A practical reference on freeze-thaw: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-04-03. Anything still debated is marked as such rather than presented as settled.
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.
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.
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.
| 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 |
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.
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.
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.
Enzymatic stability motivates the extra three residues at the carboxyl end. Native tuftsin is cleaved quickly by circulating aminopeptidases and carboxypeptidases, which limits its duration of action and its usefulness as a tool compound. Extending the chain with proline-rich segments is a common design tactic because proline constrains the backbone and slows proteolysis. The same Pro-Gly-Pro motif appears in other Russian-developed peptides of the era. Whether the full seven-residue chain is required for activity, or whether it acts mainly as a prodrug releasing tuftsin, remains unresolved.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its four N-terminal residues reproduce tuftsin, a tetrapeptide fragment of the immunoglobulin heavy chain, while the C-terminal Pro-Gly-Pro extension is a synthetic addition. The peptide has a molecular mass near 752 daltons and carries a net positive charge at physiological pH because of the arginine and lysine side chains. Published indexes list it under the name Selank and the sequence abbreviation TKPRPGP. Solid-phase peptide synthesis is the standard production route for research quantities.
Development took place at the Institute of Molecular Genetics of the Russian Academy of Sciences, where a series of short peptides were designed in the 1980s and 1990s. Selank was selected from variants of tuftsin that showed resistance to plasma peptidases. Russian regulatory approval covers it as an anxiolytic agent given intranasally. Outside that market the compound is normally handled as a research chemical rather than a medicine, and no widely recognised international pharmacopoeial monograph exists. The name Selank is a coined trade designation rather than a systematic chemical name.
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.
Reported pharmacological effects center on reduced anxiety-like behavior in animal models and on measures of memory and learning. Proposed contributing mechanisms include modulation of GABAergic signaling, shifts in monoamine turnover, and changes in the activity of enzymes that degrade neuropeptides. Effects on the expression of genes linked to neuroplasticity have also been described. No single molecular target is widely accepted, and whether the behavioral findings arise from one pathway or several remains an open question.
=== 13-31 August 2008 === An anonymous U.S. functionary said: "Saakashvili had always told us he could not stand by while Georgian villages were being shelled, and we always knew this was a point of pressure. We always told him that he should not give in to the kind of provocations we knew the Russians were capable of." In August 2008, Modest Kolerov, former head of the Department for international and cultural ties with foreign countries of the President's Office, admitted that the Kremlin had "a clear plan of action in the case of a conflict", and "the expediency with which the military operation was executed confirms that." Robert Gates, United States Secretary of Defense, said on August 14 that there had been clashes with the South Ossetian forces each August since 2004, but "This year it escalated very quickly and it seemed to me that Russians were prepared to take advantage of an opportunity and did so very aggressively." Zbigniew Brzezinski compared Russia's attack on Georgia to the Soviet attack on Finland and wrote that "Moscow was waiting for such an act to provide a pretext for the use of force." He suggested that Russia could attack Ukraine and other post-Soviet countries were not safe. Ralph Peters, a former military intelligence analyst, and several western diplomats (a western diplomat with contacts with the Georgians and a western mediator acquainted with Saakashvili) said that it was Russia who was provoking Georgia. It was reported that the United States had prevented Saakashvili from taking military action in Abkhazia in early May 2008.
==== Growth ==== From 2014 to 2016, the college completed the largest hire of new faculty in the history of the college. Many of these new hires were in partnerships with healthcare organizations in the greater Cincinnati area. Research funding at the college increased, with 51% growth from 2015 to 2016 reaching a total of $8.9 million in 2016
Mann, Adam (20 April 2021). "Making headway with the mysteries of life's origins". Proceedings of the National Academy of Sciences. 118 (16) e2105383118. doi:10.1073/pnas.2105383118. PMC 8072247. PMID 33853953. Exploring Life's Origins Archived 8 April 2023 at the Wayback Machine a virtual exhibit at the Museum of Science (Boston) How life began on Earth – Marcia Malory (Earth Facts; 2015) The Origins of Life – Richard Dawkins et al. (BBC Radio; 2004) Life in the Universe – Essay by Stephen Hawking (1996)
In mammals, the genome only contains one gene for tropoelastin, called ELN. The human ELN gene is a 45 kb segment on chromosome 7, and has 34 exons interrupted by almost 700 introns, with the first exon being a signal peptide assigning its extracellular localization. The large number of introns suggests that genetic recombination may contribute to the instability of the gene, leading to diseases such as SVAS. The expression of tropoelastin mRNA is highly regulated under at least eight different transcription start sites. Tissue specific variants of elastin are produced by alternative splicing of the tropoelastin gene. There are at least 11 known human tropoelastin isoforms. These isoforms are under developmental regulation, however there are minimal differences among tissues at the same developmental stage.
