freeze-thaw cycle is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2025-11-15. Numbers and descriptions here follow the published literature rather than marketing material.
Outside its country of origin the compound is generally handled as a research chemical rather than an approved medicine. No regulatory approval from the United States Food and Drug Administration or the European Medicines Agency has been granted for human use. Identity and purity are normally checked by reverse-phase high-performance liquid chromatography, with mass spectrometry used to confirm the molecular mass. Lyophilised material is stored cold and desiccated, and repeated freeze-thaw cycles are avoided.
Published work on this peptide almost always uses intranasal delivery, with drops or a spray applied to the nasal mucosa. Some animal experiments have used subcutaneous or intraperitoneal injection, and a smaller number have compared routes directly. Oral administration is not a focus of the literature, because short peptides of this size are broken down by digestive enzymes and cross intestinal barriers poorly. How much of an intranasal dose reaches the bloodstream intact in humans remains an open question.
Regulatory status differs sharply by region. Selank holds a Russian marketing authorization, where it is supplied mainly as nasal drops, while authorities elsewhere have not approved it for medical use. Material sold internationally is therefore usually labeled as a research chemical rather than a medicine. Peer-reviewed publications come predominantly from Russian laboratories, and sample sizes are generally small. Whether the compound produces comparable effects under independent, well-controlled replication remains an open question that the broader literature has not settled.
Selank is a synthetic heptapeptide developed in Russia as a structural analogue of tuftsin, a naturally occurring immunomodulatory tetrapeptide. Its sequence, Thr-Lys-Pro-Arg-Pro-Gly-Pro, keeps the tuftsin core at the N-terminus and appends a Pro-Gly-Pro tail. Researchers at the Institute of Molecular Genetics in Moscow synthesized the compound during the 1990s while searching for peptides with combined anxiolytic and immunomodulatory activity. The added tail was intended to resist enzymatic cleavage and prolong the molecule's presence in circulation.
The compound has a calculated molecular weight near 751.9 daltons and carries a net positive charge at physiological pH because of its arginine residue. It dissolves freely in water and in common aqueous buffers, and typically appears as a white or off-white lyophilized powder. The amide backbone makes the molecule susceptible to peptidases, which limits oral use and favors intranasal or parenteral routes. Nomenclature in the literature varies: the substance is also described by the sequence abbreviation TP-7 and by a Russian trade designation.
| Property | Value | Notes |
|---|---|---|
| Common route | Intranasal | Also injected in some animal work |
| Solubility class | Freely soluble in water | Solid form is hygroscopic |
| Typical storage | About -20 degrees Celsius | Keep desiccated and dark |
| Purity method | Reverse-phase HPLC | Reported as area percent |
| Confirmatory method | Mass spectrometry | Verifies expected molecular mass |
Identity and purity are usually assessed by reversed-phase high-performance liquid chromatography, with mass spectrometry used to confirm molecular mass and sequence information. Amino acid analysis and peptide mapping may supplement these methods. Certified reference standards are scarce, and many commercial lots are sold as research chemicals without a pharmacopoeial monograph. Regulatory treatment differs by country: Selank is a registered prescription medicine in Russia, while in the European Union and the United States it is not an approved drug and may fall under research-chemical or unapproved-product frameworks.
Selank is a hydrophilic peptide and dissolves readily in water and in aqueous buffers. The lyophilised powder is typically a white to off-white solid. Because short peptides are prone to hydrolysis and oxidation, handling benefits from limiting exposure to heat, moisture and strong light. Working solutions are commonly prepared in sterile water or saline, and repeated freeze-thaw cycles are avoided to reduce aggregation and loss of activity. These practices reflect general laboratory convention rather than published stability specifications.
Dry powder is normally held at -20 degrees Celsius or lower, in a sealed container with desiccant and protection from light. Reconstituted solutions are usually kept at 2 to 8 degrees Celsius for short periods and frozen for longer ones. Proline residues at several positions are generally associated with some resistance to peptidase attack, but chemical stability still declines at neutral to alkaline pH and at elevated temperature. Exact shelf-life figures are product-specific and are not standardised across suppliers.
