If you have been reading about Purity testing and want a single page that covers the useful parts, this is it: definitions, context, how it is studied, and the questions that come up repeatedly.
Last reviewed on 2025-10-29. Where a claim depends on a specific study, the study is described rather than over-claimed.
Cells produce NAD+ through several biosynthetic routes. The salvage pathway recycles nicotinamide, while the Preiss-Handler pathway uses nicotinic acid, and a de novo route can start from tryptophan in some organisms. In mammals, the salvage pathway is generally considered the main source under ordinary conditions. Tissue concentrations vary widely by cell type and compartment, and measured declines with age have been reported in some studies. Whether such changes drive aging or mainly accompany it remains an open question.
Nicotinamide adenine dinucleotide, commonly abbreviated NAD+, is a coenzyme present in all living cells. The molecule consists of two nucleotides linked by phosphate groups, with adenine and a nicotinamide ring as its principal features. In its oxidized form, the nicotinamide ring can accept a hydride ion, becoming NADH. This reversible conversion places NAD+ at the center of many electron-transfer reactions. Its role as a redox carrier is well established across bacteria, plants, fungi, and animals.
Beyond redox chemistry, NAD+ serves as a substrate for enzymes that cleave the molecule and transfer its ADP-ribose moiety or remove acetyl groups. Sirtuins consume NAD+ during deacetylation, poly(ADP-ribose) polymerases use it in DNA damage responses, and CD38 enzymes hydrolyze it to signaling metabolites. These consumption pathways mean that NAD+ availability can influence gene regulation, DNA repair, and calcium signaling. Cellular NAD+ concentrations decline in some tissues with age in animal models, but whether this decline is a cause or consequence of aging in humans remains an active open question.
Nicotinamide adenine dinucleotide, commonly abbreviated NAD+, is a dinucleotide coenzyme built from an adenine nucleotide and a nicotinamide nucleotide joined by a pyrophosphate linkage. Its oxidized form carries a positive charge on the nicotinamide ring, while the reduced form, NADH, carries a hydride equivalent. The molecule participates in hundreds of oxidoreductase reactions, where it accepts or donates electrons and protons. Because it can cycle between oxidized and reduced states without net consumption, NAD+ functions as a reusable electron carrier rather than a fuel molecule.
| Property | Value | Notes |
|---|---|---|
| Chemical formula | C21H27N7O14P2 | Oxidized free acid form; charge depends on pH. |
| Molar mass | 663.43 g/mol | Calculated for the free acid. |
| CAS Registry Number | 53-84-9 | For the anhydrous free acid; salts have different identifiers. |
| Appearance | White to off-white powder | Solid material; hygroscopic. |
| Solubility | Water-soluble | Dissolves in aqueous buffers; solubility varies with pH and salt. |
Beyond electron transfer, NAD+ serves as a substrate for enzymes that cleave it and attach its ADP-ribose portion to other molecules. This group includes poly(ADP-ribose) polymerases, CD38, and sirtuins. Such reactions consume NAD+ and can influence its availability for metabolism. Cells replenish NAD+ through a salvage pathway that recycles nicotinamide and through routes starting from tryptophan or vitamin B3 forms. How these synthesis and consumption routes are coordinated across tissues remains an active area of study, and compartment-specific concentrations are difficult to measure directly.
Nicotinamide adenine dinucleotide, abbreviated NAD+, is a dinucleotide built from adenine, nicotinamide, two ribose sugars, and two phosphate groups. The oxidized form carries a positive charge on the nicotinamide ring, while the reduced form, NADH, is neutral. This pair acts as a reversible electron carrier in cells. NAD+ is present in bacteria, plants, animals, and fungi. Its structure allows it to accept and donate electrons without being consumed in the reactions it supports.
In redox reactions, NAD+ accepts a hydride ion, which consists of two electrons and one proton. The hydride adds to the nicotinamide ring at a specific carbon, converting NAD+ into NADH. Dehydrogenase enzymes use this step in glycolysis, the citric acid cycle, and fatty acid oxidation. NADH later donates electrons to the mitochondrial electron transport chain, helping to drive ATP synthesis. The balance between NAD+ and NADH reflects the metabolic state of a cell, and shifts in that balance can alter how pathways operate.
