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 2026-02-10. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
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.
| 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 |
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.
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.
Peptide stability depends strongly on temperature, moisture, and pH. Lyophilized Selank is generally most stable when stored cold and dry, with freezer temperatures commonly used for long-term storage. In solution, the compound is susceptible to hydrolysis and to microbial growth if it is not handled aseptically. The C-terminal proline-rich extension appears to slow enzymatic cleavage relative to tuftsin, though quantitative degradation rates vary with the matrix and the conditions tested. Published stability data specific to Selank remain sparse.
Quality assessment of Selank samples typically combines purity determination with identity confirmation and counter-ion analysis. Purity is usually reported as a percentage by chromatographic area, with values above 95 percent often quoted for research-grade material. Water content and residual solvents are checked in lyophilized batches because they affect both stability and accurate mass determination. A reported purity figure does not by itself establish that a sample is the intended sequence, so orthogonal methods are needed to rule out sequence isomers or truncation products.
Characterization of Selank in laboratory settings relies on standard peptide analytical techniques. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities and degradation products, while mass spectrometry confirms molecular identity through accurate mass measurement. Amino acid analysis and peptide sequencing verify the primary structure when reference material is unavailable. Because Selank is a short chain, fragmentation-based analysis produces a diagnostic ion pattern that supports confident identification.
=== Cellular biophysics === By rectifying the motion of individual swimming bacteria, microfluidic structures can be used to extract mechanical motion from a population of motile bacterial cells. This way, bacteria-powered rotors can be built.
== In-gel digestion == Afterwards the eponymous step of the method is performed, the in-gel digestion of the proteins. By this procedure, the protein is cut enzymatically into a limited number of shorter fragments. These fragments are called peptides and allow for the identification of the protein with their characteristic mass and pattern. The serine protease trypsin is the most common enzyme used in protein analytics. Trypsin cuts the peptide bond specifically at the carboxyl end of the basic aminoacids arginine and lysine. If there is an acidic amino acid like aspartic acid or glutamic acid in direct neighborhood to the cutting site, the rate of hydrolysis is diminished, a proline C-terminal to the cutting site inhibits the hydrolysis completely. An undesirable side effect of the use of proteolytic enzymes is the self digestion of the protease. To avoid this, in the past Ca2+-ions were added to the digestion buffer. Nowadays most suppliers offer modified trypsin where selective methylation of the lysines limits the autolytic activity to the arginine cutting sites. Unmodified trypsin has its highest activity between 35 °C and 45 °C. After the modification, the optimal temperature is changed to the range of 50 °C to 55 °C. Other enzymes used for in-gel digestion are the endoproteases Lys-C, Glu-C, Asp-N and Lys-N. These proteases cut specifically at only one amino acid e.g. Asp-N cuts n-terminal of aspartic acid. Therefore, a lower number of longer peptides is obtained.
Tracheal intubation refers to the insertion of a tube down the trachea. This procedure is commonly performed during surgery, in order to ensure a person receives enough oxygen when sedated. The catheter is connected to a machine that monitors the airflow, oxygenation and several other metrics. This is often one of the responsibilities of an anaesthetist during surgery. In an emergency, or when tracheal intubation is deemed impossible, a tracheotomy is often performed to insert a tube for ventilation, usually when needed for particular types of surgery to be carried out so that the airway can be kept open. The provision of the opening via a tracheotomy is called a tracheostomy. Another method procedure can be carried, in an emergency situation, and this is a cricothyrotomy.
== Contraindications == Gepirone is contraindicated in people that have experienced an allergic reaction to gepirone, a corrected QT interval > 450 msec, a history of congenital long QT syndrome, use medications that strongly inhibit CYP3A4 (an enzyme involved in gepirone's metabolism), severe liver problems, or have used a monoamine oxidase inhibitor (MAOI) medication within 14 days.
