freeze-thaw cycle raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-02-15. Anything still debated is marked as such rather than presented as settled.
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.
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.
Regulatory treatment varies by jurisdiction. In Russia the compound is a registered prescription product, while in the European Union and the United States it is generally handled as a research chemical without a marketing authorization. Suppliers therefore operate outside pharmaceutical oversight, and buyers rely on supplier documentation for purity and identity claims. Chain of custody and third-party testing are the main verification tools. Analysts note that the absence of a pharmacopoeial monograph for research-grade material limits standardization across vendors.
Purity assessment relies mainly on reverse-phase high-performance liquid chromatography with ultraviolet detection. Because the peptide lacks a strong chromophore, detection often uses backbone absorbance near 214 nm. Identity is confirmed by mass spectrometry, typically electrospray ionization or matrix-assisted laser desorption, comparing the measured mass against the expected value. Amino acid analysis can verify composition after acid hydrolysis. Diastereomer content and residual counterions are reported less often, although both can influence biological assays.
| Property | Value | Notes |
|---|---|---|
| Principal proposed target | GABA-A receptor complex | Hypothesis derived mainly from animal pharmacology |
| Common behavioral assay | Elevated plus maze | Rodent test for anxiety-like behavior |
| Reported molecular marker | Hippocampal BDNF expression | Measured by immunoassay or mRNA quantification |
| Typical dosing route | Intranasal | Chosen to reduce first-pass metabolism |
| Reported plasma half-life | Minutes | Based on limited peptide stability data |
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.
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.
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.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions 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.
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.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated as TKPRPGP. It was designed as a structural analogue of tuftsin, a naturally occurring tetrapeptide released by enzymatic cleavage of the immunoglobulin heavy chain. The two additional proline residues at the C-terminal end extend the parent chain and change how the molecule behaves in solution. The free peptide has a calculated molecular mass of approximately 751.9 g/mol and is generally supplied as a lyophilised white to off-white powder.
Development work on the compound began in the 1980s and 1990s at the Institute of Molecular Genetics in Moscow, within the same research programme that produced the peptide Semax. Early investigators sought a tuftsin derivative with improved resistance to enzymatic breakdown and with activity in the central nervous system after peripheral administration. Most of the primary literature from this period was published in Russian, a factor that still shapes how easily the findings can be checked by outside groups.
Naming for this compound is not fully standardised in English sources. The spelling Selanc appears in some transliterations, and catalogue entries may instead list the peptide sequence itself as the identifier. Reference material sometimes groups it with other short synthetic peptides studied for behavioural effects, which can create confusion when citations are compared. Distinguishing the exact sequence from related tuftsin analogues is therefore a practical first step when reviewing any dataset or specification sheet.
Most terrestrial helium present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations as great as 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Terrestrial helium is a non-renewable resource because once released into the atmosphere, it promptly escapes into space. Its supply is thought to be rapidly diminishing. However, some studies suggest that helium produced deep in the Earth by radioactive decay can collect in natural gas reserves in larger-than-expected quantities, in some cases having been released by volcanic activity.
Diseases of the skin include skin infections and skin neoplasms (including skin cancer). Dermatology is the branch of medicine that deals with conditions of the skin. There are seven cervical, twelve thoracic, five lumbar, and five sacral. Certain diseases like shingles, caused by varicella-zoster infection, have pain sensations and eruptive rashes involving dermatomal distribution. Dermatomes are helpful in the diagnosis of vertebral spinal injury levels. Aside from the dermatomes, the epidermis cells are susceptible to neoplastic changes, resulting in various cancer types. The skin is also valuable for diagnosis of other conditions, since many medical signs show through the skin. Skin colour affects the visibility of these signs, a source of misdiagnosis in unaware medical personnel.
The caffeine found in energy drinks and coffee shows an increased reaction performance and feelings of energy, focus and alertness in quickness and reaction anaerobic power tests. In other words, consuming an energy drink or any drink with caffeine increases short time/rapid exercise performance (like short full-speed sprints and heavy power weight lifting). Caffeine is chemically similar to adenosine, a type of sugar that helps in the regulation of important body processes, including the firing of neurotransmitters. Caffeine takes the place of adenosine in the brain, attaching itself to the same neural receptors affected by adenosine, and causing neurons to fire more rapidly, hence caffeine's stimulating effects. Carbohydrates are also a very common form of energy supplements, as all sugars are carbohydrates. Products like Gatorade and Powerade are formulated with simple sugars such as sucrose and dextrose. Carbohydrates are necessary as they maintain blood glucose levels and restore muscle glycogen levels.
A cigarette filter or filter tip is a component of a cigarette. Filters are typically made from cellulose acetate fibre. Most factory-made cigarettes are equipped with a filter; those who roll their own can buy them separately. Filters can reduce the presence of some substances, such as tar, in cigarette smoke, but do not actually make them any safer to smoke.
