Freeze-thaw is one of those subjects where the details matter more than the headlines. This page pulls together the background, the mechanisms, and the practical points readers ask about most.
Updated 2026-04-14. Numbers and descriptions here follow the published literature rather than marketing material.
The compound was developed in the late 1980s and early 1990s by academic researchers investigating melanocortin signaling and pigmentation. Early work explored whether synthetic analogs could reproduce effects of the natural hormone under controlled conditions. The molecule never advanced through the full regulatory pathway required for approval as a medicine. From the mid-2000s onward it appeared in unregulated consumer markets, often distributed through informal channels. That gap between research origins and commercial availability shapes how the compound is discussed today.
Melanotan-2 is a synthetic peptide designed as an analog of alpha-melanocyte-stimulating hormone, a signaling molecule produced in the pituitary and skin. Its structure is a linear chain of seven amino acids that folds into a ring through an internal lactam bridge joining two side chains. The compound is sometimes written as MT-II or MEL-2 in informal and commercial contexts. It belongs to the melanocortin peptide family, a group of short signaling molecules that share a conserved core sequence recognized by melanocortin receptors.
Two structural changes distinguish the synthetic peptide from the natural hormone. A norleucine residue replaces methionine at one position, and a D-configured phenylalanine replaces the natural L-form at another. Both substitutions slow enzymatic breakdown, which extends the molecule's persistence relative to the parent hormone. The lactam bridge further constrains the backbone into a stable conformation. These features are standard design strategies in peptide chemistry and are not unique to this compound; they appear across many research peptides built for improved stability.
The peer-reviewed record is dominated by small early-phase studies, case reports and pharmacovigilance summaries rather than large randomised trials. Papers typically examine tanning response, receptor selectivity or patterns of reported adverse events. Many note that participants obtained the peptide outside a clinical setting, which limits verification of composition and administered amount. Reported events vary widely, and causality is frequently unclear because the identity and purity of self-sourced material are unknown. Open questions include whether repeated melanocortin receptor stimulation produces cumulative effects, and how often label claims match actual content.
Identification in laboratories relies on reversed-phase liquid chromatography coupled with tandem mass spectrometry, with product-ion spectra compared against a certified reference standard. High-resolution mass spectrometry supplies accurate mass confirmation, and peptide mapping after enzymatic digestion separates melanotan II from closely related analogues. Quantitation of seized material is complicated by unknown counter-ions and residual trifluoroacetate left from purification. Immunoassays raised against alpha-melanocyte-stimulating hormone can cross-react, so chromatographic confirmation is normally required. Urinary detection windows are short, and reported limits of detection differ substantially between laboratories.
| Property | Value | Notes |
|---|---|---|
| Molecular class | Synthetic cyclic heptapeptide | Analog of alpha-MSH with an internal lactam bridge |
| Molecular weight | Approximately 1024 daltons | Free base value; salt forms differ |
| Appearance | White to off-white powder | Usually supplied as a lyophilized solid |
| Solubility | Freely soluble in water | Poorly soluble in nonpolar solvents |
| Typical storage | −20 °C, dry, protected from light | Repeated freeze-thaw cycles degrade peptides |
Published pharmacokinetic information is limited and comes mainly from small studies rather than registrational trials. Plasma half-life is usually described as short, on the order of tens of minutes, followed by rapid tissue distribution and clearance of the intact peptide. Metabolites and low concentrations of parent compound have been reported in urine, a detail relevant to anti-doping and forensic testing. Whether repeated exposure changes receptor sensitivity or clearance over time remains an open question. Values differ noticeably between analytical assays, so published numbers should be read as approximate rather than definitive.
Melanotan II is a synthetic cyclic heptapeptide with the sequence Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, corresponding to a molecular formula of C50H69N15O9 and a monoisotopic mass near 1024 daltons. It was designed as a structural analogue of alpha-melanocyte-stimulating hormone, a peptide hormone produced by cleavage of proopiomelanocortin. A lactam bridge between the aspartate and lysine side chains closes the ring, and the C-terminal amide removes a free carboxyl group. Both modifications increase resistance to enzymatic degradation compared with the linear parent hormone. Four substitutions distinguish it from afamelanotide, the linear analogue studied under the name melanotan I.
Verification of a purchased sample requires documentation linking a batch to a certificate of analysis, and that document should be read for the methods used rather than the headline purity figure. A single chromatographic percentage does not establish identity. Independent laboratories can perform identity and content assays, but no such test establishes that a product is suitable for human use. Claims about efficacy rest largely on small, early studies rather than on replicated controlled trials, and that gap remains open.