Biosynthesis of NAD+ starts from nicotinamide, nicotinic acid, or nicotinamide riboside through salvage pathways. A rate-limiting enzyme, nicotinamide phosphoribosyltransferase, converts nicotinamide to nicotinamide mononucleotide. Further coupling with ATP yields NAD+. In mammals, the liver and muscle can synthesize NAD+ from dietary precursors, but tissue levels vary widely. Researchers study these pathways to understand age-related changes, metabolic disorders, and neurodegeneration. Direct causal links between NAD+ decline and disease remain an active area of investigation.
NAD+ is a dinucleotide composed of adenine, ribose, and nicotinamide groups joined by phosphate linkages. It serves as a coenzyme in oxidoreductase reactions, cycling between oxidized NAD+ and reduced NADH. The molecule is water-soluble and occurs in all living cells. Its nicotinamide ring accepts hydride ions during catabolic reactions, linking substrate oxidation to electron transport. This redox couple supports ATP production and helps maintain cytosolic and mitochondrial redox balance in many cell types.
Beyond redox catalysis, NAD+ is a substrate for enzymes that transfer ADP-ribose or remove acetyl groups from proteins. Sirtuins and poly(ADP-ribose) polymerases consume NAD+ and release nicotinamide as a byproduct. These reactions connect cellular energy status to gene regulation, DNA repair, and stress responses. Because NAD+ is used rather than merely recycled in such signaling, its concentration reflects both biosynthesis and consumption. The balance between salvage and de novo synthesis pathways determines available pools in different tissues.
Laboratory handling of NAD+ follows standard practices for hygroscopic fine chemicals. Personnel typically avoid inhalation and skin contact, use gloves and eye protection, and work in a ventilated area. Quality control may include ultraviolet absorbance at the nicotinamide maximum, chromatographic purity, water content, and identity confirmation by mass spectrometry. Because commercial preparations can contain counterions, residual solvents, or related nucleotides, a certificate of analysis helps verify the material. Researchers should confirm that the form supplied matches the intended assay.
Measuring NAD+ in biological samples requires care because the molecule is chemically reactive and present at low concentrations in some tissues. Common approaches include enzymatic cycling assays, high-performance liquid chromatography, and liquid chromatography coupled to mass spectrometry. Each method has different sensitivity and specificity, and sample preparation can affect results. Acidic or alkaline extraction steps are used in some protocols, but the choice depends on the analyte and matrix. No single method is universally optimal for every tissue or fluid.
Solid NAD+ is relatively stable when kept dry, cold, and protected from light. Aqueous solutions are more vulnerable to hydrolysis and can lose activity during repeated freeze-thaw cycles or prolonged storage at ambient temperature. Stability depends on pH, ionic strength, and the presence of degrading enzymes or metal ions. For many laboratory uses, aliquots are stored frozen and thawed only once. Exact degradation rates vary by matrix, so stability should be checked for each application rather than assumed.
Quality control for NAD+ materials typically combines identity, purity, and water content checks. Identity may be confirmed by ultraviolet spectrum, retention time in chromatography, or mass accuracy, while purity is assessed by HPLC peak area or quantitative nuclear magnetic resonance. Residual water and solvents can affect molar calculations and enzyme assays, so Karl Fischer titration or thermogravimetric analysis may be used. Commercial materials vary in grade and counterion form, and published methods should specify the exact salt or hydrate when reporting concentrations. Regulatory status depends on intended use, with research reagents, dietary ingredients, and clinical products treated under different frameworks.
Quantification of NAD+ in biological samples usually relies on separation techniques coupled to sensitive detection. High-performance liquid chromatography with ultraviolet detection can measure the oxidized form by its absorbance near 260 nm, while mass spectrometry provides greater specificity and can distinguish NAD+ from close analogs. Enzymatic cycling assays use coupled dehydrogenase reactions to amplify signal and estimate NAD+ concentrations in cell or tissue extracts. Because NAD+ and NADH interconvert rapidly, sample preparation must quench metabolism quickly and preserve the redox state before analysis.
