Reversed-phase HPLC raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-04-26 and is reviewed periodically as new material appears.
The compound is described in the literature as a derivative of epithalamin, a preparation obtained from bovine pineal tissue. Work on this peptide family was carried out mainly by a research group in Saint Petersburg beginning in the 1980s, and the substance was later registered for clinical use in Russia under the name Epitalon. Outside that region it is generally treated as a research chemical rather than an approved medicine. Statements about its biological activity rest on a relatively small number of studies, and independent replication remains limited.
In its supplied form epitalon is a white to off-white powder, usually lyophilized and often hygroscopic. It dissolves readily in water and in aqueous buffers, and it is commonly handled as the acetate or trifluoroacetate salt to improve stability during purification and drying. The amide backbone is labile in aqueous media, so solutions are less durable than the dry solid. Handling notes in the chemical literature therefore emphasize keeping the powder dry, cool and shielded from light until it is dissolved.
Epitalon is a synthetic tetrapeptide whose sequence is alanine-glutamate-aspartate-glycine, written in single-letter code as AEDG. The four residues are joined by three peptide bonds, giving a linear backbone with no branching and no disulfide bridges. Its calculated molecular mass for the free form is approximately 390.3 daltons, a figure that rises when the compound is supplied as an acetate or trifluoroacetate salt. Because the chain is short, the molecule is defined entirely by its residue order rather than by any folded three-dimensional structure.
Because epitalon has no pharmacopoeial monograph, quality assessment depends on supplier documentation and independent testing. Certificates of analysis typically report a purity figure from a single chromatographic run, a measured mass and sometimes an appearance description, but methods and acceptance criteria are not harmonised across vendors. Third-party laboratories can repeat identity and purity measurements, and mismatches between labelled and measured peptide content have been described for research peptides generally. What constitutes adequate identity confirmation for a molecule of this size stays an open question, since mass agreement alone does not separate closely related sequences.
Identity testing for epitalon relies on reversed-phase high-performance liquid chromatography for purity and mass spectrometry for mass confirmation. Because the sequence contains no tryptophan or tyrosine, ultraviolet detection at 280 nanometres is insensitive, so chromatographic methods usually monitor absorbance near 214 nanometres, where the peptide backbone absorbs. Electrospray ionisation or matrix-assisted laser desorption/ionisation then checks the intact mass against the expected value near 390 daltons. Peptide mapping or amino acid analysis after acid hydrolysis can supplement these measurements, although such confirmatory work is seldom reported on commercial certificates of analysis.
| Property | Value | Notes |
|---|---|---|
| Chemical class | Synthetic tetrapeptide | Four residues, linear chain |
| Residue sequence | Ala-Glu-Asp-Gly | Single-letter form AEDG |
| Calculated mass | 390.3 daltons | Value for the free, uncharged form |
| Appearance | White to off-white powder | Usually supplied lyophilized |
| Solubility | Freely soluble in water | Often handled as a salt form |
Several names circulate for the same molecule, including epitalon, epithalone, epithalamin tetrapeptide, and the sequence code AEDG. A CAS registry number, 307297-39-8, is commonly cited for it, though catalogue entries should be checked against supplier documentation because mislabelled records occur. In its usual form the peptide carries free amino and carboxyl termini and is neither glycosylated nor lipidated. Researchers distinguish the defined tetrapeptide from epithalamin itself, a crude pineal preparation containing many peptides that is not chemically characterised.
Material supplied for laboratory use is normally a lyophilised white to off-white powder that dissolves readily in water and in isotonic saline. Lyophilised cakes are hygroscopic and should be equilibrated to room temperature before opening to limit condensation on the solid. Solutions are typically prepared at milligram-per-millilitre concentrations and divided into single-use aliquots, because repeated freeze–thaw cycles degrade short peptides. Aqueous solutions are far less stable than the dry powder, and identity is usually verified by mass spectrometry alongside purity estimation from reversed-phase high-performance liquid chromatography.
Regulatory treatment differs by country. No formulation of epitalon holds a marketing authorisation as a medicine in the United States or the European Union, where material sold for laboratory use is handled as a research chemical and is not intended for human consumption. In Russia, several short peptide preparations from the same institute's peptide series are registered medicinal products, and epitalon appears in that national context. Elsewhere it is frequently offered as a cosmetic ingredient, a category with lighter requirements. Advertising claims about longevity or disease prevention are restricted in most jurisdictions, which limits how sellers describe the compound.
