The short version of freeze-thaw fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-12-29. Anything still debated is marked as such rather than presented as settled.
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.
Pharmacokinetic data are sparse and largely derived from animal work. After intranasal administration the peptide appears in plasma within minutes, and reported half-lives are short, on the order of minutes to tens of minutes. Degradation proceeds through ordinary proteolytic cleavage into constituent amino acids and smaller fragments. Direct evidence that intact Selank reaches brain tissue in meaningful amounts is limited, and the extent of blood-brain barrier penetration is debated. Some authors argue that fragments, not the parent peptide, carry much of the observed activity.
Published clinical work is concentrated in Russian-language journals and generally involves small samples without independent replication. Systematic reviews in English note the shortage of randomised, placebo-controlled trials and the difficulty of verifying methods from translated reports. Outcome measures vary between studies, which complicates pooling of results. Interest in the compound as a cognitive or anxiolytic agent therefore rests on a thinner evidence base than the volume of citations suggests. Replication in well-powered trials with preregistered endpoints would be needed before firm conclusions about efficacy can be drawn.
Proposed mechanisms centre on the GABAergic system. Animal and tissue studies report changes in GABA-A receptor expression and reduced activity of GABA transaminase, the enzyme that degrades GABA. Effects on monoamine turnover, including serotonin and dopamine pathways, are also described, and a separate line of work links the peptide to increased expression of brain-derived neurotrophic factor in hippocampal tissue. Most of these findings come from rodent models and cell preparations. How the individual observations combine into a single coherent mode of action is not settled.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic heptapeptide | Analog of the tetrapeptide tuftsin |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Reported consistently across pharmacopoeial descriptions |
| Appearance | White to off-white lyophilized powder | Typical form of research-grade material |
| Solubility | Freely soluble in water | Aqueous buffers; poor in nonpolar solvents |
| Typical storage temperature | -20 degrees Celsius | Lyophilized powder; protect from moisture |
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.
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.
Quality assessment of Selank samples typically combines purity determination with identity confirmation and counter-ion analysis. Purity is usually reported as a percentage by chromatographic area, with values above 95 percent often quoted for research-grade material. Water content and residual solvents are checked in lyophilized batches because they affect both stability and accurate mass determination. A reported purity figure does not by itself establish that a sample is the intended sequence, so orthogonal methods are needed to rule out sequence isomers or truncation products.
Characterization of Selank in laboratory settings relies on standard peptide analytical techniques. Reverse-phase high-performance liquid chromatography separates the peptide from related impurities and degradation products, while mass spectrometry confirms molecular identity through accurate mass measurement. Amino acid analysis and peptide sequencing verify the primary structure when reference material is unavailable. Because Selank is a short chain, fragmentation-based analysis produces a diagnostic ion pattern that supports confident identification.
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.
Flashbacks are psychological episodes where individuals re-experience some of LSD's subjective effects after the drug has worn off, persisting for days or months post-hallucinogen use. These experiences are associated with hallucinogen persisting perception disorder (HPPD), where flashbacks occur intermittently or chronically, causing distress or functional impairment. The etiology of flashbacks is varied. Some cases are attributed to somatic symptom disorder, where individuals fixate on normal somatic experiences previously unnoticed before drug consumption. Other instances are linked to associative reactions to contextual cues, similar to responses observed in individuals with past trauma or emotional experiences. The risk factors for flashbacks remain unclear, but pre-existing psychopathologies may be significant contributors. Estimating the prevalence of HPPD is challenging. It is considered rare, with occurrences ranging from 1 in 20 users experiencing the transient and less severe type 1 HPPD, to 1 in 50,000 for the more concerning type 2 HPPD. Contrary to internet rumors, LSD is not stored long-term in the spinal cord or other parts of the body. Pharmacological evidence indicates LSD has a half-life of 175 minutes and is metabolized into water-soluble compounds like 2-oxo-3-hydroxy-LSD, eliminated through urine without evidence of long-term storage. Clinical evidence also suggests that chronic use of SSRIs can potentiate LSD-induced flashbacks, even months after stopping LSD use.
