freeze-thaw comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Last reviewed on 2026-08-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
Semaglutide is a synthetic peptide analog of human glucagon-like peptide-1, a gut hormone released after meals. Its backbone retains the GLP-1 sequence but incorporates two substitutions that slow enzymatic breakdown by dipeptidyl peptidase-4. A short polyethylene glycol linker and a C18 fatty diacid are attached to the peptide chain, allowing the molecule to bind serum albumin and remain in circulation far longer than the native hormone. The result is a circulating half-life measured in days rather than the minutes typical of endogenous GLP-1.
Receptor activation occurs at GLP-1 receptors distributed across pancreatic islets, the hypothalamus, and the gastrointestinal tract. Binding triggers G protein signaling that raises cyclic AMP and enhances glucose-dependent insulin release. Because the effect depends on prevailing glucose levels, insulin secretion does not rise when blood sugar is already low. Signaling in the brain and gut also influences appetite and gastric emptying, which is why the compound appears in both metabolic and weight-related research literature.
Semaglutide 是一种经结构修饰的胰高血糖素样肽-1 类似物，其主链与内源性 GLP-1(7-36) 约有百分之九十四的序列一致性。第 8 位丙氨酸被 α-氨基异丁酸取代，使二肽基肽酶-4 无法识别原有切割位点。第 34 位赖氨酸换为精氨酸，进一步降低酶解速率。第 26 位赖氨酸经间隔基连接一条含十八个碳的二酸脂肪链，该侧链赋予分子与血浆白蛋白结合的能力。
该分子作为 GLP-1 受体的选择性激动剂发挥作用，受体属于 B 类 G 蛋白偶联受体家族，激活后经 Gs 通路提升细胞内环腺苷酸水平。在胰腺 β 细胞，信号促进葡萄糖依赖性的胰岛素释放，血糖偏低时该作用明显减弱。在胰岛 α 细胞，胰高血糖素分泌受到抑制。中枢神经系统与胃肠道同样存在受体表达，相应信号参与食欲调节以及胃排空速率的降低。
皮下注射后吸收相对缓慢，绝对生物利用度约为百分之八十九，血药浓度峰值通常出现在给药后一到三天。与白蛋白结合使清除减慢，终末半衰期约为一百六十五小时，接近一周。连续给药约四到五周后达到稳态暴露水平。表观分布容积约为每千克零点二五升，血浆蛋白结合率超过百分之九十九。代谢以蛋白水解切割和脂肪二酸侧链的 β-氧化为主，相关产物主要经尿液与粪便排出。
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic peptide, GLP-1 receptor agonist | Not a small molecule |
| Backbone substitutions | Non-natural residue at position 8, arginine at position 34 | Slows enzymatic cleavage |
| Side chain | C18 fatty diacid with PEG linker | Enables albumin binding |
| Approximate molecular mass | 4114 Da | Varies slightly with salt form |
| Reported half-life | About one week | Longer than native GLP-1 by orders of magnitude |
Lyophilised semaglutide is generally held at -20 °C or below, protected from light and moisture. Reconstituted solutions are typically kept at 2-8 °C and used within a defined window because degradation accumulates over time. Repeated freeze-thaw cycles are discouraged, since each cycle can promote aggregation and reduce monomeric content. Room-temperature stability of the solid has been examined in some studies but remains incompletely characterised for long durations, so cold storage is the conservative default for research material.
Degradation proceeds along several parallel routes. Deamidation of asparagine and glutamine residues generates charged variants that shift retention time in chromatographic analysis. Oxidation targets methionine and can be accelerated by trace metals or dissolved oxygen. Non-covalent aggregation produces dimers, oligomers, and larger species that are difficult to reverse. Isomerisation at aspartate residues is slower but measurable under thermal stress. The distribution among these pathways depends on pH, buffer composition, ionic strength, and the presence of excipients such as sugars or surfactants.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 nm is the standard purity method, reported as area percent. Mass spectrometry, usually with electrospray ionisation, confirms identity and reveals covalent modifications. Size-exclusion chromatography quantifies aggregates and fragments. Peptide mapping after enzymatic digestion localises changes to specific sequence regions. Circular dichroism and infrared spectroscopy report on secondary structure, while light scattering tracks particle formation in liquid formulations. No single technique captures every quality attribute.
Pharmacological activity arises from agonism at the glucagon-like peptide-1 receptor, a G protein-coupled receptor expressed in the pancreas, the gastrointestinal tract, and the brainstem. Receptor activation raises intracellular cyclic adenosine monophosphate and enhances insulin release in a glucose-dependent manner, an effect that diminishes when blood glucose concentration is low. Other effects include slowed gastric emptying and hypothalamic satiety signalling. These pathways are described well. Receptor desensitisation rates across tissues, relative to the endogenous hormone, are still under investigation, and reported findings differ between laboratories.
