A practical reference on electron paramagnetic resonance: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
This page was last updated on 2026-07-16 and is reviewed periodically as new material appears.
Stability depends on temperature, light exposure, moisture, and the presence of oxidizing or reducing agents. Solid material held dry and protected from light is generally more stable than aqueous solutions, which can undergo gradual degradation. Recommended storage in much of the literature is a freezer at around minus twenty degrees Celsius for long-term retention, with working aliquots kept cold and shielded from light. Repeated freeze-thaw cycles and alkaline pH are commonly noted as factors that accelerate loss of the intact complex, though exact degradation rates vary.
Analytical confirmation usually combines a separation method with a copper-specific measurement. Liquid chromatography or mass spectrometry establishes peptide identity and purity, while an elemental measurement quantifies the metal content. A frequent misconception is that any blue solution contains an intact copper peptide complex; color alone does not confirm structure, because free copper salts and degraded mixtures can also appear colored. Literature on efficacy is mixed, with in vitro findings often more dramatic than human evidence, and reviews note small sample sizes and short follow-up. Open questions include optimal concentration, skin penetration, and long-term effects.
Aqueous GHK-Cu solutions are less stable than the dry powder. Light, dissolved oxygen and elevated temperature all accelerate loss of the intact complex, and the main observable changes are fading of the blue colour and the appearance of peptide fragments. Acidic conditions protonate the histidine imidazole and weaken copper binding, while strongly alkaline conditions promote hydrolysis of the peptide backbone. Because several degradation routes operate at once, a single shelf-life figure does not describe all storage conditions.
Solid material is typically kept as a lyophilised powder in a sealed, light-protected container at minus 20 degrees Celsius, with desiccant where humidity is high. Working solutions are often prepared fresh, aliquoted and frozen to avoid repeated freeze-thaw cycles. Glassware and buffers are checked for trace metal contamination, since other transition metals can displace copper. Records of lot number, reconstitution date and storage temperature help trace unexpected colour changes. Blue colour itself is not a reliable purity test, because partly degraded solutions can remain visibly coloured.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C | Dry, protected from light |
| Appearance in solution | Blue | Tone varies with pH and concentration |
| Primary analytical method | LC-MS with ICP-MS | Identity plus copper content |
| pH sensitivity | Higher near neutral and above | Alkaline conditions can degrade it |
| Common supplied form | Freeze-dried solid | Dissolved before use |
The peptide portion consists of three amino acids: glycine, histidine and lysine. Copper(II) coordinates through the imidazole nitrogen of histidine, the alpha-amino group of glycine and a deprotonated amide nitrogen of the backbone, producing a roughly square-planar geometry. This arrangement gives the complex its characteristic blue-to-violet colour and helps it resist dissociation in water. Reported stability constants are high, although values differ between studies because of differences in ionic strength and measurement method.
The International Nomenclature of Cosmetic Ingredients lists the substance as copper tripeptide-1, the name that appears on most topical product labels. Related designations include copper peptide and GHK-Cu, and the hyphenated form is common in research literature. In cosmetics the material is regulated as an ingredient rather than as a drug, so products may reach the market without evidence of the effects claimed for them. Whether those effects are clinically meaningful is an open question, since most supportive data come from laboratory work and small trials.
GHK-Cu is the copper complex of the tripeptide glycyl-L-histidyl-L-lysine, a short sequence found naturally in human plasma, saliva and urine. Loren Pickart reported the isolation of the free peptide in 1973 while studying factors that influenced the growth of aged liver cells in culture. The peptide was later shown to bind copper(II) with high affinity, and the metal-bound form became the focus of most subsequent research. Its concentration in circulation declines markedly with age, a pattern that is well documented, though the physiological consequences of that decline remain debated.
Commercial products list GHK-Cu as copper tripeptide-1, a cosmetic ingredient. Formulators value its blue color and water solubility, which allow incorporation into serums, creams, and masks. Regulatory treatment varies: in the United States it appears in cosmetics, while some jurisdictions classify certain claims as drug-like. The compound is not an approved drug for any indication. Studies continue to examine its effects on skin, hair, and wound repair, but dosage, delivery, and long-term safety questions remain open.
