freeze-thaw cycle 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 2025-09-29. Where a claim depends on a specific study, the study is described rather than over-claimed.
Lyophilized material is generally stable for extended periods when kept dry at or below minus twenty degrees Celsius. Working solutions are less stable, and common practice is to aliquot and freeze them so that repeated freeze-thaw cycles are avoided. Aqueous solutions are sensitive to pH extremes and to microbial growth, so short-term storage at refrigerator temperature is typical. Oxidation and hydrolysis are the principal degradation routes. Reconstitution with sterile water or a mild buffer is standard, and solutions should be protected from light.
Regulatory treatment varies by jurisdiction. In Russia the compound is a registered prescription product, while in the European Union and the United States it is generally handled as a research chemical without a marketing authorization. Suppliers therefore operate outside pharmaceutical oversight, and buyers rely on supplier documentation for purity and identity claims. Chain of custody and third-party testing are the main verification tools. Analysts note that the absence of a pharmacopoeial monograph for research-grade material limits standardization across vendors.
Purity assessment relies mainly on reverse-phase high-performance liquid chromatography with ultraviolet detection. Because the peptide lacks a strong chromophore, detection often uses backbone absorbance near 214 nm. Identity is confirmed by mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, comparing the measured mass against the expected value. Amino acid analysis can verify composition after acid hydrolysis. Diastereomer content and residual counterions are reported less often, although both can influence biological assays.
Enzymatic stability motivates the extra three residues at the carboxyl end. Native tuftsin is cleaved quickly by circulating aminopeptidases and carboxypeptidases, which limits its duration of action and its usefulness as a tool compound. Extending the chain with proline-rich segments is a common design tactic because proline constrains the backbone and slows proteolysis. The same Pro-Gly-Pro motif appears in other Russian-developed peptides of the era. Whether the full seven-residue chain is required for activity, or whether it acts mainly as a prodrug releasing tuftsin, remains unresolved.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its four N-terminal residues reproduce tuftsin, a tetrapeptide fragment of the immunoglobulin heavy chain, while the C-terminal Pro-Gly-Pro extension is a synthetic addition. The peptide has a molecular mass near 752 daltons and carries a net positive charge at physiological pH because of the arginine and lysine side chains. Published indexes list it under the name Selank and the sequence abbreviation TKPRPGP. Solid-phase peptide synthesis is the standard production route for research quantities.
Development took place at the Institute of Molecular Genetics of the Russian Academy of Sciences, where a series of short peptides were designed in the 1980s and 1990s. Selank was selected from variants of tuftsin that showed resistance to plasma peptidases. Russian regulatory approval covers it as an anxiolytic agent given intranasally. Outside that market the compound is normally handled as a research chemical rather than a medicine, and no widely recognised international pharmacopoeial monograph exists. The name Selank is a coined trade designation rather than a systematic chemical name.
| Property | Value | Notes |
|---|---|---|
| Typical purity report | 95% or higher by HPLC | Area percentage at 214 nm |
| Identity confirmation | Mass spectrometry | Electrospray or MALDI |
| Powder storage | -20 C, desiccated | Protect from light |
| Solution storage | 2-8 C short term | Freeze aliquots for longer |
| Quality document | Certificate of analysis | States method and value |
Handling follows standard practice for research peptides. Material is weighed in a low-humidity environment because the powder absorbs atmospheric moisture. Purity is reported as the percentage area of the main peak in a chromatogram, with specifications commonly set at 95 percent or higher; values below that threshold indicate the presence of truncated or modified species. Residual trifluoroacetate from purification is often present and may affect mass balance. Certificates of analysis should state the analytical method, the column and gradient used, and the lot-specific retention time so that results can be compared across suppliers.
Identity and purity of selank are established with reversed-phase high-performance liquid chromatography coupled to mass spectrometry. The peptide elutes from C18 columns with acetonitrile gradients in water containing trifluoroacetic acid or formic acid, and detection is usually performed by ultraviolet absorbance near 214 nm. Electrospray ionization in positive mode gives a doubly protonated ion near m/z 377, consistent with a mass of about 752 Da. Amino acid analysis or tandem mass spectrometry of fragment ions confirms the sequence. Because the molecule has no aromatic residues, it lacks a usable 280 nm chromophore, so low-wavelength detection or mass spectrometry is required.
Once dissolved, the peptide is markedly less stable than the dry powder. Aqueous solutions are subject to backbone hydrolysis and to microbial growth when they are handled without sterile technique. Buffered solutions near neutral pH are common for short-term laboratory work, while acidic conditions are sometimes used to improve solubility. Analytical laboratories generally prepare working solutions fresh rather than storing them, and a residual water film left in a reopened vial can seed degradation even when the container appears dry.