The company that developed the compound filed it as a long-acting analogue, and it gained first approval in 2017 for type 2 diabetes. Later authorisations from several regulators extended the indication to chronic weight management, and the World Health Organization added the glucagon-like peptide-1 receptor agonist drug class to its model list of essential medicines in 2023. Production uses solid-phase peptide synthesis followed by side-chain conjugation and chromatographic purification. Supply constraints and cost differences across regions are well documented. Literature on long-term outcomes continues to grow, with many trials reporting surrogate endpoints rather than hard clinical endpoints.
Handling practices center on minimizing contamination and adsorption. Lyophilized peptide tends to accumulate static charge, so weighing is done with antistatic measures and calibrated balances. Reconstitution with appropriate solvent should be gentle, avoiding vigorous vortexing that generates foam and shear. Solutions are typically aliquoted before freezing to reduce repeated temperature cycling. Personal protective equipment and a fume hood are standard for powder handling.
Reconstituted solutions are less stable than the dry powder, and stability depends on concentration, pH, buffer composition, and container material. Low-protein-binding tubes reduce loss of peptide to plastic surfaces. Some researchers add a carrier protein to limit adsorption at low concentrations. The exact shelf life of a given solution is best determined empirically through a stability study rather than assumed from general guidance, because published data cover only a limited set of conditions.
Semaglutide dissolves readily in water and in aqueous buffers near neutral pH. Solubility decreases near the isoelectric point, where net charge is minimal. Common laboratory solvents include phosphate-buffered saline and dilute ammonium bicarbonate. Strongly acidic or basic conditions may accelerate hydrolysis. Working concentrations are usually prepared by diluting a concentrated stock. Vial surfaces can adsorb small amounts of peptide at low concentrations, so carrier proteins or low-binding tubes are sometimes used.
Reverse-phase high-performance liquid chromatography is the standard method for purity assessment, separating the peptide from truncated or oxidized variants. Mass spectrometry confirms molecular mass and detects modifications, while ultraviolet absorbance near 280 nanometers supports concentration measurement through tryptophan and tyrosine residues. Circular dichroism can indicate secondary structure, though the peptide is largely helical in solution, and ion-exchange chromatography resolves charge variants. Purity values above 95 percent are typical for research-grade material. Stability studies track degradation over time under defined conditions.
The word petroleum comes from Medieval Latin petroleum (literally 'rock oil'), which comes from Latin petra 'rock' (from Greek pétra πέτρα) and oleum 'oil' (from Greek élaion ἔλαιον). The origin of the term stems from monasteries in southern Italy where it was in use by the end of the first millennium as an alternative for the oldest term "naphtha". After that, the term was used in numerous manuscripts and books, such as in the treatise De Natura Fossilium, published in 1546 by German mineralogist Georg Bauer. After the advent of the oil industry during the second half of the 19th century, the term became commonly known for the liquid form of hydrocarbons.
For services to Life Saving. Geoffrey Francis Norris, General Medical Practitioner, London. For services to Medicine. Arthur Joseph Nutter. For services to the Lieutenancy in Lancashire. John O'Neil, lately Principal Lecturer and Course Leader of PGCE Art and Design, University of Wales Institute, Cardiff. For services to Art Education and Teacher Training. Martin Offiah. For services to Rugby Football. Enid Rosalind Oliver. For services to the community in Ashford, Kent. William James Orford. For services to Cricket in the West Midlands. Vera Overs. For services to the community in Martindale, Cumbria. Clifford Owen. For services to the Chorley and District Talking Newspaper, Lancashire. Pamela Mary Owen. For services to the community, particularly the NHS, in Welshpool, Powys. Anthony Gerald Palmer. For services to the War Pensions Committee in East Anglia. Sarah Faith, The Honourable Mrs. Palmer. For services to the community, particularly the British Red Cross Society, in Berkshire. Isobel Marilyn Park. For services to the Scout Association in Dumfries. Gordon Seymour Passmore, Member, London Borough of Wandsworth. For services to Local Government. Norman Henry Pattenden, Special Operations Manager, North & South Railways Ltd. For services to the Railways Industry. William Evans Pattison. For services to Mountain Rescue. Robert John Patton. For services to the Engineering Industry. Christine Anne Pendlebury, Personal Secretary, Home Office. Philippa Helen Perks. For services to the community in Wrington, Bristol.
