If you have been reading about freeze-thaw and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2026-04-15. Where a claim depends on a specific study, the study is described rather than over-claimed.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 nanometres is the standard purity method. Mass spectrometry, typically electrospray ionisation, confirms identity through the expected mass-to-charge pattern. Amino acid analysis can verify composition independently. Chiral purity requires separate techniques such as derivatisation followed by chromatographic separation, and such data are rarely reported for research-grade material.
Quantification in biological matrices relies on liquid chromatography coupled to tandem mass spectrometry with stable-isotope internal standards. Low plasma concentrations and adsorption to container surfaces both complicate measurement. Solid-phase extraction is often needed to reduce matrix interference before injection. Reported limits of quantification differ widely between laboratories, which makes direct comparison of pharmacokinetic results difficult and limits meta-analysis.
Peptide bonds are vulnerable to protease attack, and Selank is no exception. Measured half-life in serum is short, on the order of minutes in several reports, which explains why intranasal administration is the common route described in the literature. Absorption across the nasal mucosa partially bypasses first-pass hepatic metabolism. Quantitative data on human bioavailability remain limited and are difficult to compare across studies.
Selank is a synthetic heptapeptide developed in Russia as a structural analogue of tuftsin, a naturally occurring immunomodulatory tetrapeptide. Its sequence, Thr-Lys-Pro-Arg-Pro-Gly-Pro, keeps the tuftsin core at the N-terminus and appends a Pro-Gly-Pro tail. Researchers at the Institute of Molecular Genetics in Moscow synthesized the compound during the 1990s while searching for peptides with combined anxiolytic and immunomodulatory activity. The added tail was intended to resist enzymatic cleavage and prolong the molecule's presence in circulation.
The compound has a calculated molecular weight near 751.9 daltons and carries a net positive charge at physiological pH because of its arginine residue. It dissolves freely in water and in common aqueous buffers, and typically appears as a white or off-white lyophilized powder. The amide backbone makes the molecule susceptible to peptidases, which limits oral use and favors intranasal or parenteral routes. Nomenclature in the literature varies: the substance is also described by the sequence abbreviation TP-7 and by a Russian trade designation.
Regulatory status differs sharply by region. Selank holds a Russian marketing authorization, where it is supplied mainly as nasal drops, while authorities elsewhere have not approved it for medical use. Material sold internationally is therefore usually labeled as a research chemical rather than a medicine. Peer-reviewed publications come predominantly from Russian laboratories, and sample sizes are generally small. Whether the compound produces comparable effects under independent, well-controlled replication remains an open question that the broader literature has not settled.
| Property | Value | Notes |
|---|---|---|
| Dry storage temperature | -20 C or below | Sealed, desiccated, protected from light |
| Solution stability | Hours to days at 2-8 C | Depends on buffer and microbial load |
| Preferred pH range | Near neutral to slightly acidic | Alkaline pH accelerates hydrolysis |
| Main degradation routes | Hydrolysis and deamidation | No cysteine or methionine in sequence |
| Identity confirmation | Electrospray mass spectrometry | Observed mass compared with 751.9 Da |
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.
Quality assessment of Selank samples typically combines purity determination with identity confirmation and counter-ion analysis. Purity is usually reported as a percentage by chromatographic area, with values above 95 percent often quoted for research-grade material. Water content and residual solvents are checked in lyophilized batches because they affect both stability and accurate mass determination. A reported purity figure does not by itself establish that a sample is the intended sequence, so orthogonal methods are needed to rule out sequence isomers or truncation products.
Characterization of Selank in laboratory settings relies on standard peptide analytical techniques. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities and degradation products, while mass spectrometry confirms molecular identity through accurate mass measurement. Amino acid analysis and peptide sequencing verify the primary structure when reference material is unavailable. Because Selank is a short chain, fragmentation-based analysis produces a diagnostic ion pattern that supports confident identification.
Peptide stability depends strongly on temperature, moisture, and pH. Lyophilized Selank is generally most stable when stored cold and dry, with freezer temperatures commonly used for long-term storage. In solution, the compound is susceptible to hydrolysis and to microbial growth if it is not handled aseptically. The C-terminal proline-rich extension appears to slow enzymatic cleavage relative to tuftsin, though quantitative degradation rates vary with the matrix and the conditions tested. Published stability data specific to Selank remain sparse.
