This is a working overview of glass transition, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-23. Anything still debated is marked as such rather than presented as settled.
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.
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.
Regulatory expectations for lyophilized products focus on consistent manufacture and documented stability. Batches are often monitored for moisture, appearance, potency, and sterility where applicable. Process parameters such as shelf temperature, chamber pressure, and drying time are recorded and controlled within validated ranges. Open questions remain about how best to predict long-term stability from short accelerated studies, especially for complex biologics. Variations in freezing rate and ice crystal size can produce differences that are not always visible but may affect performance.
After drying, a lyophilized product is usually sealed under vacuum or an inert gas to limit moisture uptake. Residual water content is measured because small changes can alter chemical stability and cake appearance. Storage temperature depends on the material; many biological products are kept at 2–8 °C, while some require −20 °C or colder. Exposure to ambient humidity during handling can cause the porous solid to absorb water and collapse. Container closures and stoppers are therefore selected for low moisture transmission and compatibility.
Quality control for lyophilized materials includes visual inspection of the cake, measurement of residual moisture, and tests for reconstitution time. An acceptable cake is typically uniform and may be slightly porous; shrinkage, meltback, or cracks can indicate process deviations. Analytical methods such as Karl Fischer titration, thermogravimetric analysis, and near-infrared spectroscopy quantify water content. Reconstitution time is recorded because a very slow or incomplete dissolution can signal collapse or aggregation. Stability studies compare samples stored under defined temperature and humidity conditions over months or years.
| Property | Value | Notes |
|---|---|---|
| Physical state | Solid, porous cake or powder | Depends on formulation and container |
| Typical storage temperature | 2–25 °C, protected from moisture | Some materials require colder conditions |
| Solubility class | Usually readily soluble after reconstitution | Not an intrinsic chemical property |
| Common analytical method | Karl Fischer titration | Used for residual moisture |
| Common synonyms | Freeze-drying; lyophilisation | Lyophilisation is a spelling variant |
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 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.
After lyophilization, the dried product is often sealed under vacuum or an inert gas to limit moisture and oxygen exposure. Vials, stoppers, and seals must maintain their barrier throughout shelf life. Storage temperature depends on product sensitivity: some cakes tolerate controlled room temperature, while labile biologics require refrigeration. Humidity is a critical variable because dried cakes are hygroscopic and can absorb water when exposed to air. Handling procedures therefore limit open-vial time and use desiccated environments for sampling.
Quality control for lyophilized materials examines appearance, reconstitution time, residual moisture, and mechanical integrity. An acceptable cake is usually uniform and porous, though appearance alone does not prove stability. Karl Fischer titration is a common method for water content, while differential scanning calorimetry can reveal glass transition events. Stability studies track potency, aggregation, and moisture over time under defined temperature and humidity conditions. Specifications are product-specific and may include sterility and endotoxin tests for sterile preparations.
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.
Venter's research showed no improvement in skin scaliness and elasticity. Treatment of ageing skin has become very popular over the last decade. Ageing skin is characterised by wrinkles, sagging skin and decreased laxity. As a result, crocodile oil is used for skin repair to assist in skin quality and appearance as well as skin conditions. According to Croc City, crocodile oil and crocodile oil containing products currently on the market, are used for treatment of dermatitis, scrapes, acne, razor bumps, bed sores, haemorrhoids, inflammation of arthritic conditions, treatment of discolouration, pigmentation of skin-like brown spots, freckles, menopausal darkening, treatment of dry, flaky, itchy and ageing skin, nappy rash, athlete's foot, jock-itch and irritation of head skin. Crocodile oil lotion is proven to be a safe product to use on skin.
Studies concluded that the tone of media coverage of Sanders was more favorable than that of any other candidate, whereas his main opponent in the Democratic primary, Hillary Clinton, received the most negative coverage of any candidate. All 2016 candidates received vastly less media coverage than Donald Trump, and the Democratic primary received substantially less coverage than the Republican primary. Amy Goodman of Democracy Now! noted that on March 15, Super Tuesday III, the speeches of Trump, Clinton, Marco Rubio, and Ted Cruz were broadcast in full. Sanders was in Phoenix, Arizona, on that date, speaking to a rally larger than any of the others, yet his speech was not mentioned, let alone broadcast. However, political scientist Rachel Bitecofer wrote in her 2018 book about the 2016 election that the Democratic primary was effectively over in terms of delegate count by mid-March 2016, but that the media promoted the narrative that the contest between Sanders and Clinton was "heating up" at that time. An NBC/Wall Street Journal poll conducted in May 2016 found Clinton and Trump (by then the presumptive Republican nominee) in a "dead heat", but the same poll found that if Sanders were the Democratic nominee, 53% of voters would support him to 39% for Trump. Clinton and Trump were the least popular likely candidates ever polled, while Sanders received a 43% positive, 36% negative rating. Polls showed that Democratic voters older than 50 preferred Clinton by a large margin but that those under 50 overwhelmingly favored Sanders.
