A practical reference on freeze-thaw cycle: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-01-01 and is reviewed periodically as new material appears.
Most published work on selank originates from a small number of research groups in the Russian Federation. A large share of that record appears in Russian-language journals, which limits access for readers who rely on English-indexed databases. Independent replication by laboratories outside the original research network is sparse in publicly available sources. This concentration of origin and language is a frequently noted feature when the compound is summarized in broader reviews of synthetic peptides.
Reported pharmacological effects center on reduced anxiety-like behavior in animal models and on measures of memory and learning. Proposed contributing mechanisms include modulation of GABAergic signaling, shifts in monoamine turnover, and changes in the activity of enzymes that degrade neuropeptides. Effects on the expression of genes linked to neuroplasticity have also been described. No single molecular target is widely accepted, and whether the behavioral findings arise from one pathway or several remains an open question.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed as a stabilized analogue of tuftsin, a naturally occurring tetrapeptide fragment derived from the immunoglobulin heavy chain. The additional Pro-Gly-Pro segment at the carboxyl terminus is intended to slow enzymatic cleavage. The compound is usually described in the literature as a synthetic peptide with anxiolytic and cognitive-related activity, a label that reflects a research context rather than an approved therapeutic category.
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.
The compound was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences during the 1980s and 1990s. The stated design goal was to retain the immunomodulatory and central nervous system activity attributed to tuftsin while improving resistance to enzymatic breakdown. Adding a proline-rich tail to the short parent peptide was a deliberate strategy, because proline residues restrict the conformations available to many peptidases. The same laboratory produced Semax, an ACTH fragment analog, and both compounds were developed in parallel as short, enzymatically stabilized peptides intended for intranasal use.
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C33H57N11O9 | Derived from the seven-residue sequence |
| Molecular weight | About 751.9 g/mol | Average mass; the monoisotopic value is slightly lower |
| Residue count | Seven amino acids | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Parent compound | Tuftsin (Thr-Lys-Pro-Arg) | Selank extends tuftsin at the C-terminus |
| Compound class | Synthetic short peptide | Studied in a research setting; not a licensed drug in most markets |
Lyophilised material kept dry at minus 20 degrees Celsius or colder is the most stable form, and suppliers commonly state a shelf life of two years or more under those conditions. Once dissolved, degradation accelerates through hydrolysis and deamidation, particularly at alkaline pH or elevated temperature. Working solutions are usually divided into single-use aliquots to avoid repeated freeze-thaw cycles. The choice of reconstitution solvent affects both stability and the ionic strength of the final preparation.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 nanometres is the standard purity method. Mass spectrometry, typically electrospray ionisation, confirms identity through the expected mass-to-charge pattern. Amino acid analysis can verify composition independently. Chiral purity requires separate techniques such as derivatisation followed by chromatographic separation, and such data are rarely reported for research-grade material.
Naming conventions place Selank in the same research family as Semax, another Russian-developed peptide investigated for cognitive effects. The two compounds share a lineage but differ in sequence and in the biological systems proposed as their targets. Semax descends from ACTH fragments, whereas Selank descends from tuftsin. Publications sometimes identify Selank by its full peptide sequence or by laboratory codes rather than one uniform trade name. Because replication outside Russia is limited, reports on its properties are best read alongside the study design and the purity of the material tested.
Selank is a synthetic heptapeptide developed in Russia during the 1990s. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences designed it as a stabilized analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The compound has been studied primarily for its reported anxiolytic and nootropic effects. It remains largely unknown in Western pharmacology and is not approved as a medicine by major regulators such as the FDA or the EMA.
The primary structure of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, corresponding to the molecular formula C33H57N11O9 and a monoisotopic mass of roughly 751.9 daltons. The N-terminal threonine and the arginine residue in the fourth position are shared with tuftsin, which carries the sequence Thr-Lys-Pro-Arg. The three additional residues at the C-terminus, Pro-Gly-Pro, extend the chain and are associated with greater resistance to enzymatic degradation. This extension also separates Selank from the shorter parent peptide.
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.
==== Turkic cultures ==== Among Turkic peoples, circumcision (sünnet in Turkish, sünnət in Azerbaijani, sunnat in Uzbek, сүндет/sündet in Kazakh) is viewed as both a religious obligation and a significant rite of passage for boys. The practice is nearly universal among Turkic Muslim populations in Turkey, Azerbaijan, Uzbekistan, Kazakhstan, Kyrgyzstan, Turkmenistan, and among Turkic minorities such as the Uyghurs in China.The ceremony, known as sünnet düğünü (circumcision celebration) in Turkey, is typically one of the most important events in a boy's life, often rivaling weddings in scale and expense. Boys are usually circumcised between the ages of 2 and 14, with the timing varying by region and family preference. The celebration commonly includes the boy wearing special ceremonial attire, often resembling a prince's costume or military uniform, and parading through the community on horseback or in a decorated vehicle. Among the Uyghurs, the tradition is called xetne toyi and remains an important rite of passage. In traditional practice, the ceremony was accompanied by feasting, music, and gift-giving, serving as an important occasion for community bonding and the affirmation of cultural identity.
