Primary drying 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.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Lyophilization is a dehydration process that removes water from a frozen material by sublimation under low pressure. The material is first frozen to convert liquid water into ice. Next, the pressure is reduced below the triple point of water so that ice changes directly into vapor without passing through a liquid phase. This step is called primary drying. The result is a porous solid or cake that retains the original shape of the frozen solution.
After primary drying, secondary drying removes water that remains bound to the material. This stage raises the shelf temperature while maintaining low pressure, which encourages desorption of unfrozen water. Residual moisture can be reduced to a low percentage, improving stability for many products. The process parameters, including freezing rate, shelf temperature, and chamber pressure, influence the final pore structure and reconstitution behavior. Control of these variables helps prevent collapse or meltback during drying.
Lyophilization is a dehydration technique in which a product is frozen and the solvent is removed under reduced pressure. The low pressure allows ice to sublimate directly into vapor without passing through a bulk liquid phase. This differs from conventional drying, where heat drives evaporation and can damage heat-sensitive structures. The process is used for biological materials, pharmaceutical formulations, and some foods. Its main advantage is preservation of porous structure and rapid reconstitution.
Freezing is the first stage and sets the ice structure that later becomes the pore network. The formulation is cooled below its freezing point, often with a controlled ramp, and solutes concentrate as ice forms. Primary drying then lowers chamber pressure and supplies heat to sublime the ice. The product temperature must stay below its collapse or eutectic temperature to prevent structural loss. Secondary drying raises the temperature modestly to remove bound water and achieve a low residual moisture.
A freeze-dryer consists of a vacuum chamber, temperature-controlled shelves, a condenser, and a vacuum pump. Vials, ampoules, or bulk trays hold the product during the cycle. The condenser traps water vapor as ice at a temperature lower than the product. Cycle development balances shelf temperature, chamber pressure, and time. Scale-up can be difficult because heat and mass transfer change with equipment size, so process analytical tools and conservative validation are often used.
| Property | Value | Notes |
|---|---|---|
| Common synonyms | Freeze-drying, lyophilisation | Lyophilization is the American spelling; lyophilisation is British |
| Primary drying mechanism | Sublimation of ice | Occurs under vacuum below the triple point |
| Typical chamber pressure | 0.05-0.5 mbar | Range depends on product and equipment |
| Typical shelf temperature during freezing | -40 to -20 °C | Lower temperatures may be used for labile products |
| Resulting product form | Porous cake or powder | Appearance depends on formulation and cycle |
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.
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.
Lyophilization, also called freeze-drying, is a dehydration process in which a solvent, usually water, is frozen and then removed by sublimation under reduced pressure. The method preserves heat-sensitive materials that would degrade in conventional drying. Large-scale use grew during the mid-twentieth century for blood plasma and antibiotics, and it later expanded to vaccines, enzymes, foods, and advanced materials. The process produces a dry, porous solid that usually reconstitutes rapidly. It is distinct from simple evaporation because the solvent bypasses the liquid phase during primary removal.
The process generally proceeds in three stages: freezing, primary drying, and secondary drying. During freezing, controlled cooling converts water into ice and may also crystallize or vitrify solutes. In primary drying, the pressure is lowered below the triple point, and heat is supplied so ice sublimes directly to vapor. Secondary drying removes water that remains bound to the solid matrix, yielding a low final water content. Product temperature must stay below the collapse or glass transition temperature to maintain structure. Cycle design therefore balances shelf temperature, chamber pressure, and time.
Freeze-drying is used for materials whose activity or structure depends on low temperature and low water content. Examples include certain biologics, diagnostic reagents, starter cultures, coffee, and porous inorganic precursors. The dried product forms a cake whose porosity aids rapid wetting and dissolution. Main drawbacks are high energy use, long cycle times, and sensitivity to formulation and equipment variation. Questions remain about how freezing rates and ice morphology affect batch uniformity, especially when moving from laboratory to production scale.
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 removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Mammalian alcohol dehydrogenases also have a structural zinc site. This Zn ion plays a structural role and is crucial for protein stability. The structures of the catalytic and structural zinc sites in horse liver alcohol dehydrogenase (HLADH) as revealed in crystallographic structures, which has been studied computationally with quantum chemistry as well as with classical molecular dynamics methods. The structural zinc site is composed of four closely spaced cysteine ligands (Cys97, Cys100, Cys103, and Cys111 in the amino acid sequence) positioned in an almost symmetric tetrahedron around the Zn ion. A recent study showed that the interaction between zinc and cysteine is governed by primarily an electrostatic contribution with an additional covalent contribution to the binding.
