This is a working overview of Reversed-phase HPLC, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-10-20 and is reviewed periodically as new material appears.
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.
Practical handling follows from those properties. Bulk material is best divided into single-use portions soon after receipt, because each thaw exposes the whole container to moisture and temperature cycling. Vials should be allowed to reach room temperature before opening to prevent condensation on the powder. Low-binding plasticware reduces loss of dilute solutions, and sterile filtration is used when a preparation must remain free of microbial growth. Records of batch number, reconstitution date and storage history are what allow a later analytical result to be interpreted meaningfully.
Semax is a synthetic peptide created in the Soviet Union during the early 1980s by researchers working in Moscow. It was built from the short adrenocorticotropic hormone fragment known as ACTH(4-10), and the chain was then extended with three additional amino acids. The resulting molecule was named semax and entered clinical use in Russia in 1994. It is generally described as a nootropic and neuroprotective agent rather than as a hormone analogue.
The parent fragment ACTH(4-10) carries the sequence Met-Glu-His-Phe-Arg-Trp-Gly. Semax replaces the arginine and tryptophan positions with a proline-glycine-proline tail, giving Met-Glu-His-Phe-Pro-Gly-Pro. That change removes residues associated with adrenal stimulation, so the peptide does not drive cortisol release the way full ACTH does. This distinction shapes how the compound is grouped in the literature, where it sits with neuropeptides and peptide neuromodulators rather than with corticosteroids.
Regulatory status varies sharply by country. Semax is registered for medical use in Russia, where it appears in formularies as a nasal solution, and it also holds registration in a small number of neighbouring states. It has no approval from the United States Food and Drug Administration or the European Medicines Agency, and it is not a scheduled controlled substance in most jurisdictions. Elsewhere it circulates mainly as laboratory material, so purity documentation comes from suppliers rather than from a national pharmacopoeia.
| Property | Value | Notes |
|---|---|---|
| Typical purity specification | ≥ 95 % of peak area by HPLC | Some suppliers quote 98 % or higher |
| Identity confirmation | Mass spectrometry (electrospray or MALDI) | Observed mass is compared with the calculated mass |
| Common analytical method | Reversed-phase HPLC on a C18 column | Acetonitrile and water gradients with trifluoroacetic acid |
| Primary degradation route | Oxidation of the methionine residue | Yields a sulfoxide that separates cleanly on chromatography |
| Storage of dissolved material | Aliquoted and frozen at −20 °C or below | Single-use aliquots avoid repeated temperature cycling |
稳定性主要由水解与氧化两条路径支配。肽键在中性或弱酸性条件下相对稳定，遇到强碱或长时间高温则明显断裂；甲硫氨酸侧链容易被氧化成亚砜，使主峰前移并拉低实际含量。金属离子、光照和反复冻融会进一步促进降解或聚集。冻干粉在低温避光条件下可存放较长时间，配制后的水溶液通常需要冷藏并尽快用完。
纯度评估以反相高效液相色谱为主，通过主峰面积百分比给出粗略结果，再配合电喷雾质谱核对分子量。氨基酸分析可验证组成比例，手性色谱或毛细管电泳用于检查残基构型。常见杂质包括缺失序列的短肽、氧化产物与二聚体。由于多数市售品不附带完整检验报告，独立第三方检测常被用来核实标称值。
从分子层面看，Semax 是线性七肽，没有二硫键、糖基或脂链修饰，N 端为游离氨基，C 端为游离羧基。分子含组氨酸与谷氨酸侧链，因此在水和甲醇等极性溶剂中溶解良好，在非极性溶剂中溶解有限。计算分子量约为 814 Da，与其质子化离子的质荷比吻合，可用于质谱确认。
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.
Clinical reports describe use in ischaemic stroke, transient ischaemic attack, optic nerve conditions, and cognitive complaints, but most of these studies are small and were conducted in a single region. Systematic reviews have generally described the evidence base as limited in size and variable in methodological quality. Randomised controlled data suitable for international regulatory assessment are scarce. As a result, major treatment guidelines outside Russia do not include the peptide, and interest in it remains largely research-driven rather than routine clinical.