Furthermore, a nanoparticle could possess the capability to be activated by a trigger that is specific to the target site, such as utilizing materials that are pH responsive. Most of the body has a consistent, neutral pH. However, some areas of the body are naturally more acidic than others, and, thus, nanoparticles can take advantage of this ability by releasing the drug when it encounters a specific pH. Another specific triggering mechanism is based on the redox potential. One of the side effects of tumors is hypoxia, which alters the redox potential in the vicinity of the tumor. By modifying the redox potential that triggers the payload release the vesicles can be selective to different types of tumors. By utilizing both passive and active targeting, a drug-loaded nanoparticle has a heightened advantage over a conventional drug. It is able to circulate throughout the body for an extended period of time until it is successfully attracted to its target through the use of cell-specific ligands, magnetic positioning, or pH responsive materials. Because of these advantages, side effects from conventional drugs will be largely reduced as a result of the drug-loaded nanoparticles affecting only diseased tissue. However, an emerging field known as nanotoxicology has concerns that the nanoparticles themselves could pose a threat to both the environment and human health with side effects of their own. Active targeting can also be achieved through peptide based drug targeting system.
=== "Central pillar" cave structure === In the typical "central pillar" design, pilgrims can circumambulate around a central column incorporating a niche for a statue of the Buddha, which is a representation of the stupa. The so-called "central pillar" which appears on a plan is actually not a pillar at all but only the rock at the back of the cave, into which was bored a circular corridor allowing for circumambulation. A large vaulted chamber is located in front of the "central pillar" column and a smaller rear chamber behind with two tunnel-like corridors on the sides linking these spaces. In the front chamber, a three-dimensional image of Buddha would have been housed in a large niche serving as the focus of the interior, however, none of these sculptures have survived at Kizil. The rear chamber may feature the parinirvana scene in the form of a mural or large sculpture, and in some cases, a combination of both. The "central pillar" layout is possibly related to the structural design of Kara Tepe in northern Bactria. The program of the paintings in the "central pillar" caves generally follows a fixed arrangement: the walls of the main cella show sermons of the Buddha, the ceiling has rhomboid vignettes alluding to Jatakas, the central niche has the scene of the Indrasala Cave. The back room or corridor has scenes related to the Parinirvana, and finally the painting over the exit is related to the Tusita Heaven and the future Buddha Maitreya.
The species previously thought to be AtO2− has since been determined to be AtO(OH)2−, a hydrolysis product of AtO+ (another such hydrolysis product being AtOOH). The well characterized AtO3− anion can be obtained by, for example, the oxidation of astatine with potassium hypochlorite in a solution of potassium hydroxide. Preparation of lanthanum triastatate La(AtO3)3, following the oxidation of astatine by a hot Na2S2O8 solution, has been reported. Further oxidation of AtO3−, such as by xenon difluoride (in a hot alkaline solution) or periodate (in a neutral or alkaline solution), yields the perastatate ion AtO4−; this is only stable in neutral or alkaline solutions. Astatine is also thought to be capable of forming cations in salts with oxyanions such as iodate or dichromate; this is based on the observation that, in acidic solutions, monovalent or intermediate positive states of astatine coprecipitate with the insoluble salts of metal cations such as silver(I) iodate or thallium(I) dichromate. Astatine may form bonds to the other chalcogens; these include S7At+ and At(CSN)2− with sulfur, a coordination selenourea compound with selenium, and an astatine–tellurium colloid with tellurium.
