Everything below concerns reversed-phase HPLC. We keep the language plain, cite what the science says, and separate well-supported claims from open questions.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Quality documentation for research-grade peptide usually includes a certificate of analysis stating purity, identity, and residual counterion content. Batch-to-batch variation in purity and salt form is a recognized issue, and comparisons across suppliers require attention to the exact counterion, for example acetate versus trifluoroacetate. Sequence verification by tandem mass spectrometry provides stronger evidence than a single mass measurement. For any study reporting biological results, the analytical method and the measured purity should be stated explicitly. Independent verification of supplier claims is considered good practice.
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.
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.
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.
| Property | Value | Notes |
|---|---|---|
| Typical purity | ≥95% by HPLC | Research-grade material |
| Detection wavelength | 214 nm | Peptide bond absorbance |
| Reconstitution medium | Sterile water or saline | Prepare fresh or aliquot immediately |
| Storage (solution) | -80 °C, single-use aliquots | Avoid repeated freeze-thaw cycles |
| Common salt form | Acetate or trifluoroacetate | Affects mass and solubility |
Identity and purity are established with standard peptide methods. Reversed-phase HPLC with ultraviolet detection near 214 nm resolves the parent peak from deletion and truncation byproducts, and reports typically quote a main-peak percentage. Mass spectrometry by electrospray or MALDI-TOF confirms the expected molecular mass, while amino acid analysis or peptide mapping can verify composition when the sequence itself is in question. A certificate of analysis that pairs a chromatogram with a mass spectrum is more informative than a purity figure alone. Counter-ion content and residual solvents are separate specifications and are frequently omitted.
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.
Routine characterization relies on reversed-phase high-performance liquid chromatography to establish purity and on mass spectrometry to confirm molecular identity. Electrospray ionization and matrix-assisted laser desorption ionization are both used for mass verification. Amino acid analysis and peptide mapping can detect sequence errors. Common impurities include truncated sequences, methionine sulfoxide formed by oxidation, and deamidated products. Chromatograms are usually recorded near 214 nm, where the peptide backbone absorbs, and purity is reported as the percentage area of the principal peak.
Verification of a supplied batch generally combines a certificate of analysis with independent testing, because certificates are self-reported documents. A typical package includes a chromatographic trace, a mass spectrum, and a stated water or counter-ion content. Batch-to-batch consistency matters more than a single purity figure when results are compared across experiments. No single mandatory standard governs research-grade peptide release, so laboratories are expected to define their own acceptance criteria. Residual trifluoroacetate from purification is a frequently overlooked counter-ion.
Lyophilized material is chemically stable for extended periods when kept dry, cold, and protected from light. The powder is hygroscopic, so vials should be warmed to room temperature before opening to reduce condensation on the contents. Once dissolved, the peptide is far less stable because peptide bonds are susceptible to hydrolysis and the methionine residue can oxidize. Solutions are typically aliquoted and held at 2-8 °C for short intervals or frozen for longer ones, and repeated freeze-thaw cycles should be avoided.
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。
Material sold for laboratory use varies widely in stated purity and documentation. A certificate of analysis should list the analytical method, the column and detector used, and the observed purity value. Independent verification by an outside laboratory is the practical way to confirm identity when documentation is absent or internally inconsistent. Regulatory status differs by country, and a product legal in one jurisdiction may be unapproved or controlled in another.
Identity and purity of semax are established with reversed-phase high-performance liquid chromatography coupled to ultraviolet detection, usually at 214 nanometres. Mass spectrometry, most often electrospray ionisation in positive mode, confirms the molecular mass and reveals truncated sequences. Amino acid analysis and peptide mapping after enzymatic digestion provide additional structural confirmation. Laboratories typically report purity as the percentage area of the main peak, a figure that does not capture isomeric or oxidised variants unless the method resolves them.
=== Acidity === Thiols are easily deprotonated. Relative to the alcohols, thiols are more acidic. The conjugate base of a thiol is called a thiolate. Butanethiol has a pKa of 10.5 vs 15 for butanol. Thiophenol has a pKa of 6, versus 10 for phenol. A highly acidic thiol is pentafluorothiophenol (C6F5SH) with a pKa of 2.68. Thus, thiolates can be obtained from thiols by treatment with alkali metal hydroxides.
