A practical reference on electron paramagnetic resonance: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-02-06. Anything still debated is marked as such rather than presented as settled.
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.
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.
GHK-Cu is a coordination complex formed between the tripeptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The peptide was isolated from human plasma in the early 1970s by Loren Pickart, who observed that a plasma fraction from young donors stimulated growth in cultured liver cells. The copper-bound form is abbreviated GHK-Cu, while the metal-free peptide is written simply as GHK. In the research literature the complex also appears as copper tripeptide-1 and as glycyl-histidyl-lysine copper complex.
Copper(II) binds the peptide through four nitrogen donors: the terminal amino group, the imidazole nitrogen of histidine, and two deprotonated amide nitrogens of the peptide backbone. This tetradentate arrangement gives a roughly square-planar geometry, the thermodynamically favoured form near neutral pH. Because the amide nitrogens must lose a proton before they can coordinate, complex formation is strongly pH-dependent, and the fully coordinated species dominates only above mildly acidic conditions. Electronic transitions within the copper d orbital set produce the characteristic blue to violet colour in aqueous solution.
Endogenous GHK occurs in blood plasma, saliva, and urine, and reported plasma concentrations decline with age in several studies. Researchers have proposed that the peptide acts as a copper carrier that delivers the metal to cells and to sites of injury. That transport role is a hypothesis supported by binding measurements and tissue-distribution data rather than a settled mechanism, and the peptide is generally described as a minor contributor to total plasma copper transport. Values reported in wound fluid and certain tissue extracts are higher than in circulating plasma.
| 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 |
Quality specifications for research material commonly state peptide purity, copper stoichiometry, counter-ion identity, and residual water content. Frequent counter-ions include acetate and trifluoroacetate, which differ in mass and in their effect on solubility and handling. Whether batch-to-batch differences in reported responses trace to these parameters or to assay conditions remains an open question, since published comparisons rarely control for all of them at once. Independent verification therefore normally pairs a purity measurement with an elemental copper measurement on the same lot.
Practical handling notes centre on limiting exposure to water, oxygen, and repeated temperature cycling. Weighed powder is often equilibrated to room temperature before opening to avoid condensation on the solid. Working solutions are typically divided into single-use aliquots and frozen rather than stored refrigerated for long periods. Reported shelf lives vary widely between laboratories, and no single set of conditions is universally treated as a reference standard, which complicates direct comparison of published stability figures.
GHK-Cu is a coordination complex formed from the tripeptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The peptide binds copper through its histidine imidazole nitrogen, the terminal amino group, and the deprotonated amide nitrogen. This arrangement creates a square-planar or distorted geometry around the metal center, depending on pH and the presence of competing ligands. The complex occurs naturally in human plasma, saliva, and urine at low concentrations, and its sequence is conserved across many vertebrate species.
Discovery of GHK is generally attributed to work in the 1970s that isolated a plasma factor influencing liver cell behavior. Subsequent studies identified the copper-binding tripeptide and its ability to chelate copper with high affinity. Early reports linked the complex to wound healing and tissue remodeling in animal models. The free peptide and the copper-bound form have different properties, so the two are distinguished in the literature. Whether endogenous GHK-Cu serves a single primary physiological role remains an open question.
Stability of GHK-Cu in solution depends on pH, temperature, buffer composition, and oxygen exposure. The copper center can undergo reduction or dissociation, especially in the presence of strong metal chelators such as EDTA. Aqueous solutions are often prepared fresh or stored frozen to limit degradation. Lyophilized solid is more stable than liquid formulations, but it can absorb moisture and should be kept dry. Light exposure may also affect copper complexes, though the effect is often modest.
Purity assessment typically involves high-performance liquid chromatography for the peptide and atomic spectroscopy for copper content. The ratio of copper to peptide is a key quality parameter; a value near one indicates proper stoichiometry. Impurities can include free peptide, copper salts, and truncated sequences from synthesis. Because the complex is dynamic, sample preparation and mobile-phase conditions can shift the observed species. Reported purity values therefore depend on the analytical method and should be interpreted with that context.
Published work on GHK-Cu is dominated by in vitro experiments and small animal studies. Human trials tend to be short and small, with endpoints such as skin appearance rather than clinical outcomes. Review articles often summarize the same underlying laboratory findings, which can make the evidence base look broader than it is. Several basic questions remain open: the concentration of the intact complex in human tissue, the route by which it crosses the skin barrier, and whether effects seen in culture produce measurable changes in people.
Laboratory studies describe GHK-Cu as a source of copper that cells can take up, with reported effects on collagen, elastin, and glycosaminoglycan synthesis in cultured fibroblasts. The peptide also appears in wound-repair research, where it is linked to the activity of matrix metalloproteinases and their inhibitors. These observations come largely from cell and animal models. How directly the complex controls any single pathway in intact human skin remains an open question, and reported effects depend on concentration, vehicle, and exposure time.
Copper takes part in redox chemistry, and the same property that makes it useful in enzymes can generate reactive oxygen species when the ion is loosely bound. GHK chelates copper through imidazole, amino, and amide nitrogen donors, which reduces the amount of free copper in solution. Whether that chelation is protective, neutral, or harmful in a given tissue is not settled. Laboratory assays report both antioxidant and pro-oxidant behavior, depending on the conditions and the readout used.
