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 2025-11-06. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
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.
| 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 |
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.
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.
== Universities == According to the 2020 QS World University Rankings, Chulalongkorn University (CU) was ranked 247th in the world and earned the top ranking in Thailand for the seventh consecutive year. Also ranked were Mahidol University (314th), and Chiang Mai University and Thammasat University (both in the 601–650 tranche), and four other Thai universities in the 801–1,000 tranche. The Times Higher Education Asia University Rankings 2018 ranked Mahidol University as the top Thai institution. It ranked 97 of some 350 universities (1=best; 350=lowest). King Mongkut's University of Technology Thonburi was ranked 116, Chulalongkorn University 164, and Suranaree University of Technology 168. Thailand had no other universities in the top 200. Chulalongkorn University was ranked number one in Thailand and 45th in Asia in 2016. Mahidol University was ranked the top Thai university among the top 200 Asian (including Middle Eastern) universities in 2016 by Times Higher Education Asia University Rankings 2016.
=== Parasites === Emus can suffer from both external and internal parasites, but under farmed conditions are more parasite-free than ostriches or rheas. External parasites include the louse Dahlemhornia asymmetrica and various other lice, ticks, mites and flies. Chicks sometimes suffer from intestinal tract infections caused by coccidian protozoa, and the nematode Trichostrongylus tenuis infects the emu as well as a wide range of other birds, causing haemorrhagic diarrhoea. Other nematodes are found in the trachea and bronchi; Syngamus trachea causing haemorrhagic tracheitis and Cyathostoma variegatum causing serious respiratory problems in juveniles.
=== Alternative modulations === The DASH7 Alliance policy forbids the addition of proprietary or licensable modulation techniques in the official DASH7 Alliance Protocol. However, the layered structure of the protocol allows simple integration of alternative modulations, such as LoRa, under the network layer (D7ANL).
Sources: en.wikipedia.org
== Education and early career == Barran went to Godolphin and Latymer School. She moved to the University of Manchester to study chemistry, graduating in 1994. She joined the University of Sussex for her graduate studies, working with Harry Kroto and Tony Stace.
==== International Congress of Refrigeration ==== First held in 1908, the International Congress of Refrigeration of the IIR is a flagship event that converges industry and research. Covering all fields of refrigeration, the Congress, which takes place every four years, reunites key international stakeholders and provides perspectives on the future of the industry in line with sustainable development.
==== Pan Sahel Initiative ==== In 2002, the United States created the Pan Sahel Initiative (PSI) which was aimed at counter-terrorism and enhancing regional peace and security in Mali, Mauritania, Niger and Chad. Green Berets from the 10th SFG attached to Special Operations Command Europe (SOCEUR) of the United States European Command (EUCOM) deployed to Niger and Mali and supervised anti-terror exercises in the Sahara Desert.
Sources: en.wikipedia.org
The new tools of molecular biology changed the study of bird systematics, which changed from being based on phenotype to the underlying genotype. The use of techniques such as DNA–DNA hybridization to study evolutionary relationships was pioneered by Charles Sibley and Jon Edward Ahlquist, resulting in what is called the Sibley–Ahlquist taxonomy. These early techniques have been replaced by newer ones based on mitochondrial DNA sequences and molecular phylogenetics approaches that make use of computational procedures for sequence alignment, construction of phylogenetic trees, and calibration of molecular clocks to infer evolutionary relationships. Molecular techniques are also widely used in studies of avian population biology and ecology.
Diabetes burden and access to care vary widely between and within countries. Between 1990 and 2022, diabetes prevalence rose faster in low and middle income countries than in high-income countries. In 2022, more than half of adults aged 30 and over with diabetes were not taking medication for it, and treatment coverage was lowest in low and middle income countries. A pooled analysis of 1,108 population-based studies estimated that in most countries, especially low and middle income ones, treatment had not increased enough to keep pace with rising prevalence, and that the gap in treatment coverage between the countries widened from 56 percentage points in women and 43 in men in 1990 to 78 and 71 respectively in 2022. WHO reported in 2021 that essential diabetes medicines were available in only about half of facilities in low and lower middle income countries, compared to about 80% of facilities globally. The International Diabetes Federation estimated that 252 million adults aged 20–79 were unaware they had diabetes in 2024. Risk also differs between ethnic groups. South Asian people tend to develop type 2 diabetes earlier in life and often at a normal body mass index. In a study of British Pakistani and British Bangladeshi participants, those with a high genetic risk of both insulin deficiency and unfavourable fat distribution were diagnosed about 8 years earlier, at a BMI about 3 kg/m² lower, than those at low genetic risk. Disparities are also documented for Indigenous peoples.
==== Masculinization in rodents ==== In rodents, estrogens (which are locally aromatized from androgens in the brain) play an important role in psychosexual differentiation, for example, by masculinizing territorial behavior; the same is not true in humans. In humans, the masculinizing effects of prenatal androgens on behavior (and other tissues, with the possible exception of effects on bone) appear to act exclusively through the androgen receptor. Consequently, the utility of rodent models for studying human psychosexual differentiation has been questioned.
==== New Zealand ==== Sildenafil was reclassified in New Zealand in 2014 so it could be bought over the counter from a pharmacist. It is thought that this reduced sales over the Internet and was safer as males could be referred for medical advice if appropriate.
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.
Selank is a seven-amino-acid peptide built from the tuftsin sequence plus a Pro-Gly-Pro tail. It is produced by chemical synthesis rather than extracted from a natural source. The free peptide is usually supplied as a lyophilised powder or in an aqueous formulation.