A practical reference on freeze-thaw: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-05-01 and is reviewed periodically as new material appears.
Identity and purity are commonly assessed by reversed-phase high-performance liquid chromatography, with ultraviolet detection near 214 nanometers for the peptide backbone. Mass spectrometry, either electrospray or matrix-assisted laser desorption, confirms molecular mass and detects truncation or modification products. Amino acid analysis can verify composition. Because the sequence contains no strongly absorbing aromatic residue apart from phenylalanine, detection wavelengths are chosen carefully. Purity values above 95 percent are typical for research-grade material.
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.
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。
The peptide is prone to several degradation pathways. Oxidation of the methionine residue produces a sulfoxide that elutes close to the parent peak in many chromatographic systems. Hydrolysis of peptide bonds and deamidation of susceptible residues in related sequences also reduce purity over time. Lyophilised material kept dry at minus twenty degrees Celsius and shielded from light is the most stable form commonly described in laboratory practice.
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.
There is a consensus among the world's major medical organizations and in the academic literature that circumcision is an efficacious intervention for HIV prevention in high-risk populations if carried out by medical professionals under safe conditions. In 2007, the WHO and the Joint United Nations Programme on HIV/AIDS (UNAIDS) recommended adolescent and adult circumcision as part of a comprehensive program for prevention of HIV transmission in areas with high endemic rates of HIV, as long as the program includes "informed consent, confidentiality, and absence of coercion"—known as voluntary medical male circumcision, or VMMC. In 2010, this expanded to routine neonatal circumcision, as long as the infant's parents consented. In 2020, the WHO again concluded that male circumcision is an efficacious intervention for HIV prevention and that male circumcision is an essential strategy, in addition to other measures, to prevent heterosexually acquired HIV infection in men. Eastern and southern Africa had a particularly low prevalence of circumcised males. This region has a disproportionately high HIV infection rate, with a significant number of infections stemming from heterosexual transmission. As a result, the promotion of prophylactic circumcision has been a priority intervention in that region since the WHO's 2007 recommendations. The International Antiviral Society–USA also suggests circumcision be discussed with men who have insertive anal sex with men, especially in regions where HIV is common.
Thai iced coffee is brewed using strong black coffee, sweetened with sugar, heavy cream (or half-and-half) and cardamom, and quickly cooled and served over ice. Some variations are brewed using espresso. Thai iced coffee can be served with whipped cream on top for a layered effect and garnished with cinnamon, vanilla or anise. It is a common menu item at Thai restaurants.
Unlike normal metals, graphene's longitudinal resistance shows maxima rather than minima for integral values of the Landau filling factor in measurements of the Shubnikov–de Haas oscillations, thus the term "integral quantum Hall effect". These oscillations show a phase shift of π, known as Berry's phase. Berry's phase arises due to chirality or dependence (locking) of the pseudospin quantum number on the momentum of low-energy electrons near the Dirac points. The temperature dependence of the oscillations reveals that the carriers have a non-zero cyclotron mass, despite their zero effective mass in the Dirac-fermion formalism.
== History == Arginine was first isolated in 1886 from yellow lupin seedlings by the German chemist Ernst Schulze and his assistant Ernst Steiger. He named it from the Greek árgyros (ἄργυρος) meaning "silver" due to the silver-white appearance of arginine nitrate crystals. In 1897, Schulze and Ernst Winterstein (1865–1949) determined the structure of arginine. Schulze and Winterstein synthesized arginine from ornithine and cyanamide in 1899, but some doubts about arginine's structure lingered until Sørensen's synthesis of 1910.
The four substrates of this enzyme are 4-aminobenzoic acid, reduced nicotinamide adenine dinucleotide (NADH), oxygen and a proton. Its products are 4-aminophenol, oxidised NAD+, water, and carbon dioxide. Nicotinamide adenine dinucleotide phosphate can be used as an alternative cofactor. The enzyme is a flavin-containing monooxygenase that uses molecular oxygen as oxidant and incorporates one of its atoms into the starting material. The systematic name of this enzyme class is 4-aminobenzoate,NAD(P)H:oxygen oxidoreductase (1-hydroxylating, decarboxylating). Other names in common use include 4-aminobenzoate hydroxylase, and 4-aminobenzoate monooxygenase. It uses flavin adenine dinucleotide as a cofactor.
