Freeze-thaw cycling raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
This page was last updated on 2026-01-11 and is reviewed periodically as new material appears.
杂质谱一般包含缺失序列片段、差向异构体、氧化产物以及残留溶剂或反离子，其中组氨酸与芳香残基的氧化常被重点关注。反相色谱中这类杂质往往紧邻主峰洗脱，因此方法需要足够的分离度并经过系统适用性验证。纯度百分比的解读依赖于检测波长与梯度条件，不同实验室公布的数字不宜直接横向比较。参考标准品有助于跨批次对照，但其自身赋值同样需要可追溯来源。
冻干状态下的肽通常比溶液状态更稳定，常规做法是维持 -20 °C 或更低温度、保持干燥并避开强光。复溶后的降解主要来自水解、氧化与脱酰胺，速率受 pH、缓冲液种类、离子强度与温度共同影响，碱性条件一般会加快这些反应。反复冻融会造成聚集与容器吸附损失，分装保存能降低该风险。容器材质与金属离子也可能参与氧化过程，需与操作条件一并考虑。
Published animal and early human work describes growth hormone release that is separated from comparable rises in adrenocorticotropic hormone and cortisol. Prolactin changes are reported as small in the same studies. Selectivity is attributed to binding at the ghrelin receptor and to the downstream signaling that follows, rather than to differences in how quickly the peptide is cleared. Authors commonly label the compound selective rather than potent, because the same mass produces a smaller growth hormone response than some older secretagogues tested in parallel. Whether that profile holds across species and routes of administration remains an open question.
Human data remain limited and come mainly from small, short-term studies conducted decades ago. The peptide has not received approval as a medicine from major regulators, so current availability is largely as a research chemical. Reported effects on growth hormone pulsatility, appetite, and body composition should be read as preliminary, since few independent groups have replicated the original findings. Analytical characterization of research-grade material varies between suppliers, which complicates comparison across studies. Regulatory status also differs by country, and some jurisdictions classify it as a prescription-only or otherwise restricted item.
| Property | Value | Notes |
|---|---|---|
| 纯度检测 | RP-HPLC，214 nm | 乙腈/水梯度，含 0.1% 三氟乙酸 |
| 身份确认 | ESI-MS 或 LC-MS/MS | 比对实测与理论分子量 |
| 冻干粉储存 | -20 °C，干燥避光 | 分装可减少开盖次数 |
| 复溶液储存 | 2-8 °C，短期使用 | 避免反复冻融与长时间室温放置 |
| 主要降解途径 | 水解、氧化、脱酰胺 | 碱性 pH 与强光会加快反应 |
Long-term storage of the dry powder is typically at minus twenty degrees Celsius or lower, protected from light and moisture. Solutions are commonly kept frozen and thawed only once, because repeated freeze-thaw cycles can promote aggregation and loss of measurable peptide content. Buffers near neutral pH are preferred over strongly acidic or strongly basic conditions. Shipping at ambient temperature is acceptable for short periods when the powder remains sealed and desiccated.
Identity and purity are assessed by complementary methods rather than a single test. Reversed-phase high-performance liquid chromatography separates the peptide from related impurities and reports a percentage purity. Mass spectrometry, most often with electrospray ionization, confirms the expected molecular mass and detects sequence-related variants. Amino acid analysis can verify composition, while water content and residual counterion measurements support the mass balance of a batch. Stability studies under accelerated conditions are used to estimate shelf life, though such estimates carry uncertainty for long-term storage.
Ipamorelin is a synthetic pentapeptide that belongs to the growth hormone secretagogue class of compounds. Its sequence is Aib-His-D-2-Nal-D-Phe-Lys-NH2, a structure that differs from natural ghrelin in length and in the presence of non-natural amino acid residues. Early laboratory work described it as a comparatively selective agent that stimulates growth hormone release with limited effect on other pituitary hormones. The compound is supplied as a lyophilized solid for research use and has no identified natural source in the body.