The stability of NAD+ depends on pH, temperature, light exposure, and the presence of degradative enzymes. Aqueous solutions are generally more stable under mildly acidic to neutral conditions and degrade faster under alkaline conditions or prolonged heat. The solid is hygroscopic and should be stored desiccated, often frozen, and protected from repeated freeze-thaw cycles. In laboratory handling, aliquots reduce repeated temperature changes, and chelating agents may limit metal-catalyzed hydrolysis in some buffers. These practices matter because even small amounts of NADH or hydrolysis products can interfere with quantitative assays.
=== Elderly === A 2006 review regarding the management of insomnia and the elderly found that considerable evidence of the effectiveness and lasting benefits of nondrug treatments for insomnia exist. Compared with the benzodiazepines, the nonbenzodiazepine sedative-hypnotics offer few if any advantages in efficacy or tolerability in elderly persons. Other agents such as the melatonin receptor agonists may be more suitable and effective for the management of chronic insomnia in elderly people. Long-term use of sedative-hypnotics for insomnia lacks an evidence base and is discouraged for reasons that include concerns about such potential adverse drug effects as cognitive impairment (anterograde amnesia), daytime sedation, motor incoordination, and increased risk of motor vehicle accidents and falls.
=== Burial === Burial of food can preserve it due to a variety of factors: lack of light, lack of oxygen, cool temperatures, pH level, or desiccants in the soil. Burial may be combined with other methods such as salting or fermentation. Most foods can be preserved in soil that is very dry and salty (thus a desiccant) such as sand, or soil that is frozen. Many root vegetables are very resistant to spoilage and require no other preservation than storage in cool dark conditions, for example by burial in the ground, such as in a storage clamp (not to be confused with a root cellar). Cabbage was traditionally buried during autumn in northern US farms for preservation. Some methods keep it crispy while other methods produce sauerkraut. A similar process is used in the traditional production of kimchi. Sometimes meat is buried under conditions that cause preservation. If buried on hot coals or ashes, the heat can kill pathogens, the dry ash can desiccate, and the earth can block oxygen and further contamination. If buried where the earth is very cold, the earth acts like a refrigerator, or, in areas of permafrost, a freezer. In Odisha, India, it is practical to store rice by burying it underground. This method helps to store for three to six months during the dry season. Butter and similar substances have been preserved as bog butter in Irish peat bogs for centuries. Century eggs are traditionally created by placing eggs in alkaline mud (or other alkaline substance), resulting in their "inorganic" fermentation through raised pH instead of spoiling.
Informed consent approaches include conversations between the medical provider and person seeking care on the details of risks and outcomes, current understandings of scientific research, and how the provider can best assist the person in making decisions. Local standards of care exist in many countries, with most local standards being based on the WPATH standards, with some minor exceptions.
Alumni of Morgan State University have achieved notability in the fields of athletics, science, government, law, the arts, and the military including four members of the NFL Football Hall of Fame (Willie Lanier, Roosevelt Brown, Leroy Kelly, and Len Ford); Black Enterprise Magazine publisher Earl Graves; Clarence Dunnaville, lawyer and civil rights activist; and nearly a dozen U.S. Army generals, including Lieutenant General William "Kip" Ward, the first commanding officer of the United States Africa Command. The New York Times sports columnist William C. Rhoden, playwright, TV producer, and entrepreneur David E. Talbert, and American-Israeli Olympic sprinter Donald Sanford are also alumni. Civil rights activist and music critic for the Baltimore Afro-American newspaper Adah Jenkins graduated from Morgan State, as did scientist and inventor Valerie Thomas.