=== Protein–lipid electrostatic interactions === Any positively charged protein will be attracted to a negatively charged membrane by nonspecific electrostatic interactions. However, not all peripheral peptides and proteins are cationic, and only certain sides of membrane are negatively charged. These include the cytoplasmic side of plasma membranes, the outer leaflet of bacterial outer membranes and mitochondrial membranes. Therefore, electrostatic interactions play an important role in membrane targeting of electron carriers such as cytochrome c, cationic toxins such as charybdotoxin, and specific membrane-targeting domains such as some PH domains, C1 domains, and C2 domains. Electrostatic interactions are strongly dependent on the ionic strength of the solution. These interactions are relatively weak at the physiological ionic strength (0.14M NaCl): ~3 to 4 kcal/mol for small cationic proteins, such as cytochrome c, charybdotoxin or hisactophilin.
Neurochemistry – study of neurochemicals; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. Molecular biochemistry and genetic engineering – an area of biochemistry and molecular biology that studies the genes, their heritage and their expression. Bioorganic chemistry – combines organic chemistry and biochemistry toward biology. Biophysical chemistry – is a physical science that uses the concepts of physics and physical chemistry for the study of biological systems. Medicinal chemistry – discipline which applies chemistry for medical or drug related purposes. Organometallic chemistry – is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkaline, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and tin. Physical organic chemistry – study of the interrelationships between structure and reactivity in organic molecules. Inorganic chemistry – study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry. Bioinorganic chemistry – is a field that examines the role of metals in biology.
Sources: en.wikipedia.org
=== Molecular biology === In addition to microarrays, biochips have been designed for two-dimensional electrophoresis, transcriptome analysis, and PCR amplification. Other applications include various electrophoresis and liquid chromatography applications for proteins and DNA, cell separation, in particular, blood cell separation, protein analysis, cell manipulation and analysis including cell viability analysis and microorganism capturing.
Under Xi, China's official military budget has more than doubled, reaching a record $282 billion in 2026. Though predating Xi, his administration has taken a more assertive stance towards maritime affairs, and has boosted CCP control over the maritime security forces. The PLA Navy has grown rapidly under Xi, with China adding more warships, submarines, support ships and major amphibious vessels from 2014 to 2019 than the entire number of ships serving in the United Kingdom's fleet. Aircraft carriers Shandong and Fujian entered into service under Xi in 2019 and 2025 respectively. In 2017, China established the navy's first overseas base in Djibouti. Xi has also undertaken an expansion of China's nuclear arsenal, with him calling China to "establish a strong system of strategic deterrence." The Federation of American Scientists (FAS) has estimated China's total nuclear arsenal to be 600 in 2025, with the US Department of Defense estimating that China's arsenal could reach 1,000 by 2030.
Example 2: The reference for 'Glycoprotein hormones alpha chain' is UniProt Protein Knowledgebase, ID P01215, which besides a set of synonyms and a reference to the corresponding gene gives the full sequence of the protein.
Sources: en.wikipedia.org
I call on President Brezhnev to join us in this important first step to reduce the nuclear shadow that hangs over the peoples of the world." Ghana's former president, Hilla Limann, who had been overthrown on December 31 in a military coup, was arrested at a roadblock near Koforidua after an unsuccessful attempt to flee the African nation, northeast of the capital, Accra. President Reagan signed NSDD-17, a top secret directive granting the Central Intelligence Agency (CIA) $19 million to support the Contras, anti-communist right-wing rebels seeking to overthrow the Marxist Sandinistas government of Nicaragua. By 1984, Congress would outlaw the use of any funds to the Contras or to U.S. government agencies for the overthrow of the Nicaraguan government. In Sudan, 21 leading members of the parliament, including the Speaker of the Assembly, Samuel Aru Bol, were arrested in Juba by order of President Gaafar Nimeiry for forming an outlawed party, the Council for Unity of Southern Sudan. They would be freed after Nimeiry's overthrow in 1985. Òscar Ribas Reig took office as the first Prime Minister of the Principality of Andorra, located in the Pyrennes Mountains on the border between France and Spain, and officially ruled by the Spanish Bishop of Urgel and the President of France as co-Princes, and the 28-members of the General Council of the Valleys.
