The short version of RP-HPLC fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-05-11 and is reviewed periodically as new material appears.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical purity specification | 95 percent or higher by RP-HPLC | Area percentage of the main peak |
| Identity confirmation | Electrospray ionization mass spectrometry | Observed mass compared with the theoretical value near 751.9 Da |
| Recommended dry storage | -20 °C, desiccated | -80 °C for multi-year archival material |
| Solution handling | Prepare fresh; avoid long storage | Sterile filtration reduces microbial load |
| Common synonyms | TKPRPGP; TP-7 | Sequence code and laboratory designation used interchangeably |
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.
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.
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.
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 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.
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.
== Further reading == A. Abragam (1961). The Principles of Nuclear Magnetism. Clarendon Press. ISBN 978-0-19-852014-6. {{cite book}}: ISBN / Date incompatibility (help) J.W. Akitt; B.E. Mann (2000). NMR and Chemistry. Cheltenham, UK: Stanley Thornes. pp. 273, 287. ISBN 978-0-7487-4344-5. K.V.R. Chary, Girjesh Govil (2008) NMR in Biological Systems: From Molecules to Human. Springer. ISBN 978-1-4020-6680-1. G.M. Clore; A.M. Gronenborn (1991). "Structures of larger proteins in solution: three- and four-dimensional heteronuclear NMR spectroscopy". Science. 252 (5011): 1390–1399. Bibcode:1991Sci...252.1390M. doi:10.1126/science.2047852. OSTI 83376. PMID 2047852. John Emsley; James Feeney; Leslie Howard Sutcliffe (1965). High Resolution Nuclear Magnetic Resonance Spectroscopy. Pergamon. ISBN 978-1-4831-8408-1. The Feynman Lectures on Physics Vol. II Ch. 35: Paramagnetism and Magnetic Resonance David M. Grant; Robin Kingsley Harris (2002). "Advances in NMR". Encyclopedia of Nuclear Magnetic Resonance. John Wiley. ISBN 978-0-471-49082-1. R.L. Haner; P.A. Keifer (2009). "Flow Probes for NMR Spectroscopy". Encyclopedia of Magnetic Resonance. John Wiley. doi:10.1002/9780470034590.emrstm1085. ISBN 978-0-470-03459-0. J.P. Hornak. "The Basics of NMR". Retrieved 23 February 2009. J. Keeler (2005). Understanding NMR Spectroscopy. John Wiley & Sons. ISBN 978-0-470-01786-9. Gary E. Martin; A. S. Zektzer (1988). Two-Dimensional NMR Methods for Establishing Molecular Connectivity. New York: Wiley-VCH. p. 59. ISBN 978-0-471-18707-3. J.A.Pople; W.G.Schneider; H.J.Bernstein (1959).
Cholesterol has 256 stereoisomers that arise from its eight stereocenters. Only two of the stereoisomers have biochemical significance: nat-cholesterol and ent-cholesterol (for natural and enantiomer, respectively). The only cholesterol stereoisomer to occur naturally is nat-cholesterol.
During his 2022 gubernatorial campaign, Moore said he supported the Inclusive Schools Act, a bill introduced in the 2022 legislative session that banned schools from discriminating against students based on their sexual orientation and gender identity. He also supported the Trans Health Equity Act, a bill that would have required the state's Medicaid program to cover gender-affirming treatments. In December 2022, Moore praised the signing of the Respect for Marriage Act, which codifies same-sex and interracial marriage rights. On March 31, 2023, Moore became the first Maryland governor to recognize International Transgender Day of Visibility when he issued an official proclamation. In May 2023, Moore signed the Trans Health Equity Act into law and allowed a bill furthering an earlier repeal of the state's sodomy law to become law without his signature. In June 2023, he signed an executive order to protect people or entities that provide gender-affirming care from legal punishments by other states. During the 2024 legislative session, Moore signed into law the Trans Shield Act, which prevents states with anti-trans laws from prosecuting patients or entities within Maryland for providing gender-affirming care. In May 2025, Moore signed into law a bill decriminalizing the spread of HIV.
