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 2026-02-03. Where a claim depends on a specific study, the study is described rather than over-claimed.
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.
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.
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.
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.
| 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 |
Solid NAD+ is usually supplied as a white to off-white powder or lyophilized preparation. It is hygroscopic and should be kept desiccated at low temperature, commonly -20 °C or below for long-term storage. Aqueous solutions are less stable than dry material and are often prepared fresh or stored frozen in aliquots. Light exposure and repeated freeze-thaw cycles can promote degradation, so amber containers and single-use aliquots are preferred. Buffered solutions near neutral pH are generally less stable than acidic or frozen preparations.
Quantification of NAD+ in biological samples typically uses liquid chromatography coupled to mass spectrometry. Enzymatic cycling assays offer higher throughput and rely on NAD+ dependent dehydrogenases to amplify signal. Both approaches require careful sample quenching because NAD+ can be rapidly consumed or converted after collection. Acidic extraction is common for NAD+, while alkaline conditions favor NADH in some protocols. Isotopically labeled internal standards help correct for losses during extraction and ionization.
Commercial NAD+ is available at research grade, often with purity specifications determined by high-performance liquid chromatography. Certificates of analysis may report water content, residual solvents, and counterion identity. Identity can be confirmed by ultraviolet absorbance near 260 nm, mass spectrometry, or enzymatic activity. Because different salt forms and hydration states exist, researchers should verify that the product matches the intended molecular form. Lot-to-lot variation in purity can affect quantitative assays and should be documented.
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.
Quality control for NAD+ relies on identity, purity, and functional tests. A certificate of analysis may report high-performance liquid chromatography purity, ultraviolet spectrum, water content, and residual solvents. Because NAD+ is hygroscopic, gravimetric values can shift as material absorbs water, so purity should be interpreted alongside storage history. Mass spectrometry confirms molecular identity, while enzymatic assays show whether the material supports dehydrogenase activity. Commercial material is available as the free acid and as salts, and the counterion affects molecular weight, solubility, and how concentrations are calculated.
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.
Metrohm was founded in 1943 in Herisau by Bertold Suhner and Willi Studer. At the outset, the company produced measuring instruments for high-frequency technology and telecommunications. High-precision measuring instruments as well as radio receivers were added to its product range later on. After World War II, the company struggled as the demand for their products decreased, since it was cheaper to buy imported radios from the US. Thus, Suhner decided to venture into analytical chemistry and developed a first pH meter in 1947, followed by a titrator in 1949. In 1947, Suhner and Studer parted ways. Swiss journalist and author Peter Holenstein describes how this happened in his book on the lifework of co-founder Willi Studer: In June 1947, Emil Haefely, founder of the company Emil Haefely & Cie AG, which was one of Metrohm's first customers, asked Willi Studer, whom he had known for many years, to build a prototype for a cathode-ray oscilloscope. This being new technology for Metrohm, Bertold Suhner opposed the idea, fearing that the development wouldn't be possible within reasonable time and budget constraints. Indeed, while the development of the simpler instruments in Metrohm's portfolio had never taken Studer more than a few weeks, Studer still hadn't finished the prototype after several months at the end of November 1947. At this point, his colleague Suhner lost all hope that the project would come to a successful conclusion. A break between the co-founders was the result, and led Studer to leave the company at the end of December 1947.
To avoid transfusion reactions, the donor and recipient blood are tested, typically ordered as a "type and screen" for the recipient. The "type" in this case is the ABO and Rh type, specifically the phenotype, and the "screen" refers to testing for atypical antibodies that might cause transfusion problems. The typing and screening are also performed on donor blood. The blood groups represent antigens on the surface of the red blood cells which might react with antibodies in the recipient. The ABO blood group system has four basic phenotypes: O, A, B, and AB. In the former Soviet Union these were called I, II, III, and IV, respectively. There are two important antigens in the system: A and B. Red cells without A or B are called type O, and red cells with both are called AB. Except in unusual cases like infants or seriously immunocompromised individuals, all people will have antibodies to any ABO blood type that isn't present on their own red blood cells, and will have an immediate hemolytic reaction to a unit that is not compatible with their ABO type. In addition to the A and B antigens, there are rare variations which can further complicate transfusions, such as the Bombay phenotype. The Rh blood group system consists of around 50 different antigens, but that of the greatest clinical interest is the "D" antigen, though it has other names and is commonly just called "negative" or "positive". Unlike the ABO antigens, a recipient will not usually react to the first incompatible transfusion because the adaptive immune system does not immediately recognize it.
