If you have been reading about mass spectrometry 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 2026-06-14. Where a claim depends on a specific study, the study is described rather than over-claimed.
Lyophilized semaglutide powder is typically held at minus twenty degrees Celsius for long-term storage. At that temperature, solid-state degradation reactions proceed slowly and the peptide remains intact for extended periods. Repeated freeze-thaw cycles are best avoided because they promote aggregation and can shift the proportion of monomeric peptide present. Working aliquots are often prepared so that each portion is thawed only once, and desiccant is placed inside the vial to limit moisture uptake.
Identity and purity are usually assessed by reverse-phase high-performance liquid chromatography coupled to mass spectrometry. Retention time and observed mass are compared against a reference standard run under identical conditions. Impurity profiles reveal deamidation products, oxidized methionine variants, and truncated fragments that arise during synthesis or storage. Peptide mapping through enzymatic digestion confirms the primary sequence, while amino acid analysis offers an independent check on overall composition.
序列层面的改动同时解决了两个问题，即酶解稳定性与肾脏清除速度。天然 GLP-1 在循环中的半衰期仅约两分钟，主要被二肽基肽酶-4 迅速灭活。酰化侧链与白蛋白的可逆结合形成循环储库，使分子缓慢释放并持续激活受体。这种设计思路后来被广泛用于同类长效肽的开发，属于该类药物化学改造的典型范式。
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。
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white lyophilized powder | Batch-to-batch variation is normal |
| Solubility class | Soluble in water, buffer, and dimethyl sulfoxide | Aqueous solubility is moderate |
| Typical storage temperature | Minus 20 degrees Celsius dry, 2 to 8 degrees Celsius reconstituted | Avoid repeated freeze-thaw |
| Common analytical method | Reverse-phase HPLC with electrospray mass detection | Used for purity and mass confirmation |
| Common synonyms | GLP-1 analog, semaglutide peptide | Wording varies across suppliers |
Serum protein binding dominates the pharmacokinetic profile. The attached chain associates strongly with albumin, shielding the peptide from enzymatic attack and slowing filtration by the kidney. This interaction extends the circulation half-life to roughly one week in humans, which supports weekly administration intervals. An oral version pairs the peptide with an absorption enhancer that transiently alters gastric epithelium, permitting limited uptake; bioavailability by that route is substantially lower than by injection.
Semaglutide belongs to the glucagon-like peptide-1 receptor agonist class, a group of synthetic peptides that imitate an incretin hormone released by intestinal L cells after food intake. Native GLP-1 circulates for only a few minutes because dipeptidyl peptidase-4 cleaves it rapidly. The hormone acts on pancreatic islets, the gastrointestinal tract, and several brain regions. Because the natural peptide is short-lived, development work concentrated on analogues that keep receptor activity while resisting enzymatic breakdown and renal clearance.
Semaglutide is a synthetic peptide analogue of glucagon-like peptide-1, a gut hormone released by intestinal L cells after food intake. The natural hormone acts on pancreatic and central receptors but is degraded within minutes by dipeptidyl peptidase-4 and other peptidases. Semaglutide belongs to the class of long-acting GLP-1 receptor agonists, a group distinguished by structural changes that slow breakdown and extend circulation time. Its development followed earlier short-acting analogues and reflects a general strategy in peptide drug design: preserve receptor activity while blocking proteolytic clearance.
Three structural changes define the molecule. At position 8 an alpha-aminoisobutyric acid residue replaces alanine, which blocks dipeptidyl peptidase-4 cleavage. At position 34 arginine replaces lysine, and at position 26 a lysine carries a C18 fatty diacid attached through a short linker. The fatty chain binds serum albumin, and this albumin association reduces renal filtration and enzymatic attack. The unchanged backbone retains the receptor contacts that produce signalling. The free base has the formula C187H291N45O59 and a molecular weight near 4114 daltons.
