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 2026-08-01 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Identity confirmation | Reversed-phase HPLC retention time versus reference standard | Retention depends on column, gradient, and ion-pairing agent |
| Mass confirmation | Electrospray or MALDI mass spectrometry | Doubly protonated ion near m/z 377 is consistent with about 752 Da |
| Typical purity specification | 95 percent or higher by chromatographic peak area | Lower values suggest truncated or modified peptide species |
| Storage of lyophilized powder | -20 °C, desiccated, protected from light | Powder tolerates long storage better than solution |
| Storage of solution | 2-8 °C for short periods | Freeze-thaw cycling promotes aggregation and surface adsorption |
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
Proposed mechanisms centre on modulation of the GABAergic system, with reports of altered expression of genes related to GABA-A receptor subunits and changed monoamine turnover. Some studies describe inhibition of enkephalinase, the enzyme that degrades endogenous enkephalins, which may prolong opioid peptide signalling. Effects on brain-derived neurotrophic factor and on cytokine expression have also been reported. These findings come largely from animal models and small human studies, and the precise primary target remains unresolved.
Pharmacokinetic data are sparse and largely derived from animal work. After intranasal administration the peptide appears in plasma within minutes, and reported half-lives are short, on the order of minutes to tens of minutes. Degradation proceeds through ordinary proteolytic cleavage into constituent amino acids and smaller fragments. Direct evidence that intact Selank reaches brain tissue in meaningful amounts is limited, and the extent of blood-brain barrier penetration is debated. Some authors argue that fragments, not the parent peptide, carry much of the observed activity.
Published clinical work is concentrated in Russian-language journals and generally involves small samples without independent replication. Systematic reviews in English note the shortage of randomised, placebo-controlled trials and the difficulty of verifying methods from translated reports. Outcome measures vary between studies, which complicates pooling of results. Interest in the compound as a cognitive or anxiolytic agent therefore rests on a thinner evidence base than the volume of citations suggests. Replication in well-powered trials with preregistered endpoints would be needed before firm conclusions about efficacy can be drawn.
Proposed mechanisms centre on the GABAergic system. Animal and tissue studies report changes in GABA-A receptor expression and reduced activity of GABA transaminase, the enzyme that degrades GABA. Effects on monoamine turnover, including serotonin and dopamine pathways, are also described, and a separate line of work links the peptide to increased expression of brain-derived neurotrophic factor in hippocampal tissue. Most of these findings come from rodent models and cell preparations. How the individual observations combine into a single coherent mode of action is not settled.
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.
=== Taste === Salts can elicit all five basic tastes, e.g., salty (sodium chloride), sweet (lead diacetate, which will cause lead poisoning if ingested), sour (potassium bitartrate), bitter (magnesium sulfate), and umami or savory (monosodium glutamate).
=== Phase 2 clinical trial – Covid-19 / SARS-CoV-2 === The Brilacidin trial for the treatment of COVID-19 infection has started in February 2021 and is expected to be completed in July 2021. The study is a randomized, blinded, placebo-controlled, parallel group design and will accept 120 patients. The placebo or drug will be administered via IV infusion to patients with moderate to severe COVID-19, SARS-CoV-2 infection confirmed by positive standard polymerase chain reaction test (or equivalent/ other approved diagnostic test) within 4 days prior to starting study treatment, and hospitalized with respiratory distress but not yet requiring high-level respiratory support.
Because breasts are mostly fatty tissue, their shape can—within limits—be molded by clothing, such as foundation garments. Bras are commonly worn by about 90% of Western women, and are often worn for support. The social norm in most Western cultures is to cover breasts in public, though the extent of coverage varies depending on the social context. Some religions ascribe a special status to the female breast, either in formal teachings or through symbolism. Islam forbids free women from exposing their breasts in public. Many cultures, including Western cultures in North America, associate breasts with sexuality and tend to regard bare breasts as immodest or indecent. In some cultures, like the Himba in northern Namibia, bare-breasted women are normal. In some African cultures, for example, the thigh is regarded as highly sexualized and never exposed in public, but breast exposure is not taboo. In a few Western countries and regions female toplessness at a beach is acceptable, although it may not be acceptable in the town center. Social attitudes and laws regarding breastfeeding in public vary widely. In many countries, breastfeeding in public is common, legally protected, and generally not regarded as an issue. However, even though the practice may be legal or socially accepted, some mothers may nevertheless be reluctant to expose a breast in public to breastfeed due to actual or potential objections by other people, negative comments, or harassment. It is estimated that around 63% of mothers across the world have publicly breast-fed.
