freeze-thaw 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 2025-10-12. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
Tuftsin, the parent structure, is a naturally occurring immunomodulatory tetrapeptide released from the Fc region of immunoglobulin G by spleen enzymes. Selank extends this four-residue sequence with three additional amino acids. The stated rationale is that the added tail slows enzymatic breakdown and may influence receptor interactions. How the full heptapeptide behaves at the molecular level is not firmly established, and proposed mechanisms often involve indirect modulation of neurotransmitter or immune signaling rather than a single defined target.
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.
| 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 |
Animal studies have examined behaviour in tests of anxiety, memory retention and stress response, and several report changes in neurotrophic or neurotransmitter-related markers. The human evidence base is much smaller, consisting mainly of short trials conducted in Russia with limited reporting in English-language journals. Sample sizes are modest and outcome measures vary between studies, so the findings are best described as preliminary. Independent replication under modern trial standards has not been widely reported.
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.
Naming for this compound is not fully standardised in English sources. The spelling Selanc appears in some transliterations, and catalogue entries may instead list the peptide sequence itself as the identifier. Reference material sometimes groups it with other short synthetic peptides studied for behavioural effects, which can create confusion when citations are compared. Distinguishing the exact sequence from related tuftsin analogues is therefore a practical first step when reviewing any dataset or specification sheet.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, frequently abbreviated as TKPRPGP. It was designed as a structural analogue of tuftsin, a naturally occurring tetrapeptide released by enzymatic cleavage of the immunoglobulin heavy chain. The two additional proline residues at the C-terminal end extend the parent chain and change how the molecule behaves in solution. The free peptide has a calculated molecular mass of approximately 751.9 g/mol and is generally supplied as a lyophilised white to off-white powder.
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.
=== Popular culture === In the 2022 Australian film Everything in Between, the lead character smokes what is implied to be DMT in the opening sequence, which is followed by hallucination-like visual effects and an altered state of consciousness.
Won the Banff best Popular Science award 15 September A Very British Bomb, with interviews with Eddie Howse and John Challens who worked with William Penney at Fort Halstead; Dennis Ginns, reactor design engineer; featured Christopher Hinton (of ICI); Harold Disney of supply; Hinton decided to build the plant at Windscale; Sir John Hill worked on a computer; Tom Tuohy managed the piles; David Deverell was a senior chemical engineer; the core would be made at the new site of Aldermaston, a former RAF airfield; Air Marshal Sir John Rowlands took the two plutonium cores on an Avro Lincoln; Bill Hall, later Professor of Nuclear Engineering from 1959 at the University of Manchester; scientists travelled to Australia on HMS Campania (D48).
=== Animal studies in vivo === An in vivo study in aging mice found that epitalon treatment significantly reduced the incidence of chromosomal aberrations, both for wild-type mice and for mice characterized by an accelerated aging phenotype, which is consistent with increases in telomere length. Another study in aging rats found that epitalon increased the activities of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and glutathione-S-transferase. Epitalon reduced the number of spontaneous tumors and the number of metastases in mice that did develop spontaneous tumors in an experiment on one-year-old female mice of the C3H/He inbred strain, and is speculated to have oncostatic and anti-metastatic properties. In a study of chickens subjected to neonatal hypophysectomy and subsequent maturation, epitalon promoted the recovery of the morphological structures of the thymus, as well as the structure and function of the thyroid gland. Epitalon appears to increase the proliferation of lymphocytes in the thymus, putatively increasing production of interferon gamma by T-cells. Another study in aging rats demonstrated extension of life span for rats subjected to constant illumination or to a natural light regimen typical of northern regions.
=== Type 2 diabetes === There are contradictory reviews. From one, vitamin C supplementation cannot be recommended for management of type 2 diabetes. However, another reported that supplementation with high doses of vitamin C can decrease blood glucose, insulin and hemoglobin A1c.
There are several pressure-lowering medication groups that could be used in lowering the IOP, usually eyedrops. The choice of medication usually depends on the dose, duration, and side effects of each medication. However, in general, prostaglandin analogues are the first-line treatment for glaucoma. Prostaglandin analogues, such as latanoprost, bimatoprost, and travoprost, reduce the IOP by increasing the aqueous fluid outflow through the draining angle. It is usually prescribed once daily at night. The systemic side effects of this class are minimal. However, they can cause local side effects, including redness of the conjunctiva, a change in the iris color, and eyelash elongation. Several other classes of medications could be used as a second-line in case of treatment failure or presence of contraindications to prostaglandin analogues. These include:
Sources: en.wikipedia.org
H2S ⇌ HS− + H+ Hydrogen sulfide gas and the hydrosulfide anion are extremely toxic to mammals, due to their inhibition of the oxygen-carrying capacity of hemoglobin and certain cytochromes in a manner analogous to cyanide and azide.