Steel cars (vs wood) for better insulation protection and greater rigidity, resulting in reduced leakage around doors A minimum of 4 inches (10 cm) insulation thickness with all insulation protected from moisture Cushioned trucks and draft gear to minimize jarring and bruising of produce Standardized interior dimensions to allow improved loading methods with standardized containers Adjustable ice bunker bulkheads to allow greater floor space for shippers using top icing alone Vertically adjustable grates within the ice bunkers to allow half-stage icing to reduce icing charges where appropriate Forced air circulation within the car An additional lining to allow side wall flues to circulate air around all cargo, preventing contact with exterior car walls Perforated floor racks providing similar protection and air circulation under the cargo Provisions for pre-cooling the cars with a portable unit at the loading platforms.
=== Saturable absorption === Graphene exhibits unique saturable absorption, which saturates when the input optical intensity exceeds a threshold value. This nonlinear optical behavior, termed saturable absorption, occurs across the visible to near-infrared spectrum, due to graphene's universal optical absorption and zero band gap. This property has enabled full-band mode-locking in fiber lasers using graphene-based saturable absorbers, contributing significantly to ultrafast photonics. Additionally, the optical response of graphene/graphene oxide layers can be electrically tuned. Saturable absorption in graphene could occur at the Microwave and Terahertz band, owing to its wideband optical absorption property. The microwave-saturable absorption in graphene demonstrates the possibility of graphene microwaves and terahertz photonics devices, such as a microwave-saturable absorber, modulator, polarizer, microwave signal processing, and broadband wireless access networks.
Larger species are mostly nestbrooding (making a nest of vegetation at the water surface), and the dwarfs mostly paternal mouthbrooding, but exceptions occur; the large C. barca is a paternal mouthbrooder and the dwarf C. bleheri is a free-spawner (the eggs float to the surface where the parents take care of them, but they do not mouthbrood or built a nest). Some species in the Channa gachua group also provision their offspring with trophic eggs. Females of Channa andrao and C. gachua have been observed releasing unfertilised eggs above newly hatched larvae, which consume the eggs. Similar trophic-egg provisioning has been observed in several other species of the C. gachua group, suggesting that the behaviour may be widespread within the group.
== Production == Optimer ligands are produced via solid-phase synthesis. Solid-phase chemical synthesis was invented in the 1960s by Robert Bruce Merrifield, for which he was awarded the Nobel Prize for Chemistry in 1984. Solid-phase synthesis is carried out on a solid support held between filters, in columns that enable all reagents and solvents to pass through freely. Solid-phase synthesis has a number of advantages over cell-based manufacturing that is typically used for protein affinity reagents, such as antibodies:
Sources: en.wikipedia.org
Intracellular ice can be much more damaging than extracellular ice. For red blood cells, the optimum cooling rate is very rapid (nearly 100 °C per second), whereas for stem cells the optimum cooling rate is very slow (1 °C per minute). Cryoprotectants, such as dimethyl sulfoxide and glycerol, are used to protect cells from freezing. A variety of cell types are protected by 10% dimethyl sulfoxide. Cryobiologists attempt to optimize cryoprotectant concentration (minimizing both ice formation and toxicity) and cooling rate. Cells may be cooled at an optimum rate to a temperature between −30 and −40 °C before being plunged into liquid nitrogen. Slow cooling methods rely on the fact that cells contain few nucleating agents, but contain naturally occurring vitrifying substances that can prevent ice formation in cells that have been moderately dehydrated. Some cryobiologists are seeking mixtures of cryoprotectants for full vitrification (zero ice formation) in preservation of cells, tissues, and organs. Vitrification methods pose a challenge in the requirement to search for cryoprotectant mixtures that can minimize toxicity.
=== Etymology === The word diabetes ( or ) comes from Latin diabētēs, which in turn comes from Ancient Greek διαβήτης (diabētēs), which literally means "a passer through; a siphon". Ancient Greek physician Aretaeus of Cappadocia (fl. 2nd century CE) used that word, with the intended meaning "excessive discharge of urine", as the name for the disease. Ultimately, the word comes from Greek διαβαίνειν (diabainein), meaning "to pass through", which is composed of δια- (dia-), meaning "through" and βαίνειν (bainein), meaning "to go". The word "diabetes" is first recorded in English, in the form diabete, in a medical text written around 1425. The word mellitus ( or ) comes from the classical Latin word mellītus, meaning "mellite" (i.e. sweetened with honey; honey-sweet). The Latin word comes from mell-, which comes from mel, meaning "honey"; sweetness; pleasant thing, and the suffix -ītus, whose meaning is the same as that of the English suffix "-ite". It was Thomas Willis who in 1675 added "mellitus" to the word "diabetes" as a designation for the disease, when he noticed the urine of a person with diabetes had a sweet taste (glycosuria). This sweet taste had been noticed in urine by the ancient Greeks, Chinese, Egyptians, and Indians.
== Phytochemicals == Chemical analyses of extracts have revealed some 65 phytochemicals, including saponins, alkaloids, polyphenols, coumarin, tannins, triterpenes, and the glycoprotein compounds, eurycomanol, eurycomanone, and eurycomalactone.
