freeze-thaw cycle raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-08-01 and is reviewed periodically as new material appears.
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 hydrophilic peptide and dissolves readily in water and in aqueous buffers. The lyophilised powder is typically a white to off-white solid. Because short peptides are prone to hydrolysis and oxidation, handling benefits from limiting exposure to heat, moisture and strong light. Working solutions are commonly prepared in sterile water or saline, and repeated freeze-thaw cycles are avoided to reduce aggregation and loss of activity. These practices reflect general laboratory convention rather than published stability specifications.
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 |
|---|---|---|
| Appearance | White to off-white powder | Lyophilised solid form |
| Solubility class | Freely soluble in water | Hydrophilic heptapeptide |
| Dry storage temperature | -20 degrees Celsius or lower | Sealed, desiccated, protected from light |
| Solution storage | 2 to 8 degrees Celsius short term | Avoid repeated freeze-thaw cycles |
| Common identification method | Reversed-phase HPLC with mass spectrometry | Confirms purity and molecular mass |
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.
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.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Proposed mechanisms centre on the GABAergic system. Animal and tissue studies report changes in GABA-A receptor expression and reduced activity of GABA transaminase, the enzyme that degrades GABA. Effects on monoamine turnover, including serotonin and dopamine pathways, are also described, and a separate line of work links the peptide to increased expression of brain-derived neurotrophic factor in hippocampal tissue. Most of these findings come from rodent models and cell preparations. How the individual observations combine into a single coherent mode of action is not settled.
Pharmacokinetic data are sparse and largely derived from animal work. After intranasal administration the peptide appears in plasma within minutes, and reported half-lives are short, on the order of minutes to tens of minutes. Degradation proceeds through ordinary proteolytic cleavage into constituent amino acids and smaller fragments. Direct evidence that intact Selank reaches brain tissue in meaningful amounts is limited, and the extent of blood-brain barrier penetration is debated. Some authors argue that fragments, not the parent peptide, carry much of the observed activity.
Published clinical work is concentrated in Russian-language journals and generally involves small samples without independent replication. Systematic reviews in English note the shortage of randomised, placebo-controlled trials and the difficulty of verifying methods from translated reports. Outcome measures vary between studies, which complicates pooling of results. Interest in the compound as a cognitive or anxiolytic agent therefore rests on a thinner evidence base than the volume of citations suggests. Replication in well-powered trials with preregistered endpoints would be needed before firm conclusions about efficacy can be drawn.
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.
The team is launched into space on modified ballistic missiles and approaches the alien ship by stealth. Four of the avout destroy the ship's main weapon before dying in combat. The rest of the team boards the ship and temporarily pass out from breathing alien air. The narrative now parallelizes across multiple timelines. In one narrative, Fraa Jad awakens Erasmas and leads him through the ship toward the command center. Upon being discovered and attacked by alien soldiers, Fraa Jad detonates the neutron bombs. In another narrative, soldiers take Erasmas and Fraa Jad captive and bring them to parley with the leader of the peaceful faction. In the final narrative, Erasmas awakens in a hospital on the starship and learns that diplomatic negotiations are underway thanks to the successful destruction of the alien weapon. Erasmas is told that Fraa Jad died in an accident during the launch, contradicting the other narratives. It remains ambiguous which (or how many) of these contradictory narratives are real, or how the narratives have influenced each other. It is implied that some Millenarian avout are capable of operating simultaneously in multiple parallel timelines, and that the Millenarians had called the alien ship to Arbre to disrupt the subjugation of the Avout by the Sæcular Power. Erasmas attends a diplomatic summit where a funeral ceremony is held for those lost on both sides and a peace process begins between the aliens and the Arbrans. On Arbre itself, the Sæcular Power and the avout have agreed to cooperate as equal powers.
The People's Assembly (Arabic: مَجْلِس الشَّعْب, ALA-LC: Majlis ash-Shaʻb) is the unicameral legislative body of Syria. Currently, under the Syrian transitional government, the People's Assembly is composed of 210 members, each serving a renewable 30-month term. Of these, 119 of these members were elected in the 2025 Syrian parliamentary election through a temporary electoral college system, whilst 14 were elected in subsequent by-elections, with the remainder 70 being directly appointed by the President of Syria.
