Reversed-phase HPLC is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-08-01. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
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.
| 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 |
The compound is generally described as a synthetic analogue of a fragment isolated from a pineal gland extract. Researchers associated with the Saint Petersburg Institute of Bioregulation and Gerontology introduced it during the 1980s and 1990s while studying short peptides from animal tissue. The original extract, called epithalamin, is a heterogeneous mixture, whereas epitalon is a single defined sequence. That distinction matters because findings reported for the extract are not automatically findings about the pure tetrapeptide, and claims about broader biological effects remain a separate question from the chemical identity described here.
Residue composition is the property that most cleanly separates verified material from mislabelled samples. Alanine, glutamate, aspartate and glycine appear in that order from the N-terminus, and the two acidic residues sit in the middle of the chain. Because the peptide is short, it can be produced by solid-phase synthesis and characterised by mass spectrometry without ambiguity. Any reported sample whose measured mass departs substantially from 390 daltons is a different compound or a degraded mixture rather than epitalon.
Epitalon is a synthetic tetrapeptide whose four residues are alanine, glutamate, aspartate and glycine, commonly abbreviated AEDG. Its molecular formula is C14H22N4O9 and its monoisotopic mass is near 390.35 daltons. The peptide carries two acidic side chains, so it is neutral to negatively charged in most aqueous buffers. Published reference summaries usually list it under both spellings, epitalon and epithalon, and treat the two names as the same material.
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.
=== As a host for intracellular pathogens === In their role as a phagocytic immune cell macrophages are responsible for engulfing pathogens to destroy them. Some pathogens subvert this process and instead live inside the macrophage. This provides an environment in which the pathogen is hidden from the immune system and allows it to replicate. Diseases with this type of behaviour include tuberculosis (caused by Mycobacterium tuberculosis) and leishmaniasis (caused by Leishmania species). In order to minimize the possibility of becoming the host of an intracellular bacteria, macrophages have evolved defense mechanisms such as induction of nitric oxide and reactive oxygen intermediates, which are toxic to microbes. Macrophages have also evolved the ability to restrict the microbe's nutrient supply and induce autophagy.
Membrane lipids: Phospholipids: Phospholipids are a major component of the lipid bilayer of the cell membrane and are found in many parts of the body. Sphingolipids: Sphingolipids are mostly found in the cell membrane of neural tissue. Glycolipids: The main role of glycolipids is to maintain lipid bilayer stability and facilitate cell recognition. Glycerophospholipids: Neural tissue (including the brain) contains high amounts of glycerophospholipids. Other types of lipids: Cholesterol: Cholesterol is the main precursor for different hormones in our body such as progesterone and testosterone. The main function of cholesterol is controlling the cell membrane fluidity. Steroid – see also steroidogenesis: Steroids are one of the important cell signaling molecules. Triacylglycerols (fats) – see also lipolysis and lipogenesis: Triacylglycerols are the major form of energy storage in human body. Fatty acids – see also fatty acid metabolism: Fatty acids are one of the precursors used for lipid membrane and cholesterol biosynthesis. They are also used for energy. Bile salts: Bile salts are secreted from liver and they facilitate lipid digestion in the small intestine. Eicosanoids: Eicosanoids are made from fatty acids in the body and they are used for cell signaling. Ketone bodies: Ketone bodies are made from fatty acids in the liver. Their function is to produce energy during periods of starvation or low food intake.
==== Bangsamoro ==== In the Bangsamoro Parliament, members of the interim body, known as the Bangsamoro Transition Authority, are nominated by both the Moro Islamic Liberation Front (MILF) and the Philippine government, and appointed by the president of the Philippines.
Those peptides expressing a drug-related, non-self epitope on one of their various HLA protein forms (HLA-A, HLA-B, HLA-C, HLA-DM, HLA-DO, HLA-DP, HLA-DQ, or HLA-DR) can bind to a T-cell receptor and thereby stimulate the receptor-bearing parent T cell to initiate attacks on self tissues. Alternatively, a drug or its metabolite may stimulate these T cells by inserting into the groove on a HLA protein to serve as a non-self epitope or bind outside of this groove to alter a HLA protein so that it forms a non-self epitope. In all these cases, however, a non-self epitope must bind to a specific HLA serotype (i.e. variation) in order to stimulate T cells. Since the human population expresses some 13,000 different HLA serotypes while an individual expresses only a fraction of them and since a SJS-inducing drug or metabolite interacts with only one or a few HLA serotypes, a drug's ability to induce SCARs is limited to those individuals who express HLA serotypes targeted by the drug or its metabolite. Accordingly, only rare individuals are predisposed to develop a SCARs in response to a particular drug on the bases of their expression of HLA serotypes: Studies have identified several HLA serotypes associated with development of SJS, SJS/TEN, or TEN in response to certain drugs. In general, these associations are restricted to the cited populations. In some East Asian populations studied (Han Chinese and Thai), carbamazepine- and phenytoin-induced SJS is strongly associated with HLA-B*1502 (HLA-B75), an HLA-B serotype of the broader serotype HLA-B15.