=== Pharmacokinetics === After oral administration itopride undergoes rapid and extensive absorption with levels of itopride peaking in the blood plasma after only 35 minutes. Itopride is primarily eliminated via the kidneys having an elimination half-life of approximately 6 hours.
Sources: en.wikipedia.org
=== Mac port === A version of Half-Life for Mac OS was announced by Logicware on April 23, 1999. However, Valve canceled it a few months later in October 1999. The Valve CEO, Gabe Newell, said the port was substandard, citing a separate multiplayer network, no automatic update utility and the inability to include Valve's multiplayer mod Team Fortress Classic. He said he did not want to make Mac players "second-class customers" and preferred to write off the investment rather than "take money from Mac customers and short-change them". Rebecca Heineman, the co-founder of Logicware, denied this, saying that Valve cancelled the port as Apple had angered them by misrepresenting sales projections. She said the port was complete and three weeks from release. In 2013, Valve released a port for OS X.
Two of the most significant differences between puberty in females and puberty in males are the age at which it begins, and the major sex steroids involved, the androgens and the estrogens. Although there is a wide range of normal ages, females typically begin the process of puberty around age 10½; males at ages 11½–12. Puberty generally ends between 15–17 for females and 16–17 for males. Females attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, males accelerate more slowly but continue to grow for about six years after the first visible pubertal changes. For males, the androgen testosterone is the principal sex hormone; while testosterone is produced, all males' changes are characterized as virilization. A substantial product of testosterone metabolism in males is the estrogen estradiol. The conversion of testosterone to estradiol depends on the amount of body fat and estradiol levels in males are typically much lower than in females. The male "growth spurt" also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse. Although males are on average 2 centimetres (0.8 in) shorter than females before puberty begins, adult men are on average about 13 centimetres (5.1 in) taller than women. Most of this sex difference in adult heights is attributable to a later onset of the growth spurt and a slower progression to completion, a direct result of the later rise and lower adult male levels of estradiol. The hormonal maturation of females is considerably more complicated than in males.
In 1906, Hahn returned to Germany, where Fischer placed at his disposal a former woodworking shop (Holzwerkstatt) in the basement of the Chemical Institute to use as a laboratory. Hahn equipped it with electroscopes to measure alpha and beta particles and gamma rays. In Montreal these had been made from discarded coffee tins; Hahn made the ones in Berlin from brass, with aluminium strips insulated with amber. These were charged with hard rubber sticks that he rubbed against the sleeves of his suit. It was not possible to conduct research in the wood shop, but Alfred Stock, the head of the inorganic chemistry department, let Hahn use a space in one of his two private laboratories. Hahn purchased two milligrams of radium from Friedrich Oskar Giesel, the discoverer of emanium (radon), for 100 marks a milligram (equivalent to €700 in 2021), and obtained thorium for free from Otto Knöfler, whose Berlin firm was a major producer of thorium products. In the space of a few months Hahn discovered mesothorium I (radium-228), mesothorium II (actinium-228), and – independently from Boltwood – the mother substance of radium, ionium (later identified as thorium-230). In subsequent years, mesothorium I assumed great importance because, like radium-226 (discovered by Pierre and Marie Curie), it was ideally suited for use in medical radiation treatment, but cost only half as much to manufacture. Along the way, Hahn determined that just as he was unable to separate thorium from radiothorium, so he could not separate mesothorium I from radium.