Prokaryotes: 50S ribosomal subunit, 23S rRNA Eukaryotes: 60S ribosomal subunit, 28S rRNA See also: Ribosomal RNA § Subunits and associated ribosomal RNA, mitochondrial ribosome, and Chloroplast § Chloroplast ribosomes. Peptidyl transferases are not limited to translation, but there are relatively few enzymes with this function.
The average lifespan in the wild is 18 years, and it is quite possible for wild individuals to survive for more than 23 years. The record age of a wild individual was 39 years, while that in captivity was 44 years. The average annual survival rate is variable, ranging from 86% in Florida to 73% in Virginia and North Carolina. In Minnesota, 99% of wintering adult bears were able to survive the hibernation cycle in one study. A study of American black bears in Nevada found that the amount of annual mortality of a population of bears in wilderness areas was 0%, whereas in developed areas in the state this figure rose to 83%. Survival in subadults is generally less assured. In Alaska 14–17% of subadult males and 30–48% of subadult females were found in a study to survive to adulthood. Across the range, the estimated number of cubs who survive past their first year is 60%. With the exception of the rare confrontation with an adult brown bear or a gray wolf pack, adult black bears are not usually subject to natural predation. Scats with fur inside of them and a carcass of an adult sow with puncture marks in the skull indicate black bears may occasionally be killed by jaguars in the southern parts of their range. In such scenarios, the big cat would have the advantage if it ambushed the bear, killing it with a crushing bite to the back of the skull. Cubs tend to be more vulnerable to predation than adults, with known predators including bobcats, coyotes, cougars, gray wolves, brown bears and other bears of their own species.
For example, for the protein alkaline phosphatase, the staining solution is a mixture of 4-chloro-2-2 methylbenzenediazonium salt with 3-phospho-2-naphthoic acid-2'-4'-dimethyl aniline in Tris buffer. This stain is commercially sold as a kit for staining gels. If the protein is present, the mechanism of the reaction takes place in the following order: it starts with the de-phosphorylation of 3-phospho-2-naphthoic acid-2'-4'-dimethyl aniline by alkaline phosphatase (water is needed for the reaction). The phosphate group is released and replaced by an alcohol group from water. The electrophile 4- chloro-2-2 methylbenzenediazonium (Fast Red TR Diazonium salt) displaces the alcohol group forming the final product Red Azo dye. As its name implies, this is the final visible-red product of the reaction. In undergraduate academic experimentation of protein purification, the gel is usually run next to commercial purified samples to visualize the results and conclude whether or not purification was successful. Native gel electrophoresis is typically used in proteomics and metallomics. However, native PAGE is also used to scan genes (DNA) for unknown mutations as in single-strand conformation polymorphism.
==== Physical gels ==== In physical gels unlike covalently linked gels the polymers chains are not covalently linked together. That means that the gel could re-dissolve in a good solvent under some conditions. Thermoresponsive physical gels, also sometimes called thermoresponsive injectable gels have been used in Tissue Engineering. This involves mixing at room temperature the thermoresponsive polymer in solution with the cells and then inject the solution to the body. Due to the temperature increase (to body temperature) the polymer creates a physical gel. Within this physical gel the cells are encapsulated. Tailoring the temperature that the polymer solution gels can be challenging because this depend by many factors like the polymer composition, architecture as well as the molar mass.
Sources: en.wikipedia.org
=== Financial markets === While futures for the Dow Jones Industrial Average, the Nasdaq-100, and the S&P 500 fell before U.S. stock exchanges opened on the day after Powell's announcement, all three indexes ultimately closed higher at the end of trading on January 12. However, the U.S. Dollar Index showed the dollar falling against other major currencies in the foreign exchange markets, while the price of gold in commodity markets hit a record high, and the yield on the 10-year United States Treasury note rose, and the yield curve between the 2-year and 10-year Treasury notes steepened. The Dow Jones, the Nasdaq, and the S&P 500 saw sell-offs over the next two days with concerns among investors about Federal Reserve independence contributing to the declines, along with news about the Trump administration's response to the 2025–2026 Iranian protests, comments by Trump that Microsoft would make changes to absorb the electricity costs of the data centers used for its artificial intelligence products, as well as Trump's proposed ceiling on credit card interest rates and continued calls for the United States to acquire Greenland. The dollar weakened further on January 14 after recovering the day before on the release of U.S. Consumer Price Index data, both gold and silver prices hit record highs on both days, while yields on 2-year and 10-year Treasury notes fell despite break-even inflation on the 10-year Treasury note rising on January 13.
