The short version of freeze-thaw fits in a sentence. The long version — which is the one that helps — is below.
This page was last updated on 2026-01-06 and is reviewed periodically as new material appears.
After reconstitution, solutions are usually divided into single-use aliquots to avoid repeated freeze-thaw cycles. Aliquots should be labeled with peptide identity, concentration, solvent, and date, then stored at the temperature specified by the supplier or protocol. Many peptides tolerate -20 °C for short periods, while -80 °C is preferred for longer storage. Frost-free freezers are generally avoided because temperature fluctuations can stress samples. Aseptic technique and sterile filters reduce microbial contamination, though filtration can also remove aggregated material or bind some peptides.
Peptide handling begins with careful receipt and inventory. Containers should be inspected for damage, label information should match the certificate of analysis, and storage location should be recorded. Many lyophilized peptides are electrostatic and may cling to vial walls or weighing paper, which can complicate transfer. Allowing a cold vial to equilibrate to room temperature before opening reduces condensation on the contents. Clean tools, gloves, and a low-humidity workspace limit contamination and moisture exposure during manipulation.
Reconstitution is the process of dissolving a dried peptide in a suitable solvent. The choice of solvent depends on solubility, charge, and sequence; sterile water is common, while buffers or small amounts of organic solvent may be needed for hydrophobic peptides. Adding solvent gently down the vial wall and mixing by inversion or gentle swirling reduces foaming and shear. Vortexing or vigorous pipetting can denature some peptides or promote aggregation. The resulting solution should be visually inspected for particles, turbidity, and complete dissolution before use.
Light exposure can damage aromatic residues and certain labels, so amber vials or opaque containers are often used. pH control matters in solution, as extreme acidity or alkalinity accelerates backbone cleavage; buffers may also introduce ions that affect solubility. Microbial growth is a concern for aqueous preparations that lack preservatives, though many research peptides are handled in sterile or low-bioburden conditions. Container materials can adsorb peptides, particularly hydrophobic or positively charged sequences, reducing recovery. These factors interact, meaning storage decisions balance chemical stability, physical state, and intended use.
Peptides are short chains of amino acids whose physical and chemical stability depends on sequence, length, and conformation. The amide backbone can hydrolyze under acidic or basic conditions, while side chains such as methionine, cysteine, and tryptophan are prone to oxidation. Aggregation may occur when hydrophobic regions associate, especially near surfaces or at high concentration. Because these pathways differ among peptides, no single storage condition applies to all sequences. Stability studies therefore examine each peptide under defined temperature, pH, and humidity ranges.
Temperature is a primary variable because most degradation reactions slow as thermal energy decreases. Lyophilized powders are commonly held at -20 °C for routine work and at -80 °C for longer archival periods, though exact recommendations depend on the peptide. Solutions are less stable than dry powders in many cases, and repeated freeze-thaw cycles can promote aggregation or precipitation. Inert atmospheres, such as argon or nitrogen, can limit oxidation for oxygen-sensitive sequences. Desiccants reduce water activity, which lowers hydrolysis rates during storage.
| Property | Value | Notes |
|---|---|---|
| Reconstitution solvent | Sterile water or aqueous buffer | Organic cosolvent may be needed for hydrophobic sequences |
| pH adjustment | Sequence-dependent | Test small volumes before preparing the full solution |
| Filtration | 0.22 µm sterile filter | Can remove particles but may bind or remove aggregates |
| Aliquot size | Single-use volume | Reduces repeated freeze-thaw cycles |
| Post-reconstitution storage | -20 °C to -80 °C | Follow supplier or protocol; avoid frost-free cycles |
Cold-chain practice relies on documented temperature ranges, calibrated monitoring, and minimized excursions. Shipments may use insulated boxes, phase-change materials, or dry ice, with data loggers to record conditions. Upon receipt, the recipient should verify the logger trace and place items into long-term storage promptly. Repeated warming and cooling during transfers can be more harmful than a single controlled excursion. For solutions, dividing material into single-use aliquots reduces the number of thawing and refreezing events and limits repeated opening of the same container.
Handling begins before a peptide arrives at the bench. Containers should be inspected for cracks, loose caps, or visible moisture, and labels should record identity, lot, and receipt date. Lyophilized material is often allowed to equilibrate to room temperature before opening to prevent condensation on the powder. Gloves and a clean workspace reduce contamination and static-related loss. Once opened, the vial may be purged with inert gas and resealed if the peptide is sensitive to oxygen or humidity. These steps are procedural safeguards rather than guarantees of stability.