Freeze-dried epitalon is normally kept at minus twenty degrees Celsius in a sealed, desiccated container, protected from light. Short excursions at ambient temperature during shipping are generally tolerated, but repeated warming and cooling cycles encourage moisture uptake, which shortens shelf life. Once dissolved, the peptide is far less stable than the solid: aqueous solutions are subject to hydrolysis and to deamidation at the aspartate and glutamate residues. Working solutions are therefore held refrigerated and used within days, and repeated freezing and thawing of the same vial is best avoided.
The peptide is a synthetic analogue of epithalamin, a preparation extracted from bovine pineal glands. Investigators sought a short, chemically defined molecule that would reproduce some of the endocrine and gerontological observations attributed to the glandular extract. Proposed mechanisms centre on induction of telomerase activity, an effect reported in cultured human somatic cells in the early 2000s, together with influences on melatonin secretion and neuroendocrine regulation. Those mechanisms remain incompletely characterised, and the reported telomerase response has not been consistently reproduced by independent groups working in comparable systems.
Published work on this compound consists mainly of in vitro experiments, animal studies, and small clinical investigations, a substantial share of which appeared in Russian-language journals. Sample sizes are generally small, control conditions differ between studies, and several endpoints rely on markers whose clinical meaning is itself debated. Reviews of the longevity field treat the peptide as an early example of telomerase-directed research rather than an established intervention. Regulatory treatment varies by country: some jurisdictions place it under prescription controls, others treat it as a laboratory material, and importation may be restricted regardless of local status.
Identity confirmation uses mass spectrometry, usually electrospray ionisation in positive mode or matrix-assisted laser desorption. The protonated free peptide produces a signal near three hundred and ninety-one daltons, while salt adducts shift that value slightly. Tandem mass spectrometry or amino acid analysis supplies sequence-level confirmation, which a single mass measurement cannot. Peptides containing aspartate can cyclise into succinimide intermediates that hydrolyse to isoaspartate isomers of identical mass. Because those isomers are difficult to separate chromatographically, identity and purity results carry more weight when interpreted together.
Storage practice centres on limiting moisture, oxygen, and repeated temperature cycling. Freeze-dried powder is generally held desiccated at minus twenty degrees Celsius or colder and protected from light. Reconstituted solutions are markedly less stable, and the aspartate-glycine junction is prone to succinimide formation at neutral to mildly alkaline pH. Portioning material into single-use aliquots reduces degradation compared with repeated freeze-thaw cycles. Stability data specific to this tetrapeptide remain scarce, so most handling guidance is extrapolated from general peptide chemistry rather than measured directly.
== Research and clinical uses == Lauer-Fields et al. (2007), are using C-terminally truncated SRTX-b to act as a matrix metalloproteinase inhibitor. The removal of the C-terminal eliminates its toxic vasopressive activity and also the matrix metalloproteinase inhibitor activity, however with further amino acid changes, the matrix metalloproteinase inhibitory activity is regained and enhanced. This modified sarafotoxin is useful for treating some pathological conditions including arthritis, cardiovascular diseases and tumor cell metastasis.
==== In pregnancy ==== Pregnant women with opioid use disorder can also receive treatment with methadone, naltrexone, or buprenorphine. Buprenorphine appears to be associated with more favorable outcomes compared to methadone for treating opioid use disorder (OUD) in pregnancy. Studies show that buprenorphine is linked to lower risks of preterm birth, greater birth weight, and larger head circumference without increased harm. Compared to methadone, it consistently results in improved birth weight and gestational age, though these findings should be interpreted with caution due to potential biases. Buprenorphine use correlates with a lower risk of adverse neonatal outcomes, with similar risks of adverse maternal outcomes as methadone. Infants born to buprenorphine-treated mothers generally have higher birth weights, fewer withdrawal symptoms, and a lower likelihood of premature birth. They often require less treatment for neonatal abstinence syndrome and have mothers who are more likely to start treatment earlier in pregnancy, leading to longer gestations and larger infants.
