glass transition comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2026-04-18. Numbers and descriptions here follow the published literature rather than marketing material.
Residual moisture is a key quality attribute for lyophilized products. Water that remains after secondary drying can affect chemical stability, cake structure, and shelf life. Karl Fischer titration is a common method for measuring water content in the dried solid. The target range varies by product, but many biologics are dried to between 0.5% and 3% water by weight. Acceptable limits are set during development and confirmed by stability studies.
Stability studies examine how temperature, humidity, and time influence a lyophilized product. Accelerated conditions provide early information about degradation pathways, while long-term studies support shelf-life claims. The glass transition temperature of the dried formulation can indicate its physical stability, and storage above this temperature may increase molecular mobility and lead to collapse or aggregation. Container closure integrity also matters because moisture or oxygen ingress can degrade the product, so vial stoppers and seals are part of the quality system.
Handling and storage practices aim to keep the cake intact and dry. Vials are typically stored upright at controlled temperatures, often between 2 °C and 8 °C or at -20 °C for longer-term use. Reconstitution involves adding a suitable diluent and gently mixing until the solid dissolves. Shaking or rapid injection of diluent can create foam or damage sensitive molecules. Once reconstituted, the product may require refrigeration and use within a defined period.
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.
| Property | Value | Notes |
|---|---|---|
| Residual moisture | 0.5-3% w/w | Typical range for many biopharmaceuticals |
| Typical storage temperature | 2-8 °C | Some products require -20 °C or lower |
| Reconstitution time | Seconds to several minutes | Depends on cake porosity and diluent |
| Common moisture method | Karl Fischer titration | Measures water content in the solid |
| Container closure | Stoppered vial with seal | Protects against moisture and oxygen ingress |
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.
Lyophilization, or freeze-drying, removes water from a material by freezing it and then lowering pressure so ice changes directly to vapor. The process relies on sublimation, the phase transition from solid to gas without an intervening liquid state. It is used for heat-sensitive materials that would degrade in conventional drying. The three stages are freezing, primary drying, and secondary drying, each with distinct temperature and pressure requirements. In practice, cycle design balances these variables.
Freezing determines ice crystal structure and pore size, which affect drying speed and product uniformity. Rapid freezing creates small crystals, while slow freezing creates larger crystals and often faster sublimation. During primary drying, chamber pressure is held below the vapor pressure of ice, and shelf temperature supplies heat for sublimation. The ice front recedes, leaving a porous matrix. Thermal limits such as collapse and eutectic temperatures set safe boundaries for formulation. These limits vary with solute composition and concentration.
Secondary drying removes bound water that remains after ice sublimation. Shelf temperature is raised gradually while pressure remains low, reducing water content to a target range. Over-drying can cause brittleness or electrostatic issues, while under-drying affects stability. The endpoint is often judged by pressure rise tests, temperature measurements, or water content analysis. Scale-up depends on matching heat and mass transfer across equipment sizes. Small changes in shelf temperature or pressure can alter cycle length substantially.
After drying, a lyophilized product is usually sealed under vacuum or an inert gas to limit moisture and oxygen exposure. The container closure system matters because stoppers and seals can allow moisture ingress over time. Storage conditions are selected from stability studies that track potency, cake appearance, and reconstitution behavior. Many freeze-dried materials are kept at controlled room temperature, while some require refrigeration or protection from light.
Quality control for freeze-dried forms includes visual inspection, water content measurement, and reconstitution time. A satisfactory cake is typically uniform, porous, and intact, although minor shrinkage or cracking may be acceptable if specifications allow. Karl Fischer titration, thermal gravimetric analysis, and near-infrared spectroscopy are used to measure water content. Reconstitution is assessed by adding a specified diluent and recording the time and ease of dissolution. Microbiological and particulate tests are added when the product is sterile or intended for injection.
Stability of a lyophilized solid depends on water content, temperature, and the physical state of the formulation. Amorphous products may slowly absorb moisture and drop below their glass transition temperature, causing collapse or crystallization. Some proteins and peptides can aggregate even in a dry state, especially when exposed to heat or moisture. Accelerated stability studies at elevated temperature and humidity help estimate shelf life, but real-time data remain the basis for expiration dating.
