This is a working overview of Sublimation, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-02-09. Anything still debated is marked as such rather than presented as settled.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Common synonym | Freeze-drying | Same dehydration operation |
| Typical vacuum | 10-100 Pa | Pressure during primary drying |
| Primary drying temperature | -40 to -10 °C | Below collapse temperature for many formulations |
| Cycle duration | 12-72 hours | Varies with load, container, and formulation |
| Key phase change | Sublimation | Solid ice to water vapor |
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.
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.
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 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.
Analysis of CRISPR sequences revealed coevolution of host and viral genomes. The basic model of CRISPR evolution is newly incorporated spacers driving phages to mutate their genomes to avoid the bacterial immune response, creating diversity in both the phage and host populations. To resist a phage infection, the sequence of the CRISPR spacer must correspond perfectly to the sequence of the target phage gene. Phages can continue to infect their hosts' given point mutations in the spacer. Similar stringency is required in PAM or the bacterial strain remains phage sensitive.
A synchronous or synchronized culture is a microbiological culture or a cell culture that contains cells that are all in the same growth stage. As numerous factors influence the cell cycle (some of them stochastic) normal cultures have cells in all stages of the cell cycle. Obtaining a culture with a unified cell-cycle stage is useful for biological research where a particular stage in the cell cycle is desired (such as the culturing of parasitized cells). Since cells are too small for certain research techniques, a synchronous culture can be treated as a single cell; the number of cells in the culture can be easily estimated, and quantitative experimental results can simply be divided in the number of cells to obtain values that apply to a single cell. Synchronous cultures have been extensively used to address questions regarding cell cycle and growth, and the effects of various factors on these. Synchronous cultures can be obtained in several ways:
Adhesion G protein-coupled receptor G1 also known as GPR56 is a protein encoded by the ADGRG1 gene. ADGRG1 is a member of the adhesion GPCR family. Adhesion GPCRs are characterized by an extended extracellular region often possessing N-terminal protein modules that is linked to a TM7 region via a domain known as the GPCR-Autoproteolysis INducing (GAIN) domain. ADGRG1 is expressed in liver, muscle, tendon, neural, and cytotoxic lymphoid cells in human as well as in hematopoietic precursor, muscle, and developing neural cells in the mouse. ADGRG1 has been shown to have numerous role in cell guidance/adhesion as exemplified by its roles in tumour inhibition and neuron development. More recently it has been shown to be a marker for cytotoxic T cells and a subgroup of Natural killer cells. The ADGRG1 protein binds transglutaminase 2 to suppress tumor metastasis and binds collagen III to regulate cortical development and lamination.
Binding curves describe the binding behavior of ligand to a protein. Curves can be characterized by their shape, sigmoidal or hyperbolic, which reflect whether or not the protein exhibits cooperative or noncooperative binding behavior respectively. Typically, the x-axis describes the concentration of ligand and the y-axis describes the fractional saturation of ligands bound to all available binding sites. The Michaelis Menten equation is usually used when determining the shape of the curve. The Michaelis Menten equation is derived based on steady-state conditions and accounts for the enzyme reactions taking place in a solution. However, when the reaction takes place while the enzyme is bound to a substrate, the kinetics play out differently. Modeling with binding curves are useful when evaluating the binding affinities of oxygen to hemoglobin and myoglobin in the blood. Hemoglobin, which has four heme groups, exhibits cooperative binding. This means that the binding of oxygen to a heme group on hemoglobin induces a favorable conformation change that allows for increased binding favorability of oxygen for the next heme groups. In these circumstances, the binding curve of hemoglobin will be sigmoidal due to its increased binding favorability for oxygen. Since myoglobin has only one heme group, it exhibits noncooperative binding which is hyperbolic on a binding curve.