== History == In 1982, Dan Duchaine formulated the first pre-workout, called Ultimate Orange, in Venice, California. Ultimate Orange was commonly used among bodybuilders. Between the late 1990s and early 2000s, consumers alleged that an active ingredient in Ultimate Orange, called Ephedra, caused high blood pressure, strokes, seizures, cardiac arrhythmia, and heart attacks. The risk of using Ephedra gave rise to creatine. Creatine is a supplement that was used by a lot of athletes in the 1992 Olympics where it gained most of its popularity from. Creatine was considered a form of pre-workout in the late 1990s until the early 2000s where it was then later used with a mixture of other supplements. Creatine was negatively received when it was first introduced to the public until the last decade where it is now one of the most used supplements. In the early 2000s, supplement companies created more potent forms of pre-workout that caused the blood flow in muscles to increase temporarily, giving lifters a better "pump." These more potent supplements are called Arginine AKG, Arginine Malate, and Citrulline. In 2005, chemist Patrick Arnold formulated a pre-workout which contained a new ingredient called DMAA (dimethylamylamine). The product Jack3d gained notoriety for its potency, but its high concentrations of DMAA were suspected of causing shortness of breath, chest pain, and an elevated risk of heart attacks. Jack3d was banned in 2012 by the FDA.
1,8-Cineole 2-exo-monooxygenase (EC 1.14.14.56, CYP3A4) is an enzyme with systematic name 1,8-cineole,NADPH:oxygen oxidoreductase (2-exo-hydroxylating). This enzyme catalyses the following chemical reaction
Sources: en.wikipedia.org
== Production and content == Finely textured meat is produced by heating boneless beef trimmings (the last traces of skeletal muscle meat, scraped, shaved, or pressed from the bone) to 107–109 °F (42–43 °C), removing the melted fat by centrifugal force using a centrifuge, and flash freezing the remaining product to 15 °F (−9 °C) in 90 seconds in a roller press freezer. The roller press freezer is a type of freezer that was invented in 1971 by BPI CEO Eldon Roth that can "freeze packages of meat in two minutes" and began to be used at Beef Products Inc. in 1981. The lean finely textured beef is added to ground beef as a filler or to reduce the overall fat content of ground beef. In March 2012 about 70% of ground beef sold in US supermarkets contained the product. It is also used as a filler in hot dogs produced in the United States. The recovered beef material is extruded through long tubes that are thinner than a pencil, during which time at the BPI processing plant, the meat is exposed to gaseous ammonia. At Cargill Meat Solutions, citric acid is used to kill bacteria such as E. coli and Salmonella instead. Gaseous ammonia in contact with the water in the meat produces ammonium hydroxide. The ammonia sharply increases the pH and damages microscopic organisms, the freezing causes ice crystals to form and puncture the organisms' weakened cell walls, and the mechanical stress destroys the organisms altogether. The product is finely ground, compressed into pellets or blocks, flash frozen and then shipped for use as an additive.
== Society and culture == Prescriptions in the US for all sleeping pills (including zolpidem) steadily declined from around 57 million tablets in 2013, to around 47 million in 2017, possibly due to concern about prescribing addictive drugs amid the opioid crisis.
2 October A U.S. Navy C-2A Greyhound crashed into the Gulf of Tonkin on a flight from Naval Air Station Cubi Point to the aircraft carrier USS Constellation killing all 27 on board. Hanna E. Crews a Donut Dolly died of head injuries after a vehicle accident near Bien Hoa, becoming the first of three Donut Dollies to die in the war.
=== Neonate === Guidelines for neonatal skin care have been developed. Nevertheless, the pediatric and dermatological communities have not reached a consensus on best cleansing practices, as good quality scientific evidence is scarce. Immersion in water seems superior to washing alone, and use of synthetic detergents or mild liquid baby cleansers seems comparable or superior to water alone.
Most important of all, the Butantan Institute became a fertile school for breeding a new generation of Brazilian biochemists, physiologists and pathologists, such as José Moura Gonçalves, Carlos Ribeiro Diniz, Gastão Rosenfeld, Wilson Teixeira Beraldo and Maurício Rocha e Silva, who went on to found a growing number of schools, departments and research laboratories in São Paulo, Rio de Janeiro and Minas Gerais, giving a great impetus to the development of medical and biological research and teaching in Brazil in the second half of the 20th century.
Sources: en.wikipedia.org
Identity is confirmed by matching the retention time in reversed-phase chromatography against a reference standard and by measuring the molecular mass with mass spectrometry. Tandem mass spectrometry or amino acid analysis can verify the sequence of the seven residues. Because the peptide contains no aromatic amino acids, detection at 280 nm is not useful.
Lyophilized powder is normally stored desiccated at -20 °C, protected from light and moisture. Powder kept under these conditions is generally stable for long periods. Solutions are less stable and are usually prepared immediately before use.
A purity value from one chromatographic method does not capture every possible impurity. Related peptides with similar retention behavior, counterions, and residual solvents may not appear in the same analysis. Independent testing with an orthogonal method provides stronger assurance of identity and content.
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.