Identity testing for a cyclic peptide of this size usually relies on reversed-phase high-performance liquid chromatography coupled to mass spectrometry. The mass spectrum confirms molecular weight, while the chromatographic trace indicates the proportion of related impurities. Tandem mass spectrometry can provide sequence-level information when fragmentation data are compared against a reference standard. Nuclear magnetic resonance is sometimes used to confirm the lactam bridge, although it requires more material and greater operator expertise than routine chromatographic methods.
The 5 placebo-controlled trials include two monotherapy trials and one add-on combination therapy trial with each of the following: metformin, thiazolidinedione, or glyburide. Table shows 24-week data regardless of glycemic rescue. In February 2012, Bristol-Myers/Astra Zeneca distributed additional safety information on saxagliptin use in South Africa. The package insert is to be edited for South Africa. Contraindications will now include a history of sensitivity to saxagliptin (or another DPP4 inhibitor) as well as pancreatitis. Spontaneously reported adverse events in South Africa have included anaphylaxis, angioedema and acute pancreatitis. In a cardiovascular outcomes trial, saxagliptin treatment let to a small increase in the risk of being hospitalized for heart failure. Saxagliptin may cause joint pain that can be severe and disabling. Saxagliptin may increase the risk of heart failure.
Many of these nutrients are available in the must and skins of the grapes themselves but sometimes are supplemented by winemakers with additions such as diammonium phosphate (DAP), freeze-dried micro-nutrients (such as Go-Ferm and Ferm-K) and even the remnant of dead or extracted yeast cells such that the fermenting yeast can break down to mine for available nitrogen and nutrients. One historical winemaking tradition that is still practiced in some Italian wine regions is the ripasso method of adding the leftover pomace from the pressing of other wines into a newly fermenting batch of wine as an additional food source for the yeast. Saccharomyces cerevisiae can assimilate nitrogen from both inorganic (ammonia and ammonium) and organic forms (amino acids, particularly arginine). As yeast cells die, enzymes within the cells begin autolyzing by breaking down the cell, including the amino acids. This autolysis of the cell provides an available nitrogen source for the still-fermenting and viable yeast cells. However, this autolysis can also release sulfur-link compounds (such as the breakdown of amino acid cysteine) which can combine with other molecules and react with alcohol to create volatile thiols that can contribute to a "stinky fermentation" or later development into various wine faults.
Crystalline silica exists in seven different forms (polymorphs), depending upon the temperature of formation. The main three polymorphs are quartz, cristobalite, and tridymite. Quartz is the second most common mineral in the world (next to feldspar). Microcrystalline silica consists of minute quartz crystals bonded together with amorphous silica. Examples include flint and chert. Amorphous silica exists either as diatomaceous earth, from the skeletons of diatoms, or as vitreous silica, produced by heating and then rapid cooling of crystalline silica. Amorphous silica is less toxic than crystalline, but not biologically inert, and diatomite, when heated, can convert to tridymite or cristobalite. Silica flour is nearly pure SiO2 finely ground. Silica flour has been used as a polisher or buffer, as well as paint extender, abrasive, and filler for cosmetics. Silica flour has been associated with all types of silicosis, including acute silicosis. Silicosis is due to deposition of fine respirable dust (less than 10 micrometers in diameter) containing crystalline silicon dioxide in the form of alpha-quartz, cristobalite, or tridymite.
At birth, the liver comprises roughly 4% of body weight and weighs on average about 120 g (4 oz). Over the course of further development, it will increase to 1.4–1.6 kg (3.1–3.5 lb) but will only take up 2.5–3.5% of body weight. Hepatosomatic index (HSI) is the ratio of liver weight to body weight.
Sources: en.wikipedia.org
=== Other === In February 2026, activists announced plans for the Nuestra América Convoy, which will attempt to break the U.S. blockade and provide humanitarian aid to Cuba during the crisis. The flotilla is organized by Progressive International and contains members of the Global Sumud Flotilla that had attempted to break the Israeli blockade of the Gaza Strip. Streamer and political commentator Hasan Piker was on the Flotilla.
=== Oxidative stability === Using differential scanning calorimetry to study the stability to oxidation of samples generally requires an airtight sample chamber. It can be used to determine the oxidative-induction time (OIT) of a sample. Such tests are usually done isothermally (at constant temperature) by changing the atmosphere of the sample. First, the sample is brought to the desired test temperature under an inert atmosphere, usually nitrogen. Oxygen is then added to the system. Any oxidation that occurs is observed as a deviation in the baseline. Such analysis can be used to determine the stability and optimum storage conditions for a material or compound. DSC equipment can also be used to determine the Oxidative-Onset Temperature (OOT) of a material. In this test a sample (and a reference) are exposed to an oxygen atmosphere and subjected to a constant rate of heating (typically from 50 to 300 °C). The DSC heat flow curve will deviate when the reaction with oxygen begins (the reaction being either exothermic or endothermic). Both OIT and OOT tests are used as a tools for determining the activity of antioxidants.
