glass transition raises a handful of sensible questions. This page answers them in order, starting with the fundamentals and moving to applications.
Reviewed 2026-06-26. Anything still debated is marked as such rather than presented as settled.
Quality control for freeze-dried forms includes visual inspection, water content measurement, and reconstitution time. A satisfactory cake is typically uniform, porous, and intact, although minor shrinkage or cracking may be acceptable if specifications allow. Karl Fischer titration, thermal gravimetric analysis, and near-infrared spectroscopy are used to measure water content. Reconstitution is assessed by adding a specified diluent and recording the time and ease of dissolution. Microbiological and particulate tests are added when the product is sterile or intended for injection.
Stability of a lyophilized solid depends on water content, temperature, and the physical state of the formulation. Amorphous products may slowly absorb moisture and drop below their glass transition temperature, causing collapse or crystallization. Some proteins and peptides can aggregate even in a dry state, especially when exposed to heat or moisture. Accelerated stability studies at elevated temperature and humidity help estimate shelf life, but real-time data remain the basis for expiration dating.
The physics of freeze-drying couples heat transfer, mass transfer, and phase change. Heat supplied through the shelf must reach the sublimation front without melting the ice or degrading the product. Water vapor then travels through the already dried layer and leaves the chamber, where low pressure and cold traps keep it from returning. The dried layer acts as a resistance to vapor flow, so drying rate changes as the front recedes. Open questions remain about how pore structure and formulation heterogeneity affect drying uniformity at larger scales.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and concentrates dissolved solids. Primary drying then lowers chamber pressure so ice changes directly into vapor without passing through a liquid phase. Secondary drying raises the shelf temperature to remove bound water that remains after ice sublimation. The result is a dry, porous structure that can be reconstituted later.
Formulation composition influences whether freeze-drying produces an intact cake or a collapsed mass. Excipients such as sugars and polymers can raise the collapse temperature and provide bulk during drying. The critical temperature for primary drying is often the collapse temperature or the glass transition temperature of the maximally concentrated phase. If the product temperature exceeds this threshold, the frozen matrix may soften and lose structure. Established practice therefore links shelf temperature and chamber pressure to the formulation's thermal properties.
| Property | Value | Notes |
|---|---|---|
| Appearance | Porous cake or plug | Uniform structure suggests the drying cycle preserved the matrix. |
| Reconstitution time | Usually under 2 minutes | Depends on cake porosity, diluent volume, and excipient composition. |
| Water content range | 0.5–3% w/w | Common specification range; exact limits are product-specific. |
| Headspace oxygen | <1% v/v | Inert gas backfill reduces oxidation of sensitive materials. |
| Storage temperature | 2–8 °C or controlled room temperature | Choice depends on accelerated and real-time stability results. |
Reconstitution involves adding a suitable diluent, often sterile water or a buffer, to the dried cake. Gentle swirling or inversion helps dissolve the material without creating excessive foam. The time required for complete dissolution can range from seconds to several minutes and depends on the cake structure and the diluent. Improper reconstitution, such as vigorous shaking or using the wrong diluent, can cause protein aggregation or loss of activity. After reconstitution, the product may have a limited shelf life and should be used according to its labeling.
Lyophilized products are typically hygroscopic and require protection from moisture during storage. Manufacturers seal them in glass vials, often under vacuum or an inert gas such as nitrogen. The container closure system, including the stopper and crimp seal, must prevent water vapor ingress. Storage temperature varies from controlled room temperature to refrigerated or frozen conditions, depending on the formulation. Humidity-controlled environments are essential because even brief exposure to ambient air can degrade the product.
Freeze-drying is distinct from simple evaporation and from spray drying. Evaporation removes water at temperatures above freezing, while spray drying rapidly dries droplets in a heated gas stream. Lyophilization avoids high temperatures, which can be useful for heat-sensitive materials such as proteins, vaccines, and some foods. The porous cake produced by sublimation dissolves or rehydrates more quickly than a dense dried mass. Not all materials tolerate freezing or the pH shifts that can occur as solutes concentrate during ice formation.