As such, it is far more suitable for men for whom long-term medication is being chosen. Mineralcortocoid receptor antagonists (MRA) as a class (including spironolactone, canerenone, eplerenone and finerenone) are cornerstones of heart failure with reduced ejection fraction (HFrEF EF≤40%) management, however, the comparative magnitude of effect on mortality between agents remains uncertain. Primarily, evidence explores spironolactone and eplerenone, with limited comparative data available for canerenone. Furthermore, there is limited evidence for benefit of finerenone in a HFrEF patient cohort, a newer agent recently licensed for the treatment of chronic kidney disease (CKD) in type 2 diabetes mellitus.
A 58-hour curfew was announced in Kherson. Oleksandr Prokudin, the Ukrainian governor of Kherson Oblast, said that during the curfew: "it is forbidden to move on the streets of the city. The city will also be closed for entry and exit". Twenty-four civilians were killed in Kherson city due to Russian shelling. Russia said it had shot down two drones over the Moscow Kremlin and accused Ukraine of sending them to assassinate President Vladimir Putin. The Institute for the Study of War commented that it was "extremely unlikely that two drones could have penetrated multiple layers of air defence and detonated or been shot down just over the heart of the Kremlin in a way that provided spectacular imagery caught nicely on camera". The Ukrainian government denied the accusations, calling them fabricated. The British Ministry of Defence reported that several unmanned aerial vehicles (UAVs) struck Russia's Seshcha Airbase in Bryansk Oblast, 150 km north of the Ukrainian border, adding that an An-124 heavy transport aircraft was likely damaged.
Sources: en.wikipedia.org
RCO2H + (CH3)3OBF4 → RCO2CH3 + (CH3)2O + HBF4 Although rarely employed for esterifications, carboxylate salts (often generated in situ) react with electrophilic alkylating agents, such as alkyl halides, to give esters. Anion availability can inhibit this reaction, which correspondingly benefits from phase transfer catalysts or such highly polar aprotic solvents as DMF. An additional iodide salt may, via the Finkelstein reaction, catalyze the reaction of a recalcitrant alkyl halide. Alternatively, salts of a coordinating metal, such as silver, may improve the reaction rate by easing halide elimination.
The image of seedy underground, destitute smokers were often generated by anti-opium narratives and became a more accurate image of opium use following the effects of large scale opium prohibition in the 1880s.
== Gene == The RAGE gene lies within the major histocompatibility complex (MHC class III region) on chromosome 6 and comprises 11 exons interlaced by 10 introns. Total length of the gene is about 1400 base pairs (bp) including the promoter region, which partly overlaps with the PBX2 gene. About 30 polymorphisms are known most of which are single-nucleotide polymorphisms.
moderate to severe, diffuse abdominal pain constipation abdominal distension nausea/vomiting, especially after meals vomiting of bilious fluid (green or yellowish-green in colour) flatulence or inability to pass gas excessive belching
In 1935, Paul Gyorgy, in collaboration with chemist Richard Kuhn and physician T. Wagner-Jauregg, reported that rats kept on a B2-free diet were unable to gain weight. Isolation of B2 from yeast revealed the presence of a bright yellow-green fluorescent product that restored normal growth when fed to rats. The growth restored was directly proportional to the intensity of the fluorescence. This observation enabled the researchers to develop a rapid chemical bioassay in 1933, and then isolate the factor from egg white, calling it ovoflavin. The same group then isolated the a similar preparation from whey and called it lactoflavin. In 1934, Kuhn's group identified the chemical structure of these flavins as identical, settled on "riboflavin" as a name, and were also able to synthesize the vitamin. Circa 1937, riboflavin was also referred to as "Vitamin G". In 1938, Richard Kuhn was awarded the Nobel Prize in Chemistry for his work on vitamins, which had included B2 and B6. In 1939, it was confirmed that riboflavin is essential for human health through a clinical trial conducted by William H. Sebrell and Roy E. Butler. Women fed a diet low in riboflavin developed stomatitis and other signs of deficiency, which were reversed when treated with synthetic riboflavin. The symptoms returned when the supplements were stopped.