==== New substrate design for siRNA delivery ==== siRNA cell delivery represent a valuable tool for treatment of cancer disease, viral infections and genetic disorders. However, classical strategies involve covalent linking of cargo molecules and CPPs, which does not provide efficient protection of siRNA molecules in vivo; thus results reported in literature are not consistent. Recently, non-covalent strategies have been successfully reported. Secondary amphipathic peptides based on aromatic tryptophan and arginine residues linked with lysine as spacer have been reported under the name of CADY. CADY contains a short peptide sequence of 20 amino acids, with the sequence "Ac-GLWRALWRLLRSLWRLLWRA-cysteamide."
=== Food fortification === Countries fortify foods with nutrients to address known deficiencies. While many countries mandate or have voluntary programs to fortify wheat flour, maize (corn) flour or rice with vitamins, none include vitamin C in those programs. As described in Vitamin C Fortification of Food Aid Commodities (1997), the United States provides rations to international food relief programs, later under the auspices of the Food for Peace Act and the Bureau for Humanitarian Assistance. Vitamin C is added to corn-soy blend and wheat-soy blend products at 40 mg/100 grams. (along with minerals and other vitamins). Supplemental rations of these highly fortified, blended foods are provided to refugees and displaced persons in camps and to beneficiaries of development feeding programs that are targeted largely toward mothers and children. The report adds: "The stability of vitamin C (L-ascorbic acid) is of concern because this is one of the most labile vitamins in foods. Its main loss during processing and storage is from oxidation, which is accelerated by light, oxygen, heat, increased pH, high moisture content (water activity), and the presence of copper or ferrous salts. To reduce oxidation, the vitamin C used in commodity fortification is coated with ethyl cellulose (2.5 percent). Oxidative losses also occur during food processing and preparation, and additional vitamin C may be lost if it dissolves into cooking liquid and is then discarded."
== Screening == The United States Preventive Services Task Force stated, as of 2013, that there was insufficient evidence to recommend for or against screening for glaucoma. Therefore, there is no national screening program in the US. Screening, however, is recommended starting at age 40 by the American Academy of Ophthalmology. There is no screening program in the UK; however, opportunistic testing is recommended for at-risk groups, including free eye tests.
=== Differential diagnosis === An important differential diagnosis of OI is child abuse, as both may present to a clinician with multiple fractures in various stages of healing. Differentiating them can be difficult, especially when no other characteristic features of OI are present. This can become an issue in court; in the United States, several child abuse cases were resolved with a finding that osteogenesis imperfecta was the true cause of a child's fractures, leading to lawsuits seeking redress such as Alice Velasquez, et al. v. United States. Other differential diagnoses include rickets and osteomalacia, both caused by malnutrition, as well as rare skeletal/connective tissue syndromes such as Bruck syndrome, hypophosphatasia, geroderma osteodysplasticum, and Ehlers–Danlos syndrome. Various forms of osteoporosis, such as iatrogenic osteoporosis, idiopathic juvenile osteoporosis, disuse osteoporosis and exercise-related osteoporosis should also be considered when OI is suspected.
Sources: en.wikipedia.org
Isotope masses from: M. Wang; G. Audi; A. H. Wapstra; F. G. Kondev; M. MacCormick; X. Xu; et al. (2012). "The AME2012 atomic mass evaluation (II). Tables, graphs and references" (PDF). Chinese Physics C. 36 (12): 1603–2014. Bibcode:2012ChPhC..36....3M. doi:10.1088/1674-1137/36/12/003. hdl:11858/00-001M-0000-0010-23E8-5. S2CID 250839471. Archived from the original (PDF) on 2013-09-28. Retrieved 2013-07-03. Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001 Half-life, spin, and isomer data selected from the following sources. Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001 National Nuclear Data Center. "NuDat 3.0 database". Brookhaven National Laboratory. Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.