=== Surfactant peptides === Surfactant–like peptides that undergo self-assembly in water to form nanotubes and nanovesicles have been designed using natural lipids as guides. This class of peptides has a hydrophilic head (with one or two charged amino acids such as aspartic or glutamic acids, or lysine or histidine acids) with a hydrophobic tail (with 4 or more hydrophobic amino acids such as alanine, valine, or leucine). The peptide monomers are about 2-3 nm long and consist of seven or eight amino acids; the peptide length can be adjusted by adding or removing acids. In water, surfactant peptides undergo self-assembling to form well-ordered nanotubes and nanovesicles of 30–50 nm through intermolecular hydrogen bonds and the packing of the hydrophobic tails in between the residues, like micelle formation. Transmission electron microscopy examination on quick-frozen samples of surfactant-peptide structures showed helical open-ended nanotubes. The samples also showed dynamic behaviours and some vesicle "buds" sprouting out of the peptide nanotubes.
Sources: en.wikipedia.org
== Further reading == Coluzzi F, Mattia C (July–August 2005). "Oxycodone. Pharmacological profile and clinical data in chronic pain management" (PDF). Minerva Anestesiologica. 71 (7–8): 451–460. PMID 16012419. Archived from the original (PDF) on March 9, 2006.
13 November – The Home Office announces that the 41 police and crime commissioners in England and Wales will be scrapped from 2028, with their responsibilities moving to either directly elected mayors or council leaders. First Minister of Scotland John Swinney confirms plans for the Scottish Government to issue its first bonds in 2026–27 after Scotland is given the same rating as the UK by credit rating agencies. The House of Lords has proposed 942 amendments to the Terminally Ill Adults (End of Life) Bill. Sarah Taylor, the Norfolk Police and Crime Commissioner, resigns from the Labour Party following the UK government's decision to scrap her role, citing a lack of consultation in the matter. 14 November – Independent MP Adnan Hussain announces that he is "stepping away" from the steering group of Your Party because of what he describes as a "toxic" culture, particularly towards "Muslim men". The House of Lords has asked for more time to debate the Terminally Ill Adults (End of Life) Bill. 16 November – Horninglow and Eton Parish Council has asked Staffordshire County Councillor Peter Mason, elected in May 2025 to represent Reform UK, to stay away from its meetings after old social media posts came to light. In response, Mason says he "regrets his choice of words" in the posts, which concerned black women and the police. 18 November – The Northern Ireland Troubles Bill receives its second reading in the House of Commons and passes by 320 votes to 105.
Buddhism is the most widely practised religion, with 30.9% of residents declaring themselves adherents in the 2020 census. Christianity was the second largest religion at 17.1%, followed by Islam (15.0%), Taoism and folk beliefs (7.3%) and Hinduism (5.4%). Over one-fifth of the population had no religious affiliation. The proportion of Christians, Muslims, and the nonreligious slightly increased between 2010 and 2020, while the proportion of Buddhists and Taoists slightly decreased; Hinduism and other faiths remained largely stable in their share of the population. Singapore hosts monasteries and Dharma centres from all three major traditions of Buddhism: Theravada, Mahayana, and Vajrayana. Most Buddhists in Singapore are Chinese and adhere to the Mahayana tradition, owing to decades of missionary activity from China. However, Thailand's Theravada Buddhism has seen growing popularity among the populace (not only the Chinese) during the past decade. Soka Gakkai International, a Japanese Buddhist organisation, is practised by many people in Singapore, and mostly by those of Chinese descent. Tibetan Buddhism has also made slow inroads into the country in recent years.
Drotrecogin alfa (activated) (Xigris, marketed by Eli Lilly and Company) is a recombinant form of human activated protein C that has anti-thrombotic, anti-inflammatory, and profibrinolytic properties. Drotrecogin alpha (activated) belongs to the class of serine proteases. Drotrecogin alfa has not been found to improve outcomes in people with severe sepsis. The manufacturer's aggressive strategies in marketing its use in severe sepsis have been criticized. On October 25, 2011, Eli Lilly & Co. withdrew Xigris from the market after a major study showed no efficacy for the treatment of sepsis.