Sources: en.wikipedia.org
Dried spirulina is 5% water, 24% carbohydrates, 8% fat, and 57% protein (table). In a reference amount of 100 g (3.5 oz), dried spirulina powder supplies 290 kilocalories (1,200 kJ) and is a rich source (20% or more of the Daily Value, DV) of numerous essential nutrients, particularly B vitamins (thiamin, riboflavin, and niacin), and dietary minerals, such as iron and manganese (table). The lipid content of spirulina is about 8% by weight. The polyunsaturated fatty acids include gamma-linolenic acid and linoleic acid. In contrast to the "high" content reported in a 2003 study, two other analyses found low levels of omega-3 fatty acids in spirulina.
The role of the other BDNF receptor, p75, is less clear. While the TrkB receptor interacts with BDNF in a ligand-specific manner, all neurotrophins can interact with the p75 receptor. When the p75 receptor is activated, it leads to activation of NFkB receptor. Thus, neurotrophic signaling may trigger apoptosis rather than survival pathways in cells expressing the p75 receptor in the absence of Trk receptors. Recent studies have revealed a truncated isoform of the TrkB receptor (t-TrkB) may act as a dominant negative to the p75 neurotrophin receptor, inhibiting the activity of p75, and preventing BDNF-mediated cell death.
There are three amino acids with side chains that are cations at neutral pH: arginine (Arg, R), lysine (Lys, K) and histidine (His, H). Arginine has a charged guanidino group and lysine a charged alkyl amino group, and are fully protonated at pH 7. Histidine's imidazole group has a pKa of 6.0, and is only around 10% protonated at neutral pH. Because histidine is easily found in its basic and conjugate acid forms it often participates in catalytic proton transfers in enzyme reactions.
APEKTx1 is a highly selective blocker of the voltage-gated potassium channel Kv1.1 with no effect on other tested potassium channels (Kv1.2, Kv1.3, Kv1.4, Kv1.5, Kv1.6, Shaker IR, Kv2.1, Kv3.1, Kv4.2 and Kv4.3). APEKTx1 selectively blocks Kv1.1 channels with an IC50 value of 0.9 nM, which makes it between a 700 to 3000 times more potent inhibitor than the two known sea anemone peptides targeted against Kv channels (kalicludines and SHTX II). APEKTx1 is thought to interact with Kv1.1 through the aliphatic residue alanine (A352), an acidic residue glutamate (E353), and an aromatic residue tyrosine (Y379), as a mutation in these sites causes a loss in affinity of the toxin for Kv1.1. These residues are located in the H5-loop between the S5 and S6 domains and are part of the channel’s pore. In addition, APEKTx1 acts as a potent trypsin inhibitor (Kd= 124 nM), probably a competitive one. However, trypsin inhibition is more potent (as it has a higher affinity) in BPTI, which can be explained by the presence of Phe13 and Pro19 in APEKTx1, causing an unfavorable interaction.
The protein encoded by this gene is a member of the STAT protein family. In response to cytokines and growth factors, STAT family members are phosphorylated by the receptor associated kinases, and then form homo- or heterodimers that translocate to the cell nucleus where they act as transcription activators. In response to IFN, this protein forms a complex with STAT1 and IFN regulatory factor family protein p48 (IRF9) and form ISGF-3 (IFN-stimulated gene factor-3), in which this protein acts as a transactivator, but lacks the ability to bind DNA directly. The protein mediates innate antiviral activity. Mutations in this gene result in Immunodeficiency 44. ISGF-3 proceeds the activation of genes via the IFN-stimulated response element (ISRE). ISRE-driven genes include Ly-6C, the double-stranded RNA kinase (PKR), 2´ to 5´ oligoadenylate synthase (OAS), MX and potentially MHC class I. Transcription adaptor P300/CBP (EP300/CREBBP) has been shown to interact specifically with this protein, which is thought to be involved in the process of blocking IFN-alpha response by adenovirus. STAT2 knockout mice are unresponsive to type I IFN and extremely vulnerable to viral infection. They indicate the loss of the type I IFN autocrine loop and several defects in macrophages and T cell responses. Stat2-/- cells show differences in the biological response to IFN-α.