== History of discovery == This analgesic activity of M6G (in animals) was first noted by Yoshimura. Subsequent work at St Bartholomew's Hospital, London in the 1980s, using a sensitive and specific high-performance liquid chromatography assay, accurately defined for the first time the metabolism of morphine, and the abundance of this metabolite (along with morphine-3-glucuronide, considered an inactive metabolite). It was postulated that kidney impairment would result in accumulation of the kidney-excreted active agent M6G, leading to potentially fatal toxicity such as respiratory depression. The frequent use of morphine in critically ill patients, and the common occurrence of kidney failure in this group implied that M6G accumulation could be a common, but previously unanticipated problem. The first studies demonstrated massive levels of M6G in 3 patients with kidney failure, which resolved as kidney function returned. Accumulation of M3G and M6G also decreased with return of kidney function after kidney transplantation. A key step in defining the importance of M6G in humans came in 1992 when the substance was artificially synthesised and administered to patients with pain, the majority of whom described pain relief.
Vitamin E does not improve established liver fibrosis in those with MASLD, but seems to improve certain markers of liver function and reduce inflammation and fattiness of the liver in some people with MASLD. The Asia-Pacific Work Group advises that Vitamin E may improve liver condition and aminotransferase levels, but only in adults without diabetes or cirrhosis who have MASH. The NICE guidelines recommend Vitamin E as an option for children and adults with MASFLD with advanced liver fibrosis, regardless of whether the person has diabetes mellitus.
Examples of potent CYP1A2 inhibitors include ethinylestradiol (found in hormonal birth control), fluoroquinolones (e.g., ciprofloxacin), fluvoxamine, and St. John's wort, while potent CYP1A2 inducers include phenytoin, rifampin, ritonavir, and tobacco. A study found that ritonavir, a strong CYP3A4 and CYP2D6 inhibitor and moderate CYP1A2 inducer, increased trazodone peak levels by 1.4-fold, trazodone area-under-the-curve levels by 2.4-fold, and decreased trazodone clearance by 50%. This was associated with adverse effects such as nausea, hypotension, and syncope. Another study found that the strong CYP3A4 inducer carbamazepine reduced concentrations of trazodone by 60 to 74%. The strong CYP2D6 inhibitor thioridazine has been reported to increase trazodone levels by 1.4-fold and concentrations of mCPP by 1.5-fold. Fluoxetine, a strong inhibitor of CYP2D6 and a weak or moderate inhibitor of CYP3A4, has been reported to increase levels of trazodone by 1.3- to 1.7-fold and of mCPP by 3.0- to 3.4-fold. Conversely, CYP2D6 genotype has not been found to predict trazodone or mCPP concentrations with trazodone therapy, although CYP2D6 genotype did correlate with side effects like dizziness and prolonged corrected QT interval. Smokers have lower levels of trazodone and higher ratios of mCPP to trazodone. Trazodone levels were 30% lower in smokers and mCPP to trazodone ratio was 1.3-fold higher in smokers, whereas mCPP concentrations were not different between smokers and non-smokers. Smoking is known to induce CYP1A2, and this may be involved in these findings.
Sources: en.wikipedia.org
The properties of many polymers are affected by hydrogen bonds within and/or between the chains. Prominent examples include cellulose and its derived fibers, such as cotton and flax. In nylon, hydrogen bonds between carbonyl and the amide NH effectively link adjacent chains, which gives the material mechanical strength. Hydrogen bonds also affect the aramid fibre, where hydrogen bonds stabilize the linear chains laterally. The chain axes are aligned along the fibre axis, making the fibres extremely stiff and strong. Hydrogen-bond networks make both polymers sensitive to humidity levels in the atmosphere because water molecules can diffuse into the surface and disrupt the network. Some polymers are more sensitive than others. Thus nylons are more sensitive than aramids, and nylon 6 more sensitive than nylon-11.