Hilleman also developed the first Hepatitis B vaccine and the first varicella vaccine, for chickenpox. The company was incorporated in New Jersey in 1970. John J. Horan became CEO and Chairman in 1976, serving until 1985. Under his leadership, the company's investment in R&D grew threefold, and Merck became the largest pharmaceutical company in the world. In 1979, Merck scientists developed lovastatin (Mevacor), the first drug of the statin class. Merck scientist William C. Campbell and Satoshi Ōmura developed ivermectin for veterinary use in 1981, and later put it to human use against onchocerciasis in 1987–1988 with the name Mectizan; today the compound is also used against lymphatic filariasis, scabies and other parasitic infections. In 1982, the company formed a joint venture, KBI Inc., with AstraZeneca. During the late 1980s and 1990s, the company also established joint ventures with DuPont to access research and development expertise, and with Johnson & Johnson to sell over-the-counter consumer medications. In 1985, Merck received approval for imipenem, the first member of the carbapenem class of antibiotics. Antibiotics of the carbapenem class play an important role in treatment guidelines for certain hospital-acquired and multi-drug resistant infections. P. Roy Vagelos became CEO and Chairman that year, succeeding Horan. Vagelos served until reaching the company's mandatory retirement age in 1994, succeeded by Raymond Gilmartin. In 1991, Merck's Kelco subsidiary was responsible for volatile organic compound (VOC) emission pollution in the San Diego area.
Post-translational modification (PTM) isoforms are easily detected on 2D gels. Indeed, phosphorylation replaces neutral hydroxyl groups on serines, threonines, or tyrosines with negatively charged phosphates with pKs near 1.2 and 6.5. Thus, below pH 5.5, phosphates add a single negative charge; near pH 6.5, they add 1.5 negative charges; above pH 7.5, they add 2 negative charges. The relative amount of each isoform can also easily and rapidly be determined from staining intensity on 2D gels. In some very specific cases, the detection of the phosphorylation as a shift in the protein's electrophoretic mobility is possible on simple 1-dimensional SDS-PAGE gels, as it is described for instance for a transcriptional coactivator by Kovacs et al. Strong phosphorylation-related conformational changes (that persist in detergent-containing solutions) are thought to underlie this phenomenon. Most of the phosphorylation sites for which such a mobility shift has been described fall in the category of SP and TP sites (i.e. a proline residue follows the phosphorylated serine or threonine residue). Large-scale mass spectrometry analyses have been used to determine sites of protein phosphorylation. Dozens of studies have been published, each identifying thousands of sites, many of which were previously undescribed. Mass spectrometry is ideally suited for such analyses using HCD or ETD fragmentation, as the addition of phosphorylation results in an increase in the mass of the protein and the phosphorylated residue.
Typically, the higher the temperature the kiln operates at, the larger amount of emissions are produced (per pound of water removed). This is especially true in the drying of thin veneers and high-temperature drying of softwoods.
Sources: en.wikipedia.org
== Education == Zaffaroni was born on February 27, 1923, in Montevideo. Zaffaroni was of Italian descent, as his grandfather migrated from Italy to Uruguay at the age of 16. Both of Zaffaroni's parents died early in his life; his mother when he was 12 and his father when he was 18. His father was in the banking business. Zaffaroni received his Bachelor of Science degree from the University of the Republic in 1945, and his Ph.D. in biochemistry from the University of Rochester in 1949.
==== Lithium ==== The chemistry of lithium shows several differences from that of the rest of the group as the small Li+ cation polarises anions and gives its compounds a more covalent character. Lithium and magnesium have a diagonal relationship due to their similar atomic radii, so that they show some similarities. For example, lithium forms a stable nitride, a property common among all the alkaline earth metals (magnesium's group) but unique among the alkali metals. In addition, among their respective groups, only lithium and magnesium form organometallic compounds with significant covalent character (e.g. LiMe and MgMe2). Lithium fluoride is the only alkali metal halide that is poorly soluble in water, and lithium hydroxide is the only alkali metal hydroxide that is not deliquescent. Conversely, lithium perchlorate and other lithium salts with large anions that cannot be polarised are much more stable than the analogous compounds of the other alkali metals, probably because Li+ has a high solvation energy. This effect also means that most simple lithium salts are commonly encountered in hydrated form, because the anhydrous forms are extremely hygroscopic: this allows salts like lithium chloride and lithium bromide to be used in dehumidifiers and air-conditioners.
