RP-HPLC purity comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2025-10-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
Selank is not a naturally occurring peptide and has no known endogenous counterpart in human physiology. Russian-language sources frequently call it TP-7, while English-language sources use the name Selank almost exclusively. Database indexing is uneven, partly because early reports appeared in regional journals that are not widely cataloged. Some summaries describe the material as a tuftsin analog and others as a synthetic heptapeptide; the labels overlap rather than conflict. Citing the primary sequence resolves ambiguity more reliably than the research or trade name alone.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter notation. Its structure consists of the immunomodulatory tetrapeptide tuftsin, Thr-Lys-Pro-Arg, extended at the carboxyl terminus by a Pro-Gly-Pro segment. The molecular formula is commonly given as C33H57N11O9, corresponding to a monoisotopic mass near 751.4 Da and an average molecular mass near 751.9 Da. All seven residues are proteinogenic amino acids, and the molecule carries no modified side chains or non-natural linkages.
The compound was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences during the 1980s and 1990s. The stated design goal was to retain the immunomodulatory and central nervous system activity attributed to tuftsin while improving resistance to enzymatic breakdown. Adding a proline-rich tail to the short parent peptide was a deliberate strategy, because proline residues restrict the conformations available to many peptidases. The same laboratory produced Semax, an ACTH fragment analog, and both compounds were developed in parallel as short, enzymatically stabilized peptides intended for intranasal use.
| Property | Value | Notes |
|---|---|---|
| Solubility | Freely soluble in water | Also in aqueous buffers |
| Typical purity (HPLC) | 95 percent or higher | Lot-dependent |
| Dry powder storage | Minus 20 degrees Celsius | Sealed, dry, protected from light |
| Solution storage | 2 to 8 degrees Celsius | Short-term use |
| Identity confirmation | Mass spectrometry | ESI or MALDI-TOF |
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.
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.
Lyophilised material kept dry at minus 20 degrees Celsius or colder is the most stable form, and suppliers commonly state a shelf life of two years or more under those conditions. Once dissolved, degradation accelerates through hydrolysis and deamidation, particularly at alkaline pH or elevated temperature. Working solutions are usually divided into single-use aliquots to avoid repeated freeze-thaw cycles. The choice of reconstitution solvent affects both stability and the ionic strength of the final preparation.
Proposed mechanisms center on modulation of the GABA system, but no single molecular target has been confirmed. Rodent studies report changes in GABA-A receptor expression and in the turnover of serotonin, dopamine, and norepinephrine in several brain regions. Increases in brain-derived neurotrophic factor and its receptor have also been described after repeated administration. These findings come largely from animal models, and the degree to which they describe human neurochemistry remains an open question. The mechanism is best characterized as multi-system and not fully resolved.
Pharmacokinetic data are limited. Like most short peptides, Selank is vulnerable to plasma and tissue peptidases, and its measured half-life in circulation is short, on a minutes scale. The Pro-Gly-Pro tail slows this degradation but does not eliminate it. Intranasal administration is the route described in most reports, with absorption through the nasal mucosa and a hypothesized path into the central nervous system that avoids the blood-brain barrier. Direct measurements of human brain exposure are unavailable, so distribution claims rest on inference from animal work.
Clinical evidence comes mainly from small studies conducted in Russia, several of which were open-label or lacked robust blinding. Reported outcomes include lower anxiety scores, changes in attention measures, and effects on asthenic states following illness. Sample sizes are typically in the tens of participants, and independent replication outside the region is scarce. Reviews published in English generally note the limited methodological quality of the underlying trials. Whether the compound produces clinically meaningful effects under rigorous conditions remains unresolved.
Its use is generally restricted to severe infections largely in hospitalized patients. The recommended dosage is 250 mg to 1 gram given intravenously every 6 to 8 hours or in intramuscular doses of no more than 1.5 gm daily, usually for five to 14 days. It is commercially available as Primaxin as 250-mg or 500-mg infusion bottles for IV use or 500-mg or 750-mg vials of lyophilized powder for IM injection. The most common side effects of imipenem are diarrhea, nausea, vomiting, skin rash, pruritus, and injection-site reactions.
In addition, the HTR of 5-HTP is abolished by indolethylamine N-methyltransferase (INMT) inhibitors, which block conversion of serotonin and other endogenous tryptamines into N-methylated tryptamines, such as N-methylserotonin (NMS; norbufotenin), bufotenin (5-hydroxy-N,N-dimethyltryptamine; 5-HO-DMT), and N,N-dimethyltryptamine (DMT). These N-methylated tryptamines are well-known for their psychedelic effects, whereas serotonin itself, without biotransformation, does not seem to produce psychedelic effects. 5-HTP has not been found to produce psychedelic effects in humans, which has been attributed to the high doses required to produce such effects. The 5-HTP doses that produce the HTR in rodents are orders of magnitude higher than the doses of 5-HTP that have been used safely and therapeutically in humans. It remains unknown whether 5-HTP can produce psychedelic effects in humans. The highest dosage of 5-HTP that is known to have been evaluated in humans is about 3,000 mg per day. Serotonin syndrome and associated hallucinations have been reported with overdose of serotonin-elevating drugs, but psychedelic-like effects have not been reported. The lack of the HTR and psychedelic effects with serotonin itself has been attributed to the fact that these effects appear to be dependent on activation of a population of intracellular 5-HT2A receptors expressed in cortical neurons in the medial prefrontal cortex (mPFC) that lack the serotonin transporter (SERT) and are inaccessible to serotonin.