GHK-Cu is a coordination complex formed between the tripeptide glycyl-L-histidyl-L-lysine and copper(II). The peptide sequence consists of glycine, histidine, and lysine, and its imidazole and amino groups provide binding sites for the metal ion. In the complex, copper is held through nitrogen donors from the histidine side chain, the N-terminal amine, and deprotonated amide nitrogens. The resulting compound is intensely blue and water-soluble. It occurs naturally in human plasma, saliva, and urine at low concentrations.
The peptide was first isolated from human albumin in 1973 by Loren Pickart, who later described its copper-binding behavior. Early work linked the complex to wound healing and tissue remodeling. Plasma levels of GHK decline with age, a pattern that stimulated interest in topical and supplemental applications. Researchers have reported that the tripeptide influences collagen synthesis, antioxidant defense, and inflammatory signaling in cell and animal models. Human clinical evidence remains limited and often relies on small studies.
Handling practices for the solid material emphasise low temperature and dryness. The lyophilised or powdered form is typically kept at refrigerator or freezer temperatures together with a desiccant. Working solutions are often prepared fresh, because repeated freeze-thaw cycles and extended storage may alter the complex. Glass or inert plastic containers are preferred over materials that could leach metal ions into the preparation. Such practices follow general peptide conventions rather than substance-specific regulations.
Analytical verification commonly relies on high-performance liquid chromatography for purity assessment and mass spectrometry for identity confirmation. Spectroscopic methods such as UV-visible absorption and electron paramagnetic resonance can probe the metal centre itself, since the d9 configuration of copper(II) produces characteristic signals. Elemental analysis or plasma-based techniques quantify copper content. Because each method reports a different aspect of the same sample, purity figures are most meaningful when the technique and its detection wavelength are stated alongside the value.
In December 2016, Chipotle announced that co-CEO Monty Moran had stepped down from his role effective immediately with Ells becoming the sole CEO. Eleven months later, Ells announced in November 2017 that he would be stepping down as CEO. In December 2017, Chipotle announced it signed a 15-year lease and in late 2018 will move around 450 corporate employees—currently housed in multiple buildings around downtown Denver—into the new 1144 Fifteenth Tower and occupy around 126,000 square feet, or 5 floors, of the 40-story tower. In February 2018, Chipotle announced that Taco Bell CEO Brian Niccol would replace Ells as CEO starting on March 5 while Ells would retain his chairman position. Many industry analysts praised Niccol's appointment saying that Chipotle "needed new blood". Chipotle stock went up $30.27, or 12.04%, as a result of the announcement. However, other analysts criticized the announcement by saying that "the move goes against everything the burrito chain stands for". In May 2018, Chipotle announced that it would relocate its headquarters from Denver to Newport Beach, California. Corporate functions handled in their Denver and New York offices would move to Newport Beach or to an existing office in Columbus, Ohio. This move would impact 400 workers, some being offered relocation and retention packages. In May 2018, Chipotle announced the "Chipotlane" and began testing it in the U.S.
In the Free State of Brunswick, the eastern part of the district of Blankenburg and the exclave of Calvörde, which belonged to the district of Helmstedt fell into the Soviet Zone of Occupation and were later integrated into the state of Saxony-Anhalt. In the State of Hanover, Amt Neuhaus and the villages of Neu Bleckede and Neu Wendischthun were allotted to the Soviet Zone and thus the subsequent East Germany. They were not returned to Lower Saxony until 1993. The city of Wesermünde that then lay in the Regierungsbezirk Stade was renamed in 1947 to Bremerhaven and incorporated into the new city-state of Bremen, which became one of the federated German states. The demands of Dutch politicians that the Netherlands should be given the German regions east of the Dutch-German border as war reparations, were roundly rejected at the London Conference of 26 March 1949. In fact only about 1.3 km2 (0.50 sq mi) of west Lower Saxony was transferred to the Netherlands, in 1949. → see main article Dutch annexation of German territory after World War II
Life expectancy of people with acromegaly is dependent on how early the disease is detected. Life expectancy after the successful treatment of early disease is equal to that of the general population. Acromegaly can often go on for years before diagnosis, resulting in poorer outcome, and it is suggested that the better the growth hormone is controlled, the better the outcome. Upon successful surgical treatment, headaches and visual symptoms tend to resolve. One exception is sleep apnea, which is present in around 70% of cases but does not tend to resolve with successful treatment of growth hormone level. While hypertension is a complication of 40% of cases, it typically responds well to regular regimens of blood pressure medication. Diabetes that occurs with acromegaly is treated with the typical medications, but successful lowering of growth hormone levels often alleviates symptoms of diabetes. Hypogonadism without gonad destruction is reversible with treatment. Acromegaly is associated with a slightly elevated risk of cancer.