Sources: en.wikipedia.org
Similarly, the number of one-year-olds fully immunised against measles rose from 30% in 1985–1990 to 40% in 2000–2005, and for tuberculosis, it grew nearly 20% from 31% to 50% over the same period. The number of infants with low birth weight fell from 16 per 1,000 to 0.3, a 15% drop in total over the same time frame. Between 2005 and 2010 as compared to the 1985–1990 period, infant mortality per 1,000 births also fell from 152 to 109.6. Significantly, maternal mortality per 100,000 births fell from 1,600 in the pre-war 1985–1990 half-decade to 1,100 in the 2000–2005 period. The number of physicians per 100,000 people also rose from 3.4 to 4 over the same time frame, as did the percentage of the population with access to sanitation services, which increased from 18% to 26%. According to United Nations Population Fund data on the midwifery workforce, there is a total of 429 midwives (including nurse-midwives) in Somalia, with a density of one midwife per 1,000 live births. Eight midwifery institutions presently exist in the country, two of which are private. Midwifery is regulated by the government, and a licence is required to practice professionally. A live registry is also in place to keep track of licensed midwives. In addition, midwives in the country are officially represented by a local midwives association, with 350 registered members. According to a 2005 World Health Organization estimate, about 97.9% of Somalia's women and girls underwent female genital mutilation, a pre-marital custom mainly endemic to the Horn of Africa and parts of the Near East.
== Non-traditional sales == Due to their limited restaurant locations throughout the United States, White Castle had developed a cult following among former customers who develop a craving for their hamburger in areas not served by their restaurants. By the early 1980s, these customers would go to extreme length to obtain White Castle burgers, such as having friends and relatives ship the burgers to them. In November 1980, the town officials of Fountain Hills, Arizona, placed an order for 10,000 hamburgers to be sold at a town festival as part of a fundraiser. The following year, the town created an annual festival that was held each May called Midwest Fest or Midwest Festival in which 100,000 or more hamburgers were purchased and sold as part of a fundraiser. By the middle of the decade, several other western cities were purchasing hundreds of thousands of burgers at a time for fundraisers. In 1982, a Dayton disc jockey sent 3,000 burgers to 1,200 U.S. Marines stationed in Beirut. In late 1982, White Castle established a toll free phone line in which customers can order as few as 50 burgers to be shipped frozen to any metropolitan area in the United States serviced by Federal Express for as low as $57 as part of a program called "Hamburgers to Fly". By early 1983, White Castle was shipping 10,000 hamburgers per week via FedEx. Based on the success of the sale of hamburgers shipped via air express, White Castle decided to expand their frozen hamburgers distribution by selling the burgers through supermarkets.
=== Authorizations of COVID-19 vaccines === The COVID-19 pandemic, and sequencing of the causative virus SARS-CoV-2 at the beginning of 2020, led to the rapid development of the first approved mRNA vaccines. BioNTech and Moderna in December of the same year obtained approval for their mRNA-based COVID-19 vaccines. In December 2020, the UK Medicines and Healthcare products Regulatory Agency (MHRA) became the first global medicines regulator in history to approve an mRNA vaccine, granting emergency authorization for Pfizer–BioNTech's BNT162b2 COVID-19 vaccine for widespread use. Also, in December 2020, the US Food and Drug Administration gave emergency use authorization for the Pfizer–BioNTech COVID-19 vaccine and the Moderna COVID-19 vaccine.
== Test usage in the life insurance industry == The test has been widely used in the life insurance industry to screen applicants as part of the routine requirements when applying for a life insurance policy. It is also inexpensive and can be measured from blood samples routinely drawn as part of the application process. The test can be used to evaluate for a number of health conditions.
== State Union of Serbia and Montenegro == The Assembly of Serbia and Montenegro (Skupština Srbije i Crne Gore) had 126 members who served four-year terms, 91 from Serbia and 35 from Montenegro. The first parliament was chosen in February 1993 by the members of the parliament of the former Federal Republic of Yugoslavia, and the members of the parliaments of Serbia and of Montenegro. The seats were divided up among political parties in proportion to the number of their seats in these two parliaments, so that each time one of the parliaments was re-elected, the composition of the federal parliament changed. The president of Serbia and Montenegro was elected by the parliament. It was intended that direct elections for the Assembly of Serbia and Montenegro would be held in 2007, but the break-up of the state ended this possibility.
