Crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups. The most common crown ethers are cyclic oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e. –CH2CH2O–. Important members of this series are the tetramer, the pentamer, the hexamer; the term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, a crown sitting on a person's head. The first number in a crown ether's name refers to the number of atoms in the cycle, the second number refers to the number of those atoms that are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide. Crown ethers bind certain cations, forming complexes; the oxygen atoms are well situated to coordinate with a cation located at the interior of the ring, whereas the exterior of the ring is hydrophobic. The resulting cations form salts that are soluble in nonpolar solvents, for this reason crown ethers are useful in phase transfer catalysis; the denticity of the polyether influences the affinity of the crown ether for various cations.
For example, 18-crown-6 has high affinity for potassium cation, 15-crown-5 for sodium cation, 12-crown-4 for lithium cation. The high affinity of 18-crown-6 for potassium ions contributes to its toxicity. Crown ethers are not the only macrocyclic ligands. Ionophores such as valinomycin display a marked preference for the potassium cation over other cations. Crown ethers have been shown to coordinate to Lewis acids through electrostatic, σ-hole interactions, between the Lewis basic oxygen atoms of the crown ether and the electrophilic Lewis acid center. In 1967, Charles Pedersen, a chemist working at DuPont, discovered a simple method of synthesizing a crown ether when he was trying to prepare a complexing agent for divalent cations, his strategy entailed linking two catecholate groups through one hydroxyl on each molecule. This linking defines a polydentate ligand that could envelop the cation and, by ionization of the phenolic hydroxyls, neutralize the bound dication, he was surprised to isolate a by-product that complexed potassium cations.
Citing earlier work on the dissolution of potassium in 16-crown-4, he realized that the cyclic polyethers represented a new class of complexing agents that were capable of binding alkali metal cations. He proceeded to report systematic studies of the synthesis and binding properties of crown ethers in a seminal series of papers; the fields of organic synthesis, phase transfer catalysts, other emerging disciplines benefited from the discovery of crown ethers. Pedersen popularized the dibenzo crown ethers. Pedersen shared the 1987 Nobel Prize in Chemistry for the discovery of the synthetic routes to, binding properties of, crown ethers. Apart from its high affinity for potassium cations, 18-crown-6 can bind to protonated amines and form stable complexes in both solution and the gas phase; some amino acids, such as lysine, contain a primary amine on their side chains. Those protonated amino groups can bind to the cavity of 18-crown-6 and form stable complexes in the gas phase. Hydrogen-bonds are formed between the three hydrogen atoms of protonated amines and three oxygen atoms of 18-crown-6.
These hydrogen-bonds make the complex a stable adduct. By incorporating luminescent substituents into their backbone, these compounds have proved to be sensitive ion probes, as changes in the absorption or fluorescence of the photoactive groups can be measured for low concentrations of metal present; some attractive examples include macrocycles, incorporating oxygen and/or nitrogen donors, that are attached to polyaromatic species such as anthracenes or naphthalenes. 21- and 18-membered diazacrown ether derivatives exhibit excellent calcium and magnesium selectivities and are used in ion-selective electrodes. Some or all of the oxygen atoms in crown ethers can be replaced by nitrogens to form cryptands. A well-known tetrazacrown is cyclen. Lariat crown ethers have sidearms; the lariat is attached to an amine centre in an azacrown. 9-Crown-3 Cryptand Metallacrown Pedersen, Charles. "Nobel Lecture". Nobel Prize. Molecular crown
Sodium bromide is an inorganic compound with the formula NaBr. It is a high-melting crystalline solid that resembles sodium chloride, it is a used source of the bromide ion and has many applications. NaBr crystallizes in the same cubic motif as NaCl, NaF and NaI; the anhydrous salt crystallizes above 50.7 °C. Dihydrate salts crystallize out of water solution below 50.7 °C. NaBr is produced by treating sodium hydroxide with hydrogen bromide. Sodium bromide can be used as a source of the chemical element bromine; this can be accomplished by treating an aqueous solution of NaBr with chlorine gas: 2 NaBr + Cl2 → Br2 + 2 NaCl Sodium bromide is the most useful inorganic bromide in industry. It is used as a catalyst in TEMPO-mediated oxidation reactions. Known as Sedoneural, sodium bromide has been used as a hypnotic and sedative in medicine used as an anticonvulsant and a sedative in the late 19th and early 20th centuries, its action is due to the bromide ion, for this reason potassium bromide is effective.
