glass or a crystalline solid. Amorphous systems can collapse if product temperature rises above the glass transition temperature of the freeze concentrate. Crystalline systems may show eutectic melting, where ice and solute melt together at a fixed temperature. Formulators add bulking agents, lyoprotectants, and buffers to preserve structure and biological activity. The optimum cycle keeps product temperature below critical thresholds during primary drying while allowing efficient sublimation.
Lyophilization is a drying process in which a solvent, usually water, is removed from a frozen material by sublimation under reduced pressure. The material is first solidified, then placed under vacuum so that ice transitions directly to vapor without a bulk liquid phase. This approach suits heat-sensitive substances that would degrade during conventional evaporation. Primary drying removes unbound ice, while secondary drying reduces water that remains adsorbed to the solid matrix. The result is a porous, lightweight solid that can be reconstituted later.
A typical cycle begins with freezing, sometimes including an annealing step to control ice crystal size. Freezing conditions influence the pore network that later allows vapor escape. During primary drying, shelf temperature and chamber pressure are set so heat enters the product while its temperature stays below the collapse or eutectic point. Secondary drying then raises the shelf temperature to desorb bound water and lower residual moisture. Cycle design depends on formulation, fill volume, container type, and equipment capability.
The physics of lyophilization couples heat transfer, mass transfer, and phase behavior. Sublimation requires a vapor pressure difference between the ice front and the chamber, and the dried layer adds resistance to vapor flow. Amorphous formulations are characterized by a glass transition temperature of the maximally freeze-concentrated solute, often denoted Tg'. Crystalline bulking agents can provide structure, while amorphous excipients stabilize labile components. Open questions remain about spatial heterogeneity, edge effects, and how laboratory cycles scale to production.
=== Wet media milling (nanocrystal technology) === In wet media milling, the drug substance is suspended in an aqueous solution containing a stabilizing surfactant or polymer and circulated through a chamber filled with small (typically 0.2–0.5 mm) ceramic, glass, or polymer-coated beads. Bead-on-bead and bead-on-particle impacts progressively reduce the drug particle size to the 100–400 nm range, while the stabilizer adsorbs onto newly created surfaces and prevents agglomeration. The technology, commercialized as NanoCrystal by Elan Drug Technologies (later Alkermes), underpins several U.S. Food and Drug Administration–approved products, including sirolimus (Rapamune oral tablet, approved 2000), aprepitant (Emend, 2003), fenofibrate (Tricor 145 mg, 2004; Triglide, 2005), and megestrol acetate (Megace ES, 2005).
==== Apixaban binding to factor Xa ==== Apixaban shows a similar binding mode as rivaroxaban and forms a tight inhibitor-enzyme complex when connected to FXa. The p-methoxy group of apixaban connects to S1 pocket of FXa but does not appear to have any interaction with any residues in this region of FXa. The pyrazole N-2 nitrogen atom of apixaban interacts with Gln-192 and the carbonyl oxygen interacts with Gly-216. The phenyl lactam group of apixaban is positioned between Tyr-99 and Phe-174 and due to its orientation, it is able to interact with Trp-215 of the S4 pocket. The carbonyl oxygen group of the lactam moiety interacts with a water molecule and does not seem to interact with any residues in the S4 pocket.
Note: The following list gives the isoelectric point at 25 °C for selected materials in water. The exact value can vary widely, depending on material factors such as purity and phase as well as physical parameters such as temperature. Moreover, the precise measurement of isoelectric points can be difficult, thus many sources often cite differing values for isoelectric points of these materials. Mixed oxides may exhibit isoelectric point values that are intermediate to those of the corresponding pure oxides. For example, a synthetically prepared amorphous aluminosilicate (Al2O3-SiO2) was initially measured as having IEP of 4.5 (the electrokinetic behavior of the surface was dominated by surface Si-OH species, thus explaining the relatively low IEP value). Significantly higher IEP values (pH 6 to 8) have been reported for 3Al2O3-2SiO2 by others. Similarly, also IEP of barium titanate, BaTiO3 was reported in the range 5–6 while others got a value of 3. Mixtures of titania (TiO2) and zirconia (ZrO2) were studied and found to have an isoelectric point between 5.3–6.9, varying non-linearly with %(ZrO2). The surface charge of the mixed oxides was correlated with acidity. Greater titania content led to increased Lewis acidity, whereas zirconia-rich oxides displayed Brønsted acidity. The different types of acidities produced differences in ion adsorption rates and capacities.
Sources: en.wikipedia.org
N1,N8-bis(glutathionyl)spermidine + ADP + phosphate The 3 substrates of this enzyme are glutathione, glutathionylspermidine, and ATP, whereas its 3 products are N1,N8-bis(glutathionyl)spermidine, ADP, and phosphate. This reaction is especially important for protozoa in the order kinetoplastida as the molecule of N1,N8-bis(glutathionyl)spermidine, also known as trypanothione, is homologous to the function of glutathione in most other prokaryotic and eukaryotic cells. This means that it is a key intermediate in maintaining thiol redox within the cell and defending against harmful oxidative effects in such protozoa. This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds as acid-D-ammonia (or amine) ligases (amide synthases). The systematic name of this enzyme class is glutathionylspermidine:glutathione ligase (ADP-forming).