An important technique for characterizing metal carbonyls is infrared spectroscopy. The C–O vibration, typically denoted νCO, occurs at 2143 cm−1 for carbon monoxide gas. The energies of the νCO band for the metal carbonyls correlates with the strength of the carbon–oxygen bond, and inversely correlated with the strength of the π-backbonding between the metal and the carbon. The π-basicity of the metal center depends on a lot of factors; in the isoelectronic series (titanium to iron) at the bottom of this section, the hexacarbonyls show decreasing π-backbonding as one increases (makes more positive) the charge on the metal. π-Basic ligands increase π-electron density at the metal, and improved backbonding reduces νCO. The Tolman electronic parameter uses the Ni(CO)3 fragment to order ligands by their π-donating abilities. The number of vibrational modes of a metal carbonyl complex can be determined by group theory. Only vibrational modes that transform as the electric dipole operator will have nonzero direct products and are observed. The number of observable IR transitions (but not their energies) can thus be predicted. For example, the CO ligands of octahedral complexes, such as Cr(CO)6, transform as a1g, eg, and t1u, but only the t1u mode (antisymmetric stretch of the apical carbonyl ligands) is IR-allowed. Thus, only a single νCO band is observed in the IR spectra of the octahedral metal hexacarbonyls. Spectra for complexes of lower symmetry are more complex. For example, the IR spectrum of Fe2(CO)9 displays CO bands at 2082, 2019 and 1829 cm−1.
An ultra low temperature (ULT) freezer is a refrigerator that stores contents at −80 to −86 °C (−112 to −123 °F). An ultra low temperature freezer is commonly referred to as a "minus 80 freezer" or a "negative 80 freezer", referring to the most common temperature standard. ULT freezers come in upright and chest freezer formats.
=== May === May 15, 2009: France, Austria, Belgium, Romania, Lithuania, Luxembourg, Portugal, Hungary The French Institute of Statistics and Economic Studies announced that French gross domestic product shrank 1.2% in the first quarter of 2009 after falling by 1.5% in the final quarter of 2008. The French economy had avoided narrowly a recession in 2008. The GDP is expected to keep shrinking in 2009. Eurostat also reported at this time that Austria, Belgium, and Romania had all entered recession in the first quarter of 2009, with two consecutive quarters of shrinking GDP, while Lithuania, Luxembourg, and Portugal had already done so in the last quarter of 2008 and Hungary in the quarter before that.
Sources: en.wikipedia.org
The energy in sunlight is captured by plants, cyanobacteria, purple bacteria, green sulfur bacteria and some protists. This process is often coupled to the conversion of carbon dioxide into organic compounds, as part of photosynthesis, which is discussed below. The energy capture and carbon fixation systems can, however, operate separately in prokaryotes, as purple bacteria and green sulfur bacteria can use sunlight as a source of energy, while switching between carbon fixation and the fermentation of organic compounds. In many organisms, the capture of solar energy is similar in principle to oxidative phosphorylation, as it involves the storage of energy as a proton concentration gradient. This proton motive force then drives ATP synthesis. The electrons needed to drive this electron transport chain come from light-gathering proteins called photosynthetic reaction centres. Reaction centers are classified into two types depending on the nature of photosynthetic pigment present, with most photosynthetic bacteria only having one type, while plants and cyanobacteria have two. In plants, algae, and cyanobacteria, photosystem II uses light energy to remove electrons from water, releasing oxygen as a waste product. The electrons then flow to the cytochrome b6f complex, which uses their energy to pump protons across the thylakoid membrane in the chloroplast. These protons move back through the membrane as they drive the ATP synthase, as before. The electrons then flow through photosystem I and can then be used to reduce the coenzyme NADP+.
Oral fibromas are also termed irritation fibromas, focal fibrous hyperplasia, and traumatic fibromas. These lesions are nodules that occur on the buccal mucosa (i.e. mucous membranes lining the cheeks and back of the lips) or lateral tongue. They may be irritating or asymptomatic and are the most common tumor-like lesions in the oral cavity. Oral fibromas are not neoplasms; they are hyperplastic (i.e. overgrowth) reactions of fibrous tissue to local trauma or chronic irritation.
