counterion raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-03-05. Anything still debated is marked as such rather than presented as settled.
Purity assessment relies mainly on reversed-phase high-performance liquid chromatography, which separates the target heptapeptide from truncated sequences, deletion analogues, and oxidised forms. Mass spectrometry, usually coupled to liquid chromatography, confirms identity through the expected molecular ion and reveals modifications such as methionine sulfoxide formation. Amino acid analysis can verify composition, and tandem mass spectrometry supports sequence confirmation. Ultraviolet detection near 254 to 280 nanometres is convenient because the phenylalanine and histidine residues absorb in that region. Nuclear magnetic resonance is rarely used for routine release testing.
Common degradation pathways include oxidation of the methionine side chain, hydrolysis of the peptide backbone, and aggregation under unfavourable pH or concentration. Stability studies typically monitor the main peak by chromatography and report total related substances as a percentage. Because no official monograph exists, acceptance criteria vary between laboratories, and reported purity values are not directly comparable across suppliers. Analysts therefore document the method, column, and detection wavelength alongside each result, and open questions remain about how much biological activity the oxidised forms retain.
The C-terminal Pro-Gly-Pro extension is not incidental. Proline-rich tails are known to resist several common peptidases, and the published literature attributes the longer half-life of Semax, relative to unmodified ACTH fragments, to this feature. The modification also removes the melanocyte-stimulating and corticosteroidogenic activity that characterizes longer ACTH-derived sequences. Because the molecule is small and hydrophilic, it is typically formulated as an aqueous solution for intranasal or parenteral delivery. Acetylation or amidation at the termini appears in closely related research peptides and shifts the mass by a fixed increment.
Reported pharmacological work centers on neurotrophic signaling, including changes in BDNF and NGF expression in hippocampal tissue in animal models. Human data come largely from studies conducted in Russia, and how well those results generalize to other populations remains an open question. Regulatory status differs sharply by jurisdiction: Semax is a registered prescription medicine in Russia, while it holds no approved marketing status in the United States or the European Union. Outside such jurisdictions it is generally handled as a research chemical, which affects both documentation and quality expectations.
| Property | Value | Notes |
|---|---|---|
| Typical analytical method | Reversed-phase HPLC with UV detection | Separates target peptide from truncated and oxidised forms |
| Identity confirmation | LC-MS or ESI-MS | Compares observed and calculated molecular ion |
| Primary degradation route | Methionine oxidation | Forms the sulfoxide; monitored as an early-eluting peak |
| Short-term storage | 2 to 8 degrees Celsius | Applies to working vials and reconstituted portions |
| Common synonyms | ACTH(4–10) analogue, MEHFPGP | Descriptive names used in laboratory catalogues |
Identity and purity of Semax are established mainly by reversed-phase high-performance liquid chromatography coupled with mass spectrometry. The chromatographic trace gives a purity estimate as a percentage of total peak area, while electrospray or matrix-assisted laser desorption ionization confirms the molecular mass against the calculated value. Amino acid analysis and sequence-specific fragmentation provide further confirmation when a supplier's chain of custody is unclear. Vendors frequently quote a purity figure without stating the detection wavelength or the integration method, which limits how far one number can be compared with another.
Stability depends heavily on physical state. Lyophilized powder held dry, cold and dark retains its content over long periods, whereas dissolved peptide begins to change within days at room temperature. The most cited degradation route is oxidation of the methionine residue, which converts the peptide to a sulfoxide form that elutes differently on chromatography. Hydrolysis of amide bonds and adsorption onto container walls contribute smaller losses. Buffers that exclude oxygen from the headspace slow the oxidation pathway, but no single condition prevents all change indefinitely.
Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. It corresponds to the ACTH(4-7) fragment extended at the C-terminus by a Pro-Gly-Pro tripeptide, an addition intended to slow enzymatic breakdown. The molecular formula is C37H51N9O10S and the molecular mass is approximately 814 daltons. In the literature it is often described as an ACTH(4-10) analog, although that label reflects a naming convention as much as a precise structural relationship. The compound was developed in Russia and remains most closely associated with that research tradition.