Activity is mediated mainly through the growth hormone secretagogue receptor, now generally called the ghrelin receptor or GHS-R1a. Binding at this G-protein-coupled receptor triggers phospholipase C signaling, calcium mobilization, and release of growth hormone from pituitary somatotrophs. Reports describe less pronounced stimulation of adrenocorticotropic hormone and prolactin compared with earlier secretagogues such as hexarelin or GHRP-6. Selectivity figures vary between assay systems, so the degree of separation from other secretagogues is an area of ongoing comparison rather than a fixed constant.
Ipamorelin is a synthetic pentapeptide that acts as an agonist at the ghrelin receptor, also called the growth hormone secretagogue receptor type 1a. Its sequence incorporates non-natural residues, which slows enzymatic breakdown relative to short native peptides. In laboratory and early clinical work the compound is described as a selective growth hormone secretagogue because it raises growth hormone with comparatively little effect on other pituitary outputs. The degree to which that selectivity holds across species and dosing regimens remains an open question in the published literature.
Signal transduction begins when the peptide binds GHSR-1a on pituitary somatotrophs. The receptor couples to Gq/11 proteins, activating phospholipase C, which cleaves phosphatidylinositol bisphosphate into inositol trisphosphate and diacylglycerol. Inositol trisphosphate releases calcium from intracellular stores, and the resulting rise in cytosolic calcium drives growth hormone vesicle fusion. Concurrent Gs coupling and cyclic AMP elevation have also been reported, and the relative contribution of each arm to the overall secretory response is not fully settled.
Structural features distinguish the molecule from earlier secretagogues. An alpha-aminoisobutyric acid residue near the N-terminus and a D-naphthylalanine substitution increase receptor affinity, while C-terminal amidation improves resistance to exopeptidases. These modifications are associated with reduced stimulation of appetite and of the hypothalamic-pituitary-adrenal axis compared with hexarelin or growth hormone releasing peptide-6. Whether the same profile applies at every dose level studied is a matter of ongoing investigation rather than settled consensus.
(1933), first African-American basketball player to be selected as All-American Alfred Skrobisch (1933), Olympic fencer Cliff Montgomery (1934), led the Columbia Lions football team to victory in the Rose Bowl John O'Brien (1938), basketball player for the Akron Wingfoots Ben Johnson (1938), sprinter who rivaled Jesse Owens Sid Luckman (1939), NFL Hall of Fame Chicago Bears quarterback Ken Germann (1943), football coach, athletic director of Columbia University, and former Southern Conference commissioner Paul Governali (1943), football player for the Boston Yanks and New York Giants Walt Budko (1948), basketball player for Baltimore Bullets and Philadelphia Warriors Bruce Gehrke (1948), football player for New York Giants Bill Swiacki (1948), player for New York Giants, member of the College Football Hall of Fame Lou Kusserow (1949), football player for Hamilton Tiger-Cats and New York Yanks John Azary (1951), basketball player, recipient of the Haggerty Award Jack Molinas (1953), NBA player for the Fort Wayne Pistons Jack Rohan (1953), head coach of the Columbia Lions men's basketball team 1961–1974, and 1990–1995 George Shaw (1953), Olympic triple jumper Richard Ballantine* (1967), cyclist and cycling advocate; son of Ian Ballantine '38 of Ballantine Books James Margolis (1958), Olympic fencer James Melcher (1961), Olympian fencer, president of Fencers Club and hedge fund manager Robert Contiguglia (1963), soccer player, former president of the United States Soccer Federation Peter Salzberg (1964), head coach of Vermont Catamounts men's basketball 1972–1981 Archie Roberts (1965), former football player for the Miami Dolphins and cardiac surgeon Jim McMillian (1968), NBA player for the Los Angeles Lakers, Buffalo Braves, New York Knicks and Portland Trail Blazers Dave Newmark (1968), NBA player for the