A practical reference on freeze-thaw: what it is, how it behaves, what the literature reports, and where the honest uncertainties sit.
Reviewed 2026-06-28. Anything still debated is marked as such rather than presented as settled.
Quality checks after reconstitution include visual inspection, pH measurement, and analytical methods such as reversed-phase high-performance liquid chromatography. These tests can detect insoluble material, degradation products, and changes in concentration. Mass spectrometry is often used to confirm molecular identity when the peptide sequence is known. Because a clear solution can still contain aggregates or modified peptide, visual clarity alone is not sufficient. Analytical results are compared with a reference standard or the pre-reconstitution certificate of analysis.
Container selection matters because peptides can adsorb to glass, plastic, and filter membranes. Low-binding polypropylene tubes reduce losses for hydrophobic sequences, and filtration through a 0.22 µm membrane can remove particulates and microorganisms. Some peptides may bind to certain filter materials, so compatibility should be checked. Aliquots should be prepared before freezing to avoid repeated temperature cycling. Labels should record the peptide identity, lot number, solvent, concentration, reconstitution date, and storage condition.
After reconstitution, the peptide solution is less stable than the dried powder because water enables hydrolysis, oxidation, and microbial growth. Storage temperature, pH, buffer composition, and container material all affect how long the solution remains usable. Many peptides are kept at 2–8 °C for short-term work, while frozen aliquots at −20 °C or below are used for longer intervals. Repeated freeze-thaw cycles can cause aggregation or precipitation. The choice of storage condition should be based on stability data for the specific peptide.
Storage recommendations for reconstituted peptides vary by sequence and intended use, so general rules remain broad. A common laboratory practice is to keep solutions cold, sometimes frozen, and protected from light, but freezing itself can damage certain peptides. The pH of the solution may be adjusted to a range where the peptide is most stable, though changing pH can also alter solubility. Documentation of reconstitution date, solvent, concentration, and storage conditions supports reproducibility. Stability data for a specific peptide are generally established by direct measurement rather than assumed from related compounds.
Once a peptide is in solution, its stability depends on temperature, pH, ionic strength, and the presence of oxygen or light. Many peptides are less stable in liquid form than as dry powders because hydrolysis, oxidation, and aggregation can proceed faster in water. Storage at low temperature slows these reactions but does not eliminate them. Some sequences are particularly sensitive to repeated freezing and thawing, which can cause precipitation or conformational changes. The container material and headspace also influence adsorption and surface-induced aggregation.
Practical handling often includes dividing a reconstituted solution into single-use aliquots to limit freeze-thaw cycling. Vials made of low-binding plastic or glass with inert closures are common, and some protocols add a carrier protein or bulking agent to reduce adsorption. Filtration through a sterile filter may be used when a sterile solution is required, but filters can retain peptide if binding occurs. Mixing is usually gentle; vigorous vortexing can introduce air-liquid interfaces that promote aggregation. Each of these steps involves trade-offs between sterility, recovery, and analytical accuracy.
| Property | Value | Notes |
|---|---|---|
| Lyophilized storage | −20 °C or below | Sealed container with desiccant limits moisture ingress. |
| Reconstituted storage | 2 to 8 °C short term | Freezing aliquots at −20 °C or below may extend stability for some peptides. |
| Preferred container | Low-binding polypropylene | Reduces adsorption losses compared with untreated glass. |
| Sterilization method | 0.22 µm filtration | Filter material compatibility should be verified for each peptide. |
| Common label data | Peptide, lot, date, concentration | Supports traceability and avoids repeated freeze-thaw cycles. |
Reconstitution concentration is chosen from the mass of peptide and the volume of solvent added. Researchers often prepare a concentrated stock and then divide it into single-use aliquots to reduce freeze-thaw cycling. The actual peptide content may differ from label mass because of counterions, water, or impurities. For that reason, quantitative work may require independent measurement such as amino acid analysis or ultraviolet absorbance. Records of solvent, volume, date, and lot help trace later observations.
Lyophilized peptides are supplied as dry powders or porous cakes that remain stable during shipment and short-term storage. Reconstitution is the laboratory step of adding a suitable solvent so the solid dissolves into a liquid stock. The dried state limits hydrolysis and microbial growth, but it does not remove all residual water or salts. Sequence, counterion, and manufacturing method influence how quickly and completely a peptide enters solution. Researchers treat reconstitution as a practical starting point for later dilution, analysis, or assay work.
Dissolution involves hydration of polar and charged groups, disruption of intermolecular interactions in the lyophilized powder, and transition to a thermodynamically favored solution state. Not all powder dissolves readily; aggregation, incomplete lyophilization, or high molecular weight can slow reconstitution. The resulting solution may contain particulates or oligomers that affect downstream measurements. Researchers often verify complete dissolution by visual inspection and spectrophotometric or chromatographic methods. The relationship between reconstitution conditions and long-term stability remains an active area of study.
