If you have been reading about freeze-thaw cycle and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Updated 2025-07-30. Numbers and descriptions here follow the published literature rather than marketing material.
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.
Lyophilised material kept dry at minus 20 degrees Celsius or colder is the most stable form, and suppliers commonly state a shelf life of two years or more under those conditions. Once dissolved, degradation accelerates through hydrolysis and deamidation, particularly at alkaline pH or elevated temperature. Working solutions are usually divided into single-use aliquots to avoid repeated freeze-thaw cycles. The choice of reconstitution solvent affects both stability and the ionic strength of the final preparation.
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.
| Property | Value | Notes |
|---|---|---|
| Dry storage temperature | -20 C or below | Sealed, desiccated, protected from light |
| Solution stability | Hours to days at 2-8 C | Depends on buffer and microbial load |
| Preferred pH range | Near neutral to slightly acidic | Alkaline pH accelerates hydrolysis |
| Main degradation routes | Hydrolysis and deamidation | No cysteine or methionine in sequence |
| Identity confirmation | Electrospray mass spectrometry | Observed mass compared with 751.9 Da |
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.
As with other untreatable genetic conditions with a later onset, it is ethically questionable to perform presymptomatic testing on a child or adolescent since there would be no medical benefit for that individual. There is consensus for testing only individuals who are considered cognitively mature, although there is a counter-argument that parents have a right to make the decision on their child's behalf. With the lack of effective treatment, testing a person under legal age who is not judged to be competent is considered unethical in most cases. There are ethical concerns related to prenatal genetic testing or preimplantation genetic diagnosis to ensure a child is not born with a given disease. For example, prenatal testing raises the issue of selective abortion, a choice considered unacceptable by some. As it is a dominant disease, there are difficulties in situations in which a parent does not want to know his or her own diagnosis. This would require parts of the process to be kept secret from the parent.
==== Drug delivery ==== Block copolymers are a well-studied and versatile class of self-assembling materials characterized by chemically distinct polymer blocks that are covalently bonded. This molecular architecture of the covalent bond enhancement is what causes block copolymers to spontaneously form nanoscale patterns. In block copolymers, covalent bonds frustrate the natural tendency of each individual polymer to remain separate (in general, different polymers, do not like to mix), so the material assembles into a nano-pattern instead. These copolymers offer the ability to self-assemble into uniform, nanosized micelles and accumulate in tumors via the enhanced permeability and retention effect. Polymer composition can be chosen to control the micelle size and compatibility with the drug of choice. The challenges of this application are the difficulty of reproducing or controlling the size of self-assembly nano micelle, preparing predictable size-distribution, and the stability of the micelle with high drug load content.
Pancrustacea is the clade that comprises all crustaceans and all hexapods (insects and relatives). This grouping is contrary to the Atelocerata hypothesis, in which Hexapoda and Myriapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the Pancrustacea taxon was considered well accepted, with most studies recovering Hexapoda within Crustacea. The clade has also been called Tetraconata, referring to having a four-part cone in the ommatidium. The term "Tetraconata" is preferred by some scientists in order to avoid confusion with the use of "pan-" to indicate a clade that includes a crown group and all of its stem group representatives.
Nature magazine criticised the over-reliance on JIF, pointing not just to its statistical flaws but to negative effects on science: "The resulting pressures and disappointments are nothing but demoralizing, and in badly run labs can encourage sloppy research that, for example, fails to test assumptions thoroughly or to take all the data into account before submitting big claims." Various publishers now use a mixture of metrics on their website; the PLOS series of journals does not display the impact factor. Microsoft Academic took a similar view, stating that h-index, EI/SCI and journal impact factors are not shown because "the research literature has provided abundant evidence that these metrics are at best a rough approximation of research impact and scholarly influence." In 2021, Utrecht University promised to abandon all quantitative bibliometrics, including the impact factor. The university stated that "it has become a very sick model that goes beyond what is really relevant for science and putting science forward". This followed a 2018 decision by the main Dutch funding body for research, NWO, to remove all references to journal impact factors and the h-index in all call texts and application forms. Utrecht's decision met with some resistance. An open letter signed by over 150 Dutch academics argued that, while imperfect, the JIF is still useful, and that omitting it "will lead to randomness and a compromising of scientific quality".
