This is a working overview of freeze-thaw cycle, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2026-05-04. Anything still debated is marked as such rather than presented as settled.
Regulatory status differs sharply by region. Selank holds a Russian marketing authorization, where it is supplied mainly as nasal drops, while authorities elsewhere have not approved it for medical use. Material sold internationally is therefore usually labeled as a research chemical rather than a medicine. Peer-reviewed publications come predominantly from Russian laboratories, and sample sizes are generally small. Whether the compound produces comparable effects under independent, well-controlled replication remains an open question that the broader literature has not settled.
Selank is a synthetic heptapeptide developed in Russia as a structural analogue of tuftsin, a naturally occurring immunomodulatory tetrapeptide. Its sequence, Thr-Lys-Pro-Arg-Pro-Gly-Pro, keeps the tuftsin core at the N-terminus and appends a Pro-Gly-Pro tail. Researchers at the Institute of Molecular Genetics in Moscow synthesized the compound during the 1990s while searching for peptides with combined anxiolytic and immunomodulatory activity. The added tail was intended to resist enzymatic cleavage and prolong the molecule's presence in circulation.
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.
Tuftsin, the parent structure, is a naturally occurring immunomodulatory tetrapeptide released from the Fc region of immunoglobulin G by spleen enzymes. Selank extends this four-residue sequence with three additional amino acids. The stated rationale is that the added tail slows enzymatic breakdown and may influence receptor interactions. How the full heptapeptide behaves at the molecular level is not firmly established, and proposed mechanisms often involve indirect modulation of neurotransmitter or immune signaling rather than a single defined target.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Analog of the tetrapeptide tuftsin |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Reported consistently across pharmacopoeial descriptions |
| Appearance | White to off-white lyophilized powder | Typical form of research-grade material |
| Solubility | Freely soluble in water | Aqueous buffers; poor in nonpolar solvents |
| Typical storage temperature | -20 degrees Celsius | Lyophilized powder; protect from moisture |
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.
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.
Peptide bonds in selank are susceptible to hydrolysis under strongly acidic or basic conditions, and the terminal proline residues are vulnerable to exopeptidase activity in biological samples. Lyophilized powder stored dry at -20 °C typically remains stable for extended periods, whereas aqueous solutions degrade faster and may lose measurable purity within days to weeks depending on pH, temperature, and microbial load. Repeated freeze-thaw cycles promote aggregation and adsorption to container surfaces. For analytical work, solutions are usually prepared fresh, kept cold, and used within a single working day.
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.
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.
Wastewater treatment Macrophytes have an essential role in some forms of wastewater treatment, most commonly in small scale sewage treatment using constructed wetlands or in polishing lagoons for larger schemes.
bidirectional replication A common mechanism of DNA replication in which two replication forks move in opposite directions away from the same origin; this results in a bubble-like region where the duplex molecule is locally separated into two single strands.
== Biosynthesis == The biosynthesis of serine starts with the oxidation of 3-phosphoglycerate (an intermediate from glycolysis) to 3-phosphohydroxypyruvate and NADH by phosphoglycerate dehydrogenase (EC 1.1.1.95). Reductive amination (transamination) of this ketone by phosphoserine transaminase (EC 2.6.1.52) yields 3-phosphoserine (O-phosphoserine) which is hydrolyzed to serine by phosphoserine phosphatase (EC 3.1.3.3). In bacteria such as E. coli these enzymes are encoded by the genes serA (EC 1.1.1.95), serC (EC 2.6.1.52), and serB (EC 3.1.3.3).
==== Council house sales ==== Heseltine was a convert to the sale of council houses, a policy pioneered by some Conservative local authorities, e.g. Birmingham. He also favoured the policy of giving away houses, a policy first mooted from the backbenches by Peter Walker in the mid-1970s, not least as some local authorities were spending more on maintenance than they were recouping in rents. Thatcher, who was concerned at the reaction from those who had made financial sacrifices to buy their homes, was initially sceptical. After taking office Heseltine issued a circular enabling councils, if they chose, to sell houses at 30% discount and to offer 100% mortgages. The Housing Act 1980 enacting Right to Buy was delayed by a Lords amendment and did not reach the statute book until the end of 1980. Some councils were slow in processing applications (one even threatened to house "problem" families next door to those who bought) and Heseltine made an example of Norwich by setting up a DOE sales office there; Norwich council took him to court and lost. At the time Heseltine permitted councils to use up to 75% of sales receipts for renovating the housing stock, and was angry in later years when this was cut back by the Treasury. Heseltine also insisted on the doubling of rents to encourage buying. During the 1980s over a million council houses, around 20% of the stock, were sold, and by 1987 Labour had dropped their opposition to the Right to Buy.