Reconstitution introduces new risks because the peptide contacts solvent, air, and container surfaces. The chosen solvent should match the peptide's solubility profile, and buffer salts, pH, and ionic strength can affect dissolution and subsequent stability. Gentle mixing is preferred over vigorous vortexing, which can create interfaces and shear. If the solution is not clear, the cause may be incomplete dissolution, aggregation, or insoluble counter-ions rather than a simple concentration problem. Filtration is sometimes used, but filters can adsorb peptides and alter measured concentration.
Temperature is a primary factor in peptide storage. Lower temperatures reduce molecular motion and slow degradation reactions, but freezing can concentrate solutes and promote aggregation. Lyophilized powders are commonly held at -20°C, whereas solutions are often kept at -80°C. Repeated freeze-thaw cycles are harmful because ice crystal formation and pH shifts can damage the peptide. The glass transition temperature of a lyophilized cake influences its stability; below this temperature, molecular mobility is restricted. For solutions, the choice between -20°C and -80°C depends on the peptide's sensitivity and the intended storage duration.
Moisture, oxygen, and light also affect peptide integrity. Lyophilized powders absorb water from the air, which can enable hydrolysis and conformational changes. Oxygen promotes oxidation of sensitive residues, so storage under inert gas or in sealed vials is common. Light exposure can cause photodegradation, particularly for peptides containing aromatic amino acids. Buffer choice and pH influence charge state and solubility; extremes of pH accelerate deamidation and hydrolysis. Adding stabilizers such as sugars or polyols can protect the peptide during freezing and drying. Optimal conditions are determined empirically for each peptide.
Peptides are short chains of amino acids that can undergo both chemical and physical degradation. Chemical pathways include hydrolysis of peptide bonds, oxidation of methionine or cysteine residues, deamidation of asparagine or glutamine, and isomerization of aspartate. Physical instability leads to aggregation, precipitation, or adsorption to surfaces. The rate of these processes depends on the peptide sequence, the formulation, and the storage environment. Because each peptide has a unique composition, no single storage condition applies to all peptides. Stability studies are therefore conducted to define suitable conditions for each specific molecule.
After reconstitution, solutions are usually divided into single-use aliquots to limit repeated handling. Each aliquot is stored at a temperature appropriate for the peptide, with -20 °C or -80 °C common for longer-term laboratory storage. Freeze-thaw cycles are minimized because they can cause aggregation, precipitation, or loss of activity. Temperature monitoring and documented storage conditions support reproducibility across experiments. When a peptide is removed from storage, it is typically allowed to equilibrate before opening to reduce condensation.
Receiving a peptide begins with recording its identity, lot number, quantity, and arrival condition. Dry material is often kept in sealed containers with desiccant and an inert headspace to limit moisture and oxygen. Containers should be compatible with the peptide and solvent; some peptides adsorb to certain plastics or glass. Labels should include date, concentration, solvent, and storage location. A centralized inventory with temperature logs helps prevent loss and mix-ups.
Container and environment choices matter. Peptides may adsorb to glass, plastic, or filter membranes, especially at low concentrations. Low-binding tubes and inert containers reduce loss. Moisture barriers include sealed bags with desiccant, and light protection uses amber vials or opaque wraps. Inert gas blankets can limit oxidation for sequences containing methionine, cysteine, or tryptophan. Buffers and pH also affect solution stability; extremes of pH accelerate hydrolysis and deamidation. These practices apply to research and manufacturing settings, not to any specific clinical use.
Peptides are short amino acid polymers whose stability depends on sequence, length, and chemical modifications. In dry form, most peptides are relatively stable because low water activity slows hydrolysis and other degradation. Residual moisture, oxygen, and light can still promote oxidation, deamidation, or aggregation over time. Storage recommendations therefore usually combine low temperature, desiccation, and protection from light. Because each peptide has distinct properties, no single condition fits every sequence.
