A practical reference on freeze-thaw cycle: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-02-23. Anything still debated is marked as such rather than presented as settled.
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 are vulnerable to protease attack, and Selank is no exception. Measured half-life in serum is short, on the order of minutes in several reports, which explains why intranasal administration is the common route described in the literature. Absorption across the nasal mucosa partially bypasses first-pass hepatic metabolism. Quantitative data on human bioavailability remain limited and are difficult to compare across studies.
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.
| 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 |
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.
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.
Dry powder is normally held at -20 degrees Celsius or lower, in a sealed container with desiccant and protection from light. Reconstituted solutions are usually kept at 2 to 8 degrees Celsius for short periods and frozen for longer ones. Proline residues at several positions are generally associated with some resistance to peptidase attack, but chemical stability still declines at neutral to alkaline pH and at elevated temperature. Exact shelf-life figures are product-specific and are not standardised across suppliers.
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography, with mass spectrometry used to confirm molecular mass and sequence information. Amino acid analysis and peptide mapping may supplement these methods. Certified reference standards are scarce, and many commercial lots are sold as research chemicals without a pharmacopoeial monograph. Regulatory treatment differs by country: Selank is a registered prescription medicine in Russia, while in the European Union and the United States it is not an approved drug and may fall under research-chemical or unapproved-product frameworks.
Selank is a synthetic heptapeptide developed in Russia as a structural analogue of tuftsin, a naturally occurring immunomodulatory tetrapeptide. Its sequence, Thr-Lys-Pro-Arg-Pro-Gly-Pro, keeps the tuftsin core at the N-terminus and appends a Pro-Gly-Pro tail. Researchers at the Institute of Molecular Genetics in Moscow synthesized the compound during the 1990s while searching for peptides with combined anxiolytic and immunomodulatory activity. The added tail was intended to resist enzymatic cleavage and prolong the molecule's presence in circulation.
The compound has a calculated molecular weight near 751.9 daltons and carries a net positive charge at physiological pH because of its arginine residue. It dissolves freely in water and in common aqueous buffers, and typically appears as a white or off-white lyophilized powder. The amide backbone makes the molecule susceptible to peptidases, which limits oral use and favors intranasal or parenteral routes. Nomenclature in the literature varies: the substance is also described by the sequence abbreviation TP-7 and by a Russian trade designation.
Regulatory status differs sharply by region. Selank holds a Russian marketing authorization, where it is supplied mainly as nasal drops, while authorities elsewhere have not approved it for medical use. Material sold internationally is therefore usually labeled as a research chemical rather than a medicine. Peer-reviewed publications come predominantly from Russian laboratories, and sample sizes are generally small. Whether the compound produces comparable effects under independent, well-controlled replication remains an open question that the broader literature has not settled.
=== Retrospective views === Retrospectively, the album is viewed very positively and is often considered the band's "breakthrough". JR Moores, writing for The Guardian, called it "the most gloriously sardonic collection of caustic-yet-catchy mini-anthems of its era" and bemoaned its lack of popularity upon release. Candice Eley of Treble called it a "masterpiece [...] an album as hardcore and as cheeky as its title might imply." Kyle Fowle of Spectrum Culture considers it to be "a monumental album. It may not be the most revolutionary revision of the punk rock aesthetic or vision, but it’s definitely the most fun. There’s a perfect balance present on the record; Mclusky is focused on creating a foreboding, harsh, loud record, but never once take themselves too seriously. The overdriven guitar solos and Falkous’ shriek hit you like a freight train, but are never alienating or unwanted. There's no overarching political or creative statement, just three guys beating the shit out of their instruments and having a blast doing it.
== Etymology == The word animal comes from the Latin noun animal of the same meaning, which is itself derived from Latin animalis 'having breath or soul'. The biological definition includes all members of the kingdom Animalia. In colloquial usage, the term animal is often used to refer only to nonhuman animals. The term metazoa is derived from Ancient Greek μετα meta 'after' (in biology, the prefix meta- stands for 'later') and ζῷᾰ zōia 'animals', plural of ζῷον zōion 'animal'. A metazoan is any member of the group Metazoa.