Estradiol is available as a transdermal gel in the form of gel dispensers and gel packets. Major estradiol gel dispenser products include EstroGel and Elestrin while major estradiol gel packet products include DiviGel and Sandrena. Estradiol gels are administered daily. When estradiol is administered as a hydroalcoholic gel, it dries within 2 to 5 minutes following application to the skin. A single application of a transdermal estradiol gel results in a sustained increase in estradiol levels for at least 24 hours. The apparent elimination half-life of estradiol with transdermal estradiol gel is 36 hours. Once daily application of 1.25 g topical gel containing 0.75 mg estradiol (brand name EstroGel) for 2 weeks was found to produce mean peak estradiol and estrone levels of 46.4 pg/mL and 64.2 pg/mL, respectively. The time-averaged levels of circulating estradiol and estrone with this formulation over the 24-hour dose interval were 28.3 pg/mL and 48.6 pg/mL, respectively. Levels of estradiol and estrone are stable and change relatively little over the course of the 24 hours following an application, indicating a long duration of action of this route. Steady-state levels of estradiol are achieved after 3 days of application. A higher dosage of estradiol gel containing 1.5 mg estradiol per daily application has been found to produce mean estradiol levels of 40 to 100 pg/mL and estrone levels of 90 pg/mL, while 3 mg per day has been found to result in respective mean estradiol and estrone levels of 60 to 140 pg/mL and 45 to 155 pg/mL.
Sources: en.wikipedia.org
The role of gastric acid in digestion was established in the 1820s and 1830s by William Beaumont on Alexis St. Martin, who, as a result of an accident, had a fistula (hole) in his stomach, which allowed Beaumont to observe the process of digestion and to extract gastric acid, verifying that acid played a crucial role in digestion.
Agilent ChemStation is a software package to control Agilent liquid chromatography, gas chromatography, and ultraviolet-visible spectroscopy systems such as the 1050, 1100 and 1200 Series HPLC system and the 8453 and 8454 single-beam diode array detector spectrophotometers. It is an evolution of the Hewlett-Packard ChemStation System. Two versions are available: one ("online") in connection with the modules of the HPLC chain is designed to control instruments and run experiments, and the other ("offline"), without a connection with the HPLC chain, is designed to analyze data. ChemStation is structured around a number of registers. Two of the more important registers are CHROMREG and CHROMRES, the chromatographic data registers. Other special registers exist for the UV-vis implementation of the software. ChemStation has a command line interpreter and can run macros. Those macros are files grouping a set of commands. These files possess a .mac extension. ChemStation can import analysis lists and export result files in XML by adding new lines to the ChemStation.ini configuration file. This is a feature to implement the connection with a Laboratory information management system (LIMS).
Field rations can be eaten at any temperature, but are preferably heated or cooked. However, as the use of cooking appliances or fire may be unavailable or tactically unwise, smokeless solid fuel and a portable stove are typically included in rations to heat meals. Hexamine fuel tablets have traditionally been preferred, though gelatinized ethanol is also sometimes used. Some modern field rations use a flameless ration heater instead of fuel tablets. NATO standardization states that, while main courses and entrées must be consumable without heating, main course components and hot beverages should be provided with a heater, with such items intended to be heated to a minimum temperature of 62 °C from an ambient temperature of 20 °C within 12 minutes.
== Chemistry == The minimum requirement for adrenergic agents is a primary or secondary amine separated from a substituted benzene ring by one or two carbons. This configuration results in strong agonist activity. As the size of the substituent attached to the amine becomes greater, particularly with respect to a t-butyl group, then the molecule typically is found to have receptor affinity without intrinsic activity, and is, therefore, an antagonist. Labetalol, with its 1-methyl-3-phenylpropyl substituted amine, is greater in size relative to a t-butyl group and therefore acts predominantly as an antagonist. The overall structure of labetalol is very polar. This was created by substituting the isopropyl group in the standard beta blocker structure with an aralkyl group, including a carboxamide group on the meta position, and by adding a hydroxyl group on the para position. Labetalol has two chiral carbons and consequently exists as four stereoisomers. Two of these isomers, the (S,S)- and (R,S)- forms are inactive. The third, the (S,R)-isomer, is a powerful α1-adrenergic receptor blocker. The fourth isomer, the (R,R)-isomer which is also known as dilevalol, is a mixed non-selective β-adrenergic receptor blocker and selective α1 blocker. Labetalol is typically given as a racemic mixture to achieve both α- and β-adrenergic receptor blocking activity.
