freeze-thaw comes up often in conversation and rarely with the context attached. Here we lay out the basics in order, then work through the practical considerations.
Updated 2025-11-19. Numbers and descriptions here follow the published literature rather than marketing material.
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.
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.
| Property | Value | Notes |
|---|---|---|
| CAS number | 53-84-9 | Refers to the free acid form of NAD+. |
| Molecular formula | C21H27N7O14P2 | Free acid; salts include additional counterions. |
| UV absorbance maximum | 259-260 nm | Used for detection and concentration estimation. |
| Typical storage | -20 °C or below, desiccated | Protect from light and moisture; avoid repeated freeze-thaw. |
| Common analytical method | HPLC-UV or LC-MS | Enzymatic cycling is an alternative for low-abundance samples. |
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.
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.
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.
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.
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.
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.
The bill to allow beer and wine sales in grocery stores was withdrawn by its sponsor, Cory McCray, moments before it was poised to be killed by the Senate Finance Committee, and its House crossfile never received a vote in the House Economic Matters Committee. As of 2025, Maryland is one of five states that do not allow alcohol sales except in liquor or packaged goods stores. During the 2026 legislative session, Moore introduced the DECADE Act, which extends initiatives for companies in tax-incentive zones and eliminates certain eligibility requirements for startup businesses to qualify for assistance programs, and another bill to ban surveillance pricing and dynamic pricing in grocery stores. Moore signed the dynamic pricing ban into law in April 2026.
=== Food and Drug Administration (FDA) === In vitro diagnostic (IVD) products use the same categorization as medical devices (Class I, II, and III) to assure safety and effectiveness. Regulatory controls and premarket approval process are determined by this classification, with Class I being the lowest risk (least regulated) and Class III being the highest risk (most regulated). Under the CLIA, it is the role of the FDA to assess the complexity of the in vitro laboratory diagnostic tests. Tests are only scored after the FDA has cleared or approved a premarketing request, or upon request. Manufacturers can apply for CLIA waivers during this premarket approval/clearance process. Tests that are already cleared or approved for home use or are waived by 42 CRF 293.15(c), are classified as waived. Otherwise, the tests are either classified as moderate or high complexity based on seven categorization criteria listed in 42 CFR 493.17. If the test is classified as moderate, the manufacturer may request the test be waived through the CLIA Waiver by Application. The application must show that the test meets the criteria in 42 U.S.C. § 263a(d)(3), that the test is simple and will not cause harm to the patient if performed incorrectly. These test classifications determine the certifications needed for laboratories to perform said tests. Waived tests require the least regulation, while moderate to high complexity tests require higher regulation and standards within the laboratory.
==== Thiopeptides ==== Thiopeptide biosynthesis involves particularly extensive modification of the core peptide scaffold. Indeed, due to the highly complex structures of thiopeptides, it was commonly thought that these natural products were nonribosomal peptides. Recognition of the ribosomal origin of these molecules came in 2009 with the independent discovery of the gene clusters for several thiopeptides. The standard nomenclature for thiopeptide biosynthetic proteins follows that of the thiomuracin gene cluster. In addition to the precursor peptide, referred to as the A peptide, thiopeptide biosynthesis requires at least six genes. These include lanthipeptide-like dehydratases, designated the B and C proteins, which install dehydroalanine and dehydrobutyrine moieties by dehydrating Ser/Thr precursor residues. Azole and azoline synthesis is effected by the E protein, the dehydrogenase, and the G protein, the cyclodehydratase. The nitrogen-containing heterocycle is installed by the D protein cyclase via a putative [4+2] cycloaddition of dehydroalanine moieties to form the characteristic macrocycle. The F protein is responsible for binding of the leader peptide. Thiopeptide biosynthesis is biochemically similar to that of cyanobactins, lanthipeptides, and linear azol(in)e-containing peptides (LAPs). As with cyanobactins and LAPs, azole and azoline synthesis occurs via the action of an ATP-dependent YcaO-domain cyclodehydratase.
