This is a working overview of freeze-thaw cycle, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-07-30 and is reviewed periodically as new material appears.
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.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Route studied | Intranasal | Predominant route in published reports |
| Circulation stability | Short, minutes scale | Peptidases cleave it; the tail slows the process |
| Analytical method | RP-HPLC with mass spectrometry | Used for identity and purity assessment |
| Reported outcome domains | Anxiety and cognitive measures | Derived from small, mostly regional trials |
| Regulatory status | Marketed in Russia | Availability outside that market is limited |
Development work on the compound began in the 1980s and 1990s at the Institute of Molecular Genetics in Moscow, within the same research programme that produced the peptide Semax. Early investigators sought a tuftsin derivative with improved resistance to enzymatic breakdown and with activity in the central nervous system after peripheral administration. Most of the primary literature from this period was published in Russian, a factor that still shapes how easily the findings can be checked by outside groups.
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.
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.
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.
Reported activity for Selank centers on anxiolytic and nootropic effects. Russian clinical reports describe use in anxiety and in cognitive or attention-related complaints. Most of this evidence comes from studies conducted by the same research groups that developed the peptide. Independent replication in other countries remains limited, and no major Western regulatory agency has approved the compound for any indication. The gap between local reports and external verification is a recurring point in discussions of the peptide.
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.
Chebulagic acid is a benzopyran tannin and an antioxidant that has many potential uses in medicine. It has been found to be immunosuppressive, hepatoprotective, and a potent alpha-glucosidase inhibitor, a human gut enzyme useful in diabetic studies. It has been shown to be active against Staphylococcus aureus and Candida albicans. It is found in the plants Terminalia chebula, T. citrina and T. catappa. It is formed from geraniin through a glutathione-mediated conversion.
=== Additional effects === Semaglutide typically causes a benign increase in resting heart rate (around 3 beats per minute), which has not been associated with adverse cardiovascular events. In January 2026, the US Food and Drug Administration requested removal of suicidal behavior and ideation warning from glucagon-like peptide-1 receptor agonist (GLP-1 RA) medications. A 2024 systematic review of 6 studies found that while lean body mass was unchanged in some cases, there were instances of significant decreases in lean body mass (0–40%). However, the review concluded that in all studies the ratio of lean body mass to total body mass increased, supporting continued use of the medication. After stopping semaglutide, individuals on average regain 67% of the weight they lost during treatment within the following year, according to a 2025 systematic review. People return to their previous weight within a year and a half on average after stopping semaglutide.
==== Other types of T-cell help ==== The type of T-cell help raised is influenced by the delivery method and the type of immunogen expressed, as well as the targeting of different lymphoid compartments. Generally, saline needle injections (either IM or ID) tend to induce TH1 responses, while gene gun delivery raises TH2 responses. This is true for intracellular and plasma membrane-bound antigens, but not for secreted antigens, which seem to generate TH2 responses, regardless of the method of delivery. Generally the type of T-cell help raised is stable over time, and does not change when challenged or after subsequent immunizations that would normally have raised the opposite type of response in a naïve specimen. However, Mor et al.. (1995) immunized and boosted mice with pDNA encoding the circumsporozoite protein of the mouse malarial parasite Plasmodium yoelii (PyCSP) and found that the initial TH2 response changed, after boosting, to a TH1 response.
Sources: en.wikipedia.org
=== Controversy === Use of this class of drugs has a history of criticism in residential care. As the drugs used can make patients calmer and more compliant, critics claim that the drugs can be overused. Outside doctors can feel under pressure from care home staff. In an official review commissioned by UK government ministers it was reported that the needless use of antipsychotic medication in dementia care was widespread and was linked to 1800 deaths per year. In the US, the government has initiated legal action against the pharmaceutical company Johnson & Johnson for allegedly paying kickbacks to Omnicare to promote its antipsychotic risperidone (Risperdal) in nursing homes. There has also been controversy about the role of pharmaceutical companies in marketing and promoting antipsychotics, including allegations of downplaying or covering up adverse effects, expanding the number of conditions or illegally promoting off-label usage; influencing drug trials (or their publication) to try to show that the expensive and profitable newer atypicals were superior to the older cheaper typicals that were out of patent. Following charges of illegal marketing, settlements by two large pharmaceutical companies in the US set records for the largest criminal fines ever imposed on corporations. One case involved Eli Lilly and Company's antipsychotic Zyprexa, and the other involved Bextra. In the Bextra case, the government also charged Pfizer with illegally marketing another antipsychotic, Geodon.
==== Thyrotropin-releasing hormone ==== Thyrotropin-releasing hormone (TRH) is a potent stimulator of prolactin release, acting via phospholipase C to mobilise intracellular calcium and activate protein kinase C. In primary hypothyroidism, elevated TRH stimulates both TSH and prolactin, producing hyperprolactinaemia in approximately 20–40% of hypothyroid patients. However, TRH-knockout mice display normal prolactin levels, indicating that TRH is a modulator rather than an obligate releasing factor.
South African military decorations Military history of South Africa Conscription in South Africa South African military ranks South African National Defence Force South African Police South West African Territorial Force (SWATF)
Approximately 50% of all brain tumors are glioblastomas. Glioblastomas can contain multiple glial cell types, including astrocytes and oligodendrocytes. Glioblastomas are generally considered to be the most invasive type of glial tumor, as they grow rapidly and spread to nearby tissue. Treatment may be complicated, because one tumor cell type may die off in response to a particular treatment while the other cell types may continue to multiply.