=== Immobilized metal ion affinity chromatography === Immobilized metal ion affinity chromatography (IMAC) is based on the specific coordinate covalent bond of amino acids, particularly histidine, to metals. This technique works by allowing proteins with an affinity for metal ions to be retained in a column containing immobilized metal ions, such as cobalt, nickel, or copper for the purification of histidine-containing proteins or peptides, iron, zinc or gallium for the purification of phosphorylated proteins or peptides. Many naturally occurring proteins do not have an affinity for metal ions, therefore recombinant DNA technology can be used to introduce such a protein tag into the relevant gene. Methods used to elute the protein of interest include changing the pH, or adding a competitive molecule, such as imidazole.
Sources: en.wikipedia.org
Within hours of the attack, a search and rescue operation was launched. After months of around-the-clock operations, the World Trade Center site was cleared by the end of May 2002. The damaged section of the Pentagon was rebuilt and occupied within a year of the attacks. The temporary World Trade Center PATH station opened in late 2003 and construction of the new 7 World Trade Center was completed in 2006. Work on rebuilding the main World Trade Center site was delayed until late 2006 when leaseholder Larry Silverstein and the Port Authority of New York and New Jersey agreed on financing. The construction of One World Trade Center began in April 2006, and reached its full height in May 2013. The spire was installed atop the building at that date, putting One WTC's height at 1,776 feet (541 m), making it the tallest building in the Western Hemisphere. One WTC finished construction and opened on November 3, 2014. On the World Trade Center site, three more office towers were to be built one block east of where the original towers stood. 4 WTC, meanwhile, opened in November 2013, making it the second tower on the site to open behind 7 World Trade Center, as well as the first building on the Port Authority property. 3 WTC opened in June 2018, becoming the fourth skyscraper at the site to be completed. In December 2022, the Nicholas Greek Orthodox Church fully reopened for regular services, followed by the opening of the Ronald O. Perelman Performing Arts Center in September 2023. With construction beginning in 2008, 2 World Trade Center remains as of 2026 unfinished.
== Areas of application == Small molecules are essential components found throughout nature, playing a significant role in various fields such as drug discovery, diagnostics, food science, environmental monitoring, forensics and more. Effectively addressing many global challenges hinges on the comprehensive identification of small molecules in complex samples. These complex mixtures contain thousands of different molecules measurable in a single mass spectrometry run. The identification of unknown small molecules is considered a critical bottleneck in metabolomics, natural product research, and related fields, given that widely over 90% of all small molecules remain unknown. Commonly, analyses were based on targeted approaches that are limited to the rediscovery of known molecules. In contrast, untargeted analysis is a top-down strategy that avoids the need for a prior specific hypothesis on expected small molecules. The focus shifts from asking, "Is molecule X present in the sample?" to "Which (unknown) molecules are present in the sample and might be relevant for downstream analysis?" SIRIUS is designed for the untargeted structural elucidation of unknown molecules, addressing various challenges:
==== Netherlands ==== All major political parties in the Netherlands have state-sponsored research foundations that play a role in shaping policy. The Dutch government also has its own think tank: the Scientific Council for Government Policy. The Netherlands furthermore hosts the Netherlands Institute of International Relations Clingendael, or Clingendael Institute, an independent think tank and diplomatic academy which studies various aspects of international relations.
During his visit to Colombia, Pope Francis brought with him a message of peace and paid tribute to the victims of the conflict. The Special Jurisdiction of Peace (Jurisdicción Especial para la Paz, JEP) is the transitional justice component of the Comprehensive System, complying with Colombia's duty to investigate, clarify, prosecute, and punish serious human rights violations and grave breaches of international humanitarian law which occurred during the armed conflict. Its objectives are to satisfy victims' right to justice, offer truth to the public, contribute to the reparation of victims, contribute to the fight against impunity, and adopt decisions which give full legal security to direct and indirect participants in the conflict and contribute to the achievement of a stable and lasting peace. The Special Unit for the Search of Missing Persons in the context and due to the armed conflict (Unidad especial para la búsqueda de personas dadas por desaparecidas en el contexto y en razón del conflicto armado) would be a special high-level unit created following the signature of the final agreement. It would direct and coordinate efforts to search for and locate missing persons, or find their remains so that they may be returned to their families.
== In culture == Spider webs play a crucial role in the 1952 children's novel Charlotte's Web. Webs are also featured in many other cultural depictions of spiders. In films, illustration, and other visual arts, spider webs may be used to readily suggest a "spooky" atmosphere, or imply neglect or the passage of time. Artificial "spider webs" are a common element of Halloween decorations. Spider webs are a common image in tattoo art, often symbolizing long periods of time spent in prison, or used simply to fill gaps between other images. Some observers believe that a small spider is depicted on the United States one-dollar bill, in the upper-right corner of the front side (obverse), perched on the shield surrounding the number "1". This perception is enhanced by the resemblance of the background image of intertwining fine lines to a stylized spider web. However, other observers believe the figure is an owl. The World Wide Web is thus named because of its tangled and interlaced structure, said to resemble that of a spider web. Itsy Bitsy Spider is a popular nursery rhyme about the adventures of a spider. Artificial spider webs are used by the superhero Spider-Man to restrain enemies and to make ropes on which to swing between buildings as quick transportation. Some incarnations of the character, such as the version in the Sam Raimi film trilogy and Spider-Man 2099, are shown to be able to produce organic webs. The notable tensile strength of spider webs is often exaggerated in science fiction, often as a plot device to justify the presence of artificially giant spiders.