Sources: en.wikipedia.org
== Medical uses == Phenelzine is primarily used in the treatment of major depressive disorder, including treatment-resistant depression. Modern guidance on classic MAOIs recommends considering phenelzine, tranylcypromine, or isocarboxazid after insufficient response to other antidepressant treatments and before electroconvulsive therapy when a rapid treatment response is not required. Patients with atypical depression may respond particularly well to phenelzine, but evidence also supports the use of classic MAOIs in melancholic depression. Phenelzine may be especially useful when depression is accompanied by premorbid anxiety, comorbid panic disorder, or other treatment-resistant anxiety symptoms, reflecting its additional effects on GABA metabolism. Phenelzine has also been studied or used in anxiety-related and other psychiatric conditions including panic disorder, social anxiety disorder, post-traumatic stress disorder (PTSD), obsessive–compulsive disorder (OCD), dysthymia, bipolar depression, and bulimia nervosa.
The Nestlé product, developed by a Swiss chemist Max Morgenthaler, was composed of 50% soluble coffee solids and 50% maltodextrins. The presence of maltodextrins permitted spray drying into a stable powder. Nescafé instant coffee became known world-wide during the Second World War through inclusion in the rations of the US Army. After the war, other companies began to manufacture soluble coffee, for example Douwe Egberts Moccona, and consumption increased rapidly. In the 1950s, General Foods introduced an instant coffee product made from 100% coffee solids without the need for added carbohydrates such as maltodextrins. By extracting coffee with water at high temperature (up to 175°C) and under pressure, larger polysaccharide carbohydrates naturally present in the coffee beans are released. These larger polysaccharides in the coffee extract facilitate spray drying without the need to add maltodextrins. The resulting instant coffee may be described as pure soluble coffee. Early spray dried instant coffee powders had small particle size and were quite dusty. Agglomeration of spray dried coffee has been used since around 1968 to form the instant coffee into granules. The first freeze-dried instant coffee was launched in 1963 by General Foods under the brand Maxwell House. From the mid 1960s, techniques of capturing aroma compounds from the roasting and extraction of coffee and then adding them back to the finished product were introduced by manufacturers to improve the flavour of instant coffee.
This craze died down amid warnings of kojic acid, reports of contamination in home-made cultures, and insufficient capabilities for industrial production. In addition, Chen Jin-Shu of National Chung Hsing University noted that kombucha was briefly home-made in Taiwan under the name hóngchá gū (Chinese: 紅茶菇; from Japanese kōcha kinoko) in the 1960s.
Upon activation by light (laser) or ultrasound, the photosensitizers induced targeted and precise killing of GD2-positive cells both in vitro and in vivo. Competing methods for in vitro protein evolution include yeast display, bacterial display, ribosome display, and mRNA display.
Sources: en.wikipedia.org
The group takes its name from Mighei (Ukraine), but the most famous member is the extensively studied Murchison meteorite. Many falls of this type have been observed and CM chondrites are known to contain a rich mix of complex organic compounds such as amino-acids and purine/pyrimidine nucleobases. CM chondrite famous falls:
{\displaystyle {\begin{aligned}\Delta p={\frac {1}{2}}\rho {\overline {v}}_{\text{max}}^{2}&={\frac {1}{2}}\rho \left({\frac {Q_{\text{max}}}{\pi R^{2}}}\right)^{2}\\\Rightarrow \quad Q_{\max }{}&=\pi R^{2}{\sqrt {\frac {2\Delta p}{\rho }}},\end{aligned}}}
=== Zinc(I) compounds === Zinc(I) compounds are very rare. The [Zn2]2+ ion is implicated by the formation of a yellow diamagnetic glass by dissolving metallic zinc in molten ZnCl2. The [Zn2]2+ core would be analogous to the [Hg2]2+ cation present in mercury(I) compounds. The diamagnetic nature of the ion confirms its dimeric structure. The first zinc(I) compound containing the Zn–Zn bond, (η5-C5Me5)2Zn2 has been reported in 2004.
Sources: en.wikipedia.org
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.
Reduced pressure keeps the solvent below its triple point, allowing ice to become vapor without melting. Vacuum also helps remove water vapor from the product chamber. The exact pressure is chosen with the formulation and equipment.
Residual moisture is water that remains in the dried solid after secondary drying. It is often measured by Karl Fischer titration, near-infrared spectroscopy, or thermogravimetry. Acceptable levels depend on the material and its stability profile.
Most are held in sealed containers at controlled temperatures, often 2–8 °C, while some require frozen storage. Protection from moisture and light helps preserve the dry matrix. Exact conditions are set by the manufacturer or study protocol.