Reversed-phase high-performance liquid chromatography is the standard technique for estimating peptide purity. The result is a peak-area percentage, which describes how much of the detected material elutes as the main peak in one run. Mass spectrometry confirms the molecular mass and can reveal truncated, adducted, or otherwise modified species. Amino acid analysis or tandem mass spectrometry can address sequence fidelity when identity is in doubt. None of these measurements, taken alone, establishes that a sample is fit for any specific purpose.
Lyophilized selank is normally supplied as a dry powder and is considered stable for extended periods when kept cold and dry. Moisture uptake is the main practical threat, because absorbed water promotes both hydrolysis and aggregation in the solid state. Vials are usually warmed to room temperature before opening so that condensation does not form on the powder. Supplier documentation commonly specifies -20 °C for routine storage, with -80 °C used for material intended to be archived for years.
Selank is a synthetic heptapeptide developed in Russia. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, a seven-residue chain built around the natural tetrapeptide tuftsin. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences first described the compound in the mid-1990s. The design combined the tuftsin core with an added Pro-Gly-Pro tail, a modification intended to extend the molecule's stability in biological fluids. Published work on the peptide has appeared mainly in Russian-language journals.
Reported activity for Selank centers on anxiolytic and nootropic effects. Russian clinical reports describe use in anxiety and in cognitive or attention-related complaints. Most of this evidence comes from studies conducted by the same research groups that developed the peptide. Independent replication in other countries remains limited, and no major Western regulatory agency has approved the compound for any indication. The gap between local reports and external verification is a recurring point in discussions of the peptide.
Fbw7 is known to be a haplo-insufficient tumor suppressor gene implicated in several sporadic carcinomas, for which one mutant allele is enough to disturb the wild type phenotype. Fbxo4 is another tumor suppressor FBP that has been implicated in human carcinomas. SCF-fbxo4 plays a role in cell cycle control by targeting cyclin D1 for degradation. Cyclin F is an FBP that is associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Mutations that prevent phosphorylation of Cyclin F alter the activity of SCF-Cyclin F, which likely affects downstream processes pertinent to neuron degeneration in ALS and FTD. Normally, Cyclin F targets E2f1 for degradation.
Overseas territories of European allies, including territories in Africa. "The general area of China" – Cambodia, Laos, Vietnam, Burma, and the Philippines. In the countries referred to as being in the general area of China, the Marshall Plan (ECA) operated through Special Technical and Economic Missions (STEMs). The STEMs were set up in 1950 and 1951, and had a "Point Four character" in the sense that they emphasized services by technical experts. Minimizing overlaps with the Marshall Plan, Point Four managed assistance mainly in:
=== Agarose vs. magnetic beads === Proponents of magnetic beads claim that the beads exhibit a faster rate of protein binding over agarose beads for immunoprecipitation applications, although standard agarose bead-based immunoprecipitations have been performed in 1 hour. Claims have also been made that magnetic beads are better for immunoprecipitating extremely large protein complexes because of the complete lack of an upper size limit for such complexes, although there is no unbiased evidence stating this claim. The nature of magnetic bead technology does result in less sample handling due to the reduced physical stress on samples of magnetic separation versus repeated centrifugation when using agarose, which may contribute greatly to increasing the yield of labile (fragile) protein complexes. Additional factors, though, such as the binding capacity, cost of the reagent, the requirement of extra equipment and the capability to automate IP processes should be considered in the selection of an immunoprecipitation support.
In this study, phospholipid membrane is comparable to the model membrane which consists of POPC, ethanol, water and in some cases the addition of monovalent ions (Na+, K+, and Cl−) that are transported throughout the membrane in the presence of ethanol. The concentration of ethanol varies ranging from 2.5 to 30 mol% in an aqueous solution but there is no addition of any sterol compound. The atomic-scale molecular dynamics simulations are used to monitor the changes in the phospholipid membrane. All the simulations are carried out using GROMACS simulation suite software along with other methods that are essential to perform the simulations. The temperature and pressure are controlled at 310K and 1bar. The simulations are measured at various time frames which include ficoseconds (fs), picoseconds (ps), and nanoseconds (ns). A typical simulation is composed of approximately 128 POPC lipids and 8000 solvent molecules which include water and ethanol. In each simulation ethanol molecules, water molecules, head group regions, acyl chains, and the monovalent ions are all color-coded which aids in interpreting the results of the simulations. The concentrations of ethanol are 2.5, 5.0, 15.0 and 30 mol%. The amount of ethanol molecules depend on the concentration of ethanol present in the phospholipid membrane. Force field parameters are measured for the POPC lipids and monovalent ions (Na+, K+, and Cl−), which are very important.
