If you have been reading about freeze-thaw 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 2026-07-31. Where a claim depends on a specific study, the study is described rather than over-claimed.
Commercial NAD+ is supplied as a solid, often as the free acid or a salt, and purity is verified by chromatographic methods. Laboratories typically store it desiccated at minus 20 degrees Celsius or below. Working solutions are prepared fresh because even sterile aqueous solutions can lose activity over hours to days depending on pH and temperature. Documentation may include a certificate of analysis, an assay value, and a recommended retest date. Researchers should verify identity and purity when results depend on precise cofactor concentrations.
NAD+ is commonly measured by high-performance liquid chromatography with ultraviolet detection, often at 254 or 260 nm. Enzymatic cycling assays provide higher sensitivity by coupling NAD+ to a reporter reaction. Mass spectrometry can distinguish NAD+ from close analogues and confirm isotope labeling. Sample preparation usually involves rapid quenching of metabolism to prevent interconversion with NADH. Because NAD+ and NADH differ by one hydride, extraction conditions strongly affect the measured ratio.
In aqueous solution, NAD+ is most stable under mildly acidic to neutral conditions and degrades faster at high pH or elevated temperature. The molecule can hydrolyze at the pyrophosphate bond or undergo nonenzymatic cyclization. Buffers, chelating agents, and cold temperatures slow these losses during analysis. Repeated freeze-thaw cycles are generally avoided because they can promote degradation and concentration changes. Light exposure is also controlled, though NAD+ is less photolabile than some related nucleotides.
Related compounds include NADH, the reduced form, and NADP+, which carries an additional phosphate group. NADP+ and NADPH often serve in biosynthetic and antioxidant reactions, while NAD+ and NADH are more associated with energy-yielding catabolism. Nicotinamide, nicotinic acid, and nicotinamide riboside are precursors that can enter salvage pathways. The exact contribution of dietary precursors to tissue NAD+ pools is an area of active investigation. Some studies measure labeled precursors to trace those routes.
NAD+ is the oxidized form of nicotinamide adenine dinucleotide, a coenzyme built from two nucleotides joined by a phosphate linkage. One nucleotide carries adenine, and the other carries nicotinamide; the plus sign denotes a formal positive charge on the nicotinamide ring, not a free proton. In cells, NAD+ and its reduced partner NADH form a reversible redox pair. That pair participates in electron transfer reactions throughout metabolism. The abbreviation NAD+ is common in biochemistry, while NAD(H) sometimes denotes the combined pool.
The molecule was first described in the early twentieth century as a factor that promoted fermentation in yeast extracts. Later work linked it to hydrogen transfer and to the oxidation of nutrients in living tissues. Its structure was resolved as a dinucleotide, which explained why it could accept and donate electrons at specific enzyme sites. Today, NAD+ is recognized as a central substrate and signaling precursor, not merely a metabolic cofactor. Whether all observed NAD+ changes reflect causal signaling remains an open question.
| Property | Value | Notes |
|---|---|---|
| UV absorption maximum | 259–260 nm | Aqueous solution; pH-dependent |
| Common salt form | Disodium salt | Improves aqueous solubility |
| Typical storage temperature | -20 °C or lower | Desiccated and protected from light |
| Common analytical method | HPLC with UV detection | Often paired with mass spectrometry |
| Aqueous stability | pH and temperature dependent | Degrades faster at alkaline pH and high heat |
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+ acts as a substrate for several enzyme families. ADP-ribosyltransferases, sirtuins, and CD38 ectoenzymes cleave the molecule into nicotinamide and ADP-ribose or related products. These reactions connect NAD+ availability to processes such as DNA repair, chromatin modification, and calcium signaling. Because the coenzyme is used in both electron transfer and signaling, cells maintain separate pools in compartments including the cytosol, mitochondria, and nucleus. The relative sizes and regulation of those pools remain active areas of study.
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.
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.
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.
Laboratory measurement of NAD+ usually begins with rapid sample quenching because the molecule can change form after collection. Enzymatic cycling assays amplify signal through coupled reactions and are suited to small samples. High-performance liquid chromatography with ultraviolet detection separates NAD+ from related nucleotides. Liquid chromatography-mass spectrometry offers higher specificity and can distinguish NAD+ from close analogs. Each method has trade-offs in sensitivity, throughput, and equipment needs, so reported values depend heavily on extraction and detection choices.