Sources: en.wikipedia.org
Animal glue is an adhesive that is created by prolonged boiling of animal connective tissue in a process called rendering. In addition to being used as an adhesive, it is used for coating and sizing, in decorative composition ornaments, and as a clarifying agent. These protein colloid glues are formed through hydrolysis of the collagen from skins, bones, tendons, and other tissues, similar to gelatin. The word collagen itself derives from Greek κόλλα (kolla), meaning 'glue'. These proteins form a molecular bond with the glued object. Stereotypically, the animal in question is a horse, and horses that are euthanized are often said to have been "sent to the glue factory". However, other animals are also used, including cattle, rabbits and fish.
Franklin's underground laboratory where he witnesses several of the doctor's horrid experiments, such as dismembered heads being kept alive. Soon the player is forced to fight an army of undead Frankenstein-like monsters brought to life through Franklin's machine. Shortly after, Dr. Franklin is chased out of the area by one of his own monsters. The episode ends with the player inadvertently setting the whole asylum aflame. The player is caught in a massive explosion that ends the episode.
=== Non-flammable electrolyte === In 2023, most commercial Li-ion batteries employed alkylcarbonate solvents to assure the formation solid electrolyte interface on the negative electrode. Since such solvents are readily flammable, there has been active research to replace them with non-flammable solvents or to add fire suppressants. Another source of hazard is hexafluorophosphate anion, which is needed to passivate the negative current collector made of aluminium. Hexafluorophosphate reacts with water and releases volatile and toxic hydrogen fluoride. Several strategies have been explored for developing non-flammable Li-ion battery electrolytes. One approach uses fluorinated (co-)solvents, such as methyl-(2,2,2-trifluoroethyl)-carbonate (FEMC) or methyl-3,3,3-trifluoropropionate (MTFP). Another approach uses fluorinated anions, such as lithium bis(trifluoromethanesulfonyl)imide or lithium difluoro(oxalato)borate in high concentrations.
=== Refactoring === The process of rearranging the sets of backups in an archive file is known as refactoring. For example, if a backup system uses a single tape each day to store the incremental backups for all the protected computers, restoring one of the computers could require many tapes. Refactoring could be used to consolidate all the backups for a single computer onto a single tape, creating a "synthetic full backup". This is especially useful for backup systems that do incrementals forever style backups.
Sources: en.wikipedia.org
== USDA 1923-1942 == By now Lore Rogers had served the USDA for nearly two decades as Chief of the Research Laboratories. In 1923 the University of Maryland awarded him an honorary D. Sc. degree. He was now Dr. Rogers. Two years later his alma mater, the University of Maine, also conferred the D. Sc. degree to him. He was serving as president of the Society of American Bacteriologists and as associate editor of the Journal of Bacteriology. The World Dairy Congress was to be held in Washington in 1923, and Rogers volunteered to head the program committee. In 1928 he was off to London as a delegate to the 10th International Dairy Congress. A most remarkable book was published in 1928. Fundamentals of Dairy Science had about 31 contributing authors. The title page, however, merely states