== Chemically driven rotary molecular motors == Source: An example of a prototype for a synthetic chemically driven rotary molecular motor was reported by Kelly and co-workers in 1999. Their system is made up from a three-bladed triptycene rotor and a helicene, and is capable of performing a unidirectional 120° rotation. This rotation takes place in five steps. The amine group present on the triptycene moiety is converted to an isocyanate group by condensation with phosgene (a). Thermal or spontaneous rotation around the central bond then brings the isocyanate group in proximity of the hydroxyl group located on the helicene moiety (b), thereby allowing these two groups to react with each other (c). This reaction irreversibly traps the system as a strained cyclic urethane that is higher in energy and thus energetically closer to the rotational energy barrier than the original state. Further rotation of the triptycene moiety therefore requires only a relatively small amount of thermal activation in order to overcome this barrier, thereby releasing the strain (d). Finally, cleavage of the urethane group restores the amine and alcohol functionalities of the molecule (e). The result of this sequence of events is a unidirectional 120° rotation of the triptycene moiety with respect to the helicene moiety. Additional forward or backward rotation of the triptycene rotor is inhibited by the helicene moiety, which serves a function similar to that of the pawl of a ratchet.
However, in MHC class I of many teleost fishes, the allelic polymorphism is much more extreme than in mammals in the sense that the sequence identity levels between alleles can be very low and the variation extends far beyond the peptide binding groove. It has been speculated that this type of MHC class I allelic variation contributes to allograft rejection, which may be especially important in fish to avoid grafting of cancer cells through their mucosal skin. The MHC locus (6p21.3) has 3 other paralogous loci in the human genome, namely 19pl3.1, 9q33–q34, and 1q21–q25. It is believed that the loci arouse from the two-round duplications in vertebrates of a single ProtoMHC locus, and the new domain organizations of the MHC genes were a result of later cis-duplication and exon shuffling in a process termed "the MHC Big Bang." Genes in this locus are apparently linked to intracellular intrinsic immunity in the basal Metazoan Trichoplax adhaerens. A 2022 metaanalysis across 50 vertebrate species found that IIA genes were underrepresented in published studies, but that class IIA loci harbor considerable levels of genetic variability and are targets for positive and/or diversifying selection. The authors therefore argued that MHC Class IIA loci represent an understudied component in studies of immunogenetics, mate choice, evolutionary genetics, and other aspects of MHC variation.
=== Art history === In European pre-historic societies, sculptures of female figures with pronounced or highly exaggerated breasts were common. A typical example is the so-called Venus of Willendorf, one of many Paleolithic Venus figurines with ample hips and bosom. Artifacts such as bowls, rock carvings and sacred statues with breasts have been recorded from 15,000 BC up to late antiquity all across Europe, North Africa and the Middle East. Many female deities representing love and fertility were associated with breasts and breast milk. Figures of the Phoenician goddess Astarte were represented as pillars studded with breasts. Isis, an Egyptian goddess who represented, among many other things, ideal motherhood, was often portrayed as suckling pharaohs, thereby confirming their divine status as rulers. Even certain male deities representing regeneration and fertility were occasionally depicted with breast-like appendices, such as the river god Hapy who was considered to be responsible for the annual overflowing of the Nile.
Sources: en.wikipedia.org
==== Elimination ==== MDMA and metabolites are primarily excreted as conjugates, such as sulfates and glucuronides. MDMA is a chiral compound and has been almost exclusively administered as a racemate. However, the two enantiomers have been shown to exhibit different kinetics. The disposition of MDMA may also be stereoselective, with the S-enantiomer having a shorter elimination half-life and greater excretion than the R-enantiomer. Evidence suggests that the area under the blood plasma concentration versus time curve (AUC) was two to four times higher for the (R)-enantiomer than the (S)-enantiomer after a 40 mg oral dose in human volunteers. Likewise, the plasma half-life of (R)-MDMA was significantly longer than that of the (S)-enantiomer (5.8 ± 2.2 hours vs 3.6 ± 0.9 hours). However, because MDMA excretion and metabolism have nonlinear kinetics, the half-lives would be higher at more typical doses (100 mg is sometimes considered a typical dose).
== External links == Official website (in German) "Search results for 'Kermani'". Goethe-Institut (in German). 23 June 2021. Retrieved 25 September 2021. "German-Iranian author receives culture prize after religious row". DW.COM. 27 November 2009. Retrieved 25 September 2021.
== European Union == Source: The Principles of GLP help ensure the quality and accuracy of data in chemical testing, and help prevent scientific fraud, as adopted by the European Union (EU). European GLP Regulations and Directives also apply to European Economic Area (EEA) member states which include Iceland, Liechtenstein, and Norway. GLP principles govern the laboratory safety testing of substances in various products, mandated by product-specific legislation in the EU/EEA. Directive 2004/9/EC mandates EU/EEA countries to designate GLP inspection authorities and includes requirements for reporting and mutual acceptance of data within the internal market. Annex I of the Directive incorporates OECD Revised Guides for Compliance Monitoring Procedures for GLP, along with OECD Guidance for the Conduct of Test Facility Inspections and Study Audits. It ensures compliance with these guidelines during laboratory inspections and study audits. This directive replaced Directive 88/320/EEC as of 11 March 2004. Directive 2004/10/EC, the second core EU GLP Directive, harmonizes laws and administrative provisions for applying GLP principles and verifying their implementation in chemical substance tests. It includes GLP principles in Annex I and requires EU/EEA countries to ensure that laboratories conducting safety studies on chemical products comply with OECD GLP principles. It replaces Directive 87/18/EEC.