==== 2025 ==== Starting in January 2025, WWE began a partnership with Netflix where Raw would broadcast live worldwide weekly. Internationally outside the United States, all episodes of SmackDown and NXT, as well as livestreaming supercards, would also move to Netflix. With this partnership, WWE discontinued the WWE Network in all countries, with the exception of a few due to pre-existing contracts; by April 1, 2026, all other countries had transitioned to Netflix, bringing a complete end to the WWE Network, with the exception of Sub-Saharan Africa and Japan, which remain on SuperSport and Abema, respectively. Every livestreaming supercard in 2025 would air on Peacock in the United States until August 2025, after which, they transferred to ESPN. With the discontinuation of the WWE Network around the world, the "Network exclusive" notation is no longer valid as of January 2025.
Sources: en.wikipedia.org
=== Part Two === The Purchase Brothers had initially planned to release the second part of the film in early to mid-March 2009, but the large number of emails and phone calls the two received regarding the first part slowed development of the second. According to teaser clips at the end of the first part, the two Resistance soldiers will be joined by two additional characters, one of them a heroine, and will come into contact with headcrab zombies. The Purchase Brothers cited on their YouTube profile page that a new secret film project has heavily hampered their progress in completing Part Two, although it would be released in the near future. Another teaser clip was released on YouTube on October 13, 2009. Part Two was released on YouTube on August 19, 2011. The clip was quickly removed for unknown reasons by the end of the same day with no further comment on why it was removed. It was re-uploaded on August 24, 2011.
The world's largest producers of ethylene oxide are Dow Chemical Company (3–3.5 Mt (3.3–3.9 million short tons) in 2006), Saudi Basic Industries (2,000–2,500 tonnes (2,200–2,800 short tons) in 2006), Royal Dutch Shell (1.328 Mt (1.464 million short tons) in 2008–2009), BASF (1.175 Mt (1.295 million short tons) in 2008–2009), China Petrochemical Corporation (~1 Mt (1.1 million short tons) in 2006), Formosa Plastics (~1 Mt (1.1 million short tons) in 2006), and Ineos (0.92 Mt (1.01 million short tons) in 2008–2009).
An extension of the WAG algorithm is used, with a new PhyML (WAG+Γ4) model taking into account of sites with different evolutionary rates. Qmaker and nQmaker (2021, 2022), programs with the ability to estimate time-reversible and nonreversible matrices from very large datasets quickly. Each provide a general matrix and 5 specialized matrices, for a total of 12 precalculated substitution matrices. Matrices using a selection of proteins based on structural relatedness, as proposed by Benner et al. (1994), Fan (2004), and Steven et al. (2004). Matrices using structural alignments of proteins instead of simple sequence alignment (6 separate publications). Matrices using known physiochemical parameters of amino acid residues (5 separate publications). For a list of more models (including irreversible i.e. asymmetric and/or specialized ones), see the documentation for recent bioinformatic software including IQ-Tree, PhyML, and RAxML.
== Examples == In the built environment, evaporation limited capillary penetration is responsible for the phenomenon of rising damp in concrete and masonry, while in industry and diagnostic medicine this phenomenon is increasingly being harnessed in the field of paper-based microfluidics.
The earliest description of solid carbon dioxide (dry ice) was given by the French inventor Adrien-Jean-Pierre Thilorier, who in 1835 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO2. Carbon dioxide in combination with nitrogen was known from earlier times as Blackdamp, stythe or choke damp. Along with the other types of damp it was encountered in mining operations and well sinking. Slow oxidation of coal and biological processes replaced the oxygen to create a suffocating mixture of nitrogen and carbon dioxide.
Sources: en.wikipedia.org
NAD+ is a coenzyme found in living cells and is the oxidized form of nicotinamide adenine dinucleotide. It accepts electrons in redox reactions and also serves as a substrate for certain signaling and repair enzymes.
NAD+ becomes NADH when it accepts a hydride ion during oxidation-reduction reactions. NADH then donates electrons to other molecules, after which the carrier can return to the NAD+ form.
No, nicotinamide is a smaller molecule and a component of NAD+. Cells can use nicotinamide to rebuild NAD+ through the salvage pathway.
NAD+ is an oxidized dinucleotide coenzyme that carries electrons in metabolic reactions. It is also consumed by signaling enzymes, including sirtuins and PARPs. Its reduced form is NADH.