If you have been reading about freeze-thaw cycle and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2026-04-02. Numbers and descriptions here follow the published literature rather than marketing material.
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.
The compound has a calculated molecular weight near 751.9 daltons and carries a net positive charge at physiological pH because of its arginine residue. It dissolves freely in water and in common aqueous buffers, and typically appears as a white or off-white lyophilized powder. The amide backbone makes the molecule susceptible to peptidases, which limits oral use and favors intranasal or parenteral routes. Nomenclature in the literature varies: the substance is also described by the sequence abbreviation TP-7 and by a Russian trade designation.
Measuring peptide exposure inside the brain is technically difficult. Selank is degraded rapidly in plasma, and assays must separate intact peptide from fragments, which favors targeted mass spectrometry over immunoassays alone. Reported half-lives are short, on the order of minutes, so effects observed hours later are attributed to downstream signaling rather than to the parent compound. Blood-brain barrier permeability is debated and rarely quantified directly. Gaps include absent dose-response characterization, inconsistent reporting of purity, and almost no pharmacokinetic data from human participants.
Selank is studied chiefly as an animal-model anxiolytic with proposed secondary effects on memory and immune signaling. Reported mechanisms include modulation of the GABA-A receptor complex, inhibition of enkephalin-degrading enzymes, and shifts in monoamine turnover within limbic structures. Some experiments describe increased expression of brain-derived neurotrophic factor in the hippocampus after repeated dosing. No single molecular target has been confirmed, and the peptide does not bind any receptor with the selectivity typical of a conventional small-molecule drug. Mechanism therefore remains a set of hypotheses rather than an established pathway.
Laboratory work relies on standard behavioral paradigms. Rodents are tested in the elevated plus maze, open field, and passive avoidance tasks, with outcomes compared against diazepam or vehicle controls. Intranasal dosing is used most often because it bypasses first-pass metabolism, though intraperitoneal and intravenous routes also appear in published protocols. Biochemical endpoints include tissue BDNF concentrations, cytokine levels, and monoamine metabolites. Human data are limited to small Russian trials reporting reduced anxiety scores; most were not prospectively registered, and few employed independent outcome assessment.
| 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 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.
Selank is not a naturally occurring peptide and has no known endogenous counterpart in human physiology. Russian-language sources frequently call it TP-7, while English-language sources use the name Selank almost exclusively. Database indexing is uneven, partly because early reports appeared in regional journals that are not widely cataloged. Some summaries describe the material as a tuftsin analog and others as a synthetic heptapeptide; the labels overlap rather than conflict. Citing the primary sequence resolves ambiguity more reliably than the research or trade name alone.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter notation. Its structure consists of the immunomodulatory tetrapeptide tuftsin, Thr-Lys-Pro-Arg, extended at the carboxyl terminus by a Pro-Gly-Pro segment. The molecular formula is commonly given as C33H57N11O9, corresponding to a monoisotopic mass near 751.4 Da and an average molecular mass near 751.9 Da. All seven residues are proteinogenic amino acids, and the molecule carries no modified side chains or non-natural linkages.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
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.
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.
Radiation protection continued to develop with the invention of new measuring devices such as the chromoradiometer by Guido Holzknecht (1872-1931) in 1902, the radiometer by Raymond Sabouraud (1864-1938) and Henri Noiré (1878–1937) in 1904/05, and the quantimeter by Robert Kienböck (1873-1951) in 1905, which made it possible to determine maximum doses at which there was a high probability that no skin changes would occur. Radium was also included by the British Roentgen Society, which published its first memorandum on radium protection in 1921.
Challenges include: 1) finding a surface and a method of attachment that allows the proteins to maintain their secondary or tertiary structure and thus their biological activity and their interactions with other molecules, 2) producing an array with a long shelf life so that the proteins on the chip do not denature over a short time, 3) identifying and isolating antibodies or other capture molecules against every protein in the human genome, 4) quantifying the levels of bound protein while assuring sensitivity and avoiding background noise, 5) extracting the detected protein from the chip in order to further analyze it, 6) reducing non-specific binding by the capture agents, 7) the capacity of the chip must be sufficient to allow as complete a representation of the proteome to be visualized as possible; abundant proteins overwhelm the detection of less abundant proteins such as signaling molecules and receptors, which are generally of more therapeutic interest.