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.
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.
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.
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.
Staphylococci are considered to have a creamy consistency, while some Neisseria species are sticky, and colonies of diphtheroid bacteria and beta-hemolytic streptococci are typically dry. Bacteria that produce capsules often have a slimy (mucoid) consistency. When certain microorganisms are grown on blood agar, they may digest the blood in the medium, causing visible hemolysis (destruction of red blood cells) on the agar plate. In colonial morphology, hemolysis is classified into three types: alpha-, beta-, and gamma-hemolysis. In alpha-hemolysis, the blood is partially digested, causing the area around the colony to turn green. In beta-hemolysis, the organism digests the blood completely, leaving a clear area around each colony. Organisms that do not produce hemolysis are referred to as gamma-hemolytic. Clostridium perfringens, which causes gas gangrene, is noteworthy for producing a "double zone" of both complete and incomplete hemolysis. The odour of a culture is sometimes considered part of colonial morphology. While intentionally smelling microbial cultures is not advised, some organisms produce distinctive odours that can be detected during routine examination of the culture. Among these are Pseudomonas aeruginosa, which has a grape-like scent; Staphylococcus aureus, which is said to smell like old socks; and Proteus mirabilis, whose scent is alternately described as putrid or like chocolate cake. Other distinctive features of colonial morphology include motility and the production of pigments.
== See also == Loperamide - an μ-opioid receptor agonist that doesn't cross the BBB in significant amounts, and treats diarrhea (in contrast to methynaltrexone, a Mu-opioid receptor antagonist that doesn't cross the BBB, avoiding opiate withdrawal effects in patients, while treating constipation) Naloxegol (trade names Movantik and Moventig) - another peripherally selective opioid antagonist used to treat opioid-induced constipation (+)-Naloxone - a non-opioid drug which also reduces some side effects of opioids without significantly affecting analgesia when used in small oral doses 6β-Naltrexol (6α-hydroxynaltrexone) - another naltrexone derivative that is also a peripherally selective opioid antagonist
== A priori therapeutic drug monitoring == A priori TDM consists of determining the initial dose regimen to be given to a patient, based on clinical endpoint and on established population pharmacokinetic–pharmacodynamic (PK/PD) relationships. These relationships help to identify sub-populations of patients with different dosage requirements, by utilizing demographic data, clinical findings, clinical chemistry results, and/or, when appropriate, pharmacogenetic characteristics.
== See also == Acidosis Acids in wine: tartaric, malic and citric are the principal acids in wine. Alkalosis Arterial blood gas Chemical equilibrium Conductivity (electrolytic) Grotthuss mechanism: how protons are transferred between hydronium ions and water molecules, accounting for the exceptionally high ionic mobility of the proton (animation). Hammett acidity function: a measure of acidity that is used for very concentrated solutions of strong acids, including superacids. Ion transport number Ocean acidification: dissolution of atmospheric carbon dioxide affects seawater pH. The reaction depends on total inorganic carbon and on solubility equilibria with solid carbonates such as limestone and dolomite. Law of dilution pCO2 pH Predominance diagram: relates to equilibria involving polyoxyanions. pKa values are needed to construct these diagrams. Proton affinity: a measure of basicity in the gas phase. Stability constants of complexes: formation of a complex can often be seen as a competition between proton and metal ion for a ligand, which is the product of dissociation of an acid.
