Water content 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 2025-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
A formulation often contains excipients that protect the active ingredient during freezing and drying. Bulking agents provide structure, while lyoprotectants stabilize sensitive molecules. The freezing step can produce ice crystals whose size and distribution affect the drying rate, and cycle design includes freezing, annealing, and drying phases. If the product temperature rises above a critical value, the cake may collapse or lose its porous structure. Successful lyophilization therefore depends on the interaction between formulation, equipment, and cycle design.
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.
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.
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.
| 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 |
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.
Stability programs monitor lyophilized products under defined temperature and humidity conditions over time. Real-time studies at recommended storage conditions are the reference, while accelerated studies provide early signals of degradation pathways. Because a dry cake can still undergo oxidation, hydrolysis, or aggregation, stability depends on residual moisture, excipients, and container headspace. Open questions include how best to predict long-term stability from short accelerated runs and how vial-to-vial variability affects shelf life. Current guidance treats these predictions as product-specific rather than universally generalizable.
Freeze-dried materials are hygroscopic to varying degrees and can take up moisture after drying. Storage therefore often uses sealed glass vials, rubber stoppers, and crimp seals to limit contact with ambient humidity. A desiccant may be included for moisture-sensitive products, although it is not universal. Controlled room temperature is sufficient for many lyophilizates, while others require refrigeration or freezing. Moisture ingress remains a primary cause of cake collapse, chemical degradation, and loss of reconstitution performance.
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.
In this case, K2 > K1. The reason for this is that, in aqueous solution, the ion written as Ag+ actually exists as the four-coordinate tetrahedral aqua species [Ag(H2O)4]+. The first step is then a substitution reaction involving the displacement of a bound water molecule by ammonia forming the tetrahedral complex [Ag(NH3)(H2O)3]+. In the second step, all the aqua ligands are lost and a linear, two-coordinate product [H3N–Ag–NH3]+ is formed. Examination of the thermodynamic data shows that the difference in entropy change is the main contributor to the difference in stability constants for the two complexation reactions.
==== siRNA delivery ==== Short interfering RNA (siRNA) is a powerful new tool that can interfere with and silence the expression of specific disease gene. To improve cellular uptake of siRNA, CPP strategies have been applied to facilitate the delivery of siRNA into cells through either covalent or non-covalent linkages. In one study, siRNA is covalently linked to transportation and penetration by disulfide-linkage at 5'-end of the sense strands of siRNA to target luciferase or eGFP mRNA reporters. In another study, TAT-siRNA conjugate through a stable thiomaleimide linkage at 3'-end of siRNA was delivered into HeLa cells for eGFP gene silencing. However, non-covalent strategies appear to be better for siRNA delivery with a more significant biological response. In one study, MPG/siRNA complexes formed through stable non-covalent strategy showed successful introduction of siRNA into cultured cells and induced robust regulation of target mRNA. Furthermore, MPG/siRNA complexes have also been applied for delivery of siRNA in vivo into mouse blastocytes for gene regulation. MPG forms stable complexes with siRNA with a low degradation rate and can be easily functionalized for specific targeting, which are major advantages compared with the covalent CPP technology.
Under normal conditions, osteocytes express high amounts of TGF-β and thus repress bone resorption, but when bone grows old, the expression levels of TGF-β decrease, and the expression of osteoclast-stimulatory factors, such as RANKL and M-CSF increases, bone resorption is then enhanced, leading to net bone loss. Mechanical stimulation of osteocytes results in opening of hemichannels to release PGE2 and ATP, among other biochemical signaling molecules, which play a crucial role in maintaining the balance between bone formation and resorption. Osteocyte cell death can occur in association with pathologic conditions such as osteoporosis and osteoarthritis, which leads to increased skeletal fragility, linked to the loss of ability to sense microdamage and/or signal repair. Oxygen deprivation that occurs as the result of immobilization (bed rest), glucocorticoid treatment, and withdrawal of oxygen have all been shown to promote osteocyte apoptosis. It is now recognized that osteocytes respond in a variety of ways to the presence of implant biomaterials.
