freeze-thaw 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 2025-11-20. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Animal studies have examined behaviour in tests of anxiety, memory retention and stress response, and several report changes in neurotrophic or neurotransmitter-related markers. The human evidence base is much smaller, consisting mainly of short trials conducted in Russia with limited reporting in English-language journals. Sample sizes are modest and outcome measures vary between studies, so the findings are best described as preliminary. Independent replication under modern trial standards has not been widely reported.
Outside its country of origin the compound is generally handled as a research chemical rather than an approved medicine. No regulatory approval from the United States Food and Drug Administration or the European Medicines Agency has been granted for human use. Identity and purity are normally checked by reverse-phase high-performance liquid chromatography, with mass spectrometry used to confirm the molecular mass. Lyophilised material is stored cold and desiccated, and repeated freeze-thaw cycles are avoided.
Published work on this peptide almost always uses intranasal delivery, with drops or a spray applied to the nasal mucosa. Some animal experiments have used subcutaneous or intraperitoneal injection, and a smaller number have compared routes directly. Oral administration is not a focus of the literature, because short peptides of this size are broken down by digestive enzymes and cross intestinal barriers poorly. How much of an intranasal dose reaches the bloodstream intact in humans remains an open question.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic heptapeptide | Stabilized analog of tuftsin |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Single-letter form: TKPRPGP |
| Molecular formula | C33H57N11O9 | Monoisotopic mass about 751.9 Da |
| Appearance | White to off-white powder | Typically supplied as lyophilized solid |
| Solubility | Freely soluble in water | Also soluble in common polar solvents |
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.
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.
Naming for this compound is not fully standardised in English sources. The spelling Selanc appears in some transliterations, and catalogue entries may instead list the peptide sequence itself as the identifier. Reference material sometimes groups it with other short synthetic peptides studied for behavioural effects, which can create confusion when citations are compared. Distinguishing the exact sequence from related tuftsin analogues is therefore a practical first step when reviewing any dataset or specification sheet.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated as TKPRPGP. It was designed as a structural analogue of tuftsin, a naturally occurring tetrapeptide released by enzymatic cleavage of the immunoglobulin heavy chain. The two additional proline residues at the C-terminal end extend the parent chain and change how the molecule behaves in solution. The free peptide has a calculated molecular mass of approximately 751.9 g/mol and is generally supplied as a lyophilised white to off-white powder.
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.
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.
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.
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.
=== MAGNET designation === In 2008, Southern Ohio Medical Center became the first hospital in the tri-state region (Ohio, Kentucky, West Virginia) to earn Magnet Recognition from the American Nurses Credentialing Center. The Magnet Recognition Program recognizes healthcare organizations for quality patient care, nursing excellence and innovations in professional nursing practice. In 2011, less than 7% of hospitals in the United States were able to achieve Magnet Recognition. SOMC earned Magnet re-designation in 2013.
When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence the adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products.
The Hispanic population in Belize makes up about half of the population and consists of two main groups, the Yucatec Mestizos, better known as Mestizos, and the Central American immigrants from El Salvador, Guatemala, Honduras and Nicaragua. The Yucatec Mestizos are people of mixed Spanish and Yucatec Maya descent. They were the first to bring Catholicism and the Spanish language to Belize after various failed attempts over the century by Spanish conquistadores. They originally came to Belize in 1847, to escape the Caste War, which occurred when thousands of Mayas rose against the state in Yucatán and over one-third of the population was massacred. The survivors fled across the borders into British territory. The Mestizos are found everywhere in Belize but most make their homes in the northern districts of Corozal and Orange Walk. In the 1980s a wave of Central American migrants from El Salvador, Guatemala, Honduras, and Nicaragua came to settle in Belize. The Government of Belize with the help of the United Nations opened the nation's doors to Central American neighbours fleeing from civil war and persecution. Due to the influences of Belizean Creole and English, many Mestizos speak what is known as "Kitchen Spanish". The mixture of Yucatec Mestizo and Yucatec Maya foods like tamales, escabeche, chirmole, relleno, and empanadas came from their Mexican side and corn tortillas were handed down by their Mayan side. Music comes mainly from the marimba, but they also play and sing with the guitar.
