If you have been reading about peptide purity 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.
Last reviewed on 2026-07-25. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Peptide sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues; tuftsin plus a Pro-Gly-Pro tail |
| Molecular formula | C33H57N11O9 | Commonly reported value for the free peptide |
| Monoisotopic mass | Roughly 751.4 Da | Average molecular mass near 751.9 Da |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Freely soluble in water | Also dissolves in saline and other polar solvents |
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.
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.
Lyophilized Selank, the dry powder form, is generally stored frozen at minus 20 degrees Celsius or colder for long-term keeping. The solid is hygroscopic and should stay sealed, dry, and protected from light. Once dissolved, the peptide is less stable and is usually held refrigerated at 2 to 8 degrees Celsius for short periods. Repeated freezing and thawing is avoided because it can promote aggregation and loss of activity. Buffers and pH choice also affect how long a solution remains usable.
Solubility behavior is a practical concern for handling. Selank dissolves readily in water and in common aqueous buffers, which simplifies preparation of working solutions. The choice of solvent, ionic strength, and pH can influence aggregation over time, particularly at higher concentrations. Aqueous solutions are typically sterile-filtered before use. Because stability depends on several variables, storage and handling notes should be treated as general guidance rather than fixed rules, and specific values are best confirmed against a certificate of analysis for each batch.
Cartels have engaged in kidnapping, ransom, murder, robbery, and extortion of migrants traveling from Central America through Mexico on their way to the United States and Canada. Cartels have also forced migrants to join their organization and work for them, a situation that has been described as slavery. Mass graves have been also discovered in Mexico containing bodies of migrants. In 2011, 177 bodies were found in a mass grave in San Fernando, Tamaulipas, the same area where the bodies of 72 migrants were found in 2010, where most victims "died of blunt force trauma to the head." Cartels have also infiltrated the Mexican government's immigration agencies and attacked and threatened immigration officers. The National Human Rights Commission of Mexico (Comisión Nacional de los Derechos Humanos, CNDH) said that 11,000 migrants had been kidnapped in 6 months in 2010 by drug cartels.
A modification of the Koenigs-Knorr reaction for building glycosides from 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (acetobromoglucose) originates from S. Hanessian who used the silver salt silver trifluoromethanesulfonate (TfOAg) and as a proton acceptor tetramethylurea. This process variant is characterized by a simplified process control, high anomeric purity and high yields of the products. If the reaction is carried out with acetobromoglucose and silver triflate/tetramethylurea at room temperature, then tetramethylurea reacts not only as a base, but also with the glycosyl to form a good isolable uroniumtriflates in 56% yield.
Buprenorphine is metabolized by the liver, primarily via the cytochrome P450 (CYP) isozyme CYP3A4, into norbuprenorphine. The glucuronidation of buprenorphine is primarily carried out by the UDP-glucuronosyltransferases (UGTs) UGT1A1 and UGT2B7, while norbuprenorphine is glucuronidated by UGT1A1 and UGT1A3. These glucuronides are then eliminated mainly through excretion into bile. The elimination half-life of buprenorphine is 20 to 73 hours (mean 37 hours). Due to the mainly hepatic elimination, there is no risk of accumulation in people with kidney problems.
=== Regulatory status === Selegiline is a prescription drug. It is not specifically a controlled substance in the United States and hence is not an illegal drug. However, deprenyl and selegiline are controlled substances in Japan. They are classified as "Stimulants", alongside a variety of other amphetamines, under Article 2 of Japan's Narcotics and Psychotropics Control Law. Selegiline is known to metabolize into small amounts of levoamphetamine and levomethamphetamine but is thought to have little to no misuse potential or dependence liability.
Sources: en.wikipedia.org
==== Electrolyte imbalances ==== Electrolytes like Na, K, Ca, and P can all cause mimicking symptoms when high or low. Most commonly, hypokalemia, or low K, is the culprit, since many common drugs decrease this electrolyte.
