This is a working overview of RP-HPLC, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-10-02 and is reviewed periodically as new material appears.
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.
Reported activity for Selank centers on anxiolytic and nootropic effects. Russian clinical reports describe use in anxiety and in cognitive or attention-related complaints. Most of this evidence comes from studies conducted by the same research groups that developed the peptide. Independent replication in other countries remains limited, and no major Western regulatory agency has approved the compound for any indication. The gap between local reports and external verification is a recurring point in discussions of the peptide.
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.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Modeled on tuftsin |
| Amino acid sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues |
| Approximate molecular mass | Around 750 Da | Depends on counter-ion and hydration |
| Common forms | Lyophilized powder | Also described as aqueous solution |
| Primary origin of research | Russian laboratories | Mid-1990s onward |
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.
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.
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.
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.
== External links == Human Health Campus, The official website of the International Atomic Energy Agency dedicated to Professionals in Radiation Medicine. This site is managed by the Division of Human Health, Department of Nuclear Sciences and Applications Canadian Organization of Medical Physicist - Organisation canadienne des physiciens médicaux The American Association of Physicists in Medicine medicalphysicsweb.org from the Institute of Physics AIP Medical Physics portal University of Toronto - Medical Biophysics Department Journal of Biophysics Institute of Physics & Engineering in Medicine (IPEM) - UK European Federation of Organizations for Medical Physics (EFOMP)
=== Split-&-Pool DNA Encoding === In order to apply combinatorial chemistry for the synthesis of DNA-encoded chemical libraries, a Split-&-Pool approach was pursued. Initially a set of unique DNA-oligonucleotides (n) each containing a specific coding sequence is chemically conjugated to a corresponding set of small organic molecules. Consequently, the oligonucleotide-conjugate compounds are mixed ("Pool") and divided ("Split") into a number of groups (m). In appropriate conditions a second set of building blocks (m) are coupled to the first one and a further oligonucleotide which is coding for the second modification is enzymatically introduced before mixing again. This “split-&-pool” steps can be iterated a number of times (r) increasing at each round the library size in a combinatorial manner (i.e. (n x m)r). Alternatively, peptide nucleic acids have been used to encode libraries prepared by "split-&-pool" method. A benefit of PNA-encoding is that the chemistry can be performed by standard SPPS.
Gelatine art desserts, also known as 3D gelatine desserts, are made by injecting colourful shapes into a flavoured gelatine base. Creations by Lourdes Reyes Rosas of Mexico City kicked off the growth in popularity of this 3D gelation art technique in the early 1990s, which spread to Western and Pacific countries. These desserts are made using high-quality gelatine that has a high bloom value and low odour and taste. The clear gelatine base is prepared using gelatine, water, sugar, citric acid and food flavouring. When the clear gelatine base sets, colourful shapes are injected using a syringe. The injected material usually consists of a sweetener (most commonly sugar), some type of edible liquid (milk, cream, water, etc.), food colouring and a thickening agent such as starch or additional gelatine. The shapes are drawn by making incisions in the clear gelatine base using sharp objects. Coloured liquid is then allowed to fill the crevice and make the cut shape visible. Most commonly, the shapes are drawn using sterile medical needles or specialised pre-cut gelatine art tools that allow the shape to be cut and filled with colour at the same time. Gelatine art tools are attached to a syringe and used to inject a predetermined shape into gelatine. When combined with other ingredients, such as whipping cream or mousse, gelatine art desserts can be assembled into formations resembling a cake.
The vaginal wall from the lumen outwards consists firstly of a mucosa of stratified squamous epithelium that is not keratinized, with a lamina propria (a thin layer of connective tissue) underneath it. Secondly, there is a layer of smooth muscle with bundles of circular fibers internal to longitudinal fibers (those that run lengthwise). Lastly, is an outer layer of connective tissue called the adventitia. Some texts list four layers by counting the two sublayers of the mucosa (epithelium and lamina propria) separately. The smooth muscular layer within the vagina has a weak contractive force that can create some pressure in the lumen of the vagina. Much stronger contractive force, such as during childbirth, comes from muscles in the pelvic floor that are attached to the adventitia around the vagina. The lamina propria is rich in blood vessels and lymphatic channels. The muscular layer is composed of smooth muscle fibers, with an outer layer of longitudinal muscle, an inner layer of circular muscle, and oblique muscle fibers between. The outer layer, the adventitia, is a thin dense layer of connective tissue and it blends with loose connective tissue containing blood vessels, lymphatic vessels and nerve fibers that are between pelvic organs. The vaginal mucosa is absent of glands. It forms folds (transverse ridges or rugae), which are more prominent in the outer third of the vagina; their function is to provide the vagina with increased surface area for extension and stretching.
Sources: en.wikipedia.org
== Brumation == In the colder winter months, some rattlesnake species enter a period of brumation, which is dormancy similar to hibernation. They often gather for brumation in large numbers, sometimes over 1,000 snakes, and huddle together inside underground "rattlesnake dens" or hibernacula. They regularly share their winter burrows with a wide variety of other species (such as turtles, small mammals, invertebrates, and other types of snakes). Rattlesnakes often return to the same den every year, sometimes traveling several miles to get there. How the rattlesnakes find their way back to the dens each year is unknown, but it may involve a combination of pheromone trails and visual cues such as topography, celestial navigation, and solar orientation. Species with long periods of brumation tend to have much lower reproductive rates than those with shorter brumation periods or those that do not brumate at all. Female timber rattlesnakes in high peaks in the Appalachian Mountains of New England reproduce every three years on average; the lance-headed rattlesnake (C. polystictus), native to the warm climate of Mexico, reproduces annually. Like most other snakes, rattlesnakes aestivate during very hot or dry periods, which is why they are rarely seen during the hottest and driest months of summer.
