freeze-thaw 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 2025-11-11. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. It was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences as a structural analogue of tuftsin, a naturally occurring tetrapeptide fragment of the immunoglobulin heavy chain. The added Pro-Gly-Pro tail was intended to slow enzymatic degradation and extend biological activity. In Russia it is registered as an anxiolytic nasal preparation, while regulators elsewhere have not approved it for clinical use.
Proposed mechanisms centre on modulation of the GABAergic system, with reports of altered expression of genes related to GABA-A receptor subunits and changed monoamine turnover. Some studies describe inhibition of enkephalinase, the enzyme that degrades endogenous enkephalins, which may prolong opioid peptide signalling. Effects on brain-derived neurotrophic factor and on cytokine expression have also been reported. These findings come largely from animal models and small human studies, and the precise primary target remains unresolved.
Published clinical evidence is limited. Most controlled trials were conducted in Russia, enrolled modest numbers of participants, and appeared in Russian-language journals, which restricts independent verification. Reported outcomes include lower anxiety scores, improved attention and memory measures, and changes in fatigue ratings. Reviews written in English note methodological limitations such as small samples and inconsistent endpoints. Whether the compound produces clinically meaningful benefit relative to established anxiolytics is therefore an open question rather than an established finding.
| Property | Value | Notes |
|---|---|---|
| Identity confirmation | Reversed-phase HPLC retention time versus reference standard | Retention depends on column, gradient, and ion-pairing agent |
| Mass confirmation | Electrospray or MALDI mass spectrometry | Doubly protonated ion near m/z 377 is consistent with about 752 Da |
| Typical purity specification | 95 percent or higher by chromatographic peak area | Lower values suggest truncated or modified peptide species |
| Storage of lyophilized powder | -20 °C, desiccated, protected from light | Powder tolerates long storage better than solution |
| Storage of solution | 2-8 °C for short periods | Freeze-thaw cycling promotes aggregation and surface adsorption |
The primary structure of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, corresponding to the molecular formula C33H57N11O9 and a monoisotopic mass of roughly 751.9 daltons. The N-terminal threonine and the arginine residue in the fourth position are shared with tuftsin, which carries the sequence Thr-Lys-Pro-Arg. The three additional residues at the C-terminus, Pro-Gly-Pro, extend the chain and are associated with greater resistance to enzymatic degradation. This extension also separates Selank from the shorter parent peptide.
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.
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.
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.
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 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.
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.
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.
The use of high-resolution ion-mobility mass spectrometry (IMS-MS) on HPLC-purified alpha-synuclein in vitro has shown alpha-synuclein to be autoproteolytic (self-proteolytic), generating a variety of small molecular weight fragments upon incubation. The 14.46 kDa protein was found to generate numerous smaller fragments, including 12.16 kDa (amino acids 14–133) and 10.44 kDa (40–140) fragments formed through C- and N-terminal truncation and a 7.27 kDa C-terminal fragment (72–140). The 7.27 kDa fragment, which contains the majority of the NAC region, aggregated considerably faster than full-length alpha-synuclein. It is possible that these autoproteolytic products play a role as intermediates or cofactors in the aggregation of alpha-synuclein in vivo.
Tbr1 forms a complex with CASK and regulates gene expression in cortical development. Tbr1 binds to the guanylate kinase (GK) domain of CASK. It was determined that the C-terminal domain of Tbr1 in crucial and solely capable of this process. Through luciferase reporter assays of neurons in the hippocampus, it was found that increased Tbr1/CASK complex expression results in enhanced promoter activity in genes downstream of TBR1 such as NMDAR subunit 2b (NMDAR2b), glycine transporter, interleukin-7 receptor (IL-7R) and OX-2 genes. NMDAR2b experienced the greatest change in activity. Tbr1 and CASK also play an important role in activation of the RELN gene. One study suggests that CASK acts as a coactivator of TBR1, interacting with CINAP (CASK-interacting nucleosome assembly protein) to form a complex with Tbr1. The Tbr1/CASK/CINAP complex regulates expression of NMDAR2b and RELN, which both play important roles in long-term potentiation. Sox5 is another co-regulatory protein of Tbr1. Sox5 is a marker of layer VI neurons in the neocortex. It aids in the suppression of layer V neuron identity within layer VI cortical neurons through suppression of Fezf2. TBR1 is involved in the downstream regulation of Sox5. Sox5 expression was reduced in Tbr1 null mutants. It has been found that Sox5 interacts with Tbr1 to regulate Fezf2 transcription in layer VI cortical neurons.