In 1975, bromides were removed from drugs in the U. S. such as Bromo-Seltzer due to toxicity. Sodium bromide is used for the preparation of other bromides in organic synthesis and other areas, it is a source of the bromide nucleophile to convert alkyl chlorides to more reactive alkyl bromides by the Finkelstein reaction: NaBr + RCl → RBr + NaCl Once a large need in photography, but now shrinking, the photosensitive salt silver bromide is prepared using NaBr. Sodium bromide is used in conjunction with chlorine as a disinfectant for hot tubs and swimming pools. Sodium bromide is used to prepare dense fluids used in oil wells. NaBr has a low toxicity with an oral LD50 estimated at 3.5 g/kg for rats. However, this is a single-dose value. Bromide ion is a cumulative toxin with a long half life: see potassium bromide. Information about NaBr. Bromide Poisoning in Angola
Green chemistry called sustainable chemistry, is an area of chemistry and chemical engineering focused on the designing of products and processes that minimize the use and generation of hazardous substances. Whereas environmental chemistry focuses on the effects of polluting chemicals on nature, green chemistry focuses on the environmental impact of chemistry, including technological approaches to preventing pollution and reducing consumption of nonrenewable resources; the overarching goals of green chemistry—namely, more resource-efficient and inherently safer design of molecules, materials and processes—can be pursued in a wide range of contexts. Green chemistry emerged from a variety of existing ideas and research efforts in the period leading up to the 1990s, in the context of increasing attention to problems of chemical pollution and resource depletion; the development of green chemistry in Europe and the United States was linked to a shift in environmental problem-solving strategies: a movement from command and control regulation and mandated reduction of industrial emissions at the "end of the pipe," toward the active prevention of pollution through the innovative design of production technologies themselves.
The set of concepts now recognized as green chemistry coalesced in the mid- to late-1990s, along with broader adoption of the term. In the United States, the Environmental Protection Agency played a significant early role in fostering green chemistry through its pollution prevention programs and professional coordination. At the same time in the United Kingdom, researchers at the University of York contributed to the establishment of the Green Chemistry Network within the Royal Society of Chemistry, the launch of the journal Green Chemistry. In 1998, Paul Anastas and John C. Warner published a set of principles to guide the practice of green chemistry; the twelve principles address a range of ways to reduce the environmental and health impacts of chemical production, indicate research priorities for the development of green chemistry technologies. The principles cover such concepts as: the design of processes to maximize the amount of raw material that ends up in the product; the twelve principles of green chemistry are: Prevention.
Preventing waste is better than cleaning up waste after it is created. Atom economy. Synthetic methods should try to maximize the incorporation of all materials used in the process into the final product. Less hazardous chemical syntheses. Synthetic methods should avoid using or generating substances toxic to humans and/or the environment. Designing safer chemicals. Chemical products should be designed to achieve their desired function while being as non-toxic as possible. Safer auxiliaries. Auxiliary substances should be avoided wherever possible, as non-hazardous as possible when they must be used. Design for energy efficiency. Energy requirements should be minimized, processes should be conducted at ambient temperature and pressure whenever possible. Use of renewable feedstocks. Whenever it is practical to do so, renewable feedstocks or raw materials are preferable to non-renewable ones. Reduce derivatives. Unnecessary generation of derivatives—such as the use of protecting groups—should be minimized or avoided if possible.
Catalysis. Catalytic reagents that can be used in small quantities to repeat a reaction are superior to stoichiometric reagents. Design for degradation. Chemical products should be designed. Real-time analysis for pollution prevention. Analytical methodologies need to be further developed to permit real-time, in-process monitoring and control before hazardous substances form. Inherently safer chemistry for accident prevention. Whenever possible, the substances in a process, the forms of those substances, should be chosen to minimize risks such as explosions and accidental releases. Attempts are being made not only to quantify the greenness of a chemical process but to factor in other variables such as chemical yield, the price of reaction components, safety in handling chemicals, hardware demands, energy profile and ease of product workup and purification. In one quantitative study, the reduction of nitrobenzene to aniline receives 64 points out of 100 marking it as an acceptable synthesis overall whereas a synthesis of an amide using HMDS is only described as adequate with a combined 32 points.