Inflammatory arthritides such as ankylosing spondylitis, psoriatic arthritis, rheumatoid arthritis and systemic lupus erythematosus can all cause varying levels of joint destruction. Among the inflammatory arthritides, ankylosing spondylitis is most closely associated with back pain because of the inflammatory destruction of the bony components of the spine. Ankylosing spondylitis is common in young men and presents with a range of possible symptoms such as uveitis, psoriasis and inflammatory bowel disease.
Sources: en.wikipedia.org
=== Non-clinical use === SR-17018 has emerged as a novel designer drug and has been extensively discussed online, for instance on the social media website Reddit. Thorough online documentation of the drug, for instance use protocols and experiences, have emerged. The drug is anecdotally reported to have very different effects relative to other opioids. Rather than being used to produce euphoria, SR-17018 is employed to help dependent individuals discontinue opioids, to prevent opioid withdrawal, and to reduce opioid tolerance. It has been used to facilitate discontinuation of a wide range of opioids, including fentanyl, heroin, methadone, buprenorphine, prescription opioids, synthetic opioids like nitazenes, and kratom, among others. SR-17018 itself is said to produce minimal euphoria or analgesia, in contrast to conventional opioids. A risk of SR-17018 is accidental overdose of opioids after tolerance has reduced, with at least one fatal case having been reported. It is not said to address psychological opioid addiction.
== Toxicity == Azacitidine causes anemia (low red blood cell counts), neutropenia (low white blood cell counts), and thrombocytopenia (low platelet counts), and patients should have frequent monitoring of their complete blood counts, at least prior to each dosing cycle. The dose may have to be adjusted based on nadir counts and hematologic response. It can also be hepatotoxic in patients with severe liver impairment, and patients with extensive liver tumors due to metastatic disease have developed progressive hepatic coma and death during azacitidine treatment, especially when their albumin levels are less than 30 g/L. It is contraindicated in patients with advanced malignant hepatic tumors. Kidney toxicity, ranging from elevated serum creatinine to kidney failure and death, have been reported in patients treated with intravenous azacitidine in combination with other chemotherapeutic agents for conditions other than myelodysplastic syndrome. Renal tubular acidosis developed in five patients with chronic myelogenous leukemia (an unapproved use) treated with azacitidine and etoposide, and patients with renal impairment may be at increased risk for renal toxicity. Azacitidine and its metabolites are primarily excreted by the kidneys, so patients with chronic kidney disease should be closely monitored for other side effects, since their levels of azacitidine may progressively increase. Based on animal studies and its mechanism of action, azacitidine can cause severe fetal damage.
These models tend to recognize partial molecular structures early in training but require significantly longer to accurately distinguish between enantiomers, sometimes exhibiting periods of confusion where @ and @@ tokens are frequently interchanged. The interpretability of neural network-based descriptors is often limited compared to traditional physically-motivated descriptors. Additionally, these methods typically perform best for compounds structurally similar to training data and may not generalize well to novel scaffolds or unusual stereochemical arrangements.
=== Simmering hostilities === Although the Vaal uprising marked the beginning of an open and sustained revolt, it was preceded by an "underground war" or "series of localised confrontations", for example clashes in Pietermaritzburg in 1982; in Durban and Mdantsane in 1983; and in Crossroads, Atteridgeville, Cradock, Tumahole, and the East Rand earlier in 1984. Over the same period, in Soweto and some other areas, there was a demonstrable upswing in a longstanding habit of persecution of black local councillors. The boycott of the 1984 election, held in the last week of August, was accompanied by large-scale protests, resulting in a large number of arrests. Some of the candidates for the Tricameral Parliament were also targeted in petrol bomb attacks.
