If you have been reading about Freeze-thaw 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 2026-06-01. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
市售注射用制剂通常要求在二至八摄氏度冷藏保存，并避免光照与冻结。部分多剂量笔在首次使用后允许在不超过三十摄氏度的环境中存放有限周数，具体期限由辅料与防腐剂体系决定。反复冻融会促进肽链聚集并改变可见颗粒计数，因此应予避免。冻干粉末在干燥、避光、低温条件下更为稳定。溶液配制后宜使用低吸附容器，以减少肽类在塑料或玻璃表面的损失。
纯度评价多采用反相高效液相色谱，流动相常加入三氟乙酸或甲酸作为离子对改性剂，检测波长设在二百一十四纳米或二百二十纳米。分子量确认依靠电喷雾电离质谱或基质辅助激光解吸电离质谱，实测值应与理论值在数 ppm 内吻合。肽图分析通过酶切后液相色谱串联质谱完成，用于核查序列与修饰位点。体积排阻色谱用于定量共价与非共价聚集体。生物基质浓度测定则采用免疫分析或液相色谱串联质谱。
肽类的主要降解路径包括天冬酰胺脱酰胺、甲硫氨酸氧化、天冬氨酸异构化以及由 β-折叠驱动的聚集，这些反应对 pH 与缓冲液种类较为敏感。磷酸盐、丙二醇与苯酚等辅料会影响局部微环境与界面行为。强制降解研究借助高温、强光、氧化剂与极端 pH 暴露来预测产物谱。关于长期室温存放的数据相对有限，超出标签条件的稳定性仍属开放问题，需要在具体制剂中通过实时与加速试验加以确认。
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C187H291N45O59 | free base, without counter-ion |
| Molecular weight | About 4114 Da | peptide backbone plus attached lipid chain |
| Plasma half-life | About 165 hours | supports once-weekly dosing in humans |
| Plasma protein binding | Greater than 99 percent | attributed mainly to serum albumin |
| Receptor target | GLP-1 receptor | Gs-coupled, raises intracellular cyclic AMP |
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.
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.
Quantification and purity assessment rely on separation methods coupled to optical or mass detection. Reversed-phase high-performance liquid chromatography resolves the intact peptide from related impurities and is the standard assay technique. Size-exclusion chromatography measures aggregates, while ion-exchange chromatography separates charge variants produced by deamidation. Mass spectrometry confirms identity and detects mass shifts of a few daltons. In biological matrices, liquid chromatography with tandem mass spectrometry is often used because immunoassays can cross-react with endogenous GLP-1 or with circulating fragments.
As a peptide, semaglutide is sensitive to conditions that break amide bonds or modify side chains. Deamidation of asparagine and glutamine residues, oxidation of methionine and tryptophan, and non-covalent aggregation are the main degradation routes described in published stability work. Rate depends strongly on pH, buffer species, ionic strength, temperature and exposure to light. Formulators therefore choose a defined solution pH and often add excipients such as phosphate buffer, propylene glycol and phenol, each of which plays a separate role in pH control, tonicity or preservation.
Storage guidance for the finished injectable product distinguishes the unused state from the in-use state. Before first use, pens are kept refrigerated between 2 and 8 degrees Celsius, protected from light, and never frozen, since freezing can disrupt the peptide or the device. After first use, label instructions in several markets permit storage at room temperature up to about 30 degrees Celsius for a limited number of days. Solid research-grade material is normally held at or below minus 20 degrees Celsius, often with desiccant, and allowed to equilibrate before opening.
Activation of the GLP-1 receptor couples to Gs signalling and raises intracellular cyclic AMP in pancreatic beta cells. The resulting insulin release depends on prevailing glucose concentrations, so the effect is greater when glucose is elevated. Receptor engagement also suppresses glucagon secretion and slows gastric emptying, which flattens post-meal glucose excursions. In the central nervous system, signalling in hypothalamic and brainstem regions is associated with reduced appetite and lower energy intake. Studies continue to examine effects on cardiac, renal and hepatic endpoints; whether those benefits are independent of weight change remains an open question.