Chicago Bulls; also played for Israeli team Hapoel Tel Aviv B.C. Marty Domres (1969), football player for San Diego Chargers and Baltimore Colts Heyward Dotson (1970), basketball player George Starke (1971), offensive lineman for the Washington Redskins Henry Bunis (1975), two-time All-American tennis player, runner-up in 1977 Chilean Open Rick Fagel (1975), professional tennis player Vitas Gerulaitis* (1975), champion tennis player Thomas Losonczy (1975), Olympic fencer, winner of the Congressional Gold Medal Alton Byrd (1979), basketball player Eric Fromm (1980), tennis player John Witkowski (1983), football player for Detroit Lions and Houston Oilers Gene Larkin (1984), member of the Minnesota Twins 1987 and 1991 World Series championship teams Amr Aly (1985), soccer player who won the Hermann Trophy as the top college player of the year 1984; member of the 1984 U.S. Olympic Soccer Team and indoor soccer team Los Angeles Lazers Stephen Trevor (1986), Olympic fencer Kyra Tirana Barry (1987), team leader for U.S. women's national wrestling team Caitlin Bilodeaux (1987), Olympic fencer Howard Endelman (1987), tennis player Phil Williamson (1987), tennis player for Antigua and Barbuda Bob Cottingham (1988), Olympic fencer Jon Normile (1989), Olympic fencer Frank Seminara (1989), Major League Baseball pitcher for the San Diego Padres and the New York Mets Tom Auth (1990), Olympic rower Christine Vardaros (1991), professional cyclist Ann Marsh (1994), Olympic fencer Ríkharður Daðason (1996), Icelandic soccer player Marcellus Wiley (1997), football player for the Buffalo Bills, San Diego Chargers and Dallas Cowboys Dan Kellner (1998), fencer Pellegrino Matarazzo (1999), head coach of VfB Stuttgart Matt Napoleon (1999), Olympic soccer goalkeeper Cristina Teuscher (2000), Olympic gold medalist swimmer Jedediah Dupree (2001), NCAA Champion fencer Veljko Urošević (2003), Serbian Olympic rower Fernando Perez (2004), outfielder for the Tampa Bay Rays Jeremiah Boswell (2005), professional basketball player for BC Sliven, KK Strumica, and KK Torus Delilah DiCrescenzo (2005), long-distance runner, inspiration and subject of the Grammy-nominated song Hey There Delilah Michael Quarshie (2005), Finnish American football player who played for the Oakland Raiders and Frankfurt Galaxy Lisa Nemec (2006), Croatian long-distance runner Miloš Tomić (2006), Serbian Olympic rower Erison Hurtault (2007), Dominican sprinter James Leighman Williams (2007), fencer who won silver in the 2008 Summer Olympics Emily Jacobson (2008), fencer İhsan Emre Vural (2008), Turkish rower for Galatasaray S.K. Sherif Farrag (2009), Egyptian-American Olympic fencer Nicholas la Cava (2009), Olympic rower Jeff Spear (2010), Olympic fencer Daria Schneider (2010), fencer Jeff Adams (2011), Houston Texans offensive tackle Nicole Ross (2011), Olympic fencer Isadora Cerullo (2013), Brazilian-American Olympic rugby player Katie Meili (2013), Olympic swimmer, Pan American Games and 2016 Summer Olympics gold medalist Josh Martin (2013), Kansas City Chiefs linebacker John Gregorek Jr. (2014), middle-distance runner David Najem (2014), American soccer player for New Mexico United and the Afghanistan national football team Nadia Eke (2015), Ghanaian triple jumper, African Championships gold medalist in 2016 Kristine Musademba (2015), figure skater Max Schnur (2015), tennis player playing on the ATP Challenger Tour Nzingha Prescod (2015), Olympic fencer Ramit Tandon (2015), professional squash player Jakub Buczek (2016), Canadian Olympic rower Sasha DiGiulian (2016), world champion climber Jacqueline Dubrovich (2016), Olympic fencer Maodo Lô (2016), German basketball player for Brose Bamberg Robb Paller (2016), American-Israeli Olympic baseball player Jeff Coby (2017), American basketball player for Xuventude Baloncesto Cameron Nizialek (2017), football player for Atlanta Falcons Akua Obeng-Akrofi (2018), Ghanaian sprinter Charlotte Buck (2018), Olympic rower Osama Khalifa (2018), #1 ranked college squash player in the U.S. for the 2016–17 season Camille Zimmerman (2018), American basketball player for Norrköping Dolphins Yasmeen Al-Dabbagh (2019), Saudi Arabian