The short version of freeze-thaw cycling fits in a sentence. The long version — which is the one that helps — is below.
Reviewed 2025-11-29. Anything still debated is marked as such rather than presented as settled.
胸腺素α1（thymosin alpha 1，Tα1）是一种由28个氨基酸组成的酸性肽，N端被乙酰化，分子量约为3108道尔顿。该肽最早从牛胸腺组织提取物中分离，属于胸腺素组分5的一个成分。其序列在不同哺乳动物中高度保守，提示其具有基本的生物学功能。名称中的“α1”指其在电泳中的迁移位置，并非表示亚型编号。它既存在于胸腺，也存在于脾脏和淋巴结等免疫组织。
20世纪70年代，研究者从胸腺提取物中纯化出多种小肽，Tα1是其中被较早表征的一种。最初的制备依赖组织匀浆和层析步骤，产量低且成分复杂。随着固相肽合成技术成熟，实验室和工业界能够生产与天然序列一致的合成版本。合成肽的纯度可达95%以上，并可通过反相高效液相色谱和质谱进行鉴定。这一转变使研究不再依赖动物胸腺来源。
Quantifying thymosin alpha-1 in a sample usually relies on reverse-phase high-performance liquid chromatography. The peptide lacks strong chromophores, so detection often occurs at 214 nm, where the peptide backbone absorbs. Mass spectrometry provides confirmatory identification and can detect sequence variants or truncations. Immunoassays have been used in biological matrices, but they may cross-react with related fragments. For purity assessment, chromatographic peak area gives the main component percentage, while mass accuracy verifies molecular identity.
The lyophilized peptide is generally stable for extended periods when kept cold and dry. Once dissolved, aqueous solutions are less stable; hydrolysis, oxidation, and aggregation can degrade the material. Storage at -20 °C or lower slows these processes. Repeated freeze-thaw cycles are best avoided because they can promote aggregation. The exact shelf life depends on formulation, pH, and concentration, so stability studies are typically performed for each specific product.
Quality control for thymosin alpha-1 focuses on identity, purity, and potency. Identity is confirmed by mass spectrometry and amino acid analysis, while purity is assessed by chromatography with limits on related substances and residual solvents. Potency assays may use cell-based immune readouts, but these are not standardized across laboratories. Regulatory status differs by jurisdiction; no product is approved in the United States for clinical use, whereas some other countries register injectable forms for specific indications.
| Property | Value | Notes |
|---|---|---|
| 化学分类 | 线性肽 | 由28个氨基酸组成 |
| 分子量 | 约3108 Da | 合成版本一致 |
| 外观 | 白色至类白色粉末 | 冻干品 |
| 溶解度 | 易溶于水 | 微溶于有机溶剂 |
| 储存温度 | -20°C（冻干） | 溶解后2-8°C |
Lyophilized material is typically treated as a hygroscopic solid that should be brought to room temperature before the container is opened, which limits condensation on the powder. Reconstitution is commonly done with sterile water or a buffered diluent, and gentle mixing is preferred over vigorous agitation to reduce foaming and surface adsorption. Because peptides can bind to plastic and glass, diluents containing a small amount of carrier protein are sometimes used in laboratory work. Working solutions are generally aliquoted and prepared fresh rather than subjected to repeated freezing and thawing.
Stability depends on temperature, pH, and the number of freeze-thaw events the sample has experienced. Freeze-dried material is commonly held at -20 °C or colder, while reconstituted liquid is kept cold and used within a short window. Extreme pH and prolonged light exposure can promote deamidation, oxidation, or aggregation, particularly at asparagine and methionine positions. Adsorption to container walls can lower the measured concentration of a dilute solution even when the peptide molecules themselves remain intact.
Like most short peptides, thymosin alpha-1 is susceptible to hydrolysis under strongly acidic or basic conditions and to oxidation when exposed to air over long periods. The acetylated amino terminus blocks one common degradation route, which contributes to the molecule's relative robustness in solution. Lyophilized material generally retains potency for extended periods when kept cold and dry. Once reconstituted, aqueous solutions are less stable and are typically used within a defined window rather than held indefinitely at ambient temperature.
