This is a working overview of peptide purity, written for readers who want more than a one-paragraph summary but less than a textbook.
Reviewed 2025-11-17. Anything still debated is marked as such rather than presented as settled.
Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter notation. Its structure consists of the immunomodulatory tetrapeptide tuftsin, Thr-Lys-Pro-Arg, extended at the carboxyl terminus by a Pro-Gly-Pro segment. The molecular formula is commonly given as C33H57N11O9, corresponding to a monoisotopic mass near 751.4 Da and an average molecular mass near 751.9 Da. All seven residues are proteinogenic amino acids, and the molecule carries no modified side chains or non-natural linkages.
The compound was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences during the 1980s and 1990s. The stated design goal was to retain the immunomodulatory and central nervous system activity attributed to tuftsin while improving resistance to enzymatic breakdown. Adding a proline-rich tail to the short parent peptide was a deliberate strategy, because proline residues restrict the conformations available to many peptidases. The same laboratory produced Semax, an ACTH fragment analog, and both compounds were developed in parallel as short, enzymatically stabilized peptides intended for intranasal use.
Selank is not a naturally occurring peptide and has no known endogenous counterpart in human physiology. Russian-language sources frequently call it TP-7, while English-language sources use the name Selank almost exclusively. Database indexing is uneven, partly because early reports appeared in regional journals that are not widely cataloged. Some summaries describe the material as a tuftsin analog and others as a synthetic heptapeptide; the labels overlap rather than conflict. Citing the primary sequence resolves ambiguity more reliably than the research or trade name alone.
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.
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 |
|---|---|---|
| Peptide sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Seven residues; tuftsin plus a Pro-Gly-Pro tail |
| Molecular formula | C33H57N11O9 | Commonly reported value for the free peptide |
| Monoisotopic mass | Roughly 751.4 Da | Average molecular mass near 751.9 Da |
| Appearance | White to off-white powder | Typically supplied as a lyophilized solid |
| Solubility class | Freely soluble in water | Also dissolves in saline and other polar solvents |
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.
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.
Lyophilized Selank, the dry powder form, is generally stored frozen at minus 20 degrees Celsius or colder for long-term keeping. The solid is hygroscopic and should stay sealed, dry, and protected from light. Once dissolved, the peptide is less stable and is usually held refrigerated at 2 to 8 degrees Celsius for short periods. Repeated freezing and thawing is avoided because it can promote aggregation and loss of activity. Buffers and pH choice also affect how long a solution remains usable.
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.
== Instant tea == In 1946, Nestle USA introduced the first instant tea, Nestea. Instant teas are produced from black tea by extracting the liquor from processed portion of tea typically from offgrade black teas; green tea in a smaller proportion has traditionally been used by the instant tea makers as a "clarification agent" - again, in effort to maximize the clarity of color and minimize off-colors created by certain teas that cloud. The extract is concentrated under low pressure, and drying the concentrate to a powder by freeze-drying, spray-drying, or vacuum-drying. Low temperatures tend to be used to minimize loss of flavor. The American market for instant tea powders, which developed quickly following Nestle's introduction, has slackened off considerably over the past quarter century, as Americans have more and more turned to naturally icing their favorite loose teas, as well as preparing iced tea from tea bags, and to ready-to-drink iced teas where the smaller sizes are found in the supermarkets' refrigerated drinks sections and the larger gallon sizes are found in the supermarkets' non-refrigerated drinks sections.
By the mid-2020s, Zipline had become an example of a Silicon Valley startup whose most visible commercial activity occurred abroad rather than domestically, with most of its business based on government contracts for transporting medical supplies to remote or hard-to-reach areas in multiple African countries. In April 2024, Zipline completed its millionth commercial delivery, having flown more than 70 million autonomous commercial miles. In January 2026, Zipline completed its two millionth commercial delivery, with over 120 million autonomous miles flown.