Clinical development of this compound followed earlier short-acting GLP-1 analogues that required frequent injection. Once-weekly subcutaneous formulations entered use after 2017, and an oral formulation using a permeation enhancer later became available. The oral version pairs the peptide with sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, a carrier that improves uptake across the gastric epithelium. Interest has expanded from glycaemic control into weight management and metabolic liver disease. Regulatory status and approved indications differ between countries, and the product remains subject to ongoing safety monitoring.
Semaglutide is a synthetic peptide that acts as an agonist at the glucagon-like peptide-1 receptor. It is a structural analogue of human GLP-1(7-37), modified to resist enzymatic degradation by dipeptidyl peptidase-4. The peptide backbone contains alpha-aminoisobutyric acid at position 8, a substitution that stabilises the helix and slows cleavage. A fatty diacid side chain attached through a linker at lysine 34 promotes binding to serum albumin, which extends the circulating half-life. These two modifications together allow less frequent administration than native GLP-1 requires.
Development began in the early 2010s with the goal of extending GLP-1 activity beyond the brief window achieved by native peptide infusion. The earliest approved formulation was a subcutaneous injection given once weekly. A later oral tablet pairs the peptide with an absorption enhancer, sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, usually shortened to SNAC. That carrier lowers local pH and helps the peptide cross gastric tissue. Both routes deliver the same active molecule.
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.
Newer research has focused on methods of identifying healthier obese people by clinicians, and not treating obese people as a monolithic group. Obese people who do not experience medical complications from their obesity are sometimes called (metabolically) healthy obese, but the extent to which this group exists (especially among older people) is in dispute. The number of people considered metabolically healthy depends on the definition used, and there is no universally accepted definition. There are numerous obese people who have relatively few metabolic abnormalities, and a minority of obese people have no medical complications. The guidelines of the American Association of Clinical Endocrinologists call for physicians to use risk stratification with obese patients when considering how to assess their risk of developing type 2 diabetes. In 2014, the BioSHaRE–EU Healthy Obese Project (sponsored by Maelstrom Research, a team under the Research Institute of the McGill University Health Centre) came up with two definitions for healthy obesity, one more strict and one less so:
=== CD8+ T-cells === Tetramer stains usually analyze cytotoxic T lymphocyte (CTL) populations. CTLs are also called CD8+ T-cells, because they have CD8 co-receptors that bind to MHC class I molecules. Most cells in the body express MHC class I molecules, which are responsible for processing intracellular antigens and presenting at the cell's surface. If the peptides being presented by MHC class I molecules are foreign—for example, derived from viral proteins instead of the cell's own proteins—the CTL with a receptor that matches the peptide will destroy the cell. Tetramer stains allow for the visualization, quantification, and sorting of these cells by flow cytometry, which is extremely useful in immunology. T-cell populations can be tracked over the duration of a virus or after the application of a vaccine. Tetramer stains can also be paired with functional assays like ELIspot, which detects the number of cytokine secreting cells in a sample.
They take an intact bone image sample (region of interest, ROI, reference site) and a sample of the implantation site (second ROI, test site) can be assessed numerically/objectively to what extent the implantation site imitates a healthy bone and how advanced is the process of bone regeneration Fast-Versus Slow-Resorbable Calcium Phosphate Bone Substitute Materials—Texture Analysis after 12 Months of Observation New Oral Surgery Materials for Bone Reconstruction—A Comparison of Five Bone Substitute Materials for Dentoalveolar Augmentation. It is also possible to check whether the bone healing process is influenced by some systemic factors Influence of General Mineral Condition on Collagen-Guided Alveolar Crest Augmentation.
Morpholinos can interfere with pre-mRNA processing steps either by preventing splice-directing small nuclear ribonucleoproteins (snRNP) complexes from binding to their targets at the borders of introns on a strand of pre-mRNA, or by blocking the nucleophilic adenine base and preventing it from forming the splice lariat structure, or by interfering with the binding of splice regulatory proteins such as splice silencers and splice enhancers. Preventing the binding of snRNP U1 (at the donor site) or U2/U5 (at the polypyrimidine moiety and acceptor site) can cause modified splicing, commonly excluding exons from the mature mRNA. Targeting some splice targets results in intron inclusions, while activation of cryptic splice sites can lead to partial inclusions or exclusions. Targets of U11/U12 snRNPs can also be blocked. Splice modification can be conveniently assayed by reverse-transcriptase polymerase chain reaction (RT-PCR) and is seen as a band shift after gel electrophoresis of RT-PCR products.