Sources: en.wikipedia.org
By contrast, the Biden administration's 2022 Review, while prioritizing Ground-based Midcourse Defense, emphasized that it is "neither intended nor capable of defeating" peer-level threats from Russia or China, noting "the interrelationship between strategic offensive arms and strategic defensive systems." While terrestrial defenses developed, the vision of a full space-based shield remained a consistent goal for its proponents. The modern groundwork for the Golden Dome was laid in 2017 by the SDI's former Deputy of Technology, and prominent Team B leader, Michael D. Griffin, who formed the Space Development Agency during the first Trump administration. Griffin long advocated for reusable launch vehicles to make the mass launching of weapons into space economically feasible. While the original Strategic Defense Initiative's attempts at this were short-lived, with the DC-X failing after a series of test flights, Griffin later encouraged and promoted funding of commercial reusable launch vehicles, which have since proven successful. The Heritage Foundation's Project 2025 effort advocated for a Golden Dome-like effort, writing that SpaceX's development of Starlink proves the feasibility of a space-based "overlayer" of thousands of networked satellites and interceptors, broadly similar to the Brilliant Pebbles concept of the 1980s. During his 2024 presidential campaign, Trump repeatedly mentioned the missile shield concept, often to mixed reception.
=== CANOPUS: Compound class prediction === CANOPUS is short for class assignment and ontology prediction using mass spectrometry. It predicts the compound classes from the molecular fingerprint predicted by CSI:FingerID. This approach is completely database-free, i.e. it is not even limited to molecules that are listed in structure databases. CANOPUS employs a deep neural network (DNN) to predict 2,497 compound classes. The DNN was trained on 4.10 million compound structures with compound classes assigned by ClassyFire. No MS/MS data was used for training, but instead simulated 'realistic' probabilistic fingerprints for the training molecular structures were used. The DNN predicts all compound classes simultaneously. For full biological datasets, CANOPUS provides a comprehensive overview of compound classes present in the sample and allows for comparisons between different cohorts at compound class level.
== History == The therapeutic efficacy of subcutaneous pegcetacoplan in treating paroxysmal nocturnal hemoglobinuria has been established through several clinical trials. Initial phase I and II trials, such as PADDOCK, PALOMINO, and PHAROAH, evaluated pegcetacoplan in participants with paroxysmal nocturnal hemoglobinuria who had not received a complement inhibitor or had previously received eculizumab. These trials demonstrated that 1–2 years of pegcetacoplan treatment effectively controlled hemolysis and improved quality of life in participants with paroxysmal nocturnal hemoglobinuria. Building upon these findings, the efficacy of pegcetacoplan was further assessed in phase III trials. The PRINCE trial, a 26-week study, focused on complement inhibitor-naïve participants with paroxysmal nocturnal hemoglobinuria, while the PEGASUS trial, a 48-week multinational study, included complement inhibitor-treated participants with paroxysmal nocturnal hemoglobinuria. In these trials, subcutaneous pegcetacoplan was administered at a dosage of 1080 mg twice weekly, delivered as a 20-mL subcutaneous infusion. Participants had the option to self-administer the medication or have it administered by qualified research personnel.
5 November – Ross McDonnell, 44, director, cinematographer and photographer. 7 November – Dean Byrne, 39, professional boxer. 10 November – Miah Dennehy, 73, footballer (Walsall, Bristol Rovers, national team). 11 November – Louis Belton, 79, politician, TD (1989–1992 and 1997–2002) and Senator (1993–1997). 12 November – Anna Scher, 78, British-Irish drama school founder. 17 November – Seóirse Bodley, 90, composer. 18 November Ben Dunne, 74, businessman. Anthony Farquhar, 83, Roman Catholic prelate, Auxiliary Bishop of Down and Connor (1983–2015). 19 November – Eddie Linden, 88, poet and editor. Born in Scotland. 20 November – Frankie Connolly, 78, footballer (Cork Hibernians, Cork Alberts). 26 November – Tras Honan, 93, politician, Senator (1977–1992) and Cathaoirleach (1982–1983 and 1987–1989). 30 November – Shane MacGowan, 65, singer-songwriter (The Pogues). Born in England.
Sources: en.wikipedia.org
Native GLP-1 is degraded within minutes by circulating enzymes. The synthetic version carries substitutions at positions that block enzymatic cleavage, plus a fatty acid side chain that promotes albumin binding. These two changes together extend circulation time from minutes to roughly a week.
Albumin binding keeps a large fraction of the compound in a slowly released reservoir within the bloodstream. Plasma levels decline gradually rather than falling sharply after each administration. That profile supports dosing intervals measured in days instead of hours.
The active peptide sequence is the same in both formats. The oral version adds an absorption enhancer that is not present in the injected solution. Differences in excipients and formulation affect uptake rather than the identity of the active molecule.
差别集中在三处：第 8 位残基被非天然氨基酸取代，第 34 位换成精氨酸，第 26 位增加一条脂肪酸侧链。前两处改动降低酶解速率，侧链则通过白蛋白结合延长循环时间。综合结果是半衰期从约两分钟延长到约一周。