The photosynthetic partners, or photobionts, of X. parietina belong to the green algal genus Trebouxia, including Trebouxia arboricola and T. irregularis. These algae also exist independently in nature, occurring on both lichen-colonized and lichen-free bark. A study found that the photobiont occupies 7% of the thallus volume in X. parietina. Pigmentation density in the upper cortex varies, regulating light exposure to the algae. The Trebouxia photobiont adjusts its photosynthetic activity seasonally, supporting X. parietina in sunlit environments. As sunlight increases in spring, the photobiont reduces chlorophyll levels and produces protective pigments to dissipate excess light as heat. Chlorophyll concentrations are lowest in spring and peak in winter, balancing light absorption and photoprotection throughout the year. X. parietina associates with diverse photobionts. It primarily partners with Trebouxia decolorans when growing on bark and with T. arboricola on rock. Even within local populations, genetically distinct photobionts often coexist in adjacent thalli. One study identified 36 algal genotypes among 38 epiphytic samples from a single site. Despite T. decolorans being assumed to reproduce asexually, multiple algal strains sometimes occur within a single thallus, suggesting photobiont switching or thallus fusion. This diversity may contribute to X. parietina's adaptability across varied environments. Although free-living algae are abundant, X. parietina selectively associates with Trebouxia species.
== Selected bibliography == Gitashri Naiya, Paromita Raha, Manas Mondal, Uttam Pal, Rajesh Saha, Susobhan Choudhury, Subrata Batabyal, Samir Kumar Pal, Dhananjay Bhattacharyya, Nakul Chandra Maiti, Siddhartha Roy (June 2016). "Conformational Selection Underpins Recognition of Multiple DNA sequences by Proteins and Consequent Functional Actions". Physical Chemistry Chemical Physics. 18 (31): 21618–21628. Bibcode:2016PCCP...1821618N. doi:10.1039/C6CP03278H. PMID 27426617.{{cite journal}}: CS1 maint: multiple names: authors list (link) Samir Kumar Pal, Susobhan Choudhury, Basusree Ghosh, Priya Singh, Raka Ghosh, Siddhartha Roy (June 2016). "Ultrafast Differential Flexibility of Cro-protein Binding Domains of Two Operator DNAs with Different Sequences". Physical Chemistry Chemical Physics. 18 (27): 17983–17990. Bibcode:2016PCCP...1817983C. doi:10.1039/C6CP02522F. PMID 27326896.{{cite journal}}: CS1 maint: multiple names: authors list (link) Sk Kayum Alam, Vinod Yadav, Swati Bajaj, Arindam Datta, Shamit Kumar Dutta, Madhumita Bhattacharyya, Santanu Bhattacharya, Subrata Debnath, Siddhartha Roy, Lisa A Boardman, Thomas Smyrk, Julian R. Molina, Saikat Chakrabarty, Shantanu Chowdhury, Debabrata Mukhopadhyay, Susanta Roychoudhury (April 2016). "DNA Damage-Induced Ephrin-B2 Reverse Signaling Promotes Chemoresistance and Drives EMT in Colorectal Carcinoma Harboring Mutant p53". Cell Death and Differentiation. 23 (4): 707–722. doi:10.1038/cdd.2015.133. PMC 4986638.
Robin Begley of the American Hospital Association said the case was likely to have a "chilling effect on the culture of safety in health care." The American Nurses Association, the American Association of Critical-Care Nurses, and the National Medical Association all expressed concern that Vaught's prosecution set a "dangerous precedent." The American Nurses Association stated:
=== Consumer Products === The General Product Safety Regulation (GPSR) is a European regulation on consumer protection. It replaces Directive 2001/95/EC on general product safety. The regulation is intended to ensure that products placed on the market in the European internal market do not endanger the health and safety of consumers through a high level of consumer protection. The GPSR mandates a risk-based approach to product safety, requiring manufacturers and other economic operators to conduct comprehensive risk assessments before placing products on the market. These assessments must consider:
=== Visas === Seeking to reverse a policy of Bolsonaro — which, according to the current government, made the decision to "break with the pattern of Brazilian migration policy, historically grounded in the principles of reciprocity and equal treatment" — the government instructed the Itamaraty to once again require visas for entry into Brazil by citizens of Australia, Canada, the United States, and Japan, just as these countries already do when it comes to Brazilian citizens. The decision was taken after consultations with the governments of these four countries regarding the possibility of also exempting Brazilians from visas, in accordance with the principle of reciprocity; a principle that the Ministry of Foreign Affairs had already defended since 2017, when it opposed a proposal by the Ministry of Tourism to permanently remove the visa requirement for these countries. The Itamaraty's decision had also taken into account a decree issued by then president Donald Trump in January 2017, intended to complicate the granting of visas to citizens of several countries, among which Brazil was included.
