This is a working overview of electron paramagnetic resonance, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2025-09-08 and is reviewed periodically as new material appears.
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.
Stability of the complex in solution depends on pH, temperature, and the presence of competing ligands. It is generally described as more resistant to breakdown than the metal-free chain, since coordination reduces susceptibility to enzymatic attack. Oxidation and hydrolysis can nevertheless proceed over time in aqueous media. Storage guidance in laboratory settings commonly involves refrigeration, protection from light, and avoidance of strongly alkaline conditions. Published data on long-term behaviour vary considerably and depend on the specific matrix.
The copper-binding activity of this sequence was described in the 1970s during studies of liver tissue and plasma factors. Early work identified the peptide as a component that influenced copper uptake by cells and that appeared in wound fluid. Later investigations examined its presence across species, reporting the same chain in human and animal samples. A decline in measured concentration with age became a recurring observation, although the underlying causes remain incompletely characterised.
Published studies describe the complex in several research contexts, including collagen synthesis, antioxidant behaviour, and wound repair models. Much of this work is conducted in cultured cells or in small animal systems, and the findings are frequently cited in reviews of copper peptides. Direct clinical evidence in humans is comparatively limited, and reported outcomes vary with formulation and study design. Whether free chain or metal-bound form was used is not always stated, a point that complicates comparison between reports.
GHK-Cu is a coordination complex formed between the peptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The unbound chain, abbreviated GHK, consists of three amino acids and occurs naturally in human plasma, saliva, and urine. Binding of the metal is mediated mainly by the imidazole nitrogen of the histidine residue together with backbone amides, producing a stable chelate. Ingredient nomenclature often lists the same substance as copper tripeptide-1. Its charge and solubility behaviour differ from those of the metal-free chain.
| Property | Value | Notes |
|---|---|---|
| Appearance | Blue crystalline solid | Colour arises from copper(II) d-d transitions |
| Water solubility | Readily soluble | Extent varies with pH and counterion |
| Typical storage | Minus 20 degrees Celsius, desiccated | Protect from light and moisture |
| Purity method | Reverse-phase HPLC, UV detection | Wavelength typically 214 or 220 nanometres |
| Identity method | Mass spectrometry | Confirms peptide mass and copper content |
Aqueous solutions of GHK-Cu are less stable than the dry powder. The peptide backbone is vulnerable to hydrolysis at extreme pH, and copper can be stripped from the complex by strong chelating agents such as EDTA or citrate. Oxidising agents and high concentrations of ascorbic acid can reduce copper(II) and change the complex, which is one reason formulators often keep such ingredients in separate phases. How quickly these changes occur under real storage conditions depends on pH, buffer, temperature and packaging, and quantitative data on the subject are limited.
Dry material is normally held cold, commonly at -20 °C for long-term storage and 2 to 8 °C for working quantities, protected from light and moisture. Vials should be allowed to reach room temperature before opening so that condensation does not form on the powder. In liquid formulations the complex is generally kept near neutral to slightly acidic pH, because strongly alkaline conditions favour precipitation of copper hydroxide. Antioxidants or chelate-stabilising excipients are often added, though the specific approaches are proprietary and rarely published in detail.
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.
Copper peptide solutions tend to resist degradation better than many free peptides, because the bound metal protects the N-terminus and reduces susceptibility to some peptidases. Backbone hydrolysis, oxidation of the histidine imidazole ring, and photochemical reactions remain the principal degradation routes. Aqueous solutions are generally most stable near neutral to mildly acidic pH, while strongly alkaline conditions accelerate hydrolysis. Light exposure is usually avoided, since both the peptide and the copper center can take part in photochemical processes. Stability data published by suppliers often describe short-term behavior rather than multi-year shelf life.
Identity and purity are commonly assessed by reversed-phase high-performance liquid chromatography, frequently paired with mass spectrometry to confirm the molecular ion. Copper content is measured separately, typically by inductively coupled plasma mass spectrometry or atomic absorption spectroscopy, because the chromatographic signal reports the peptide rather than the metal. Ultraviolet-visible spectroscopy provides a fast check on complex formation, since copper(II) peptide complexes absorb in the visible region. Elemental analysis and amino acid analysis are used less often but remain useful for reference standards. A gap between reported peptide purity and measured copper content is a recurring source of confusion.