Sources: en.wikipedia.org
== Lactation == No human data is available if the drug is distributed into human milk. Nursing women should either discontinue breast-feeding or Neumega, the decision should take into account the importance of the drug to the mother.
==== Codon models ==== Codon models describe the evolution of protein-coding nucleic acid sequences. The simplest codon model, MG, estimates one parameter: nonsynonymous/synonymous mutation ratio. The more complex GY also estimates transition/transversion rate ratios. Both of these are mechanistic models. They can be expanded by the addition of rate parameters. Empirical codon models directly describe the odds of one non-stop codon (61 in the standard code) being replaced by another, making them similar to amino acid exchangability matrices. By their construction, they are tied to the genetic code found in the data used to construct them. They can also be combined with a mechanistic model by multiplying the two estimated rates, adding back the ability to adapt to the data being processed.
== See also == Mr. Holland's Opus, a 1995 film starring Richard Dreyfuss Magnum opus (disambiguation) Opera (disambiguation) (plural form of opus) Opus Dei (disambiguation) All pages with titles beginning with Opus All pages with titles containing Opus
Sources: en.wikipedia.org
==== Neutron Activation Analysis ==== Neutron activation analysis is a powerful non-destructive method of analyzing elements of mid to high atomic number. This method combines excitation by nuclear reaction and the radiation counting techniques to detect various materials. The measurement of characteristic radiation, following the bombardment completion, is indicative of the elements of interest. The equation for the production product is given by:
Pizotifen is a serotonin antagonist acting mainly at the 5-HT2A, 5-HT2B, and 5-HT2C receptors. It also has some activity as an antihistamine as well as some anticholinergic activity. The drug binds non-selectively to many targets, including serotonin, dopamine, adrenergic, histamine, and muscarinic acetylcholine receptors. Besides its serotonin 5-HT2 receptor antagonism, pizotifen is a low-potency moderate-efficacy partial agonist of the serotonin 5-HT1A receptor. Pizotifen is able to dose-dependently and fully antagonize the discriminative stimulus effects of the serotonin–norepinephrine–dopamine releasing agent and serotonin 5-HT2 receptor agonist MDMA in rodent drug discrimination tests. Conversely, the related drug cyproheptadine was only partially effective and clozapine was ineffective. All three of these agents, pizotifen, cyproheptadine, and clozapine act as non-selective monoamine receptor antagonists. Pizotifen also fully blocks the effects of serotonergic psychedelics, including LSD, mescaline, 5-MeO-DMT, and DOM, in drug discrimination tests. The antimigraine activity of pizotifen might be specifically due to serotonin 5-HT2B receptor blockade.
== Production == As of 2021, the main industrial process for the production of myo-inositol (mostly in China and Japan) started with phytate (IP6) extracted from the soaking water resulting from corn and rice bran processing. After purification, the phytate is hydrolized, and myo-inositol is separated by crystallization. Another route is microbial fermentation of carbohydrates by various organisms, such as the fungus Neurospora crassa (Beadle and Tatum, 1945), Candida boidini (Shirai et al., 1997), Saccharomyces cerevisiae (Culbertson et al., 1976), Escherichia coli (Hansen, 1999). Alternatively, enzyme extracts from microbial cultures can be used in vitro to obtain myo-inositol from various substrates, including glucose, sucrose, starch, xylose, and amylose.
== Treatment == Treatment is focused on reducing stroke episodes and damage from a distending artery. Four treatment modalities have been reported in the treatment of vertebral artery dissection. The two main treatments involve medication: anticoagulation (using heparin and warfarin) and antiplatelet drugs (usually aspirin). More rarely, thrombolysis (medication that dissolves blood clots) may be administered, and occasionally obstruction may be treated with angioplasty and stenting. No randomized controlled trials have been performed to compare the different treatment modalities. Surgery is only used in exceptional cases.
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.
Most published work uses intranasal application, either as drops or as a nasal spray. Injection routes appear in a smaller set of animal experiments. Oral use is uncommon in the literature because peptide breakdown and poor absorption limit this route.