===== Sliding-rebinding model ===== The sliding-rebinding model differs from the allosteric model in that the allosteric model posits that only one binding site exists and can be altered, but the sliding-rebinding model states that multiple binding sites exist and aren't changed by EGF extension. Rather, in the bent conformation which is favored at low applied forces, the applied force is perpendicular to the line of possible binding sites. Thus, when the association between ligand and lectin domain is interrupted, the bond quickly dissociates. At larger applied forces, however, the protein is extended and the line of possible binding sites is aligned with the applied force, allowing the ligand to quickly re-associate with a new binding site after the initial interaction is disrupted. With multiple binding sites, and even the ability to re-associate with the original binding site, the rate of ligand dissociation would be decreased as is typical of catch bonds.
Sources: en.wikipedia.org
The European Journal of Mass Spectrometry is a peer-reviewed scientific journal covering all areas of mass spectrometry. It is published by SAGE Publishing and the editor-in-chief is Jürgen Grotemeyer (Kiel University).
=== Ports === Half-Life 2 was released on the Xbox console by Electronic Arts in November 2005. In 2006, Valve partnered with Taito to release Half-Life 2: Survivor, an arcade game, for the Japanese market. Valve re-released Half-Life 2 as part of the 2007 compilation The Orange Box for Windows, Xbox 360 and PlayStation 3. On May 26, 2010, Half-Life 2, Episode One and Episode Two were released for Mac OS X. In 2013, Valve ported Half-Life 2 to Linux and released a free update adding support for the Oculus Rift virtual reality headset. An Nvidia Shield Tablet-exclusive port for Android was released on May 12, 2014.
===== India, Russia and CIS countries ===== Valparin Chrono by Sanofi India Valprol CR by Intas Pharmaceutical (India) Encorate Chrono by Sun Pharmaceutical (India) Serven Chrono by Leeven APL Biotech (India)
The committee finished its work in April 1978 and the Constitutional Affairs Commission began to debate the preliminary draft on May 5. But the real negotiation was carried out outside the commission by Fernando Abril Martorell on behalf of the UCD and the government and the deputy secretary general of the PSOE Alfonso Guerra, who met privately to reach a consensus on the controversial issues, which allowed the rapid approval of the articles of the preliminary draft. The consensus was extended to Communists and Catalan nationalists but a part of Alianza Popular, which rejected among other things the incorporation of the term "nationalities", and the PNV, which demanded the recognition of the national sovereignty of the Basques, did not join it. Finally, on October 31, 1978, the Constitutional bill was voted in the Congress and in the Senate. In the Congress, 325 deputies voted in favor, 6 against (five deputies of AP and the deputy of Euskadiko Ezkerra), and 14 abstained (the 8 deputies of the PNV, plus 6 of AP and the mixed group). In the Senate, 226 senators supported it and 5 voted against it. The Constitution thus obtained enormous parliamentary support. On December 6, 1978, the Constitution was submitted to referendum, being approved by 88% of the voters, and rejected by 8%, with a participation of 67.11% of the census. In the Basque Country, the abstentionist campaign promoted by the PNV was successful so that there the Constitution was approved by only 43.6% of the electoral roll.
The preferred and most reliable diagnosis of malaria is microscopic examination of blood smears, because each of the four major parasite species has distinguishing characteristics. Two sorts of blood smear are traditionally used.
Sources: en.wikipedia.org
Selank is a synthetic heptapeptide designed as a stabilized analog of the natural tetrapeptide tuftsin. It has been investigated mainly for anxiolytic and cognitive effects. It is not an approved pharmaceutical in most countries.
It was developed in Russia, at the Institute of Molecular Genetics of the Russian Academy of Sciences, during the 1990s. Most published research originates from Russian institutions. Independent international replication remains limited.
Tuftsin is a natural tetrapeptide with the sequence Thr-Lys-Pro-Arg that participates in immune signaling. Selank extends that sequence with Pro-Gly-Pro at the C-terminus. The added residues are linked to greater resistance to enzymatic breakdown.
Most published work uses intranasal application, either as drops or as a nasal spray. Injection routes appear in a smaller set of animal experiments. Oral use is uncommon in the literature because peptide breakdown and poor absorption limit this route.