Routine handling calls for storage of the lyophilized powder at refrigerated temperatures, away from light, in a sealed container. Working solutions are often prepared in sterile water or buffer and kept cold between uses. Repeated freeze-thaw cycles are generally avoided because they can promote aggregation and loss of material. Laboratories usually record lot number, reconstitution date, and storage conditions so that any change in behavior can be traced to a specific preparation.
Thymosin alpha-1 is a synthetic peptide of 28 amino acids whose sequence matches the amino-terminal region of prothymosin alpha. The chain is acetylated at its first residue and contains one disulfide bridge between two cysteine residues, which folds the molecule into a compact loop. Its molecular formula, C129H215N33O55, corresponds to a monoisotopic mass of roughly 3,106 daltons. Material used in laboratories is made by solid-phase synthesis rather than isolated from animal tissue.
Early work on thymic extracts in the 1960s described a heat-stable acidic fraction containing many polypeptides. Separation of that mixture yielded individual components, and thymosin alpha-1 was named as one of them on the basis of assays for T-cell activity. The first preparations came from calf thymus, while subsequent research and clinical material has been chemically synthesized. Nomenclature in older papers is inconsistent, and the same peptide sometimes appears under different designations, which complicates literature searches.
Lyophilized thymosin alpha 1 is typically stored refrigerated at 2 to 8 degrees Celsius and kept away from light. Reconstituted solutions are less stable and are usually used promptly after preparation. Repeated freeze-thaw cycles are avoided because they can promote aggregation and loss of activity. The peptide adsorbs to some plastic and glass surfaces, so a carrier protein is often added to dilute working solutions. Manufacturer instructions and published protocols both govern handling.
Identity and purity testing for thymosin alpha 1 relies mainly on reversed-phase high-performance liquid chromatography and mass spectrometry. Chromatography separates the parent peptide from truncated or modified variants, while mass spectrometry confirms the expected molecular mass. Amino acid analysis and peptide mapping provide additional sequence confirmation. Counterion content, water content, and residual solvents are measured separately as part of specification testing. No single method captures every attribute, so laboratories combine several techniques.
=== Movement of NAPLs in the unsaturated zone === The unsaturated zone involves a porous media which consists of small particles, around which exist a thin film of water which acts as a membrane. The rest of the space between these particles consists of air. Thus, NAPLs can either remain as an immiscible hydrocarbon, dissolve into water, adsorb onto solid porous material, or vaporize into gaseous form. This four-phase model is highly variable and can even change within a particular site during different stages of site remediation. As such, it is important to continuously monitor the phase distribution on a case-by-case basis. Each of these phases differs in terms of their mobility and their available remediation techniques. The most mobile phases of NAPL are the volatilized/gaseous phase and the solubilized/aqueous phase, while the least mobile phases of NAPL are the adsorbed/solid phase and the immiscible liquid phase. Because of these complexities, flow is more difficult to measure in the unsaturated zone than in the saturated zone. Contamination of the unsaturated zone is dangerous because of both the potential to seep into the saturated zone, where aquifers are contained, and the potential to harm ecological life. Whether or not the NAPL reaches the saturated zone is determined by a parameter called residual saturation. Residual saturation is caused by capillary action, which immobilizes NAPLs and restricts their infiltration into the saturated zone.
Diuretics act primarily by reducing the reabsorption of sodium at different sites of the renal tubular system and consequently promoting the elimination of sodium and water with increased urine output.
Boletus edulis fruit bodies contain diverse phytochemicals, including 500 mg of ergosterol per 100 g of dried mushroom, and ergothioneine. The fruit bodies contain numerous polyphenols, especially a high content of rosmarinic acid, and organic acids (such as oxalic, citric, malic, succinic and fumaric acids), and alkaloids.
Sources: en.wikipedia.org
=== Mantle minerals === Ferropericlase (Mg,Fe)O, a solid solution of periclase (MgO) and wüstite (FeO), makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO3; it also is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction γ-(Mg,Fe)2SiO4 ⇌ (Mg,Fe)SiO3 + (Mg,Fe)O transforms γ-olivine into a mixture of silicate perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite. Silicate perovskite may form up to 93% of the lower mantle, and the magnesium iron form, (Mg,Fe)SiO3, is considered to be the most abundant mineral in the Earth, making up 38% of its volume.
