mass spectrometry 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 2026-05-24 and is reviewed periodically as new material appears.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical purity report | 95% or higher by HPLC | Area percentage at 214 nm |
| Identity confirmation | Mass spectrometry | Electrospray or MALDI |
| Powder storage | -20 C, desiccated | Protect from light |
| Solution storage | 2-8 C short term | Freeze aliquots for longer |
| Quality document | Certificate of analysis | States method and value |
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 with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its four N-terminal residues reproduce tuftsin, a tetrapeptide fragment of the immunoglobulin heavy chain, while the C-terminal Pro-Gly-Pro extension is a synthetic addition. The peptide has a molecular mass near 752 daltons and carries a net positive charge at physiological pH because of the arginine and lysine side chains. Published indexes list it under the name Selank and the sequence abbreviation TKPRPGP. Solid-phase peptide synthesis is the standard production route for research quantities.
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.
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.
The biological effects of hexobarbital depend primarily on its ability to penetrate the central nervous system. Hexobarbital can potentiate GABAA receptors, like all barbiturates. It has been found over the years that the S(+) enantiomer of hexobarbital potentiates GABAA receptors more effectively than its R(-) enantiomer. When GABA binds to the GABAA receptor, the chloride ion channels open such that chloride ions can flow into the neuron. This causes a hyperpolarization in the membrane potential of the neuron, which makes it less likely for the neuron to start an action potential. Therefore, this type of receptor is the major inhibitory neurotransmitter receptor in the mammalian central nervous system. As a GABAA receptor potentiator, hexobarbital binds to the barbiturate binding site localized in the chloride ion channel, thereby increasing the binding of GABA and benzodiazepines to their respective binding site, allosterically. Moreover, hexobarbital causes the chloride ion channel opening to their longest open state of 9 milli seconds, thereby causing the postsynaptic inhibitory effect to be extended. In contrast to GABA, glutamate is the major excitatory neurotransmitter in the mammalian brain. In addition to the inhibitory effect, hexobarbital blocks, like all barbiturates, AMPA receptors, kainate receptors, neural acetylcholine receptors. And above all, barbiturates inhibit glutamate release by causing an open channel block on P/Q‐type high‐voltage activated calcium channels.
All Gram-positive bacteria are bounded by a single unit lipid membrane (i.e. monoderm); they generally contain a thick layer (20-80 nm) of peptidoglycan responsible for retaining the Gram-stain. A number of other bacteria which are bounded by a single membrane but stain gram-negative due to either lack of the peptidoglycan layer (viz., mycoplasmas) or their inability to retain the Gram-stain due to their cell wall composition, also show close relationship to the Gram-positive bacteria. For the bacterial (prokaryotic) cells that are bounded by a single cell membrane the term "monoderm bacteria" or "monoderm prokaryotes" has been proposed. In contrast to gram-positive bacteria, all archetypical Gram-negative bacteria are bounded by a cytoplasmic membrane as well as an outer cell membrane; they contain only a thin layer of peptidoglycan (2–3 nm) between these membranes. The presence of both inner and outer cell membranes forms and define the periplasmic space or periplasmic compartment. These bacterial cells with two membranes have been designated as diderm bacteria. The distinction between the monoderm and diderm prokaryotes is supported by conserved signature indels in a number of important proteins (for example, DnaK and GroEL).
In 1927, a Southland Ice Company employee named John Jefferson Green began selling ice, eggs, milk, and bread from 16 ice house storefronts in Dallas, with permission from one of Southland's founding directors, Joe C. Thompson Sr. Although small grocery stores and general merchandisers were available, Thompson theorized that selling products like bread and milk in convenience stores would reduce the need for customers to travel long distances for basic items. Thompson eventually bought the Southland Ice Company and turned it into the Southland Corporation, which oversaw several locations in the Dallas area. In 1928, a manager named Jenna Lira brought a totem pole from Alaska and placed it in front of her store. The pole served as a marketing tool for the company, as it attracted a great deal of attention. Soon, executives added totem poles in front of every store and eventually adopted an Alaska Native-inspired theme. Later on, the stores began operating under the name "Tote'm Stores". That same year, the company began constructing filling stations at some of its Dallas locations as an experiment. Joe Thompson introduced staff training to ensure that customers would receive the same quality and service in every store. Additionally, Southland introduced a uniform for its ice station service boys. In 1931, the Great Depression affected the company, sending it toward bankruptcy. Nevertheless, the company continued its operations through re-organization and receivership. A Dallas banker, W. W.
Sources: en.wikipedia.org
== Combinatorial libraries == A combinatorial library is a set of compounds prepared by Combinatorial chemistry, typically by systematically combining sets of chemical building blocks . Such libraries may be organized in pools or sublibraries. Combinatorial synthesis is particularly suited to DNA-encoded chemical libraries because large numbers of compounds can be generated through repeated combination of building blocks, while the associated DNA tags provide a way to identify the individual library members.