He will be strong enough to get up and two days later he leaves the home.However, even in 1934 he was suspicious of the idea that the treatment was pure conditioned reflex – "though vomiting is one of the ways that apomorphine relives the patient, I do not believe it to be its main therapeutic effect." – and by 1948 he wrote:It is now twenty-five years since I began treating cases of anxiety and alcoholism with apomorphine, and I read my first paper before this Society fourteen years ago. Up till then I had thought, and, unfortunately, I said in my paper, that the virtue of the treatment lay in the conditioned reflex of aversion produced in the patient. This statement is not even a half truth… I have been forced to the conclusion that apomorphine has some further action than the production of a vomit.This led to his development of lower-dose and non-aversive methods, which would inspire a positive trial of his method in Switzerland by Dr Harry Feldmann.
=== Co-evolution of lens and cornea through gene sharing === Based on the similarities between lens and cornea, such as abundant water-soluble enzymes, and being derived from ectoderm, the lens and cornea are thought to be co-evolved as a "refraction unit." Gene sharing would maximize light transmission and refraction to the retina by this refraction unit. Studies have shown that many water-soluble enzymes/proteins expressed by cornea are identical to taxon-specific lens crystallins, such as ALDH1A1/ η-crystallin, α-enolase/τ-crystallin, and lactic dehydrogenase/ -crystallin. Also, the anuran corneal epithelium, which can transdifferentiate to regenerate the lens, abundantly expresses ubiquitous lens crystallins, α, β and γ, in addition to the taxon-specific crystallin α-enolase/τ-crystallin. Overall, the similarity in expression of these proteins in the cornea and lens, both in abundance and taxon-specificity, supports the idea of co-evolution of lens and cornea through gene sharing.
Sources: en.wikipedia.org
The following day, Lee insisted that Peart's remarks had been taken out of context, and suggested he was "simply taking a break". Lifeson confirmed in 2016 that the R40 tour was the band's last large-scale tour. A documentary, Time Stand Still, was announced in November 2016. On January 16, 2018, Lifeson told The Globe and Mail that it was unlikely that Rush would play any more shows or record new material. He said, "We have no plans to tour or record anymore. We're basically done. After 41 years, we felt it was enough." In October 2018, Rolling Stone published an interview with Lee, who said:
=== Phenylbutyrate therapy === Sodium phenylacetate/benzoate or sodium phenylbutyrate has been shown to reduce BCAA in a clinical trial done February 2011. Phenylbutyrate treatment reduced the blood concentration of BCAA and their corresponding BCKA in certain groups of MSUD patients and may be a possible adjunctive treatment.
Tohme, researcher recognized for his work on the genetic diversity of food, Manuel Elkin Patarroyo who is known for his groundbreaking work on synthetic vaccines for malaria, Francisco Lopera who discovered the "Paisa Mutation" or a type of early-onset Alzheimer's, Rodolfo Llinás known for his study of the intrinsic neurons properties and the theory of a syndrome that had changed the way of understanding the functioning of the brain, Jairo Quiroga Puello recognized for his studies on the characterization of synthetic substances which can be used to fight fungus, tumors, tuberculosis and even some viruses and Ángela Restrepo who established accurate diagnoses and treatments to combat the effects of a disease caused by Paracoccidioides brasiliensis.
Professor Juan J. Calvete is a researcher in venomics at the biomedical institute in Valencia and has extensively explained the process involved in untangling and analysing venom (Once in 2007 and recently in 2017.) These involve the following steps: (1) Venom collection, (2) Separation and quantification, (3) Identification and (4) Representation of components found.
=== Non-specific biotinylation === Photoactivatable biotinylation reagents are ideal when primary amines, sulfhydryls, carboxyls and carbohydrates are not available for labeling. These reagents rely on aryl azides, which become activated by ultraviolet light (UV; >350 nm), which then react at C-H and N-H bonds. Because these types of bonds occur independent of the type of amino acid, this type of biotinylation is termed "non-specific". Photoactivatable biotinylation reagents can also be used to activate biotinylation at specific times in an experiment or during certain reaction conditions, by simply exposing the reaction to UV light at the specific time or condition.
Sources: en.wikipedia.org
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, designed as a metabolically stabilized analogue of the endogenous tetrapeptide tuftsin. It has been studied mainly against anxiety-related and cognitive endpoints rather than as an approved medicine in most jurisdictions.
Tuftsin contains four residues, while selank carries an additional Pro-Gly-Pro segment at the carboxyl end. That extension is intended to reduce enzymatic cleavage. Comparative pharmacokinetic data in humans remain limited.
No single receptor target is widely accepted as the definitive mediator of the reported effects. Proposed contributors include GABAergic modulation, shifts in monoamine turnover, and altered neuropeptide degradation. The mechanism is treated in the literature as unresolved.
The sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code. It combines the tetrapeptide tuftsin with a carboxyl-terminal Pro-Gly-Pro extension. This full sequence identifies the molecule more precisely than the research name.