Sources: en.wikipedia.org
=== Chairmen === R.S. Sharma, 1972 - 1977 A.R. Kulkarni, 1978 - 1981 Niharranjan Ray, 1981 - 1981 Lokesh Chandra, 1982 - 1985 Irfan Habib, 1986 - 1993 Ravinder Kumar, 1993 - 1996 S. Settar, 1996 - 1999 K.S. Sarma (acting), 1999 - 1999 B.R. Grover, 1999 - 2001 K.S. Lal, 2001 - 2001 M.G.S. Narayanan, 2001 - 2003 Kumud Bansal (acting), 2003 - 2004 D.N. Tripathi, 2004 - 2007 K.M. Acharya (acting), 2007 - 2007 Sabyasachi Bhattacharya, 4 March 2007 – 3 March 2010 Sabyasachi Bhattacharya (acting), 4 April 2010 – 20 May 2011 Basudev Chatterjee, 20 May 2011 - 2014 Yellapragada Sudershan Rao, 28 June 2014 - 26 June 2017 A.P Jamkhedkar, 15 February 2018 – 14 January 2022 Raghuvendra Tanwar, 14 January 2022 - present
On August 23, 1879, 26 members of the Christian Scientists' Association were granted a charter to form the Church of Christ (Scientist). Services were held in people's homes in Lynn and later in Hawthorne Hall, Boston. On January 31, 1881, Eddy was granted a charter to form the Massachusetts Metaphysical College to teach "pathology, ontology, therapeutics, moral science, metaphysics, and their application to the treatment of disease." The college lived wherever Eddy did; a new sign appeared on 8 Broad Street. In October 1881 there was a revolt. Eight church members resigned, signing a document complaining of Eddy's "frequent ebullitions of temper, love of money, and the appearance of hypocrisy." Only a few students remained, including Calvin Frye, who became Eddy's most loyal personal assistant. They appointed Eddy pastor of the church in November 1881, and drew up a resolution in February 1882 that she was "the chosen messenger of God to the nations." Despite the support, the resignations ended Eddy's time in Lynn. The church was struggling and her reputation had been damaged by the disputes. By now 61 years old, she decided to move to Boston, and in early 1882 rented a house at 569 Columbus Avenue, a silver plaque announcing the arrival of the Massachusetts Metaphysical College.
Booker Brooks (George Clooney) – The original foreman at Wellman. Booker wasn't always taken seriously by the workers, but compared to their future boss, Roseanne and the others appreciate him more. He dated Jackie for a while, and they tried to keep it a secret. He set the quotas at Wellman at 5,500, much lower than the 8,000 set by their next boss Keith Faber (Fred Thompson). Vonda Green (Charlayne Woodard, credited as Charlaine Woodard)- Spirited and perky friend of Jackie and Roseanne, also has a great singing voice. Sylvia Foster (Anne Faulkner)- Older Wellman employee working there since the late 1950s, she occasionally hangs out with Jackie, Roseanne, and the rest of the gang at the Lobo. Has a husband named Joe who is hard of hearing. Juanita Herrara (Evelina Fernandez)- Hispanic co-worker who after leaving Wellman with the rest of the gang opens a successful small business in Lanford with her husband Emilio and their teenage son. Meg Wellman (Debra Mooney) – Owner of the Wellman factory, who believes she and Roseanne are good friends. Unaware she's getting their names wrong, she comically refers to Roseanne as "Roxanne Conway" and Jackie as Janet. Accidentally hits Roseanne's car with her car in one episode.
== Applications == Enzyme inhibitors are found in nature and also produced artificially in the laboratory. Naturally occurring enzyme inhibitors regulate many metabolic processes and are essential for life. In addition, naturally produced poisons are often enzyme inhibitors that have evolved for use as toxic agents against predators, prey, and competing organisms. These natural toxins include some of the most poisonous substances known. Artificial inhibitors are often used as drugs, but can also be insecticides such as malathion, herbicides such as glyphosate, or disinfectants such as triclosan. Other artificial enzyme inhibitors block acetylcholinesterase, an enzyme which breaks down acetylcholine, and are used as nerve agents in chemical warfare.
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.
Common methods include LC-MS, HPLC with UV detection, and enzymatic cycling assays. Rapid quenching is needed because NAD+ and NADH interconvert. The chosen method should be validated for the sample matrix.