Green chemistry is seen as a powerful tool that researchers must use to evaluate the environmental impact of nanotechnology. As nanomaterials are developed, the environmental and human health impacts of both the products themselves and the processes to make them must be considered to ensure their long-term economic viability. Solvents are consumed in large quantities in many chemical syntheses as well as for cleaning and degreasing. Traditional solvents are toxic or are chlorinated. Green solvents, on the other hand, are derived from renewable resources and biodegrade to innocuous a occurring product. Novel or enhanced synthetic techniques can provide improved environment
Chemistry is the scientific discipline involved with elements and compounds composed of atoms and ions: their composition, properties and the changes they undergo during a reaction with other substances. In the scope of its subject, chemistry occupies an intermediate position between physics and biology, it is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry, the formation of igneous rocks, how atmospheric ozone is formed and how environmental pollutants are degraded, the properties of the soil on the moon, how medications work, how to collect DNA evidence at a crime scene. Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron; the word chemistry comes from alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, philosophy, astronomy and medicine.
It is seen as linked to the quest to turn lead or another common starting material into gold, though in ancient times the study encompassed many of the questions of modern chemistry being defined as the study of the composition of waters, growth, disembodying, drawing the spirits from bodies and bonding the spirits within bodies by the early 4th century Greek-Egyptian alchemist Zosimos. An alchemist was called a'chemist' in popular speech, the suffix "-ry" was added to this to describe the art of the chemist as "chemistry"; the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία; this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, in turn derived from the word Kemet, the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία, meaning "cast together"; the current model of atomic structure is the quantum mechanical model. Traditional chemistry starts with the study of elementary particles, molecules, metals and other aggregates of matter.
This matter can be studied in isolation or in combination. The interactions and transformations that are studied in chemistry are the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together; such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware; however glassware is not central to chemistry, a great deal of experimental chemistry is done without it. A chemical reaction is a transformation of some substances into one or more different substances; the basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation, which involves atoms as subjects; the number of atoms on the left and the right in the equation for a chemical transformation is equal. The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws.
Energy and entropy considerations are invariably important in all chemical studies. Chemical substances are classified in terms of their structure, phase, as well as their chemical compositions, they can be analyzed using the tools of e.g. spectroscopy and chromatography. Scientists engaged in chemical research are known as chemists. Most chemists specialize in one or more sub-disciplines. Several concepts are essential for the study of chemistry; the particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. Matter can be a mixture of substances; the atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space occupied by an electron cloud; the nucleus is made up of positively charged protons and uncharged neutrons, while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons.
The nucleus is dense. The atom is the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state, coordination number, preferred types of bonds to form. A chemical element is a pure substance, composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z; the mass number is the sum of the number of neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same
A detergent is a surfactant or a mixture of surfactants with cleaning properties in dilute solutions. These substances are alkylbenzenesulfonates, a family of compounds that are similar to soap but are more soluble in hard water, because the polar sulfonate is less than the polar carboxylate to bind to calcium and other ions found in hard water. In most household contexts, the term detergent by itself refers to laundry detergent or dish detergent, as opposed to hand soap or other types of cleaning agents. Detergents are available as powders or concentrated solutions. Detergents, like soaps, work because they are amphiphilic: hydrophilic and hydrophobic, their dual nature facilitates the mixture of hydrophobic compounds with water. Because air is not hydrophilic, detergents are foaming agents to varying degrees. Detergents are classified into three broad groupings, depending on the electrical charge of the surfactants. Typical anionic detergents are alkylbenzenesulfonates; the alkylbenzene portion of these anions is lipophilic and the sulfonate is hydrophilic.
Two different varieties have been popularized, those with branched alkyl groups and those with linear alkyl groups. The former were phased out in economically advanced societies because they are poorly biodegradable. An estimated 6 billion kilograms of anionic detergents are produced annually for domestic markets. Bile acids, such as deoxycholic acid, are anionic detergents produced by the liver to aid in digestion and absorption of fats and oils. Cationic detergents that are similar to the anionic ones, with a hydrophilic component, instead of the anionic sulfonate group, the cationic surfactants have quaternary ammonium as the polar end; the ammonium sulfate center is positively charged. Non-ionic detergents are characterized by their hydrophilic headgroups. Typical non-ionic detergents are based on a glycoside. Common examples of the former include Tween and the Brij series; these materials are known as ethoxylates or PEGylates and their metabolites, nonylphenol. Glycosides have a sugar as their uncharged hydrophilic headgroup.