Apixaban During the SAR development of apixaban there were three groups that needed to be tested to attain maximum potency and bioavailability. The first group to be tested was the non-active site as it needs to be stabilized before SAR testing on the p-methoxyphenyl group (S1 binding moiety). There are several of groups that increase the potency of the compound, mostly amides, amines and tetrazoles but also methylsulfonyl and trifluoromethyl groups. Of these groups, carboxamide has the greatest binding and had similar clotting activity as the compounds. In dog testing, this compound with a carboxamide group called 13F, showed a great pharmacokinetical profile, a low clearance and adequate half-life and volume of distribution. Due to the success of finding a stabilizing group, SAR research for S1 binding moiety (p-methoxyphenyl) was discontinued. In the S4 binding group, N-methylacetyl and lactam analogues proved to have a very high binding affinity for FXa, showed great clotting and selectivity versus other proteases. Orientation turned out to be important as N-methyl acetyl, compared to acetamide, had a 300 fold lower binding ability to FXa due to unfavorable planarity close to the S4 region binding site.
In the two examples (on the right) the isoelectric point is shown by the green vertical line. In glycine the pK values are separated by nearly 7 units. Thus in the gas phase, the concentration of the neutral species, glycine (GlyH), is effectively 100% of the analytical glycine concentration. Glycine may exist as a zwitterion at the isoelectric point, but the equilibrium constant for the isomerization reaction in solution
Wnt comprises a diverse family of secreted lipid-modified signaling glycoproteins that are 350–400 amino acids in length. The lipid modification of all Wnts is palmitoleoylation of a single totally conserved cysteine residue. Palmitoleoylation is necessary because it is required for Wnt to bind to its carrier protein Wntless (WLS) so it can be transported to the plasma membrane for secretion and it allows the Wnt protein to bind its receptor Frizzled Wnt proteins also undergo glycosylation, which attaches a carbohydrate in order to ensure proper secretion. In Wnt signaling, these proteins act as ligands to activate the different Wnt pathways via paracrine and autocrine routes. These proteins are highly conserved across species. They can be found in mice, humans, Xenopus, zebrafish, Drosophila and many others.
Sources: en.wikipedia.org
Procyanidin A2 is an A type proanthocyanidin. It is found in avocado, chestnut, cranberry juice concentrate, lychee fruit pericarp, peanut skins, Cinchona cortex, cinnamon cortex, Urvillea ulmaceae, and Ecdysanthera utilis.
== Drug interaction == The administration of cisplatin and vitamin B12 concomitantly does not modify the pharmacokinetics of the pemetrexed. It was recently shown that pemetrexed may play a role in cisplatin resistance in lung cancer by increasing the expression of Orai3 calcium channels as well as the expression of certain ABC transporters like MDR1 and MRP-5 responsible for cisplatin efflux and therefore a reduction of the effect of cisplatin As current therapies are based on the co-administration of pemetrexed and cisplatin, there may be interactions between pemetrexed and cisplatin, including a reduction in the therapeutic effects of cisplatin caused by pemetrexed.
=== Desorption ionization === Desorption ionization (DI) is a family of ionization techniques. The main examples are secondary-ion mass spectrometry (SIMS), fast atom bombardment (FAB), and matrix-assisted laser desorption ionization (MALDI). In DI, the sample is dissolved or dispersed in a matrix, and bombarded by a high-energy (1-10 keV) beam of ions (SIMS), neutral atoms (FAB), or photons (MALDI). The beam ionizes and expels (desorbs) some sample molecules off the matrix. The ion is then accelerated electrostatically, as in EI. The matrix should be nonvolatile and relatively inert, so that it would not react with the analyte. It should also be a good electrolyte to allow ion formation. Ionized fragments of the matrix itself forms usually have
Sources: en.wikipedia.org
Unlike traditional techniques such as embryo gene editing, which directly alter the genome of an existing embryo and are therefore person-affecting, these synthetic gametes are built de novo and give rise to individuals who would not have existed otherwise, making the intervention non-person-affecting in the sense of Parfit. Gametes produced in this way, which are distinct from artificial gametes obtained through in vitro–derived gametogenesis, raise ethical questions regarding reproductive autonomy, identity, and the design of human traits without impacting pre-existing persons.
=== Other === Deformity type Erlenmeyer flask gives a distal femur similar to an Erlenmeyer flask. It may result from Gaucher disease. Kashin–Beck disease Melnick–Needles syndrome Ovine chondrodysplasia Familial osteodysplasia, Anderson type Ulna metaphyseal dysplasia syndrome
== Cause == Causes may include trauma or repetitive activities. Less common causes include infection, arthritis, gout, thyroid disease, and diabetes. Obesity, or more specifically, adiposity or fatness, is linked to increasing incidence of tendinopathy. Quinolone antibiotics are associated with increased risk of tendinitis and tendon rupture. A 2013 review found the incidence of tendon injury among those taking fluoroquinolones to be between 0.08 and 0.2%. Fluoroquinolones most frequently affect large load-bearing tendons in the lower limb, especially the Achilles tendon.
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.
It consists of a three-amino-acid peptide, glycine-histidine-lysine, bound to one copper(II) ion. The peptide supplies four nitrogen donor atoms, and the resulting complex is stable in neutral aqueous solution. The metal-free peptide is usually called GHK.