Alcoholic liver disease (ALD, or alcoholic cirrhosis) develops in 10–20% of individuals who drink heavily for a decade or more. Alcohol seems to injure the liver by blocking the normal metabolism of protein, fats, and carbohydrates. This injury happens through the formation of acetaldehyde from alcohol. Acetaldehyde is reactive and leads to the accumulation of other reactive products in the liver. People with ALD may also have concurrent alcoholic hepatitis. Associated symptoms are fever, hepatomegaly, jaundice, and anorexia. AST and ALT blood levels are both elevated, but at less than 300 IU/liter, with an AST:ALT ratio > 2.0, a value rarely seen in other liver diseases. In the United States, 40% of cirrhosis-related deaths are due to alcohol. In non-alcoholic fatty liver disease (NAFLD), fat builds up in the liver and eventually causes scar tissue. This type of disorder can be caused by obesity, diabetes, malnutrition, coronary artery disease, and steroids. Though similar in signs to alcoholic liver disease, no history of notable alcohol use is found. Blood tests and medical imaging are used to diagnose NAFLD and NASH, and sometimes a liver biopsy is needed. Chronic hepatitis C, an infection with the hepatitis C virus, causes inflammation of the liver and a variable grade of damage to the organ. Over several decades, this inflammation and damage can lead to cirrhosis. Among people with chronic hepatitis C, 20–30% develop cirrhosis. Cirrhosis caused by hepatitis C and alcoholic liver disease are the most common reasons for liver transplant.
== Radiolabeled somatostatin receptor antagonists in Peptide Radionuclide Receptor Therapy (PRRT) == Somatostatin receptor antagonists are also being developed as therapeutic agents in peptide radionuclide receptor therapy (PRRT) due to the wider binding of antagonists compared to agonists. Research indicated the antagonist Lu-DOTA-JR11 showed higher tumor uptake, more double-strand breaks within tumor cells, longer adherence time to tumors and improved tumor-to-kidney dose ratio. Moreover, another study finds out that radioactive atom, terbium-161 (161Tb), that can release short-ranged electrons, can combine with somatostatin receptor antagonists which localize at the cell membrane, giving an alternative solution, rather than the currently clinically used lutetium-somatostatin receptor agonist, which localize at the cytoplasm and nucleus. Moreover, Tb-antagonist in vitro shows 102-fold more potent than Lu-antagonist in inhibiting tumor cell growth and prolonging survival of mice, which is trusted to be due to its high linear energy transfer. This result is further repeated and confirmed in vivo, showing the high potential and strengths of radiolabeled somatostatin receptor antagonists to treat neuroendocrine neoplasms.
== Reactions == HATU is commonly encountered in amine acylation reactions (i.e., amide formation). Such reactions are typically performed in two distinct reaction steps: (1) reaction of a carboxylic acid with HATU to form the OAt-active ester; then (2) addition of the nucleophile (amine) to the active ester solution to afford the acylated product. The reaction mechanism of carboxylic acid activation by HATU and subsequent N-acylation is summarised in the figure below. The mechanism is shown using the more commonly encountered and commercially available iminium isomer; a similar mechanism, however, is likely to apply to the uronium form. In the first step, the carboxylate anion (formed by deprotonation by an organic base [not shown]) attacks HATU to form the unstable O-acyl(tetramethyl)isouronium salt. The OAt anion rapidly attacks the isouronium salt, affording the OAt-active ester and liberating a stoichiometric quantity of tetramethylurea. Addition of a nucleophile, such as an amine, to the OAt-active ester results in acylation. The high coupling efficiencies and fast reaction rates associated with HATU coupling are thought to arise from a neighbouring group effect brought about by the pyridine nitrogen atom, which stabilises the incoming amine through a hydrogen-bonded 7-membered cyclic transition state.
Sources: en.wikipedia.org
Lyophilization removes water by sublimation from a frozen material, while evaporation changes liquid water into vapor. The low-pressure freezing step avoids the liquid phase and can preserve heat-sensitive structures.
Vacuum lowers the pressure below the triple point of water, allowing ice to sublimate directly into vapor. It also helps remove water vapor from the product chamber and shortens primary drying.
Many aqueous solutions and suspensions can be freeze-dried, but some formulations collapse or do not form a stable cake. The process requires careful formulation and cycle development.
Yes, the terms are generally interchangeable. Lyophilization is more common in pharmaceutical and laboratory contexts, while freeze-drying appears widely in food science and general writing. Both describe removal of solvent by sublimation under vacuum after freezing.