sprinter Jessica Antiles (2019), swimmer who won silver and bronze medals in the 2017 Maccabiah Games Dylan Castanheira (2019), soccer player, goalkeeper for Fort Lauderdale CF Sophie Whitehouse (2019), goalkeeper for Republic of Ireland women's national football team Mike Smith (2020), basketball player Anthony Jackie Tang (2020), Hong Kong tennis player John Tanguay (2020), rower who won a silver medal in the 2020 Summer Paralympics Dylan Geick* (2021), wrestler and internet personality Velavan Senthilkumar (2021), British Junior Open Squash champion and Asian Junior Squash champion Nastasya Generalova (2023), gymnast and model Olivia Giaccio (2024), Olympic freestyle skier Evita Griskenas (2024), rhythmic gymnast Camden Pulkinen (2024), figure skater Abbey Hsu (2024), basketball player
== Career and research == Biemann was born in Innsbruck, Austria in 1926. He was drafted into the Wehrmacht during the final months of World War II and was sent to aid the divisions fighting against Allied forces then retreating before the Soviet Army on the Eastern Front. Fearing capture, he deserted with a friend to travel back to Innsbruck. Following in the footsteps of his father, he studied pharmacy at the University of Innsbruck where he graduated in 1948. He received his PhD at the University of Innsbruck supervised by Hermann Bretschneider in 1951. He started his work on his habilitation, but instead moved to the MIT in 1955 to work as a postdoctoral fellow in the group of George Büchi. Two years later with the assistance of Büchi, he was offered a faculty position at MIT in the analytical chemistry division where he turned his focus to peptide analysis and sequencing. Before embarking on his new research, however, Biemann decided to buy a mass spectrometer and use it to study peptides instead. He used his background in organic chemistry to modify peptides so that they become volatile and entered the gas phase, making them amenable to electron ionization, the only feasible ionization technique at the time. He partnered on the NASA Viking mission project to Mars which failed to detect organic matter on its the surface in 1976.
== History == 4-HO-DPT was first described in the scientific literature by David Repke and colleagues in 1977. Subsequently, it was described in further detail by Alexander Shulgin in his 1997 book TiHKAL (Tryptamines I Have Known and Loved). The drug was encountered as a novel designer drug in Europe in 2012.
1 January – New Year's Day 2 January – Day after New Year's Day 6 February – Waitangi Day 18 April – Good Friday 21 April – Easter Monday 25 April – Anzac Day 2 June – King's Birthday 20 June – Matariki 27 October – Labour Day 25 December – Christmas Day 26 December – Boxing Day
== J == Jacksonian seizure A type of focal seizure that begins in one area of the body (typically a finger or toe) and "marches" to adjacent areas, reflecting orderly spread of abnormal activity in the motor cortex. James–Lange theory A historical theory of emotion proposing that emotions result from physiological responses to stimuli (e.g., "We are afraid because we tremble"). While outdated, it laid groundwork for modern affective neuroscience. Jaw jerk reflex A stretch reflex elicited by tapping the chin, which causes the jaw to jerk upward. Used clinically to assess integrity of the trigeminal nerve and brainstem reflex circuits. Jitter The variability in timing of neural spike trains or signal transmission, especially in motor units or brain-computer interface systems. High jitter can affect signal fidelity. JNK pathway (c-Jun N-terminal kinase pathway) A signaling cascade involved in stress responses, apoptosis, and neurodegeneration. Dysregulation of the JNK pathway is linked to Alzheimer’s disease and neuronal injury. Joubert syndrome A rare genetic disorder characterized by abnormal development of the cerebellar vermis and brainstem, leading to hypotonia, ataxia, abnormal breathing, and developmental delay. Juxtacrine signaling A form of cell-to-cell communication where signaling molecules are transmitted directly through contact, rather than being secreted. Important in neural development and synaptogenesis.