== Music and lyrics == With songs written primarily on the road, the material is darker than Facelift. "We did a lot of soul searching on this album. There's a lot of intense feelings." Cantrell said, "We deal with our daily demons through music. All of the poison that builds up during the day we cleanse when we play". Drug use was front and center as a lyrical theme on the album. Three tracks ("Junkhead", "God Smack", and "Hate to Feel") specifically reference heroin use and its effects. Staley revealed that the album is semi-conceptual and that there are two basic themes in it. The first theme is about "dealing with kind of a personal anguish and turmoil, which turns into drugs to ease that pain, and being confident that that was the answer in a way. Then later on the songs start to slip down closer and closer to hell, and then he figures out that drugs were not, and are not, the way to ease that pain. Basically, it's the whole story of the last three years of my life." Staley described the other theme as being about "painful relationships and involvements with persons." Staley later expressed regret about the lyrical content of some songs on Dirt, explaining, "I wrote about drugs, and I didn't think I was being unsafe or careless by writing about them ... I didn't want my fans to think that heroin was cool. But then I've had fans come up to me and give me the thumbs up, telling me they're high. That's exactly what I didn't want to happen." Cantrell said in 2013: "That darkness was always part of the band, but it wasn't all about that.
Sources: en.wikipedia.org
== Biography == Stephen Kent received his chemistry Ph.D. from the University of California, Berkeley in 1975, his M.Sc. from Massey University, Palmerston North, New Zealand in 1970, and his B.Sc. degree in 1968 from Victoria University of Wellington, New Zealand. Following post-doctoral work in the laboratory of Robert Bruce Merrifield at the Rockefeller University, Stephen Kent continued research there as an assistant professor through 1981. He has also held faculty positions at the California Institute of Technology, Bond University in Australia, and The Scripps Research Institute in California. Currently, Stephen Kent is Professor Emeritus of Biochemistry and Molecular Biology and Professor Emeritus of Chemistry at the University of Chicago, where from 2003-2009 he served as Director of the Institute for Biophysical Dynamics. In addition to his academic achievements, in the 1990s Kent was the founder of two San Francisco Bay Area biotech companies: Ciphergen Biosytems and Gryphon Sciences. Stephen Kent has received international recognition for his research achievements.
== Further reading == Mullbacher A, Waring P, Eichner RD (1985). "Identification of an Agent in Cultures of Aspergillus fumigatus Displaying Anti-phagocytic and Immunomodulating Activity in vitro". Microbiology. 131 (5): 1251–1258. doi:10.1099/00221287-131-5-1251. PMID 2410548. Shah DT, Larsen B (1991). "Clinical isolates of yeast produce a gliotoxin-like substance". Mycopathologia. 116 (3): 203–208. doi:10.1007/BF00436836. PMID 1724551. S2CID 12919491. Jones RW, Hancock JG (1988). "Mechanism of Gliotoxin Action and Factors Mediating Gliotoxin Sensitivity". Microbiology. 134 (7): 2067–2075. doi:10.1099/00221287-134-7-2067. Schweizer M, Richter C (1994). "Gliotoxin Stimulates Ca2+ Release from Intact Rat Liver Mitochondria". Biochemistry. 33 (45): 13401–13405. doi:10.1021/bi00249a028. PMID 7524661. Scharf DH, Brakhage AA, Mukherjee PK (2016). "Gliotoxin - bane or boon?". Environmental Microbiology. 18 (4): 1096–1109. Bibcode:2016EnvMi..18.1096S. doi:10.1111/1462-2920.13080. PMID 26443473. Puri A, Ahmad A, Panda BP (2009). "Development of an HPTLC-based diagnostic method for invasive aspergillosis". Biomedical Chromatography. 24 (8): 887–92. doi:10.1002/bmc.1382. PMID 20033890.
=== Meteoritic quinones === A proposed alternative source to chemiosmotic energy developing across membranous structures is if an electron acceptor, ferricyanide, is within a vesicle and the electron donor is outside, quinones transported by carbonaceous meteorites pick up electrons and protons from the donor. They would release electrons across the lipid membrane by diffusion to ferricyanide within the vesicles and release protons which produces gradients above pH 2, the process is conducive to the development of proton gradients.
==== Breast-filler toxicity ==== Biological risks to the health of a sucking infant arise from the possibility of breast-filler toxicity, that the filler-material (saline solution or silicone gel) might leak from the breast-implant into the body of the mother, then into her breast milk, and then into the infant organism; yet the biological risk to the breastfeeding infant is minimal, because silicone is indigestible and saline-solution is digestible. The study Silicone Breast Implants and Breastfeeding (1996) indicated that possible medical complications that impede breastfeeding can arise among women with silicone-filled prosthetic breasts, and found no causal relation between the presence of breast prostheses and neurological and physical impairment of the breastfeeding function of the augmented breasts.