=== Sweden and Norway === The sale and production of absinthe has never been prohibited in Sweden or Norway. However, the only outlet that may sell alcoholic beverages containing more than 3.5% ABV in Sweden and 4.75% ABV in Norway is the government-owned chain of liquor stores known as Systembolaget in Sweden and Vinmonopolet in Norway. Systembolaget and Vinmonopolet did not import or sell absinthe for many years after the ban in France; however, today several absinthes are available for purchase in Systembolaget stores, including Swedish made distilled absinthe. In Norway, on the other hand, one is less likely to find many absinthes since Norwegian alcohol law prohibits the sale and importation of alcoholic beverages above 60% ABV, which eliminates most absinthes.
== Diseases affected by IGF == Studies of recent interest show that the Insulin/IGF axis play an important role in aging. Nematodes, fruit-flies, and other organisms have an increased life span when the gene equivalent to the mammalian insulin is knocked out. It is somewhat difficult to relate this finding to mammals, however, because there are many genes (at least 37 in the nematode Caenorhabditis elegans) in smaller organisms that are "insulin-like" or "IGF-1-like", whereas in mammals insulin-like proteins comprise only seven members (insulin, IGFs, relaxins, EPIL, and relaxin-like factor). The human insulin-like genes have apparently distinct roles with some but less crosstalk presumably because there are multiple insulin-receptor-like proteins in humans. Simpler organisms typically have fewer receptors; for example, only one insulin-like receptor exists in the nematode C. elegans. Additionally, C. elegans do not have specialized organs such as the (Islets of Langerhans), which sense insulin in response to glucose homeostasis. Moreover, IGF1 affects lifespan in nematodes by causing dauer formation, a developmental stage of C. elegans larva. There is no mammalian correlate. Therefore, it is an open question as to whether either IGF-1 or insulin in the mammal may perturb aging, although there is the suggestion that dietary restriction phenomena may be related. Other studies are beginning to uncover the important role the IGFs play in diseases such as cancer and diabetes, showing for instance that IGF-1 stimulates growth of both prostate and breast cancer cells.
=== Counterculture === By the mid-1960s, the youth countercultures in California, particularly in San Francisco, had widely adopted the use of hallucinogenic drugs, including LSD. The first major underground LSD factory was established by Owsley Stanley. Around this time, the Merry Pranksters, associated with novelist Ken Kesey, organized the Acid Tests, events in San Francisco involving LSD consumption, accompanied by light shows and improvised music. Their activities, including cross-country trips in a psychedelically-decorated bus and interactions with major figures of the beat movement, were later documented in Tom Wolfe's The Electric Kool-Aid Acid Test (1968). In San Francisco's Haight-Ashbury neighborhood, the Psychedelic Shop was opened in January 1966 by brothers Ron and Jay Thelin to promote the safe use of LSD. This shop played a significant role in popularizing LSD in the area and establishing Haight-Ashbury as the epicenter of the hippie counterculture. The Thelins also organized the Love Pageant Rally in Golden Gate Park in October 1966, protesting against California's ban on LSD. A similar movement developed in London, led by British academic Michael Hollingshead, who first tried LSD in America in 1961. After experiencing LSD and interacting with notable figures such as Aldous Huxley, Timothy Leary, and Richard Alpert, Hollingshead played a key role in the famous LSD research at Millbrook before moving to New York City for his experiments. In 1965, he returned to the UK and founded the World Psychedelic Center in Chelsea, London.
Sources: en.wikipedia.org
It is a synthetic seven-amino-acid peptide modeled on alpha-melanocyte-stimulating hormone. It carries two non-natural substitutions and a cyclic bridge that increase its stability relative to the natural hormone. It circulates as a research chemical and is not an approved medicine.
Melanotan-1, also called afamelanotide, is a shorter linear analog with a different amino acid sequence and no lactam ring. It has been evaluated in formal clinical programs, while melanotan-2 has not. The two are distinct molecules and are not interchangeable.
No. Bremelanotide is a related but distinct cyclic peptide that reached approved status for one specific clinical indication. Melanotan-2 is a separate molecule with its own sequence and properties. Shared ancestry in the melanocortin family does not make them the same substance.
Regulatory treatment varies by country. In the United States, the European Union and Australia it is an unapproved drug and its sale is restricted, while some other jurisdictions list it as prescription-only or controlled. The applicable rules depend on the country of import.