If you have been reading about reversed-phase HPLC and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-12-26. Where a claim depends on a specific study, the study is described rather than over-claimed.
Semax is normally supplied as a lyophilized powder, and that form is the most stable. Suppliers commonly recommend storage at -20 °C in a desiccated container protected from light, with short-term handling at room temperature limited to weighing and transfer. Powder that has absorbed moisture degrades faster, so vials should be warmed to ambient temperature before opening to prevent condensation on the contents. Hygroscopic behavior is typical of short hydrophilic peptides, and humidity control matters more than temperature alone for long-term retention.
Once dissolved, the peptide is considerably less stable than the solid. Aqueous solutions are usually prepared at neutral to slightly acidic pH, filtered, and divided into single-use aliquots before freezing. Repeated freeze-thaw cycles are a common cause of avoidable loss and are best prevented by never refreezing a thawed aliquot. Adsorption to plastic and glass surfaces can lower the measured concentration of dilute solutions, particularly below roughly 0.1 mg/mL. Buffer choice, salt content, and container material all influence how much peptide remains detectable after storage.
Lyophilised powder is normally kept at -20 °C in a desiccated container, with some suppliers recommending -80 °C for long-term archival storage. Repeated freeze-thaw cycles are the most common cause of avoidable loss, so aliquoting before freezing reduces variability between working sessions. Dissolved peptide is far less stable than the dry solid and is usually prepared fresh or held briefly at 4 °C. Aqueous solutions support both hydrolysis of the backbone and oxidation of the N-terminal methionine, and these two routes dominate degradation under ordinary laboratory conditions.
Identity and purity are confirmed with reversed-phase high-performance liquid chromatography, typically monitored at 214 nanometres where the peptide bond absorbs. Mass spectrometry, either electrospray or MALDI-TOF, verifies molecular mass against the theoretical value and detects truncation or adduct formation. Amino acid analysis and peptide mapping provide additional confirmation when required. The most frequently reported impurities are deletion sequences from incomplete coupling, methionine sulfoxide from oxidation, and dimeric species formed through non-covalent aggregation. Impurity profiles depend strongly on the synthesis and purification route chosen by the producer.
| Property | Value | Notes |
|---|---|---|
| Solid storage temperature | -20 °C or below | Desiccated and protected from light |
| Solution storage temperature | -80 °C as single-use aliquots | Avoid repeated freeze-thaw cycles |
| Purity assessment method | RP-HPLC, around 214 nm | Reported as main-peak area percent |
| Identity confirmation method | ESI-MS or MALDI-TOF | Measured mass compared with calculated mass |
| Common synonyms | ACTH(4-10) analog; Met-Glu-His-Phe-Pro-Gly-Pro | Also written as Semaxum in some sources |
Solid semax is typically supplied as a lyophilised powder that is hygroscopic and sensitive to moisture, light, and repeated temperature cycling. Long-term storage of the dry peptide is generally recommended at approximately -20 degrees Celsius, while shorter working periods may use refrigeration at 2 to 8 degrees Celsius. Vials should remain tightly closed and desiccated when brought to room temperature, because condensation can damage the material before it is weighed. Dividing a batch into aliquots is preferable to thawing one container repeatedly.
Dissolution is normally performed in water, phosphate-buffered saline, or normal saline, since the peptide is freely soluble in aqueous media and is rarely handled with strong organic solvents. Solution pH should be kept near neutral, because extreme acidity or alkalinity accelerates backbone hydrolysis and encourages oxidation of the methionine side chain. Once dissolved, the material is less stable than the dry powder and is commonly divided into single-use portions and frozen. Buffers containing primary amines, such as Tris, are often avoided because of possible side reactions.
Circulation time for the peptide is short because peptidases cleave it readily. The Pro-Gly-Pro tail is thought to slow breakdown compared with the bare ACTH fragment, but the gain appears modest. Absorption after intranasal dosing is limited, and only a fraction of a dose is expected to reach the central nervous system. Laboratory concentrations therefore sit well above levels achieved systemically, a gap that complicates translation from bench findings to clinical claims.
The mechanisms attributed to semax are inferred from animal and cell studies rather than traced to one confirmed target. The most frequently cited pathway involves increased expression of brain-derived neurotrophic factor and nerve growth factor in hippocampal and cortical tissue. Some work points to engagement of melanocortin receptors, particularly MC4, which the parent ACTH fragment can activate. Effects on dopaminergic and serotonergic signalling have also been reported. No single account explains all observed results, and the relative weight of each pathway remains unsettled.
Published studies examine a fairly narrow set of endpoints. Rodent experiments commonly measure maze learning, infarct volume after induced ischemia, and tissue levels of neurotrophic factors. Clinical reports from Russian centres describe attention, memory and recovery scores in patients after stroke or transient ischemic attack. Most of those human studies are small and few have been repeated by independent groups. Outcome measures differ between studies, which limits direct comparison.