Half a Life is a 2001 novel by Nobel laureate V. S. Naipaul published by Alfred A. Knopf. The novel is set in India, Africa and Europe (London, Berlin and Portugal). Half a Life was long listed for the Booker prize (2001).
Sources: en.wikipedia.org
=== Q: Congenital malformations, deformations and chromosomal abnormalities === (Q18.0) Sinus, fistula and cyst of branchial cleft Congenital preauricular fistula: A small pit in front of the ear. Also known as an ear pit or preauricular sinus. (Q26.6) Portal vein-hepatic artery fistula (Q38.0) Congenital fistula of lip (Q38.4) Congenital fistula of salivary gland (Q42.0) Congenital absence, atresia and stenosis of rectum with fistula (Q42.2) Congenital absence, atresia and stenosis of anus with fistula (Q43.6) Congenital fistula of rectum and anus (Q51.7) Congenital fistulae between uterus and digestive and urinary tracts (Q52.2) Congenital rectovaginal fistula
== External links == Biggest Collection of Medical Abbreviations Glossary of Medical Terms - Tufts University Medical Abbreviations EN English Medical Abbreviations for Android JD.MD, Inc. online Medical & Dental Abbreviations Glossary Acronyms for Medical & Dental professional organizations Medical Abbreviations for iPhone Medical abbreviations on mediLexicon Medical acronyms and abbreviations on allacronyms.com Over 20,000 medical abbreviations sorted into specialist categories Medical abbreviations in various categories such as Physiology, Oncology, Laboratory and more
Ooi and Skilling surmise that making wheels on this scale was a devotional practice particular to Dvaravati, since it is not found in other regions where Theravada was practised. The pairing of the wheel with deer, which stands for the Deer Park at Sarnath, developed in India and is seen in stone reliefs from south to north. It appears on the clay seals of the vihāra at Nālandā and on the sculptures of Phanagiri in Telangana, and it still stands on the roof-ridges of Tibetan monasteries. The four-lion capitals of Aśoka at Sarnath and Sanchi are thought to have carried dharmachakras as well. According to Harrison, the symbolism of "the wheel of the law" and the order of Nature is also visible in the Tibetan prayer wheels. The moving wheels symbolize the movement of cosmic order (ṛta).
Sources: en.wikipedia.org
== Treatment == There is no standard medical or surgical treatment for acrocyanosis, and treatment, other than reassurance and avoidance of cold, is usually unnecessary. The patient is reassured that no serious illness is present. A sympathectomy would alleviate the cyanosis by disrupting the fibers of the sympathetic nervous system to the area. However, such an extreme procedure would rarely be appropriate. Treatment with vasoactive drugs is not recommended but traditionally is mentioned as optional. However, there is little, if any, empirical evidence that vasoactive drugs (α-adrenergic blocking agents or calcium channel blockers) are effective.
== Signs and symptoms == Symptoms seen on plants infected with this virus can vary depending on the plant. However typical symptoms include vein clearing, mottling, and necrotic lines or etching. Symptoms can occur on leaves and fruit and the plants can become stunted. Like other potyviruses, TEV makes viral inclusions that can be seen in the light microscope if properly stained. This particular potyvirus makes two kinds of inclusions that can be diagnostic in a known host. One of the inclusions is the cylindrical inclusions found in the cytoplasm of infected cells and the second inclusion is found in the nucleus. Neither inclusion type stains in the nucleic acid stain (AzureA). (Inclusions of tobacco etch virus in various hosts.)
This hypothesis posits that the physiological processes of mitochondrial stress induction (affecting neuronal plasticity) and vasodilation, which cooperatively increase microvascular blood flow and tissue oxygenation, are the basis of the natural neurostimulation. It is also thought to be a foundation of many non-invasive artificial neuromodulation techniques. Because if the mother-fetus interactions allow the child's nervous system to grow with adequate biological sentience, similar (while scaling) environmental interactions can heal the damaged nervous system in adults.
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.
Dry powder is best kept sealed, protected from light, and held at minus 20 degrees Celsius or below. Desiccant packaging helps limit moisture uptake because the material is hygroscopic. A sealed vial should be allowed to equilibrate to room temperature before opening to reduce condensation.