Sources: en.wikipedia.org
A man is arrested on suspicion of attempted murder after four people were injured when they were hit by a car being driven on the wrong side of the road in Shaftesbury Avenue, central London. King Charles III delivers the Royal Christmas Message from London's Fitzrovia Chapel, where he praises health workers and calls for unity following the summer riots. Archbishop of York Stephen Cottrell delivers a Christmas message in place of the Archbishop of Canterbury, doing so as he prepares to assume acting charge of the Church of England. 26 December – Data collected by MRI Software indicates a 4% decrease in the number of Boxing Day shoppers compared to the same day in 2023. 27 December The Prime Minister pays tribute to Nick Starmer, his younger brother who died from cancer the previous day. Conservative leader Kemi Badenoch expresses her condolences. Flights to and from some of the UK's major airports, including Gatwick and Manchester, are disrupted due to fog. Former Conservative Justice Secretary David Gauke, who is leading a review into sentencing and prison overcrowding, calls for greater use of open prisons in order to ease the pressure on closed category prisons. A man is charged with four counts of attempted murder and remanded in custody over an incident involving a car in London on Christmas Day. 28 December – Fog continues to disrupt flights at UK airports. 29 December Weather warnings for rain, snow, and winds of up to 70 mph are issued for parts of the UK on New Year's Eve and New Year's Day.
== Society and culture == Many societies have a system for organ donation, in which a living or deceased donor's organ are transplanted into a person with a failing organ. The transplantation of larger solid organs often requires immunosuppression to prevent organ rejection or graft-versus-host disease. There is considerable interest throughout the world in creating laboratory-grown or artificial organs.
== Function == This gene encodes the alpha chain of type VII collagen. The type VII collagen fibril, composed of three identical alpha collagen chains, is restricted to the basement zone beneath stratified squamous epithelia. It functions as an anchoring fibril between the external epithelia and the underlying stroma. Mutations in this gene are associated with all forms of dystrophic epidermolysis bullosa. In the absence of mutations, however, an autoimmune response against type VII collagen can result in an acquired form of this disease called epidermolysis bullosa acquisita. Type VII collagen is also found in the retina; its function in this organ is unknown. COL7A1 is located on the short arm of human chromosome 3, in the chromosomal region denoted 3p21.31. The gene is approximately 31,000 base pairs in size and is remarkable for the extreme fragmentation of its coding sequence into 118 exons. COL7A1 is transcribed into an mRNA of 9,287 bases. In the skin, the type VII collagen protein is synthesized by keratinocytes and dermal fibroblasts. The symbol for the orthologous gene in the mouse is Col7a1.
The Balfour Declaration (2 November 1917) was a public statement issued by the British Government in 1917 during the First World War announcing its support for the establishment of a "national home for the Jewish people" in Palestine, then an Ottoman region with a small Jewish minority among an overwhelming Arab majority, mostly Muslim but also including Christians. The declaration was contained in a letter dated 2 November 1917 from Arthur Balfour, the British foreign secretary, to Lord Rothschild, a leader of the British Jewish community, for transmission to the Zionist Federation of Great Britain and Ireland. The text of the declaration was published in the press on 9 November 1917. Following Britain's declaration of war on the Ottoman Empire in November 1914, it had begun to consider the future of Palestine. Within two months a memorandum was circulated to the War Cabinet by a Zionist member, Herbert Samuel, proposing support of Zionist ambitions in order to gain the support of Jews in the current war. A committee was established in April 1915 by British prime minister H. H. Asquith to determine policy towards the Ottoman Empire including Palestine. Asquith, who had favoured post-war reform of the Ottoman Empire, resigned in December 1916; his replacement David Lloyd George favoured partition of the Empire. The first negotiations between the British and the Zionists took place at a conference on 7 February 1917 that included Sir Mark Sykes and the Zionist leadership.