The major long-term complications of diabetes relate to damage to blood vessels at both macrovascular and microvascular levels. Diabetes doubles the risk of cardiovascular disease, and about 75% of deaths in people with diabetes are due to coronary artery disease. Other macrovascular morbidities include stroke and peripheral artery disease. Microvascular disease affects the eyes, kidneys, and nerves. Damage to the retina, known as diabetic retinopathy, is the most common cause of blindness in people of working age. The eyes can also be affected in other ways, including development of cataract and glaucoma. It is recommended that people with diabetes visit an optometrist or ophthalmologist once a year. Diabetic nephropathy is a major cause of chronic kidney disease, accounting for over 50% of patients on dialysis in the United States. Diabetic neuropathy, damage to nerves, manifests in various ways, including sensory loss, neuropathic pain, and autonomic dysfunction (such as postural hypotension, diarrhea, and erectile dysfunction). Loss of pain sensation predisposes to trauma that can lead to diabetic foot problems (such as ulceration), the most common cause of non-traumatic lower-limb amputation. Hearing loss is another long-term complication associated with diabetes. Based on extensive data and numerous cases of gallstone disease, it appears that a causal link might exist between type 2 diabetes and gallstones. People with diabetes are at a higher risk of developing gallstones compared to those without diabetes.
=== Neurohormone === GnRH is considered a neurohormone, a hormone produced in a specific neural cell and released at its neural terminal. A key area for production of GnRH is the preoptic area of the hypothalamus, which contains most of the GnRH-secreting neurons. GnRH neurons originate in the nose and migrate into the brain, where they are scattered throughout the medial septum and hypothalamus and connected by very long >1-millimeter-long dendrites. These bundle together so they receive shared synaptic input, a process that allows them to synchronize their GnRH release. The GnRH neurons are regulated by many different afferent neurons, using several different transmitters (including norepinephrine, GABA, glutamate). For instance, dopamine appears to stimulate LH release (through GnRH) in estrogen-progesterone-primed females; dopamine may inhibit LH release in ovariectomized females. Kisspeptin appears to be an important regulator of GnRH release. GnRH release can also be regulated by estrogen. It has been reported that there are kisspeptin-producing neurons that also express estrogen receptor alpha.
In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties p of the system, the partial derivative with respect to time is zero and remains so:
Sources: en.wikipedia.org
Gram-positive organisms: Staphylococcus aureus (including methicillin-resistant [MRSA] and methicillin-susceptible [MSSA] isolates), Staphylococcus haemolyticus, Staphylococcus lugdunensis, Streptococcus agalactiae, Streptococcus anginosus group (including Streptococcus anginosus, Streptococcus intermedius, and Streptococcus constellatus), Streptococcus pyogenes, and Enterococcus faecalis Gram-negative organisms: Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Susceptible bacteria for CABP are: Streptococcus pneumoniae, Staphylococcus aureus (methicillin-susceptible [MSSA] isolates only), Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Haemophilus influenzae, Haemophilus parainfluenzae, Chlamydia pneumoniae, Legionella pneumophila, and Mycoplasma pneumoniae. It has not been tested in pregnant women. In the European Union, it is indicated for the treatment of acute bacterial skin and skin structure infections (ABSSSI) in adults when it is considered inappropriate to use other antibacterial agents that are commonly recommended for the initial treatment of these infections.
== AMPA Receptors in Disease Beyond Epilepsy == AMPA receptors are essential to excitatory neurotransmission in the CNS. Beyond their established role in epilepsy, recent research indicates that AMPARs are implicated in various neurological and psychiatric disorders, including excitotoxicity in stroke and neurodegeneration, as well as conditions such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Huntington's disease, schizophrenia, and autism spectrum disorders (ASD).
Schleiden was a microscopist and an early plant anatomist who co-founded the cell theory with Theodor Schwann and Rudolf Virchow and was among the first to grasp the significance of the cell nucleus that had been described by Robert Brown in 1831. In 1855, Adolf Fick formulated Fick's laws that enabled the calculation of the rates of molecular diffusion in biological systems.
Peppermint (Mentha × piperita) is a hybrid species of mint, a cross between watermint and spearmint. Indigenous to Europe and the Middle East, the plant is now widely spread and cultivated in many regions of the world. It is occasionally found in the wild with its parent species. Although the genus Mentha comprises more than 25 species, peppermint is the most widely used variant. While Western peppermint is derived from Mentha × piperita, Chinese peppermint, or bohe, is derived from the fresh leaves of M. haplocalyx. M. × piperita and M. haplocalyx are both recognised as plant sources of menthol and menthone, and are among the oldest herbs used for both culinary and medicinal products.