Site-specific recombination makes use of phage integrases instead of restriction enzymes, eliminating the need for having restriction sites in the DNA fragments. Instead, integrases make use of unique attachment (att) sites, and catalyse DNA rearrangement between the target fragment and the destination vector. The Invitrogen Gateway cloning system was invented in the late 1990s and uses two proprietary enzyme mixtures, BP clonase and LR clonase. The BP clonase mix catalyses the recombination between attB and attP sites, generating hybrid attL and attR sites, while the LR clonase mix catalyse the recombination of attL and attR sites to give attB and attP sites. As each enzyme mix recognises only specific att sites, recombination is highly specific and the fragments can be assembled in the desired sequence. Vector design and assembly Because Gateway cloning is a proprietary technology, all Gateway reactions must be carried out with the Gateway kit that is provided by the manufacturer. The reaction can be summarised into two steps. The first step involves assembling the entry clones containing the DNA fragment of interest, while the second step involves inserting this fragment of interest into the destination clone.
Secret Chiefs 3 created an auditory adaptation on their "The Electromagnetic Azoth - Ubik / Ishraqiyun - Balance of the 19" 7" record. The "Ubik" track features musicians Trey Spruance (Faith No More, Mr. Bungle) and Bill Horist. In 2000, Art Zoyd released a musical interpretation of the novel titled u.B.I.Q.U.e.. It is also the name of a Timo Maas single. In 1992, Richard Pinhas released an album titled DWW featuring the tracks called "Ubik" and "The Joe Chip Song". In 2006, C-Jeff started a chiptune net-label called Ubiktune. In 2012, Cristian Vogel released The Inertials album named after characters from the novel.
=== Cancer === Heejin et al. showed that trimebutine is effective at stopping ovarian cancer cells from growing in vitro. This effect is believed to be exerted through G0/G1 phase switch arrest, voltage-gated calcium channels and calcium-activated potassium channels inhibition and suppressing Wnt, Notch and Hedgehog pathways. Yi-pu Fan et al. found that trimebutine can inhibit glioma and glioblastoma cells from proliferating by promoting apoptosis and downregulation of Bcl-2, thereby upregulating Bax pro-apoptotic factor.
Sources: en.wikipedia.org
Without the fully functional sar1B protein, the COPll coatomer proteins engulf pre-chylomicrons exiting the ER but are unable to disassemble upon arrival at the cis-Golgi, preventing membrane fusion with this organelle.
A member of parliament refers to the elected members of the federal Bundestag at the Reichstag building in Berlin. In German a member is called Mitglied des Bundestages (member of the Federal Diet) or officially Mitglied des Deutschen Bundestages (member of the German Federal Diet), abbreviated MdB and attached . Unofficially the term Abgeordneter (lit. 'delegate', i.e. of a certain electorate) is also common (abbreviated Abg., never follows the name but precedes it). In accordance with article 38 of the Basic Law for the Federal Republic of Germany, which is the German constitution, "[m]embers of the German Bundestag shall be elected in general, direct, free, equal, and secret elections. They shall be representatives of the whole people, not bound by orders or instructions, and responsible only to their conscience." An important though not constitutionally required feature of German parliamentarianism is a slightly modified proportional representation. The 16 federal states of Germany (Länder) are represented by the Bundesrat at the former Prussian House of Lords, whose members are representatives of the respective Länder's governments and not directly elected by the people.
== History == As techniques began developing the ancient Greeks and Romans began writing down and collecting everything they knew involving these procedures. Aulus Cornelius Celsus, a first-century Roman, described making an excision in the skin to relax the eyelids in his book De Medicina. Karl Ferdinand von Gräfe coined the phrase blepharoplasty in 1818 when the technique was used for repairing deformities caused by cancer in the eyelids.
This process can also be further adjusted by manipulating factors such as pH, temperature, exudate dilution and plant origin to produce different shapes of nanoparticles, including triangles, spheres, rods, and spirals. These biogenic metallic nanoparticles then have applications as catalysts, glass window coatings to insulate heat, in biomedicine, and in biosensor devices.