In randomized controlled trials, meanwhile, these rates were 28%, 23.4% and 13.3%, respectively. In contrast to other selective serotonin reuptake inhibitors (SSRIs), initial trials showed that vilazodone did not cause decreased sexual desire/function, which often cause people to abandon their use. However, post-marketing experience led the FDA to warn that vilazodone may cause sexual dysfunction.
During the 1990s, Brazil saw a surge of critical and commercial success with films such as O Quatrilho (Fábio Barreto, 1995), O Que É Isso, Companheiro? (Bruno Barreto, 1997) and Central do Brasil (Walter Salles, 1998), all of which were nominated for the Academy Award for Best Foreign Language Film, the latter receiving a Best Actress nomination for Fernanda Montenegro. The 2002 crime film City of God, directed by Fernando Meirelles, was critically acclaimed, scoring 90% on Rotten Tomatoes, being placed in Roger Ebert's Best Films of the Decade list and receiving four Academy Award nominations in 2004, including Best Director. Notable film festivals in Brazil include the São Paulo and Rio de Janeiro International Film Festivals and the Gramado Festival. The film I'm Still Here, directed by Walter Salles, was nominated for Best Actress (Torres) and Best Picture at the 97th Academy Awards, and won Best International Feature Film, becoming the first-ever Brazilian produced film to win an Academy Award. The film The Secret Agent had its world premiere at the main competition of the 2025 Cannes Film Festival on 18 May 2025, where it won the Best Actor prize for Wagner Moura, the Best Director prize for Mendonça and the FIPRESCI Prize. It received further widespread critical acclaim.
Sources: en.wikipedia.org
== Causes == Childhood obesity can be brought on by a range of factors which often act in combination. "Obesogenic environment" refers to a mixture of environmental factors that are permissive of obesity, especially for those who are genetically predisposed. The greatest risk factor for child obesity is the obesity of both parents. This may be reflected by the family's environment and genetics. Other reasons may also be due to psychological factors and the child's body type. A 2010 review stated that childhood obesity likely is the result of the interaction of natural selection favouring those with more parsimonious energy metabolism and today's consumerist society with easy access to cheap, energy-dense foods and less energy requirements in daily life. Factors include the increase in use of technology, increase in snacks and portion size of meals, and the decrease in the physical activity of children. A study found that children who use electronic devices three or more hours a day had between a 17–44% increased risk of being overweight, or a 10–61% increased risk of obesity (Cespedes 2011). Childhood obesity is common among children from low-income, African American and Hispanic communities. This is mainly because minority children spend less time playing outside the house and staying active. Parents may prefer their children stay inside the home because they fear gang and drug violence and other dangers.
As shown above, E. coli can grow with reducing agents such as formate, hydrogen, or lactate as electron donors, and nitrate, DMSO, or oxygen as acceptors. The larger the difference in midpoint potential between an oxidizing and reducing agent, the more energy is released when they react. Out of these compounds, the succinate/fumarate pair is unusual, as its midpoint potential is close to zero. Succinate can therefore be oxidized to fumarate if a strong oxidizing agent such as oxygen is available, or fumarate can be reduced to succinate using a strong reducing agent such as formate. These alternative reactions are catalyzed by succinate dehydrogenase and fumarate reductase, respectively. Some prokaryotes use redox pairs that have only a small difference in midpoint potential. For example, nitrifying bacteria such as Nitrobacter oxidize nitrite to nitrate, donating the electrons to oxygen. The small amount of energy released in this reaction is enough to pump protons and generate ATP, but not enough to produce NADH or NADPH directly for use in anabolism. This problem is solved by using a nitrite oxidoreductase to produce enough proton-motive force to run part of the electron transport chain in reverse, causing complex I to generate NADH. Prokaryotes control their use of these electron donors and acceptors by varying which enzymes are produced in response to environmental conditions. This flexibility is possible because different oxidases and reductases use the same ubiquinone pool.
At the Battle of Carabobo on 24 June, the Gran Colombian forces decisively defeated the royalist forces, assuring control of Venezuela save for Puerto Cabello and guaranteeing Venezuelan independence. Bolívar could now concentrate on Gran Colombia's claims to southern New Granada and Quito.