Stability of NAD+ depends on form, temperature, pH, and water content. The solid is generally more stable than solutions, and it should be kept dry and cold. In solution, hydrolysis can cleave the dinucleotide, especially under alkaline conditions or at elevated temperature. Light exposure may also contribute to degradation. Buffers, chelating agents, and sterile handling can reduce losses, but no single condition preserves all preparations indefinitely. Researchers often prepare working solutions shortly before use and verify activity or purity after storage.
=== Healthcare === In July 2018, Premier Ford named Rueben Devlin, an orthopedic surgeon who was CEO of Toronto's Humber River Hospital and a "key Tory adviser" and former Ontario PCs president—to a $348,000 a year three-year appointment on the Council on Improving Healthcare and Ending Hallway Medicine, to curb hospital overcrowding. Devlin is the Ford family's "closest health-care adviser." Health costs in Ontario were over $60 billion annually, according to TVO's Steve Paikin. Devlin is tasked with the selection of the other Council members, and with "ending hallway medicine, dental care for seniors, improved mental-health services), all while ensuring stable, long-term funding for the system—Premier Ford's election promises. Since coming into power in June 2018, Premier Ford's government put an approved injection site in Toronto—and several other places—on pause while Health Minister Christine Elliott studied the issue. In February 2019, the Ontario NDP said that two sets of leaked documents show that the Ford government was creating a health "super agency" that "would be in charge of managing health services, quality improvement, patient relations, digital health and tissue donation and transplants, among other responsibilities." The documents said that "long-term care inspections" and the Ontario's "air ambulance service" Ornge would be "outsourced". According to a CTV News report, Minister Elliot was "forced to make assurances" that these services would not be "privatized".
Early medical texts, especially the Carakasaṃhitā and Suśrutasaṃhitā, are often claimed to contain early references to rasaśāstra. Where these texts use the word rasa, later commentators interpret rasa as mercury, despite the word having various other meanings. The earliest mentions of mercury are to the unprocessed substance and it is not until the 9th century Kalyāṇakāraka that we find recipes for purifying and calcination. The 13th century Śārṅgadharasaṃhitā also contains elaborate descriptions of the processing and uses of mercury. An important feature is the use of metals, including several that are toxic. In addition to mercury, gold, silver, iron, copper, tin, lead, zinc and bell metal are used. In addition to these metals, salts and other substances such as coral, seashells, and feathers are also used. The usual means used to administer these substances is by preparations called bhasma, Sanskrit for "ash". Calcination, which is described in the literature of the art as śodhana, "purification", is the process used to prepare these bhasma for administration. Sublimation and the preparation of a mercury sulfide are also in use in the preparation of its materia medica. A variety of methods are used to achieve this. One involves the heating of thin sheets of metal and then immersing them in oil (taila), extract (takra), cow urine (gomutra) and other substances. Others are calcined in crucibles heated with fires of cow dung (puttam). Ayurvedic practitioners believe that this process of purification removes undesirable qualities and enhances their therapeutic power.
== Description == Most Scutellaria are annual or perennial herbaceous plants from 5 to 100 cm (2 to 39 in) tall, however a few are subshrubs. Some Scutellaria are aquatic. Scutellaria have four-angled stems and opposite leaves, and flowers with upper and lower lips. The genus is most easily recognized by the typical shield on the calyx that has also prompted its common name.
== Cellular immunotherapy == Immune cell-based therapies for solid tumors may be limited by tumor-antigen heterogeneity, restricted immune-cell trafficking, an immunosuppressive tumor microenvironment, limited cell persistence, treatment-related toxicities, and complex manufacturing requirements.