== History == Phage display was first described by George P. Smith in 1985, when he demonstrated the display of peptides on filamentous phage (long, thin viruses that infect bacteria) by fusing the virus's capsid protein to one peptide out of a collection of peptide sequences. This displayed the different peptides on the outer surfaces of the collection of viral clones, where the screening step of the process isolated the peptides with the highest binding affinity. In 1988, Stephen Parmley and George Smith described biopanning for affinity selection and demonstrated that recursive rounds of selection could enrich for clones present at 1 in a billion or less. In 1990, Jamie Scott and George Smith described creation of large random peptide libraries displayed on filamentous phage. Phage display technology was further developed and improved by groups at the Laboratory of Molecular Biology with Greg Winter and John McCafferty, The Scripps Research Institute with Richard Lerner and Carlos Barbas and the German Cancer Research Center with Frank Breitling and Stefan Dübel for display of proteins such as antibodies for therapeutic protein engineering. Smith and Winter were awarded a half share of the 2018 Nobel Prize in chemistry for their contribution to developing phage display. A patent by George Pieczenik claiming priority from 1985 also describes the generation of peptide libraries.
Sources: en.wikipedia.org
It’s a fight for our national security." He advocated for a special inspector general to monitor the aid given to Ukraine following Russia's invasion. Kennedy expressed concern that money was being misspent, saying, "Ukraine is not without flaws. We've heard several unsettling reports of bad actors exploiting our generosity… We trust that our friends in Ukraine take corruption seriously. We must verify, too."
Cannabis (Cannabis sativa) [3.8–37.5% of cannabis flower essential oil] Black caraway (Carum nigrum) [7.8%] Cloves (Syzygium aromaticum) [1.7–19.5% of clove bud essential oil] Hops (Humulus lupulus) [5.1–14.5%] Basil (Ocimum spp.) [5.3–10.5% O. gratissimum; 4.0–19.8% O. micranthum] Oregano (Origanum vulgare) [4.9–15.7%] Black pepper (Piper nigrum) [7.29%] Lavender (Lavandula angustifolia) [4.62–7.55% of lavender oil] Rosemary (Rosmarinus officinalis) [0.1–8.3%] True cinnamon (Cinnamomum verum) [6.9–11.1%] Malabathrum (Cinnamomum tamala) [25.3%] Ylang-ylang (Cananga odorata) [3.1–10.7%] Copaiba oil (Copaifera)
The retribution stoked renewed rebellion, which, combined with a weakened Spain, made possible a successful rebellion led by the Venezuelan-born Simón Bolívar, who finally proclaimed independence in 1819. The pro-Spanish resistance was defeated in 1822 in the present territory of Colombia and in 1823 in Venezuela. During the Independence War, between 250 and 400 thousand people died (12–20% of the pre-war population).
The Pharmacyclics name was retained, and it operated as a subsidiary of AbbVie from its previous Sunnyvale, California headquarters until the consolidation of AbbVie Bay Area sites in a new building in South San Francisco. In June 2015, AbbVie and Halozyme Therapeutics entered into a global collaboration and licensing agreement to develop and commercialize products that combine AbbVie's treatments and Halozyme's ENHANZE drug-delivery technology, this was terminated in November 2016. In February 2016, AbbVie and Cambridge, Massachusetts-based Synlogic announced a multi-year R&D collaboration. Synlogic is a synthetic biology company built on research from the labs of James Collins and Tim Lu at MIT. As part of the collaboration, AbbVie is getting worldwide rights to Synlogic's probiotic-based technology for treating inflammatory bowel disease, and the research teams will focus on Crohn's disease and ulcerative colitis. In April 2016, the company announced it would acquire Stemcentrx for up to $9.8 billion. A day later, the company announced an expansion of a two and a half-year-old cystic fibrosis deal with Galapagos NV, potentially doubling milestone payments to $600 million. Also in April 2016, the company partnered with the University of Chicago to investigate several areas of oncology: breast, lung, prostate, colorectal and hematological cancers. Also in April 2016, the company announced it would co-commercialize Argenx's preclinical immunotherapy, ARGX-115.
Sources: en.wikipedia.org
Dry powder is best kept sealed, protected from light, and held at minus 20 degrees Celsius or below. Desiccant packaging helps limit moisture uptake because the material is hygroscopic. A sealed vial should be allowed to equilibrate to room temperature before opening to reduce condensation.
Hydrolysis of peptide bonds and deamidation of arginine and proline residues are the main degradation routes. Alkaline pH and higher temperatures accelerate both processes. Buffered, near-neutral solutions stored cold generally degrade more slowly than unbuffered ones.
Reverse-phase chromatography gives the clearest single view of related impurities and truncated sequences. Mass spectrometry then confirms that the main peak carries the expected mass. Neither test detects enantiomeric impurities, which require a separate chiral assay.
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.