In 2003, arsenic trioxide (under the trade name Trisenox) was re-introduced for the treatment of acute promyelocytic leukaemia, a cancer of the blood and bone marrow. Arsenic in drinking water, which causes lung and bladder cancer, has been associated with a reduction in breast cancer mortality rates. Metallic antimony is relatively non-toxic, but most antimony compounds are poisonous. Two antimony compounds, sodium stibogluconate and stibophen, are used as antiparasitical drugs. Elemental tellurium is not considered particularly toxic; two grams of sodium tellurate, if administered, can be lethal. People exposed to small amounts of airborne tellurium exude a foul and persistent garlic-like odour. Tellurium dioxide has been used to treat seborrhoeic dermatitis; other tellurium compounds were used as antimicrobial agents before the development of antibiotics. In the future, such compounds may need to be substituted for antibiotics that have become ineffective due to bacterial resistance. Of the elements less often recognised as metalloids, beryllium and lead are noted for their toxicity; lead arsenate has been extensively used as an insecticide. Sulfur is one of the oldest of the fungicides and pesticides. Phosphorus, sulfur, zinc, selenium, and iodine are essential nutrients, and aluminium, tin, and lead may be. Sulfur, gallium, selenium, iodine, and bismuth have medicinal applications. Sulfur is a constituent of sulfonamide drugs, still widely used for conditions such as acne and urinary tract infections.
== Names == Calcitriol refers specifically to 1,25-dihydroxycholecalciferol. Because cholecalciferol already has one hydroxyl group, only two (1,25) are further specified in this nomenclature, but in fact there are three (1,3,25-triol), as indicated by the name calcitriol. The 1-hydroxy group is in the alpha position, and this may be specified in the name, for instance in the abbreviation 1α,25-(OH)2D3. It is also known as cholecalcitriol to emphasize its derivation from vitamin D3. Calcitriol is, strictly, the 1-hydroxylation product of calcifediol (25-OH vitamin D3), derived from cholecalciferol (vitamin D3), rather than the product of hydroxylations of ergocalciferol (vitamin D2). 1α,25-Dihydroxyergocalciferol (ercalcitriol) should be used for the vitamin D2 product. However, the terminology of 1,25-dihydroxyvitamin D, or 1,25(OH)2D, is often used to refer to both types of active forms of vitamin D. Indeed, both bind to the vitamin D receptor and produce biological effects. In clinical use, the differences are unlikely to have major importance. Calcitriol is marketed as a pharmaceutical for medical use under various brand names including Rocaltrol (Roche), Calcijex (Abbott), Decostriol (Mibe, Jesalis), Vectical (Galderma), and Rolsical (Sun Pharma).
===== Pharmacokinetics ===== Gonadotropin-releasing hormone agonists are largely parenterally administered to the body, that is, via subcutaneous or intramuscular injection. At the same time, nafarelin is an exception in which its prescription is a nasal spray, and some may be implanted into fats. In general, their half-lives are approximately two to four hours. Some agonists are mainly excreted via urine while other agonists are mainly excreted via faeces.
Sources: en.wikipedia.org
The widespread nature of Gulf of Mexico chemosynthetic communities was first documented during contracted investigations by the Geological and Environmental Research Group (GERG) of Texas A&M University for the Offshore Operators Committee. This survey remains the most widespread and comprehensive, although numerous additional communities have been documented since that time. Industry exploration for energy reserves in the Gulf of Mexico has also documented numerous new communities through a wide range of depths, including the deepest-known occurrence in the Central Gulf of Mexico in Alaminos Canyon Block 818 at a depth of 2,750 metres (9,020 feet). The occurrence of chemosynthetic organisms dependent on hydrocarbon seepage has been documented in water depths as shallow as 290 metres (950 feet) and as deep as 2,744 metres (9,003 feet). This depth range specifically places chemosynthetic communities in the deepwater region of the Gulf of Mexico, which is defined as water depths greater than 305 metres (1,001 feet). Chemosynthetic communities are not found on the continental shelf, although they do appear in the fossil record in water shallower than 200 metres (660 feet). One theory explaining this is that predation pressure has varied substantially over the time period involved (Callender and Powell 1999). More than 50 communities are now known to exist in 43 Outer Continental Shelf (OCS) blocks.
Inca cuisine originated in pre-Columbian times within the Inca civilization from the 13th to the 16th century. The Inca civilization stretched across many regions on the western coast of South America (specifically Peru), and so there was a great diversity of unique plants and animals used for food. The most important plant staples involved various tubers, roots, and grains; and the most common sources of meat were guinea pigs, llamas, fish, and other aquatic and terrestrial organisms (305-307). Cuisine was heavily influenced by the Inca's food storage system, social gatherings and celebrations, and social status (308-315).