Sources: en.wikipedia.org
Byzantine music is eclectically descended from early Christian plainsong, Jewish music, and a variety of ancient music; its exact connections to ancient Greek music remain uncertain. It included both sacred and secular traditions, but the latter is little known, whereas the former remains the central music of Eastern Orthodox liturgy into the 21st century. The empire's church music, known as Byzantine chant, was exclusively unaccompanied monodic vocal music, sung in Greek. From the 8th century, chant melodies were governed by the Oktōēchos framework, a set of eight modes—echos (ἦχος; lit. 'sound')—which each provide predetermined motivic formulae for composition. These formulae were chosen for proper text stress and occasionally for text painting, then collated through centonisation into hymns or psalms. Byzantine chant was central to the Byzantine Rite; the earliest music was not notated, including early monostrophic short hymns like the troparion. Proto-Ekphonetic notation (9th century onwards) marked simple recitation patterns. The neumatic Palaeo-Byzantine notation system emerged in the 10th century, and the Middle Byzantine "Round Notation" from the mid-12th century onwards is the first fully diastematic scheme. Several major forms developed alongside well-known composers: the long kontakion (5th century onwards), popularised by Romanos the Melodist; the also-extensive kanōn (late 7th century onwards), developed by Andrew of Crete; and the shorter sticheron (at least 8th century onwards), championed by Kassia.
=== As a medication target === Circulating levels of adiponectin can indirectly be increased through lifestyle modifications and certain medications such as statins. A small molecule adiponectin receptor AdipoR1 and AdipoR2 agonist, AdipoRon, has been reported. In 2016, the University of Tokyo announced it was launching an investigation into anonymously made claims of fabricated and falsified data on AdipoR1, AdipoR2, and AdipoRon. Extracts of sweet potatoes have been reported to increase levels of adiponectin and thereby improve glycemic control in humans. However, a systematic review concluded there is insufficient evidence to support the consumption of sweet potatoes to treat type 2 diabetes mellitus. Adiponectin is apparently able to cross the blood-brain-barrier. However, conflicting data on this issue exist. Adiponectin has a half-life of 2.5 hours in humans.
In a report published in JAMA Pediatrics, 37.5% of all fatal pediatric opioid poisonings between 1999 and 2021 were related to fentanyl; most of the deaths were among adolescents (89.6%) (15–19 years) and children aged 0 to 4 years (6.6%). According to the UNODC, "the opioid crisis in North America is unabated, fueled by an unprecedented number of overdose deaths."
Sources: en.wikipedia.org
肽键在 214 nm 附近有较强吸收，适合检测缺少芳香侧链的短肽。该波长的基线受流动相组成与梯度影响较大。因此流动相与梯度条件需要固定并完整记录。
仅凭保留时间不足以定性，通常需要质谱给出与理论值一致的分子量。进一步可用碎裂谱与参考谱比对。保留时间、分子量与碎裂谱三者吻合时，身份判断较为可靠。
这取决于缓冲液、pH、温度与微生物负荷，并不存在通用时限。常见做法是分装冷冻并尽量缩短室温放置时间。出现浑浊或沉淀时应弃用并重新配制。
碱性 pH、较高温度、强光照射与反复冻融都会加快水解、氧化或脱酰胺。溶液中的金属离子也可能催化氧化。控制这些变量比单纯降低浓度更有效。