Receptor activation follows the canonical Gs pathway: binding increases intracellular cyclic AMP, which promotes protein kinase A activity. In pancreatic beta cells this amplifies glucose-dependent insulin release, so secretion rises when blood glucose is high and changes little when it is low. The same signalling suppresses glucagon release from alpha cells and slows gastric emptying. Receptors in the hypothalamus and brainstem are thought to contribute to reduced appetite and lower energy intake. Which of these effects dominates clinical outcomes remains an area of active study.
The primary target is the GLP-1 receptor, a class B G protein-coupled receptor expressed on pancreatic beta cells, in the gut, and in several brain regions. Receptor activation raises intracellular cyclic AMP, which potentiates glucose-dependent insulin secretion and lowers glucagon release when blood glucose is elevated. Signalling in the hypothalamus and brainstem is associated with reduced appetite and slower gastric emptying. Because the insulinotropic effect depends on prevailing glucose levels, the hypoglycaemic risk of the peptide alone is described as low in most study settings. The relative contribution of peripheral and central actions remains an active research question.
Large randomised trials in adults with type 2 diabetes and in adults with obesity have reported reductions in body weight and improvements in several cardiovascular risk markers. One outcome trial found a lower incidence of major adverse cardiovascular events in participants with diabetes and established cardiovascular disease. Gastrointestinal effects such as nausea and vomiting are the most frequently reported adverse events and often diminish over time. Changes in lean body mass during weight loss are an area of ongoing investigation. Effects in adolescents and in pregnancy are less well characterised, and current labelling advises against use during pregnancy.
Semaglutide is a synthetic peptide analogue of glucagon-like peptide-1, a gut hormone released after nutrient intake. The molecule contains 31 amino acid residues and differs from the native sequence at several positions. A non-natural residue at position eight resists the enzyme that normally truncates the hormone, while a lysine-linked fatty diacid side chain promotes binding to serum albumin. These two modifications extend the circulating half-life from minutes to roughly one week. The peptide is produced by solid-phase synthesis followed by selective acylation, and its identity and purity are confirmed by spectrometric and chromatographic techniques.
Lyophilised material appears as a white to off-white cake or powder that is hygroscopic, and containers are usually equilibrated to room temperature before opening to limit condensation. Dissolution is performed in water, phosphate-buffered saline, or a mildly alkaline buffer, since solubility rises above neutral pH. Gentle inversion or low-speed mixing is preferred, because vigorous vortexing can promote surface denaturation and aggregation. Complete dissolution may require several minutes, and brief sonication is sometimes applied. Passing the solution through a 0.22 micrometre membrane removes particulates but does not by itself sterilise the liquid.
Storage at minus 20 degrees Celsius or lower in a desiccated container preserves the peptide for extended periods, while working solutions are commonly held at two to eight degrees Celsius for short intervals. Light exposure and repeated freeze-thaw cycles accelerate degradation, so dividing material into single-use aliquots is generally recommended. Adsorption to glass and plastic surfaces can lower the measured concentration of dilute solutions, particularly below one milligram per millilitre. The degradation routes most often reported for GLP-1 analogues are deamidation, methionine oxidation, and backbone hydrolysis. Relative rates under specific conditions are frequently described only for individual formulations.
Reverse-phase high-performance liquid chromatography with ultraviolet detection near 214 or 280 nanometres is widely used to assess purity and to resolve related impurities. Liquid chromatography coupled to mass spectrometry confirms identity through the protonated molecular ion and fragment ions formed in tandem experiments. Capillary electrophoresis and peptide mapping after enzymatic digestion supply complementary information on charge variants and modification sites. Circular dichroism and nuclear magnetic resonance can report on secondary structure in solution. Absolute quantification usually depends on an external standard, and reported purity depends on the detection wavelength and integration parameters chosen.
== Commercial performance == The album debuted at No. 145 on Billboard 200, and No. 5 on Top Dance/Electronic Albums for charts dated November 24, 2012, selling 4,000 copies in the first week. The album reached No. 77 on Billboard 200 the following week, and No. 2 on Dance/Electronic Albums. The album has sold 52,000 copies in the United States as of August 2016.