== Mechanism of action == Imipenem/cilastatin has the ability to kill a wide variety of bacteria. Imipenem is the active antibiotic agent and works by interfering with their ability to form cell walls, so the bacteria break up and die. Imipenem is rapidly degraded by the renal enzyme dehydropeptidase if administered alone (making it less effective); the metabolites can cause kidney damage. Imipenem is a broad-spectrum betalactam antibiotic used for severe bacterial infections caused by susceptible organisms. Because imipenem is rapidly inactivated by renal dehydropeptidase I, it is given in combination with cilastatin, a DHP-I inhibitor which increases half-life and tissue penetration of imipenem. Imipenem/cilastatin, like other carbapenems, binds to bacterial penicillin-binding proteins and interferes with bacterial cell wall integrity and synthesis. It has activity against many aerobic and anaerobic Gram-positive and Gram-negative organisms, including Staphylococcus aureus, Streptococcus pyogenes, S. agalactiae, S. viridans- group streptococci, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, Bacteroides fragilis and Peptostreptococcus species. Imipenem/cilastatin was approved for use in the United States in 1985. Imipenem/cilastatin is indicated for the treatment of severe or complicated skin, tissue, joint, respiratory tract, intra-abdominal, urinary tract and urogenital infections, but not meningitis (as it does not pass through the blood brain barrier), endocarditis, and sepsis due to susceptible organisms.
=== Death and legacy === Several retrospective sources state that Liu was greatly saddened by Zhou Enlai's death in January 1976 and, according to Guangming Daily, even had himself carried on a stretcher to the Beijing Hospital to bid farewell to Zhou's remains. Having been diagnosed with cancer in 1975, Liu's own health deteriorated shortly after, and he died of his illness in Beijing on June 24, 1976. He was 81. His memorial service was held at the Babaoshan Revolutionary Cemetery and was presided by Vice Premier and general Chen Xilian. The June 30, 1976 issue of the People's Daily reported that Vice Chairperson Li Suwen delivered Liu's eulogy. According to the eulogy, Liu Wenhui supported Chairman Mao, the Cultural Revolution, the movement to criticize Lin Biao and Confucius, and finally the ongoing campaign against Deng Xiaoping. He had also called for the liberation of Taiwan from Kuomintang rule. Present at his funeral were several politicians including Wu De, Li Jingquan, Ngapoi Ngawang Jigme, and Zhou Jianren, among others. Marshals Zhu De, Ye Jianying, and Liu Bocheng sent wreaths to the funeral, as well as Hua Guofeng and Song Qingling.
Raw potatoes contain toxic glycoalkaloids, of which the most prevalent are solanine and chaconine. Solanine is found in other plants in the same family, Solanaceae, which includes such plants as deadly nightshade (Atropa belladonna), henbane (Hyoscyamus niger) and tobacco (Nicotiana spp.), as well as food plants like tomato. These compounds, which protect the potato plant from its predators, are especially concentrated in the aerial parts of the plant. The tubers are low in these toxins, unless they are exposed to light, which makes them go green. Exposure to light, physical damage, and age increase glycoalkaloid content within the tuber. Different potato varieties contain different levels of glycoalkaloids. The 'Lenape' variety, released in 1967, was withdrawn in 1970 as it contained high levels of glycoalkaloids. Since then, breeders of new varieties test for this, sometimes discarding an otherwise promising cultivar. Breeders try to keep glycoalkaloid levels below 200 mg/kg (0.0032 oz/lb). However, when these commercial varieties turn green, their solanine concentrations can go well above this limit, with higher levels in the potato's skin.
Sources: en.wikipedia.org
Solid peptide is best kept frozen at about minus 20 degrees Celsius in a sealed container with desiccant. It should be allowed to reach room temperature before opening to prevent condensation. Repeated warming and cooling of the same vial is discouraged.
Reversed-phase liquid chromatography establishes purity, while mass spectrometry confirms molecular mass. The two techniques are normally used together. Retention time alone is not sufficient evidence of identity.
Different counterions change the mass per unit of peptide and can shift chromatographic behavior. Two samples of equal stated purity may therefore not be directly comparable. Reports should specify the counterion whenever quantitative comparisons are made.
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.