Lyophilization removes water from a frozen material by sublimation under reduced pressure. The process begins with freezing, which converts liquid water into ice and fixes the structure of the sample. After freezing, primary drying lowers pressure so ice changes directly to vapor without passing through a liquid phase. Secondary drying then removes bound water that remains after ice sublimation. The result is a dry, porous solid that often retains its original shape.
The low pressure used during drying allows water vapor to move from the ice surface to a cold condenser. Energy supplied as heat drives sublimation but must stay below the collapse temperature of the frozen matrix. If the product becomes too warm, the frozen structure may soften or melt, reducing pore formation and slowing drying. Formulations often include bulking agents, stabilizers, or buffers to support a rigid cake. The final moisture content depends on formulation, freezing rate, and the length of secondary drying.
A 2004 essay on the relation between car colour and safety stated that no previous studies had been scientifically conclusive. Since then, a Swedish study found that pink cars are involved in the fewest and black cars are involved in the most crashes (Land transport NZ 2005). In Auckland New Zealand, a study found that there was a significantly lower rate of serious injury in silver cars, with higher rates in brown, black, and green cars. The Vehicle Colour Study, conducted by Monash University Accident Research Centre (MUARC) and published in 2007, analysed 855,258 crashes that occurring between 1987 and 2004 in the Australian states of Victoria and Western Australia that resulted in injury or in a vehicle being towed away. The study analysed risk by light condition. It found that in daylight, black cars were 12% more likely than white to be involved in a collision, followed by grey cars at 11%, silver cars at 10%, and red and blue cars at 7%, with no other colours found to be significantly more or less risky than white. At dawn or dusk, the risk ratio for black cars jumped to 47% more likely than white, and that for silver cars to 15%. In the hours of darkness, only red and silver cars were found to be significantly more risky than white, by 10% and 8% respectively.
Stability of isotopes is affected by the ratio of protons to neutrons, and also by presence of certain magic numbers of neutrons or protons which represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. As in the case of tin, a magic number for Z, the atomic number, tends to increase the number of stable isotopes for the element. Just as electrons have the lowest energy state when they occur in pairs in a given orbital, nucleons (both protons and neutrons) exhibit a lower energy state when their number is even, rather than odd. This stability tends to prevent beta decay (in two steps) of many even–even nuclides into another even–even nuclide of the same mass number but lower energy (and of course with two more protons and two fewer neutrons), because decay proceeding one step at a time would have to pass through an odd–odd nuclide of higher energy. Such nuclei thus instead undergo double beta decay (or are theorized to do so) with half-lives several orders of magnitude larger than the age of the universe. This makes for a larger number of stable even–even nuclides, which account for 150 of the 251 total. Stable even–even nuclides number as many as three isobars for some mass numbers, and up to seven isotopes for some atomic numbers.
== Side effects == The most common side effect in all insulin analogues is low blood sugar, while in more serious cases, side effects may include low blood potassium. Insulin allergies are also a concern, although they are not prevalent, affecting only about 2% of people in some form. Insulin analogues are generally considered safe during pregnancy, and many are used in the treatment of gestational diabetes.
