freeze-thaw raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-03-08. Anything still debated is marked as such rather than presented as settled.
After reconstitution, a peptide solution is typically stored under conditions that limit degradation. Cool temperatures slow hydrolysis and oxidation, while freezing can preserve samples for longer periods. Repeated freeze-thaw cycles may promote aggregation or precipitation, so aliquoting before freezing is a common laboratory practice. The optimal storage temperature depends on the peptide sequence, buffer composition, and expected duration. Solutions containing oxidizable residues may benefit from inert gas overlays or antioxidants, though compatibility with the specific peptide must be considered.
Aseptic technique matters because aqueous peptide solutions can support microbial growth. Sterile solvents, clean workspaces, and sterile filtration can reduce contamination. The choice of filter material and pore size must avoid peptide loss through adsorption, especially for hydrophobic or low-concentration samples. Visual inspection for particles, turbidity, or color change provides a simple initial check, but it cannot confirm identity or purity. Analytical methods such as reversed-phase high-performance liquid chromatography and mass spectrometry are used to verify composition and detect degradation products.
After a peptide is reconstituted, handling practices affect its chemical and physical stability over time. Aqueous solutions can support microbial growth unless they are prepared with aseptic technique or contain preservatives. Container material matters because peptides can adsorb to glass or plastic surfaces, reducing the amount available in solution. Repeated transfers increase exposure to air and potential contaminants, and temperature fluctuations can accelerate degradation. These factors are separate from the peptide's intrinsic sequence-based stability.
Storage conditions for reconstituted peptides are product-specific. Cool temperatures slow many degradation pathways, but freezing can concentrate solutes and promote aggregation. Light exposure can oxidize susceptible residues such as methionine, cysteine, or tryptophan. Oxygen in headspace can contribute to oxidation, while acidic or basic pH can drive hydrolysis and deamidation. The best storage condition for a given sequence is often determined empirically because general rules do not capture all sequence-specific effects.
| Property | Value | Notes |
|---|---|---|
| Typical storage temperature (lyophilized) | -20 °C or lower | Desiccant and sealed container limit moisture |
| Typical storage temperature (reconstituted) | 2-8 °C short term; frozen for longer | Freeze-thaw cycles may damage peptide |
| Appearance of solution | Clear to slightly opalescent | Turbidity or particles suggest aggregation or contamination |
| Identity method | Mass spectrometry | Confirms molecular mass and detects modifications |
| Purity method | Reversed-phase HPLC | Separates peptide from related impurities |
The choice of solvent depends on the peptide's sequence, charge, and solubility profile. Water is common for hydrophilic peptides, while aqueous mixtures containing acetonitrile, methanol, or a small amount of acid may be needed for hydrophobic or basic sequences. Adding the liquid to the powder, rather than the reverse, can reduce clumping and improve wetting. Gentle mixing or brief vortexing may help, but vigorous agitation can create foam and shear sensitive structures. Complete dissolution is judged by a clear solution with no visible particles.
Buffer components and ionic strength affect how a peptide dissolves and remains in solution. Some sequences require a defined pH range to avoid precipitation or aggregation, while others tolerate pure water. The optimal conditions are often determined empirically because solubility cannot be predicted reliably from sequence alone. Even when a peptide dissolves, the resulting solution may contain aggregates that are not visible to the eye. Analytical methods such as reversed-phase high-performance liquid chromatography and mass spectrometry are used to confirm identity and purity after reconstitution.
After reconstitution, peptide solutions are generally less stable than lyophilized powders, and hydrolysis, oxidation, deamidation, and aggregation can occur in solution. Stability depends on peptide sequence, concentration, pH, buffer composition, temperature, light exposure, and dissolved oxygen. Many research protocols store reconstituted solutions at 4 °C for short periods or at -20 °C or -80 °C for longer periods. Repeated freeze-thaw cycles can promote aggregation and loss of activity. The optimal storage condition is peptide-specific and often determined empirically rather than predicted from sequence alone.
Quality control after reconstitution often includes visual inspection for particulates, pH measurement, and concentration determination by ultraviolet absorbance at 280 nm when aromatic residues are present. Reverse-phase high-performance liquid chromatography can assess purity and reveal degradation peaks. Mass spectrometry confirms molecular identity and detects modifications such as oxidation or truncation. Size-exclusion chromatography can quantify aggregates and oligomers. These methods are established for many peptides but may require optimization for hydrophobic or chemically modified sequences.
Microbial contamination is a concern for aqueous peptide solutions, especially those without preservatives. Bacteriostatic water contains an antimicrobial preservative and is used in some laboratory settings, while sterile water lacks preservatives. Filtration through a sterile filter can reduce particulates and microbes, but some peptides adsorb to filter membranes. The effect of preservatives on peptide stability is peptide-dependent and not fully predictable. Documentation of lot number, solvent, date, and storage conditions supports traceability and reproducibility.