=== Entry into bacteria === Penicillin can easily enter bacterial cells in the case of gram-positive species. This is because Gram-positive bacteria do not have an outer cell membrane and are simply enclosed in a thick cell wall. Penicillin molecules are small enough to pass through the spaces of glycoproteins in the cell wall. For this reason Gram-positive bacteria are very susceptible to penicillin (as first evidenced by the discovery of penicillin in 1928). Penicillin, or any other molecule, enters gram-negative bacteria in a different manner. The bacteria have thinner cell walls but the external surface is coated with an additional cell membrane, called the outer membrane. The outer membrane is a lipid layer (lipopolysaccharide chain) that blocks passage of water-soluble (hydrophilic) molecules like penicillin. It thus acts as the first line of defence against any toxic substance, which is the reason for relative resistance to antibiotics compared to gram-positive species. But penicillin can still enter gram-negative species by diffusing through aqueous channels called porins (outer membrane proteins), which are dispersed among the fatty molecules and can transport nutrients and antibiotics into the bacteria. Porins are large enough to allow diffusion of most penicillins, but the rate of diffusion through them is determined by the specific size of the drug molecules. For instance, penicillin G is large and enters through porins slowly; while smaller ampicillin and amoxicillin diffuse much faster.
== Preparation == DraxImage MAA kits for preparing 99mTc-MAA are available in the United States from only a single manufacturer; Jubilant DraxImage Inc. The kits are delivered to nuclear pharmacies as lyophilized powders of non-radioactive ingredients sealed under nitrogen. A nuclear pharmacist adds anywhere from 50 - 100 mCi of Na[99mTcO4] to the reaction vial to make the final product, in the pH range of 3.8 to 8.0. After being allowed to react at room temperature for 15 minutes to ensure maximum labeling of the human albumin with 99mTc, the kit can then be diluted with sterile normal saline as needed. Once prepared the product will have a turbid white appearance.
=== Foreign nationals === The people on death row include foreign nationals, many of whom were convicted of drug-related offences. These inmates come from a diverse range of countries, including Australia, Bangladesh, China, Ghana, India, Indonesia, Malaysia, the Netherlands, Nigeria, Pakistan, the Philippines, Portugal, Sri Lanka, Thailand, the United Kingdom, and Vietnam. Figures released by the Singapore government show that between 1993 and 2003, 36% of those executed were foreigners, including some residents in Singapore (half of Singapore residents are foreigners).
Sources: en.wikipedia.org
This abnormal chromosome was dubbed the Philadelphia chromosome - as both scientists were doing their research in Philadelphia, Pennsylvania. Thirteen years later, with the development of more advanced techniques, the abnormal chromosome was shown by Janet Rowley to be the result of a translocation of chromosomes 9 and 22. Identification of the Philadelphia chromosome by cytogenetics is diagnostic for CML. More than 780 leukemias and hundreds of solid tumors (lung, prostate, kidney, etc.) are now characterized by an acquired chromosomal abnormality, whose prognostic value is crucial. The identification of these chromosomal abnormalities has led to the discovery of a very large number of "cancer genes" (or oncogenes). The increasing knowledge of these cancer genes now allows the development of targeted therapies, which transforms the prospects of patient survival. Thus, cytogenetics has had and continues to have an essential role in the progress of cancer understanding. Large databases (Atlas of Genetics and Cytogenetics in Oncology and Haematology, COSMIC cancer database, Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer) allow researchers and clinicians to have the necessary corpus for their work in this field.
== Indications == There are no clinical guidelines outlining the use and implementation of opioid rotation. However, this strategy is commonly used for these various situations: pain not controlled by current opioid, pain controlled but in the presence of intolerable adverse events, pain not controlled despite rapid increase in opioid dose, switching to utilize different alternative routes of administration, or switching due to high cost of current opioid (or other patient-specific cost considerations).
=== National infrastructure === The WHO has implemented an "Effective Vaccine Management" system, which includes constructing priorities to prepare national and subnational personnel and facilities for vaccine distribution, including:
=== Mechanisms of moisture movement === Water in wood normally moves from zones of higher to zones of lower moisture content. Drying starts from the exterior of the wood and moves towards the centre, and drying at the outside is also necessary to expel moisture from the inner zones of the wood. Wood subsequently attains equilibrium with the surrounding air in moisture content.
Sources: en.wikipedia.org
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.
The first four residues of Selank reproduce the tuftsin sequence Thr-Lys-Pro-Arg. A Pro-Gly-Pro extension at the C-terminus was added to slow enzymatic breakdown and extend residence time.
It holds marketing authorization in Russia, where nasal drop formulations are sold. No equivalent approval exists in the European Union, the United States, or most other countries.
Reports describe modulation of GABA signalling, changes in monoamine turnover and effects on neurotrophic factor expression. These observations come mainly from animal and cell studies. A single unifying mechanism has not been demonstrated.