Sources: en.wikipedia.org
Bisoprolol is used for prevention of cardiovascular events following a heart attack in patients with risk factors for disease progression, in the management of congestive heart failure with reduced ejection fraction, and as a second-line agent for hypertension. Bisoprolol may be beneficial in the treatment of high blood pressure, but it is not recommended as a first-line antihypertensive agent. It can be an adjunct to first-line antihypertensive agents in patients with accompanying comorbidities, for example, congestive heart failure, where selected beta blockers can be added in patients who remain mildly to moderately symptomatic despite appropriate doses of an angiotensin-converting-enzyme inhibitor. In cardiac ischemia, the drug is used to reduce the activity of the heart muscle, thereby reducing its oxygen and nutrient demands and allowing its reduced blood supply to still transport sufficient amounts of oxygen and nutrients to meet its needs.
Chemical information and Biochemical information. The chemical information includes more than 2,700 metabolite structures with detailed metabolite descriptions, extensive chemical classifications, synthesis information and observed/calculated chemical properties. It also contains nearly 5,000 NMR, GC-MS and LC-MS spectra from more than 600 different metabolites. The biochemical information includes >1,600 protein (and DNA) sequences and >3,100 biochemical reactions that are linked to these metabolite entries. The ECMDB supports many different types of online queries including text searches, chemical structure searches, sequence similarity searches and spectral similarity searches. This makes it particularly useful for metabolomic researchers who are studying E. coli as a model organism. Secondary electrospray ionization (SESI-MS) can discriminate between eleven E. Coli strains thanks to the volatile organic compound profiling.
== Efficacy == The use of lasers in treating periodontal disease has been seen by some dental professionals as controversial. The American Academy of Periodontology stated in 1999 that it was "not aware of any randomized blinded controlled longitudinal clinical trials, cohort or longitudinal studies, or case-controlled studies indicating that 'laser excisional new attachment procedure (or Laser ENAP)' or 'laser curettage' offers any advantageous clinical result not achieved by traditional periodontal therapy. Moreover, published studies suggest that use of lasers for ENAP procedures and/or gingival curettage could render root surfaces and adjacent alveolar bone incompatible with normal cell attachment and healing." A 2015 systematic review from the AAP regeneration workshop acknowledged peer-reviewed studies reporting periodontal regeneration, and further suggested that the LANAP protocol's minimally invasive nature may offer advantages in the regeneration of defects where minimal soft tissue change is required. The AAP consumer information page on laser therapy for gum disease notes that lasers can be used to treat periodontal disease and that controlled studies have reported similar results to some other treatment options (including scaling and root planing alone), and also states that different laser wavelengths have different applications in periodontal treatment.
==== Eastern copperhead ==== The eastern copperhead (Agkistrodon contortrix) is a species of venomous snake, a pit viper, endemic to eastern North America; it is a member of the subfamily Crotalinae in the family Viperidae. The generic name is derived from the Greek words ancistro (hooked) and odon (tooth), and the specific name comes from the Latin contortus (twisted, intricate, complex); thus, the scientific name translates into "twisted hook-tooth".
Sources: en.wikipedia.org
=== Environmental benefits === Hydroponic farming offers several environmental benefits when compared to traditional agriculture. The most significant of these is reduced water consumption and controlled nutrient usage. Hydroponic systems can use up to 90% less water when compared to conventional farming. Also, in hydroponic systems, water and nutrients are recirculated in a controlled environment, eliminating runoff and the discharge of pollutants into local waterways. By using hydroponics to grow crops indoors or in greenhouses, land use is minimized, reserving arable soil and land for other purposes. Also, utilizing the controlled environment created for hydroponic farming reduces the need for pesticides and other chemicals. This is due to the fact that many pests and diseases in farming are soil-borne. Since hydroponics uses other substrates, eliminating soil use, these farming obstacles are reduced. Using hydroponics systems that grow vertically in a space-efficient manner also makes cultivating crops in urban areas possible. However, These systems can use large amounts of energy due to the use of water filtration systems and artificial lighting. Due to this, the carbon footprint of a hydroponic farm can vary depending on factors like the energy source, local climate, and the scale of the operation. Using renewable energy sources such as solar panels has the possibility of making hydroponic farms more sustainable.