Examples maltosides. HEGA and MEGA series detergents are similar. Zwitterionic detergents possess a net zero charge arising from the presence of equal numbers of +1 and −1 charged chemical groups. Examples include CHAPS. See surfactants for more applications. In World War I, there was a shortage of oils. Synthetic detergents were first made in Germany. One of the largest applications of detergents is for household and shop cleaning including dish washing and washing laundry; the formulations are complex, reflecting the diverse demands of the application and the competitive consumer market. Both carburetors and fuel injector components of Otto engines benefit from detergents in the fuels to prevent fouling. Concentrations are about 300 ppm. Typical detergents are long-chain amines and amides such as polyisobuteneamine and polyisobuteneamide/succinimide. Reagent grade detergents are employed for the isolation and purification of integral membrane proteins found in biological cells. Solubilization of cell membrane bilayers requires a detergent that can enter the inner membrane monolayer.
Advancements in the purity and sophistication of detergents have facilitated structural and biophysical characterization of important membrane proteins such as ion channels the disrupt membrane by binding Lipopolysaccharide, signaling receptors, photosystem II. Soap Cleavable detergent Dishwashing liquid Dispersant Green cleaning Hard-surface cleaner Laundry detergent List of cleaning products Triton X-100 About.com: How Do Detergents Clean Campbell tips for detergents chemistry and history related to laundry washing, destaining methods and soil
Polyethylene glycol is a polyether compound with many applications, from industrial manufacturing to medicine. PEG is known as polyethylene oxide or polyoxyethylene, depending on its molecular weight; the structure of PEG is expressed as H−n−OH. PEG is the basis of a number of laxatives. Whole bowel irrigation with polyethylene glycol and added electrolytes is used for bowel preparation before surgery or colonoscopy. PEG is used as an excipient in many pharmaceutical products; when attached to various protein medications, polyethylene glycol allows a slowed clearance of the carried protein from the blood. The possibility that PEG could be used to fuse nerve cells is being explored by researchers studying spinal cord injury; because PEG is hydrophilic molecule, it has been used to passivate microscope glass slides for avoiding non-specific sticking of proteins in single-molecule fluorescence studies. Polyethylene glycol is used in a variety of products; the polymer is used as a lubricating coating for various surfaces in aqueous and non-aqueous environments.
Since PEG is a flexible, water-soluble polymer, it can be used to create high osmotic pressures. It is unlikely to have specific interactions with biological chemicals; these properties make PEG one of the most useful molecules for applying osmotic pressure in biochemistry and biomembranes experiments, in particular when using the osmotic stress technique. Polyethylene glycol is commonly used as a polar stationary phase for gas chromatography, as well as a heat transfer fluid in electronic testers. PEG has been used to preserve objects that have been salvaged from underwater, as was the case with the warship Vasa in Stockholm, similar cases, it replaces water in wooden objects, making the wood dimensionally stable and preventing warping or shrinking of the wood when it dries. In addition, PEG is used when working with green wood as a stabilizer, to prevent shrinkage. PEG has been used to preserve the painted colors on Terracotta Warriors unearthed at a UNESCO World Heritage site in China; these painted artifacts were created during the Qin Shi Huang Di dynasty.
Within 15 seconds of the terra-cotta pieces being unearthed during excavations, the lacquer beneath the paint begins to curl after being exposed to the dry Xian air. The paint would subsequently flake off in about four minutes; the German Bavarian State Conservation Office developed a PEG preservative that when applied to unearthed artifacts has aided in preserving the colors painted on the pieces of clay soldiers. PEG is used in mass spectrometry experiments, with its characteristic fragmentation pattern allowing accurate and reproducible tuning. PEG derivatives, such as narrow range ethoxylates, are used as surfactants. PEG can be reacted with an isocyanate to make polyurethane. PEG has been used as the hydrophilic block of amphiphilic block copolymers used to create some polymersomes. PEG is used as a crowding agent in in vitro assays to mimic crowded cellular conditions. PEG is used as a precipitant for plasmid DNA isolation and protein crystallization. X-ray diffraction of protein crystals can reveal the atomic structure of the proteins.
PEG is used to fuse two different types of cells, most B-cells and myelomas in order to create hybridomas. César Milstein and Georges J. F. Köhler originated this technique, which they used for antibody production, winning a Nobel Prize in Physiology or Medicine in 1984. Polymer segments derived from PEG polyols impart flexibility to polyurethanes for applications such as elastomeric fibers and foam cushions. In microbiology, PEG precipitation is used to concentrate viruses. PEG is used to induce complete fusion in liposomes reconstituted in vitro. Gene therapy vectors can be PEG-coated to shield them from inactivation by the immune system and to de-target them from organs where they may build up and have a toxic effect; the size of the PEG polymer has been shown to be important, with larger polymers achieving the best immune protection. PEG is a component of stable nucleic acid lipid particles used to package siRNA for use in vivo. In blood banking, PEG is used as a potentiator to enhance detection of antibodies.