== Genetics == The human OPRK1 gene is located on chromosome 8 and comprises four exons separated by three introns, spanning approximately 25 kilobases. The gene utilizes at least three transcription initiation sites, generating mRNAs with 5′-UTRs of 215–299 nucleotides, with the predominant isoform containing 238 nucleotides of 5′-UTR sequence. The exon-intron organization is conserved between human, mouse, and rat OPRK1 genes.
=== Developments in production === Until the end of the 19th century, vaccination was performed either directly with vaccine produced on the skin of calves or, particularly in England, with vaccine obtained from the calf but then maintained by arm-to-arm transfer; initially in both cases vaccine could be dried on ivory points for short-term storage or transport but increasing use was made of glass capillary tubes for this purpose towards the end of the century. During this period there were no adequate methods for assessing the safety of the vaccine and there were instances of contaminated vaccine transmitting infections such as erysipelas, tetanus, septicaemia and tuberculosis. In the case of arm-to-arm transfer there was also the risk of transmitting syphilis. Although this did occur occasionally, estimated as 750 cases in 100 million vaccinations, some critics of vaccination e.g. Charles Creighton believed that uncontaminated vaccine itself was a cause of syphilis. Smallpox vaccine was the only vaccine available during this period, and so the determined opposition to it initiated a number of vaccine controversies that spread to other vaccines and into the 21st century. Sydney Arthur Monckton Copeman, an English Government bacteriologist interested in smallpox vaccine, investigated the effects on the bacteria in it of various treatments, including glycerine. Glycerine was sometimes used simply as a diluent by some continental vaccine producers.
== Methylation of arsenic == Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised (detoxified) through a process of methylation. The methylation occurs through alternating reductive and oxidative methylation reactions, that is, reduction of pentavalent to trivalent arsenic followed by addition of a methyl group (CH3).
Sources: en.wikipedia.org
Botha wanted all the Cuban military personnel to be withdrawn, and over a period of twelve months rather than three years. He also countered that the Namibian independence process could only take place once the Cuban withdrawal was initiated. The Lusaka Accords were abandoned in the wake of Operation Argon, a failed sabotage mission carried out by South African special forces in Angola's oil-rich Cabinda exclave. Four years of military escalation and massive defence expenditures had a drastic impact on Angola's state finances, which were only being balanced by petroleum revenue. The largest oil refinery in the country was located on the Cabindan coast and operated by a US firm, Gulf Oil, under the auspices of the Cabina-Gulf Oil National Petroleum Company of Angola (SONAGOL). By 1984 Gulf had invested over 1.3 billion dollars in its Cabinda operation, which was exporting 165,495 barrels of oil per day. At the time, the revenue from the Gulf refinery generated 90% of Angola's foreign exchange. The Reagan administration separated its political positions on Angola from its position on SONAGOL, with Crocker hoping that American multinational companies in general, and Gulf in particular, would be a moderating force on the Marxist government. South Africa had noted the critical importance of the refinery's contribution to the FAPLA war effort and had begun investigating ways to disrupt it without incurring the ire of the US, which would have to react if American commercial interests were threatened.
== Dynamic structures and modifications == As in the broader field of DNA nanotechnology, DNA origami may be made dynamic in nature through the use of a variety of methods. The three primary methods of creating a dynamic DNA origami machine are toehold mediated strand displacement, enzymatic reactions, and base stacking. While these methods are most commonly used, additional methods for creating dynamic DNA origami machines exist, such as designing a directional component and using brownian motion to drive rotational movement of structures or leveraging less commonly used DNA self-assembly phenomena like G-quadruplexes or i-motifs which can be pH sensitive.
== Two step non-laser == In two-step non-laser methods, the material removal from the sample and the ionization steps are separate. Probe electrospray ionization (PESI) is a modified version of conventional electrospray ionization in which the capillary for sample solution transferring is replaced by a solid needle with a sharp tip. Compared with conventional electrospray ionization, high salt tolerance, direct sampling, and low sample consumption are found with PESI. PESI is not a continuous process; the needle for sampling and spraying is driven up and down at a frequency of 3–5 Hz.
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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.
Intranasal administration predominates in both animal and human research because it avoids hepatic first-pass metabolism. Injectable and intraperitoneal routes appear in animal work mainly for comparison.