Sources: en.wikipedia.org
The influence of the art of Gandhara in some of the paintings at the Kizil Caves, dated to circa 500 CE, is considered as a consequence of the political unification of the area between Bactria and Kucha under the Hephthalites. The paintings of the Caves of the Painters have been carbon dated to 478–536 CE. Albert Grünwedel in 1912 considered that the murals of the "Cave of the Statues" had been "made by the same artists as those of the Cave of the Painters", and that they were in "pure Gandhara style". Also, a self-portraited painter in the Caves of the Statues, holding a cup of paint, has clothes which "exactly match" those of the painters in the "Cave of the Painters" (caftan, boots...). The clothing style of the painters at Kizil has often been described as Sasanian, but is now rather considered as Hephthalite due to the similarities with the figures in Bamiyan, Dilberjin Tepe or Balalyk Tepe. Grünwedel attributed both caves to the same "Stage I" period (500–600 CE). The main cella contains 18 scenes of the Buddha preaching. The niche must have contained a monumental statue of the Buddha, and paintings related to the Indrasala Cave narrative. The ceiling is prismatic, reproducing a type of architecture known from Bamiyan. The right corridor contained murals related to the War for the Relics and the Sharing of the relics of the Buddha, one of them showing armoured warriors on horses. The murals of the back corridor were almost entirely gone by 1912. Only a few traces remained, suggesting scenes of the Parinirvana.
Acid–base extraction is a subclass of liquid–liquid extractions and involves the separation of chemical species from other acidic or basic compounds. It is typically performed during the work-up step following a chemical synthesis to purify crude compounds and results in the product being largely free of acidic or basic impurities. A separatory funnel is commonly used to perform an acid-base extraction. Acid-base extraction utilizes the difference in solubility of a compound in its acid or base form to induce separation. Typically, the desired compound is changed into its charged acid or base form, causing it to become soluble in aqueous solution and thus be extracted from the non-aqueous (organic) layer. Acid-base extraction is a simple alternative to more complex methods like chromatography. It is not possible to separate chemically similar acids or bases using this simple method.
The International Atomic Energy Agency (IAEA) estimates that between 170 and 1,700 tonnes of depleted uranium was dropped in Iraq by the US military since 2003, whereas the UK reported firing 1.9 tonnes of depleted uranium weapons in Iraq In March 2023, the UK government confirmed it was sending DU rounds to Ukraine along with its Challenger 2 tanks with its 120mm ammunition during the Russian invasion.
== Medical uses == Canagliflozin is indicated to be used with diet and exercise to lower blood sugar in adults with type 2 diabetes; to reduce the risk of major heart-related events such as heart attack, stroke, or death in people with type 2 diabetes who have known heart disease; and to reduce the risk of end-stage kidney disease, worsening of kidney function, heart-related death, and being hospitalized for heart failure in certain people with type 2 diabetes and diabetic kidney disease. Canagliflozin is an anti-diabetic medication used to improve blood sugar control in people with type 2 diabetes. It is a third-line medication to metformin. Per the British National Formulary it is also less preferred than a sulfonylurea as of 2019, while the American Diabetes Association and European Association for the Study of Diabetes consider either a SGLT2 inhibitor or GLP-1 receptor agonist a reasonable second line medication in those with heart disease. Canagliflozin decreases HbA1c levels by 0.77% to 1.16% when given by itself, in combination with metformin, in combination with metformin and a sulfonylurea, in combination with metformin and pioglitazone, or in combination with insulin, from initial HbA1c levels of 7.8% to 8.1%. When added to metformin, canagliflozin does not appear worse than sitagliptin or glimepiride in reducing HbA1c levels, while canagliflozin maybe better than sitagliptin and glimiperide in decreasing HbA1c. It is unclear whether or not it has any unique cardiovascular benefits beyond lowering blood sugar.
