The short version of electrospray ionization fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-07-10 and is reviewed periodically as new material appears.
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.
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.
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.
| 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 |
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.
Selank is a synthetic heptapeptide developed in Russia during the 1990s. Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences designed it as a stabilized analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The compound has been studied primarily for its reported anxiolytic and nootropic effects. It remains largely unknown in Western pharmacology and is not approved as a medicine by major regulators such as the FDA or the EMA.
The primary structure of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, corresponding to the molecular formula C33H57N11O9 and a monoisotopic mass of roughly 751.9 daltons. The N-terminal threonine and the arginine residue in the fourth position are shared with tuftsin, which carries the sequence Thr-Lys-Pro-Arg. The three additional residues at the C-terminus, Pro-Gly-Pro, extend the chain and are associated with greater resistance to enzymatic degradation. This extension also separates Selank from the shorter parent peptide.
Naming conventions place Selank in the same research family as Semax, another Russian-developed peptide investigated for cognitive effects. The two compounds share a lineage but differ in sequence and in the biological systems proposed as their targets. Semax descends from ACTH fragments, whereas Selank descends from tuftsin. Publications sometimes identify Selank by its full peptide sequence or by laboratory codes rather than one uniform trade name. Because replication outside Russia is limited, reports on its properties are best read alongside the study design and the purity of the material tested.
Lyophilized material is generally stable for extended periods when kept dry at or below minus twenty degrees Celsius. Working solutions are less stable, and common practice is to aliquot and freeze them so that repeated freeze-thaw cycles are avoided. Aqueous solutions are sensitive to pH extremes and to microbial growth, so short-term storage at refrigerator temperature is typical. Oxidation and hydrolysis are the principal degradation routes. Reconstitution with sterile water or a mild buffer is standard, and solutions should be protected from light.
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.
===== Methane ===== Methane produced by marine methanogens is typically more D-enriched than methane produced by methanogens grown in freshwater. δDs for thermogenic methane range from −275‰ to −100‰, and from −400‰ to −150‰ for microbial methane.
Overcoming serious difficulties, President Suárez achieved these two objectives and the first free elections since 1936 could be held on June 15, 1977. Union of the Democratic Centre (UCD), the party organized by President Suárez, won the elections, although not by absolute majority, and sought the consensus of the rest of the political forces ─ and especially of the other great winner, the PSOE ─ to create the new legal framework that was to replace the fundamental laws of the Franco regime, as well as to face the economic crisis, the reappearance of the "regional question" and the increase of terrorism by ETA. This led to the creation of the political transition to democracy model, which was based on the Amnesty Law of 1977 that included everything that had happened during the Franco dictatorship ─ thus constituting a so-called "pact of oblivion" ─ and in the approval of a Consensus Constitution in exchange for the leftist parties abandoning their claim to establish the Republic. On December 6, 1978, the referendum was held and the new democratic Constitution was approved. Once the Constitution was endorsed, President Suárez called elections for March 1979, which were won by UCD but again without an absolute majority. During the following two years, the governing party suffered an acute process of internal decomposition that culminated with the resignation of Adolfo Suárez in January 1981.
The cell counters of that time used LED screens for result review. In 1982, Medonic AB, another Swedish company with focus on hematology, was founded. The founders, Ingemar Berndtsson and Abraham Bottema, both had a long history and experience in hematology, clinical chemistry, and blood banking engineering. In 1985, Medonic AB launched the Cellanalyzer CA 480 system, its first own-developed cell counter with a built-in display that also showed the cell histograms. When computers began to be incorporated into the analyzers, other brands, like the Swelab analyzers, also came with a display. Both targeting the smaller clinical laboratories, Swelab Instrument AB and Medonic AB were competitors on the decentralized hematology testing market. In the late 90s, both Swelab Instrument AB and Medonic AB were acquired by Boule Diagnostics AB. The company has kept the parallel brands and the analyzers are still manufactured from its facilities in Stockholm, Sweden and supplied under the Swelab and Medonic trademarks for the decentralized hematology testing market. When Coulter was acquired by Beckman, former Coulter employees Dr. Harold R Crews, Andrew C Swanson, and Donald Grantham founded Clinical Diagnostic Solutions, Inc. (CDS) in 1997, focusing on the development and production of generic reagents and control material. In 2004, CDS was acquired by Boule. By this acquisition, Boule came to master the skills of the development and production of both instruments and the consumables included in a complete hematology system.