Peptide reconstitution is the process of dissolving a lyophilized peptide powder in a liquid solvent to produce a solution of defined concentration. Lyophilization removes water under vacuum from a frozen peptide solution, leaving a porous cake or powder. The dry form is often more stable for shipping and storage. Reconstitution restores the peptide to a liquid state for analytical, biochemical, or formulation work. The exact solvent depends on peptide sequence and intended assay.
Water is common, but not universal; hydrophobic peptides may require organic co-solvents like acetonitrile or dimethyl sulfoxide. Acidic peptides may dissolve better in dilute acetic acid or ammonium hydroxide, while basic peptides may favor slightly acidic conditions. Buffer choice matters because pH can affect charge, solubility, and aggregation. Some peptides require sonication or gentle mixing, whereas vigorous vortexing can cause foaming and surface denaturation. The target concentration is typically calculated from the labeled peptide mass and the volume of solvent added.
Cloudiness, particles, or gel formation after reconstitution can signal incomplete dissolution, aggregation, or contamination. A clear solution is not proof of purity, and a cloudy one is not always unusable if the peptide is designed to form suspensions. pH measurement can identify whether the solution matches the intended range, and buffer exchange may be needed when the original solvent is incompatible. Sterile filtration is sometimes used for microbial control, but filters can adsorb peptides and reduce concentration. Documentation of lot number, solvent, volume, date, and storage condition supports later traceability in laboratory records.
Once a peptide is in liquid form, its stability depends on temperature, pH, concentration, and the presence of oxygen or microbes. Refrigeration slows many degradation pathways, while freezing can extend storage for longer periods. Repeated freeze-thaw cycles are generally avoided because ice crystal formation and concentration changes can promote aggregation. Light exposure can also damage peptides that contain aromatic or sulfur-containing residues. A common laboratory practice is to divide a reconstituted stock into single-use aliquots before freezing, but the optimal storage condition remains peptide-specific and is often determined empirically.
Analytical checks help determine whether a reconstituted peptide matches its expected identity and purity; reverse-phase high-performance liquid chromatography separates components by hydrophobicity and can reveal degradation products or impurities. Mass spectrometry provides a mass measurement that supports sequence identity when compared with the theoretical value. Ultraviolet absorbance at 280 nm can estimate concentration for peptides containing tryptophan or tyrosine, though sequence-dependent extinction coefficients are needed. For shorter or non-aromatic peptides, other methods such as amino acid analysis may be required. These techniques describe the material rather than guarantee its biological effect.
Human ASH1L protein is 2969 amino acids long with a molecular weight of 333 kDa. ASH1L has an associated with SET domain (AWS), a SET domain, a post-set domain, a bromodomain, a bromo-adjacent homology domain, and a plant homeodomain finger (PHD finger). Human and Drosophila Ash1 share 66% and 77% similarity in their SET and PHD finger domains, respectively. A bromodomain is not present in Drosophila Ash1. The SET domain is responsible for ASH1L's histone methyltransferase (HMTase) activity. Unlike other proteins that contain a SET domain at their C terminus, ASH1L has a SET domain in the middle of the protein. The crystal structure of the human ASH1L catalytic domain, including the AWS, SET, and post-SET domains, has been solved to 2.9 angstrom resolution. The structure shows that the substrate binding pocket is blocked by a loop from the post-SET domain, and because mutation of the loop stimulates ASH1L HMTase activity, it was proposed that this loop serves a regulatory role.
Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging. Functions of a healthy kidney include maintaining a person's fluid balance, maintaining an acid-base balance; regulating sodium and other electrolytes; clearing toxins; regulating blood pressure; and regulating hormones, such as erythropoietin; and activation of vitamin D. The kidney is also involved in maintaining blood pH balance.
Chemistry... Key to Better Living. Diamond Jubilee Volume: A Record of Chemical Progress During the First 75 Years of the American Chemical Society. American Chemical Society. 1951. Skolnik, Herman; Reese, Kenneth M., eds. (1976). A Century of chemistry: the role of chemists and the American Chemical Society. Washington, D.C.: American Chemical Society. ISBN 978-0841203075. J. J. Bohning 2001. American Chemical Society Founded 1876. ACS, Washington, D.C. Reese, Kenneth M., ed. (2002). The American Chemical Society at 125: A recent history 1976–2001. American Chemical Society. ISBN 978-0-8412-3851-0. ACS website ACS Publications website ACS Chemical & Engineering News ACS Chemical Abstracts Service (CAS) International Year of Chemistry 2011(archived) A Cauldron Bubbles: PubChem and the American Chemical Society — Information Today, June 2005 ACS Chemical Biology WIKI(archived) ACS Chemical Biology Community(archived) ACS Green Chemistry Institute ACS Organic Division Leete Award Gassman Award
In order for a protonated acid to lose a proton, the pH of the system must rise above the pKa of the acid. The decreased concentration of H+ in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) solutions, there is a high enough H+ concentration in the solution to cause the acid to remain in its protonated form. Solutions of weak acids and salts of their conjugate bases form buffer solutions. To determine the concentration of an acid in an aqueous solution, an acid–base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added. The titration curve of an acid titrated by a base has two axes, with the base volume on the x-axis and the solution's pH value on the y-axis. The pH of the solution always goes up as the base is added to the solution.