An estimated 160 TBq (about 250 kg) of technetium-99 was released into the environment by atmospheric nuclear tests. The amount of technetium-99 from civilian nuclear power released into the environment up to 1986 is estimated to be on the order of 1000 TBq (about 1600 kg), primarily by outdated methods of nuclear fuel reprocessing; most of this was discharged into the sea. In recent years, reprocessing methods have improved to reduce emissions, but the Sellafield plant, which operated until 2022, released an estimated 550 TBq (about 900 kg) from 1995–1999 into the Irish Sea; afterward the amount was limited by regulation to 90 TBq (about 140 kg) per year.
=== Energy intake === 5-HT2C receptor agonists reduce appetite by working on serotonin receptors in a region of the brain called the hypothalamus. Lorcaserin (Belviq) was FDA approved for weight loss but was withdrawn from the market because a safety clinical trial shows an increased occurrence of cancer. Cannabinoid receptor antagonists were developed to treat obesity because researchers noticed that cannabinoid agonists (such as THC, the main pharmacologically active component of cannabis), increased appetite. However, some drugs in this class such as rimonabant were withdrawn or ceased development due to concerns about mental health and suicide. More selective drugs—some are in development that act only in peripheral tissues, not the brain—may be able to achieve this result with fewer adverse effects. GLP-1 agonists such as tirzepatide, semaglutide, and liraglutide slow gastric emptying and also have neurologically driven effects on appetite. It is unknown if GLP-1 agonists or dual/triple agonists of GLP-1 and/or the glucagon or GIP receptors act solely by reducing energy intake or if they also increase energy expenditure. Setmelanotide is an agonist of the melanocortin 4 receptor and is used in people with certain rare genetic conditions that cause obesity. It is less effective and not approved for general obesity.
Bolivian officials also asserted that more than 1,660 antidrug operations during 1988 had resulted in the destruction of from 1,000 to 1,400 clandestine cocaine factories and laboratories (80 percent of them in Cochabamba and Santa Cruz departments), the confiscation of about 10,000 kilograms of cocaine, and the arrest of some 700 individuals. The minister of planning and coordination stated in December that 2,900 hectares of coca crops had been eradicated under the financial compensation program. Bolivia's anti-narcotics units apprehended several prominent traffickers in 1988. At the same time that the 1988 Antinarcotics Law was promulgated, the Umopar arrested Suárez at his hacienda in Beni Department. According to one theory, Suárez allowed himself to be arrested in a bid to avoid extradition to the United States. In October 1988, the Special Antinarcotics Forces captured an alleged drug "godfather," Mario Araoz Morales ("El Chichin"), by chance during a training exercise in a jungle area. In November antidrug police in the Chapare also arrested Rosa Flores de Cabrera, alias Rosa Romero de Humérez ("La Chola Rosa"), described as one of the most-wanted women in the Bolivian drugtrafficking network, with connections to the Medellín Cartel. In 1991, under pressure from the United States, Bolivia involved its military forces in anti-drugs actions, despite local opposition. Under the government of Jaime Paz Zamora (1989-1993), antidrug institutions were restructured, but Conalid remained the regulatory body.
Sources: en.wikipedia.org
Whereas testosterone is the major circulating androgen, DHT is the major androgen in the prostate gland. DHT levels in circulation are relatively low and only approximately 10% of those of circulating testosterone levels. Conversely, local concentrations of DHT in the prostate gland are 8- to 10-fold higher than circulating levels of DHT. This is due to high expression of 5α-reductase in the prostate gland, which very efficiently catalyzes the formation of DHT from testosterone such that over 90% of intraprostatic testosterone is converted into DHT. Relative to testosterone, DHT is 2.5- to 10-fold as potent as an AR agonist in bioassays, and hence, is a much stronger androgen in comparison. As such, AR signaling is exceptionally high in the prostate gland, and the effectiveness of bicalutamide monotherapy in the treatment of prostate cancer, which is roughly equivalent to that of gonadotropin-releasing hormone analogues (GnRH analogues), demonstrates a capacity of bicalutamide to strongly antagonize the AR. On the other hand, GnRH analogue monotherapy achieves only a 50 to 60% reduction in levels of DHT in the prostate gland, and combined androgen blockade (CAB), the combination of surgical castration or a GnRH analogue and bicalutamide, is significantly more effective than either modality alone in the treatment of prostate cancer.
== History == The origin of the term food noise is unknown, but it first appeared in a Google search in 2006. Google searches for “food noise” increased markedly in 2022, possibly due to the rising use of GLP-1 receptor agonist drugs (GLP-1 RA drugs) for weight loss. Growing public interest spurred attention from researchers, and the concept was first incorporated into a model of food cue reactivity (how the body and brain respond when a person sees, smells, or thinks about food) in 2023. However, other researchers do not see food cue reactivity as the sole trigger for food noise.