When working with phenol in a laboratory situation, PEG 300 can be used on phenol skin burns to deactivate any residual phenol. In biophysics, polyethylene glycols are the molecules of choice for the functioning ion channels diameter studies, because in aqueous solutions they have a spherical shape and can block ion channel conductance. PEG is the basis of personal lubricants. PEG is used in a number of toothpastes as a dispersant. In this application, it binds water and helps keep xanthan gum uniformly distributed throughout the toothpaste. PEG is under investigation for use in body armor, in tattoos to monitor diabetes. In low-molecular-weight formulations, it is used in Hewlett-Packard designjet printers as an ink solvent and lubricant for the print heads. PEG is one of the main ingredients in paintball fills, because of its thickness and flexibility. However, as early as 2006, some paintball manufacturers began substituting cheaper oil-based alternatives for PEG. PEG is used as an anti-foaming agent in food – its INS number is 1521 or E1521 in the EU.
A nitrate ester-plasticized polyethylene glycol is used in Trident II submarine-launched ballistic missile solid rocket fuel. Dimethyl ethers of PEG are the key ingredient of Selexol, a solvent used by co
In the physical sciences, a phase is a region of space, throughout which all physical properties of a material are uniform. Examples of physical properties include density, index of refraction and chemical composition. A simple description is that a phase is a region of material, chemically uniform, physically distinct, mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, the humid air is a third phase over the ice and water; the glass of the jar is another separate phase. The term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter; the term phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. Because phase boundaries relate to changes in the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal structure to another, this latter usage is similar to the use of "phase" as a synonym for state of matter.
However, the state of matter and phase diagram usages are not commensurate with the formal definition given above and the intended meaning must be determined in part from the context in which the term is used. Distinct phases may be described as different states of matter such as gas, solid, plasma or Bose–Einstein condensate. Useful mesophases between solid and liquid form other states of matter. Distinct phases may exist within a given state of matter; as shown in the diagram for iron alloys, several phases exist for both the liquid states. Phases may be differentiated based on solubility as in polar or non-polar. A mixture of water and oil will spontaneously separate into two phases. Water has a low solubility in oil, oil has a low solubility in water. Solubility is the maximum amount of a solute that can dissolve in a solvent before the solute ceases to dissolve and remains in a separate phase. A mixture can separate into more than two liquid phases and the concept of phase separation extends to solids, i.e. solids can form solid solutions or crystallize into distinct crystal phases.
Metal pairs that are mutually soluble can form alloys, whereas metal pairs that are mutually insoluble cannot. As many as eight immiscible liquid phases have been observed. Mutually immiscible liquid phases are formed from water, hydrophobic organic solvents, silicones, several different metals, from molten phosphorus. Not all organic solvents are miscible, e.g. a mixture of ethylene glycol and toluene may separate into two distinct organic phases. Phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of immiscible phase pair combinations that do not physically separate. Left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ. Water in a closed jar with an air space over it forms a two phase system. Most of the water is in the liquid phase, where it is held by the mutual attraction of water molecules.
At equilibrium molecules are in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to break away from the liquid phase and enter the gas phase. Every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid. At equilibrium and condensation processes balance and there is no net change in the volume of either phase. At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%; this percentage increases. At 100 °C and atmospheric pressure, equilibrium is not reached. If the liquid is heated a little over 100 °C, the transition from liquid to gas will occur not only at the surface, but throughout the liquid volume: the water boils. For a given composition, only certain phases are possible at pressure; the number and type of phases that will form is hard to predict and is determined by experiment. The results of such experiments can be plotted in phase diagrams; the phase diagram shown here is for a single component system.
In this simple system, which phases that are possible depends only on pressure and temperature. The markings show points. At temperatures and pressures away from the markings, there will be only one phase at equilibrium. In the diagram, the blue line marking the boundary between liquid and gas does not continue indefinitely, but terminates at a point called the critical point; as the temperature and pressure approach the critical point, the properties of the liquid and gas become progressively more similar. At the critical point, the liquid and gas become indistinguishable. Above the critical point, there are no longer separate liquid and gas phases: there is only a generic fluid phase referred to as a supercritical fluid. In water, the critical point occurs at 22.064 MPa. An unusual feature of the water phase diagram is that the solid–liquid phase line has a negative slope. For most substances, the slope is positive; this unusual feature of water is related to ice having a lowe