When the elastic fibers are relaxed the elastic chains appear disorganized, when tensile pressure is give the elastic chains appear organized and return to a disorganized state when the pressure is released. Collagen fibers form networks to provide strength and structural framework for the molecules within the extracellular matrix.
Vaginal intracavity brachytherapy (VBT) is used to treat endometrial, vaginal and cervical cancer. An applicator is inserted into the vagina to allow the administration of radiation as close to the site of the cancer as possible. Survival rates increase with VBT when compared to external beam radiation therapy. By using the vagina to place the emitter as close to the cancerous growth as possible, the systemic effects of radiation therapy are reduced and cure rates for vaginal cancer are higher. Research is unclear on whether treating cervical cancer with radiation therapy increases the risk of vaginal cancer.
Stratum basale (basal layer) Stratum spinosum (spinous layer) Stratum granulosum (granular layer) Stratum corneum (keratinized/superficial layer) Depending on the region of the mouth the epithelium may be keratinized or non-keratinized. Non-keratinized squamous epithelium covers the soft palate, lips, cheeks and the floor of the mouth. Keratinized squamous epithelium is present in the gingiva and hard palate. Keratinization is the differentiation of keratinocytes in the granular layer into dead surface cells to form the stratum corneum. The cells terminally differentiate as they migrate to the surface (from the basal layer where the progenitor cells are located to the dead superficial surface). The lamina propria is a fibrous connective tissue layer that consists of a network of type I and III collagen and elastin fibers. The main cells of the lamina propria are the fibroblasts, which are responsible for the production of the extracellular matrix. The basement membrane forms the border between the epithelial layer and the lamina propria.
Sources: en.wikipedia.org
==== Insects ==== Freeze-drying is used extensively to preserve insects for the purposes of consumption. Whole freeze-dried insects are sold as exotic pet food, bird feed, fish bait, and increasingly for human consumption. Powdered freeze-dried insects are used as a protein base in animal feeds, and in some markets, as a nutritional supplement for human use. Farmed insects are generally used for all of the aforementioned purposes versus harvesting wild insects, except in the case of grasshoppers which are often harvested out of field crops.
=== The no common mechanism (NCM) model and maximum parsimony === In 1997, Tuffley and Steel described a model that they named the no common mechanism (NCM) model. The topology of the maximum likelihood tree for a specific dataset given the NCM model is identical to the topology of the optimal tree for the same data given the maximum parsimony criterion. The NCM model assumes all of the data (e.g., homologous nucleotides, amino acids, or morphological characters) are related by a common phylogenetic tree. Then
There are also the testimonies of Raymond Queneau (1903–1976), born in Le Havre, the city served as a framework for his novel Un rude hiver (A harsh winter) (1939). The plot of Une maison soufflée aux vents (A house blown to the winds) by Émile Danoën, winner of the Popular Novel Prize in 1951, and its sequel Idylle dans un quartier muré (Idyll in a walled neighbourhood) were located in Le Havre during the Second World War. Under the name Port de Brume Le Havre is the setting for three other novels by this author: Cerfs-volants (Kites), L'Aventure de Noël (The Adventure at Christmas), and La Queue à la pègre (Queue to the underworld). Michel Leiris wrote De la littérature considérée comme une tauromachie (Of literature considered like a bullfight) in December 1945. Diana Gabaldon set the second novel in her Outlander series, Dragonfly in Amber (1992), partly in Le Havre. Two mystery novels take place in Le Havre: Le Bilan Maletras (The Maletras Balance) by Georges Simenon and Le Crime de Rouletabille (Crime at the Roulette table) by Gaston Leroux. In Rouge Brésil (Red Brazil), winner of the Goncourt Prize in 2001, Jean-Christophe Rufin describes Le Havre in the 16th century as the port of departure of French expeditions to the New World: the hero Villegagnon leaves of the port to conquer new lands for the French crown which become Brazil. Martine–Marie Muller tells the saga of a clan of Stevedores from Le Havre in the 1950s to the 1970s in Quai des Amériques (Quay of the Americas).
Sources: en.wikipedia.org
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.
Dry powder is kept frozen, desiccated, and shielded from light. Dissolved material is aliquoted and frozen to limit freeze-thaw cycles. Short-term refrigerated storage is common for working solutions.
Russia registers it as a prescription nasal product. Most other markets classify it as a research chemical with no approved medical use. Oversight of purity and labeling is consequently minimal in those markets.
Selank is a synthetic heptapeptide designed as a stabilized analog of the natural tetrapeptide tuftsin. It has been investigated mainly for anxiolytic and cognitive effects. It is not an approved pharmaceutical in most countries.