=== Research tool === Due to its high proteolytic specificity, thrombin is a valuable biochemical tool. The thrombin cleavage site (Leu-Val-Pro-Arg-Gly-Ser) is commonly included in linker regions of recombinant fusion protein constructs. Following purification of the fusion protein, thrombin can be used to selectively cleave between the arginine and glycine residues of the cleavage site, effectively removing the purification tag from the protein of interest with a high degree of specificity.
Sources: en.wikipedia.org
On January 6, 2021, following the U.S. Capitol attack, Bush denounced the violence and attack alongside the three other living former presidents, Obama, Clinton, and Carter, releasing a statement saying that "this is how election results are disputed in a banana republic, not our democratic republic", and that "it is a sickening and heartbreaking sight". He also echoed president-elect Biden's message saying that what occurred at the Capitol was an "insurrection". On January 20, Bush and his wife attended Biden's inauguration. Bush opposed President Biden's withdrawal of American troops from Afghanistan, saying that the withdrawal made him "concerned" and that it had the potential to "create a vacuum, and into that vacuum is likely to come people who treat women as second-class citizens". During an interview with Deutsche Welle on July 14, 2021, Bush reaffirmed his opposition to the troop withdrawal, calling the plan "a mistake". On September 11, 2021, the 20th anniversary of the September 11 attacks, Bush gave a speech at the Flight 93 National Memorial, praising the heroism of the people on Flight 93 and the spirit of America. He also said that he "saw millions of people instinctively grab for a neighbor's hand and rally to the cause of one another. That is the America I know." Bush condemned the assassination attempt on then-former president Trump, who was the presumptive Republican nominee, on July 13, 2024, calling it "cowardly" and applauding the Secret Service's response.
== Pharmacokinetics == Cefadroxil is almost completely absorbed from the gastrointestinal tract. After doses of 500 mg and 1 g by mouth, peak plasma concentrations of about 16 and 30 micrograms/ml, respectively, are obtained after 1.5 to 2.0 hours. Although peak concentrations are similar to those of cefalexin, plasma concentrations are more sustained. Dosage with food does not appear to affect the absorption of cefadroxil. About 20% of cefadroxil is reported to be bound to plasma proteins. Its plasma half-life is about 1.5 hours and is prolonged in patients with renal impairment. Cefadroxil is widely distributed to body tissues and fluids. It crosses the placenta and appears in breast milk. More than 90% of a dose of cefadroxil may be excreted unchanged in the urine within 24 hours by glomerular filtration and tubular secretion; peak urinary concentrations of 1.8 mg/ml have been reported after a dose of 500 mg. Cefadroxil is removed by haemodialysis.
Cider has also been popular in the Basque Country for centuries. While Txakoli and Rioja wines became more popular in Biscay, Álava, and Navarre during the 19th century, there is still a strong Basque cider culture in Gipuzkoa. From the 1980s, government and gastronomic associations have worked to revive this culture in all Basque regions. Known as sagardoa (IPA: /s̺a'gardoa/), it is drunk either bottled or in a cider house (called a sagardotegi), where it is poured from barrels. Most of "sagardotegis" are in the north of Gipuzkoa (Astigarraga, Hernani, Urnieta, and Usurbil), but they can be found everywhere in Gipuzkoa, the northwest of Navarre and the northern Basque country. Cider tasting events are popular in the Basque province of Gipuzkoa, where stalls are set up on the street selling the drink from several producers at cheap prices and served until stock runs out.
Shunting inhibition has no direct effect on the membrane potential of the cell; however, it reduces the effect of any coincident synaptic input by reducing the electrical resistance of the cell's membrane. Shunting inhibition can "override" the excitatory effect of depolarising GABA, resulting in overall inhibition even if the membrane potential becomes less negative. It was thought that a developmental switch in the molecular machinery controlling the concentration of chloride inside the cell changes the functional role of GABA between neonatal and adult stages. As the brain develops into adulthood, GABA's role changes from excitatory to inhibitory.
=== Sniper: Rogue Mission (2022) === After discovering a human sex trafficking ring working with a corrupt agent, Brandon Beckett teams up with allies from his past, Agent Zeke "Zero" Rosenberg and Yuki "Lady Death" Mifune, to discover the identity of the agent and stop the ring.