=== Beginning of hostilities and responsibility === The cables also describe the chronology of events on 7 and 8 August. The cable, sent on 7 August from Tbilisi, described the hostilities which broke out on the evening of 6 August in Avnevi and Nuli as "atypical". The ambassador cited available evidence that South Ossetia was responsible for starting the conflict to which Georgia was reacting. The cable also noted the Georgian evacuation from Nuli on August 7. Later on 7 August, Deputy Foreign Minister Grigol Vashadze reported to the US Ambassador about the casualties among Georgian peacekeepers after 16:00. Vashadze told the Ambassador that "heavy Russian equipment was being moved south from Java - a military base north of the conflict zone, which Georgians have not seen – even in tense times – in the past." Ambassador told on the same day the Foreign Minister and the Deputy Minister of Defense "to remain calm, not overreact". The cable reported that OSCE monitors had reported the Georgian military deployment. When General Marat Kulakhmetov, the head of the Russian peacekeepers in Tskhinvali, met with Temur Iakobashvili, Kulakhmetov said that he "does not control anything" and that the South Ossetians were "shooting at the Georgians behind my back." Tefft wrote on 8 August, "As late as 22:30 Georgian Ministry of Defense and Ministry of Foreign Affairs officials were still hopeful that the unilateral cease-fire announced by President Saakashvili will hold.
Cave paintings from more than 3,500 years ago document burns and their management. The earliest Egyptian records on treating burns describes dressings prepared with milk from mothers of baby boys, and the 1500 BCE Edwin Smith Papyrus describes treatments using honey and the salve of resin. Many other treatments have been used over the ages, including the use of tea leaves by the Chinese documented to 600 BCE, pig fat and vinegar by Hippocrates documented to 400 BCE, and wine and myrrh by Celsus documented to the 1st century CE. French barber-surgeon Ambroise Paré was the first to describe different degrees of burns in the 1500s. Guillaume Dupuytren expanded these degrees into six different severities in 1832. The first hospital to treat burns opened in 1843 in London, England, and the development of modern burn care began in the late 1800s and early 1900s. During World War I, Henry D. Dakin and Alexis Carrel developed standards for the cleaning and disinfecting of burns and wounds using sodium hypochlorite solutions, which significantly reduced mortality. In the 1940s, the importance of early excision and skin grafting was acknowledged, and around the same time, fluid resuscitation and formulas to guide it were developed. In the 1970s, researchers demonstrated the significance of the hypermetabolic state that follows large burns. The "Evans formula", described in 1952, was the first burn resuscitation formula based on body weight and surface area (BSA) damaged.
Sources: en.wikipedia.org
== Immune system == Movement of cells is vital for the function of the immune system, and especially for antigen presenting cells. Dendritic cells (one of the main antigen presenting cells in the immune system), move towards the lymph nodes after phagocytizing an antigen in order to present the antigen to T cells. Chemokines influence these movements, especially CCL21, which is bound to lymphatic endothelial cell membranes. The influence is short range, but causes movement of the dendritic cells up a fixed chemical gradient. Other leukocytes also exhibit haptotactic movement: neutrophils undergo IL-8 mediated migration, while monocytes, basophils, eosinophils and some T cells are influenced by RANTES chemokines. In the autoimmune disorder rheumatoid arthritis and in osteoarthritis, the associated swelling and migration of neutrophils to the affected site has been shown to be linked to membrane bound midkine cytokine. This cytokine operates in a haptotactic fashion, attracting local neutrophils to the site of expression.
Aldi Süd, Lidl and Asda join Sainsbury's and Tesco in cutting the retail price of milk. Several thousand workers with the Environment Agency belonging to the UNISON trade union begin a three-day strike over pay and conditions. Coronation of Charles III and Camilla Official chinaware manufactured by the Royal Collection Trust, in Stoke-on-Trent is unveiled. Media, including BBC News, report that Sarah, Duchess of York has not been invited to the coronation. Some details of the Coronation Concert are revealed, with acts including Katy Perry, Lionel Richie and Take That confirmed as part of the line-up. 15 April The SNP's National Executive Committee orders a review of the party's transparency and governance. Merseyside Police say that 118 people have been arrested at Aintree Racecourse after protestors delay the start of the 2023 Grand National. The race, which is delayed by 14 minutes, is won by Corach Rambler, ridden by Derek Fox. 16 April – The building of all new smart motorways is cancelled over cost and safety concerns. 17 April The 2023 World Snooker Championship is disrupted by a protestor from Just Stop Oil who climbs onto the snooker table during a match between Robert Milkins and Joe Perry and pours orange powder over it. Two people are later arrested by South Yorkshire Police. The Parliamentary Commissioner for Standards is to investigate Prime Minister Rishi Sunak over a possible failure to declare an interest over a childcare company in which his wife has shares.