Sources: en.wikipedia.org
Mass media, lawmakers, and Donald Trump raised concerns about Biden's age, including his cognitive state, during and after the 2020 United States presidential election. According to a February 2024 poll, Biden's age and health were major or moderate concerns for 86% of voters generally, up from 76% in 2020. According to another February 2024 poll, most of those who voted for Biden in 2020 believed he was too old to be an effective president; The New York Times noted that these concerns "cut across generations, gender, race and education". Concerns about Biden's age and health increased after a poor performance by Biden during a debate against Trump in June 2024. That performance led a number of commentators and Democratic lawmakers to call for Biden to drop out of the 2024 presidential race. In July 2024, Biden ultimately withdrew from the race while stating that he would continue serving as president until the conclusion of his term.
=== Non-fraternization === Fraternization between senior cadres and PLA officers is prohibited without authorization. Politburo members must apply to the Politburo Standing Committee before visiting PLA units and once approved, visits must be arranged by the CMC. CMC approval is required before a PLA general can be involved in national or regional civil affairs.
glutathione + formaldehyde This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is S-(hydroxymethyl)glutathione formaldehyde-lyase (glutathione-forming). Other names in common use include glutathione-dependent formaldehyde-activating enzyme, Gfa, and S-(hydroxymethyl)glutathione formaldehyde-lyase. This enzyme participates in methane metabolism.
Sources: en.wikipedia.org
It insured the lives of its members for $1,000 and that of members' wives for half that amount. Sick benefits were administered by the subordinate lodges and death benefits by the Supreme Lodge. The ritual was based on the covenant between God, Noah, Abraham, and Moses. The emblem was the All Seeing Eye above three pillars with the tablets of the Ten Commandments between them. Independent Order of B'rith Abraham - Founded in 1887 as a split from the Order of Brith Abraham, whose leadership they felt was incompetent. Some sources give the name as the Improved Order of B'rith Abraham. Admitted women and was smoothly run. Added social membership option to what was already essentially an insurance society in 1924. Had a peak membership of 206,000 in 1917. In 1923 it had 585 lodges and a benefit membership of 142,812. Had 58,000 immediately before World War II. Changed name to simply B'rith Abraham in 1968. Merged with B'nai Zion in 1981. Headquarters in 1923 at 37 Seventh Street New York City. New York was still the headquarters in 1979. The Order's stated objectives in 1969 were to "foster fraternity in the context of Jewish ideals, tradition, and welfare", provide fraternal benefits to its members, and support programs for underprivileged children and seniors. It also promoted Zionism. Independent Order of American Israelites - Founded in 1894 in New York City by a group of men, some or all of whom had been members of the Independent Order, Free Sons of Israel, and the Sons of Benjamin. Order paid a $1,000 death benefit for male members and $500 for female members.
=== Mitochondrial genetics === Mitochondrial genetics concerns the diagnosis and management of mitochondrial disorders, which have a molecular basis but often result in biochemical abnormalities due to deficient energy production. There exists some overlap between medical genetic diagnostic laboratories and molecular pathology. In the UK, the NHS Highly Specialised Service for Rare Mitochondrial Disorders offers diagnostic testing for patients. Based in laboratories in Newcastle upon Tyne , Oxford and London which are integrated within the NHS Genomic Medicine Service (GMS).
Another common technique typically used in NanoSIMS analysis is stable isotope probing. This method involves the introduction of stable isotopically labelled biologically relevant compounds to organisms for consumption and integration into organic matter. When analyzed via NanoSIMS, the technique is referred to as nanoSIP. NanoSIMS can be used to detect which organisms incorporated which molecules, how much of the labeled molecules was incorporated in a semi-quantitative manner, and where in the cell the incorporation occurred. Previous quantitative analysis techniques at a lower resolution than NanoSIMS of stable isotopically labeled molecules was limited to analyzed bulk material, which did not allow for insights about the contributions of individual cells or subcellular compartments to be made. Additionally, the removal of large foreign molecules (such as antibodies or gold particles) from the experimental setup alleviates concerns that tagged molecules required for other microscopy techniques may have different biochemical responses or properties than normal. This technique can be used to study nutrient exchange. The mouse gut microbiome was investigated to determine which microbes fed on host-derived compounds. For this, mice were given food enriched in the stable isotopically labelled amino acids and the microbial biomass examined. NanoSIMS allows for the metabolic contributions of individual microbes to be examined.
=== Motivational disorders === Levodopa has been found to increase the willingness to exert effort for rewards in humans and hence appears to show pro-motivational effects. Other dopaminergic agents have also shown pro-motivational effects and may be useful in the treatment of motivational disorders.
Sources: en.wikipedia.org
Selank is a synthetic seven-amino-acid peptide modeled on tuftsin, a fragment of the immunoglobulin G heavy chain. It was designed in Russia to combine anxiolytic and immunomodulatory properties in one molecule.
The first four residues of Selank reproduce the tuftsin sequence Thr-Lys-Pro-Arg. A Pro-Gly-Pro extension at the C-terminus was added to slow enzymatic breakdown and extend residence time.
It holds marketing authorization in Russia, where nasal drop formulations are sold. No equivalent approval exists in the European Union, the United States, or most other countries.
Selank is a synthetic peptide made of seven amino acids. It is modeled on tuftsin, a natural tetrapeptide, with an added three-residue tail. It is not a small-molecule drug.