Laboratory descriptions of the material are consistent across suppliers. It appears as a white to off-white lyophilized powder that dissolves readily in water and in polar organic solvents such as dimethyl sulfoxide. Aqueous solutions are clear and colorless at low concentrations. Because the peptide contains methionine, oxidation at the sulfur atom is a recognized degradation pathway, and handling notes usually call for protected, desiccated storage. Reported purity for research-grade lots is generally above 95 percent as measured by reversed-phase high-performance liquid chromatography.
The compound is registered in Russia as a pharmaceutical product, most commonly formulated as a nasal solution, and has been used in that setting since the 1990s. Outside that jurisdiction it is generally handled as a research chemical rather than an approved medicine. Regulatory status therefore differs sharply between countries, and material sold internationally may not correspond to the Russian pharmaceutical formulation. Documentation with commercial samples is typically limited to a certificate of analysis covering purity and identity, not clinical status or local legal classification.
Semax is supplied as a lyophilized powder that appears white to off-white. It dissolves readily in water, phosphate-buffered saline, and other aqueous media, which simplifies preparation of working solutions for laboratory use. The nasal products registered in Russia are dilute aqueous solutions, typically around 0.1 percent peptide by weight. Organic solvents are rarely necessary and can complicate handling. Because the peptide is hygroscopic, weighing should be performed quickly and with minimal exposure to ambient humidity.
Solid material is normally kept at minus 20 degrees Celsius in a sealed, desiccated container. Reconstituted solutions are less stable and are usually divided into single-use aliquots before freezing. Repeated freeze-thaw cycles are avoided because they promote aggregation and loss of activity. Light exposure is minimized by using amber glassware or foil wrapping. Published stability data for this peptide are sparse, so recommended storage conditions rest mainly on general practice for short synthetic peptides rather than on dedicated study.
Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. It is described in the literature as an analogue of the ACTH(4–10) fragment, a short N-terminal portion of adrenocorticotropic hormone that retains some neurotropic activity without the full hormonal effects of the parent peptide. The molecule carries a methionine residue at the N-terminus and two proline residues near the C-terminus, features that shape both its interactions with receptor systems and its chemical stability. The free peptide corresponds to the formula C37H51N9O10S and a molecular mass near 813.9 Da.
The compound was developed in the 1980s at the Institute of Molecular Genetics in Moscow, where it emerged from research on short ACTH fragments and their effects on the central nervous system. Russian pharmaceutical listings describe it as a nootropic and neuroprotective agent, most often formulated as nasal drops. It is not a marketed medicine in the United States or the European Union, and no pharmacopoeial monograph covers it. Consequently, most published clinical experience with the substance originates from a small number of research centres, mainly in Russia and neighbouring countries.
Pharmacological accounts link semax to melanocortin signalling and to modulation of neurotrophic factor expression, particularly brain-derived neurotrophic factor and nerve growth factor. Much of this evidence comes from rodent studies using intranasal delivery, a route chosen because it allows peptides to reach the central nervous system with limited systemic exposure. Whether the same mechanisms operate in humans at comparable magnitude remains an open question. The precise receptor or receptors responsible for the reported behavioural and neuroprotective effects have not been conclusively identified.
A clinical biologist is a health professional such as a doctor of medicine, pharmacist, biologist that is specialized in clinical biology, a medical specialty derived from clinical pathology. The concept includes interventional biology, including assisted reproductive technology. These professionals follow a medical residency whose duration varies between countries (from 3 to 5 years). This term is frequently used in France, Switzerland, Belgium, and other countries in Western Europe, Africa or Asia.
Tofisopam has been shown to act as an inhibitor of the liver enzyme CYP3A4, and some researches suspect that this could cause dangerous drug interactions with other medications metabolised by this enzyme, although the clinical significance of these findings remains unclear.