== Structure == Most sv-LAAOs are reported as being homodimers with multiple subunits that have molecular weights around 50–70 kDa and the interaction between the subunits occurs via non-covalent interactions. Sv-LAAOs are present in the acidic, basic, and neutral forms of the protein. Studies that look at x-ray crystal structures have confirmed that sv-LAAOs are often found as functional dimers, with each dimer having three domains. The three domains are the substrate-binding site, FAD-binding site, and a helical domain. The substrate-binding site lies at the bottom of a funnel-shaped cavity approximately 25 Å deep, enabling substrate specificity among sv-LAAOs. Structural differences in active site topology likely account for species-dependent substrate preferences. Additionally, LAAOs are thermolabile, with cold inactivation and heat reactivation properties, necessitating specific storage and pre-activation conditions to preserve enzymatic activity. It has also been determined that the FAD prosthetic group becomes deeply entrenched in the enzyme structure, which allows for pervasive interactions with both neighboring atoms and conserved water molecules. Additionally, this flavin-containing prosthetic group has been classified as providing snake venom with its quintessential dark yellow coloration, which is shown in Figure 2. One unusual characteristic reported for sv-LAAOs regards the cold inactivation and heat reactivation properties of the protein. Thereby, most sv-LAAOs are considered to be thermolabile enzymes.
Sources: en.wikipedia.org
The concentration of free electrons is effectively zero as the electrons are transferred directly from the reductant to the oxidant. The standard electrode potential, E0 for the each half-reaction is related to the standard free energy change by
==== United States ==== The dietary reference intake for vitamin D issued in 2011 by the Institute of Medicine (IoM) (renamed National Academy of Medicine in 2015), superseded previous recommendations which were expressed in terms of adequate intake. The recommendations were formed assuming the individual has no skin synthesis of vitamin D because of inadequate sun exposure. The reference intake for vitamin D refers to total intake from food, beverages, and supplements, and assumes that calcium requirements are being met. The tolerable upper intake level (UL) is defined as "the highest average daily intake of a nutrient that is likely to pose no risk of adverse health effects for nearly all persons in the general population". Although ULs are believed to be safe, information on the long-term effects is incomplete and these levels of intake are not recommended for long-term consumption. For US food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For vitamin D labeling purposes, 100% of the daily value was 400 IU (10 μg), but in May 2016, it was revised to 800 IU (20 μg) to bring it into agreement with the recommended dietary allowance (RDA). A table of the old and new adult daily values is provided at Reference Daily Intake. In 2024, the Endocrine Society advised healthy adult under age 75 not to take vitamin D above the recommended daily amount unless there is a specific reason. It also advised against routine vitamin D blood testing for healthy adults.
== Academic career == Broadbent initially trained as an electronic engineer at the University of Canterbury, completing a Bachelor of Engineering degree with Honours (Electrical and Electronic). She worked at companies Transpower, Électricité de Tahiti, and Robotechnology before continuing her education with a graduate Diploma of Arts from Massey University, and Master of Arts and Doctor of Philosophy degrees at the University of Auckland. Her 2002 master's thesis was on the effects of stress, social support and beliefs on wound healing following surgery. Her PhD thesis, completed in 2005, was titled New approaches to the assessment of illness perceptions. Broadbent was promoted to full professor at the University of Auckland in 2019. Broadbent has worked on how robots might help in school situations, both in the classroom and the sick bay, and also how might robots help patients managing chronic lung condition COPD. About 75% of patients in a controlled trial found that having robot assistance at home helped with medication adherence and companionship. Her work on how writing can help recovery from injury and weightloss surgery has been featured in Scientific American Mind, Time magazine, and The Guardian.
Haptophytes are similar and closely related to cryptophytes or heterokontophytes. Their chloroplasts lack a nucleomorph, their thylakoids are in stacks of three, and they synthesize chrysolaminarin sugar, which are stored in granules completely outside of the chloroplast, in the cytoplasm of the haptophyte.
Sources: en.wikipedia.org
It should first equilibrate to room temperature in a sealed container to prevent condensation on the cold contents. Opening too soon can introduce moisture and reduce stability, and the waiting period depends on vial size and packaging.
Hydrophobic peptides may require buffers, organic cosolvents, or a stepwise solvent approach. Small amounts of acetonitrile, methanol, or dimethyl sulfoxide are sometimes used, followed by dilution into aqueous buffer. The exact solvent system should be tested for the specific sequence.
Single-use aliquots limit freeze-thaw cycling, which can cause aggregation, precipitation, or loss of activity. They also reduce repeated opening of the same container and lower contamination risk. Labeling each aliquot supports traceability and consistent use.
Freezing slows hydrolysis and oxidation by reducing molecular motion and available water. Lyophilized powders contain little moisture, so they can remain stable for extended periods when kept cold and dry. The exact temperature depends on peptide sequence and expected storage duration.