==== Economic impact on Denmark ==== By 2023, Novo Nordisk was the most valuable corporation in the European Union, worth more than US$500 billion, and accounted for almost all economic growth in Denmark. The large amounts of foreign currency earned by Novo Nordisk from Wegovy and Ozempic sales, when converted to Danish krone, have exerted upward pressure on the value of the krone, making it necessary for Danmarks Nationalbank to maintain lower interest rates than the European Central Bank. Poor clinical trial results published by Novo Nordisk in December 2024 contributed to a drop in the krone's value. Profits from Novo Nordisk result in increased Danish tax revenues and employment. Novo Nordisk added 3,500 jobs in Denmark in 2022, bringing the total in the country to 21,000 employees, out of 59,000 worldwide. As of February 2026, Novo Nordisk has a market capitalization of $220.42 billion.
===== Parity Violation ===== Parity, a physical property of symmetry, is conserved for strong, electromagnetic, and gravitational interactions. However, experimental work involving weak forces, such as the interactions between subatomic particles, found that parity is not conserved in these interactions (see Parity Violation). This theoretically would result in slight energy differences between mirror-image enantiomers of a single compound, which could cause a small stereochemical bias for the lower-energy enantiomer. However, a definitive relationship between molecular chirality and parity-violating energy differences have not yet been experimentally demonstrated.
Sources: en.wikipedia.org
== History == B-cell activating factor is a naturally occurring protein that was discovered by researchers from National Jewish Health (previously the National Jewish Medical and Research Center) and the University of Colorado, who jointly published a paper detailing their findings in May 1999 and named the protein TALL-1. The same protein was named BAFF in another paper published in June 1999, and in a paper published in July of that year, Human Genome Sciences (HGS) referred to it as BLyS (short for B lymphocyte stimulator). Six years later, research showing the key role of BLyS in B cell differentiation, survival, and activation was published. In October 2000, HGS and Cambridge Antibody Technology (CAT) agreed to co-develop monoclonal antibodies targeted at BLyS. Under this agreement, CAT would identify antibodies and HGS would select appropriate ones to take into clinical trials. In 2003, CAT researchers reported that, by using phage display technology, they had elicited an array of more than 1,000 distinct antibodies, half of which inhibited binding of BLyS to its receptor. Later that year, one of these antibodies was isolated and characterized. It was named LymphoStat-B and subsequently called belimumab. In August 2006, HGS and GlaxoSmithKline (GSK) entered into a co-development and commercialization agreement under which HGS would conduct Phase III trials for belimumab with assistance from GSK. The companies would share equally in Phase III/IV development costs, sales and marketing expenses, and profits of any product commercialized under the agreement.
=== Acidity === The methyl groups of DMSO are only weakly acidic, with a pKa = 35. For this reason, the basicities of many weakly basic organic compounds have been examined in this solvent. Deprotonation of DMSO requires strong bases like lithium diisopropylamide and sodium hydride. Stabilization of the resultant carbanion is provided by the S(O)R group. The sodium derivative of DMSO formed in this way is referred to as dimsyl sodium. It is a base, e.g., for the deprotonation of ketones to form sodium enolates, phosphonium salts to form Wittig reagents, and formamidinium salts to form diaminocarbenes. The dimsyl anion is a potent nucleophile.
The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of 5,150 km (3,200 mi). Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock. Orientation with the stellar compass depends on the position of the constellations surrounding Polaris. These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.
== Ecology == Xanthoria parietina demonstrates a range of physiological and morphological adaptations that facilitate its survival in diverse habitats. Populations in drier, more exposed habitats produce longer-chain surface hydrocarbons (alkanes), whereas those in more humid, cooler regions synthesize shorter-chain alkanes—a response that helps reduce water loss, similar to adaptations seen in vascular plants. Its thallus morphology is plastic; forms in moist stream beds tend to be semi-erect and orange-yellow, whereas those in drier, sun-exposed sites are more compact and darker orange. These differences appear to be induced by environment conditions rather than genetic differences.
Sources: en.wikipedia.org
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.
Freezing determines ice crystal size, pore structure, and the concentration of solutes in remaining liquid. Faster freezing generally creates smaller ice crystals and a denser dried matrix. These features affect drying rate and reconstitution behavior.
Lyophilization reduces water content but usually leaves a small amount of water in the dried material. Some water remains bound to solids or trapped in the dried matrix. Very low water targets can require extended secondary drying, which may alter product stability.
Simple drying usually removes water by evaporation from a liquid or solid, often with heat. Lyophilization first freezes the material and then removes ice by sublimation under vacuum. This avoids prolonged exposure to liquid water and high temperatures.