=== Selegiline inhibition of cytochrome P450 enzymes === Selegiline has been reported to inhibit several cytochrome P450 enzymes, including CYP2D6, CYP3A4/5, CYP2C19, CYP2B6, and CYP2A6. It is a mechanism-based inhibitor (suicide inhibitor) of CYP2B6 and has been said to "potently" or "strongly" inhibit this enzyme in vitro. It may inhibit the metabolism of bupropion, a major CYP2B6 substrate, into its active metabolite hydroxybupropion. However, a study predicted that inhibition of CYP2B6 by selegiline would non-significantly affect exposure to bupropion. Selegiline has not been listed or described as a clinically significant CYP2B6 inhibitor by the Food and Drug Administration (FDA) as of 2023. One small study observing three patients found that selegiline was safe and well-tolerated in combination with bupropion. In addition to CYP2B6 and other cytochrome P450 enzymes, selegiline is a potent mechanism-based inhibitor of CYP2A6 and may increase exposure to nicotine (a major CYP2A6 substrate). By inhibiting cytochrome P450 enzymes like CYP2B6 and CYP1A2, selegiline may inhibit its own metabolism and thereby interact with itself.
Note that in the context of metal-ligand complex formation, the equilibrium constants for the formation of metal complexes are usually defined as association constants. In that case, the equilibrium constants for ligand protonation are also defined as association constants. The numbering of association constants is the reverse of the numbering of dissociation constants; in this example
Sources: en.wikipedia.org
He received the Hirschmann Award in Peptide Chemistry from the American Chemical Societyin 1994, the (inaugural) Kaiser Award from the Protein Society in 2002, the du Vigneaud Award from the American Peptide Society (2004), the 2009 Merrifield award from the American Peptide Society, the Rudinger Medal from the European Peptide Society (2010), the Akabori Medal from the Japanese Peptide Society (2010), the Bader Award in Bioorganic Chemistry (2011) from the American Chemical Society, the Leach Medal from the Lorne Protein Conference (2013), the Prelog Medal from the ETH Zurich (2017), the (inaugural) Scoffone Award from the Italian Peptide Society (2018), and the Meienhofer Award of the Boulder Peptide Society (2022). Dr. Kent is Honorary Fellow of the Royal Society of New Zealand. He was elected Fellow of the American Association for the Advancement of Science in 2000, and Fellow of the Royal Society of Chemistry in 2008. In May 2016 the Journal of Peptide Science, edited by Luis_Moroder, published a Festschrift in celebration of Stephen Kent's 70th birthday. In 2022, Stephen Kent's scientific autobiography was published as the first English language contribution to the book series Lives-in-Chemistry; this series is steered by an Advisory Board appointed by the Executive Committee of the Fachgruppe Geschichte der Chemie (History of Chemistry Division) of the Gesellschaft Deutscher Chemiker (GDCh).
=== Gag order === Syngenta sued to stop communication by Swiss health authorities with the Swiss public regarding the "relevance" of specific metabolites of chlorothalonil that Swiss authorities detected in high concentrations in the groundwater from which hundreds of thousands of Swiss people obtain drinking water. The court banned Swiss health authorities from communicating with the public about the dangers posed by some of the metabolites.
To emphasise that there was now only one Indian Army, and that all units were to be trained and deployed without regard for their regional origins, the regiments were renumbered into single sequences of cavalry, artillery, infantry of the line, and Gurkha Rifles. Regimental designations were altered to remove all references to the former Presidency Armies. Where appropriate subsidiary titles recalling other identifying details were adopted. Thus the 2nd Bengal Lancers became the 2nd Lancers (Gardner's Horse). The new order began with the Bengal regiments, followed by the Punjab Frontier Force, then the regiments of Madras, the Hyderabad Contingent, and Bombay. Wherever possible a significant digit was retained in the new number. Thus the 1st Sikh Infantry became the 51st Sikhs, the 1st Madras Pioneers became the 61st Pioneers, and the 1st Bombay Grenadiers became the 101st Grenadiers. The Gurkha Regiments had developed into their own Line of rifle regiments since 1861. They were five of these until they were joined by the former 42nd, 43rd, & 44th Gurkha Regiments of the Bengal Army, who became the 6th, 7th, & 8th Gurkha Rifles. The numbers 42, 43, & 44 were allocated respectively to the Deoli and Erinpura Irregular Forces and the Mhairwara Battalion from Rajputana.