Turin is split up into 8 boroughs, locally called circoscrizioni; these do not necessarily correspond to the historical districts of the city, which are rather called quartieri, rioni, borghi, borgate or zone. The circoscrizioni system originally comprised 10 of them, that were reduced to 8 by merging borough 9 into 8, and 10 into 2. The following list enumerates the boroughs and the location of the historical districts inside them:
Sources: en.wikipedia.org
=== Film === The rotoscoped film A Scanner Darkly was authorized by Dick's estate. It was released in July 2006 and stars Keanu Reeves as Fred/Bob Arctor and Winona Ryder as Donna. Rory Cochrane, Robert Downey Jr., and Woody Harrelson co-star as Arctor's drugged-out housemates and friends. The film was directed by Richard Linklater.
=== Precursor to other peroxide compounds === Hydrogen peroxide is a weak acid, forming hydroperoxide or peroxide salts with many metals. It also converts metal oxides into the corresponding peroxides. For example, upon treatment with hydrogen peroxide, chromic acid (CrO3 and H2SO4) forms a blue peroxide CrO(O2)2.
== Historical understanding == Historically, there has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD. Following Plato, however, even the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, itself, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite literally nothing at all, which cannot rightly be said to exist. Aristotle believed that no void could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void. In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. In the medieval Muslim world, the physicist and Islamic scholar Al-Farabi wrote a treatise rejecting the existence of the vacuum in the 10th century. He concluded that air's volume can expand to fill available space, and therefore the concept of a perfect vacuum was incoherent.
23 August – It is reported that doctors at Oxford's Churchill Hospital have carried out the UK's first womb transplant, with a 34-year-old woman receiving her sister's womb in a 17-hour operation that took place in February 2023. 24 August Data released by the Home Office shows that 175,000 people were waiting to have their claims for asylum assessed at the end of June 2023, an increase of 44% on the same time in 2022. GCSE results are published in England, Wales and Northern Ireland, with 68.2% of all entries marked at grades 4/C and above. It is the second fall in overall results, taking them almost back to pre-pandemic levels. 25 August Ofgem confirms the energy price cap will fall again in October, with an annual gas and electricity bill at around £1,923. The National Crime Agency launches a criminal investigation after linking 88 UK deaths with an online seller from Canada accused of selling them a poisonous substance so they could commit suicide. 26 August – Conservative MP Nadine Dorries resigns her Parliamentary seat two months after originally saying she would do so, accusing Prime Minister Rishi Sunak of abandoning "the fundamental principles of Conservatism" and that "history will not judge [him] kindly". 28 August – Hundreds of flights to and from the UK are delayed following technical problems with the UK's air traffic control system.
Cellular thermal shift assay (CETSA) and proteome integral solubility alteration (PISA)-based proteomics are widely used in drug discovery as label-free, mass spectrometry–compatible methods for quantifying cellular target engagement (confirming that a drug binds its intended target), deconvoluting drug targets (identifying the protein target of compounds with unknown targets), and profiling off-target interactions at the proteome scale. CETSA measures drug-induced changes in protein thermal stability in intact cells or tissues and, when combined with proteomics, enables the unbiased identification and ranking of on- and off-targets, as well as supporting phenotypic hit mechanism-of-action studies. PISA extends thermal-shift principles by integrating protein solubility changes across a temperature gradient, substantially increasing throughput and enabling multiplexed analysis of multiple compounds, concentrations, or time points. This approach facilitates high-content target deconvolution and comparative mechanism-of-action profiling, including applications in low-input or automated workflows.
Sources: en.wikipedia.org
The ruby laser was developed in 1960 by Theodore Maiman (1927-2007) as the first laser based on the ruby maser. Soon after, the dangers of lasers were discovered, especially for the eyes and skin, due to the laser's low penetration depth. Lasers have numerous applications in technology and research as well as in everyday life, from simple laser pointers to distance measuring devices, cutting and welding tools, reproduction of optical storage media such as CDs, DVDs and Blu-ray discs, communication, laser scalpels and other devices using laser light in everyday medical practice. The Radiation Protection Commission requires that laser applications on human skin be performed only by a specially trained physician. Lasers are also used for show effects in discotheques and at events.