=== Subtypes === There are several subtypes of catatonia recognized: stuporous catatonia, excited catatonia, malignant catatonia, and periodic catatonia. Subtypes are defined by the group of symptoms and associated features that a person is experiencing or displaying. Although catatonia can be divided into subtypes, its presentation is often dynamic, and the same individual may exhibit different subtypes at different times. Stuporous catatonia is characterized by immobility, mutism, and a lack of response to the world around them. They may appear frozen in one position for long periods of time unable to eat, drink, or speak. Excited catatonia is characterized by odd mannerisms and gestures, purposeless or inappropriate actions, excessive motor activity, restlessness, stereotypy, impulsivity, agitation, and combativeness. Patients suffering from excited catatonia may have speech and actions that are repetitive or mimic another person's. This state is often characterized by hyperactivity, and the patient may have delusions and hallucinations. Malignant catatonia is characterized by fever, dramatic and rapid changes in blood pressure, increased heart rate and respiratory rate, and excessive sweating. This condition is life-threatening, and the patient's laboratory tests may come back abnormal. Periodic catatonia is characterized by a person having recurrent episodes of catatonia. Individuals will experience multiple episodes over time, with no signs of catatonia between episodes.
The Free Movement of Workers Regulation articles 1 to 7 set out the main provisions on equal treatment of workers. First, articles 1 to 4 generally require that workers can take up employment, conclude contracts, and not suffer discrimination compared to nationals of the member state. In a famous case, the Belgian Football Association v Bosman, a Belgian footballer named Jean-Marc Bosman claimed that he should be able to transfer from R.F.C. de Liège to USL Dunkerque when his contract finished, regardless of whether Dunkerque could afford to pay Liège the habitual transfer fees. The Court of Justice held "the transfer rules constitute[d] an obstacle to free movement" and were unlawful unless they could be justified in the public interest, but this was unlikely. In Groener v Minister for Education the Court of Justice accepted that a requirement to speak Gaelic to teach in a Dublin design college could be justified as part of the public policy of promoting the Irish language, but only if the measure was not disproportionate. By contrast in Angonese v Cassa di Risparmio di Bolzano SpA a bank in Bolzano, Italy, was not allowed to require Mr Angonese to have a bilingual certificate that could only be obtained in Bolzano. The Court of Justice, giving "horizontal" direct effect to TFEU article 45, reasoned that people from other countries would have little chance of acquiring the certificate, and because it was "impossible to submit proof of the required linguistic knowledge by any other means", the measure was disproportionate.
== Mentions in culture == In the 2009 film inspired by Edgar Allan Poe's "The Tell-Tale Heart", Tell-Tale, Eastlack is mentioned and referred to as Harry Erlich. The mention occurs in a scene where characters are in a museum, and a skeleton is referred to. The scene provides some genuine facts, such as how Eastlack's skeleton does not require any wiring or glue to be held together in the museum because the fused bones hold it all in one piece.
=== Benefits of plasma over serum === Plasma preparation is quick, as it is not coagulated. Serum sample preparation requires about 30 minutes of waiting time before it can be centrifuged and then analyzed. However, coagulation can be hastened down to a few minutes by adding thrombin or similar agents to the serum sample. Compared to serum, 15–20% larger volume of plasma can be obtained from a blood sample of certain size. Serum lacks some proteins that partake in coagulation and increase the sample volume. Serum preparation can cause measurement errors by increasing or decreasing the concentration of the analyte that is meant to be measured. For example, during coagulation, blood cells consume blood glucose and platelets increase the sample content of compounds like potassium, phosphates and aspartate transaminase by secreting them. Glucose or these other compounds may be the analytes.
Sources: en.wikipedia.org
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.
No peptide with this exact sequence has been identified as an endogenous substance. It is a laboratory-designed analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The Pro-Gly-Pro extension has no known natural source.
Proline introduces conformational constraints that make a peptide less accessible to common peptidases. This is a standard stabilization strategy in peptide design. The added residues also increase the distance between the active tuftsin portion and typical cleavage sites.
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.