Ebselen (also called PZ 51, DR3305, and SPI-1005), is a synthetic organoselenium molecule under preliminary investigation as a drug candidate. It belongs to the class of compounds related to benzene and its derivatives. It is being developed by the Seattle biotechnology company, Sound Pharmaceuticals, Inc. It has also been reported to target tubulin, blocking its polymerization. Ebselen has been entered into clinical trials as a lead compound intended for the potential treatment of various diseases. Its most advanced clinical trial is a Phase III study in people with Meniere's disease, completed in July 2024. In vitro, ebselen is a mimic of glutathione peroxidase and reacts with peroxynitrite. It is purported to have antioxidant and anti-inflammatory properties.
=== Proteins === In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and i + 4, an alpha helix is formed. When the spacing is less, between positions i and i + 3, then a 310 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding). Bifurcated H-bond systems are common in alpha-helical transmembrane proteins between the backbone amide C=O of residue i as the H-bond acceptor and two H-bond donors from residue i + 4: the backbone amide N−H and a side-chain hydroxyl or thiol H+. The energy preference of the bifurcated H-bond hydroxyl or thiol system is −14 or 167 kJ/mol (−3.4 or 40 kcal/mol) respectively. This type of bifurcated H-bond provides an intrahelical H-bonding partner for polar side-chains, such as serine, threonine, and cysteine within the hydrophobic membrane environments. The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol, shift the protein folding equilibrium toward the folded state, in a concentration dependent manner.
Sources: en.wikipedia.org
In the cobalamins, cobalt normally exists in the trivalent state, Co(III). However, under reducing conditions, the cobalt center is reduced to Co(II) or even Co(I), which are usually denoted as B12r and B12s, for reduced and super reduced respectively. B12r and B12s can be prepared from cyanocobalamin by controlled potential reduction, or chemical reduction using sodium borohydride in alkaline solution, zinc in acetic acid, or by the action of thiols. Both B12r and B12s are stable indefinitely under oxygen-free conditions. B12r appears orange-brown in solution, while B12s appears bluish-green under natural daylight, and purple under artificial light. B12s is one of the most nucleophilic species known in aqueous solution. This property allows the convenient preparation of cobalamin analogs with different substituents, via nucleophilic attack on alkyl halides and vinyl halides. For example, cyanocobalamin can be converted to its analog cobalamins via reduction to B12s, followed by the addition of the corresponding alkyl halides, acyl halides, alkene or alkyne. Steric hindrance is the major limiting factor in the synthesis of the B12 coenzyme analogs. For example, no reaction occurs between neopentyl chloride and B12s, whereas the secondary alkyl halide analogs are too unstable to be isolated. This effect may be due to the strong coordination between benzimidazole and the central cobalt atom, pulling it down into the plane of the corrin ring. The trans effect determines the polarizability of the Co–C bond so formed.
=== Body mass index (BMI) === A body mass index (BMI) level not within normal range can also affect semen quality negatively. Being underweight, presented by a low BMI value, was observed in an analysis to decrease the total sperm count and semen volume. No significant changes were observed in sperm concentration and motility due to a low BMI. However, due to the lack of raw data, further research is needed to clarify the role of BMI in semen quality. On the other hand, an overweight (BMI of 25.9–29.9) or obese status (BMI over 30) is similarly associated with low semen quality through a decrease of semen volume, concentration, motility, count, and morphology. Alteration of sex hormone levels were also concluded to result from a high BMI status, with affected hormones such as inhibin B or testosterone observed to decrease in concentration, whereas estradiol was increased. The reduction in hormone levels can subsequently result in being diagnosed with hypogonadism.
Funding for research in this field was in part provided by the Muscular Dystrophy Association and the Acid Maltase Deficiency Association in the US and by the Association of Glycogen Storage Disease in the UK, as well as the International Pompe Association. John Crowley became involved in the fund-raising efforts in 1998 after two of his children were diagnosed with Pompe. He joined the company Novazyme in 1999, which was working on enzyme replacement treatment for Pompe. Novazyme was sold to Genzyme in 2001 for over US$100 million. The 2010 film Extraordinary Measures is based on Crowley's search for a cure. As of 2019, many biomedical companies are developing gene therapy in hopes of helping the body create alpha-glucosidase on its own. In 2021, in-utero enzyme replacement therapy infusions were provided to the fetus of an Ottawa, Ontario, mother who had had two previous children with Pompe disease. The medical team was a collaboration between Ottawa Hospital, Children's Hospital of Eastern Ontario, the University of California, San Francisco, and Duke University. The child, born in June 2021, is thriving as of November 2022.
Sources: en.wikipedia.org
Short-term storage is often at refrigerated temperatures, while longer storage may use freezing. Repeated freeze-thaw cycles are generally avoided because they can promote aggregation. Container material and headspace can also affect stability.
Mass spectrometry is commonly used to confirm molecular mass and detect modifications. Reversed-phase high-performance liquid chromatography can assess purity and separate related impurities. These methods are complementary rather than interchangeable.
Turbidity can indicate aggregation, precipitation, or microbial contamination. It may also result from incomplete dissolution or undissolved excipients. The cause is not identifiable from appearance alone.
There is no universal storage time because stability depends on sequence, solvent, pH, concentration, and temperature. Product-specific data or stability studies provide the most reliable guidance. In the absence of such data, short-term cold storage is common.