Sources: en.wikipedia.org
In vitro testing suggests that unidentified wolfberry phytochemicals in goji tea may inhibit metabolism of medications, such as those processed by the cytochrome P450 liver enzymes, including such drugs as warfarin. Organochlorine pesticides are conventionally used in commercial wolfberry cultivation to mitigate infestation by insects. China's Green Food Standard, administered by the Chinese Ministry of Agriculture's China Green Food Development Center, permits some pesticide and herbicide use. Agriculture in the Tibetan Plateau (where many "Himalayan" or "Tibetan"-branded berries supposedly originate) conventionally uses fertilizers and pesticides, making organic claims for berries originating there dubious. Since the early 21st century, high levels of insecticide residues (including fenvalerate, cypermethrin, and acetamiprid) and fungicide residues (such as triadimenol and isoprothiolane), have been detected by the United States Food and Drug Administration in some imported wolfberries and wolfberry products of Chinese origin, leading to the seizure of these products.
Cells of one type may release the 5(S)-HETE that they make to nearby cells of a second type which then oxidize the 5(S)-HETE to 5-oxo-ETE. This transcellular production typically involves the limited variety of cell types that express active 5-lipoxygenase, lack HEDH activity because of their high levels of NADPH compared to NADP+ levels, and therefore accumulate 5(S)-HETE, not 5-oxo-ETE, upon stimulation. This 5(S)-ETE can leave these cells, enter various cell types that possess 5-HEDH activity along with lower NADPH to NADP+ levels, and thereby be converted to 5-oxo-ETE. Transcellular production of 5-oxo-eicosatetraenoates has been demonstrated in vitro with human neutrophils as the 5(S)-HETE producing cells and human PC-3 prostate cancer cells, platelets, and monocyte-derived dendritic cells as the oxidizing cells. It is theorized that this transcellular metabolism occurs in vivo and provides a mechanism for controlling 5-oxo-ETE production by allowing it to occur or be augmented at sites were 5-lipoxygenase-containing cells congregate with cell types possessing 5-HEDH and favorable NADPH/NADP+ ratios; such sites, it is theorized, might include those involving allergy, inflammation, oxidative stress, and rapidly growing cancers.
The NAD-I riboswitch (also called the nadA motif) was identified in species of the bacterial phylum Acidobacteriota, where it typically resides upstream of nadA genes encoding quinolate synthase, an enzyme in the de novo NAD⁺ biosynthesis pathway. Unusually, despite regulating genes relevant to NAD⁺ metabolism, neither binding domain of the NAD⁺-I riboswitch's dual-aptamer architecture has been shown to specifically recognize the nicotinamide portion of the coenzyme; instead, the RNA robustly binds the adenosine 5′-diphosphate (ADP) moiety of NAD⁺.
Pyocyanin inactivates catalase by reducing its gene’s transcription as well as directly targeting the enzyme itself. Glutathione is an important antioxidant modulated by pyocyanin. In particular the pool of the reduced form is depleted while the oxidised form is promoted by hydrogen peroxide which is not dismutated by catalase. In the cystic fibrosis lung, intracellular pyocyanin converts molecular oxygen to the superoxide free radical by oxidizing NADPH to NADP+. This has a doubly negative effect on the lungs. Firstly, the NADPH used by pyocyanin depletes the available substrate for the reaction catalysed by the NADPH oxidase enzyme. Secondly, the superoxide radical generated can inhibit cytokines, such as IL-4, IL-13 and IFN-γ, which usually upregulate NADPH oxidase. When the lung is confronted with pyocyanin, an increased concentration of catalase and superoxide dismutase is seen in order to deal with the barrage of radicals being produced.
Sources: en.wikipedia.org
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.
Sublimation requires the solvent to remain solid so vapor leaves without passing through a liquid phase. If the product melts, the porous structure can collapse and drying becomes uneven. Maintaining frozen conditions preserves the intended physical form.
No, freeze-drying is a dehydration method, not a sterilization step. It can reduce water activity and limit microbial growth during storage, but it does not reliably kill microbes or remove endotoxins. Sterility must come from separate validated processes.
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.