Physiologic antagonism refers to the behaviour in which an antagonist behaves the opposite of the agonist but does not bind to the same active site as the agonist does. A physiologic antagonist binds to a different receptor but not the original agonist receptor. Both insulin and glucagon are synthesised naturally in the human body to regulate blood glucose levels at homeostasis. Insulin binds to insulin receptors to decrease blood glucose levels, whilst glucagon binds to glucagon receptors to increase blood glucose levels. In cases of insulin-induced hypoglycaemia, glucagon injection could help increase blood glucose levels. Another example is epinephrine (a bronchodilator) and histamine (a bronchoconstrictor). Epinephrine binds to adrenergic receptors to promote bronchodilation whilst histamine binds to histamine receptors which leads to bronchoconstriction. Since they have opposite effects in different pathways, they are considered physiological antagonists, and they are not advised to be taken together.
Sources: en.wikipedia.org
An investigational device exemption (IDE) allows an investigational device (i.e. a device that is the subject of a clinical study) to be used in order to collect safety and effectiveness data required to support a premarket approval (PMA) application or a premarket notification [510(k)] submission to Food and Drug Administration (FDA). Clinical studies are most often conducted to support a PMA. Only a small percentage of 510(k)'s require clinical data to support the application. Investigational use also includes clinical evaluation of certain modifications or new intended uses of legally marketed devices. All clinical evaluations of investigational devices, unless exempt, must have an approved IDE before the study is initiated. Clinical evaluation of devices that have not been cleared for marketing requires:
From studies and predictions such as Dreyer and Bennett's, it shows that the light chains and heavy chains are encoded by separate multigene families on different chromosomes. They are referred to as gene segments and are separated by non-coding regions. The rearrangement and organization of these gene segments during the maturation of B cells produce functional proteins. The entire process of rearrangement and organization of these gene segments is the vital source where our body immune system gets its capabilities to recognize and respond to variety of antigens.
Effective on new passenger cars sold in the United States after January 1, 1964. front outboard lap belts were required. On September 9, 1966, the National Traffic and Motor Vehicle Safety Act became law in the U.S., the first mandatory federal safety standards for motor vehicles. Effective in 1966, US-market passenger cars were required to be equipped with padded instrument panels, front and rear outboard lap belts, and white reverse (backup) lamps. In 1966, the U.S. established the United States Department of Transportation (DOT) with automobile safety as one of its purposes. The National Transportation Safety Board (NTSB) was created as an independent organization on April 1, 1967, but was reliant on the DOT for administration and funding. However, in 1975 the organization was made completely independent by the Independent Safety Board Act (in P.L. 93-633; 49 U.S.C. 1901). In 1967, equipment specifications by such major fleet purchasers as the City and County of Los Angeles, California, encouraged the voluntary installation in most new cars sold in the US of safety devices, systems, and design features including:
A transcriptor is a transistor-like device composed of DNA and RNA rather than a semiconducting material such as silicon. Prior to its invention in 2013, the transcriptor was considered an important component to build biological computers. To function, a modern computer needs three different capabilities: It must be able to store information, transmit information between components, and possess a basic system of logic. Prior to March 2013, scientists had successfully demonstrated the ability to store and transmit data using biological components made of proteins and DNA. Simple two-terminal logic gates had been demonstrated, but required multiple layers of inputs and thus were impractical due to scaling difficulties.
Unlike anandamide, formation of 2-AG is calcium-dependent and is mediated by the activities of phospholipase C (PLC) and diacylglycerol lipase (DAGL). 2-AG acts as a full agonist at the CB1 receptor. At a concentration of 0.3 nM, 2-AG induces a rapid, transient increase in intracellular free calcium in NG108-15 neuroblastoma X glioma cells through a CB1 receptor-dependent mechanism. 2-AG is hydrolyzed in vitro by monoacylglycerol lipase (MAGL), fatty acid amide hydrolase (FAAH), and the uncharacterized serine hydrolase enzymes ABHD2, ABHD6 and ABHD12. The exact contribution of each of these enzymes to the termination of 2-AG signaling in vivo is unknown, though it is estimated that MAGL is responsible for ~85% of this activity in the brain. There have been identified transport proteins for 2-arachidonoylglycerol and anandamide. These include the heat shock proteins (Hsp70s) and fatty acid binding proteins (FABPs).
