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Camphorquinone
Camphorquinone, also known as 2,3-bornanedione, is an organic compound derived from camphor. A yellow solid, it is used as a photoinitiator in curing dental composites. Camphorquinone is produced by the oxidation of camphor with selenium dioxide. Photocuring details Polymerization is induced very slowly by camphorquinone, so amines such as N,N-dimethyl-p-toluidine, 2-ethyl-dimethylbenzoate, N-phenylglycine are generally added to increase the rate of curing. It absorbs very weakly at 468 nm ( extinction coefficient of 40 M−1·cm−1) giving it a pale yellow color. Photoexcitation results in nearly quantitative formation of its triplet state through intersystem crossing and very faint fluorescence. Reactions It can be hydrolyzed by the enzyme 6-oxocamphor hydrolase. Camphorquinone has been examined as a reagent in organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dental Composite
Dental composite resins (better referred to as "resin-based composites" or simply "filled resins") are dental cements made of synthetic resins. Synthetic resins evolved as restorative materials since they were insoluble, of good tooth-like appearance, insensitive to dehydration, easy to manipulate and inexpensive. Composite resins are most commonly composed of Bis-GMA and other dimethacrylate monomers (TEGMA, UDMA, HDDMA), a filler material such as silica and in most applications, a photoinitiator. Dimethylglyoxime is also commonly added to achieve certain physical properties such as flow-ability. Further tailoring of physical properties is achieved by formulating unique concentrations of each constituent. Many studies have compared the lesser longevity of resin-based composite restorations to the longevity of silver- mercury amalgam restorations. Depending on the skill of the dentist, patient characteristics and the type and location of damage, composite restorations can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Camphor
Camphor () is a waxy, colorless solid with a strong aroma. It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel ('' Cinnamomum camphora''), a large evergreen tree found in East Asia; and in the kapur tree ( ''Dryobalanops'' sp.), a tall timber tree from South East Asia. It also occurs in some other related trees in the laurel family, notably '' Ocotea usambarensis''. Rosemary leaves ('' Rosmarinus officinalis'') contain 0.05 to 0.5% camphor, while camphorweed ('' Heterotheca'') contains some 5%. A major source of camphor in Asia is camphor basil (the parent of African blue basil). Camphor can also be synthetically produced from oil of turpentine. The compound is chiral, existing in two possible enantiomers as shown in the structural diagrams. The structure on the left is the naturally occurring (+)-camphor ((1''R'',4''R'')-bornan-2-one), while its mirror image shown on the right is the (−)-camphor ((1''S'',4''S'')-bornan-2-o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonate salts and cyanide salts), along with a few other exceptions (e.g., carbon dioxide, hydrogen cyanide), are not classified as organic compounds and are considered inorganic. Other than those just named, little consensus exists among chemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive. Although organic compounds make up only a small percentage of Earth's crust, they are of central importance because all known life is based on organic compounds. Livin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoinitiator
A photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (UV or visible). Synthetic photoinitiators are key components in photopolymers (for example, photo-curable coatings, adhesives and dental restoratives). Some small molecules in the atmosphere can also act as photoinitiators by decomposing to give free radicals (in photochemical smog). For instance, nitrogen dioxide (NO2) is produced in large quantities by gasoline-burning internal combustion engines. NO2 in the troposphere gives smog its brown coloration and catalyzes production of toxic ground-level ozone (O3). Molecular oxygen (O2) also serves as a photoinitiator in the stratosphere, breaking down into atomic oxygen and combining with O2 in order to form the ozone in the ozone layer. Reactions Photoinitators can create reactive species by different pathways including photodissociation and electron transfer. As an example of dissociation, hydrogen peroxide ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Selenium Dioxide
Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium. Properties Solid SeO2 is a one-dimensional polymer, the chain consisting of alternating selenium and oxygen atoms. Each Se atom is pyramidal and bears a terminal oxide group. The bridging Se-O bond lengths are 179 pm and the terminal Se-O distance is 162 pm.Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium, Franceso A. Devillanova, Royal Society of Chemistry, 2007, The relative stereochemistry at Se alternates along the polymer chain (syndiotactic). In the gas phase selenium dioxide is present as dimers and other oligomeric species, at higher temperatures it is monomeric. The monomeric form adopts a bent structure very similar to that of sulfur dioxide with a bond length of 161 pm. The dimeric form has been isolated in a low temperature argon matrix and vibrational spectra indicate that it has ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mass Extinction Coefficient
The mass attenuation coefficient, or mass narrow beam attenuation coefficient of a material is the attenuation coefficient normalized by the density of the material; that is, the attenuation per unit mass (rather than per unit of distance). Thus, it characterizes how easily a mass of material can be penetrated by a beam of light, sound, particles, or other energy or matter. In addition to visible light, mass attenuation coefficients can be defined for other electromagnetic radiation (such as X-rays), sound, or any other beam that can be attenuated. The SI unit of mass attenuation coefficient is the square metre per kilogram (). Other common units include cm2/g (the most common unit for X-ray mass attenuation coefficients) and mL⋅g−1⋅cm−1 (sometimes used in solution chemistry). Mass extinction coefficient is an old term for this quantity. The mass attenuation coefficient can be thought of as a variant of absorption cross section where the effective area is defined per unit ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intersystem Crossing
Intersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different spin multiplicity. Excited Singlet and Triplet States When an electron in a molecule with a singlet ground state is excited (''via'' absorption of radiation) to a higher energy level, either an excited singlet state or an excited triplet state will form. Singlet state is a molecular electronic state such that all electron spins are paired. That is, the spin of the excited electron is still paired with the ground state electron (a pair of electrons in the same energy level must have opposite spins, per the Pauli exclusion principle). In a triplet state the excited electron is no longer paired with the ground state electron; that is, they are parallel (same spin). Since excitation to a triplet state involves an additional "forbidden" spin transition, it is less probable that a triplet state will form when the molecule absorbs radiation. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
6-oxocamphor Hydrolase
6-oxocamphor hydrolase (, ''OCH'', ''camK (gene)'') is an enzyme with systematic name ''bornane-2,6-dione hydrolase''. This enzyme catalyses the following chemical reaction : bornane-2,6-dione + H2O \rightleftharpoons 1S)-4-hydroxy-2,2,3-trimethylcyclopent-3-enylcetate This enzyme is isolated from ''Rhodococcus ''Rhodococcus'' is a genus of aerobic, nonsporulating, nonmotile Gram-positive bacteria closely related to ''Mycobacterium'' and ''Corynebacterium''. While a few species are pathogenic, most are benign, and have been found to thrive in a broad ...'' sp. References External links * {{Portal bar, Biology, border=no EC 3.7.1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organic Synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one of the most important branches of organic chemistry. There are several main areas of research within the general area of organic synthesis: '' total synthesis'', '' semisynthesis'', and ''methodology''. Total synthesis A total synthesis is the complete chemical synthesis of complex organic molecules from simple, commercially available petrochemical or natural precursors. Total synthesis may be accomplished either via a linear or convergent approach. In a ''linear'' synthesis—often adequate for simple structures—several steps are performed one after another until the molecule is complete; the chemical compounds made in each step are called synthetic intermediates. Most often, each step in a synthesis refers to a separate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ketones
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bond C=O). The simplest ketone is acetone (where R and R' is methyl), with the formula . Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids (e.g., testosterone), and the solvent acetone. Nomenclature and etymology The word ''ketone'' is derived from ''Aketon'', an old German word for ''acetone''. According to the rules of IUPAC nomenclature, ketone names are derived by changing the suffix ''-ane'' of the parent alkane to ''-anone''. Typically, the position of the carbonyl group is denoted by a number, but traditional nonsystematic names are still generally used for the most important ketones, for example acetone and benzophenone. These nonsystematic names are considered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