Sources: en.wikipedia.org
=== Learning and memory === The first learning and memory mutants (dunce, rutabaga, etc.) were isolated by William "Chip" Quinn while in Benzer's lab, and were eventually shown to encode components of an intracellular signaling pathway involving cyclic AMP, protein kinase A, and a transcription factor known as CREB. These molecules were shown to be also involved in synaptic plasticity in Aplysia and mammals. The initial report by William Quinn et al. described a basic conditioned preference assay. Over the next decade, the assay evolved into the classical olfactory conditioning paradigm in the T-maze: ~100 flies in a vial are connected to a short hallway that splits in two directions, a T-maze. On either end of the T-maze are two odors that are initially neutral, i.e. flies do not show preference for one odor or the other. The assay involves counting the number of flies in each side of the T-maze corridor. Before training half of the flies, on average, will before in each end. During training, the flies also encounter a stimulus in one of the two ends, typically either a sugar reward or an electric shock. After training, flies will show a preference for one odor or another. The two odors are referred to as the conditioned stimulus (CS), and the reward is the unconditioned stimulus (US). The T-maze assay was used to show where in the fly brain the association is made between the unconditioned stimulus and the conditioned stimulus. Olfactory sensory information is carried by antennal lobe projection neurons to the Kenyon cells of the mushroom body of the fly brain.
Using amino acids and protein synthesis, the specific sequence in DNA of these nucleobase-pairs helps to keep and send coded instructions as genes. In RNA, base-pair sequencing helps to make new proteins that determine most chemical processes of all life forms.
=== Books === Two biographies have been written about Staley, both authored by Adriana Rubio—Layne Staley: Angry Chair released in 2003, which contains an alleged final interview of Staley that Rubio claimed to have conducted less than three months before his death, and Layne Staley: Get Born Again, released in 2009, a revised and updated version of her earlier book. Staley's family has disputed Rubio's work, stating they do not believe she interviewed him in 2002. When questioned about the authenticity of the book, Rubio refused to confirm the interview was genuine. Staley's last interview was for the radio program Rockline on July 19, 1999, promoting the release of the compilation album Nothing Safe: Best of the Box with the other members of Alice in Chains. The content of Rubio's book, including what she referred to as Staley's final interview, was called into question in journalist David De Sola's 2015 book Alice in Chains: The Untold Story. De Sola questions not only the content of the interview, which portrays Staley as using his lyrics in casual conversation, it also indicates that Rubio never spoke to him, citing her refusal to release the tape with the interview and the fact that not even her publisher had access to the tape. One of Staley's sisters, Liz Coats, likewise doubted the veracity of the book. Staley was featured on the books Grunge Is Dead: The Oral History of Seattle Rock Music (2009) by Greg Prato, and Everybody Loves Our Town: An Oral History of Grunge (2011) by Mark Yarm.
Constitutionally, the USSR was a federation of constituent Union Republics, which were either unitary states, such as Ukraine or Byelorussia (SSRs), or federations, such as Russia or Transcaucasia (SFSRs), all four being the founding republics who signed the Treaty on the Creation of the USSR in December 1922. In 1924, during the national delimitation in Central Asia, Uzbekistan and Turkmenistan were formed from parts of Russia's Turkestan ASSR and two Soviet dependencies, the Khorezm and Bukharan PSPs. In 1929, Tajikistan was split off from the Uzbekistan SSR. With the constitution of 1936, the Transcaucasian SFSR was dissolved, resulting in its constituent republics of Armenia, Georgia and Azerbaijan being elevated to Union Republics, while Kazakhstan and Kirghizia were split off from the Russian SFSR, resulting in the same status. In August 1940, Moldavia was formed from parts of Ukraine and Soviet-occupied Bessarabia, and Ukrainian SSR. Estonia, Latvia and Lithuania were also annexed by the Soviet Union and turned into SSRs, which was not recognized by most of the international community and was considered an illegal occupation. After the Soviet invasion of Finland, the Karelo-Finnish SSR was formed on annexed territory as a Union Republic in March 1940 and then incorporated into Russia as the Karelian ASSR in 1956. Between July 1956 and September 1991, there were 15 union republics (see map below).
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.