== Definition == Urea and creatinine are nitrogenous end products of metabolism. Urea is the primary metabolite derived from dietary protein and tissue protein turnover. Creatinine is the product of muscle creatine catabolism. Both are relatively small molecules (60 and 113 daltons, respectively) that distribute throughout total body water. In Europe, the whole urea molecule is assayed, whereas in the United States only the nitrogen component of urea (the blood or serum urea nitrogen, i.e., BUN or SUN) is measured. The BUN, then, is roughly one-half (7/15 or 0.466) of the blood urea. The normal range of urea nitrogen in blood or serum is 5 to 20 mg/dl, or 1.8 to 7.1 mmol urea per liter. The range is wide because of normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis, and renal urea excretion. A BUN of 15 mg/dl would represent significantly impaired function for a woman in the thirtieth week of gestation. Her higher glomerular filtration rate (GFR), expanded extracellular fluid volume, and anabolism in the developing fetus contribute to her relatively low BUN of 5 to 7 mg/dl. In contrast, the rugged rancher who eats in excess of 125 g protein each day may have a normal BUN of 20 mg/dl. The normal serum creatinine (sCr) varies with the subject's body muscle mass and with the technique used to measure it. For the adult male, the normal range is 0.6 to 1.2 mg/dl, or 53 to 106 μmol/L by the kinetic or enzymatic method, and 0.8 to 1.5 mg/dl, or 70 to 133 μmol/L by the older manual Jaffé reaction.
As seen in Fig. 1, the engineered aldehyde tag consists of six amino acids. A set of organisms from all domains of life was chosen and the sequence homology of the sulfatase motif was determined. The sequence used is the best consensus for sequences found in bacteria, archaea, worms and higher vertebrates.
Sources: en.wikipedia.org
pressure The force applied perpendicular to the surface of an object per unit area. The SI unit for pressure is the pascal (Pa), though many other units of pressure are also commonly used in chemistry.
Enzyme inhibitors are molecules that reduce or abolish enzyme activity, while enzyme activators are molecules that increase the catalytic rate of enzymes. These interactions can be either reversible (i.e., removal of the inhibitor restores enzyme activity) or irreversible (i.e., the inhibitor permanently inactivates the enzyme).
== Gas separation discovery and development == At Innsbruck, Cremer researched the hydrogenation of acetylene and found difficulty separating two gases with similar adsorption heats using the common methods of the day. She was aware of the liquid absorption chromatography research going on at Innsbruck, so she thought of a parallel method to separate gases which used an inert carrier gas as the mobile phase. She developed mathematical relationships and equations and instrumentation for the first gas chromatograph. Separate components were detected by a thermal conductivity detector. She initially submitted a short academic paper in 1944 to Naturwissenschaften, which was accepted and she informed them that future experimental work would follow. The paper however was not published at the time, because the journal's printing press was destroyed during air bombardment. It was finally published thirty years later in 1976 at which point it was considered a historical document. In December 1944, the university's facilities were badly damaged in an air bombardment and after the war, Cremer, as a German citizen, was not allowed to use the limited facilities. Fritz Prior was one of her postwar students and a high school chemistry teacher. He chose her idea of the gas chromatograph for his dissertation. Until facilities at the University of Innsbruck were usable again, he used his high school's laboratory to continue Cremer's research with her.
Sources: en.wikipedia.org
它不是经典的内分泌激素，而是一种免疫调节肽。其作用主要通过局部免疫细胞间的信号传递实现，而非经血液循环作用于远隔器官。
天然胸腺素α1主要从胸腺组织提取，也可在脾脏和淋巴结中检出。目前研究和临床使用的多为化学合成版本，不再依赖动物组织。
胸腺素组分5是牛胸腺提取物的粗组分，包含多种肽。胸腺素α1是其中一种被纯化和表征的单一肽，具有明确的28个氨基酸序列。
Reverse-phase HPLC with ultraviolet detection at 214 nm is common. Mass spectrometry is used to confirm molecular identity and detect modifications. Immunoassays exist but may not distinguish the intact peptide from fragments.