== Predicting from DNA/RNA sequences == In biology, proteins are produced by translation of messenger RNA (mRNA) with the protein sequence deriving from the sequence of codons in the mRNA. The mRNA is itself formed by the transcription of genes and may be further modified. These processes are sufficiently understood to use computer algorithms to automate predictions of protein sequences from DNA sequences, such as from whole-genome DNA-sequencing projects, and have led to the generation of large databases of protein sequences such as UniProt. Predicted protein sequences are an important resource for protein identification by mass spectrometry. Historically, short protein sequences (10 to 15 residues) determined by Edman degradation were back-translated into DNA sequences that could be used as probes or primers to isolate molecular clones of the corresponding gene or complementary DNA. The sequence of the cloned DNA was then determined and used to deduce the full amino-acid sequence of the protein.
Richard Küch (1860-1915) was able to melt quartz glass - the basis for UV radiation sources - for the first time in 1890 and founded the Heraeus Quarzschmelze. He developed the first quartz lamp (sun lamp) for generating UV radiation in 1904, thus laying the foundation for this form of light therapy. Despite the dosage problems, doctors increasingly used quartz lamps in the early 20th century. Internal medicine specialists and dermatologists were among the most eager testers. After successful treatment of skin tuberculosis, internal medicine began to treat tuberculous pleurisy, glandular tuberculosis and intestinal tuberculosis. In addition, doctors tested the effect of quartz lamps on other infectious diseases such as syphilis, metabolic diseases, cardiovascular diseases, nerve pain such as sciatica, or nervous diseases such as neurasthenia and hysteria. In dermatology, fungal diseases, ulcers and wounds, psoriasis, acne, freckles and hair loss were also treated with quartz lamps, while in gynecology, abdominal diseases were treated with quartz lamps. Rejuvenation specialists used artificial high-altitude sunlight to stimulate gonadal activity and treated infertility, impotentia generandi (inability to conceive), and lack of sexual desire by irradiating the genitals. For this purpose, Philipp Keller (1891-1973) developed an erythema dosimeter with which he measured the amount of radiation not in Finsen units (UV radiation with a wavelength λ of 296.7 nm and an irradiance E of 10−5 W/m2), but in height solar units (HSE).
Selected ion monitoring (SIM) is a mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted/detected by the instrument, as opposed to the full spectrum range. This mode of operation typically results in significantly increased sensitivity. Due to their inherent nature, this technique is most effective—and therefore most common—on quadrupole mass spectrometers, Orbitrap, and Fourier transform ion cyclotron resonance mass spectrometers.
Sources: en.wikipedia.org
=== Pharmacodynamics === As a glucocorticoid, the lipophilic structure of prednisolone allows for easy passage through the cell membrane where it then binds to its respective glucocorticoid receptor (GCR) located in the cytoplasm. Upon binding, the formation of the GC/GCR complex causes dissociation of chaperone proteins from the glucocorticoid receptor enabling the GC/GCR complex to translocate inside the nucleus. This process occurs within 20 minutes of binding. Once inside the nucleus, the homodimer GC/GCR complex binds to specific DNA binding sites known as glucocorticoid response elements (GREs) resulting in gene expression or inhibition. Complex binding to positive GREs leads to the synthesis of anti-inflammatory proteins while binding to negative GREs blocks the transcription of inflammatory genes. They inhibit the release of signals that promote inflammation such as nuclear factor-Kappa B (NF-κB), Activator protein 1 (AP-1), nuclear factor of activated T-cells (NFAT), and stimulate anti-inflammatory signals such as the interleukin-10 gene. All of them will collectively cause a sequence of events, including the inhibition of prostaglandin synthesis and additional inflammatory mediators. Glucocorticoids also inhibit neutrophil cell death and demargination. As well as phospholipase A2, which in turn lessens arachidonic acid derivative genesis.
