The short version of glass transition fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-11-26. Anything still debated is marked as such rather than presented as settled.
Lyophilized products are typically hygroscopic and require protection from moisture during storage. Manufacturers seal them in glass vials, often under vacuum or an inert gas such as nitrogen. The container closure system, including the stopper and crimp seal, must prevent water vapor ingress. Storage temperature varies from controlled room temperature to refrigerated or frozen conditions, depending on the formulation. Humidity-controlled environments are essential because even brief exposure to ambient air can degrade the product.
Stability of a lyophilized product depends on its glass transition temperature, the temperature at which the amorphous cake transitions from a glassy to a rubbery state. Storage below this temperature minimizes molecular mobility and slows chemical degradation. If the storage temperature exceeds the glass transition temperature, the cake may collapse, shrink, or become sticky. Accelerated stability studies at elevated temperatures and humidity help predict shelf life, but they do not always reflect real-time behavior. Residual moisture content also plays a critical role in long-term stability.
Reconstitution involves adding a suitable diluent, often sterile water or a buffer, to the dried cake. Gentle swirling or inversion helps dissolve the material without creating excessive foam. The time required for complete dissolution can range from seconds to several minutes and depends on the cake structure and the diluent. Improper reconstitution, such as vigorous shaking or using the wrong diluent, can cause protein aggregation or loss of activity. After reconstitution, the product may have a limited shelf life and should be used according to its labeling.
Lyophilization removes water by freezing a material and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intermediate liquid state. Because the material remains frozen during primary drying, the structure often stays porous. This porous matrix can rehydrate quickly when water is added back. The low pressure also allows vapor to leave the solid matrix without boiling.
A typical cycle begins with freezing, which fixes the material into a solid and determines ice crystal size. Primary drying then raises heat under vacuum so ice sublimes, often near or below the collapse temperature of the formulation. Secondary drying removes bound water that remains after ice is gone, usually by gently warming the product. Each stage balances heat input against pressure to avoid melting or structural damage. Temperature probes and pressure sensors guide the transition between stages.
In practice, lyophilization is slower and more energy intensive than simple drying. Cycle times can range from hours to several days depending on load, container, and formulation. Amorphous materials may require excipients that help preserve structure during freezing and drying. The method is widely used for biological materials, pharmaceuticals, and foods where heat drying would cause unacceptable change. Open questions remain about scaling cycles between laboratory and production equipment, and this gap affects technology transfer.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white porous cake | Color depends on formulation. |
| Typical storage temperature | 2–8 °C | Refrigerated for many biologics. |
| Residual moisture | <1% to 3% | Low moisture improves stability. |
| Container | Sealed glass vial | Often with rubber stopper and aluminum crimp. |
| Reconstitution time | Seconds to minutes | Varies with cake density and diluent. |
Storage conditions depend on the formulation and the intended shelf life. Many pharmaceutical and biological freeze-dried products are kept at 2–8 °C, while some stable foods and reagents tolerate room temperature. Others require −20 °C or colder to slow chemical degradation or aggregation. Protection from light and oxygen is common because oxidation can continue in the dry state. Stability studies usually monitor potency, appearance, moisture, and reconstitution time over months or years. Predictions from accelerated studies are useful but may not fully capture real-time changes.
Quality control for freeze-dried lots combines visual inspection with instrumental tests. Cake appearance, color, and shrinkage are recorded against a reference, while residual moisture is measured by Karl Fischer titration or loss on drying. Thermal analysis can reveal phase transitions and crystallization events, and X-ray diffraction distinguishes amorphous from crystalline solids. Microbiological tests and container closure integrity checks are also routine for sterile products. Analytical methods must be validated for the matrix, because excipients and low moisture can affect accuracy. Open questions include how best to predict long-term stability from short-term data.
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 dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen so that water becomes ice; then the surrounding pressure is lowered below the vapor pressure of ice. Heat is applied gently so ice changes directly to vapor without passing through a bulk liquid phase. The vapor is collected on a cold condenser, leaving a dry porous matrix. This process differs from simple evaporation because the material remains frozen during the main drying stage.
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.
==== Possible prebiotic environments ==== The symmetry-breaking and chiral amplification of racemic RAO only requires a prebiotic environment where RAO is available and can interact with spin-polarized magnetic surfaces. One suggested environment is an evaporative lake with magnetic sediments, such as magnetite or greigite, which gain a statistically uniform net magnetization on a hemisphere scale from the Earth's geomagnetic field. These environments could have been widespread on the early Earth, and wet-drying cycling within and at the edges of these lakes could facilitate both crystallization and replenishment of RAO, along with other prebiotic precursors important for early life.
Protonitazene is a benzimidazole derivative with potent opioid effects which has been sold over the internet as a designer drug since 2019, and has been identified in various European countries, as well as Canada, the US and Australia. It has been linked to numerous cases of drug overdose, and is a Schedule I drug in the US. It was developed by a Swiss pharmaceutical company in the 1950s as an alternative to morphine, but was never adopted due to severe side effects.
