freeze-thaw is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-02-17. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical purity specification | 95 percent or higher by RP-HPLC | Area percentage of the main peak |
| Identity confirmation | Electrospray ionization mass spectrometry | Observed mass compared with the theoretical value near 751.9 Da |
| Recommended dry storage | -20 °C, desiccated | -80 °C for multi-year archival material |
| Solution handling | Prepare fresh; avoid long storage | Sterile filtration reduces microbial load |
| Common synonyms | TKPRPGP; TP-7 | Sequence code and laboratory designation used interchangeably |
Characterization of Selank in a laboratory setting relies on standard peptide methods. Reverse-phase high-performance liquid chromatography separates the target from related impurities and provides a purity figure, commonly reported as 95 percent or higher. Mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, confirms the molecular mass and helps detect truncation or modification. Amino acid analysis can verify composition when a sequence-level check is needed. These techniques together establish identity and purity for a given lot.
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.
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.
=== Wnt signalling === One of the first discovered examples of a highly dynamic intracellular liquid biomolecular condensate with a clear physiological function were the supramolecular complexes (Wnt signalosomes) formed by components of the Wnt signaling pathway. The Dishevelled (Dsh or Dvl) protein undergoes clustering in the cytoplasm via its DIX domain, which mediates protein clustering (polymerisation) and phase separation, and is important for signal transduction. The Dsh protein functions both in planar polarity and Wnt signalling, where it recruits another supramolecular complex (the Axin complex) to Wnt receptors at the plasma membrane. The formation of these Dishevelled and Axin containing droplets is conserved across metazoans, including in Drosophila, Xenopus, and human cells.
CAKKRNWCGK NEDCCCPMKC IYAWYNQQGS CQTTITGLFK KC Cysteine bridges exist between Cys1 and Cys15, Cys8 and Cys20, Cys14 and Cys31, and Cys16 and Cys42. The structure consists of a small triple-stranded beta-sheet stabilized by a disulfide knot, followed by a C-terminal extension comprising three classic or inverse y-turns. The disulfide knot is a ring consisting of two disulfide bonds (1-15 and 8-20) and the connecting backbone, through which a third disulfide bond (14–31) passes. The β-sheet, defined on the basis of inter-sheet hydrogen bonds, consists of residues 6-8 (strand I), 19-21 (strand II) and 29-32 (strand III), with a topology of +2x, —1. The two hydrogen bonds (one amide of which has a slowly exchanging amide proton) between strands I and III are distorted (NH to CO distance between 2.5 and 3.0 A). There are four hydrogen bonds between strands II and III (all of which have corresponding slowly exchanging amide protons), three being present in most of the structures and one in half of the structures. The structure contains a number of chain reversals. The first is not well defined and is either a type II β-turn (Lys3-Asn6) or a y-turn centered on Arg5. Chain reversal II is a y turn centered on Gly9. Chain reversal III is not well defined, being either a type I β-turn (Asnn-Cys14) or an inverse y-turn centered on Asn11. Chain reversal IV (Cys15-Met18) is not stabilized by a hydrogen bond but has a cis peptide bond between Cys16 and Pro17 and resembles a type Via turn.
{\displaystyle {\begin{aligned}\nabla \varphi &=\left({\frac {\partial \varphi }{\partial x}},\,{\frac {\partial \varphi }{\partial y}}\right)^{\mathsf {T}},\\[5pt]\nabla \times \varphi &=\left({\frac {\partial \varphi }{\partial y}},\,-{\frac {\partial \varphi }{\partial x}}\right)^{\mathsf {T}}.\end{aligned}}}
Sources: en.wikipedia.org
Lactobacillales (order) as the most abundant; primarily upstream of pnuC, and sometimes pncB or pnuC–nadR operons. Notable organisms include species of Fructobacillus and many other lactic acid bacteria. Planctomycetota (phylum), commonly upstream of nadA. Pseudomonadota, found in Pseudomonas laurylsulfatiphila and related species, upstream of an annotated nucleoside transporter. Actinobacteriota, in isolated instances from metagenome-assembled genomes. The prevalence of mini-NAD⁺-II riboswitches in lactic acid bacteria is thought to be functionally significant, as these organisms rely on various anaerobic fermentation strategies (e.g., lactic acid or ethanol production) to maintain a balanced NAD⁺/NADH ratio. The prevalence of mini-NAD⁺-II riboswitches in lactic acid bacteria is thought to be functionally significant, as these organisms rely on various anaerobic fermentation strategies (e.g., lactic acid or ethanol production) to maintain a balanced NAD⁺/NADH ratio.
A period of rule under the Swedish House of Vasa began in the Commonwealth in the year 1587. The first two kings from this dynasty, Sigismund III (r. 1587–1632) and Władysław IV (r. 1632–1648), repeatedly attempted to intrigue for accession to the throne of Sweden, which was a constant source of distraction for the affairs of the Commonwealth. At that time, the Catholic Church embarked on an ideological counter-offensive and the Counter-Reformation claimed many converts from Polish and Lithuanian Protestant circles. In 1596, the Union of Brest split the Eastern Christians of the Commonwealth to create the Uniate Church of the Eastern Rite, but subject to the authority of the pope. The Zebrzydowski rebellion against Sigismund III unfolded in 1606–1608. Seeking supremacy in Eastern Europe, the Commonwealth fought wars with Russia between 1605 and 1618 in the wake of Russia's Time of Troubles; the series of conflicts is referred to as the Polish–Russian War or the Dymitriads. The efforts resulted in expansion of the eastern territories of the Polish–Lithuanian Commonwealth, but the goal of taking over the Russian throne for the Polish ruling dynasty was not achieved. Sweden sought supremacy in the Baltic during the Polish–Swedish wars of 1617–1629, and the Ottoman Empire pressed from the south in the Battles at Cecora in 1620 and Khotyn in 1621. The agricultural expansion and serfdom policies in Polish Ukraine resulted in a series of Cossack uprisings.
=== 1925: White Castle Official House Organ, success, expansion and imitators === The company also began publishing its own internal employee magazine, the White Castle Official House Organ, circa November 1925 (it was originally named The Hot Hamburger). The bulk of the material was contributed by company personnel and consisted mostly of letters and photographs of workers, promotional announcements, 25-year milestones, retirements, and similar items of interest arranged by geographic area. "Employees could... read about the progress and innovations made by those in other areas which made everyone aware of the entire system's direction and condition." The White Castle Official House Organ was published quarterly at least through the early 1980s, and at some point was renamed The Slider Times. The Ohio History Connection houses an extensive archive of White Castle System, Inc. records from 1921 to 1991, including issues dating from 1927 to 1970 of the White Castle Official House Organ.
Sources: en.wikipedia.org
Sealed, desiccated storage at -20 °C or colder is the standard recommendation for research-grade material. Vials should reach room temperature before they are opened, which limits condensation. Repeated temperature cycling is discouraged.
A reported purity value reflects the share of the main peak in one chromatographic run and says nothing about identity. Confirming that the expected sequence is present requires a separate measurement such as mass spectrometry. Purity and identity are distinct questions.
A mass spectrum reports the molecular masses present in a sample and shows whether they match the value expected for selank, near 751.9 Da. It also flags common artifacts such as truncation or adduct formation. It does not establish correct stereochemistry or complete sequence order on its own.
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.