A practical reference on ICP-MS: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2025-11-09. Anything still debated is marked as such rather than presented as settled.
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.
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.
The compound was first isolated from human plasma in the 1970s by Loren Pickart, who later described copper-binding activity in liver and other tissues. Early reports focused on its presence in blood and its ability to carry copper between proteins. Commercial and cosmetic use of the term 'copper peptide' has since broadened, and labels rarely distinguish GHK-Cu from other copper-binding fragments. This naming overlap makes literature searching harder, because cosmetic ingredient lists, supplier catalogues and laboratory papers use different vocabularies for the same molecule.
GHK-Cu is the copper-binding complex formed by the tripeptide glycyl-L-histidyl-L-lysine and a copper(II) ion. The free peptide is usually written as GHK, and the complex is written as GHK-Cu or Cu-GHK. The sequence was identified in human plasma and later detected in saliva and urine. Its name comes from the single-letter codes of glycine, histidine and lysine. The complex is widely described as a naturally occurring carrier of copper in blood rather than as a free peptide with its own hormonal role.
Copper binds to the peptide through the histidine imidazole nitrogen and the terminal amino group, forming a stable square-planar complex. Binding constants reported for copper(II) with GHK are high, so the peptide competes effectively for copper in solution. The complex absorbs visible light, which gives solutions a blue to violet colour. Whether the metal-free peptide has a distinct biological function of its own is still an open question; some work treats it mainly as a copper delivery vehicle, while other work reports peptide-specific effects.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature | -20 °C for solid; 2-8 °C for short-term solution use | Avoid repeated freeze-thaw cycles |
| Preferred solvent | Water or aqueous buffer near neutral pH | Nonpolar solvents give poor dissolution |
| Typical analytical method | Reversed-phase HPLC with mass spectrometry | Copper quantified separately by ICP-MS |
| Principal degradation routes | Backbone hydrolysis, histidine oxidation, photolysis | Alkaline pH accelerates hydrolysis |
| Counterion form | Acetate salt is common | Counterion contributes to measured mass |
The tripeptide was first isolated from a human plasma filtrate in 1973 during studies of tissue repair factors. Later work detected the free peptide and its copper complex in saliva, urine, and wound fluid, suggesting a natural role in tissue remodeling. Plasma concentrations reported in early literature decline with age, a pattern often cited in discussions of skin aging. Whether these endogenous levels are directly functional or largely incidental remains an open question. The peptide sequence is conserved across mammalian species.
Material described in research and cosmetic supply chains is typically a synthetic peptide supplied as a lyophilized powder. Purity is commonly reported through chromatographic separation, often at 95 percent or higher, while copper content is confirmed by separate elemental analysis. Batch variation in color and solubility can reflect residual counter-ions, moisture, or partial oxidation of the peptide. Because the complex is not a single regulatory entity, specifications differ between suppliers and are not standardized internationally.
The molecular weight and charge of GHK-Cu depend on the pH and the number of coordinated ligands. At neutral pH, the peptide typically binds one copper ion, but ternary complexes with other biomolecules can form. Spectroscopic methods such as electron paramagnetic resonance and circular dichroism are used to study the coordination environment. Reports on the exact geometry vary because the complex is dynamic in solution. Researchers often use synthetic GHK-Cu rather than extracted material to control stoichiometry and purity.
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.
Dry material is typically held at low temperature, often around minus twenty degrees Celsius, and protected from moisture and light. Copper complexes can release their metal ion under acidic conditions or in the presence of competing chelators. Hydrolysis of the peptide backbone is a slower but real pathway, and the histidine residue is susceptible to oxidation over long periods. Stability statements therefore depend on formulation, pH, and container, and they should be read as conditional rather than absolute.
Identity and purity are usually assessed with reversed-phase high-performance liquid chromatography, often paired with mass spectrometry. Copper content is measured separately by techniques such as inductively coupled plasma mass spectrometry or atomic absorption. Amino acid analysis confirms the peptide sequence after hydrolysis. Because the metal and the peptide can be quantified independently, a complete certificate of analysis normally reports both values rather than a single purity figure. This separation of measurements is important when comparing suppliers.