Sources: en.wikipedia.org
== Medical uses == As of January 2017, plecanatide is approved in the United States for the treatment of chronic idiopathic constipation in adults. later it was also approved for irritable bowel syndrome with constipation (IBS-C). The presence of this condition is determined using the Rome III diagnostic criteria for chronic constipation which requires that the patient meet stool frequency, stool consistency, incomplete evacuation, and straining requirements in addition to not being a likely candidate for irritable bowel syndrome. The symptoms should also have been present for at least three of the last six months to establish the chronic nature of the condition before treatment with plecanatide is indicated. Plecanatide has been shown to be safe and effective. It has shown to be at least equally as effective as its main competitor, linaclotide (brand name Linzess), but has been shown to have a lower rate of diarrhea as an adverse drug reaction.
Lorenzo Feritta, who at the time was one of the presidents of the UFC, said, "We want 100 percent of the fighters tested the night they compete". Also, in addition to the drug testing protocols in place for competitors on fight night, the UFC conducts additional testing for main event fighters or any fighters that are due to compete in championship matches. This includes enhanced, random 'out of competition' testing for performance-enhancing drugs, with both urine and blood samples being taken. The UFC also announced that all potential UFC signees would be subject to mandatory pre-contract screening for performance-enhancing drugs prior to being offered a contract with the promotion.
Because β-alanine dipeptides are not incorporated into proteins, they can be stored at relatively high concentrations. Occurring at 17–25 mmol/kg (dry muscle), carnosine (β-alanyl-L-histidine) is an important intramuscular buffer, constituting 10-20% of the total buffering capacity in type I and II muscle fibres. In carnosine, the pKa of the imidazolium group is 6.83, which is ideal for buffering.
Sources: en.wikipedia.org
== Early life == Khloé Alexandra Kardashian was born on June 27, 1984, in Los Angeles, California, to Kris (née Houghton), a homemaker, and Robert, an attorney. She has two older sisters, Kourtney and Kim, and a younger brother, Rob. Their mother is of Dutch, English, Irish and Scottish ancestry, while their father was a third-generation Armenian-American. After her parents divorced in 1991, her mother married 1976 Summer Olympics decathlon winner Caitlyn Jenner (then Bruce) in 1991. Through their marriage, Kardashian gained stepbrothers Burt, Brandon, and Brody; stepsister Casey; and half-sisters Kendall and Kylie. In 1994, her father garnered public attention as a defense lawyer for football player O. J. Simpson during his murder trial. Kardashian went to Bel Air Prep, Saint Martin of Tours School, Daniel Webster Middle School, A.E. Wright Middle School, and Montclair Prep. As a teenager, she briefly attended Marymount High School, a Roman Catholic all-girls' school in Los Angeles. She left the high school and enrolled in Alexandria Academy, an alternative one-to-one school, after her sisters' graduations, later saying "there was no reason for me to stay" since she "felt like I didn't have any friends." She graduated with honors a year early at age 17. Before her family reality TV show, Kardashian worked as Nicole Richie's assistant.
=== Linear trap and FTICR === Linear traps can be used to improve the performance of FT-ICR (or FTMS) systems. As with 3D ion traps, the duty cycle can be increased to nearly 100% if ions are accumulated in a linear trap, while the FTMS performs other functions. Unwanted ions that can cause space charge problems in the FTMS can be ejected in the linear trap to improve the resolution, sensitivity, and dynamic range of the system, although the system parameters used to optimize such signal characteristics co-vary with one another.
Argon–argon (Ar–Ar) Iodine–xenon (I–Xe) Lanthanum–barium (La–Ba) Lead–lead (Pb–Pb) Lutetium–hafnium (Lu–Hf) Hafnium–tungsten dating (Hf-W) Potassium–calcium (K–Ca) Rhenium–osmium (Re–Os) Uranium–uranium (U–U) Krypton–krypton (Kr–Kr) Beryllium (10Be–9Be)
While most carcinoids are asymptomatic through the natural life and are discovered only upon surgery for unrelated reasons (so-called coincidental carcinoids), all carcinoids are considered to have malignant potential. About 10% of carcinoids secrete excessive levels of a range of hormones, most notably serotonin (5-hydroxytryptamine), causing:
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.
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.