In 2009, Lilly pleaded guilty for illegally marketing antipsychotic medication Zyprexa and agreed to pay a $1.415 billion penalty that included a criminal fine of $515 million, the largest ever in a healthcare case and the largest criminal fine for an individual corporation ever imposed in a US criminal prosecution of any kind at the time. Eli Lilly has faced many lawsuits from people who claimed they developed diabetes or other diseases after taking olanzapine (branded Zyprexa), an antipsychotic medication, as well as by various governmental entities, insurance companies, and others. Internal documents provided to The New York Times revealed that Lilly had downplayed the risks of Zyprexa. According to the documents, 16 percent of people taking Zyprexa gained more than 66 pounds in their first year, a much larger figure than Eli Lilly had shared with doctors. In 2006, Lilly paid $700 million to settle around 8,000 of these lawsuits, and in early 2007, Lilly settled around 18,000 suits for $500 million, which brought the total Lilly had paid to settle suits related to the drug to $1.2 billion. In March 2008, Lilly settled a suit with the state of Alaska, and in October 2008, Lilly agreed to pay $62 million to 32 states and the District of Columbia to settle suits brought under state consumer protection laws. In 2009, four sales representatives for Eli Lilly filed separate qui tam lawsuits against the company for illegally marketing Zyprexa for uses not approved by the Food and Drug Administration.
Zinc is an essential trace element for humans and other animals, for plants and for microorganisms. Zinc is required for the function of over 300 enzymes and 1000 transcription factors, and is stored and transferred in metallothioneins. It is the second most abundant trace metal in humans after iron and it is the only metal which appears in all enzyme classes. In proteins, zinc ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult. Roughly 2–4 grams of zinc are distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, a key factor in prostate gland function and reproductive organ growth. Zinc homeostasis of the body is mainly controlled by the intestine. Here, ZIP4 and especially TRPM7 were linked to intestinal zinc uptake essential for postnatal survival. In humans, the biological roles of zinc are ubiquitous. It interacts with "a wide range of organic ligands", and has roles in the metabolism of RNA and DNA, signal transduction, and gene expression. It also regulates apoptosis. A review from 2015 indicated that about 10% of human proteins (~3000) bind zinc, in addition to hundreds more that transport and traffic zinc; a similar in silico study in the plant Arabidopsis thaliana found 2367 zinc-related proteins.
Sources: en.wikipedia.org
=== Possible complications === Complications are present with an affected or injured system, such as the lesions and long-term inflammation in the pulmonary system, interstitial lung disease (in 88% of cases, severe interstitial lung disease) or pulmonary fibrosis. If the heart is affected, hypertrophy can occur, leading to cardiomegaly. Organs can also be affected (neurological or renal manifestations), and life-threatening conditions can occur. Affected pregnant women should follow careful clinical observation because they are more likely to see disease progression. Those with the disease at the beginning of pregnancy will keep the disease undifferentiated against 25% who progress to a defined disease at the end of pregnancy. In addition, 45% of pregnancies with the disease end in preterm birth.
=== Liver toxicity === Chronic use of kratom can be hepatotoxic, and may cause acute liver injury; symptoms include abdominal discomfort, dark urine, itching and jaundice. Liver injury has been reported with a latency (time from first use to the onset of symptoms) of median 20.6 days. Reported liver biopsies tend to show cholestasis; however, blood biomarkers can show a range of cholestatic, mixed, or hepatocellular injury patterns. Although cases are likely underreported, many users do not seem to develop liver injury, and it is unclear which users are at heightened risk. The mechanism by which kratom causes liver damage in some people is unknown and poorly studied, but a model has been proposed.
== Statement on the Islamic State Offensive in the Middle East (2014) == In August 2014 in the daily newspaper Berliner Zeitung, Kermani called for the Islamic State (IS) in Iraq to be stopped, even by military means. He compared the conflict’s significance to that of World War I and warned of a genocide against Christians, Yazidis, and other religious minorities. In his statement, he emphasized the importance of humanitarian corridors for refugees and warned of a Pol Pot-style version of Islam stretching from the borders of Iran to the Mediterranean coast. In his Peace Prize acceptance speech in October 2015, Kermani called for action against the Islamic State, action that would have to be taken militarily, if necessary, but, above all, through diplomacy and civil society, however, much more resolutely than before. While saying that he was not calling for war, he pointed out that the war could no longer be ended in Syria and Iraq alone. It could only be ended by the powers behind the opposing armies and militias: Iran, Turkey, the Gulf states, Russia, and also the West.
Sources: en.wikipedia.org
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.
Freeze-dried material is kept frozen, often at minus 20 degrees Celsius, and protected from light and moisture. Dissolved peptide is refrigerated for short-term use. Repeated freeze-thaw cycles are avoided.
A certificate of analysis typically lists purity by HPLC, the confirmed mass, appearance, and sometimes water or counter-ion content. It documents results for a specific batch. Details vary by supplier.
The sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code. It combines the tetrapeptide tuftsin with a carboxyl-terminal Pro-Gly-Pro extension. This full sequence identifies the molecule more precisely than the research name.