The triangular teeth can reach 7.5 cm (3.0 in). In juveniles, they are elongated and pointy but become broader and more serrated as they develop into adults. This reflects a shift from a diet mainly of fish to the incorporation of marine mammals. The front teeth are adapted for penetrating prey while the rear teeth, flattened at the sides and bent backwards, are designed for tearing. A total of around 300 teeth are arranged in rows like a conveyor belt, with teeth at the back moving to replace those at the front. The jaws are separate from the skull and are connected to the body entirely by muscles and tendons, allowing them to extend forward. A 2008 study using a computer scan of a 2.5 m (8.2 ft) long and 240 kg (530 lb) juvenile white shark determined that the specimen could exert a bite force of 1,602 newtons (360 lbf) in the front and 3,131 newtons (704 lbf) in the back. From this, the researchers calculated that a specimen 6.4 m (21 ft) long and weighing 3,324 kg (7,328 lb) could exert a bite force of 9,320 newtons (2,100 lbf) in the front and 18,216 newtons (4,095 lbf) in the back. The jaws are strengthened by mineralized cartilage; this is lacking in young white sharks, which have to eat softer food.
=== Engine === Chainsaw engines are traditionally either a two-stroke single-cylinder gasoline (petrol) internal combustion engine (usually with a cylinder volume of 30 to 120 cc) or an electric motor driven by a battery or electric power cord. In a petrol chainsaw, fuel is generally supplied to the engine by a carburetor at the intake. Two-stroke engines have been preferred for chainsaws due to their higher power-to-weight ratio and simplicity. Hydraulic power may be used for chainsaws for underwater use. To allow use in any orientation, modern gasoline chainsaws use a diaphragm carburetor, which draws fuel from the tank using the alternating pressure differential within the crankcase. Early engines used carburetors with gravity fed float chambers, which caused the engine to stall when tilted. The carburetor may need to be adjusted to maintain an appropriate idle speed and air-fuel ratio, such as when moving to a higher/lower altitude or as the air filter clogs. Carburetors are adjusted either by the operator or, in some saws, automatically by an electronic control unit. To prevent vibration induced injury and reduce user fatigue, saws generally have an anti-vibration system to physically decouple the handles from the engine and bar. This is achieved by constructing the saw in two pieces, connected by springs or rubber in the same way an automobile suspension isolates the chassis from the wheels and road. In cold weather, carburetor icing can occur, so many saws have a vent between the cylinders and carburetor which may be opened to allow hot air to pass.
==== July 2025 rescissions ("claw backs"), but not for PEPFAR ==== In June 2025, the White House requested that Congress pass a package of rescissions, or "claw backs", of approximately $8 billion in foreign aid and $1 billion for the Corporation for Public Broadcasting including NPR and PBS. The House of Representatives passed the cuts as requested. The Senate excluded the PEPFAR cuts, which is the program started in 2003 during the presidency of George W Bush to help provide HIV medicines to lower-income countries. The Senate passed two preliminary votes in close 51-50 fashion with Vice President JD Vance casting the tie-breaking votes. A rescission is one of the exceptions to the Senate's 60-vote filibuster rule. President Trump focused on the public broadcasting aspect, criticizing CNN and also "MSDNC" which is a mix of MSNBC and DNC (Democratic National Committee). In a Truth Social post, he wrote, "It is very important that all Republicans adhere to my Recissions Bill and, in particular, DEFUND THE CORPORATION FOR PUBLIC BROADCASTING (PBS and NPR), which is worse than CNN & MSDNC put together." In a late night session at 2:00 AM on July 17, the Senate voted 51–48 in favor of the cuts. Later that same day, the House of Representatives voted 216 - 213 for the Senate version, meaning PEPFAR was protected in the amount of $400 million. Regarding the cuts to public broadcasting, service to rural areas became one of the political issues.
Inflammation (from Latin: inflammatio) is part of the biological defence response of body tissues. Inflammatory immunovascular responses can be triggered by a broad range of stimuli, including physical trauma, "dead, damaged, malfunctioning or stressed tissues", pathogens, irritants, toxins, overuse, autoimmunity, allergens, and foreign bodies (e.g. silica and asbestos). The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin calor, dolor, rubor, tumor, and functio laesa). Inflammation is a generic response, and therefore is considered a mechanism of innate immunity, not adaptive immunity. It involves immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out damaged cells and tissues, and initiate tissue repair. Too little inflammation can lead to progressive tissue destruction by the harmful stimulus (e.g. bacteria) and compromise the survival of the organism, but too much inflammation, in the form of chronic inflammation, is associated with various diseases, such as hay fever, periodontal disease, atherosclerosis, and osteoarthritis. Inflammation can be classified as acute or chronic. Acute inflammation is the initial response of the body to harmful stimuli, and is achieved by the increased movement of plasma and leukocytes (in particular granulocytes) from the blood into the injured tissues.