Sources: en.wikipedia.org
The budget document often begins with the president's proposal to Congress recommending funding levels for the next fiscal year, beginning October 1 and ending on September 30 of the year following. The fiscal year refers to the year in which it ends. However, Congress is the body required by law to pass appropriations annually and to submit funding bills passed by both houses to the president for signature. Congressional decisions are governed by rules and legislation regarding the federal budget process. Budget committees set spending limits for the House and Senate committees and for Appropriations subcommittees, which then approve individual appropriations bills to allocate funding to various federal programs. If Congress fails to pass an annual budget, then several appropriations bills must be passed as "stop gap" measures. After Congress approves an appropriations bill, it is then sent to the president, who may either sign it into law or veto it. A vetoed bill is sent back to Congress, which can pass it into law with a two-thirds majority in each legislative chamber. Congress may also combine all or some appropriations bills into one omnibus reconciliation bill. In addition, the president may request and the Congress may pass supplemental appropriations bills or emergency supplemental appropriations bills. Several government agencies provide budget data and analysis. These include the Government Accountability Office (GAO), the Congressional Budget Office (CBO), the Office of Management and Budget (OMB), and the Treasury Department.
== Reactions == 2-Mercaptoethanol cleaves disulfide bonds. 2-Mercaptoethanol reacts with aldehydes and ketones to give the corresponding oxathiolanes. This makes 2-mercaptoethanol useful as a protecting group, giving a derivative whose stability is between that of a dioxolane and a dithiolane.
== Precautions == THF is a relatively acutely nontoxic solvent, with the median lethal dose (LD50) comparable to that for acetone. However, chronic exposure is suspected of causing cancer. Reflecting its remarkable solvent properties, it penetrates the skin, causing rapid dehydration. It is highly flammable. THF dissolves or penetrates most polymer glove materials in a very short period of time; only Linear low-density polyethylene (LLDPE) laminated gloves are capable of protecting against it for long time periods, similar to most ketones. Polyvinyl alcohol (PVA) coated gloves are capable of providing protection for nearly an hour, but because PVA is water soluble they are only effective in low humidity environments and when working with anhydrous solvents. Even very thick nitrile or nitrile-neoprene gloves degrade in under 10 minutes. One danger posed by THF is its tendency to form explosive peroxides upon reaction with air:
Habiger of the United States Air Force who was Commander in Chief from 1996 to 1998 of United States Strategic Command; Richard Lugar, former senator for Indiana; Ash Carter, later United States Secretary of Defense, from 2015 to 2017; the US spent around $2.5 billion sending former nuclear missiles back to Russia in the early 1990s; Matthew Bunn, writer on nuclear security; the Soviet Union had 8 main radar sites in its early warning system - a main site in Latvia was dismantled, and nine satellites became three; General Vladimir Dvorkin (Russian), who wanted missiles to be less 'launchable', known as de-alerting; Lieutenant-General William Eldridge Odom, who was sceptical of 1990s meetings between US and Russian generals; Alexei Yablokov (Russian and the danger of suitcase nuclear devices, and Alexander Lebed; Armimex and a June 1997 commercial plot; William Cohen, United States Secretary of Defense from 1997 to 2001. Written by June Cross, directed by Dan Chambers, produced by David Dugan, made by Windfall Films and WGBH. Shown on PBS Frontline on 23 February 1999
== Sample collection == There are no set rules for sample selection in detrital zircon geochronology studies. The objective and scale of the research project govern the type and number of samples taken. In some cases, the sedimentary rock type and depositional setting can significantly affect the result. Examples include:
Sources: en.wikipedia.org
Dry powder is best kept sealed, protected from light, and held at minus 20 degrees Celsius or below. Desiccant packaging helps limit moisture uptake because the material is hygroscopic. A sealed vial should be allowed to equilibrate to room temperature before opening to reduce condensation.
Hydrolysis of peptide bonds and deamidation of arginine and proline residues are the main degradation routes. Alkaline pH and higher temperatures accelerate both processes. Buffered, near-neutral solutions stored cold generally degrade more slowly than unbuffered ones.
Reverse-phase chromatography gives the clearest single view of related impurities and truncated sequences. Mass spectrometry then confirms that the main peak carries the expected mass. Neither test detects enantiomeric impurities, which require a separate chiral assay.
Selank is a synthetic seven-amino-acid peptide modeled on tuftsin, a fragment of the immunoglobulin G heavy chain. It was designed in Russia to combine anxiolytic and immunomodulatory properties in one molecule.