=== January === 3 January – There were 931 patients without beds in Irish hospitals as the trolley crisis reached a record high. 4 January – The Irish data privacy board fined Meta Platforms €390 million for violations of the General Data Protection Regulation on Facebook and Instagram. 21 January – Thousands of people marched in Limerick to protest against continued overcrowding at University Hospital Limerick.
=== Electrochemical sensors === Electrochemical sensors can be used for label-free sensing of biomolecules. They detect changes and measure current between a probed metal electrode and an electrolyte containing the target analyte. A known potential to the electrode is then applied from a feedback current and the resulting current can be measured. For example, one technique using electrochemical sensing includes slowly raising the voltage causing chemical species at the electrode to be oxidized or reduced. Cell current vs voltage is plotted which can ultimately identify the quantity of chemical species consumed or produced at the electrode. Fluorescent tags can be used in conjunction with electrochemical sensors for ease of detection in a biological system.
In the north, either a single new state consisting of Schleswig-Holstein, Hamburg, Bremen and Lower Saxony should be created (solution A) or two new states, one in the northeast consisting of Schleswig-Holstein, Hamburg and the northern part of Lower Saxony (from Cuxhaven to Lüchow-Dannenberg) and one in the northwest consisting of Bremen and the rest of Lower Saxony (solution B). In the center and southwest, one alternative was that Rhineland-Palatinate (with the exception of the Germersheim district but including the Rhine-Neckar region) should be merged with Hesse and the Saarland (solution C), the district of Germersheim would then become part of Baden-Württemberg. The other alternative was that the Palatinate (including the region of Worms) could be merged with the Saarland and Baden-Württemberg, and the rest of Rhineland-Palatinate would then merge with Hesse (solution D). Both alternatives could be combined (AC, BC, AD, BD). At the same time, the commission developed criteria for classifying the terms of Article 29 Paragraph 1. The capacity to perform functions effectively was considered most important, whereas regional, historical, and cultural ties were considered as hardly verifiable. To fulfill administrative duties adequately, a population of at least five million per state was considered as necessary. After a relatively brief discussion and mostly negative responses from the affected states, the proposals were shelved. Public interest was limited or nonexistent. The referendum in Baden was held on 7 June 1970.
== Background == Glutathione plays a central role in cellular redox balance, detoxification, and immune regulation. Its synthesis depends on the availability of several amino acid substrates, of which cysteine is typically the rate-limiting precursor under physiological conditions. Free L-cysteine is chemically unstable and readily oxidized in the gastrointestinal tract, which can limit its effectiveness when administered directly as a supplement. For this reason, a variety of cysteine-delivery strategies have been explored, including N-acetylcysteine (NAC) and other cysteine prodrugs. D-Ribose-L-cysteine was developed as an alternative cysteine-delivery compound intended to improve cysteine stability and intracellular availability for glutathione synthesis.
Sources: en.wikipedia.org
Sealed vials or containers should be kept at the temperature specified by stability data, often controlled room temperature or 2–8 °C. Moisture and oxygen barriers are important because both can degrade sensitive materials. Opened containers may need immediate use or protection from ambient humidity.
It usually appears as a uniform porous plug or cake that fills the container without excessive shrinkage. Color should match the specification, and there should be no meltback or visible foreign matter. Minor cracking may be acceptable if the product still meets moisture and potency limits.
Water content is a key stability parameter because excess water can promote hydrolysis, aggregation, or cake collapse. It also affects reconstitution and product weight. Each product has a target range, and methods such as Karl Fischer titration are used to verify it.
Primary drying removes ice by sublimation at low pressure and low shelf temperature. Secondary drying removes bound water by raising the shelf temperature, often under the same vacuum. The two stages differ in the water state being removed.