The germ contains oil that is exposed by grinding, thus whole-grain cornmeal and grits turn rancid quickly at room temperature and should be refrigerated. Whole-grain cornmeal and grits require extended cooking times as seen in the following cooking directions for whole-grain grits: "Place the grits in a pan and cover them with water. Allow the grits to settle a full minute, tilt the pan, and skim off and discard the chaff and hulls with a fine tea strainer. Cook the grits for 50 minutes if the grits were soaked overnight or else 90 minutes if not." The milling of corn removes the aleurone and germ layers, removing much of the (already low) amounts of bioavailable niacin and tryptophan found within. The milling and degerming of corn in the preparation of cornmeal became feasible with the development of the Beall degerminator, which was originally patented in 1901 and was used to separate the grit from the germ in corn processing. Casimir Funk, who helped elucidate the role of thiamin in the etiology of beriberi, was an early investigator of the problem of pellagra. Funk suggested that a change in the method of milling corn was responsible for the outbreak of pellagra, but no attention was paid to his article on this subject.
Sources: en.wikipedia.org
== Further reading == Greenwood, David. Antimicrobial Drugs: Chronicle of a twentieth century medical triumph (Oxford University Press, 2008) summary Kingston W (July 2004). "Streptomycin, Schatz v. Waksman, and the balance of credit for discovery". Journal of the History of Medicine and Allied Sciences. 59 (3): 441–462. doi:10.1093/jhmas/jrh091. PMID 15270337. S2CID 27465970. Mistiaen V (November 2, 2002). "Time, and the great healer". The Guardian.. The history behind the discovery of streptomycin. Pringle P (June 12, 2012). "Notebooks Shed Light on an Antibiotic's Contested Discovery". The New York Times. Office of Prevention, Pesticides And Toxic Substances (September 1992). "Streptomycin and Streptomycin Sulfate Pesticide Reregistration" (PDF). R.E.D. Facts. United States Environmental Protection Agency. EPA-738-F-92-009.
=== Mutational convergence === The most well-studied example is the Spike protein of SARS-CoV-2, which independently evolved at the same positions regardless of the underlying sublineage. The most eminent examples from the pre-Omicron era were E484K and N501Y, while in the Omicron era examples include R493Q, R346X, N444X, L452X, N460X, F486X, and F490X.
I do not know that it contains any branch of science which Congress would wish to exclude from their collection; there is, in fact, no subject to which a Member of Congress may not have occasion to refer. Jefferson's library was a working collection for a scholar, not for display. It doubled the size of the original library, transforming it from a specialist's library to a more general one. He organized his books based on Francis Bacon's organization of knowledge, grouping them into Memory, Reason, and Imagination with 44 subdivisions. The library used this scheme until the late 19th century when librarian Herbert Putnam introduced the Library of Congress Classification, now applying to over 138 million items. A February 24, 1824, report from the Committee of Ways and Means recommended a $5,000 appropriation for the Library of Congress, noting the need to improve its collections in "Law, Politics, Commerce, History, and Geography," which were crucial for Congress.
The normal resting heart rate is called the sinus rhythm, created and sustained by the sinoatrial node, a group of pacemaking cells found in the wall of the right atrium. Cells in the sinoatrial node do this by creating an action potential. The cardiac action potential is created by the movement of specific electrolytes into and out of the pacemaker cells. The action potential then spreads to nearby cells. When the sinoatrial cells are resting, they have a negative charge on their membranes. A rapid influx of sodium ions causes the membrane's charge to become positive; this is called depolarisation and occurs spontaneously. Once the cell has a sufficiently high charge, the sodium channels close and calcium ions then begin to enter the cell, shortly after which potassium begins to leave it. All the ions travel through ion channels in the membrane of the sinoatrial cells. The potassium and calcium start to move out of and into the cell only once it has a sufficiently high charge, and so are called voltage-gated. Shortly after this, the calcium channels close and potassium channels open, allowing potassium to leave the cell. This causes the cell to have a negative resting charge and is called repolarisation. When the membrane potential reaches approximately −60 mV, the potassium channels close and the process may begin again. The ions move from areas where they are concentrated to where they are not. For this reason sodium moves into the cell from outside, and potassium moves from within the cell to outside the cell. Calcium also plays a critical role.