=== Hierarchical structure === While the secondary structures are determined by energy state and hydrogen bonds formed between amino acids, hierarchical structures are determined by the hydrophobicity of the peptide. Exon 1 encoded peptide is mainly hydrophilic, and is more extended when immersed in water. In contrast, exon 3 encoded peptide contains both hydrophobic and hydrophilic blocks, suggesting the formation of micelles, where the hydrophobic block will cluster on the inside with the hydrophilic portion surrounding it. Thus, a single complete resilin protein, when immersed in water, takes on the structure in which exon 1 encoded segment extends out from the micelle exon 3 encoded peptide forms. Once resilin is transferred to the outside of the cell, their exon 2 encoded peptides, the chitin binding segments, bind to chitin. Meanwhile, di- or tri-tyrosine crosslinking is formed by oxidative coupling, mediated by peroxidase, between tyrosine residuals. Like other elastomeric proteins, the degree of cross linking in resilin is low, which ensures the low stiffness and high resilience. Cross linked peptides encoded by exon 1 have a resilience greater than 93%, while that encoded by exon 3 has a resilience of 86%. In addition, natural resilin has a resilience of 92%, similar to that of exon 1, suggesting again that exon 1 may play a more important role in the elastic property of resilin.
Sources: en.wikipedia.org
== Early life and career == An Israeli-American, Ashkenazi earned a degree in finance and economics from the Hebrew University of Jerusalem and an MBA from Tel Aviv University. She worked in the financial services sector in Israel, including for Ma'alot Standard & Poor's and Bank Hapoalim.
Amphetamines have an effect on norepinephrine levels similar to that of cocaine in that they both increase NE levels in the brain. Amphetamine-like drugs are substrates for monoamine transporters, include NET, that cause a reversal in the direction of neurotransmitter transport. Amphetamines cause a large accumulation of extracellular NE. High levels of NE in the brain account for most of the profound effects of amphetamines, including alertness and anorectic, locomotor and sympathomimetic effects. However, the effects that amphetamines have on the brain are slower but last longer than the effects cocaine has on the brain. MDMA (3,4-Methylenedioxymethamphetamine or "ecstasy") is an amphetamine with wide recreational use. A study reported that the NET inhibitor reboxetine reduced the stimulant effects of MDMA in humans, demonstrating the crucial role NET has in the cardiovascular and stimulant-like effects of MDMA.
Bragg was influential in the effort to beat a leading American chemist, Linus Pauling, to the discovery of DNA's structure (after having been pipped at the post by Pauling's success in determining the alpha helix structure of proteins). At the same time Bragg's Cavendish Laboratory was also effectively competing with King's College London, whose Biophysics department was under the direction of Randall (Randall had refused Crick's application to work at King's College). Francis Crick and Maurice Wilkins of King's College were personal friends, which influenced subsequent scientific events as much as the close friendship between Crick and James Watson. Crick and Wilkins first met at King's College and not, as erroneously recorded by two authors, at the Admiralty during World War II. In 1995 Francis Crick signed the Ashley Montagu Resolution petitioning the International Court of Justice (previously the World Court) to help end genital mutation of children, including female genital mutilation, circumcision, and penile subincision.
== Side effects == Common side effects of the ixazomib+lenalidomide+dexamethasone study therapy included diarrhea (42% versus 36% under placebo+lenalidomide+dexamethasone), constipation (34% versus 25%), thrombocytopenia (low platelet count; 28% versus 14%), peripheral neuropathy (28% versus 21%), nausea (26% versus 21%), peripheral oedema (swelling; 25% versus 18%), vomiting (22% versus 11%), and back pain (21% versus 16%). Serious diarrhoea or thrombocytopenia occurred in 2% of patients, respectively. Side effects of ixazomib alone were only assessed in a small number of people. Diarrhea grade 2 or higher was found in 24% of these patients, thrombocytopenia grade 3 or higher in 28%, and fatigue grade 2 or higher in 26%.
Sources: en.wikipedia.org
Lyophilized products should be stored in airtight containers, protected from moisture and light, at the temperature specified by the manufacturer. Many require refrigeration at 2–8 °C, while some need frozen storage. Always check the product label for specific conditions.
Moisture can cause the porous cake to collapse, increase molecular mobility, and accelerate chemical degradation. It may also promote microbial growth if the product lacks preservatives. Proper sealing and handling are essential to maintain stability.
Some formulations contain labile biological molecules that degrade even in the dry state at higher temperatures. Others have a low glass transition temperature, meaning the cake can soften or collapse at room temperature. Cold storage reduces molecular motion and slows degradation.
Primary drying removes ice by sublimation under vacuum. Secondary drying removes water that is bound to the material, often by warming the product after most ice has left. Both stages occur below temperatures that would cause unwanted melting.