=== Carrier gas selection and flow rates === Typical carrier gases include helium, nitrogen, argon, and hydrogen. Which gas to use is usually determined by the detector being used, for example, a DID requires helium as the carrier gas. When analyzing gas samples the carrier is also selected based on the sample's matrix, for example, when analyzing a mixture in argon, an argon carrier is preferred because the argon in the sample does not show up on the chromatogram. Safety and availability can also influence carrier selection. The purity of the carrier gas is also frequently determined by the detector, though the level of sensitivity needed can also play a significant role. Typically, purities of 99.995% or higher are used. The most common purity grades required by modern instruments for the majority of sensitivities are 5.0 grades, or 99.999% pure meaning that there is a total of 10 ppm of impurities in the carrier gas that could affect the results. The highest purity grades in common use are 6.0 grades, but the need for detection at very low levels in some forensic and environmental applications has driven the need for carrier gases at 7.0 grade purity and these are now commercially available. Trade names for typical purities include "Zero Grade", "Ultra-High Purity (UHP) Grade", "4.5 Grade" and "5.0 Grade". The carrier gas linear velocity affects the analysis in the same way that temperature does (see above). The higher the linear velocity the faster the analysis, but the lower the separation between analytes.
Factors contributing to the anarchist animosity towards the USSR included the Soviet destruction of the Makhnovist movement after an initial alliance, the suppression of the anarchist Kronstadt rebellion, and the defeat of the rival anarchist factions by the Soviet-supported Communist faction during the Spanish Civil War. Maoists also have a mixed opinion on the USSR, viewing it negatively during the Sino-Soviet Split and denouncing it as revisionist and reverted to capitalism. The Chinese government in 1963 articulated its criticism of the USSR's system and promoted China's ideological line as an alternative. After the dissolution of the Soviet Union, the Japanese Communist Party (JCP) released a press statement titled "We welcome the end of a party which embodied the historical evil of great power chauvinism and hegemonism". Noam Chomsky called the collapse of the Soviet Union "a small victory for socialism, not only because of the fall of one of the most anti-socialist states in the world, where working people had fewer rights than in the West, but also because it freed the term 'socialism' from the burden of being associated in the propaganda systems of East and West with Soviet tyranny—for the East, in order to benefit from the aura of authentic socialism, for the West, in order to demonize the concept."
==== Continuous ==== Continuous capillaries are continuous in the sense that the endothelial cells provide an uninterrupted lining, and they only allow smaller molecules, such as water and ions, to pass through their intercellular clefts. Lipid-soluble molecules can passively diffuse through the endothelial cell membranes along concentration gradients. Continuous capillaries can be further divided into two subtypes:
Sources: en.wikipedia.org
Microbats and a few megabats emit ultrasonic sounds to produce echoes. The sound intensity of these echoes is dependent on subglottic pressure. The bats' cricothyroid muscle, located inside the larynx, controls the orientation pulse frequency, which is an important function. By comparing the outgoing pulse with the returning echoes, bats can learn about their environment and detect prey in darkness. Some bat calls can reach over 140 decibels. Microbats use their larynx to emit echolocation signals through the mouth or the nose. Bat call frequencies range from as low as 11 kHz to as high as 212 kHz. The noses of various groups of bats have fleshy extensions, known as nose-leaves, which play a role in sound transmission. In low-duty cycle echolocation, bats can separate their calls and returning echoes by time. They have to time their short calls to finish before echoes return. In high-duty cycle echolocation, bats emit a continuous call and separate pulse and echo in frequency using the Doppler effect of their motion in flight. The shift of the returning echoes yields information relating to the motion and location of the bat's prey. These bats must deal with changes in the Doppler shift due to changes in their flight speed. They have adapted to change their pulse emission frequency in relation to their flight speed so echoes still return in the optimal hearing range. In addition to echolocating prey, bat ears are sensitive to sounds made by their prey, such as the fluttering of moth wings.
== Chemistry == Vortioxetine (1-[2-(2,4-dimethylphenylsulfanyl)phenyl]piperazine) is a bis-aryl-sulfanyl amine as well as piperazine derivative. The acid dissociation constant (pKa) values for vortioxetine hydrobromide were determined to be 9.1 (± 0.1) and 3.0 (± 0.2) according to an Australian Public Assessment Report.