Sources: en.wikipedia.org
A number of very specialised chain types have emerged over recent years. These include chains made of steel alloys optimised for cutting in extremely cold conditions, chains with tungsten carbide teeth for very dirty conditions and rescue work, ripping chains with altered blade geometry for making ripping cuts, and milling chains for chainsaw mills. Chain mortisers, used to cut the mortice of large mortice and tenon timber framing, use a number of chains, riveted side-by-side. They are used with a vertical tip-first plunge. Owing to the difficulty of resharpening the multiple teeth, these are usually made of long-lasting tungsten carbide.
=== Mental === A 2018 survey by the American Psychological Association revealed that Generation Z had the weakest mental health of any living generation; some 91% of this demographic cohort reported physical or emotion symptoms associated with stress. Surgeon General of the United States Vivek Murthy stated in a 2021 advisory that the shares of young people having suicidal ideation and suffering from persistent feelings of sadness or hopelessness had grown precipitously compared to the previous decade. There is a growing body of evidence that there is a direct link between having access to social media at a young age and weak mental health, especially among teenage girls. Parents who are overly involved in their children's lives are likely making matters worse by preventing their children from developing emotional resilience. Across the United States, university students are seeking mental health support. Many are discussing their distress over climate change with their psychotherapists. Compared to the 2000s, the 2010s saw a marked increase in the rate of suicide among adolescents, due to an increased willingness by families and coroners to label a death as a result of suicide, depression or opioid usage. Nadine Kaslow, a psychiatrist and behavioral scientist at the Emory University School of Medicine, pointed to the weakening of familial and other social bonds and the heavy use of modern communications technology, which exposes people to the risk of cyber-bullying. The number of American teenagers who exhibited the classic symptoms of depression jumped during the 2010s.
== External links == Classification of Instructional Programs (CIP 2000): Developed by the U.S. Department of Education's National Center for Education Statistics to provide a taxonomic scheme that will support the accurate tracking, assessment, and reporting of fields of study and program completions activity. Complete JACS (Joint Academic Classification of Subjects) from Higher Education Statistics Agency (HESA) in the United Kingdom Australian and New Zealand Standard Research Classification (ANZSRC 2008) (web-page Archived 2010-12-12 at the Wayback Machine) Chapter 3 and Appendix 1: Fields of research classification. Fields of Knowledge, a zoomable map allowing the academic disciplines and sub-disciplines in this article be visualised. Sandoz, R. (ed.), Interactive Historical Atlas of the Disciplines, University of Geneva
When analyzed in the lower-dimensional PCA space, clustering of samples with similar metabolic fingerprints can be detected. PCA algorithms aim to replace all correlated variables with a much smaller number of uncorrelated variables (referred to as principal components (PCs)) and retain most of the information in the original dataset. This clustering can elucidate patterns and assist in the determination of disease biomarkers – metabolites that correlate most with class membership. Linear models are commonly used for metabolomics data, but are affected by multicollinearity. On the other hand, multivariate statistics are thriving methods for high-dimensional correlated metabolomics data, of which the most popular one is Projection to Latent Structures (PLS) regression and its classification version PLS-DA. Other data mining methods, such as random forest, support-vector machines, etc. are received increasing attention for untargeted metabolomics data analysis. In the case of univariate methods, variables are analyzed one by one using classical statistics tools (such as Student's t-test, ANOVA or mixed models) and only these with sufficient small p-values are considered relevant. However, correction strategies should be used to reduce false discoveries when multiple comparisons are conducted since there is no standard method for measuring the total amount of metabolites directly in untargeted metabolomics. For multivariate analysis, models should always be validated to ensure that the results can be generalized.
Sources: en.wikipedia.org
Intranasal administration predominates in both animal and human research because it avoids hepatic first-pass metabolism. Injectable and intraperitoneal routes appear in animal work mainly for comparison.
Behavioral endpoints include time spent in open arms of the elevated plus maze and avoidance latencies. Biochemical endpoints include BDNF concentration, cytokine levels, and monoamine metabolite ratios in brain tissue.
Most published studies are small, originate from a limited number of laboratories, and lack independent replication. Dose-response relationships, measured brain exposure, and long-term outcomes are not well characterized.
Purity is usually reported as an HPLC area percentage, most often measured at 214 nm. Identity is confirmed separately by mass spectrometry. A certificate of analysis should state both the method and the observed value.