Anger over the treatment of demonstrators following the death of Benno Ohnesorg and the attack on Rudi Dutschke, coupled with growing frustration over the lack of success in achieving their aims led to growing militance among students and their supporters. In May 1968, three young people set fire to two department stores in Frankfurt; they were brought to trial and made clear to the court that they regarded their action as a legitimate act in what they described as the "struggle against imperialism". The student movement began to split into different factions, ranging from the unattached liberals to the Maoists and supporters of direct action in every form—the anarchists. Several groups set as their objective the aim of radicalising the industrial workers; taking an example from activities in Italy of the Red Brigades (Brigate Rosse), many students went to work in the factories, but with little or no success. The most notorious of the underground groups was the Red Army Faction, which began by making bank raids to finance their activities and eventually went underground having killed a number of policemen, several bystanders and eventually two prominent West Germans, whom they had taken captive in order to force the release of prisoners sympathetic to their ideas. In the 1990s, attacks were still being committed under the name "RAF". The last action took place in 1993 and the group announced it was giving up its activities in 1998.
As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous iron(III) oxide precipitates out of solution. Although Fe3+ has a d5 configuration, its absorption spectrum is not like that of Mn2+ with its weak, spin-forbidden d–d bands, because Fe3+ has higher positive charge and is more polarizing, lowering the energy of its ligand-to-metal charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region. On the other hand, the pale green iron(II) hexaquo ion [Fe(H2O)6]2+ does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises quickly in air to form iron(III) oxide that accounts for the brown deposits present in a sizeable number of streams.
== History == SPAR began in 1994 at the New England Deaconess Hospital (now Beth Israel Deaconess Medical Center) as a support group for couples wishing to parent when one of them had an incurable sexually transmitted disease. The patient couples began raising money to fund the research needed to develop the methods to improve the safety of attempting pregnancy. By 1996 sufficient funds were available to begin, but a merger between the Beth Israel Hospital and the New England Deaconess Hospital (now Beth Israel Deaconess Medical Center) necessitated the creation of an independent Massachusetts public charity, the Assisted Reproduction Foundation (now the Bedford Stem Cell Research Foundation directed by Dr. Ann Kiessling), to continue the work. Within two years, the methods for reducing, and perhaps eliminating, the risks of infection to the mother and the child were developed and Baby Ryan was born in 1999. The goal of SPAR was to provide semen testing by experts that would ensure improved safety of sperm that could then be shipped to infertility clinics near the couple's home. In this way, couples could be cared for in the same manner as other couples in their community. Fortunately, a few clinics were willing to help with this effort, and by 2002, seven collaborating clinics around the country were caring for couples living with HIV disease. In the Spring of 2000 a ground breaking study was completed, giving significant insight to the role of semen producing organs in HIV anti-viral therapy.
=== Inhibin === In both females and males, inhibin inhibits FSH production. Inhibin does not inhibit the secretion of GnRH from the hypothalamus. However, the overall mechanism differs between the sexes:
Sources: en.wikipedia.org
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.
A reported purity value reflects the share of the main peak in one chromatographic run and says nothing about identity. Confirming that the expected sequence is present requires a separate measurement such as mass spectrometry. Purity and identity are distinct questions.
A mass spectrum reports the molecular masses present in a sample and shows whether they match the value expected for selank, near 751.9 Da. It also flags common artifacts such as truncation or adduct formation. It does not establish correct stereochemistry or complete sequence order on its own.
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.