== Middle Ages == With the fall of the western Roman Empire in 476, Italy was taken over by the Germanic chieftain Odoacer and later became part of the Ostrogothic Kingdom in 489. The Ostrogothic kings ruled officially as Magistri Militum of the Byzantine Emperors. All government and administrative positions were held by Romans, while all primary laws were legislated by the Byzantine Emperor. During the sixth century, under the Ostrogoths' rule, Romans remained the center of government and cultural life. The Roman Cassiodorus, like Boethius and Symmachus, emerged as one of the most prominent men of his time. He was an administrator, politician, scholar and historian who was born in Scylletium (near Catanzaro). He spent most of his career trying to bridge the divides of East and West, Greek and Latin cultures, Romans and Goths, and official Christianity and Arian Christianity, which was the form of Christianity adopted by the Ostrogoths and which had earlier been banned. He established the Vivarium (monastery) in Scylletium. He oversaw the collation of three editions of the Bible in Latin. Seeing the value of collecting all the books of the Bible in one volume, he was the first to produce Latin Bibles in single volumes. The most well-known was the Codex Grandior which became the ancestor of all modern western Bibles. Cassiodorus was the heart of the administration of the Ostrogothic kingdom.
==== Anti-Coercion Instrument ==== Several European leaders including France's Emmanuel Macron advocated using the EU's Anti-Coercion Instrument, a security and trade policy tool known as the "trade bazooka", to target the United States in retaliation. Under the not-previously-used instrument, the EU may adopt countermeasures, sometimes described as sanctions, including tariffs, restrictions on public procurement, and measures affecting trade and investment. Bernd Lange, chair of the European Parliament Committee on International Trade, supported its activation. By 21 January EU countries were described as being increasingly open to using the ACI against the United States, with Germany stating it will ask the Commission to explore its use.
== Clinical significance == Due to their role in phagocytosis, macrophages are involved in many diseases of the immune system. For example, they participate in the formation of granulomas, inflammatory lesions that may be caused by a large number of diseases. Some disorders, mostly rare, of ineffective phagocytosis and macrophage function have been described, for example.
Sources: en.wikipedia.org
Other low-carbohydrate diets in the 1960s included the Air Force diet, "Martinis & Whipped Cream" in 1966, and the Drinking Man's Diet. In 1972, Robert Atkins published Dr. Atkins' Diet Revolution, which advocated the low-carbohydrate diet he had successfully used in treating people in the 1960s. The book was a publishing success, but was widely criticized by the mainstream medical community as being dangerous and misleading, thereby limiting its appeal at the time. The concept of the glycemic index was developed in 1981 by David Jenkins to account for variances in speed of digestion of different types of carbohydrates. This concept classifies foods according to the rapidity of their effect on blood sugar levels – with fast-digesting simple carbohydrates causing a sharper increase and slower-digesting complex carbohydrates, such as whole grains, a slower one. Jenkins's research laid the scientific groundwork for subsequent low-carbohydrate diets. In 1992, Atkins published an update from his 1972 book, Dr. Atkins' New Diet Revolution, and other doctors began to publish books based on the same principles. During the late 1990s and early 2000s, low-carbohydrate diets became some of the most popular diets in the US. By some accounts, up to 18% of the population was using one type of low-carbohydrate diet or another at the peak of their popularity. Food manufacturers and restaurant chains noted the trend, as it affected their businesses.
This early research helped establish that while some morphological features remain stable regardless of environment, others show significant plasticity in response to new conditions. The transplantation technique proved valuable for studying both taxonomic relationships and ecological adaptations in lichens, helping lay groundwork for future experimental studies. In 1986, researchers performed the first complete laboratory resynthesis of X. parietina from its separate fungal and algal components. The experiment involved isolating fungal spores and algal cells, growing them separately, and then allowing them to recombine on an agar substrate. After 8–12 months, the symbionts formed new lichen thalli 2–5 mm across, complete with apothecia. While these artificially created lichens showed a similar basic structure to natural specimens, they differed in some aspects, including paler pigmentation and the absence of some characteristic lichen products. This achievement represented a breakthrough in understanding lichen biology, as successful laboratory synthesis of lichens had been a challenge for over a century.
Osteomimicry occurs when cancer cells begin to express genes normally restricted to cells present within the bone. These genes include osteocalcin, osteopontin, bone sialoprotein, osteonectin, RANK ligand (NF-κB receptor activator) and parathyroid hormone related peptide (PTHrP). This change in gene expression allows cancer cells to avoid detection by the immune system and establish colonies in the bone microenvironment. Cancer cells expressing these genes secrete normal bone ECM protein products, abnormally altering the bone matrix and activity of osteoblasts and osteoclasts in the local microenvironment.
Rubisco side activities can lead to useless or inhibitory by-products. Important inhibitory by-products include xylulose 1,5-bisphosphate and glycero-2,3-pentodiulose 1,5-bisphosphate, both caused by "misfires" halfway in the enolisation-carboxylation reaction. In higher plants, this process causes RuBisCO self-inhibition, which can be triggered by saturating CO2 and RuBP concentrations and solved by Rubisco activase (see below).
ATP4− + H2O ⇌ ADP3− + HPO2−3 + H+ releases ΔG°' = −30.5 kJ/mol (−7.3 kcal/mol) of Gibbs free energy under standard conditions when all metabolite concentrations are 1 mol/L. This may differ under physiological conditions if the reactant and products are not exactly in these ionization states. The values of the free energy released by cleaving either a phosphate (Pi) or a pyrophosphate (PPi) unit from ATP at standard state concentrations of 1 mol/L at pH 7 are:
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.
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.