Liu's governance of Sichuan was challenged by various natural disasters, exacerbated by war. The National Gazette reported the existence of famine in Shunqing and Jintang, as well as other areas of the province. The measures Liu took to address these crises are not known. Liu Wenhui continued his emphasis on promoting education, founding the Jianguo Middle School in Chengdu and serving as its chairman. The school reportedly had high academic standards and included stringent political training. Geographically, the wealthiest and most productive areas in central Sichuan were under Liu Wenhui's sway. This included Chengdu, but also the important salt production centers of Zilujing-Gongjing and the major river port of Yibin, as well as other agricultural and commercial facilities across the Chengdu Plain. Control of the lucrative Yunnan-Sichuan of opium, salt, and weapons in Yibin in particular was dominated by his older brother Liu Wencai, who was a key part of Liu's government. Liu funded some of his garrisons with the salt tax of Leshan, earning around 800 taels per month. These resources helped sustain Liu's armies and secure his power base.
To promote better consistency between a trial's objective and analysis methods, the International Committee for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) has published a new international trial regulatory guidance in Nov 2019, the ICH E9(R1) Addendum on Estimands and Sensitivity Analysis in Clinical Trials. The guidance calls for clearly defining the research question of a trial by specifying its estimand. An estimand is a clear description of the treatment effect a trial aims to quantify. The guidance provides a structured framework for defining estimands, which consists of five attributes: (i) population of patients; (ii) treatment conditions being compared; (iii) the endpoint; (iv) the summary measure; and (v) how intercurrent events are handled. Tutorials on how to implement the estimand framework is available.
Sources: en.wikipedia.org
The first point to note is that, when pKa is positive, the standard free energy change for the dissociation reaction is also positive. Second, some reactions are exothermic and some are endothermic, but, when ΔH⊖ is negative TΔS⊖ is the dominant factor, which determines that ΔG⊖ is positive. Last, the entropy contribution is always unfavourable (ΔS⊖ < 0) in these reactions. Ions in aqueous solution tend to orient the surrounding water molecules, which orders the solution and decreases the entropy. The contribution of an ion to the entropy is the partial molar entropy which is often negative, especially for small or highly charged ions. The ionization of a neutral acid involves formation of two ions so that the entropy decreases (ΔS⊖ < 0). On the second ionization of the same acid, there are now three ions and the anion has a charge, so the entropy again decreases. Note that the standard free energy change for the reaction is for the changes from the reactants in their standard states to the products in their standard states. The free energy change at equilibrium is zero since the chemical potentials of reactants and products are equal at equilibrium.
== Operations == Each Waffle House location is open 24 hours daily. This schedule has inspired the urban myth that "Waffle House doors have no locks". The chain's restaurants almost always have jukeboxes, which traditionally play 45-rpm singles and, in some cases, CDs. Waffle House has released music through its own record label, Waffle Records. It has released songs from "Saturday Night At My Place" by Gary Garcia released in 1995 to "They're Cooking Up My Order" by Alfreda Gerald released in 2006. The co-founder Joe Rogers Sr. had high standards and said, "If it sounded like a commercial, it got the ax." If the song makes the cut, it will be recorded and make its way to Waffle House jukeboxes. The songs are on ordinary discs, which are produced for Waffle House and are not commercially sold, but the chain has made a CD of some of the songs available for sale. Other artists that recorded for Waffle Records include Eddie Middleton who recorded "Good Food Fast" and "Waffle Doo-Wop," which was composed and produced by Jerry Buckner. The company claims to be the world's leading seller of several of its menu items—the namesake waffles, ham, pork chops, grits, and T-bone steaks. It also claims that it serves 2% of all eggs in the U.S. In the 1960s, S. Truett Cathy, the owner of a local diner called the Dwarf House, contracted with Waffle House to sell his proprietary chicken sandwich, the Chick-fil-A chicken sandwich.
Chlorphenamine acts primarily as a potent H1 antihistamine. It is specifically a potent inverse agonist of the histamine H1 receptor. The drug is also commonly described as possessing weak anticholinergic activity by acting as an antagonist of the muscarinic acetylcholine receptors. The dextrorotatory stereoisomer, dexchlorpheniramine, has been reported to possess Kd values of 15 nM for the H1 receptor and 1,300 nM for the muscarinic acetylcholine receptors in human brain tissue. The smaller the Kd value, the greater the binding affinity of the ligand for its target. In addition to acting as an inverse agonist at the H1 receptor, chlorphenamine has been found to act as a serotonin reuptake inhibitor (Kd = 15.2 nM for the serotonin transporter). It has only weak affinity for the norepinephrine and dopamine transporters (Kd = 1,440 nM and 1,060 nM, respectively). A study found that dexchlorphenamine had Ki values for the human cloned H1 receptor of 2.67 to 4.81 nM while levchlorphenamine had Ki values of 211 to 361 nM for this receptor, indicating that dexchlorphenamine is the active enantiomer. Another study found that dexchlorphenamine had a Ki value of 20 to 30 μM for the muscarinic acetylcholine receptor using rat brain tissue while levchlorphenamine had a Ki value of 40 to 50 μM for this receptor, indicating that both enantiomers have very low affinity for it.
Sources: en.wikipedia.org
Selank is a synthetic peptide made of seven amino acids. It is modeled on tuftsin, a natural tetrapeptide, with an added three-residue tail. It is not a small-molecule drug.
It originates from research in Russia, associated with the Institute of Molecular Genetics of the Russian Academy of Sciences. The first descriptions date to the mid-1990s. Most published studies come from Russian laboratories.
No, Selank itself does not occur naturally. Its backbone is based on tuftsin, which is produced in the body, but the seven-residue version is a synthetic construct. It is supplied as a manufactured peptide.
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.