== Sports == A 2017 INSEE study reported persistent gender disparities in physical and sports activities. Women were underrepresented in racket and team sports. In media coverage, women's sports accounted for less than 20% of televised sports airtime. Leadership roles in sports organizations remain limited for women. Despite the 2014 law for real gender equality, in 2019 only one Olympic sports federation and eleven non-Olympic federations were led by women.
==== France ==== The first location in France opened in Paris in May 2012. Expansion in France was much slower than that in the United Kingdom or Canada, with a second location in Paris opening in 2013 and a third location in 2014. At the time of its opening in 2014, the restaurant at La Défense was the largest Chipotle location in the world at 7,000 square feet (650 m2), while a typical Chipotle restaurant is usually between 2,200 square feet (200 m2) and 2,500 square feet (230 m2). A fourth Parisian location was opened in Levallois-Perret in 2015 followed by a fifth Parisian location in Saint-Germain-des-Prés in 2016. The company opened its seventh location in France and its first location outside the Paris region, inside Lyon's La Part-Dieu shopping mall in 2021.
Sources: en.wikipedia.org
Many North American sports leagues are made up of teams from different countries—three of the four largest professional leagues have teams representing cities on both sides of the U.S.-Canada border. The same is true for soccer leagues. Although foreign clubs can and do participate in leagues based in the United States, no such team is eligible to participate in the U.S. Open Cup, which is only open to teams affiliated with the United States Soccer Federation (U.S. Soccer). Previously, Canadian teams playing in Major League Soccer (MLS) were not eligible to qualify for the CONCACAF Champions League through the MLS regular season or playoffs; their only method of qualification was through the Canadian Championship, the cup competition run by the Canadian Soccer Association. However, starting from the 2023 MLS season, Canadian teams can qualify for the expanded 2024 CONCACAF Champions League through the MLS regular season or playoffs, or through the Leagues Cup, a competition run by MLS and Liga MX. Those teams that do participate in U.S. leagues also participate in various competitions under their local federations to gain entry into the Champions League and the now defunct CONCACAF League.
=== Intragenic complementation === Multiple copies of a polypeptide encoded by a gene often can form an aggregate referred to as a multimer. When a multimer is formed from polypeptides produced by two different mutant alleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. When a mixed multimer displays increased functionality relative to the unmixed multimers, the phenomenon is referred to as intragenic complementation. In humans, argininosuccinate lyase (ASL) is a homotetrameric enzyme that can undergo intragenic complementation. An ASL disorder in humans can arise from mutations in the ASL gene, particularly mutations that affect the active site of the tetrameric enzyme. ASL disorder is associated with considerable clinical and genetic heterogeneity which is considered to reflect the extensive intragenic complementation occurring among different individual patients.
Deficiency of leptin has been shown to alter brain proteins and neuronal functions of obese mice that can be restored by leptin injection Leptin receptor signaling in the hippocampus enhances learning and memory Treatment with leptin has been shown to enhance learning and memory in animal models. In humans, low circulating plasma leptin has been associated with cognitive changes associated with anorexia, depression, and Alzheimer's Disease Studies in transgenic mouse models of Alzheimer's disease have shown that chronic administration of leptin can ameliorate brain pathology and improve cognitive performance, by reducing b-amyloid and hyperphosphorylated Tau, two hallmarks of Alzheimer's pathology. Generally, leptin is thought to enter the brain at the choroid plexus, where the intense expression of a form of leptin receptor molecule could act as a transport mechanism. Increased levels of melatonin causes a downregulation of leptin, however, melatonin also appears to increase leptin levels in the presence of insulin, therefore causing a decrease in appetite during sleeping. Partial sleep deprivation has also been associated with decreased leptin levels. Mice with type 1 diabetes treated with leptin or leptin plus insulin, compared to insulin alone had better metabolic profiles: blood sugar did not fluctuate so much; cholesterol levels decreased; less body fat formed.