Acquired progressive lymphangioma (benign lymphangioendothelioma) Acral fibrokeratoma (acquired digital fibrokeratoma, acquired periungual fibrokeratoma) Acrochordon (cutaneous papilloma, cutaneous tag, fibroepithelial polyp, fibroma molluscum, fibroma pendulum, papilloma colli, skin tag, soft fibroma, Templeton skin tag) Adenoma sebaceum Adult type of generalized eruption of cutaneous mastocytosis African cutaneous Kaposi sarcoma African lymphadenopathic Kaposi sarcoma Aggressive infantile fibromatosis AIDS-associated Kaposi sarcoma Ainhum (bankokerend, dactylolysis spontanea, sukhapakla) Angiofibroma Angiokeratoma Angiokeratoma of Fordyce (angiokeratoma of the scrotum and vulva) Angiokeratoma of Mibelli (Mibelli's angiokeratoma, telangiectatic warts) Angioleiomyoma (vascular leiomyoma) Angiolipoleiomyoma Angiolipoma Angioma serpiginosum Angiosarcoma Aponeurotic fibroma (calcifying aponeurotic fibroma, juvenile aponeurotic fibroma) Atypical fibroxanthoma Benign lipoblastomatosis (embryonic lipoma) Buschke–Ollendorff syndrome (dermatofibrosis lenticularis disseminata) Capillary aneurysms Carcinoid Cellular angiofibroma Cherry angioma (De Morgan spot, senile angioma) Chondrodermatitis nodularis chronica helicis (chondrodermatitis nodularis helicis) Chondroid lipoma Chordoma Classic Kaposi sarcoma Collagenous fibroma (desmoplastic fibroblastoma) Composite hemangioendothelioma Connective tissue nevus (collagenoma, elastoma, shagreen patch) Cutaneous endometriosis Cutaneous meningioma (heterotopic meningeal tissue, rudimentary meningocele) Cutaneous myelofibrosis Cutaneous myxoma Cutis marmorata telangiectatica congenita (congenital generalized phlebectasia, Van Lohuizen syndrome) Dermal dendrocyte hamartoma Dermatofibroma (benign fibrous histiocytoma, dermal dendrocytoma, fibrous dermatofibroma, fibrous histiocytoma, fibroma simplex, histiocytoma, nodular subepidermal fibrosis, sclerosing hemangioma) Dermatofibrosarcoma protuberans Desmoid tumor Diffuse cutaneous mastocytosis Diffuse infantile fibromatosis Dupuytren's contracture (Dupuytren's diathesis, Dupuytren's disease, palmar fibromatosis) Eccrine angiomatous hamartoma Elastofibroma dorsi Endovascular papillary angioendothelioma (Dabska tumor, Dabska-type hemangioendothelioma, hobnail hemangioendothelioma, malignant endovascular papillary angioendothelioma, papillary intralymphatic angioendothelioma) Epithelioid cell histiocytoma Epithelioid hemangioendothelioma Epithelioid sarcoma Erythrodermic mastocytosis Extraskeletal chondroma (chondroma of soft parts) Familial myxovascular fibromas Fascial hernia Fibroma of tendon sheath Fibromatosis colli (sternomastoid tumor of infancy) Fibrous hamartoma of infancy Fibrous papule of the nose (benign solitary fibrous papule, fibrous papule of the face) Folded skin with scarring (Michelin tire baby syndrome) Fordyce's spot (Fordyce's disease) Ganglion cyst Ganglioneuroma Gardner fibroma Genital leiomyoma (dartoic leiomyoma) Giant cell fibroblastoma Giant cell tumor of the tendon sheath (giant cell synovioma, localized nodular tenosynovitis, pigmented villonodular synovitis) Glomeruloid hemangioma Glomus tumor (glomangioma, solid glomus tumor, solitary glomus tumor) Granular cell tumor (Abrikossoff's tumor, Abrikossov's tumor, granular cell myoblastoma, granular cell nerve sheath tumor, granular cell schwannoma) Hamartoma Hemangiopericytoma Hemangiosarcoma Hibernoma (fetal lipoma, lipoma of embryonic fat, lipoma of immature adipose tissue) Hypertrophic scar Immunosuppression-associated Kaposi sarcoma Infantile digital fibromatosis (inclusion body fibromatosis, infantile digital myofibroblastoma, Reye tumor) Infantile hemangiopericytoma (congenital hemangiopericytoma) Infantile myofibromatosis (congenital generalized fibromatosis, congenital multicentric fibromatosis) Infantile systemic hyalinosis (juvenile systemic hyalinosis) Intradermal spindle cell lipoma Intravascular papillary endothelial hyperplasia (Masson's hemangio-endotheliome vegetant intravasculaire, Masson's lesion, Masson's pseudoangiosarcoma, Masson's tumor, papillary endothelial