Sources: en.wikipedia.org
=== Organometallic clusters === Organometallic Fe–S clusters include the sulfido carbonyls with the formula Fe2S2(CO)6, H2Fe3S(CO)9, and Fe3S2(CO)9. Compounds are also known that incorporate cyclopentadienyl ligands, such as (C5H5)4Fe4S4.
The typical dinoflagellate chloroplast has three membranes, but considerable diversity exists in chloroplasts within the group, and a number of endosymbiotic events apparently occurred. The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts, which are not photosynthetic. The Chromerida are the closest relatives of apicomplexans, and some have retained their chloroplasts. The three alveolate groups evolved from a common myzozoan ancestor that obtained chloroplasts.
== History == LFTs derive from paper chromatography, which was developed in 1943 by Martin and Synge, and elaborated in 1944 by Consden, Gordon and Martin. There was an explosion of activity in this field after 1945. The ELISA technology was developed in 1971. A set of LFT patents, including the litigated US 6,485,982 described below, were filed by Armkel LLC starting in 1988. The first commercially available lateral flow device was Unipath's Clearblue One Step in 1988. This product combined Paired Monoclonal Antibody technology (patented in 1980 by Unipath's Prof. Philip Porter and colleagues including Paul Davis and Keith May) and the original Clearblue product launched in June 1985.
Any drug (including a biological product for human use), medical device for human use, human food additive, color additive, electronic product, or any other article subject to regulation under the FD&C Act (21CFR50.3) Toxicity
Sources: en.wikipedia.org
== Prevention == Hypervitaminosis A can be prevented by not ingesting more than the US Institute of Medicine Daily Tolerable Upper Level of intake for Vitamin A. This level is for synthetic and natural retinol ester forms of vitamin A. Carotene forms from dietary sources are not toxic. Possible pregnancy, liver disease, high alcohol consumption, and smoking are indications for close monitoring and limitation of vitamin A administration.
Hyperuricemia associated with classic primary gout, which is caused by low uric acid renal clearance rather than uric acid overproduction, is not associated with neuropathology. Hypouricemia occurs in a number of purine disorders, in particular xanthinuria. Despite having complete absence of blood uric acid, xanthinuria patients do not have any neuropathology, nor any other disease states – other than the kidney stones caused by accumulation of insoluble xanthine in lieu of uric acid. Similarly, uric acid does not penetrate the blood–brain barrier well. However, oxidative stress due to uric acid is now thought to figure in metabolic syndrome, atherosclerosis, and stroke, all syndromes associated with high uric acid levels. Similarly, Superoxide dismutase ( "SOD" ) and SOD-mimetics such as TEMPOL ameliorate the effects of hyperuricemia. Likewise, 6-hydroxydopamine (the putative animal model for Lesch–Nyhan's neuropathy) apparently acts as a neurotoxin by generation of reactive oxygen species. It may be that oxidative stress induced by some other oxypurine such as xanthine causes the disease.
According to the elders, roads to the districts had been closed for nearly two months because of cross-border fire by Pakistani forces, and Taliban authorities had neither reopened the routes nor built alternative roads as promised. Residents said that food supplies in local markets had been exhausted, and warned of a shortage of wheat and medicine in health centres. Later on the day, the roads leading to Kamdesh and Bargi Matal districts were temporarily reopened following a meeting between tribal elders of these districts and tribal elders of Pakistan's Chitral district. A polio vaccination team was attacked by militants in Hangu District with the subsequent clash resulting in the death of two militant whereas a policeman was killed and four more were injured. On 14 April, Punjab CTD claimed to have captured 16 "suspected terrorists" including a TTP suicide bomber. On 15 April, tribal elders from eastern Afghanistan and Pakistan's Chitral district reached an agreement to reopen key routes linking Kamdesh and Barg-i Matal in Nuristan after nearly two months of closure caused by firing from Pakistani border guards. The talks were held on the Pakistani side of the border, at a Pakistani military facility, and did not include Taliban representatives. Under the agreement, both sides committed to a ceasefire across areas including Nari, Kamdesh, Bargi Matal, Arandu, and Chitral. Local elders also said Pakistani forces asked communities not to allow Pakistani Taliban to shelter in the area, and that if anyone did so, local people should stand against them.
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.
Reverse-phase HPLC is the usual method and gives a percentage purity value. Mass spectrometry then confirms the molecular mass. Together they provide a basic identity and purity profile for a lot.