== Activities == In August 1987 Schabort attended and spoke at a commemorative service for Rudolf Hess organised by the Afrikaner Weerstandsbeweging (AWB). The BBB would organise inflammatory meeting and marches. The BBB sought to link with international right-wing organisations. The BBB ran a "blatantly racist" bilingual magazine Kommando: Stem van die Blankedom/Kommando: Voice of the White Race published by Alan Harvey. Harvey was deputy leader of the South Natal branch (its leader was Peter Smith); Harvey had previously published and edited the South African Patriot magazine in Durban, under the "Patriotic Press" imprint. This magazine carried advertisements of several far right organisations around the world, including David Duke's the National Association for the Advancement of White People, National Vanguard magazine issued by the National Alliance, Instauration magazine, the British cultural magazine Heritage and Destiny, the National Front's Nationalism Today (to which Harvey contributed both under his own name and under the pseudonym "John Humphries"), and NF News. Harvey contributed to the BBB's publication under his own name.
Sources: en.wikipedia.org
== Other uses == The trust-inducing property of oxytocin might help those with social anxiety and depression, anxiety, fear, and social dysfunctions, such as generalized anxiety disorder, post-traumatic stress disorder, and social anxiety disorder, as well as autism and schizophrenia, among others. However, a 2013 meta-analysis only autism spectrum disorder showed a significant combined effect size. A 2022 study found an indication of an effect among autistic children aged 3–5, but not among autistic children aged 5-12. People using oxytocin show improved recognition for positive social cues over threatening social cues and improved recognition of fear.
inborn error of metabolism Any genetically determined biochemical variation affecting one or more metabolic functions in a way that causes a congenital disease or disorder in humans. Most such errors are due to mutations in single genes encoding enzymes that facilitate important metabolic reactions such as the conversion of specific substrates into unique products, which may affect numerous downstream steps in one or more metabolic pathways and thereby contribute to a diverse variety of symptoms; often they cause the accumulation of toxic intermediates or impair the body's ability to synthesize essential compounds.
=== Christmas bombings === On 14 December 1972, Nixon sent an ultimatum demanding that Tho return to Paris to "negotiate seriously" within 72 hours or else he would bomb North Vietnam without limit. Knowing that Nixon was considering sacking him, Kissinger approved of his decision to resume bombing North Vietnam. Kissinger told the media that while the peace agreement was "99 percent completed…we will not be blackmailed into an agreement. We will not be stampeded into an agreement and, if I may say so, we will not be charmed into an agreement until its conditions are right". At the same time, Nixon ordered Admiral Thomas Hinman Moorer, the Chairman of the Joint Chiefs of Staff: "I don't want any more of this crap about the fact that we couldn't hit this target or that one. This is your chance to use military power to win this war, and if you don't, I'll hold you responsible". Following the rejection of Nixon's ultimatum, on 18 December, Operation Linebacker II was launched, the so-called Christmas Bombings that lasted until 29 December 1972. During these 11 days of bombing that were the heaviest bombing of the entire war, B-52 bombers flew 3,000 sorties and dropped 40,000 tons of bombs on Hanoi and Haiphong. About 1,261 people were killed in Hanoi and another 305 in Haiphong, as the North Vietnamese authorities had pulled out most people from the two cities beforehand to escape the expected bombings.
Sources: en.wikipedia.org
Manufacturers commonly state multi-year stability when the powder is kept dry and frozen. Actual shelf life depends on residual moisture, vial sealing, and storage temperature. A re-test by chromatography is the only way to confirm remaining purity.
Deamidated and oxidized forms are the most frequently reported impurities. Truncated peptide fragments from incomplete synthesis also appear at low levels. Their relative abundance grows with time, heat exposure, and unfavorable pH.
Retention time matching on a validated column provides strong circumstantial evidence. It does not distinguish compounds with similar hydrophobicity. Mass measurement or peptide mapping is needed for unambiguous identification.
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。