==== Monte Carlo and simulated annealing ==== Monte Carlo is one of the most widely used algorithms for protein design. In its simplest form, a Monte Carlo algorithm selects a residue at random, and in that residue a randomly chosen rotamer (of any amino acid) is evaluated. The new energy of the protein, Enew is compared against the old energy Eold and the new rotamer is accepted with a probability of:
Collagenase 3 is an enzyme that in humans is encoded by the MMP13 gene. It is a member of the matrix metalloproteinase (MMP) family. Like most MMPs, it is secreted as an inactive pro-form. MMP-13 has a predicted molecular weight around 54 kDa. It is activated once the pro-domain is cleaved, leaving an active enzyme composed of the catalytic domain and the hemopexin-like domain PDB: 1PEX. Although the actual mechanism has not been described, the hemopexin domain participates in collagen degradation, the catalytic domain alone being particularly inefficient in collagen degradation. During embryonic development, MMP-13 is expressed in the skeleton as required for restructuring the collagen matrix for bone mineralization. In pathological situations it is highly overexpressed; this occurs in human carcinomas, rheumatoid arthritis and osteoarthritis. Proteins of the matrix metalloproteinase (MMP) family are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, and tissue remodeling, as well as in disease processes, such as arthritis and metastasis. Most MMPs are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases. The protein encoded by this gene cleaves type II collagen more efficiently than types I and III. It may be involved in articular cartilage turnover and cartilage pathophysiology associated with osteoarthritis. The gene is part of a cluster of MMP genes which localize to chromosome 11q22.3.
Type 1 is Goodpasture syndrome, an autoimmune disease also affecting the lung. In Goodpasture syndrome, IgG antibodies directed against the glomerular basement membrane trigger an inflammatory reaction, causing a nephritic syndrome and the coughing up of blood. High dose immunosuppression is required (intravenous methylprednisolone) and cyclophosphamide, plus plasmapheresis. Immunohistochemistry staining of tissue specimens shows linear IgG deposits. Type 2 is characterised by immune-complex-mediated damage, and may be associated with systemic lupus erythematosus, post-infective glomerulonephritis, IgA nephropathy, and IgA vasculitis. Type 3 rapidly progressive glomerulonephritis, also called pauciimmune type, is associated with causes of vascular inflammation including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis. No immune deposits can be seen on staining, however blood tests may be positive for the ANCA antibody. Histopathologically, the majority of glomeruli present "crescents". Formation of crescents is initiated by passage of fibrin into the Bowman space as a result of increased permeability of glomerular basement membrane. Fibrin stimulates the proliferation of endothelial cells of Bowman capsule, and an influx of monocytes. Rapid growing and fibrosis of crescents compresses the capillary loops and decreases the Bowman space, which leads to kidney failure within weeks or months.
Sources: en.wikipedia.org
, is the probability, after time t, that there is a base j at a given position, conditional on there being a base i in that position at time 0. When the model is time reversible, this can be performed between any two sequences, even if one is not the ancestor of the other, if you know the total branch length between them. The asymptotic properties of Pij(t) are such that Pij(0) = δij, where δij is the Kronecker delta function. That is, there is no change in base composition between a sequence and itself. At the other extreme,
==== Gel electrophoresis under denaturing conditions ==== Denaturing gel electrophoresis, commonly performed using SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), involves treating proteins with SDS, a detergent that denatures proteins and imparts a uniform negative charge. This allows proteins to be separated solely based on their molecular weight, providing a clear picture of the protein composition of a sample.
=== Excretion === Excretion is performed mainly by two small kidneys. In diapsids, uric acid is the main nitrogenous waste product; turtles, like mammals, excrete mainly urea. Unlike the kidneys of mammals and birds, reptile kidneys are unable to produce liquid urine more concentrated than their body fluid. This is because they lack a specialized structure called a loop of Henle, which is present in the nephrons of birds and mammals. Because of this, many reptiles use the colon to aid in the reabsorption of water. Some are also able to take up water stored in the bladder. Excess salts are also excreted by nasal and lingual salt glands in some reptiles. In all reptiles, the urinogenital ducts and the rectum both empty into an organ called a cloaca. In some reptiles, a midventral wall in the cloaca may open into a urinary bladder, but not all. It is present in all turtles and tortoises as well as most lizards, but is lacking in the monitor lizard, the legless lizards. It is absent in the snakes, alligators, and crocodiles. Many turtles and lizards have proportionally very large bladders. Charles Darwin noted that the Galapagos tortoise had a bladder which could store up to 20% of its body weight. Such adaptations are the result of environments such as remote islands and deserts where water is very scarce. Other desert-dwelling reptiles have large bladders that can store a long-term reservoir of water for up to several months and aid in osmoregulation.