Sources: en.wikipedia.org
Korvezee was the youngest of two daughters of the pastor Willem Korvezee (1858–1913) and his wife Baukje Andringa (1874–1952). Her older sister, Elisabeth “Bets” Korvezee, later became the first female national archivist in the Netherlands. After their father's death in 1913, the family lived in The Hague, where both sisters attended the third municipal HBS, known as the “HBS-voor-jongens” (boys’ HBS), and Antonia showed particular talent for mathematics. She went on to study chemical technology at the Delft Institute of Technology, graduating cum laude in 1922. She then worked as an assistant, first in the department of analytical chemistry and from 1924 to 1938 in the laboratory of Scheffer. Under Frans Everhardus Cornelis Scheffer, she completed her doctorate cum laude in 1930 with a thesis titled “Copper chlorides as a catalyst for the Deacon process.” Between 1930 and 1932, she spent two six-month periods in Paris conducting research on radioactivity in Marie Curie’s laboratory. In 1935, her temporary appointment at Delft was made permanent, and she was appointed lecturer in radioactive decay. Korvezee was passed over for a professorship three times, first nominated in 1936 for the chair of analytical chemistry, and again in 1940 for the chair of physical chemistry despite ranking third in the nomination process.
Transcriptional gene regulation process depends on many spatial and temporal factors in the nucleus such as global or local chromatin states, nucleosome positioning, TF binding, enhancer/promoter activities. Variant that alter the function of any of these biological processes may alter the gene regulation and cause phenotypic abnormality. Genetic variants that located in distal regulatory region can affect the binding motif of TFs, chromatin regulators and other distal transcriptional factors, which disturb the interaction between enhancer/silencer and its target gene.
Viral induction of apoptosis occurs when one or several cells of a living organism are infected with a virus, leading to cell death. Cell death in organisms is necessary for the normal development of cells and the cell cycle maturation. It is also important in maintaining the regular functions and activities of cells. Viruses can trigger apoptosis of infected cells via a range of mechanisms including:
The fragment molecular orbital method (FMO) was developed by Kazuo Kitaura and coworkers in 1999. FMO is deeply interconnected with the energy decomposition analysis (EDA) by Kazuo Kitaura and Keiji Morokuma, developed in 1976. The main use of FMO is to compute very large molecular systems by dividing them into fragments and performing ab initio or density functional quantum-mechanical calculations of fragments and their dimers, whereby the Coulomb field from the whole system is included. The latter feature allows fragment calculations without using caps. The mutually consistent field (MCF) method had introduced the idea of self-consistent fragment calculations in their embedding potential, which was later used with some modifications in various methods including FMO. There had been other methods related to FMO including the incremental correlation method by H. Stoll (1992). Later, other methods closely related to FMO were proposed including the kernel energy method of L. Huang and the electrostatically embedded many-body expansion by E. Dahlke, S. Hirata and later M. Kamiya suggested approaches also very closely related to FMO. Effective fragment molecular orbital (EFMO) method combines some features of the effective fragment potentials (EFP) and FMO. A detailed perspective on the fragment-based method development can be found in a review.
Though an effective antibiotic when all others fail, against extremely drug resistant infections, it has many side effects. including inhibition of monoamine oxidase, and as with other nitrofurans generally, minimum inhibitory concentrations also produce systemic toxicity, resulting in tremors, convulsions, peripheral neuritis, gastrointestinal disturbances, and depression of spermatogenesis. Nitrofurans are recognized by FDA as mutagens/carcinogens, and can no longer be used in food-producing animals in the United States as of 1991. Nitrofurazone Nitrofurantoin Norwich Pharmacal Co. & Others v Customs and Excise Commissioners Peptic ulcers and Helicobacter pylori
Sources: en.wikipedia.org
Short-term storage is often at 2 to 8 °C, while longer storage may use frozen aliquots at −20 °C or below. Repeated freeze-thaw cycles should be avoided because they can promote aggregation.
Cloudiness may indicate incomplete dissolution, aggregation, or precipitation. Gentle mixing, pH adjustment, or filtration can sometimes resolve it, but the cause should be identified before use.
Bacteriostatic water contains a preservative that can interfere with some assays or react with certain peptides. Sterile water or a defined buffer may be preferable depending on the downstream application.
Storage time depends on peptide sequence, concentration, solvent, and temperature. No single shelf life applies to all peptides. Stability should be determined by analytical testing for the specific preparation.