The golden age of taxidermy was during the Victorian era, when mounted animals became a popular part of interior design and decor. English ornithologist John Hancock is considered to be the father of modern taxidermy. An avid collector of birds, which he had shot personally, he began modeling them with clay and casting in plaster. For the Great Exhibition of 1851 in London, he mounted a series of stuffed birds as an exhibit. They generated much interest among the public and scientists alike who considered them superior to earlier models, and they were regarded as the first lifelike and artistic specimens on display. A judge remarked that Hancock's exhibit "... will go far towards raising the art of taxidermy to a level with other arts which have hitherto held higher pretensions". Hancock's display sparked great national interest in taxidermy, and amateur and professional collections for public view proliferated rapidly. Displays of birds were particularly common in middle-class Victorian homes – even Queen Victoria amassed an impressive bird collection. Taxidermy was also increasingly used by the bereaved owners of dead pets to 'resurrect' them.
Sources: en.wikipedia.org
Sodium thiopental, also known as thiopental sodium or thiopentone and sold under the brand name Pentothal, is a rapid-onset short-acting barbiturate general anesthetic. It is the thiobarbiturate analog of pentobarbital, and an analog of thiobarbital. Sodium thiopental is a therapeutic alternative on the World Health Organization's List of Essential Medicines. It was the first of three drugs administered during most lethal injections in the United States until the US division of Hospira objected and stopped manufacturing the drug for this purpose in 2011, and the European Union additionally banned the export of the drug for this purpose. Although thiopental abuse carries a dependency risk, its recreational use is rare. Sodium thiopental is well-known in popular culture, especially under the name "sodium pentothal," as a "truth serum," although its efficacy in this role is questioned.
Forensic analysis at the Hospital das Clínicas in São Paulo identified an incision in the jugular vein used to inject a solution of aromatic substances, such as camphor and myrrh, during the 19th century embalming. The preservation was attributed to this chemical process combined with the hermetic seal of her lead-lined casket, which prevented the growth of microorganisms. Before reinterment, researchers re-embalmed the remains using techniques analogous to the original vascular method.
Chromatographic methods coupled to mass spectrometry This technique is extremely useful for the analysis of multiple toxins. It has numerous advantages over the other techniques used. It is a sensitive and selective analytical method, making it ideal for the analysis of complex samples and those with low analyte concentrations. The method is also beneficial in that it provides important structural information on the analyte which is helpful for aiding analyte identification and when unknown analytes are present in the sample. The technique has benefits over LC-FLD as the derivatisation and purification extraction steps are not necessary. YTX analysis limits of detection of 30 mg/g of shellfish tissue for chromatographic methods coupled to mass spectrometry have been recorded. The major drawback to LC-MS is that the equipment is very expensive.
=== November 2005 === -173 detainees found in an Iraqi government bunker in Baghdad were found starved, beaten and tortured. -Colin Powell's former Chief of Staff, Colonel Lawrence Wilkerson, stated in an interview with Amy Goodman on November 22 that:
Historically, red blood cell transfusion was considered when the hemoglobin level fell below 100g/L or hematocrit fell below 30%. Because each unit of blood given carries risks, a trigger level lower than that, at 70 to 80g/L, is now usually used, as it has been shown to have better patient outcomes. The administration of a single unit of blood (approximately 450ml) is the standard for hospitalized people who are not bleeding, with this treatment followed with re-assessment and consideration of symptoms and hemoglobin concentration. Patients with poor oxygen saturation may need more blood. The advisory caution to use blood transfusion only with more severe anemia is in part due to evidence that outcomes are worsened if larger amounts are given. One may consider transfusion for people with symptoms of cardiovascular disease such as chest pain or shortness of breath. In cases where patients have low levels of hemoglobin due to iron deficiency, but are cardiovascularly stable, oral or parenteral iron is a preferred option based on both efficacy and safety. Other blood products are given where appropriate, e.g., fresh frozen plasma to treat clotting deficiencies and platelets to treat or prevent bleeding in thrombocytopenic patients.
Sources: en.wikipedia.org
NAD+ and NADH can interconvert quickly after a sample is collected, which can alter the measured ratio. Rapid quenching and cold handling limit enzymatic and chemical changes.
Purity is often checked by HPLC with UV detection, sometimes paired with mass spectrometry for identity. An assay against a standard can quantify the active cofactor content.
Solid NAD+ is usually kept dry, cold, and protected from light. Aqueous working solutions are best prepared fresh because degradation depends on pH, temperature, and time.
It indicates a formal positive charge on the nicotinamide ring. The molecule is not simply a protonated acid, and the charge is part of its redox chemistry.