Sources: en.wikipedia.org
In Colombia, the laundering of billions of dollars, which come from drug trafficking, is carried out through imports of contraband from the parallel exchange market. In Central American countries such as Guatemala and Honduras, money laundering continues to increase in the absence of adequate legislation and regulations in these countries. Money laundering activities in Costa Rica have experienced substantial growth, especially using large-scale currency smuggling and investments of drug cartels in real estate, within the tourism sector. Furthermore, the Colon Free Zone in Panama, continues to be the area of operations for money laundering where cash is exchanged for products of different nature that are then put up for sale at prices below those of production for a return fast of the capital. In Mexico, the preferred techniques continue to be the smuggling of currency abroad, in addition to electronic transfers, bank drafts with Mexican banks and operations in the parallel exchange market. Money Laundering in the Caribbean countries continues to be a serious problem that seems to be very dangerous. Specifically, in Antigua, the Dominican Republic, Jamaica, Saint Vincent and the Grenadines. Citizens of the Dominican Republic who have been involved in money laundering in the United States, use companies that are dedicated to transferring funds sent to the Dominican Republic in amounts of less than $10,000 under the use of false names. Moreover, in Jamaica, multimillion-dollar asset laundering cases were discovered through telephone betting operations abroad.
=== Additional evidence and deaths === A review of ephedra-related adverse reactions, published in the New England Journal of Medicine in 2000, found a number of cases of sudden cardiac death or severe disability resulting from ephedra use, many of which occurred in young adults using ephedra in the labeled dosages. Subsequently, in response to pressure from the consumer advocacy group Public Citizen, Metabolife was compelled by the Department of Justice in 2002 to turn over reports of over 15,000 ephedra-related adverse events, ranging from insomnia to death, which the company had previously withheld from the FDA. Use of ephedra was considered to have possibly contributed to the death of Minnesota Vikings offensive lineman Korey Stringer from heatstroke in 2001. Steve Bechler, a pitcher for the Baltimore Orioles, died of complications from heatstroke following a spring training workout on February 17, 2003. The medical examiner found that ephedra toxicity played a "significant role" in Bechler's sudden death. Following Bechler's death, the FDA re-opened its efforts to regulate ephedra use. According to Bruce Silverglade, legal director for the Center for Science in the Public Interest, "All of a sudden [after Bechler's death] Congress dropped objections to an ephedra ban and started demanding that the FDA act." Senator Orrin Hatch (R. Utah), who in 1999 had helped block the FDA's attempts to regulate ephedra, said in March 2003 that "...it has been obvious to even the most casual observer that problems exist", and called FDA action to regulate ephedra "long overdue."
=== Head and neck === Due to weakness of the muscles of facial expression and muscles of mastication, facial weakness may manifest as the inability to hold the mouth closed (the "hanging jaw sign") and as a snarling expression when attempting to smile. With drooping eyelids, facial weakness may make the individual appear sleepy or sad. Difficulty in holding the head upright may occur.
==== 900–999 ==== Act of Sederunt (Rules of the Court of Session Amendment No. 2) (Fees of Solicitors) 1993 (S.I. 1993/900) Further Education (Exclusion of Land from Transfer) Order 1993 (S.I. 1993/901) Greater Manchester and Lancashire (County and Metropolitan Borough Boundaries) Order 1993 (S.I. 1993/902) Dyfed-Powys Police (Amalgamation) (Amendment) Order 1993 (S.I. 1993/909) National Rivers Authority (Anglian Region) (Reconstitution of the Witham Third District Internal Drainage Board) Order 1993 (S.I. 1993/910) Plymouth Development Corporation (Area and Constitution) Order 1993 (S.I. 1993/911) Electricity (Restrictive Trade Practices Act 1976) (Exemption) Order 1993 (S.I. 1993/912) Child Support (Miscellaneous Amendments) Regulations 1993 (S.I. 1993/913) Act of Sederunt (Child Support Act 1991) (Amendment of Ordinary Cause and Summary Cause Rules) 1993 (S.I. 1993/919) Act of Sederunt (Child Support Rules) 1993 (S.I. 1993/920) Act of Sederunt (Bankruptcy Rules) 1993 (S.I. 1993/921) Land Registration (Scotland) Act 1979 (Commencement No. 7) Order 1993 (S.I. 1993/922) Dairy Produce Quotas Regulations 1993 (S.I. 1993/923) Education (Dissolution of the Council for National Academic Awards) Order 1993 (S.I. 1993/924) Child Support (Maintenance Assessments and Special Cases) Amendment Regulations 1993 (S.I. 1993/925) Greater Manchester and Lancashire (County and District Boundaries) Order 1993 (S.I. 1993/926) Secure Tenancies (Designated Courses) (Amendment) Regulations 1993 (S.I.
== External links == Chronological History of the Development of Insecticides and Control Equipment from 1854 through 1954 Background on History of Pesticide Use and Regulation in the United States, Part Two (PDF, 54 kB). The Value of Fungicides in U.S. Crop Production, (PDF, 1.1 MB)
Sources: en.wikipedia.org
Reports describe effects on GABA-A receptor expression, monoamine turnover, and neurotrophic factor levels. These are proposed mechanisms drawn mainly from animal models. No single molecular target has been established.
Intranasal delivery is the route described in most published work. It is used because the peptide is degraded quickly once it reaches circulation. Direct evidence of brain penetration in humans is lacking.
Most trials are small, regionally concentrated, and often lack rigorous blinding or placebo control. Independent replication is limited. Reviews in English generally rate the evidence as preliminary.
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.