Material described as GHK-Cu appears in several distinct markets, including cosmetic ingredients, laboratory reagents, and consumer products, and the quality expectations attached to each differ. A certificate of analysis generally reports peptide purity by chromatography, copper content, appearance, and residual solvents or counterions. Counterion identity matters, because the complex is usually supplied as an acetate or a similar salt, and the counterion contributes to the measured mass. Independent verification of sequence and metal stoichiometry is advisable when a material is used for quantitative work. Batch-to-batch variation is common and should be documented rather than assumed negligible.
Systemic scleroderma, or systemic sclerosis, is an autoimmune rheumatic disease characterised by excessive production and accumulation of collagen, called fibrosis, in the skin and internal organs and by injuries to small arteries. There are two major subgroups of systemic sclerosis based on the extent of skin involvement: limited and diffuse. The limited form affects areas below, but not above, the elbows and knees with or without involvement of the face. The diffuse form also affects the skin above the elbows and knees and can also spread to the torso. Visceral organs, including the kidneys, heart, lungs, and gastrointestinal tract can also be affected by the fibrotic process. Prognosis is determined by the form of the disease and the extent of visceral involvement. Patients with limited systemic sclerosis have a better prognosis than those with the diffuse form. Death is most often caused by lung, heart, and kidney involvement. The risk of cancer is increased slightly. Survival rates have greatly increased with effective treatment for kidney failure. Therapies include immunosuppressive drugs, and in some cases, glucocorticoids.
== External links == GeneReviews/NCBI/NIH/UW entry on Stickler Syndrome COL2A1 at Genetics Home Reference small deletion defects nucleotide substitutions Definition of COL2A1 Archived 2012-08-09 at the Wayback Machine GeneCard
== Society and culture == Methocarbamol was approved as a muscle relaxant for acute, painful musculoskeletal conditions in the United States in 1957. Muscle relaxants are widely used to treat low back pain, one of the most frequent health problems in industrialized countries. Currently, there are more than 3 million prescriptions filled yearly. Methocarbamol and orphenadrine are each used in more than 250,000 U.S. emergency department visits for lower back pain each year. In the United States, low back pain is the fifth most common reason for all physician visits and the second most common symptomatic reason. In 80% of primary care visits for low back pain, at least one medication was prescribed at the initial office visit and more than one third were prescribed two or more medications. The most commonly prescribed drugs for low back pain included skeletal muscle relaxants. Cyclobenzaprine and methocarbamol are on the U.S. Medicare formulary, which may account for the higher use of these products.
In September 2026, a UN-commissioned fact-finding mission panel found "reasonable grounds" to believe that the United States had committed war crimes during military strikes in Iran during the 2026 Iran war. The report highlighted two 28 February strikes that killed at least 178 civilians. U.S. president Donald Trump's threats to completely destroy Iranian power plants and other essential infrastructure during the 2026 Iran war have been widely condemned by human rights organizations, legal experts, and lawmakers as potential war crimes. The report published by the Independent International Fact-Finding Mission on Iran detailed two specific U.S. military operations on the first day of the 2026 Iran war that it determined constituted indiscriminate attacks on civilian infrastructure, the Minab School Bombing, where a U.S. Tomahawk missile strike targeted the Shajareh Tayyebeh Primary School in the southern city of Minab. The attack killed more than 150 people, including approximately 120 children. The UN mission concluded that the school was the intended point of impact rather than collateral damage, as well as the Lamerd Sports Complex Strike, where a separate U.S. airstrike utilized precision strike missiles to disperse tungsten pellets over a clearly identifiable sports complex and residential area in Lamerd. The attack resulted in the deaths of 22 civilian men and women. The Trump administration firmly rejected the allegations. White House spokeswoman Anna Kelly dismissed the findings as "unserious nonsense," stating that the U.S.
Sources: en.wikipedia.org
The Pd2(dba)3/MePhos catalytic system has been applied to late stage Suzuki cross couplings. This reaction has been conducted on a kilogram (2.2 lbs)scale, and no specific palladium-removal treatment was required as the excess imidazole present in the final amide coupling step coordinated to the Pd and generated a removable byproduct.