Even though this reaction proceeds effectively at biological conditions, copper in this range of dosage is cytotoxic. Solutions to this problem have been presented, such as using water-soluble ligands on the copper to enhance cell penetration of the catalyst and thereby minimize the dosage needed, An analogous "RuAAC reaction" (catalyzed by ruthenium, instead of copper) allows for the selective production of 1,5-isomers.
Keller also plans on opening his own burger restaurant inspired by his Los Angeles experience of In-N-Out. Julia Child, one of the first celebrities to champion the chain, admitted to knowing every location of the restaurant between Santa Barbara and San Francisco. Child also had the burgers delivered to her during a hospital stay. Anthony Bourdain reportedly said that In-N-Out was his favorite fast food meal, later naming the restaurant as "the best restaurant in Los Angeles". Ina Garten at an interview at Today show said "I have to say, I don't eat fast food at all, with one exception. When we're in California doing book tours, we always have to go to In-N-Out Burger. It's so good and I know it was Julia Child's favorite too, so it's okay." In-N-Out was one of the few restaurant chains mentioned positively in the book Fast Food Nation. The book commended the chain for using natural and fresh ingredients and for looking after the interests of employees regarding pay and benefits. An In-N-Out food truck catered Vanity Fair's 2012 Academy Awards after party.
Sources: en.wikipedia.org
The source of blood to be transfused can either be the potential recipient (autologous transfusion) or someone else (allogeneic or homologous transfusion). The latter is much more common than the former. Using another's blood must first start with the donation of blood. Blood is most commonly donated as whole blood obtained intravenously and mixed with an anticoagulant. In first-world countries, donations are usually anonymous to the recipient, but products in a blood bank are always individually traceable through the whole cycle of donation, testing, separation into components, storage, and administration to the recipient. This enables management and investigation of any suspected transfusion-related disease transmission or transfusion reaction. Developing countries rely heavily on replacement and remunerated donors rather than voluntary nonremunerated donors due to concerns regarding donation- and transfusion-transmitted infection as well as local and cultural beliefs. It is unclear whether applying an alcohol swab alone or an alcohol swab followed by an antiseptic can reduce contamination of the donor's blood. Studies show that the main motivators to blood donation tend to be prosocial (e.g., altruism, selflessness, charity), while the main deterrents include fear, distrust, or perceived racial discrimination in historic contexts.
catalyst Any chemical species or substance whose presence increases the reaction rate of one or more particular chemical reactions but which is itself unchanged by the reaction, being neither a reactant nor a product of the reaction. Catalysts often need only be present in very low concentrations relative to the reactants in order for catalysis to occur. They may be simple molecules which catalyze reactions spontaneously, though most biochemical reactions are catalyzed by specifically evolved enzymes which allow them to proceed at rates millions or billions of times faster than they otherwise would.
=== Error-prone replication bypass === There is increasing evidence that the majority of spontaneously arising mutations are due to error-prone replication (translesion synthesis) past DNA damage in the template strand. In mice, the majority of mutations are caused by translesion synthesis. Likewise, in yeast, Kunz et al. found that more than 60% of the spontaneous single base pair substitutions and deletions were caused by translesion synthesis.
Sources: en.wikipedia.org
From the late 1960s to the early 1970s, with the rapid surge in recreational drug use in the U.S., the production of narcotics in Mexico, particularly marijuana, expanded exponentially, and Mexican criminals started to smuggle drugs on a major scale. During the 1960s and 1970s, Mexico participated in a series of U.S.-backed anti-narcotics initiatives, including Operation Intercept and Operation Condor. These operations were formally justified on the grounds of combating the cultivation of opium poppies and marijuana in Mexico's so-called "Golden Triangle" region, an area encompassing parts of the states of Sinaloa, Durango, and Chihuahua. As part of the campaign, the Mexican government deployed about 10,000 soldiers and police. The operation resulted in mass arrests, torture, and imprisonment of peasants who were often accused of aiding leftist insurgency groups, but no major traffickers were captured. Contemporary assessments deemed the initiatives a failure, citing their inability to curb narcotics production, enabling military corruption, and their record of human rights abuses in rural areas. As U.S. efforts in the war on drugs intensified, crackdowns in Florida and the Caribbean during the Miami drug war forced Colombian traffickers to develop new routes for smuggling cocaine into the United States. By the early 1980s, the Medellin Cartel and Cali Cartel oversaw production, while distribution increasingly relied on Mexican traffickers.