Sources: en.wikipedia.org
=== Physicians and researchers === Among the renowned individuals who have worked with the University of Pittsburgh's medical center through its history are Jonas Salk who developed the polio vaccine while at the University of Pittsburgh, pediatric psychoanalyst Benjamin Spock, Peter Safar who pioneered CPR and the world's first intensive care training program at the medical center, and surgeon Thomas Starzl who perfected organ transplantation there. Other doctors include pathologist Maud Menten who is famous for her contributions to enzyme kinetics, leading orthopedic surgeon and sports medicine expert Freddie Fu, pioneering immunologist Niels Kaj Jerne, forensic pathologist and Allegheny County Coroner Cyril Wecht, Vitamin C's discoverer Charles Glen King, pediatrician Jack Paradise, leading head and neck cancer surgeon and otolaryngologist Eugene Nicholas Myers, laparoscopic liver resection pioneer David Geller, breast cancer treatment pioneer Bernard Fisher, and virologists Patrick Moore and Yuan Chang, who co-discovered Kaposi's sarcoma-associated herpesvirus.
== Chemistry == Phenazepam is a drug of the benzodiazepine class. Benzodiazepine drugs contain a benzene ring fused to a diazepine ring, which is a seven membered ring with the two nitrogen constituents located at R1 and R4. The benzyl ring of phenazepam is substituted at R7 with a bromine group. Like most benzodiazepines, phenazepam has a phenyl ring in R5 which is substituted by chlorine in the R2' group. Phenazepam also contains an oxygen group double bonded to R2 of its diazepine ring to form a ketone. This oxygen substitution at R2 is shared with other benzodiazepine drugs with the suffix -azepam. Like other benzodiazepines, phenazepam (7-bromo-5-(2-chlorophenyl)-1,3-dihydro-1,4-benzodiazepin-2-one) is composed of a benzene ring fused to a seven-membered 1,4-diazepine ring. A 2-chlorophenyl ring is attached at the 5-position and a bromine is attached at the 7-position. Phenazepam has a molecular formula of C15H10BrClN2O and a molecular weight of 349.6 g/mol.
==== Emulsification freeze-drying ==== This technique does not require the use of a solid porogen like SCPL. First, a synthetic polymer is dissolved into a suitable solvent (e.g. polylactic acid in dichloromethane) then water is added to the polymeric solution and the two liquids are mixed in order to obtain an emulsion. Before the two phases can separate, the emulsion is cast into a mold and quickly frozen by means of immersion into liquid nitrogen. The frozen emulsion is subsequently freeze-dried to remove the dispersed water and the solvent, thus leaving a solidified, porous polymeric structure. While emulsification and freeze-drying allow for a faster preparation when compared to SCPL (since it does not require a time-consuming leaching step), it still requires the use of solvents. Moreover, pore size is relatively small and porosity is often irregular. Freeze-drying by itself is also a commonly employed technique for the fabrication of scaffolds. In particular, it is used to prepare collagen sponges: collagen is dissolved into acidic solutions of acetic acid or hydrochloric acid that are cast into a mold, frozen with liquid nitrogen and then lyophilized.
Ship Minds One of the main activities of Ship Minds is the guidance of spaceships from a certain minimum size upwards. A culture spaceship is the Mind and vice versa; there are no different names for the two, and a spaceship without a Mind would be considered damaged or incomplete to the Culture. Ship Mind classes include General Systems Vehicle (GSV), Medium Systems Vehicle (MSV), Limited Systems Vehicle (LSV), General Contact Vehicle (GCV), General Contact Unit (GCU), Limited Contact Unit (LCU), Rapid Offensive Unit (ROU), General Offensive Unit (GOU), Limited Offensive Unit (LOU), Demilitarised ROU (dROU), Demilitarised GOU (dGOU), Demilitarised LOU (dLOU), Very Fast Picket (VFP–synonym for dROU), Fast Picket (FP–synonym for dGOU or dLOU), and Superlifter. These ships provide a convenient 'body' for a Mind, which is too large and too important to be contained within smaller, more fragile shells. Following the 'body' analogy, it also provides the Mind with the capability of physical movement. As Minds are living beings with curiosity, emotion and wishes of their own, such mobility is likely very important to most. Culture Minds (mostly also being ships) usually give themselves whimsical names, though these often hint at their function as well. Even the names of warships retain this humorous approach, though the implications are much darker.
Sources: en.wikipedia.org
Purity is usually reported as an HPLC area percentage, most often measured at 214 nm. Identity is confirmed separately by mass spectrometry. A certificate of analysis should state both the method and the observed value.
Dry powder is kept frozen, desiccated, and shielded from light. Dissolved material is aliquoted and frozen to limit freeze-thaw cycles. Short-term refrigerated storage is common for working solutions.
Russia registers it as a prescription nasal product. Most other markets classify it as a research chemical with no approved medical use. Oversight of purity and labeling is consequently minimal in those markets.
Selank is a seven-amino-acid peptide built from the tuftsin sequence plus a Pro-Gly-Pro tail. It is produced by chemical synthesis rather than extracted from a natural source. The free peptide is usually supplied as a lyophilised powder or in an aqueous formulation.