Dehydroepiandrosterone (DHEA) is a steroid hormone produced by the adrenal glands (and by the testes in men), which can be converted in the body to male and female sex hormones, including estrogen and testosterone. DHEA is used to treat a variety of conditions (without FDA approval) including aging, Alzheimer's disease, schizophrenia, erectile dysfunction, systemic lupus erythematosus, and for aiding in weight loss. There is insufficient data to support DHEA’s efficacy for weight loss. The DHEA content in the daily recommended dose of Dexatrim Max ranges from 100–200 mg per day. Side effects at this dose can include acne, hair loss, facial hair growth and deeper voice in women, stomach upset, and high blood pressure, particularly if the supplement is used for a longer period of time. There are many conditions in which DHEA use has special precautions and warnings. These include pregnancy and breast-feeding, hormone-sensitive conditions and cancers, liver problems, diabetes, and cholesterol problems. DHEA use is banned by the National Collegiate Athletic Association (NCAA).
Sources: en.wikipedia.org
== Causes == Lactose intolerance is a consequence of lactase deficiency, which may be genetic (primary hypolactasia and primary congenital alactasia) or environmentally induced (secondary or acquired hypolactasia). In either case, symptoms are caused by insufficient levels of lactase in the lining of the duodenum. Lactose, a disaccharide molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream, so, in the absence of lactase, passes intact into the colon. Bacteria in the colon can metabolise lactose, and the resulting fermentation produces copious amounts of gas (a mixture of hydrogen, carbon dioxide, and methane) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raise the osmotic pressure of the colon, causing an increased flow of water into the bowels (diarrhea). Lactose intolerance in infants (congenital lactase deficiency) is caused by mutations in the LCT gene. The LCT gene provides the instructions for making lactase. Mutations are believed to interfere with the function of lactase, causing affected infants to have a severely impaired ability to digest lactose in breast milk or formula. Lactose intolerance in adulthood is a result of gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans. The specific DNA sequence in the MCM6 gene helps control whether the LCT gene is turned on or off.
=== Labor relations === In 2010, when the Industrial Workers of the World attempted to unionize ten Minneapolis locations, The New York Times called the effort "one of the few efforts to organize fast-food workers in American history". In July 2017, the United States Court of Appeals for the Eighth Circuit found that the National Labor Relations Act did not protect Jimmy John's employees from being fired for exhibiting legally disloyal conduct by attacking the company's product to oppose a franchisee's sick leave policy. In October 2014, it was revealed that employees at Jimmy John's, including sandwich makers and delivery drivers, were required to sign non-compete agreements as a condition of employment. The agreement restricted the employee from working for a competitor for two years, where a competitor was defined as a business that derives more than ten percent of its revenue from selling sandwiches and is located within three miles of any Jimmy John's. Additionally, the employee could not work for another Jimmy John's franchisee for a year. Jimmy John's has since settled related lawsuits filed by the Attorneys General of New York and Illinois. In statements, the company clarified that it had taken steps to remove non-compete agreements from their new hire paperwork long before they were contacted by the Attorneys General, and that "enforcement of non-compete agreements against our own hourly store employees is not a part of Jimmy John's culture or business model."
Endless Chain Ridge is a 16-kilometre-long (9.9-mile), 2,867-metre-high (9,406-foot), mountainous ridge located in Jasper National Park, in the Canadian Rockies of Alberta, Canada. The ridge is situated at the southern end of the Maligne Range, and east of the confluence of the Sunwapta River with the Athabasca River. Seen from the Icefields Parkway, the ridge is relatively unimpressive, but from the east side it appears as a rugged chain of peaks, all quite difficult to climb.