Sources: en.wikipedia.org
will lead to a dimension-different PseAA composition. Using Eq.6 is just one of the many modes for deriving the correlation factors in PseAAC or its components. The others, such as the physicochemical distance mode and amphiphilic pattern mode, can also be used to derive different types of PseAAC, as summarized in a 2009 review article. In 2011, the formulation of PseAAC (Eq.3) was extended to a form of the general PseAAC as given by:
Once we draw out the potential stereoisomers, we see that the two structures are super-imposable in three dimensions, and therefore are the self-same molecule. For this reason fentanyl does not have R/S assignments. The second case studied here is of 3-methylfentanyl. There are two potential stereocenters, at the 4-carbon and also at the 3-carbon, where there is additionally a methyl group. Now, we mark both 3 and 4 carbon as potential stereocenters with an asterisk (*), and see how many potential stereoisomers we can eliminate. We see that of the four permutations of stereoisomers, none are super-imposable in three dimensions, meaning each is a unique stereoisomer and that both potential stereocenters were true. This gives four potential R/S assignments, 1R3S, 1R3R, 1S3S, 1S3R. What is particularly interesting and quite a contrast from the previous example of cyclohexanol, is the stereocenter at C-4 is indeed a true stereocenter here, whereas in the previous example of cyclohexanol as an analogy to fentanyl, the C-4 was not a true stereocenter. This changed because the modification of the C-3 carbon without an equivalent change on the C-2 carbon created an imbalance between two formerly identical substituents, creating a novel stereocenter where there was not one previously. This is why it is so important to follow the 4 steps in the above procedure every time, as "inherited procedural wisdom" may hold an organic chemist back in finding the true or correct answer.
Hypoxic-anoxic events may affect the fetus at various stages of fetal development, during labor and delivery, and in the postnatal period. Sometimes, even an infant that is still in the womb may exhibit signs of HIE or other hypoxic-ischemic injury. Fetal distress is one of the most common signs of HIE or other oxygen-depriving event. Other problems during pregnancy may include preeclampsia, maternal diabetes with vascular disease, congenital fetal infections, substance/alcohol use, severe fetal anemia, cardiac disease, lung malformations, or problems with blood flow to the placenta. Problems during labor and delivery can include umbilical cord occlusion, torsion or prolapse, rupture of the placenta or uterus, excessive bleeding from the placenta, abnormal fetal position such as the breech position, prolonged late stages of labor, or very low blood pressure in the mother. Problems after delivery can include severe prematurity, severe lung or heart disease, serious infections, trauma to the brain or skull, congenital malformations of the brain or very low blood pressure in the baby and due to suffocation in cases of Münchausen syndrome by proxy. The severity of a neonatal hypoxic-ischaemic brain injury may be assessed using Sarnat staging, which is based on clinical presentation and EEG findings, and also using MRI. Signs and symptoms of HIE may include:
Sources: en.wikipedia.org
Dry powder is usually kept at about -20 degrees Celsius for long-term storage and at 2 to 8 degrees Celsius for short working periods. Containers should stay sealed and protected from light and moisture to limit degradation.
Oxidation of the methionine residue to the sulfoxide is a frequently reported change, and it usually appears as an earlier-eluting peak in reversed-phase chromatography. Backbone hydrolysis products can also accumulate in aqueous solution.
Liquid chromatography coupled with mass spectrometry is the usual approach, because the observed molecular ion can be compared with a calculated mass of about 813.9 Da. Retention time alone does not establish identity.
The sequence is Met-Glu-His-Phe-Pro-Gly-Pro, a seven-residue peptide. The first four residues correspond to the ACTH(4-10) fragment, and Pro-Gly-Pro is added at the C-terminus. N-acetylated versions also appear in the literature and differ in mass.