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The thyroid hormones function via a well-studied set of nuclear receptors, termed the thyroid hormone receptors. These receptors, together with corepressor molecules, bind DNA regions called thyroid hormone response elements (TREs) near genes. This receptor-corepressor-DNA complex can block gene transcription. Triiodothyronine (T3), which is the active form of thyroxine (T4), goes on to bind to receptors. The deiodinase catalyzed reaction removes an iodine atom from the 5′ position of the outer aromatic ring of thyroxine's (T4) structure. When triiodothyronine (T3) binds a receptor, it induces a conformational change in the receptor, displacing the corepressor from the complex. This leads to recruitment of coactivator proteins and RNA polymerase, activating transcription of the gene. Although this general functional model has considerable experimental support, there remain many open questions. More recently genetic evidence has been obtained for a second mechanism of thyroid hormone action involving one of the same nuclear receptors, TRβ, acting rapidly in the cytoplasm through the PI3K. This mechanism is conserved in all mammals but not fish or amphibians, and regulates brain development and adult metabolism. The mechanism itself parallels the actions of the nuclear receptor in the nucleus: in the absence of hormone, TRβ binds to PI3K and inhibits its activity, but when hormone binds the complex dissociates, PI3K activity increases, and the hormone bound receptor diffuses into the nucleus.
Some glycerol-based ear medications for use in removing excess wax as well as relieving ear conditions such as otitis media and swimmer's ear. Some previous diet products such as Ayds. Some condoms designed to prevent premature ejaculation. Benzocaine largely inhibits sensitivity on the penis, and can allow for an erection to be maintained longer (in a continuous act) by delaying ejaculation. Conversely, an erection will also fade faster if stimulus is interrupted. Benzocaine mucoadhesive patches have been used in reducing orthodontic pain. In Poland it is included, together with menthol and zinc oxide, in the liquid powder (not to be confused with the liquid face powder) used mainly after mosquito bites. Today's ready-made Pudroderm was once used there as pharmaceutical compound.
=== 1982 === February 24: President Ronald Reagan announces the "Caribbean Basin Initiative" to prevent the overthrow of governments in the region by the forces of communism. March 22: President Ronald Reagan signs P.L. 97-157 denouncing the government of the Soviet Union that it should cease its abuses of the basic human rights of its citizens. April 2: Argentina invades the Falkland Islands, starting the Falklands War. May 30: Spain joins NATO. June 6: Israel invades Lebanon to end raids and clashes with Syrian troops based there. June 14: Falkland Islands liberated by British task force. End of the Falklands War. August 1: Rebels attempt to seize control of Kenya, with the supposed assist of the communists in a coup d'état. The coup failed. November 10: Leonid Brezhnev dies from a heart failure with his funeral being held five days later. November 14: Yuri Andropov becomes General Secretary of the Soviet Union.
==== Aluminium salts ==== There are many adjuvants, some of which are inorganic, that carry the potential to augment immunogenicity. Alum (hydrated potassium double sulfate) was the first aluminium (Al) salt used for this purpose, but has been almost completely replaced by aluminium hydroxide and aluminium phosphate for commercial vaccines. These newer types are also customarily called "alum" in some contexts (distinguished in this article by capitalization). Al salts are the most commonly used adjuvants in human vaccines. Their adjuvant activity was described in 1926. The precise mechanism of Al salts ("Alum") remains unclear but some insights have been gained. It was formerly thought that they function as delivery systems by generating depots that trap antigens at the injection site, providing a slow release that continues to stimulate the immune system. However, studies have shown that surgical removal of these depots had no impact on the magnitude of IgG1 response. Depot formation is downstream to the adsorption of antigens onto the molecular structure of the adjuvant driven by electrostatic interactions and phosphate exchange. Conventional wisdom holds that one should maximize the adsorbed % of antigens when using an Alum. There is mixed evidence regarding the role of adsorption in the action of Alum, with some studies showing no effect and others showing a positive effect with low antigen doses in antigens of 10–100 kDa.
=== Concerns about the medical evidence === Much of the medical evidence presented at trial has been criticised by experts across several specialties, including neonatology, pathology, nursing, biochemistry and forensic toxicology. Points of scrutiny have included the prosecution's assertions that the infants were clinically stable before their collapses, that alternative explanations could be excluded, and that the alleged mechanisms of harm were medically plausible. Controversy has also arisen from the fact that the original post‑mortem reports for the infants—most of whom underwent autopsy—did not identify suspicious or unnatural causes of death. In February 2025, a panel organised and instructed by Letby's defence team that was led by neonatologist Shoo Lee released findings from their own review of the deaths and collapses (see: § Expert panel investigation). The panel claimed that all of the incidents could be explained by natural causes, substandard care, or a combination of both, and claimed no evidence of deliberate harm.
Sources: en.wikipedia.org
Each freeze-thaw cycle can degrade a fraction of the peptide and promote aggregation. Dividing a stock solution into single-use volumes removes repeated cycling as a variable. It also limits the time a thawed solution spends at room temperature.
A high main-peak percentage says little about identity, counter-ion content, or residual solvents. It also does not distinguish an isomer or a closely eluting analog. Mass confirmation and the accompanying documentation cover those gaps.
Salt form changes mass, solubility, and hygroscopicity, and acetate and trifluoroacetate salts behave differently in solution. Storage guidance still centers on -20 °C for powder and lower temperatures for solutions. The certificate should state which salt is present.
Reversed-phase HPLC gives the main purity figure, most often with UV detection near 214 nanometres. Mass spectrometry then confirms the molecular mass. Together the two methods distinguish a correct sequence from a closely related impurity.