=== Approved drugs === Escitalopram (Cipralex; Entact; Lexapro; LU-26054; MLD-55; (S)-citalopram; Seroplex; Sipralex; Sipralexa) – selective serotonin reuptake inhibitor (SSRI) [14] Fluoxetine (LY-110140; Prozac; Reneuron; Sarafem) – selective serotonin reuptake inhibitor (SSRI) [15] Fluoxetine (Fluoxetine Tablets) – selective serotonin reuptake inhibitor (SSRI) [16] Paroxetine (Aropax; BRL-29060; Deroxat; Divarius; FG-7051; Frosinor; Motivan; NNC-207051; Paxil; Seroxat; SI-211103; Tagonis) – selective serotonin reuptake inhibitor (SSRI) [17] Paroxetine (Dropax; Dropaxin; Serestill) – selective serotonin reuptake inhibitor (SSRI) [18] Sertraline (Aremis; Besitran; CP-51974; Gladem; Lustral; Serad; Serlain; Tatig; Zoloft) – selective serotonin reuptake inhibitor (SSRI) [19] Venlafaxine (Dobupal; Efexor XR; Effexor; Effexor XR; Elafax; WY-45030; WY-45651; WY-45655) – serotonin–norepinephrine reuptake inhibitor (SNRI) [20]
Sources: en.wikipedia.org
Hazard research is published: a study finds the likelihood of receiving a dementia diagnosis varies 2-fold based on place of residence in the U.S. after adjusting for underlying sociodemographic and population dementia risk factors, indicating there to be further regional risk factors or especially worse diagnostics (16 Aug.), and a study shows of the infant and toddler foods in 10 major grocery chains, 60% failed to meet the nutritional requirements of the WHO's nutrient and promotion profile model (NPPM) (21 Aug.).
ATP synthase, also called complex V, is the final enzyme in the oxidative phosphorylation pathway. This enzyme is found in all forms of life and functions in the same way in both prokaryotes and eukaryotes. The enzyme uses the energy stored in a proton gradient across a membrane to drive the synthesis of ATP from ADP and phosphate (Pi). Estimates of the number of protons required to synthesize one ATP have ranged from three to four, with some suggesting cells can vary this ratio, to suit different conditions.
25 November Two Britons are among 17 people reported missing after a tourist boat sank in the Red Sea. Following the impact of Storm Bert, further rain is forecast over the coming two days for northern England and Wales. In an attempt to reassure industry there will not be further tax rises for business, Chancellor Rachel Reeves tells the CBI conference she is "not coming back with more borrowing or more taxes". It is reported that the UK Supreme Court is to decide on the definition of a woman following a case brought by campaigners in Scotland. 26 November Vauxhall owner Stellantis announces the closure of its van making facility in Luton, with the loss of 1,100 jobs. Starmer announces an overhaul of the UK jobs market that will see young people guaranteed places on apprenticeships or in training. A yellow weather warning is issued for flooding ahead of the arrival of Storm Conall, which is expected to affect southern England and Wales. The UK government says it has no plans for an extra bank holiday in 2025 to mark the 80th anniversary of VE Day. The City of London Corporation announces that two of Britain's most famous and historic markets – Smithfield and Billingsgate – will close after 850 years of operation. 28 November Former British army soldier Daniel Khalife is found guilty of spying for Iran. Justice Bobbie Cheema-Grubb at Woolwich Crown Court says that Khalife will face "a long custodial sentence" when he is sentenced in early 2025. Official figures indicate that net migration reached 906,000 in the year to June 2024, much higher than previously stated.
Sources: en.wikipedia.org
Dry powder is normally held at -20 degrees Celsius or below in a sealed, light-protected container with desiccant. Brief room-temperature handling during weighing is generally tolerated. Storage instructions vary between suppliers, so the accompanying certificate of analysis should be followed.
Reversed-phase HPLC establishes purity, while mass spectrometry confirms the expected molecular mass. Sequence confirmation may use tandem mass spectrometry or peptide mapping. A certificate of analysis typically reports these results alongside the analytical method applied.
In Russia it is a registered medicine available by prescription. In many other countries it is not approved for human use and is supplied only as a research chemical. Import and possession rules differ by jurisdiction, and buyers are responsible for checking local requirements.
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.