Jackson, A. Y. (1943). Banting as an Artist. Ryerson Press. Shaw, Margaret Mason (1976). Frederick Banting. Fitzhenry & Whiteside. ISBN 978-0-88902-229-4. Stevenson, Lloyd (1946). Sir Frederick Banting. Ryerson Press. Harris, Seale (1946). Banting's miracle; the story of the discoverer of insulin. Lippincott. Walters, Eric (2005). Elixir. Puffin Canada. ISBN 978-0-14-301641-0. Raju, T. N. (1998). "The Nobel Chronicles. 1923: Frederick G Banting (1891–1941), John J R Macleod (1876–1935)". Lancet. 352 (9138): 1482. doi:10.1016/s0140-6736(05)61319-0. PMID 9808029. S2CID 54323266. Hudson, R. P. (1979). "New light on the insulin controversy (Frederick G. Banting and J. J. R. Macleod)". Annals of Internal Medicine. 91 (2): 311. doi:10.7326/0003-4819-91-2-311. PMID 380438. Fletcher, K. (2007). "Sir Frederick Banting homestead sold to developer, family outraged". Canadian Medical Association Journal. 176 (12): 1691–92. doi:10.1503/cmaj.070613. PMC 1877854. PMID 17548378. Shampo, M. A.; Kyle, R. A. (2005). "Frederick Banting – Nobel Laureate for Discovery of Insulin". Mayo Clinic Proceedings. 80 (5): 576. doi:10.4065/80.5.576. PMID 15887423. MacLeod, J. B. A. (2006). "Frederick G. Banting: Giving Prospects for Life from the Past to the New Millennium". Archives of Surgery. 141 (7): 705–07. doi:10.1001/archsurg.141.7.705. PMID 16847245. Elliot, J. C. (2004). "Banting – a Nobel artist". The Medical Journal of Australia. 181 (11–12): 631. doi:10.5694/j.1326-5377.2004.tb06494.x. PMID 15588191. S2CID 10131078. Todhunter, E. N. (1953). "Frederick G.
Sources: en.wikipedia.org
A tea made of the leaves and stem has been used to treat tooth pain. For cases of cough and bronchitis, a water extract (decoction) of Mimosa tenuiflora is drunk. A handful of bark in one liter of water is used by itself or in a syrup. The solution is drunk until the symptoms subside. One preliminary clinical study found Mimosa tenuiflora to be effective in treating venous leg ulcerations. Aqueous extracts of Mimosa are widely used for wound healing and burns in Central and South America. Consequently, the products of the plant (generally grouped under the term "Tepezcohuite") have become a popular and easily produced cosmetic ingredient in commercial skincare products.
Globally there are about 114 million and 20 million cases of hepatitis A and hepatitis E respectively, but these generally resolve and do not become chronic. Hepatitis D virus is a "satellite" of hepatitis B virus (it can only infect in the presence of hepatitis B), and co-infects nearly 20 million people with hepatitis B, globally. Hepatic encephalopathy is caused by an accumulation of toxins in the bloodstream that are normally removed by the liver. This condition can result in coma or death if not treated. Budd–Chiari syndrome is a condition caused by blockage of the hepatic veins (including thrombosis) that drain the liver. It presents with the classical triad of abdominal pain, ascites and liver enlargement. Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile. Other disorders caused by excessive alcohol consumption are grouped under alcoholic liver diseases and these include alcoholic hepatitis, fatty liver, and cirrhosis. Factors contributing to the development of alcoholic liver diseases are not only the quantity and frequency of alcohol consumption, but can also include gender, genetics, and liver insult. Liver damage can also be caused by drugs, particularly paracetamol and drugs used to treat cancer. A rupture of the liver can be caused by a liver shot used in combat sports. Primary biliary cholangitis is an autoimmune disease of the liver.
pressure The force applied perpendicular to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), though many other units of pressure are also commonly used in chemistry.
Sources: en.wikipedia.org
Residual moisture can influence chemical degradation, cake collapse, and long-term stability. Low moisture levels usually improve stability, but each product has an optimal range.
Most lyophilized products are stored upright at controlled temperatures, often refrigerated or frozen. Protection from moisture and light helps maintain the dried cake.
A diluent is added to the dried cake, which dissolves to form a solution or suspension. Gentle mixing avoids foaming and preserves sensitive molecules.
Freezing only converts liquid to solid. Lyophilization adds vacuum and controlled warming so frozen solvent sublimes, leaving a dry porous solid. The two steps are related but not interchangeable.