The short version of freeze-thaw fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2026-01-20. 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.
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.
Lyophilized selank is normally supplied as a dry powder and is considered stable for extended periods when kept cold and dry. Moisture uptake is the main practical threat, because absorbed water promotes both hydrolysis and aggregation in the solid state. Vials are usually warmed to room temperature before opening so that condensation does not form on the powder. Supplier documentation commonly specifies -20 °C for routine storage, with -80 °C used for material intended to be archived for years.
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.
| 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 |
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.
Tuftsin, the parent structure, is a naturally occurring immunomodulatory tetrapeptide released from the Fc region of immunoglobulin G by spleen enzymes. Selank extends this four-residue sequence with three additional amino acids. The stated rationale is that the added tail slows enzymatic breakdown and may influence receptor interactions. How the full heptapeptide behaves at the molecular level is not firmly established, and proposed mechanisms often involve indirect modulation of neurotransmitter or immune signaling rather than a single defined target.
Selank is a synthetic heptapeptide developed in Russia. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, a seven-residue chain built around the natural tetrapeptide tuftsin. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences first described the compound in the mid-1990s. The design combined the tuftsin core with an added Pro-Gly-Pro tail, a modification intended to extend the molecule's stability in biological fluids. Published work on the peptide has appeared mainly in Russian-language journals.
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.
== Clinical use == Regenerative medicine is the "process of replacing or regenerating human cells, tissues or organs to restore or establish normal function." Heparan sulfate analogues are one of the early examples of regenerative medicine that reached daily clinical use. Multiple articles of animal wound models demonstrated vast effects on improving wound healing heparan sulfate analogues. These findings formed a rationale for its clinical application. The first clinical studies also show a significant improvement in wound healing. Different cases have shown improvement and better wound healing over time and persistent ulcer healing after usage of heparan sulfate analogues. Even though several studies show that heparan sulfate analogues contribute to the wound healing, more research in the form of a Randomized controlled trial is needed to obtain conclusive evidence.
=== Pests === Common herbarium pests include: silverfish, book lice (psocids), cigarette or tobacco beetles (Lasioderma), dermestids, drugstore beetles (Stegobium paniceum) A reoccurring threat to the longevity of herbarium specimens is insects, a number of which find dried plants palatable. Historically, various methods have been used to kill insects, which either come in with the plants when they are collected or are in the building where the plants are stored. Pests are commonly treated with two different methods:
13 December Mark Drakeford resigns as First minister of Wales after five years in incumbent. Bernard Looney, the former chief executive of BP, is to forfeit up to £32.4m in salary and benefits after an investigation found he committed "serious misconduct" in failing to disclose relationships with colleagues. 14 December The Bank of England keeps interest rates on hold for a third consecutive time at 5.25%. 17-year-old Alex Batty, a boy from Oldham who went missing in 2017 while on holiday in Spain, is reported by French Police to have been found at Revel, a town east of Toulouse in France. Three men are convicted of attempted murder after two children (including an 11-year-old girl) were shot while playing on a climbing frame, in Wolverhampton. Panini Group launches the first sticker album for the Women's Super League. 15 December The High Court rules that Prince Harry was the victim of phone hacking by Mirror Group Newspapers and awards him £140,600 in damages. Separately, the judge rules that Piers Morgan knew about phone hacking – and was involved – while editor of the Daily Mirror. Muslim convert Edward Little, who planned to kill a Christian preacher at Speaker's Corner in London's Hyde Park, is sentenced to life imprisonment with a minimum term of 16 years following a trial at the Old Bailey. Network Rail regional manager Michelle Handforth resigns from her post following a power outage at Ladbroke Grove earlier in the month which left hundreds of train passengers stranded for several hours.
Photosynthesis impairment occurs when bacteria release toxins that disrupt photosynthetic electron transport, lowering energy production and weakening algae cells. A specific example includes the production of 3,3′,5,5′‑tetrabromo‑2,2′‑biphenyldiol (4‑BP), which is a small molecule secreted by a certain strain of marine bacteria called Gammaproteobacteria. The algicidal effect of 4‑BP occurs due to interference with plastoquinone synthesis, which is a key molecule in the photosynthetic electron transport chain of phytoplankton. 4‑BP competitively binds to the active site of the enzyme responsible for plastoquinone synthesis, blocking its function and disrupting the phytoplankton's ability to photosynthesize. This disruption causes pigment loss, reduces photosynthetic efficiency, and leads to cell damage or death (lysis). This algicidal compound has been found to kill a range of different phytoplankton, including diatoms, chlorophytes, dinoflagellates and cyanobacteria.