Sources: en.wikipedia.org
At a White House press briefing on September 22, 2025, President Trump, joined by Kennedy and other senior officials, said the FDA would revise drug labels to discourage the use of acetaminophen (sold under the brand name Tylenol) during pregnancy, citing a possible link to autism. Medical and public health experts disputed the claim. Steven J. Fleischman, president of the American College of Obstetricians and Gynecologists, wrote, "It is highly unsettling that our federal health agencies are willing to make an announcement that will affect the health and well-being of millions of people without the backing of reliable data." A month later, on October 29, Kennedy retracted his statements from the press conference, stating that acetaminophen use in pregnancy is not linked to autism. On November 10, 2025, in response to President Trump's false claim, a 2025 British Medical Journal umbrella review was fast-tracked and confirmed no convincing evidence that paracetamol (acetaminophen) use during pregnancy increases the risk of autism spectrum disorder (ASD) or attention deficit hyperactivity disorder (ADHD) in children. The review, led by researchers at the University of Liverpool, analysed nine systematic reviews covering 40 observational studies and concluded that any apparent associations were likely due to family genetics, maternal health, or other shared factors rather than the drug itself.
The Southern Rhodesian economy grew considerably during the war despite the concurrent rise of war expenditure to pay for the expansion of the military and the air training scheme. Expenditure on the war grew from £1,793,367 in the financial year 1940–41 to £5,334,701 in 1943–44—total Southern Rhodesian expenditure on the air training scheme was £11,215,522. These sums, while tiny compared to those incurred by larger nations, were enormous when scaled against the white population of less than 70,000 that accounted for most of the colony's economic output. Annual costs for the air training scheme alone far exceeded the pre-war national budget. Southern Rhodesia was then the second largest gold producer in the world, after South Africa. The colony's gold output had expanded greatly during the 1930s, and it remained the territory's main source of income during the war, though many extracting operations were diverted towards strategic minerals, most prominently chrome and asbestos. Southern Rhodesia became one of the two main sources of chrome for the Allies (South Africa was the other) and the world's third largest producer of asbestos after Canada and the Soviet Union. By the end of the war the mines at Shabani and Mashaba were turning out 1.5 million tonnes of asbestos a year, in addition to 600,000 tonnes of chrome. Gold output reached peak levels in 1941–42 and thereafter subsided. Southern Rhodesia also exported tungsten, mica and tin, and provided coal for the copper mines of Northern Rhodesia and the Congo.
=== Mortars === Two-inch mortar – Fielded until the 1980s ML 3-inch mortar – in service through to the 1960s L16 81mm mortar – Main Cold War mortar. ML 4.2-inch mortar – saw service in 1960s L10A1 51mm mortar – Introduced in the 1980s
The female lays three to seven eggs, which both sexes help to incubate. Its breeding range extends from central and western Alaska across northern Canada to Nova Scotia, and south throughout North America, into central Mexico and the Caribbean. It is a local breeder in Central America and is widely distributed throughout South America. Most birds breeding in Canada and the northern United States migrate south in the winter. It is an occasional vagrant to Western Europe. The American kestrel is often used in falconry, especially by beginners. Though not as strong a flyer as many other, larger falcons, proper training and weight control by the falconer can allow captive American kestrels to become effective hunters of birds in the size range of sparrows and starlings, with occasional success against birds up to approximately twice their own weight.
Sources: en.wikipedia.org
Freezer temperatures are common for long-term retention. Light and moisture exposure should be limited. Working portions are best kept cold and used without repeated freeze-thaw cycles.
Sequence assays confirm the amino acids but say nothing about the metal. Copper content links the peptide to the ion that defines the complex. An elemental technique is used for this step.
No. Several copper species and degraded mixtures can also look blue. Confirmation needs both separation data and elemental data.
The colour depends on copper held in a specific coordination environment. When the complex dissociates or the peptide is cleaved, that environment changes and the visible absorption weakens.