Hydrogen–deuterium exchange mass spectrometry (HX-MS or HDX-MS) can determine the overall deuterium content of molecules which have undergone H/D exchange. Because of the sample preparation required, it is typically considered to provide an accurate measurement of non-exchangeable hydrogen atoms only. It can also involve H/D exchange in the gas phase or solution phase exchange prior to ionization. HDX-MS of proteins has several advantages when compared to HDX monitored using NMR spectroscopy: much less sample material is needed, the concentration of sample can be very low (as low as 0.1 uM), the size limit is much greater, and data can usually be collected and interpreted much more quickly. The deuterium nucleus is twice as heavy as the hydrogen nucleus because it contains a neutron as well as a proton. Thus a molecule that contains some deuterium will be heavier than one that contains all hydrogen. As a protein is increasingly deuterated, the molecular mass increases correspondingly. Detecting the change in the mass of a protein upon deuteration was made possible by modern protein mass spectrometry, first reported in 1991 by Katta and Chait. Determining site specific deuteration via mass spectrometry is more complicated than using NMR spectroscopy. For example, the location and relative amount of deuterium exchange along the peptide backbone can be determined roughly by subjecting the protein to proteolysis after the exchange reaction has been quenched. Individual peptides are then analyzed for overall deuteration of each peptide fragment.
=== Fuels === Another use of cryogenics is cryogenic fuels for rockets with liquid hydrogen as the most widely used example, with liquid methane starting to become more prevalent in recent years. Liquid oxygen (LOX) is even more widely used but as an oxidizer, not a fuel. NASA's workhorse Space Shuttle used cryogenic hydrogen/oxygen propellant as its primary means of getting into orbit. LOX is also widely used with RP-1 kerosene, a non-cryogenic hydrocarbon, such as in the rockets built for the Soviet space program by Sergei Korolev. Russian aircraft manufacturer Tupolev developed a version of its popular design Tu-154 with a cryogenic fuel system, known as the Tu-155. The plane uses a fuel referred to as liquefied natural gas or LNG, and made its first flight in 1989.
==== Behavioral treatment ==== Behavioral treatment is less effective without medical treatment during the initial detoxification. It has similarly been shown that medical treatments tend to get better results when accompanied by behavioral treatment. For opioid dependence, popular non-pharmacological treatment options include cognitive behavioral therapy (CBT), group or individual therapy, residential treatment centers, and twelve-step programs such as Narcotics Anonymous. Since addictive behavior is a learned behavior in opioid dependence, cognitive behavioral therapy aims to promote positive motivation to change that behavior. Studies such as the Rat Park series indicate that a greater focus on improving the environments of those with opioid use disorders could also be beneficial.
Sources: en.wikipedia.org
The sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, written TKPRPGP in one-letter code. It combines the tetrapeptide tuftsin with a carboxyl-terminal Pro-Gly-Pro extension. This full sequence identifies the molecule more precisely than the research name.
No peptide with this exact sequence has been identified as an endogenous substance. It is a laboratory-designed analog of tuftsin, a naturally occurring immunomodulatory tetrapeptide. The Pro-Gly-Pro extension has no known natural source.
Proline introduces conformational constraints that make a peptide less accessible to common peptidases. This is a standard stabilization strategy in peptide design. The added residues also increase the distance between the active tuftsin portion and typical cleavage sites.
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.