An alkane has only C–H and C–C single bonds. The former result from the overlap of an sp3 orbital of carbon with the 1s orbital of a hydrogen; the latter by the overlap of two sp3 orbitals on adjacent carbon atoms. The bond lengths amount to 1.09 × 10−10 m for a C–H bond and 1.54 × 10−10 m for a C–C bond. The spatial arrangement of the bonds is similar to that of the four sp3 orbitals—they are tetrahedrally arranged, with an angle of 109.47° between them. Structural formulae that represent the bonds as being at right angles to one another, while both common and useful, do not accurately depict the geometry.
. In other words, as a rule, there is an infection-free steady state. This solution, also usually ensures that the disease-free equilibrium is also an equilibrium of the system. There is another fixed point known as an Endemic Equilibrium (EE) where the disease is not totally eradicated and remains in the population. Mathematically,
Daphne Walker, singer (born 1930). 19 July – Lee Mummery, cricketer (Central Districts) (born 1935). 20 July – Jim Tomlin, artist, musician (Chants R&B), and art educator (Otago Polytechnic) (born 1940). 23 July – Kathryn Smits, Germanist (University of Auckland) (born 1935). 25 July – Ian Leggat, school teacher and university administrator, principal of Hagley High School (1971–1976) and Christchurch Boys' High School (1976–1988), University of Canterbury chancellor (1992–1998) (born 1929). 26 July Ian Carter, sociologist (University of Auckland) (born 1943). Keith Sorrenson, historian (University of Auckland), president of the Citizens' Association for Racial Equality (1971–1973), member of the Waitangi Tribunal (1986–2011) (born 1932). John Werry, child and adolescent psychiatrist (University of Auckland) (born 1931). 29 July – Sir Michael Hill, jeweller, businessman (Michael Hill Jeweller), and philanthropist (born 1938).
=== 2000s === 2000: Venezuelan astrophysicist Kathy Vivas presented her discovery of approximately 100 "new and very distant" RR Lyrae stars, providing insight into the structure and history of the Milky Way galaxy. 2000: Russian gynaecologist Galina Savelyeva founded the Department of Obstetrics and Gynaecology at Moscow State University. Savelyeva was one of the first scientists in the world to demonstrate the feasibility of using craniocerebral hypothermia in the treatment of babies born with asphyxia, which formed the basis for the Russian Ministry of Health's order on the primary resuscitation of babies born with asphyxia. 2001: Danish physicist Lene Hau led a Harvard University team who used a Bose–Einstein condensate to slow down a beam of light to about 17 metres per second, then were able to stop a beam completely. 2003: Danish structural chemist and crystallographer Sine Larsen became the first female scientific research director at the European Synchrotron Radiation Facility (ESRF), where she was responsible for research in the fields of structural biology and structural chemistry. 2003: American geophysicist Claudia Alexander oversaw the final stages of Project Galileo, a space exploration mission that ended at the planet Jupiter. 2004: American biologist Linda B. Buck received the Nobel Prize in Physiology or Medicine along with Richard Axel "for their discoveries of odorant receptors and the organization of the olfactory system". 2004: American astrophysicist and radio astronomer Naomi McClure-Griffiths identified a new spiral arm of the Milky Way galaxy.
Sources: en.wikipedia.org
Native GLP-1 is a short-lived peptide cleared within one to two minutes by dipeptidyl peptidase-4 and related enzymes. Semaglutide keeps the receptor-binding backbone but adds substitutions and a lipid chain. These changes block the main cleavage site and allow reversible albumin binding, extending the half-life to roughly 165 hours.
Albumin is the most abundant protein in plasma and carries molecules that bear fatty-acid chains. Binding shields the peptide from renal filtration and from peptidases, keeping a circulating reservoir. Slow release from this reservoir produces sustained receptor occupancy and supports infrequent dosing.
The insulinotropic effect is glucose-dependent, meaning secretion increases mainly when glucose is elevated. This property is often described as lowering the chance of hypoglycaemia when the compound is used alone. Other glucose-lowering agents used at the same time can still cause low blood glucose.
冻融过程中冰晶形成与局部浓度升高会促使肽链发生界面吸附和聚集。聚集不仅降低有效含量，还会改变可见异物与不溶性微粒的计数结果。将溶液分装为单次使用的小体积等份可减少循环次数。