=== Phenazines === Phenazines are redox-active pigments produced by P. aeruginosa. These pigments are involved in quorum sensing, virulence, and iron acquisition. P. aeruginosa produces several pigments all by the same biosynthetic pathway: phenazine-1-carboxamide (PCA), 1-hydroxyphenazine, 5-methylphenazine-1-carboxylic acid betaine, pyocyanin and aeruginosin A. Two nearly identical operons are involved in phenazine biosynthesis: phzA1B1C1D1E1F1G1 and phzA2B2C2D2E2F2G2. The enzymes encoded by these operons convert chorismic acid to PCA. The products of three key genes, phzH, phzM, and phzS then convert PCA to the other phenazines mentioned above. Though phenazine biosynthesis is well studied, questions remain as to the final structure of the brown phenazine pyomelanin. When pyocyanin biosynthesis is inhibited, a decrease in P. aeruginosa pathogenicity is observed in vitro. It has therefore been suggested that pyocyanin is mostly responsible for the initial colonization of P. aeruginosa in vivo.
Sources: en.wikipedia.org
=== Regulation === Paralogs are often regulated differently, e.g. by having different tissue-specific expression patterns (see Hox genes). However, they can also be regulated differently on the protein level. For instance, Bacillus subtilis encodes two paralogues of glutamate dehydrogenase: GudB is constitutively transcribed whereas RocG is tightly regulated. In their active, oligomeric states, both enzymes show similar enzymatic rates. However, swaps of enzymes and promoters cause severe fitness losses, thus indicating promoter–enzyme coevolution. Characterization of the proteins shows that, compared to RocG, GudB's enzymatic activity is highly dependent on glutamate and pH.
However, its toxicity to microorganisms is not overtly observed since the free silver ion is found in low concentrations in wastewater treatment systems and the natural environment due to its complexation with ligands such as chloride, sulfide, and thiosulfate.
Compound 544678-85 is the latest pyrimidine based inhibitor, the compound is a pyrimidine-4,6-dicarboxamide that is very potent and MMP-13 selective. The compound has a specificity loop that within the S1’ pocket and its 3-methyl-4-fluoro group is proximal enough to the zinc to change the water entity. These compounds have good oral bioavailability and properties that promote them to be a good candidate for a subtype inhibitor of MMP-13 based diseases and future development. Pyrimidine dicarboxamides are highly selective MMP-13 inhibitors. In the S1’ pocket of MMP-13 is an S1’ side pocket that is unique to the matrix metalloproteiase. Pyrimidine dicarboxamides bind to this side pocket, which increases the selectivity. The role of MMP-13 is cleaving fibrillar collagen at neutral pH and higher mRNA levels of MMP-13 is detected in breast carcinoma and osteoarthritis joints. The pyrimidine dicarboxamide inhibitor example in the image does not interact with the catalytic zinc ion but rather binds to the S1’ side pocket. One pyridyl arm is situated to the entrance of the S1’ pocket while the other pyridyl arm goes through the S1’ pocket into the side pocket.
3-phosphoglycerate can be separated and measured using paper chromatography as well as with column chromatography and other chromatographic separation methods. It can be identified using both gas-chromatography and liquid-chromatography mass spectrometry and has been optimized for evaluation using tandem MS techniques. 2-Phosphoglyceric acid Calvin-Benson cycle Photosynthesis Ribulose 1,5-bisphosphate
=== Rare decay modes === Spontaneous fission accounts for about 1.1×10−9% of thorium-232 decays, corresponding to a partial half-life of about 1.3×1021 years. Double beta decay to uranium-232 is also theoretically possible. A 2020 experimental search set lower half-life limits for such decays to excited states of uranium-232.
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.
Sealed vials or containers should be kept at the temperature specified by stability data, often controlled room temperature or 2–8 °C. Moisture and oxygen barriers are important because both can degrade sensitive materials. Opened containers may need immediate use or protection from ambient humidity.