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.
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Eli Lilly and Company, doing business as Lilly, is an American multinational pharmaceutical company headquartered in Indianapolis, Indiana, with offices in 18 countries. Its products are sold in approximately 125 countries. The company was founded in 1876 by Eli Lilly, a pharmaceutical chemist and Union army veteran during the American Civil War for whom the company was later named. The company is ranked 4th on the list of largest biomedical companies by revenue and is the most valuable pharmaceutical company worldwide. It is ranked 100th on the Fortune 500 and 138th on the Forbes Global 2000. In November 2025, the company reached a $1 trillion market capitalization, the first health-care company in the world to do so. The company's primary products are tirzepatide (Mounjaro and Zepbound) for the treatment of type 2 diabetes, weight loss, and obstructive sleep apnea (56% of 2025 revenues); abemaciclib (Verzenio) for the treatment of advanced or metastatic breast cancers (9% of 2025 revenues); dulaglutide (Trulicity) for the treatment of type 2 diabetes (7% of 2025 revenues); ixekizumab (Taltz) for the treatment of autoimmune diseases (6% of 2025 revenues); and empagliflozin (Jardiance) for the treatment of type 2 diabetes (5% of 2025 revenues).
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covalent bond Also molecular bond. A bond that involves the sharing of electron pairs between atoms. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as covalent bonding.
=== Termination === The phosphorylation of PAR1's cytoplasmic tail and subsequent binding to arrestin uncouples the protein from G protein signaling. These phosphorylated PAR1s are transported back into the cell via endosomes where they are sent to Golgi bodies. The cleaved PAR1s are then sorted and transported to lysosomes where they are degraded. This internalization and degradation process is necessary for the termination of receptor signaling.
The valence of an element can be defined either as the number of hydrogen atoms that can combine with it to form a simple binary hydride, or as twice the number of oxygen atoms that can combine with it to form a simple binary oxide (that is, not a peroxide or a superoxide). The valences of the main-group elements are directly related to the group number: the hydrides in the main groups 1–2 and 13–17 follow the formulae MH, MH2, MH3, MH4, MH3, MH2, and finally MH. The highest oxides instead increase in valence, following the formulae M2O, MO, M2O3, MO2, M2O5, MO3, M2O7. Today the notion of valence has been extended by that of the oxidation state, which is the formal charge left on an element when all other elements in a compound have been removed as their ions. The electron configuration suggests a ready explanation from the number of electrons available for bonding; indeed, the number of valence electrons starts at 1 in group 1, and then increases towards the right side of the periodic table, only resetting at 3 whenever each new block starts. Thus in period 6, Cs–Ba have 1–2 valence electrons; La–Yb have 3–16; Lu–Hg have 3–12; and Tl–Rn have 3–8. However, towards the right side of the d- and f-blocks, the theoretical maximum corresponding to using all valence electrons is not achievable at all; the same situation affects oxygen, fluorine, and the light noble gases up to krypton.
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Suppliers normally quote a percentage of total chromatographic peak area, most often from reversed-phase HPLC. That figure says nothing about what the remaining percentage contains, and it depends on the detection wavelength used. A mass spectrometry result is a separate and stronger check on identity.
The methionine residue at the start of the chain is vulnerable to oxidation, producing a sulfoxide variant. Amide bonds can also hydrolyze, though more slowly under neutral conditions. Cold storage, oxygen exclusion and minimization of freeze-thaw cycles slow both processes but do not stop them.
A purity number on a certificate does not establish that a powder is the same product as a registered nasal medicine. Counter-ion content, residual solvents and peptide-related impurities may differ between the two. Independent verification is the only way to narrow that gap.
Registered medical products are most often 0.1% nasal drops. Research suppliers ship lyophilized powder, usually in milligram quantities, which is dissolved before use. The active peptide is the same in both cases; presentation and excipients differ.