=== Mi === August Michaelis (1847–1916), German chemist who discovered the Michaelis–Arbuzov reaction Leonor Michaelis (1875–1949), German biochemist and physical chemist known for fundamental advances in enzyme chemistry Hartmut Michel (born 1948), German biochemist, 1988 Nobel Prize in Chemistry for determination of the first crystal structure of an integral membrane protein Huang Minlon (1889–1979), Chinese chemist, pioneer of modern pharmaceutical industries in China Stanley Miller (1930–2007), American chemist, best known for the Miller–Urey experiment Eugène Millon (1812–1867), French military chemist and physician who discovered the reaction of mercury and nitric acid with egg albumen David P. Mills (PhD 2007), British chemist who investigates lanthanide and actinide f-block elements Luis E. Miramontes (1925–2004), Mexican co-inventor of the combined oral contraceptive pill Peter D. Mitchell (1920–1992), British biochemist known for the theory of chemiosmosis, 1978 Nobel Prize in Chemistry Eilhardt Mitscherlich (1794–1863), German chemist, remembered for the law of isomorphism. Alexander Mitscherlich (1836–1918), German chemist known for discovering crystallographic isomorphism
Sources: en.wikipedia.org
Gene defects in the leptin gene (ob) are rare in human obesity. As of July 2010, only 14 individuals from five families have been identified worldwide who carry a mutated ob gene (one of which was the first ever identified cause of genetic obesity in humans)—two families of Pakistani origin living in the UK, one family living in Turkey, one in Egypt, and one in Austria—and two other families have been found that carry a mutated ob receptor. Others have been identified as genetically partially deficient in leptin, and, in these individuals, leptin levels on the low end of the normal range can predict obesity. Several mutations of genes involving the melanocortins (used in brain signaling associated with appetite) and their receptors have also been identified as causing obesity in a larger portion of the population than leptin mutations.
=== As a feed additive === Guanidinoacetic acid is a nutritional feed additive approved by the European Commission for chickens for fattening, weaned piglets and pigs for fattening. It is supposed to lead with a "vegetarian diet" (meaning without feeding of animal protein) to higher feed conversion, higher weight gain and improved muscle increase already at a low dosage (600 g/to feed). Possible benefits of glycocyamine supplementation can not yet be conclusively assessed, neither in other breeding, fattening and domestic animals nor for high-performance athletes, analogous to the glycocyamine metabolite creatine. The simultaneous intake of methyl providing substances such as betaine appears advisable because of the risk of homocysteine formation with glycocyamine alone.
Continuing Arab disquiet over Allied intentions also led during 1918 to the British Declaration to the Seven and the Anglo-French Declaration, the latter promising "the complete and final liberation of the peoples who have for so long been oppressed by the Turks, and the setting up of national governments and administrations deriving their authority from the free exercise of the initiative and choice of the indigenous populations". In 1919, King Hussein refused to ratify the Treaty of Versailles. After February 1920, the British ceased to pay subsidy to him. In August 1920, five days after the signing of the Treaty of Sèvres, which formally recognized the Kingdom of Hejaz, Curzon asked Cairo to procure Hussein's signature to both treaties and agreed to make a payment of £30,000 conditional on signature. Hussein declined and in 1921, stated that he could not be expected to "affix his name to a document assigning Palestine to the Zionists and Syria to foreigners." Following the 1921 Cairo Conference, Lawrence was sent to try and obtain the King's signature to a treaty as well as to Versailles and Sèvres, a £60,000 annual subsidy being proposed; this attempt also failed. During 1923, the British made one further attempt to settle outstanding issues with Hussein and once again, the attempt foundered, Hussein continued in his refusal to recognize the Balfour Declaration or any of the Mandates that he perceived as being his domain.
Sulfur may be found by itself and historically was usually obtained in this form; pyrite has also been a source of sulfur. In volcanic regions in Sicily, in ancient times, it was found on the surface of the Earth, and the "Sicilian process" was used: sulfur deposits were piled and stacked in brick kilns built on sloping hillsides, with airspaces between them. Then, some sulfur was pulverized, spread over the stacked ore and ignited, causing the free sulfur to melt down the hills. Eventually the surface-borne deposits played out, and miners excavated veins that ultimately dotted the Sicilian landscape with labyrinthine mines. Mining was unmechanized and labor-intensive, with pickmen freeing the ore from the rock, and mine-boys or carusi carrying baskets of ore to the surface, often through a mile or more of tunnels. Once the ore was at the surface, it was reduced and extracted in smelting ovens. The conditions in Sicilian sulfur mines were horrific, prompting Booker T. Washington to write "I am not prepared just now to say to what extent I believe in a physical hell in the next world, but a sulfur mine in Sicily is about the nearest thing to hell that I expect to see in this life." Sulfur is still mined from surface deposits in poorer nations with volcanoes, such as Indonesia, and problems with working conditions still exist. Elemental sulfur was extracted from salt domes (where it sometimes occurs in nearly pure form) until the late 20th century, when it became a side product of other industrial processes such as in oil refining, in which sulfur is undesirable.
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.
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.