==== Huo and Wang ==== In 1989–1993, Huo and Wang (中国社会科学院考古研究所, Zhongguo shehui kexueyuan kaogu yanjiusuo) tested the following caves: 224, 76, 4, 8, 34, 68, 77, 98, 104, 114, 117, 118, 119, 125, 129, 135, 162, 171, 180, 189, 196, 198, 206, 212, 219, 227, 27, 39, 48, 60, 69, 84, 91, 92, 99, 123, 139, 161, 165, 178, 207. They proposed a chronology which has some significant differences with the chronology previously proposed by Su Bai. Japanese teams of Nagoya University (日本名古屋大学) tested in 1995, 1997, 1998 and 2011 the following caves: 8, 171, 224, 13, 67, 76, 77, 92, 205. Many of the results remain inconclusive, sometimes even contradictory, and the historical period in question is rather too short in relation to the uncertainty margin of Carbon 14 datation, to provide a meaningful segmentation of the caves. Most narrow Carbon dates given for the Kizil Caves refer to a 68% probability level (1σ), which implies a significant level of uncertainty, and when dates are adjusted to the 95% probability level (2σ) as standard archaeological practice requires, then the timespan between the earliest and lowest dates becomes so large (about 200 to 300 years), as to make individual comparisons between the caves meaningless. Most researchers now use an approach combining artistic and architectural analysis together with carbon-dating, as a way to approach a reliable nomenclature, as proposed by Marylin Martin Rhie from 2001.
Sources: en.wikipedia.org
The strong tornado widened again and curved northward as it exited Hodonín and moved into a rural area, completely mowing down a large swath of trees as it impacted a patch of forest. Metal truss transmission towers were blown over in this area, crops were damaged in farm fields, and damage along this segment of the path was rated F2. The tornado briefly strengthened again one final time as it struck the village of Pánov at high-end F3 strength. Almost every structure in the small village was damaged in some way, and multiple homes were significantly damaged or destroyed, a few of which were leveled. Outbuildings were destroyed, cars were damaged by flying debris, and large trees were snapped and denuded as well. The tornado continued past Pánov and moved through another densely forested area, weakening back to F2 strength as it flattened another large swath of trees. The tornado continued to weaken, and trees beyond this point were downed at F1 intensity as the tornado continued to the northeast before it abruptly dissipated near Ratíškovice. In all, at least 1,200 buildings were damaged or destroyed by the tornado along its 27.1 kilometer (17 mi)-long path. 6 people were killed by the tornado, and at least 200 more were injured, some critically.
=== Sampling calorimeters for detectors in high-energy particle physics === Depleted uranium has been used in a number of sampling calorimeters (such as in the D0 and ZEUS detectors) because of its high density and natural radioactivity.
Although canagliflozin produces beneficial effects on HDL cholesterol, it has also been shown to increase LDL cholesterol to produce no change in total cholesterol. Evidence shows that apart from positive effects on glycemic levels, canagliflozin also reduces the risk of heart attacks and heart failures. SGLT2 inhibitors, including canagliflozin, reduce the likelihood of hospitalization for congestive heart failure or progression of renal disease in persons with diabetes mellitus type 2 and reduce the likelihood of stroke and heart attack in persons with diabetes mellitus type 2 who have known atherosclerotic vascular disease.
One form of C-terminal modification is prenylation. During prenylation, a farnesyl- or geranylgeranyl-isoprenoid membrane anchor is added to a cysteine residue near the C-terminus. Small, membrane-bound G proteins are often modified this way.
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 solid is kept cold, dry and dark, typically at minus twenty degrees Celsius, in a sealed container with desiccant. Dissolved material is kept refrigerated and used promptly. Freezing and thawing a solution repeatedly is avoided because it accelerates degradation.