=== Education and early law career === Duterte went to Laboon Elementary School in Maasin for a year. He spent his remaining elementary days at Santa Ana Elementary School in Davao City, where he completed his primary education in 1956. He finished his secondary education in the High School Department of Holy Cross College of Digos (now Cor Jesu College) in Digos, Davao province, after being expelled twice from previous schools, including one in the Ateneo de Davao University (AdDU) High School due to misconduct. He graduated in 1968 with a Bachelor of Arts degree in political science at the Lyceum of the Philippines in Manila. Duterte obtained a law degree from San Beda College of Law in 1972, passing the bar exam in the same year. He worked as a professor in the national police academy, and was a member of an organization called Nationalist Alliance for Justice, Freedom and Democracy. He later served as the OIC vice mayor of Davao City, assisting evacuees from Davao City remote areas and working for the release of soldiers captured by the New Peoples Army (NPA). Eventually, he became a special counsel at the City Prosecution Office in Davao City from 1977 to 1979, fourth assistant city prosecutor from 1979 to 1981, third assistant city prosecutor from 1981 to 1983, and second assistant city prosecutor from 1983 to 1986.
Singapore has a tropical rainforest climate (Köppen: Af) with no distinctive seasons, uniform temperature and pressure, high humidity, and abundant rainfall. Temperatures usually range from 23 to 32 °C (73 to 90 °F). While temperature does not vary greatly throughout the year, there is a wetter monsoon season from November to February. From July to October, there is often haze caused by bush fires in neighbouring Indonesia, usually from the island of Sumatra. Singapore follows the GMT+8 time zone, one hour ahead of the typical zone for its geographical location. This causes the sun to rise and set particularly late during February, where the sun rises at 7:15 am and sets around 7:20 pm. During July, the sun sets at around 7:15 pm. The earliest the sun rises and sets is in late October and early November when the sun rises at 6:46 am and sets at 6:50 pm. Singapore recognises that climate change and rising sea levels in the decades ahead will have major implications for its low-lying coastline. It estimates that the nation will need to spend $100 billion over the course of the next century to address the issue. In its 2020 budget, the government set aside an initial $5 billion towards a Coastline and Flood Protection Fund. Singapore is the first country in Southeast Asia to levy a carbon tax on its largest carbon-emitting corporations producing more than 25,000 tons of carbon dioxide per year, at $5 per ton.
=== Hunter-case watches === A hunter-case pocket watch is a case with a spring-hinged circular metal lid or cover, that closes over the watch-dial and crystal, protecting them from dust, scratches and other damage or debris. The name originated from England where "fox hunting men found it convenient to be able to open their watch and read the time with one hand, while holding the reins of their 'hunter' (horse) in the other hand". It is also known as a "savonnette", after the French word for soap (savon) due to its resemblance to a round soap bar. The majority of antique and vintage hunter-case watches have the lid-hinges at the 9 o'clock position and the stem, crown and bow of the watch at the 3 o'clock position. Modern hunter-case pocket watches usually have the hinges for the lid at the 6 o'clock position and the stem, crown and bow at the 12 o'clock position, as with open-face watches. In both styles of watch-cases, the sub-seconds dial was always at the 6 o'clock position. A hunter-case pocket watch with a spring-ring chain is pictured at the top of this page. An intermediate type, known as the demi-hunter (or half-hunter), is a case style in which the outer lid has a glass panel or hole in the centre giving a view of the hands. The hours are marked, often in blue enamel, on the outer lid itself; thus with this type of case one can tell the time without opening the lid.
Sources: en.wikipedia.org
The peptide contains four residues in the order alanine, glutamate, aspartate and glycine, abbreviated AEDG. The chain is linear and held together by three peptide bonds. Its calculated mass for the uncharged free form is about 390.3 daltons.
Epithalamin refers to a crude preparation derived from bovine pineal tissue, which contains many components. Epitalon is a single synthetic tetrapeptide identified from that material and produced by chemical synthesis. The two names are sometimes confused because early reports treated the synthetic peptide as an active fragment of the extract.
It has been registered for clinical use in Russia, where it is associated with a small family of short peptides. In most other jurisdictions it is not an approved medicine and is traded as a research chemical. Regulatory status varies by country and changes over time.
The molecule lacks aromatic residues, so it absorbs weakly near 280 nanometres, the wavelength applied to many other peptides. The peptide bond absorbs strongly below 220 nanometres, making 214 nanometres a practical compromise. Gradient methods must therefore use mobile phases with low ultraviolet absorbance to keep the baseline clean.