Sources: en.wikipedia.org
Where S is the salinity of the fluid, βT is the thermal expansion coefficient at constant pressure and βS is the coefficient of saline expansion at constant pressure and temperature. Non dimensionalizing using the scale:
=== Toxicology === A method for detecting arsenious oxide, simple arsenic, in corpses was devised in 1773 by the Swedish chemist, Carl Wilhelm Scheele. His work was expanded upon, in 1806, by German chemist Valentin Ross, who learned to detect the poison in the walls of a victim's stomach. Toxicology, a subfield of forensic chemistry, focuses on detecting and identifying drugs, poisons, and other toxic substances in biological samples. Forensic toxicologists work on cases involving drug overdoses, poisoning, and substance abuse. Their work is critical in determining whether harmful substances play a role in a person's death or impairment. read more
Valve enlisted Gearbox Software to develop three expansions for Half-Life: Opposing Force (1999), Blue Shift (2001) and Decay (2001). In 1998, Valve acquired TF Software, a group that had made the popular Team Fortress mod for Quake, and remade it for GoldSrc as Team Fortress Classic in 1999. Valve released the software development kit (SDK) for the GoldSrc engine, facilitating numerous user-created mods. They acquired the developers of one popular mod, Counter-Strike, to create a standalone Counter-Strike game. Happy with Valve's success, Harrington sold his stake in Valve to Newell in 2000. Valve's publishing agreement meant Sierra owned the Half-Life intellectual property and held exclusive publishing rights to future Valve games. In 2001, Valve renegotiated by threatening to cease game development and develop other software, using an offer of a partnership from Amazon to create a digital storefront as a bargaining chip. After the agreement with Sierra was amended, Valve gained the Half-Life intellectual property and online distribution rights for its games.
Due to the presence of its valeric acid ester and differences in molecular weight, estradiol valerate contains about 76% of the same amount of estradiol by weight. As a result, 2 mg oral estradiol valerate produces equivalent estradiol levels to about 1.5 mg oral estradiol.
During the six decades of its rule, the security apparatus banned all social, political and economic groups independent of the Ba'ath party or the regime; ensuring that the state had total monopoly over all forms of organizations. A state of emergency was in effect from 1963 until April 2011, giving security forces sweeping powers of arbitrary arrests and detentions of civilians; including prisoners of conscience. From 1973 to 2012, Syria was a single-party state. While the 2012 Syrian constitution nominally affirmed the formation of political parties; registration process in practice was difficult and thoroughly scrutinized by the regime. Political activities independent of the Ba'ath were discouraged in regime-controlled territories and strictly monitored by the Mukhabarat. There was no independent judiciary, as it was mandatory for all judges and prosecutors to be approved members of the Ba'ath party. The Ba'athist military forces had the power to arbitrarily arrest civilians and put them to trial. The authorities have been accused of harassing and imprisoning human rights activists and other critics of the government. Freedom of expression, association and assembly were strictly controlled, and ethnic minorities faced discrimination. Throughout the decades-long reign of Assad dynasty between 1970 and 2011; over 70,000 Syrians were subjected to forced disappearances, more than 40,000 were executed through extrajudicial killings and hundreds of thousands of civilians became displaced through deportations.
Sources: en.wikipedia.org
The solid is typically held cold and dry, and solutions are kept for shorter periods because hydrolysis proceeds in water. Repeated freeze-thaw cycles are usually avoided, since they can degrade both the peptide and the complex. Container material and headspace also affect how long a sample remains unchanged.
Copper is quantified by an elemental technique such as inductively coupled plasma mass spectrometry, not by peptide chromatography. The chromatographic result describes the peptide chain, while the elemental result describes the metal. Reporting both is what makes the stoichiometry checkable.
It normally lists the analytical methods used, the measured purity, the appearance, and any residuals or counterions detected. It is a statement about a specific batch rather than a general property of the material. Independent testing is still needed when results must be traceable to a reference standard.
The letters GHK are the one-letter codes for glycine, histidine and lysine, the three amino acids in the peptide. The suffix Cu indicates that the peptide is bound to a copper ion, normally copper(II).