== Treatment == There is no cure for McLeod syndrome; the treatment is supportive depending on symptoms. Medication may assist with management of epilepsy, and cardiac and psychiatric features, although patients may respond poorly to treatment for chorea.
Sources: en.wikipedia.org
==== Bones ==== Together with [18F]sodium floride, PET for bone imaging has been in use for 60 years for measuring regional bone metabolism and blood flow using static and dynamic scans. Researchers have recently started using [18F]sodium fluoride to study bone metastasis as well.
To distribute the compressive forces exerted on the heel during gait, and especially the stance phase when the heel contacts the ground, the sole of the foot is covered by a layer of subcutaneous connective tissue up to 2 cm thick (under the heel). This tissue has a system of pressure chambers that both acts as a shock absorber and stabilises the sole. Each of these chambers contains fibrofatty tissue covered by a layer of tough connective tissue made of collagen fibers. These septa ("walls") are firmly attached both to the plantar aponeurosis above and the sole's skin below. The sole of the foot is one of the most highly vascularized regions of the body surface, and the dense system of blood vessels further stabilize the septa.
Acute poisoning can be fatal, leading to cardiovascular collapse and death in 2–18 hours, and in general, is treated using a symptomatic and supportive approach. Diagnosis of toxicity is based on history and clinical presentation, and in general, precise plasma levels do not appear to provide useful relevant clinical information. Several levels of evidence strongly indicate diphenhydramine (similar to chlorpheniramine) can block the delayed rectifier potassium channel and, as a consequence, prolong the QT interval, leading to cardiac arrhythmias such as torsades de pointes. No specific antidote for diphenhydramine toxicity is known, but the anticholinergic syndrome has been treated with physostigmine for severe delirium or tachycardia. Benzodiazepines may be administered to decrease the likelihood of psychosis, agitation, and seizures in people who are prone to these symptoms.
Drug Delivery: Developing Countries The drug delivery mechanisms have the potential to enhance the health of all parts of the world despite the fact that most of the advanced systems are quite costly to the poor nations. Simple system, orals or skin patch, is more feasible in low resource countries. Most countries have used vaccines that are administered orally to combat such diseases as polio (Yenet et al., 2023). The government and the hospital organizations need to collaborate in order to reduce the cost and offer the new means of drug distribution that will allow giving the new medications everywhere. Ethical and Safety Issues Emerging drug delivery devices such as nanoparticles or gene therapies are highly dangerous in terms of safety and equity. For example, we should make sure that the treatments would not negatively affect the environment or cause any incidental side effects. The regulation of other agencies such as FDA are applied in the process of ensuring the safety of new practices but vary across countries (World Health Organization, 2024). The government has the mandate of making sure that medicine is not only affordable to the wealthy members of the society, but also to the vulnerable ones as well. The issue of drug delivery has raised a number of ethical concerns with respect to patients and healthcare systems. One common concern is the accessibility of specific medications within a health organization.
Sources: en.wikipedia.org
Most published work uses intranasal application, either as drops or as a nasal spray. Injection routes appear in a smaller set of animal experiments. Oral use is uncommon in the literature because peptide breakdown and poor absorption limit this route.
Reported human trials are few, brief and originate mainly from one country. They describe effects on anxiety-related measures, but sample sizes are small and reporting is limited. The results are widely regarded as preliminary rather than confirmed.
Reverse-phase liquid chromatography is used to assess purity and separation of related impurities. Mass spectrometry confirms that the observed molecular mass matches the expected peptide. A certificate of analysis from the supplier is the usual document of record.
Selank is a synthetic seven-amino-acid peptide modeled on tuftsin, a fragment of the immunoglobulin G heavy chain. It was designed in Russia to combine anxiolytic and immunomodulatory properties in one molecule.