Ann Lawthom, lately Headteacher, Rhondda Special School, Trealaw, Rhondda. For services to Education. Hilda Blanche Le Cras. For services to Horse Driving for the Disabled and to the Royal British Legion on Guernsey. Elizabeth May Leake. For charitable services in Clenchwarton, Norfolk. William Gordon John Leckie, Managing Director, Cneff Hydro Hotel, Perthshire. For services to the Hotel Industry and to Tourism. Bryan Neville Lee. For services to the Samaritans and to the community in Doncaster. Winifred Elizabeth Lees. For political and public service. Jacqueline Margaret Leete. For services to the community in Headley, Hampshire. Donald Clement Lefever. For services to the Butler Trust. Shiu-Wing Leung, Executive Officer, Ministry of Defence. Joan Lewin. For services to the Historical Association. Ann Lewis, Teacher in Charge, Widden Family Centre, Gloucester. For services to Pre-School Education. Peter Reginald Lewis, Sub-Officer (Retained), North Wales Fire Service. For services to the Fire Service. Maurice George Lihou. For services to Young Handicapped People on Guernsey. Sandra Elizabeth Linnett, lately Sales and Computer Clerk, Kopex International Ltd. For services to Industry. Rose Helena Lloyd. For services to St. David's Church, Hundleton. Adrian Neville Barrett Loach, Assistant Group Scout Leader, Bristol. For services to Scouting. Rebecca McCausland Lockhead. For public service Jean Elizabeth Lockwood. For services to the community in Amersham, Buckinghamshire. The Reverend Roy Frederick Lodge, Chaplain, Her Majesty's Prison Brockhill.
Sources: en.wikipedia.org
The Ukrainian Defence Ministry said that its forces had retaken about 20sq km (7.5sq miles) of territory from Russian forces in the north and south of the outskirts of Bakhmut in recent days while acknowledging continued Russian advances inside the city. The Wagner Group's head Yevgeny Prigozhin claimed that an American citizen was killed fighting in Bakhmut, in a video posted on Telegram that showed him inspecting a body and what he claimed to be US identification documents. In Kharkiv Oblast, two people where killed in another bout of Russian shelling in Dvorichna. South African President Cyril Ramaphosa said both Presidents Putin and Zelenskyy had agreed to receive an African mission that would propose a peace plan. He said the plan was backed by the presidents of Senegal, Uganda and Egypt and that UN Secretary-General António Guterres, the United States and the United Kingdom had also been briefed. The commander of the land forces of the South African National Defence Force, Lieutenant-General Lawrence Mbatha, visited Moscow. A Moscow court sentenced Colombian resident and Russian passport-holder Alberto Enrique Giraldo Saray to five years and two months in prison for spreading "fake news" about the actions of the Russian military in Ukraine. The US State Department condemned the arrest of a local embassy employee in Russia for alleged spying.
The role that microRNAs play in cancer development and metastasis is under much scientific investigation and it is yet to be demonstrated whether microRNA mimics or antagomirs may serve as standard clinical treatments to suppress EMT or oncogenic microRNAs in cancers.
=== Burnt sugars and caramels === Heating sugar to near 200 °C for several minutes yields a product called burnt sugar. Often additives are used to modify the resulting caramels, e.g. alkali or sulfites. Several volatile products evolve in the heating process including butanone, several furans (2-Acetylfuran, furanone, hydroxymethyl furfural), and levoglucosan and more. Because sugars burn easily when exposed to flame, the handling of sugar powders risks dust explosion. The 2008 Georgia Imperial sugar refinery explosion, which killed 14 people and injured 36, and destroyed most of the refinery, was caused by the ignition of sugar dust.
This is usually done by adding more space to the colony with honey supers, empty boxes placed on top of an existing colony. The bees can then usually be enticed to develop this empty space instead of dividing their colony through swarming.
Bags of potatoes are sometimes stacked in customer spaces due to an occasional lack of storage space, or, in some franchises, for aesthetic reasons. Restaurants are decorated with white and red checkered tile throughout and generally use wooden tables along with counter-high level seating.
Sources: en.wikipedia.org
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.
Lyophilized powder is normally stored desiccated at -20 °C, protected from light and moisture. Powder kept under these conditions is generally stable for long periods. Solutions are less stable and are usually prepared immediately before use.
A purity value from one chromatographic method does not capture every possible impurity. Related peptides with similar retention behavior, counterions, and residual solvents may not appear in the same analysis. Independent testing with an orthogonal method provides stronger assurance of identity and content.
It is a seven-amino-acid peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, produced by chemical synthesis rather than extracted from biological tissue. Its design is based on tuftsin, a natural immunomodulatory tetrapeptide. The C-terminal Pro-Gly-Pro segment is a common stabilising motif in short regulatory peptides.