hyperplasia) Juvenile hyaline fibromatosis (fibromatosis hyalinica multiplex juvenilis, Murray–Puretic–Drescher syndrome) Kaposiform hemangioendothelioma (infantile kaposiform hemangioendothelioma) Kasabach–Merritt syndrome (hemangioma with thrombocytopenia) Keloid (Keloidal scar) Keratinizing metaplasia Keratocyst Klippel–Trenaunay syndrome (angioosteohypertrophy syndrome, hemangiectatic hypertrophy) Knuckle pads (heloderma) Leiomyosarcoma Lipoma Liposarcoma (atypical lipoma, atypical lipomatous tumor) Lymphangiectasis (lymphangioma) Lymphangiomatosis Malignant fibrous histiocytoma Malignant peripheral nerve sheath tumor (malignant schwannoma, neurofibrosarcoma, neurosarcoma) Mast cell sarcoma Meningocele Metastatic carcinoma Microvenular hemangioma (microcapillary hemangioma) Midline nevus flammeus (angel's kiss, salmon patch) Multifocal lymphangioendotheliomatosis (congenital cutaneovisceral angiomatosis with thrombocytopenia, multifocal lymphangioendotheliomatosis with thrombocytopenia) Multinucleate cell angiohistocytoma Multiple cutaneous and uterine leiomyomatosis syndrome (leiomyomatosis cutis et uteri, multiple leiomyomatosis, Reed's syndrome) Multiple cutaneous leiomyoma (pilar leiomyoma) Neural fibrolipoma Neuroblastoma (infantile neuroblastoma, neuroepithelioma) Neuroma cutis Neurothekeoma (bizarre cutaneous neurofibroma, cutaneous lobular neuromyxoma, myxoma of the nerve sheath, myxomatous perineurioma, nerve sheath myxoma) Nevus flammeus (capillary malformation, port-wine stain) Nevus flammeus nuchae (stork bite) Nevus lipomatosus superficialis (nevus lipomatosis of Hoffman and Zurhelle) Nevus oligemicus Nodular fasciitis (nodular pseudosarcomatous fasciits, pseudosarcomatous fasciitis, subcutaneous pseudosarcomatous fibromatosis) Oral submucous fibrosis Pachydermodactyly Palisaded encapsulated neuroma Paraneoplastic syndrome Pearly penile papules (hirsuties coronae glandis, hirsutoid papillomas) Peyronie's disease (induratio penis plastica) Phakomatosis pigmentovascularis Piloleiomyoma Plantar fibromatosis (Ledderhose's disease) Pleomorphic fibroma Pleomorphic lipoma Plexiform fibrohistiocytic tumor Porokeratotic eccrine ostial and dermal duct nevus Progressive nodular histiocytoma Proliferating angioendotheliomatosis Prominent inferior labial artery Pseudo-ainhum
==== Short-term ==== Acute adverse effects are usually the result of high or multiple doses, although single dose toxicity can occur in susceptible individuals. The most serious short-term physical health risks of MDMA are hyperthermia and dehydration. Cases of life-threatening or fatal hyponatremia (excessively low sodium concentration in the blood) have developed in MDMA users attempting to prevent dehydration by consuming excessive amounts of water without replenishing electrolytes. The immediate adverse effects of MDMA use can include:
Sources: en.wikipedia.org
Common methods include enzymatic cycling assays, HPLC with UV detection, and LC-MS. The choice depends on sample size, specificity needs, and available equipment. Rapid quenching before analysis is important because NAD+ and NADH can interconvert.
Water promotes hydrolysis, and heat accelerates degradation. Cold, dry storage slows these processes. Repeated warming and cooling can introduce moisture and condensation, so aliquoting is often used.
Yes. They may be free acid or salts, with different counterions and purity grades. The counterion changes molecular weight, so concentration calculations should account for the actual form. Certificates of analysis provide batch-specific information.
Aqueous NAD+ solutions are best kept frozen in aliquots and protected from light. Repeated freezing and thawing is avoided because it can accelerate breakdown. Dry powder stored desiccated at -20 °C or lower typically remains stable for longer periods.