The price of real estate in Moscow continues to increase. The expected price averages $4,000 per square meter (11 sq ft) near the perimeter of the city or $6,500–8,000 per square meter in a prestigious district. The price sometimes exceeds $40,000 per square meter for a flat. Renting costs about $1,200 per month for a one-bedroom apartment and about $1,000 per month for a studio in the city center. A typical one-bedroom apartment in Moscow is about 30 square meters (320 square feet) in area; a typical two-bedroom apartment is 45 square meters (480 square feet); and a typical three-bedroom apartment is 70 square meters (750 square feet). Many residents cannot move out of their apartments, especially if a family lives in a two-room apartment originally granted by the state during the Soviet era. Some city residents have attempted to cope with the cost of living by renting out their apartments while staying in dachas (country houses) outside the city. In 2006, Mercer Human Resources Consulting named Moscow the world's most expensive city for expatriate employees, ahead of recurring winner Tokyo, because of the stable Russian ruble as well as increasing housing prices. Moscow also ranked first in the 2007 edition and 2008 edition of the survey. However, in 2009, Tokyo overtook Moscow, which came in third after Osaka. In 2014, according to Forbes magazine, Moscow was ranked the world's ninth most expensive city. This magazine ranked Moscow the second most expensive city the previous year.
== Structure == Mammalian GPX1, GPX2, GPX3, and GPX4 (this protein) have been shown to be selenium-containing enzymes, whereas GPX6 is a selenoprotein in humans with cysteine-containing homologues in rodents. In selenoproteins, the amino acid selenocysteine is inserted in the nascent polypeptide chain during the process of translational recoding of the UGA stop codon. GPX4 shares the amino acid motif of selenocysteine, glutamine, and tryptophan (catalytic triad) with other glutathione peroxidases.
Sources: en.wikipedia.org
=== Other uses in science === Electron transport chain, a sequence of chemical reactions yielding the transport of an electron through a membrane Food chain, a hierarchical or recursive list of predators and prey
Sublimation is a technique used by chemists to purify compounds. A solid is typically placed in a sublimation apparatus and heated under vacuum. Under this reduced pressure, the solid volatilizes and condenses as a purified compound on a cooled surface (cold finger), leaving a non-volatile residue of impurities behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface. For even higher purification efficiencies, a temperature gradient is applied, which also allows for the separation of different fractions. Typical setups use an evacuated glass tube that is heated gradually in a controlled manner. The material flow is from the hot end, where the initial material is placed, to the cold end that is connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation, with very volatile compounds being pumped out of the system completely (or caught by a separate cold trap), moderately volatile compounds re-condensing along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end. Vacuum sublimation of this type is also the method of choice for purification of organic compounds for use in the organic electronics industry, where very high purities (often > 99.99%) are needed to satisfy the standards for consumer electronics and other applications.
=== Marine alkaloids === Marine alkaloids are extracted from marine organisms living in oceans, including animals, plants, certain marine bacteria and marine fungi. They are characterized in their chemical structure by halogens, which are atypical of higher organisms and terrestrial plants. An example is tetrodotoxin, a non-protein neurotoxin about 10,000 times more toxic than cyanide. It is mainly produced by the pufferfish and blue-ringed octopus, but occurs in 140 animal species worldwide. Although numerous theories address the origin of tetrodotoxin, the involvement of endogenous symbiotic bacteria producing toxins is prevalent.
However, recent medical literature has proposed reclassifying insulin specifically as a reponic hormone (from the Latin repono, meaning "to store") to better distinguish its metabolic role from that of classic anabolic hormones like testosterone or growth hormone. While classic anabolic hormones drive energy-intensive processes to build metabolically active lean tissue, the primary physiological function of a reponic hormone is to conserve and store systemic energy. Insulin achieves this by driving the cellular uptake of glucose and lipids for storage (lipogenesis and glycogenesis) while simultaneously inhibiting the breakdown of stored energy (lipolysis and glycogenolysis). Researchers argue this distinction provides a clearer framework for understanding why hyperinsulinemia is uniquely characterized by central adiposity and metabolic syndrome rather than lean tissue growth.
Sources: en.wikipedia.org
Reverse-phase high-performance liquid chromatography with ultraviolet detection is the most common approach. Purity is expressed as a share of total peak area at a specified wavelength. Mass spectrometry is then used to confirm molecular identity.
Solid material is often held at refrigerator or freezer temperatures, typically between minus 20 and 4 degrees Celsius. Desiccation limits moisture uptake. Solution stability is generally shorter and varies with pH and buffer composition.
Electron paramagnetic resonance is suited to copper(II) because of its unpaired electron. UV-visible spectroscopy reveals ligand-to-metal charge transfer bands. Both methods report on coordination rather than on peptide purity.
GHK denotes the unbound chain of three amino acids. GHK-Cu describes the form in which a copper(II) ion is held by that chain. The two are not interchangeable in solution, since charge, molecular weight, and reactivity differ.